_D 


THE ORIGIN AND 
EVOLUTION OF LIFE 

ON THE THEORY OF ACTION 
REACTION AND INTERACTION OF ENERGY 


HALE LECTURES OF THE NATIONAL ACADEMY OF 
SCIENCES, WASHINGTON, APRIL, 1916 


BY THE SAME AUTHOR 


MEN OF THE OLD STONE AGE. Illus- 
trated. 8vo iiel S.5.00 

••The book is the ripe fruit of tlie author's life 
study, served in a •popular' form that van be en- 
joyed by any educated reader; in another sense it is 
the first authoritative summary of the wondeiful 
series of archceological discoveries made in recent 
years."- — New York Times. 


Charles Scribner's Sons 


Tyrannosaunis rex, the King of the Tyrant Saurians. 
The climax among carnivorous reptiles of a complex mechanism for the 
capture, storage, and release of energy. Contemporary with and de- 
stroyer of the large herbivorous dinosaurs. Compare p. 224. 


o?; 


THE ORIGIN AND 
EVOLUTION OF LIFE 

ON THE THEORY OF ACTION 
REACTION AND INTERACTION OF ENERGY 


BY 

HENRY FAIRFIELD OSBORN 

SC.D. PRINCETON, HON. LL.D. TRIXITY, PRINCETON, COLUMBIA, HON. D.SC. CAMBRIDGE 
HON. PH.D. CHRISTIANIA 

RESEARCH PROFESSOR OF ZOOLOGY, COLUMBIA UNIVERSITY 

VERTEBRATE PALEONTOLOGIST U. S. GEOLOGICAL SURVEY, CURATOR EMERITUS OF VERTEBRATE 

PALAEONTOLOGY IN THE AMERICAN MUSEUM OF NATURAL HISTORY 

AUTHOR OF "from THE GREEKS TO DARWIN " 

"the AGE OF M.^MMALS," "MEN OF THE OLD STONE AGE 


WITH 1^6 ILLUSTRATIONS 


NEW YORK 

CHARLES SCRIBNER'S SONS 

1917 


Copyright, 1916, by 
THE SCIENCE PRESS 


Copyright, 191 7, by 
CHARLES SCRIBNER'S SONS 


Published September, 1917 


DEDICATED TO 
MY COLLEAGUE AND FRIEND 

GEORGE ELLERY HALE 

HEAD OF THE MOUNT WILSON OBSERVATORY OF THE CARNEGIE 

institution; ardent advocate OF 

THE synthesis OF THE SCIENCES IN RESEARCH 


PREFACE 

In these lectures we may take some of the initial steps 
toward an energy conception of Evolution and an energy 
conception of Heredity and away from the matter and form 
conceptions which have prevailed for over a century. 

The first half of this volume is therefore devoted to what 
we know of the capture, storage, release, and reproduction of 
energy in its simplest and most elementary living phases; 
the second half is devoted to the evolution of matter and 
form in plants and animals, also interpreted largely in terms 
of energy and mechanics. Lest the reader imagine that 
through the energy conception I am at present even pretend- 
ing to offer an explanation of the miracles of adaptation and 
of heredity, some of these miracles are recited in the second 
part of this volume to show that the germ evolution is the 
most incomprehensible phenomenon which has yet been dis- 
covered in the universe, for the greater part of what we see in 
animal and plant forms is only the visible expression of the in- 
visible evolution of the heredity-germ. 

We are not ready for a clearly developed energy conception 
of the origin of life, still less of evolution and of heredity; yet 
we believe our theory of the actions, reactions, and interactions 
of living energy will prove ^ to be a step in the right direction. 

It is true that in the organism itself, apart from the 
heredity-germ, we have made great advances- in the energy 

' Some of the reasons for this assertion are presented in the successive chapters of 
this voKime and summarized in the Conclusion. 

- One of the most influential works in this direction is Jacques Loeb's Dynamics of 
Living Mailer, a synthesis of many years of physicochemical research on the actions and 
reactions of living organisms. See also Loeb's more recent work, The Organism as a 
Whole, published since these lectures were written. 

vii 


viii PREFACE 

conception. We observe many of the means by which energy 
is stored, and some of the compHcated methods by which it 
is captured, protected, and released. We shall see that highly 
evolved organisms, such as the large reptiles and mammals 
and man, present to the eye of the anatomist and physiologist 
an inconceivable complexity of energy and form; but this we 
may in part resolve by reading the pages of this volume back- 
ward, Chinese fashion, from the mammaP to the monad, in 
which we reach a stage of relative simplicity. Thus the or- 
ganism as an arena for energy and matter, as a complex of in- 
tricate actions, becomes in a measure conceivable. The 
heredity-germ, on the contrary, remains inconceivable in each 
of its three powers, namely, in the Organism which it produces, 
in the succession of germs to which it gives rise, and in its own 
evolution in course of time. 

Having now stated the main object of these lectures, I 
invite the reader to study the following pages with care, be- 
cause they review some of the past history and introduce some 
of the new spirit and purpose of the search for causes in the 
domain of energy. I begin with matters which are well known 
to all biologists and proceed to matters which are somewhat 
more difhcult to understand and more novel in purpose. 

In this review we need not devote any time or space to 
fresh arguments for the truth of evolution. The demonstra- 
tion of evolution as a universal law of living nature is the 
great intellectual achievement of the nineteenth century. 
Evolution has outgrown the rank of a theory, for it has w^on 
a place in natural law beside Newton's law of gravitation, 
and in one sense holds a still higher rank, because evolution is 
the universal master, while gravitation is one among its many 

' Man is not treated at all in this volume, the subject being reserved for the final 
lectures in the Hale Series. 


PREFACE ix 

agents. Nor is the law of evolution any longer to be associ- 
ated with any single name, not even with that of Darwin, 
who was its greatest exponent.^ It is natural that evolution 
and Darwinism should be closely connected in many minds, 
but we must keep clear the distinction that evolution is a law, 
while Darwinism is merely one of the several ways of inter- 
preting the workings of this law. 

In contrast to the unity of opinion on the law of evolution 
is the wide diversity of opinion on the causes of evolution. 
In fact, the causes of the evolution of life are as mysterious as 
the law of evolution is certain. Some contend that we already 
know the chief causes of evolution, others contend that we 
know little or nothing of them. In this open court of con- 
jecture, of hypothesis, of more or less heated controversy, the 
great names of Lamarck, of Darwin, of Weismann figure promi- 
nently as leaders of different schools of opinion; while there 
are others, like myself,- who for various reasons belong to no 
school, and are as agnostic about Lamarckism as they are 
about Darwinism or Weismannism, or the more recent form 
of Darwinism, termed Mutation by de Vries. 

In truth, from the period of the earliest stages of Greek 
thought man has been eager to discover some natural cause of 
evolution, and to abandon the idea of supernatural interven- 
tion in the order of nature. Between the appearance of The 
Origin of Species, in 1859, and the present time there have 
been great waves of faith in one explanation and then in an- 
other: each of these waves of confidence has ended in disap- 
pointment, until finally we have reached a stage of very general 

1 See From the Greeks to Darwin (Macmillan & Co., 1894), by the present author, in 
which the whole history of the evolution idea is traced from its first conception down to 
the time of Darwin. 

* Osborn, H. F., "The Hereditary Mechanism and the Search for the Unknown Factors 
of Evolution," The Amer. Naturalist, May, 1895, pp. 418-439. 


X PREFACE 

scepticism. Thus the long period of observation, experiment, 
and reasoning which began with the French natural philosopher 
Buffon, one hundred and fifty years ago, ends in 1916 with the 
general feeling that our search for causes, far from being near 
completion, has only just begun. 

Our present state of opinion is this: we know to some 
extent how plants and animals and man evolve; we do not 
know why they evolve. We know, for example, that there 
has existed a more or less complete chain of beings from monad 
to man, that the one-toed horse had a four-toed ancestor, that 
man has descended from an unknown ape-like form somewhere 
in the Tertiary. We know not only those larger chains of 
descent, but many of the minute details of these transforma- 
tions. We do not know their internal causes, for none of the 
explanations which have in turn been olTered during the last 
hundred years satisfies the demands of observation, of experi- 
ment, of reason. It is best frankly to acknowledge that the 
chief causes of the orderly evolution of the germ are still en- 
tirely unknown, and that our search must take an entirely 
fresh start. 

As regards the continuous adaptability and fitness of liv- 
ing things, we have a reasonable interpretation of the causes 
of some of the phenomena of adaptation, but they are the 
smaller part of the whole. Especially mysterious are the chief 
phenomena of adaptation in the germ; the marvellous and 
continuous fitness and beauty of form and function remain 
largely unaccounted for. We have no scientific explana- 
tion for those processes of development from within, which 
Bergson^ has termed "revolution creatrice," and for which 
Driesch- has abandoned a natural explanation and assumed 

' Bergson, Henri, 1907, U Evolution Creatrice. 

' Driesch, Hans, 1908, The Science and Philosophy of the Organism. 


PREFACE xi 

the existence of an entelechy, that is, an internal perfecting 
influence. 

This confession of failure is part of the essential honesty of 
scientific thought. We recall the fact that our baffled state 
of mind is by no means new, for in Kant's work of 1790, his 
Methodical System of the Teleological Faculty of Judgment, he 
divides all things in nature into the "inorganic," in which 
natural causes prevail, and the "organic," in which the active 
teleological (i. e., purposive) principle of adaptation is sup- 
posed to prevail. There was in Kant's mind a cleft between 
the domain of primeval matter and the domain of life, for in 
the latter he assumes the presence of a supernatural principle, 
of final causes acting toward definite ends. This view is ex- 
pressed in his Teleological Faculty of Judgment as follows : 

"But he" (the archaeologist of Nature) "must for this end 
ascribe to the common mother an organization ordained pur- 
posely with a view to the needs of all her offspring, otherwise 
the possibility of suitability of form in the products of the 
animal and vegetable kingdoms cannot be conceived at all."^ 

"It is cjuite certain that we cannot become sufficiently 
acquainted with organized creatures and their hidden poten- 
tialities by aid of purely mechanical natural principles; much 
less can we explain them; and this is so certain, that we may 
boldl}' assert that it is absurd for man even to conceive such 
an idea, or to hope that a Newton may one day arise able to 
make the production of a blade of grass comprehensible, ac- 
cording to natural laws ordained by no intention; such an 
insight we must absolutely deny to man."- 

For a long period after The Origin of Species appeared, 
Haeckel and many others believed that Darwin had arisen 
as the Newton for whom Kant did not dare to hope; but no 

' Kant, Emmanuel, 1790, § 79. -Ibid., § 74. 


xii PREFACE 

one now claims for Darwin's law of natural selection a rank 
equal to that of Newton's law of gravitation. 

If we admit the possibility that Kant was right, and that 
we can never become sufhciently acquainted with organized 
creatures and their hidden potentialities by aid of purely 
natural principles, we may be compelled to regard the origin 
and evolution of life as an ultimate law like the law of gravita- 
tion, which may be mathematically and physically defined, 
but cannot be resolved into any causes. We are not willing, 
however, to make such an admission at the present time and 
to abandon the search for causes. 

The question then arises, why has our long and arduous 
search after the causes of evolution so far been unsuccessful? 
One reason why our search may have failed appears to be that 
the chief explorers have been trained in one school of thought, 
namely, the school of the naturalist. They all began their studies 
with observations on the external form and color of animals 
and plants; they have all observed the end results of long 
processes of evolution. Buffon derived his ideas of the causes 
of evolution from the comparison of the wild and domestic 
animals of the Old and New Worlds; Goethe observed the com- 
parative anatomy of man and of the higher animals; Lamarck 
observed the higher phases of the vertebrate and invertebrate 
animals; Darwin observed the form of most of the domestic 
animals and cultivated plants and, finally, of man, and noted 
the adaptive significance of the colors of flowers and birds, 
and the relations of flowers with birds and insects; de Vries 
compared the wild and cultivated species of plants. Thus all 
the great naturalists in turn — Buffon, Goethe, Lamarck, Dar- 
win, and de Vries — have attempted to reason backward, as it 
were, from the highly organized appearances of form and color 
to their causes. The same is true of the palaeontologists: 


PREFACE xiii 

Cope turned from the form of the teeth and skeleton backward 
to considerations of cause and energy, Osborn^ reached a con- 
ception of evolution as of the relations of fourfold form, and 
hence proposed the word tetraplasy. 

The Heredity theories of Darwin, of de Vries, of Weis- 
mann have also been largely in the material conceptions of 
fine particles of matter such as "pangens" and "determinants." 
There has been some consideration of function and of the 
internal phenomena of organisms, but there has been little 
or no serious attempt to reverse the mental processes of the 
naturalist and substitute those of the physicist in considering 
the causes of evolution. - 

Moreover, all the explanations of evolution which have 
been offered by three generations of naturalists align themselves 
under two main ideas only. The first is the idea that the 
causes of evolution are chiefly from without inward, namely, 
beginning in the environment of the body and extending into 
the germ: this idea is centripetal. The second idea is just the 
reverse: it is centrifugal, namely, that the causes begin in the 
germ and extend outward into the body and into the environ- 
ment. 

The pioneer of the first order of ideas is Buff on, who early 
reached the opinion that favorable or unfavorable changes 
of environment directly alter the hereditary form of succeed- 
ing generations. Lamarck,^ the founder of a broader and 
more modern conception of evolution, concluded that the 
changes of form and function in the body and nervous system 
induced by habit and environment accumulate in the germ, 

' Osborn, H. F., "Tetraplasy, the Law of the Four Inseparable Factors of Evolution," 
Jour. Acad. Nat. Sci. Pliila., special anniversary volume issued September 14, 1912, pp. 
275-309- 

^ See fuller exposition on pp. 10-23 of this volume. 

' For a fuller exposition of the theory of Lamarck, see pp. 143, 144. 


xiv PREFACE 

and are handed on by heredity to succeeding generations. 
This essential idea of Lamarckism was refined and extended 
by Herbert Spencer, by Darwin himself, by Cope and many 
others; but it has thus far failed of the crucial test of observa- 
tion and experiment, and has far fewer adherents to-day than 
it had forty years ago. 

We now perceive that Darwin's original thought turned 
to the opposite idea, namely, to sudden changes in the heredity- 
germ itself^ as giving rise spontaneously to more or less adap- 
tive changes of body form and function which, if faA'orable to 
survival, might be preserved and accumulated through natural 
selection. This pure Darwinism has been refined and extended 
by Wallace, Weismann, and especially of late by de Vries, 
whose "mutation theory" is pure Darwinism in a new guise. 

Weismann's great contribution to thought has been to 
point out the very sharp distinction which undoubtedly exists 
between the hereditary forces and predispositions in the hered- 
ity-germ and the visible expression of these forces in the or- 
ganism. It is in the "germ-plasm," as Weismann terms it — 
in this volume termed the '"heredity-chromatin" — that the real 
evolution of all predispositions to form and function is taking 
place, and the problem of causes of evolution has become an 
infinitely more difficult one since Weismann has compelled us 
to realize that the essential question is the causes of germinal 
evolution rather than the causes of bodily evolution or of en- 
vironmental evolution. 

Again, despite the powerful advocacy of pure Darwinism 
by Weismann and de Vries in the new turn that has been 
given to our search for causes by the rediscovery of the law of 
Mendel and the heredity doctrines which group under Men- 

* Osborn, H. F., "Darwin's Theory of Evolution by the Selection of Minor Saltations," 
The Amer. Naturalist, February, 191 2, pp. 76-82. 


PREFACE XV 

delism/ it may be said that Darwin's law of selection as a 
natural explanation of the origin of all fitness in form and func- 
tion has also lost its prestige at the present time, and all of 
Darwinism which now meets with universal acceptance is the 
law of the survival of the fittest, a limited application of Darwin's 
great idea as expressed by Herbert Spencer. Few biologists 
to-day question the simple principle that the fittest tend to 
survive, that the unfit tend to be eliminated, and that the 
present aspect of the entire living world is due to this great 
pruning-knife which is constantly sparing those which are best 
fitted or adapted to any conditions of environment and cutting 
out those which are less adaptive. But as Cope pointed out, 
the survival of fitness and the origin of fitness are two very 
different phenomena. 

If the naturalists have failed to make progress in the search 
for causes, I believe it is chiefly because they have attempted 
to reason backward from highly complex plant and animal 
forms to causes. The cart has always been placed before the 
horse; or, to express it in another way, thought has turned 
from the forms of living matter toward a problem which involves 
the phenomena of living energy ; or, still more briefly, we have 
been thinking from matter backward into energy rather than 
from energy forward into matter and form. 

All speculation on the origin of life, fruitless as it may at 
first appear, has the advantage that it compels a sudden re- 
versal of the naturalist's point of view, for we are forced to 
work from energy upward into form, because, at the begin- 
ning, form is nothing, energy is everything. Energy appears 
to be the chief end of life — the first efforts of life work toward 
the capture of energy, the storage of energy, the release of 

' Mendelism chiefly refers to the distinction and laws of distribution of separable or 
unit characters in the germ and in the individual in course of its development. 


xvi PREFACE 

energy. The earliest adaptations we know of are designed for 
the capture and storage of energy. 

Matter in the state of relative rest know^n as plant and 
animal form is present, but, in the simplest and lowliest types 
of life, form does not conceal and mask the processes of energy 
as it does in the higher types. Similarly, the earliest fitness 
we discover in the bacteria or monads is the fitness of group- 
ing and organizing different kinds of energy — the energy of 
molecules, of atoms, of electrons as displayed in the twenty- 
six or more chemical elements which enter into life. 

In searching among these early episodes of life in its origin 
we discover that four complexes of energy are successively 
added and combined. The Inorganic Environment of the sun, 
of the earth, of the water, of the atmosphere is exploited thor- 
oughly in search of energy by the Organism: the organism 
itself becomes an organism only by utilizing the energy of the 
environment and by coordinating its own internal energies. 
Whether the Germ as the special centre of heredity and repro- 
duction of energy is as ancient as the organism we do not 
know; but we do know that it becomes a distinct and highly 
complex centre of potential energy which directs the way to 
the entire energy complex of the newly developing organism. 
Finally, as organisms multiply and acquire various kinds of 
energy, the Life Environment arises as a new factor in the 
energy complex. Thus in the process of the origin and early 
evolution of life, complexes of four greater and lesser energy 
groups arise, namely: inorganic environment: the energy 
content in the sun, the earth, the water, and the air; organism: 
the energy of the individual, developing and changing the cells 
and tissues of the body, including that part of the germ which 
enters every cell; heredity-germ: the energies of the heredity 
substance (heredity-chromatin) concentrated in the reproduc- 


PREFACE xvii 

tive cells of continuous and successive generations, as well as 
in all the cells and tissues of the organism; and life environ- 
ment: beginning with the monads and algae and ascending in a 
developing scale of plants and animals. 

There are here four evolutions of energy rather than one, 
and the problem of causes is how the four evolutions are ad- 
justed to each other; and especially how the evolution of the 
germ adjusts itself to that of the inorganic environment and 
of the life environment, and to the temporary evolution of the 
organism itself. 

I do not propose to evade the difficulties of the problem 
of the origin and evolution of life by minimizing any of them. 

Whether our approach through energy will lead to the dis- 
covery of some at least of the unknown causes of evolution 
remains to be determined by many years of observation and 
experiment. Whereas our increasing knowledge of energy in 
matter reveals an infinity of energized particles even in the in- 
finitely minute aggregations known as molecules — an infinity 
which we observe but do not comprehend — we find in our 
search for causes of the origin and evolution of life that we have 
reached an entirely new point of departure, namely, that of 
the physicist and chemist rather than the old point of departure 
of the naturalist. We have obtained a starting-point for new 
and untried paths of exploration which may be followed dur- 
ing the present century — paths which have long been trodden 
with a different purpose by physicists and chemists, and by 
physiologists and biochemists in the study of the organism it- 
self. 

The reader may thus follow, step by step, my own experi- 
ence and development of thought in preparing these lectures. 
The reason why I happened to begin this volume with the prob- 


xviii PREFACE 

lem of energy and end with that of the evolution of form is 
that these lectures were prepared and delivered midway in a 
cosmic-evolution series which opened with Sir Ernest Ruther- 
ford's^ discourse on "The Constitution of Matter and the 
Evolution of the Elements," and continued with "The Evolu- 
tion of the Stars and the Formation of the Earth," by Doctor 
William Wallace Campbell,- and "The Evolution of the Earth," 
by Professor Thomas Chrowder Chamberlin.^ My friend 
George Ellery Hale placed upon me the responsibility of 
weaving the partly known and still more largely unknown 
narrative which connects the forms of energy and matter ob- 
served in the sun and stars with the forms of energy and matter 
which we observe in the bodies of our own mammalian ances- 
tors. Certainly we appear to inherit some, if not all, of our 
physicochemical characters from the sun; and to this degree 
we may claim kinship with the stellar universe. Some of our 
distinctive characters and functions are actually properties of 
our ancestral star. Physically and chemically we are the off- 
spring of our great luminary, which certainly contributes to 
us all our chemical elements and all the physical properties 
which bind them together. 

Some day a constellation of genius will unite in one labora- 
tory on the life problem. This not being possible at present, 
I have endeavored during the past two years^ for the purposes 

1 Rutherford, Sir Ernest, "The Constitution of Matter and the Evokition of the 
Elements," first series of lectures on the William Ellery Hale foundation, delivered in 
April, 1914; Pop. Sci. Mon., August, 1915, pp. 105-142. 

2 Campbell, William Wallace, "The Evolution of the Stars and the Formation of the 
Earth," second series of lectures on the WilUam Ellery Hale foundation, delivered De- 
cember 7 and 8, 1914; Pop. Sci. Man., September, 1915, pp. 209-235; Scientific Monthly, 
October, 1915, pp. 1-17; November, 1915, pp. 177-194; December, 1915, pp. 238-255. 

' Chamberlin, Thomas Chrowder, "The Evolution of the Earth," third series of lec- 
tures on the William Ellery Hale foundation, delivered April 19-21, 1915; Scientific 
Monthly, May, 1916, pp. 417-437; June, 1916, pp. 536-556. 

'' I first opened a note-book on this subject in the month of April, 19 15, when I was 
invited by Doctor George Ellery Hale to undertake the preparation of these lectures. 


PREFACE xix 

of my own task to draw a large number of specialists together 
in correspondence and in a series of personal conferences and 
discussions; and whatever merits this volume may possess are 
partly due to their generous response in time and thought to 
my invitation. Their suggestions are duly acknowledged in 
footnotes throughout the text. I have myself approached the 
problem through a synthesis of astronomy, geology, physics, 
chemistry, and biology. 

In consulting authorities on this subject I have made one 
exception, namely, the problem of the origin of life itself with 
its vast literature going back to the ancients — I have read none 
of it and quoted none of it. In order to consider the problem 
from a fresh and unbiassed point of view, I have also purposely 
refrained from reading any of the recent and authoritative 
treatises of Schafer,^ Moore,'- and others on the origin of life. 
It will be interesting for the reader to compare the conclusions 
previously reached by these distinguished chemists with those 
presented in the following pages. 

For invaluable guidance in the phenomena of physics I 
am deeply indebted to my colleague Professor Michael I. 
Pupin, of Columbia University, who has given me his views 
as to the fundamental relation of Newton's laws of motion to 
the modern laws of heat and energy (thermodynamics), and has 
clarified the laws of action, reaction, and interaction from the 
physical standpoint. Without this aid I could never have 
developed what I believe to be the new biological principle set 
forth in this work. I owe to him the confirmation of the use 
of the word interaction as a physical term, which had occurred 
to me first as a biological term. 

' Schafer, Sir Edward A., Life, Its Nature, Origin, and Maintenance, Longmans, Green 
& Co., New York, igi2. 

-Moore, Benjamin, The Origin and Nature of Life, Henr}' Holt & Co., New York; 
Williams & Norgate, London, 1913. 


XX PREFACE 

As to the physicochemical actions and reactions of the 
hving organism I have drawn especially from Loeb's Dynamics 
of Living Matter. In the physicochemical section I am also 
greatly indebted to the very suggestive work of Henderson 
entitled The Fitness of the Environment, from which I have 
especially derived the notion that fitness long antedates the 
origin of life. Professor Hans Zinsser, of Columbia University, 
has aided in a review of Ehrlich's theory of antibodies and the 
results of later research concerning them. Professor Ulric 
Dahlgren, of Princeton University, has aided the preparation of 
this work with valuable notes and suggestions on the light, 
heat, and chemical rays of the sun, and on phosphorescence 
and electric phenomena in the higher organisms. 

In the geochemical and geophysical section I am indebted 
to my colleagues in the National Academy, F. W. Clarke and 
George F. Becker, not only for the revision of parts of the 
text, but for many valuable suggestions and criticisms. 

For suggestions as to the chemical conditions which may 
have prevailed in the earth during the earliest period in the 
origin of life, as well as for criticisms and careful revision of 
the chemical text I am especially indebted to my colleague in 
Columbia University, Professor William J, Gies. 

In the astronomic section I desire to express my indebted- 
ness to George Ellery Hale, of the Mount Wilson Observatory, 
for the use of photographs, and to Henry Norris Russell, of 
Princeton University, for notes upon the heat of the primordial 
earth's surface. In the early narrative of the earth's history 
and in the subsequent geographic and physiographic charts 
and maps Professor Charles Schuchert and Professor Joseph 
Barrell, of Yale University, kindly cooperated with the loan of 
illustrations and otherwise. In the section on the evolution of 
bacteria, which is a part pertaining to the idea of the early 


PREFACE xxi 

evolution of energy in living matter, I enjoyed the cooperation 
of Doctor I. J. Kligler, formerly of the American Museum of 
Natural History, and now at the Rockefeller Institute for 
Medical Research. 

In the botanical section I am especially indebted to Pro- 
fessor T. H. Goodspeed, of the University of California, and tO' 
Doctor Marshall Avery Howe, of the Botanical Gardens, for 
many valuable notes and suggestions, as well as for certain 
illustrations. In the early zoological section I am indebted 
to my colleagues at Columbia University, Professor Edmund 
B. Wilson and Professor Gary N. Calkins. Especial thanks 
are due to Mr. Roy W. Miner, of the American Museum, for his 
careful comparisons of recent forms of marine life with the Cam- 
brian forms discovered by Doctor Charles Walcott, who sup- 
plied me with the beautiful photographs shown in Chapter IV. 

In preparing the chapters on the evolution of the verte- 
brates, I have turned to my colleague Professor W. K. Gregory, 
of the American Museum and Columbia University, who has 
aided both with notes and suggestions, and in the supervision 
of various illustrations relating to the evolution of vertebrate 
form. The illustrations are chiefly from the collections of the 
American Museum of Natural History, as portrayed in original 
drawings by Charles R. Knight, Erwin S, Christman, and 
Richard Deckert. The entire work has been faithfully collated 
and put through the press by my research assistant. Miss 
Christina D. Matthew. 

It affords me great pleasure to dedicate this work to the 
astronomer friend whose enthusiasm for my own field of work 
in biology and palaeontology has always been a source of en- 
couragement and inspiration. 

Henry Fairtield Osborn. 

American Museum of Natural History, 
February 26, 191 7. 


CONTENTS 

INTRODUCTION 

PAGE 

Four questions regarding life i 

The energy concept of life lo 

The four complexes of energy i8 

PART I. THE ADAPTATION OF ENERGY 
CHAPTER I 

Preparation of the Earth for Life 

The lifeless earth 24 

The lifeless water 34 

The atmosphere 39 

CHAPTER II 

The Sun and the Physicochemical Origins of Life 

Heat and light 43 

Life elements in the sun 45 

Heat and electric energy 48 

The capture of sunlight 51 

Ionization — the electric energy of atoms 53 

Coordination of activities by means of interaction ... 56 

Functions of the chemical life elements 59 

Primary stages of life 67 

xxiii 


xxiv CONTENTS 


PAGE 


New organic compounds 60 

Interactions — enzymes, antibodies, hormones, and chalones . 71 

Chemical messengers 72 

Physicochemical differentiation 78 

CHAPTER III 

Energy Evolution of Bacteria, Alg^, and Plants 

Evolution of bacteria 80 

Protoplasm and heredity-chromatin 91 

Chlorophyll — the sunlight converter of plants .... 99 

Evolution of ALGiE^THE most primitive plants loi 

Plant and animal evolution contrasted 105 

PART 11. THE EVOLUTION OF ANIMAL FORM 

CHAPTER IV 

The Origins of Animal Life and Evolution of the 
Invertebrates 

Evolution of Protozoa no 

Evolution of Metazoa 117 

Cambrian invertebrates 118 

Environmental changes 134 

Mutations of Waagen 138 

CHAPTER V 

Visible and Invisible Evolution of the Vertebrates 

Evolution of the germ 141 

Character evolution 146 

The laws of adaptation 152 


CONTENTS XXV 

CHAPTER VI 

Evolution of Body Form in the Fishes and Amphibians 

PAGE 

Earliest known fishes i6o 

Early armored fishes 165 

Primordial sharks 167 

Rise of modern fishes 169 

Evolution of the amphibians 177 

CHAPTER Vn 

Form Evolution of the Reptiles and Birds 

Earliest reptiles 184 

Mammal-like reptiles 191 

Adaptive radiation of reptiles 193 

Aquatic reptiles 198 

Carnivorous dinosaurs 210 

Herbivorous dinosaurs 216 

Flying reptiles 226 

Origin of birds 226 

Arrested reptilian evolution 231 

CHAPTER VHI 

Evolution of the IVIamm.als 

Origin of mammals 234 

Character evolution 27,8 

Causes of evolution 245 

Modes of evolution 251 


xxvi CONTENTS 


PAGE 


Adaptation to environment 253 

Geographic distribution 259 

Changes of proportion 263 

Retrospect and prospect 275 

Conclusion . . . 281 


APPENDIX 

NOTE 

I. Different modes of storage and release of energy in 

living organisms 285 

II. Blue-green alg^ possibly among the first settlers of 

OUR PLANET 285 

III. One secret of life — synthetic transformation of in- 

different MATERIAL 286 

IV. Interaction through catalysis — the acceleration of 

CHEMICAL REACTIONS THROUGH THE PRESENCE OF ANOTHER 
SUBSTANCE WHICH IS NOT CONSUMED BY THE REACTION . 286 

V. The causes or agents of speed and order in the reac- 
tions OF LIVING BODIES — ENZYMES, COLLOIDS, ETC. . . 287 

VI. Interactions of the organs of internal secretion and 

HEREDITY 289 

VII. Table — relations of the principal groups of animals 

referred to in the text 29o 

Bibliography 293 

Index 307 


ILLUSTRATIONS 

Plate. Tyrannosanrus rex, the "king of the tyrant saurians" . . Frontispiece 

FIG. PAGE 

1. The moon's surface 30 

2. Deep-sea ooze, the foraminifera 32 

3. Light, heat, and chemical influence of the sun 44 

4. Chemical life elements in the sun 46 

5. The earliest phyla of plant and animal life 50 

6. Hydrogen vapor in the solar atmosphere 60 

7. Hydrogen flocculi surrounding sun-spots 61 

8. The sun, showing sun-spots and calcium vapor 64 

9. Chemical life elements in the sun 65 

10. Hand form, determined by heredity and secretions 76 

11. Fossil and living bacteria compared 85 

12. Protoplasm and chromatin of Anuvba 93 

13. The two structural components of the living world 94 

14. Chromatin in Sequoia and Trillium compared 96 

15. Fossil and living algae compared 102 

16. Typical forms of Protozoa 112 

17. Light, heat, and chemical influence of the sun 113 

18. Skeletons of typical Protozoa 115 

19. Map — Late Low^er Cambrian world environment 119 

20. A Mid-Cambrian trilobite 121 

21. Brachiopods, Cambrian and recent 123 

22. Horseshoe crab and shrimp, Cambrian and recent 124 

23. Map — Middle Cambrian world environment 125 

24. Sea-cucumbers, Cambrian and recent 127 

xxvii 


xxviii ILLUSTRATIONS 

FIG. PAGE 

25. Worms, Middle Cambrian and recent . 128 

26. Chaetognaths, Cambrian and recent . 129 

27. Jellyfish, Cambrian and recent 130 

28. The twelve chief habitat zones 131 

29. Life zones of Cambrian and recent invertebrates 131 

30. Map — North America in Cambrian times 132 

31. Sea-scorpions of Silurian times 133 

32. Map — North America in Middle Devonian times 134 

2$. Changing environment during fifty million years 135 

34. Fossil starfishes 136 

35. Mutations of Waagen in ammonites 139 

36. Mutations of Spirifer mucronatus 140 

37. Shell pattern and tooth pattern of Glyptodon 148 

38. Teeth of Euprotogonia and Mcniscotherium 149 

39. Adaptation of the fingers in a lemur 150 

40. Total geologic time scale 153 

41. Adaptation of form in three marine vertebrates — shark, ichthyosaur, 

and dolphin 155 

42. Chronologic chart of vertebrate succession 161 

43. The existing lancelets (Amphioxus) 162 

44. Five types of body form in fishes 163 

45. Map — North America in Upper Silurian time 164 

46. The Ostracoderm Palcraspis 165 

47. The Antiarchi. Bothriolepis 165 

48. The Arthrodira. Dinichthys intermedius 166 

49. A primitive Devonian shark, Cladoselache 167 

50. Adaptive radiation of the fishes 168 

51. Fish types from the Old Red Sandstone 170 

52. Map — the world in Early Lower Devonian times 171 

53. Change of adaptation in the limbs of vertebrates 172 


ILLUSTRATIONS xxix 

FIG. PAGE 

54. Deep-sea fishes — extremes of adaptation in locomotion and illumina- 

tion 173 

55. Phosphorescent illuminating organs of deep-sea fishes 174 

56. Map — North America in Upper Devonian time 175 

57. The earliest known limbed animal 176 

58. A primitive amphibian 177 

59. Descent of the Amphibia 178 

60. Chief amphibian types of the Carboniferous 179 

61. Skull and vertebral column of Diplocaidiis 180 

62. Map — the world in Earliest Permian time 181 

63. Amphibia of the American Permo-Carboniferous 182 

64. Skeleton of Eryops 183 

65. JNIap — the world in Earliest Permian time 185 

66. Ancestral reptilian types 186 

67. Reptiles with skulls transitional from the amphibian 187 

68. ]Map — the w^orld in Middle Permian time 188 

69. The fin-back Permian reptiles 189 

70. Mammal-like reptiles of South Africa 190 

71. A South African "dog-toothed" reptile 192 

72. Adaptive radiation of the Reptilia 193 

73. Geologic records of reptilian evolution 195 

74. Dinosaur mummy — a relic of flood-plain conditions 197 

75. Reptiles leaving a terrestrial for an aquatic habitat 199 

76. Convergent adaptation of amphibians and reptiles 200 

77. Adaptation of reptiles to the aquatic habitat zones 201 

78. Alternating adaptation of the "leatherback" turtles 202 

79. The existing "leatherback" turtle 202 

80. Marine adaptation of terrestrial Chelonia 203 

81. Marine pelagic adaptation of the ichthyosaurs 204 

82. Restorations of two ichthyosaurs 205 


XXX ILLUSTRATIONS 


TIG 


87 


90 

91 
92 

93 
94 
95 
96 

97 

98 

99 


PAGE 


83. Map — North America in Upper Cretaceous time 206 

84. Convergent forms of aquatic reptiles 207 

85. A plesiosaur from the Jurassic of England 207 

Types of marine pelagic plesiosaurs 20S 

Tylosaurus, a sea lizard 209 

Upper Triassic life of the Connecticut River 211 

Terrestrial evolution of the dinosaurs 211 

Map — North America in Upper Triassic time 212 

A carnivorous dinosaur preying upon a sauropod 213 

Extreme adaptation in the "tyrant" and "ostrich" dinosaurs . . 214 

Four restorations of the "ostrich" dinosaur 215 

Aiicliisaiirus and Platcosauriis compared 216 

Map — the world in Lower Cretaceous time 217 

Map — North America in Lower Cretaceous time 218 

Three principal types of sauropods 219 

Terrestrio-fluviatile theory of the habits of Apatosaiints .... 220 

Primitive iguanodont Camptosaunis 221 

100. Upper Cretaceous iguanodonts from Montana 222 

loi. Adaptive radiation of the iguanodont dinosaurs 223 

102. Tyrannosaurus and Ceratopsia — offensive and defensive energy 

complexes 224 

103. Restoration of the Pterodactyl 226 

104. Ancestral tree of the birds 227 

105. Skeletons of Archccoptcryx and pigeon compared 228 

106. Silhouettes of ArcJicroptcryx and pheasant 22S 

107. Four evolutionary stages in the four-winged bird 22S 

108. Parachute flight of the primitive bird 229 

109. Restoration of Archccoptcryx 229 

no. Reversed aquatic evolution of wing and body form 230 

III. The sei whale, Balcoioptcra boreal is 234 


ILLUSTRATIONS xxxi 

FIG. PAGE 

112. The tree shrew, Tnpaia 235 

113. Primitive types of monotreme and marsupial ....... 235 

114. Ancestral tree of the mammals 236 

115. Adaptive radiation of the mammals 239 

116. Alternating adaptation in the kangaroo marsupials 243 

117. Evolution of proportion. Okapi and giraffe 24S 

118. Brachydactyly and dolichodactyly 249 

119. Result of removing the thyroid and parathyroid glands . . . . 250 

120. Result of removing the pituitary body 251 

121. Main subdivisions of geologic time 256 

122. Map — North Polar theory of the distribution of mammals . . . 257 

123. Scene in western Wyoming in Middle Eocene times 258 

124. Two stages in the early evolution of the ungulates 259 

125. A primitive whale from the Eocene of Alabama 260 

126. Map — North America in Upper Oligocene time 262 

127. Two stages in the evolution of the titanotheres 263 

128. Evolution of the horn in the titanotheres 264 

129. Horses of Oligocene time 266 

130. Stages in the evolution of the horse 267 

131. Epitome of proportion evolution in the Proboscidea 269 

132. Map — the ice-fields of the fourth glaciation 270 

133. Groups of reindeer and woolly mammoth 271 

134. Glacial environment of the woolly rhinoceros 272 

135- Pygmies and plainsmen of New Guinea 273 

TABLES 

I. Distribution of the chemical elements t,^ 

II. Functions of the life elements (0 face 67 


THE ORIGIN AND EVOLUTION 

OF LIFE 

INTRODUCTION 

Four questions as to the origin of life. Vitalism or mechanism? Creation 
or evolution? Law or chance? The energy concept of life. Newton's 
laws of motion. Action and reaction. Interaction. The four complexes 
of energy. Darwin's law of Natural Selection. 

We may introduce this great subject by putting to ourselves 
four leading questions: First, Is life upon the earth something 
new? Second, Does life evolution externally resemble stel- 
lar evolution? Third, Is there evidence that similar internal 
physicochemical laws prevail in life evolution and in lifeless 
evolution? Fourth, Are life forms the result of law or of 
chance ? 

Four Questions as to the Origin of Life 

Our first question is one which has not yet been answered 
by science,^ although there are two opinions regarding it. Does 
the origin of life represent the beginning of something new in 
the cosmos, or does it represent the continuation and evolu- 
tion of forms of matter and energy already found in the earth, 
in the sun, and in the other stars ? 

The traditional opinion is that something new entered this 
and possibly other planets with the appearance of life; this 
view is also involved in all the older and newer hypotheses 

' Science consists of the body of well-ascertained and verified facts and laws of nature. 
It is clearly to be distinguished from the mass of theories, hypotheses, and opinions which 
are of value in the progress of science. 


2 THE ORIGIN AND EVOLUTION OF LIFE 

which group around the idea of vitalism or the existence of 
specific, distinctive, and adaptive energies in living matter — 
energies which do not occur in lifeless matter. 

The more modern scientific opinion is that life arose from 
a recombination of forces pre-existing in the cosmos. To hold 
to this opinion, that life does not represent the entrance either 
of a new form of energy or of a new series of laws, but is sim- 
ply another step in the general evolutionary process, is cer- 
tainly consistent with the development of mechanics, physics, 
and chemistry since the time of Newton and of evolutionary 
thought since Buffon, Lamarck, and Darwin. Descartes (1644) 
led all the modern natural philosophers in perceiving that the 
explanation of life should be sought in the physical terms of 
motion and matter. Kant at first (lysS'-iyys) adopted and 
later (1790) receded from this opinion. 

These contrasting opinions, which are certainly as old as 
Greek philosophy and probably much older, are respectively 
known as the vitalistic and the mechanistic. 

We may express as our own opinion, based upon the appli- 
cation of uniformitarian evolutionary principles, that when 
life appeared on the earth some energies pre-existing in the 
cosmos were brought into relation with the chemical elements 
already existing. In other words, since every advance thus 
far in the quest as to the nature of life has been in the direc- 
tion of a physicochemical rather than of a vitalistic explanation, 
from the time when Lavoisier (i 743-1 794) put the life of plants 
on a solar-chemical basis, if we logically follow the same direc- 
tion we arrive at the belief that the last step into the unknown 
— one which possibly may never be taken by man — will also be 
physicochemical in all its measurable and observable proper- 
ties, and that the origin of life, as well as its development, will 
ultimately prove to be a true evolution within the pre-existing 


FOUR QUESTIONS REGARDING LIFE 3 

cosmos. Without being either a mechanist or a materialist, one 
may hold the opinion that Hfe is a continuation of the evolu- 
tionary process rather than an exception to the rest of the 
cosmos, because both mechanism and materialism are words 
borrowed from other sources which do not in the least con- 
vey the impression which the activities of the cosmos make 
upon us. This impression is that of limitless and ordered 
energy. 

Our second great question relates to the exact significance 
of the term evolutioii when applied to lifeless and to living 
matter. Is the development of life evolutionary in the same 
sense or is it essentially different from that of the inorganic 
world? Let us critically examine this question by comparing 
the evolution of life with what is known of the evolution of 
the stars, of the formation of the earth; in brief, of the com- 
parative anatomy and physiology of the universe as developed 
by the physicist Rutherford,' by the astronomer Campbell,- 
and by the geologist Chamberlin.'^ Or we may compare the 
evolution of life to the possible evolution of the chemical ele- 
ments themselves from simpler forms, in passing from primitive 
nebuliE through the hotter stars to the planets, as first pointed 
out by Clarke* in 1873, ^^^ by Lockyer in 1874. 

In such comparisons do we find a correspondence between 
the orderly development of the stars and the orderly develop- 
ment of life? Do we observe in life a continuation of processes 
which in general present a picture of the universe slowly cool- 
ing off and running down? Or, after hundreds of millions of 
years of more or less monotonous repetition of purely physico- 
chemical and mechanical reaction, do we find that electrons, 

1 Rutherford, Sir Ernest, 1915. = Campbell, William Wallace, 1915. 

sChamberlin, Thomas Chrowder, 1916. ^ Clarke, F. W., 1873, P- 323- 


4 THE ORIGIN AND EVOLUTION OF LIFE 

atoms, and molecules break forth into new forms and mani- 
festations of energy which appear to be "creative," convey- 
ing to our eyes at least the impression of incessant genesis of 
new combinations of energy, of matter, of form, of function, 
of character? 

To our senses it appears as if the latter view were the cor- 
rect one, as if something new is breathed into the aging dust, 
as if the first appearance of life on this planet marks an actual 
reversal of the previous order of things. Certainly the cosmic 
processes cease to run down and begin to build up, abandoning 
old forms and constructing new ones. Through these activities 
within matter in the living state the dying earth, itself a mere 
cinder from the sun, develops new chemical compounds; the 
chemical elements of the ocean are enriched from new sources 
of supply, as additional amounts of chemical compounds, pro- 
duced by organisms from the soil or by elements in the earth 
that were not previously dissolved, are liberated by life proc- 
esses and ultimately carried out to sea; the very composition 
of the rocks is changed; a new life crust begins to cover the 
earth and to spread over the bottom of the sea. Our old in- 
organic planet is reorganized, and we see in living matter a 
reversal of the melancholy conclusion reached by CampbelP 
that ''Everything in nature is growing older and changing in 
condition; slowly or rapidly, depending upon circumstances; 
the meteorological elements and gravitation are tearing down 
the high places of the earth; the eroded materials are trans- 
ported to the bottoms of valleys, lakes, and seas; and these 
results beget further consecjuences." 

Thus it certainly appears, in answer to our second ques- 
tion, that living matter does not follow the old evolutionary or- 
der, but represents a new assemblage of energies and new types 

1 Campbell, William Wallace, 1915, p. 209. 


FOUR QUESTIONS REGARDING LIFE 5 

of action, reaction, and interaction — to use the terms of ther- 
modynamics — between those chemical elements which may be 
as old as the cosmos itself, unless they prove to represent an 
evolution from still simpler elements. 

Such evolution, we repeat with emphasis, is not like that 
of the chemical elements or of the stars; the evolutionary proc- 
ess now takes an entirely new and different direction. Al- 
though it may arise through combinations of pre-existing ener- 
gies, it is essentially constructive and apparently though not 
actually creative;^ it is continually giving birth to an infinite 
variety of new forms and functions which never appeared in 
the universe before. It is a continuous creation or creative 
evolution. Although this creative power is something new 
derived from the old, it presents the first of the numerous con- 
trasts between the living and the lifeless world. 

Our third great question, however, relates to the continua- 
tion of the same physicochemical laws in living as in lifeless 
matter, and puts the second question in another aspect. Is 
there a creation in the strict sense of the term, namely, that 
some new form of energy arises? No, so far as we observe, 
the process is still evolutionary ratlier than creative, because all 
the new characters and forms of life appear to arise out of new 
combinations of pre-existing matter. In other words, the old 
forms of energy transformations appear to be taking a new 
direction. 

I shall attempt to show that since in their simple forms 
living processes are known to be physicochemical and are 

1 Creation (L. creatio, crcarc, pp. crcaliis; akin to Gr. Kpalveiv, complete; Sanskrit, 
i/kar, make), in contradistinction to evolution, is the production of something new out 
of nothing, the act of producing both the material and the form of that which is made. 
Evolution is the production of something new out of the building-up and recombination 
of something which already exists. 


6 THE ORIGIN AND EVOLUTION OF LIFE 

more or less clearly interpretable in terms of action, reaction, 
and interaction, we are compelled to believe that complex forms 
will also prove to be interpretable in the same terms. None 
the less, if we affirm that the entire trend of our observation 
is in the direction of physicochemical explanations rather than 
of vitalism and vitalistic hypotheses, this is very far from 
affirming that the explanation of life is purely materialistic, 
or purely mechanistic, or that any of the present physico- 
chemical explanations are final or satisfying to our reason. 

Chemists and biological chemists have very much more to 
discover. May there not be in the assemblage of cosmic chem- 
ical elements necessary to life, which we shall distinguish as 
the "/i/c element s,^^ some knoivn element which thus far has 
not betrayed itself in chemical analysis ? This is not impossi- 
ble, because a known element like radium, for example, might 
well be wrapped up in living matter but remain as yet unde- 
tected, owing to its suffusion or presence in excessively small 
quantities or to its possession of properties that have escaped 
notice. Or, again, some unknown chemical element, to which 
the hypothetical term bion might be given, may lie awaiting 
discovery within this complex of known elements. Or an 
unknown source of energy may be active here. 

It is, however, far more probable from our present state of 
knowledge that unknown principles of action, reaction, and 
interaction between living forms await discovery; such prin- 
ciples are indeed adumbrated in the as yet partially explored 
activities of various chemical messengers in the bodies of 
plants and animals. 

We are now prepared for the fourth of our leading questions. 
If it be determined that the evolution of non-living matter 
follows certain physical laws, and that the living world con- 


FOUR QUESTIONS REGARDING LIFE 7 

forms to many if not to all of these laws, the final question 
which arises is: Does the living world also conform to law in 
its most important aspect, namely, that of fitness or adapta- 
tion, or does law emerge from chance? In other words, in 
the origin and evolution of living things, does nature make a 
departure from its previous orderly procedure and substitute 
chance for law? This is perhaps the very oldest biologic 
question that has entered the human mind, and it is one on 
which the widest difference of opinion exists even to-day. 

Let us first make clear what we mean by the distinction 
between law and chance. 

Astronomers have described the orderly development of 
the stars, and geologists the orderly development of the earth: 
is there also an orderly development of life? Are life forms, 
like celestial forms, the result of law or are they the result of 
chance ? 

That life forms have reached their present stage through 
the operations of chance has been the opinion held by a great 
line of natural philosophers from Democritus and Empedocles 
to Darwin, and including Poulton, de Vries, Bateson, Morgan, 
Loeb, and many others of our own day. 

Chance is the very essence of the original Darwinian selec- 
tion hypothesis of evolution. William James^ and many other 
eminent philosophers have adopted the "chance" view as if 
it had been actually demonstrated. Thus James observes: 
"Absolutely impersonal reasons would be in duty bound to 
show more general convincingness. Causation is indeed too 
obscure a principle to bear the weight of the whole structure 
of theology. As for the argument from design, see how Dar- 
winian ideas have revolutionized it. Conceived as we now 
conceive them, as so many fortunate escapes from almost lim- 

' James, William, 1902, pp. 437-439. 


8 THE ORIGIN AND EVOLUTION OF LIFE 

itless processes of destruction, the benevolent adaptations 
which we find in nature suggest a deity very different from the 
one who figured in the earher versions of the argument. The 
fact is that these arguments do but follow the combined sug- 
gestions of the facts and of our feeling. They prove nothing 
rigorously. They only corroborate our pre-existent partiali- 
ties." Again, to quote the opinion of a recent biological writer: 
"And why not? Nature has always preferred to work by the 
hit-or-miss methods of chance. In biological evolution mil- 
lions of variations have been produced that one useful one 
might occur." ^ 

I have long maintained that this opinion is a biological 
dogma;- it is one of the string of hypotheses upon which Dar- 
win hung his theory of the origin of adaptations and of species, 
a hypothesis which has gained credence through constant re- 
iteration, for I do not know that it has ever been demon- 
strated through the actual observation of any evolutionary 
series. 

That life forms have arisen through law has been the opinion 
of another school of natural philosophers, headed by Aristotle, 
the opponent of Democritus and Empedocles. This opinion 
has fewer scientific and philosophical adherents; yet Eucken,'^ 
following Schopenhauer, has recently expressed it as follows: 
"From the very beginning the predominant philosophical ten- 
dency has been against the idea that all the forms we see around 
us have come into existence solely through an accumulation of 
accidental individual variations, by the mere blind concurrence 
of these variations and their actual survival, without the op- 

* Davies, G. R., 1916, p. 583. 

2 Biology, like theology, has its dogmas. Leaders have their disciples and blind fol- 
lowers. All great truths, like Darwin's law of selection, acquire a momentum which 
sustains half-truths and pure dogmas. 

3 Eucken, Rudolf, 1912, p. 257. 


FOUR QUESTIONS REGARDING LIFE 9 

eration of any inner law. Natural science, too, has more and 
more demonstrated its inadequacy." 

A modern chemist also questions the probability of the en- 
vironmental fitness of the earth for life being a mere chance 
process, for Henderson remarks: "There is, in truth, not one 
chance in countless millions of millions that the many unique 
properties of carbon, hydrogen, and oxygen, and especially of 
their stable compounds, water and carbonic acid, which chiefly 
make up the atmosphere of a new planet, should simultaneously 
occur in the three elements otherwise than through the opera- 
tion of a natural law which somehow connects them together. 
There is no greater probability that these uniciue properties 
should be without due cause uniquely favorable to the organic 
mechanism. These are no mere accidents; an explanation is 
to seek. It must be admitted, however, that no explanation 
is at hand."^ 

Unlike our first question as to whether the principle of life 
introduced something new in the cosmos, a cjuestion which is 
still in the stage of pure speculation, this fourth question of 
law versus chance in the evolution of life is no longer a matter 
of opinion, but of direct observation. So far as law is con- 
cerned, we observe that the evolution of life forms is like that 
of the stars: their origin and evolution as revealed through 
palaeontology go to prove that Aristotle was essentially right 
when he said that "Nature produces those things which, being 
continually moved by a certain principle contained in them- 
selves, arrive at a certain end."- What this internal moving 
principle is remains to be discovered. We may first exclude 
the possibility that it acts either through supernatural or teleo- 
logic interposition through an externally creative power. Al- 
though its visible results are in a high degree purposeful, we 

1 Henderson, Lawrence J., 1913, p. 276. - Osborn, H. F., 1894, p. 56. 


lo THE ORIGIN AND EVOLUTION OF LIFE 

may also exclude as unscientific the vitalistic theory of an 
entelechy or any other form of internal perfecting agency dis- 
tinct from known or unknown physicochemical energies. 

Since certain forms of adaptation which were formerly 
mysterious can now be explained without the assumption of 
an entelechy we are encouraged to hope that all forms may 
be thus explained. The fact that the causes underlying the 
origin of many forms of adaptation are still unknown, uncon- 
ceived, and perhaps inconceivable, does not inhibit our opinion 
that adaptation will prove to be a continuation of the previous 
cosmic order rather than the introduction of a new order of 
things. If, however, we reject the vitalistic hypotheses of the 
ancient Greeks, and the modern vitalism of Driesch, of Bergson, 
and of others, we are driven back to the necessity of further 
experiment, observation, and research, guided by the imagina- 
tion and checked by verification. As indicated in our Pref- 
ace, the old paths of research have led nowhere, and the 
question arises: What lines shall new researches and experi- 
ments follow? 

The Energy Concept of Life 

While we owe to matter and form the revelation of the 
existence of the great law of evolution, we must reverse our 
thought in the search for causes and take steps toward an 
energy conception of the origin of life and an energy conception 
of the nature of heredity. 

So far as the creative power of energy is concerned, we 
are on sure ground: in physics energy controls matter and 
form; in physiology function controls the organ; in animal 
mechanics motion controls and, in a sense, creates the form of 
muscles and bones. In every instance some kind of energy 


THE ENERGY CONCEPT OF LIFE ii 

or work precedes some kind of form, rendering it probable 
that energy also precedes and controls the evolution of life. 

The total disparity between invisible energy and visible 
form is the second point which strikes us as in favor of such 
a conception, because the most phenomenal thing about the 
heredity-germ is its microscopic size as contrasted with the 
titanic beings which may rise out of it. The electric energy 
transmitted through a small copper wire is yet capable of mov- 
ing a long and heavy train of cars. The discovery by Bec- 
c^uerel and Curie of radiant energy and of the properties of 
radium helps us in the same way to understand an energy 
conception of the heredity-germ, for in radium the energy 
per unit of mass is enormously greater than the energy quanta 
which we were accustomed to associate with units of mass; 
whereas, in most man-made machines with metallic wheels 
and levers, and in certain parts of the animal machine con- 
structed of muscle and bone, the work done is proportionate 
to the size and form. The slow dissipation or degradation of 
energy in radium has been shown by Curie to be concomitant 
with the giving off of an enormous amount of heat, while 
Rutherford and Strutt declare that in a very minute amount 
of active radium the energy of degradation would entirely 
dominate and mask all other cosmic modes of transformation 
of energy; for example, it far outweighs that arising from the 
gravitational energy which is an ample supply for our cosmic 
system, the explanation being that the minutest energy ele- 
ments of which radium is composed are moving at incredible 
velocities, approaching often the velocity of light, /. c., 180,000 
miles per second. The energy of radium differs from the 
supposed energy of life in being constantly dissipated and de- 
graded; its apparently unlimited power is being lost and scat- 
tered. 


12 


THE ORIGIN AND EVOLUTION OF LIFE 


We may imagine that the energy which Hes in the Hfe-germ 
of heredity is very great per unit of mass of the matter which 
contains it, but that the Kfe-germ energy, unhke that of radium, 
is in process of accumulation, construction, conservation, rather 
than of dissipation and destruction. 

Following the time (1620) when Francis Bacon divined that 
heat consists of a kind of motion or brisk agitation of the par- 
ticles of matter, it has step by step been demonstrated that 
the energy of heat, of light, of electricity, the electric energy 
of chemical configurations, the energy of gravitation, are all 
utilized in living as well as in lifeless substances. Moreover, 
as remarked above (p. 5), no form of energy has thus far 
been discovered in living substances which is peculiar to them 
and not derived from the inorganic world. In a broad sense 
all these manifestations of energy are subject to Newton's dy- 
namical laws^ which were formulated in connection with the 
motions of the heavenly bodies, but are found to apply equally 
to all motions great or little. 

These three fundamental laws are as follows:- 


Corpus omne perseverare in statu 
suo quiescendi vel movendi uni- 
formiter in directum, nisi quatenus 
illud a viribus impressis cogitur 
statum suum mutare. 


Every body perseveres in its 
state of rest, or of uniform motion 
in a right line, unless it is compelled 
to change that state by forces im- 
pressed thereon. 


^ I am indebted to my colleague M. I. Pupin for valuable suggestions in formulating 
the physical aspect of the principles of action and reaction. He interprets Newton's 
third law of motion as the foundation not only of modern dynamics in the Newtonian 
sense but in the most general sense, including biological phenomena. With regard to the 
first law of thermodynamics, it is a particular form of the principle of conservation of en- 
ergy as applied to heat energy; Helmholtz, who first stated the principle of conservation 
of energy, derived it from Newtonian dynamics. The second law of thermodynamics 
started from a new principle, that of Carnot, which apparently had no direct connection 
with Newton's third law of motion; this second law, however, in its most general form 
cannot be fully interpreted except by statistical dynamics, which are a modern offshoot 
of Newtonian dynamics. 

-Newton's three laws of motion, first published in Newton's Principia in 1687. 


THE ENERGY CONCEPT OF LIFE 
II II 


13 


Mutationem motus proportio- 
nalem esse vi motrici impressae, et 
fieri secundum lineam rectam qua 
vis ilia imprimitur. 


Ill 

Actioni contrariam semper et 
aequalem esse reactionem: sive cor- 
porum duorum actiones in se mutuo 
semper esse asquales et in partes 
contrarias dirigi. 


The alteration of motion is ever 
proportional to the motive force 
impressed; and is made in the direc- 
tion of the right line in which that 
force is impressed. 

Ill 

To every action there is always 
opposed an equal reaction: or the 
mutual actions of two bodies upon 
each other are always equal, and 
directed to contrary parts. 


Newton's third law of the equahty of action and reaction is 
the foundation of the modern doctrine of energy,^ not only in 
the Newtonian sense but in the most general sense.- Newton 
divined the principle of the conservation of energy in mechanics; 
Rumford (1798) maintained the universality of the laws of 
energy; Joule (1843) established the particular principle of the 
conservation of energy, namely of the exact equivalence be- 
tween the amount of heat produced and the amount of mechan- 
ical energy destroyed; and Helmholtz in his great memoir 
Uher die Erlialtiing dcr Kraft extended this system of conser- 
vation of energy throughout the whole range of natural phe- 
nomena. A familiar instance of the so-called transformation of 
energy is where the sudden arrest of a cool but rapidly moving 
body produces heat. This was developed as the first law of 
thermodynam ics. 

At the same time there arose the distinction between po- 
tential energy, which is stored away in some latent form or 
manner so that it can be drawn upon for work — such energy 

> The lerm Energy (Gr. svspYsta; sv in; epyov, work) in physical science denotes an 
accumulated capacity for doing mechanical work, and may be either kinetic (energy of 
heat or motion) or potential (latent or stored energy). 
- M. I. Pupin, see note above. 


14 THE ORIGIN AND EVOLUTION OF LIFE 

being exemplified mechanically by the bent spring, chemi- 
cally by gunpowder, and electrically by a Leyden jar — and 
kinetic energy, the active energy of motion and of heat. 

While all active mechanical energy or work may be con- 
verted into an equivalent amount of heat, the opposite process 
of turning heat into work involves more or less loss, dissipa- 
tion, or degradation of energy. This is known as the second 
law of thermodynamics and is the outgrowth of a principle dis- 
covered by Sadi Carnot (1824), and developed by Kelvin (1852, 
1853). The far-reaching conception of cyclic processes in en- 
ergy enunciated in Kelvin's principle of the dissipation of 
available energy puts a diminishing limit upon the amount of 
heat energy available for mechanical purposes. The available 
kinetic energy of motion and of heat which we can turn into 
work or mechanical effect is possessed by any system of two 
or more bodies in virtue of the relative rates of motion of their 
parts, velocity being essentially relative. 

These two great dynamical principles that the energy of 
motion can be converted into an equivalent amount of heat, 
and that a certain amount of heat can be converted into a 
more limited amount of power were discovered through obser- 
vations on the motions of larger masses of matter, but they 
are believed to apply equally to such motions as are involved 
in the smallest electrically charged atoms (ions) of the chem- 
ical elements and the particles flying off in radiant energy as 
phosphorescence. Such movements of infinitesimal particles 
underlie all the physicochemical laws of action and reaction 
which have been observed to occur within living things. In 
all physicochemical processes within and without the organism 
by which energy is captured, stored, transformed, or released 
the actions and reactions are equal, as expressed in Newton's 
third law. 


THE ENERGY CONCEPT OF LIFE 15 

Actions and reactions refer chiefly to what is going on be- 
tween the parts of the organism in chemical or physical con- 
tact, and are subject to the two dynamical principles referred 
to above. Interactions, on the other hand, refer to what is 
going on between material parts which are connected with 
each other by other parts, and cannot be analyzed at all by the 
two great dynamical principles alone without a knowledge of 
the structure which connects the interacting parts. For ex- 
ample, in interaction between distant bodies the cause may be 
very feeble, yet the potential or stored energy which may be 
liberated at a distant point may be tremendous. Action and 
reaction are chiefly simultaneous, whereas interaction connects 
actions and reactions which are not simultaneous; to use a 
simple illustration: when one pulls at the reins the horse feels 
it a little later than the moment at which the reins are pulled 
— there is interaction between the hand and the horse's mouth, 
the reins being the interacting part. An interacting nerve- 
impulse starting from a microscopic cell in the brain may give 
rise to a powerful muscular action and reaction at some distant 
point. An interacting enzyme, hormone, or other chemical 
messenger circulating in the blood may profoundly modify the 
growth of a great organism. 

Out of these physicochemical principles has arisen the con- 
ception of a living organism as composed of an incessant series 
of actions and reactions operating under the dynamical laws 
which govern the transfer and transformation of energy. 

The central theory which is developed in our speculation 
on the Origin of Life is that every physicochemical action and 
reaction concerned in the transformation, conservation, and 
dissipation of energy, produces also, either as a direct result or 
as a by-product, a physicochemical agent of interaction which 
permeates and afects the organism as a whole or afects only some 


i6 


THE ORIGIN AND EVOLUTION OF LIFE 


special part. Through such interaction the organism is made 
a unit and acts as one, because the activities of all its parts 
are correlated. This idea may be expressed in the follov\dng 
simplified scheme of the functions or physiology of the organism; 


ACTION ] 

AND \ 

REACTION J 

Functions of the 

Capture, Storage, 

and Release of 

Energy. 


INTERACTION 


Functions of the 

Coordination, Balance, 

Cooperation, Compensation, 

Acceleration, Retardation, 

of Actions and Reactions. 


ACTION 
AND 
[ REACTION 

Functions of the 

Capture, Storage, 

and Release of 

Energy. 


Since it is known that many actions and reactions of the 
organism — such as those of general and localized growth, of 
nutrition, of respiration — are coordinated with other actions 
and reactions through interaction, it is but a step to extend 
the principle and suppose that all actions and reactions are sim- 
ilarly coordinated; and that while there was an evolution of 
action and reaction there was also a corresponding evolution 
of interaction, for without this the organism would not evolve 
harmoniously. 

Evidence for such universality of the interaction principle 
has been accumulating rapidly of late, especially in experi- 
mental medicine^ and in experimental biology.- It is a further 
step in our theory to suppose that the directing power of he' 
redlty which regulates the initial and all the subsequent steps 
of development in action and reaction, gives the orders, hastens 
development at one point, retards it at another, is an elab- 
oration of the principle of interaction. In lowly organisms 


* See the works of Gushing and Crile cited below. 
- See the recent experiments of Morgan and Goodale. 


THE ENERGY CONCEPT OF LIFE 17 

like the monads these interactions are very simple; in higher 
organisms like man these interactions are elaborated through 
physicochemical and other agents, some of which have already 
been discovered although doubtless many more await discovery. 
Thus we conceive of the origin and development of the or- 
ganism as a concomitant evolution of the action, reaction, and 
interaction of energy. Actions and reactions are borrowed 
from the inorganic world, and elaborated through the produc- 
tion of the new organic chemical compounds; it is the peculiar 
evolution and elaboration of the physical principle of inter- 
action which distinguishes the living organism. 

Thus the evolution of life may be rewritten in terms of in- 
visible energy, as it has long since been written in terms of 
visible form. All visible tissues, organs, and structures are 
seen to be the more or less simple or elaborate agents of the 
different modes of energy. One after another special groups of 
tissues and organs are created and coordinated — organs for the 
capture of energy from the inorganic environment and from the 
life environment, organs for the storage of energy, organs for 
the transformation of energy from the potential state into the 
states of motion and heat. Other agents of control are evolved 
to bring about a harmonious balance between the various or- 
gans and tissues in which energy is released, hastened or ac- 
celerated, slowed down or retarded, or actually arrested or 
inhibited. 

In the simplest organisms energy may be captured while the 
organism as a whole is in a state of rest; but at an early stage of 
life special organs of locomotion are evolved by which energy is 
sought out, and organs of prehension by which it may be seized. 
Along with these motor organs are developed organs of ojfense 
and defense of many kinds, by means of which stored energy is 


i8 THE ORIGIN AND EVOLUTION OF LIFE 

protected from capture or invasion by other organisms. Finally, 
there is the most mysterious and comprehensive process of all, 
by which aU these manifold modes of energy are reproduced in 
another organism. The evolution of these complex modes of 
action, reaction, and interaction is traced through all the early 
chapters of this volume and is summed up in Chapter V (p. 
152) as a physicochemical introduction to the evolution of ver- 
tebrate form. 

The Four Coivjplexes of Energy 

The theoretic evolution of the four complexes is somewhat 
as follows: 

(i) In the order of time the Inorganic Environment comes 
first; energy and matter are first seen in the sun, in the earth, 
in the air, and in the water — each a very wonderful complex 
of energies in itself. They form, nevertheless, an entirely 
orderly system, held together by gravitation, moving under 
Newton's laws of motion, subject to the more newly discovered 
laws of thermodynamics. In this complex we observe actions 
and reactions, the sum of the taking in and the giving out of 
energy, the conservation of energy. We also observe inter- 
actions wherein the energy released at certain points may be 
greater than the energy received, which is merely a stimulus for 
the beginning of the local energy transformations. This energy 
is distributed among the eighty or more chemical elements of 
the sun and other stars. These elements are combined in plants 
into complex substances, generally with a storage of energy. 
Such substances are disintegrated into simple substances in ani- 
mals, generally with a release of energy. All these processes 
are termed by us physicochemical. 


THE FOUR COMPLEXES OF ENERGY 19 

(2) With life something new appears in the universe, 
namely, a union of the internal and external adjustment of 
energy which we appropriately call an Organism. In the course 
of the evolution of life every law and property in the physico- 
chemical world is turned to advantage; every chemical ele- 
ment is assembled in which inorganic properties may serve 
organic functions. There is an immediate or gradual separa- 
tion of the organism into two complexes of energy, namely, 
first, the energy complex of the organism, which is perishable 
with the term of the life of the individual, and second, the germ 
or heredity substance, which is perpetual. 

(3) The idea that the germ is an energy complex is an as 
yet unproved hypothesis; it has not been demonstrated. The 
Heredity-germ in some respects bears a likeness to latent or 
potential interacting energy, while in other respects it is en- 
tirely unique. The supposed germ energy is not only cumula- 
tive but is in a sense imperishable, self-perpetuating, and con- 
tinuous during the whole period of the evolution of life upon 
the earth, a conception which we owe chiefly to the law of the 
continuity of the germ-plasm formulated by Weismann. Some 
of the observed phenomena of the germ in Heredity are chiefly 
analogous to those of interaction in the Organism, namely, 
directive of a series of actions and reactions, but in general we 
know no complete physical or inorganic analogy to the phe- 
nomena of heredity; they are unique in nature. 

(4) With the multiplication and diversification of individual 
organisms there enters a new factor in the environment, namely, 
the energy complex of the Life Environment. 

Thus there are combined certainly three, and possibly four, 
complexes of energy, of which each has its own actions, reac- 
tions, and interactions. The evolution of life proceeds by sus- 


20 THE ORIGIN AND EVOLUTION OF LIFE 

taining these actions, reactions, and interactions and con- 
stantly building up new ones : at the same time the potentiality 
of reproducing these actions, reactions, and interactions in the 
course of the development of each new organism is gradually 
being accumulated and perpetuated in the germ. 

From the very beginning every individual organism is 
competing with other organisms of its own kind and of other 
kinds, and the law of the survival of the fittest is operating 
between the forms and functions of organisms as a whole and 
between their separate actions, reactions, and interactions. 
This, as Weismann pointed out, while apparently a selection 
of the individual organism itself, is actually a selection of the 
heredity-germ complex, of its potentialities, powers, and pre- 
dispositions. Thus Selection is not a form of energy nor a part 
of the energy complex; it is an arbiter between different com- 
plexes and forms of energy; it antedates the origin of life just 
as adaptation or fitness antedates the origin of life, as re- 
marked by Henderson. 

Thus we arrive at a conception of the relations of organisms 
to each other and to their environment as of an enormous and 
always increasing complexity, sustained through the interchange 
of energy. Darwin's principle of the survival or elimination 
of various forms of living energy is, in fact, adumbrated in the 
survival or elimination of various forms of lifeless energy as 
witnessed among the stars and planets. In other words, Dar- 
win's principle operates as one of the causes of evolution in mak- 
ing the lifeless and living worlds what they now appear to be, 
but not as one of the energies of evolution. Selection merely 
determines which one of a combination of energies shall survive 
and which shall perish. 

The complex of four interrelated sets of physicochemical 
energies which I have previously set forth (p. xvi) as the most 


THE FOUR COMPLEXES OF ENERGY 21 

fundamental biologic scheme or principle of development may 
now be restated as follows: 

In each organism the phenomena of life represent the action, 
reaction, and interaction of Jour complexes of physicochemical 
energy, namely, those of (i) the Inorganic Environment, (2) the 
developing Organism {protoplasm and body-chromatin), (3) the 
germ or Ileredity-chromatin, (4) the Life Environment. Upon 
the resultant actions, reactions, and interactions of potential and 
kinetic energy in each organism Selection is constantly operating 
wherever there is competition witJi the corresponding actions, re- 
actions, and interactions of other organisms.'^ 

This principle I shall put forth in different aspects as the 
central thought of these lectures, stating at the outset and 
often recurring to the admission that it involves several unknown 
principles and especially the largely hypothetical question 
whether there is a relation between the action, reaction, and 
interaction of the internal energies of the germ or heredity- 
chromatin with the external energies of the inorganic environ- 
ment, of the developing organism, and of its life environment. 
In other words, while this is a principle which largely governs 
the Organism, it remains to be discovered whether it also 
governs the causes of the Evolution of the Germ. 

As observed in the Preface (p. xvii) we are studying not one 
but four simultaneous evolutions. Each of these evolutions 
appears to be almost infinite in itself as soon as we examine 
it in detail, but of the four that of the germ or heredity- 
chromatin so far surpasses all the others in complexity that it 
appears to us infinite. 

The physicochemical relations between these four evolu- 
tions, including the activities of the single and of the multiply- 
ing organisms of the Life Environment, may be expressed in 

' Compare Osborn, H. F., 191 7, p. 8. 


22 


THE ORIGIN AND EVOLUTION OF LIFE 


diagrammatic form, and somewhat more technically than in the 
Preface, as follows: 


Organism A 
Under 

Newton's Laws of Motion 

and 
Modern Thermodynamics 

Actions, Reactions, and 

Interactions 

of the 

1. Inorganic Environment: 

physicochemical en- 
ergies of space, of 
the sun, earth, air, 
and water. 

2. Organism: 

physicochemical en- 
ergies of the devel- 
oping individual in 
the tissues, cells, 
protoplasm, and 
cell-chromatin. 

3. Heredity-Germ: 

physicochemical en- 
ergies of the hered- 
ity-chromatin, in- 
cluded in the re- 
productive cells 
and tissues. 

4. Life Environment: 

physicochemical en- 
ergies of other or- 
ganisms. 


Under 

Danvins Laiv 

of 

Natural Selection 

Survival of the 
fittest: com- 
petition, selec- 
tion, and elim- 
ination of the 
energies and 
forms. 


Organisms B-Z 
Under 

Newton s Laws of Motion 

and 
Modern Thermodynamics 

Actions, Reactions, and 

Interactions 

of the 

I. Inorganic Environment: 

physicochemical en- 
ergies of space, of 
the sun, earth, air, 
and water. 

;. Organism: 

physicochemical en- 
ergies of the devel- 
oping individual in 
the tissues, cells, 
protoplasm, and 
cell-chromatin. 

,. Heredity-Germ: 

physicochemical en- 
ergies of the hered- 
ity-chromatin in- 
cluded in the re- 
productive cells 
and tissues. 

4. Life Environment : 

physicochemical en- 
ergies of other or- 
ganisms. 


If a single name is demanded for this conception of evolu- 
tion it might be termed the tetrakinetic theory in reference to 


THE FOUR COMPLEXES OF ENERGY 23 

the four sets of internal and external energies which play upon 
and within every individual and every race. In respect to 
form it is a tctraplastic^ theory in the sense that every living 
plant and animal form is plastically moulded by four sets of 
energies. The derivation of this conception of life and of the 
possible causes of evolution from the laws which have been 
developed out of the Newtonian system, and from those of the 
other great Cambridge philosopher, Charles Darwin, are clearly 
shown in the above diagram. 

In these lectures we shall consider in order, first, the evo- 
lution of the inorganic environment necessary to life; second, 
theories of the origin of life in regard to the time when it oc- 
curred and the accumulation of various kinds of energy through 
which it probably originated; and, third, the orderly develop- 
ment of the differentiation and adaptation of the most primi- 
tive forms. Throughout we shall point out some of the more 
notable examples of the apparent operation of our fundamental 
biologic principle of the action, reaction, and interaction be- 
tween the inorganic environment, the organism, the germ, and 
the life environment. 

The apparently insuperable difficulties of the problem of 
the causes of evolution in the germ or heredity-chromatin — 
causes which are at present almost entirely beyond the realm 
of observation and experiment — will be made more evident 
through the development of the second part of our subject, 
namely, the evolution of the higher living forms of energy 
upon the earth so far as they have been followed from the 
stage of monads or bacteria up to that of the higher mammals. 

^ Osborn, H. F., 1912.2. 


PART I. THE ADAPTATION OF ENERGY 

CHAPTER I 
PREPARATION OF THE EARTH FOR LIFE 

Primordial environment — the lifeless earth. Age of the earth and beginning 
of the life period. Primordial environment — the lifeless water. Salt as 
a measure of the age of the ocean. Primordial chemical environment. 
Primordial environment — the atmosphere. 

In the spirit of the preparatory work of the great pioneers 
of geology, such as Hutton, Scrope, and Lyell, and of the his- 
tory of the evolution of the working mechanism of organic 
evolution, as developed by Darwin and Wallace,^ our infer- 
ences as to past processes are founded upon the observation 
of present processes. In general, our narrative will therefore 
follow the "uniformitarian" method of interpretation first 
presented in 1788 by Hutton,- who may be termed the Newton 
of geology, and elaborated in 1830 by Lyell,'' the master of 
Charles Darwin. The uniformitarian doctrine is this: present 
continuity implies the improbability of past catastrophism and 
violence of change, either in the lifeless or in the living world; 
moreover, we seek to interpret the changes and laws of past 
time through those which we observe at the present time. 
This was Darwin's secret, learned from Lyell. 

Cosmic Primordial Environment — The Lifeless Earth 

Let us first look at the cosmic environment, the inorganic 
world before the entrance of life. Since 1825, when Cuvier"* 

1 Judd, John W., igio. -Hutton, James, 1795. 

^ Lyell, Charles, 1830. * Cuvier, Baron Georges L. C. F. D., 1825. 

24 


THE LIFELESS EARTH 25 

published his famous Discours sur Ics Revolutions de la Surface 
du Globe, the past history of the earth, of its waters, of the 
atmosphere, and of the sun — the four great complexes of in- 
organic environment — has been written with some approach to 
precision. Astronomy, physics, chemistry, geology, and pa- 
laeontology have each pursued their respective lines of obser- 
vation, resulting in some concordance and much discordance 
of opinion and theory. In general we shall find that opinion 
founded upon life data has not agreed with opinion founded 
upon physical or chemical data, arousing discord, especially in 
connection with the problems of the age of the earth and the 
stability of the earth's surface. 

In our review of these matters we may glance at opinions, 
whatever their source, but our narrative of the chemical origin 
and history of life on the earth will be followed by observations 
on living matter mainly as it is revealed in palaeontology and 
as it exists to-day, rather than on hypotheses and speculations 
upon pre-existing states. 

The formation of the earth's surface is a prelude to our 
considering the first stage of the environment of life. Accord- 
ing to the planetesimal theory, as set forth by Chamberlin,^ the 
earth, instead of consisting of a primitive molten globe as pos- 
tulated by the old nebular hypothesis of Laplace, originated in 
a nebulous knot of solid matter as a nucleus of growth which 
was fed by the infall or accretion of scattered nebulous matter 
(planetesimals) coming within the sphere of control of this 
knot. The temperature of these accretions to the early earth 
could scarcely have been high, and the mode of addition of 
these planetesimals one by one explains the very heterogeneous 
matter and differentiated specific gravity of the continents and 
oceanic basins. The present form of the earth's surface is the 

' Chamberlin, Thomas Chrowder, igi6. 


26 THE ORIGIN AND EVOLUTION OF LIFE 

result of the combined action of the hthosphere (the rocks), 
hydrosphere (the water), and atmosphere (the air). Liquefac- 
tion of the rocks occurred locally and occasionally as the result 
of heat generated by increased pressure and by radioactivity; 
but the planetesimal hypothesis assumes that the present 
elastic rigid condition of the earth prevailed — at least in its 
outer half — throughout the history of its growth from the small 
original nebular knot to its present proportions and caused the 
permanence of its continents and of its oceanic basins. We 
are thus brought to conditions that are fundamental to the 
evolution of life on the earth. According to the opinion of 
Chamberlin, cited by Pirsson and Schuchert,^ life on the earth 
may have been possible when it attained the present size of 
Mars. 

According to Becker,- who follows the traditional theory of 
a primitive molten globe, the earth first presented a nearly 
smooth, equipotential surface, determined not by its mineral 
composition, but by its density. As the surface cooled down 
a temperature was reached at which the waters of the gaseous 
envelope united with the superficial rocks and led to an aqueo- 
igneous state. After further cooling the second and final con- 
sohdation followed, dating the origin of the granites and grani- 
tary rocks. The areas which cooled most rapidly and best 
conducted heat formed shallow oceanic basins, whereas the 
areas of poor conductivity which cooled more slowly stood out 
as low continents. The internal heat of the cooling globe still 
continues to do its work, and the cyclic history of its surface 
is completed by the erosion of rocks, by the accumulation of 
sediments, and by the following subsidence of the areas loaded 

' Pirsson, Louis V., and Schuchert, Charles, 1915, p. 535- 
- George F. Becker, letter of October 15, 1915. 


THE LIFELESS EARTH 27 

down by these sediments. It appears that the internal heat 
engine is far more active in the slowly cooling continental areas 
than in the rapidly cooling areas underlying the oceans, as 
manifested in the continuous outflows of igneous rocks, which, 
especially in the early history of the earth — at or before the 
time when life appeared — covered the greater part of the earth's 
surface. The ocean beds, being less subject to the work of the 
internal heat engine, have always been relatively plane; except 
near the shores, no erosion has taken place. 

The Age of the Earth and Beginning of the Life Period 

The age of the earth as a solid body affords our first in- 
stance of the very wide discordance between physical and 
biological opinion. Among the chief physical computations 
are those of Lord Kelvin, Sir George Darwin, Clarence King, 
and Carl Barus.^ In 1879 Sir George Darwin allowed 56,000,- 
000 years as a probable lapse of time since the earth parted 
company with the moon, and this birthtime of the moon was 
naturally long prior to that stage when the earth, as a cool, 
crusted body, became the environment of living matter. Far 
more elastic than this estimate was that of Kelvin, who, in 
1862, placed the age of the earth as a cooling body between 
20,000,000 and 400,000,000 years, with a probability of 98,000,- 
000 years. Later, in 1897, accepting the conclusions of King 
and Barus calculated from data for the period of tidal stability, 
Kelvin placed the age limit between 20,000,000 and 40,000,000 
years, a conclusion very unwelcome to evolutionists. 

As early as 1859 Charles Darwin led the biologists in de- 
manding an enormous period of time for the processes of evo- 

' Becker, George F., 1910, p. 5. 


28 THE ORIGIN AND EVOLUTION OF LIFE 

lution, being the first to point out that the high degree of evo- 
lution and speciaHzation seen in the invertebrate fossils at the 
very base of the Palaeozoic was in itself a proof that pre-Palaeo- 
zoic evolution occupied a period as long as or even longer than 
the post-Palseozoic. In 1869 Huxley renewed this demand for 
an enormous stretch of pre-Palaeozoic or pre-Cambrian time; 
and as recently as 1896 Poulton^ found that 400,000,000 years, 
the greater limit of Kelvin's original estimate, was none too 
much. 

Later physical computations greatly exceeded this biological 
demand, for in 1908 Rutherford- estimated the time required 
for the accumulation of the radium content of a uranium min- 
eral found in the Glastonbury granitic gneiss of the Early 
Cambrian as no less than 500,000,000 years. This physical 
estimate of the age of the Early Cambrian is eighteen times as 
great as that attained by Walcott'' in 1893 from his purely 
geologic computation of the time rates of deposition and max- 
imum thickness of strata from the base of the Cambrian up- 
ward; but recent advances in our knowledge of the radioactive 
elements preclude the possibility of any trustworthy deter- 
mination of the age of the elements through the methods sug- 
gested by Joly and Rutherford. 

We thus return to the estimates based upon the time 
required for the deposition of sediments as by far the most 
reliable, especially for our quest of the beginning of the life 
period, because erosion and sedimentation imply conditions of 
the earth, of the water, and of the atmosphere more or less 
comparable to those under which life is known to exist. These 
geologic estimates, which begin with that of John Phillips in 
i860, may be tabulated as follows: 

^ Poulton, Edward B., 1896, p. 808. - Rutherford, Sir Ernest, 1906, p. i8g. 

^ Walcott, Charles D., 1893, p. 675. 


THE LIFELESS EARTH 29 

Estimates of Time Required eor the Processes of Past Deposition and 

Sedimentation at Rates Similar to Those Observed at 

THE Present Day ' 


i860. John Phillips 38- 96 million years. 

1890. De Lapparent 67- 90 million years. 

1893. Walcolt 55- 70 million years. 

(27,640,000 years since the base of the Cam- 
brian Palaeozoic; 17,500,000 years or up- 
ward for the pre-Palaeozoic.) 

1899. Geikie 100-400 million years. 

(Minimum 100 million years; maximum — 
slowest known rates of deposition — 400 
million years.) 

1909. Sollas 34- 80 million years. 

(The larger estimate of 80 million years on the 
theory that pre-Pala?ozoic sediments took 
as much time as those from the base of 
the Cambrian upward, allowing for gaps 
in the stratigraphic column.) 


These estimates give a maximum of sixty-four miles as the 
total accumulation of sedimentary rocks, which is equivalent 
to a layer 2,300 feet thick over the entire face of the earth. '-^ 
From these purely geologic data the time ratio of the entire 
life period is now calculated in terms of millions of years, 
assuming the approximate reliability of the geologic time scale. 
The actual amount of rock weathered and deposited was prob- 
ably far greater than that which has been preserved. 

In general, these estimates are broadly concordant with 
those reached by an entirely different method, namely, the 
amount of sodium chloride (common salt) contained in the 
ocean,'' to understand which we must first take another glance 
at the geography and chemistry of the primordial earth. 

The lifeless primordial earth can best be imagined by look- 
ing at the lifeless surface of the moon, featured by volcanic 

' Becker, George F., 1910, pp. 2, 3, 5. 

^ Clarke, F. W., 1916, p. 30. 

^ See Salt as a Measure of the Age of the Ocean, p. 35. 


30 


THE ORIGIN AND EVOLUTION OF LIFE 


action with little erosion or sedimentation because of the lack 
of water. 

The surface of the earth, then, was chiefly spread with 
granitic masses known as batholiths and with the more super- 
ficial volcanic outpourings. There were volcanic ashes; there 


W - ^ y^ ..^.-- ."t^i^ -V---, '■•..*• -■^■^ 


>_ 


l''i(;. I. Tiiii Moon's SL:RrAcK. 

"The lifeless primordial earth can best be imagined by looking at the lifeless surface of 
the moon." A portion of the moon's surface, many miles in diameter, illuminated 
by the rising or setting sun and showing the craters and areas of lava outflow. The 
Meteor Crater of Arizona, formerly known as Coon Butte — a huge hole, 4,500 feet in 
diameter and 600 feet in depth, made by a falling meteorite — is strikingly similar to 
these lunar craters and suggests the possibility that, instead of being the result of 
volcanic action, the craters of the moon may have been formed by terrific impacts of 
meteoric masses. Photograph from the Mt. Wilson Observatory. 

were gravels, sands, and micas derived from the granites; there 
were clays from the dissolution of granitic feldspars; there were 
loam mixtures of clay and sand; there was gypsum from min- 
eral springs. 

Bare rocks and soils were inhospitable ingredients for any 
but the most rudimentary forms of life such as were adapted 
to feed directly upon the chemical elements and their simplest 


THE LIFELESS EARTH 


31 


compounds, or to transform their energy without the friendly 
aid of sunshine. The only forms of hfe to-day which can exist 
in such an inhospitable environment as that of the lifeless 
earth are certain of the simplest bacteria, which, as we shall 
see, feed directly upon the chemical elements. 

It is interesting to note that, in the period when the sun's 
light was partly shut off by watery and gaseous vapors, the 
early volcanic condition of the earth^s surface may have supplied 
life with fundamentally important chemical elements, as well 
as with the heat-energy of the waters or of the soils. Volcanic 
emanations contain^ free hydrogen, both oxides of carbon, and 
frequently hydrocarbons such as methane (CH4) and ammo- 
nium chloride: the last compound is often very abundant. 
Volcanic waters sometimes contain ammonium (NH4) salts, 
from which life may have derived its first nitrogen supply. 
For example, in the Devil's Inkpot, Yellowstone Park, ammo- 
nium sulphate forms ^^^ per cent of the dissolved saline matter: 
it is also the principal constituent of the mother liquor of the 
boric fumaroles of Tuscany, after the boric acid has crystallized 
out. A hot spring on the margin of Clear Lake, California, 
contains 107.76 grains per gallon of ammonium bicarbonate. 

There were absent from the primordial earth the greater 
part of the fine sediments and detrital material which now 
cover three-fourths of its surface, and from which a large part 
of the sodium content has been leached. The original surface 
of the earth was thus composed of granitic and other igneous 
rocks to the exclusion of all others,'- the essential constituents 
of these rocks being the lime-soda feldspars from which the 
sodium of the ocean has since been leached. Waters issuing 
from such rocks are, as a rule, relatively richer in silica than 

1 Clarke, F. W., 1916, chap. VIII., also pp. 197, 199, 243, 244. 
^Becker, George F., 1910, p. 12. 


THE ORIGIN AND EVOLUTION OF LIFE 


waters issuing from modern sedimentary areas. They thus 
furnish a favorable environment for the development of such 
low organisms (or their ancestors) as the existing diatoms, 
radiolarians, and sponges, which have skeletons composed of 

hydrated silica, mineralogi- 
cally of opal. 

The decomposition and 
therefore the erosion of the 
massive rocks was slower then 
than at present, for none of 
the life agencies of bacteria, 
of algae, of lichens, and of the 
higher plants, which are now 
at work on granites and vol- 
canic rocks in all the humid 
portions of the earth, had yet 
appeared. On the other hand, 
much larger areas of these 
rocks were exposed than at 
present. 

In brief, to imagine the 
primal lifeless earth we must 
subtract all those portions of 
mineral deposits which as they 
exist to-day are mainly of organic origin, such as the organic car- 
bonates and phosphates of lime,^ the carbonaceous shales as well 
as the carbonaceous limestones, the graphites derived from car- 
bon, the silicates derived from diatoms, the iron deposits made 

^ It seems improbable that organisms originally began to use carbon or phosphorus 
in elementary form: carbonates and phosphates were probably available at the very be- 
ginning and resulted from oxidations or decompositions. — VV. J. Gies. 

Phosphate of lime, apatite, is an almost ubiquitous component of igneous rocks, but 
in very small amount. In more than a thousand analyses of such rocks, the average 
percentage of P2O5 is 0.25 per cent. — F. W. Clarke. 


Fig. 2. Deep-Sea Ooze, the Forami- 

NIFERA. 

Photograph of a small portion of a cal- 
careous deposit on the sea bottom formed 
by the dropping down from the sea sur- 
face of the dead shells of foraminifera, 
chiefly Glohigerina, greatly magnified. 
Such calcareous deposits extend over 
large areas of the sea bottom. Repro- 
duced from The Depths of the Ocean, by 
Sir John Murray and Doctor Johan 
Hjort by permission of the Macmillan 
Company. 


THE LIFELESS EARTH 


33 


by bacteria, the humus of the soil containing organic acids, 
the soil derived from rocks which are broken up by bacteria, 
and even the ooze from the ocean floor, both calcareous and 


TABLE I 

Average Distribution of the Chemical Elements in Earth, Air, and 
Water at the Present Time ^ 

{Life Elements in Italics) 


The Rocks, 
Lithosphere, 
g3 per cent 


The Waters, 

Hydrosphere, 

7 per cent 


The Atmosphere 


Average, 

Including 

Atmosphere 


Oxygen 

Silicon 

Aluminum 


47-33 

27.74 

7.85 

4 5° 

3-47 

2. 24 

2 .46 

2.46 

. 22 

.46 

.19 

.06 

. 12 
. 12 
.08 
.08 
.02 

. 10 
•50 


85.79 

■05 

.14 

I. 14 

.04 

10.67 

.002 

2.07 
.008 

■ OQ 


20.8 

(variable to some 
extent) 

variable 
variable 


50.02 
25.80 

7 30 

4.18 
3.22 
2.08 
2.36 
2.28 

•95 
•43 
.18 
.20 

. II 
. II 

.08 
.08 
.02 


Iron 

Calcium 


Magnesium 


Sodium 


Potassium 

Hydrogen 

Titanium 


Carbon 

Chlorine 


Bromine 


Phosphorus 


Sulphur 

Barium 

Manganese 


Strontium 


Nitrogen 


78 1 .0? 1 


Fluorine 


(variable to some 
extent) 


. 10 

•47 


All other elements. . . . 


silicious, formed from the shells of foraminifera and the skele- 
tons of diatoms. Thus, before the appearance of bacteria, of 
algas, of foraminifera, and of the lower plants and lowly inver- 
tebrates, the surface of the earth was totally different from 

' Clarke, F. W., 1916, p. 34. 


34 THE ORIGIN AND EVOLUTION OF LIFE 

what it is at present; and thus the present chemical composi- 
tion of terrestrial matter, of the sea, and of the air, as indi- 
cated by Table I, is by no means the same as its primordial 
composition 80.000,000 years ago. 

In Table I all the chemical "life elements" which enter 
more or less freely into organic compounds are indicated by 
italics, shoiving that life has taken up and ?nade use of practically 
all the chemical elements of frequent occurrence in the rocks, 
waters, and air, with the exception of aluminum, barium, and 
strontium, which are extremely rare in life compounds, and 
of titanium, which thus far has not been found in any. But 
even these elements appear in artificial organic compounds, 
showing combining capacity without biological "inclination" 
thereto. In the life compounds, as in the lithosphere and 
hydrosphere, it is noteworthy that the elements of least atomic 
weight (Table II) predominate over the heavier elements. 

Primordial Environment — The Lifeless Water 

According to the nebular theory of Laplace the waters 
originated in the primordial atmosphere; according to the 
planetesimal theory of Chamberlin^ and Moulton,- the greater 
volume of water has been gradually added from the interior 
of the earth through the vaporous discharges of hot springs. 
As Suess observes: "The body of the earth has given forth its 
ocean." 

From the beginning of Archaeozoic time, namely, back to a 
period of 80,000,000 years, we have little biologic or geologic 
evidence as to the stability of the earth. From the beginning 
of the Palaeozoic, namely, for the period of the last 30,000,000 
years, the earth has been in a condition of such stability that 

1 Chamberlin, Thomas Chrowder, 1916. - Moulton, F. R., 191 2, p. 244. 


THE LIFELESS WATER 35 

the oceanic tides and tidal currents were similar to those of the 
present day; for the early strata are full of such evidences as 
ripple marks, beach footprints, and other proofs of regularly 
recurrent tides.' 

As in the case of the earth, the chemistry of the lifeless 
primordial seas is a matter of inference, /. c, of subtraction of 
those chemical elements which have been added as the infant 
earth has grown older. The relatively simple chemical con- 
tent of the primordial seas must be inferred by deducting the 
mineral and organic products which have been sweeping into 
the ocean from the earth during the last So, 000, 000 to 90,000,000 
years; and also by deducting those that have been precipitated 
as a result of chemical reactions, calcium chloride reacting with 
sodium phosphate, for example, to yield precipitated calcium 
phosphate and dissolved sodium chloride.' The present waters 
of the ocean are rich in salts which have been derived by solu- 
tion from the rocks of the continents. 

Thus we reach our first conclusion as to the origin of life, 
namely: it is probable that life originated on the continents, 
either in the moist crevices of rocks or soils, in the fresh waters 
of continental pools, or in the slightly saline waters of the 
bordering primordial seas. 

Salt as a Measure of the Age of the Ocean 

As long ago as 1715 Edmund Halley suggested that the 
amount of salt in the ocean might afford a means of computing 
its age. Assuming a primitive fresh-water ocean, Becker'' in 
1 9 10 estimated its age as between 50,000,000 and 70,000,000 
years, probably closer to the upper limit. The accumulation 
of sodium was probably more rapid in the early geologic periods 

' Becker, George F., 1910, p. 18. - W. J. Gies. 

^Becker, George F., 1910, pp. 16, 17. 


36 THE ORIGIN AND EVOLUTION OF LIFE 

than at the present time, because the greater part of the earth's 
surface was covered with the granitic and igneous rocks which 
have since been largely covered or replaced by sedimentary 
rocks, a diminution causing the sodium content from the earth 
to be constantly decreasing.^ This is on the assumption that 
the primitive ocean had no continents in its basins and that the 
continental areas were not much greater than at the present 
time, namely, 20.6 per cent to 25 per cent of the surface of 
the globe. 

Age of the Ocean Calculated from its Sodium Content - 


1S76. T. Mellard Reade. 

1899. J. Joly 80- 90 million years. 

1900. J. Joly 90-100 million years. 

1909. Sollas 80-150 million years. 

1910. Becker 50- 70 million years. 

1911. F. W. Clarke and Becker 94,712,000 years. 

1915. Becker 60-100 million years. 

1916. Clarke somewhat less than loo million years. 


From the mean of the foregoing computations it is inferred 
that the age of the ocean since the earth assumed its present 
form is somewhat less than 100,000,000 years. The 63,000,000 
tons of sodium which the sea has received yearly by solution 
from the rocks has been continually uniting with its equivalent 
of chlorine to form the salt (NaCl) of the existing seas.^ So 
with the entire present content of the sea, its sulphates as well 
as its chlorides of sodium and of magnesium, its potassium, its 
calcium as well as those rare chemical elements which occasion- 
ally enter into the life compounds, such as copper, fluorine, 
boron, barium — all these earth-derived elements were much 

1 Becker, George F., 1015, p. 201; igio, p. 12. 

-After Becker, George F., 1910, pp. 3-5; and Clarke, F. W., 1916, pp. 150, 152. 

^ Becker, George F., 1910, pp. 7, 8, 10, 12. 


THE LIFELESS WATER 


37 


rarer in the primordial seas than at the present time. Yet 
from the first the air in sea-water was much richer in oxygen 
than the atmosphere.^ 

As compared with primordial sea- water, which was relatively 
fresh and free from salts and from nitrogen, existing sea-water 
is an ideal chemical medium for life. As a proof of the special 
adaptability of existing sea-water to present biochemical con- 
ditions, a very interesting comparison is that between the 
chemical composition of the chief body fluid of the highest 
animals, namely, the blood serum, and the chemical composi- 
tion of sea-water, as given b}^ Henderson. - 

Chemical Composition of Present Sea-Water and of Blood Serum 


"Life Elements" 


In Sea-Water 


In Blood Serum 


Sodium 


30.59 

3-79 
I. 20 
I . II 

55 ■ 27 
7.66 
0. 21 
0. 19 


390 
0.4 
I .0 

2.7 
450 

12.0 
0.4 


Mcignesiuni 


Calcium 


Potassium 


Chlori)ie 


SO4 (sulphur tetroxide) 

CO3 (carbon trioxide) 

Bromine 


P'>Ot (phosphorous pen I oxide) 


Primordial Chemical Environment 

Since the primal sea was devoid of those earth-borne nitro- 
gen compounds which are indirectly derived first from the 
atmosphere and then from the earth through the agency of the 
nitrifying bacteria, those who hold to the hypothesis of the 
marine origin of protoplasm fail to account for the necessary 
proportion of nitrogenous matter there to begin with. 


1 Pirsson, Louis V., and Schuchert, Charles, 1915, p. 84. 
-Henderson, Lawrence J., 1913, p. 187. 


38 THE ORIGIN AND EVOLUTION OF LIFE 

When we consider that those chemical "hfe elements" 
which are most essential to living matter were for a great period 
of time either absent or present in a highly dilute condition in 
the ocean, it appears that we must abandon the ancient Greek 
conception of the origin of life in the sea, and reaffirm our 
conclusion that the lowliest organisms originated either in 
moist earths or in those terrestrial waters which contained 
nitrogen. Nitrate and nitrite occasionally arise from the union 
of nitrogen and oxygen in electrical discharges during thunder- 
storms, and were presumably thus produced before Hfe began. 
These and related nitrogen compounds, so essential for the 
development of protoplasm, may have been specially concen- 
trated in pools of water to degrees particularly favorable for the 
origin of protoplasm} 

It appears, too, that every great subsequent higher life 
phase — the bacterial phase, the chlorophyllic algal phase, the 
protozoan phase — was also primarily of fresh-water and sec- 
ondarily of marine habitat. From terrestrial waters or soils 
life may have gradually extended into the sea. It is probable 
that the succession of marine forms was itself determined to 
some extent by adaptation to the increasing concentration of 
saline constituents in sea-water. That the invasion of the sea 
upon the continental areas occurred at a very early period is 
demonstrated by the extreme richness and profusion of marine 
life at the base of the Cambrian. 

That life originated in water (H2O) there can be little doubt, 
hydrogen and oxygen ranking as primary elements with nitro- 
gen. The fitness of water to life is maximal - both as a solvent 
in all the bodily fluids, and as a vehicle for most of the other 
chemical compounds. Further, since water itself is a solvent 

' Suggested by Professor W. J. Gies. 

- These notes upon water are chiefly from the v'ery suggestive treatise, "The Fitness 
of the Environment," by Henderson, Lawrence J., 1913. 


THE ATMOSPHERE 39 

that fails to react with many substances (with nearl}- all bio- 
logical substances) it serves also as a factor of biochemical 
stability. 

In relation to the application of our theory of action, re- 
action, and interaction to the processes of life, the most im- 
portant property of water is its electric property, known as 
the dielectric constant. Although itself only to a slight degree 
dissociated into ions, it is the bearer of dissolved electrolytic 
substances and thus possesses a high power of electric conduc- 
tivity, properties of great importance in the development of the 
electric energy of the molecules and atoms in ionization. Thus 
water is the very best medium of electric ionization in solution, 
and was probably essential to the mechanism of life from its 
very origin.^ 

Through all the electric changes of its contained solvents 
water itself remains very stable, because the molecules of 
hydrogen and oxygen are not easily dissociated; their union 
in water contributes to the living organism a series of proper- 
ties which are the prime conditions of all physiological and 
functional activity. The great surface tension of water as 
manifested in capillary action is of the highest importance to 
plant growth; it is also an important force acting within the 
formed colloids, the protoplasmic substance of life. 

Primordial Environment — The Atmosphere 

It is significant that the simplest known living forms derive 
their chemical "life elements" partly from the earth, partly 
from the water, and partly from the atmosphere. This was 
not improbably true also of the earliest living forms. 

One of the mooted questions concerning the primordial 

^Henderson, Lawrence J., 1913, p. 256. 


40 THE ORIGIN AND EVOLUTION OF LIFE 

atmosphere^ is whether or no it contained free oxygen. The 
earliest forms of hfe were probably dependent on atmospheric 
oxygen, although certain existing bacterial organisms, known 
as "anaerobic," are now capable of existing without it. 

The primordial atmosphere was heavily charged with water 
vapor (HoO) which has since been largely condensed by cooling. 
In the early period of the earth's history volcanoes- were also 
pouring into the atmosphere much greater amounts of car- 
bon dioxide (CO2) than at the present time. At present the 
amount of carbon dioxide in the atmosphere averages about 
three parts in 10,000, but there is little doubt that the primor- 
dial atmosphere was richer in this compound, w^hich next to 
water and nitrogen is by far the most important both in the 
origin and in the development of living matter. The atmos- 
pheric carbon dioxide is at present continually being withdrawn 
by the absorption of carbon in living plants and the release of 
free oxygen; it is also washed out of the air by rains. On the 
other hand, the respiration of animals, the combustion of car- 
bonaceous matter, and the discharges from volcanoes are con- 
tinually returning it to the air in large quantities. 

As to carbon, from our present knowledge we cannot con- 
ceive of organisms that did not consist, from the instant of 
initial development, of protoplasm containing hydrogen, oxygen, 
nitrogen, and carbon. Probably carbon dioxide, the most likely 
source of carbon from the beginning, was reduced in the pri- 
mordial environment by other than chlorophyllic agencies, by 
simple chemical influences. 

Since carbon is a less dominant element^ than nitrogen in 
the life processes of the simplest bacteria, we cannot agree 
with the theory that carbon dioxide was coequal with water 

1 Becker, George F., letter of October 15, 1915. 
- Henderson, Lawrence J., 1913, p. 134. 
3 Jordan, Edwin O., 1908, p. 66. 


THE ATMOSPHERE 


41 


as a primary compound in the origin of life; it probably was 
more widely utilized after the chlorophyllic stage of plant 
evolution, for not until chlorophyll appeared was life equipped 
with the best means of extracting large quantities of carbon 
dioxide from the atmosphere. 

The stable elements of the present atmosphere, for which 
alone estimates can be given, are essentially as follows:^ 


Oxygen. . 
Nitrogen 
Argon. . . 


By Weight 


23.024 

75-539 
1-437 

I 00 . 000 


By Volume 


20. 941 

78. 122 

-037 


Atmospheric carbon dioxide (CO2), which averages about three 
parts in every 10,000, and water (HoO) are always present 
in varying amounts; besides argon, the rare gases helium, 
xenon, neon, and krypton are present in traces. None of the 
rare gases which have been discovered in the atmosphere, such 
as helium, argon, xenon, neon, krypton, and niton — the latter 
a radium emanation — are at present known to have any rela- 
tion to the life processes. Carbon dioxide- exists in the atmos- 
phere as an inexhaustible reservoir of carbon, only slightly 
depleted by the drafts made upon it by the action of chloro- 
phyllic plants or by its solution in the waters of the conti- 
nents and oceans. Soluble in water and thus equally mobile, 
of high absorption coefficient, and of universal occurrence, 
it constitutes a reservoir of carbon for the development of 
plants and animals, radiant energy being required to make this 
carbon available for biological use. Carbon dioxide in water 


1 Clarke, F. W., letter of March 7, 1916. 
"Henderson, Lawrence J., 1913, pp. 136-139. 


42 THE ORIGIN AND EVOLUTION OF LIFE 

forms carbonic acid, one of the few instances of biological 
decomposition of water. This compound is so unstable that it 
has never been obtained. Carbon dioxide is derived not only 
through chlorophyllic agencies by means of free oxygen, but 
also by the action of certain anaerobic bacteria and moulds 
without the presence of free oxygen, as, for example, through 
the catalytic action of zymase, the enzyme of yeast, which is 
soluble in water, Loeb^ dwells upon the importance of the 
bicarbonates as regulators in the development of the marine 
organisms by keeping neutral the water and the solutions in 
which marine animals live. Similarly the life of fresh-water 
animals is also prolonged by the addition of bicarbonates. 

^ Loeb, Jacques, 1906, pp. 96, 97. 


CHAPTER II 

THE SUN AND THE PHYSICOCHEMICAL ORIGINS 

OF LIFE 

Heat and light. Chemical '' life elements " as they exist in the sun. Primor- 
dial environment — electric energy and the sun's heat. Capture of the 
energy of sunlight. Action and reaction as adaptive properties of the 
life elements. Interaction or coordination of the properties of the life 
elements. Adaptation in the colloidal state. Cosmic properties and life 
functions of the chief chemical life elements. Pure speculation as to the 
primary physicochemical stages of life. Evolution of actions and reac- 
tions. Evolution of interactions. New organic compounds. 

We will now consider the sun as the source of heat, light, 
and other forms of energy which conditioned the origin of life. 

Heat and Light 

It is possible that in the earher stages of the earth's history 
the sun's light and heat may have been different in amount from 
what they are at present; so far as can be judged from the 
available data it seems probable that, if perceptibly different, 
they were greater then than now. But if they were greater, 
the atmosphere must have been more full of clouds — as that of 
Venus apparently is to-day — and have reflected away into space 
much more than the 45 per cent of the incident radiation which 
it reflects at present. On the earth's surface, beneath the cloud 
layer, the temperature need not have been much higher than 
the present mean temperature, but was doubtless much more 
equable, with more moisture, while the amount of sunlight 
reaching the earth's surface may have been less intense and 
continuous than at present. 

43 


44 


THE ORIGIN AND EVOLUTION OF LIFE 


The following are among the reasons why the primordial 
solar influences upon the earth may have differed from the 
present solar influences. It appears probable that the lifeless 
surface of the primordial earth was like that of the moon — 
covered not only with igneous rocks but with piles of heat-stor- 


HEAT LIGJ 


Billion vibratijlds per secondnn/^^ 


CHEMrC4L 


WIRA VIOLET 


Fig. 3. Light, Heat, and Chemical Influence of the Sun. 

Diagram showing how the increase, maximum, and decrease of heat, Hght, and chemical 
energy derived from the sun correspond to the velocity of the vibrations. After Ulric 
Dahlgren. 


ing debris, as recently described by Russell ^ — and if, like the 
moon, the earth had had no atmosphere, then the reflecting 
power of its surface would have represented a loss of only 40 
per cent of the sun's heat. But a large amount of aqueous 
vapor and of carbon dioxide in the primordial atmosphere prob- 
ably served to form an atmospheric blanket which inhibited 
the radiation from the earth's surface of such solar heat as pen- 
etrated to it, and also prevented excessive changes of temper- 
ature. Thus there was on the primal earth a greater reg- 
ularity of the sun's heat-supply, with more moisture. 

J Russell, H. N., 1916, p. 75. 


LIFE ELEMENTS IN THE SUN 45 

To sum up, if the primordial atmosphere contained more 
aqueous vapor and carbon dioxide than at present, the greater 
cloudiness of the atmosphere would have very considerably in- 
creased the albedo, that is, the reflection of solar heat, as well 
as hght, away into space. If the earth's surface was covered 
with loose debris, it would have retained more of the solar heat 
which reached it directly ; but, with such an atmosphere as is 
postulated, very Httle of the solar radiation would have reached 
the surface directly. What is true of the indirect access of the 
supply of light from the sun would also be true of the supply 
of heat. On the other hand, the greater blanketing power of 
the atmosphere would tend to keep the surface as warm as it 
is now, in spite of the smaller direct supply of heat. 

It is also possible that, through the agency of thermal 
springs and the heat of volcanic regions, primordial life forms 
may have derived their energy from the heat of the earth as 
well as from that of the sun. This is in general accord with 
the fact that the most primitive organisms surviving upon the 
earth to-day, the bacteria, are dependent upon heat rather 
than upon light for their energy. 

We have thus far observed that the primal earth, air, and 
water contained all the chemical elements and three of the 
most simple but important chemical compounds, namely, 
water, nitrates, and carbon dioxide, which are known to be 
essential to the bacterial or prechlorophyllic, and algal and 
higher chlorophyllic stages of the life process. 

Chemical "Life Elements" as They Exist in the Sun 

An initial step in the origin of life was the coordination or 
bringing together of these elements which, so far as we know, 
had never been chemically coordinated before and which are 


46 


THE ORIGIN AND EVOLUTION OF LIFE 


widely distributed in the solar spectrum. Therefore, before 
examining the properties of these elements, it is interesting to 
trace them back from the earth into the sun and thus into 
the cosmos. It is through these "properties" which in life 


■|] .1 : 


i.i 


FT 


M-46NE5IUM 


55M ip ?IC 3i5 JKT 

' 1 i i'H'i||ii,!Mi| 


IRON 


iin 


HI 


jSCO 10 


J.O i^ 


TT 

i i 


I III " r 


Fig. 4. Chemical Life Elements in the Sun. 

Three regions of the solar spectrum with lines showing the presence of such essential life 
elements as carbon, nitrogen, calcium, iron, magnesium, sodium, and hydrogen. From 
the Mount Wilson Observatory. 

subserve "functions" and "adaptations" that all forms of life, 
from monad to man, are linked with the universe. 

Excepting hydrogen and oxygen, the principal elements 
which enter into the formation of living protoplasm are minor 
constituents of the mass of matter sown throughout space in 
comparison with the rock-forming elements.^ Again excepting 
hydrogen, their lines in the solar spectrum are for the most 

1 Russell, Henry Norris, letter of March 6, 1916. 


LIFE ELEMENTS IN THE SUN 47 

part weak, and only shown on high dispersion plates, while 
hydrogen is represented by very strong lines, as shown by 
spectroheliograms of solar prominences. The lines of oxygen 
are relatively faint; it appears principally as a compound, 
titanium oxide (Ti02) in sun-spots, although a triple line in the 
extreme red seems also to be due to it. In the chromosphere, 
or higher atmosphere of the sun, hydrogen is not in a state of 
combustion, and the fine hydrogen prominences show radia- 
tions comparable to those in a vacuum tube.^ 

Nitrogen, the next most important life element, is displayed 
in the so-called cyanogen bands of the ultra-violet, made visible 
by high-dispersion photographs. 

Carbon is shown in many lines in green, which are relatively 
bright near the sun's edge; it is also present in comets, and 
carbonaceous meteorites (Orgueil, Kold Bokkeveld, etc.) are 
well known. Graphite occurs in meteoric irons. 

In the solar spectrum so far as studied no lines of the "life 
elements," phosphorus, sulphur, and chlorine, have been de- 
tected. On the other hand, the metallic elements which enter 
into the life compounds, iron, sodium, and calcium, are all 
represented by strong lines in the solar spectrum, the excep- 
tion being potassium in which the lines are faint. Of the eight 
metallic elements which are most abundant in the earth's crust, 
as well as the non-metallic elements carbon and silicon, six 
are also among the eight strongest in the solar spectrum. In 
general, however, the important life elements are very widely 
distributed in the stellar universe, showing most prominently 
in the hotter stars, and in the case of hydrogen being uni- 
versal. 

We have now considered the source of four "life elements," 
namely, hydrogen, oxygen, nitrogen, and carbon, also the 

1 Hale, George Ellery, letter of March lo, 19 16. 


48 THE ORIGIN AND EVOLUTION OF LIFE 

presence iii the sun and stars of the metallic elements. Before 
passing to the properties of these and other life elements let us 
consider how lifeless energy is transformed into living energy. 


Primordial Environment — Electric Energy and the 

Sun's Heat 

As remarked above, in the change from the lifeless to the 
life world, the properties of the chemical life elements become 
known as the fimctions of living matter. Stored energy becomes 
known as nutriment or food. 

The earliest function of living matter appears to have been 
to capture and transform the electric energy of those chemical 
elements which throughout we designate as the '4ife elements." 
This function appears to have developed only in the presence 
of heat energy, derived either from the earth or from the sun 
or from both; this is the first example in the life process of 
the capture and utiKzation of energy wherever it may be found. 
At a later stage of evolution life captured the light energy of 
the sun through the agency of chlorophyll, the green coloring 
matter of plants. In the final stage of evolution the intellect 
of man is capturing and controlling physicochemical energy in 
many of its forms. 

The primal dependence of the electric energy of life on the 
original heat energy of the earth or on solar heat is demon- 
strated by the universal behavior of the most primitive organ- 
isms, because when the temperature of protoplasm is lowered to 
o° C: the velocity of the chemical reactions becomes so small 
that in most cases all manifestations of life are suspended, 
that is, Hfe becomes latent. Some bacteria grow at or very 
near the freezing-point of water (o° C.) and possibly primordial 
bacteria-like organisms grew below that point. Even now the 


HEAT AND ELECTRIC ENERGY 49 

common "hay bacillus" grows at 6° C.^ Rising temperatures 
increase the velocity of the biochemical reactions of proto- 
plasm up to an optimum temperature, beyond which they are in- 
creasingly injurious and finally fatal to all organisms. In hot 
springs some of the Cyanophyceaj (blue-green algae), primitive 
plants intermediate in evolution between bacteria and algae, 
sustain temperatures as high as 63° C. and, as a rule, are killed 
by a temperature of 73° C, which is probably the coagulation 
point of their proteins. Setchell found bacteria living in water 
of hot springs at 89° C.- In the next higher order of the Chlo- 
rophyceas (green algae) the temperature fatal to life is lower, 
being 43° C.^ Very much higher temperatures are endured by 
the spores of certain bacilli which survive until temperatures 
of from 105° C. to 120° C. are reached. There appears to be 
no known limit to the amount of dry cold which they can 
withstand.^ 

It is this power of the relatively water-free spores to resist 
heat and cold which has suggested to Richter (1865), to Kel- 
vin, and to Arrhenius (1908) that living germs may have per- 
vaded space and may have reached our planet either in com- 
pany with meteorites (Kelvin)'^ or driven by the pressure of 
light (Arrhenius).^ The fact that so far as we know Hfe on the 
earth has only originated once or during one period, and not 
repeatedly, does not appear to favor these hypotheses; nor is 
it courageous to put off the problem of life origin into cosmic 

^Jordan, Edwin 0., 1908, pp. 67, 68. "Op. ciL, p. 68. 

^ Loeb, Jacques, 1906, p. 106. 

^ Cultures of bacteria have even been exposed to the temperature of liquid hydrogen 
(about — 250° C.) without destroying their vitality or sensibly impairing their biologic 
qualities. This temperature is far below that at which any chemical reaction is known 
to take place, and is only about 23 degrees above the absolute zero point at which, it is 
believed, molecular movement ceases. On the other hand, when bacteria are frozen in 
water during the formation of natural ice the death rate is high. See Jordan, Edwin O., 
1908, p. 69. 

* Poulton, Edward B., 1896, p. 818. 

* Pirsson, Louis V., and Schuchert, Charles, 1915, pp. 535, 536. 


50 


THE ORIGIN AND EVOLUTION OF LIFE 


space instead of resolutely seeking it within the forces and 
elements of our own humble planet. 

The thermal conditions of living matter point to the prob- 
ability that life originated at a time when portions at least 


Fig. 5. The Earliest Phyla of Plant and Animal Life. 

Chart showing the theoretic derivation of chordates and vertebrates from some inverte- 
brate stock, and of the invertebrates from some of the protozoa. The diagonal lines 
indicate the geologic date of the earliest known fossil forms in the middle Algonkian. 
The earliest well-known invertebrate fauna is in the Middle Cambrian (see pp. 
118-134; and Figs. 20-27). Although diatoms are among the simplest known liv- 
ing forms and probably represent a very early stage in the evolution of life, no fossil 
forms are known earlier than two species from the Lias, while all the rest date 
from the Cretaceous. 

of the earth's surface and waters had temperatures of between 
89° C. and 6° C; and also to the possibility of the origin of 
life before the atmospheric vapors admitted a regular supply 
of sunlight. 


THE CAPTURE OF SUNLIGHT 51 

Capture of tlie Energy of SunUgJd 

After the sun's heat Hving matter appears to have captured 
the sun's hght, which is essential, directly or indirectly, to all 
living energy higher than that of the most primitive bacteria. 
The discovery by Lavoisier (i 743-1794) and the development 
(1804) by de Saussure' of the theory of photosynthesis, namely, 
that sunshine combining solar heat and light is a perpetual 
source of living energy, laid the foundations of biochemistry 
and opened the way for the establishment of the law of the 
conservation of energy within the living organism. 

Thus arose the first conception of the cycle of the elements 
continually passing through plants and animals which was so 
grandly formulated by Cuvier in 181 7:- "La vie est done un 
tourbillon plus ou moins rapide, plus ou moins complique, 
dont la direction est constante, et qui entraine toujours des 
molecules de memes sortes, mais ou les molecules individuelles 
entrent et d'ou elles sortent continuellement, de maniere que 
\3i forme du corps vivant lui est plus essentielle que sa matiere.'" 

Chemical Composition of Chlorophyll^ 


Carbon 73.34 

Hydrogen 9.72 

Nitrogen 5-68 

Oxygen 9.54 

Phosphorus 1.38 

Magnesium 0.34 


The green coloring matter of plants is known as chloro- 
phyll; its chemical composition according to Hoppe-Seyler's 

' De Saussure, N. T., 1804. 

- Cuvier, Baron Georges L. C. F. D., 181 7, p. 13. 

3 Sachs, Julius, 1882, p. 758. 


52 THE ORIGIN AND EVOLUTION OF LIFE 

analysis is given here. Potassium is essential for its assimi- 
lating activity. Iron (often accompanied by manganese), al- 
though essential to the production of chlorophyll, is not con- 
tained in it. The chlorophyll-bearing leaves of the plant in 
the presence of sunlight separate oxygen atoms from the 
carbon and hydrogen atoms in the molecules of carbon dioxide 
(COo) and of water (HoO), storing up the energy of the hydro- 
gen and carbon products in the carbohydrate substances of the 
plant, an energy which is stored by deoxidation (separation of 
oxygen), and which can be released only through reoxidation 
(addition of oxygen). Thus the celluloses, sugars, starches, 
and other similar substances deposit their kinetic or stored 
energy in the tissues of the plant and release that energy 
through the addition of oxygen, the amount of oxygen required 
being the same as that needed to burn these substances in 
the air to the same degree; in brief, through a combustion 
which generates heat.^ Thus living matter utilizes the energy 
of the sun to draw a continuous stream of electric energy from 
the chemical elements in the earth, the water, and the atmos- 
phere. 

This was the first step in the interpretation of life processes 
in the terms of physics and chemistry, rather than in terms 
of a peculiar vitalism. What had previously been regarded 
as a special vital force in the life of plants thus proved to be 
an adaptation of physicochemical forces. The chemical action 
of chlorophyll is even now not fully understood, but it is known 
to absorb most vigorously the solar rays between B and C of 
the spectrum,' and these rays are most effective in the assim- 
ilation of energy or food by the plant. While the effect of the 
solar rays between D and E is minimal, those beyond F are 
again effective. In heliotropic movements both of plants and 

1 W. J. Gies. -Loeb, Jacques, 1906, p. 115. 


IONIZATION 53 

animals the blue rays are more effective than the red.' Spores 
given off as ciliated cells from the algae seek first the blue rays. 
Since the food supply of animals is primarily derived from 
chlorophyll-bearing plants, animals are less directly dependent 
on the solar light and solar heat, while the chemical life of 
plants fluctuates throughout the day with the variations of 
light and temperature. Thus Richards- finds in the cacti that 
the breaking down of the acids through the splitting of the 
acid compounds is a respiratory process caused by the alternate 
oxidation and deoxidation of the tissues through the action of 
the sun. 

The solar energy transformed into the chemical potential 
energy of the compounds of carbon, hydrogen, and oxygen in 
the plants is transmuted by the animal into motion and heat 
and then dissipated. Thus in the life cycle we observe both 
the conservation and the degradation of energy, corresponding 
with the first and second laws of thermodynamics developed 
in physics by the researches of Newton, Helmholtz, Phillips, 
Kelvin, and others.^ The remaining life processes correspond 
in many ways to Newton's third law of motion. 

Action and Reaction as Adaptive Properties of the Life 

Elements 

The adaptation of the chemical elements to life processes 
is due to their incessant action and reaction, each element 
having its peculiar and distinctive forms of action and reaction, 
which in the organism are transmuted into functions. Such 
activity of the life elements is largely connected with forms 
of electric energy which the physicists call ionization, while 
the correlated or coordinated interaction of various groups 

^Op. cit., p. 127. - Richards, Herbert M., 1915, pp. 34, 73-75. 

'Henderson, Lawrence J., 1913, pp. 15-1S. 


54 


THE ORIGIN AND EVOLUTION OF LIFE 


of life elements is largely connected with processes which the 
chemists term catalysis. 

Ionization J the actions and reactions of all the elements and 
electrolytic compounds — according to the hypothesis of Arrhe- 
nius, first put forth in 1887 — is primarily due to electrolytic 
dissociation whereby the molecules of all acids {e. g., carbonic 
acid, H2CO3), bases (e. g., sodium hydroxide, NaOH), and salts 
{e. g., sodium chloride, NaCl) give off streams of the electrically 
charged particles known as ions. Ionization is dependent on 
the law of Nernst that the greater the dielectric capacity of 
the solvent {e. g., water) the more rapid will be the dissociation 
of the substances dissolved in it, other conditions remaining 
the same. 


Ionization of the Elements thus far Discovered in Living Organisms 


Mainly or Wholly with or in Negative Ions' 


Mainly or Wholly with or in 


'ositive Ions ' 


Non-metallic 


Metallic 


Carbon^ (c g./ carbonates) 


Silicon 


Hydrogen^ 


Iron^ 


Lithium 


Oxygen = {c. g.,'* sulphates) 


Iodine 


Potassium 


Copper 


Nickel 


Nitrogen-'^ (r. g.,'' nitrates) 


Bromine 


Sodium 


Aluminum 


Radium 


Phosphorus- (c. g.,^ phosphates) 


Fluorine 


Calcium 


Barium 


Strontium 


Sulphur- (c. g.,'» sulphates) 


Boron 


Magnesium 


Cobalt 


Zinc 


Chlorine [c. g.,^ chlorides) 


Arsenic'' 


Manganese 


Lead 


' An ion is an atom or group of atoms carrying an electric charge. The positiv^e ions 
(cations) of the metallic elements move toward the cathode; the negative ions (anions) 
given off by the non-metallic elements move toward the anode. 

- Together with hydrogen conspicuous in living colloids and non-electrolytes — very 
little in the indicated ionized forms. 

^ Occurs also, as NH4, in positive ions. Here the hydrogen overbalances the nitrogen. 

* Substances occurring in living matter. 

* Arsenic itself is a metal, but in living compounds it is an analogue of phosphorus 
and occurs in negative ions when ionized. 

^ Pictet has obtained results indicating that liquid and solid hydrogen are metallic. 
Hydrogen is metallic in behavior, though non-metallic in appearance. 

' Iron in living compounds is chiefly non-ionized, colloidal. Apparently this is also 
true of copper, aluminum, barium, cobalt, lead, nickel, strontium, and zinc. As to ra- 
dium, however, there is no information on this point. 

Thus, ions are atoms or groups of atoms carrying electric 
charges which are positive when given off from metallic ele- 


IONIZATION 5 5 

ments, and negative when given off from non-metallic elements. 
Electrolytic molecules, according to this theory, are constantly 
dissociating to form ions, and the ions are as constantly recom- 
bining to form molecules. Since the salts of the various min- 
eral elements are constantly being decomposed through elec- 
trolytic ionization, they play an important part in all the life 
phenomena; and since similar decomposition is induced by 
currents of electricity, indications are that all the development 
of living energy is in a sense electric. 

The ionizing electric properties of the life elements are a 
matter of prime importance. We observe at once in the table 
above that all the great structural elements which make up 
the bulk of plant and animal tissues are of the non-metallic 
group with negative ions, with the single exception of hydro- 
gen which has positive ions. All these elements are of low 
atomic weight, and several of them develop a great amount 
of heat in combustion, hydrogen and carbon leading in this 
function of the release of energy, which invariably takes place 
in the presence of oxygen. On the other hand, the lesser com- 
ponents of living compounds are the metallic elements with 
positive ions, such as potassium, sodium, calcium, and mag- 
nesium, calcium combining with carbon or with phosphorus 
as the great structural or skeletal builder in animals. There is 
also so much carbonaceous protein in the animal skeleton that 
calcium in animals takes the place of carbon in plants only in 
the sense that it reduces the proportion of carbon in the skele- 
ton: it shares the honors with carbon. 

In general the electric action and reaction of the non- 
metallic and the metallic elements dissolved or suspended in 
water are now believed to be the chief phenomena of the in- 
ternal functions of life, for these functions are developed always 
in the presence of oxygen and with the energy either of the 


56 THE ORIGIN AND EVOLUTION OF LIFE 

heat of the earth or of the sun, or of both the heat and light 
of the sun. 

Finally, we observe that ionization is connected with the 
radioactive elements, of which thus far only radium has been 
detected in the organic compounds, although the others may 
be present. 

Phosphorescence in plants and animals is treated by Loeb^ 
and others as a form of radiant energy. While developed in a 
number of living animals — including the typical glowworms in 
which the phenomenon was first investigated by Faraday — the 
living condition is not essential to it because phosphorescence 
continues after death and may be produced in animals by 
non-living material. Many organisms show phosphorescence 
at comparatively low temperatures, yet the presence of free 
oxygen appears to be necessary. 

In Rutherford's experiments on radioactive matter- he tells 
us that in the phosphorescence caused by the approach of an 
emanation of radium to zinc sulphate the atoms throw off the 
alpha particles to the number of five billion each second, with 
velocities of 10,000 miles a second; that the alpha particles in 
their passage through air or other medium produce from the 
neutral molecules a large number of negatively charged ions, 
and that this ionization is readily measurable. 

Interaction or Coordination of the Properties of the 

Life Elements 

The actions and reactions of the life elements, which are 
mainly contemporaneous, direct, and immediate, do not suffice 
to form an organism. As soon as the grouping of chemical 
elements reaches the stage of an organism interaction also be- 
comes essential, for the chemical activities of one region of the 

^Loeb, Jacques, 1906, pp. 66-68. -Rutherford, Sir Ernest, 1915, p. 115. 


COORDINATION 57 

organism must be harmonized with those of all other regions; 
the principle of interaction may apply at a distance and the 
results may not be contemporaneous. This is actually inferred 
to be the case in single-celled organisms, such as the Amoeba} 

The interacting and coordinating form of lifeless energy 
which has proved to be of the utmost importance in the life 
processes is that recognized in the early part of the nineteenth 
century and denoted by the term catalysis, first applied by 
Berzelius in 1835. A catalyzer is a substance which modifies 
the velocity of any chemical reaction without itself being 
used up by the reaction. Thus chemical reactions may be 
accelerated or retarded, and yet the catalyzer lose none of 
its energy. In a few cases it has been definitely ascertained 
that the catalytic agent does itself experience a series of 
changes. The theory is that catalytic phenomena depend 
upon the alternate decomposition and recomposition, or the 
alternate attachment and detachment of the catalytic agent. 

Discovered as a property in the inorganic world, catalysis 
has proved to underlie the great series of functions in the 
organic world which may be comprised in the physical term 
interaction. The researches of Ehrlich and others fully justify 
Huxley's prediction of 1881 that through therapeutics it would 
become possible "to introduce into the economy a molecular 
mechanism which, like a cunningly contrived torpedo, shall 
find its way to some particular group of living elements and 
cause an explosion among them, leaving the rest untouched." 
In fact, the interacting agents known as "enzymes" are such 
living catalyzers,- and accelerate or retard reactions in the 
body by forming intermediary unstable compounds which are 
rapidly decomposed, leaving the catalyzer (/. c, enzyme) free 
to repeat the action. Thus a small quantity of an enzyme 

' Calkins, Gary N., 1916, pp. 259, 260. - Loeb, Jacques, 1906, pp. 26, 28. 


58 THE ORIGIN AND EVOLUTION OF LIFE 

can decompose indefinite quantities of a compound. The 
activity of enzymes is rather in the nature of the "interaction" 
of our theory than of direct action and reaction, because the 
results are produced at a distance and the energy Uberated 
may be entirely out of proportion to the internal energy of the 
catalyzer. The enzymes, being themselves complex organic 
compounds, act specifically because they do not affect alike the 
different organic compounds which they encounter in the fluid 
circulation. 

Adaptation in the Colloidal State 

In the lifeless world matter occurred both in the crystal- 
loidal and colloidal states. It is in the latter state that life 
originated. It is a state peculiarly favorable to action, reac- 
tion, and interaction, or the free interchange of physicochemi- 
cal energies. Each organism is in a sense a container full of 
a watery solution in which various kinds of colloids are sus- 
pended.^ Such a suspension involves a play of the energies of 
the free particles of matter in the most delicate equilibrium, 
and the suspended particles exhibit the vibrating movement 
attributed to the impact of the molecules.- These free parti- 
cles are of greater magnitude than the individual molecules; in 
fact, they represent molecules and multimolecules, and all the 
known properties of the compounds known as "colloids" can 
be traced to feeble molecular affinities between the molecules 
themselves, causing them to unite and to separate in multi- 
molecules. Among the existing living colloids are certain car- 
bohydrates, like starch or glycogen, proteins (compounds of 
carbon, hydrogen, oxygen, and nitrogen with sulphur or phos- 
phorus), and the higher fats. The colloids of protoplasm are 
dependent for their stability on the constancy of acidity and 

^ Bechhold, Heinrich, 191 2. - Smith, Alexander, 1914, p. 305. 


FUNCTIONS OF LIFE ELEMENTS 59 

alkalinity, which is more or less regulated by the presence of 
bicarbonates.^ 

Electrical charges in the colloids'- are demonstrated by cur- 
rents of electricity sent through a colloidal solution, and are 
interpreted by Freundlich as due to electrolytic dissociation of 
the colloidal particles, alkaline colloids being positively charged, 
while acid colloids are negatively charged. The concentration 
of hydrogen and hydroxyl ions in the ocean and in the organ- 
ism is automatically regulated by carbonic acid.'' 

Among the colloidal substances in living organisms the so- 
called enzymes are very important, since they are responsible 
for many of the processes in the organism. Possibly enzymes 
are not typical colloids and perhaps, in pure form, they may 
not be classified as such; but if they are not colloids they cer- 
tainly behave like colloids.^ 

Cosmic Properties and Life Functions of the Chief 
Chemical Life Elements 

Of the total of eighty-two or more chemical elements thus 
far discovered at least twenty-nine are known to occur in liv- 
ing organisms either invariably, frequently, or rarely, as shown 
in Table II of the Life Elements. Whether essential, fre- 
quent, or of rare occurrence, each one of these elements — as 
described below — has its single or multiple services to render 
to the organism. 

Hydrogen, the life element of least atomic weight, is always 
near the surface of the typical hot stars. Rutherford^ tells us 
that, while the hydrogen atom is the lightest known, its nega- 
tively charged electrons are only about 1/1800 of the mass of 

^Henderson, Lawrence J., 1913, pp. 157-160. - Loeb, Jacques, 1906, pp. 34, 35. 

* Henderson, Lawrence J., 1913, p. 257. * Hedin, Sven G., 1915, pp. 164, 173. 

* Rutherford, Sir Ernest, 1915, p. 113. 


6o 


THE ORIGIN AND EVOLUTION OF LIFE 


the hydrogen atom: they are hberated from metals on which 
ultra-violet light falls, and can be released from atoms of mat- 


FiG. 6. H\T)ROGEN Vapor in the Solar Atmosphere 

Hydrogen, which far exceeds any other element in the amount of heat it yields upon 
oxidation (see Table II, p. 67) and ranks among the four most important of the chemical 
life elements, is also invariably present at the surface of all typical hot stars, includ- 
ing the sun. The large masses of hydrogen vapor known as "solar prominences" 
which burst forth from ever}^ part of the sun, are here shown as photographed during a 
total eclipse. The upper figure presents a detail from the lower, greatly enlarged 
From the Mount Wilson Observatory. 

ter by a variety of agencies. Hydrogen is present in all acids 
and in most organic compounds. It also has the highest 


FUNCTIONS OF LIFE ELEMENTS 


6i 


power of combustion.' Its ions are very important factors in 
animal respiration and in gastric digestion.'- It is very active 
in dissociating or separating oxygen from various compounds, 
and through its affinity for oxygen forms water (H2O), the 
principal constituent of protoplasm. 


Fig. 7. Hm>rogen Flocculi Surrounding a Group of Sun-Spots. 

The vortex structure is clearly shown. After Hale. From the Mount Wilson 

Observatory. 

Oxygen, like hydrogen, has an attractive power which brings 
into the organism other elements useful in its various functions. 
It makes up two- thirds of all animal tissue, as it makes up 
one-half of the earth's crust. Besides these attractive and syn- 
thetic functions, its great service is as an oxidizer in the release 
of energy; it is thus always circulating in the tissues. Through 
this it is involved in all heat production and in all mechanical 
work, and affects cell division and growth.^ 

1 Henderson, Lawrence J., 1913, pp. 218, 239, 245. 

^ W. J. Gies. ^ Loeb, Jacques, 1906, p. 16. 


62 THE ORIGIN AND EVOLUTION OF LIFE 

Nitrogen comes next in importance to hydrogen and oxygen 
as structural material^ and when combined with carbon and 
sulphur gives the plant and animal world one of the chief 
organic food constituents, protein. It was present on the 
primordial earth, not only in the atmosphere but also in the 
gases and waters emitted by volcanoes. Combined with hy- 
drogen it forms various radicles of a basic character {e. g., NHo 
in amino-acids, NHj in ammonium compounds) ; combined with 
oxygen it yields acidic radicles, such as NO3 in nitrates. It 
combines with carbon in — C ^ N radicles and in ^ C — NH2 
and = C = NH forms, the latter being particularly important 
in protoplasmic chemistry.- This life element forms the basis 
of all explosives, it also confers the necessary instability upon 
the molecules of protoplasm because it is loath to combine 
with and easy to dissociate from most other elements. Thus 
we find nitrogen playing an important part in the physiology 
of the most primitive organisms known, the nitrifying bacteria. 

Carbon also exists at or near the surface of cooling stars 
which are becoming red.'^ It unites vigorously with oxygen, 
tearing it away from neighboring elements, while its tendency 
to unite with hydrogen is less marked. At lower heats the 
carbon compounds are remarkably stable, but they are by no 
means able to resist great heats; thus Barrel^ observes that a 
chemist would immediately put his finger on the element car- 
bon as that which is needed to endow organic substance with 
complexity of form and function, and its selection in the origin 
of plant life was by no means fortuitous. Including the arti- 
ficial products, the known carbon compounds exceed 100,000, 
while there are thousands of compounds of C, H, and O, and 
hundreds of C and H.^ Carbon is so dominant in living mat- 

^ Henderson, Lawrence J., 1913, p. 241. - W. J. Gies. 

^ Henderson, Lawrence J., 1913, p. 55. * Joseph Barrell, letter of March 20, 1916. 

5 Henderson, Lawrence J., 1913, pp. 193, 194. 


FUNCTIONS OF LIFE ELEMENTS 6 


o 


ter that biochemistry is very largely the chemistry of carbon 
compounds; and it is interesting to observe that in the evolu- 
tion of life each of these biological compounds must have arisen 
suddenly as a saltation or mutation, there being no continuity 
between one chemical compound and another. 

Phosphorus is essential in the nucleus of the cell,^ being a 
large constituent of the intranuclear germ-plasm known as 
chromatin, which is the seat of heredity. It enters largely 
into the structure of nerves and brain and also, in the form 
of phosphates of calcium and magnesium, serves an entirely 
diverse function as building material for the skeletons of 
animals. Phosphates are important factors in the maintenance 
of normal uniformity of reaction in the blood. 

Sulphur, uniting with nitrogen, oxygen, hydrogen, and car- 
bon, is an essential constituent of the proteins of plants and 
animals.- It is especially conspicuous in the epidermal protein 
known as keratin, which by its insolubility mechanically pro- 
tects the underlying tissues.^ Sulphur is also contained in 
one of the physiologically important substances of bile.^ Sul- 
phates are important factors in the protective destruction, in 
the liver, of poisons of bacterial origin normally produced in 
and absorbed from the large intestine. 

Potassium is able to separate hydrogen from its union with 
oxygen in water, and is the most active of the metals, biologi- 
cally considered, in its positive ionization.-^ Through stimula- 
tion and inhibition potassium salts play an important part in 
the regulation of life phenomena, and they are essential to the 
living tissues of plants and animals, fresh-water and marine 
plants in particular storing up large quantities in their tissues.^ 

^Op. cit., p. 241. -Op. cit.. p. 242. 

^ Pirsson, Louis V., and Schuchert, Charles, 19 15, p. 434. ■* W. J. Gies. 

* Caesium is more electropositive. — F. W. Clarice. 

* Loeb, Jacques, 1906, p. 94. 


64 THE ORIGIN AND EVOLUTION OF LIFE 

Potassium is of service to life in building up complex com- 
pounds from which the potassium cannot be dissociated as a 
free ion; it is thus one of the building stones of living 
matter.^ 

Magnesium is fourth in order of activity among the metallic 
elements. It is essential to chlorophyll, the green coloring 
matter of plants, which in the presence of sunshine is able 


Fig. 8. The Sun, Showing Sun-Spots and Calcium Vapor. 

Calcium, a life element essential to all plants and animals, and especially abundant in 
the bones and teeth of vertebrates, is also a constituent of the solar atmosphere, as 
shown by these two photographs of the sun, both displaying the same view and the 
same group of sun-spots. The one at the left, made by calcium rays alone with the 
spectro-heliographji shows in addition the clouds of calcium vapor which are not 
evident in the photograph at the right. From the Mount Wilson Observatory. 

• An instrument devised by Professor George E. Hale for taking photographs of the sun by the light of a 
single ray of the spectrum (calcium, hydrogen, etc.). 

to dissociate oxygen from the carbon of carbon dioxide and 
from the hydrogen of water. It is also found in the skeletons 
of many invertebrates and in the coralline algae, and is an im- 
portant factor in inhibiting or restraining many biochemical 
processes. 

Calcium is third in order of activity among the metallic 
elements. According to Loeb- it plays an important part in 

1 Op. ciL, p. .72. 2 Op. ciL, 1906, p. 94. 


FUNCTIONS OF LIFE ELEMENTS 


65 


the life phenomena through stimulation (irritability) and in- 
hibition. It unites with carbon as carbonate of lime and is 
contained in many of those animal skeletons which, through 
deposition, make up an important part of the earth's crust. 


MAiNCiiUM 


i I! ! ' 


III 


i500 ro 20 


So . 410 

iiliihl:! 


I 


{-"If] 


IRON MVDROGEN 


Fig. g. Chemical Life Elemextr ix the Sux. 

Three regions of the solar spectrum with lines showing the presence of such essential 
life elements as carbon, nitrogen, calcium, iron, magnesium, sodium, and h\'drogen. 
From the Mount Wilson Observatory. 


In invertebrates the carbonates, except in certain brachiopods, 
are far more important as skeletal material than the phosphates: 
the limestones form only about live per cent of the sedimen- 
taries. Shales and sandstones are far more abundant. 

Iron is essential for the production of chlorophyll,^ though, 
unlike magnesium, it is not contained in it. It is present as 
well in all protoplasm, while in the higher animals it serves, in 

1 Sachs, Julius, 188.3, p. 699. 


66 THE ORIGIN AND EVOLUTION OF LIFE 

the form of oxyhemoglobin, as a carrier of oxygen from the 
lungs to the tissues.^ 

Sodium is less important in the nutrition of plant tissues, 
but serves an essential function in all animal life in relation to 
movement through muscular contraction,- Its salts, like those 
of calcium, play an important part in the regulation of life phe- 
nomena through stimulation and inhibition.^ 

Iodine, with its negative ionization, becomes useful through 
its capacity to unite with hydrogen in the functioning of the 
brown algae and in many other marine organisms. It is also 
an organic constituent in the thyroid gland of the vertebrates.* 
The iodine content of crinoids — stalked echinoderms — varies 
widely in organisms gathered from different parts of the ocean 
according to the temperature and the iodine content of the 
sea-water. Iodine and bromine are important constituents of 
the organic axes of gorgonias. 

Chlorine, like iodine, a non-metallic element with negative 
ions, is abundant in marine algae and present in many other 
plants, while in animals it is present in both blood and lymph. 
In union with hydrogen as hydrochloric acid it serves a very 
important function in the gastric digestion of proteins.^ 

Barium, rarely present in plants, has been used in animal 
experimentation by Loeb, who has shown that its salts induce 
muscular peristalsis and accelerate the secretory action of the 
kidneys.^ 

Copper ranks first in electric conductivity. In the inverte- 
brates, in the form of hemocyanine, it acts as an oxygen carrier 
in the fluid circulation to the tissues.'^ It is always present in 
certain molluscs, such as the oyster, and also in the plumage 

^ Henderson, Lawrence J., 1913, p. 241. - Loeb, Jacques, 1906, p. 79. 

^Op. cit., pp. 94, 95. * Henderson, Lawrence J., 1913, p. 242. 

^Op. cit., p. 242. ^Loeb, Jacques, 1906, p. 93. 
'Henderson, Lawrence J., 1913, p. 241. 


TABLE II. ADAPTIVE FUNCTIONS OF THE LIFE ELEMENTS IN PLANTS AND ANIMALS 


ELEMENTS INVARIABLY PRESENT IN LIVING ORGANISMS 


Atomic 
Weiihl 


.008 


34- 
8. 


.04 


5- 


.06 


I. 


■i2 


6, 


07 

84 


}■ 


702 cal. (H,) 


Hydrogen 

Carbon 

Oxygen 

Nitrogen 

Phosphorus 


? Sodium 
?Chlorine 
? Silicon 


Hydrogen, carbon, oxygen, „.. 
with sulphur, practically all 


and nitrogen — "H, C, O, N" — are csscnlial and of chief rank in all life processes; forming, 
"" plant and animal proteins and, with phosphorus, forming the nucleoproteins. 


In nucleoproteins and phospholipins. 

In most proteins, o.i-*5.o per cent. 

Abundant in marine plants, esp. "kelps" (larger Phaophy- 
cea); activity of chlorophyll depends on it. 

Present in large quantities in Corallinacccs (a family of cal- 
cified red algse). 

Present in large quantities in certain algae {chiefly marine). 

Essential in the formation of protoplasm; present in chlo- 
rophyll. 

Believed essential to all plants, but not demonstrated; 

found in marine plants, esp. Phceophycece. 
Present in many plants; believed by some to be essential; 

abundant in marine algas, esp. in the Phaophycea. 
Found in all plants; present in large quantities in the Dia- 

lomace<B, both fresh-water and marine ; in form of ' ' silica ' ' 

constitutes 0.5-7.0 per cent of the ash of ordinary marine 


In nucleoproteins and phosphoUpins; in some brachiopods 

in blood; and in vertebrate bone and teeth. 
In most proteins, 0.1-5.0 per cent. 
In blood, muscle, etc. 


Present in ecbinoderms and alcyonarians; present in all 

parts of vertebrates, esp. in bones. 
In all parts of vertebrates; abundant in bones and teeth. 
Essential in the formation of protoplasm, and in the 

higher animals; essential in hemoglobin as an o.xygen- 

Present in all animals; abundant in blood and lymph. 

Present in all animals; abundant in blood and lymph; 

present in the gastric juice. 
Present in radiolarians and siliceous sponges; also in all 

the higher animals. 


ELEMENTS FREQUENTLY PRESENT IN LIVING ORGANISMS 


Iodine 


I 


Manganese 
Bromine 


Mn 
Br 


Fluorine 


F 


In marine plants, esp. the "brow;i alga." Phmophycew; 

in Laminaria and Fiicus; also in some Gorgonias. 
In some plants. 
In marine plants, esp. the "brown alga;," Phffophycca; ; in 

some Gorgonias. 
In a few plants. 


Essential in the higher animals (thyroid). 


, very slight proportions. 
1 very slight proportions. 


27 

74 


96 


.?7 


37 


11 


S8 


07 


03 


57 


207 


20 


b 


94 


ss 


58 


22(1 


87 


6<! 


65 


37 


.463 cal. 


0.585 
0.243 


ELEMENTS RARELY PRESENT IN LIVING ORGANISMS 


Aluminum ' 
Arsenic ' 
Barium * 
Boron 
Cobalt • 
Copper ' 

Lead' 
Lithium 
Nickel ' 
Radium ' 
Strontium ' 
Zinc' 


In a few plants. 

In a few plants. 
In some plants. 
In a few plants. 
In a few plants. 


In some plants. 
In a few plants. 
In some plants. 
In a few plants. 
In a few plants. 


' corals; essential in some lower animals 


In some animals. 

In a few animals; traces in some corals, 


The exceedingly rare occurrence of cerium, chromium, didymium, lanthanum, molybdenum, and vanAdium is in all probability merely adventitious. 
' Commonly regarded as poisons when present in m'tnerd (ionic) forms, even in small proportions. 


PRIMARY STAGES OF LIFE 67 

of a bird, the Turaco. Although among the rare Hfe elements 
it ranks first in toxic action upon fungi, algse, and in general 
upon all plants, yet it is occasionally found in the tissues of 
trees growing in copper-ore regions.^ 

In general most of the metallic compounds and several of 
the non-metallic compounds are toxic or destructive to life 
when present in large quantities. All the mineral elements of 
high atomic weight are toxic in comparatively minute propor- 
tions, while the essential life elements of low atomic weight 
are toxic only in comparatively large proportions. Toxicity 
depends largely upon the liberation of ions, and non-ionized 
and non-ionizable organic compounds — such as hemoglobin 
containing non-ionizable iron — are wholly non-toxic. 

Pure Speculation as to the Primary Physicochemical 

Stages of Life 

The mode of the origin of life is a matter of pure specula- 
tion, in which we have as yet little observation or uniformitarian 
reasoning to guide us, for all the experiments of Biitschli and 
others to imitate the original life process have proved fruitless. 
We shall, however, from our knowledge of bacteria (see Chap. 
Ill) put forward five hypotheses in regard to it, considering 
the life process as probably a gradual one, marked by short leaps 
or accessions of energy, and not as a sudden one. 

First: We may advance the hypothesis that an early step 
in the organization of living matter was the assemblage one by 
one of sev^eral of the ten elements now essential to life, namely, 
hydrogen, oxygen, nitrogen, carbon, phosphorus, sulphur, po- 
tassium, calcium, magnesium, and iron (also perhaps silicon), 
which are present in all living organisms, with the exception 
of some of the most primitive forms of bacteria which may 

' M. A. Howe, letter of February 24, 1916. 


68 THE ORIGIN AND EVOLUTION OF LIFE 

lack magnesium, iron, and silica. Of these the four most im- 
portant elements were obtained from their previous combina- 
tion in water (H2O), from the nitrogen compounds of volcanic 
emanations or from the atmosphere' consisting largely of 
nitrogen, and from atmospheric carbon dioxide (CO2). The 
remaining six elements, phosphorus, sulphur, potassium, cal- 
cium, magnesium, and iron, came from the earth. 

Second: Whether there was a sudden or a more or less serial 
grouping of these elements, one by one, we are led to a second 
hypothesis that they were gradually bound by a new form of 
mutual attraction whereby the actions and reactions of a group 
of life elements established a new form of unity in the cosmos, 
an organic unity, an individual or organism quite distinct from 
the larger and smaller aggregations of inorganic matter pre- 
viously held or brought together by the forces of gravity. 
Some such stage of mutual attraction may have been ancestral 
to the cell, the primordial unity and individuality of which we 
shall describe later. 

Third: This leads to the hypothesis that this grouping oc- 
curred in the gelatinous state described as "colloidal" by 
Graham.'- Since all living cells are colloidal, it appears prob- 
able that this grouping of the "life elements" took place in a 
state of colloidal suspension, for it is in this state that the life 
elements best display their incessant action, reaction, and 
interaction. Bechhold^ observes that "Whatever the arrange- 
ment of matter in living organisms in other worlds may be, it 
must be of colloidal nature. What other condition except the 

' Ammonia is also formed by electrical action in the atmosphere and unites with the 
nitric oxides to form ammonium nitrate or nitrite; these compounds fall to earth in rain. 
— F. W. Clarke. 

^ Over fifty years ago Thomas Graham introduced the term "colloid" (L. colla, glue) 
to denote non-crystalloid indiffusible substances, like gelatine, a typical colloid, as dis- 
tinguished from diffusible crj'stalloids. Proteins belong to that class of colloids which, 
once coagulated, cannot, as a rule, be redissolved in water. 

^ Bechhold, Heinrich, 1912, p. 194. 


NEW ORGANIC COMPOUNDS 6q 

colloidal could develop such changeable and plastic forms, and 
yet be able, if necessary, to preserve these forms unaltered?" 

Fourth: As a fourth hypothesis relating to the origin of 
organisms, we may advocate the idea that the evolution and 
specialization of various " chemical messengers " known as 
catalyzers (including enzymes or "unformed ferments") has 
proceeded step by step with the evolution of plant and animal 
functions. In the evolution from the single-celled to the many- 
celled forms of life and the multiplication of these cells into 
hundreds of millions, into billions, and into trillions, as in the 
larger plants and animals, biochemical coordination and cor- 
relation became increasingly essential. This cooperation was 
also an application of energy new to the cosmos. 

Fifth: With this assemblage, mutual attraction, colloidal 
condition, and chemical coordination, a fifth hypothesis is 
that there arose the rudiments of competition and Natural 
Selection which tested all the actions, reactions, and inter- 
actions of two competing individuals. Was there any stage in 
this grouping, assemblage, and organization of life forms, how- 
ever remote or rudimentary, when the law of natural selection 
did not operate between different unit aggregations of matter? 
Probably not, because each of the chemical life elements possesses 
its peculiar properties which in living compounds best serve cer- 
tain functions. 

Evolution of New Organic Compounds 

Special actions and reactions appear to be characteristic of 
each of the life elements, issuing in new compounds. 

The central idea in our five hypotheses (see p. 67) of suc- 
cessive physicochemical stages is that in the origin and early 
evolution of the life organism there was a gradual attraction 
and grouping of the ten chief life elements, followed by the 


70 THE ORIGIN AND EVOLUTION OF LIFE 

grouping of the nineteen or more chemical elements which were 
subsequently added. The creation of new chemical compounds 
may have been analogous to the successive addition of new 
characters and functions, such as we now observe through 
palaeontology in the origin and development of the higher 
plants and animals, resembling a series of inventions and dis- 
coveries by the organism. 

Conceivable steps in the process were as follows: From 
earth, air, and water there may have been an early grouping 
of oxygen, nitrogen, hydrogen, and carbon, such as we witness 
in the lowliest bacterial stages of life. Even those lifeless com- 
pounds which contain neither hydrogen, carbon, nor oxygen, 
make up but a very small percentage of the substance of known 
bodies. The compounds of carbon, hydrogen, and oxygen 
(C, H, 0)^ constitute a unique ensemble of fitness among all 
the possible chemical substances for the exchange of matter 
and energy within the life organism and between it and its 
environment. As the higher forms of life are constituted to- 
day, water and the carbon dioxide of the atmosphere are the 
chief materials of the complicated life compounds, and also 
the common end products of the materials yielding energy to 
the body. Proteins are made from materials containing nitro- 
gen in addition. 

Thus may have arisen the utilization of the binary com- 
pounds of carbon and oxygen (CO2), and of hydrogen and 
oxygen (H2O), to the attractive power of which Henderson- 
has especially drawn our attention. It is this attractive power 
of oxygen or of hydrogen or of both elements combined which 
is now bringing, and in the past may have brought into the 
life organism other elements useful to it in its various func- 

^ Henderson, Lawrence J., 1913, pp. 71, 194, 195, 207, 231, 232. 
-Op. cit., pp. 239, 240. 


INTERACTIONS 71 

tions. Thus in the origin of Hfe hydrogen and oxygen, ele- 
ments unrivalled in chemical activity, functioned as ''attrac- 
tive" agents to enable the life organism to draw in other chem- 
ical elements to serve new purposes and functions. 

Through such attraction or other means the incorporation 
of the active metals — ^potassium, sodium, calcium, magnesium, 
iron, manganese, and copper — into the substance of living 
organisms may have occurred in the order of their utility in 
capturing energy from the environment and storing it within 
the organism. For example, an immense period of geologic 
time may have elapsed before the addition of magnesium and 
iron to certain hydrocarbons enabled the plant to draw upon 
the energy of solar light. This marked the appearance of 
chlorophyll in the earliest algal stage of plant life. 

Evolution of Interactions 

The organism as a whole is made a harmonious unit 
through interaction. Its actions and reactions must be regu- 
lated, balanced, coordinated, correlated, protected from foreign 
invasion, accelerated, retarded. This harmony seems in large 
part to be due to the principle that every action and reaction 
sends off as a by-product a "chemical messenger" which sooner 
or later produces an interaction at some more or less distant 
point. 

The regulating and balancing of actions and reactions within 
the organism was provided for by the presence in the fluid cir- 
culation of outside chemical agents, for many of the primordial 
actions and reactions are known to give rise to chemical by- 
products which circulate throughout the life organism. Among 
such regulating and balancing influences we observe that ex- 
erted by the phosphates upon the acidifying tendency of carbon 


72 THE ORIGIN AND EVOLUTION OF LIFE 

dioxide;^ in respiration carbon dioxide raises the hydrogen con- 
centration of the blood; the phosphates restrain this tendency, 
while the breathing apparatus, in response to stimuli from the 
respiratory centres irritated by the hydrogen, throws out the 
excess of this element. 

Thus there evolved step by step the function of coordinating 
and correlating the activities of various parts of the life organ- 
ism remote from each other by means of chemical messen- 
gers adapted to effect not only a general interaction between 
general parts, but also special interactions between special 
parts; for it is now known that, as Huxley prophesied (see 
p. 57), certain chemical messengers do reach particular groups 
of living elements and leave others entirely untouched. For 
example, the enzyme developed in the yeast ferment produces 
a different result in each one of a series of closely related carbo- 
hydrates.- 

These chemical messengers are doubtless highly diversified; 
they are now known to exist in at least three or four forms, 
as follows: 

First: The simplest forms of such chemical messengers are 
those which originate as by-products of single chemical reactions. 
For example, the carbon dioxide (CO2) liberated in the cell by 
the reactions of respiration acts at a distance on other portions 
of the cell and of the organism. Thus every cell of the body 
furnishes in the carbon dioxide which it ehminates a chemical 
messenger,'^ since under normal conditions the carbon dioxide 
of the blood is one of the chief regulators of the respiratory 
centre, influencing this centre by virtue of its acidic properties. 

Second: Of prime importance among the various ''chemical 
messengers" are the organic catalyzers'^ known as enzymes, the 

' W. J. Gies. - Moore, F. J., 1915 p. 170; Loeb, Jacques, 1906, pp. 21, 22. 

^ Abel, John J., 1915, p. 168. ■'Loeb, Jacques, 1906, pp. 8, 28. 


CHEMICAL MESSENGERS 73 

action of which has already been described (see p. 57). They 
appear to be present in all cells, and in most cases the ac- 
tivity of the cell itself depends upon them.^ These enzymes 
are very probably of a protein nature and are readily destroyed 
by heat in the presence of water. The active agents of the 
external secretions when present are always of the nature of a 
ferment or enzyme. Driesch- has suggested that the nucleus 
of the cell is a storehouse of these ferments which pass out 
into the protoplasm tissues and there set up specific activities. 

Third: Antigens, antibodies including the agents of immunity.^ 
The active and inactive protein compounds termed antigens in- 
clude certain known proteins and possibly a few other com- 
pounds of kindred nature. Among the active protein compounds 
are certain enzymes, bacterial poisons, snake venoms, spider 
poisons, and some vegetable poisons; antigens of this class are 
all powerfully active and possess properties which suggest that 
they may eventually be classed as enzymes. On the invasion 
of an organism by any foreign protein of this class in any 
region except the interior of the alimentary canal it would 
seem that certain chemical messengers called antibodies arise 
which are especially fitted to protect the tissues of the body 
against such invasion; these antibodies are true agents of im- 
munity and serve to increase the resistance of the organism to 
any future attack of the invading antigen; it is to this forma- 
tion of neutralizing antibodies, known as antitoxins, that the 
curative powers for such infections as diphtheria and tetanus 
are due. 

There are also antigens of another kind, consisting of inac- 
tive protein compounds, which, when they invade an organism, 
induce the formation of antibodies acting in an entirely dif- 

1 Schafer, Sir Edward A., 1916, pp. 4, 5. "Wilson, lidniund B., 1906, p. 427. 

'Zinsser, Hans, 1915, pp. 223-226, 247, 24S. 


74 THE ORIGIN AND EVOLUTION OF LIFE 

ferent manner from the antitoxins. While antibodies of this 
kind tend to assimilate or remove the invading antigen, they 
do not confer immunity against a future invasion: on the con- 
trary, they render the organism increasingly susceptible. Ex- 
periments on animals show that, while the first injection of 
such inactive proteins may be entirely harmless, subsequent 
injections may result in severe injury or even death. 

It is, therefore, evident that the invasion of an organism 
either by a powerfully active or by an inactive antigen causes 
changes of a physicochemical nature which appear to originate 
in the body cell itself, resulting in the formation of chemical 
messengers known as antibodies which appear in the circulat- 
ing blood. 

Fourth: Of vital importance to the life organism are those 
chemical messengers known as internal secretions, due for the 
most part to the so-called endocrine (Gr. evhov, within, and 
Kpivoi, to separate) organs or ductless glands, which liberate 
some specific substance within their cells that passes directly 
into the blood stream and has a stimulating or inhibiting effect 
upon other organs. To certain of these stimulating internal 
messengers Starling applied the term ''hormone" (Gr. op/xdo), 
to awaken, to stir up). Recently Schafer,^ in reviewing all 
the organs of internal secretion, has proposed the opposite 
term "chalone" (Gr. x"^'^'^, to make slack) for those messen- 
gers which depress, retard, or inhibit the activity of distant 
parts of the body. The interactions between different parts 
of the organism produced by these chemical messengers depend 
upon a simpler chemical constitution than that of the enzymes,- 
as hormones and chalones, for the most part, are not rendered 
inactive, even by prolonged boiling. 

We may suppose that in the course of evolution certain 

' Schafcr, Sir Edward A., 1916, p. 5. - Loc. cit. 


CHEMICAL MESSENGERS 75 

special cells and, finally, special groups of cells gave rise to 
the glands, and none of the discoveries we have hitherto de- 
scribed throws greater illumination on the whole process of 
building up an elaborate life organism than those connected 
with the products of internal secretion. Among the special 
glands of internal secretion known in man are the thyroids, 
parathyroids, thymus, suprarenals, pituitary body, and pineal 
gland, rudiments of which doubtless occur in the very oldest 
vertebrates and even among their invertebrate ancestors; al- 
though their functions have been discovered chiefly through 
experiment upon the lower mammals and man. 

Of the chemical messengers produced by these glands some 
affect the growth of the entire organism, while others affect 
only certain parts of the organism ; some arrest growth entirely, 
others stimulate growth at certain points only, and others again 
entirely change the proportions of certain parts of the body. 
Thus an injury to the pituitary body, which lies beneath the 
vertebrate brain, results in stunted stature, marked adiposity, 
and delayed or imperfect sexual development; on the other 
hand, a diseased condition of the pituitary body, rousing it 
to excessive function, is followed by a great increase in the 
general size of the head, as well as by a complete change in 
the proportions of the face from broad to long and narrow, 
and an abnormal growth of the long limb-bones, while at the 
same time the proportions of the hands are changed from nor- 
mal to the short and broad condition known as brachydactyly.^ 
In other words, the regulation and balance resulting in the 
normal size and proportions of certain parts of the skeleton 
are dependent upon chemical messengers coming from these 
glands. 

1 Schafer, Sir Edward A., 1916, pp. 107, 108, no. Gushing, Harvey, 1911, pp. 
253, 256. 


76 


THE ORIGIN AND EVOLUTION OF LIFE 


It has also been discovered that the source of such internal 
secretions is not confined to the ductless glands, but that cer- 
tain duct-glands, such as the ovaries, testes, and pancreas, 
serve a double function, for they secrete not only through 
their ducts, but they also produce an internal secretion 
which enters the circulation of the blood. It is, of course, a 
fact known from remote antiquity that removal of the sex 


Fig. io. Hantd Form Determined by Heredity (.4) and by Abnormal Internal 

Secretions (B, C). 

A. Hereditary brachydaclyly (partial) attributed to congenital causes. After Drinkwater. 

B. Acquired brachydactyly. This abnormally broad and stumpy hand shows one of the 

results of abnormally excessive secretions of the pituitary gland. After Gushing. 

C. Acquired dolichodactyly. This slender hand with tapering fingers shows one of the 

results of abnormally insufficient secretions of the pituitary gland. After Gushing. 


glands from a young animal of either sex not only inhibits the 
development of all the so-called secondary sexual characters, 
but favors the development of characters of the opposite sex. 
During the last and present centuries it has been discovered 
that all these inhibited characters may be restored by success- 
fully transplanting or grafting into some part of the body the 
ovary or testicle, either from the same or another individual, 
thus proving that in both sexes the secondary sexual characters 


CHEMICAL MESSENGERS 77 

are dependent upon some internal secretion from the ovaries 
and testes and not upon the normal production of the male 
and female germ-cells, or ova and spermatozoa. 

The classic demonstration of this internal messenger sys- 
tem is that made experimentally by Berthold in fowls. In 
1849 he transplanted the testicles of young cocks which after- 
ward developed the masculine voice, comb, sexual desire, and 
love of combat, thus anticipating the theories of Brown- 
Sequard, who committed himself to the view that a gland, 
ductless or not, sends into the circulation substances essential 
to the normal growth and maintenance of many if not all parts 
of the body. 

With the discovery that the regulating and balancing func- 
tions, as well as the accelerating or retarding of the activities 
of certain characters of organisms, are phenomena of physico- 
chemical action, reaction, and interaction in individual devel- 
opment, we obtain a distant glimpse of the possible causes of 
the balance, development, or degeneration of certain parts of 
organisms through successive generations, and conceivably of 
the long-sought means of interaction between the actions and 
reactions of individual development (body-protoplasm and 
body-chromatin) and of the germ-cells in race development 
(heredity-chromatin) . 

In fact, a heredity hypothesis was proposed by Cunning- 
ham' in 1906 based upon Berthold's discovery that the connec- 
tion between the germ-cells and the secondary sexual organs of 
the body was really of a chemical rather than of a nervous 
nature as had previously been supposed. To paraphrase Cun- 
ningham's hypothesis in modern terms, since hormones and 
chalones issuing as internal secretions from the groups of germ- 
cells (ovaries and testes) determine the development of many 

^ Cunningham, J. T., 1908, pp. 372-42S. 


78 THE ORIGIN AND EVOLUTION OF LIFE 

other organs, it is possible that hormones and chalones arising 
from the various cellular activities of the body itself may act 
upon the physicochemical elements in the germ-cells which 
correspond potentially to the tissues from which these hor- 
mones and chalones are derived. Cunningham was a strong 
believer in the Lamarckian explanation (see p. xiii) of evolu- 
tion, and his heredity hypothesis was designed to suggest a 
means by which the modifications of the body due to environ- 
mental and developmental conditions could so modify the 
corresponding tissues and physicochemical constitution of the 
chromatin in the germ-cells as to become hereditary and re- 
appear in subsequent generations. 

Physicochemical Differentiation 

As the result of recent investigations of cancer, Loeb^ comes 
to the following conclusions: 

"We must assume that every individual of a certain species 
differs in a definite chemical way from every other of that 
species, and that in its chemical constitution an animal of one 
species differs still more from an animal of another. Every 
cell of the body has a chemical character in common with ev- 
ery other cell of that body and also in common with the body 
fluids; and this particular chemical group differs from that of 
every other individual of the species and to a still greater de- 
gree from that of any individual of another group or species. 
Thus it happens that cells belonging to the same organism are 
adapted to all the other cells of that organism and also to the 
body fluids. . . . 

"It has been possible to demonstrate by experimental 
methods that there are fine chemical differences not only be- 
tween different species and between different individuals of 

^ Loeb, Leo, 1916, pp. 209-226. 


PHYSICOCHEMICAL DIFFERENTIATION 79 

the same species, but also between different sets of families 
which constitute a strain, for certain chemical characters dif- 
ferentiate them from other strains of the same species. It 
has been shown, for instance, that white mice bred in Europe 
differ chemically from white mice bred in America, although 
the appearance of both strains may be identical." 

The investigations of Reichert and Brown (cited in Chapter 
VIII, p. 247) give an insight into the almost inconceivable 
physicochemical complexity of a single element of the blood, 
namely, the oxyhemoglobin crystals. 


CHAPTER III 

ENERGY EVOLUTION OF BACTERIA, ALG^., 
AND PLANTS 

Energy and form. Primary stages of biochemical evolution in bacteria. Evo- 
lution of protoplasm and chromatin, the two structural components of the 
living world. Chlorophyll and the energy of sunlight. Evolution of the 
algje. Some physicochemical contrasts between plant and animal evo- 
lution. 

We shall now trace some of the physicochemical principles 
of action, reaction, and interaction as they actually appear in 
operation in some of the simpler forms of life, beginning with 
the bacteria. In the bacterial organisms the capture, storage, 
release, and interaction of energy are what is best known and 
apparently most important, while their Jorm is less known and 
apparently less important. 

Primary Stages of Biochemical Evolution in Bacteria 

A bacterialess earth and a bacterialess ocean would soon 
be uninhabitable either for plants or animals; conversely, it is 
probable that bacteria-like organisms prepared both the earth 
and the ocean for the further evolution of plants and animals, 
and that life passed through a very long bacterial stage. 

In the origin of life bacteria appear to lie half-way be- 
tween our hypothetical chemical precellular stages (pp. 67-71) 
and the chemistry and definite cell structure of the lowliest 
plants, or algae. Owing to their minute size or actual invisibil- 
ity, bacteria are classified less by their shape than by their 
chemical actions, reactions, and interactions, the analysis of 

which is one of the triumphs of modern research. 

80 


EVOLUTION OF BACTERIA 8i 

The size of bacteria is in inverse ratio to their importance 
in the primordial and present history of the earth. The largest 
known are slightly above i /20 of a millimetre in length and 
1/200 of a millimetre in width. ^ The smaller forms range 
from I /2000 of a millimetre to organisms on the very limit of 
microscopic vision, i /5000 of a millimetre in size, and to the 
bacteria beyond the limits of microscopic vision, the existence 
of which is inferred in certain diseases. The chemical consti- 
tution of these microscopic and ultramicroscopic forms is 
doubtless highly complex. The number of these organisms is 
inconceivable. In the daily excretion of a normal adult human 
being it is estimated that there are from 128,000,000,000 to 
33,000,000,000,000 bacteria, which would weigh approximately 
5 5/10 grams when dried, and that the nitrogen in this dried 
mass would be about 0.6 gram, constituting nearly one-half 
the total intestinal nitrogen.- 

The discovery of the chemical life of the lowliest bacteria 
marks an advance toward the solution of the problem of the 
origin of life as important as that attending the long-prior dis- 
covery of the chemical action of chlorophyll in plants. 

In their power of finding energy or food in a lifeless world 
the bacteria known as prototrophic, or "primitive feeders," are 
not only the simplest known organisms, but it is probable 
that they represent the survival of a primordial stage of life 
chemistry. These bacteria derive both their energy and their 
nutrition directly from inorganic chemical compounds: such 
types were thus capable of living and flourishing on the lifeless 
earth even before the advent of continuous sunshine and long 

^ The influenza bacillus, s/io X 2/10 of a micron (i/iooo mm.) in size, and the germ 
of infantile paralysis, measuring 2/ 10 of a micron, are on the limit of microscopic vision. 
Beyond these are the ultramicroscopic bacteria, beyond the range of vision, some of 
which can pass through a porcelain filter. See Jordan, Edwin O., 1908, pp. 52, 53. 

- Kendall, A.. I., 1915, p. 209. 


82 THE ORIGIN AND EVOLUTION OF LIFE 

before the first chlorophyllic stage (Algas) of the evolution of 
plant life. Among such bacteria, possibly surviving from 
Archaeozoic time, is one of these "primitive feeders," namely, 
the Nitroso monas of Europe.^ For combustion it takes in 
oxygen directly through the intermediate action of iron, phos- 
phorus, or manganese, each of the single cells being a powerful 
little chemical laboratory which contains oxidizing catalyzers, 
the activity of which is accelerated by the presence of iron and 
of manganese. Still in the primordial stage, Nitroso monas 
lives on ammonium sulphate, taking its energy (food) from 
the nitrogen of ammonium and forming nitrites. Living sym- 
biotically with it is Nitrobacter, which takes its energy (food) 
from the nitrites formed by Nitroso monas, oxidizing them 
into nitrates. Thus these two species illustrate in its simplest 
form our law of the interaction of an organism {Nitrobacter) with 
its life environment {Nitroso monas). - 

These organisms are wide-spread: Nitroso monas is found 
in Europe, Asia, and Africa, while Nitrobacter appears to be 
almost universally distributed. 

These "primitive feeders" are classed among the nitrifying 
bacteria because they take up the nitrogen of ammonia com- 
pounds. Heraeus and Hlippe (1887) were the first to observe 
these nitrifiers in action in the soils and to prove that pre- 
chlorophyllic organisms were capable of development, with 
ammonium and carbon dioxide as their only sources of energy. 
Nine chemical "life elements" are involved in the life reac- 
tions of these organisms, namely, sodium, potassium, phos- 
phorus, magnesium, sulphur, calcium, chlorine, nitrogen, and 
carbon. This discovery was confirmed by Winogradsky (1890, 
1895), who showed that the above two symbiotic groups ex- 
isted; one the nitrite formers, Nitroso monas, and the other the 

1 Fischer, Alfred, 1900, pp. 51, 104. ^ Jordan, Edwin O., 1908, pp. 492-497. 


EVOLUTION OF BACTERIA 83 

nitrate formers, Nitrobactcr. These bacteria are not only in- 
dependent of life compounds, but even small traces of organic 
carbon and nitrogen compounds are injurious to them. Later 
Nathanson (1902) and Beyjerinck (1904) showed that certain 
sulphur bacteria possess similar powers of converting ferrous to 
ferric oxide, and HoS to SOo. 

Such bacterial organisms may have flourished on the lifeless 
earth and chemically prepared both the earth and the waters 
for the lowly forms of plant life. The relation of the nitrifying 
bacteria to the decomposition of rocks is well summarized by 
Clarke in the following passage:^ "Even forms of life so low 
as the bacteria seem to exert a definite influence in the decom- 
position of rocks. A. Miintz has found the decayed rocks of 
Alpine summits, where no other life exists, swarming with the 
nitrifying ferment. The limestones and micaceous schists of 
the Pic du Midi, in the Pyrenees, and the decayed calcareous 
schists of the Faulhorn, in the Bernese Oberland, offer good 
examples of this kind. The organisms draw their nourishment 
from the nitrogen compounds brought down in snow and rain; 
they convert the ammonia into nitric acid, and that in turn 
corrodes the calcareous portions of the "rocks. A. Stutzer and 
R. Hartleb have observed a similar decomposition of cement 
by nitrifying bacteria. The effects thus produced at any one 
point may be small, but in the aggregate they may become 
appreciable. J. C. Branner, however, has cast doubts upon 
the validity of Muntz's argument, and further investigation 
of the subject seems to be necessary." 

It is noteworthy that it is the nitrogen derived from waters 
and soils, rather than from the atmosphere, which plays the 
chief part in the life of these organisms; in a sense they repre- 
sent an early carbon stage of chemical evolution, since carbon 

1 Clarke, F. W., 1916, p. 485. 


84 THE ORIGIN AND EVOLUTION OF LIFE 

is not their prime constituent, also adaptation to an earth-and- 
water environment rather than to an atmospheric one. 

In our portrayal of the chemistry of the Hfeless earth it is 
shown how the chief hfe elements essential for the energy and 
nutrition of the nitrifying bacteria, namely, sodium, potassium, 
calcium, and magnesium, with potassium nitrite and ammo- 
nium salts as a source of nitrogen, may have accumulated in 
the waters, pools, and soils. These bacteria were at once the 
soil-forming and the soil-nourishing agents of the primal earth; 
they throve in the presence of energy-liberating compounds of 
extremely primitive character. It is important to note that 
water and air are essential to vigorous ammonium reactions, 
whether at or near the surface. In arid regions at the present 
time the ammonifying bacteria do not exist on the dry surface 
rocks, but act vigorously in the soils, not only at the surface, 
but also in the lower layers at depths of from six to ten feet, 
where moisture is constant and the porous soil well aerated,^ 
thus giving rise to a nitrogen-nourished substratum, which 
explains the deep rooting of desert-dwelling plants. 

A second point of great significance is that these nitrifying 
organisms are heat-loving and light-avoiding; they are dependent 
on the heat of the earth or of the sun, for, like all other bac- 
teria, they carry on their activities best in the absence of sun- 
shine, direct sunlight being generally fatal. The sterilizing 
effect of sunlight is due partly to the coagulation of the bac- 
terial colloids by the rays of ultra-violet light. The sensitive- 
ness of bacteria to sunlight cannot, however, be viewed as 
evidence against their geologic antiquity, because their undif- 
ferentiated structure and their ability to live on inorganic 
foodstuffs even without the aid of sunshine seem to favor the 
idea that they represent a very primitive form of life.'- 

iLipman, Charles B., 191 2, pp. 7, 8, 16, 17, 20. -I. J. Kligler. 


EVOLUTION OF BACTERIA 85 

The great geologic antiquity even of certain lower forms 
of bacteria which feed on nitrogen is proved by the discovery, 
announced by Walcott^ in 191 5, of a species of pre-Palaeozoic 

ABC 


'■■^r -^ 


V-- . ' 5»/| 


N 


D E F 

Fig. II. Fossil .\nd Living B.\cteri.\ Compared. 

Extremely ancient fossil bacteria (.1) compared \vith similar t\-pcs of Ii\-ing bacteria 
{B-F). 

A. Fossil bacteria from the pre-Cambrian Xewland limestone (Algonkian), after Walcott. 

B. E.xisting nitrifying bacteria found in soils — the arrow indicates a chain series similar 

to that of Walcott's fossil bacteria. 

C. A more complex type of nitrifying bacteria found in soils. 

D. Nitrogen-fixing bacteria from the root nodules of legumes. Note the granular struc- 

ture of the supposed "chromatin." 

E. Denitrifying bacteria found in soil and water. 

F. Bacteria stained to bring out the chromatin granules or "nuclei" in the centre of 

each rod-like bacterial cell. 

fossil bacteria attributed to '''Micrococcus,'' but probably 
related rather to the existing Xitroso coccus, which derives its 
nitrogen from ammonium salts. 

These fossil bacteria were found in a section of a chlorophyll- 

■ Walcott, Charles D., 1915, p. 256. 


86 THE ORIGIN AND EVOLUTION OF LIFE 

bearing algal plant from the Newland limestone of the Algon- 
kian of Montana, the age of which is estimated to be about 
33,000,000 years. They point to a very long antecedent stage 
of bacterial evolution. In this section (Fig. 11, A), at the 
points indicated by the arrows, there is a little chain of cells 
closely similar to those in the existing species of Azotohader, an 
organism that fixes atmospheric nitrogen and converts it into 
a form utilizable by the plant. The Algonkian form is related 
to the other nitrifiers, Nitroso coccus, Nitroso monas, and to 
Nitrohacter which lives on simple salts with carbon dioxide 
(CO2) as a source of carbon. 

The gradual evolution of a cellular structure in these organ- 
isms can be partly traced despite their excessively minute size. 
The cell structure of the Algonkian and of the recent Nitroso 
coccus bacteria (Fig. 11, A, B) is very primitive and uniform in 
appearance, the protoplasm being naked or unprotected; this 
primitive structure is also seen in C, another type of nitrogen- 
fixer of the soil, which is chemically more complex because it 
can obtain its nitrogen either from the inorganic nitrogen 
compounds or from the organic nitrogen compounds (amino- 
acids), which are fatal to the Nitroso monas and the Nitro- 
hacter forms. The arrow points to a group of cells similar in 
appearance to those in B. A higher stage of granular structure 
appears in D, a nitrogen-fixer from the root nodules of legumes, 
which like B and C lives on inorganic chemical compounds, 
but draws upon the atmosphere for nitrogen and upon sugar 
for its carbon; we observe an uneven granular structure in this 
cell. This may be an illustration of an early type of parasitic 
adaptation. The next type of bacterium {E) is a denitrifer, 
which derives its oxygen from the nitrates, reducing them to 
nitrites and free nitrogen and ammonia. A further stage of 
structural and chemical evolution is seen (F) in four elongated 


EVOLUTION OF BACTERIA 87 

bacteria, each showing a rod-Hke but cellular form with a 
deeply staining chromatin or nuclear mass; the arrows point 
to cells showing these chromatin granules. This organism is 
chemically more complex in that it can secrete a powerful 
tryptic-like enzyme which enables it to utilize complex poly- 
pep tids and proteins (casein). Also it is an obligatory aerobic 
type, being unable to function in the absence of free oxygen. 

It was only after the chlorophyllic, carbon-storing true 
plants had evolved that the second great group of parasitic 
nitrifying bacteria arose to develop the power of capturing and 
storing the nitrogen of the atmosphere through life association or 
symbiosis with plants, also of deriving their carbon, not from 
inorganic compounds, but from the carbohydrates of plants. 
Such users of atmospheric nitrogen and of plant carbon include 
three general types: B. radicicola, associated with the root 
formation of legumes (compare D, Fig. 11), Clostridium (anaer- 
obic, i. c., independent of free oxygen), and Azotohacter (aerobic, 
i. e., requiring free oxygen).^ 

It seems that the early course of bacterial evolution was in 
the line of developing a variety of complex molecules for per- 
forming a number of metabolic functions, and that the visible 
cell differentiation came later.- Step by step the chemical 
evolution and addition of increasingly complex actions, reac- 
tions, and interactions appear to correspond broadly with the 
structural evolution of the bacterial organism in its approach 
to the condition of a typical cell with its cell-wall, protoplasm, 
and chromatin nucleus. 

To sum up, the existing bacteria exhibit a series of primor- 
dial physicochemical phases in the capture, storage, and utiHza- 
tion of energy, and in the development of products useful to 
themselves and to other organisms and of by-products which 

^Jordan, Edwin 0., 1908, pp. 484-491. -I. J. Kligler. 


88 THE ORIGIN AND EVOLUTION OF LIFE 

as chemical messengers cause interactions in other organisms. 
With the simplest bacteria which live directly on the lifeless 
world we find that most of the fundamental chemical energies 
of the living world are already established, namely: 
(a) the colloidal cell interior, with all the adaptations of col- 
loidal suspensions, including 
{[)) the stimulating electric action and reaction of the metallic 
on the non- metallic elements; for example, the accelera- 
tions by iron, manganese, and other metals. Some bac- 
teria carry positive, others negative ion charges; 

(c) the catalytic messenger, or enzyme action, both within and 

without the organism; 

(d) the protein and carbon energy storage, the primary food 

supply of the living world. 
Thus the chemical reactions of bacteria are analogous to those 
of the higher plant and animal cells. 

Considering bacteria as the primordial food supply, it is 
the invariable presence of nitrogen which distinguishes the 
bacteria making up their proteins; nitrogen is also a large con- 
stituent of all animal proteins. 

Percentage or Elements in the Proteins ^ 


Carbon 50.0-55.0 

Hydrogen 6.9- 7.3 

Oxygen I g. 0-24.0 

Nitrogen 18. 0-19.0 

Sulphur 0.3- 2.4 


Bacterial suspensions manifest the characteristics of col- 
loidal suspensions, namely, of fluids containing minute gelat- 
inous particles which are kept in motion by molecular move- 

^ Moore, F. J., 1915, p. 199. Nucleic proteins contain a notable amount of phos- 
phorus as well. 


EVOLUTION OF BACTERIA 89 

ment: these colloidal substances have the food-value of protein 
and form the primary food of many Protozoa, the most ele- 
mentary forms of animal life. Chemical messengers in the 
form of enzymes of three kinds exist, proteolytic, oxidizing, and 
synthetic.^ The proteolytic enzymes are similar to the tryptic 
enzymes of animals, being able to digest only the proteoses 
and simple proteins (casein, albumin) but not the complex 
proteins. Powerful oxidizing enzymes are present, but their 
character is not known. Synthetic enzymes, bringing together 
new living chemical compounds^ must also exist, though as yet 
there is no positive information concerning them. 

Armed with these physicochemical powers, which may 
have been acquired one by one, the primordial bacteria begin 
to mimic the subsec|uent evolution of the higher plant and 
animal world by an adaptive radiation into groups which 
respectively seek new sources of energy, either directly from 
the inorganic world or parasitically from the developing organic 
bacterial and plant foods in protein and carbohydrate form, 
the different groups living together in large communities and 
interacting chemically upon one another by the changes pro- 
duced in their environment. 

The parasitic life of bacteria, beginning with their symbiotic 
relations with other bacteria, was extended into intimate rela- 
tions with the plants and finally with the entire living world. 

Like other forms of life, bacteria need oxygen for combus- 
tion in their intracellular actions and reactions; but free oxygen 
is not only unnecessary but actually toxic to the anaerobic 
bacteria, discovered by Pasteur in 1861, which derive their 
oxygen from inorganic and organic compounds. There is, 
however, a transitional group of bacteria, known as the faculta- 
tive anaerobes, which can use either free or combined oxygen, 

1 1. J. Kligler. 


90 THE ORIGIN AND EVOLUTION OF LIFE 

thus forming a link to all the higher forms of life in which free 
oxygen is an absolute essential. There is a group of the higher 
spore-forming bacteria which must have free oxygen. These 
constitute probably a late stage in bacterial evolution and 
form the link to the higher forms. 

The iron bacteria discovered by Ehrenberg in 1838 obtain 
their energy from the oxidation of iron compounds, the insolu- 
ble oxide remaining stored in the cell and accumulating into 
iron as the bacteria die.^ In general the beds of iron ore found 
in certain of the pre-Cambrian stratified rocks, which have an 
estimated age of 60,000,000 years, are believed to be of bac- 
terial origin. Sulphur bacteria similarly obtain their energy 
from the oxidation of hydrogen sulphide. 

Bacteria in the Balance of Life 

Bacteria thus anticipate the plant world of alg£e, diatoms, 
and carbon-formers, as well as the animal world of Protozoa 
and Mollusca, by playing an important role in the formation 
of the new crust of the earth. This is observed in the primor- 
dial limestone depositions composed of calcium carbonate 
formed by bacterial action on the various soluble salts of cal- 
cium present in solution in sea-water, a process exemplified 
to-day- in the Great Bahama Banks, where chalk mud is now 
precipitated through accumulation by B. calcis. Doubtless in 
the shallow continental seas of the primal earth such bacteria 
swarmed, as in the shallow coastal seas of to-day, having both 
the power of secreting and precipitating Hme and, at the same 

' It is claimed that iron bacteria play an important part in the formation of numerous 
small deposits of bog-iron ore, and it seems possible that their activities may be respon- 
sible for extensive sedimentary deposits as well. Further, the fact of finding iron bac- 
teria in underground mines opens the possibility that certain underground deposits of 
iron ore may have been formed by them. — Harder, E. C, 1915, p. 311. 

- Drew, George H., 1914, p. 44. 


PROTOPLASM AND CHROMATIN 91 

time, of converting nitrogen combinations. In the warm 
oceanic waters the amount of Hme deposited is larger and the 
variety of Hving forms is greater; but the number of Hving forms 
which depend for food on the algae is less because the denitrify- 
ing bacteria which flourish in warm tropical waters deprive the 
algae of the nitrates so necessary for their development. Again, 
where algal growth is scarce, the protozoic unicellular and 
multicellular life (plankton) of the sea, which lives upon the 
algae, is also less abundant. This affords an excellent illustra- 
tion of the great law of the balance of the life environment through 
the equilibrium of supply of energy^ one aspect of the interaction 
of organisms with their life environment. The denitrifying 
bacteria rob the waters of the energy needed for the lowest 
forms of plants, and these in turn are not available for the 
lowest forms of animal life. Thus in the colder waters of the 
oceans, where the denitrifying bacteria do not exist, the num- 
ber of living forms is far greater, although their variety is far 
less.^ 

The so-called luminous bacteria also anticipate the plants 
and animals in light production,'- which is believed to be con- 
nected with the oxidation of a phosphorescing substance in 
the presence of water and of free oxygen. 

Evolution of Protoplasm and Chromatin, the Two 
Structural Components of the Living World 

It is still a matter of discussion'' whether any bacteria, even 
at the present time, have reached the evolutionary stage of 
the typical cell with its cell-wall, its contained protoplasm, and 
its distinct nuclear form and inner substance known as chro- 
matin. Some bacteriologists (Fischer) maintain that bacteria 

1 Pirsson, Louis V., and Schuchert, Charles, 1915, p. 104. 

2 Harvey, E. Newton, 191,5, pp. 230, 238. 'I. J. Kligler. 


92 THE ORIGIN AND EVOLUTION OF LIFE 

have neither nucleus nor chromatin; others admit the presence 
of chromatin, but deny the existence of a formal nucleus; others 
contend that the entire bacterial cell has a chromatin content; 
while still others claim the presence of a distinctly differenti- 
ated nucleus containing chromatin. Most of them, however, 
are agreed as to the presence in bacteria of granules of a chro- 
matin nature, while they leave as an open question the pres- 
ence or absence of a structurally distinct nucleus. This con- 
servative point of view is borne out by the fact that all the 
common bacteria have been found to contain nude in, the spe- 
cific nuclear protein complex. Nuclei and chromatin were 
ascribed to the Cyanophyce^, by KohP as early as 1903 and 
by Phillips'- and by Olive^ in 1904. 

It is also a matter of controversy among bacteriologists 
whether protoplasm or chromatin is the more ancient. Cell 
observers (Boveri, Wilson, Minchin), however, are thoroughly 
agreed on this point. Thus Minchin is unable to accept any 
theory of the evolution of the earliest forms of living beings 
which assumes the existence of forms of life composed entirely 
of protoplasm without chromatin.' All the results of modern 
investigations — the combined results, that is to say, of cytology 
and protistology — appear to him to indicate that the chroma- 
tin elements represent the primary and original living units or 
individuals, and that the protoplasm represents a secondary 
product. As to whether chromatin or protoplasm is the more 
ancient, Boveri suggests that true cells arose through sym- 
biosis between protoplasm and chromatin, and that the chro- 
matin elements were primitively independent, living symbioti- 
cally with protoplasm. The more probable view is that of 
Wilson, that chromatin and protoplasm are coexistent in cells 

iKohl, F. G., 1903. = Phillips, O. P., 1904. = Olive, E. W., 1904. 

* Minchin, E. A., 1916, p. 32. 


PROTOPLASJM AND CHROMATIN 


93 


from the earliest known stages, in the bacteria and even prob- 
ably in the ultramicroscopic forms. 

The development of the cell theory after its enunciation in 
1838 by Schleiden and Schwann followed first the differentia- 


FiG. 12. Protoplasm (gray) axd Chromatin (black) of Amoeba , A Typical Protozoan. 

A group of six specimens of Amceha Umax magnified 1000 diameters; /> = protoplasm; 
(7;;-. = chromatin substance of nucleus; d = vacuoles. 

I and 5. Two amoebse with the chromatin nucleus {chr.) in the "resting stage." 

2. An amoeba with the chromatin nucleus dividing into two chromatin nuclei. 

3. A parent amceha with chromatin nuclei completely separated. 

4. Protoplasm and chromatin nuclei separated to form two young amoebae. 

After a photograph by Gary N. Calkins. 


tion of protoplasmic structure in the cellular tissues (histology). 
Since 1880 it has taken a new direction in investigating the 
chemical and Junctional separation of the chromatin. As proto- 
plasm is now known to be the expression, so chromatin is now 
known to be the seat of heredity which Nageli (1884) was the 
first to discuss as having a physicochemical basis; the ^'idio- 
plasm" postulated in his theory being realized in the actual 


94 


THE ORIGIN AND EVOLUTION OF LIFE 


structure of the chromatin as developed in 
the researches of Hertwig, Strasburger, 
KolHker, and Weismann, who indepen- 
dently and almost simultaneously (1884, 
1885) were led to the conclusion that the 
nucleus of the cell contains the physical 
basis of inheritance and that the chroma- 
tin is its essential constituent.^ In the 
development from unicellular (Protozoa) 
into multicellular (Metazoa) organisms 
the chromatin is distributed through the 
nuclei to all the cells of the body, but 
Boveri has demonstrated that all the 
body-cells lose a portion of their chroma- 
tin and only the germ-cells retain the 
entire ancestral heritage. 

Chemically, the most characteristic 
peculiarity of chromatin (Fig. 13), as 


D 


t^ 


^ 


Fig. 13. 


^1^^ 


1 Wilson, E. B., 190O, p. 403. 

The Two Structural Components of 
THE Living World. 


^t%®^ 


Protoplasm or cytoplasm represents the chicj visible fortn 

|«v , "■ •xftll'^'!^''^ or substance of the cell m the growing condition. Chro- 

^ T^ - lis ■' matin is the chief visible centre of heredity; there are 

doubtless other visible and invisible centres of energy 

concerned in heredity. 

Protoplasm (grayish dotted areas) and Chromatin (black, 

waving rods, threads, crescents, and paired spindles) in 

single cells {A-C) and in clusters of cells {D, E). 

A. Achromaliitm, bacteria-like organisms with network of 
chromatin threads and dots. 

B, C. Single-cell eggs in the ovaries of a sea-urchin (resting 
stage), the chromatin concentrated into a small 
black sphere within the nucleolus (inner circle). 

D. Many cells in the root-tip of an onion. Chromatin 
(division stage) in black, wavy lines and threads. 
E. Many cells in the embryo of the giant redwood-tree of California. Chromatin (division 
stage) in black, waving rods, threads, crescents, and spindles. The cell boundaries 
in thin black lines and the dotted protoplasm are clearly shown. After Lawson. 


PROTOPLASM AND CHROMATIN 95 

contrasted with protoplasm, is its phosphorus content.^ It is 
also distinguished by a strong affinity for certain stains which 
cause its scattered or collected particles to appear intensely 
dark (Fig. 13, A-E). Nuclein, which is probably identical with 
chromatin, is a complex albuminoid substance rich in phos- 
phorus. The chemical, or molecular and atomic, constitution 
of chromatin infinitely exceeds in complexity that of any other 
form of matter or energy known. As intimated above (pp. 6, 77), 
it not improbably contains undetected chemical elements. Ex- 
periments made by Oskar, Gunther, and Paula Hertwig (191 1- 
19 1 4) resulted in the conclusion that in cells exposed to radium 
rays the seat of injury is chiefly, if not exclusively, in the chro- 
matin:- these experiments point also to the separate and dis- 
tinct chemical constitution of the chromatin. 

The principle formulated by Cuvier, that the distinctive 
property of life is the maintenance of the individual specific 
form throughout the incessant changes of matter which occur 
in the inflow and outflow of energy, acquires wider scope in 
the law of the continuity of the germ-plasm (?'. c, chromatin) 
announced by Weismann in 1883, for it is in the heredity- 
chromatin^ that the ideal form is not only preserved, but 
through subdivision carried into the germ-cells of all the 
present and succeeding generations. 

It would appear, according to this interpretation, that the 
continuity of life since it first appeared in Archaeozoic time is 
the continuity of the physicochemical energies of the chroma- 
tin; the development of the individual life is an unfolding of 
the energies taken within the body under the directing agency 

^ Minchin, E. A., 1916, pp. 18,19. - Richards, A., 1915, p. 291. 

'The term " chromatin " or " heredity-chromatin " as here used is equivalent to the 
" germ-plasm " of Weismann or the " stirp " of Galton. It is the visible centre of the 
energy complex of heredity, the larger part of which is by its nature invisible. Chro- 
matin, although within our microscopic vision, is to be conceived as a gross manifesta- 
tion of the infinite energy complex of heredity, which is a cosmos in itself. 


Fig. 14. Bulk of Curomatin ix Sequoia and Trillium Compared. 

Chromatin rods in an embryonic cell of the Sequoia compared with those in an embryonic cell of the small 
wood-plant known as the Trinity-flower (Trillium). The chromatin of Sequoia (Sc), which contains all 
the characters, potential and casual, of the giant tree, is less in bulk than the chromatin of Trillium (Tc). 
S. Sequoia washingtoiiia, or gj.?a«/ea, the Big Tree of California. The tree known as "General Sherman," 

shown here, is 279% feet high above ground, its largest circumference is 102^ feet, and its greatest 

diameter is ,56 i feet. 
Sc. Part of the germcell of the nearly allied species. Sequoia semperdrens, the redwood, with the darkly stained 

chromatin rods in the centre. About 1,000 times actual size. The redwood is but little inferior in size 

to the "Big Tree." After Goodspeed. 
T. Trillium. 
To. Part of the germ cell of Trillium sessile, showing the darkly stained chromatin rods in the same phase and 

with the same magnification as in the cell of Sequoia. After Goodspeed. 

96 


PROTOPLASM AND CHROMATIN 97 

of the chromatin; and the evolution of Hfe is essentially the 
evolution of the chromatin energies. It is in the inconceivable 
physicochemical complexity of the microscopic specks of 
chromatin that life presents its most marked contrast to any 
of the phenomena observed within the lifeless world. 

Although each organism has its specific constant in the 
cubic content of its chromatin, the bulk of this content bears 
little relation to the size of the individual. This is illustrated 
by a comparison of the chromatin content of the cell-nucleus 
of Trillium, a plant about sixteen inches high, with that of 
Sequoia sempervircns, the giant redwood-tree of California, 
which reaches a height of from 200 to 340 feet' and attains an 
age of several thousand years (Fig. 14); we observe that the 
chromatin bulk in Sequoia is apparently less than that in 
Trillium. 

The chromatin content of such a nucleus is measured by 
the bulk of the chromosome rods of which it is composed. In 
the sea-urchin the size of the sperm-nucleus, the most compact 
type of chromatin, has been estimated as about i /ioo,ooo,ooo 
of a cubic millimetre, or 10 cubic microns, in bulk.- Within 
such a chromatin bulk there is yet ample space for an incal- 
culable number of minute particles of matter. According to the 
figures given by Rutherford'^ in the first Hale Lecture the dia- 
meter of the sphere of action of an atom is about i / 100,000,000 

^ Jepson, Willis Linn, 191 1, p. 23. - E. B. Wilson, letter of June 28, 1916. 

^ It is necessary, observes Rutherford, to be cautious in speaking of the diameter of 
an atom, for it is not at all certain that the actual atomic structure is nearly so extensive 
as the region through which the atomic forces are appreciable. The hydrogen atom is the 
lightest known to science, and the average diameter of an atom is about 1/100,000,000 
of a centimetre; but the negatively charged particles known as electrons are about 1/1800 
of the mass of the hydrogen atom. . . . These particles travel with enormous velocities 
of from 10,000 to 100,000 miles a second. . . . The alpha particles produce from the 
neutral molecules a large number of negatively charged particles called ions. The ioniza- 
tion due to these alpha particles is measurable. ... In the phosphorescence of an 
emanation of pure radium the atoms throw off the alpha particles with velocities of 
10,000 miles a second, and each second five billion alpha particles are projected. — Ruth- 
erford, Sir Ernest, 1915, pp. 113, 128. 


98 THE ORIGIN AND EVOLUTION OF LIFE 

of a centimetre, or i /lo, 000,000 of a millimetre, or i /io,ooo 
of a micron — the unit of microscopic measurement. The elec- 
trons released from atoms of matter are only 1/1800 of the 
mass of the hydrogen atom, the lightest known to science, and 
thus the mass of an electron would be only 1/18,000,000 of a 
micron. 

These figures help us in some measure to conceive of the 
chromatin as a microcosm made up of an almost unlimited 
number of mutually acting, reacting, and interacting particles; 
but while we know the heredity-chromatin to be the physical 
basis of inheritance and the presiding genius of all phases of 
development, we cannot form the slightest conception of the 
mode in which the chromatin speck of the germ cell controls 
the destinies of Sequoia gigantea and lays down all the laws of 
its being for its long life period of five thousand years. 

In observing the trunk of "General Sherman" (Fig. 14), 
the largest and oldest living thing known, one finds that an 
active regeneration of the bark and woody layers is still in 
progress, tending to heal scars caused by fire many centuries ago. 
This regeneration is attributable to the action of the heredity- 
chromatin in the plant tissues. 

We are equally ignorant as to how the chromatin responds 
to the actions, reactions, and interactions of the body cells, of 
the life environment, and of the physical environment, so as 
to call forth a new adaptive character,^ unless it be through 
some infinitely complex system of chemical messengers and 
other catalytic agencies (p. 77). Yet in pursuing the history 
of the evolution of life upon the earth we may constantly keep 
before us our fundamental biologic law- that the causes of 
evolution are to be sought within four complexes of energies, 
which are partly visible and partly invisible, namely: 

1 Wilson, E. B., 1906, p. 434. - Osborn, H. F., 1912.2. 


CHLOROPHYLL 


99 


Physicochemical energies in the evo- 
lution of the physical environ- 
ment; 

Physicochemical energies in the in- 
dividual development of the or- 
ganism, namely, of its protoplasm 
controlled and directed by its 
chromatin; 

Physicochemical energies in the evo- 
lution of the heredity-chromatin 
with its constant addition of new 
powers and energies; 

Physicochemical energies in the evo- 
lution of the life environment, 
beginning with the protocellular 
chemical organisms, and such in- 
termediate organisms as bacteria, 
and followed by such cellular and 
multicellular organisms as the 
higher plants and animals. 


Selection and Elimination 

Incessant competition, selection, 
intraselection (Roux), and elim- 
ination between all parts of or- 
ganisms in their chromatin ener- 
gies, in their protoplasmic ener- 
gies, and in their actions, reac- 
tions, and interactions with the 
living environment and with the 
physical environment. 


Chlorophyll and the Energy of Sunlight 

As bacteria seek their energy in the geosphere and hydro- 
sphere, chlorophyll is the agent v^hich connects Hfe with the 
atmosphere, disrupting and collecting the carbon from its union 
with oxygen in carbon dioxide. The utilization of the energy 
of sunlight in the capture of carbon from the atmosphere 
through the agency of chlorophyll in algae marked the second 
great phase in the evolution of life, following the first bacterial 
phase. This capture of atmospheric carbon, the chief energy 
element of plants, always takes place in the presence of sun- 
light; while the chief energy elements of bacteria, nitrogen and 
(less frequently) carbon, are captured through molecule-splitting 
in the presence of heat, but without the powerful aid of sun- 
light. 

It is the metamorphosed, fossilized tissue of plants which 
leads us to the conclusion that the agency of chlorophyll is 


lOO THE ORIGIN AND EVOLUTION OF LIFE 

also extremely ancient. Near the base of the Archaean rocks^ 
graphites, possibly formed from fossilized plant tissue, are 
observed in the Grenville series and in the Adirondacks. The 
very oldest metamorphosed sedimentaries are mainly composed 
of shales containing carbon which may have been deposited by 
plants. 

As a reservoir of life energy which is liberated by oxidation, 
hydrogen exceeds any other element in the heat it yields, 
namely, 34.5 calories per gram, while carbon yields 8.1 calories 
per gram.- Since the carbohydrates constitute the basal 
energy-supply of the entire plant and animal world, ^ we may, 
with reference to the laws of action and reaction, examine the 
process even more closely than we have done above (p. 51). The 
results of the most recent researches are presented by Wager:"* 

"The plant organ responds to the directive influence of 
light by a curvature which places it either in a direct line with 
the rays of light, as in grass seedlings, or at right angles to the 
light, as in ordinary foliage leaves." "Of the light that falls 
upon a green leaf a part is reflected from its surface, a part is 
transmitted, and another part is absorbed. That which is 
reflected and transmitted gives to the leaf its green color; that 
which is absorbed, consisting of certain red, blue, and violet 
rays, is the source of the energy by means of which the leaf is 
enabled to carry on its work. 

"The extraordinary molecular complexity of chlorophyll has 
recently been made clear to us by the researches of Willstatter 
and his pupils; Usher and Priestley and others have shown us 
something of what takes place in chlorophyll when light acts 
upon it; and we are now beginning to realize more fully what 
a very complex photosensitive system the chlorophyll must 

' Pirsson, Louis V., and Schuchert, Charles, 1915, p. 545. 

2 Henderson, Lawrence J., 1913, p. 245. ^ Moore, F. J., 1915, p. 213. 

* Wager, Harold, 1915, p. 468. 


EVOLUTION OF ALG^E loi 

be, and how much has yet to be accompHshed before we can 
picture to our minds with any degree of certainty the changes 
that take place when Hght is absorbed by it. But the evidence 
afforded by the action of hght upon other organic compounds, 
especially those which, like chlorophyll, are fluorescent, and 
the conclusion according to modern physics teaching that we 
may regard it as practically certain that the first stage in any 
photochemical reaction consists in the separation, either par- 
tial or complete, of negative electrons under the influence of 
light, leads us to conjecture that, when absorbed by chloro- 
phyll, the energy of the light-waves becomes transformed into 
the energy of electrified particles, and that this initiates a whole 
train of chemical reactions resulting in the building up of the 
complex organic molecules which are the ultimate products of 
the plant's activity." 

Chlorophyll absorbs most vigorously the rays between B 
and C of the solar spectrum,^ which are the most energizing; 
the efl'ect of the rays between D and E is minimal; while the 
rays beyond F again become effective. As compared with the 
primitive bacteria in which nitrogen figures so largely, chloro- 
phyllic plant tissues consist chiefly of carbon, hydrogen, and 
oxygen, the chief substance being cellulose (CeHioOo),- while in 
some cases small amounts of nitrogen are found, and also min- 
eral substances — potassium, magnesium, phosphorus, sulphur, 
and manganese. Chlorophyllic algal life is thus in contrast 
with bacterial life, the prime function of which is to capture 
nitrogen. 

Evolution of the Alg.^ 

Closest to the bacteria in their visible structure are the so- 
called "blue-green algae" or Cyanophyceoe, found almost every- 

' Loeb, Jacques, 1906, p. 115. 

^ Pirsson, Louis V., and Schuchert, Charles, 1915, p. 164. 


I02 


THE ORIGIN AND EVOLUTION OF LIFE 


where in fresh and salt water and even in hot springs, as well 
as on damp soil, rocks, and bark. The characteristic color of 

the Red Sea is due to a 

free-floating form of 
these blue-green algae, 
which in this case are 
red. Unlike the true 
algtC, the cell-nucleus of 
the Cyanophyceae or- 
dinarily is not sharply 
limited by a membrane, 
and there is no evidence 
of distinct chlorophyll 
bodies, although chloro- 
phyll is present. In the 
simpler of the unicel- 
lular Cyanophyceae the 
only method of repro- 
duction is that known 
as vegetative multipli- 

FiG. 15. Fossil and Living 
Alg-E Compared 

C. A living algal pool colony near 

the Great Fountain Geyser, 

Yellowstone Park. After 

Walcott. 

B. Fossil calcareous algas, Crypto- 

zoon prolifcrum Hall, from 

the Cryptozoon Ledge in 

Lester Park near Saratoga 

Springs, N. Y. These algse, 

which are among the oldest 

plants of the earth, grew in cabbage-shaped heads on the bottom of the ancient 

Cambrian sea and deposited lime in their tissue. The ledge has been planed down 

by the action of a great glacier which cut the plants across, showing their concentric 

interior structure. Photographed by H. P. Gushing. 

Fossil alga;, NnvJandia conccntrica, Newlandia Jrondosa, from the Algonkian Belt 

Series of Montana. After Walcott. 


EVOLUTION OF ALG^ 103 

cation, in which an ordinary working cell (individual) divides 
to form two new individuals. In certain of the higher forms, 
in which there is some differentiation of connected cells and in 
which we seem justified in considering the " individual" to be 
multicellular, multiplication is accomplished through the agency 
of cells of special character known as the spores. No evidences 
of sexual reproduction have been observed in the Cyanophyceae. 
The sinter deposits of hot springs and geysers in Yellowstone 
Park are attributed to the presence of Cyanophyceae.^ 

With the appearance of the true algae the earth-forming 
powers of life become still more manifest, and few geologic 
discoveries of recent times are more important than those 
growing out of the recognition of algae as earth-forming agents. 
As early as 1831 Lyell remarked their rock-forming powers. 
It is now known that there are formations in which the algae 
rank first among the various lower organisms concerned in 
earth-building. In a forthcoming work by F. W. Clarke and 
W. C. Wheeler, they remark upon these earth-building activ- 
ities as follows: "The calcareous algae are so important as 
reef-builders that, although they are not marine invertebrates 
in the ordinary acceptance of the term, it seemed eminently 
proper to include them in this investigation. In many cases 
they far outrank the corals in importance, and of late years 
much attention has been paid to them. On the atoll of Funa- 
futi, for example, the algae Lithothamniiim and Halimeda rank 
first and second in importance, followed by the foraminifera, 
third, and the corals, fourth." 

Algae are probably responsible for the formation of the 
very ancient limestones; those of the Grenville series at the 
very base of the pre-Cambrian are believed to be over 60,000,- 
000 years of age. The algal flora of the relatively recent Al- 

* Coulter, John Merle, 1910, pp. 10-14. 


I04 THE ORIGIN AND EVOLUTION OF LIFE 

gonkian time,^ together with calcareous bacteria, developed 
the massive limestones of the Tetons. Clarke observes: "We 
are now beginning to see where the magnesia of the limestones 
comes from and the algae are probably the most important 
contributors of that constituent." 

Thus representatives of the Rhodophyceae contribute as 
high as 87 per cent of calcium carbonate and 25 per cent of 
magnesium carbonate. Species of IJalimeda, however, calci- 
fied algas belonging to the very different class Chlorophyceae, 
are important agents in reef-building and land-forming, yet are 
almost non-magnesian.- 

The Grenville series at the base of the Palaeozoic is essen- 
tially calcareous, with a thickness of over 94,000 feet, nearly 
eighteen miles, more than half of which is calcareous.^ Thus 
it appears probable that the surface of the primordial conti- 
nental seas swarmed with these minute algae, which served as 
the chief food magazine for the floating Protozoa; but it is very 
important to note that algal life is absolutely dependent upon 
phosphorus and other earth-borne constituents of sea-water, as 
well as upon nitrogen, also earth-borne, and due to bacterial 
action; for where the denitrifying bacteria rob the sea-water 
of its nitrogen content the alga? are much less numerous.^ 
Silica is also an earth-borne, though mineral, constituent of 
sea-water which forms the principal skeletal constituent of the 
shells of diatoms, minute floating plants especially charac- 
teristic of the cooler seas, which form the siliceous ooze of the 
sea-bottoms. 

1 Walcott, Charles D., 1914. - M. A. Howe, letter of February 24, 1916. 

' Pirsson, Louis V., and Schuchert, Charles, 191 5, pp. 545, 546. 
^ Op. cit., p. 104. 


PLANT AND ANIMAL EVOLUTION 105 

Some Physicochemical Contrasts Between Plant 
AND Animal Evolution 

In their evolution, while there is a continuous specialization 
and differentiation of the modes of obtaining energy, plants 
may not attain a higher chemical stage than that observed 
among the bacteria and alga?, except in the parasitic forms 
which feed both upon plant and animal compounds. In the 
energy which they derive from the soil plants continue to be 
closely dependent upon bacteria, because they derive their 
nitrogen from nitrates generated by bacteria and absorbed 
along with water by the roots. In reaching out into the air 
and sunlight the chlorophyllic organs differentiate into the 
marvellous variety of leaf forms, and these in turn are sup- 
ported upon stems and branches which finally lead into the 
creation of woody tissues and the clothing of the earth with 
forests. Through the specialization of leaves in connection 
with the germ-cells flowers are developed, and plan-ts establish 
a marvellous series of balanced relations with their life environ- 
ment, first with the developing insect life, and finally with the 
developing bird life. 

The main lines of the ascent and classification of plants are 
traced by palgeobotanists partly from their structural evolu- 
tion, which is almost invariably adapted to keep their chloro- 
phyllic organs in the sunlight^ in competition with other plants, 
and partly from the evolution of their reproductive organs, 
which pass through the primitive spore stage into various 
forms of sexuality, with, finally, the development of the seed 
habit and the dominance of the sporophyte.' It is a striking 
peculiarity of plants that the powers of motion evolve chiefly 
in connection with their reproductive activities, namely, with 

1 Wager, Harold, 1915, p. 468. - M. A. Howe. 


io6 THE ORIGIN AND EVOLUTION OF LIFE 

the movements of the germ cells. We follow the development 
of a great variety of automatic migrating organs, especially in 
the seed and embryonic stages, by which the germs, or chro- 
matin bearers, are mechanically propelled through the air or 
water. Plants are otherwise dependent on the motion of the 
atmosphere and of animals to which they become attached 
for the migration of their germs and embryos and of their 
adult forms into favorable conditions of environment. In 
these respects and in their fundamentally different sources of 
energy they present the widest contrast to animal evolution. 

In the absence of a nervous system the remarkable actions 
and reactions to environmental stimuli which plants exhibit 
are purely of a physicochemical nature. The interactions be- 
tween different tissues of plants, which become extraordinarily 
complex in the higher and larger forms, are probably sustained 
through catalysis and the circulation through the tissues of 
chemical messengers analogous to the enzymes, hormones (ac- 
celerators), and chalones (retarders) of the animal circulation. 
It is a very striking feature of plant development and evolu- 
tion that, although entirely without the coordinating agency 
of a nervous system, all parts are kept in a condition of perfect 
correlation. This fact is consistent with the comparatively 
recent discovery that a large part of the coordination of animal 
organs and tissues which was formerly attributed to the ner- 
vous system is now known to be catalytic. 

Throughout the evolution of plants the fundamental dis- 
tinctions between the heredity-chromatin and the body-proto- 
plasm are sustained exactly as among animals. 

It would appear from the researches of de Vries^ and other 
botanists that the sudden hereditary alterations of plant struc- 
ture and function which may be known as mutations of de 

* De Vries, Hugo, 1901, 1903, 1905. 


PLANT AND ANIMAL EVOLUTION 107 

Vries'^ are of more general occurrence among plants than 
among animals. Such mutations are attributable to sudden 
alterations of molecular and atomic constitution in the hered- 
ity-chromatin, or to the altered forms of energy supplied to 
the chromatin during development. Sensitiveness to the bio- 
chemical reactions of the physical environment should theo- 
retically be more evident in organisms like plants which derive 
their energy directly from inorganic compounds that are con- 
stantly changing their chemical formulae with the conditions 
of moisture, of aridity, of temperature, of chemical soil con- 
tent, than in organisms like animals which secure their food 
compounds ready-made by the plants and possessing com- 
paratively similar and stable chemical formulas. Thus a plant 
transferred from one environment to another may exhibit much 
more sudden and profound changes than an animal, for the 
reason that all the sources of plant energy are profoundly 
changed while the sources of animal energy in a new environ- 
ment are only slightly changed. The highly varied chemical 
sources of plant energy are in striking contrast with the com- 
paratively uniform sources of animal energy which are primarily 
the starches, sugars, and proteins formed by the plants. 

In respect to character origin, or the appearance of new 
characters, therefore, plants may in accordance with the de 
Vries mutation hypothesis exhibit discontinuity or sudden 
changes of form and function more frequently than animals. 
In respect to character coordination , or the harmonious relations 
of all their parts, plants are inferior to animals only in their 
sole dependence on catalytic chemical messengers, while animal 
characters are coordinated both through catalytic chemical 
messengers and through the nervous system. 

In respect to character velocity, or the relative rates of move- 

^ As distinguished from the earlier defined Mutations of Waagcn (see p. 138). 


io8 THE ORIGIN AND EVOLUTION OF LIFE 

ment of different parts of plants in individual development 
and in evolution, plants appear to agree very closely with 
animals. In both we observe that some characters evolve more 
rapidly or more slowly than others in geologic time; also that 
some characters develop more rapidly or slowly than others in 
the course of individual growth. This may be termed charac- 
ter motion or character velocity. 

This law of changes in character velocity, both in individ- 
ual development (ontogeny) and in racial evolution (phylog- 
eny), is one of the most mysterious and difficult to understand 
in the whole order of biologic phenomena. One character is 
hurried forward so that it appears in earlier and earlier stages 
of individual development (Hyatt's law of acceleration), while 
another is held back so that it appears in later and later 
stages (Hyatt's law of retardation). Osborn has also pointed 
out that corresponding characters have different velocities in 
different lines of descent — a character may evolve very rapidly 
in one line and very slowly in another. This is distinctively a 
heredity-chromatin phenomenon, although visible in protoplas- 
mic form. Among plants it is illustrated by the recent obser- 
vations of Coulter on the relative time of appearance of the 
archegonia in the two great groups of gymnosperms (/. e., 
naked-seeded plants), the Cycads (sago-palms, etc.) and the 
Conifers (pines, spruces, etc.), as follows: In the Cycads, which 
are confined to warmer climates, the belated appearance of the 
archegonium persists; in the Conifers, in adaptation to colder 
climates and the shortened reproductive season, the appearance 
of the archegonium is thrust forward into the early embryonic 
stages. Finally, in the flowering plants (Angiosperms) with 
their brief reproductive season, the forward movement of the 
archegonium continues until the third cellular stage of the em- 
bryo is reached. This is but one illustration among hundreds 


PLANT AND ANIMAL EVOLUTION 109 

which might be chosen to show how character velocity in 
plants follows exactly the same laws as in animals, namely, 
characters are accelerated or retarded in race evolution and in 
individual development in adaptation to the environmental and 
individual needs of the organism. 

We shall see this mysterious law of character velocity 
beautifully illustrated among the vertebrates, where of two 
characters, lying side by side, one exhibits inertia, the other 
momentum. 

It is difficult to resist the speculation that character velocity 
in individual development and in evolution is also a phenom- 
enon of physicochemical interaction in some way connected 
with and under the control of chemical messengers which are 
circulating in the system. 


PART II. THE EVOLUTION OF ANIMAL FORM 

CHAPTER IV 

THE ORIGINS OF ANIMAL LIFE AND EVOLUTION 
OF THE INVERTEBRATES 

Evolution of single-celled animals or Protozoa. Evolution of many-celled 
animals or Metazoa. Pre-Cambrian and Cambrian forms of Inverte- 
brates. Reactions to climatic and other environmental changes of geo- 
logic time. The mutations of Waagen. 

A prime biochemical characteristic in the origin of animal 
life is the derivation of energy neither directly from the water, 
from the earth, nor from the earth's or sun's heat, as in the 
most primitive bacterial stages; nor from sunshine, as in the 
chlorophyllic stage of plant life; but from its stored form in 
the bacterial and plant world. All animal life is chemically 
dependent upon bacterial and plant life. 

Many of the single-celled animals like the single-celled bac- 
teria and plants appear to act, react, and interact directly 
with their lifeless and life environment, their protoplasm be- 
ing relatively so simple. We do not know how far this action, 
reaction, and interaction affects the protoplasm only, and how 
far it affects both protoplasm and chromatin. It would seem 
as if even at this early stage of evolution the organism-proto- 
plasm was sensitive while the heredity- chromatin was relatively 
insensitive to environment, stable, and as capable of conserving 
and reproducing hereditary characters true to type as in the 
many-celled animals in which the heredity-chromatin is deeply 
buried within the tissues of the organism remote from direct 
environmental reactions. 


EVOLUTION OF PROTOZOA iii 

Evolution of Single-Celled Animals or Protozoa 

We have no idea when the first unicellular animals known 
as Protozoa appeared. Since the Protozoa feed freely upon 
bacteria, it is possible they may have evolved during the bac- 
terial epoch; it is known that Protozoa are at present one of 
the limiting factors of bacterial activity in the soil, and it is 
even claimed^ that they have a material effect on the fertility 
of the soil through the consumption of nitrifying bacteria. 

On the other hand, it may be that the Protozoa appeared 
during the algal epoch or subsequent to the chlorophyllic plant 
organisms which now form the primary food supply of the 
freely floating and swimming protozoan types. A great num- 
ber of primitive flagellates are saprophytic, using only dis- 
solved proteids as food.- 

Apart from the parasitic mode of deriving their energy, 
even the lowest forms of animal life are distinguished both in 
the embryonic and adult stages by their locomotive powers. 
Heliotropic or sun reactions, or movements toward sunlight, 
are manifested at an early stage of animal evolution. In this 
function there appear to be no boundaries between animals 
and the motile spores, gametes, and seedlings of certain plants.^ 
As cited by Loeb and Wasteneys, Paul Bert in 1869 discovered 
that the little water-flea Daphnia swims toward the light in all 
parts of the visible spectrum, but most rapidly in the yellow or 
in the green. More definitely, Loeb observes that there are 
two particular regions of the spectrum, the rays of which are 
especially effective in causing organisms to turn, or to congre- 
gate, toward them; these regions lie (i) in the blue, in the 

'Russell, Edward John, and Hutchinson, Henry Brougham, 1909, p. 118; 1913, pp. 
191, 219. 

2 Gary N. Calkins. 

' Loeb, Jacques, and Wasteneys, Hardolph, 1915.1, pp. 44-47; 1915.2, pp. 32S-330. 


A 


f^ 


f 


?) 


Ji^V ^^^^-^v 


i;- 


/»\/, 


i^ /I >'ir 

( ^ V rv 
\ 

i 


\ 


D 


E 


^/''^'W 

^^* 


.A,.^^ 


Fig. i6. Typical Forms of Protozoa or Single-Celled Organisms. 

A. Amccba proteus, one of the soft, unprotected, jelly-like organisms which rank among the simplest known 
animals. They are continually changing form by thrusting out or withdrawing the lobe-like projections 
known as pseudopodia, which are temporary prolongations of the cell-body for purposes of locomotion or 
food capture. Any part of the body may serve for the purpose of food ingestion, which is accomplished 
by simply extending the body so as to surround the food. Magnified 200 times life-size. After Leidy. 

D. A colony of flagellates or Mastigophora, showing a number of individuals in variou.s stages of their life his- 

tory. They are distinguished by one or more whip-like prolongations which serve chiefly for purposes of 
locomotion. As, contrasted with the Amxha. many of the flagellates have definite, characteristic body 
forms, and have the function of food ingestion limited to a special area of the body. Magnified 285 times 
life-size. Photographed from a model in the .\merican Museum. 

E. A typical ciliate, one of the most highly organized single-celled forms, distinguished by a multitude of fine 

hair-like cilia, distributed over the whole or a part of the body, which are used for locomotion and for 
the capture of food. In some forms these cilia are grouped or specialized for further effectiveness. After 
BUtschli Magnified 180 times life-size. 


EVOLUTION OF PROTOZOA 


113 


neighborhood of a wave-length of 477 /iyu, and (2) in the 
yellowish-green, in the region of X = 534 /u/a; and these two 
wave-lengths affect different organisms, with no very evident 
relation to the nature of these latter. Thus the blue rays 
(of 477 ixfx) attract the protozoan flagellate Euglena, the hydroid 


HEAT 


Billion ■vibraiijlds per second'-i^^'^ 


CHEMICAL 


ULTRA VIOLET 


Fig. 17. Light, Heat, and Chemical Influence of the Sun. 

Diagram showing the increase, maximum, and decrease of heat, light, and chemical 
energy derived from the sun. The shaded area represents that portion of the spec- 
trum included in the phosphorescent light emitted by our common fire-flies. It is 
probable that it corresponds more closely with the light sensitiveness of the fire-fly's 
eye than with that of the human eye as represented by the wave marked "Light." 
After Ulric Dahlgren. 


coelenterate Eudendrium, and the seedlings of oats; while the 
yellowish-green rays (of 534 /x^i) in turn affect the protozoan 
Chlamydomonas, the crustacean Daphnia, and the crustacean 
larvae of barnacles. 

Aside from these heliotropic movements which they share 
with plants, animals show higher powers of individuality, of 
initiation, of experiment, and of what Jennings cautiously 
terms "a conscious aspect of behavior." In his remarkable 
studies this author traces the genesis of animal behavior to 


114 THE ORIGIN AND EVOLUTION OF LIFE 

reaction and trial. Thus the behavior of organisms is of such 
a character as to provide for its own development. Through 
the principle of the production of varied movements and that 
of the resolution of one physiological state into another, any- 
thing that is possible is tried and anything that turns out to 
be advantageous is held and made permanent.^ Thus the sub- 
psychic stages when they evolve into the higher stages give us 
the rudiments of discrimination, of choice, of attention, of 
desire for food, of sensitiveness to pain, and also give us the 
foundation of the psychic properties of habit, of memory, and 
of consciousness.'- These profound and extremely ancient 
powers of animal life exert indirectly a creative influence on 
animal form, whether we adopt the Lamarckian or Darwinian 
explanation of the origin of animal form, or find elements of 
truth in both explanations.^ The reason is that choice, dis- 
crimination, attention, desire for food, and other psychic 
powers are constantly acting on individual development and 
directing its course. Such action in turn controls the habits 
and migrations of animals, which finally influence the laws of 
adaptive radiation^ and of selection. In this indirect way these 
psychic powers are creative of new form and new function. 

In the evolution of the Protozoa^ the starting-point is a 
simple cell consisting of a small mass of protoplasm contain- 
ing a nucleus within which lies the heredity-chromatin 
(Fig. 12). This passes into the plasmodial condition of 
the Rhizopods, in which the protoplasm increases enormously 
to form the relatively large, unprotected masses adapted to 

'Jennings, H. S., 1906, pp. 318, 319. . "Op. cit., pp. 329-335- 

^ These two explanations are fully set forth below (see pp. 143-146) in the introduc- 
tion to the evolution of the vertebrates. 

■* Adaptive radiation — the development of widely divergent forms in animals ances- 
trally of the same stock or of related stocks, as a result of bodily adaptation to widely 
different environments (see p. 157). 

^ Minchin, E. A., 1916, p. 277. 


EVOLUTION OF PROTOZOA 115 

the creeping or semiterrestrial mode of life. From these 
evolve the forms specialized for the floating pelagic habit, 
namely, the Foramiiiijera and Radiolaria, protected by an 
excessive development and elaboration of their skeletal struc- 
tures.^ Less cautious observers- than Jennings find in the 


Fig. 18. Skeletons of Typical Protozoa. 

B. Siliceous skeleton or shell of a typical radiolarian, Stauraspis siaiiracantha Haeckel, 

170 times the actual size. Owing to their vast numbers, these microscopic, glassy 
skeletons are an appreciable factor in earth-building. A large part of the island 
of Barbados is formed of radiolarian ooze. Photographed from a model in the 
American Museum. 

C. Calcareous skeleton or shell of a typical foraminifer. Globigcn'na bidloidc; d'Orbigny, 

30 times the actual size. As the animal increases in size it forms successively 
larger shells adjoining the earlier ones until, as shown in the figure, a cluster of 
shells of increasing size is formed. The name foraminifer refers to the many 
minute openings, plainly seen in this figure, through which the pseudopodia can 
pass. Photographed from a model in the American Museum. (Compare Fig. i6, 
p. 112.) 

Foraminifera the rudiments of the highest functions and the 
most intelligent behavior of which undifferentiated protoplasm 
has been found capable. In the Mastigoplwra the body de- 
velops flagellate organs of locomotion and food-capture. As 
an offshoot from the ancestors of these forms arose the Ciliata, 
the most highly organized unicellular typts of living beings, 

^Op. cit., p. 278. - Heron- Allen, Edward, 1915, p. 270. 


ii6 THE ORIGIN AND EVOLUTION OF LIFE 

for a Ciliate, like every other protozoan, is a complete and 
independent organism, and is specialized for each and all of 
the vital functions performed by the higher multicellular or- 
ganisms as a whole. 

In the chemical life of the Protozoa^ (Amceba) the proto- 
plasm is made up of colloidal and of crystalloidal substances 
of different density, between which there is a constant, orderly 
chemical activity. The relative speed of these orderly proc- 
esses is attributed to specific catalyzers which control each 
successive step in the long chain of chemical actions. Thus 
in the breaking-down process (destructive metabolism) the by- 
i:)roducts act as poisons to other organisms or they may play 
an important part in the vital activities of the organism itself, 
as in the phosphorescence of Noctiluca, or as in reproduction 
and regeneration. Since regrowth or regeneration- takes place 
in artificially separated fragments of cells in which the nuclear 
substance (chromatin) is believed to be absent, the formation 
of new parts may be due to a specific enzyme, or perhaps to 
some chemical body analogous to hormones and formed as a 
result of mutual interaction of the nucleus and the protoplasm. 
Reproduction through cell-division is also interpreted theoreti- 
cally as due to action set up by enzymes or other chemical 
bodies produced as a result of interaction between the nucleus 
and cell body. The protoplasm is regenerated, including both 
the nuclei and the cell-plasm, by the distribution of large quan- 
tities of nucleoproteins, the specific chemical substance of 
chromatin. 

The latest word as to the part played by natural selection 
in the heredity-chromatin is that of Jennings^ who, after many 
years of experiment, has proved that the congenital charac- 

I Calkins, Gary N., 1916, p. 260. = Op. cit., pp. 261-264, 266. 

3 Jennings, H. S., 1916, pp. 522-526. 


EVOLUTION OF METAZOA 117 

ters arising from the heredity-chromatin are changed by long- 
continued selection through a great number of generations in 
the form of slow gradations which would not be revealed by 
imperfect selection for a few generations. This is doubtless 
the way in which nature works. In the protozoan known as 
Diffiugia the inherited changes produced by selection seem as 
gradual as could well be observed. Large steps do occur, but 
much more frequent is the slow alteration of the stock with 
the passage of generations. The question is asked whether 
even such slight and seemingly gradual hereditary changes 
may not really be little jumps or mutations, since all chemical 
change is discontinuous. In reply, Jennings observes that it is 
highly probable that every inherited variation does involve a 
chemical change, for there is no character change so slight that 
it may not be chemical in nature. In the relatively immense 
organic molecule, with its thousands of groups, the simple trans- 
fer of one atom, one ion, perhaps one electron, is a chemical 
change and, in this sense, discontinuous even though its effect 
is below our powers of perception with the most refined instru- 
ments. 

Through this modern chemical interpretation of the pro- 
tozoan life cycle we may conceive how the laws of thermody- 
namics may be apphed to single-celled organisms, and espe- 
cially our fundamental biologic law of action, reaction, and inter- 
action. By far the most difficult problem in biologic evolution 
is the mode of working of this law among the many-celled or- 
ganisms (Metazoa) including both invertebrates and vertebrates. 

Evolution of Many- Celled Animals or Metazoa 

It is possible that during the long period of pre-Cambrian 
time, which, from the actual thickness of the Canadian pre- 
Cambrian rocks, is estimated at not less than thirty million 


ii8 THE ORIGIN AND EVOLUTION OF LIFE 

years, some of the simpler Protozoa gave rise to the next higher 

stage of animal evolution and to the adaptive radiation on 

land and sea of the Invertebrata. 

We are compelled to assume that the physicochemical actions, 

reactions, and interactions were sustained and became step by 

step more complex as the single-celled 

-,.. r /r. . \ 11-^ Phyla of Fossil 

hfe forms (Protozoa) evolved mto or- Invertebrata 

ganisms with groups of cells (Metazoa), Protozoa 

and these into organisms with two chief Porifera, 

cell-layers (Coelenterata), and later Coelenterata, 

. . 1 . r n Molluscoida, 

into organisms with three chief cell- Echinodermata 

layers. Annulata, 

The metamorphosis by heat and Mollu''s?a'^^' 

pressure of the pre-Cambrian rocks has 

for the most part concealed or destroyed all the life impressions 
which were undoubtedly made in the various continental or 
oceanic basins of sedimentation. Indirect evidences of the 
long process of life evolution are found in the great accumula- 
tions of limestone and in the deposits of iron and graphite^ 
which, as we have already observed, are considered proofs of 
the existence at enormously remote periods of limestone- 
forming algae, of iron-forming bacteria, and of a variety of 
chlorophyll-bearing plants. These evidences begin with the 
metamorphosed sedimentaries overlying the basal rocks of the 
crust of the primal earth. 

Pre-Cambrian and Cambrian Forms of Invertebrates 

The discovery by Walcotf- of a world of highly specialized 
and diversified invertebrate life in the Middle Cambrian seas 
completely confirms the prophecy made by Charles Darwin in 

1 Joseph Barrell. See Pirsson, Louis V., and Schuchert, Charles, 1915, p. 547. 
- Walcott, Charles D., 1911, 1912. 


CAMBRIAN INVERTEBRATES 


119 


1859^ as to the great duration that must be assigned to pre- 
Cambrian time to allow for the evolution of highly specialized 
life forms. 

By Middle Cambrian time the adaptive radiation of the 
Invertebrata to all the conditions of life — ^in continental waters, 


PALEOGEOGRAPHY. LATE LOWER CAMBRIAN (WAUCOBIAN OR OLENELLUS) TIME 
AFTER SCHUCHERT, APRIL, 1916 
^^MARINE DEPOSITS «»" ACTIVE VOLCANOES IM SCOTLAND *-" MOUNTAINS A ■ ARCMAEOCYATHINAE 


Fig. 19. Theoretic World Environment in Late Lower Cambrian Time. 

This period corresponds with that of the first well-known marine fauna with trilobites 
and brachiopods as the dominant forms. No land life of any kind is known, and the 
climate appears to have been warm and equable the world over. After Schuchert. 


along the shore-lines, and in the littoral and pelagic environ- 
ment of the seas — appears to have been governed by mechan- 
ical and chemical principles fundamentally similar to those 
observed among the Protozoa, but distributed through myriads 
of cells and highly complicated tissues and organs, instead of 
being differentiated within a single cell as in the ciliate Pro- 
tozoa. Among the elaborate functions thus evolved, showing 

■ Darwin. Charles, 1850, pp. 306, 307. 


I20 THE ORIGIN AND EVOLUTION OF LIFE 

a more complicated system of action, reaction, and interaction 
with the environment and within the organism, were, first, 
a more efficient locomotion in the quest of food, in the capture 
of food, and in the escape from enemies, giving rise in some 
cases to skeletal structures of various types; second, the evolu- 
tion of offensive and defensive weapons and armature; third, 
various chemical modes of offense and defense; fourth, protec- 
tion and concealment by methods of burrowing.^ 

There are heavy protective coverings for slowly moving 
and sessile animals. In contrast we find swiftly moving types 
(c. g., Sagitta and other chaetognaths) with the lines of modern 
submarines, whose mechanical means of propulsion resemble 
those of the most primitive darting fishes. Other types, such 
as the Crustacea, have skeletal parts for the triple purposes of 
defense, offense, and locomotion, some being adapted to less 
swift motion. In Palaeozoic time they include the slowly 
moving, bottom-living, armored types of trilobites. Then 
there are other slowly moving, bottom-living forms, such as 
the brachiopods and gastropods, with very dense armature of 
phosphate and carbonate of lime. Finally, there are pelagic 
or surface-floating t}q3es, such as the jellyfishes, which are 
chemically protected by the poisonous secretions of their 
"sting-cells." 

This highly varied life of mid-Cambrian time affords abun- 
dant evidence that in pre-Cambrian time certain of the inver- 
tebrates had already passed through first, second, and even 
third phases of form in adaptation to as many different life 
zones. 

Our first actual knowledge of such extremely ancient adap- 
tations dates back to the pre-Cambrian and is afforded by Wal- 
cott's discovery- in the Greyson shales of the Algonkian Belt 

1 R. W. Miner. " Walcott, Charles D., 1899, pp. 235-244. 


CAMBRIAN INVERTEBRATES 


121 


Series of fragmentary remains of that problematic fossil, Bcl- 
tina danai, which he refers to the Merostomata and near to the 
eurypterids, thus making it probable that either eurypterids, or 
forms ancestral both to trilobites and eurypterids existed in pre- 
Cambrian times. More extensive adaptive radiations are found 
in the Lower Cambrian life period of Olenelliis. This trilobite 
is not primitive but a compound phase of evolution, and rep- 
resents the highest trilobite 
development. Trilobites 
are beautifully preserved as 
fossils because of their dense 
chitinous armature, which 
protected them and at the 
same time admitted of con- 
siderable freedom of mo- 
tion. The relationships of 
the trilobites to other in- 
vertebrates have long been 
in dispute, but the dis- 
covery of the ventral sur- 
face and appendages in the mid-Cambrian Ncolcnus serratus 
(Fig. 20) seems to place the trilobites definitely as a subclass 
of the Crustacea, with affinities to the freely swimming phyl- 
lopods, which swarm on the surface of the existing oceans. 

A most significant biological fact is that certain of the 
primitively armored and sessile brachiopods of the Cambrian 
seas have remained almost unchanged generically for a period 
of nearly thirty million years, down to the present time. These 
animals afford a classic illustration of the rather exceptional 
condition known to evolutionists as "balance," resulting in 
absolute stability of type. One example is found in Lingulella 
(Lingula), of which the fossil form, Lingulella acuminata, char- 


FiG. 20. A Mid-Cambrian Trilobite. 
N^coloius serratus (Rominger). After Walcott. 


122 THE ORIGIN AND EVOLUTION OF LIFE 

acteristic of Cambrian and Ordovician times, is closely similar 
to that of Lingiila anatina, a species living to-day. Represen- 
tatives of the genus Lingula {Lingulella) have persisted from 
Cambrian to Recent times. The great antiquity of the brachi- 
opods as a group is well illustrated by the persistence of Lingula 
(Cambrian — Ordovician — Recent), on the one hand, and of 
Terehratula (Devonian — Recent), belonging to a widely differ- 
ing family, on the other. These lamp-shells are thus charac- 
teristic of all geologic ages, including the present. Reaching 
their maximum radiation during the Ordovician and Silurian, 
they gradually lost their importance during the Devonian and 
Permian, and at the present time have dwindled into a rela- 
tively insignificant group, members of which range from the 
oceanic shore-line to the deep-sea or abyssal habitat. 

By the Middle Cambrian the continental seas covered the 
whole region of the present Cordilleras of the Pacific coast. 
In the present region of Mount Stephen, B. C, in the unusually 
favorable marine oily shales of the Burgess formation, the 
remarkable evolution of invertebrate life prior to Cambrian 
time has been revealed through Walcott's epoch-making dis- 
coveries between 1909 and 1912.^ It is at once evident (Figs. 
20-27) that the seashore and pelagic life of this time exhibits 
types as widely divergent as those which now occur among 
the aquatic Invertebrata; in other words, the extremes of 
invertebrate evolution in the seas were reached some thirty 
million years ago. Not only are the characteristic external 
features of these soft-bodied invertebrates evident in the fossil 
remains, but in some cases (Fig. 22) even the internal organs 
show through the imprint of the transparent integument. 
Walcott's researches on this superb series have brought out 
two important points: First, the great antiquity of the chief 

1 Walcott, Charles D., 1911, 1912. 


CAMBRIAN INVERTEBRATES 


123 


aquatic invertebrate groups and their high degree of special- 
ization in Early Cambrian times, which makes it necessary to 
look for their origin far back in the pre-Cambrian ages; and, 
second, the extraordinary persistence of type, not only among 
the lamp-shells (brachiopods) but among members of all the 
invertebrate phyla from the mid- Cambrian to the present 


Tercbratu la 

Devon -Rece nt 


Fig. 21. Brachiopods. Cambrian axd Recent. 

Lingulella (Lingula) acuminata, a fossil form ranging from Cambrian to Ordovician, 
and the verj- similar existing form, Lingula anatina, which shows that the genus has 
persisted from Cambrian times down to the present day. 

Lingulella (^fossil), Cambrian to Ordovician, contrasted with a living specimen of the 
wideh- differing Tcrchratiihi, which ranges from Devonian to recent times. 


time, so that sea forms with an antiquity estimated at twenty- 
five million years can be placed side by side with existing sea 
forms with very obvious similarities of function and structure, 
as in the series arranged for these lectures by Mr. Roy W. 
Miner, of the American Museum of Natural History (Figs. 21, 
22, 24-27). 

Except for the trilobites, the existence of Crustacea in 
Cambrian times was unknown until the discovery of the prim- 


124 


THE ORIGIN AND EVOLUTION OF LIFE 


itive shrimp-like form, Burgessia hella (Fig. 22), a true crusta- 
cean, which may be compared with Apus lucasanus, a mem- 
ber of the most nearly allied recent group. We observe a 
close correspondence in the shape of the chitinous shield (car- 
apace), in the arrangement of the leaf-like locomotor appen- 
dages at the base of the tail, and in the clear internal impres- 


MEROSTOMATA 


RUSTACEA 


Fig. 22. Horseshoe Crab and Shrimp, Cambrian and Recent. 

Molaria spinifcra, a mid-Cambrian merostome (after Walcott), compared witli the 

recent "horseshoe crab," Limiilus polyplicmus. 
Btirg<:ss:a bclla, a shrimp-like crustacean of the Middle Cambrian (after Walcott), 

compared with the very similar Apus lucasanus of recent times. 


sions in Burgessia of the so-called "kidneys," with their 
branched tubules. The position of these organs in Apus is 
indicated by the two light areas on the carapace. Other 
specimens of Burgessia found by Walcott show that the taper- 
ing abdominal region and tail are jointed as in Apus. 

The age of the armored merostome arthropods is also 
thrust back to mid-Cambrian times by the discovery of several 
genera of Aglaspidas, the t}qDical species of which, Molaria 
spinijera Walcott, may be compared with that "living fossil," 


CAMBRIAN INVERTEBRATES 


125 


the horseshoe crab {Limulus polyphemns), its nearest modern 
relative, which is beheved to be not so closely related to the 
phyllopod crustaceans as would at first appear, but rather to 
the Arachnida through the eurypterids and scorpions. Mo- 
laria and Limulus are strikingly similar in their cephalic shield, 


Fig. 23. Theoretic World Environment in Middle Cambrian Time. 

The period of the trilobite Paradoxidcs. This shows the theoretic South Atlantic con- 
tinent "Gondwana" of Suess, connecting Africa and South America. 

segmentation, and telson; but the latter shows an advance 
upon the earlier type in the coalescence of the abdominal seg- 
ments into a single abdominal shield-plate. The trilobate 
character of the cephalic shield in Molaria is an indication of 
its trilobite affinities; hence we apparently have good reason 
to refer both the merostomes and phyllopods to an ancestral 
trilobite stock. 

Another mode of defense is presented by some of the 
sessile, rock-clinging sea-cucumbers (Holothuroidea) protected 


126 THE ORIGIN AND EVOLUTION OF LIFE 

not only by their habit of hiding in crevices, but by their 
leathery epidermis, in which are scattered a number of cal- 
careous plates, as among certain members of the modern eden- 
tate mammals. Fossils of this group have been known here- 
tofore only through scattered spicules and calcareous plates 
dating back no earlier than Carboniferous times (Goodrich); 
therefore Walcott's holothurian material from the Cambrian 
constitutes new records for invertebrate palaeontology, not 
only for the preservation of the soft parts, but for the great 
antiquity of these Cambrian strata. In Louisella pedunculata 
(Fig. 24) we observe the preservation of a double row of tube- 
feet, and the indication at the top of oral tentacles around the 
mouth like those of the modern Elpidiidae. A typical rock- 
clinging holothurian is the recent Pentacta frondosa. 

Besides these sessile, rock-clinging forms, the adaptive 
radiation of the holothurians developed burrowing or fossorial 
types, an example of which is the mid-Cambrian Mackenzia 
costalis (Fig. 24) which strikingly suggests one of the existing 
burrowing sea-cucumbers, Synapta girardil. The character- 
istic elongated cyhndrical body-form with longitudinal muscle- 
bands is clearly preserved in the fossil, while around the mouth 
is a ring of tubercles interpreted by Walcott as calcareous 
ossicles from above which the oral tentacles have been torn 
away. 

A remarkable and problematic mid-Cambrian fossil, Eldonia 
ludwigi (Fig. 24), is regarded by Walcott as a free-swimming 
or pelagic animal. It bears a superficial resemblance to a 
medusa, or jellyfish, while the lines radiating from a central 
ring suggest the existence of a water vascular system; but the 
cylindrical body coiled around the centre shows a spiral intes- 
tine through its transparent body-wall, and it is therefore con- 
sidered to be a swimming holothurian, or sea-cucumber, with 


CAMBRIAN INVERTEBRATES 


127 


a medusa-like umbrella. The existing holothuroid Pelagothuria 
natatrix Ludwig, shown at the right, is somewhat analogous, 


Fig. 24. Sea-Cucumbers of Cambrian and Recent Seas. 

Eldonia luiwigioi the mid-Cambrian (after Walcott), regarded as pelagic and somewhat 
resembling a jellyfish, is thought rather to be a form analogous to Pelagothuria nata- 
trix, a swimming sea-cucumber, although it shows wide differences. The mouth of 
Pelagothuria is above the swimming umbrella, the posterior part of the body and the 
anal opening are below: in the fossil Eldonia both mouth and anus hang below. 

Mackenzia coslalis, a mid-Cambrian form (after Walcott), strongly resembling the bur- 
rowing sea-cucumbers, a recent form of which, Synapta girardii, is shown at the right. 
Loiiisella pedunculata, another mid-Cambrian form (after Walcott), and a recent 
rock-clinging form, Pentacta frondosa. 


although it also displays wide differences of structure. If 
Eldonia ludwigi proves to be a holothurian, we witness in mid- 


128 


THE ORIGIN AND EVOLUTION OF LIFE 


Cambrian strata members of this order differentiated into at 

least three widely distinct famiUes. 

The worms, including swimming and burrowing annulates, 

are represented in the Bur- 
gess fauna by a very large 
number of specimens, com- 
prising nineteen species, dis- 
tributed through eleven 
genera and six families. 
Most of these are of the 
order Polycha?ta, as, for ex- 
ample, Worthenella cambria, 
in which the head is armed 
with tentacles, while the 
segmented body and the 
continuous series of bilobed 
parapodia are very clear. 
When compared with such 
typical living polychaetes as 
Nereis virens and Arabella 
op alma (Fig. 25), we have 
clear proof of the modern 
relationships of these mid- 
Cambrian species, as well as 
of Cambrian sea-shore and 
tidal conditions closely 
similar to those of the pres- 
ent time. A specialization 
toward the spiny or scaly 
annulates at this period is 

emphasized in such forms as Canadia spinosa (Fig. 25), a slowly 

moving form which shows a development of lateral cha^tae and 


Fig. 25. Worms (Annulata) of the IMiddle 
Cambrian and Recent Seashores. 

Canadia spinosa, a mid- Cambrian form (after 
Walcott) with overlappinj^ groups of scale- 
like dorsal spines, resembling those of the liv- 
ing AphroditidcE, such as Polyno'e sqiiamata. 

Worthenella cambria, a worm of mid-Cambrian 
times (after Walcott) , compared with Nereis 
virens and Arabella opalina, recent marine 
worms. 


CAMBRIAN INVERTEBRATES 


129 


CH/ETOGNATHA 


overlapping groups of scale-like dorsal spines comparable only 
to those of the living Aphroditidae. An example of this latter 
family is Polynoe sguamala, furnished with dorsal scales. Still 
other recent forms, such as Palmyra aiirij'era Savigny, have 
groups of spinous scales closely 
resembling those of Canadia. 

Even the modern freely pro- 
pelled Chcrtognatha have their 
representatives in the mid- 
Cambrian, for to no other group 
of invertebrates can Amlskwia 
sagittiformis Walcott (Fig. 26) 
be referred, so far as we can 
judge by its external form. As 
in the recent Sagitta the body 
is divided into head, trunk, and 
a somewhat fish-like tail. Its 
single pair of fins of chaetognath 
type would perhaps give a 
clearer aflfinity to the genus 
Spadella. The conspicuous pair 
of tentacles which surmounts 
the head is absent in modern 

chaetognaths, although some recent species show a pair of sen- 
sory papillae mounted on a stalk on either side of the head, as 
in Spadella cephaloptera Bush. The digestive canal and other 
digestive organs appear through the thin walls of the body. 

A modern group of jellyfishes, the Scyphomedusa? (Fig. 27), 
is represented by the Middle Cambrian Peyioia nathorsti, the 
elliptical disk of which is seen from below. Although this 
fossil species is ascribed by Walcott to the group Rhizostomae 
because of a lack of marginal tentacles, the thirty-two radiat- 


FiG. 26. Freely Swimming Ch^tog- 
NATHS, Cambrian and Recent. 

Amishcia sagittiformis, a mid-Cambrian 
form (after Walcott), has a body di- 
vided into head, trunk, and tail like the 
recent Sagitta, as seen in S. gardincri. 


I30 


THE ORIGIN AND EVOLUTION OF LIFE 


ing lobes which are so beautifully preserved in the fossil cor. 
respond closely with those of the existing genus Dactylometra 
of the suborder Semostomae. It is possible that the marginal 
tentacles may have been lost in Peytoia, as so frequently hap- 
pens in living jellyfishes when in a dying condition. 

From the Burgess fauna it appears that the pre- Cambrian 
invertebrates had entered and become completely adapted to 

all the life zones of the 
continental and oceanic 
waters, except possibly 
the abyssal. All the 
principal phyla — the 
segmented Annulata, 
the jointed Arthropoda 
(including trilobites, 
merostomes, crusta- 
ceans, arachnids, and 
insects), medusae and 
other coelenterates, 
echinoderms, brachio- 
pods, molluscs (includ- 
ing pelycypods, gastro- 
pods, ammonites, and other cephalopods), and sponges — ^w^ere all 
clearly established in pre- Cambrian times. Which one of these 
great invertebrate divisions gave rise to the vertebrates remains 
to be determined by future discovery. At present the Annulata, 
Arthropoda, and Echinodermata all have their advocates as 
being theoretically related to the ancestors of the vertebrates. 
The evolution of each of these invertebrate t^^Des follows the 
laws of adaptive radiation, and in the case of the articulates and 
molluscs extends into the terrestrial and arboreal habitat zones, 
while many branches of the articulates enter the aerial zone. 


Fig. 27. Jellyfish, Cambrian and Recent. 

Peytoia nathorsti, mid-Cambrian (after Walcott), 
and Dactylometra quinquecirra, recent. The 
thirty-two lobes of the fossil specimen corre- 
spond with the same number often observed in 
Dactylometra, and the characteristic marginal 
tentacles may have been lost in Peytoia. 


EVOLUTION OF DIVERGENT AND ANALOGOUS MODES OF RESPIRATION, MOTION. FEEDING. OFFENSE AND DEFENSE. 


AERIAL 


AER5 ARBORt 


ARBOREAL 
ARB0R5TERR!= 


TERRESTRIAL 
TERR2 FOSSORt 
FOSSORIAL 


TERR5 AQUATIC 


AQUATIC, FLUVt-^ 


LITTORAL 


PELAGIC 


ABYSSAL 


uw of adaptive radiation 
Fig. 28. The Twelve Chief Habitat Zones of Animal Life. 

These twelve zones compose the environment, aerial to abyssal, into which the Inver- 
tebrata and Vertebrata have adaptively radiated in the course of geologic time. The 
Invertebrates range from the abyssal to the aerial zones. The fishes, ranging only 
from the terrestrio-aquatic to the abyssal habitat zones, nevertheless evolve body 
forms and types of locomotion similar to those observed in the Amphibia, which range 
from the littoral to the arboreal habitat zones. The reptiles, birds, and mammals, 
ranging from the aerial to the pelagic habitat zones, independently evolve through 
the law of adaptive radiation many convergent, parallel, or similar types of body 
form, as well as similar modes of locomotion and of offense and defense. 


ZONAL DISTRIBUTION OF INVERTEBRATE PHYLATYPICALLY OF MARINE ORIGIN 
MID-CAMBRIAN RECENT 


«.,WM,«..™,U,S,S 


ARBOREAL 


ARB0R5TERR!. 


Ji 1/ 


TERRESTRIAL 


II II 1 


) t) 1 


FOSSORIAL 


TERRS AQUATIC 


11 


AflUATIC.FLUVti 


AJl 


m 


C! i (1U( 11 \ 


•• LfTTORAL 


II ) 


, 


wn{j 


ri ( \) ) 


•• PELAGIC 


\l 


1( 


1 M 


1/ if i \ 


il J 


■■ ABYSSAL 


V 1 


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1 2 


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POLYZOA 
ECHINODERMA 

BRACHIOPODA 


i i i 1 1 M. 

1 r n M 1 


H 111 

i i ^ i 1 


MARINE PELAGIC. LITTORAL. ABYSSAL. 


SECONDARILr AQUATIC AND TERRESTRIAL 


Fig. 29. Life Zones of Cambrian ant) Recent Invertebrates. 

Chart showing in shaded areas the limited habitat zones — Littoral, Pelagic, Abyssal — of 
the known Cambrian forms (left) compared with the wide adaptive radiation (Abyssal 
to Arboreal) of recent forms (right). By Roy W. Miner. 

131 


132 


THE ORIGIN AND EVOLUTION OF LIFE 


The evolution of the articulates^ is believed to be as follows: 
From a pre-Cambrian annelidan (worm-like) stock arose the 
trilobites with their chitinous armature and many-jointed 
bodies. The same stock gave rise also to the chitin-armored 


Fig. 30. Environment. North America in Cambrian Times. 

Theoretic restoration of the North American continent (white), continental seas (gray), 
and ocean (dark gray) in Upper Cambrian (Lower Saint-Croixian) time, during which 
there occurred the earhest known great invasion of land by the oceans. This period 
marks the rise of invertebrate gastropods, limulids, eurypterids, and articulate brach- 
iopods, and the greatest differentiation of trilobites. The lands were probably all 
low and the climate warm. Detail from the globe model in the American Museum 
by Chester A. Reeds and George Robertson, after Schuchert. 

sea-scorpions, or eurypterids, which attained a great size and 
dominated the seas of Silurian times (Fig. 31). Another line 
from the same stock is that of the chitin-armored horseshoe 
crab (Limulus). Out of the eurypterid stock of Silurian times 
may have come the terrestrial scorpions, fossils of which are 

1 Pirsson, Louis V., and Schuchert, Charles, 1915, p. 608. 


CAMBRIAN INVERTEBRATES 


^33 


first known in the Silurian, and through it arose the entire 
group of arachnoid (spider-hke) animals, including the existing 
•scorpions, spiders, and mites. It is also possible that the 


Fig. 31. EuRYPTERiDS OR Sea-Scorpions of Silurian Times. 

A. Restoration of the giant eurypterid, Stylonurus excelsior, from the Catskill sandstone. 

Natural length, four feet. 

B. Restoration of Eusar.cus, from the Bertie water-lime. Natural length, three feet. 

C. Restoration of Eiisarcus, age of the Bertie water-lime. (After John M. Clarke.) 


amphibious, terrestrial, and aerial Insecta were derived from 
some Silurian or Devonian chitin-armored articulate. The 
true Crustacea also have probably developed out of the same 


134 


THE ORIGIN AND EVOLUTION OF LIFE 


pre-Cambrian stock, giving rise to the phyllopods and other 
true Crustacea of the Cambrian, and to the cirripedes or bar- 
nacles of the Ordovician. 


Fig. 


America in Middle Devonian Times. 


Theoretic restoration of the North American continent (white), continental seas (gray), 
and ocean (dark gray), in Middle Devonian (Hamilton) time. This period is 
marked by the last extensive inundation of the Arctic seas, by the rise of the Schick- 
chockian Mountains and many volcanoes in Acadia, and by the beginning of the 
great Catskill delta built up by rivers from the rising Acadian region. Marine shark 
and arthrodires become abundant, the American fauna of the Mississippi Sea shows 
numerous brachiopods and bivalves, and the first evidence of a land flora with large 
conifers (Dadoxylon) is found. Detail from a globe model in the American Museum 
by Chester A. Reeds and George Robertson, after Schuchert. 


Reactions to Climatic and Other Environmental 
Changes of Geologic Time 

Schuchert observes that there is no more significant period 
in the history of the world than the Devonian^ (Fig. 32), for 
at this time the increasing verdure of the land invited the 

^Pirsson, Louis V., and Schuchert, Charles, 1915, p. 714- 


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136 


THE ORIGIN AND EVOLUTION OF LIFE 


invasion of life from the waters, the first conquest of the terres- 
trial environment being attained by the scorpions, shell-fish, 
worms, and insects. 

This is an instance of the constant dispersion of animal 
forms into new environments in search of their food-supply, 

the chief instinctive 
cause of all migration. 
This impulse is con- 
stantly acting and react- 
ing throughout geologic 
time with the migration 
of the environment, 
which is graphically pre- 
sented by Huntington's 
chart (Fig. ;2^;^), from the 
researches of Barrell, 
Schuchert, and others. 
The periodic readjust- 
ment of the earth crust 
of North America^ is 
witnessed in fourteen 
periods of mountain- 
making (oblique lines), 
concluding with the Appalachian Range, the Sierra Nevada 
(Sierran), the Rocky Mountains (Laramide), and the Pacific 
Coast Range. 

Between these relatively short periods of mountain up- 
heaval came'- periods of continental depression and oceanic 
invasion (horizontal lines) when the continent was more or 
less flooded by the oceans. There are certainly twelve and 
probably not less than seventeen periods of continental flood- 

' Pirsson, Louis V., and Schuchert, Charles, 1915, p. 979. ° Op. ciL, p. 98::. 


. ,*-*t 


■ n 


'-:*: f\. 


L ^ 


^ c- 


..V 


■;•■■■■ 1, 


^* . fr 


f.^ ^> '^ 


-• * 


* '^ - 


^ ■ 


- 


- *" * 


» 


» . 'V ■ 


4* - 


V^' ^^ 


•. s * . 


J^ 


*:^, 

___,^^^^ 


IT ~ 


Fig. 34. Fossil Starfishes. 

A portion of petrified sea bottom of Devonian age, 
showing fossil starfishes associated with and 
devouring bivalves as starfishes attack oyster- 
beds at the present time. Hamilton group, 
Saugerties, N. Y. After John INI. Clarke. 


ENVIRONMENTAL CHANGES 137 

ing which vary in extent up to the submergence of 4,000,000 
square miles of surface. 

Each of these changes, which by some geologists are be- 
lieved to be cyclic, included long epochs especially favorable 
to certain forms of life, resulting in the majority of cases in 
high specialization like that of the sea-scorpions (eurypterids) 
followed by more or less sudden extinction. In the oceans the 
life most directly influenced was that of the lime-secreting 
organisms which resulted in maximum and minimum periods 
of limestone formation (oblique lines) by algae, pelagic fora- 
minifera, and corals. On land there were two greater (Car- 
boniferous, Upper Cretaceous) and several lesser periods of 
coal formation. 

Changes of environment play so large and conspicuous a 
part in the selection and elimination of the invertebrates that 
the assertion is often made that environment is the cause of 
evolution, a statement only partly consistent with our funda- 
mental biologic law, which finds that the causes of evolution 
lie within the four complexes of action, reaction, and inter- 
action (see p. 21). 

Perrin Smith, who has made a most exhaustive analysis of 
the evolution of the cephalopod molluscs and especially of 
the Triassic ammonites, observes that the evolution of form 
continues uninterruptedly, even where there is no evidence 
whatever of environmental change. Conversely, environmen- 
tal change does not necessarily induce evolution — for exam- 
ple, during the Age of Mammals, although the mammals de- 
veloped an infinite variety of widely divergent forms, the rep- 
tiles (p. 231) show very little change. 


138 THE ORIGIN AND EVOLUTION OF LIFE 

The Mutations of Waagen 

When Darwin published the "Origin of Species," in 1859, 
no one had actually observed how one form of animal or plant 
actually passes into another, whether according to some definite 
law or principle, or whether fortuitously or by chance. So 
far as we know, the honor of first observing how new specific 
forms arise belongs to Wilhelm Heinrich Waagen.^ It was 
among the fossil ammonites of the Jurassic, which are repre- 
sented by the existing pearly nautilus, that Waagen first ob- 
served the actual mode of transformation of one animal form 
into another, as set forth in his classic paper of 1869, "Die 
Formenreihe des Ammonites subradiatus.'''''^ The essential fea- 
ture of the "mutation of Waagen"^ is that it established the 
law of minute and inconspicuous changes of form which ac- 
cumulate so gradually that they are observable only after a 
considerable passage of time, and which take a definite direc- 
tion as expressed in the word Mutationsrichtung. We now 
recognize that they represent a true evolution of the heredity- 
chromatin. This law of definitely directed evolution is illus- 
trated in the detailed structure of the type series of ammon- 
ites (Fig. 35) in which Waagen's discovery was made. It has 
proved to be a fundamental law of the evolution of form, for 
it is observed alike in invertebrates and vertebrates wherever 
a closely successive series can be obtained. 

Among the fossil invertebrates a mutation series of the 
brachiopod, Spirifer mucronatus of the Middle Devonian or 
Hamilton time, is one of the most tyi^ical (Fig. 36). 

The essential law discovered by Waagen is one of the most 

1 Born in 1841, died in 1900. An Austrian palaeontologist and stratigraphic geologist. 

-Waagen, Wilhelm, 1869. 

* The term " mutation " used in this sense was introduced by Waagen in 1869. Twenty 
years later the great Austrian palaeontologist Neumayr defined the " Mutationsrichtung " 
as the tendency of form to evolve in certain definite directions. See Neumayr, M., 1889, 
pp. 60; 61. 


MUTATIONS OF WAAGEN 


139 


important in the whole history of biology. It is that certain 
new characters arise definitely and continuously, and, as 
Osborn has subsequently shown, ^ adaptively. This law of the 


A. MACROCEPHALUS 


Zone des 
A. ASPIOOIDES 


Zone der 
TERDIGONA 


Zone des 
A, PARKINSONI 


Zone .des 
A. HUMPHRIESIANUS 


A, MAMERTENSIS 


A. SUBCOSTARIUS 


A. LATILOBATUS 


A, SUBRADIATUS 


COLLECTIVART- A. SUBRADIATUS 
Fig. 35. Continuous Character Changes Known as the Mutations of Waagen. 

Successive geologic mutations of A mmonilcs siihradialus, drawn and rearranged from the 
original plates published by Waagen in i86q, showing his type series of the contin- 
uous character changes Icnown as the Mutations of Waagen. 

1 Osborn, Henry Fairfield, 1912.1. 


140 


THE ORIGIN AND EVOLUTION OF LIFE 


gradual evolution of adaptive form is directly contrary to 
Darwin's theoretic principle of the selection of chance varia- 
tions. It is unfortunate that the same term, mutation, was 
chosen by the botanist, Hugo de Vries, in 1901, to express his 
observation that certain characters in plants arise by sudden 


MULTIPLICATUS 


U3) '" 


i*^^ 


m 


mW 


V, 


212 

(347) 


°*'y*^* 


(21) 


^^#^^ 


(177) 
COLLECTIVART-SPIRIFER MUCRONATUS 


THOWBRlCXiE MILLS 


ALPtNA UMESTONE 


SOUMERVILLE UMESTONE 

EUCAJONCLAy 

SUNNYSIOE UMESTONE 

MtDOLE LAKE SHAL£ 


Fig. 36. Successive Mutations of Spirifer mucronalns. 

Specimens from the geologic section at Alpena, Mich., on the shore of Lake Huron, 
and from the corresponding section at Thedford across the lake on the Canadian 
shore, arranged by A. Grabau to show the relationships of the various mutations. 
In the scale of strata at the right 8J4 mm. ec^uals 100 feet depth. 


changes (saltations) or discontinuously, and without any defi- 
nite direction or adaptive trend {Mutationsrichtung) . The 
essential feature of de Vries's observations, in contrast to 
Waagen's, is that of discontinuous saltations in directions that 
are entirely fortuitous — that is, either in an adaptive or in- 
adaptive direction, the direction to be subsequently deter- 
mined by selection — a theoretic principle agreeing closely with 
that of Darwin. 


CHAPTER V 

VISIBLE AND INVISIBLE EVOLUTION OF THE 
VERTEBRATES 

Chromatin evolution. Errors and truths in the Lamarckian and Darwinian 
explanations of the processes of evolution. Character evolution more 
important than species evolution. Individuality in character origin, 
velocity, and cooperation. Origin of the vertebrate type. The laws 
of convergence, divergence, and adaptive radiation of form. 

Simon Newcomb^ considered the concept of the rapid 
movement of the solar system toward Lyra as the greatest 
which has ever entered the human mind. He remarks: ''If I 
were asked what is the greatest fact that the intellect of man 
has ever brought to light, I should say it was this: Through all 
human history, nay, so far as we can discover, from the infancy 
of time, our solar system — sun, planets, and moons — has been 
flying through space toward the constellation Lyra with a 
speed of which we have no example on earth. To form a con- 
ception of this fact the reader has only to look at the beauti- 
ful Lyra and reflect that for every second that the clock tells 
off we are ten miles nearer to that constellation." 

The history of the back-boned animals (Vertebrata) as the 
visible expression of the invisible evolution of the microscopic 
chromatin presents an equally great concept of the potential- 
ities of matter in the infinitely minute state. 

According to this concept our study of the evolution of 
the back-boned animals at once resolves itself into two parallel 
lines of inquiry and speculation, which can never be divorced 
and are always to be followed in observation and inference: 

' Newcomb, Simon, 1902 (ed. of 1904, p. 325). 
141 


142 THE ORIGIN AND EVOLUTION OF LIFE 

The Visible Body The Invisible Germ 

The evolution of somatic (z*. e., The evolution of heredity- 
bodily) FORM and FUNCTION as ob- chromatin as inferred from the in- 
served in anatomy, embryology, pa- cessant visible evolution of Form 
[geontology, and physiology. The and Function. The rise and decline 
rise, differentiation, and change of of potentialities, predispositions, and 
function in bodily characters. other germinal characters. 

A clear distinction exists between the slow, stable heredity- 
chromatin, or germ evolution, and the unstable body cell evolu- 
tion as viewed by the experimental zoologist. The body is un- 
stable because it is immediately sensitive to all variations of 
environment, growth, and habit, while the chromatin alters very 
slowly. The peculiar significance of heredity-chromatin, when 
viewed in the long perspective of geologic time, is its stability 
in combination with incessant plasticity and adaptability to 
varying environmental conditions and new forms of bodily 
action. Chromatin is far more stable than the surface of the 
earth. Throughout, the potentiality of constant changes of 
proportion, gain and loss of characters, genesis of new charac- 
ters, there is always preserved a large part of the history of 
antecedent form and function. In the vertebrates chromatin 
evolution is mirrored in the many continuous series of forms 
which have been discovered, also in the perfection of mechani- 
cal detail in organisms of titanic size and inconceivable com- 
plexity, like the dinosaurs among reptiles and the whales among 
mammals, which rank with the Sequoia among plants. 

Adaptive Characters of Internal-External Action, 
Reaction, Interaction 

Of the causes^ of this slow but wonderful process of chroma- 
tin evolution there are two historic explanations, each adum- 
brated in the Greek period of inquiry. 

' See Preface, p. ix. 


EVOLUTION OF THE GERM 


143 


The older, known as the Lamarckian/ expressed in modern 
terms, is that the causes of tlic genesis of new form and new func- 
tion are to be sought in the body 
cells (soma), on the hypothesis 
that cellular actions, reactions, 
and interactions with each other 
and with the environment are 
in some way impressed physico- 
chemically upon and are heri- 
table by the chromatin. This 
idea was originally suggested 
by the accurate observation of 
early naturalists and anatomists 
that bodily function not only 
controls and perfects form but 
is generally adaptive or pur- 
posive in its effects upon form. 
According to this Lamarck- 
Spencer-Cope explanation a 
change of environment, of 
habit, and of function should al- 
ways be antecedent to changes 
of form in succeeding genera- 
tions; moreover, if this explana- 
tion were the true one, succes- 
sive changes in evolutionary 
series would be like growth, 
they would be observed to fol- 
low the direct lines of individ- 
ual action, reaction, and inter- 
action, and the young would 

' Cf. Preface, pp. xiii, xiv 


Adaptations of Environmental Cor- 
relation : 
respiratory, olfactory, visual, 
altditory, thermal, gravity 
functions and organs 
coordinatlve and correlative to 

variations of LIGHT, HEAT, HU- 
midity, aridity, caused by mi- 
grations of the individual or 
of the enwronment. 

Adaptations of Internal Correlation: 
correlation and coordination of 
the internal growth and func- 
tions through internal secre- 
tions, enzymes, and the ner- 
vous system. 

/\x)aptations of nutrition 

(1) on inorganic compounds. 

(2) on bacteria. 

(3) on protophyta, alg.e, etc. 

(4) on protozoa. 

(5) on higher plants, herbivo- 

rous diet. 

(6) on higher animals, carntv'o- 

rous diet. 

(7) parasitic, without or within 

plants ant) animals. 
Adaptations of Individual Competi- 
tion AND Selection: 

(a) selection, AFFECTING VARIA- 

TION, RECTIGRADATION, MUTA- 
TION, ORIGIN, AND DE\'ELOP- 
MENT OF SINGLE CHARACTERS, 
PROPORTIONS, ETC. 

(b) AFFECTING ALL REPRODUCTR'E 

ORGANS, PRIMARY AND SEC- 
ONDARY. 

Adaptations of Racial Competition 
AND Selection, 

AFFECTING CHIEFLY ALL MOTOR, PRO- 
TECTmS, OFFENSIVE, AND DEFEN- 
SIVE STRUCTURES OF THE ENDO- 
ANT) EXOSKELETON; ALSO REPRO- 
DUCTION RATE. 

The peculiar significance of 

THE HEREDITY-CHROMATIN is itS Sta- 
bility in combination with incessant 
plasticity and adaptability to vary- 
ing environmental conditions and 
new forms of bodily action. 


144 THE ORIGIN AND EVOLUTION OF LIFE 

be increasingly similar to the adults of antecedent genera- 
tions, which is frequently the case but unfortunately for the 
Lamarckian explanation is not invariably the case. In many 
parts of the skeleton chromatin development and degeneration 
so obviously follow bodily use and disuse that Cope was led to 
propose a law which he termed baihmism (growth force) and to 
explain the energy phenomena of use and disuse in the body 
tissues as the cause of the appearance of corresponding energy 
potentialities in the chromatin. In other words, he believed 
that the energy of development or of degeneration in the bodily 
parts of the individual is inherited by corresponding parts in 
the germ. Similar opinions prevail among most anatomists 
(c. g., Cunningham) and among many palaeontologists and zo- 
ologists {c. g., Semon). 

The opposed explanation, the pure Darwinian,^ as restated 
by Weismann and de Vries, is that the genesis of new form and 
function is to be sought in the germ cells or chromatin. This is 
based upon an hypothesis which is directly anti-Lamarckian, 
that the actions, reactions, and interactions which cause cer- 
tain bodily organs to originate, to develop, or to degenerate, 
to exhibit momentum or inertia in development, do not give 
rise to corresponding sets of predispositions in the chromatin, 
and are thus not heritable. According to this explanation, 
body cell changes do not exert any corresponding specific in- 
fluence on the germ cells. All predispositions to new form and 
function not only begin in the germ cells but are more or less 
lawless or experimental; they are constantly being tested or 
tried out by bodily experience, habits, and functions. Techni- 
cally stated, they are "fortuitous" or chance variations, fol- 
lowed by selection of the fittest variations, and thus giving 
rise to adaptations. Thus Darwin's disciple, Poulton, also de 

' Cf. Preface, p. xiv. 


EVOLUTION OF THE GERM 145 

Vries, who has merely restated in his law of "mutation" Dar- 
win's original principle of 1859, and Bateson, the most radical 
thinker of the three, hold the opinion that there is no adaptive 
law observed in germ variation, but that the chromatin is con- 
tinuously experimenting, and that from these experiments se- 
lection guides the organism into adaptive and purposive lines. 
This is the prevailing opinion among most modern experimental 
zoologists and many other biologists. 

Neither the Lamarckian nor the Darwinian explanation 
accords with all that we are learning through palaeontology 
and experimental zoology of the actual modes of the origin and 
development of adaptive characters. That there may be ele- 
ments of truth in each explanation is evident from the follow- 
ing consideration of our fundamental biologic law. Adaptive 
characters present three phases: first, tJie origin of character 
form and character function; second, the more or less rapid 
acceleration or retardation of character form and function; third, 
the coordination and coo peration of character form and func- 
tion. If we adopt the physicochemical theory of the origin 
and development of life it follows that the causes of such 
origin, velocity (acceleration or retardation) and cooperation 
must lie somewhere within the actions, reactions, and interac- 
tions of the four physicochemical complexes, namely, the 
physical environment, the developing organism, the heredity- 
chromatin, the living environment, because these are the only 
reservoirs of matter and energy we know of in life history. 

While it is possible that the relations of these four energy 
complexes will never be fathomed, it is certain that our search 
for causes must proceed along the line of determining which 
actions, reactions, and interactions invariably precede and 
which invariably follow those of the body cells (Lamarckian 
view) or those of the chromatin (Darwin- Weismann view). 


146 THE ORIGIN AND EVOLUTION OF LIFE 

The Lamarckian view that adaptation in the body cells invari- 
ably precedes similar adaptive reaction in the chromatin is not 
supported either by experiment or by observation; such pre- 
cedence, while occasional and even frequent, is by no means 
invariable. The Darwinian view, namely, that chromatin 
evolution is a matter of chance and displays itself in a variety 
of directions, is contradicted by palaeontological evidence both 
in the Invertebrata and Vertebrata, among which we observe 
that continuity and law in chromatin evolution prevails over the 
evidence either of fortuity or of sudden leaps or mutations, that 
in the genesis of many characters there is a slow and prolonged 
rectigradation or direct evolution of the chromatin toward adaptive 
ends. This is what is meant in our introduction (p. 9) by 
the statement that in evolution law prevails over chance. 

Visible Characters, Invisible Chromatin Determiners 

The chief quest of evolutionists to-day in every field of 
observation is the mode and cause of the origin and subsequent 
history of single characters. The quest of Darwin for the causes 
of the origin of species has now become an incidental or side 
issue, since, given a number of new or modified heredity char- 
acters,^ presto, we have a new species. In this present aspect 
of research the discoveries of modern palaeontology are in 
accord with many of the recently discovered laws of heredity. 
The palaeontologist supports the observer of heredity in dem- 
onstrating that every vertebrate organism is a mosaic of an 

' Character (Greek, xapax.TTjp, metaph., a distinctive mark, characteristic, character) 
is the most elastic term in modern biology; we may apply it to every part and function 
of the organism, large or small, which may evolve separately and be inherited separately. 
Mendel has shown that "characters" are far more minutely separable in the invisible 
chromatin than they are in the visible organism; also that every bodily "character" is 
a complex of numerous germ "characters," which are technically known as determiners or 
factors. For example, such a simple visible character as eye color in the fruit-fly is known 
to have determiners in the chromatin. Morgan, Thomas Hunt, 1916, pp. 118-124. 


CHARACTER EVOLUTION 147 

inconceivably large number of "characters" or "character 
complexes," structural and functional, some indissolubly and 
invariably grouped and cooperating, others singularly inde- 
pendent. For example, the zoologist infers that every one of 
the most minute scales of a reptile or hairs of a mammal is a 
"character complex" having its particular chemical formulae 
and chemical energies which condition the shape, the color, 
the function, and all other features of the complex. Through 
researches on heredity each of these characters and character 
complexes is now believed to have a corresponding physico- 
chemical determiner or group of determiners in the germ- 
chromatin, the chromatin existing not as a miniature, but as 
an individual potential and causal. 

In the course of normal physicochemical environment, of 
normal life environment, of normal individual development, 
and of normal selection and competition, an organism will tend 
to more or less closely reproduce its normal ancestral charac- 
ters. But a new or abnormal physicochemical intruder either 
into the environment, the developing individual, the heredity- 
chromatin or the life environment may produce a new or abnor- 
mal visible character type. This cjuadruple nature of the 
physicochemical energies directed upon each and every char- 
acter is tetrakinetic in the sense that it represents four complexes 
of energy; it is tetraplastic in the sense that it moulds bodily 
development from four different complexes of causes. This law 
largely underlies what we call variation of type. 

In other words, the normal actions, reactions, and inter- 
actions must prevail throughout the whole course of growth 
from the germ to the adult; otherwise the visible body (pheno- 
type, Johannsen) may not correspond with the normal expres- 
sion of the potentialities of the invisible germ (genotype, Jo- 
hannsen). 


148 


THE ORIGIN AND EVOLUTION OF LIFE 


The principle of individuality, namely, of separate develop- 
ment and existence, which we have seen to be the prime char- 
acteristic of the first chemical assemblage into an organism 
(p. 68), also governs each of the character complexes, as ob- 
served by the palaeontologist. In some vertebrates we observe 
an infinity of similar character com- 
plexes, evolving in an exactly similar 
manner, as in the beautiful mark- 
ings of the shell and the exquisite 


Fig. 37. Similarly Formed Characters in the Glvptodon. 

Shell pattern and tooth pattern of the Glvptodon, a heavily armored fossil armadillo 
found in North and South America. The entire shell is covered with rosettes, composed 
of small plates nearly uniform in design, similar to those in the very small section repre- 
sented {A). The entire series of upper and lower teeth bear within a uniform "glyptic" 
pattern, like that of the tooth shown here {B), to which the name Glyptodon refers. 


enamel pattern of the teeth of the heavily armored armadillo 
known as the glyptodon (Fig. 37), in which respectively every 
portion of the shell evolves similarly and every one of the 
teeth evolves similarly, from which we might conclude that 
there is an absence of separability or individuality in form 
characters and that some homomorphic (similarly formative) 
impulse is present in all characters of similar chromatin origin. 
But such a rash conclusion is offset by the existence of other 


CHARACTER EVOLUTION 


149 


character complexes of similar ancestry in which each char- 
acter evolves differently and is in a high degree heteromorphic 
(diversely formative), as, for example, in the grinding teeth of 
mammals (Fig. 38). 

This individuality and separability inherent in character 
form is equally observed in character velocity and is the basis 
of the shifting of characters from adult to youthful stages, 
or vice versa, as well as of all the pro- 
portionate and quantitative changes 
which make up four-fifths of verte- 
brate evolution. Increasing character 
velocity is a process of acceleration; 
decreasing character velocity is a proc- 
ess of retardation. For example, in 
the evolution of any group of ani- 
mals, as in plants (p. 108), two char- 
acter forms side by side, like the 
fingers of the hand or toes of the 
foot, may evolve with equal velocity 
and maintain a perfect symmetry, or 
one may be accelerated into a very 
rapid momentum^ while another may be held in a state of 
absolute inertia or equilibrium, and a third may be retarded. 
These are the extremes of character velocity which result in 
the anatomical or visible conditions respectively known as de- 
velopment, balance, and degeneration. 

^ In physics momentum equals mass X velocity. In biology momentum and inertia 
refer to the relative rate of character change, both in individual development (ontogeny) 
and in evolution (phylogeny). Character parallax would express the differing velocities 
of two characters. Thus the character parallax of the right and left horns in the Bron- 
totheriinae (titanotheres) is very small, i. c, they evolve at nearly or quite the same 
rate; on the other hand, the character parallax between the first and second premolar 
teeth in these animals is very great. The character-parallax idea has innumerable ap- 
plications and can be expressed quantitatively. W. K. Gregory. 


Fig. 38. Dissimilarly 
Formed Characters of 
Similar Origin. 

Surface of the upper grinding 
teeth of two ancient Eocene 
mammals. Type B is 
known to be related to 
type A. In Euprologonia 
{A) all the cusps are of a 
somewhat similar rounded 
form. In Mcniscotherium 
(B) each cusp has its own 
peculiar form. 


ISO 


THE ORIGIN AND EVOLUTION OF LIFE 


The ever changing velocity and changing bodily form and 
function in character complexes are to be regarded as expressions 
of physicochemical energy resulting from the actions, reactions, 
and interactions of different parts of the organism. As we 
have repeatedly stated, these changes proceed according to 
some unknown laws. The only vista which we enjoy at pres- 

sent of a possible fu- 
ture explanation of the 
causes of character 
origin, character veloc- 
ity, and character co- 
operation is through 
chemical catalysis, 
namely, through the 
hypothesis that all ac- 
tions and reactions of 
form and of motion 
liberate specific cata- 
lytic messengers, such 
as ferments, enzymes, 
hormones, chalones, 
and other as yet un- 
discovered chemical messengers, which produce specific and 
cooperating interactions in every character complex of the organ- 
ism and corresponding predispositions in the physicochemical 
energies of the germ; in other words, that the chemical accelera- 
tors, balancers, and retarders of body cell development also 
affect the germ. 

In our survey of the marvellous visible evolution of the 
vertebrates we may constantly keep in our imagination this 
conception of the invisible actions, reactions, and interactions 
of the hard parts of the structural tissues, which are preserved 


Fig. 39. Proportional Adaptation in the 
Fingers of a Lemur. 
This peculiar hand of the Aye-Aye {Cheiromys) of 
Madagascar affords an excellent example of un- 
equal velocity in the development of adjacent 
characters. In this hand each finger has its own 
proportionate rate of evolution. The thumb 
(upper) is extremely short; the index finger is 
normal; the middle finger is excessively slender, 
in adaptation to a very special purpose, namely, 
for insertion into small spaces and crevices in 
search of larv£e; the fourth and fifth fingers (two 
lower) are normal. 


CHARACTER EVOLUTION 151 

in visible form in fossils. In this field of observation the nature 
of the chemical and physiological influences of the body can 
only be inferred, while the relations of these physicochemical 
influences to those of the chromatin are absolutely unknown. 

Such a form of explanation would, however, only apply to a 
part of the characters of adaptation (table, page 143). The 
visible and invisible evolution of the hard parts in adaptation 
resolves itself into six chief and concurrent processes, namely: 

Ever changing character form and character function, 

Ever changing character velocity, acceleration, balance, re- 
tardation, in individual development and in the chromatin. 

Ever changing character cooperation, coordination and corre- 
lation. Characters 

Incessant character origin in the heredity-chromatin, some- I and 
times following, sometimes antecedent to similar charac- [ Character 
ter origin in the developing individual. Complexes 

Relatively rapid disappearance of character form and charac- 
ter function in the developing individual. 

Relatively slow disappearance of the determiners and predis- 
positions of character form and character function in the 
heredity-chromatin. 

Changes in the visible bodily hard parts invariably mirror 
the invisible evolution of the chromatin; in fact, this invisible 
evolution is nowhere revealed in a more extraordinary manner 
than in the incessantly changing characters in such structures 
as the labyrinthine foldings of the deep layers of enamel in the 
grinding teeth of the horse. 

The chromatin as the potential energy of form and func- 
tion is at once the most conservative and the most progressive 
centre of physicochemical evolution; it records the body form 
of past adaptations, it meets the emergencies of the present 
through the adaptability to new conditions which it imparts 
to the organism in its distribution throughout every living cell; 
it is continuously giving rise to new characters and functions. 


152 THE ORIGIN AND EVOLUTION OF LIFE 

Taking the whole history of vertebrate Hfe from the beginning, 
we observe that every prolonged, old adaptive phase in a sim- 
ilar habitat becomes impressed in the hereditary characters of 
the chromatin. Throughout the development of new adaptive 
phases the chromatin always retains more or less potentiality 
of repeating the embryonic, immature, and more rarely some 
of the mature structures of older adaptive phases in the older 
environments. This is the basis of the law of ancestral repeti- 
tion, formulated by Louis Agassiz and developed by Haeckel 
and Hyatt, which dominated biological thought during thirty 
years of the nineteenth century (1865-1895). It yielded with 
more or less success a highly speculative solution of the ances- 
tral form history of the vertebrates, through the study of em- 
bryonic development and comparative anatomy, long before 
the actual lines of evolutionary descent were determined 
through palaeontology. 

Laws of Form Evolution in Adaptation to the Mechani- 
cal AND PhYSICOCHEMICAL ACTIONS, REACTIONS, AND 

Interactions of Locomotion, Offense and 
Defense, and Reproduction 

The form evolution of the back-boned animals, beginning 
with the pro-fishes of Cambrian and pre-Cambrian time, ex- 
tends over a period estimated at not less than 30,000,000 
years. The supremely adaptable vertebrate body type be- 
gins to dominate the living world, overcoming one mechan- 
ical difficulty after another as it passes through the habitat 
zones of water, land, and air. Adaptations in the motions 
necessary for the capture, storage, and release of plant and 
animal energy continue to control the form of the body and 
of its appendages, but simultaneously the organism through me- 
chanical and chemical means protects itself either offensively 


THE LAWS OF ADAPTATION 


153 


or defensively and also adapts 
itself to reproduce and protect 
its kind, according to Darwin's 
original conception of the strug- 
gle for existence as involving 
both the life of the individual 
and the life of its progeny. 
Among all defenseless forms 
either speed or chemical or elec- 
trical protection is a prime 
necessity, while all heavily ar- 
mored forms gradually aban- 
don mobility. As among the 
Invertebrata, calcium carbon- 
ate and phosphate and various 
compounds of keratin and chi- 
tin are the chief chemical ma- 
terials of defensive armature. 

Locomotion, as distinguished 
from that in all invertebrates, 
is in an elongate body stiffened 
by a central axis, hence the 
name chordatc or Chord ata for 
the vertebrate division. The 
evolution of the cartilaginous 
skeletal supports (endoskeleton) 
and of the limbs is generally 
from the centre of the body 
toward the periphery, the evolu- 
tion of the epidermal defensive 
armature (exoskeleton) is from 
the periphery toward the centre. 


AGE OF MAN 


^ 


QUATERNARY 


OF 


s.s 


AGE 


g 


YEARS 


|S 


OF 

MAMMALS 


S 


TERTIARY ~ 


UPPER 


S 


K 


£ 


CRETACEOUS 


Z 


g 


U 


^ 2 


i 


LOWER 


AGE 


N 


CRETACEOUS 


1 


REPTILES 


U 


ICOMANCMEAN' 


JURASSIC 


10 - 


> a. 

IT 


2 


;< 


I 


°= 


TRTASSIC 


PERMIAN 


QO5 


15 - 


inuj'*' 


AGE 


i 


lUPPER 


c^h 


■OF 


Ul 


AMPHIBIANS 


i 


ll^ 


< 


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MISSISSIPPIAN 


2zin 


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<0-J 


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5 S 


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AGE 

OF 

FISHES 


s 

UJ 


j 


DEVONIAN 


h 2 
5 ° 


2 


< 
< 


i 


SILURIAN 


u Z 


^ 


Q. 


:£. 


^ 


25 - 


I 


AGE 

OF 

INVERTEBRATES 


i 


ORDOVICIAN 


CAMBRIAN 


MILLIONS 


KEWEENAWAN 


OF 


i 


s 


!! 


ANIMIKIAN 


35 - 


h-' U 


EVOLUTION 


5 


iii 


OF 


HURONIAN 


in 


INVERTEBRATES 


UJ 


si"" 


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a. 


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ALGOMIAN 


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SUDBURIAN 


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d 


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Z 
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I 
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LAURENTIAN 


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1 


EVOLUTION 


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UNICELLULAR 
LIFE 


UJ 


g 1 


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u 

< 


GRENVILLE 


60 


Fio. 40. Total Geologic Time Scale, 
Estimated at Sixty Million Years. 

These estimates are based upon the 
relative thickness of the pre-Cambrian 
and post-Cambrian rocks. Prepared 
by the author and C. A. Reeds after 
the time estimates of Walcott and 
Schuchert. 


154 THE ORIGIN AND EVOLUTION OF LIFE 

The defensive armature finally through change of function 
makes important contributions to the inner skeleton. 

The chief advance which has been made in the last fifty 
years is our abundant knowledge of the modes of adaptation 
as contrasted with the very limited knowledge yet attained 
as to the causes of adaptation. 

The theoretic application of the fundamental law of action, 
reaction, and interaction becomes increasingly difficult and 
almost inconceivable as adaptations multiply and are super- 
posed upon each other with the evolution of the four physico- 
chemical relations, as follows: 

Physical environment: succession, reversal, and alternation 
of habitat zones. 

Individual development: succession, reversal, and alterna- 
tion of adaptive habitat phases. 

Chromatin evohition: addition of the determiners of new 
habitat adaptations while preserving the determiners of 
old habitat adaptations, 

Succession of life environments: caused by the migrations 
of the individual and of the life environment itself. 

The Law of Convergence or Parallelism of Form in 
Locomotor, Offensive, and Defensive Adaptations 

There arise hundreds of adaptive parallels between the 
evolution of the Vertebrata and the antecedent evolution of 
the Invertebrata. Although the structural body t}pe and 
mechanism of locomotion is profoundly diverse, the combined 
necessity for protection and locomotion brings about close 
parallels in body form between such primitive Silurian euryp- 
terids as Biinodes and the vertebrate armored fishes known as 
ostracoderms, a superficial resemblance which has led Patten' 
to defend the view that the two groups are genetically related. 

1 Patten, Wm., 191 2. 


Incessant 

Selection 

and 

Competition 


THE LAWS OF ADAPTATION 


155 


iM(.yo 


>iUn<(Atj>Mt 


It must be the similarity of the internal physicochemical 
energies of protoplasm, the similarity in the mechanics of 
motion, of offense and defense, together with the constant simi- 
larity of selection, which under- 
lies the law of convergence or 
parallelism in adaptation, name- 
ly, the production of externally 
similar forms in adaptation to 
similar external natural forces, a 
law which escaped the keen ob- 
servation of Huxley^ in his re- 
markable analysis of the modes 
of vertebrate evolution pub- 
lished in 1880. 

The whole process of motor 
adaptation in the vertebrates, 
whether among fishes, amphib- 
ians, reptiles, birds, or mam- 
mals, is the solution of a series 
of mechanical problems, namely, 
of adjustment to gravity, of 
overcoming the resistance of 
water or air in the develop- 
ment of speed, of the evolution 
of the limbs in creating levers, 
fulcra (joints), and pulleys. 
The fore and hind fins of fishes 
and the fore and hind limbs of mammals evolve uniformly 
where they are hemodynamic and divergently where they are 
heterodynamic. This principle of homodynamy and hetero- 
dynamy applies to the body as a whole and to every one of its 

"Huxley, T. H., 1880. 


Fig. 41. Convergent Adaptation of 
Form in Three Wholly Unrelated 
Marine Vertebrates. 

Analogous evolution of the swift-swim- 
ming, fusiform body type (upper) in 
the shark, a fish; (middle) in the 
ichthyosaur, a reptile; and (lower) in 
the dolphin, a mammal — three wholly 
unrelated animals in which the in- 
ternal skeletal structure is radically 
different. After Osborn and Knight. 


156 


THE ORIGIN AND EVOLUTION OF LIFE 


parts, according to two laws: first, that each individual part 
has its own mechanical evolution, and, second, that the same 
mechanical problem is generally solved on the same principle. 

This, we observe, is invariably 
the ideal principle, for, unlike 
man, nature wastes little time 
on inferior inventions but imme- 
diately proceeds to superior in- 
ventions. 

The three mechanical prob- 
lems of existence in the water 
habitat are: First, overcoming 
the buoyancy of water either by 
weighting down and increasing 
the gravity of the body or by 
the development of special grav- 
itating organs, which enable 
animals to rise and descend in 
this medium; second, the me- 
chanical problem of overcom- 
ing the resistance of water in 
rapid motion, which is accom- 
plished by means of warped sur- 
faces and well-designed entrant 
and re-entrant angles of the 
body similar to the ''stream- 
lines" of the fastest modern 
yachts; third, the problem of 
propulsion of the body, which is 
accomplished, first, by sinuous motion of the entire body, ter- 
minating in powerful propulsion by the tail fin; secondly, by 
supplementary action of the four lateral fins; third, by the 


HABITAT ADAPTATIONS OF THE VER- 
TEBRATES TO THE CHANGES OF 
ENVIRONMENT 

AERIAL 

(flying, volant types) 

AERO-ARBOREAL 

^PARACHUTE, VOLPLANING TYPEs) 

ARBOREAL 

^CLIMBING, LEAPING, AND BRACHIATING TYPEs) 

ARBOREO-TERRESTRIAL 

(walking and CLIMBING, SCANSORIAL TYPEsJ 


TERRESTRIAL 

(ambulatory, slow: cursoria 
saltatory, leaping ; ghavipoht 
cumbrous) 

TERRESTRIO-FOSSOHIAL 

(walking AND BURROWING TYPEs) 

FOSSORIAL 

(burrowing types) 

TERRESTRIO-AQUATIC 

(amphibious types) 

AQUATIC 

PALUSTRAL, LACUSTRINE 

(surface-living, bottom-livk 


FLUVIATILE 

(fresh-water, swift current, slow- 
current; fluvio-marine types) 

MARINE LITTORAL 

(surface- living and burrowing types) 

marine pelagic 

(free surface-living, drifting, float- 
ing, self-propelling types) 

marine abyssal 

(deep bottom-living types, slow- and 
swift-moving) 

Each of the chief habitat zones may be divided 
into many subzones. The vertebrates may mi- 
grate from one to another of these habitats, or 
through geophysical changes the environments 
themselves may migrate. Conditions of locomo- 
tion result in forms that are quadrupedal, bipedal, 
pinnipedal, apodal, etc. 


THE LAWS OF ADAPTATION 157 

horizontal steering of the body by means of the median sys- 
tem of fins. 

The terrestrial and aerial evolution of the four-limbed 
types (Tetrapoda) is designed chiefly to overcome the resis- 
tance of gravity and in a less degree the resistance of the atmos- 
phere through which the body moves. When the aerial stage 
evolves, with increasing speed the resistance of the air becomes 
only slightly less than that of the water in the fish stage, and 
the warped surfaces, the entrant and re-entrant angles evolved 
by the flying body are similar to those previously evolved in 
the rapidly moving fishes. 

In contrast with this convergence brought about by the sim- 
ilarity above described of the physicochemical laws of action, 
reaction, and interaction, and the similarity of the mechanical 
obstacles encountered by the different races of animals in 
similar habitats and environmental media, is the law of diver- 
gence. 

Branching or Divergence of Form, the Law of Adaptive 

Radiation 

In general the law of divergence of form, perceived by La- 
marck and rediscovered by Darwin, has been expanded by 
Osborn into the modern law of adaptive radiation, which ex- 
presses the differentiation of animal form radiating in every 
direction in response to the necessities of the quest for nour- 
ishment and the development of new forms of motion in the 
different habitat zones. The psychic rudiments of this ten- 
dency to divergence are observed among the single-celled Pro- 
tozoa (p. 114). Divergence is constantly giving rise to differ- 
ences in structure, while convergence is constantly giving rise 
to resemblances of structure. 

The law of adaptive radiation is a law expressing the modes 


158 


THE ORIGIN AND EVOLUTION OF LIFE 


of adaptation of form, which fall under the following great 
principles of convergence and divergence: 


1. Divergent adaptation, by which the members of a primitive 

stock tend to develop differences of form while radiating 
into a number of habitat zones. 

2. Convergent adaptation, parallel or homoplastic, whereby an- 

imals from different habitat zones enter a similar habitat 
zone and acquire many superficial similarities of form. 

3. Direct adaptation, for example, in primary migration through 

an ascending series of habitat zones, aquatic to terres- 
trial, arboreal, aerial. 

4. Reversed adaptation, where secondary migration takes a re- 

verse or descending direction from aerial to arboreal, 
from arboreal to terrestrial, from terrestrial to aquatic 
habitat zones. 

5. Alternate adaptation, where the animal departs from an orig- 

inal habitat and primary phase of adaptation into a sec- 
ondary phase, and then returns from the secondary phase 
of adaptation into a more or less perfect repetition of the 
primary phase by returning to the primary habitat zone. 

6. Change of adaptation {function), by which an organ serving a 

certain function in one zone is not lost but takes up an 
entirely new function in a new zone. 

7. Symbiotic adaptation, where vertebrate forms exhibit recip- 

rocal or interlocking adaptations with the form evolution 
of other vertebrates or invertebrates. 


Law 

of 

Adaptive 

Radiation 

in the 

External 

Body 

Form 


It is very important to keep in mind that the body and 
limb form developed in each adaptive phase is the starting 
point of the next succeeding phase. 

Prolonged residence by an animal type in a single habitat 
zone results in profound alterations in its chromatin and in 
consequence the history of past phases is more or less clearly 
recorded. 

Among the disadvantages of prolonged existence in one life 
zone are the following: Through the law of compensation, dis- 
covered by Geoffroy St. Hilaire early in the last century, every 
vertebrate, in developing and specializing certain organs sacri- 


THE LAWS OF ADAPTATION 159 

fices others; for example, the lateral digits of the foot of the 
horse are sacrificed for the evolution of the central digit as the 
animal evolves from tridactylism to monodactylism. These 
sacrificed parts are never regained; the horse can never regain 
the tridactyl condition although it may re-enter a habitat 
zone in which three digits on each foot would serve the pur- 
poses of locomotion better than one. In this sense chromatin 
evolution is irreversible. The extinction of vertebrate races 
has generally been due to the fact that the various types have 
sacrificed too many characters in their structural and func- 
tional reactions to a particular life habitat zone. A finely spe- 
cialized form representing a perfect mechanism in itself which 
closely interlocks with its physical and living environment 
reaches a cul-de-sac of structure from which there is no possible 
emergence by adaptation to a different physical environment 
or habitat zone. It is these two principles of too close adjust- 
ment to a single environment and of the non-revival of char- 
acters once lost by the chromatin which underly the law that 
the highly specialized and most perfectly adapted types become 
extinct, while primitive, conservative, and relatively unspe- 
cialized types invariably become the centres of new adaptive 
radiations. 


CHAPTER VI 

EVOLUTION OF BODY FORM IN THE FISHES AND 

AMPHIBIANS 

Rapid evolution in a relatively constant environment. Mechanism of motion, 
of offense, and defense. Early armored fishes. Primordial sharks. Rise 
of existing groups of fishes. Form evolution of the amphibians. Maxi- 
mum radiation and extinction. 

A SIGNIFICANT law of fish evolution is that in a practically 
unchanging environment, that of salt and fresh water, which is 
relatively constant both as to temperature and chemical con- 
stitution as compared with the variations of the terrestrial 
environment, it is steadily progressive and reaches the great- 
est extremes of form and of function. This indicates that a 
changing physicochemical environment, although important, is 
not an essential cause of the evolution of form. The same 
law holds true in the case of the marine invertebrates (p. 137), 
as observed by Perrin Smith. A second principle of signifi- 
cance is that even the lowliest fishes establish the chief glandu- 
lar and other organs of action, reaction, and interaction which 
we observe in the higher types of the vertebrates. Especially 
the glands of internal secretion (p. 74), the centres of inter- 
action and coordination, are fully developed. 

Mechanism of Motion, of Offense, and Defense 

Ordovician time, the early Palaeozoic Epoch next above the 
Cambrian, is the period of the first vertebrates known, namely, 
the fossil remains of fish dermal defenses found near Canon 
City, Col., as announced by Walcott in 1891, and subse- 
quently discovered in the region of the present Bighorn 

160 


EARLIEST KNOWN FISHES 


i6i 


Mountains of Wyoming and the Black Hills of South Dakota. 
Small spines referred to acanthodian sharks are also abundant 
in the Ordovician of Canon City, Col. Since they were slow- 
moving types protected with the beginnings of a dorsal arma- 
ture composed of small calcareous tubercles, to which the 


BIRDS MAMMALS 


ORDER OF APPEARANCE AND EXPANSION OF THE CLASSES OF VERTEBRATE ANIMALS 


Fig. 42. Chronologic Chart of Vertebrate Succession. 

Successive geologic appearance and epochs of maximum adaptive radiation (expansion) 
and diminution (contraction) of the five classes of vertebrates, namely, fishes, amphi- 
bians, reptiles, birds, and mammals. 

group name Ostracoderm refers, probably these earliest known 
pro-fishes were not primitive in external form but followed 
upon a long antecedent stage of vertebrate evolution. In the 
form evolution of the vertebrates relatively swift-moving, de- 
fenseless types are invariably antecedent and ancestral to slow- 
moving, armored types. Ancestral to these Ordovician chor- 
dates there doubtless existed free-swimming, quickly darting 


l62 


THE ORIGIN AND EVOLUTION OF LIFE 


types of unarmored fishes. The double-pointed, fusiform body, 
in which the segmented propelHng muscles are external and a 
stiffening notochord is central, is the fish prototype, which 

MYOMERES 
iscfe segments) 


SPIKAi KEHV[ CORD 


=v r t'T—i.-— ^l^i- :n-T, 


:???:?rr^p-^ 


". -«,,t=s.'""';-is=-^sr'-..i^. - w 


^//>^ 


w///AM^ym^y/^'\^ 


,V\ 


^ 


OIGEST/te TRUCr 


more or less clearly 
survives in the exist- 
ing lancelets (Aniphi- 
oxus) and in the lar- 
val stages of the de- 
generate ascidians. 
These animals also 
furnish numerous 
embryonic and lar- 
val proofs of de- 
scent from nobler 
types. 

Following the 
pro-fishes of Ordovi- 
cian time, the great group of true fishes begins its form evolu- 
tion with (^4) active, free-swimming, double-pointed types of 
fusiform shape, adapted to rapid motion through the water 
and to predaceous habits in pursuit of swift-moving prey. 


I'lG. 43. TuK Existing Lanceleis [Aiiipliioxns). 

Fusiform protochordates living in the littoral zone of 
the ocean shores, sole survivors of an extremely 
ancient stage of chordate (pro-vertebrate) evolution. 
The body is fusiform or doubly pointed, hence the 
name Amphioxiis. It is stiffened by the continuous 
central axis (chorda, notochord). All the other or- 
gans are more or less sharply segmented. After Willey. 


EARLIEST KNOWN FISHES 


163 


From this type there radiated many others: {B) the deep, 
narrow-bodied fishes of relatively slow movements, frequenting 
the middle depths of the waters ; {D) the swift-moving, elongate 


DEPRESSED (GROVELINGI 


Fig. 44. The Yive Principal Types of Body Form in Fishes. 

These begin with {A) the swift-moving, compressed, fusiform t3'pes which pass, on the 
one hand, into {B) laterally compressed, slow-moving, deep-bodied types, and, on the 
other, into (C) laterally depressed, round, bottom-dwelling, slow-moving types, also 
into (D) elongate, swift-moving fusiform types which grade into (£) the eel-like, swift- 
moving, bottom-living types without lateral fins. These five types of body form in 
fishes arise independently over and over again in the various groups of this class of 
vertebrates. Partially convergent forms subsequently appear among amphibians, rep- 
tiles, and mammals. Prepared for the author by W. K. Gregory and Erwin S. Christman. 


164 


THE ORIGIN AND EVOLUTION OF LIFE 


types which increasingly depend upon lateral motions of the 

body for propulsion and thus tend to lose the lateral fins and 

finally to assume (E) an 
elongate, eel shape, en- 
tirely finless, for pro- 
gression along the bot- 
tom; (C) the bottom- 
living forms, in which 
the body becomes later- 
ally broadened, the head 
very large relatively and 
covered with protective 
dermal armature, the 
movements of the ani- 
mals becoming slower 
and slower as the dermal 
defenses develop. This 
law applies to all the 
vertebrates, including 
man, namely: the de- 
velopment of armor is 
pari passu with the loss 
of speed. Conversely, 
the gain of speed neces- 
sitates the loss of ar- 
mor. Smith Wood- 
ward^ has traced similar 

radiations of body form in the historic evolution of each of the 

great groups of fishes. 

The interest of this fivefold law of body-form radiation is 

greatly enhanced when we find it repeated successively under 

' Smith Woodward, A., 1915. 


UPPERS 
SILURIAN.' 


PALEOGEOGnAPHY, UPPER SILURIAN (SALINA) TIME 
AFTER SCHUCHERT, , 
NE DEPOSITS ^- CONTINENTAL DEPOSITS ^,V SALT DEPOSITS 


Fig. 45. 


North America in Upper Silurian 
Time. 


During this period of depression of the Appala- 
chian region and elevation of the western half of 
the North American continent occurred the 
maximum evolution of the most primitive armored 
fishes, known as Ostracoderms, which were 
widely distributed in Europe, America, and the 
Antarctic. After Schuchert, 1916. 


EARLY ARMORED FISHES 


165 


Fig. 46. The Ostracoderm Palceaspis 
OF Claypole as Restored by Dean. 


the law of convergence among the aquatic amphibia, reptiles, 
and mammals as one of the invariable effects of the coordina- 
tion of the mechanism of locomotion with that of offense and 
defense. In each of these four or five great radiations of body 
form, from the swift-moving 
to the bottom- or ground- 
living, slow, armored types, 
there is usually an increase of 
bodily size, also an increase of 

specialization, the maximum in both being reached just before 
the period of extinction arrives. 

Early Armored Fishes 

The armored Ordovician ostracoderms are very little 
known. The Upper Silurian ostracoderms enjoyed a wide 

distribution in Europe and 
America. They include 
both the fusiform, free-swim- 
ming type (Birkenia) and 
the broadly depressed ray- 
like types {Lanark ia, etc.). 
Apparently they had not 
yet acquired cartilaginous 
lower jaws and were in a 
lower stage of evolution than 
the true fishes. 

The armature is from 
the first arranged in shield 
and plate form, as seen in 
Palceaspis, from the Upper 
Silurian Salina time of Schu- 
chert. In this epoch we 


Fig. 47. The Antiarchi. 

Armored, bottom-living Ostracoderm type, Bo- 
///r/o/f/^w, from the Upper Devonian of Canada, 
with chitinous armature and a pair of anterior 
appendages analogous to those of the euryp- 
terid crustaceans. This cluster of animals was 
undoubtedly buried simultaneously while 
headed against the current in search of food 
or for purposes of respiration. After Patten. 


i66 


THE ORIGIN AND EVOLUTION OF LIFE 


obtain our first glimpses of North American land life in the 
presence of the oldest known air-breathing animals, the scorpion 

spiders, also of the first known 
land plants. There are indica- 
tions of an arid climate in many 
parts of the world. 

In Upper Silurian time the 
ostracoderms attain the slow, 
armored, bottom-living stage of 
evolution, typified in the ptera- 
spidians and cephalaspidians, 
which were widely distributed 
in Europe, in America, and pos- 
sibly in the Antarctic regions, 
as indicated by recent explora- 
tions there. Belonging to an- 
other and very distinct order, or 
subclass (Antiarchi), are certain 
armored Devonian forms {Botli- 
riolepis, Pterichthys, etc.), which 
possessed a pair of jointed lat- 
eral appendages. Some of 
these fishes, which are propelled 
by a pair of appendages at- 
tached to the anterior portion 
of the body, present analogies to 
the eurypterids (Merostomata, 
or Arachnida) . 

In the fresh-water deposits 
of Lower Devonian age have 
been discovered the ancestors of 
the heavily armored fishes 


Fig. 48. The Arthrodira. 

(Above.) Restoration of the gigantic 
Middle Devonian Arthrodiran (jointed 
neck) fish Dinichthys intermedins, eight 
feet in length, of the Cleveland shales 
(Ohio), showing the bony teeth and 
bony armature of the head region. 
(Below.) Lateral view of the same. 
Model by Dr. Louis Hussakof and ISIr. 
Horter, in the American Museum of 
Natural History. 


PRIMORDIAL SHARKS 


167 


known as the Arthrodira, a group of uncertain relationships. 
They have many adaptations in common with Bothriolcpis, 
such as the jointed neck, dermal jaws, carapace, plastron, and 
paired appendages (Acanthaspis). Some authorities regard 
the Arthrodira as aberrant lung-fishes. Dean, Hussakof, and 
others regard the balance of evidence as in favor of relationship 
with the stem of the Antiarchi {Bothriolepis). In the Middle 
Devonian (the Cleveland shales 
of Ohio) they attain the formi- 
dable size shown in the species 
Dinichthys intermedins (Fig. 48). 
Like the ostracoderms, these 
animals are not in the central 
or main lines of fish evolution 
but represent collateral lines 
which early attained a very high 
degree of specialization which 
was followed by extinction. 

Primordial Sharks, Ances- 
tral TO Higher Ver- 
tebrates 


Fig. 49. A Primitive Devonian Shark. 

(Above.) CJadosclachc, the type of the 
primitive Devonian shark of Ohio with 
paired and median lappet fins provided 
with rod-Hke cartilaginous supports, 
from which type by fusion the limbs of 
all the higher land vertebrates have 
been derived. Model by Dean, Hussa- 
kof, and Hortcr from specimens in the 
American Museum of Natural History. 
(Below.) The interior structure of 
the lappet fins of Cladoselache showing 
the cartilaginous rays (white) within 
the fin (black). After Dean. 


The central line of fish 
evolution, destined to give rise 
to all the higher and modern 
fish types, is found in the typical cartilaginous skeleton and jaws 
and four fins of the primordial sharks, the primitive fusiform 
stage of which appears in the spine-finned type (acanthodian, 
Diplacanthus , Fig. 51) of Upper Silurian time. The relatively 
large-headed, bottom-living types of sharks do not appear until 
the Devonian, during which epoch the early swift-moving, 
fusiform, predaceous types through a partly reversed adaptation 


i68 


THE ORIGIN AND EVOLUTION OF LIFE 


branch off into the elongated eel-shaped forms of the Car- 
boniferous. 

The prototype of the shark group is the Cladoselache (Fig. 
49), a fish famed in the annals of comparative anatomy since 
it demonstrates that the fins of fishes arise from lateral skin 


ORIGrN AND ADAPTIVE RADIATION OF THE FISHES 


Fig. 50. Origin and Adaptive Radiation of the Fishes. 

This chart shows the now extinct Siluro-Devonian groups, the Ostracoderms and Arthro- 
dires, in relation to the surviving lampreys (Cyclostomes) ; sharks and rays (Elasmo- 
branchs); sturgeons, garpikes, and bowfins (Ganoids); bon}' fishes (Teleosts); primi- 
tive and recent lung-fishes (Dipnoi); and finally the fringe-finned or lobe-finned Ganoids 
(Crossopterygii) from the cartilaginous fins of which the fore and hind limbs of the 
first land-living vertebrates (Tetrapoda) were derived. Dotted areas represent groups 
which still exist. Hatched areas represent extinct groups. Prepared for the author 
by W. K. Gregory. 

folds of the body, into which are extended internal stiffening 
cartilaginous rods (Fig. 49). In course of evolution these 
rods are concentrated to form the central axis of a freely jointed 
fin, while in a further step of evolution they transform into the 
cartilages and bones of the limb girdles and limb segments of 
the four-footed land vertebrates, the Tetrapoda. 

The manner of this fin and limb transformation has been 
one of the greatest problems in the history of the origin of 


RISE OF MODERN FISHES 169 

animal form since the earliest researches of Carl Gegenbaur, 
of Heidelberg, who sought to derive the lateral fins from a 
modification through a profound change of adaptation (func- 
tion) of the cartilaginous rods which support the respiratory 
gill arches. While palaeontology has disproved Gegenbaur's 
hypothesis that the Hmbs of the higher vertebrates, including 
those of man, are derived from the cartilaginous gill arches of 
fishes, it has helped to demonstrate the truth of Reichert's 
anatomical hypothesis that the bony chain of the middle ear 
of man has been derived through change of adaptation from a 
portion of a modified gill arch, namely, the mandibular carti- 
lage of the fish. 

The cycle of shark evolution in course of geologic time 
embraces a majority of the swift-moving, predaceous types, 
which radiate into the sinuous, elongate body of the frilled 
shark {Chlamydoselache) and into forms with broadly depressed 
bodies, such as the bottom-living skates and rays. Under the 
law of adaptive radiation the sharks seek every possible habitat 
zone except the abyssal in the search for food. The nearest 
approach to the evolution of the eel-shaped type among the 
sharks are certain forms discovered in Carboniferous time. 

Rise of Modern Fishes 

By Upper Devonian time the fishes in general had already 
radiated into all the great existing groups. The primitive 
armored arthrodires and ostracoderms were nearing extinc- 
tion. The sharks were still in the early lappet-fin stage of 
evolution above described, a common characteristic of the 
members of this entire order being that they never evolved a 
solid bony armature, finding sufficient protection in the sha- 
green covering. 

The scaled armature of the first true ganoid, enamel-cov- 


lyo 


THE ORIGIN AND EVOLUTION OF LIFE 


ered fishes {Osteolepis, Cheirolepis) now makes its first appear- 
ance. These armored knights of the sea are descended from 
simpler scaly forms which also gave rise to the rich stock of 
sturgeons, garpikes, bowfins, and true bony fishes (teleosts) 
which now dominate all other fish groups both in the fresh 


Fig. 51. Fish Types from the Old Red Sandstone of Scotland. 

Upper Devonian time. Primitive ganoids, primitive spine-finned sharks, bottom-living 
Ostracoderms, partly armored ganoids, and the first lung-fishes, i. Osteolepis, primitive 
lobe-finned ganoid. 2. Holoptychius, fringe-finned ganoid. 3, 6. Cheiracanthus, spine- 
finned shark (Acanthodian). 4. Diplacanthus, spine-finned shark (Acanthodian). 
5. Coccosteus, primitive Arthrodiran. 7. Cheirolepis, primitive ganoid. 8, 9. Dipterus, 
primitive lung-fish. Pterichthys, bottom-living Ostracoderm allied to Bothriolepis. 
Restorations by Dean, Hussakof, and Horter, partly after Traquair. Models in the 
American Museum of Natural History. 

waters and the seas. Remotely allied to this stock are the 
first air-breathing lung-fishes (Dipnoi), represented by Dipterus; 
also the "lobe-finned," or "fringe-finned" ganoids from which 
the first land vertebrates were derived. From a single locality, 
in the Old Red Sandstone of Scotland, Traquair has recovered 


RISE OF MODERN FISHES 


171 


a whole fossil series of these archaic fish types as they lived 
together in the fresh water or the brackish pools of Upper De- 
vonian time. (Fig. 51). 

In this period the palaeogeographers (Schuchert) obtain their 
first knowledge of the evolution of the terrestrial environment 
in the indications of the existence of parallel mountain ranges 
on the British Isles, of active volcanoes in the Gaspe region of 


PALEOOEOGHAPHY. EARLY LOWER DEVONIAN (HELDERBERGIAN-GEOINNlAN-HEHOYNfAN-KONIEPRUSSIAN) TIME 

AFTER SCHUCHEnr. APRIL. 1916 

^ ^^MARINE DEPOSITS ^-^CONnNENTAL DEPOSITS ^' MOUNTAINS AND VOLCANOES 


Fig. 52. Theoretic World Environment in Early Lower Devonian Times. 

The period of the early appearance of terrestrial invertebrates and vertebrates. This 
shows the hypothetical South Atlantic continent Gondivana and the Eurasiatic inland 
sea Tethys, according to the hypotheses of Suess. Modified after Schuchert, 1916. 

New Brunswick, of the mountain formations of South Africa, 
and of the depressions of the centre of the Eurasiatic continent 
into the great central Mediterranean Sea, known as the Tethys 
of the great Austrian geologist, Suess. In the seas of this time, 
as compared with Cambrian seas, we observe that the trilo- 
bites are in a degenerate phase, the brachiopods are relatively 
less numerous, the echinoderms are represented by the bottom- 


172 THE ORIGIN AND EVOLUTION OF LIFE 

living starfishes, sharks are abundant, and arthrodiran fishes are 
still abundant in Germany. 

It was long believed that the air-and-water-breathing Am- 
phibia evolved from the Dipnoi, the air-breathing fishes of the 
inland fresh waters, and this hypothesis was stoutly main- 


y -■-■ o* 


FIN STAGE 

RHIPIDISTIAN FISH 
(DEVONIAN! 


FOOT STAGE 

AMPHIBIAN 
(CARBONIFEROUS) 


Fig. 53. Change of Adaptation in the Limbs of Vertebrates. 

The upper figures represent the theoretic mode of metamorphosis of the fringe-fin of the 
Crossopterygian lish (left) into the foot of an amphibian (right) through loss of the 
dermal fringe border and rearrangement of the cartilaginous supports of the lobe. 
After Klaatsch. 

The lower figures represent (left) the theoretic mode of direct original evolution of the 
bones of the fringe-fin (A, B) of a Crossopterygian tish — the Rhipidistia type of Cope — • 
into the bony, five-rayed limb (C) of an amphibian of the Carboniferous Epoch (after 
Gregory); and (right) the secondary, reversed evolution of the five-rayed liml) of a 
land reptile (.4) into the fin or paddle (B, C) of an ichthyosaur (after Osborn). 

tained by Carl Gegenbaur, who also upheld what he termed 
the archipterygian theory of the origin of the vertebrate limb, 
namely, that the prototype of the modern limbed forms of 
terrestrial vertebrates is to be found in the fin of the modern 
Australian lung-fish, Ccratodus. This hypothesis of Gegen- 
baur, which has been warmly supported by a talented group of 
his students, is memorable as the last of the great hypotheses 
regarding vertebrate descent to be founded exclusively upon 


RISE OF MODERN FISHES 


173 


Fig. 54. Extremes of x^daptation in 
Locomotion axd Illumination. 
Extremes of adaptation in the existing bony 
fishes (Teleosts) of the Abyssal Zone of 
the Oceans. Although man\^ different or- 
ders of Teleosts are represented, each type 
has independenth^ acquired phosphores- 
cent organs, affording a fine example of 
the law of adaptive convergence. The 
body form in these fishes is of great 
diversity. i. Thread-eel, Nemichlhys 
scolopaceus Richardson. 2. Barathromis 
diaphanus BTiiuer. 3. Neoscopelus macrole- 
pidotus Johnson. 4, 5. Gastroslomns bairdi Gill and Ryder. 6. Gigantaclis ranhocj/cni- 
Brauer. 7. Sknioptyx diaphana Lowe. 8. Gigantitya chiini Brauer. 9. Mdanostomias 
mdanops Brauer. 10. Stylo phlhahniis paradoxus Brauer. 11. Opisthoprocliis solcatus 
Vaillant. After models in the American Museum of Xatural History. 


comparative anatomy and embryology as opposed to the 
triple evidence afforded by these sciences when reinforced by 
palaeontology. 


174 


THE ORIGIN AND EVOLUTION OF LIFE 


It is through the discovery of primitive types of the fringe- 
finned ganoids, to which Huxley gave the appropriate name 
Crossopterygia, in reference to the fringe of dermal rays around 
a central lobe-iin of cartilaginous rods, that the true ancestry 
of the Amphibia and of the amphibian limb has been traced. 
This is now regarded as due to a partial change of adaptation, 


Fig. 55- Phosphorescent Illuminating Organs. 

The abyssal fishes represented in Fig. 54 as they are supposed to appear in the darkness 
of the ocean depths. .A.fter models in the American Museum of Natural History. 

incident to the passage of the animal from the littoral life zone 
to the shore zone, whereby the propelling fin was gradually 
transformed into the propelling limb. This transformation 
implies a long terrestrio-aquatic phase, in which the fin was 
partly used for propulsion on muddy surfaces (Fig. 53). 

In the reversed parallel retrogressive evolution of the lung- 
fishes {Lepidosiren, Gymnotus), of the fringe-finned fishes {Cala- 
moichthys) and of the bony fishes {Angicilla), the final eel-shaped. 


RISE OF MODERN FISHES 


175 


finless stage is through convergent adaptation either approached 
or actually passed. 

The bony fishes (teleosts), which first emerge as a distinct 
group in Jurassic time, radiate adaptively into all the great 
body-form types which 
had been previously at- 
tained by the older 
groups, more or less 
closely imitating each 
in turn, so that it is not 
easy to distinguish su- 
perficially between the 
armored catfishes {Lori- 
caria) of the existing 
South American waters 
and their prototypes 
(Cephalaspis) of the 
early Palaeozoic. The 
most extreme specializa- 
tion in the great group 
of bony fishes is to be 
found in the radiations 
of abyssal fishes into 
slow- and swift-moving 
forms which inhabit the 
great depths of the 
ocean and are adapted 
to tons of water-pres- 
sure, to temperatures 
just above the freezing 
point, and to total absence of sunlight which is compensated 
for by the evolution of a great variety of phosphorescent light- 


FiG. 56. NorthAmerica in Upper Devonian Time. 

The maximum evolution of the Arthrodiran fishes 
{Dinic/illiys, etc.) and of the ganoids of the Upper 
Devonian of Scotland, the establishment of all the 
great modern orders of fishes excepting the bony- 
fishes (Teleosts), and the appearance of the first 
land vertebrates, the amphibians (Tliiuopus), 
took place during this period of depression of the 
western centre of the North American continent. 
Modified after Schuchert. 


176 


THE ORIGIN AND EVOLUTION OF LIFE 


producing organs in the fishes themselves and in other animals 
on which they prey. 

Another extreme of chemical evolution among the fishes is 
the production of electricity as a protective function, which is 

even more effective than bony arma- 
ture because it does not interfere with 
rapid locomotion. In only a few of 
the fishes is electricity generated in 
sufficient amounts to thoroughly pro- 
tect the organism. It develops through 
modified body tissues in the form of 
superimposed plates (electroplaxes) se- 
parated equally from one another by 
layers of a peculiar jelly-like connec- 
tive tissue, all lying parallel to each 
other and at right angles to the direc- 
tion of discharge.^ The electric organ 
is formed from modified muscle and 
connective tissue and is innervated by 
motor nerves. The physical principle 
involved is that of the concentration 
cell, and the electrolyte used in the 
process is probably sodium chloride. 
The theory is that at the moment of 
discharge a membrane is formed on one 
surface of the electroplax which prevents the negative ions 
from passing through while the positive ions do pass through 
and form the current. The strength of the current varies 
from four volts in Mormyriis up to as much as 250 or more 
in Gymnotus, the electric eel, and consists of a series of shocks 
discharged 3/1000 of a second apart. 

1 Dahlgren, Ulric, iqo6, pp. 389-398; 1910, p. 200. 


Fig. 57. The Earliest 
Known Limbed Animal. 
Footprint of Tliinopus anli- 
qiius Marsh, an amphibian 
from the Upper Devonian of 
Pennsylvania. Type in the 
Peabody Museum of Yale 
University. Photograph of 
cast presented to the Ameri- 
can Museum of Natural His- 
tory by the Peabody 
Museum. 


EVOLUTION OF THE AMPHIBIANS 


177 


%i:.'-\ 


Form Evolution of the Amphibians 

A single impression of a three-toed footprint (Thinopus 
antiques) in the Upper Devonian shales of Pennsylvania con- 
stitutes at present the sole palaeontologic proof of the long 
period of transition of the vertebrates from the fish type to 
the amphibian type. This transition was a matter of thousands 
of years. It took place in Lower Devonian if not in Upper 
Silurian time. Under the 
influence of the heredity- 
chromatin it is now re- 
hearsed or recapitulated in 
a few days in the metamor- 
phosis from the tadpole to 
the frog. 

As compared with 
fishes, the significant prin- 
ciple of the evolution of 
amphibians, as the earliest terrestrial vertebrates, is their reac- 
tion to marked environmental change. Their entire life re- 
sponds to the changes of the seasons. They also respond to 
secular changes of environment in the evolution of types 
adapted to extremely arid conditions. 

The adaptive radiation of the primordial Amphibia prob- 
ably began in Middle Devonian time and extended through 
the great swamp, coal-forming period of the Carboniferous, 
which afforded over vast areas of the earth's surface ideal con- 
ditions for amphibian evolution, the stages of which are best 
preserved in the Coal Measures of Scotland, Saxony, Bohemia, 
Ohio, and Pennsylvania, and have been revealed through the 
studies of von Meyer, Owen, Fritsch, Cope, Credner, and 
Moodie. The earliest of these terrestrio-aquatic types have 


Fig. 58. A Primitive Amphibian. 

Theoretic reconstruction of a primitive sala- 
mander-like type with large, solidly roofed 
skull, four limbs, and five fingers on each of 
the fore and hind feet, such as may have ex- 
isted in Upper Devonian time. After Fritsch. 


178 


THE ORIGIN AND EVOLUTION OF LIFE 


not only a dual breathing system of gills and lungs, but a dual 
motor equipment of limbs and of a propelling median fin in 
the tail region. 

So far as known, the primordial Amphibia in their form were 
chiefly of the small-headed, long-bodied, small-Hmbed, tail-pro- 


FiG 59. Descent of the Amphibia 

The Amphibia — in which the fin is transformed into a limb (Thinopus) — are believed to 
have evolved from an ancestral ganoid fish stock of Silurian age through the fringe- 
finned ganoids. From this group diverge the ancestors of the Reptilia and the sala- 
mander-like Amphibia which give rise to the various salamander types, also to branches 
of limbless and snake-like forms (Aistopoda, modern Coecilians). The other great 
branch of the solid-skulled Amphibia, the Stegocephalia, was widespread all over the 
northern continents in Permian and Triassic time (Cricotas, Eryops), and from this 
stock descended the modern frogs and toads (Anura). Prepared for the author by 
W. K. Gregory. 

pelled type of the modern salamander and newt. The large- 
headed, short-bodied types (Amphibamus) were precocious 
descendants of such primordial forms. In Upper Carbonifer- 


EVOLUTION OF THE AMPHIBIANS 


179 


ous and early Permian time the terrestrial amphibians began 
to be favored by the land elevation and recession of the sea 
which distinguished the close of the Carboniferous and early 
Permian time. Under these varied zonal conditions, aquatic, 
palustral, terrestrio-aquatic, fossorial, and terrestrial, the Am- 


EUMICRERPETON 
AMPHIBIA CARBONIFEROUS 


CARBONIFEROUS, 


AMPHIBAMUS 
AMPHIBIA CARBONIFEROUS AMPHIBIA 


DIPLOCAULUS 


PERMO- 
CARBONIFEROUS 


Fig. 60. Chief Amphibian Types of the Carboniferous. 

Restorations of the early short-tailed, land-living Amphibamus, the salamander-like 
Etimicrerpcton, the eel-bodied Ptyoniits, and the broad-headed, bottom-living Diplo- 
cauliis. Prepared for the author by W. K. Gregory and Richard Deckert. 

phibia began to radiate into several habitat zones and adaptive 
phases, and thus to imitate the chief types of body form which 
had previously evolved among the fishes as well as to anticipate 
many of the types of body form which were to evolve subse- 
quently among the reptiles. One ancestral feature of the 
amphibians is a layer of superficial body scales in some types, 
which appear to be derived from those of their lobe- finned fish 
ancestors; with the loss of these scales most of the Amphibia 
also lost the power of forming a bony dermal armature. 


i8o 


THE ORIGIN AND EVOLUTION OF LIFE 


Recent researches in this country, chiefly by WilHston, 
Case, and Moodie, indicate that the soKd-headed Amphibia 
(Stegocephaha) and primary forms of the ReptiKa chiefly be- 
long to late Carboniferous (Pennsylvania) and early Permian 
time. They are found abundantly in ancient pool deposits, 
which are now widespread over the southwestern United States 

and Europe deposited in 
rocks of a reddish color. 
This reddish color points 
to aridity of climate in 
the northern hemis- 
phere during the period 
in which the terrestrial 
adaptive radiation of the 
Amphibia occurred. 
These arid conditions 
continued during the 
greater part of Permian 
time, especially in the 
northern hemisphere. 
In the southern hemisphere there is evidence, on the con- 
trary, of a period of humidity, cold, and extensive glaciaticn, 
which was accompanied by the disappearance of the old lyco- 
pod flora (club-mosses) and arrival of the cool fern flora (GIos- 
sopteris), which appeared simultaneously in South America, 
South Africa, Australia, Tasmania, and southern India. The 
widespread distribution of this flora in the southern hemisphere 
furnishes one of the arguments for the existence of the great 
South Atlantic continent Goudwana, a transatlantic land bridge 
of animal and plant migration, postulated by Suess and sup- 
ported by the palaeogeographic studies of Schuchert. In 
North America the glaciation of Permian time is believed to 


Fig. 6i. Skull and Vertebral Column of 

Diplocaidus. 

A typical solid-, broad-headed amphibian from the 
Permian of northern Texas. Specimen in the 
American Museum of Natural History. (Com- 
pare Fig. 60.) 


EVOLUTION OF THE AMPHIBIANS 


i»i 


have been only local. The last of the great Palaeozoic seas dis- 
appeared from the surface of the continents, while the border 
seas give evidence of the rise of the ammonite cephalopods. 
Toward the close of Permian time the continent was com- 
pletely drained. Along the eastern seaboard the Appalachian 


^^^:^ 


PALEOGEOGRAPHY. EARLIEST PERMIAN (LOWER ARTCNSKIAN-ROTLIEGENDE-AUTUNIAN). A GLACIAL TIME 
AFTER SCMUCHERT, APRIL, 1916 

E FIELDS t 


Fig. 62. Theoretic World En\tronment in Earliest Permian Time. 
A period of marked glacial conditions in the Antarctic region. Vanishing of the coal 
floras and rise of the cycad-conifer floras, along with the rise of more modern insects and 
the beginning of the dominance of reptiles. Modified after Schuchert, 1916. 

revolution occurred, and the mountains rose to heights esti- 
mated at from three to five miles. 

An opposite extreme, of slender body structure, is found 
in the active predaceous types of water-loving amphibians such 
as Cricotus, of rapid movements, propelled by a long tail fin, 
and with sharp teeth adapted to seizing an actively moving 
prey. This type retrogresses into the eel-like, bottom-loving 
Lysorophus with its slender skull, elongate body propelled by 


l82 


THE ORIGIN AND EVOLUTION OF LIFE 


lateral swimming undulations, the limbs relatively useless. 
Corresponding to the bottom-living fishes are the large, slug- 
gish, broad-headed, bottom-living amphibians, such as Diplo- 
caulus, with heads heavily armored, limbs small and weak, the 
body propelled by lateral motions of the tail. There were also 


.^^^M^wm. 


.^\[,i/l,.)i L 


./, / 


Fig. 63. Amphibia of the American Permo-Carboniferous. 

Here are found the free-swimming Cricotiis, the short-bodied Cacops, and abundance of 
the amphibious terrestrial type, the large, solid-headed Eryops. Restorations for the 
author by W. K. Gregory and Richard Deckert. 

more powerful, slow-moving, long-headed, alligator-like, terres- 
trio-aquatic forms, such as the Archegosaiirus of Europe and 
the fully aquatic Trimerorachis of America. An extreme 
stage of terrestrial, ground-living evolution with marked reduc- 
tion of the use of the tail for propulsion is the large-headed 
Cacops, short-bodied, with limbs of medium size, but with 
feeble powers of prehension in the feet. Radiating around 
these animals were a number of terrestrial types exhibiting 
the evolution of dorsal protective armature and spines {Aspi- 
dosaurus); other types lead into the pointed-headed structure 
and pointed teeth of Trematops. 


EVOLUTION OF THE AMPHIBIANS 


183 


The Age of Amphibians passes its cHmax in Permian time 
(Fig 63.). In Triassic time there still survive the giant terres- 
trial forms. 

Evidences of extensive intercontinental connections in the 
northern hemisphere are also found in the similarity of type 
between the great terrestrial amphibians of such widely sepa- 
rated areas as Texas and Wiirtemberg, which develop into simi- 
lar resemblances between the great labyrinthodont amphibians 
of Lower Triassic times of Europe, North America, and Africa. 
Ancestral to these Triassic giants is the large, sluggish, water- 
and shore-living Eryops of the Texas Permian, with massive 
head, depending on its short, powerful limbs and broad, spread- 
ing feet for land propulsion, and in a less degree upon its tail for 
propulsion in the water. This animal may be regarded as a 
collateral ancestor of the labyrinthodonts; it belongs to a type 
which spread all over Europe and North America and persisted 
into the Mdopias of the Triassic. 


Fig. 64. Skeleton of Eryops from the Permo-Carboniferous of Texas. 
A type of the stegocephalian Amphibia which were structurally ancestral to the Laby- 
rinthodonts of the Triassic. Mounted in the Amerjcan Museum of Natural History. 


CHAPTER VII 
FORM EVOLUTION OF THE REPTILES AND BIRDS 

Appearance of earliest reptile-like forms, the pro-Reptilia, followed by the first 
higher reptiles. Geologic distribution and environment of the various 
extinct and existing orders of reptilia. Evolutionary laws exemplified in 
the origin and development of this great group of animal life. Direct, 
reversed, alternate, and convergent adaptation. Modes of offense and 
defense. Terrestrial, fossorial, aquatic, and marine radiation. Aerial 
adaptation. The Pterosaurs. First appearance of bird-like animals. 
Theories regarding the evolution of flight in birds. Theories as to the 
causes of arrested evolution. 

The environment of the ancestor of all the reptiles was a 
warm, terrestrial, and semi-arid region, favorable to a sensitive 
nervous system, alert motions, scaly armature, slender limbs, 
a vibratile tail, and the capture of food both by sharply pointed, 
recurved teeth and by the claws of a five-fingered hand and 
foot. The mechanically adaptive evolution of the Reptilia 
from such an ancestor is as marvellous and extreme as the 
subsequent evolution of the mammals; it far exceeds in di- 
versity the radiation of the Amphibia and extends over a pe- 
riod estimated at from 15,000,000 to 20,000,000 years. 

The Permian Reptiles of North America and South 

Africa 

The experiments of the Amphibia in adapting themselves 
to the Permian continents with their relatively dry surfaces 
and seasonal water pools and lagoons are contemporaneous 
with the first terrestrial experiments and adaptive radiations 
of the Reptilia, a group which was particularly favored in its 


EARLIEST REPTILES 


185 


origin by arid environmental conditions. The result is the 
creation in Permian time of many externally analogous or con- 
vergent groups of amphibians and reptiles which in external 
appearance are difficult to distinguish. Yet as divergent from 
the primitive salamander-like Amphibia and clearly of another 


PALEOGEOGRAPHY. EARLIEST PERMIAN ILOWER ARTINSKIAN-ROTLIEGENDE-AUTUNIAN). A GLACIAL TIME 

AFTER SCHUCHERT, APRIL. 1916 

Y MARINE DEPOSITS <v^' CONTINENTAL DEPOSITS ^5i5.hCE FIELDS f DIRECTION OF ICE FLOW 

^UNCERTAIN ICE FIELDS .-■VOLCANOES wol.nT4is 


Fig. 65. Theoretic World Environment in Earliest Permian Time. 
A period of marked glacial conditions in the Antarctic region. Vanishing of the coal 
floras and rise of the cycad-conifer floras, along with the rise of more modern insects 
and the beginning of the dominance of reptiles. Modified after Schuchert, 191 6. 

type these pro-reptiles are different in the inner skeletal struc- 
ture and in the anatomy of the skull they are exclusively 
air-breathing, primarily terrestrial in habit rather than ter- 
restrio-aquatic, superior in their nervous reactions and in the 
development of all the sensory organs, and have a more 
highly perfected cold-blooded circulatory system. Neverthe- 
less, the most ancient solid-headed reptilian skull type (Cotylo- 
sauria, Pareiasauria, of Texas and South Africa, respectively) 


i86 


THE ORIGIN AND EVOLUTION OF LIFE 


is very similar to that of the solid-headed Amphibia (Steg- 
ocephalia). Bone by bone its parts indicate a common descent 

from the skull type of the fringe- 
finned fishes (Crossopterygia, 
Fig. 53)- 

As revealed by the researches 
of Cope, Williston, and Case, 
the adaptive radiation of the 
reptile life of western America 
in Permian time is as follows: 
First there is a variety of swift- 
moving, alert, predaceous forms 
corresponding to the fusiform, 
swift-moving stage in the evolu- 
tion of the fishes. Some of 
these reptiles (Varanops) re- 
semble the modern monitor liz- 
ards (Varanus); others {Oplii- 
acodon and Theropleura) are 
provided wath four well-devel- 
oped limbs and feet, the long tail 
being utilized as a balancing 
organ. These were littoral or 
lowland reptiles, insectivorous 
or carnivorous in habit. The 
primitive, lizard-like pelycosaur Varanops, with a long tail 
and four limbs of equal proportions, represents more nearly 
than any known ancient reptile, apart from certain special 
characters, a generalized prototype from which all the eighteen 
Orders of the Reptilia might have descended; its structure could 
well be ancestral to that of the lizards, the alligators, and the 
dinosaurs. At present, however, it is not determined whether 


ARAEOSCELIS 
PEPTILIA 

Fig. 66. Ancestral Reptilian T\tes. 

Two of the defenseless, swift-moving, 
terrestrial reptilian types, Varanops 
and Arwoscelis, of the Permo-Carbonif- 
erous period of Texas. The skull and 
skeleton of ArcBoscelis foreshadow the 
existing lizard (Lacertilian) type and 
Williston regards it as the most nearly 
related Permian representative known 
of the true Squamata (ancestors of 
the lizards, snakes, and mosasaurs). 
Restorations of Varanops and ArcBos- 
celis modified from Williston. Drawn 
for the author by Richard Deckert. 


EARLIEST REPTILES 


187 


LABIDOSAURUS 


PERMO- 
CARBONIFEROUS 


,5355?-^,X n 


the primitive ancestors from which the various orders of reptiles 
descended belong to a single, a double, or a multiple stock. 

Passing to the widely different amphibian-like order known 
as cotylosaurs, we see animals ^-r*^-F)7^\ 
which, on the one hand, grade ^^^^^^'^j-^^' 
into the more fully aquatic, pad- 
dle-footed, free-swimming Lim- 
noscelis with a short, crocodile- 
like head, which propelled itself 
by means of its long tail, and, 
on the other hand, there devel- 
oped short-tailed, semi-acjuatic 
forms, such as the Lahido- 
saurus. In adaptation to the 
more purely terrestrial habitats 
there is sometimes a reduction 
in the length of the tail and 
greater perfection in the struc- 
ture of the limbs and the various 
forms of armature. In Pantyliis 
these defenses appear in the 
form of bony ossicles of the skin 
and scutes; in Chilonyx the 
skull top is covered with tuber- 
culated defenses; in the slow- 
moving Diadedes the body is 
partly armored, the animal be- 
ing proportioned like the exist- 
ing Gila monster and probably 
of nocturnal habits, which is in- 
ferred from the large size of the 
eyes. 


i3 


Fig. 67. Reptiles with Skulls Trans- 
itional IN Structitre from the 
Amphibian Skull. 

Typical solid-headed reptiles (Coty- 
losaurs) characteristic of Permo-Car- 
boniferous time in northern Texas, 
including the three forms Seynioiiria, 
Labidosaiints, and the powerful Dia- 
dedes, which resembles the existing 
Gila monster. The head in the mounted 
skeleton of Diadcctcs (lower) in the 
American Museum of Natural History 
is probably bent too sharply on the 
neck. Restorations for the author by 
W. K. Gregory and Richard Deckert. 
Labidosaiirus and Seymouria chiefly 
after Williston. 


1 88 THE ORIGIN AND EVOLUTION OF LIFE 

The most remarkable types in this complex reptilian society 
of Permian Texas are the giant fin-backed lizards, Clepsydrops, 
Dimetrodon, Edaphosaiirus, of Cope, probably terrestrial and 
carnivorous in habit. In these animals the neural spines of 
the dorsal vertebrae are vertically elongated to support a power- 
ful median membranous fin, the spines of which are sometimes 


Fig. 68. Theoretic World Environment in Middle Permian Tuvle. 

Great extension of the Baltic Sea and of the Eurasiatic Mediterranean Tethys. Rise of 
the Appalachian, Northern European Alps, and many other mountains. Modified 
after Schuchert. 

smooth (Dimetrodon), sometimes provided with transverse rods 
{Edaphosaurus cruciger). These structures may have devel- 
oped through social or racial competition and selection within 
this reptile family rather than as offensive or defensive organs 
in relation to other reptile families. 

We now glance at the Permian life of another great zoologic 
region. Africa has been throughout all geologic time the 
most stable of the continents, especially since the begin- 


EARLIEST REPTILES 


189 


ning of the Permian Epoch. 
The contemporaneous evo- 
lution of the pro-ReptiUa, 
traced in a continuous earth 
section from the base of the 
Permian to the Lower Trias- 
sic, as successively explored 
by Bain, Owen, Seeley, 
Broom, and Watson, has re- 
realed a far more extensive 
and more varied adaptive 
radiation of the reptiles than 
that which is known on the 
American continent. Al- 
though the adaptations are 
chiefly terrestrial, we trace 
certain strong analogies if 
not actual relationships to 
the Permo-Triassic reptiles 
of North America. 

While the drying pools 
and lagoons of arid North 
America were entombing the 
life of the Permian and 
Triassic Epochs, there were 
being deposited in the Karoo 
series of South Africa some 
9,500 feet of strata consist- 
ing of shales and sandstones, 
chiefly of river flood-plain 
and delta origin, and rang- 
ing in time from the basal 


^ > 


^" t 


ITt 


■^>.^ii^ 


-*\ 


CARBONIFEROUS 


Fig. 


The Fin-Back Permian 
Reptiles. 


Restorations (middle and upper figures) of 
the giant carnivorous reptiles of northern 
Texas in Permian time; the large-headed 
Djmctrodon and the contemporary small- 
headed Edaphosauriis cruciger. In both 
animals the neural spines of the vertebrae 
are greatly elongated, hence the popular 
name "fin-back." Skeleton of Dimctrodon 
(lower) in the American Museum of Natural 
History. Restorations for the author by 
W. K. Gregory and Richard Deckert. 


igo 


THE ORIGIN AND EVOLUTION OF LIFE 


Permian into the Upper Triassic. Here, up to the year 1909, 
twenty-two species of fossil fishes had been recorded, mostly 
ganoids of Triassic age. The eleven species of amphibians dis- 
covered are of the solid-headed (Stegocephalia) type, broadly 

similar in external appearance to 
those of the same age discovered 
in Europe. The one hundred and 
fifteen species of reptiles described 
from the Lower and Middle Per- 
mian deposits include solid-headed 
pareiasaurs — great, round-bodied, 
herbivorous reptiles with massive 
limbs and round heads — which are 
allied to the cotylosaurs of the 
Permo-Carboniferous of America, 
the agile dromosaurs, similar to the 
lizard-like reptiles of the Texas 
Permian, with large eye-sockets, 
and adapted to swift, cursorial 
movements, also reptiles known 
as therocephalians in reference to 
the analogy which the skull bears 
to that of the mammals, gorganop- 
sians, and numerous slender- 
limbed, predatory reptiles with 
sharp caniniform teeth. The giant 
predaceous Reptilia of the time 
are the dinocephalians (z. e., "terri- 
ble-headed"), very massive animals with a highly arched back, 
broad, swollen forehead, short, wide jaws provided with mar- 
ginal teeth. Surpassing these in size are the anomodonts {i. c, 
"lawless-toothed") in which the skull ranges from a couple 


Fig. 70. Mammal-like Reptiles of 
South Africa. 

The relative stability of the African 
continent favored the early evolu- 
tion of the free-limbed forms of 
reptiles known as Anomodonts, in- 
cluding the powerful Eudothiodon, 
in which the jaws are sheathed in 
horn like those of turtles; and also 
of the Cynodonts (dog-toothed 
reptiles), including the carnivorous, 
strongly toothed Cynognalhiis which 
is allied to the ancestors of the 
Mammalia. Restorations for the 
author by W. K. Gregory and 
Richard Deckert. 


MAMMAL-LIKE REPTILES I91 

of inches to a yard in length, and the toothless jaws are sheathed 
in horn and beaked like those of turtles. This is a nearly 
typical social group: large and small, herbivorous, omnivorous, 
and carnivorous, toothed, toothless and horny-beaked, swift- 
moving, slow-moving, unarmored, partly armored; it lacks 
only the completely armored, slow-moving type to be a perfect 
complex. 

In the Upper Permian the fauna includes pareiasaurs and 
gorganopsians, which are similar to a large group of reptiles of 
the same geologic age discovered in Russia by Amalitzky. 

In Lower and Middle Triassic time the last and most highly 
specialized of the beaked anomodonts appear together with di- 
minished survivors (ProcolopJion) of the very ancient solid-headed 
order (Pareiasauria of South Africa, Cotylosauria of Texas). 
Here also are found the true cynodonts, which are the most 
mammal-like of all known reptiles. In the Upper Triassic of 
South Africa occur carnivorous dinosaurs, also crocodile-like phy- 
tosaurs (Fig. 75), allied to those of Europe and North America. 

Origin of the Mammals and Adaptive Radiation of the 
Eighteen Orders of Reptiles 

The most notable element in this complex reptilian society 
of South Africa are those remarkable pro-mammalian types of 
reptiles (cynodont, theriodont), from which our own most 
remote ancestors, the stem forms of the Mammalia, the next 
higher class of vertebrates above the Reptilia, were destined to 
arise. This is another instance where palaeontology has dis- 
lodged a descent theory based upon anatomy, for at one time 
from anatomical evidence alone Huxley was disposed to derive 
the mammals directly from the amphibians. 

The question at once arises, why were these particular reptiles 
so highly favored as to become the potential ancestors of the 


192 


THE ORIGIN AND EVOLUTION OF LIFE 


SCYMNOGNATHUS 


mammals? At least two reasons are apparent. First, these 
larger and smaller types of South African pro-mammals exhibit 
an exceptional evolution of the four limbs, enabling them to 
travel with relative rapidity, which is connected with ability 
to migrate, powers doubtless associated with increasing in- 
telligence. Another marked characteristic which favors de- 
velopment of intelligence is the adaptability of their teeth to 
different kinds of food, insectivorous, carnivorous, and herbiv- 
orous, which leads to development and 
diversity of the powers of observation 
and choice. In this adaptability they 
in a limited degree anticipate the evo- 
lution of the mammals, for the other 
reptiles generally are distinguished by a 
singular arrest or inertia in tooth de- 
velopment. Rapid specialization of the 
teeth is one of the chief features in the 
history of the mammals, which display 
a continuous momentum and advance 
in tooth structure, associated with 
specialization of the organs of taste. 
Of greater importance in its influence on the brain evolu- 
tion of the early pro-mammalian forms is the internal tem- 
perature change, whereby a cold-blooded, scaly reptile is 
transformed into a warm-blooded mammal through a change 
which produced the four-chambered heart and complete sep- 
aration of the arterial and venous circulation. This change 
may have been initiated in some of the cynodonts. This new 
constant and higher temperature favors the nervous evolution 
of the mammals but has no influence whatever upon the me- 
chanical evolution. As pure mechanisms the cold-blooded rep- 
tiles exhibit as great plasticity, as great diversity, and perhaps 


Fig. 71. A South African 
"Dog-Toothed" Reptile. 

Head of one of the South 
African Cynodonts or "dog- 
toothed " reptiles, related to 
the ancestors of the mam- 
mals. Restoration for the 
author by W. K. Gregory 
and Richard Deckert. 


ADAPTIVE RADIATION OF REPTILES 


193 


higher stages of perfection than the mammals. Nor does increas- 
ing intelligence, as we shall see, favor mechanical perfection. 

Turning our survey to the origin and adaptive radiation of 
the reptiles as a whole, we find that in Permian time all of the 


ORIGIN AND ADAPTIVE RADIATION OF THE REPTILES v». k. c«ecci«y, 1 


Fig. 72. Adaptive Radiation of the Reptilia. 

The reptiles first appear in Upper Carboniferous and Lower Permian time and radiate into 
eighteen different orders, three of which — the Cotylosaurs, Anomodonts, and Pely- 
cosaurs — attain their full evolution in Permian and Triassic time and later become 
extinct. Six orders — the Ichthyosaurs, Plesiosaurs, Dinosaurs, Phytosaurs, Pterosaurs, 
and Turtles — are first discovered in Triassic time, while five of the orders — the Ich- 
thyosaurs, Plesiosaurs, jMosasaurs, Dinosaurs, and Pterosaurs — dominate the Cretace- 
ous Period and become suddenly extinct at its close, leaving the five surviving modern 
orders — Testudinata (turtles, tortoises), Rhyncocephalia (tuateras), Lacertilia (lizards), 
Ophidia (snakes), and Crocodilia (crocodiles). These great reptilian dynasties seem 
to have extended over the estimated ten million years of the Mesozoic Era, namely, the 
Triassic, Jurassic, and Upper Cretaceous Epochs. Prepared for the author by W. K. 
Gregory. 

ten early adaptive branches of the reptilian stem had radiated 
and become established as prototypes and ancestors of the 
great Mesozoic Reptilia. Five divisions, namely, the coty- 
losaurs, anomodonts, pelycosaurs, proganosaurs, and phyto- 
saurs, were destined to become extinct in Permian or Triassic 
time, in each instance as the penalty of excessive and prema- 


194 THE ORIGIN AND EVOLUTION OF LIFE 

ture specialization. Five other great branches, namely, the 
ichthyosaurs, plesiosaurs, two great branches of the dinosaurs, 
and the pterosaurs, were destined to dominate the waters, 
the earth, and the air during the Mesozoic Era, i. e., the Tri- 
assic, Jurassic, and Cretaceous Epochs. Thus altogether thir- 
teen great branches of the reptilian stock became extinct either 
before or near the close of the Age of Reptiles. Out of the 
total of eighteen reptilian branches only five were destined to 
survive into Tertiary time, namely, the orders which include 
the existing turtles, tuateras, lizards, snakes, and crocodiles. 

Geologic Blanks and Vistas of Reptilian Evolution 

As pointed out in the introduction of this chapter, the rep- 
tile ancestor of these eighteen branches of the class Reptilia — 
a class with an adaptive radiation which represents the mechan- 
ical conquest of every one of the great life zones, from the aerial 
to the deep sea — will some day be discovered as a small, lizard- 
like, cold-blooded, egg-laying, four-limbed, long-tailed terres- 
trial form, with a solid skull roof, of carnivorous or more prob- 
ably insectivorous habit, which lived somewhere on the land 
surfaces of Carboniferous time. Such undoubtedly was the 
reptilian protot>q3e from which evolved every one of the 
marvellous mechanical types which we may now briefly re- 
view. By methods first clearly enunciated by Huxley in 1880 
several of the ideal vertebrate prototypes have been theoreti- 
cally reconstructed, and in more than one instance discovery 
has confirmed these hypothetical reconstructions. 

The early geologic vistas of this entire radiation are seen 
in the reptilian life of the Permian Epoch of North America, 
Europe, and Africa just described, consisting exclusively of ter- 
restrial and terrestrio-aquatic forms. In the Triassic we obtain 
succeeding vistas of the terrestrial and fluviatile life of North 


ADAPTIVE RADIATION OF REPTILES 


195 


America, Europe, and Africa, as well as our first glimpses of the 
early marine life of North America. In Jurassic time deposits 
at the bottom of the great interior continental seas give us the 


TERRESTRIAL AND 
FLUVIATILE 


N. AMER. [ EUROPE I AFRICA ] S. AMER. 


N. AMER. I EUROPE I AFRICA 


QUATERNARY 


LOWER 
CRETACEOUS 
(COMANCHEANt 


r^^^SlA 


SECOND REPTILIAN SEA FAUNA 
IPLESIOSAURS AND ICHTHYOSAURS) 


Fig. 


73- 


Geologic Records of Reptilian Evolution, Terrestrial and 
IMarine. 


Shaded areas represent the geologic vistas of reptilian life which have been discovered 
from fossils entombed in ancient terrestrial, fluviatile, and marine habitats of 
different portions of the northern and southern hemispheres. 

Triassic. We begin with the deposits of the continental surfaces of North America, 
Fvurope, and Africa. During Triassic time the first dinosaur stages appear, as well 
as some of the semi-aquatic forms which frequented flu\aatile regions, while the primi- 
tive ICHTHYOSAURS Were then fully adapted to marine life. 

Jurassic and Lo\\^r Cretaceous. We continue with geologic vistas of the succeeding 
marine life and the evolution of the second reptilian sea fauna, indicated by the 
shaded areas of the Jurassic and the Lower Cretaceous of North America and Europe. 
The remains of these animals are found in the deposits of deep or shallow sea waters. 
There is one great vista, the second dinosaur stages, which includes the terrestrial 
dinosaurs known as Sauropoda, found in Upper Jurassic and Lower Cretaceous de- 
posits in North America, Europe, Africa, and South America. 

Upper Cretaceous. Then there was a long interval, followed by the final dinosaur 
stages and a long vista of the terrestrial reptilian life of Upper Cretaceous time, especi- 
ally in North America. Contemporary with this is the final reptilian sea fauna. 

Chart by the author. 

second reptilian sea fauna of plesiosaurs and ichthyosaurs within 
the continents of North America and Europe. The story of the 
marine pelagic evolution of the reptiles is continued with some 
interruptions through the Lower Cretaceous into the final rep- 


196 THE ORIGIN AND EVOLUTION OF LIFE 

tilian sea fauna of plesiosaurs and mosasaurs of Upper Creta- 
ceous time. 

In the meanwhile the Ufe of the continents is revealed in 
the terrestrial and fluviatile deposits of the Triassic Epoch, 
in the first stages of the terrestrial evolution of the dinosaurs, 
in the early stages of the fluviatile evolution of the Crocodilia, 
and in the final stages of the terrestrial phases of the Amphibia 
and pro-Reptilia. A long interval of time elapses at this 
period in the earth's history, during which the life of the con- 
tinents is entirely unknown, until the close of the Jurassic 
and beginning of Cretaceous time, when there appears a sec- 
ond great stage of dinosaur evolution, revealed especially in 
the lagoon deposits of North Africa and South America, which 
have yielded remains of giant Sauropoda. Then another gap 
occurs in the story as told by continental deposits. Finally, in 
Upper Cretaceous time we again discover great flood-plain and 
shore-line deposits, which give a prolonged vista of the ter- 
restrial life of the Reptilia, especially in North America and 
Europe. 

Thus it will be understood that, while the great tree of 
reptilian descent has been worked out through a century of 
scientific researches, beginning with those of Cuvier and con- 
tinued by Owen, Leidy, Cope, Marsh, and our contemporary 
palaeontologists, there are enormous gaps in both the terres- 
trial and the marine history of several of the reptilian orders 
which remain to be filled by future exploration. We piece to- 
gether fossil history on the continents and in the seas from 
the animals entombed in these deposits, partly by means 
of the real relationships observed in widely migrating forms, 
such as the land dinosaurs and the marine ichthyosaurs, ple- 
siosaurs, and mosasaurs. Many of these reptiles ranged over 
every continent and in every sea. On the whole, the physio- 


ADAPTIVE RADIATION OF REPTILES 


197 


graphic condition most favorable to the preservation of Hfe 
in the fossil condition is that known as the flood-plain, in which 
the rising waters and sediments of the rainy season rapidly 
entomb animal remains which are deposited on the surface 


Fig. 74. Close of the Age of Reptiles. A Relic of Ancient Flood-plain Condi- 
tions. 

Iguanodont dinosaur lying upon its back. Integument impressions preserved. The 
"dinosaur mummy," Trachodon, from the Upper Cretaceous flood-plain deposits of 
Converse County, Wyoming. Due to arid seasonal desiccation, the skin folds and 
impressions are preserved over the greater part of the body and limbs. Discovered 
by Sternberg. Mounted specimen in the American Museum of Natural History. 

or in small water pools during the drier seasons. Fossils 
buried in old flood-plain areas of South Africa tell us the story 
of the life evolution which is continued by the ancient shore 
and lagoon deposits in other parts of the world as well as by 
fossils found in the broad, intermittent flood-plain areas of 
the American Triassic and Cretaceous, which close with the 


198 THE ORIGIN AND EVOLUTION OF LIFE 

great delta deposits of the Upper Cretaceous lying to the 
east of the present Rocky Mountain range. The more re- 
stricted deposition areas of drying pools and lagoons, such as 
those observed in the Permian and Triassic shales and sand- 
stones of Texas, entomb many forms of terrestrial life. Vistas 
of the contemporaneous evolution of fluviatile, aquatic, and 
marine life are afforded by the animals which perish at the 
surface and sink to the calcareous bottom oozes of the conti- 
nental seas of Triassic, Jurassic, and Cretaceous time. It is 
only in the Tertiary of the Rocky Mountain region of North 
America that we obtain a nearly continuous and uninterrupted 
story of the successive forms of continental life, among the 
mammals entombed in the ancient flood-plains, in the volcanic 
ash-beds, in the lagoons, and more rarely in the littoral deposits. 

Aquatic Adaptation of the Reptilia, Direct and 

Reversed 

From the distinctively terrestrial radiations of Permian 
time we turn to the development of aquatic habitat phases 
among the reptiles which lived along the borders of the great 
interior rivers and continental seas of Permian, Triassic, and 
Jurassic time. 

This reversal of adaptation from terrestrial into aquatic 
life is, as we might theoretically anticipate, a reversal of func- 
tion rather than of structure, because, as above stated (p. 159), 
it is a universal law of form evolution that ancient adaptive 
characters once lost by the heredity-chromatin are never 
reacquired. In geologic race evolution there is no process 
analogous to the wonderful phenomena of individual regenera- 
tion or regrowth, such as is seen among amphibians and other 
primitive vertebrates, whereby the original limb may be com- 
pletely restored from the mutilated remnant of an amputation. 


AQUATIC REPTILES 


199 


CMAMPSOSAURUS 


CRETACEOUS 


Such regeneration is attributable to the potentiahty of the 
heredity-chromatin which still resides in the cells of the am- 
putated surfaces. The heredity-chromatin determiners of the 
bones of the separate digits or separate phalanges if once lost 
in geologic time are never reacquired; on the contrary, each 
phase of habitat adapta- 


tion is forced to commence 
with the elements remain- 
ing in the organism's hered- 
ity-chromatin, which may 
have been impoverished in 
previous habitats. When 
an ancient habitat zone is 
reentered there must be 
readaptation of the parts 
which remain. Thus, 
when the terrestrial rep- 
tiles reenter the aquatic 
zone of their amphibian 
ancestors they cannot re- 
sume the amphibian char- 
acters, for these have been 
lost by the chromatin. 
This invariable princi- 


REPTILIA RHVTIDODON ^^,^^^,^ 

Fig. 75. Reptiles Leaving a Terrestrial 
FOR AN Aquatic Habitat, the Beginning 
OF Aquatic Adaptation. 

Littoral-fluviatile types independently evolve 
in the Triassic {Rhytidodon, a phytosaur) and 
in the Upper Cretaceous (Cliampsosaitrus). 
These animals belong to two widely different 
orders of reptiles, neither of which is closely 
akin to the modern alligators and crocodiles. 
The adaptation is convergent to that of the 
existing gavials and crocodiles. Restorations 
for the author by W. K. Gregory and Richard 
Deckert. 


pie underlying reversed 
evolution is partly illustrated (Fig. 53) in the passage from the 
reptilian foot into the fin of the aquatic reptile and with equal 
clearness in the passage of the wing of the flying bird into the 
fin of the swimming bird (Fig. no). 

In no less than eleven out of the eighteen orders of reptiles 
reversed adaptation to a renewal of aquatic life, like that of 
the fishes and amphibians, took place in the long and slow 


200 


THE ORIGIN AND EVOLUTION OF LIFE 


CYMBOSPONDYLUS 


GEOSAURUS 


REPTiuA TYLOSAURUS 


CRE7ACEOUS 


Fig. 76. Convergent Aquatic Adap- 
tation INTO Elongate Fusiform Type 
in Four Different Orders of 
Amphibians and Reptiles. 

Independently convergent evolution of four long- 
bodied, free-swimming, swift-moving, surface-liv- 
ing aquatic types in which the fins and limbs are 
retained as paddles: Cn'co^Mi, an amphibian; Ty- 
losaurus, an Upper Cretaceous mosasaur; Geo- 
saurus, a Jurassic crocodilian; C ymhos pondylus , a 
Triassic ichthyosaur. A very similar fusiform type 
evolves among the mammals in the Eocene ceta- 
ceans (Zeuglodon) , as seen in Fig. 123. Restora- 
tions prepared for the author, independent of 
scale, by W. K. Gregory and Richard Deckert. 


passage from a terrestrial phase, 
through palustral, swamp-living 
phases into a littoral, fluviatile 
phase, and from this into littoral 
and marine salt-water phases; 
so that finally in no less than 
six orders of reptiles the pelagic 
phase of the high seas was inde- 
pendently reached. 

The role in the economy of 
oceanic life which is now taken 
by the whales, dolphins, and por- 
poises was assumed by families 
of the plesiosaurs, ichthyosaurs, 
mosasaurs, snakes, and croco- 
diles, all flourishing in the high 
seas, together with families of 
the turtles, which are the only 
high-sea reptiles surviving at the 
present day. Moreover, under 
the alternating adaptations to 
terrestrial and marine life, which 
prevailed during the 10,000,000 
years of late Palaeozoic and 
Mesozoic time, several families 
of the existing orders of reptiles 
sought a seafaring existence 
more than once and gave off 
numerous side branches from 
the main stem. The adapta- 
tions to marine life have been 
especially studied by Fraas, 


AQUATIC REPTILES 


20I 


Even to-day there are tendencies toward marine invasion 
observed among several of the surviving families of Hzards 
and crocodiles of seashore frequenting habits. 


ADAPTIVE RADIATION OF AQUATIC REPTILES 


Fig. 77. Independent Reversed Adaptation to the Aquatic Zones in Twelve 
Orders of Reptiles, Originating on Land and Entering the Seas. 

Diagram showing the manner in which twelve of the eighteen orders of reptiles descend 
from the terrestrial (land-living) zone into the paludal (swamp-frequenting) zone, thence 
into the littoral-fluviatile (fresh-water and brackish-water) zone, thence into the littoral- 
marine (salt-water) zone, and finally into the pelagic zones of the high seas. This final 
marine pelagic phase of evolution is attained in only six orders, namely, the plesiosaurs, 
Chelonia (sea- tortoises), ichthyosaurs, mosasaurs (marine lizards), crocodiles, and 
certain ophidians (true sea-snakes found far out at sea in the Indian Ocean). Nine of 
the reptilian orders give off not only one but from two to five independent branches 
seeking ac^uatic life, of which si.\ independently reach the full pelagic high-sea phase. 

Still more remarkable than the law of reversed adaptation 
is that of alternate adaptation, which has been brilliantly 


202 


THE ORIGIN AND EVOLUTION OF LIFE 


developed by Louis Dollo, of Brussels. This is applied hypo- 
thetically to the evolution of the existing leatherbacks (Sphar- 


ABYSSAL 


Fig. 78. Chelonia. Diagram Illustrating the Alternate Habitat Migration 
OF THE Ancestral "Leatherbacks," SpHARGiD.i. 

DoUo's theory is that these animals originate in armored land forms with a solid bony 
shell, and pass from the terrestrio-aquatic into the littoral and then into the pelagic 
zone, in which the solid bony shell, being no longer of use, is gradually atrophied. After 
prolonged marine pelagic existence these animals return secondarily to the littoral 
zone and acquire a new armature of rounded dermal ossicles which develop on the 
upper and lower shields of the body. The animals (Sphargis) then for a second time 
take up existence in the pelagic zone, during which the dermal ossicles again tend to 
disappear. 

gidae), an extremely sj^ecialized type of sea turtles. It is be- 
lieved that after a long period of primary terrestrial evolution 

^^^_^ ^__^ ii^ which the ancestors of 

these turtles acquired a firm, 
bony carapace for land de- 
fense, they then passed 
through various transitions 
into a primary marine phase 
during which they gradually 
lost all their first bony arma- 

FiG. 79. The Existing "Leatherback" ture. Following this sea 


The Existing "Leatherback" 
Chelonian Sphargis. 

In this form the solid armature adapted to a 
former terrestrial existence is being replaced 
by a leathery shield in which are embedded 
small polygonal ossicles. After Lydekker. 


phase the animals returned 
to shore and entered a 
secondary littoral, shore-liv- 
ing phase, also of long dur- 
ation, in course of which they developed a second bony 
armature quite distinct in plan and pattern from the first. 


AQUATIC REPTILES 


203 


Descendants of these secondarily armored, shore-living types 
again sought the sea and entered a secondary marine pelagic 
phase in course of which they lost the greater part of their 


REPTILIA ARCHELON cRE^tTcIou: REPTILIA PLACOCHELYS 

Fig. 80. Armored Terrestrial Cheloxia ^^ 
In\'.«)e the Seas and Lose Their Araia- f 

TURE. 

Convergent or analogous evolution (two 

upper figures) in the inland seas of the 

paddle-propelled chelonian Archelon (after 

Williston), the gigantic marine turtle of 

the Upper Cretaceous continental seas of 

North America, and of Placochclys (after 

Jaekel in part), a Triassic reptile belonging 

to the entirely distinct order Placodontia. 
Skeleton of Archelon (lower) in which the 

bony armature of the carapace has largely 

disappeared, exposing the ribs. Specimen 

in the Peabody Museum of Yale Univer- 
sity. After Wieland. 

second armature and acquired their present leathery covering, 
to which the popular name ''leatherbacks" applies.^ 

In general the law of reversed aquatic adaptation is most 
brilliantly illustrated in the fossil ichthyosaurs, in the internal 

' This law of alternate adaptation may be regarded as absolutely established in the 
case of certain land-living marsupials in which anatomical records remain of an alterna- 
tion of adaptations from the terrestrial to the arboreal phase, from an arboreal into a 
secondary terrestrial phase, and from this terrestrial repetition to a secondary arboreal 
phase. The relics of successive adaptations to alternations of habitat zones and adap- 
tive phases are clearly observed in the so-called tree kangaroos {Dendrolagiis) of Australia. 


204 


THE ORIGIN AND EVOLUTION OF LIFE 


anatomy of which land-living ancestry is clearly written, while 
reversed adaptation for marine pelagic life has resulted in a 
superficial type of body which presents close analogies to that 
of the sharks, porpoises, and shark-dolphins (Fig. 41). Integu- 
mentary median and tail fins precisely similar to those of the 


Fig. 81. Extreme Adaptation of the Ichthyosaurs to Marine Pelagic Life. 

Although primarily of terrestrial origin the ichthyosaurs become quite independent of 
the shores through the viviparous birth of the young as evidenced by a fossil female 
ichthyosaur (upper figures) with the foetal skeletons of seven young ichthyosaurs 
within or near the abdominal cavity. 

A fossil ichthyosaur (lower figure) with preserved body integument and fin outlines re- 
sembling those of the sharks and dolphins (see Fig. 41). 

Both specimens in the American Museum of Natural History from Holzmaden, Wiirtem- 
berg. 

sharks evolve, the anterior lateral limbs are secondarily con- 
verted into fin-paddles, which are externally similar to those 
of sharks and dolphins, while the posterior limbs are reduced. 
As in the shark, the tail fin is vertical, while in the dolphin the 
tail fin is horizontal. In the early history of their marine 
pelagic existence the ichthyosaurs undoubtedly returned to 
shore to deposit their eggs, but a climax of imitation of the dol- 
phins and of certain of the sharks is reached in the develop- 
ment of the power of viviparity, the growth of the young within 


AQUATIC REPTILES 


205 


BAPTANODON 


CRETACEOUS 


CYMOOSPONDYLUS 


the body cavity of the mother, resulting in the young ichthyo- 
saurs being born in the water fully formed and able to take 
care of themselves immediately after birth like the young of 
modern whales and dolphins. When this viviparous habit 
finally released the ichthyosaurs from the necessity of return- 
ing to land for breeding they developed the extraordinary 
powers of migration which car- 
ried them into the Arctic seas 
of Spitzbergen, the Cordilleran 
seas of western North America, 
and doubtless into the Antarc- 
tic. So far as we know this 
viviparous habit was never de- 
veloped among the seafaring 
turtles, which always return 
to shore to deposit their eggs. 
While the ichthyosaurs vary 
greatly in size, they present a 
reversed evolution from the ter- 
restrial, quadrupedal type into 
the swift-moving, fusiform body 
type of the fishes, which is 
finally reduced in predaceous 
power through the degeneration of the teeth, as observed in 
the Baptanodon, an ichthyosaur of the Upper Jurassic seas of 
the ancient Rocky Mountain region. 

While the continental seas of Jurassic time were favorable 
to this remarkable aquatic marine phase of the reptiles, still 
greater inundations both of North America and of Europe 
occurred during Upper Cretaceous time. This was the period 
of the maximum evolution of the sea reptiles, the ultimate 
food supply of which was the surface life of the oceans, the 


Fig. 82. 


Restorations of Two Ich- 
thyosaurs. 

Cymhospcmdylns, a primitive ichthyosaur 
from the Triassic seas of Nevada (after 
Merriam), and the highly speciahzed 
Baptanodon, a Cretaceous ichthyosaur 
of the seas of that period in the region 
of Wyoming, in which the teeth are 
greatly reduced. Restorations for the 
author by W. K. Gregory and Richard 
Deckert. 


2o6 


THE ORIGIN AND EVOLUTION OF LIFE 


marine Protozoa, skeletons of which were depositing the great 
chalk beds of Europe and of western North America. 

The Plesiosaurs had begun their invasion of the sea during 
Upper Triassic time, as shown in the primitive half-lizard 


Fig. 83. North America in Upper Cretaceous Time. 

The great inland continental sea extending from the Gulf to the Arctic Ocean, was favor- 
able to the evolution of the mosasaurs, plesiosaurs, and giant sea turtles (Airhelon). 
This period is marked by the greatest inundation of North America during Mesozoic 
time, by mountains slowly rising along the Pacific coast from Mexico to Alaska, and by 
volcanic activity in Antillia. Detail from the globe model in the American Museum by 
Chester A. Reeds and George Robertson, after Schuchert. 

Lariosaurus, discovered in northern Italy, which still retains 
its original lacertilian appearance, due to the fact that the 
limbs and feet are not as yet transformed into paddles. In 
the subsequent evolution of paddles the number of digits re- 
mains the same, namely, five, but the number of the phalanges 
on each digit is greatly increased through the process known 
as hyperphalangy, an example of the numerical addition of 


AQUATIC REPTILES 


207 


new characters. Propulsion through the water was rather by 
means of the paddles than by the combined lateral body-and- 


FiG. 84. Convergent Forms of Aquatic Reptiles of Different Origin. 

Lariosaurus (left), the Triassic ancestor of the plesiosaurs from northern Italy, and 
Mesosaurus (right), from the Permian of Brazil and South Africa, representing another 
extinct order of the Reptilia, the Proganosauria. Drawn by Deckert after McGregor. 

tail motion seen among the ichthyosaurs, because all plesiosaurs 
exhibit a more or less abbreviated tail and a more or less 
broadly depressed body. It is also significant that the fore 


Fig. 85. A Plesiosaur from the Jurassic of England. 

Skeleton of Cryptodcidus oxonicnsis seen from above. Mounted in the American Museum 

of Natural History. 


208 


THE ORIGIN AND EVOLUTION OF LIFE 


and hind paddles are homodynamic, i. e., exerting equal power; 
they are so exactly alike that it is very difficult to distinguish 
them, whether they are provided with four broad paddles or 
with four long, narrow, slender paddles. The plesiosaurs 

afford the first illustration we 
have noted of another of the 
great laws of form evolution, 
namely, adaptation occurs far 
more frequently through 
changes of existing proportions 
than through numerical addi- 
tion of new characters. It is 
proportional changes which 
separate the swift-moving 
plesiosaurs {Trinacromerion os- 
horni), which are invariably 
provided with long heads, short 
necks, and broad paddles, from 
the slow-moving plesiosaurs 
(Elasmosaurus) , which are pro- 
vided with narrow paddles, 
short bodies, extremely long 
necks, and small heads. 

It is believed that the lizard- 
like ancestors of the mosasaurs 
left the land early in Cretaceous 
time ; it is certain that through- 
out the three or four million years of the Cretaceous epoch 
they spread into all the oceans of the world, from the conti- 
nental seas of northern Europe and North America to those 
of New Zealand. In Europe these animals survived to the 
very close of Mesozoic time since the type genus of the great 


TRINACROMERION 


CRETACEOUS 


Fig. 86. Types of Marine Pelagic 
Plesiosaurs of the American Con- 
tinental Cretaceous Seas. 

The slow-moving, long-necked Elasmo- 
saurus and the swift-moving, short- 
necked Trinacromerion. The limbs 
are completely transformed into pad- 
dles. The great differences in the pro- 
portions of the neck and body repre- 
sent adaptations to greater or less 
speed. Restorations for the author by 
W. K. Gregory and Richard Deckert, 
chiefly after Williston. 


AQUATIC REPTILES 


209 


order Mosasauria (Mosasaurus), taking its name from the 

River Meuse, was found in the uppermost marine Cretaceous. 

Detailed knowledge of the structure of these remarkable 

sea lizards is due chiefly to the researches of Williston and 


Fig. 87. A Sea Lizard. 

Tylosaurus, a giant mosasaur from the inland Cretaceous seas of Kansas, chasing the giant 
fish Porlheiis. After a restoration in the American Museum of Natural History, by 
Charles R. Knight under the author's direction. 

Osborn of this country and to those of Dollo in Europe. The 
head is long and provided with recurved teeth adapted to seiz- 
ing active fish prey (Fig. 87); the neck is extremely short; as 
in the plesiosaurs the fore and hind limbs are converted into 
paddles, symmetrical in proportion; the body is elongate and 


2IO THE ORIGIN AND EVOLUTION OF LIFE 

propulsion is not chiefly by means of the fins but by the sinu- 
ous motions of the body, and especially of the very elongate, 
broad, fin-like tail. These sea lizards of Upper Cretaceous 
time (Fig. 76) are analogous or convergent to the sea Croco- 
dilia (Geosaurus) of Jurassic time and present further analogies 
with the Triassic ichthyosaur Cymbospondylus and the small 
Permo- Carboniferous amphibian Cricotiis (Fig. 76), In the 
American continental seas these animals radiated into the 
small, relatively slender Clidastes, into the somewhat more 
broadly finned Platecarpus, and into the giant Tylosaurus, 
which was capable (Fig. 87) of capturing the great fish of the 
Cretaceous seas (Porlheus). 

Terrestrial Life. Carnivorous Dinosaurs 

Widely contrasting with these extreme adaptations to 
aquatic marine life, the climax of terrestrial adaptation in the 
reptilian skeleton is reached among the dinosaurs, a branch 
which separated in late Permian or early Triassic time from 
small quadrupedal, swiftly moving, lizard-like reptiles and 
before the time of their extinction at the close of the Creta- 
ceous had evolved into a marvellous abundance and variety 
of types. In the Upper Triassic of North America, late New- 
ark time, the main separation of the dinosaurs into two great 
divisions, (a) those with a crocodile-like pelvis, known as 
Saurischia, and (b) those with a bird-like pelvis, known as Orni- 
thischia, had already taken place, and the dinosaurs domi- 
nated all other terrestrial forms. 

When Hitchcock in 1836 explored the giant footprints in 
the ancient mud flats of the Connecticut valley he quite nat- 
urally attributed many of them to gigantic birds, since at the 
time the law of parallel mechanical evolution between birds 
and dinosaurs was not comprehended and the order Dino- 


CARNIVOROUS DINOSAURS 


211 


ANCHISAURUS 


RHYTIDODON 


CONNECTICUT TRJASSIC REPTILES 

Fig. 88. Life of the Connecticut Ri\ er Valley in Upper Triassic (Newark) Time. 

Anchisaurus, a primitive carnivorous bipedal dinosaur. Rhytidodon, a phytosaur analo- 
gous but not related to the modern gavials. Stegomus, a small armored phytosaur 
related to Rhytidodon. Anomospus, a herbivorous bipedal dinosaur related to the 
"duckbills" or Iguanodonts. Podokcsaurus, a light, swift-moving, carnivorous dino- 
saur of the bird-like type. Restorations (except Rhytidodon) after R. S. Lull of Yale 
University. Drawn to uniform scale for the author by Richard Deckert. 


PHYLOGENY AND ADAPTIVE RADIATION OF THE DINOSAURS 


UPPER 


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T ^^^"~ 


Y ""^'"' 


— ... 


:y -•---: 


— 


fc£?£^S 


'— — ° 


■~ — — 


..SS,C 


™ 


._ 


URS 


TRIASSIC 


c""°'°" 


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Fig. 


Terrestrial Evolution of the Dlnosaurs. 


The ancestral tree of the dinosaurs, originating in Lower Permian time, and branching 
into five great lines during a period estimated at twelve million years. A , The giant 
herbivorous Sauropoda which sprang from Lower Triassic carnivorous ancestors. 

B, Giant carnivorous dinosaurs, which prey upon all the larger herbivorous forms. 

C, Swift-moving, ostrich-like, carnivorous dinosaurs, related to B. D, Herbivorous 
Iguanodonts, swift-moving, beaked, or "duck-bill" dinosaurs, related to E. E, Slow- 
moving, quadrupedal, heavily armored or horned herbivorous dinosaurs, related to D. 
Prepared for the author by W. K. Gregory, chiefly after Lull. 


212 


THE ORIGIN AND EVOLUTION OF LIFE 


sauria was not known. It has since been discovered that 
many of the ancient dinosaurs, especially those of carnivorous 
habit, were bird-footed and adapted in structure for rapid, 
cursorial locomotion; the body was completely raised above 


Fig. 90. North America ix Uppkr Triassic (,.\'i:\v\rkj Timk. 

The period of the primitive bipedal dinosaurs, with semi-arid, cool to warm climate, and 
a prevailing flora of cycads and conifers. Remains of amphibians, primitive crocodiles, 
and dinosaurs are found in the reddish continental deposits. Detail from the globe 
model in the American Museum by Chester A. Reeds and George Robertson, after 
Schuchert. 

the ground, the forward part being balanced with the aid of 
the long tail. This primitive type of body structure is com- 
mon to all the dinosaurs, and is evidence that the group 
underwent a long period of evolution under semi-arid conti- 
nental conditions in late Permian and early Triassic time. 
The reptilian group discovered in the Connecticut valley (Fig. 


CARNIVOROUS DINOSAURS 


213 


88) is not inconsistent with the theory of a semi-arid climate 
advocated by Barrell to explain the reddish continental de- 
posits not only in the region of the Connecticut valley but 
over the southwestern Great Plains. The flora of ferns, cycads, 
and conifers indicates moderate conditions of temperature. 
Along the Pacific coast there was a great overflow of the seas 
along the western continental border and an archipelago of 
volcanic islands. In this region there were numerous coral 
reefs and an abundance of cephalopod ammonites. In the 


Fig. qi. A Carm\(jR(h:s Uknusaur Preying upon a Sauropou. 

Skeletons (left) and restoration (right) of the bipedal dinosaur Allosaunis of Upper Jurassic 
and Lower Cretaceous time in the act of feeding upon the carcass of Apatosaitnis, one 
of the giant herbivorous Sauropoda of the same period. Mounted specimens and 
restoration by Osborn and Knight in the American Museum of Natural History. 

interior continental seas great marine reptiles (Cymbospondylus, 
Fig. 82), related to the ichthyosaurs, were abundant. 

The primitive light-bodied, long-tailed type of dinosaur of 
bipedal locomotion originates in this country with Marsh's 
Anchisaurus of the Connecticut valley (Fig. 88) and develops 
into the more powerful form of the Allosaurus of Marsh from 
the Jurassic flood-plains east of the Rocky Mountains (Fig. 91). 
Contemporaneous with this powerful animal is the much more 
delicate Ornitholestes, which is departing from the carnivorous 
habits of its ancestors and seeking some new form of food. It 
is in turn ancestral to the remarkable "ostrich dinosaur" of 
the Upper Cretaceous, Struthiomimus {Ornithomimus) , which 
is bird-like both in the structure of its limbs and feet and in 


214 


THE ORIGIN AND EVOLUTION OF LIFE 


Recently restored skeleton of the light-limbed, 
bird-like, toothless "ostrich'' dinosaur, Slriith- 
iomimus {Ornithomimus), after Osborn. 


its toothless jaw sheathed in horn. In this animal the car- 
nivorous habit is completely lost; it is secondarily herbivorous. 

Its limbs are adapted to 
very rapid motion. 

In the meantime the 
true carnivorous dinosaur 
line was evolving over 
the entire northern hemis- 
phere stage by stage with 
the evolution of the varied 
herbivorous group of the 
dinosaurs. These animals 
preserved perfect me- 
chanical unity in the evo- 
lution of the very swift 
motions of the hind limb 
and prehensile powers 
both of the jaws and of 
the hind feet, adapted to 
seizing and rapidly over- 
coming a struggling 
powerful prey. This series 
reaches an astounding 
climax in the gigantic 
Tyrannosaurus rex, de- 
scribed by Osborn from 
the Upper Cretaceous of 
Montana (see frontis- 
piece). This "king of the tyrant saurians" is in respect to 
speed, size, power, and ferocity the most destructive life 
engine which has ever evolved. The excessively small size of 
the brain, probably weighing less than a pound, which is less 


Lateral view of the "tyrant" dinosaur, Tyran- 
nosaurus (left), and the "ostrich" dinosaur, 
Slruthiomimus (right), to the same scale. 

Fig. 92. Extremes of Adaptation in the 
"Tyrant" and the "Ostrich" Dinosaurs. 

Skeletons mounted in the American Museum of 
Natural History. 


CARNIVOROUS DINOSAURS 


215 


than I /4000 of the estimated body weight, indicates that in 
animals mechanical evolution is quite independent of the 
evolution of their intelligence; in fact, intelligence compensates 
for the absence of mechanical perfection. Tyrannosaums is 


^^(f? 'y^<^ 


Fig. 93. Four Restorations of the "Ostrich" Dinosaur, Stnithiomimus 

{Ornithomimus). 

A. Showing the mode of progression. 

B. Illustrating the hypothesis that the animal was an anteater which used the front 

claws like those of sloths in tearing down anthills. 

C. Illustrating the hypothesis that it was a browser which supported the fore part of the 

body by means of the long, curved claws of the fore limb while browsing on trees. 

D. Illustrating the hypothesis that it was a wading type, feeding upon shrimps and 

smaller crustaceans. 
Restorations by Osbom. No satisfactory theory of the habits of this animal has as 
yet been advanced. 

an illustration of the law of compensation, first enunciated by 
Geoffroy St. Hilaire, first, in the disproportion between the 
diminutive fore limb and the gigantic hind limb, and second, 
in the fact that the feeble grasping power and consequent 
degeneration of the fore limb and hand are more than com- 
pensated for by the development of the tail and the hind claws. 


2l6 


THE ORIGIN AND EVOLUTION OF LIFE 


PLATEOSAURUS 


which enables these animals to feed practically in the same 
manner as the raptorial birds. 

Herbivorous Dinosaurs, Sauropoda 

As analyzed by Lull along the lines of modern interpreta- 
tion, beside the small carnivorous dinosaurs there may be 

traced in the Connecticut 
Triassic footprints the be- 
ginnings of an herbivorous 
offshoot of the primitive 
carnivorous dinosaur stock, 
leading into the elephantine 
types of herbivorous dino- 
saurs known as the Sauro- 
poda, which were first 
brought to our knowledge 
in this country through the 
pioneer studies of Marsh 
and Cope. 

As there is never any 
need of haste in the capture 
of plant life these animals 
underwent a reversed evo- 
lution of the limbs from the 
swift-moving primitive bi- 
pedal type into a secon- 
dary slow-moving quadru- 
pedal ambulatory type. 
The original power of occa- 
sionally raising the body 
on the hind limbs was «Jtil] retained in some of these gigantic 
forms. The half-way stage between the bipedal and the 


ANCHISAURUS 


Fig. 94. Analogy Between the Carnivo- 
rous Anchisaunis Type of the Triassic 
AND the Ancestral Herbivorous Sauro- 
POD Type Platcosaiirus. 

The upper restoration (Plalcosaurus) repre- 
sents a bipedal stage of sauropod evolution 
which was discovered in the German Trias, 
in which the transition from carnivorous to 
herbivorous habits is observed. Recent 
discovery renders it probable that the 
herbivorous Sauropoda descend from carniv- 
orous ancestors like Anchisaunis. 

Restoration of Plaleosaurus modified from Jae- 
kel. Restoration of Anchisaurus after Lull. 


HERBIVOROUS DINOSAURS 


217 


quadrupedal mode of progression is revealed in the recently 
described Plateosaiirus of Jaekel from the Trias of Germany 
(Fig. 94), an animal which could progress either on two or on 
four legs. 

The Sauropoda reached the climax of their evolution dur- 
ing the close of Jurassic (Morrison formation) and the be- 


PALEOOEOGRftPHY. LOWER CRETACEOUS (UPPER NEOCOMIAN-VELANGIAN-HILS-WEALDEN 
AFTER SCHUCHERT. APRIL 1918 
»..^ MARINE DEPOSITS T; CONTINENTAL DEPOSITS \ SIERRA NEVADA 


ITY-MORISSON) 1 


Fig. 95. Theoretic World Environment in Lower Cretaceous Time. 

The dominant period of the great sauropod dinosaurs. This shows the theoretic South 
Atlantic continent Gondwana connecting South America and Africa, and the Eurasiatic 
Mediterranean sea Tclhys. Shortly afterward comes the rise of the modern flowering 
plants and the hardwood forests. The shaded patch over the existing region of Wyo- 
ming and Colorado is the flood-plain (Morrison) centre of the giant Sauropoda (see Fig. 
97). After Schuchert, 1916. 

ginning of Cretaceous time (Comanchean Epoch). Meanwhile 
they attained world-wide distribution, migrating throughout a 
long stretch of the present Rocky Mountain region of North 
America, into southern Argentina, into the Upper Jurassic of 
Great Britain, France, and Germany, and into eastern Africa. 
The last named region is the one most recently explored, and 


2l8 


THE ORIGIN AND EVOLUTION OF LIFE 


the widely heralded Giganiosaurus (= Brachiosaurus) , de- 
scribed as the largest land-Hving vertebrate ever found, is 


Fig. 


gO. -\uKTii Ami.ru'a i.\ Lu.w.u Lrktaceous (Comanchian) Time. 

This period, also known as the Trinity-Morrison time, is marked by the maximum develop- 
ment of the giant herbivorous dinosaurs, the Sauropoda. The Sierra Nevada and coast 
ranges are elevated, also the mountain ranges of the Great Basin which give rise east- 
ward to the flood-plain deposits (Morrison) in which the remains of the Sauropoda are 
entombed. This epoch is prior to the birth of the Rocky IMountains, which arose be- 
tween Cretaceous and Eocene time. Detail from the globe model in the American 
Museum by Chester A. Reeds and George Robertson, after Schuchert. 

structurally closely related to and does not exceed in size the 
sauropods discovered in the Black Hills of South Dakota. 
Their size is indeed titanic, the length being loo feet, while the 


HERBIVOROUS DINOSAURS 


219 


longest whales do not exceed 90 feet. In height these sauropods 
dwarf the straight-tusked elephant of Pleistocene time, which 
is the largest land product of mammalian evolution. The 
Sauropoda for the most part inhabited the swampy meadows 
and flood-plains of Morrison time. They include, besides the 


CRETACEOUS 


CRETACEOUS 


Fig. 97. Three Principal Types of Sauropods. 

The body form of the three principal types of giant herbivorous Sauropoda which ap- 
pear to have been almost world-wide in distribution. 

Camarasaiirus, a heavy-bodied, short-limbed quadrupedal type. Diplodocus, a light- 
bodied, relatively swift-moving quadrupedal type. Brachiosauriis, a short-bodied 
quadrupedal type in which the fore limbs are more elevated than the hind limbs. 
Brachiosaurus attained gigantic size, being related to the recently discovered Giganlo- 
saiinis of East .Africa. Restorations by Osborn, Matthew, and Deckert. 

gigantic type Bracl/iosannts (- Gigantosaurics), with its greatly 
elevated shoulder and forearm, massive quadrupedal types like 
Camarasaurus Cope and Apatosaurus (=^ Brontosaurus) Marsh, 
and the relatively long, slender, swiftly moving Diplodocus. 
According to Lull and Deperet the Sauropoda survived until 
the close of the Cretaceous Epoch in Patagonia and in southern 
France. In North America they became extinct in Lower 
Cretaceous time. 


220 


THE ORIGIN AND EVOLUTION OF LIFE 


In the final extinction of the herbivorous sauropod type we 
find an example of the selection laiv of elimination^ attributable 


Fig. 98. .\\ii'iiiiiii 


i)R TlCKklCSrRID-lM.HXTATILE THEORY ( )i.' TiiK IlAliirS OF 

Apatosaurus. 


(Upper.) Apatosaurus { = Brontosaurus), a typical sauropod of Morrison age, quad- 
rupedal, heavy-limbed, herbivorous, inhabiting the flood-plains (Morrison) and lagoons 
of the region now elevated into the Rocky Mountain chain of Wyoming and Colorado. 

(Lower.) Mounted skeleton of Apatosaurus { = Brontosaimis) in the American Museum 
of Natural History. 


to the fact that these types had reached a cul-de-sac of mechan- 
ical evolution from which they could not adaptively emerge 


HERBIVOROUS DINOSAURS 


221 


when they encountered in all parts of the world the new en- 
vironmental conditions of advancing Cretaceous time. 

The Iguanodontia 

Contemporaneous with the culminating period of the evo- 
lution of the Sauropoda is the world-wide appearance of an 


J 

Fig. 99. Primitive Iguaxodont Camptosaurus from the Upper Jurassic of 

Wyoming. 
This swift bipedal form was contemporary with the giant sauropod Apatosaunis and the 
lighter-bodied Diplodocus. These iguanodonts were defenseless and dependent wholly 
on alertness and speed, or perhaps on resort to the water, for escape from their enemies. 
They were the prey of AUosaiirus (see Fig. 91). Mounted specimen in the American 
Museum of Natural History. 

entirely different stock of bipedal herbivorous dinosaurs in 
which the pelvis is bird-like (Ornithischia, Seeley). These 
animals may be traced back (von Huene) to the Triassic 
Naosaurus. The front of the jaws at an early stage lost the 
teeth and developed a horny sheath or beak like that of the 
birds, within which a new bone (predentary) evolves, giving to 
this order the name Predentata. Entirely defenseless at this 
stage {Camptosaurus), these relatively small, bipedal types 


222 


THE ORIGIN AND EVOLUTION OF LIFE 


Fig. loo. A Pair of Upper Cretaceous Iguano- 

DONTS FROM MONTANA. 

After a lapse of 500,000 years of Cretaceous time the 
Camptosaurus (Fig. gg) evolved into the giant " duck- 
billed " dinosaur Trachodon, described by Leidy and 
Cope from the Upper Cretaceous of New Jersey and 
Dakota. 

Two skeletons of Trachodon annedens (upper) discovered 
in Montana, as mounted in the American Museum of 
Natural History, and restoration of the same (lower) 
by Osborn and Knight. (Compare Fig. 74.) 


spread all over the 
northern hemisphere 
and attained an extra- 
ordinary adaptive radi- 
ation in the river- and 
shore-living "duck- 
bill" dinosaurs, the 
iguanodonts of the Cre- 
taceous Epoch (Fig. 
loi). The adaptive 
radiation of these ani- 
mals has only recently 
been fully determined; 
it led into three great 
types of body form, all 
unarmored. First, the 
less specialized types 
which retain more or 
less the body structure 
of the earlier Jurassic 
forms and the famous 
iguanodont of Bernis- 
sart, Belgium. Related 
to these are the krito- 
saurs of the Cretaceous 
of Alberta, with a com- 
paratively narrow head, 
the protection of which 
was facilitated by a 
long, backwardly pro- 
jecting spine. Second, 
there are the broadl\' 


HERBIVOROUS DINOSAURS 


223 


duck-billed, wading dinosaurs {Trachodon), with stalking limbs 
and elevated bodies. Third, there are more fully aquatic, free- 
swimming forms with crested skulls iCorytliosaiirus). The 


: :»ijyj&»m»^ 


Fig. ioi. Adaptive Radiation of the Iguanodont Dinosaurs into Three Groups. 

(Upper.) Three characteristic types: A, Typical "duck-bill" Trachodon; B, Corytho- 
saitrus, the hooded "duck-bill," with a head like a cassowary, probably aquatic; C, 
Kritosaiirus, the crested "duck-bill " dinosaur. Restorations by Brown and Deckert. 

(Lower.) Mounted skeleton of Corythosaurus in the American Museum of Natural His- 
tory, recently discovered in the Upper Cretaceous of Alberta, Canada, with the integ- 
ument impressions and body lines preserved. 

anatomy and habits of all these forms have been made known 
recently by American Museum explorations in Alberta, Canada, 
under Barnum Brown (Fig. loi). 

The partly armored dinosaurs known as stegosaurs are 
related to the iguanodonts and belong to the bird-pelvis group 


224 


THE ORIGIN AND EVOLUTION OF LIFE 


(Ornithischia) . The small Triassic ancestors of this great 
group of herbivorous, ornithischian dinosaurs also gave rise 
to a number of secondarily quadrupedal, slow-moving forms, 
in which there developed various forms of defensive and offen- 
sive armature. Of these the Jurassic stegosaurs exhibit a 
reversed evolution in their locomotion since they pass from a 
bipedal into a quadrupedal type in which the armature takes 


Fig. I02. Offensive and Defensh'e Energy Complexes. 

The carnivorous "tyrant" dinosaur Tyrannosaiirus approaching a group of the horned 
herbivorous dinosaurs known as Ceratopsia. Compare frontispiece. 

The Ceratopsia are related to the armored Stegosaurus and to the armorless, swift-moving 
Iguanodontia. Restoration by Osborn in the American Museum of Natural History, 
painted by Charles R. Knight. 


the form of sharp dorsal plates and spiny defenses, the exact 
arrangement of which has been recently worked out by Gil- 
more. Doubtless when this animal was attacked it drew its 
head and limbs under its body, like the armadillo or porcu- 
pine, and relied for protection upon its dorsal armature, aided 
by rapid lateral motions of the great spines of the tail to ward 
off its enemies. During the progress of Cretaceous time these 
stegosaurs became extinct, and by the beginning of the Middle 
Cretaceous two other herbivorous types are given off from the 
predentate stock. 

The first of these are the aggressively and defensively 
horned Ceratopsia, in which two or three front horns evolved 


HERBIVOROUS DINOSAURS 225 

step by step, with a great bony frill protecting the neck. This 
evolution took place stage by stage with the evolution of the 
predatory mechanism of the carnivorous dinosaurs, so that 
the climax of ceratopsian defense {Triceratops) was reached 
simultaneously with the climax of Tyrannosaurus offense. This 
is an example of the counteracting evolution of offensive and 
defensive adaptations, analogous to that which we observe 
to-day in the evolution of the lions, tigers, and leopards, which 
counteracts with that of the horned cattle and antelopes of 
Africa, and again in the evolution of the wolves simultaneously 
with the horned bison and deer in the northern hemisphere. 
It is a case where the struggle for existence is very severe at 
every stage of development and where advantageous or dis- 
advantageous chromatin predispositions in evolution come con- 
stantly under the operation of the law of selection. Thus in the 
balance between the reptilian carnivora and herbivora we find 
a complete protophase of the more recent balance between the 
mammalian carnivora and herbivora. 

The climax of defense was reached, however, in another 
line of Predentata, in the herbivorous dinosaurs, known as 
Ankylosaurus, in which there developed a close imitation of the 
armadillo or glyptodon type of mammal, with the head and 
entire body sheathed in a very dense, bony armature. In 
these animals not only is motion abandoned as a means of 
escape, but the teeth become diminutive and feeble, as in most 
other heavily armored forms of reptiles and mammals. The 
herbivorous function of the teeth is replaced by the develop- 
ment of horny beaks. Thus these animals reach a ground- 
dwelling, slow-moving, heavily armored existence. 


226 


THE ORIGIN AND EVOLUTION OF LIFE 


Pterosaurs 

There is no doubt that the pterosaurs, flying reptiles, were 
adapted to fly far out to sea, for their remains are found min- 
gled with those of the mosasaurs in deposits far from the 
ancient shore-lines. There is no relation whatever between 
the feathered birds and these animals, whose analogies in their 
modes of flight are rather with the bats among the mammals. 

These flying reptiles are 
perhaps the most extraor- 
dinary of all extinct ani- 
mals. While some ptero- 
saurs were hardly larger 
than sparrows, others sur- 
passed all living birds in 
the spread of the wings, 
although inferior to many 
birds in the bulk of the 
body. It is believed that 
they depended almost entirely upon soaring for progression. 
The head in the largest types of the family {Pteranodon) is 
converted into a great vertical fin, used, no doubt, in directing 
flight, with a long, backwardly projecting bony crest which 
served in the balancing of the elongate and compressed bill. 
The feeble development of the muscles of flight in these an- 
cient forms is compensated for by the extreme lightness of the 
body and the hollowness of the bones. 

Origin of Birds 

It is believed that in late Permian or early Triassic time a 
small lizard-like reptile of partly bipedal habit and remotely 
related to the bipedal ancestors of the dinosaurs passed from 


Fig. 103. Restoration of the Pterodactyl, 
Showing the Soaring Flight. 

After the Aeronautical Journal. London. 


ORIGIN OF BIRDS 227 

a terrestrial into a terrestrio-arboreal mode of life, probably 
for purposes of safety. This early arboreo-terrestrial phase is 
indicated in the most ancient known birds {Archceopteryx) by 
the presence of claws at the ends of the bones of the wing, fit- 
ting them for clinging to trees, it is argued, through analogy 
to the tree-clinging habits of existing young hoatzins of South 


QUATERNARY 


CRETACEOUS 


CRETACEOUS 


PENNSYLVANIAN 


,.^_ 


RELATIVELY *■ 


., CURSORIAL, CLIMBING <l 


OF CROCODILES. PHYTOSAURS. 
PTEROSAURS AND BIRDS 


Fig. 104. Ancestral Tree of the Birds. 

The ancestors of the birds branch off in Permian time from the same stock that gives rise 
to the dinosaurs, adding to swift, bipedal locomotion along the ground the power of 
tree climbing and, with their very active life, the development of a high and uniform 
body temperature. Primitive types of birds exhibit a fore limb terminating in claws, 
probably for grasping tree branches. The power of flight began to develop in Triassic 
time through the conversion of scales into feathers either on the fore limbs (two-wing 
theory) or on both fore and hind limbs (four-wing theory). From the Jurassic birds 
{ Archceopteryx), capable of only feeble flight, there arises an adaptive radiation into 
aerial, arboreal, arboreo-terrestrial, terrestrial, and aquatic forms, the last exhibiting a 
reversal of evolution. Diagram prepared for the author by W. K. Gregory. 

America. Ancestral tree existence is rendered still more prob- 
able by the fact that the origin of flight was apparently sub- 
served in the parachute function of the fore limb and perhaps 
of both the fore and hind limbs for descent from the branches 
of trees to the ground. 

Two theories have been advanced as to the origin of flight 
in the stages succeeding the arboreal phase of bird evolution. 
First, the pair-wing theory, developed from the earlier studies 
on Archceopteryx, in which the transformation of lateral scales 


228 


THE ORIGIN AND EVOLUTION OF LIFE 


Fig. 105. Skeleton of Archceoptcryx 
(left) Compared with That of the 
Pigeon (right). 

Showing the abbreviation of the tail into 
the pygostyle and the conversion of 
the grasping fore limb into the bones 
of the wing. After Heilman. 


into long primary feathers on 
the fore Umbs and at the sides 
of the extended tail would afford 
a glissant parachute support 
for short flights from trees to 
the ground (Fig. 106). Quite 
recently a Jour-wing theory, the 
tetrapteryx theory, has been pro- 
posed by Beebe, based on the 
observation of the presence of 
great feathers on the thighs of 
embryos of modern birds and 
of supposed traces of similar feathers on the thighs of the old- 
est known fossil bird, the Ar- 
chceopteryx of Jurassic age. Ac- 
cording to this hypothesis after 
the four-wing stage was reached 
the two hind-leg wings degen- 
erated as the flight function 
evolved in the spreading feathers 
of the forearm-wings and the 
rudder function was perfected ^^ , c ^ 7 >, 

^ Fig. 106. Silhouettes of Archaop- 

in the spreading feathers of the tcryx (A) and pheasant (B). 

tail (Fig. 107). Both of these ^^''^ °" '^' '^^^^^l '^'"'y- ^^'" 


Fig. 107. Four Evolutionary Stages in the Hypothetical Four-winged Bird. 

After Beebe. 


ORIGIN OF BIRDS 


229 


hypotheses assign two phases to the origin of flight in birds: 

first, a primary terrestrial phase, during which the pecuUar 

characters of the hind limbs 

and feet were developed with 

their strong analogies to the 

bipedal feet of dinosaurs; 

second, a purely arboreal 

phase. It is believed by the 

adherents of both the two- 


FiG. 108. Theoretic Mode of Para- 
chute Flight of the Primitive 
Bird. 

Based on the four-wing theory. After 
Beebe. 

wing and the four-wing theory 
that following the arboreal 
phase, in which the powers of 
flight were fully developed, 
there occurred among the 
struthious birds, such as the 
ostriches, a secondary terres- 
trial phase in which the 
powers of flight were secon- 
darily lost and rapid cursorial 
locomotion on the ground was 
secondarily developed. This 
interpretation of the foot and 
limb structure associated 
with the loss of teeth, which 
is characteristic of all the higher birds, will explain the close 
analogies which exist between the ostrich-like dinosaur Stru- 


FiG. 109. Restoration of the Ancient 
Jurassic Bird, Archaopteryx. 

Capable of relatively feeble flight. After 
Heilman. 


230 


THE ORIGIN AND EVOLUTION OF LIFE 


thiomimus and the modern cursorial flightless forms of birds, 
such as the ostriches, rheas, and cassowaries. 

In the opposite extreme to these purely terrestrial forms, 
the flying arboreal birds also gave off the water-living birds, 
one phase in the evolution of which is represented in the loon- 
like Hesperornis, the companion of the pterosaurs and mosa- 
saurs in the Upper Cretaceous seas. It was on the jaws of the 


Fig. iio. Reversed Aquatic Evoli;ti(l\ ok Wim, axd Body Form. 

Wing of a penguin (.4) transformed into a fin externally resembling the fin of a shark (B). 
Skeleton of Hesperornis (C) in the American Museum of Natural History and restora- 
tion of Hesperornis (D) by Heilman, both showing the transformation of the flying bird 
into a swimming, aquatic type, and its convergent evolution toward the body shape of 
the shark, ichthyosaur, and dolphin (compare Fig. 41). 

Hesperornis and smaller Ichthyornis that Marsh made his sen- 
sational announcement of the discovery of birds with teeth, 
a discovery confirmed by his renewed studies of the classic 
fossil bird type, the Jurassic Archceopteryx. These divers of 
the Cretaceous seas {Hesperornis) are analogous to the modern 
loons, and represent one of the many instances in which the 
tempting food of the aquatic habitat has been sought by ani- 
mals venturing out from the shore-lines. As in the most highly 
specialized modern swimming birds, the Antarctic penguins, 
the wing secondarily evolves into a Im or paddle, while the 


ARRESTED REPTILIAN EVOLUTION 231 

body secondarily develops a fusiform shape in order to dimin- 
ish resistance to the water in rapid swimming. 

Possible Causes of the Arrested Evolution of the 

Reptiles 

Of the eighteen great orders of reptiles which evolved on 
land, in the sea, and in the air during the long Reptilian Era 
of 12,000,000 years, only five orders survive to-day, namely, 
the turtles (Testudinata), tuateras (Rhynchocephalia), lizards 
(Lacertilia), snakes (Ophidia), and crocodiles (Crocodilia). 

The evolution of the members of these five surviving or- 
ders has either been extremely slow or entirely arrested during 
the 3,000,000 years which are generally assigned to Tertiary 
time; we can distinguish only by relatively minor changes the 
turtles and crocodiles of the base of the Tertiary from those 
living to-day. In other words, during this period of 3,000,000 
years the entire plant world, the invertebrate world, the fish, 
the amphibian, and the reptilian worlds have all remained 
as relatively balanced, static, unchanged or persistent types, 
while the mammals, radiating 3,000,000 years ago from very 
small and inconspicuous forms, have undergone a phenomenal 
evolution, spreading into every geographic region formerly 
occupied by the Reptilia and passing through multitudinously 
varied phases not only of direct but of alternating and of 
reversed evolution. During the same epoch the warm-blooded 
birds were doubtless evolving, although there are relatively 
few fossil records of this bird evolution. 

This is a most striking instance of the differences in chroma- 
tin potentiality or the internal evolutionary impulses under- 
lying all visible changes of function and of form. If we apply 
our law of the actions, reactions, and interactions of the four 
physicochemical energies (p. 21), there are four reasons why 


232 THE ORIGIN AND EVOLUTION OF LIFE 

we may not attribute this relatively arrested development of 
the reptiles either to an arrested physicochemical environment, 
to an arrested life environment, or to the relative bodily iner- 
tia of reptiles which affects the body-protoplasm and body- 
chromatin. These four reasons appear to be as follows: 

First: We have noted that among the reptiles the velocity 
of purely mechanical adaptation is quite independent both of 
brain power and of nervous activity, a fact which seems to 
strike a blow at the psychic-direction hypothesis (p. 143), on 
which the explanations of evolution by Lamarck, Spencer, and 
Cope so largely depend. The law that perfection of mechan- 
ical adaptation is quite independent of brain power also holds 
true among the mammals, because the small-brained mammals 
of early Tertiary time, the first mammals to appear, evolve as 
mechanisms quite as rapidly or more rapidly than the large- 
brained mammals. 

Second: The law of rapidity of character evolution is inde- 
pendent also of body temperature, for, while the mechanical 
evolution of the warm-blooded birds and mammals is very 
rapid and very remarkable it can hardly be said to have ex- 
ceeded that of the cold-blooded reptiles. Thus the causes of 
the velocity of character evolution in mechanism need not be 
sought in the psychic influence of the brain, in the nervous 
system, in the "Lamarckian" influence of the constant exer- 
cise of the body, nor in a higher or lower temperature of the 
circulatory system. 

Third: Nor has the relatively arrested evolution of the 
Reptilia during the period of the Age of Mammals been due 
to arrested environmental conditions, for during this time the 
environment underwent a change as great as or greater than 
that during the preceding Age of Reptiles. 

Fourth, and finally, there is no evidence that natural selec- 


ARRESTED REPTILIAN EVOLUTION 233 

tion has exerted less influence on reptilian evolution during the 
Age of Mammals than previously. Thus we shut out four out 
of five factors, namely, physical environment, individual habit 
and development, life environment, and selection as reasonable 
causes of the relative arrest of evolution among the reptiles. 

Consequently the causes of the arrest of evolution among 
the Reptilia appear to lie in the internal heredity-chromatin, 
i. e., to be due to a slowing down of physicochemical inter- 
actions, to a reduced activity of the chemical messengers which 
theoretically are among the causes of rapid evolution. 

The inertia witnessed in the entire body form of static or per- 
sistent types is also found to occur in certain single characters 
of the individual. Recurring to the view that evolution is in 
part the sum of the acceleration, balance, or retardation of 
the velocity of single characters, the five surviving orders of 
the reptiles appear to represent organisms in which the greater 
number of characters lost their velocity at the close of the 
Age of Reptiles, and consequently the order as a whole re- 
mained relatively static. 


CHAPTER VIII 
EVOLUTION OF THE MAMMALS 

First mammals, of insectivorous and tree-living habits. Single character 
evolution, physicochemical interaction, coordination, and complexity. 
Problem as to the causes of the origin of new characters and of new 
bodily proportions. Adaptations of the teeth and of the limbs as observed 
in direct, reversed, alternate, and counteracting evolution. Physiographic 
and climatic environment during the period of mammalian evolution, in a 
measure deduced from adaptive variations in teeth and feet of mammals. 
Conclusions, present knowledge of biologic evolution among the verte- 
brate animals. Future lines of inquiry into the causes of evolution. 

It required a man of genius like Linnaeus to conceive the 
inclusion within the single class Mammalia of such diverse 


TK,. 111. 1 Ui. blA W'iiALL, LiAL.L;.ui'il.i:.v Imjrlali.--, 

Which attains a total length of forty-nine feet. Restoration (upper) and photograph 

(lower) after Andrews. 

forms as the tiny insect-loving shrew and the gigantic preda- 
ceous whale. It has required one hundred and twenty-five 
years of continuous exploration and research to establish the 
fact that the whale type (Fig. iii), is not only akin to but 

234 


ORIGIN OF MAMMALS 


235 


is probably a remote descendant of an insectivorous type 
not very distant from the existing tree shrews (Fig. 112), the 

transformation of size, of func- 
tion, and of form between these 
two extremes having taken 
place within a period broadly 
estimated in our geologic time 
scale at about 10,000,000 
years. 


Fig. 112. The Tree Shrew Tiipaia. 
Insectivore, considered to be near the pro- 
totype form of all the higher placental 
mammals. 

Origin of the Mammals, Insec- 
tivorous, Arboreal 

To the descent of the mammals 
Huxley was the first, in essaying the 
reconstruction of the great ancestral 
tree, to apply Darwin's principles 
on a large scale and to prophesy 
that the very remote ancestral 
form of all the mammals was of an 
insectivore type. Subsequent re- 
search' has all tended in the same 
direction, pointing to insectivorous 
habits and in many ways to arboreal 
modes of existence as characteristic 


Fig. 113. rKiiUiTUE Types of 

MONOTREME AND MARSUPIAL. 

(Below.) Monotreme type — Echid- 
na, the spiny ant-eater. 

(Above.) Marsupial type — Didel- 
pliys, the arboreal opossum of 
South America. After photo- 
graphs of specimens in the New 
York Zoological Park. 


* This insectivorous and tree-inhabiting theory of mammalian origin has recently 
been advocated by Doctor William Diller Matthew of the American Museum of Natural 
History, by Doctor William K. Gregory of Columbia University ("The Orders of Mam- 
mals"), and Doctor Elliot Smith of the University of Glasgow. 


236 


THE ORIGIN AND EVOLUTION OF LIFE 


of the earliest mammals. Proofs of arboreal habit are seen in 
the limb-grasping adaptations of the hind foot in many prim- 
itive mammals, and even in the human infant. Thus the 


Fig. 114. Ancestral Tree of the Mammals. 
Adaptive radiation of the Mammalia, originating from Triassic cynodont reptiles and 
dividing into three main branches: (A) the primitive, egg-laying, reptile-like mammals 
(Monotremes) ; (B) the intermediate pouched, viviparous mammals (Marsupials- 
opossums, etc.); and (C) the true Placental which branch off from small, primitive, 
arboreo-insectivorous forms (Trituberculata) of late Triassic time into the four grand 
divisions (i) the clawed mammals, (2) the Primates, (3) the hoofed mammals, and (4) 
the cetaceans. Dividing into some thirty orders, this grand evolution and adaptive 
radiation takes place chiefly during the four million years of Upper Cretaceous and 
Tertiary time. As among the Reptilia, the primary arboreo-terrestrial adaptive phases 
radiate by direct evolution into all the habitat zones, and by reversed and alternate evolu- 
tion develop backward and forward in adaptation to one or another habitat zone. Dia- 
gram prepared for the author by W. K. Gregory. 

existing tree shrews, the tupaias of Africa (Fig. 112), in many 
characters resemble the hypothetic ancestral forms of Creta- 
ceous time from which the primates (monkeys, apes, and man) 
may have radiated. 


ORIGIN OF MAMMALS 237 

Following Cuvier, Owen, and Huxley in Europe, a period 
of active research in this country began with Leidy in the 
middle of the nineteenth century and was continued in the 
arid regions of the West by Cope, Marsh, and their succes- 
sors with such energy that America has become the chief cen- 
tre of vertebrate palaeontology. When we connect this research 
with the older and the more recent explorations by men of all 
countries in Europe, Asia, Africa, Australia, and South Amer- 
ica, we are enabled to reconstruct the great tree of mammalian 
descent (Fig. 114) with far greater fulness and accuracy than 
that of the reptiles, amphibians, or fishes (Pisces). 

The connection of the ancestral mammals with a reptilian 
type of Permian time is theoretically established through the 
survival of a single branch of primitive egg-laying mammals 
(Monotremata, Fig. 113) in Australia and New Guinea; while 
the whole intermediate division, consisting of the pouched 
mammals (Marsupialia) of Australia, which bring forth their 
young in a very immature condition, represents on the great 
continent of AustraHa an adaptive radiation which also sprang 
from a small, primitive, tree-living j Whales. 
type of mammal, typified by the ex- 2. Seals (marine carnivores). 

... r AT ^-u J c <-i, S- Carnivores (terrestrial). 

istmg opossums of North and bouth -^ -, . 

° ^ 4. Insectivores. 

America (Fig. 113). The third great 5. Bats, 
group (Place ntalia) includes the 6. Primates: 

1 • I,- 1 4^1, u Lemurs, 

mammals m which the unborn Monkevs 

young are retained a longer period Apes, 

within the mother and are nourished Man. 

, , . , . . . . 7. Hoofed mammals, 

through the circulation 01 nutrition g j^^^atees 

in the placenta. 9. Rodents. 

The adaptive radiation of the ten ^°- Edentates. 
great branches of the placental stock from the primitive insec- 
tivorous arboreal ancestors produced a mammalian fauna which 


238 THE ORIGIN AND EVOLUTION OF LIFE 

inhabited the entire globe until the comparatively recent period 
of extermination by man, who through the invention of tools 
in Middle Pleistocene time, about 125,000 years ago, became 
the destroyer of creation. 

Single Character Evolution and Physicochemical 
Correlation 

The principal modes of evolution as we observe them among 
the mammals are threefold, namely: 

I. The modes in which new characters first appear, whether 
suddenly or gradually and continuously, whether accidentally 
or according to some law. 

II. The modes in which characters change in proportion, 
quantitatively or intensively, both as to form and color. 

III. The modes in which all the characters of an organism 
respond to a change of environment and of individual habit. 

The key to the understanding of these three modes is to be 
sought first in changes of food and in changes of the medium 
in which the mammals move, whether on the earth, in the 
water, or in the air. The complexity of the environmental 
influence becomes like that of a lock with an unlimited number 
of combinations, because the adaptations of the teeth to varied 
forms of insectivorous, carnivorous, and herbivorous diet may 
be similar among mammals living in widely different habitat 
zones, while the adaptations of the locomotor apparatus, the 
limbs and feet, to the primary arboreal zone may radiate 
into structures suited to any one of the remaining ten life 
zones. Thus there is invariably a double adaptive and inde- 
pendent radiation of the teeth to food and of the limbs to pro- 
gression, and therefore two series of organs are evolving. For 
example, there always arises a more or less close analogy be- 
tween the teeth of all insect-eating mammals, irrespective of 


CHARACTER EVOLUTION 


239 


the habitat in which they find their food. Similarly there 
arises a more or less close analogy between the motor organs of 
all the mammals living in any particular habitat; thus the glis- 
sant or volplaning limbs of all aero-arboreal types are exter- 
nally similar, irrespective of the ancestral orders from which 


HABITAT CHANGE ACCOMPANYING CHANGE OF FUNCTION 


motor adaptations of different animals to similar life zones 
Fig. 115. Adaptive Radiation of the Mammals. 

The mammals, probably originating in arboreal leaping or climbing phases, radiate 
aclaptively into all the other habitat zones and thus acquire many types of body form 
and of locomotion more or less convergent and analogous to those previously evolved 
among the reptiles (shown in the right-hand column), the amphibians, and the fishes. 
Diagram by Osborn and Clregory. 

they are derived. A mammal may seek any one of twelve 
different habitat zones in search of the same general kind of 
food; conversely, a mammal living in a single habitat zone 
may seek within it six entirely different kinds of food. 

This principle of the independent adaptation of each organ 
of the body to its own particular function is in keeping with 
the heredity law of individual and separate evolution of "char- 
acters" and "character complexes" (p. 147), and is fatal to 


240 THE ORIGIN AND EVOLUTION OF LIFE 

some of the hypotheses regarding animal structure and evolu- 
tion which have been entertained since the first analyses of 
animal form were made by Cuvier at the beginning of the last 
century. The independent adaptation of each character group 
to its own particular function proves that there is no such essen- 
tial correlation between the structure of the teeth and the struc- 
ture of the feet as Cuvier claimed in what was perhaps his 
most famous generalization, namely, his "Law of Correlation."^ 

Again this principle, of twofold, threefold, or manifold adap- 
tation, is fatal to any form of belief in an internal perfecting 
tendency which may drive animal evolution in any particular 
direction or directions. Finally, it is fatal to Darwin's original 
natural-selection hypothesis, which would imply that the teeth, 
limbs, and feet are varying fortuitously rather than evolving 
under certain definite although still unknown laws. 

The adaptations which arise in the search of many varieties 
of food and in overcoming the mechanical problems of loco- 
motion, offense, and defense in the twelve different habitat 
zones are not fortuitous. On the contrary, observations on 
successive members of families of mammals in process either 
of direct, of reversed, or of alternate adaptation admit of but 
one interpretation, namely, that the evolution of characters is 
in definite directions toward adaptive ends; nor is this definite 
direction limited by the ancestral constitution of the heredity- 
chromatin as conceived in the logical mind of Huxley. The 
passage in which Huxley expressed this conception is as follows : 

"The importance of natural selection will not be impaired 
even if further inquiries should prove that variability is definite, 
and is determined in certain directions rather than in others, by 

1 Cuvier's law of correlation has been restated by Osborn. There is a fundamental 
correlation, coordination, and cooperation of all parts of the organism, but not of the 
kind conceived by Cuvier, who was at heart a special creationist. Contrary to Cuvier's 
claim, it is impossible to predict from the structure of the teeth what the structure of 
the feet may prove to be. 


CHARACTER EVOLUTION 241 

conditions inherent in that which varies. It is quite conceiv- 
able that every species tends to produce varieties of a Hmited 
number and kind, and that the effect of natural selection is to 
favor the development of some of these, while it opposes the 
development of others along their predetermined lines of 
modification."^ It is true that the variations of the organ- 
ism are in some respects limited in the heredity-chromatin, as 
Huxley imagined; on the contrary, every part of a mammal 
may exhibit such plasticity in course of geologic time as enables 
it to pass from one habitat zone into another, and from that 
into still others until finally traces of the adaptations to pre- 
vious habitats and anatomical phases may be almost if not 
entirely lost. The heredity-chromatin never determines be- 
forehand into what new environment the lot of a mammal 
family may be cast; this is determined by cosmic and plane- 
tary changes as well as by the appetites and initiative of the 
organism (p. 114). For example, one of the most remarkable 
instances which have been discovered is that of the reversed 
aquatic adaptation of Z en gl odour first terrestrial, then aquatic, 
in succession a dog-like, a fish-like, and finally an eel-like 
mammal. These peculiar whales (Archasoceti) appear to have 
originated in the littoral and pelagic waters of Africa in Eocene 
time from a purely terrestrial ancestral form of mammal 
(allied to Hycsnodon), in which the body is proportioned like 
that of the wolf or dog, and this terrestrial mammal in turn 
was descended from a very remote arboreal ancestor. Thus 
in its long history the Zeuglodon passed through at least three 
habitat zones and as many life phases. 

Yet in another sense Huxley was right, for palaeontolo- 

1 Huxley, Thomas, 1893, p. 223 (first published in 1878). 

-Zeuglodon itself is a highly specialized side branch of the primitive toothed whales. 
The true whales may have arisen from the genera Protocetus, probably ancestral to the 
toothed whales, and Patriocctiis which combines characters of the zeuglodonts and 
whalebone whales. 


242 THE ORIGIN AND EVOLUTION OF LIFE 

gists actually observe in the characters springing from the 
heredity-chromatin a predetermination of another kind, namely, 
the origin through causes we do not understand of a tendency 
toward the independent appearance or birth at different periods 
of geologic time of similar new and useful characters. In fact, 
a very large number of characters spring not from the visible 
ancestral body forms but from invisible predispositions and 
tendencies in the ancestral heredity-chromatin. For example, 
all the radiating descendants of a group of hornless mammals 
may at different periods of geologic time give rise to similar 
horny outgrowths upon the forehead. This heredity principle 
partly underlies what Osborn has termed the law of rectigra- 
dation. Moreover, once a new character or group of characters 
makes its visible appearance in the body its invisible chromatin 
evolution may assume certain definite directions and become 
cumulative in successive generations in accordance with the 
principle of Mutationsrichtung, first perceived by Neumayr 
(p. 138); in other words, the tendency of a character to evolve 
in one direction often accumulates in successive generations 
until it reaches an extreme. 

The application of our law of quadruple causes, namely, of 
the incessant action, reaction, and interaction of the four 
physicochemical complexes under the influence of natural 
selection, to the definite and orderly origin of myriads of char- 
acters such as are involved in the transformation of a shrew 
type of mammal into the quadrupedal wolf type and of the 
wolf type into the Zeuglodon eel type, has not yet even ap- 
proached the dignity of a working hypothesis, much less of an 
explanation. The truth is that the causes of the orderly co- 
adaptation of separable and independent characters still remain 
a mystery which we are only beginning to dimly penetrate. 

As another illustration of the complexity of the evolution 


CHARACTER EVOLUTION 243 

process in mammals, let us observe the operation of Dollo's 
law of alternate adaptation (p. 202) in the evolution of the tree 
kangaroo {Dendrolagus) , belonging to the marsupial or pouched 
division of the Mammalia. This is a case where many of the 
intermediate stages are known to survive in existing types. 
These tree kangaroos theoretically have passed through four 
phases, as follows: (i) An arboreo- terrestrial phase, including 
primitive marsupials like the opossum, with no special adap- 


AERIAL 
AER9 ARBORt 
ARBOREAL 
ARB0R5TERRt 
TERRESTRIAL 


H SPE'^IAlHED 
FEET OF CLIMBING TYPE, GREAT TOE OPPOSABLE 
i FOURTH TOE ENLARGED 


PRIMITIVE MARSUPIALS 

WITH NO SPECIAL ADAPTATIONS 

FOR CLIMBING 


Fig. 116. Four Phases of Alternating Adaptation ix the Kangaroo Marsupials, 
According to Dollo's Law. 

1. Primitive arboreo-terrestrial phase — tree and ground living forms. 

2. Primitive arboreal phalanger phase — tree-living forms. 

3. Kangaroos — terrestrial, saltatorial phase — ground-living, jumping forms. 

4. Tree kangaroos — secondaril\' arboreal, climbing i)hase. 

tations for climbing; (2) a true arboreal phase of primitive tree 
phalangers with the feet specialized for climbing purposes 
through the opposability of the great toe (hallux), the fourth 
toe enlarged; (3) a cursorial terrestrial phase, t^qpified by the 
kangaroos, with feet of the leaping type, the big toe (hallux) 
reduced or absent, the fourth toe greatly enlarged; (4) a second 
arboreal phase, typified by the tree kangaroos {Dendrolagus), 
with limbs fundamentally of the cursorial terrestrial leaping 
type but superficially readapted for climbing purposes. It 
is clear that there can be no internal perfecting tendency 
or predetermination of the heredity-chromatin to anticipate 
such a tortuous course of evolution from terrestrial into arbo- 
real life, from arboreal back to a highly specialized terrestrial 


244 THE ORIGIN AND EVOLUTION OF LIFE 

life, and finally from the leaping over the ground of the kan- 
garoo into the incipiently specialized arboreal phase of the 
tree kangaroo. In the evolution of the tree kangaroos adap- 
tation is certainly not limited by the inherent tendencies of 
the heredity-chromatin to evolve in certain directions. The 
physicochemical theory of these remarkable alternate adap- 
tations is that an animal leaving the terrestrial habitat and 
taking on arboreal habits initiates an entirely new series of 
actions, reactions, and interactions with its physical environ- 
ment, with its life environment, in its body cell and individual 
development, and, in some manner entirely unknown to us, in 
its heredity-chromatin, which begins to show new or modified 
determiners of bodily character. That natural selection is 
continuously operating at every stage of the transformation 
there can be no doubt. 

One interpretation which has been offered up to the pres- 
ent time of the mode of transformation of a terrestrial into an 
arboreal mammal is through a form of Darwinism known as 
the "organic selection" or "coincident selection" hypothesis, 
which was independently proposed by Osborn,' Baldwin, and 
Lloyd Morgan, namely: that the individual bodily modifications 
and adaptations caused by growth and habit (while not them- 
selves heritable) would tend to preserve the organism during the 
long transition into arboreal life; they would tend to nurse the 
family over the critical period and allow time to favor all pre- 
dispositions and tendencies in the heredity-chromatin toward 
arboreal function and structure, and would tend also to elim- 
inate all structural and functional predispositions in the hered- 
ity-chromatin which would naturally adapt a mammal to life 
in any one of the other habitat zones. This interpretation is 
consistent with our law that selection is constantly operating 

•Osborn, H. F., 1S97. 


CAUSES OF EVOLUTION 245 

on all the actions, reactions, and interactions of the body, but 
it does not help to explain the definite origin of new characters 
which cannot enter into "organic selection" before they exist. 
Nor is there any evidence that while adapting itself to one 
mode of life fortuitous variations in the heredity-chromatin for 
every other mode of life are occurring. 

Theoretic Causes of Evolution in Mammals 

We have thus far described only the modes of evolution and 
said nothing of the causes. In speculating on the causes of 
character evolution in the mammals, in comparison with similar 
body forms and characters in the lower vertebrates and even 
in the invertebrates, it is very important to keep in mind the 
preceding evidence that mammalian heredity-chromatin may 
preserve all the useful functional and structural properties of 
action, reaction, and interaction which have accumulated in 
the long series of ancestral life forms from the protozoan and 
even the bacterial stage. 

Since structurally the mammalian embryo passes through 
primitive protozoan (single-celled) and metazoan (many-celled) 
phases, it is probable that chemically it passes through the 
same. The heredity-chromatin even in the development of 
the highest mammals still recalls primitive stages in the devel- 
opment of the fishes, for example, the gill-arch structure at 
the side of the throat, which through change of function serves 
to form the primary cartilaginous jaws (Meckelian cartilages) 
of mammals as well as the bony ossicles which are connected 
with the auditory function of the middle ear (Reichert's 
theory). Similarly profound structural ancestral phases in 
protozoan, fish, and reptile structure pervade every part of the 
mammalian body. In race evolution there may be changes of 
adaptation as in the law of change of function {Prinzip des Funk- 


246 THE ORIGIN AND EVOLUTION OF LIFE 

tionswediscls), first clearly enunciated by Anton Dohrn in 1875. 
But no function is lost without good cause, and the heredity- 
chromatin retains every character which through change of 
function and adaptation can be made useful. 

The same law which we observe in the conservation of all 
adaptive characters and functions will probably be discovered 
also in the conservation of ancestral physicochemical actions, 
reactions, and interactions of the organism from the protozoan 
stages onward. The primordial chemical messengers — enzymes 
or organic catalyzers, hormones and chalones, and other accele- 
rators, retarders, and balancers of organ formation (see p. 72) — 
are certainly not lost; if useful, they are retained, built up, and 
unceasingly complicated to control the marvellous coordina- 
tions and correlations of the various organs of the mammalian 
body. The principal endocrine (internal secretory) as well as 
duct secretory glands established in the fish stage of evolution 
(p. 160), through which they can be partly traced back even to the 
lancelet stage (chordate), doubtless had their beginnings among 
the ancestors (protochordates) of the vertebrated animals, which 
extend back into Cambrian and pre-Cambrian time. Since 
these chemical messenger functions among the mammals are 
enormously ancient, we may attribute an equal antiquity to the 
powers of chemical storage and entertain the idea that the 
chromatin potentiality of storing phosphate and carbonate of 
lime for skeletal and defensive armature in the protozoan 
stage of 50,000,000 years' antiquity is the same chromatin 
potentiality which builds up the superb internal skeletal struc- 
tures of the Mammalia and the highly varied forms of offen- 
sive and defensive armature either of the calcium compound 
or the chitinous type. 

It is, moreover, through the fundamental similarity of the 
physicochemical constitution of the fishes, amphibians, reptiles, 


CAUSES OF EVOLUTION 247 

birds, and mammals that we may interpret the similarities of 
form evolution and understand why, the other three causes 
being similar, mammals repeat so many of the habitat form 
phases in adaptation to the environments previously passed 
through by the lower orders of life. Thus advancing struc- 
tural complexity is the reflection or the mirror of the invisible 
physicochemical complexity; the visible structural complexity 
of a great animal like the whale (Fig. 234), for example, is 
something we can grasp through its anatomy; the physico- 
chemical complexity of the whale is quite inconceivable. 

In research relating to the physicochemical complexity of 
the mammals, so notably stimulated by the work of Ehrlich 
and further advanced by later investigators, there are perhaps 
few studies more illuminating than those of Reichert and 
Brown^ on the crystals of oxyhemoglobin, the red coloring 
matter of the mammalian blood. Their research proves that 
every species of mammal has its highly distinctive specific 
and generic form of hemoglobin crystals, that various degrees 
of kinship and specific affinity are indicated in the crystallog- 
raphy of the hemoglobin. For example, varieties of the dog 
family, such as the domestic dog, the wolf, the Australian 
dingo, the red, Arctic, and gray fox, are all distinguished by 
only slightly differing crystalline forms of oxyhemoglobin. The 
authors' philosophic conclusions arising from this research are 
as follows:^ 

"The possibilities of an inconceivable number of constitu- 
tional differences in any given protein are instanced in the fact 
that the serum-albumin molecule may, as has been estimated, 
have as many as 1,000,000,000 stereoisomers. If we assume 
that serum-globulin, myoalbumin, and other of the highest pro- 

1 Reichert, E. T., and Brown, A. P., 1909, pp. iii-iv. 

' Certain insertions in brackets being made for purposes of comparison with other 
portions of this series of lectures. 


248 


THE ORIGIN AND EVOLUTION OF LIFE 


teins may have a similar number, and that the simpler proteins 
and the fats and carbohydrates and perhaps other complex 
organic substances, may each have only a fraction of this 
number, it can readily be conceived how, primarily by differ- 
ences in chemical constitution of vital substances, and secon- 


k r -"-1 , .'; ' V. 


Fig. 117. Evolution of Proportion. Adaptation in Length of Neck. 

Short-necked okapi (left), the forest-living giraffe of the Congo, which browses upon the 
lower branches of trees. 

Long-necked giraffe (right), the plains-living tvpe of the African savannas, which browses 
on the higher branches of trees. After Lang. 


darily by differences in chemical composition, there might be 
brought about all of those differences which serve to charac- 
terize genera, species, and individuals. Furthermore, since the 
factors which give rise to constitutional changes in one vital 
substance would probably operate at the same time to cause 
related changes in certain others, the alterations in one may 
logically be assumed to serve as a common index to all. 

"In accordance with the foregoing statement it can readily 
be understood how environment, for instance, might so affect 


CAUSES OF EVOLUTION 


249 


the individual's metabolic processes as to give rise to modifica- 
tions of the constitutions of certain corresponding proteins and 
other vital molecules which, even though they be of too subtle 
a character for the chemist to detect by his present methods, 
may nevertheless be sufficient to cause not only physiological 
and morphological differentiations in the individual, but also 


Fig. 118. Short-Fingeredness (Brachydactyly) and Long-Fingeredness (Dolicho- 
DACTYLv). Congenital, and Due to Internal Secretion. 

(Left.) Congenital brachydactyly, theoretically due either to a sudden alteration in the 
chromatin or to a congenital defect in the pituitary gland. After Drinkwater. 

(Centre.) Brachydactyly, after birth, due to abnormally excessive secretions of the 
pituitary gland. After Gushing. 

(Right.) Dolichodactyly, after birth, due to abnormally insufficient secretions of the 
pituitary gland. After Gushing. ' 

become manifested physiologically [functionally] and morpho- 
logically [structurally] in the offspring." 

The above summary adumbrates the lines along which some 
of the chemical interactions, if not causes, of mammalian ev- 
olution may be investigated during the present century. 

The cause of different bodily proportions, such as the very 
long neck of the tree-top browsing giraffe, is one of the classic 
problems of adaptation. In the early part of the nineteenth 
century Lamarck (p. 143) attributed the lengthening of the neck 


250 


THE ORIGIN AND EVOLUTION OF LIFE 


to the inheritance of bodily modifications caused by the neck- 
stretching habit. Darwin attributed the lengthening of the 
neck to the constant selection of individuals and races which 
were born with the longest necks. Darwin was probably right. 
This is an instance where length or shortness of neck is ob- 
viously a selective survival 
character in the struggle for 
existence, because it directly 
affects the food supply. 

But there are many other 
changes of proportion in mam- 
mals, which are not known to 
have a selective survival value. 
We may instance in man, for 
example, the long head-form 
(dolichocephaly) and the broad 
head-form (brachycephaly) , or 
the long-fingered form (dolicho- 
dactyly) and the short-fingered 
form (brachydactyly), which 
have been interpreted as con- 
genital characters appearing at 
birth and tending to be transmitted to offspring. Brachy- 
dactyly may be transmitted through several generations, but 
until recently no one has suggested what may be its possible 
cause. 

It has now been found^ that both the short-fingered con- 
dition (brachydactyly) and the slender-fingered condition may 
be induced during the lifetime of the individual in a previously 
healthy and normal pair of hands by a diseased or injured con- 
dition of the pituitary body at the base of the brain. If the 

1 Gushing, Harvey, 1911, pp. 253, 256. 


Fig. 119. Result of Removing the 
Thyroid and Parathyroid Glands. 

(Right.) Normal sheep fourteen months 
old. 

(Left.) A sheep of the same age from 
which the thyroids and parathyroids 
were removed twelve months previ- 
ously. 

After Sutherland Simpson. 


MODES OF EVOLUTION 


251 


Fic. 120. 


secretions of the pituitary are abnormally active (hyperpitui- 
tarism) the hand becomes broad and the fingers stumpy (Fig. 
118, B). If the secretions of the pituitary are abnormally re- 
duced (hypopituitarism) the fingers become tapering and slender 
(Fig. 118, C). Thus in a most remarkable manner the internal 
secretions of a very ancient 
ductless gland, attached to the 
brain and originating in the 
roof of the mouth in our most 
remote fish-like ancestors, affect 
the proportions both of flesh 
and bones in the fingers, as 
well as the proportions of many 
other parts of the body. 

Whether this is a mere co- 
incidence of a heredity-chro- 
matin congenital character 
with a mere bodily chemical 
messenger character it would 
be premature to say. It cer- 
tainly appears that chemical in- 
teractions from the pituitary body control the normal and ab- 
normal development of proportions in distant parts of the body. 

Chief Modes of Evolution of Mammalian Characters 

What we have gained during the past century is positive 
knowledge of the cliiej modes of evolution; we know almost the 
entire history of the transformation of many different kinds of 
mammals. 

These modes as distinguished from the unknown causes are 
expressed in the following general laws: first, the law of con- 
tinuity; Natura non facit saltum, there is prevailing continuity 


Result of Removing the 
Pituitary Body. 

twelve months 


(Right.) Normal do, 
old. 

(Left.) A dog of the same age and litter 
from which the pituitary body was 
removed at the age of two months. 

After Aschner. 


252 THE ORIGIN AND EVOLUTION OF LIFE 

in the changes of form and proportion in evolution as in 
growth. Second, the law of rectigradation, under which many 
important new characters appear definitely and take an adap- 
tive direction from the start; third, the law of acceleration and 
retardation, witnessed both in racial and individual develop- 
ment, whereby each character has its own velocity, or rate of 
development, which displays itself both in the time of its origin, 
in its rate of evolution, and its rate of individual development. 
This last law underlies the profound changes of proportion in 
the head and different parts of the body and limbs which are 
among the dominant features of mammalian evolution. In 
the skeleton of mammals very few new characters originate; 
most of the changes are in the loss of characters and in the 
profound changes of proportion. For example, by the addi- 
tion of many teeth and by stretching or pulling, swelling or 
contracting, the skeleton of a tree shrew may almost be trans- 
formed into that of a whale. 

The above laws are the controlling ones and make up four- 
fifths of mammalian evolution in the hard parts of the body. 
So far as has been observed the remaining fifth or even a 
much smaller fraction of mammalian evolution is attributable 
to the law of saltation, or discontinuity, namely, to the sudden 
appearance of new characters and new functions in the hered- 
ity-chromatin. For example, the sudden addition of a new 
vertebra or vertebrae to the backbone, which gives rise to the 
varied vertebral formulae in different orders and even the dif- 
ferent genera of mammals, or the sudden addition of a new 
tooth are instances of saltatory evolution in the hard parts 
of the body. There are also many instances of the sudden 
appearance of new functional, physiological, or physicochem- 
ical characters, such as immunity or non-immunity to certain 
diseases. 


ADAPTATION TO ENVIRONMENT 253 

Responses of Mammal Characters to Changing 
Environment 

Buffon was the first to observe the direct responses of mam- 
mals to their environment and naturally supposed that en- 
vironment was the cause of animal modification, chiefly in 
adaptation to changes of climate. It did not occur to him 
to inquire whether these modifications were heritable or not, 
any more than it did to Lamarck. 

It is now generally believed that these reactions are for 
the most part modifications of the body cells and body chro- 
matin only, which give rise to what may be known as environ- 
mental species, as distinguished from true chromatin species 
which are founded upon new or altered hereditary characters. 
Of the former order are many geographic varieties and doubtless 
many geographic species. These visible species of body cell 
characters are quite distinct from the invisible species of 
heredity-chromatin characters. Both occur in nature. 

Geologic and secular changes of environment have preceded 
many of the most profound changes in the evolution of the 
mammals, which interlock and counteract with their physical 
and life environments quite as closely as do the reptiles, am- 
phibians, and fishes; yet a very large part of mammalian evo- 
lution has proceeded and is proceeding quite independently of 
change of environment. Thus environment holds its rank as 
one of the four complexes of the causes of evolution instead of 
being the cause par excellence as it was regarded in the brilliant 
speculations of Buffon. 

The interlocking of mammals with their life environment is 
extremely close, namely, with Bacteria, Protozoa, Insecta, and 
many other kinds of Invertebrata, with other Vertebrata, as 
well as with the constantly evolving food supply of the plant 


254 THE ORIGIN AND EVOLUTION OF LIFE 

world; consequently the vicissitudes of the physical environ- 
ment as causes of the vicissitudes of the life environment of 
mammals afford the most complex examples of interlocking 
which we know of in the whole animal world. In other words, 
the mammals interlock in relation to all the surviving forms of 
the life which evolved on the earth before them. Although 
suggested nearly a century ago by Lyell, the demonstration is 
comparatively recent that one of the principal causes of the 
extinction of certain highly adaptive groups of mammals is 
their non-immunity to the infections spread by Bacteria and 
Protozoa.' Thus a change of environment and of climate may 
not affect a mammal directly but may profoundly affect it in- 
directly through insect life. 

These closely interlocking relations of the mammals with 
their physicochemical environment and their life environment 
have been subject to constant disturbances through the geo- 
logic and geographic shifting of the twelve or more habitat 
zones which they occupy. Yet the earth changes during the 
Tertiary, the era during which mammalian evolution mainly 
took place, were less extreme than those during Mesozoic and 
Palaeozoic time. This is because the trend of development of 
the earth's surface and of its climate during the past 3,000,000 
years has been toward continental stability and lowering of 
general temperature in both the northern and southern hemi- 
spheres, terminating in the geologically sudden advent of the 
Glacial Epoch, with its alternating periods of moisture and 
aridity, cold and heat, which exerted the most profound influ- 
ence upon the food supply, insect barriers, and other causes 
affecting the migrations of the Mammalia. These causes com- 
pletely change the general aspect of the mammalian world in 

^ For the history and discussion of this entire subject see Osborn, H. F.: "The Causes 
of Extinction of Mammalia," Amcr. Naturalist, vol. XL, November and December, 
1906, pp. 769-795, 829-859. 


ADAPTATION TO ENVIRONMENT 255 

the whole northern hemisphere, South America, and AustraUa, 
and leave only the world of African mammalian life untouched. 
The water content of the atmosphere during the 3,000,000 years 
of the Age of Mammals has tended toward a repetition of the 
environmental conditions of Permian and Triassic times in 
the development of areas of extreme humidity as well as areas 
of extreme aridity, interrupted, however, by widespread humid 
conditions in the Pleistocene Epoch. Marine invasion of the 
continents of Europe and North America, while far less ex- 
treme than during Cretaceous time, has served to give us the 
complete history of the littoral and marine Mollusca, both in 
the eastern and western hemispheres, which is the chief basis 
of the geologic time scale as discovered in the Paris basin by 
Brogniart at the beginning of the eighteenth century. 

The clearest conception of the length of Tertiary time is 
afforded (Fig. 121) by the completion in Eocene time of the 
Rocky Mountain uplift of America and the eastern Alps of 
Europe, by the elevation of the Pyrenees in Oligocene time, 
by the rise of the wondrous Swiss Alps between the Oligocene 
and Miocene Epochs, and finally by the creation of the titanic 
Himalaya chain in the latter part of Miocene time. 

Through the phenomena of the migration of various kinds 
of mammals from continent to continent, we are able to date 
with some precision the rise and fall of the land bridges and 
the alternating periods of connection and separation of the 
two northern continental masses, Eurasia and America, as well 
as of the northern and southern continents. Few writers 
maintain seriously for Tertiary time the "equatorial theory" of 
connection between the eastern and western hemispheres such 
as figures largely in the speculations of Suess, Schuchert, and 
others in relation to plant and animal migrations of Palaeozoic 
and Mesozoic time. The less radical "bipolar theory" that 


256 


THE ORIGIN AND EVOLUTION OF LIFE 


the eastern and western hemispheres were connected both at 
the north pole and at the south pole, or through Arctic and 
Antarctic land areas, still has many adherents, especially in 


PER I O D S 

GLACIAL kQUATERK ABV 4000 


HIMALAYAS 

SWISS ALPS 
PYRENEES 


PLIOCENE 5000 


i I ■ Ml I I 
, PREJACEOUS 


-+^T^ 


I I I 
TRiA^sic I I I I 

I I I ' I I '13000 


P^RMi , ; , , 

I L j j J I , | i^° 9° i, 


THE HERCYNIAN BELT OF 

CENTRAL EUROPE? ////'// ''^'/ 

// CAJ^BONIFERJlyS- ' 


•/-^/OEWINIAN^/^ 
;x//.^/g?OO0 


SCOTTISH HIGHUNDS/ 


FINLAND 

E.SCANDir 

S.BOHEMM 


ORDOVICIAN 

17000 


E. SCANDINAVIA 


CERTAIN MOUNTAIN CHIEF MOUNTAIN 

REVOLUTIONS OF' REVOLUTIONS OF 

EUROPE AND ASIA NORTH AMERICA 


AGE 

OF 
MAMMALS 


Fig. 121. Main Subdivisions of Geologic Time. 

The subdivisions are not to the same scale. The notches at the sides of the scale (which 
is simplified from that on p. 153) represent chiefly the periods of mountain uplift in the 
northern hemisphere of the Old World (left) and of the New World (right). 


regard to the former relations of the Australian continent 
and South America through the now partly sunken continent 
of Antarctica. The still more conservative ''north polar 


ADAPTATION TO ENVIRONMENT 


257 


DISTRIBUTION OF PRIMATI 


^n 


^^.^ 


theory" of Wallace, of an exclusively northern land connection 
of the eastern and western hemispheres during Tertiary time, 
has recently been maintained by Matthew^ as adequate to 
explain all the chief facts of mammalian migration and geo- 
graphic evolution. 

The feet and the teeth of mammals become so closely 
adapted to the medium in which they move and the kind of 
food consumed that 
through the interpreta- 
tion of their structure 
we shall in time write a 
fairly complete physio- 
graphic and climatic his- 
tory of the Tertiary 
Epoch along the lines of 
the investigations in- 
itiated by Gaudry and 
Kowalevsky. Through 
the successive adapta- 
tions of the limbs and 
sole of the foot and the 
adaptations of the teeth, 
which are most delicately 
adjusted — the former to impact with varying soils and the 
latter to the requirements of the consumption of various forms 
of nourishment — we may definitely trace the influences or 
rather the adaptive responses to the habitat subzones, such as 
the forest, forest-border, meadow, meadow-border, river-border, 
the lowland, the upland, the meadow-fertile, the meadow-arid, 
the plains, and the desert-arid. This mirror of past geography, 
climate, evolution of plant life in the anatomy of the limbs 


Fig. 122. The North Polar Theory of the 
Distribution of Mammals. 

A zenith view of the earth from the north pole, 
showing (arrows) the North Polar theory of the 
geographic migrations and distribution of the 
mammals, especially of the Primates (monkeys, 
lemurs, and apes). After W. D.Matthew, 1915. 


Matthew, W. D., 1915. 


258 


THE ORIGIN AND EVOLUTION OF LIFE 


and feet, is one of the most fascinating fields of philosophic 
study. 

In the more humid, semi-forested regions, which preserve 
the physiographic conditions of early Eocene times (Fig. 123), 
we discover most of the examples of the survival of primitive 
mammalian forms and functions. The borderland between 
the extremes of aridity and humidity has afforded the most 


Fig. 123. Scene in Western Wyoming in Middle Eocene Time. 

The period of the four-toed mountain horse, Orohippiis (right), of the Uintathere (left), 
and of the Titanothere (left lower). From study for a mural decoration in the American 
Museum of Natural History by Charles R. Knight under the author's direction. 

favorable habitats for the rapid evolution of all the forms of 
terrestrial life. From these favored regions the mammals 
have entered the semi-arid and arid deserts, in which also 
evolution has been relatively rapid. Since Tertiary geologic 
succession is nearly unbroken we can now trace the evolution 
of many families of the carnivores, the greater number of the 
hoofed mammals, and the rodents, with few interruptions 
through the entire 3,000,000 years of Tertiary time. It is 
through our very close observation of the origin and history 
of numerous single characters as exhibited in palaeontologic 
lines of evolution that the three chief modes (p. 251) of mam- 


GEOGRAPHIC DISTRIBUTION 


259 


malian evolution and the continued definite direction and dif- 
ferences of velocity in the development of characters have 
been discovered. 


General Succession of Mammalian Life in North 

America 

In Upper Cretaceous and Pakeocene time we find that the 
northern hemisphere is covered with an archaic adaptive radi- 
ation of mammals distinguished 
by the extremely small size of 
the brain and clumsy mechanics 
of the skeleton. Of these the 
carnivorous forms radiate into a 
number of families adapted to a 
great variety of feeding and lo- 
comotor habits which are anal- 
ogous to the families of existing 
Carnivora. Similarly the hoofed 
mammals (Condylarthra, Am- 
blypoda) divide into swift- 
footed (cursorial) and heavy- 
footed (graviportal) forms, the 
latter including the Amblypoda 
{Coryphodon and Dinoccras) . 
From surviving members of this 
archaic adaptive radiation of small-brained mammals there arise 
all the stem forms of the orders existing to-day, which almost 
without exception have now been traced back to the close of 
Eocene time, namely, the ancestors of the whales, of the modern 
families of carnivores, insectivores, bats, lemurs, rodents, and 
the edentates (armadillos and ant-eaters). Especially remark- 
able is the discovery in the Lower Eocene of the ancestors of 


Fig. 124. Two Stages in the Early 
Evolution of the Ungulates. 

Pantolambda {A), an archaic Palaeocene 
form which transforms into Coryphodon 
(B), a Lower Eocene form of increased 
size, with greatly enlarged head, ab- 
breviated tail, and defensive tusks. 
This transformation occupied a period 
estimated at 500,000 years, nearly one- 
sixth of Tertiary time. Restorations 
in the American Museum of Natural 
Historv, bv Osborn and Knight. 


26o 


THE ORIGIN AND EVOLUTION OF LIFE 


the modern horses, tapirs, rhinoceroses, and various types of 
cloven-footed animals. 

A very general principle of mammalian evolution is illus- 
trated in Fig. 124 (.4, B), namely, the increase of size character- 
istic of all the herbivorous mammals, which almost without 
exception are in the beginning extremely small forms that 
evolve into massive forms possessing for defense either power- 


FiG. 125. A Primitue Whale from the Eocene of Alabama. 

Zeiiglodon cdoides exhibits a secondary elongate, eel-shaped body form analogous to that 
of many of the aquatic, free-swimming, surface-dwelling reptiles, aquatic amphibians, 
and fusiform fishes. Restoration by Gidley and Knight in the American IVIuseum of 
Natural History. 

ful tusks or horns. The most conspicuous example of very 
rapid evolution which has taken place prior to the close of 
Eocene time is that of the great primitive whale Zeuglodon 
cetoides, discovered in the Upper Eocen,e of Alabama, and now 
known to have been distributed eastward to the region of the 
Mediterranean. As described above (p. 241), as an example of 
reversed adaptation and evolution, this animal had already 
passed through a prior terrestrial phase and had reached a 
stage of extreme specialization for marine life. These zeu- 
glodonts parallel several of the marine groups of reptiles (Figs. 
76, 87), also certain of the amphibians and fishes (Figs. 60, 44), 


GEOGRAPHIC DISTRIBUTION 261 

in the extreme elongation and eel-like mode of propulsion of 
the body. 

A zoogeographic feature of Eocene life is the strong and in- 
creasing evidence of migration between South America and 
North America by means of land connection in late Cretaceous 
or basal Eocene time, between the northern and southern 
hemispheres, which was then interrupted for 1,000,000 or per- 
haps 1,500,000 years until the middle of the Pliocene Epoch, 
when the South American types again appear in North Amer- 
ica. Another relation which has been established by recent 
discoveries is seen in the resemblance between certain Rocky 
Mountain primates (lemurs) and those existing at the present 
time in the IVIalayan Peninsula. 

North America and western Europe pass alike through 
three great phases of mammalian life in Eocene time: first, the 
archaic phase of the Palaeocene; second, a long phase in which 
the archaic and modern mammals of the Lower Eocene inter- 
mingle; third, a very prolonged period from the Lower to the 
Upper Eocene, in which Europe and North /Vmerica are widely 
separated and each of the ancestral types of mammals undergoes 
an independent evolution. This is followed in Oligocene time 
by a phase in which the animal life of western Europe and 
North America was reunited. Again in Miocene time a fur- 
ther wave of European mammalian life sweeps over North 
America, including the advance wave of the great order Pro- 
boscidea embracing both mastodons and elephants which ap- 
pear to have originated in Africa or in southern Asia. During 
the entire Miocene and Pliocene Epochs there is more or less 
unity of evolution between North America, Europe, and Asia, 
but it is a very striking fact that in Middle Pliocene time, 
when a wave of South American life enters North America, 
certain very highly characteristic forms of North American 


262 


THE ORIGIN AND EVOLUTION OF LIFE 


mammals (camels) enter Europe. In late Pliocene and early 
Pleistocene time the grandest epoch of mammalian life is 
reached; certain great orders like the proboscidians and the 
horses, with very high powers of adaptation as well as of migra- 
tion, spread over every continent except Australia. 


Fig. 126. North America in Upper Oligocene Time. 

East of the recently born Rocky Mountains the region of the Great Plains was made up 
of broad fluviatile flood-plains, fan-deltas, and lagoons, accumulating the detritus of the 
Rocky Mountains on the west and with a general eastern drainage. It was the scene 
of a continuous evolution of a plains fauna of mammals for a period of 1,500,000 years. 
Detail from the globe model in the American Museum by Chester A. Reeds and George 
Robertson, after Schuchert. 

This great epoch of mammalian distribution is followed by 
the Pleistocene phases in the northern and southern hemi- 
spheres, at the close of which the world wears a greatly im- 
poverished aspect; the northern hemisphere banishes all the 
forms of mammalian life evolving in the southern hemisphere 


CHANGES OF PROPORTION 263 

and in the tropics, and the high table-lands of Africa alone 
retain the grandeur of the Pliocene Epoch. 

The Definite Couuse of Chroiviatin Evolution in 

THE Origin of New Characters Partly 

Predetermined by Ancestry 

Some of the most universal laws as to the modes (p. 251) of 
evolution emerge from the comparative study of the horses, 


127. Two Stalls i.\ lin, Jadlltiux or thi; Titaxutiieres. 

Transformation of the small hoofed quadruped Eotitanops {A) of the Eocene — a relatively 
light-hmbcd, swift-moving, cursorial herbivore — into the gigantic Brontothcriitm (B) of 
the Lower Oligocene — a ponderous, slow-moving, graviportal type, horned for offense 
and defense. These titanotheres were remotely related to the existing rhinoceroses, 
horses, and tapirs, but they became suddenly extinct on attaining this impressive 
stage of evolution. They exemplify the increase of size characteristic of the evolution 
of the greater number of the hoofed Herbivora. The time during which this trans- 
formation occurred is estimated at 1,200,000 years — about one-third of the whole 
Tertiary Epoch. 

the proboscidians, and the rhinoceroses, from areas so widely 
separated geographically that there was no possibility of hy- 
bridizing or of a mingling of strains. For example, during a 
period estimated at not less than 500,000 years the horses of 
France, Switzerland, and North America evolve in these widely 


264 


THE ORIGIN AND EVOLUTION OF LIFE 


separated regions in a closely similar manner and develop 
closely similar characteristics in approximately a similar length 
of time. The same is true of the widely separated lines of 

descendants from the mas- 
todons, elephants, and rhi- 
noceroses. This law of 
uniform evolution and of 
the development inde- 
pendently in descendants 
from the same ancestors of 
closely similar characters 
is confirmed in Osborn's 
study of the evolution of 
the titanotheres (Fig. 127). 
In these animals, which 
have been traced through 
discoveries of their fossil 
remains over a period of 
time extending from the 
beginning of the Lower 
Eocene to the beginning 
of the Middle Oligocene, 
inclusive, is exhibited a 
nearly continuous, ^ un- 
broken transformation 
from the diminutive Eoti- 
tanops of the Lower Eocene 
to the massive Brontothe- 
rium of the Lower Oligocene, the latter form being so far as 
known the most imposing product of mammalian evolution, 

1 The continuity is broken by the extinction of one branch and the survival of an- 
other.^ It IS a continuity of character rather than of lines of descent. In some cases 
there is a continuity both of characters and of branches. 


Fig. 128. Stages in the Evolution of the 
Horn in the Titanotheres. 

This shows that these important weapons arise 
as rectigradations, /. c, orthogenetically and 
not as the result of the selection of chance or 
fortuitous variations. Horns, large, 4, Bron- 
totheriinn platyccras, Lower Oligocene; horns, 
small, 3, Protitanothcrium emarginaliim, Upper 
Eocene; horns, rudimentary, 2, Manteoccras 
manteoceras, Middle Eocene; hornless stage, 
I, Eotitanops horealis, Lower Eocene. 

Models in the American Museum of Natural 
History, prepared for the author by Erwin S. 
Christman. 


CHANGES OF PROPORTION 265 

with the exception of the Proboscidea. Every known step in 
this transformation is determinate and definite, every additional 
character which has been observed arises according to a fixed 
law and not according to any principle of chance. In the 
eleven principal branches which radiate from the earliest known 
forms {Eotltanops gregoryi) of this family exactly similar new 
characters arise quite independently at different periods of 
geologic time which are separated by the lapse of tens of thou- 
sands of years. 

The titanotheres exhibit an absolutely independent but 
definite origin and development in each branch; so far as ob- 
served, every new character has its own rate of evolution 
and its own peculiar kind of form change; for example, in cer- 
tain branches of the family the horns will appear many thou- 
sands of years later in the evolution history than in other 
branches, and after their appearance in many instances they 
may exhibit a singular inertia, or lack of momentum, over a 
long period of time, which is exactly in accord with our gen- 
eral principle (p. 149) that every character has its own rate 
of velocity both in individual development and in racial de- 
velopment. 

The Origin of New Proportional Characters Not 
Predetermined by Ancestry 

The titanotheres exhibit another very important principle, 
namely, that the linear proportions of the bones of the limbs 
are exactly adapted to the weight they are destined to carry 
and to the speed which they are destined to develop; in other 
words, the speed and the weight of all these great herbivora 
may be very precisely estimated by ratios and indices of the 
proportionate lengths of the different segments of the limbs, 
upper, middle, and lower. These proportionate lengths are 


266 


THE ORIGIN AND EVOLUTION OF LIFE 


not predetermined by the heredity-chromatin, because the 
same law of limb proportion prevails in all heavy, slow-mov- 
ing mammals, whatever their descent; for example, this law 
holds among the heavy, slow-moving reptiles, the Sauropoda 
(Fig. 97), as well as among the heavy, slow-moving mammals. 
The most beautiful adjustment of the proportions of the 
limb segments to speed is observed in the evolution of the 

horses (Fig. 130). Here we see 
that the upper segments (hu- 
merus, femur) are abbreviated, 
while the lower segments (fore- 
arm, lower leg, manus, and pes) 
are elongated. This is precisely 
the reverse of the conditions 
obtaining among the slow-mov- 
ing titanotheres and proboscid- 
ians (Fig. 131). Among the 
horses, too, the same law pre- 
vails and governs the very 
precise adjustment of the ratios 
of each of the limb segments, 
quite irrespective of ancestry. 
In the swift Hipparion of Amer- 
ica, for example, the highest 
phase of equine adaptation to 
speed, the indices and ratios of the limb segments are very 
similar to those in the existing prong-horn antelopes {Antiloca- 
pra) of our western plains. Contemporary with the Hipparion 
of Pliocene time, adapted to racing over hard, stony ground, 
is the relatively slow-moving, forest-living horse (Hypohippus) 
of the river borders of western North America (Fig. 130), in 
which the limb proportions are quite different. There is reason 


Fig. 129. Horses of Oligocexe Time. 

The horses frequenting the semi-arid 
plains of Oligocene times present an 
intermediate stage in the evokition of 
of cursorial motion — Mcsohippus, with 
a narrow, three-toed type of foot, 
elongate, graceful limbs, and teeth with 
crowns beginning to be adapted to the 
comminution of silicious grasses in 
accommodation to the contemporane- 
ous world-wide evolution of grassy 
plains. This law of the contemporane- 
ous evolution of an environment of 
grassy plains and of swift-moving 
Herbivora was first clearly enunciated 
by Kowalevsky in 1873. 

Restorations by Osborn, painted by 
Charles R. Knight, in the American 
Museum of Natural History. 


e^i^';'r>^ 


JXJtULJlStSt . mlOl£_t.U«J-El-IIJ 

B 


TUttl LPJJi—l^ oust 


11 


Fig. 130. Stages in the Evolution of the Horse. 

(Left.) An ascending series of Oligocene three-toed horses {A, B, C), showing their evolu- 
tion in size, form, and dental structure, which involved continuous change in thousands 
of distinct characters and occupied a period of time estimated at 100,000 to 200,000 years. 

(Right.) Two Upper IMiocene American types of horses, Hipparion {F), with limbs pro- 
portioned like those of the deer, representing the climax of the swift-moving, grassy 
plains type, in contrast with Hypohippus {D, E), a conservative forest and browsing 
type. This is an instance of the survival of an ancient browsing type in an ancient 
forested environment {D, £), while in the adjacent grassy plains there exists contem- 
poraneously the fleet Hipparion (F). 

Skeletons mounted in the American Museum of Natural History. Restoration under 
the direction of the author, painted by Charles R. Knight. 


267 


268 THE ORIGIN AND EVOLUTION OF LIFE 

to believe that this animal, like the existing okapi, was protected 
by coloration and by its swamp-living habits. 

The above examples illustrate the general fact that changes 
of proportion make up the larger part of mammalian evolution 
and adaptation. The gain and loss of parts, the presence and 
absence of parts, which is so conspicuous a phenomenon in 
heredity as studied from the Mendelian standpoint, is a com- 
paratively rare phenomenon. These changes of proportion are 
brought about through the greater or less velocity of single 
characters and of groups of characters; for example, the trans- 
formation of the four-toed horse of the base of the Lower 
Eocene^ into the three-toed embryo of the modern horse is 
brought about by the acceleration of the central digit and the 
retardation of the side digits. This process is so gradual that 
it required 1,000,000 years to accomplish the reduction of the 
fifth digit, which left the originally tetradactyl horse in the 
tridactyl stage (Fig. 130); and it has required 2,000,000 years 
more to complete the retardation of the second and fourth 
digits, which are still retained in the chromatin and develop 
side by side with the third digit for many months during the 
early intrauterine life of the horse. 

No form of sudden change of character (saltation, muta- 
tion of de Vries) or of the chance theory of evolution (pp. 7, 8) 
accounts for such precise steps in mechanical adjustment; be- 
cause for all proportional changes, which make up ninety-five per 
cent of mammalian evolution, we must seek a similar cause, 
namely, the cause of acceleration, balance or persistence, and 
retardation. This cause may prove to be in the nature of phys- 
icochemical interactions (p. 71) regulated by selection. The 
great importance of selection in the evolution of proportion is 

^The earliest-known fossil horses are four-toed, having lost the first digit (thumb). 
No five-toed fossil horse has yet been found. 


CHANGES OF PROPORTION 


269 


demonstrated by the universal law that the limb proportions 
of mammals are closely adjusted to provide for escape from 
enemies at each stage of development. 


Africa as a Great Theatre of Radiation 

The part which Africa has played in the early stages of 
mammalian evolution is a matter of comparatively recent dis- 
covery, and we are not yet 

. i 
positive whether the great life 

centre of North Africa was not 
closely related to that of south- 
ern Asia in Eocene and early 
Oligocene time, as the most re- 
cent discoveries appear to indi- 
cate. At all stages of geologic 
history Africa was, as it is to- 
day, a great theatre of evolu- 
tion of terrestrial life. Accord- 
ing to present knowledge. North 
Africa developed a highly varied 
fauna, including three chief ele- 
ments: first, types which are 
closely ancestral to the higher 
monkeys and apes, and which 
may thus be related to man him- 
self; second, a series of forms 
which attained gigantic size and 
never migrated from the con- 
tinent of Africa, but became 
extinct; and, thirdly, a series of forms, such as the zeuglodons, 
ancestral whales, sirenians, manatees, and dugongs, which 
emerged from this African home and enjoyed a very wide dis- 


FiG. 131. Epitome of Proportion Evo- 
lution IN THE PrOBOSCIDEA. 

These animals originated in the Palcco- 
niastodon (lower), frequenting the an- 
cient borders of the Nile in Egypt dur- 
ing Oligocene time, which developed 
during a period of 1,500,000 years into 
the existing types of the Indian and 
African elephants and into the ancient 
type of the Elephas (upper). 

Restoration in the American Museum of 
Natural History under the direction of 
the author, painted by Charles R. 
Knight. 


270 


THE ORIGIN AND EVOLUTION OF LIFE 


tribution in the northern hemisphere and in the equatorial 
regions. 

Among the giant tribes which issued from this ancient con- 
tinent the evolution of the proboscidians gives us an instance 
of the most extreme divergence of a terrestrial type from a 
related family, the sirenians, which evolve into the aquatic, 

fluviatile, and littoral t>'pe of 
the existing sea-cows and man- 
atees. 

In the transformation of 
PalcEomastodon (Fig. 131) into 
Elephas there are notable 
changes of proportion as well 
as the loss of many characters, 
as seen in the disappearance of 
the lower tusks, the enlarge- 
ment and curvature of the up- 
per tusks, the elongation of the 
proboscis, the abbreviation of 
the skull, the elongation of the 
limbs, the relative abbreviation 
of the vertebrae of the neck and of the backbone, the reduction 
of the tail. The limbs become of the weight-bearing type, the 
hind limbs attaining proportions which converge toward those 
of the titanothere BrontotJicrium (Fig. 127). The final numerical 
loss of characters as witnessed in the very gradual reduction of 
the lower tusks affords an instance of the leisurely methods of 
nature, for the process requires 2,000,000 years in the elephant 
line while in the mastodon line the lower tusks were still pres- 
ent at the time of the comparatively recent extinction of this 
animal, which occurred since the final glaciation of North 
America. The loss of parts through retardation is also seen 


Fig. 132. The Ice-Fii: i,1)> (jf the 
Fourth Glaciation. 

Southward extension of the ice-fields 
over the northeastern United States 
during the period of the fourth glacia- 
tion. After studies of Chamberlain. 
Modelled by Howell. 


CHANGES OF PROPORTION 271 

in the reduction of the number of the pairs of grinding teeth, 
from seven to six and finally in the adult modern elephant 
stage to one. The addition of new characters is principally 
observed in the remarkable evolution of the plates of the grind- 
ing teeth and of the elaborate muscular system of the pro- 
boscis. It is very important to note that, as in the evolution 
of the horses (p. 263), this evolution independently follows sim- 
ilar lines among the Proboscidea throughout all parts of the 
world. In other words, the unity of the evolution of the 
proboscidians in various parts of the world was not main- 


- 3» j^, 

Fig. 133. Groups of Reindeer (Ra>i(>ifci- taraudus) and Woolly Mammoth {Elcphas 

primi genius). 

Conditions of the reindeer-mammoth period of Europe during the maximum cold of the 
fourth glaciation of the Glacial Epoch. Mural painting in the American Museum of 
Natural History, painted by Charles R. Knight, under the direction of the author. 

tained by interbreeding^ but by the unity of ancestral heredity 
and the unity of the actions, reactions, and interactions of 
the animals with their environment. Widely separated de- 
scendants of similar ancestors may evolve in a closely but not 
entirely similar manner. The resemblances are due to the 
independent gain of similar new characters and loss of old 
characters. The differences are chiefly due to the unequal ve- 
locity of characters; in some lines certain characters appear or 
disappear more rapidly than others. 

The general fact that the slow-breeding elephants evolved 
very much more rapidly than the frequently breeding rodents, 
such as the mice and rats (Muridae), is one of the many evi- 
dences that the rate of evolution may not be governed by the 
frequency of natural selection and elimination. For example, 


272 THE ORIGIN AND EVOLUTION OF LIFE 

in the murine family of rodents, the annual progeny is very 
numerous and reproduction is very frequent, while among the 
elephants there is only a single offspring and reproduction is 
comparatively infrequent, yet the grinding teeth of the Pro- 
boscidea evolve far more rapidly and into much more highly 
complicated structures than the grinding teeth of any of the 


Fig. 134. Pleistocene or Glacial Environment of the Woolly Rhinoceros. 

Rhinoceros tichor/iiniis, of northern Europe, a contemporary of the woolly mammoth. 
Restoration in the American Museum of Natural History, painted by Charles R. 
Knight, under the direction of the author. 

rapidly breeding rodents. If evolution were due to the natural 
selection of chance variations this would not be the case. 

The elephants, like the horses, afTord an example of superb 
mechanical perfection in a single organ, the teeth, evolved in 
relatively slow-breeding forms, within a relatively short period 
of geologic time. In their grinding-tooth structure the Probos- 
cidea closely interlock with their environment, that is, there 
are complete transitions of dental structure between partly 
grazing, partly browsing, and exclusively browsing forms, such 


CHANGES OF PROPORTION 


273 


as the mastodon. The psychic and bodily adaptabiUty and 
plasticity of the Proboscidea to extreme ranges of habitat is 
paralleled only by the human adaptation to extremes of climate 
which is achieved through the intelligence of man. The woolly 


Fig. 135. Pygmies of the Hills Compared with the Plainsmen of West Central 

New Guinea. 

From Rawling's Land of the New Guinea Pigmies, by permission of Seeley, Service & 
Co. — The question arises whether the dwarfing is due to natural selection, to prolonged 
unfavorable environment, or to abnormal internal secretions of certain glands like the 
thyroid. It will be observed that the dwarfing is disproportional, the heads being 
relatively large. Compare the dwarfed sheep and dog in Figs. 119 and 120. 

mammoth (Fig. 131) presents one extreme of proboscidian 
adaptation, comparable to the Eskimo among human races as 
superbly adapted to the rigors of the arctic climate, while the 
hairless African and Indian elephants are comparable to the 
hairless human races living under the equator. 


2 74 THE ORIGIN AND EVOLUTION OF LIFE 

Undoubtedly the most promising field for future palaeon- 
tological research and discovery is in Asia. The links in the 
series of mammals — especially in the line known as the Pri- 
mates leading into the ancestors of man, namely, the Lemurs, 
Monkeys, and Apes — are probably destined to be found in 
this still very imperfectly explored continent, for it is indicated 
by much evidence that the still unexplored region of northern 
Asia was a great centre of animal population and of adaptive 
radiation into Europe on the west and into North America 
on the northeast. Ancient vertebrate fossils from this vast 
region are as yet absolutely unknown, but will doubtless be 
discovered, and it is here that the Eocene, and perhaps the 
Oligocene ancestors of man are likely to be unearthed, that 
is, in deposits of the first half of the Tertiary Period. Fos- 
sil records of the descent of man during the second half of 
the Tertiary also, namely, from the Oligocene Epoch to the 
close of the Pliocene time, we believe may be discovered in 
Asia, most probably in the region lying south of the Hima- 
layas. 

This subject of prehuman ancestry and evolution is re- 
served for the concluding series of Hale Lectures, but in our 
search for suggestions as to the causes of evolution, especially 
along the lines of internal physicochemical factors and the 
doctrine of energy, man himself is proving to be one of the 
most helpful of all mammals because chemically, physically, 
and experimentally man is the best known of all organisms at 
the present time. 


RETROSPECT AND PROSPECT 275 

Retrospect and Prospect 

The initial question raised in this volume arises as soon 
as we undertake a summary of evolution as we see it in the 
retrospect of the ages. 

Does the energy conception of evolution bring us nearer 
to the causes either of the origin or of the transformation of 
characters? Before answering these crucial questions let us 
see what our brief survey has taught us as to the kind of causes 
to look for. 

The foregoing comparison in the second part of this vol- 
ume of the evolutionary development that has taken place 
in many series of animals belonging to the five great classes 
of vertebrates — fishes, reptiles, amphibians, birds, and mam- 
mals — in response to twelve different kinds of environment, 
gives repeated evidence of their continuous powers of ever- 
plastic adaptation, not only to one kind of physical and 
life environment, but to any direct, reversed, or alternating 
change of environment which a group of animals may en- 
counter either on its own initiative or by force of circum- 
stances. 

In the large vertebrates we are enabled to observe and 
often to follow in minute details this continuous adaptation 
not merely in one, but in hundreds and sometimes in thou- 
sands of characters. In this respect a vertebrate differs from 
a relatively simple plant organism like the pea or the bean 
on which some of the prevailing conceptions of evolution have 
been grounded. In the well-ordered evolution of these single 
characters we have a picture like that of a vast army of sol- 
diers; the organism as a whole is Hke the army; the "char- 
acters" are like the individual soldiers; and the evolution of 
each character is coordinated with that of every other char- 


276 THE ORIGIN AND EVOLUTION OF LIFE 

acter. Sometimes a character lags behind and through failure 
to keep pace produces the dysteleogy or imperfect fitness of 
certain parts of the organism observed by Metchnikoff in the 
human body. 

Sometimes there are serial regiments of such well-ordered 
characters which are exactly or closely alike — for example, 
the 1092 teeth in the upper jaw of the iguanodont dinosaur, 
Trachodon, all very similar in appearance, all evolving and all 
perfectly coordinated in form and function with the 910 teeth 
in the lower jaw of the same animal. There are other serial 
regiments of characters, however, like the vertebrae in the 
backbone of a large dinosaur, for example, in which every 
single character, large and small, is different in form from 
every other. These are among the many miracles of adapta- 
tion referred to in the Preface. 

The evidence for this continuous and more or less adaptive 
direction in the simultaneous evolution of numberless char- 
acters which can be observed only by means of an ancestral 
fossil series was unknown to the master mind of Darwin 
during the preparation of his "Origin of Species" through 
his observations on the variations of domestic animals and 
plants between 1845 ^^'^ 18585 ^oi" it was not until the dis- 
covery by Waagen, in 1869, of a continuous series of fossil 
ammonites, in which minute changes originate and can be 
followed continuously, that the rudiment^ of a true concep- 
tion of the orderly and continuous modes of evolution which 
prevail in nature were reached. Among invertebrates and 
vertebrates, this conception has been abundantly confirmed 
by modern palaeontology in all its branches, namely, that 
of a well-ordered continuity as the prevailing mode of evolu- 
tion. This is the greatest contribution which palaeontology 
has made to biology and to natural philosophy. 


RETROSPECT AND PROSPECT 277 

Discontinuity is found chiefly in those characters in which 
a continuous mode of change is impossible. As to the physico- 
chemical constitution of animals and plants it has been well 
said that there can be no continuity between two distinct 
chemical formulas, or in many physicochemical functions and 
reactions. There are also certain form and proportion char- 
acters in which continuity is impossible — for example, the 
sudden addition of a new tooth to the jaw, or of a new verte- 
bra to the backbone. 

From these well-ascertained facts of the sudden or salta- 
tory appearance of characters, some have rashly inferred 
that there can be no continuity between species, whereas it 
is now known in mammalogy, in palaeontology, and to a less 
extent in ornithology that a large number of so-called species 
in nature show a complete continuity. Although the part 
which sudden changes or "saltations" from character to char- 
acter play in experimental evolution and artificial selection 
is very prominent, it remains to be seen how large a part they 
play under natural conditions. 

We realize that it is far more dif!icult to ascertain the causes 
of such continuous independent and more or less orderly and 
adaptive evolution of single characters than to comprehend 
evolution as Darwin's adherents of the present day imagine it 
to be, namely fortuitous and saltatory, for it is incumbent upon 
us to discover the cause of the orderly origin of every single 
character. The nature of such a law we cannot even dream 
of at present, for the causes of the majority of vertebrate adap- 
tations remain wholly unknown. 

Negatively we may say from palaeontology that there is 
positive disproof of the existence of an internal perfecting 
principle or entelechy of any kind which would impel animals 
to evolve in a given direction regardless of the direct, reversed, 


278 THE ORIGIN AND EVOLUTION OF LIFE 

or alternating directions taken by the organism in seeking its 
life environment or physical environment. 

It is true, we have found (p. 264) among the descendants 
of similar, though remote, ancestors something determinate or 
definite — a similarity which reminds us of the potential of the 
physicist — as to the origin of certain characters rather than 
others in the heredity-chromatin. It is as if certain latent 
power or potency of character-origin in the chromatin were 
there waiting to be called forth. It is partly due to this, 
as well as to inheritance of a similar ancestral form, that the 
mammals, as studied by the comparative anatomist, are so 
much alike, despite their superficial differences as seen by the 
student of adaptation. This definite or determinate origin 
of certain new characters appears to be partly a matter of 
hereditary predisposition. That is, animals from a common 
stock independently give rise at different times to similar new 
characters, as seen, for example, in the origin of similar horn 
defenses and similar bony and dental structures. 

The conclusive evidence against an elan vital or internal 
perfecting tendency, however, is that these characters do 
not spring up autonomously at any time; they may lie dor- 
mant or remain rudimentary for great periods of time, and 
here we find a correspondence which may be only an analogy 
with the principle of latent energy in physics. They require 
something to call them forth, to make them active, so to 
speak. 

It is in this function of arousing such character predis- 
positions that the chemical messenger phenomena of inter- 
action in the organism present some analogy to latent energy, 
although future experiment may prove that this does not con- 
stitute a real cause or likeness. If the transformation of energy 
is accelerated in certain organs or parts of existing organs by the 


RETROSPECT AND PROSPECT 279 

arrival of interacting chemical messengers and these parts 
thereby change their form and proportions, it is not incon- 
ceivable that chemical messengers may arouse a latent new 
character by stimulating the transformation of energy at a 
specific point. 

Then character-velocity must be considered. Although 
we may find that in the course of evolution in one group of 
animals a character moves extremely slowly, it lags along, 
it is retarded, as if partly suffering from inertia, or perhaps, 
for a while it stops altogether; yet in another group we may 
find that the very same character is full of life and velocity, 
it is accelerated like the alert soldier in the regiment. Here 
again is a point where the energy conception of evolution may 
throw a gleam of light. Some of the phenomena of interaction 
in the organism give us the first insight into the possible causes 
of the slow or rapid movement of character evolution — of its 
acceleration and retardation. Such individual character move- 
ments may govern the proportions of certain parts as well 
as of all parts of the organism. 

Combined, these character velocities and movements create 
all the extraordinary differences of proportion which dis- 
tinguish the mammals — for example, the extraordinarily long 
neck of the giraffe, the short neck of the elephant, the elongated 
skull of the ant-eater, the abbreviated head of the tree sloth. 
Wherever such changes of proportion weigh in the struggle 
for existence they may be hastened or retarded by natural 
selection. 

We discover that the chief principles of comparative 
anatomy formulated by Aristotle, Cuvier, Lamarck, Goethe, 
St. Hilaire, Dohrn, and other philosophic anatomists^ may 
all be expressed anew in terms treating the organism as a 

' Russell, E. S., 1916. 


28o 


THE ORIGIN AND EVOLUTION OF LIFE 


complex of energies. This is shown in a final scheme of 
action, reaction, and interaction^ which is an elaboration of the 
simplified scheme expressed on page i6 of the Introduction, as 
follows : 


Coordinated Activity of the Organism Within Itself 


ACTION 

AND > 

REACTION J 

of certain parts 

Chemical synthesis 
proteins, fats, 
carbohydrates 

Heat and Motion 

Nutrition, digestion 

Respiration 
oxidation, etc. 

Secretion 

Circulation 

Muscular and Skeletal 
system, etc. 
organs of locomotion 

Reproductive system: 
ovary and testis tis- 
sues surrounding 
heredity-germ cells 

All other phenomena 
under the laws of 
Transformation, Stor- 
age, and Release of 
Energy. 


INTERACTION 


Physicochcmical Agents 
Catalyzers 

enzymes 
Internal secretions 

hormones (accelerators), 

chalones (retarders), 
Nervous system 

accelerators, retarders, 

inhibitors 

Functions of Organs 
Balance, Equilibrium 

arrested development 
Acceleration 

growth, development 
Retardation 

atrophy, degeneration 
Correlation 
Compensation 

reciprocal atrophy 

and hypertrophy 


ACTION 

S^-^ \ AND 

[ REACTION 

of other parts 

Chemical synthesis 
proteins, fats, 
carbohydrates 

Heat and Motion 

Nutrition, digestion 

Respiration 
oxidation, etc. 

Secretion 

Circulation 

Muscular and Skeletal 
system, etc. 
organs of locomotion 

Reproductive system: 
ovary and testis tis- 
sues surrounding 
heredity-germ cells 

All other phenomena 
under the laws of 
Transformation, Stor- 
age, and Release of 
Energy. 


The eternal question remains, How do these energy phe- 
nomena which govern the life, form, and function of the organ- 
ism interact with the supposed latent and potential energy 
phenomena of the heredity-germ cells? As stated in the Pref- 
ace and Introduction, this question can only be answered by 
experiment. There is no proof at present. 

^ This notion of coordinated activity is particularly well expressed in Mathews's 
Physiological Chemistry (191 6), a volume which came to the author after this work was 
written (see Appendix, Notes V and VI). 


CONCLUSION 281 

Conclusion 

In the foregoing pages we have attempted to sketch in 
broad outHnes the course of the origin and evolution of hfe 
upon the earth in the Hght of our present imperfect knowl- 
edge, which offers few certainties to guide us and probabilities 
and possibilities innumerable among which to choose. 

The difference between the non-living world and the living 
world seems like a vast chasm when we think of a very high 
organism like man, the result of perhaps a hundred million 
years of evolution. But the difference between primordial 
earth, water, and atmosphere and the lowliest known organisms 
which secure their energy directly from simple chemical com- 
pounds is not so vast a chasm that we need despair of bridging 
it some day by solving at least one problem as to the actual 
nature of life —