The Doctrine of Evolution - Its Basis and Its Scope

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Title: The Doctrine of Evolution - Its Basis and Its Scope
Author: Crampton, Henry Edward
Language: English
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Columbia University Lectures

THE DOCTRINE OF EVOLUTION

THE HEWITT LECTURES

1906-1907

COLUMBIA UNIVERSITY PRESS
SALES AGENTS

NEW YORK:
LEMCKE & BUECHNER
30-32 WEST 27TH STREET

LONDON:
HUMPHREY MILFORD
AMEN CORNER, E.C.

_COLUMBIA UNIVERSITY LECTURES_

THE DOCTRINE OF EVOLUTION

ITS BASIS AND ITS SCOPE

HENRY EDWARD CRAMPTON, PH.D.

PROFESSOR OF ZOÖLOGY, COLUMBIA UNIVERSITY

New York

COLUMBIA UNIVERSITY PRESS

1916

_All rights reserved_

By THE COLUMBIA UNIVERSITY PRESS

Set up and electrotyped. Published June, 1911.
Reprinted December, 1912; September, 1916.

Norwood Press
J.S. Cushing Co.--Berwick & Smith Co.
Norwood, Mass., U.S.A.

PREFACE

The present volume consists of a series of eight addresses delivered as
the Hewitt Lectures of Columbia University at Cooper Union in New York
City during the months of February and March, 1907. The purpose of these
lectures was to describe in concise outline the Doctrine of Evolution, its
basis in the facts of natural history, and its wide and universal scope.
They fall naturally into two groups. Those of the first part deal with
matters of definition, with the essential characteristics of living
things, and, at greater length, with the evidences of organic evolution.
The lectures of the second group take up the various aspects of human
evolution as a special instance of the general organic process. In this
latter part of the series, the subject of physical evolution is first
considered, and this is followed by an analysis of human mental evolution;
the chapter on social evolution extends the fundamental principles to a
field which is not usually considered by biologists, and its purpose is to
demonstrate the efficiency of the genetic method in this department as in
all others; finally, the principles are extended to what is called "the
higher human life," the realm, namely, of ethical, religious, and
theological ideas and ideals.

Naturally, so broad a survey of knowledge could not include any extensive
array of specific details in any one of its divisions; it was possible
only to set forth some of the more striking and significant facts which
would demonstrate the nature and meaning of that department from which
they were selected. The illustrations were usually made concrete through
the use of photographs, which must naturally be lacking in the present
volume. In preparing the addresses for publication, the verbal form of
each evening's discussion has been somewhat changed, but there has been no
substantial alteration of the subjects actually discussed.

The choice of materials and the mode of their presentations were
determined by the general purpose of the whole course. The audiences were
made up almost exclusively of mature persons of cultivated minds, but who
were on the whole quite unfamiliar with the technical facts of natural
history. It was necessary to disregard most of the problematical elements
of the doctrine so as to bring out only the basic and thoroughly
substantiated principles of evolution. The course was, in a word, a simple
message to the unscientific; and while it may seem at first that the
discussions of the latter chapters lead to somewhat insecure positions, it
should be remembered that their purpose was to bring forward the proof
that even the so-called higher elements of human life are subject to
classification and analysis, like the facts of the lower organic world.

It may seem that the biologist is straying beyond his subject when he
undertakes to extend the principles of organic evolution to those
possessions of mankind that seem to be unique. The task was undertaken in
the Hewitt Lectures because the writer holds the deeply grounded
conviction that evolution has been continuous throughout, and that the
study of lower organic forms where laws reveal themselves in more
fundamental simplicity must lead the investigator to employ and apply
those laws in the study of the highest natural phenomena that can be
found. Another motive was equally strong. Too frequently men of science
are accused of restricting the application of their results to their own
particular fields of inquiry. As individuals they use their knowledge for
the development of world conceptions, which they are usually reluctant to
display before the world. It is because I believe that the accusation is
often only too well merited that I have endeavored to show as well as
circumstances permit how universal is the scope of the doctrine based upon
the facts of biology, and how supreme are its practical and dynamic
values.

It remains only to state that the present volume contains nothing new,
either in fact or in principle; the particular form and mode of presenting
the evolutionary history of nature may be considered as the author's
personal contribution to the subject. Nothing has been stated that has not
the sanction of high authority as well as of the writer's own conviction;
but it will be clear that the believers in the truth of the analysis as
made in the later chapters may become progressively fewer, as the various
aspects of human life and of human nature are severally treated.
Nevertheless, I believe that this volume presents a consistent reasonable
view that will not be essentially different from the conceptions of all
men of science who believe in evolution.

CONTENTS

CHAPTER PAGE

I. EVOLUTION. THE LIVING ORGANISM AND ITS NATURAL HISTORY 1

II. THE STRUCTURE AND DEVELOPMENT OF ANIMALS AS EVIDENCE OF EVOLUTION 35

III. THE EVIDENCE OF FOSSIL REMAINS 73

IV. EVOLUTION AS A NATURAL PROCESS 106

V. THE PHYSICAL EVOLUTION OF THE HUMAN SPECIES AND OF HUMAN RACES 150

VI. THE MENTAL EVOLUTION OF MAN 197

VII. SOCIAL EVOLUTION AS A BIOLOGICAL PROCESS 241

VIII. EVOLUTION AND THE HIGHER HUMAN LIFE 278

INDEX 313

EVOLUTION. THE LIVING ORGANISM AND ITS NATURAL HISTORY

The Doctrine of Evolution is a body of principles and facts concerning the
present condition and past history of the living and lifeless things that
make up the universe. It teaches that natural processes have gone on in
the earlier ages of the world as they do to-day, and that natural forces
have ordered the production of all things about which we know.

It is difficult to find the right words with which to begin the discussion
of so vast a subject. As a general statement the doctrine is perhaps the
simplest formula of natural science, although the facts and processes
which it summarizes are the most complex that the human intellect can
contemplate. Nothing in natural history seems to be surer than evolution,
and yet the final solution of evolutionary problems defies the most subtle
skill of the trained analyst of nature's order. No single human mind can
contain all the facts of a single small department of natural science, nor
can one mind comprehend fully the relations of all the various departments
of knowledge, but nevertheless evolution seems to describe the history of
all facts and their relations throughout the entire field of knowledge.
Were it possible for a man to live a hundred years, he could only begin
the exploration of the vast domains of science, and were his life
prolonged indefinitely, his task would remain forever unaccomplished, for
progress in any direction would bring him inevitably to newer and still
unexplored regions of thought.

Therefore it would seem that we are attempting an impossible task when we
undertake in the brief time before us the study of this universal
principle and its fundamental concepts and applications. But are the
difficulties insuperable? Truly our efforts would be foredoomed to failure
were it not that the materials of knowledge are grouped in classes and
departments which may be illustrated by a few representative data. And it
is also true that every one has thought more or less widely and deeply
about human nature, about the living world to which we belong, and about
the circumstances that control our own lives and those of our fellow
creatures. Many times we withdraw from the world of strenuous endeavor to
think about the "meaning of things," and upon the "why" and "wherefore" of
existence itself. Every one possesses already a fund of information that
can be directly utilized during the coming discussions; for if evolution
is true as a universal principle, then it is as natural and everyday a
matter as nature and existence themselves, and its materials must include
the facts of daily life and observation.

Although the doctrine of evolution was stated in very nearly its present
form more than a century ago, much misunderstanding still exists as to its
exact meaning and nature and value; and it is one of the primary objects
of these discussions to do away with certain current errors of judgment
about it. It is often supposed to be a remote and recondite subject,
intelligible only to the technical expert in knowledge, and apart from the
everyday world of life. It is more often conceived as a metaphysical and
philosophical system, something antagonistic to the deep-rooted religious
instincts and the theological beliefs of mankind. Truly all the facts of
knowledge are the materials of science, but science is not metaphysics or
philosophy or belief, even though the student who employs scientific
method is inevitably brought to consider problems belonging to these
diverse fields of thought. A study of nervous mechanism and organic
structure leads to the philosophical problem of the freedom of the will;
questions as to the evolution of mind and the way mind and matter are
related force the investigator to consider the problem of immortality. But
these and similar subjects in the field of extra-science are beyond its
sphere for the very good reason that scientific method, which we are to
define shortly, cannot be employed for their solution. Evolution is a
science; it is a description of nature's order, and its materials are
facts only. In method and content it is the very science of sciences,
describing all and holding true throughout each one.

The overwhelming importance of knowing about natural laws and universal
principles is not often realized. What have we to do with evolution and
science? Are we not too busy with the ordering of our immediate affairs to
concern ourselves with such remote matters? So it may appear to many, who
think that the study of life and its origin, and of the vital facts about
plants and animals may be interesting and may possess a certain
intellectual value, but nothing more. The investigation of man and of men
and of human life is regarded by the majority as a mere cultural exercise
which has no further result than the recording of present facts and past
histories; but it is far otherwise. Science and evolution must deal with
mere details about the world at large, and with human ideals and with life
and conduct; and while their purpose is to describe how nature works now
and how it has progressed in the past, their fullest value is realized in
the sure guidance they provide for our lives. This cannot be clear until
we reach the later portions of our subject, but even at the outset we must
recognize that knowledge of the great rules of nature's game, in which we
must play our parts, is the most valuable intellectual possession we can
obtain. If man and his place in nature, his mind and social obligations,
become intelligible, if right and wrong, good and evil, and duty come to
have more definite and assignable values through an understanding of the
results of science, then life may be fuller and richer, better and more
effective, in direct proportion to this understanding of the harmony of
the universe.

And so we must approach the study of the several divisions of our subject
in this frame of mind. We must meet many difficulties, of which the chief
one is perhaps our own human nature. For we as men are involved, and it is
hard indeed to take an impersonal point of view,--to put aside all
thoughts of the consequences to us of evolution, if it is true. Yet
emotion and purely human interest are disturbing elements in intellectual
development which hamper the efforts of reason to form assured
conceptions. We must disregard for the time those insistent questions as
to higher human nature, even though we must inevitably consider them at
the last. Indeed, all the human problems must be put aside until we have
prepared the way for their study by learning what evolution means, what a
living organism is, and how sure is the evidence of organic
transformation. When we know what nature is like and what natural
processes are, then we may take up the questions of supreme and deep
concern about our own human lives.

* * * * *

Human curiosity has ever demanded answers to questions about the world and
its make-up. The primitive savage was concerned primarily with the
everyday work of seeking food and building huts and carrying on warfare,
and yet even he found time to classify the objects of his world and to
construct some theory about the powers that made them. His attainments may
seem crude and childish to-day, but they were the beginnings of classified
knowledge, which advanced or stood still as men found more or less time
for observation and thought. Freed from the strife of primeval and
medieval life, more and more observers and thinkers have enlarged the
boundaries and developed the territory of the known. The history of human
thought itself demonstrates an evolution which began with the savages'
vague interpretation of the "what" and the "why" of the universe, and
culminates in the science of to-day.

What, now, is a science? To many people the word denotes something cold
and unfeeling and rigid, or something that is somehow apart from daily
life and antagonistic to freedom of thought. But this is far from being
true. Karl Pearson defines science as _organized knowledge_, and Huxley
calls it _organized common sense_. These definitions mean the same thing.
They mean that in order to know anything that deserves confidence, in
order to obtain a real result, it is necessary in the first place to
establish the reality of facts and to discriminate between the true, the
not so sure, the merely possible, and the false. Having accurate and
verified data, scientific method then proceeds to classify them, and this
is the _organizing_ of knowledge. The final process involves a summary of
the facts and their relations by some simple expression or formula. A good
illustration of a scientific principle is the natural law of gravitation.
It states simply that two bodies of matter attract one another directly in
proportion to their mass, and inversely in proportion to the square of the
distance between them. In this concise rule are described the relations
which have been actually determined for masses of varying sizes and at
different distances apart,--for snowflakes falling to the earth, for the
avalanche on the mountain slope, and for the planets of the solar system,
moving in celestial coördination.

Such a principle as the law of gravitation, like evolution, is true if the
basic facts are true, if they are reasonably related, and if the
conclusion is drawn reasonably from them. It is true for all persons who
possess normal minds, and this is why Huxley speaks of science as "common
sense,"--that is, something which is a reasonable and sensible part of the
mental make-up of thinking persons that they can hold in common. The form
and method of science are fully set forth by these definitions, and the
purpose also is clearly revealed. For the results of investigation are not
merely formulæ which summarize experience as so much "conceptual
shorthand," as Karl Pearson puts it, but they must serve also to describe
what will probably be the orderly workings of nature as future experience
unfolds. Human endeavor based upon a knowledge of scientific principles
must be far more reliable than where it is guided by mere intuition or
unreasoned belief, which may or may not harmonize with the everyday world
laws. Just as the law of gravitation based upon past experience provides
the bridge builder and the architect with a statement of conditions to be
met, so we shall find that the principles of evolution demonstrate the
best means of meeting the circumstances of life.

Evolution has developed, like all sciences, as the method we have
described has been employed. Alchemy became chemistry when the so-called
facts of the medievalist were scrutinized and the false were discarded.
Astrology was reorganized into astronomy when real facts about the planets
and stars were separated from the belief that human lives were influenced
by the heavenly bodies. Likewise the science of life has undergone
far-reaching changes in coming down to its present form. All the principles
of these sciences are complete only in so far as they sum up in the best
way the whole range of facts that they describe. They cannot be final until
all that can be known is known,--until the end of all knowledge and of
time. It is because he feels so sure of what has been gained that the man
of science seems to the unscientific to claim finality for his results. He
himself is the first to point out that dogmatism is unjustified when its
assertions are not so thoroughly grounded in reasonable fact as to render
their contrary unthinkable. He seeks only for truth, realizing that new
discoveries must oblige him to amend his statement of the laws of nature
with every decade. But the great bulk of knowledge concerning life and
living forms is so sure that science asserts, with a decision often
mistaken for dogmatism, that evolution is a real natural process.

* * * * *

The conception of evolution in its turn now demands a definite
description. How are we to regard the material things of the earth? Are
they permanent and unchanged since the beginning of time, unchanging and
unchangeable at the present? We do not need Herbert Spencer's elaborate
demonstration that this is unthinkable, for we all know from daily
experience that things do change and that nothing is immutable. Did things
have a finite beginning, and have they been "made" by some _supernatural_
force or forces, personified or impersonal, different from those agencies
which we may see in operation at the present time? So says the doctrine of
special creation. Finally, we may ask if things have changed as they now
change under the influence of what we call the natural laws of the
present, and which if they operated in the past would bring the world and
all that is therein to be just what we find now. This is the teaching of
the doctrine of evolution. It is a simple brief statement of natural
order. And because it has followed the method of common sense, science
asserts that changes have taken place, that they are now taking place, and
furthermore that it is unnecessary to appeal to other than everyday
processes for an explanation of the present order of things.

Wherever we look we see evidence of nature's change; every rain that falls
washes the earth from the hills and mountains into the valleys and into
the streams to be transported somewhere else; every wind that blows
produces its small or greater effect upon the face of the earth; the
beating of the ocean's waves upon the shore, the sweep of the great
tides,--these, too, have their transforming power. The geologists tell us
that such natural forces have remodeled and recast the various areas of
the earth and that they account for the present structure of its surface.
These men of science and the astronomers and the physicists tell us that
in some early age the world was not a solid globe, with continents and
oceans on its surface, as now; that it was so very hot as to be semi-fluid
or semi-solid in consistency. They tell us that before this time it was
still more fluid, and even a mass of fiery vapors. The earth's molten bulk
was part of a mass which was still more vast, and which included portions
which have since condensed to form the other bodies of the solar
system,--Mars and Jupiter and Venus and the rest,--while the sun remains as
the still fiery central core of the former nebulous materials, which have
undergone a natural history of change to become the solar system. The
whole sweep of events included in this long history is called cosmic
evolution; it is the greater and more inclusive process comprising all the
transformations which can be observed now and which have occurred in the
past.

At a certain time in the earth's history, after the hard outer crust had
been formed, it became possible for living materials to arise and for
simple primitive creatures to exist. Thus began the process of organic
evolution--_the natural history of living things_--with which we are
concerned in this and later addresses. Organic evolution is thus a part of
the greater cosmic process. As such it does not deal with the origin of
life, but it begins with life, and concerns itself with the evolution of
living things. And while the investigator is inevitably brought to
consider the fundamental question as to the way the first life began, as a
student of organic forms he takes life for granted and studies only the
relationships and characteristics of animals and plants, and their
origins.

But even as a preliminary definition, the statement that organic evolution
means _natural change_ does not satisfy us. We need a fuller statement of
what it is and what it involves, and I think that it would be best to
begin, not with the human being in which we are so directly interested,
nor even with one of the lower creatures, but with something, as an
analogy, which will make it possible for us to understand immediately what
is meant by the evolution of a man, or of a horse, or of an oak tree. The
first steam locomotive that we know about, like that of Stephenson, was a
crude mechanism with a primitive boiler and steam-chest and drive-wheels,
and as a whole it had but a low degree of efficiency measured by our
modern standard; but as time went on inventive genius changed one little
part after another until greater and greater efficiency was obtained, and
at the present time we find many varied products of locomotive evolution.
The great freight locomotive of the transcontinental lines, the swift
engine of the express trains, the little coughing switch engine of the
railroad yards, and the now extinct type that used to run so recently on
the elevated railroads, are all in a true sense the descendants of a
common ancestor, namely the locomotive of Stephenson. Each one has evolved
by transformations of its various parts, and in its evolution it has
become adapted or fitted to peculiar circumstances. We do not expect the
freight locomotive with its eight or ten powerful drive-wheels to carry
the light loads of suburban traffic, nor do we expect to see a little
switch engine attempt to draw "the Twentieth Century Limited" to Chicago.
In the evolution, then, of modern locomotives, differences have come
about, even though the common ancestor is one single type; and these
differences have an adaptive value to certain specific conditions. A
second illustration will be useful. Fulton's steamboat of just a century
ago was in a certain true sense the ancestor of the "Lusitania," with its
deep keel and screw propellers, of the side-wheel steamship for river and
harbor traffic like the "Priscilla," of the stern-wheel flat-bottom boats
of the Mississippi, and of the battleship, and the tug boat. As in the
first instance, we know that each modern type has developed through the
accumulation of changes, which changes are likewise adjustments to
different conditions. The diversity of modern types of steamships may be
attributed therefore to adaptation.

The several kinds are no more interchangeable than are the different forms
of locomotives that we have mentioned. The flat-bottom boat of the
Mississippi would not venture to cross the Atlantic Ocean in winter, nor
would the "Lusitania" attempt to plow a way up the shallow mud-banked
Mississippi. These products of mechanical development are not efficient
unless they run under the circumstances which have controlled their
construction, unless they are fitted or adapted to the conditions under
which they must operate.

Evolution, then, means _descent with adaptive modification_. We must
examine the various kinds of living creatures everywhere to see if they,
like the machines, exhibit in their make-up similar elements which
indicate their common ancestry in an earlier age, and if we can interpret
their differences as the results of modifications which fit them to occupy
different place in nature.

Two objections to the employment of these analogies will present
themselves at once. The definition may be all very well as far as the
machines are concerned, but, it may be asked, should a living thing like a
horse or a dog be compared with the steamship or the locomotive? Can we
look upon the living thing as a mechanism in the proper sense of the word?
A second objection will be that human invention and ingenuity have
controlled the evolution of the steamship and engine by the perfection of
newer and more efficient parts. It is certainly true that organic
evolution cannot be controlled in the same way by men, and that science
has not yet found out what all the factors are. And yet we are going to
learn in a later discussion that nature's method of transforming organisms
in the course of evolution is strikingly similar to the human process of
trial and error which has brought the diverse modern mechanisms to their
present conditions of efficiency. This matter, however, must remain for
the time just as it stands. The first objection, namely, that an organism
ought not to be viewed as a machine, is one that we must meet immediately,
because it is necessary at the very outset to gain a clear idea of the
essentially mechanical nature of living things and of their relations to
the conditions under which they live. It is only when we have such a clear
understanding that we can profitably pursue the further inquiries into the
evidence of evolution. Our first real task, therefore, is an inquiry into
certain fundamental questions about life and living things, upon which we
shall build as we proceed.

* * * * *

All living things possess three general properties which seem to be
unique; these are a peculiar chemical constitution, the power of repairing
themselves as their tissues wear out, and the ability to grow and
multiply. The third property is so familiar that we fail to see how
sharply it distinguishes the creatures of the organic world. To realize
this we have only to imagine how strange it would seem if locomotives and
steamships detached small portions of themselves which could grow into the
full forms of the parent mechanisms. Equally distinctive is the marvelous
natural power which enables an animal to re-build its tissues as they are
continually used up in the processes of living; for no man-made,
self-sustaining mechanism has ever been perfected. The property of chemical
composition is believed by science to be the basis of the second and the
third; but this matter of chemical constitution must take its proper place
in the series of structural characters, which we shall discuss further on
as we develop the conception of organic mechanism.

Whatever definition we may employ for a machine or an engine, we cannot
exclude the living organism from its scope. As a "device for transforming
and utilizing energy" the living organism differs not at all from any
"dead" machine, however complex or simple. The greatest lesson of
physiological science is that the operations of the different parts of the
living thing, as well as of the whole organism itself, are mechanical;
that is, they are the same under similar circumstances. The living
creature secures fresh supplies of matter and energy from the environment
outside of itself; these provide the fuel and power for the performance of
the various tasks demanded of an efficient living thing, and they are the
sources upon which the organism draws when it rebuilds its wasted tissues
and replenishes its energies. The vital tasks of all organisms must be
considered in due course, but at first it is necessary to justify our
analogies by analyzing the structural characteristics of animals and
plants, just as we might study locomotives in a mechanical museum before
we should see how they work upon the rails.

Among the familiar facts which science reveals in a new light are the
peculiarly definite qualities of living things as regards size and form.
There is no general agreement in these matters among the things of the
inorganic world. Water is water, whether it is a drop or the Pacific
Ocean; stone is stone, whether it is a pebble, a granite block, or a solid
peak of the Rocky Mountains. It is true that there is a considerable range
in size between the microscopic bacterium at one extreme and the elephant
or whale at the other, but this is far less extensive than in the case of
lifeless things like water and stone. In physical respects, water may be a
fluid, or a gas in the form of steam, or a solid, as a crystal of snow or
a block of ice. But the essential materials of living things agree
throughout the entire range of plant and animal forms in having a
jellylike consistency.

But by far the most striking and important characteristic of living things
is their definite and restricted chemical composition. Out of the eighty
and more chemical elements known to science, the essential substance of
living creatures is formed by only six to twelve. These are the simple and
obvious characteristics of living things which are denoted by the word
"organic." Everyone has a general idea of what this expression signifies,
but it is important to realize that it means, in exact scientific
terms,--_constituted in definite and peculiar ways_.

The living thing, then, possesses a definite constitution, which is a
mechanical characteristic, while furthermore it is related to its
surroundings in a hard and fast way. Just as locomotives are different in
structure so that they may operate successfully under different
conditions, so the definite characteristics of living things are exactly
what they should be in order that organisms may be adjusted or fitted into
the places in nature which they occupy. This universal relation to the
environment is called _adaptation_. It is only too obvious when our
attention is directed to it, but it is something which may have escaped
our notice because it is so natural and universal. The trunk of a tree
bears the limbs and branches and leaves above the ground, while the roots
run out into the surrounding soil from the foot of the trunk; they do not
grow up into the air. An animal walks upon its legs, the wings of a bird
are just where they should be in order that they may be useful as organs
of flight. And these mechanical adjustments in the case of living
creatures occur for the same reason as in mechanisms like the steamship,
which has the propeller at its hinder end and not elsewhere, and which
bears its masts erect instead of in any other way.

The next step in the analysis of organisms reveals the same wonderful
though familiar characteristics. The living organism is composed of parts
which are called _organs_, and these differ from one another in structural
and functional respects. Each of them performs a special task which the
others do not, and each differentiated organ does its part to make the
whole creature an efficient mechanism. The leg of the frog is an organ of
locomotion, the heart is a device for pumping blood, the stomach
accomplishes digestion, while the brain and nerves keep the parts working
in harmony and also provide for the proper relation of the whole creature
to its environment. So rigidly are these organs specialized in structure
and in function that they cannot replace one another, any more than the
drive wheels of the locomotive could replace the smokestack, or the boiler
be interchanged with either of these. All of the organs are thus fitted or
adjusted to a particular place in the body where they may most efficiently
perform their duties. Each organ therefore occupies a particular place in
an organic environment, so to speak. Thus the principle of adaptation
holds true for the organs which constitute an organism, as well as for
organisms themselves in their relations to their surroundings.

The various organs of living things are grouped so as to form the several
organic systems. There are eight of these, and each performs a group of
related tasks which are necessary for complete life. The alimentary system
concerns itself with three things: it gets food into the body, or ingests;
it transforms the insoluble foods by the intricate chemical processes of
digestion; and it absorbs or takes into itself the transformed food
substances, which are then passed on to the other parts of the body. It is
hardly necessary to point out that the ingestive structures for taking
food and preparing it mechanically lie at and near the mouth, while the
digesting parts, like the stomach, come next, because chemical
transformation is the next thing to be done; while finally the absorbing
portions of the tract, or the intestines, come last. The second group of
organs, like gills and lungs, supplies the oxygen, which is as necessary
for life as food itself; this respiratory system also provides for the
passage from the body of certain of the waste gases, like carbonic acid
gas and water vapor. The excretory system of kidneys and similar
structures collects the ash-waste produced by the burning tissues, and
discharges this from the whole mechanism, like the ash hoist of a
steamship. The circulatory system, made up of smaller and larger vessels,
with or without a heart, transports and propels the blood through the
body, carrying the absorbed foods, the supplies of oxygen, and the waste
substances of various kinds. All of these four systems are concerned with
"commissary" problems, so to speak, which every individual must solve for
and by itself.

Another group of systems is concerned with wider relations of the
individual and its activities. For example, the motor system accomplishes
the movements of the various organs within the body, and it also enables
the organism to move about; thus it provides for motion and locomotion.
Systems of support, comprising bones or shells, occur in many animals
where the other organs are soft or weak. Perhaps the most interesting of
the individual systems of relation is the nervous system. The strands of
its nerve fibers and its groups of cells keep the various organs of the
body properly coördinated, whereas in the second place, through the
sensitive structures at the surface of the body, they receive the
impressions from the outside world and so enable the organism to relate
itself properly to its environment. The last organic system differs from
the other seven in that the performance of its task is of far less
importance to the individual than it is to the race as a whole. It is the
reproductive system, with a function that must be always biologically
supreme. We can very readily see why this must be so; it is because nature
has no place for a species which permits the performance of any individual
function to gain ascendency over the necessary task of perpetuating the
kind. Nature does not tolerate race suicide.

All organisms must perform these eight functions in one way or another.
The bacterium, the simplest animal, the lowest plant, the higher plants
and animals,--all of these have a biological problem to solve which
comprises eight terms or parts, no more and no less. This is surely an
astonishing agreement when we consider the varied forms of living
creatures. And perhaps when we see that this is true we may understand why
adaptation is a characteristic of all organisms, for they all have similar
biological problems to solve, and their lives must necessarily be adjusted
in somewhat similar ways to their surroundings.

Carrying the analysis of organic structure one step further, it is found
that the various organisms are themselves complex, being composed of
_tissues_. A frog's leg as an organ of locomotion is composed of the
protecting skin on the outside, the muscles, blood vessels, and nerves
below, and in the center the bony supports of the whole limb. Like the
organs, these tissues are differentiated, structurally and functionally,
and they also are so placed and related as to exhibit the kind of
mechanical adjustment which we call adaptation. The tissues, then, in
their relations to the organs are like the organs in their relations to
the whole creature, i.e. adapted to specific situations where they may
most satisfactorily perform their tasks.

Finally, in the last analysis, all organisms and organs and tissues can be
resolved into elements which are called _cells_. They are not little
hollow cases, it is true, although for historical reasons we employ a word
that implies such a condition. They are unitary masses of living matter
with a peculiar central body or nucleus, and every tissue of every living
thing is composed of them.

The cells of bone differ from those of cartilage mainly in the different
consistency of the substances secreted by the cells to lie between them;
skin cells are soft-walled masses lying close together; even blood is a
tissue, although it is fluid and its cells are the corpuscles which float
freely in a liquid serum. Thus an organism proves to be a complex
mechanism composed of cells as structural units, just as a building is
ultimately a collection of bricks and girders and bolts, related to one
another in definite ways.

Our analysis reveals the living creature in an entirely new light, not
only as a machinelike structure whose parts are marvelously formed and
coordinated in material respects, but also as one whose activities or
workings are ultimately cellular in origin. Structure and function are
inseparable, and if an animal or a plant is an aggregate of cells, then
its whole varied life must be the sum total of the lives of its
constituent cells. Should these units be subtracted from an animal, one by
one, there would be no material organism left when the last cells had been
disassociated, and there would be no organic activity remaining when the
last individual cell-life was destroyed. All the various things we do in
the performance of our daily tasks are done by the combined action of our
muscle and nerve and other tissue cells; our life is all of their lives,
and nothing more. The cell, then, is the physiological or functional unit,
as truly as it is the material element of the organic world. Being
combined with countless others, specialized in various ways, relations are
established which are like those exhibited by the human beings
constituting a nation. In this case the life of the community consists of
the activities of the diverse human units that make it up. The farmer, the
manufacturer, the soldier, clerk, and artisan do not all work in the same
way; they undertake one or another of the economic tasks which they may be
best fitted by circumstances to perform. Their differentiation and
division of labor are identical with the diversity in structure and in
function as well, exhibited by the cells of a living creature. We might
speak of the several states as so many organs of our own nation; the
commercial or farming or manufacturing communities of a state would be
like the tissues forming an organ, made up ultimately of human units,
which, like cells, are engaged in similar activities. As the individual
human lives and the activities of differentiated economic groups
constitute the life of a nation and national existence, so cell-lives make
the living of an organism, and the expressions "division of labor" and
"differentiation" come to have a biological meaning and application.

* * * * *

The cell, then, is in all respects the very unit of the organic world. Not
only is it the ultimate structural element of all the more familiar
animals and plants that we know, as the foregoing analysis demonstrates,
but, in the second place, the microscope reveals simple little organisms,
like _Amoeba_, the yeast plant and bacteria, which consist throughout
their lives of just one cell and nothing more. Still more wonderful is the
fact that the larger complex organisms actually begin existence as single
cells. In three ways, therefore,--the analytic, the comparative, and the
developmental,--the cell proves to be the "organic individual of the first
order." As the ultimate biological unit, its essential nature must possess
a profound interest, for in its substance resides the secret of life.

This wonderful physical basis of life is called _protoplasm_. It contains
three kinds of chemical compounds known as the proteins, carbohydrates,
and hydrocarbons. Proteins are invariably present in living cells, and are
made up of carbon, hydrogen, nitrogen, sulphur, and usually a little
phosphorus. The elements are also combined in a very complex chemical way.
For example, the substance called hæmoglobin is the protein which exists
in the red blood cells and which causes those cells to appear light red or
yellow when seen singly. Its chemical formula states the precise number of
atoms which enter into the constitution of a single molecule as:
C_{600}H_{960}N_{154}FeO_{179}. This is truly a marvelously complex
substance when compared with the materials of the inorganic world, like
water, for example, which has the formula H_{2}O. And just as the peculiar
properties of H_{2}O are given to it by the properties of the hydrogen and
the oxygen which combine to form it, just so, the scientist believes, the
marvelous properties of protein are due to the assemblage of the
properties of the carbon and hydrogen and other elements which enter into
its composition.

It would be interesting to see how each one of these elements contributes
some particular characteristic to the whole compound. The carbon atom, for
example, is prone to combine with other atoms in definite varied ways, and
the high degree of complexity which the protein molecule possesses may
depend in greater part upon the combining power of its carbon elements.
The nitrogen atom makes the protein an extremely volatile compound, so
that the latter burns readily in the tissue cells; and the hydrogen and
oxygen bring their specific characteristics to the total molecule. And
furthermore, it is evident that the great complexity of this constituent,
protein, gives to protoplasm its power of doing work, or, in a word, its
power of living. In constructing it, much energy has been absorbed and
stored up as potential energy, and so, like the stored-up energy in a
watch spring or in gunpowder, this may be converted, under proper
conditions, into the kinetic energy and the work of actual operation. On
account of its peculiar and complex nature, it possesses great capacity
for burning or oxidization, thus serving as a source of vital power. It
burns in the living tissue just as coal oxidizes in the boiler of an
engine; its atoms fly apart and unite with oxygen so as to satisfy their
chemical affinities for this substance. If we could only see what happens
to the protein molecule when it undergoes oxidization, we would witness a
violent explosion, like that of a mass of gunpowder. And the astonishing
fact is that this process is actually the same for the living molecule,
for exploding gunpowder, and for the fuel which burns in the locomotive
boiler. Does this mean that the essential process of what we call life is
a chemical one? So it would seem on the basis of this fact alone, but a
conclusion must be deferred until we reach a later point.

The second kind of substance which we find in protoplasm is the
carbohydrate. A typical member of this group is common sugar,
C_{6}H_{12}O_{6}; another sugar has the formula C_{12}H_{22}O_{11}. Starch
is again a typical carbohydrate, and its formula is C_{6}H_{10}O_{5}, or
some multiple of this. One sees at a glance that these substances agree in
having twice as many hydrogen atoms as there are oxygen atoms, the same
proportion that the hydrogen bears to the oxygen in the compound water,--a
characteristic which makes it easy to remember the general constitution of
carbohydrate as compared with the protein. The substances of this second
class are obviously much less complex, both as regards the different kinds
of atoms and in respect to the numbers of each kind that enter into the
formation of a single molecule. Therefore the carbohydrates do not possess
so much power or energy as the protein molecule; in short, they are not
such good fuels for the living mechanism.

Finally, we find almost always in protoplasm other substances composed of
carbon and hydrogen and oxygen which are called hydrocarbons,
distinguished from carbohydrates by the fact that the number of oxygen
atoms is less than half the number of hydrogen atoms. These substances are
the fats and oils of various kinds, less powerful sources of energy than
the proteins, but they contain more potential energy than the
carbohydrates because they are more oxidizable.

Besides the characteristic substances of these three classes, protoplasm
contains certain other chemical compounds, like the various salts of
sodium, chlorine, magnesium and potassium, and a few others, which bring
the list of chemical elements to the number twelve. We have already noted
how strikingly small and restricted is the list of elements composing
living matter as compared with the long array of eighty-odd different
kinds of chemical atoms existing in the world as a whole.

But an astonishing result is reached through the brief analysis we have
just made. It is this: we do not find _peculiar_ kinds of atoms which
occur exclusively in living matter; the materials are exactly the same as
those of the outer world. In short, the elements of both the organic and
inorganic divisions of the universe prove to be the same. Carbon is
carbon, whether it is part of the substance of a living brain cell, or
black inert coal, or the glistening diamond, or an incandescent part of
the fiery sun. Hydrogen is the same, whether it be a constituent of the
ocean, of the air, or of the living muscle fiber. And so it is with all of
the other elements of the living mechanism. This starts us upon a line of
thought which leads to a significant conclusion, namely, that a living
thing which seems so distinct and permanent is after all only a temporary
aggregate of elements which come to it from the not-living world; existing
for a time in peculiar combinations which render life possible, they pass
incessantly away from the living thing and return to the inorganic world.
Every breath we draw sends out particles which were at one time living
portions of ourselves; every movement we make involves the destruction of
living muscle cells, whose protoplasm breaks down into the ash and gas and
fluid wastes which eventually return to the world of dead things. A tree
loses its living leaves with each recurring season, and the antlers of the
stag are lost annually, to be replaced anew. Indeed the major part of some
organisms is itself actually dead. The bones and hair and nails of such an
animal as a cat are almost entirely lifeless, even though they are
integral and necessary portions of the organism as a whole. They are
constructed by living protoplasm which has died in their making. Thus
without going beyond the boundaries of the individual body, these
substances have passed from the sphere of life, and are dead. The apparent
gap on the other side between the lifeless and living world is equally
imaginary, for our living substance is continually replenished and rebuilt
from the elements of our dead foods. So, as Huxley says, a living organism
is like a flame or a whirlpool, which is an ever changing though seemingly
constant individuality. We look at a gas flame, and we see in the flame
itself those particles of gas which have come through the pipe to be
agitated violently in the higher temperature of the flame as they are
oxidized or burnt. These particles immediately pass off as carbonic acid
gas and water vapor which are no longer parts of the flame. A fountain is
continually replenished by the water which is not-fountain, but which
becomes for the time a part of the graceful jet, falling out and away as
it leaves the fountain itself. Just so a living organism is an ever
changing, ever renewed, and ever destroyed mass of little particles--the
atoms of the inorganic world which combine and come to life for a time,
but which return inevitably to the world of lifeless things. This is one
of the most fundamental facts of biology. The independence of a living
thing like a human being or a crustacean is a product of the imagination.
How can we be independent of the environment when we are interlocked in so
many ways with inorganic nature? Our very substance with its energies has
been wrested from the environment; and as we, like all other living
things, must replenish our tissues as we wear out in the very act of
living, we cannot cease to maintain the closest possible relations with
the environment without surrendering our existence in the battle of life.

From the foregoing discussion, it will be evident, I am sure, that there
is ample justification for the biological dictum that a living individual
is a mechanism. Not only is the organism composed always of cell units
grouped mechanically in tissues and organs and organic systems; not only
are the operations which make up its life constant and regular under
similar conditions; not only is the whole creature mechanically connected
with the inorganic world; but above all the whole activity of a biological
individual is concerned necessarily and again mechanically with the
acquisition of materials endowed with energy, which materials and energy
are mechanically transformed into living matter and its life. Even though
an organism is so much more complex than a locomotive, and so plastic,
nevertheless, in so far as both are mechanisms, the conception of the
evolution of the former may be much more readily understood through a
knowledge of the historical transformation of the latter.

* * * * *

What, now, is life? To most people "life seems to be something which
enters into a combination of carbon and hydrogen and the other elements,
and makes this complex substance, the protoplasm, perform its various
activities." Nearly every one finds it difficult to regard life and
vitality as anything but actuating principles that exist apart from the
materials into which they enter, and which they seem to make alive.
According to this general conception, "life is something like an engineer
who climbs into the cab of the locomotive and pulls the levers which make
it go," as health might supposedly be regarded as something that does not
inhere in well-being, but gets into the body to alter it. But is this
conception really justified by the facts of animal structure and
physiology? Let us recall the steps of our analysis. The living organism
is a collection of differentiated parts, the organs; the life of an
organism is a series of activities of the several organic systems and
organs. If we could take away one organ after another, there would be
nothing left after the last part had been subtracted. In a similar manner,
the activities of organs prove to be the combined activities of the
tissue-cells, and again the truth of this statement will be clear when we
imagine the result of taking away one cell after another from organisms
like the frog or tree. When the last cell had been withdrawn, there would
be nothing left of the frog's structure, and there would be no element of
the frog's life. It is true that the particular way the tissue-cells are
combined is of primary importance, but it is none the less true that the
life of a cell is the kind of element out of which the life of even the
most complex organism is built. And we have seen that the essential
substance of a cell is a complex chemical compound we call protoplasm,
whose elements are identical with chemical substances outside the living
world. Is there any ground for supposing that the properties of protoplasm
are due to any other causes than those which may be found in the chemical
and physical constitution of protoplasm? In brief, is life physics and
chemistry? Nowadays the majority of biologists believe that it is. Just as
the properties of water are contributed by the elements hydrogen and
oxygen which unite to form it, just so the marvelous properties of
protoplasm are regarded as the inevitable derivatives of the combined
properties of the various chemical elements which constitute protoplasm.
Biologists have known for more than a century, since the work of Lavoisier
and Laplace in 1780, that the fundamental process of the living mechanism
is oxidation, and that this process is the same, as they said, for the
burning candle and the guinea pig. Beginning with Woehler, in 1828, scores
of students of physiological chemistry have duplicated the chemical
processes of living matter, which were regarded as so peculiar to the
living organism that they seemed to be due to the operation of a
non-mechanical and vital cause. The investigator mentioned was the first to
construct artificially from inorganic substances the nitrogen-containing
ash product of the living organism called urea. Now hundreds of so-called
organic compounds have been made synthetically and their number is added
to week after week. Therefore, the biologist who finds that a physical and
chemical analysis of some vital processes is possible, and that the
analysis is being extended with astonishing rapidity, finds himself unable
to regard protoplasmic activity as anything different in kind or category
from the processes of physics and chemistry which go on in the world of
dead things.

It is true that even at the present time some biologists are reluctant to
accept the thoroughgoing mechanical interpretation of organic phenomena,
partly because these are so complex that their ultimate constituents
cannot be discerned, but more often on account of the apparently
purposeful nature of biological processes. Some, indeed, have gone so far
as to postulate something like consciousness which controls and directs
the formation of protoplasm, and the exercise of its distinctive
properties in the way of growth, reproduction, and embryonic development
into the adapted adult. But the fact remains that wherever analysis has
been possible the constituent elements of an organic process prove to be
physical and chemical. Protoplasm differs from inorganic materials only in
its complexity and in the properties which seem to owe their existence to
this complexity. As Huxley points out, it is no more justifiable to
postulate the existence of a vitalistic principle in protoplasm than it
would be to set up an "aquosity" to account for the properties of water,
or a "saltness" for the qualities of a certain combination of sodium and
chlorine. We may not know how the elements produce the properties of the
compound, but we do know that such properties are the invariable products
of their respective constituents in combination. As far as the evidence
goes, it tells strongly and invariably in favor of the mechanistic
interpretation.

Under the present limitations, it is impossible to give this subject the
further discussion it deserves. It is not our purpose to review the origin
of life in times past, and the origin of living matter from inorganic
constituents, though the subject is one of the most important in the field
of cosmic evolution. We must begin with the living organism; and how the
first one arose must be of less importance to us than the knowledge of its
mechanical constitution and of its mechanical operation. Of far greater
value is the realization that a living creature is not an independent
thing, but that, on the contrary, it must hold the closest possible
relations with the world of materials and energies constituting its
environment. We must again insist upon the importance of that mechanical
adjustment to the conditions of life which is the universal characteristic
of plants and animals. It is the history of these creatures and the origin
of their adapted conditions that we are called upon to study. We must
scrutinize the nature of to-day to see if we can find evidence that
evolution is true, and if we can discern the forces which, acting upon the
living mechanism as man has dealt with machines, might bring the various
species of the present day to their modern forms.

* * * * *

We have now learned that evolution means a common ancestry of living forms
that have come to differ in the course of time; our common reason has
shown us also that organisms are in a true sense complicated chemical
mechanisms adapted to meet the conditions under which they must operate.
We come now to the evidences offered by the organic world that evolution
is true and that natural forces control its workings. Clearly the
examination of the matter of _fact_ is independent of the question of
_method_. For just as the chemist may experiment with various substances
to see if they will dissolve in water and not in alcohol before it is
necessary or desirable for him to take up the further studies of the laws
of solution, so reasonable grounds must be found for regarding evolution
as true before passing to its method of accomplishment. And in the
following discussions, the animals will be used almost exclusively, not
because the study of plants fails to discover the same relations and
principles, but because the better known animal series is more varied and
extensive, and above all for the reason that the human organism arrays
itself as the highest term of the animal series.

In the complete scheme adopted by most naturalists, five categories
include the evidences bearing upon the fact of evolution. These are
_Classification_; Comparative Anatomy, or _Morphology_; Comparative
Development, or _Embryology; _Palæontology_, which comprises the facts
provided by fossil relics of animals and plants of earlier geological
ages; and _Geographical Distribution_. Each of these divisions includes a
descriptive and analytical series of facts, whose characteristics are
"explained" or summarized in the form of the general principles of the
respective divisions. Such principles, taken singly and collectively,
constitute the evidences of evolution.

The particular nature of any one of these categories, evolved in the
development of science practically in the order stated, depends upon the
special quality of an animal which it selects for comparison and
organization in connection with other similar facts, and also in its own
mode of viewing its facts. One and the same organism may present materials
for two, three, or even all five of these divisions, for they are by no
means mutually exclusive. For example, a common cat possesses certain
definite characteristics which give it a particular place when animals
more or less like it are grouped or classified according to their degrees
of resemblance and difference, in small _genera_ of very similar forms, in
larger _tribes_ or _orders_ of similar genera, and in more and more
inclusive groups of these lesser divisions, such as the _classes_ and
_phyla_, or main branches of the animal tree. The common cat and its
relatives are even earlier to be regarded as anatomical subjects, and
their thorough analysis belongs to comparative anatomy,--a name which
explains itself. The purpose of this department of natural history is to
explore the entire range of animal forms and animal structures, and to
determine the degree of resemblance and difference exhibited by the
general characters of entire organisms and by the special qualities of
their several systems of organs. It provides the data from which
classification selects those which indicate mutual affinities with
greatest precision and surety. But its materials are _all_ the facts of
animal structure, and because each and every known organism can be and
must be studied, the investigator engaged in formulating the evidence of
evolution has at his disposal all the data referring to the entire realm
of animals. The data of embryology are likewise coextensive with the
territory of the animal world, for we do not know of any form which does
not change in the course of its life history. An adult cat is the product
of a kitten which is itself the result of a long series of changes from
earlier and simpler conditions. In so far as it deals with structures in
the making, embryology is a study of anatomy, but as it is concerned
primarily with all of the plastic remodeling which animals undergo during
the production of their final forms, it is an independent study.
Nevertheless we shall learn how intimate are the relations of these two
divisions of zoölogy and how the evolutionary teachings of each body of
fact support and supplement those of the other.

Palæontology searches everywhere among the deposits of earlier ages for
links to be fitted into their proper sequence of time, from which it
constructs the chain of diverse types leading down to the species of the
present. A cat of to-day is therefore viewed in an entirely different
connection, as the last term in a consecutive series of species. Forming
alliances with geology, and even with physics and chemistry, this
department of zoölogy endeavors to reconstruct the past from what it
learns to-day about organisms and the conditions under which they live.
Finally the observations that cats of various kinds do not occur
everywhere in the world, but only in certain more or less restricted
localities, belong to the subject of geographical distribution, and
illustrate its nature.

Our task is to learn the teachings of these several divisions by recalling
and putting together what we know already about the commonest animals, or
noting what can be observed in a visit to a zoölogical garden and
aquarium. On account of the present limitations of time, the subject of
classification will be combined with comparative anatomy; embryology will
be taken up together with these subjects; palæontology will be the main
subject of the next discussion, which will include also a brief statement
of the meaning of distribution. Then we will be prepared to study nature
to see how evolution works.

THE STRUCTURE AND DEVELOPMENT OF ANIMALS AS EVIDENCE OF EVOLUTION

In order to become acquainted with the way the structures of animals
provide evidences of evolution, it is by no means necessary to review the
entire range of their forms, because research has discovered that the
principles of relationship are universal among animals, and that any group
of examples will demonstrate what is taught by comparative anatomy as a
whole. The commonest creatures may serve us best in order that we may come
to view evolution as a process that involves each and every living thing
that we know, and not as something which belongs only to the remote and
unknown past.

Let us begin with the common cat and the group of carnivora or
flesh-eating animals to which it belongs. As we pass along the streets of
the city, we will see many cats which differ in some details, though they
resemble one another closely. While they vary somewhat in form, the range
in this quality is not so noticeable as in the matter of color; some of
them will be gray, some maltese, while others will be yellowish or black,
and they will differ in the striped or spotted character of their
coloration. We readily classify them all as "cats" in spite of their
differences, because they are alike in so many ways that we have learned
to associate as the distinguishing characteristics of these animals, and
to label--"cat." The animals which we might see in a walk of several
blocks may reasonably be regarded as offspring of the same pair of
ancestors of a few years back, even though they are dissimilar. We all
know that the kittens of one and the same litter vary: no two of them are
ever exactly alike in color or disposition or voice or size, nor is any
one identical with either of its parents, although it may be necessary to
employ exact means of measuring them in order to demonstrate their
variation. The fact of difference, then, is surely not inconsistent with
even the closest ties of blood, and we do not need to go beyond the scope
of daily observation to find that this is true in nature wherever we look.

Should we extend our observations so as to include the cats of Boston and
Philadelphia and San Francisco, the animals would probably vary over a
wider range, but they would be so similar to New York cats in their
make-up that we would have no difficulty in regarding them and all the
others of the United States as the descendants of a single pairs of
ancestors, perhaps brought over in the "Mayflower." But why does this view
seem justified? Because experience has taught us that the living things
which resemble each other most closely are those which are most intimately
bound by ties of blood and common heritage. It is "natural" for relatives
to resemble one another more than persons not related, and for brothers and
sisters to be more alike than cousins. Science does not refer to something
outside everyday observation when it states that _the possession by two
animals of a great body of similar characters beneath their minor
differences is an indication of their common ancestry_.

Thus at the very outset our simple illustration establishes the most
fundamental principle of comparative anatomy. Let us see how it works
further. The Manx cat possesses an abbreviated tail, although in other
respects it is practically the same as the familiar long-tailed form; the
Angora and the Persian differ in having long hair. All of these animals
are so much alike in so many respects, and so closely resemble the wild
cats, that it is not unreasonable to regard them all as the descendants of
the same original wild ancestors, and as the varying products of lines
which branched out from the same stock in different directions and at
different times. It is, in a word, their "cat-_ness_" which demonstrates
their relationships. But common sense need not stop here. Guided by the
facts of anatomical similarity, it convinces us that the dun-colored lion
and puma, the striped tiger and the spotted leopard are simply cats of a
larger growth whose remoter ancestry is one with that of the previously
cited forms. Not until we explore and compare their several systems do we
see how thoroughgoing is their uniformity in structural plan. And because
reason justifies the view regarding the origin of domestic cats from wild
ancestors, the evolution of all the various members of the cat tribe must
be acknowledged. These animals exhibit a fundamental likeness, which, to
employ a musical analogy, is the "theme" of "cat-_ness_," and they are so
many variations of this theme.

The members of another tribe of the familiar carnivora display in their
own way the same kind of evidences of relationship. The varieties of
domesticated dogs differ far more widely among themselves than do common
cats, yet their community of ancestry is demonstrated not only by
structural resemblances, but also by the striking fact that forms as
diverse as the greyhound and the fox terrier can be crossed. Here again
there are wild forms, like the wolf and fox and jackal, so like the
domesticated members of the dog tribe that we cannot fail to recognize a
common "dog-_ness_" and its significance as evidence of the relationship
in ancestry of all these animals.

Extending our survey so as to include the other tribes of flesh-eaters,
identical principles come to light. One is compelled to regard the polar
and grizzly bears as obvious blood relatives of the brown bear, and even
of the raccoon of our own territory. Instead of walking upon their toes
like cats and dogs, these animals plant their feet flat upon the ground;
and they agree in many other details of structure that place them
together, but somewhat apart from the other tribes. The many kinds of
seals and walruses and sea elephants form still another group displaying
similar bodily characters, but differing more widely from the "cat theme"
in these differences. They are all true carnivora, but in the course of
their evolution they have progressively changed so as to be adapted to
life in the water where they find their prey. The bones of the limbs are
the same in number and arrangement as in the cat's limb, but the seal's
anterior appendage or "arm" has altered in numerous ways so as to become
an efficient flexible paddle, while the hind limbs have shifted
posteriorly, very much as screw propellers have evolved in the history of
steam vessels. How the members of the seal tribe have changed in their
descent from purely terrestrial ancestors is partly explained by such
intermediate animals as the otter. This form is adapted by its slender
body and partly webbed feet to a semi-aquatic life; it seems to have
halted at a point beyond which all of the seals have passed in their
evolution.

Each one of these tribes by itself provides conclusive evidence of
evolution, for it is most reasonable to regard the "theme" in every case
as a product of common inheritance, while the variations of any theme are
best understood as the results of adaptive changes in various directions.
But the examples have disclosed a larger relation and a principle of wider
scope, as indeed the assignment of all these tribes to the single natural
group of the _carnivora_ implies. These tribes are put together because
comparative anatomy finds that the common characters of all cats are
fundamentally like those of all dogs and bears and seals, and in these
common qualities the carnivora differ from all other mammalia. Does this
mean that the branches which bear respectively the various members of the
several tribes are outgrowths of a single limb of the evolving animal
tree? Science does not hesitate to give an affirmative answer, because, as
in the case of the similar but varying domestic cats, no other explanation
of tribal resemblance in structure seems so reasonable and natural.

So far the examples have been taken from one order of the highest class of
backboned animals, called mammalia. When our survey is extended to other
divisions of this class, additional laws of organic relationship are
discovered. If in a series of evolving generations the line of
modification proceeding from a terrestrial animal like a cat to
semi-aquatic and marine types substantially like an otter and a seal should
be carried further, it will inevitably lead to forms possessing characters
such as those displayed by whales and the related porpoises, dolphins, and
narwhals of the order cetacea. In their make-up all of these animals
clearly possess the general characteristics of mammals, and they
constitute collectively another limb which has sprung from the same stock
as the carnivora, although at an earlier time. This we believe because of
their plan of body and because their peculiar organization fits them even
more perfectly than the seals for aquatic existence that is their only
possible mode of life. In the case of the whales the bony framework of the
fore limb is again like that of the cat's leg, although the whole
structure is a flexible finlike paddle. The hind limb has disappeared as
an efficient organ, but the significant fact is that small rudiments of
hind limbs are present just where corresponding structures are placed in
the seal. These vestiges cannot be reasonably accounted for, unless they
are the degenerate hinder limbs of a remote four-footed ancestor.
Furthermore the unborn whale possesses a complete coat of hair, which is
afterwards replaced by blubber; but hair is a thatchlike coat to shed
rain, as the way the hairs lie on a terrestrial mammal indicates. We are
therefore forced to conclude that whales have originated from four-footed
animals walking about on land, because no opposed explanation gives so
reasonable an interpretation of the observed facts.

Another group of familiar animals materially reinforces the results
already established. After what has been said, it will not be difficult to
perceive the meaning of the resemblances among mice of the house and
field, and of rats and rabbits and squirrels. All of them possess heavy
curved gnawing teeth, or incisors, and lack the flesh-tearing or canine
teeth. They agree in many other respects which distinguish them as a
separate natural order of the mammals called the rodentia. Again we find a
highly aberrant form in the flying squirrel, which leads toward an order
with another plan of body. This animal is a true rodent, which lengthens
its leap from branch to branch by means of a fold of skin stretching
between its fore and its hind limbs. It is an animated aeroplane, and it
shows in part how bats have originated. The wing of a bat is an elastic
membrane stretching not only between the two legs of one side, but also
between the greatly lengthened "fingers" of the fore limb. But the bones
of arm, wrist, and fingers are almost precisely the same in number and
relation as in walking forms. The fact that this peculiar wing adheres to
a plan belonging to the anterior legs of walking or climbing types has no
reasonable explanation save that of evolution.

The well-known group of hoofed animals, including horses and cattle, is
also valuable for our present purposes, as well as in a later connection
when the evidence of fossils is described. The elephant possesses five
toes armed with well-developed nails or hoofs. A tapir has four or three
toes, and it would seem that its ancestor had had five toes, of which one
or two had been lost. A rhinoceros possesses three toes, and its foot is
constructed internally like the elephant's with the outer elements absent.
The horse comes last with one large toe and hoof, but on either side of
the main bones of this digit are vestiges of what must have been toes in
its ancestors. Among the even-toed forms the hippopotamus has four which
reach the ground, with a vestige of a fifth, so this animal has apparently
descended from a typical mammal with the full number along a different
line from that taken by the odd-toed forms. A pig has a cloven hoof, made
up of what we may call the third and fourth members of a series of five
digits, but the second and fifth fingers and toes are present, though they
are withdrawn from the ground so as to be no longer functional; this
animal seems to have proceeded further along the same line taken by the
hippopotamus. A deer, with still smaller rudiments at the sides of its
double foot, leads in the comparative series to the camel with a cloven
hoof devoid of any such relics.

We must pass with only brief mention the lower orders of mammalia, like
the insect-eating forms to which armadillos and ant-bears belong. Of
greater interest are the pouched mammals like the kangaroo and opossums,
which live almost exclusively in the Australian realm. The kangaroo is
endowed with a head somewhat like that of a goat, and well-developed hind
legs that enable it to make leaps of astonishing length. Some of its
relatives, such as the bandicoot, are like rats, or like bears, as in the
case of the wombat. The Tasmanian wolf is another true marsupial, even
though divergent adaptation has brought it to resemble the carnivora of
the dog tribe in general appearance and in special structures like the
teeth. Finally at the very bottom of the mammalian scale are two small
forms living in the Australian faunal region. The duckbill or
_Ornithorhynchus_ is the better known animal, with its close fur, webbed
feet, and flattened ducklike beak, while its only other near relative, the
_Echidna_, is somewhat similar to the spiny hedgehog in external
appearance. A unique peculiarity of these two forms is that they produce
eggs much like those of reptiles and birds, and this fact, together with
others of a structural nature, brings the whole group of mammals near to
the lower classes of the Vertebrata.

Looking back on the several orders of mammals, it will be seen that the
last mentioned are much less differentiated or specialized in their
general organization. Above the level of the egg-layers and the pouched
mammals, the higher orders branch out in different directions and reach up
to various levels of the scale of animal organization.

The foregoing structural evidences of organic transformation in the past
histories of cats and seals and whales insistently recall the analogies of
the locomotive and the ship employed at the outset. All these animals,
like the mechanical examples, have come to differ in their derivation from
the same original parents, and their lines of descent have diverged so as
to fit the products of evolutionary modification to diverse circumstances.
Even the vestigial organs of animals have their counterparts in the
machines. The cowcatcher was a large and important structure in the early
days of railroading, but it has become relatively useless with the
decrease of grade crossings and the construction of more complete lines of
fence. The structure still persists, sometimes in a greatly reduced form.
Even more obvious is the change of structure in the case of masts of
vessels, which originally bore the sails for propelling the ship. When
steam engines were employed to give motive power, masts did not disappear.
They now provide the derrick supports of trading steamers; in battleships
their function is changed to that of fighting tops and signal yards. Even
the poles carried by canal boats to bear windmills must be regarded as the
reduced vestiges of masts originally constructed to carry sails; and their
adaptive evolution, like that of countless structures in animals, has been
accomplished by degeneration.

* * * * *

The birds are another class of backboned animals which exhibit identical
principles of relationship. A heron has long legs and wide-spreading toes,
which keep its body out of the water as it stalks about the marshes where
it seeks its food; its bill is a long slender pincers. Compare it with an
eagle; the latter has a short and heavily hooked beak to tear flesh, while
its stout legs bear strongly curved talons to hold its struggling prey.
Swimming birds like the swan and duck and loon possess feet which are
constructed in general like those of the former examples, but they are
webbed and shortened to serve as paddles. In the penguin we find a
counterpart of the seal among mammals; its feathers are much reduced and
its fore limbs are no longer wings enabling the animal to fly, but they
are paddles which it uses when it swims in pursuit of fish. Finally the
ostrich and wingless bird of New Zealand--the _Apteryx_--have wings that
are useless vestiges, which, in the latter case, are hidden under the
brushlike feathers covering the body. It is unnecessary to add more
examples, for even these few illustrations establish exactly the same
principles of relationship and evidences of evolution that are to be found
in the series of mammalia.

Reptiles also are grouped, like the mammals and birds, as variations about
a central theme. An ordinary lizard is perhaps the nearest in form to the
remote ancestor from which all have sprung. Some lizards are long and very
slender, with all four limbs of greatly reduced size. Others, which are
still true lizards, have lost the hind limbs, or even all the legs, as in
the "blind worms" of England. One step more, and an animal which has
progressed further along a similar line of descent would be a snake. Just
as whales as a group are derivable from forms which resemble types
belonging to another order, so snakes as an order are to be regarded as
more radically altered derivatives of some four-footed lizardlike
creature. Alligators are very much like lizards in general form, and their
order is a diverging branch from the same limb. Finally the evolution of
turtles from the same ancestors is intelligible if we begin with a short
stout animal like the so-called "horned toad" of Arizona, and proceed to
the soft-shelled tortoise of the Mississippi River system; the
establishment of a bony armor completes the evolution of the familiar and
more characteristic turtle.

Frogs and salamanders constitute another lower class, called the amphibia,
whose members are gilled during the earlier stages of development. An
adult frog is essentially a salamander without a tail and with highly
developed hinder limbs. The salamanders differ as regards the number of
fishlike gill clefts that they all possess in their young stages, but
which disappear entirely or in part during later life. In comparison with
the lizard as a typical reptile, a salamander is more primitive in all of
its inner organic systems, while in its nearly continuous body, with head
and tail gradually merging into the trunk, it also displays a somewhat
simpler form of body.

The fishes are the lowest among the common vertebrates, and they offer an
abundance of independent testimony as to the truth of the principles of
comparative anatomy. The common shark is perhaps the most fundamental
form, with a hull-like body undivided into head, trunk, and tail, and from
it have originated such peculiar variations as the hammerhead and skate.
Among fishes with true bones, a cod or trout is the most typical in
general features. Without ceasing to be true bony fishes, the trunk-fish
and cow-fish are adapted by their peculiar characters of spine and armor
plate to repel many enemies. The puff fish can take in a great amount of
water, when disturbed, so as to become too large to be swallowed by some
of its foes, illustrating another adaptive modification for self-defense.
The wonderful colors and color patterns of the tropical fish of the reef,
or of the open water forms like the mouse-fish of the Sargossa Sea, often
render them more or less completely hidden from the foraging enemy. A
flounder looks like a fish which was originally symmetrical, but which had
come to lie flat on its side upon the bottom, whereupon the eye underneath
had left its original place to appear on the upper surface. The difficult
and unusual conditions of deep-sea existence have been met by fishes in
two ways; some forms possess luminous frilled and weedlike fins, which
lure their prey to within easy reach of their jaws, while others have
enormous eyes, so as to make use of all possible rays of light in their
pursuit of food organisms. But all of these diverse forms are true
_fishes_, possessing a common heritage of structure which demonstrates
their unity of origin.

The brief review of backboned animals has shown how comprehensive are the
principles of relationship. The families and tribes of each order, such as
the carnivora, are like branches arising from a single limb; the orders in
their turn exhibit common qualities of structure which mean that they have
grown from the same antecedents, while even the larger divisions or
classes of mammals, birds, reptiles, amphibia, and fishes, possess a deep
underlying theme whose dominant motif is the backbone, which proves their
ultimate unity in ancestry. The greater and lesser branches have reached
different levels, for the fish is clearly simpler in its make-up than the
highly specialized bird. But the great fact is that structural evidences
demonstrating the reality of genealogical affinities are displayed by the
entire series of vertebrates; although they differ much or little in many
or fewer respects they have one and the same ground-plan.

* * * * *

The lower animals devoid of backbones, and therefore called invertebrates,
are not so well-known except to the student of comparative anatomy,
because they are not so often met with, and because they are usually very
small or microscopic; but in many respects their importance to the
evolutionist surpasses that of the vertebrates. Their structural plans are
far more varied, and they range more widely from higher and relatively
complicated organisms to the unitary one-celled animals. A knowledge of
some of them is essential for our present purpose, which is to learn how
sure is the basis for the principles of relationship and how complete is
the structural evidence of evolution.

Worms are represented in the minds of most people by the common earthworm
or sandworm. The body in either case is made up of a series of segments or
joints which agree closely throughout the animal in external appearance
and in internal constitution. A section of the digestive tract, a pair of
nerve centers, two funnel-like tubes for excretion, and similar blood
vessels occur in each portion.

Precisely similar features are displayed by the crustacea, which seem to
be so different. Every one is familiar with the appearance of lobsters and
crabs. Even in these animals the body is composed of segments, but these
are not like one another, nor are they freely movable throughout the body.
Five are fused in all crustacea to make a head; in lower members of the
order the eight succeeding segments are free, but in the lobster they are
joined together and united with the head. The hinder part of this animal
is a long abdomen whose segments remain more primitive and independent.
But in a crab, the whole plan has been modified by the shortening and
broadening of the head-thorax, and by the reduction of the abdomen, which
is also turned under the anterior part of the body. The internal organic
systems are constructed upon a worm plan with modifications. Nearly every
one of the segments bears one pair of appendages, which can be referred by
their forked nature to the two-parted, oarlike flaps of sandworms, but the
appendages of crustacea have departed from their prototypes in functional
respects and in details of structure. They are variously feelers, jaws,
legs, pincers, and swimming paddles, evolved to serve different purposes,
just as the limbs of the vertebrates we have described have become
variously arms, wings, flippers and paddles in apes, bats, seals, and
whales.

Butterflies, beetles, bees, and grasshoppers seem at first sight to be
entirely different, even though they agree in being more or less
segmented. But all of them have heads with four pairs of appendages of the
same essential plan, middle thoracic regions of three segments more or
less united, bearing three pairs of legs and usually two pairs of wings,
while the hinder part is a freely jointed abdomen without real limbs. In
these respects the countless varieties of insects agree so that they also
like crustacea of various kinds seem to have been derived from wormlike
animals with more simply segmented bodies. Indeed spiders and scorpions
and their relatives of the group arachnida prove for similar reasons to be
derivatives of the same original stock, and own cousins of the insects.

In nearly every one of the invertebrate branches we find representatives
which interest us chiefly because they appear to have reached their
present condition by retrograde evolution. Barnacles are really crustacea,
but they have lost their eyes as well as some other structures that are
most useful in animals with a free existence, because they have adopted a
fixed mode of life, which has also brought about the loss of the original
freely jointed character of the body. A tapeworm as an example of internal
parasites is an extremely degenerate form which lacks a digestive tract,
because this is superfluous in an animal which lives bathed in the
nutrient fluids of its host. Comparing it in other respects with other low
wormlike creatures, it appears to be a relative of peculiar simple worms
with complete organization and independence of life. All these degenerate
forms enlarge our conception of adaptation by adding the essential point
that progress is not always the result of evolution. Indeed we have
learned this in the case of vestigial and rudimentary structures of higher
forms like whales, and now we find that entire animals may degenerate as a
result of changes no less adaptive than progressive modifications.

Passing by other invertebrate groups made up of species arranged like
higher animals in smaller and larger branches according to their degree of
fundamental similarity, we arrive at a place in the scale occupied by
two-layer animals without the highly developed and clearly differentiated
organic systems of the forms above. The fresh-water animal _Hydra_
exemplifies the creatures of this level, where also we find sea-anemones
and the soft polyps which form corals and coral reefs by their combined
skeletons. _Hydra_ is an animal to which we must return again and again as
we study one or another aspect of organic evolution. In general form it is
a hollow cylinder closed at one end, by which it attaches itself, while at
the upper end, surrounded by a group of tentacles, is the mouth which
leads to the central cavity. The wall of this simple body is composed of
two layers of cells, between which there is a gelatinous layer rarely
invaded by cells. The inner layer lines the central space into which food
organisms are thrust by the tentacles, and it is concerned primarily with
digestion. The outer layer comprises cells for protection and sensation
primarily. Cells of both layers have muscular prolongations which by their
operation enable the whole animal to change its form and to move from one
place to another.

It may seem that such an animal is totally unlike any of the higher and
more complex types. In certain respects, however, it is identical with the
other forms inasmuch as it performs all of the eight biological tasks
demanded by nature. It is also similar in so far as its inner layer, like
the innermost sheet of cells in higher forms, is concerned with problems
of taking and preparing food, while the protective outer layer resembles
in function the outermost covering of all animals higher in the scale.
Beyond these a still more fundamental agreement is found in its cellular
composition.

At the lower end of the animal scale are organisms which consist of one
cell and nothing more. _Amoeba_, to which we must refer again and again,
is an example of this group which possesses an overwhelming importance to
the comparative student because the origins of all the characteristics of
animals higher in the scale are to be found within it. _Amoeba_ itself
is a naked mass of protoplasm, about 1/100 of an inch in diameter,
enclosing a nucleus. Its form is not constant during activity, for
fingerlike processes called pseudopodia are pushed out tentatively in many
directions to be followed as circumstances direct by the materials of the
whole cell body. Other protozoa differ in possessing constant forms, or in
having constant vibratile processes, or shells of some kind, while in
still other cases like individuals combine to make colonies which are more
or less definite and permanent. Here at the very foot of the organic scale
are found animals which seem to be entirely different from those above.
Upon examination they, like _Hydra_, prove to be the same as regards the
number and kind of functions they perform, but in structural regards their
evolutionary relation to all higher animals is indicated solely by the
fact that they are cells composed of protoplasm. Nevertheless the
principle which states that resemblance means consanguinity still holds
true, for cellular constitution is a unique possession of things of the
living world,--something which demonstrates the common origin of all
living things just as truly as the "cat-_ness_" of our first series of
examples reveals for a smaller group the significance of likeness and the
nature of the basic law of comparative anatomy.

* * * * *

Employing a figure of speech, we have climbed down the animal tree from
the higher regions where the mammals belong. Having reached the very foot
of the trunk we are in a position to review and summarize the evidences
which we have discovered all about us as we have descended. The various
examples we have mentioned and the groups to which they belong clearly
occupy different places in the scale which begins with the protozoa and
extends upward to the most complicated and differentiated animals. _Hydra_
takes its place above the protozoa for obvious structural reasons; worms
belong to a still higher zone, surpassed by the more complex jointed
animals like crustacea and insects. Far above these are the vertebrates,
among which we have already demonstrated the occurrence of different
grades of organization, from the fish up to the higher amphibia and
reptiles, and beyond in two directions to the diverging birds and mammals.
The basic characteristics of every group in a high position may be traced
back to some one or another of the divisions at a lower level, so that the
general sequence of the structural levels from low to high becomes
intelligible as the order of their evolution.

To my mind the rudimentary and vestigial structures of animals are in
themselves proof positive of a natural history of change. The few
illustrations can be reinforced by countless examples offered by every
group of living animals. If such structures have not evolved naturally by
degenerating from more efficient counterparts in ancestors of earlier
times, and if they have been specially created, they are utterly
meaningless and their very existence is unreasonable. If common sense is
to be employed, they demonstrate evolution.

Everywhere throughout the whole series animals place themselves in a
treelike arrangement, for in their respective levels they occur like
leaves at the ends of the lines of descent which have led up to them and
which are comparable to the branches and limbs arising from the trunk of a
tree. Thus the major and minor divisions of animals do not follow in the
order of the rungs of a ladder, even though they must be assigned to
different levels according to the complexity of their construction. The
summary given above, namely, that the occurrence of lower and higher
levels reveals an order of evolution, is amplified and not contradicted by
the statement that the species of animals are group in a treelike
arrangement. It is the task of the evolutionist, provided with all the
facts of comparative anatomy and dealing only with the various species as
separate leaves, so to speak, to reconstruct the now invisible but not
unreal twigs and branches and limbs of the animal tree, and to show how
they have diverged at one time or another as they have grown and spread to
produce the species of the present day. This he may do in so far as he may
find sufficient materials to enable him to employ the methods of
comparative anatomy and the great natural principle established by this
method--that essential likeness means consanguinity.

* * * * *

No evidence of evolution could be more significant and interesting than
the results provided by the comparative study of development. In the first
place it is an obvious fact that every living thing changes in the course
of its life-history, and if as an adult it occupies a high place in the
animal scale, its embryological transformation is more elaborate and
intricate than in the case of a lower form. Every one knows that organisms
do develop, and yet I believe that few appreciate the tremendous
significance of the mere fact that this is true, while still fewer are
aware that the peculiar and characteristic early stages through which an
animal passes in becoming an adult are even more striking than the fact of
development itself. We shall learn something of these earlier conditions
in the development of some of our most familiar animals, but at the outset
nothing can be more important than an appreciation of the first great
lesson of this department of natural history--namely that organic
transformation is real and natural. We do not need to employ the methods
of formal logic to know that in growing up a human infant undergoes the
changes of childhood and adolescence, that kittens become cats, and that
an oak tree is produced by an acorn, for we know these things directly by
observing them. It is natural for development to take place under normal
conditions, and if it does not, then something has interfered with nature.
Inasmuch as "growing up" is accomplished by the alteration of an organic
mechanism with one structure into an individual with a changed plan of
body, it is in essence the actual process of evolution which the
comparative study of grown animals of to-day demonstrates in the way we
have learned. The study of animal structure discovers the process of
evolution because the most reasonable interpretation of the similarities
and minor differences exhibited everywhere by the various groups of
animals is that descent with adaptive and divergent modification has taken
place; the result is reached by inference, it is true, but by scientific
and logical inference. With development it is otherwise. No reasoning is
necessary to tell us that organic transformation is a real and a natural
process. We see it everywhere about us and we ourselves have come to be
what we are by a natural history of change. Can we consistently deny that
it is possible for a species to alter in the long course of time when a
few brief weeks are sufficient for the new-laid egg of the fowl to develop
into a fledgling? Many indeed strain at the gnat of the longer process in
the past when without hesitation they recognize the real and obvious fact
of individual development in a brief period.

I have said that development is a "natural" process. We employ this word
for the familiar and everyday occurrence or thing; it does not imply that
everything is known about the object or phenomenon, because science knows
that complete and final knowledge is impossible. We say that it is natural
for rain to fall to the earth, and we speak of the law of gravitation
according to which this takes place as a natural principle, but it may not
have occurred to many to inquire _what_ makes rain fall and _why_ do
masses of matter everywhere behave toward one another in the consistent
manner described by the law in question. Sunshine is natural, but we do
not know _why_ light travels as it does from the sun to the earth, and
this is another question which, like the inquiry into the ultimate cause
of the familiar and natural phenomenon of gravitation, has not yet been
answered. But it is still regarded as natural for the rain to fall and for
the sun to shine. In the same way does science view development, denoting
it natural because it is an ordinary everyday matter. And we are under no
more obligation to postulate supernatural control for the changing forms
in the life-history of a chick or a cat than we need to assume that
gravitation and the radiation of light demand immediate supernatural
direction. The embryology of no form is fully understood or described or
explained, but no intelligent person would be willing to assert that
because complete knowledge is lacking, it is unnatural for organic
transformation to take place during growth. Whatever may be the ultimate
origin and nature of the directing powers behind gravitation and
development and other phenomena, we have no concern with such matters
because they cannot be handled by scientific methods and one belief about
them is on the same plane with any other. Our task is to deal with the
everyday phenomena of life and the production of living species.

* * * * *

It is not necessary to go far afield to find an animal which will
introduce us to the general principles of embryology. In the present
instance as in the case of comparative anatomy almost any form will
disclose the meaning of development, for animate nature is uniform and
consistent in its methods of operation throughout its wide range. We shall
begin with the familiar frog which every one knows is a product of a
tadpole; passing on to the chick we will learn more facts that will enable
us to formulate the main principle of comparative embryology in definite
terms; we will then be prepared to extend our survey so as to include
somewhat less familiar facts and animals that are even more significant
than the first illustrations.

If we should visit a woodland pond in early spring, we would find
somewhere among the leaves and sticks in the water large masses of a clear
jellylike consistency enclosing hundreds of little black spheres about an
eighth of an inch in diameter. These are the egg masses and eggs of a
common frog. Watching them day by day we see the small one-celled egg
spheres divide into more and more numerous portions which are the
daughter-cells, destined to form by their products the many varied tissues
and organs of the developing larva and adult frog. After three or four
days the egg changes from its globular form into an oval or elliptical
mass, and from one end of this a small knob projects to become a flattened
waving tail a few days later. On the sides of the larger anterior portion
shallow grooves make their appearance and soon break through from the
throat or pharynx to the exterior as gill-slits. Shortly afterwards the
little embryo wriggles out of its encasing coat of jelly, develops a
mouth, and begins its independent existence as a small tadpole, with eyes,
nasal and auditory organs, and all other parts that are necessary for a
free life. Thus the one-celled egg has transformed into something that it
was not at first, and in doing this it has proved the possibility and the
reality of organic reconstruction.

The tadpole breathes by means of its gills, and it is at first entirely
devoid of the lungs which the adult frog possesses and uses. When we speak
of the larval respiratory organs as gills we imply that they are like the
organs of a fish which have the same name; they are truly like those of
fishes, for the blood-vessels which go to them are essentially the same as
in the lower types and they are supported by simple skeletal rods like the
gill-bars of the fish. In a word, they are the same things.

The animal feeds and grows during the months of its first summer, and
hibernates the following winter; with the warmth of spring it revives and
proceeds further along the course of its development. Near the base of the
tail two minute legs grow out from the hinder part of the body, and while
these are enlarging two front legs make their appearance a little behind
the gills. The tadpole now rises more frequently to the surface where it
takes small mouthfuls of air. Meanwhile great changes are effected inside
the body where the various systems of fishlike organs become remodeled
into amphibian structures. A sac is formed from the wall of the esophagus,
and this enlarges and divides to form the two simple lungs. The legs
increase in size, the tail dwindles more and more, the gills close up, and
soon the animal hops out on land as a complete young frog. From this time
on it breathes by means of its lungs instead of gills, even though it
returns to the water to escape its foes, to seek its prey, and to
hibernate in the mud of the lake bed during the winter months.

All these changes are familiar and natural, but until science places them
and similar facts in their proper relations their significance is lost to
us. The tadpole is essentially a fish in its general structure and mode of
life, even though its heritage is such that it can develop into a higher
animal. When it does become a frog it proves beyond a doubt that there is
no impassable barrier between fishes and amphibia. Our earlier comparison
of the structures of these two classes of vertebrates led to the
conclusion that the latter had evolved from antecedents like the former,
and had thus followed them upon the earth; now that sequence seems to have
some connection with the method by which a tadpole, obviously not a fish
but nevertheless actually fishlike, changes into a frog, a member of a
higher class of vertebrates. This method is employed by developing frogs
apparently because it follows the ancestral order of events, and because,
so to speak, the only way a frog knows how to become a frog is to develop
from an egg first into a fishlike tadpole and then to alter itself as its
ancestors did during their evolution in the past. We begin to see, then,
that in addition to the impressive fact of development itself, the mode of
organic transformation is far more conclusive evidence of evolution,
because it reveals an order of events which parallels the order
established by comparative anatomy as the evolutionary sequence.

However it is well to review some of the changes by which a chick comes
into existence before attempting to comprehend fully the fundamental
principle of development that the tadpole's history discloses to us. The
egg of a common fowl is certainly not a chick. Within the calcareous shell
are two delicate membranes that enclose the white or albumen; within this,
swung by two thickened cords of the albumen, is the yellow yolk ball
enclosed by a proper membrane of its own. In the earliest condition, even
before the albumen and the shell are added and before the egg is laid, on
one side of the yolk-mass there is a tiny protoplasmic spot which is at
first a single cell and nothing more. The hen's egg is relatively
enormous, but nevertheless, like that of the frog, it starts upon its
course of development as a single unitary biological element--a cell.
During the earliest subsequent hours the first cell divides again and
again to form a small disk upon the surface of the yolk. Soon the cells
along the middle line of this small sheet become rearranged to make an
obvious streak or band, and about this line a simple tube is constructed
which is destined to become the future brain and spinal cord. The whole
disk continues to enlarge by further division of its constituent elements
so that it encloses more and more of the yolk mass, but the little chick
itself is made out of the cells along the central line of the original
plate, from which it folds at the sides and in front and behind so as to
lie somewhat above and apart from the flatter enclosing cell layers which
partly surround the yolk.

At the sides of the primitive nerve-tube small blocks of cells arise to
develop into primitive muscles and other structures. As nourishment is
brought to the embryo from the surrounding layers enclosing the nutrient
yolk, one system after another takes its shape and builds its several
parts into organs which can be recognized as elementary structures of a
chick. Among the more interesting ones are small clefts or slits formed in
the side walls of the rudimentary throat or pharynx. Blood-vessels go
forward from the simple heart to run up through the intervening bars
exactly as in the tadpole and the fish. In brief, the young chick
possesses a series of gill-slits, for these structures are the same in
essential plan and relations as the clefts of tadpoles and fishes. Does
this mean that even birds have descended from gill-breathing ancestors?
Science answers in the affirmative, because evolution gives the only
reasonable explanation of such facts as these. The case seems different
from that of the frog, because gills are used by the tadpole, but
gill-slits and gill-bars can have no conceivable value for the chick as
organs concerned with the purification of the blood. None the less, if the
transition from a gilled tadpole to the adult with lungs means an
evolution of amphibia from fishlike ancestors, then the change of a chick
embryo with gill-clefts into the fledgling without them is most reasonably
interpreted as proof that birds as well as amphibia have had ancestors as
simple as fishes.

As development progresses four small pads make their appearance; two of
these lie on either side of the body back of the head and the other two
arise near the posterior end. They are far from being wings and legs, but
as day follows day they become molded into somewhat similar limbs, as much
alike in general plan as the four legs of a lizard; subsequently the ones
at the front change into real wings and the hinder ones become legs.
Meanwhile the internal organs slowly transform from fishlike structures
into things that display the characteristics of reptilian counterparts,
and only later do they become truly avian. Last of all the finishing
touches are made, and the whole creature becomes a particular kind of a
bird which picks its way out of the shell and shifts for itself as a
chick.

Only a few of the countless details have been mentioned which demonstrate
the resemblance of the successive stages first to fishes, and later to
amphibia and reptiles. We have a wide choice of materials, but even the
foregoing brief list of illustrations shows that the order in which the
stages follow is the one which comparative anatomy independently proves to
be the order of the evolution of fishes, amphibia, reptiles, and birds.
Why, now, should it be necessary for a developing bird to follow this
order? The answer has been found in the immense array of embryological
facts that investigators have verified and classified, that all tell the
same story. It is, that birds have arisen by evolution from ancestors
which were really as simple as the members of these lower classes. It
seems then that the only way a bird of to-day can become itself is to
traverse the path along which its progenitors had progressed in evolution.
Stating its conclusions precisely, science formulates the principle in the
following words: _individual development is a brief résumé of the history
of the species in past times_, or, more technically, _ontogeny
recapitulates phylogeny_. To be sure, the full history is not reviewed in
detail, for the chick embryo does not actually swim in water and breathe
by means of gills. Only a condensed account of evolution of its kind is
presented by an embryo during its development; as Huxley and Haeckel have
put it, whole lines and paragraphs and even pages are left out; many false
passages of a later date are inserted as the result of peculiar larval and
embryonic needs and adjustments. But in its major statements and as a
general outline, the account is a trustworthy natural document submitted
as evidence that higher species of to-day have evolved from ancestors
which must have been like some of the present lower animals.

Coming now to the mammalia, it might seem that we have reached forms so
highly developed that they would not exhibit the same kind of
developmental history, but would have their own mode of growing up. This
is not so, for like the adult fish, the larval tadpole, and the embryo
chick, an embryo of a cat or a man is at one time constructed with a
series of gill-clefts and with blood-vessels and skeletal supports of
fishlike nature that are everywhere associated with gills. The embryos of
wildcats and dogs, rabbits and rats, pigs, deer, and sheep, and of all
other mammalia, possess similar structures. Thus they all pass through a
stage which is found also in the development of reptiles, birds, and
amphibia,--a stage which corresponds to the fish throughout its life.
Unless these facts mean that the great classes of vertebrates have
originated together from the same or closely similar ancestors, they are
unintelligible; for we cannot see why a cat or a chick should have to be
essentially fishlike at any time unless this is so. Comparative anatomy
states as we have learned that the amphibia as a class have evolved from
and have out-developed the fishes, that reptiles have progressed still
higher, and that birds and mammals have originated from reptilian
ancestors along roads that have diverged beyond the immediate parent
class. Because the members of each class have to pass along the same path
trodden by their many varied ancestors, although at express speed, as it
were, the similarity of the earliest stages in their development is
explained, for during these periods they are traversing a path over which
their ancestors passed together.

The places where the developing embryos depart from the common mode show
where the several divisions took leave of one another in their
evolution,--a point that comes out with great clearness when the facts of
mammalian development are broadly compared. The embryos of carnivora and
rodents and hoofed animals are alike in their earlier development, and
their agreement means a community of origin. At a certain point the cat and
dog depart from the common mode, but they remain alike up to a far later
stage than the one in which they are similar to the embryos of rats and
sheep. The rat and squirrel and rabbit, on their part, remain together
until long after they take leave of the carnivora and ungulates; while the
sheep and cattle and pigs have their own branch line, which they follow in
company after leaving the embryos of the other orders. The reasons for
these facts seem to be that the members of the three orders exemplified
have evolved from the same stock, which accounts for their embryonic
similarity for a long time after they collectively come to differ from
amphibia and reptiles, while the members in each order became
differentiated only later, wherefore their embryonic paths coincide for a
longer period. Thus the degree of adult resemblance which indicates the
closeness of relationship corresponds with the degree of embryonic
agreement; that is, the cat and dog are much alike and their modes of
development are essentially the same to the latest stages, while the cat
and horse agree only during the earliest and middle stages, and their lines
diverge before those of the cat and dog on the one hand, or those of the
horse and pig on the other.

* * * * *

Like the fundamental principle of comparative anatomy in its sphere, the
Law of Recapitulation, formulated as a summary description of the
foregoing and similar facts, is one that holds true throughout the entire
range of embryology and for every division of the animal series, however
large or small. We have discussed its broader application, and now we may
take up some of the more or less special cases mentioned in the earlier
section of the present chapter, to see how it may work in detail.

The flounder was noted as a variant of the fish theme which seemed to be a
descendant of a symmetrical ancestor because its structural plan was like
that of other bony fishes. If this be true, and if in its development a
flounder must review its mode of evolution as a species, the young fish
ought to be symmetrical; and it actually is. The grotesque skate and
hammerhead shark were demonstrated to be derivatives of a simpler type of
shark; their embryos are practically indistinguishable from those of
ordinary dogfish and sharks.

Among the jointed animals a wealth of interesting material is found by the
embryologist. All crabs seemed to be modified lobsterlike creatures; to
confirm this interpretation, based solely upon details of adult structure,
young crabs pass through a stage when to all intents and purposes they are
counterparts of lobsters. Even the twisted hermit crab, which has a
soft-skinned hinder part coiled to fit the curve of the snail shell used as
a protection, is symmetrical and lobster-like when it is a larva.

Among the insects many examples occur that are already familiar to every
one. The egg of a common house-fly hatches into a larva called a maggot;
in this condition the body destined to become the vastly different fly is
composed of soft-skinned segments very much alike and also similar to the
joints of a worm. Comparative anatomy demonstrates that the fly and all
other insects have arisen from wormlike ancestors, whose originally
similar segments later differentiated in various ways to become the
diverse segments of adult insects; the embryonic history of flies of
to-day corroborates these assertions, in so far as every individual fly
actually does become a wormlike larva before it changes into the final and
complete adult insect. The other kinds of insects are equally striking in
their life-histories. All beetles, such as the potato bug and June bug,
develop from grubs which, like the maggots of flies, are similar to worms
in numerous respects. Butterflies and moths pass through a caterpillar
stage having even more striking resemblances to worms. All the larvæ of
insects are therefore like one another, and like worms also, in certain
fundamental characters of internal and external structure; so the
conclusion that the whole group of insects has arisen by evolution from
more primitive ancestors resembling the worms of to-day is based upon
mutually explanatory details of comparative anatomy and embryology.

* * * * *

Let us now turn back to some of the earlier pages of the embryological
record which we passed over in order that we might translate the later
portions dealing with more familiar and intelligible structures like
gills. Before the egg of the frog becomes an elliptical mass of cells, it
is at one time a double-walled sac enclosing a central cavity; in this
stage it is called a _gastrula_. Tracing back the mode of its formation,
we find that it is produced from a hollow sphere of fewer cells that are
essentially alike; this stage also is so important that the special term
_blastula_ is applied to it. Still earlier, there are fewer cells--128 or
thereabouts, 64, 32, 16, 8, 4, 2, and 1. In other words, the starting
point in the development of the frog is a _single biological unit_; this
divides and its products redivide to constitute the many-celled blastula
and the double-walled gastrula. All the other animals we have mentioned
begin like the frog, as eggs which are single cells and nothing more; they
too pass on to become blastulæ and gastrulæ, similar to those of the frog
in all essential respects, particularly as regards the nature of the
organs produced by each of the two primary layers, and the mode of their
formation. Does the occurrence of blastulæ and gastrulæ and one-celled
beginnings mean that the higher animals composed of numerous and much
differentiated cells have evolved in company from two-layered saccular
ancestors which were themselves the descendants of spherical colonies of
like cells, and ultimately of one-celled animals?

Comparative anatomy has asserted that this is so, as we have already
learned, for it finds that adult animals array themselves at different
levels of a scale beginning at the bottom with the protozoa, continuing on
to the two-layered animals like _Hydra_ and jellyfish and sea-anemones,
and then extending upwards to the region of the more complicated
invertebrates and vertebrates. It was difficult perhaps to believe that
these successive grades of organic structure indicated an order of
evolution, because it seemed impossible that an animal so simple as a
protozoan could produce offspring with the complex organization of a frog
or a cat, even in long ages. But development delivers its evidence
relating to this matter with telling and impressive force. How can we
doubt the possibility of an evolution of higher animals from ancestors as
simple as _Hydra_ and _Amoeba_ when a frog and a cat, like all other
complicated organisms, begin individual existence as single cells, and
pass through gastrula stages? If we deny it, we contradict the evidence of
our senses, for the development is actually accomplished by the
transformation of a single cell into a double-walled sac, and of this into
different and more intricate organic mechanisms. The process _can_ take
place, for it _does_ take place. Not until the investigator becomes
familiar with a wide range of diverse animals and the peculiar qualities
of their similar early stages, can he estimate the tremendous weight of
the facts of comparative embryology. Were the statement iterated and
reiterated on every page and in every paragraph, there would be no undue
emphasis put upon the astounding fact that the apparently impassable gap
between a one-celled animal like _Amoeba_ and a mammal like a cat is
actually compassed during the development of the last-named organisms from
single cells. The occurrence of gill-slits in the embryos of lizards,
birds, and mammals now seems a small thing when compared with the
correspondences disclosed by the earliest stages of development. But in
spite of their complexity, all the changes of "growing up" are explained
and understood by the simple formula that the mode of individual
development owes its nature primarily to the hereditary influence of
earlier ancestors back to the original animals which were protozoa.

* * * * *

Embryology as a distinct division of zoölogy has grown out of studies of
classification and comparative anatomy. Its beginnings may be found in
medieval natural history, for as far back as 1651 Harvey had pointed out
that all living things originate from somewhat similar germs, the terse
dictum being "Ex ovo omnia." By the end of the eighteenth century many had
turned to the study of developing organisms, though their views by no
means agreed as to the way an adult was related to the egg. Some, like
Bonnet, held that the germ was a minute and complete replica of its
parent, which simply unfolded and enlarged like a bud to produce a similar
organism. Even if this were true, little would be gained, for it would
still remain unknown how the germinal miniature originated to be just what
it was conceived and assumed to be. Wolff was the originator of the view
that is now practically universal among naturalists, namely, that
development is a real process of transformation from simpler to more
complex conditions.

The subject of comparative embryology grew rapidly during the nineteenth
century as the field of comparative anatomy became better known, and when
naturalists became interested in animals, not only as specific types, but
also as the finished products of an intricate series of transformations.
When life-histories were more closely compared, the meaning of the
resemblances between early stages of diverse adult organisms was read by
the same method which in comparative anatomy finds that consanguinity is
expressed by resemblance. The great law of recapitulation, stated in one
form by Von Baer and more definitely by Haeckel in the terms employed in
the foregoing sections, was for a time too freely used and too rigidly
applied by naturalists whose enthusiasm clouded their judgment. A strong
reaction set in during the latter part of the nineteenth century, when
attention was directed to the anachronisms of the embryonic record and to
the alterations that are the results of larval or embryonic adaptation as
short cuts in development. Nevertheless, it is not seriously questioned, I
believe, that the main facts of a single life-history owe their nature to
the past evolution of the species to which a given animal belongs.

Nowadays the problems in this well-organized department are concerned not
only with more accurate accounts of the development of animals, but also
with the mechanics of development, with the relative value of external and
internal influences, and above all with the physical basis of inheritance.
It is clear that the factors that direct the development of a wood frog's
egg so that it becomes a wood-frog and not a tree-toad must lie in the egg
itself, as derivatives from the two parent organisms. Weismann and his
followers have proved that a peculiar substance in the nuclei of the egg
and its daughter-products contains the essential factors of development,
whatever these may be. Experiments dealing with the phenomena of heredity
in pure and mixed breeds have largely confirmed Weismann's doctrine, and
they have prepared the way for a deeper investigation of the marvelous
process of biological inheritance.

However much he may be interested in the details of embryological science,
the general student of natural history is more concerned with the bearing
of its primary laws upon the great problem of evolution. In the foregoing
brief review of the fundamental facts and principles of this subject, the
purpose has been to show how the phenomena of development are viewed by
men of science, and how they take their place in the doctrine of organic
evolution. And it has also been made plain that comparative anatomy and
comparative embryology support and supplement one another in countless
ways and places, although each in itself is a complete demonstration that
evolution is a real and a natural process.

III

THE EVIDENCE OF FOSSIL REMAINS

Few natural objects appeal to the interest and imagination of the student
with more force than the fragments of animals and plants released from the
rocks where they have been entombed for ages. Our lives are so brief that
it is impossible for us to comprehend the full duration of the slow
process which constructed the burial shrouds of these creatures of long
ago. We try to picture the earth and its inhabitants as they were when
lizards were the highest forms of animals, and we wonder how life was
lived in the dense forests of the coal age. Science can never learn all
about the ancient history of the earth and of the organisms of bygone
times; yet it has been able to accomplish much through its endeavors to
reconstruct the past, for its method is one by which sure results can
always be obtained whenever there are definite facts with which it can
work. In our present study of evolution we reach the point when we must
examine the testimony of the rocks, and the results and methods of that
department of knowledge called palæontology, which is concerned with
fossils and their interpretation.

The word "palæontology" means literally the "science of living things of
long ago." It deals directly with the remains of animals and plants found
as fossils, and it interprets them through its knowledge of the way modern
animals are constructed and of the changes the earth's crust has
undergone. A skull-like object may be found in a coal field and may come
into the hands of the palæontologist: from his acquaintance with the head
skeletons of recent types he will be able to assign the extinct creature
which possessed the skull to a definite place in the animal scale and to
understand its nearer or wider affinities with other animals of later
times and of earlier epochs. In doing these things palæontology employs
the methods of comparative anatomy with which we have now become familiar.
In the performance of its other tasks, however, palæontology must work
independently. It is necessary to know when a fossilized animal lived, not
that its time need be measured by an absolute number of a few thousands or
millions of years antedating our own era, for that is impossible. But the
important thing is to know its relative age, and whether it preceded or
followed other similar animals of its own group or of different divisions.
The rocks themselves must be understood, how they have been formed and how
they are related in mineralogical nature and in historical succession.
Palæontology also deals with a number of subjects that are not in
themselves biological, such as the combination of circumstances necessary
for the adequate preservation of fossil relics. In so far as it is
concerned with physical matters, as contrasted with strictly biological
data, it is one with geology. Indeed, the investigators in these two
departments must always work side by side and render mutual assistance to
one another in countless ways, for each division needs the results of the
other in order to accomplish its own distinct purposes. It must be evident
to every one that it is impossible to understand the meaning of fossils
and the place of the testimony of the rocks in the doctrine of evolution
without knowing much about the geological history of the earth and the
influences at work in the past. For these reasons palæontology differs
somewhat from the other divisions of zoölogy where direct observation
gives the materials for arrangement and study; in this case the individual
data, that is, the fossil fragments themselves, can be made available only
through a knowledge of their exact situations, of the reasons for their
occurrence in particular places in the rock series and of the way rocks
themselves are constructed and worked over by natural agencies. Our task
is therefore twofold: certain physical matters of a geological nature must
first be investigated before the biological facts can be described.

No doubt most people feel justified in believing that the whole doctrine
of evolution must stand or fall according to the cogency of the
palæontological evidences. Plain common sense says that the owners of
shelly or bony fragments found in the deeply-laid strata of the earth must
have lived countless years ago, and if the evolutionist asserts that
primitive organic forms of ancient times have produced changed descendants
of later times, it would seem that fossil evidence would be supremely and
overwhelmingly important. It is true, of course, that this evidence is
peculiarly significant, because in some ways it is more direct than that
of the other categories already outlined. But it must not be forgotten
that the doctrine is already securely founded upon the basic principles of
anatomy and embryology. Science must treat the data of this category by
different methods and must view them in different ways. Therefore we are
interested in palæontology because of the way it tells the story of
evolution in its own words, and because we are justified in expecting that
its account should include a description of some such order of events as
that revealed by the developing embryos of modern organisms and that
demonstrated by the comparative anatomy of the varied species of adult
animals.

It is true that palæontology gives direct testimony about the evolutionary
succession of animals in geologic time. But we now know that embryology is
even more direct in its proof that organic transformation is natural and
real; while at the same time there is a completeness in the full series of
developmental stages connecting the one-celled egg with the adult creature
that must be forever lacking in the case of the fossil sequence of
species. If paragraphs and pages are missing from the brief embryonic
recapitulation, whole chapters and volumes of the fossil series have been
lost for all time. The investigators whose task it has been to decipher
the story of the earth's evolution have had to meet numerous and
exasperating difficulties which do not confront the embryologist and
anatomist who study living materials. Nevertheless the library of
palæontological documents is one which has been founded for over a
century, and it has grown fast during recent decades, so that consistent
accounts may now be read of the great changes in organic life as the earth
has altered and grown older. And in all this record, there is not a single
line or word of fact that contradicts evolution. What definite evidence
there is tells uniformly in favor of the doctrine, for it is possible, in
the first place, to work out the order of succession of many of the great
groups of animals, and this order is found to be the same as that
established by the other bodies of evidence. Secondly, some fossil groups
are astonishingly complete, so that the ancient history of a form like the
horse can be written with something approaching fullness. Finally, the
remains of certain animals have been found so situated in geological ways,
and so constructed anatomically, that the zoölogist is justified in
denoting them "missing links," because they seem to have been intermediate
between groups that have diverged so widely during recent epochs as to
render their common ancestry scarcely credible.

With these general results in mind, we must now become acquainted with
such subjects as the interpretation of fossils, the causes for the
incompleteness of the series, the conditions for fossilization, the forces
of geological nature, and other matters that make the fossils themselves
intelligible as scientific evidence.

* * * * *

Many views have been entertained regarding the actual nature of the relics
of antiquity exhumed from the rocks or exposed upon the surface by the
wear and tear of natural agencies. In earliest times such things were
variously considered as curious freaks of geological formation, as sports
of nature, or as the remains of the slain left upon the battle-ground of
mythical Titans. Some of the Greeks supposed that fossils were parts of
animals formed in the bowels of the earth by a process of spontaneous
generation, which had died before they could make their way to the
surface. They were sometimes described as the bones of creatures stranded
upon the dry land by tidal waves, or by some such catastrophe as the
traditional flood of the scriptures. In medieval times, and even in our
own day, some people who have been opposed to the acceptance of any
portion of the doctrine of evolution have actually defended the view that
the things called fossils were never the shells or bones of animals living
in bygone times, but that they only simulate such things and have been
created as such together with the layers of rock from which they may have
been taken. If we employed the same arguments in dealing with the broken
fragments of vases and jewelry taken from the Egyptian tombs or from the
buried ruins of Pompeii, we would have to believe that such pieces were
created as fragments and that they were never portions of complete
objects, just because no one alive to-day has ever seen the perfect vessel
or bracelet fashioned so long ago. Common sense directs us to discard such
a fantastic interpretation in favor of the view that fossils are what they
seem to be--simply relics of creatures that lived when the earth was
younger.

Until this common sense view was adopted there was no science of
palæontology. Cuvier was the first great naturalist to devote particular
attention to the mainly unrelated and unverified facts that had been
discovered before his time. He was truly the originator of this branch of
zoölogy, for he brought together the observations of earlier men and
extended his own studies widely and surely, emphasizing particularly the
necessity for noting carefully the geological situation of a fossil in
rocks of an older or later period of formation. His great result was the
demonstration that many groups of animals existed in earlier ages that
seem to have no descendants of the same nature to-day, and also that many
or most of our modern groups are not represented in the earliest formed
sedimentary rocks, although these recent forms possess hard parts which
would surely be present somewhere in these levels if the animals actually
existed in those times. But the meaning of these facts escaped Cuvier's
mind. He was a believer in special creation, like Linnæus and all but a
few among his predecessors, and he explained the diversity of the faunas
of different geological times in what seems to us a very simple and naïve
way. In the beginning, he held, when the world was created, it was
furnished with a complete set of animals and plants. Then some great
upheaval of nature occurred which overwhelmed and destroyed all living
creatures. The Creator then, in Cuvier's view, proceeded to construct a
new series of animals and plants, which were not identical with those of
the former time, but were created according to the same general working
plans or architectural schemes employed before. Another cataclysm was
supposed to have occurred, which destroyed the second series of organisms
and laid a new covering of rocks over the earth's surface for a subsequent
period of relative quiet; and so the process was continued. By this
account, Cuvier endeavored to reconcile the doctrine of supernatural
creation and intervention with the obvious facts that organisms have
differed at various times in the earth's history. Although he saw that
animals of successive periods displayed similar structures, like the
skeleton of vertebrates, which testified to some connection, Cuvier could
not bring himself to believe that this connection was a genealogical one.

Mainly through the influence of the renowned English man of science,
Charles Lyell, the students of the earth came to the conclusion that its
manifold structures had developed by a slow and orderly process that was
entirely natural; for they found no evidence of any sudden and drastic
world-wide remodeling such as that postulated by the Cuvierian hypothesis
of catastrophe. The battle waged for many years; but now naturalists
believe that the forces, of nature, whose workings may be seen on all
sides at the present time, have reconstructed the continents and ocean
beds in the past in the same way that they work to-day. The long name of
"uniformitarianism" is given to Lyell's doctrine, which has exerted an
influence upon knowledge far outside the department of geology. Darwin
tells us how much he himself was impressed by it, and how it led him to
study the factors at work upon organic things to see if he could discern
evidence of a biological uniformitarianism, according to which the past
history of living things might be interpreted through an understanding of
their present lives.

* * * * *

What, now, are the reasons why the palæontological evidence is not
complete and why it cannot be? In the first place the seeker after fossil
remains finds about three fifths of the earth's surface under water so
that he cannot explore vast areas of the present ocean beds which were
formerly dry land and the homes of now extinct animals. Thus the field of
investigation is seriously restricted at the outset, but the naturalist
finds his work still more limited, in so far as much of the dry land
itself is not accessible. The perennial snows of the Arctic region render
it impossible to make a thorough search in the frigid zone, and there are
many portions of the temperate and torrid zones that are equally
unapproachable for other reasons. But even where exploration is possible,
the surface rocks are the only ones from which remains can be readily
obtained, for the layers formed in earlier ages are buried so deeply that
their contents must remain forever unknown in their entirety. Only a few
scratches upon the earth's hard crust have been made here and there, so it
is small wonder that the complete series of extinct organisms has not been
produced by the palæontologist.

A brief survey of the varied groups of animals themselves is sufficient to
bring to light many biological reasons which account for still more of the
vacant spaces in the palæontological record. We would hardly expect to
find remains of ancient microscopic animals like the protozoa, unless they
possessed shells or other skeletal structures which in their aggregate
might form masses like the chalk beds of Europe. Jellyfish and worms and
naked mollusks are examples of the numerous orders of lower animals having
no hard parts to be preserved, and so all or nearly all of the extinct
species belonging to these groups can never be known. But when an animal
like a clam dies its shell can resist the disintegrating effects of
bacteria and other organic and inorganic agencies which destroy the soft
parts, and when a form like a lobster or a crab, possessing a body
protected by closely joined shell segments, falls to the bottom of the
sea, the chances are that much of the animal's skeleton will be preserved.
Thus it is that corals, crustacea, insects, mollusks, and a few other
kinds of lower forms constitute the greater mass of invertebrate
palæontological materials because of their supporting structures of one
kind or another. Perhaps the skeletal remains of the vertebrates of the
past provide the student of fossils with his best facts, on account of the
resistant nature of the bones themselves, and because the backboned
animals are relatively modern; then, too, the rocks in which their remains
occur have not been so much altered by geological agencies, or buried so
deeply under the strata formed later. Of course only the hardest kinds of
shells would remain as such after their burial in materials destined to
turn into rock; in the majority of cases, an entombed bone is infiltrated
or replaced by various mineral substances so that in time little or
nothing of the original thing would remain, though a mold or a cast would
persist.

But even if an animal of the past possessed hard structures, it must have
satisfied certain limited conditions to have its remains prove serviceable
to students of to-day. A dead mammal must fall upon ground that has just
the right consistency to receive it; if the soil is too soft, its several
parts will be separated and scattered as readily as though it had fallen
upon hard ground where it would be torn to pieces by carnivorous animals.
The dead body must then be covered up by a blanket of silt or sand like
that which would be deposited as the result of a freshet. If a skeleton is
too greatly broken up or scattered, it may be difficult or even impossible
for its discoverer to piece together the various fragments and assemble
them in their original relations. Very few individuals have been so buried
and preserved as to meet the conditions for the formation of an ideal
fossil. To realize how little may be left of even the most abundant of
higher organisms, we have only to recall that less than a century ago
immense herds of bison and wild horses roamed the Western plains, but very
few of their skulls or other bones remain to be enclosed and fossilized in
future strata of rocks. When we appreciate all these difficulties, both
geological and biological, we begin to see clearly why the ancient lines
of descent cannot be known as we know the path and mode of embryonic
transformation. The wonder is not that the palæontological record is
incomplete, but that there is any coherent and decipherable record at all.
Yet in view of the many and varied obstacles that must be surmounted by
the investigator, and the adverse factors which reduce the available
evidence, the rapidly growing body of palæontological facts is amply
sufficient for the naturalist to use in formulating definite and
conclusive principles of evolution.

* * * * *

For the purposes of palæontology, the most essential data of geology are
those which indicate the relative ages of the strata that make up the hard
outer crust of the earth, for only through them can the order of animal
succession be ascertained. It does not matter exactly how old the earth
may be. While it is possible to determine the approximate length of time
required for the construction of sedimentary rocks like those which
natural agencies are producing to-day, there are few definite facts to
guide speculation as to the mode or duration of the process by which the
first hard crystalline surface of the earth was formed. But palæontology
does not care so much about the earliest geological happenings, for it is
concerned with the manifold animal forms that arose and evolved after life
appeared on the globe. Questions as to the way life arose, and as to the
earliest transformations of the materials by which the earth was first
formed are not within the scope of organic evolution, although they relate
to intensely interesting problems for the student of the process of cosmic
evolution.

According to the account now generally accepted, the original material of
the earth seems to have been a semi-solid or semi-fluid mass formed by the
condensation of the still more fluid or even gaseous nebula out of which
all the planets of the solar system have been formed and of which the sun
is the still fiery core. As soon as the earth had cooled sufficiently its
substances crystallized and wrinkled to form the first mountains and
ridges; between and among these were the basins which soon filled with the
condensing waters to become the earliest lakes and oceans. The wear and
tear of rains and snows and winds so worked upon the surfaces of the
higher regions that sediments of a finer or coarser character like sand
and mud and gravel were washed down into the lower levels. These sediments
were afterwards converted into the first rocks of the so-called stratified
or sedimentary series, as contrasted with the crystalline or plutonic
rocks like the original mass of the earth and the kinds forced to the
surface by volcanic eruptions. Later the earth wrinkled again in various
ways and places so that new ridges and mountains were formed with new
systems of lakes and oceans and rivers; and again the elements continued
to erode and partially destroy the higher masses and to lay down new and
later series of sedimentary rocks upon the old.

It seems scarcely credible that the apparently weak forces of nature like
those we have mentioned are sufficiently powerful to work over the massive
crust of the earth as geology says they have. Our attention is caught, as
a rule, only by the greater things, like the earthquakes at San Francisco
and Valparaiso, and the tidal waves and cyclones of the South Seas; but
the results of these sporadic and local cataclysms are far less than the
effects of the persistent everyday forces of erosion, each one of which
seems so small and futile. When we look at the Rocky Mountains with their
high and rugged peaks, it seems almost impossible that rain and frost and
snow could ever break them up and wear them down so that they would become
like the rounded hills of the Appalachian Mountain chain, yet this is what
will happen unless nature's ways suddenly change to something which they
are not now. A visitor to the Grand Cañon of the Colorado sees a
magnificent chasm over a mile in depth and two hundred miles long which
has actually been carved through layer after layer of solid rock by the
rushing torrents of the river. Perhaps it is easier to estimate the
geological effects of a river in such a case as Niagara. Here we find a
deep gorge below the famous falls, which runs for twenty miles or so to
open out into Lake Ontario. The water passing over the brim of the falls
wears away the edge at a rate which varies somewhat according to the
harder or softer consistency of the rocks, but which, since 1843, has
averaged about 104 inches a year. Knowing this rate, the length of the
gorge, and the character of the rocky walls already carved out, the length
of time necessary for its production can be safely estimated. It is about
30,000 to 40,000 years, not a long period when the whole history of the
earth is taken into account. A similar length of time is indicated for the
recession of the Falls of St. Anthony, of the Mississippi River, an
agreement that is of much interest, for it proves that the two rivers
began to make their respective cuttings when the great ice-sheet receded
to the north at the end of the Glacial epoch.

What has become of the masses washed away during the formation of these
gorges? As gravel and mud and silt the detritus has been carried to the
still waters of the lower levels, to be laid down and later solidified
into sandstone and slate and shale. All over the continents these things
are going on, and indefatigable forces are at work that slowly but surely
shear from the surface almost immeasurable quantities of earth and rock to
be transported far away. In some instances it is possible to find out just
how much effect is produced in a given period of time, especially in the
case of the great river systems. For example, the mass of the fine
particles of mud and silt carried in a given quantity of the water of the
Mississippi as it passes New Orleans can be accurately measured, and a
satisfactory determination can also be made of the total amount of water
carried by in a year. From these figures the amount of materials in
suspension discharged into the Gulf of Mexico becomes known. It is
sufficient to cover one square mile to the depth of 269 feet; in twenty
years it is one cubic mile, or five cubic miles in a century. Turning now
to the other aspect of this process, and the antecedent causes which
produce these effects, it appears that the area of the Mississippi River
basin is 1,147,000 square miles--about one third of the total area of the
United States. Knowing this, and the annual waste from its surface, it is
easy to demonstrate that it will take 6000 years to plane off an average
of one foot of soil and rock from the whole of this immense area. Of
course only an inch or a few inches will be taken from some regions where
the ground is harder or rockier, or where little rain falls, while many
feet will be washed away from other places. The waters of the Hoang-ho
come from about 700,000 square miles of country, from which one foot of
soil is washed away in 1464 years. The Ganges River, draining about
143,000 square miles, carries off a similar depth of eroded materials from
its basin in 823 years! Should we add to the above figures those that
specify the bulk of the chemical substances in solution carried by these
waters, the total would be even greater. We know that in the case of the
Thames River, calcareous substances to the amount of 10,000 tons a year
are carried past London, and all this mineral has been dissolved by
rain-water from the chalky cliffs and uplands of England, so that the land
has become less by this amount. Thus we learn that vast alterations are
being made in the structure of great continents by rain and rivers, as well
as by glaciers and other geological agencies. And at the same time that old
strata are undergoing destruction new ones are in process of construction
at other places, where animal remains can be embedded and preserved as
fossils. The forces at work seem weak, but they continue their operations
through ages that are beyond our comprehension and they accomplish results
of world-building magnitude.

Thus the whole process of geological construction is such that older
exposed strata continually undergo disintegration, but this involves the
destruction of any fossils that they might contain. The very forces that
preserve the relics of extinct animals at one time undo their work at a
later period. There are many other influences besides that destroy the
regularity of rock layers or change their mineralogical characters by
metamorphosis. It is easier to see how volcanic outbursts alter their
neighboring territory. The intense subterranean heat and imprisoned steam
melt the deeper substances of the earth's crust, so that these materials
boil out, as it were, where the pressure is greatest, and where lines of
fracture and lesser resistance can be found. Because so much detritus is
annually added to the ocean floors--enough to raise the levels of the
oceans by inches in a century--it is natural that greater pressures should
be exerted in these areas than in the slowly thinning continental regions.
These are some of the reasons why volcanoes arise almost invariably along
the shores or from the floors of great ocean beds. The chain that extends
from Alaska to Chili within the eastern shore of the Pacific Ocean, and
the many hundreds of volcanoes of the Pacific Islands bring to the surface
vast quantities of eruptive rocks which break up and overlie the
sedimentary strata formed regularly in other ways and at other times. The
volcanoes of the Java region alone have thrown out at least 100 cubic
miles of lava, cinders, and ashes during the last 100 years--twenty times
the bulk of the materials discharged into the Gulf of Mexico by the
Mississippi River in the same period of time.

From these and similar facts, the naturalist finds how agencies of the
present construct new rocks and alter the old; and so in the light of this
knowledge, he proceeds with his task of analyzing the remote past,
confident that the same natural forces have done the work of constructing
the lower geological levels because these earlier products are similar to
those being formed to-day. After learning this much, he must immediately
undertake to arrange the strata according to their ages. This might seem a
difficult or even an impossible task, but the rocks themselves provide him
with sure guidance.

Wherever a river has graven its deep way through an area of hard rocks, as
in the case of Niagara, the walls display on their cut surfaces a series
of lines and planes showing that they are superimposed layers formed
serially by deposits that have differed some or much at different times
according to the circumstances controlling the erosion of their
constituent particles. A layer of several feet in thickness may be
composed of compact shale, while above it will be a zone of limestone, and
again above this another layer of shale. Successive strata like these,
where they are parallel and obviously undisturbed, are evidently arranged
in the order of their formation and age. But by far the most impressive
demonstration of the basic principle of geology employed for the
determination of the relative ages of rocks is the mighty Cañon of the
Colorado. As the traveler stands on the winding rim of this vast chasm,
his eye ranges across 13 miles of space to the opposite walls, which
stretch for scores of miles to the right and left; upon this serried face
he will see zone after zone of yellow and red and gray rock arranged with
mathematical precision and level in the same order as on the steep slopes
beneath him. Plain common sense tells him that the great sheets of rock
stretched continuously at one time between the now separate walls, and
that the various strata of sandstone and limestone were deposited in
successive ages from below upwards in the order of their exposure. When
now he extends his explorations to another state like Utah or Wyoming, he
may find some but not all of the series exhibited in the Grand Cañon,
overlaid or underlaid by other strata which in their turn can be assigned
to definite places in the sequence. By the same method, the geologist
correlates and arranges the rocks not only of different parts of the same
state, or of neighboring states, but even those of widely separated parts
of North America and of different continents. But he learns that he must
refrain from over-hasty conclusions, for he soon finds that the
sedimentary rocks have not been constructed at the same rate in different
places during one and the same epoch, and that rocks formed even at one
period are not always identical in nature. But his guiding principle is
sensible and reasonable, and by employing it with due caution he provides
the palæontologist with the requisite knowledge for his special task,
which is to arrange the extinct animals whose remains are found as fossils
of various earth ages in the order of their succession in time.

CONDENSED TABLE OF PALAEONTOLOGICAL FACTS

__________________________________________________________________________
| | | |
YEARS | NUMBER OF | | | ORDER OF
NECESSARY FOR | FEET IN | GEOLOGICAL | GEOLOGICAL | APPEARANCE OF
FORMATION | THICKNESS | AGE | EPOCH | CHARACTERISTIC
| | | | GROUPS
______________|___________|______________|_______________|________________
| | | |
| | | | M B R A F I
| | | | a i e m i n b
| | | | m r p p s v r
| | Recent | | m d t h h e a
| | or | | a s i i e r t
| | Quaternary | | l l b s t e
| | | | s e i e s
| | | | s a -
______________|___________|______________|_______________|_|_|_|_|_|_|____
| | | | | | | | | |
| | | Pleistocene | | | | | | |
| | Cenozoic | Pliocene | | | | | | |
5,000,000 | 25,000 | or | Miocene | | | | | | |
| | Tertiary | Oligocene | | | | | | |
| | | Eocene | | | | | | |
______________|___________|______________|_______________|_|_|_|_|_|_|____
| | | | | | | | | |
| | Mesozoic | Cretaceous | | | | | | |
4,000,000 | 23,000 | or | Jurassic | | | | | | |
| | Secondary | Triassic | | | | | |
______________|___________|______________|_______________|_____|_|_|_|____
| | | | | | | |
| | | Permian | | | | |
| | Palæozoic | Carboniferous | | | |
21,000,000 | 106,000 | or | Devonian | | |
| | Primary | Silurian | | |
| | | Cambrian | | |
______________|___________|______________|_______________|________________
| | | |
20,000,000 | 30,000 | Azoic | Archæn |
______________|___________|______________|_______________|________________

After what seems an unduly long preparation, we now come to the actual
biological evidence of evolution provided by the results of this division
of zoölogical science. But all of the foregoing is fundamentally part of
this department of knowledge and it is absolutely essential for any one
who desires to understand what the fossils themselves demonstrate.

The oldest sedimentary rocks are devoid of fossil remains and so they are
called the Azoic or Archæan. They comprise about 30,000 feet of strata
which seem to have required at least 20,000,000 years for their formation.
This period is roughly two-fifths of the whole time necessary for the
formation of _all_ the sedimentary rocks, and this proportion holds true
even if the entire period of years should be taken as 100,000,000 instead
of 50,000,000 or less. The earth during this early age was slowly
organizing in chemical and physical respects so that living matter could
be and indeed was formed out of antecedent substances--but this process
does not concern us here. The important fact is that the second major
period, called the Palæozoic, or "age of ancient animals," saw the
evolution of the lowest members of the series,--the invertebrates,--and
the most primitive of the backboned animals, like fishes and amphibia. The
rocks of this long age include about 106,000 feet of strata, demanding
some 21,000,000 or 22,000,000 years for their deposition. Thus it is
proved that the invertebrate animals were succeeded in time by the higher
vertebrates, which is exactly what the evidences of the previous
categories have shown. When we remember that the lower animals are devoid
as a rule of skeletal structures that might be fossilized, and when we
recall the fact that the strata of the palæozoic provided the materials
out of which the upper layers were formed afterwards, we can understand
why the ancient members of the invertebrate groups are not known as well
as the later and higher forms like vertebrates. Yet all the fossils of
these relatively unfamiliar creatures clearly prove that no complex animal
appears upon a geological horizon until after some simple type belonging
to a class from which it may have taken its origin; in brief, there are no
anachronisms in the record, which always corresponds with the record
written by comparative anatomy, wherever the facts enable a comparison to
be made.

But the extinct animals of the third and fourth ages are more interesting
to us, because there are more of them and because they are more like the
well-known organisms of our present era. These two ages are called the
Mesozoic or Secondary, and the Cenozoic or Tertiary. The former is so
named because it was a transitional age of animals that are intermediate
in a general way between the primitive forms of the preceding age and
those of the next period; the latter name means the "recent-animal" age,
when evolution produced not only the larger groups of our present animal
series, but also many of the smaller branches of the genealogical tree
like orders and families to which the species of to-day belong.

Confining our attention to the large vertebrate classes, the testimony of
the rocks proves, as we have said, that fishes appeared first in what are
called the Silurian and Devonian epochs, where they developed into a rich
and varied array of types unequaled in modern times. At that period, they
were the highest existing animals--the "lords of creation," as it were. To
change the figure, their branch constituted the top of the animal tree of
the time, but as other branches grew upwards to bear their twigs and
leaves, as the counterparts of species, the species of the branch of
fishes decreased in number and variety, as do the leaves of a lower part
of a tree when higher limbs grow to overshadow them.

Following the fishes, the amphibia arose during the coal age or
Carboniferous, usurping the proud position of the lower vertebrate class.
The reptiles then appeared and gained ascendancy over the amphibia, to
become in the Mesozoic age the highest and most varied of the existing
vertebrates. At that time there were the great land dinosaurs with a
length of 80 feet, like _Brontosaurus_; aquatic forms like _Ichthyosaurus_
and _Plesiosaurus_, whose mode of evolution from terrestrial to swimming
habits was like that of seals and penguins of far later eras. Flying
reptiles also evolved, to set an example for the bats of the mammalian
class, for both kinds of flying organisms converted their anterior limbs
into wings, although in different ways.

During the Triassic and Jurassic periods of the Mesozoic age, the first
birds and mammals appeared to follow out their diverging and independent
lines of descent. Palæontology makes it possible to trace the origin and
development of many of the different branches that grew out of the
mammalian limb from different places and at different times during the
Mesozoic and the following age, called the Cenozoic, or age of recent
animals. It is unnecessary, however, for us to review more of the details:
the main result is obvious; namely, that the appearance of the great
classes of vertebrates is in the order of comparative anatomy and
embryology. Not only, then, is the fact of evolution rendered trebly sure,
but the general order of events is thrice and independently demonstrated
to be one and the same. Surely we must see that no reasonable explanation
other than evolution can be given for these basic facts and principles.

Turning now to the second division of palæontological evidence, we come to
those groups where abundant materials make it possible to arrange the
animals of successive epochs in series that may be remarkably complete.
For the reasons specified, the backboned animals provide the richest
arrays of these series, and such histories as those of horses and
elephants have taken their places in zoölogical science as classics. But
even among the invertebrates significant cases may be found. For example,
in one restricted locality in Germany the shells of snails belonging to
the genus _Paludina_ have been found in superimposed strata in the order
of their geological sequence. The ample material shows how the several
species altered from age to age by the addition of knobs and ridges to the
surface of the shell, until the fossils in the latest rocks are far
different from their ancestors in the lowermost levels. Yet the
intervening shells fill in the gaps in such a way as to show almost
perfectly how the animals worked out their evolutionary history. This
example illustrates the nature of many other known series of mollusks and
of brachiopods, extending over longer intervals and connecting more widely
separated ages like the Secondary and the present period.

Since the doctrine of evolution and its evidences began to occupy the
thoughts of the intellectual world at large, no fossil forms have received
more attention than the ancient members of the horse tribe. As we have
learned, a modern horse is described by comparative anatomy as a one-toed
descendant of remote five-toed ancestors. When the hoofed animals of
modern times were reviewed as subjects for comparative anatomical study,
the odd-toed forms arranged themselves in a series beginning with an
animal like an elephant with the full number of five digits on each foot
and ending at the opposite extreme with the horse. A reasonable
interpretation of these facts was that the animals with fewer toes had
evolved from ancestors with five digits, of which the outer ones had
progressively disappeared during successive geological periods, while the
middle one enlarged correspondingly. The facts provided by palæontology
sustain this contention with absolutely independent testimony.
Disregarding some problematical five-toed forms like _Phenacodus_, the
first type of undoubted relationship to modern horses is _Hyracotherium_,
a little animal about three feet long that lived during the Eocene period
of the Cenozoic epoch. Its forefeet had four toes each, and its hinder
limbs ended with three toes armed with small hoofs, but one of its
relatives of the same time has a vestige of another digit on the hind
foot. By the geological time mentioned, therefore, the earliest true
horses had already lost some of the toes that their progenitors possessed.
In the Miocene the extinct species, obviously descended from the Eocene
forms, had lost more of their toes; still higher, that is, in the rocks
formed during succeeding periods of time, the animals of this division are
much larger and each of their feet has only three toes, of which the
middle one is the largest while the ones on the sides are small and
withdrawn from the ground so as to appear as useless vestiges. To produce
modern horses and zebras from these nearer ancestors, few additional
changes in the structure of the feet are necessary, for the lateral toes
need only to become a little more reduced and the middle one to enlarge
slightly to give the one-toed limb of modern types, with its splint-like
vestiges still in evidence to show that the ancestor's foot comprised more
of these terminal elements. Comparing the animals of successive periods,
these and other skeletal structures demonstrate that the ancestry of each
group of species is to be found in the animals of the preceding epoch, and
that the whole history of horses is one of natural transformation,--in a
word, of evolution.

No less interesting in their own way are the remains of other hoofed forms
that lead down to the elephants of to-day and to the mammoth and mastodon
of relatively recent geologic times. Common sense would lead to the
conclusion that a form like a modern tapir was the prototype from which
these creatures have arisen, and common sense would lead us to expect that
if any fossils of the ancestors of the modern group of elephants occurred
at all they would be like tapirs. Thus a fossil of much significance in
this connection is _Moeritherium_, whose remains have been found in the
rocks exposed in the Libyan desert, for this creature was practically a
tapir, while at the same time its characters of muzzle and tusk mark it as
very close to the ancestors of the larger woolly elephants of later
geological times, when the trunk had grown considerably and the tusks had
become greatly prolonged. Again the fossil sequence confirms the
conclusions of comparative anatomy, regarding the mode by which certain
modern animals have evolved.

The fossil deer of North America, as well as many other even-toed members
of the group of mammalia possessing hoofs, provide the same kind of
conclusive evidence. The feature of particular interest in the case of
their horns, is a correspondence between the fossil sequence and the order
of events in the life-history of existing species,--that is, between the
results of palæontology and of embryology. Horns of the earliest known
fossil deer have only two prongs; in the rocks above are remains of deer
with additional prongs, and point after point is added as the ancient
history of deer is traced upwards through the rocks to modern species. We
know that the life-history of a modern species of animals reviews the
ancestral record of the species, and what happens during the development
of deer can be directly compared with the fossil series. It is a matter of
common knowledge that the year-old stag has simple spikes as horns, and
that these are shed to be replaced the following year by larger forked
horns. Every year the horns are lost and new ones grow out, and become
more and more elaborately branched as time goes on, thus giving a series
of developmental stages that faithfully repeats the general order of
fossil horns. Even Agassiz, who was a believer in special creation and an
opponent of evolution, was constrained to point out many other instances,
mainly among the invertebrata, where there was a like correspondence
between the ontogeny of existing species and their phylogenetic history as
revealed by the fossil remains of their ancestors.

* * * * *

In the last place, we must give more than a passing consideration to some
of the extinct types of animals that occupy the position of "links"
between groups now widely separated by their divergence in evolution from
the same ancestors. Perhaps the most famous example is _Archæopteryx_
found in a series of slates in Germany. This animal is at once a
feathered, flying reptile, and a primitive bird with countless reptilian
structures. Its short head possesses lizard-like jaws, all of which bear
teeth; its wings comprise five clawed digits; its tail is composed of a
long series of joints or vertebræ, bearing large feathers in pairs; its
breastbone is flat and like a plate, thus resembling that of reptiles and
differing markedly from the great keeled breastbone of modern flying
birds, whose large muscles have necessitated the development of the keel
for purposes of firm attachment. In brief, this animal was close to the
point where reptiles and birds parted company in evolution, and although
it was a primitive bird, it is in a true sense a "missing link" between
reptiles and the group of modern birds. Other fossil forms like
_Hesperornis_ and _Ichthyornis_, whose remains occur in the strata of a
later date, fill in the gap between _Archæopteryx_ and the birds at the
present time, for among other things they possess teeth which indicate
their origin from forms like _Archæopteryx_, while in other respects they
are far nearer the birds of later epochs. That these links are not unique
is proved by numerous other examples known to science, such as those which
connect amphibia and reptiles, ancient reptiles and primitive mammals, as
well as those which come between the different orders of certain
vertebrate classes.

In summarizing the foregoing facts, and the larger bodies of evidence that
they exemplify, we learn how surely the testimony of the rocks establishes
evolution in its own way, how it confirms the law of recapitulation
demonstrated by comparative embryology, and how it proves that the greater
and smaller divisions of animals have followed the identical order in
their evolution that the comparative study of the present day animals has
independently described.

* * * * *

The facts of geographical distribution constitute the fifth division of
zoölogy, and an independent class of evidences proving the occurrence of
evolution. This department of zoölogy assumed its rightful status only
after the other divisions had attained considerable growth. Many
naturalists before Darwin and Wallace and Wagner had noticed that animals
and plants were by no means evenly distributed over the surface of the
globe, but until the doctrine of evolution cleared their vision they did
not see the meaning of these facts. As in the case of all the other
departments of zoölogy the immediate data themselves are familiar, but
because they are so obvious the mind does not look for their
interpretation but accepts the facts at their face value. While the
phenomena of distribution are no less fascinating to the naturalist, and
no less effective in their demonstration of evolution, their comprehensive
treatment would demand more space than the whole purpose of the present
description of organic evolution would justify. Thus a brief outline only
can be given of the salient principles of this subject in order that their
bearing upon the problem of species may be indicated.

Even as children we learn many facts of animal distribution; every one
knows that lions occur in Africa and not in America, that tigers live in
Asia and Malaysia, that the jaguar is an inhabitant of the Brazilian
forests, and that the American puma or mountain lion spreads from north to
south and from east to west throughout the American continents. The
occurrence of differing human races in widely separated localities is no
less familiar and striking, for the red man in America, the Zulu in
Africa, the Mongol and Malay in their own territories, display the same
discontinuity in distribution that is characteristic of all other groups
of animals and of plants as well. As our sphere of knowledge increases, we
are impressed more and more forcibly by the diversity and unequal extent
of the ranges occupied by the members of every one of the varied divisions
of the organic world. Another fact which becomes significant only when
science calls our attention to it is the absence from a land like
Australia of higher mammals such as the rabbit of Europe. The hypothesis
of special creation cannot explain this absence on the assumption that the
rabbit is unsuited to the conditions obtaining in the country named, for
when the species was introduced into Australia by man, it developed and
spread with marvelous rapidity and destructive effect. It may seem
impossible that facts like these could possess an evolutionary
significance, but they are actual examples of the great mass of data
brought together by the naturalists who have seen in them something to be
interpreted, and who have sought and found an explanation in the
formularies of science.

The general principles of distribution appear with greatest clearness when
an examination is made of the animals and plants of isolated regions like
islands. The Galapagos Islands constitute a group that has figured largely
in the literature of the subject, partly because Darwin himself was so
impressed by what he found there in the course of his famous voyage around
the world in the "Beagle." They form a cluster on the Equator about six
hundred miles west of the nearest point of the neighboring coast of South
America. Although the lizards and birds that live in the group differ
somewhat among themselves as one passes from island to island, on the
whole they are most like the species of the corresponding classes
inhabiting South America. Why should this be so? On the hypothesis of
special creation there is no reason why they should not be more like the
species of Africa or Australia than like those of the nearest body of the
mainland. The explanation given by evolution is clear, simple, and
reasonable. It is that the characteristic island forms are the descendants
of immigrants which in greatest probability would be wanderers from the
neighboring continent and not from far distant lands. Reaching the
isolated area in question the natural factors of evolution would lead
their offspring of later generations to vary from the original parental
types, and so the peculiar Galapagos species would come into being. The
fact that the organisms living on the various islands of this group differ
somewhat in lesser details adds further justification for the evolutionary
interpretation, because it is not probable that all the islands would be
populated at the same time by similar stragglers from the mainland. The
first settlers in one place would send out colonies to others, where
independent evolution would result in the appearance of minor differences
peculiar to the single island. In this manner science interprets the
general agreement between the animals of the Azores Islands and the fauna
of the northwestern part of Africa, the nearest body of land, from which
it would be most natural for the ancestors of the island fauna to come.

The land-snails inhabiting the various groups of islands scattered
throughout the vast extent of the Pacific Ocean provide the richest and
most ideal material for the demonstration of the principles of
geographical distribution. In the Hawaiian Islands snails of the family of
Achatinellidæ occur in great abundance, and like the lizards of the
Galapagos Islands different species occur on the different members of the
group. Within the confines of one and the same island, they vary from
valley to valley, and the correlation between their isolation in
geographical respects and specific differences on the other hand, first
pointed out by Gulick, makes this tribe of animals classical material. In
Polynesia and Melanesia are found close relatives of the Achatinellidæ,
namely, the Partulæ, which are thus in relative proximity to the
Achatinellidæ and not on the other side of the world. Furthermore, the
Partulæ are not alike in all of the groups of Polynesia where they occur;
the species of the Society Islands are absolutely distinct from those of
the Marquesas, Tonga, Samoan, and Solomon Islands, although they agree
closely in the basic characters that justify their reference to a single
genus. The geological evidence tells us that these islands were once the
peaks of mountain ranges rising from a Pacific continent which has since
subsided to such an extent that the mountain tops have become separate
islands. Thus the resemblances between Hawaiian and Polynesian snails, and
the closer similarities exhibited by the species of the various groups of
Polynesia, are intelligible as the marks of a common ancestry in a
widespread continental stock, while the observed differences show the
extent of subsequent evolution along independent lines followed out after
the isolation of the now separated islands. The principle may be worked
out in even greater detail, for it appears that within the limits of one
group diverse forms occupy different islands, evolved in different ways in
their own neighborhoods; while in one and the same island, the populations
of the different valleys show marked effects of divergence in later
evolution, precisely as in the case of the classic Achatinellidæ of the
Hawaiian Islands.

The broad and consistent principle underlying these and related facts is
this: _there is a general correspondence between the differences displayed
by the organisms of two regions and the degree of isolation or proximity
of these two areas_. Thus the disconnected but neighboring areas of the
Galapagos Islands and South America support species that resemble each
other closely, for the reasons given before; long isolated areas like
Australia and its surroundings possess peculiar creatures like the
egg-laying mammals, and all of the pouched animals or marsupials with only
one or two exceptions like our own American opossum,--a correlation
between a geological and geographical discontinuity on the one hand and a
peculiarity on the other that reinforces our confidence in the
faunal evolutionary interpretation of the facts of distribution.

It is true that the various classes of animals do not always appear with
coextensive ranges. The barriers between two groups of related species
will not be the same in all cases. A range like the Rocky Mountains will
keep fresh-water fish apart, while birds and mammals can get across
somewhere at some time. All these things must be taken into account in
analyzing the phenomena of distribution, and many factors must be given
due attention; but in all cases the reasons for the particular state of
affairs in geographical and biological respects possess an evolutionary
significance.

Having then all the facts of animal natural history at his disposal, and
the uniform principles in each body of fact that demonstrate evolution, it
is small wonder that the evolutionist seems to dogmatize when he asserts
that descent with adaptive and divergent modification is true for all
species of living things. The case is complete as it stands to-day, while
it is even more significant that every new discovery falls into line with
what is already known, and takes its natural place in the all-inclusive
doctrine of organic evolution. Because this explanation of the
characteristics of the living world is more reasonable than any other,
science teaches that it is true.

EVOLUTION AS A NATURAL PROCESS

The purpose of the discussions up to this point has been to present the
reasons drawn from the principal classes of zoölogical facts for believing
that living things have transformed naturally to become what they now are.
Even if it were possible to make an exhaustive analysis of all of the
known phenomena of animal structure, development, and fossil succession,
the complete bodies of knowledge could not make the evolutionary
explanation more real and evident than it is shown to be by the simple
facts and principles selected to constitute the foregoing outline. We have
dealt solely with the evidences as to the fact of evolution; and now,
having assured ourselves that it is worth while to so do, we may turn to
the intelligible and reasonable evidence found by science which proves
that the familiar and everyday "forces" of nature are competent to bring
about evolution if they have operated in the past as they do to-day.
Investigation has brought to light many of the subsidiary elements of the
whole process, and these are so real and obvious that they are simply
taken for granted without a suspicion on our part of their power until
science directs our attention to them.

For one reason or another, those who take up this subject for the first
time find it difficult to banish from their minds the idea that evolution,
even if it ever took place, has been ended. They think it futile to expect
that a scrutiny of to-day's order can possibly find influences powerful
enough to have any share in the marvelous process of past evolution
demonstrated by science. The naturalists of a century ago held a similar
opinion regarding the earth, viewing it as an immutable and unchanged
product of supernatural creation, until Lyell led them to see that the
world is a plastic mass slowly altering in countless ways. It is no more
true that living things have ceased to evolve than that mountains and
rivers and glaciers are fixed in their final forms; they may seem
everlasting and permanent only because a human life is so brief in
comparison with their full histories. Like the development of a continent
as science describes it, the origin of a new species by evolution, its
rise, culmination, and final extinction may demand thousands of years; so
that an onlooker who is himself only a conscious atom of the turbulent
stream of evolving organic life does not live long enough to observe more
than a small fraction of the whole process. Therefore living species seem
unchanged and unchangeable until a conviction that evolution is true, and
a knowledge of the method of science by which this conviction is borne
upon one, guide the student onwards in the further search for the
efficient causes of the process.

The biologist employs the identical methods used by the geologist in
working out the past history of the earth's crust. The latter observes the
forces at work to-day, and compares the new layers of rock now being
formed with the strata of deeper levels; these are so much alike that he
is led to regard the constructive influences of the past as identical with
those he can now watch at work. Similarly the biologist must first learn,
as we have done, the principles of animal construction and development,
and of other classes of zoölogical facts, and then he must turn his
attention from the dead object of laboratory analysis to the workings of
organic machines. The way an organism lives its life in dynamic relations
to the varied conditions of existence, as well as the mutual physiological
relations of the manifold parts of a single organism, reveal certain
definite natural forces at work. Therefore his next task is to compare the
results accomplished by these factors in the brief time they may be seen
in operation with the products of the whole process of organic evolution,
to learn, like the geologist in his sphere, that the present-day natural
forces are able to do what reason says they have done in the past.

When the subject of inquiry was the reality of evolution, it was perhaps
surprising to find that even the most familiar animals like cats and frogs
provided adequate data for science to use in formulating its principles.
So it is with the matter of method; it is unnecessary to go beyond the
observations of a day or a week of human life to find forces at work, as
real and vital as animal existence and organic life themselves. This is
true, because evolution is true, and because the lives of all creatures
follow one consistent law. Our task is therefore much more simple than
most people suppose it to be; let us look about us and classify what we
may observe, increasing our knowledge from the wide array of equally
natural facts supplied by the biologist.

The analogies of the steamship and the locomotive proved useful at many
times during the discussion of the fact of evolution, and even in the
present connection they will still be of service. The evolution of these
dead machines has been brought about by man, who, as an element of their
environment, has been their creator as well as the director of their
historical transformations. The result of their changes has been greater
efficiency and better adjustment or adaptation to certain requirements
fixed by man himself. The whole process of improvement has been one, in
brief, of trial and error; new inventions have often been worthless, and
they have been relegated to the scrap-heap, while the better part has been
finally incorporated in the type machine. In brief, then, the important
elements in the evolution of these examples have been three; first,
_adaptation_, second, the _origination of new parts_, and third, the
_retention of the better invention_.

Are the creatures of the living world so constituted that biological
equivalents of these three essential elements of mechanical evolution can
be found? Are organisms adapted to the circumstances controlling their
lives, and are they capable of changing naturally from generation to
generation, and of transmitting their qualities to their offspring? These
are definite questions that bring us face to face with the fundamental
problems relating to the dynamics or workings of evolution. We need not
ask for or expect to find complete answers, for we know that it is
impossible to obtain them. But we may expect to accomplish our immediate
object, which is to see that evolution is natural. Our attention must be
concentrated upon the three biological subjects of _adaptation_,
_variation,_ and _inheritance_, and we must learn why science describes
them as real organic phenomena and the results of natural causes.

* * * * *

At the very outset, when the general characteristics of living things were
considered, much was said on the subject of adaptation as a universal
phenomenon of nature. It was not contended that perfection is attained by
any living mechanism, but it was held that no place exists in nature for
an organism that is incapable of adjusting itself to the manifold
conditions of life. A _modus vivendi_ must be established and some
satisfactory degree of adaptation must be attained, or else an animal or a
species must perish. With this fundamental point as a basis, we look to
nature for two kinds of natural processes or factors, first, those which
may originate variations as _primary factors_,--the counterparts of human
ingenuity and invention in the case of locomotive evolution,--and the
_secondary factors_ of a preservative nature which will perpetuate the
more adaptive organic changes produced by the first influences; it is
clear that the latter are no less essential for evolution than the first
causes for the appearance of variations.

The term "variation" is employed for the natural phenomenon of being or
becoming different. It is an obvious fact that no child is ever exactly
like either of its parents or like any one of its earlier ancestors; while
furthermore in no case does an individual resemble perfectly another of
its own generation or family. This departure from the parental condition,
and the lack of agreement with others even of its closest blood-relatives,
are two familiar forms of variation. As a rule, the degree to which a
given organism is said to vary in a given character is most conveniently
measured by the difference between its actual condition and the general
average of its species, even though there is no such thing as a specimen
of average nature in all of its qualities. In brief, then, variation means
the existence of some differences between an individual and its parents,
its fraternity, and, in a wider sense, all others of its species.

Passing now to the causes of variation, all of the countless deviations of
living things can be referred to three kinds of primary factors; namely,
the _environmental_, _functional_, and _congenital_ influences that work
upon the organism in different ways and at different times during its
life. We shall learn that the evolutionary values of these three classes
are by no means equal, but we take a long step forward when we realize
that among the things we see every day are facts demonstrating the reality
of three kinds of natural powers quite able to change the characters of
organic mechanisms.

The "environment" of an organism is everything outside the creature
itself. In the case of an animal it therefore includes other members of
its own kind, and other organisms which prey upon its species or which
serve it as food, as well as the whole series of inorganic influences
which first come to mind when the term is used. For example, the
environment of a lion includes other lions which are either members of its
own family, or else, if they live in the same region, they are its more or
less active rivals and competitors. In the next place, other kinds of
animals exist whose lives are intimately related to the lion's life, such
as the antelopes or zebras that are preyed upon, and the human hunter to
whom the lion itself may fall a victim. In addition, there are the
contrasted influences of inorganic nature which demand certain adjustments
of the lion's activities. Light and darkness, heat and cold, and other
factors have their direct and larger or smaller effects upon the life of a
lion, although these effects are less obvious in this instance than in the
case of lower organisms.

The reality of variations due to the inorganic elements of the environment
is everywhere evident. Those who have spent much time in the sun are aware
that sunburn may result as a product of a factor of this class. The amount
of sunlight falling upon a forest will filter through the tree-tops so as
to cause some of the plants beneath to grow better than others, thus
bringing about variations among individuals that may have sprung from the
myriad seeds of a single parent plant. In times of prolonged drought,
plants cannot grow at the rate which is usual and normal for their
species, and so many variations in the way of inhibited development may
arise.

Then there are the variations of a second class, more complex in nature
than the direct effects of environment,--namely, the functional results of
use and disuse. A blacksmith uses his arm muscles more constantly than do
most other men, and his prolonged exercise leads to an increase of his
muscular capacity. All of the several organic systems are capable of
considerable development by judicious exercise, as every one knows. If the
functional modifications through use were unreal, then the routine of the
gymnasium and the schoolroom would leave the body and the mind as they
were before. Furthermore, we are all familiar with the opposite effects of
disuse. Paralysis of an arm results in the cessation of its growth. When a
fall has injured the muscles and nerves of a child's limb, that structure
may fail to keep pace with the growth of the other parts of the body as a
result of its disuse. These are simple examples of a wide range of
phenomena exhibited everywhere by animals and even by the human organism,
demonstrating the plasticity of the organic mechanism and its modification
by functional primary factors of variation.

But by far the greater number of variations seem to be due to the
so-called congenital causes, which are sharply contrasted with the
influences of the first and second classes. It is quite true that the
influences of the third class cannot be surely and directly demonstrated
like the others, but however remote and vague they themselves may appear to
be, their effects are obvious and real, while at the same time their
effects are to be clearly distinguished from the products of the other two
kinds. Congenital factors reside in the physical heritage of an organism,
and their results are often evident before an individual is subjected to
environmental influences and before it begins to use its various organs.
For example, it is a matter of common observation that a child with light
hair and blue eyes may have dark-eyed and brown-haired parents. The fact
of difference is a phenomenon of variation; the causes for this fact
cannot be found in any other category than that comprising the hereditary
and congenital influences of parent upon offspring. _How_ the effect is
produced by such causes is less important in the present connection than
the natural _fact_ of congenital variation. Science, however, has learned
much about the causes in question, as we shall see at a later point.

Thus the first step which is necessary for an evolution and transformation
of organic mechanisms proves to be entirely natural when we give only
passing attention to certain obvious phenomena of life. The fact of
"becoming different" cannot be questioned without indicting our powers of
observation, and we must believe in it on account of its reality, even
though the ultimate analysis of the way variations of different kinds are
produced remains for the future.

Having learned that animals are able to change in various ways, the next
question is whether variations can be transmitted to future generations
through the operation of secondary factors. Long ago Buffon held that the
direct effects of the environment are immediately heritable, although the
mode of this inheritance was not described; it was simply assumed and
taken for granted. Thus the darker color of the skin of tropical human
races would be viewed by Buffon as the cumulative result of the sun's
direct effects. Lamarck laid greater stress upon the indirect or
functional variations due to the factors of use and disuse, and he also
assumed as self-evident that such effects were transmissible as "acquired
characters." This expression has a technical significance, for it refers
to variations that are added during individual life to the whole group of
hereditary qualities that make any animal a particular kind of organism.
If evolution takes place at all, any new kind of organism originating from
a different parental type must truly acquire its new characteristics, but
few indeed of the variations appearing during the lifetime of an animal
owe their origin to the functional and environmental influences, whose
effects only deserve the name of "acquired characters" in the special
biological sense.

In sharp contrast to Lamarckianism, so called,--although it did not
originate in the mind of the noted man of science whose name it bears,--is
the doctrine of natural selection, first proposed in its full form by
Charles Darwin. This doctrine presents a wholly natural description of the
method by which organisms evolve, putting all of the emphasis upon the
congenital causes of variation, although the reality of other kinds of
change is not questioned. But the contrast between Darwinism and the other
descriptions of secondary factors can best be made after a somewhat
detailed discussion of the former, which has gained the adherence of the
majority of the naturalists of to-day. However, we must not pass on
without pointing out that however much the explanations given by various
men of science may differ, they all agree in expressly recognizing the
complete naturalness of the secondary as well as of the primary factors of
evolution.

* * * * *

The doctrine of natural selection forms the best basis for the detailed
discussion of the way evolution has come about in the past and how it is
going on to-day. This is true because it was the first description of
nature's program to carry conviction to the scientific world, and because
its major elements have stood the test of time as no other doctrine has
done. Much has been added to our knowledge of natural processes during
post-Darwinian times, and new discoveries have supplemented and
strengthened the original doctrine in numerous ways, although they have
corrected certain of the minor details on the basis of fuller
investigation.

At the outset it must be clearly understood that Darwin's doctrine is
concerned primarily with the _method_ and not with the evidences as to the
actual _fact_ of evolution. Most of those who are not familiar with the
principles of science believe that Darwin discovered this process; but
their opinion is not correct. The reality of natural change as a universal
attribute of living things had been clearly demonstrated long before
Darwin wrote the remarkable series of books whose influence has been felt
outside the domains of biology and to the very confines of organized
knowledge everywhere. The "Origin of Species" was published in 1859, and
only the last of its fourteen chapters is devoted to a statement of the
evidence that evolution is true. In this volume Darwin presented the
results of more than twenty-five years of patient study of the phenomena
of nature, utilizing the observations of wild life in many regions visited
by him when he was the naturalist of the "Beagle" during its famous voyage
around the world. He also considered at length the results of the
breeder's work with domesticated animals, and he showed for the first time
that the latter have an evolutionary significance. Because his logical
assembly of wide series of facts in this and later volumes did so much to
convince the intellectual world of the reasonableness of evolution, Darwin
is usually and wrongly hailed as the founder of the doctrine. It is
interesting to note in passing that Alfred Russel Wallace presented a
precisely similar outline of nature's workings at about the same time as
the statement by Darwin of his theory of natural selection. But Wallace
himself has said that the greater credit belongs to the latter
investigator who had worked out a more complete analysis on the basis of
far more extensive observation and research.

The fundamental point from which the doctrine of natural selection
proceeds is the fact that all creatures are more or less perfectly adapted
to the circumstances which they must meet in carrying on their lives; this
is the reason why so much has been said in earlier connections regarding
the universal occurrence of organic adaptation. An animal is not an
independent thing; its life is intertwined with the lives of countless
other creatures, and its very living substance has been built up out of
materials which with their endowments of energy have been wrested from the
environment. Every animal, therefore is engaged in an unceasing struggle
to gain fresh food and new energy, while at the same time it is involved
in a many-sided conflict with hordes of lesser and greater foes. It must
prevail over all of them, or it must surrender unconditionally and die.
There is no compromise, for the vast totality we individualize as the
environment is stern and unyielding, and it never relents for even a
moment's truce.

To live, then, is to be adapted for successful warfare; and the question
as to the mode of origin of species may be restated as an inquiry into the
origin of the manifold adaptations by which species are enabled to meet
the conditions of life. Why is adaptation a universal phenomenon of
organic nature?

The answer to this query given by Darwinism may be stated so simply as to
seem almost an absurdity. It is, that if there ever were any unadapted
organisms, they have disappeared, leaving the world to their more
efficient kin. Natural selection proves to be a continuous process of
trial and error on a gigantic scale, for all of living nature is involved.
Its elements are clear and real; indeed, they are so obvious when our
attention is called to them that we wonder why their effects were not
understood ages ago. These elements are (1) the universal occurrence of
variation, (2) an excessive natural rate of multiplication, (3) the
struggle for existence entailed by the foregoing, (4) the consequent
elimination of the unfit and the survival of only those that are
satisfactorily adapted, and (5) the inheritance of the congenital
variations that make for success in the struggle for existence. It is true
that these elements are by no means the ultimate causes of evolution, but
their complexity does not lessen their validity and efficiency as the
immediate factors of the process.

* * * * *

Taking up the first proposition, we return to the subject of variation
that has been discussed previously for the purpose of demonstrating its
reality. The observations of every day are enough to convince us that no
two living things are ever exactly alike in all respects. The reason is
that the many details of organic structure are themselves variable, so
that an entire organism cannot be similar to another either in material or
in functional regards, while furthermore it would be impossible for an
animal to be related to environmental circumstances in the same way as
another member of its species unless it was possible for two things to
occupy the same space at the same time! Individual differences in physical
constitution are displayed by any litter of kittens, with identical
parents; it needs only a careful examination to find the variations in the
shape of the heads, the length of their tails, and in every other
character. Sometimes the differences are less evident in physical
qualities than in disposition and mental make-up, for such variations can
be found among related kittens just as surely as among the children
belonging to a single human family.

Not only do all organisms vary, but they seem to vary in somewhat similar
ways. While modern investigations have thrown much light upon the
relations between variations and their causes, of particular value in the
case of the congenital phenomena, the greatest advance since Darwin's time
consists in the demonstration by the naturalists who have employed the
laborious methods of statistical analysis that the laws according to which
differences occur are the same where-ever the facts have been examined. A
single illustration will suffice to indicate the general nature of this
result. If the men of a large assemblage should group themselves according
to their different heights in inches, we would find that perhaps one half
of them would agree in being between five feet eight inches and five feet
nine inches tall. The next largest groups would be those just below and
above this average class,--namely, the classes of five feet seven to eight
inches and five feet nine to ten inches. Fewer individuals would be in the
groups of five feet five to six inches and five feet ten to eleven inches,
and still smaller numbers would constitute the more extreme groups on
opposite sides of these. If the whole assemblage comprised a sufficient
number of men, it would be found that a class with a given deviation from
the average in one direction would contain about the same number of
individuals as the class at the same distance from the average in the
opposite direction. Taking into account the relative numbers in the
several classes and the various degrees to which they depart from the
average, the mathematician describes the whole phenomenon of variation in
human stature by a concise formula which outlines the so-called "curve of
error." From his study of a thousand men, he can tell how many there would
be in the various classes if he had the measurements of ten thousand
individuals, and how many there would be in the still more extreme classes
of very short and very tall men which might not be represented among one
thousand people.

It is not possible to explain why variation should follow this or any
other mathematical law without entering into an unduly extensive
discussion of the laws of error. The mathematicians themselves tell us in
general terms that the observations they describe so simply by their
formulæ follow as the result of so-called chance, by which they mean that
the combined operation of numerous, diverse, and uncorrelated factors
brings about this result, and not, of course, that there is such a thing
as an uncaused event or phenomenon.

Whenever any extensive series of like organisms has been studied with
reference to the variations of a particular character, the variations
group themselves so as to be described by identical or similar curves of
error. It is certainly significant that this is true for such diverse
characters, cited at random from the lists of the literature, as the
number of ray-flowers of white daisies, the number of ribs of beech
leaves, and of the bands upon the capsules of poppies, for the shades of
color of human eyes, for the number of spines on the backs of shrimps, and
for the number of days that caterpillars feed before they turn into pupæ.

To summarize the foregoing facts, we have learned that variation is
universal throughout the living world, and that the primary factors
causing organic difference--the counterparts of human ingenuity in the
case of dead mechanisms--are the natural influences of the environment, of
organic physiological activity, and of congenital inheritance. These
factors are accorded different values in the evolution of new species, as
we may see more clearly at a later juncture, but the essential point here
is that they are not unreal, although they may not as yet be described by
science in final analytical terms.

* * * * *

We come now to the second element of the whole process of evolution,
namely, what we may call overproduction or excessive multiplication. Like
variation and so many other phenomena of nature, this is so real and
natural that it escapes our attention until science places it before us in
a new light. The normal rate of reproduction _in all species of animals_
is such that if it were unchecked, any kind of organism would cumber the
earth or fill the sea in a relatively short time. That this is universally
true is apparent from any illustration that might be selected. Let us take
the case of a plant that lives for a single year, and that produces two
seeds before it withers and dies; let us suppose that each of these seeds
produces an adult plant which in its turn lives one year and forms two
seeds. If this process should continue without any interference, the
twentieth generation after as many years would consist of more than one
million descendants of the original two-seeded annual plant, provided only
that each individual of the intervening years should live a normal life
and should multiply at the natural rate. But such a result as this is
rendered impossible by the very nature which makes annual plants multiply
in the way they do. Let us take the case of a pair of birds which produce
four young in each of four seasons. Few would be prepared for the figures
enumerating the offspring of a single pair of birds at the end of fifteen
years, if again all individuals lived complete and normal lives: at the
end of the time specified there would be more than two thousand millions
of descendants. The English sparrow has been on this continent little more
than fifty years; it has found the conditions in this country favorable
because few natural enemies like those of its original home have been met,
and as a consequence it has multiplied at an astounding rate so as to
invade nearly all parts of North America, driving out many species of song
birds before it. About twenty years ago David Starr Jordan wrote that if
the English sparrow continued to multiply at the natural rate of that
time, in twenty years more there would be one sparrow to every square inch
of the state of Indiana; but of course nature has seen to it that this
result has not come about. A single conger-eel may produce fifteen million
eggs in a single season, and if this natural rate of increase were
unchecked, the ocean would be filled solid with conger-eels in a few
years. Sometimes a single tapeworm, parasitic in the human body, will
produce three hundred million embryos; the fact that this animal is
relatively rare diverts our attention from the alarming fertility of the
species and the excessive rate of its natural increase. Perhaps the most
amazing figures are those established by the students of bacteria and
other micro-organisms. Many kinds of these primitive creatures are known
where the descendants of a single individual will number sixteen to
seventeen millions after twenty-four hours of development under ordinarily
favorable conditions. Though a single rodlike individual taken as a
starting-point may be less than one five-thousandth of an inch in length,
under natural circumstances it multiplies at a rate which _within five
days_ would cause its descendants _to fill all the oceans to the depth of
one mile_. This is a fact, not a conjecture; the size of one organism is
known, and the rate of its natural increase is known, so that it is merely
a matter of simple arithmetic to find out what the result would be in a
given time.

Even in the case of those animals that reproduce more slowly, an
overcrowding of the earth would follow in a very short time. Darwin wrote
that even the slow-breeding human species had doubled in the preceding
quarter century. An elephant normally lives to the age of one hundred
years; it begins to breed at the age of thirty, and usually produces six
young by the time it is ninety. Beginning with a single pair of elephants
and assuming that each individual born should live a complete life, only
eight hundred years would be requisite to produce nineteen million
elephants; a century or two more and there would be no standing room for
the latest generation of elephants. It is only too obvious that such a
result is not realized in nature, but it is on account of other natural
checks, and not because the natural rate of reproductive increase is
anything but excessive.

The third element of the process of natural selection is the struggle for
existence which is to a large extent the direct consequence of
over-multiplication. Because nature brings more individuals into existence
than it can support, every animal is involved in many-sided battles with
countless foes, and the victory is sometimes with one and sometimes with
another participant in the conflict. A survivor turns from one vanquished
enemy only to find itself engaged in mortal combat with other attacking
forces. Wherever we look, we find evidence of an unceasing struggle for
life, and an apparently peaceful meadow or pond is often the scene of
fierce battles and tragic death that escape our notice only because the
contending armies are dumb.

A community of ants, often comprising more individuals than an entire
European state, depends for its national existence upon its ability to
prevail over other communities with which it may engage in sanguinary wars
where the losses of a single battle may exceed those of Gettysburg. The
developing conger-eels find a host of enemies which greatly deplete their
numbers before they can grow even into infancy. An annual plant does not
produce a million living offspring in twenty years because seeds do not
always fall upon favorable soil, nor do they always receive the proper
amount of sunlight and moisture, or escape the eye of birds and other
seed-eating animals. These three illustrations bring out the fact that
there are three classes of natural conditions which must be met by every
living creature if it is to succeed in life. In detail, the struggle for
existence is _intra-specific_, involving some form of competition or
rivalry among the members of a single species; it is _inter-specific_, as
a conflict is waged by every species with other kinds of living things;
and finally it involves an adjustment of life to _inorganic environmental_
influences. While it may seem unjustifiable to speak of heat and cold and
sunlight as enemies, the direct effects produced by these forces are to be
reckoned with no less certainty than the attacks of living foes.

The three divisions of the struggle for existence are so important not
only in purely scientific respects, but also in connection with the
analysis of human biology, that we may look a little further into their
details, taking them up in the reverse order. Regarding the environmental
influences, the way that unfavorable surroundings decimate the numbers of
the plants of any one generation has already been noted, and it is typical
of the vital situation everywhere. English sparrows are killed by
prolonged cold and snow as surely as by the hawk. The pond in which
bacteria and protozoa are living may dry up, and these organisms may be
killed by the billion. Even the human species cannot be regarded as exempt
from the necessity of carrying on this kind of natural strife, for scores
and hundreds die every year from freezing and sunstroke and the thirsts of
the desert. Unknown thousands perish at sea from storm and shipwreck,
while the recorded casualties from earthquakes and volcanic eruptions and
tidal waves have numbered nearly one hundred and fifty thousand in the
past twenty-eight years. The effects of inorganic influences upon all
forms of organic life must not be underestimated in view of such facts as
these.

In the second place, the vital struggle includes the battles of every
species with other kinds of living things whose interests are in
opposition. The relations of protozoa and bacteria, conger-eels and other
fish, English sparrows and hawks, plants and herbivorous animals, are
typical examples of the universal conflict in which all organisms are
involved in some way. Again it is only too evident that human beings must
participate every day in some form of warfare with other species. In order
that food may be provided for mankind the lives of countless wild
organisms must be sacrificed in addition to the great numbers of
domesticated animals reared by man only that they may be destroyed. The
wolf and the wildcat and the panther have disappeared from many of our
Eastern states where they formerly lived, while no longer do vast herds of
bison and wild horses roam the Western prairies. Because one or another
human interest was incompatible with the welfare of these animals they
have been driven out by the stronger invaders.

That the victory does not always fall to the human contestant is
tragically demonstrated by the effects of the incessant assaults upon man
made by just one kind of living enemy,--the bacillus of tuberculosis.
Every year more than one hundred and twenty-five thousand people of the
United States die because they are unable to withstand its persistent
attacks; five million Americans now living are doomed to death at the
hands of these executioners, and the figures must be more than doubled to
cover the casualties on the human side in the battles with the regiments
of all the species of bacteria causing disease.

The competition between and among the individuals of one and the same
species is the third part of the struggle for existence, and it is often
unsurpassed in its ferocity. When two lion cubs of the same litter begin
to shift for themselves, they must naturally compete in the same
territory, and their contest is keener than that which involves either of
them and a young lion born ten or fifteen miles away. The seeds of one
parent plant falling in a restricted area will be engaged in a competitive
struggle for existence that is much more intense than many other parts of
nature's warfare. In brief, the intensity of the competition will be
directly proportional to the similarity of two organisms in constitution
and situation, and to the consequent similarity of vital welfare. The
interests of the white man and the Indian ran counter to each other a few
hundred years ago, and the more powerful colonists won. The assumption of
the white man's burden too often demonstrates the natural effect of
diversity of interest, and the domination of the stronger over the weaker.
In any civilized community the manufacturer, farmer, financier, lawyer,
and doctor must struggle to maintain themselves under the conditions of
their total inorganic and social environments; and in so far as the object
of each is to make a living for himself, they are competitors. But the
contest becomes more absorbing when it involves broker and broker, lawyer
and lawyer, financier and magnate, because in each case the contestants
are striving for an identical need of success.

Although the severity of the conflict imposed by nature is somewhat
modified in the case of social organisms, where community competes with
community and nation with nation, no form of social organization has yet
been developed where the individual contest carried on by the members of
one community has been done away with. It is an inexorable law of nature
that all living things must fight daily and hourly for their very lives,
because so many are brought into the world with each new generation that
there is not sufficient room for all. No organism can escape the struggle
for existence except by an unconditional surrender that results in death.
Everywhere we turn to examine the happenings of organic life we can find
nothing but a wearisome warfare in which it is the ultimate and cruel lot
of every contestant to admit defeat.

* * * * *

What now are the results of variation, over-multiplication, and
competition? Since some must die because nature cannot support all that
she produces, since only a small proportion of those that enter upon life
can find a foothold or successfully meet the hordes of their enemies,
which will be the ones to survive? Surely those that have even the
slightest advantage over their fellows will live when their companions
perish. It is impossible that the result could be otherwise; it must
follow inevitably from what has been described before. The whole process
has its positive and its negative aspects: the survival of the fittest and
the elimination of the unfit. Perhaps it would be more correct to say the
more real element is the negative one, for those which are least capable
of meeting their living foes and the decimating conditions of inorganic
nature are the first to die, while the others will be able to prolong the
struggle for a longer or shorter period before they too succumb. Thus the
destruction of the unfit leaves the field to the better adapted, that is,
to those that vary in such a way as to be completely or at least partially
adapted to carry on an efficient life. In this way Darwinism explains the
universal condition of organic adjustment, showing that it exists because
there is no place in nature for the incompetent.

* * * * *

Finally we come to the process of inheritance as viewed by Darwin, and its
part in the production and perfection of new species. In every case,
Darwin said, the efficiency or inefficiency of an animal depends upon its
characteristics of an inherited or congenital nature. Variations in these
qualities provide the array of more or less different individuals from
which impersonal nature selects the better by throwing out first the
inferior ones. An organism can certainly change in direct response to
environmental influence or by the indirect results of use and disuse, but
not unless it is so constituted by heredity as to be able to change
adaptively. Therefore the final basis of success in life must be sought in
the inherited constitutions of organic forms.

For the reason that the qualities which preserve an animal's existence are
already congenital, they are already transmissible, as Darwin contended.
Since his time much has been learned about the course of inheritance and
its physical basis, and the new discoveries have confirmed the essential
truth of Darwin's statement that the congenital characters only possess a
real power in the evolution of species.

We must devote some time to the subject of inheritance at a later
juncture, but before leaving the matter an additional point must be
established here; the selective process deals immediately with congenital
results, as the heritable characters that make for success or failure in
life, but by doing this it really selects the group of congenital factors
behind and antecedent to their effects. For example, an ape that survives
because of its superior cunning, does so because it varies congenitally in
an improved direction; and the factors that have made it superior are
indirectly but no less certainly preserved through the survival of their
results in the way of efficiency. Hereditary strains are thus the ultimate
things selected through the organic constitutions that they determine and
produce.

Natural selection, as the whole of this intricate process, is simply trial
and error on a gigantic scale. Nature is such that thousands of varying
individuals are produced in order that a mere handful or only one survivor
may be chosen to bear the burden of carrying on the species for another
generation. The effect of nature's process is judicial, as it were. We may
liken the many and varied conditions of life to as many jurymen, before
which every living thing must appear for judgment as to its fitness or
lack of it. A unanimous verdict of complete or partial approval must be
rendered, or an animal dies, for the failure to meet a single vital
condition results in sure destruction. Of course, we cannot regard
selection as involving anything like a primitive conscious choice. It is
because we individualize all of the complex totality of the world as
"Nature" with a capital N that so many people unconsciously come to think
of it as a human-like personality. He who would go further and hold that
all of nature is actually conscious and the dwelling-place of the
supernatural ultimate, must beware of the logical results of such a view.
What must we think of the ethical status of such a conscious power who
causes countless millions of creatures to come into the world and
ruthlessly compels them to battle with one another until a cruel and
tragic death ends their existence?

But that is a metaphysical matter, with which we need not concern
ourselves in this discussion; the important point is that among the
everyday happenings of life are processes that are quite competent to
account for the condition of adaptation exhibited by various animal forms.
These processes are real and natural, not imaginative or artificial, and
so they will remain even though it will become clear that much is still to
be learned about the causes of variation and the course of biological
inheritance. Darwin was the first to contend that natural selection is but
a part of nature's method of accomplishing evolution. As such it is
content to recognize variations and does not concern itself with the
origin of modifications; it accepts the obvious fact that congenital
variations are inherited, although it leaves the question as to how they
are inherited for further examination. Because the doctrine of natural
selection does not profess to answer all the questions propounded by
scientific inquisitiveness, it must not be supposed that it fails in its
immediate purpose of giving a natural explanation of how evolution may be
partly accounted for.

* * * * *

Before proceeding to the post-Darwinian investigations that have done so
much to amplify the account of natural evolution, let us consider the
contrasted explanation given by Lamarck and his followers. As we have
stated earlier, Lamarckianism is the name given to the doctrine that
modifications other than those due to congenital factors may enter into
the heritage of a species, and may add themselves to those already
combined as the peculiar characteristics of a particular species. Let us
take the giraffe and its long neck as a concrete example. The great length
of this part is obviously an adaptive character, enabling the animal to
browse upon the softer leafy shoots of shrubs and trees. The vertebral
column of the neck comprises just the same number of bones that are
present in the short-necked relatives of this form, so that we are
justified in accepting as a fact the evolution of the giraffe's long neck
by the lengthening of each one of originally shorter vertebræ. The
Lamarckian explanation of this fact would be that the earliest forms in
the ancestry of the giraffe as such stretched their necks as they fed, and
that this peculiar function with its correlated structural modification
became habitual. The slight increase brought about by any single
individual would be inherited and transmitted to the giraffes of the next
generation; in other words, an individually acquired character would be
inherited. The young giraffes of this next generation would then begin,
not where their parents did, but from an advanced condition. Thus, by
continued stretching of the neck and by continued transmission of the
elongated condition, the great length of this part of the body in the
modern giraffe would be attained.

The explanation of natural selection would be quite different. The
Darwinian would say that all the young giraffes of any one generation
would vary with respect to the length of the neck. Those with longer necks
would have a slight advantage over their fellows in the extended sphere of
their grazing territory. Being better nourished than the others, they
would be stronger and so they would be more able to escape from their
flesh-eating foes, like the lion. For the reason that their variation
would be congenital and therefore already transmissible, their offspring
would vary about the advanced condition, and further selection of the
longer necked individuals would lead to the modern result.

The Lamarckian explanation encounters one grave difficulty which is not
met by the second one, in so far as it demands some method by which a
bodily change may be introduced into the stream of inheritance. So far,
this difficulty has not been overcome, and the present verdict of science
is that the transmission of characters acquired as the result of other
than congenital factors is not proved. It would be unscientific to say
that it cannot be proved in the future, but there are good _a priori_
grounds for disbelief in the principle, while furthermore the results of
experiments that have been undertaken to test its truth have been entirely
negative. Rats and mice have had their tails cut off to see if this
mutilation would have its effect upon their young, and though this has
been done for more than one hundred successive generations the length of
the tail has not been altered. Quite unconscious of the scientific
problem, many human races have performed precisely similar experiments
through centuries of time. In some classes of Chinese, the feet of young
girls have been bound in such a way as to produce a small, malformed foot,
but this has not resulted in any hereditary diminution in the size of the
feet of Chinese females. Many other similar mutilations have been
practised, as for example, the flattening of the skull of some North
American Indians, but the deformity must be produced again with each
recurring generation. One after another, the cases that were supposed to
give positive evidence have been reinvestigated, with the result that has
been stated above. It would seem, therefore, that heredity and congenital
modification must play by far the greater part in the evolution of
species.

* * * * *

The doctrine of natural selection took form in the mind of Darwin mainly
on account of three potent influences; these were, first, the geological
doctrine of uniformitarianism proposed by Lyell, second, his own
observations of wild life in many lands and his analysis of the breeder's
results with domesticated animals, and third, the writings of Malthus
dealing with overpopulation. As Darwin had read the works of Buffon,
Lamarck, and Erasmus Darwin, his grandfather, who had written a famous
treatise under the title of "Zoonomia," he was familiar with the evidences
known in his student days tending to prove that organic evolution was a
real natural process. Lyell's doctrine of uniform geological history made
an early and deep impression upon his mind, and it led him to ask himself
whether the efficient causes of past evolution might not be revealed by an
analysis of the present workings of nature. As naturalist of the "Beagle"
during its four years' cruise around the world, Darwin saw many new lands
and observed varied circumstances under which the organisms of the tropics
and other regions lived their lives. The fierce struggle for existence
waged by the denizens of the jungle recalled to him the views of Malthus
regarding overpopulation and its results. These and other influences led
him to begin the remarkable series of note-books, from which it is
interesting indeed to learn how the doctrine of natural selection began to
assume a definite and permanent form in his mind, as year followed year,
and evidence was added to evidence. And it is a valuable lesson to the
student of science that for twenty-five years Darwin devoted all his time
to the acquisition of facts before he gave his doctrine to the world in
the famous "Origin of Species."

Darwin was particularly impressed by the way mankind has dealt with the
various species of domesticated animals, and he was the first naturalist
to point out the correspondence between the breeder's method of
"artificial selection," and the world-wide process of natural selection.
As every one knows, the breeder of race horses finds that colts vary much
in their speed; discarding the slower animals, he uses only the swifter
for breeding purposes, and so he perfects one type of horse. With other
objects in view, the heavy draught horse, the spirited hackney, and the
agile polo pony have been severally bred by exactly the same method. Among
cattle many kinds occur, again the products of an artificial or human
selection; hornless breeds have been originated, as well as others with
wide-spreading or sharply curved horns; the Holstein has been bred for an
abundant supply of milk as an object, while Jerseys and Alderneys excel in
the rich quality of their milk. Various kinds of domesticated sheep and
rabbits and cats also owe their existence to the employment of the
selfsame method, unconsciously copied by man from nature; for men have
found variations arising naturally among their domesticated animals, and
they have simply substituted their practical purposes or their fancy for
nature's criterion of adaptive fitness, preserving those that they wish to
perfect and eliminating those unfitted to their requirements or ideas.

In the case of many of these and other examples, wild forms still occur
which seem to be like the ancestral stock from which the domesticated
forms have been produced. All the varied forms of dogs--from mastiff to
toy-terrier, and from greyhound to dachshund and bulldog--find their
prototypes in wild carnivora like the wolf and jackal. In Asia and
Malaysia the jungle fowl still lives, while its domesticated descendants
have altered under human direction to become the diverse strains of the
barnyard, and even the peculiar Japanese product with tail feathers
sometimes as long as twenty feet. That far-reaching changes can be brought
about in a relatively short time is proved by the history of the game
cock, which has nearly doubled in height since 1850, while at the same
time its slender legs, long spurs, and other qualities have been perfected
for the cruel sport for which it has been bred. Again, the wild rock
pigeon seems to be the ancestral form from which the fantail and pouter
and carrier-pigeon with their diverse characters have taken their origin.

It is true that some biologists have urged certain technical objections to
the employment of domesticated animals and their history as analogies to
the processes and results in wild nature. To my mind, however, artificial
selection is truly a part of the whole process of natural selection. Man
is but one element of the environment of tame forms, and his fancy or need
is therefore one of the varied series of external criteria that must be
met if survival is to be the result; failing this, elimination follows as
surely as under the conditions of an area uninhabited or uninfluenced by
mankind. Congenital variation is real, selection is real and the heredity
of the more fit modification is equally real. Surely Darwin was right in
contending that the facts of this class amplify the conception of natural
selection developed on the basis of an analysis of wild life.

* * * * *

Knowing the elements of the selective process, it is possible to analyze
and to understand many significant phenomena of nature, and to gain a
clearer conception of the results of the struggle for existence,
especially when the human factor is involved. Let us see how much is
revealed when the foregoing results are employed in a further study of
some of nature's vital situations.

As a consequence of the many-sided struggle for existence, the
interrelations of a series of species will approach a condition of
equilibrium in an area where the natural circumstances remain relatively
undisturbed for a long time. For example, among the field-mice of one
generation, just as many individuals will survive as will be able to find
food and to escape hereditary foes such as cats and snakes and owls. The
number of owls, in their turn, will be determined by the number of
available mice and other food organisms, as well as by the severity of the
adverse circumstances that cause elimination of the less fit among the
fledglings brought into the world. The vital chain of connections is
sometimes astonishingly long and intricate. One remarkable illustration is
given by Fiske, as an elaboration of an example cited by Darwin. He points
out that the fine quality of the traditional roast beef of England is
directly determined by the number of elderly spinsters in that country.
The chain of circumstances is as follows: the quality of the clover
fields, furnishing the best food for cattle, depends largely upon the
visits to the clover-blossoms by wild bees, that accomplish the
fertilization of the flowers by carrying pollen upon their bodies from one
plant to another. Field-mice devour the young in the nests of these bees,
so if there are few field-mice there will be many bees, and consequently
better grazing for the cattle. The number of field-mice will vary
according to the abundance of cats, and so the number of these domestic
animals will exert an influence upon the whole foregoing chain of forms.
But, as Fiske points out, cats are the favorite companions of elderly
spinsters; therefore, if there are many of the latter, there will be more
cats, fewer field-mice, more bees, richer clover fields, and finer cattle!
Each link is real and the whole chain is a characteristic example of the
countless ways that the natural destinies of living things are
interrelated and intertwined.

The reality of such organic interrelationships is revealed with wonderful
clearness in the numerous instances where some disturbing factor has
altered one or another element of the balanced system. The invasion of the
new world by Europeans has directly led to the partial or complete
extinction of the tribes of Indians to whom the land formerly belonged;
they have disappeared almost entirely from our state of New York, together
with the bear and wolf and many other species of animals that formerly
existed here. Wild horses and bison have also vanished before the advances
of civilization and the alteration of their homes. Sometimes the
extermination of one pest has resulted in an increase in the number of
another through human interference with nature's equilibrium. In some of
our Western states, a bounty was offered for the scalps of wolves, so as
to lessen the number of these predatory foes of sheep. But when the wolves
were diminished in number, their wild food-animals, the prairie dogs,
found their lot much bettered, and they have multiplied so rapidly that in
some places they have become even more destructive than the wolves.

One of the most remarkable illustrations is that of the rabbits introduced
into Australia. This island continent was cut off from the surrounding
lands long before the higher mammals evolved in far distant regions, so
that the balance of nature was worked out without reference to animals
like the rabbit. When the first of these were introduced they found a
territory without natural enemies where everything was favorable. They
promptly multiplied so rapidly that within a few years their descendants
were numerous enough to eat up practically every green thing they could
reach. Two decades ago, the single province of Queensland was forced to
expend $85,000,000 in a vain effort to put down the rabbit plague. The
remarkable statement has been made that in some places nature has taken a
hand in causing a new type of rabbit to evolve. Finding the situation
desperate, some of the animals have begun to develop into tree-climbing
creatures. The animals exist in such numbers that the available food upon
the ground is insufficient for all, and so some elimination results. But
the young rabbits with longer claws, varying in this way on account of
congenital factors, have an advantage over their fellows because they can
climb some of the trees and so obtain food inaccessible to the others. If
the facts are correctly reported, and if the process of selection on the
basis of longer claws and the climbing habit is continued, the original
type of animal is splitting up into a form that will remain the same and
live upon the ground, and another that will be to all intents and purposes
a counterpart of our familiar squirrel. All the evidence goes to show that
squirrels have evolved from terrestrial rodents; if the data relating to
Australian rabbits are correct, nature is again producing a squirrel-like
animal by evolution in a region where the former natural situation has
been interfered with by man.

The laws of biological inheritance have received close and deep study by
numerous investigators of Darwinian and post-Darwinian times, because from
the first it was clearly recognized that a complete description of
nature's method of accomplishing evolution must show how species maintain
the same general characteristics from generation to generation, and also
how new qualities may be fixed in heredity as species transform in the
course of time. Before our modern era in biology, the fact of inheritance
was accepted as self-sufficient; now much is known that supplements and
extends the incomplete account given by natural selection of the way
evolution takes place.

It is not possible in the present brief outline to describe all the
results of recent investigations, but some of them are too important to be
passed over. Perhaps the most interesting one is that the laws of heredity
seem to be the same for man and other kinds of living creatures, as proved
by Galton and Pearson and many others who have dealt with such characters
as human stature, human eye color, and an extensive series of the
peculiarities of lower animals and even of plants.

The researches dealing with the physical basis of inheritance and its
location in the organism have yielded the most striking and brilliant
results. Darwin himself realized that the doctrine of natural selection
was incomplete, as it accepted at its face value the inheritance of
congenital racial qualities without attempting to describe the way an egg
or any other germ bears them, and he endeavored to round out his doctrine
of selection by adding the theory of pangenesis. According to this, every
cell of every tissue and organ of the body produces minute particles
called gemmules, which partake of the characters of the cells that produce
them. The gemmules were supposed to be transported throughout the entire
body, and to congregate in the germ-cells, which in a sense would be
minute editions of the body which bears them, and would then be capable of
producing the same kind of a body. If true, this view would lead to the
acceptance of Lamarck's or even Buffon's doctrine, for changes induced in
any organ by other than congenital factors could be impressed upon the
germ-cell, and would then be transported together with the original
specific characters to future generations. Darwin was indeed a good
Lamarckian.

But the researches of post-Darwinians, and especially those of the
students of cellular phenomena, have demonstrated that such a view has no
real basis in fact. Many naturalists, like Naegeli and Wiesner, were
convinced that there was a specific substance concerned with hereditary
qualities as in a larger way protoplasm is the physical basis of life. It
remained for Weismann to identify this theoretical substance with a
specific part of the cell, namely, the deeply staining substance, or
chromatin, contained in the nucleus of every cell. Bringing together the
accumulating observations of the numerous cytologists of his time, and
utilizing them for the development of his somewhat speculative theories,
Weismann published in 1882 a volume called "The Germ Plasm," which is an
immortal foundation for all later work on inheritance. The essential
principles of the germ-plasm theory are somewhat as follows. The chromatin
of the nucleus contains the determinants of hereditary qualities. In
reproduction, the male sex-cell, which is scarcely more than a minute mass
of chromatin provided with a thin coat of protoplasm and a motile organ,
fuses with the egg, and the nuclei of the two cells unite to form a double
body, which contains equal contributions of chromatin from the two
parental organisms. This gives the physical basis for paternal inheritance
as well as for maternal inheritance, and it shows why they may be of the
same or equivalent degree. When, now, the egg divides, at the first and
later cleavages, the chromatin masses or chromosomes contained in the
double nucleus are split lengthwise and the twin portions separate to go
into the nuclei of the daughter-cells. As the same process seems to hold
for all the later divisions of the cleavage-cells whose products are
destined to be the various tissue elements of the adult body, it follows
that all tissue-cells would contain chromatin determinants derived equally
from the male and female parents. As of course only the germ-cells of an
adult organism pass on to form later generations, and as their content of
chromatin is derived not from the sister organs of the body, but from the
original fertilized egg, there is a direct stream of the germ plasm which
flows continuously from the germ-cell to germ-cell through succeeding
generations. It would seem, therefore, that the various organic systems
are, so to speak, sister products in embryonic origin. The reproductive
organs are not produced by the other parts of the body, but their cells
are the direct descendants of the common starting-point namely, the egg.
As the cells of the reproductive organs are the only ones that pass over
and into the next and later generations, it will be evident, in the first
place, that the germ plasm of their nuclei is the only essential substance
that connects parent and offspring. This stream of germ plasm passes on in
direct continuity through successive generations--from egg to the complete
adult, including its own germ-cells, through these to the next adult, with
its germ-cells, and so on and on as long as the species exists. It does
not flow circuitously from egg to adult and then to new germ-cells, but it
is direct and continuous, and apparently it cannot pick up any of the
body-changes of an acquired nature. Now we see why individual acquisitions
are not transmitted. The hereditary stream of germ plasm is already
constituted before an animal uses its parts in adult life; we cannot see
how alterations in the structure of mature body parts through use and
adjustment to the environment can be introduced into it to become new
qualities of the species.

It must be clear, I am sure, that this theory supplements natural
selection, for it describes the physical basis of inheritance, it
demonstrates the efficiency of congenital or germ-plasmal factors of
variation in contrast with the Lamarckian factors, and finally in the way
that in the view of Weismann it accounts for the origin of variations as
the result of the commingling of two differing parental streams of germ
plasm.

At first, for many reasons, Weismann's theories did not meet with general
acceptance, but during recent years there has been a marked return to many
of his positions, mainly as the result of further cytological discoveries,
and of the formulation of Mendel's Law and of De Vries's mutation theory.
The first-named law was propounded by Gregor Mendel on the basis of
extensive experiments upon plants conducted during many years, 1860 and
later, in the obscurity of his monastery garden at Altbrünn, in Austria.
It was rescued from oblivion by De Vries, who found it buried in a mass of
literature and brought it to light when he published his renowned Mutation
Theory in 1901. Mendelian phenomena of inheritance, confirmed and extended
by numerous workers with plants and animals, prove that in many cases
portions of the streams of germ plasm that combine to form the hereditary
content of organisms may retain their individuality during embryonic and
later development, and that they may emerge in their original purity when
the germ-cells destined to form a later generation undergo the preparatory
processes of maturation. They demonstrate also the apparent chance nature
of the phenomena of inheritance. To my mind the most striking and
significant result in this field is the demonstration that a particular
chromosome or chromatin mass determines a particular character of an adult
organism, which is quite a different matter from the reference of all the
hereditary characters to the chromatin as a whole. Wilson and others have
brought forward convincing proof that the complex character of sex in
insects actually resides in or is determined by particular and definite
masses of this wonderful physical basis of inheritance.

Mendel's principles also account in the most remarkable way for many
previously obscure phenomena, like reversion, or a case where a child
resembles its grandparent more than it does either of its parents; such
phenomena are due, so to speak, to the rise to the surface of a hidden
stream of germ plasm that had flowed for one or many generations beneath
its accompanying currents. I believe that the law is replacing more and
more the laws of Galton and Pearson, formulated as statistical summaries
of certain phenomena of human inheritance taken _en masse_. According to
Galton's celebrated law of ancestral inheritance, the qualities of any
organism are determined to the extent of a certain fraction by its two
parents taken together as a "mid-parent," that a smaller definite fraction
is contributed by the grandparents taken together as a mid-grandparent,
and so on to earlier generations. But Mendel's Law has far greater
definiteness, it explains more accurately the cases of alternative
inheritance, and it may be shown to hold for blended and mosaic
inheritance as well.

De Vries's new "mutation theory" is clearly not an alternative but a
complementary theory to natural selection, the Weismannian and Mendelian
theories. Like these last, it emphasizes the importance of the congenital
hereditary qualities contained in the germ plasm, though unlike the
Darwinian doctrine it shows that sometimes new forms may arise by sudden
leaps and not necessarily by the slow and gradual accumulation of slight
modifications or fluctuations. The mutants like any other variants must
present themselves before the jury of environmental circumstances, which
passes judgment upon their condition of adaptation, and they, too, must
abide by the verdict that means life or death.

From what has been said of these post-Darwinian discoveries, the
Lamarckian doctrine, which teaches that acquired non-congenital characters
are transmitted, seems to be ruled out. I would not lead you to believe
that the matter is settled. I would say only that the non-transmission of
racial mutilations, negative breeding experiments upon mutilated rats and
mice, the results of further study of supposedly transmitted immunity to
poisons--that all these have led zoölogists to render the verdict of "not
proved." The future may bring to light positive evidence, and cases like
Brown-Séquard's guinea-pigs, and results like those of MacDougal with
plants, and of Tower with beetles, may lead us to alter the opinion
stated. But as it stands now most investigators hold that there are strong
general grounds for disbelief in the principle, and also that it lacks
experimental proof.

* * * * *

The explanation of natural evolution given by Darwinism and the principles
of Weismann, Mendel, and De Vries, still fails to solve the mystery
completely, and appeal has been made to other agencies, even to teleology
and to "unknown" and "unknowable" causes as well as to circumstantial
factors. A combination of Lamarckian and Darwinian factors has been
proposed by Osborn, Baldwin, and Lloyd Morgan, in the theory of organic
selection. The theory of orthogenesis propounded by Naegeli and Eimer, now
gaining much ground, holds that evolution takes place in direct lines of
progressive modification, and is not the result of apparent chance. Of
these and similar theories, all we can say is that if they are true, they
are not so well substantiated as the ones we have reviewed at greater
length.

The task of experimental zoölogy is to work more extensively and deeply
upon inheritance and variation, combining the methods and results of
cellular biology, biometrics, and experimental breeding. We may safely
predict that great advances will be made during the next few years in
analyzing the method of evolution; and that a few decades hence men will
look back to the present time as a period of transition like the era of
reawakened interest and renewed investigation that followed the appearance
of the "Origin of Species." For the present, we can justly say "that
evolution, so far as it is understood, is a real and natural process."

THE PHYSICAL EVOLUTION OF THE HUMAN SPECIES AND OF HUMAN RACES

The teachings of science that relate to the origin and history of the
human species constitute for us the most important part of the whole
doctrine of organic evolution and now, having completely outlined this
doctrine as a general one, we are brought to the point where we must deal
frankly and squarely with the insistent questions arising on all sides as
to the way that mankind is involved in the vast mechanism of nature's
order. These questions have been ignored heretofore, in order that the
natural history of animals in general might be discussed without any
interference on the part of purely human interest and concern. It now
becomes our privilege, and our duty as well, to employ and apply the
principles we have learned in order to understand more completely the
origin of the human body as an organic type, the history of human races,
the development of human faculty and of social institutions, and the
evolution finally of even the highest elements of human life. These are
scientific problems, and if we are to solve them we must employ the now
familiar methods of science which only yield sure results.

We must not underestimate the many difficulties to be encountered, for the
field before us is a vast territory of complex human life and of manifold
human relations. Without prolonged exercise in scientific methods, it is
impossible to view our own kind impersonally, as we do the creatures of
lower nature. Furthermore it seems to many that an analysis of human life
and biological history, even if it is possible, must alter or degrade
mankind in some degree; this is no more true than that a knowledge of the
principles of engineering according to which the Brooklyn Bridge has been
constructed renders that structure any different or unsafe for travel. Man
remains man, whether we are in utter ignorance of his mode of origin, or
whether we know all about his ancestry and about the factors that have
made him human. It is because our species appears to occupy a superior and
isolated position above the rest of nature that the mind seems reluctant
to follow the guidance of science when it conducts its investigations into
the history of seemingly privileged human nature. And it is feared also,
that if evolution is proven for man as well as for all other kinds of
animals, our cherished ideas and our outlook upon many departments of
human life must be profoundly affected. This may be so, but science
endeavors only to find out the truth; it cannot alter truth, nor does it
seek to do so. We might well wish that the world were different in many
respects and that we were free from the control of many natural laws
besides that of evolution, but if the real is what it is, then our duty is
plain before us; as we think more widely and deeply on the basis of
ripened experience, it becomes ever clearer that a knowledge of human
history gives the only sure guidance for human life.

To the zoölogist it seems strange that so many are opposed to a scientific
inquiry into the facts of human evolution, and to the conclusions
established by such an inquiry,--though, to be sure, this opposition is
directly proportional to ignorance or misunderstanding of the nature and
purpose of scientific investigation and of human evolution. The naturalist
comes to view our species as a kind of animal, and as a single one of the
hundreds of thousands of known forms of life; thus the question of human
origin is but a small part of organic evolution, which is itself only an
episode in the great sweep of cosmic evolution, endless in past time and
in the future. Were we some other order of beings, and not men, human
evolution would appear to us in its proper scientific proportions, namely,
as a minute fraction of the whole progress of the world.

While the foregoing statements are true, it is nevertheless right that a
close study should be made of the particular case of mankind. No doubt
much of the naturalist's interest in nature at large is due to his
conviction that the laws revealed by the organisms of a lower sphere must
hold true for man, and may explain many things that cannot be so clearly
discerned when only the highest type is the subject of investigation. It
is only too evident that little more than a general outline can be given
of the wide subject or group of subjects included under the head of human
evolution. We must divide the subject logically into parts, so that each
one may be taken up without being complicated by questions relating to
topics of another category, although the findings in any one department
must surely be of importance for comparison with the results established
in another section; for if evolution is universally true, the main
conclusion in any case must assist the investigation of another, just as
comparative anatomy and embryology supplement and corroborate each other
in the larger survey of organic evolution. As before, the illustrations of
each department of the subject must be selected from the stock of everyday
observation and information that we already possess, for we gain much when
we realize that evolution includes all the happenings of everyday life and
thought, as well as the occurrences of the remote past.

For the present, then, the questions relating to the higher aspects of
human life must be put aside, only that they may be taken up at the last.
Social evolution likewise finds its place in a later section, after the
phenomena of mind and mental evolution receive due attention and
description. At the present juncture, the human species presents itself as
a subject for organic analysis and classification, merely as a physical
organism. Just as the study of locomotives must begin with the detailed
structure of machines in the workshop before they can be profitably
understood as working mechanisms, so the physical evolution of mankind
must first be made intelligible before it is possible to prosecute
successfully the studies dealing with the psychology, social relations,
and higher conceptions that seem at first to be the exclusive properties
of our species.

The problems of physical evolution of man and of men fall into two groups.
Those of the first deal with the origin of the human species as a unit,
and its comparative relation to lower organisms, while those of the second
part are concerned with the further evolution of human races that have
come to be different in certain details of structure since the human type
as such arose. In the first part, all men will be assumed to be alike and
the members of a homogeneous species whose fundamental attributes are to
be compared with those of other animals; only afterwards will attention be
directed to the differences, previously ignored, that divide human beings
into well-marked varieties. It must be evident even at this point that the
mode of evolution demonstrated by the first investigation will be likely
to bear some close relation to the methods by which human races have
evolved to their present diverse anatomical situations.

* * * * *

The foregoing classification of the problems concerned with the nature and
origin of the human species renders it possible to restrict the immediate
inquiry to a definite and precise question. It is this: does the evidence
relating to the physical characteristics of our species prove that man is
the product of a supernatural act of creation, or does it show that man's
place in nature has been reached by a gradual process of natural
evolution? In order to obtain an equally precise and definite answer to
this question, referring to the particular case of most concern to us, it
is obvious that the method to be employed is the one which has given us an
understanding of organic evolution as an all-inclusive natural process.
The data must be verified, related, and classified, so that their meaning
may be concisely stated in the form of scientific principles. What are the
facts of human structure, comparatively treated? How does the human body
develop? Does palæontology throw any light on the antiquity of man? Do the
rules of nature's order control the lives of men? Our course is now clear;
we shall take up serially the anatomy, embryology, and fossil history of
the human species, in order to see that there is ample proof of the actual
occurrence of evolution, and then, as before, we may look about for the
causes which have produced this result by natural methods.

While it is necessary to treat the subject directly, namely, by examining
the actual evidences relating to the particular case in question, it is
worthwhile before doing so to point out that, as the whole includes a
part, human evolution has already been proved beyond question. This
conclusion must be accepted, unless reasons can be given for excluding
mankind from the rest of the living world as an absolutely unique type,
supreme and isolated because of some peculiar endowments not shared with
the rest of animate nature. If these reasons are lacking, and the unity of
organic nature be recognized, human evolution cannot be denied unless some
interpretation more reasonable and logical than evolution can be given for
the whole mass of facts exemplified and discussed in the foregoing
chapters. We may accordingly approach the main questions by asking if
there are any reasons for regarding the human species as a unique and
isolated type of organism.

At the outset, we must recognize that in so far as the human body is
material, its movements and mass relations are controlled by physical
principles, like all other masses of matter. It is well, indeed, that this
is so, for if gravitation and the laws of inertia were not consistent and
reliable principles holding true at all times and not intermittently, it
would be difficult to order our lives with confidence. In the next place,
the general principles of biology hold true for the structure and
physiology of the human species as they do for all other living things. A
human body is composed of eight systems of organs, whose functions are
identical with the eight vital tasks of every other animal. All these
organs are made up of cells as ultimate vital units, and the materials of
which human cells are composed belong to the class of substances called
protoplasm. Human protoplasm, like all other living materials, must
replenish itself, and respire and oxidize in obedience to biological laws
that have been found to be uniform everywhere. Thus the human organism is
no more unique in fundamental organic respects than it is apart from the
world of physical processes and laws.

How does the matter stand when the general structural plan of a human
being is examined? Is it entirely different from everything else? It is a
fact of common knowledge that the human body is supported by a bony axis,
the vertebral column, to which the skull is articulated and to which also
the skeletal framework of the limbs is attached. These characteristics
place man inevitably among the so-called vertebrata; he is certainly not
an invertebrate, nor is the basic structure of his body such that a third
group, outside the invertebrata and vertebrata, can be made to include
only the single type--man.

Passing now to the classes that make up the group of vertebrates, we meet
first the lampreys or cyclostomes without jaws, and the others with jaws,
such as the fishes, amphibia, reptiles, birds, and mammals, each class
distinguished by certain definite characters in addition to the vertebral
column. The fishes have gills and scales; amphibia of to-day are
scaleless, and they are provided with gills when they are young and lungs
as adults; reptiles have scales and lungs; birds are warm-blooded and
feathered; while mammals are warm-blooded and haired. Is the human species
a unique kind of vertebrate, or does it find a place in one of these
classes? The occurrence of hair, of a four-chambered heart which propels
warm blood, of mammary glands, and of other systematic characters marks
this species as a kind of mammal and not as a vertebrate in a section by
itself.

The members of the class mammalia differ much among themselves; and now
that we recognize clearly that man is a mammalian vertebrate, the next
question is whether an order exists to which our type must be assigned, or
whether we have at last reached a point where it is justifiable to
establish an isolated division to contain the human species alone. We are
familiar with many representatives of different mammalian orders and with
the kind of structural characteristics that serve as convenient
distinctions in denoting their relationships. Horses and cattle, sheep,
and goats and pigs resemble one another in many respects besides their
hoofs, and they form one natural order; the well-developed gnawing teeth
of rats and rabbits and squirrels place these forms together in the order
rodentia; the structures adapting their possessors for a flesh-eating and
predatory life unite the tribes of the lion, wolf, bear, and seal, in the
order carnivora. Among these and other orders of mammalia is one to which
the lemurs, monkeys, and apes are assigned, because all these forms agree
in certain structural respects that place them apart from the other
mammalia, in the same way, for example, that the races of white men may be
recognized as a group distinct from the black and red races. But
comparative studies, prosecuted not only by those who have been forced to
adopt the evolutionary interpretation, but also by believers in special
creation like Linnæus and Cuvier and other more modern opponents of
evolution, have shown that the peculiar qualities of this order are shared
by the human species. Indeed, the name of primates was given to this
section by Linnæus himself, because the human body found a place in the
array which begins at the lower extreme with the lemurs and the monkeys
and ends with man at the other end. Again it is found that no separate
order of mammals exists to include only the genus _Homo_.

To one unacquainted with the facts of vertebrate comparative anatomy, the
distinguishing characteristics of the primates seem to be trivial in
nature. It is surprising to find how insignificant are the details to
which appeal must be made in order to draw a line between our own division
of mammalia and the others. It is well to review them as they are given in
the standard text-books of comparative anatomy. Primates are eutheria, or
true mammalia possessing a placental attachment of the young within the
parent. The first digits, namely, the "great toe" and the "thumb," are
freely movable and opposable to the others, so that the limbs are
prehensile and clasping structures; usually but not always the animals of
this order are tree-dwellers in correlation with the grasping powers of
the feet and hands. The permanent teeth succeed a shorter series of
so-called "milk teeth," and they are diverse in structure, being incisors,
canines, or "eye teeth," premolars, and molars; the particular numbers of
each kind are almost invariable throughout the order and markedly
different from those of other orders. The number of digits is always five,
and with few exceptions they bear nails instead of claws. The clavicles,
or "collar bones," are well developed in correlation with the prehensile
nature of the fore limbs; a bony ring surrounds the orbit or eye socket.
Finally there are two mammary glands by which the young are suckled. It is
because any other details of difference between man and other forms are
far less marked than the agreements in these respects, that the human
species must be regarded as a primate mammalian vertebrate.

* * * * *

The comparative study of the human organism as a structural type has now
been narrowed down to a review of the various members of the order of
primates. It is the duty of science to arrange these organisms according
to the minor differences beneath the agreements in major qualities, and to
show how they are related in an order of evolution. It will appear, when
this is done, that the supreme place is given to the human species on
account of four and only four characteristics; these are (1) an entirely
erect posture, (2) greater brain development, (3) the power of articulate
speech, and (4) the power of reason. As we are treating the human body as
a subject for comparative structural study, the third and fourth
characters do not concern us here; but it is well to point out that they
depend entirely upon the second, and that they are the functional
concomitants of the improved type of brain belonging to the highest type.
Two characters remain, and in both cases it is significant that
differences in degree only are to be found by even the closest analysis.
The human brain is the same kind of brain that lower primates possess; its
structure is unique in no general respect. And as regards the
first-mentioned character, comparative anatomy shows, in the first place,
that this also is something differing only in degree, and in the second
place, that it is due directly to the development of the brain. For these
reasons a survey of the various members of the order of primates must deal
largely with the progressive elaboration of the brain and the entailed
effects of this enlargement.

The order of primates is subdivided as follows :--

Sub-order 1. _PROSIMII_. Lemurs.
Sub-order 2. _ANTHROPOIDEA_.
Family 1. _Hapalidæ_. The marmosets.
Family 2. _Cebidæ_. The American or tailed monkeys.
Family 3. _Cercopithecidæ_. The baboons.
Family 4. _Simiidæ_. The true apes.
Family 5. _Hominidæ_. The human species. Primates

Each one of these subdivisions is interesting in its own way, either
because its members depart from the typical condition of the whole order
in some respects, or because of some character that foreshadows and leads
to a more developed element of the animals placed in the higher sections.

The lemurs are small animals very much like squirrels in their general
form and in their tree-climbing habits. They live now almost exclusively
on the island of Madagascar, but palæontology shows that they were more
widely spread at an earlier time. Their teeth are exactly like our own,
except that there is one more premolar on each side of each jaw. The
"fingers" and "toes" bear nails like ours, again with an exception in the
case of the second digits of the hind limbs, which bear claws. The details
of structure that set these animals apart from all the rest of the
primates are too small to deserve comment in the present connection.

Passing to the true anthropoids, or man-like primates and man himself, the
first forms encountered are the little marmosets, which are like the
lemurs in some ways, but in other respects they resemble the familiar
tailed monkeys. They are peculiar in having three premolars and two molars
on either side of both upper and lower jaws, and also in the fact that the
"thumb" is not opposable to the other fingers, while all the digits except
the "great toes" bear claws instead of manlike nails. The proportion of
brain-case and face does not differ much from that in the lemurs and even
lower forms like cats, for the brain has not increased greatly in total
mass, though the cerebrum is more convoluted than in the lower forms.

The true monkeys, or Cebidæ, are more interesting, and at the same time
they are much more familiar to every one, as they are the commonest
anthropoids of the menagerie and circus. Their wonderful agility and
sureness in climbing about is partly due to the perfect grasping power of
the lower limb. To all intents and purposes the foot is a hand; the first
toe is shorter than the others, and its free motion is unrestricted as in
the thumb of the hand. These animals usually possess a long tail which
they can use as a prehensile organ, curling it about the branch of a tree
with hand-like ease and grasp. When they run on all fours, they plant the
palms and soles flat upon the ground. The feature of primary importance in
a comparative sense is the advanced structure of the skull. These
anthropoids are much more intelligent than the lower forms, which is a
correlate of their larger and more convoluted brains. The increase in the
total bulk of the brain has wrought considerable change, not only in the
head, but also in the relation of head to the trunk. The cranium, or
brain-case of bone, is relatively larger than the "face," and it bulges
upward so as to lie no longer behind the latter as it does in the lower
mammalia. In consequence of this cranial enlargement, the face and eyes
are swung downward, as it were, so that the line of vision is not straight
ahead, but depressed below the horizontal. In order to look to the front
and to the immediate foreground to which it is progressing or to where its
food or enemies may be, the monkey must bend back its head; if it is
still, it finds greater ease in the upright sitting posture which it
assumes readily and naturally.

The next division, called the Cercopithecidæ, includes the baboons of the
Old World. These animals also run upon all fours, and their feet are
handlike as before, but the tail is much reduced. The general appearance
of the head is doglike, and the brain-case arches little more than it does
in the monkeys, but the face projects forward as a long muzzle, with
terminal nostrils close together. In some respects the baboons stand
somewhat away from the line leading from the lower to higher anthropoids;
in other characters they approach the latter, for in the teeth especially
they are identical with the apes and with the human species.

The Simiidæ, or true apes, possess an overwhelming importance, far beyond
that of the baboons and monkeys. There are only four principal kinds now
existing, namely, the gibbon, orang-outang, chimpanzee, and the gorilla,
of which the first is much less familiar than the others. The known
species of gibbons occur in Indo-China and the Malay Peninsula. The
typical animal stands about three feet high; its overarching braincase,
enlarged in conformity with the much greater brain development, has pushed
the eyes and face still further around underneath, so that if the animal
walks upon all fours the eyes look almost straight into the ground.
Therefore it must bend back its head at an extremely uncomfortable angle
if it is to remain upon all four feet, but it prefers to raise itself up
into the human sitting posture, or, when it walks, it stands erect upon
its hind limbs. Hence we who are accustomed to think of ourselves as the
only erect animals must revise our opinion, for we find in the gibbon an
organism that is nearly, if not quite, as advanced in this respect as we
are. One peculiar difference may be pointed out,--the walking gibbon
stretches out its great long arms to the sides in order to preserve its
balance. The animal seems awkward to us, perhaps, but it is possible that
the human method of balancing the body by vigorously swinging the arms
might seem quite as awkward to a gibbon as its grotesque posture does to
us.

The orang-outang comes next in this series. It inhabits the islands of
Borneo and Sumatra, where we find two distinct species. It is a reddish
colored animal standing about four feet four inches high, with rather long
hair. It is bulky, slow and deliberate in action, and when it walks in a
semi-erect position it rests its knuckles upon the ground, swinging its
long arms as crutch-like supports. Like the gibbon, it does not walk upon
all four feet in the way that the monkeys and baboons do, and we find in
the still further development of the brain and the higher arch of the
cranium the reasons for its semi-erectness. It cannot remain with its
hands and feet upon the ground and bend back its head so as to direct its
vision forward.

The chimpanzee of intertropical Africa brings us to a still less
monkey-like and more manlike stage. This creature attains the height of
five feet, which is more than that of some of the lower races of man. It
possesses large ears and heavy overarching brows; its thumb and great toe
are more like those of man, though its foot is still practically a hand.
Its lower limb curves like those of the other apes, and its soles are
turned toward one another; in brief, it is naturally bow-legged, a
character that adapts it for a tree-climbing life. This animal also is
nearly, though not quite, erect. It shows a most marked advance in the
matter of the brain, for the cerebrum is richly folded or convoluted, and
with this higher degree of physical complexity is correlated its superior
intelligence; it is well known that chimpanzees can be taught to wear
clothing and to use a cup and spoon and bowl like a human child. Indeed,
in mental respects, the chimpanzee surpasses all of the other mammalia,
with the sole exception of man. An eminent psychologist has stated that it
is about the equal, in mental ability, of a nine months' old human infant.

The last form among the apes, the gorilla, is one that brings us to a
realization of our own human physical degeneracy. The animal lives in West
Equatorial Africa, and it is a veritable giant in bulk, though its height
may not exceed five feet six inches. The heavy ridges over the eyes, the
upturned nostrils and triangular nose, place it near to the orang-outang,
but it is superior to that form in its relatively greater brain-box, and
in the fact that its heavy lower jaws do not protrude so greatly. It, too,
is semi-erect, so that the line of the vertebral axis makes an angle with
the plane of the ground of about seventy degrees. Its anterior limbs, or
arms, are again very long and bulky; and like the chimpanzee, it rests its
knuckles upon the ground in walking.

It is a short step further to the human organism, whose brain has become
larger and more complex, with a corresponding advance in the functional
powers of reason and the like that owe their existence to the improved
structural basis. After what has been said earlier regarding the relation
between the erect attitude in walking and the increased size of the
cranial part of the skull as compared with the face, it will not be
difficult to see how inevitably the former is the result of the latter.
Should we get upon the ground upon our hands and knees in the position of
a tailed monkey, the eyes look straight into the ground, for the bulging
cranium has pushed out over the jaws and face so that they lie _under_ the
brain-case instead of in front. A person in this position can bend back
the head so as to look ahead, but the strain is too great for comfort.
Rising to the knees, and lifting the hands from the ground, a feeling of
ease at once succeeds that of tension. In the course of evolution
accomplished primarily by the increase of the higher portions of the
brain, the erect position has been assumed gradually and naturally, and to
maintain it has necessitated many other changes in skeleton and muscles;
for example, the pelvis has broadened to support the intestines, which
bear downwards instead of upon the abdominal walls; a double curve has
arisen in the axis of the vertebral column, giving an easier balance to
the upper part of the body and the head. Countless structures of the human
frame testify to an originally four-footed position and to a rotation of
the longer axis through an angle of ninety degrees, as evolution has
produced the human type.

The conclusion that the human brain has made mankind is thus established
as one of fundamental importance. Proceeding further, we learn that this
organ proves to be essentially the same as the brain of lower primates; it
does not gain its greater size and efficiency by the origination of wholly
new and unique parts, but solely by the further elaboration of the ones
present in lower forms. In a word, it is only a difference in _degree_ and
not in essential _kind_ that separates man from the apes and other
primates. Human nature is animal nature, and human structure is animal
structure, for nowhere can final and absolute differences be found. This
does not mean that no differences appear, for it would be absurd to
contend that man and the apes are identical in every respect; but it does
mean that the resemblances are fundamental and comprehensive, and any
details of dissimilarity are in the degree of complexity only. The supreme
place in nature attained by man is therefore due to progressive evolution
in the nervous system. The other systems have degenerated to a greater or
less degree, but such regressive changes are more than compensated for by
the superior control exerted by the improved brain. In purely physical and
mechanical respects, the human body is a degenerate as compared with a
gorilla; the arm of the latter is more powerful than the lower limb of the
former, while the gorilla's chest is more than twice as broad as the
human, and more than four times as capacious. It is not through superior
physique, but by superior ability to direct the activities of his body,
that man excels in the struggle for existence with the lower animals.

* * * * *

Moreover, the human body is a veritable museum of rare and interesting
relics of antiquity. This characterization is justified by those vestigial
and rudimentary structures that represent organs of value to human
relatives among the lower animals, though they play a less active part at
the present time in human economy. There is scarcely a single system that
does not exhibit many or fewer of these rudimentary structures, but only a
few need be specified. As compared with those of the apes, the human
wisdom teeth are degenerate; in the gorilla they are cut at the same time
as the other molars; and in the lower human races they come through the
gums in early youth, while in the more advanced Caucasic races they are
cut only in later life or not at all. The reduced vermiform appendix of
man, a source of much ill health, is another structure that is a
counterpart of a relatively larger and useful part of the digestive tract
in the lower primates and other animals. Furthermore, the human tail is a
reality, not a fiction. Now and then an individual is born with a tail
that may reach a length in later life of eight or ten inches; such
structures are, of course, abnormal. But in every normal human being there
is a series of little bones at the lower end of the vertebral column,
constituting the coccyx, and this is just where the abbreviated tail of
the ape and the still longer prehensile tail of the monkey arises from the
body. Unless the coccyx is a tail, what can it be? And if it does not
represent a reduced counterpart of the tails of other mammals, what does
it represent?

Many of the vestigial structures of man appear more clearly in infancy and
in embryonic development. The human embryo possesses a complete coat of
hair, called the lanugo, which usually disappears before birth. This hair
cannot be regarded as any less significant than the coat of hair which the
infant whale possesses; it means a completely haired ancestor. The
elements of this coat are arranged precisely as they are in the apes; upon
the arm, for example, they point from shoulder to elbow and from wrist to
elbow. Unless the anterior limb of the hairy human ancestor was held in
the position of the climbing ape's, this arrangement would be
disadvantageous, for the hair as a rain-shedding thatch would be effective
only upon the upper arm, while the hairs upon the forearm would catch the
rain. In a word, this vestigial coat indicates in the clearest possible
manner that the ancestor of the human species was not only hairy, but also
arboreal in its mode of life.

Every human infant is bow-legged at birth, and the natural position of its
curved limbs is like that of the gorilla's, for the soles of the feet are
turned toward one another. Again, the so-called great toe is at first
shorter than the others, and for a time it retains the power of free
movement that indicates a handlike character of the lower limb in the
ancestor. Many savage human races, however, whose feet remain unshod, make
use of the primitive grasping power of the foot which the higher races
lose completely. An Australian and Polynesian can pick up small objects
with the foot very much as we may with the hand.

Among the wonderful reminiscent characters displayed by the human infant
is the firm clasping power of the hand, which it possesses for a time
after birth and which enables it to hang suspended for several minutes
from a stick placed in its grasp. The muscles which enable the infant to
do this gradually dwindle, so that the two-year-old child can hang
suspended for only a few seconds. This grasping muscle is a heritage from
the ape, where there is an obvious necessity for the newborn individual to
have a firm hold upon the hairy coat of its tree-climbing mother. When the
newborn child hangs in this way, it bends its curved lower limbs so that
the soles of the feet are turned toward one another, thus increasing its
resemblance to the ape.

Let us realize that these curious relics found in so many places in the
framework of man are not unique, and that they are reduced counterparts of
larger and more valuable structures in the ape. Unless evolution is true,
they have absolutely no sensible reasons for existence. Science prefers
the evolutionary explanation of their occurrence because this explanation
is more in harmony with the facts known about other organisms, and it is
more reasonable than any other.

* * * * *

When we dealt with the general doctrine of natural transformation, it
appeared that the evidence of embryology was in many respects more cogent
and conclusive than that derived from the comparative study of animal
structures. In the case of man, as before, no one could demand any surer
or more convincing proof that an organic mechanism with one structure can
change into an organic mechanism with a different structure, than the
obvious facts of development. The embryo, which is not an infant or an
adult, becomes an infant which must work its way onward by the gradual
accumulation of slight changes here and there and everywhere in its
anatomy, until it becomes mature. Each and every one of us has actually
undergone the process of organic change in becoming what we are, and we
cannot deny the reality of such a process without challenging the evidence
of our senses.

When the full import of this history is realized, and when we look further
into the nature of these preliminary conditions through which the human
organism passes in development, we are forcibly impressed by other facts
than the one to which I have directed your attention, for not only do we
find natural transformation, as in the other mammals, but the embryonic
stages are marvelously similar to the earlier conditions in other mammals.
Not very long before birth the human embryo is strikingly similar to the
embryo of the ape; still earlier, it presents an appearance very like that
of the embryos of other mammals lower in the scale, like the cat and the
rabbit,--forms which comparative anatomy independently holds to be more
remote relatives of the human species. Indeed, as we trace back the still
earlier history, more and more characters are found which are the common
properties of wider and wider arrays of organisms, for at one time the
embryo exhibits gill-slits in the sides of its throat which in all
essential respects are just like those of the embryos of birds and
reptiles and amphibia, as well as of other embryo mammals and these
gill-slits are furthermore like those of the fishes which use them
throughout life. All the other organic systems exhibit everywhere the
common characteristics in which the embryos of the so-called higher animals
agree with one another and with the adult forms among lower creatures; the
human embryo possesses a fishlike heart and brain and primitive backbone,
fishlike muscles and alimentary tract. Can we reasonably regard these
resemblances as indications of anything else but a community of ancestry
of the forms that exhibit them?

Yet a still more wonderful fact is revealed by the study of the very
earliest stages of individual development. The human embryo begins its
very existence as a single cell,--nothing more and nothing less; in
general structure the human egg, like the eggs of all other many-celled
organisms, is just one of the unitary building blocks of the entire
organic world. And yet the egg may ultimately become the adult man. Does
this mean that man and all the other higher forms have evolved from
protozoa in the course of long ages? Science asks if it can mean anything
else. When the comparative anatomist bids us look upon the wide and varied
series of adult animals lower than man as his relatives, because they
display similar structural plans beneath their minor differences, it may
be difficult at first to obey him. But in the brief time necessary for the
human egg to develop into an adult, the entire range is compassed from the
single cell to the highest adult we know. There are no breaks in the
series of embryonic stages like those between the diverse adult animals of
the comparative array. I do not think we could ask nature for more
complete proof that human beings have evolved from one-cell ancestors as
simple as modern protozoa beyond the obvious facts of human transformation
during development. They at least are real and not the logical deductions
of reason; yet their very reality and familiarity render us blind to the
deeper meaning revealed to us only when science places the facts in
intelligible order.

* * * * *

And now, in the third place, we may look to nature for fossil evidence
regarding the ancestry of our species. Much is known about the remains of
many kinds of men who lived in prehistoric times, but we need consider
here only one form which lived long before the glacial period in the
so-called Tertiary times. In 1894 a scientist named Dubois discovered in
Java some of the remains of an animal which was partly ape and partly man.
So well did these remains exhibit the characters of Haeckel's hypothetical
ape-man, _Pithecanthropus_, that the name fitted the creature like a
glove. Specifically, the cranium presents an arch which is intermediate
between that of the average ape and of the lowest human beings. It
possessed protruding brows like those of the gorilla. The estimated brain
capacity was about one thousand cubic centimeters, four hundred more than
that of any known ape, and much less than the average of the lower human
races. Even without other characters, these would indicate that the animal
was actually a "missing link" in the scientific sense,--that is, a form
which is near the common progenitors of the modern species of apes and of
man. We would not expect to find a missing link that was actually
intermediate in all respects between modern apes and modern men, any more
than we should look for actual connecting bands of tissue between any two
leaves upon a tree. A missing link, in the true sense, is like a bud of
earlier years which stood near the point from which two twigs of the
present day now diverge. So _Pithecanthropus_ is a part of the chain
leading to man, not far from the place where the human line sprang from a
lower primate ancestor.

Of the fossil remains of true prehistoric men, little need be said. We
cannot know whether the races now living in the regions where these
remains are found are really the descendants of the older types, and so a
direct comparison cannot be made. It is true that the brain capacities of
the man of Spy, of the Neanderthal, and of the English caverns are lower
than those of modern civilized races, but the differences are not so
striking and not so clearly indicative of the apelike ancestor of man as
in the case of the previous comparison of _Pithecanthropus_ with apes and
men.

* * * * *

The foregoing facts illustrate the conclusive evidence brought forward by
science that human evolution in physical respects is true. Even if we
wished to do so, we cannot do away with the facts of structure and
development and fossil history, nor is there any other explanation more
reasonable than evolution for these facts. If now we should inquire into
the causes of this process, we would find again that the present study of
man and men reveals their subjection to the laws of nature which
accomplish evolution elsewhere in the organic world.

The fact of human variation requires no elucidation; it is as real for men
as for insects and trees. Indeed, some of the most significant facts of
variation have been first made out in the case of the human species. The
struggle for existence can be seen in everyday life. We cannot doubt its
reality when scores perish annually because of their failure to withstand
the extreme degrees of temperature during midwinter and midsummer; when
starvation causes so many deaths, and when the incessant combat with
bacterial enemies alone brings the list of casualties on the human side in
our own country to more than two hundred and fifty thousand a year. As in
nature at large, the more unfit are eliminated as a result of this
struggle, while the more adapted succeed. In the long run, that particular
applicant for a clerkship or any other work who may be the more fitted is
the one who gets it. While the severity of competition may be somewhat
mitigated as the result of social organization, and while our altruistic
charitable institutions enable many to prolong a more or less efficient
existence, the struggle for existence cannot be entirely done away with.
Heredity also is a real human process, and it follows the same course as
in animals at large; as in the case of variation, some of the fundamental
laws of its operation have been first worked out in the case of human
phenomena, and have been found subsequently to be of general application.

Reverting to the specific question as to the earliest divergence of man
from the apes, we can readily see how the superior development of the
ape-man's brain gave him a great advantage over his nearest competitors,
and how truly human ingenuity enabled the earliest men to employ weapons
and crude instruments instead of brute force. Thus the gap between men and
apes widened more and more, as reasoning power increased through
successive generations. This is another aspect of the statement that the
supreme position of man has been gained, not by superior organization in
physical respects outside of the nervous system, but by the superior
control of human organization by the higher organs of this system.

The unity of nature and of its processes is established more and more
surely as the naturalist classifies the facts of structure, development,
fossil history, and evolutionary method. Our own species is not unique; it
takes its high place among other organic forms whose lives are controlled
in every way by the uniform consistent laws of the world.

* * * * *

The physical evolution of human races is the next major division of the
large subject before us. Heretofore the obvious differences displayed by
various races have been disregarded and the species has been treated as a
unit, in order that its evolution from pre-human ancestors might be made
clear. Knowing now how the facts of structure show that the supreme
position of our kind has been attained mainly as the result of the
progressive elaboration of the higher portions of the brain, and not
because new and unique structures have been developed, we are prepared to
turn our attention to the diverse characteristics of human races; and
during this inquiry anatomical matters will still be the only ones to be
reviewed. The intellectual and social characters of numerous races belong
to the category of physiological or functional phenomena, which are to
receive due consideration at a later time. It is the meaning of the facts
of racial diversity for which we are now to look.

For many reasons this subject is more difficult to describe in a concise
outline than those taken up before. It is true that every one is familiar
with different types of human beings, such as the Negro and Japanese and
Chinese, while furthermore the obvious differences between such races as
the Norwegian and Italian are sufficiently marked to strike the attention
of any one who looks about at his fellow-passengers in a crowded street
car. But few indeed have a comprehensive knowledge of the wider range of
racial variation in which these familiar examples find their place.
Anthropology, or the science of mankind, is a large and well-organized
department of knowledge, dealing with the entire array of structural and
physiological characters of all men. One of its subdivisions,
anthropometry, is almost an independent discipline with methods of its
own; it describes the characteristics of human races as these are
determined by statistical methods of a somewhat technical nature. There is
still another science, ethnology, which deals more particularly with
institutions, customs, beliefs, and languages rather than with physical
matters, although it is clear that ethnology and anthropology cannot be
sharply separated, and that each must employ the results of the other for
its own particular purposes.

Because men have always been interested in the study of themselves, the
subject of racial evolution is literally enormous, and the attempt to give
anything like a complete description of what is known would obviously be
futile. But it is possible to obtain a clear conception of certain of the
fundamental principles that fall into line with the other parts of the
doctrine of organic evolution with which we have now become acquainted.
The main questions, therefore, may be stated in simple terms. The first
deals with the evidences as to the reality of evolution during the
historical and prehistoric development of the various types of man from
earlier common ancestors; the second asks whether the lines of racial
evolution are further continuations of the line leading from ape-like
ancestors to the human species as a type. In order to give the proper
perspective, it will be well to state at the present juncture, first, that
the various kinds of men do not vary from each other in a chance manner so
as to show all possible types and varieties, but that they fall into
natural groups or families distinguished by certain common
characteristics, just as do all other kinds of species of animals; in the
second place, it appears that some of the differences between the races
denoted higher on structural accounts and the lowest forms of man are of
the same nature as those observed in the review of the various species of
primates from the lemurs to man.

* * * * *

It is best to look at the whole question in a very simple and common-sense
way before undertaking an extended examination of the details of human
diversity. The most casual survey of the peoples that we know best because
of our own individual nearness to them enables us to realize that the
races now upon the earth have not existed forever and ever, or even for
the age of 6000 years as contended by Archbishop Ussher. They have all
come into existence as such, and they differ from their known antecedents;
so that at the very outset common-sense leads us to accept evolution as
true, if we admit that human races have changed during the course of
recent centuries. We know, for example, that the so-called Mexicans of
to-day are a people produced by a fusion of Spanish conquerors and Indian
aborigines the Mexican is neither Spaniard nor Indian, though he may
resemble both in certain respects; he is a product of natural evolution,
accomplished in this case by an amalgamation of two contrasted types. When
we speak of the American people, we must realize that it too has come into
existence as such, and even, indeed, that it is in the actual process of
evolution at the present time. The various foreign elements that have been
added during the last few decades by the hundreds of thousands are
becoming merged with the people who preceded them, just as the Dutch and
the French and the English coalesced during the days of early settlement
to form the young American nation. Perhaps most of us call ourselves
Anglo-Saxon, but we are in reality somewhat different even in physical
respects from the Englishmen of Queen Elizabeth's time, who alone deserved
the name Anglo-Saxon. This very term indicates an evolution of a type that
differs from both the Angles and the early Saxons of King Alfred's age.
These are simple examples which illustrate many features of the universal
history of human races wherever they are to be found. Even in the
comparatively peaceful times of our modern era the history of any race is
a veritable turmoil of constant changes; conquerors impress their
characters upon the vanquished, while the victors often adopt some of the
features of the conquered. Colonies split off from the mother nation to
follow out their destinies under other conditions. Nowhere does the
naturalist find evidence of long-established permanence, or an unentwined
course of an uninterrupted and unmodified line of racial descent.

It is the task of the student of human evolution to unravel the tangled
threads of human histories. The task is relatively simple when it is
concerned with recent times where the aid of written history may be
summoned but when the events of remote and prehistoric ages are to be
placed in order, the difficulties seem well-nigh insuperable. All is not
known, nor can it ever be known; but wherever facts can be established,
science can deal with them. By a study of the present races of mankind,
much of their earlier history can be worked out, for their genetic
relations may be determined by employing the principle that likeness means
consanguinity. Let us suppose an alien visitor to reach our planet from
somewhere else; if he were endowed with only ordinary human common-sense,
he would very soon ascertain the common origin of the English-speaking
people in Canada, the United States, Australia and New Zealand, South
Africa, and many other places. Even if he could not understand a word of
the English language, he would be justified in regarding them all as the
descendants of common ancestors because they agree in so many physical
qualities. The anthropologist works according to the same common-sense
principle, obtaining results that find no explanation other than evolution
when the varying characters that are used to determine social relationship
are properly classified and related. It is to these characters that we
must now give some attention.

* * * * *

The average stature of adults varies in different races from four feet one
inch in certain blacks to nearly six feet and seven inches, as among the
Patagonians. These are the extreme values for normal averages, although
dwarfs only fifteen inches high have been known, while "giants" sometimes
occur with a height of nine feet and five inches. Such individuals are of
course rare and abnormal, and are not to be taken into account in
establishing the average stature of a race for use in comparison with that
of another group.

The color of the skin is another criterion of racial relationship, though
it is more variable in races of common descent than we are wont to assume.
We are familiar with the fair and florid skin of the northern European,
the fair and pale skin in middle and southern Europe, the coppery red of
the American Indian, the brown of the Malay, of the Polynesian and of the
Moor, the yellowish cast of the Chinese and Japanese, and the deeper
velvety black of the Zulu; but it has been found that many of the close
relatives of the black are lighter in skin color than some of our
Caucasian relatives, so that this character cannot be taken by itself as a
single criterion of racial affinity.

Perhaps the most conservative and most reliable character that serves for
the broad classification of the human races is the shape of the individual
hairs of the head. We are familiar with the straight lank hair of the
Mongolian peoples and of the various tribes of American Indians, in whom
the hair possesses these peculiarities because each element grows as a
nearly perfect cylinder from the cells of the skin at the bottom of a tiny
pit or hair-follicle. The familiar wavy hair of white men owes its
character to the fact that the individual elements are formed by the skin,
not as pencil-like rods, but as flattened cylinders. They are oval or
elliptical in cross-section, and when they emerge from the skin they grow
into a long spiral. If, now, the hair is formed as a very much flattened
rod about one-half as wide in one diameter as in the other, it curls into
a very tight close spiral and gives the frizzly or woolly head-covering of
the Papuan and of the Negro.

In the next place, the shape of the cranium is a character of much value.
This is determined as the proportion between the transverse diameter of
the skull above the ears to the long diameter, namely, the line that runs
from the middle of the brow to the most posterior point of the skull. In
the so-called "long-headed" or dolichocephalic races, the proportion is
seventy-five to one hundred, while in those forms that have more rounded
or brachycephalic heads, like the Polynesian and the black pygmy, the
relation is eighty-three to one hundred. The cranial capacity again varies
considerably, from nine hundred cubic centimeters to twenty-two hundred
cubic centimeters. Many striking variations are also found in the
projection of the jaws. A line drawn from the lower end of the nose to the
chin makes a certain angle with the line drawn from the chin to the
posterior end of the lower jaw; if the jaw projects very greatly, this
angle will be much less than when they do not. In most of the Caucasian
peoples, the lines meet at an angle of eighty-nine degrees, or very nearly
a right angle, but in some of the lower races the figure may be only
fifty-one degrees. Additional characters of the teeth and of the palate
are also taken into account, and have proved their utility. Finally, the
nose exhibits a wide range of variation from the small delicate feature of
the Chinaman to the large, well-arched nose of the Indian. It may be
hollowed out at the bridge instead of arched; again, it may be nearly an
equilateral triangle in outline, as in the Veddahs, and the nostrils may
open somewhat forward instead of downward. As many as fifteen distinct
varieties of the human nose have been catalogued by Bertillon.

These are the principal bodily characters which the anthropologist uses to
distinguish races and by their means to determine the more immediate or
remote community of origin of comparable types. Many of these
characteristics, as indeed we may already see, are decidedly important in
connection with the second problem specified above, for in the case of the
flat triangular nose and projecting jaws of a low negroid we may discern
clear resemblances to certain features of the apes.

* * * * *

Long before the doctrine of evolution was understood and adopted, students
of the human races had been deeply impressed by their natural
resemblances. As early as 1672 Bernier divided human beings according to
certain of these fundamental similarities into four groups; namely, the
white European, the black African, the yellow Asiatic, and the Laplander.
Linnæus, in the eighteenth century, included _Homo sapiens_ in his list of
species, recognizing four subspecies in the European, Asiatic, African,
and Indian of America. Blumenbach in 1775 added the Malay, thus giving the
five types that most of us learned in our school days. But the different
varieties of men recognized by these observers were believed to be created
in their modern forms and with their present-day characteristics; the
common character of skin color exhibited by any group of peoples of a
single continent was to them only a convenient label for purposes of
description and classification. It was not until years later that
fundamental resemblances were recognized as indicating an actual blood
relationship of the races displaying them, and therefore of evolution.
Since the doctrine of human descent and of the divergence of human races
in later evolution has been accepted, those who have attempted to work out
fully the complete ancestry of different peoples have found that no single
character can be taken by itself, while the various criteria themselves
differ in reliability; the color of the skin is not so sure a guide as the
character of the hair and skull, wherefore the classifications of recent
times, notably those of Huxley and Haeckel, have been based largely upon
the latter. The latest systems have been more rigidly scientific and more
in accord with the most modern conceptions of organic relationships in
general, as evidenced by the thoroughgoing methods of Duckworth in his
recent treatise on human classification.

It now remains to present the salient facts regarding the genetic
relationships of typical human races, although it is obviously impossible
to go into all of the details of the subject. But these are not essential
for the main purpose, which is to show that the evolutionary explanation
is the only one that is reasonable and self-consistent. Opinions are
sometimes widely at variance regarding countless minor points, but no
anthropologist of to-day can be anything but an evolutionist, because the
main principles upon which the specialists agree fall directly into line
with those established elsewhere in zoölogy. It seems best to state these
principles without reverting to controversial matters which find their
place in the monographs of the experts. Any comprehensive account such as
that of Keane, even if it may not give the final word, will be entirely
sufficient to demonstrate how fruitful are the methods of evolution when
they are employed for the study of human races, and indeed how impossible
it is to discuss human histories without finding conclusive evidences of
their evolutionary nature.

The facts that are available indicate that the first members of our
species evolved in an equatorial continent which is now submerged, and
which occupied a position between the present continents of Asia and
Africa. From this center hordes of primitive men migrated to distant
centers where they differentiated into three primary and distinct groups.
The first of these was gradually resolved into the darker-skinned peoples
most of whom now live in the continent of Africa, although many dwell also
in the islands of the western Pacific Ocean. The second branch divided
almost immediately to produce, on the one hand, the Indians of the new
world and, on the other, the yellow-skinned inhabitants of Asia and other
places. The third branch developed as such in the neighborhood of the
Mediterranean Sea, and produced the series of so-called Caucasian peoples,
which are by far the most familiar to us and to which most of us belong.
But so early did the second branch divide that there are virtually four
main divisions of the human species that are to be examined in serial
order.

It is best to begin with our own division, because its greater familiarity
makes it easier to become acquainted with the methods and results of
anthropology, on the basis of facts that we already know. Three
subordinate types exist, located primarily in northern, central, and
southern Europe respectively, but many other races dwell elsewhere that
are assignable to one or another of these subdivisions. In northeastern
Europe we find people such as the Norwegians, Swedes, Danes, and north
Germans, that average five feet eight inches in height. They have the
long, wavy, and soft hair which is a general characteristic of the whole
Caucasian group, although its light flaxen color is distinctive. The blue
eye and florid complexion accompany the light color of the hair. The skull
is of the longer type, the jaws and forehead are straight and square, the
nose is large and long without a distinct arch, and the teeth are
relatively small. It is not so well known that the Scandinavian type is so
closely copied by many people of Asia, such as the western Persians,
Afghans, and certain of the Hindus, living in a continent that we are
inclined to assign to the Mongol only. In the possession of these
characters the Northern Europeans and other races specified display
evidences of their common ancestry and evolution quite as conclusively as
in the case of the cats discussed in an earlier chapter where the meaning
of essential likeness was first demonstrated.

A broad zone may be drawn from Wales, across Europe and Asia, and even to
the eastern islands of the South Seas, in which we find peoples that are
obviously of Caucasian descent, but they differ from the members of the
first group in some details of structure. On the average they are about
five feet five or six inches in height, the hair is dark and wavy, but it
is not the pencil-like structure of the Mongol. The complexion is pale,
the skull is rounder, and the eyes are usually brown in color. These
peoples agree also in their volatile temperament and vivacious manner and
are thus markedly different from the more stolid northerners. To this
minor branch of the Caucasian stock belong the Welsh, most of the French,
South Germans and Swiss, Russians and Poles, Armenians, eastern Persians,
and finally some of the inhabitants of Polynesia. The last, it is true,
form a well-marked group of darker-skinned and taller races, but in spite
of the admixture of these and other unusual features, we can still discern
the bodily characters that supplement their traditions, telling of an
Asian origin, in demonstrating their common ancestry with round-headed
Persians and middle Europeans. Below the zone of middle Europe and Asia is
another broad region inhabited by the "Mediterranean" type of Caucasian.
The Spaniard, Italian, Greek, and Arab are sufficiently familiar to
illustrate the distinctive qualities of this subdivision. These people
have the smaller stature, dark hair, dark eyes, and paler skin of the
middle Europeans, but the skull is of the long instead of the rounded
type. A well-marked subordinate group is formed by the so-called Semitic
peoples, such as the Arabs and their Hebrew relatives. The Berbers and
other North African races possess a darker skin probably because of the
admixture of Ethiopian stock, and they, too, are so well characterized
that they form a clearly marked outlying group as the so-called Hamites.
Passing over into Asia we find relatives of the Mediterranean man in the
Dravidas and Todas of India, possibly in the degenerate Veddahs of Ceylon,
and finally in the Ainus or "hairy men" of some of the Japanese islands.
The last-named people certainly possess some Mongolian features, but these
seem to have been added to a more fundamental form of body that is
distinctly Caucasian.

All of the races we have mentioned, together with their relatives, may be
compared to the leaves borne upon three branches that take their origin
from a single limb of the widespread human part of the tree. They cannot
be classified in any mode on the basis of their primary and secondary
resemblances without employing the treelike plan of arrangement, which to
the man of science is a sure indication of their evolutionary
relationships.

* * * * *

The people of the second or Mongolian group agree in certain well-marked
characteristics in such a way as to be well separated from the other
divisions of mankind; these characteristics we may speak of as
constituting a second "theme," of which the various peoples of the group
are so many variations. To visualize them we need only to recall the
appearance of the Chinaman, perhaps the most familiar example of the
entire series. Here the hair is coarse and black, and straight because of
its round transverse section; the mustache and beard of the Caucasians are
seldom found except in later life; the skin is a fleshy yellow in color;
the skull is round, indeed, it is one of the roundest that we know; the
jaws are not so straight as in the Caucasian, for the angle at the point
of the chin is about sixty-eight degrees. The cheek bones project
laterally, with greater or less prominence; the nose is very small, tilted
up slightly at the end, and is usually hollowed instead of arched. The
eyes are small and black in color, set somewhat obliquely, and the upper
lid is drawn down over the eye at its inner corner so as to make the
obliquity still more marked. The teeth are larger than those of the
Caucasian. Finally, the Mongol is below the average of all men as regards
height, being usually about five feet four inches tall.

The original Mongolians probably developed the characteristic features we
have just noted in a Central Asiatic region, and then almost immediately
they divided into two great groups. Each of these evolved along certain
lines of its own, one sweeping northward to develop into what are now
called the Northern Mongols, the other working its way eastward and
southward to produce the peoples of China proper, Indo-China, and many
parts of Malaysia. Considering first the peoples of the Northern Mongolian
division, we find in the typical Manchurian what is perhaps the nearest
among modern people to the original race. Spreading northward and westward
from the middle Asiatic plains, this great wave has produced the nomadic
tribes of Siberia, like the Chukchi, the Buryats, and the Yukaghir. The
present inhabitants of Turkestan connect those forms which have remained
near the original home with the races of Mongolian origin that live
farther to the westward, like the Turks of Asia. But the Mongolian tide
originally swept much farther to the west, although it was driven back
later by conquering Caucasian peoples; and it has left behind such
remnants as the Finlander and the Laplander, the Bulgar, and the Magyar.
It is evident that these western branches of the Mongol stock are not at
all pure in their racial characteristics, for they clearly show the
effects of a mixture with alien European peoples. To assign them to the
Northern Mongol division means only that their dominant characteristics
are mainly those of Mongolian nature. We have referred the Russians to the
middle Caucasian division even though the Slav or Tartar infusion is very
great, but it does not dominate over the Caucasian peculiarities as it
does in the case of the peoples we have mentioned. As regards the
remaining types we must add to this brief list the Koreans and the
Japanese, the former being far purer in Mongolian nature than the latter
people, which has apparently been affected by a Malay influence from the
south.

Turning now to the southern Mongol, we find that from their cradle in the
Tibetan plateau they too have spread widely, and their descendants have
also come to differ in certain respects as they have established
themselves in other lands. Most of the present people of Tibet belong to
this section; the Gurkhas of Hindustan, the people of Burma proper, of
Annam, and Cochin China are close relatives of one another and of the more
characteristic Mongolians of China proper who make up the vast bulk of the
population. From this stock we may also derive the Malays of Sumatra and
Java, of Borneo and Celebes, and the Tagals and Bisayans of the Philippine
Islands. Even the Hovars and other tribes of Madagascar may be referred to
this division, for although in them the skin has become somewhat darker,
we may still discern the characteristics which indicate their common
ancestry with the Oceanic Mongols.

* * * * *

The American Indians taken collectively constitute a group that is well
set off from the rest of mankind by such characters as taller stature,
small, straight, and black eyes, a large nose that is usually bridged or
aquiline, a skull of medium roundness, and the yellow copper color of the
skin. The common origin with the Mongols is demonstrated by the straight
and long, coarse, black hair and by the absence of a beard; the mustache
also is almost always absent.

All of us have seen Indians belonging to the tribes of the plains, which
serve as excellent examples of this grand division. Many have also visited
the homes of the Pueblo Indians, and have learned how uniform is the
physical appearance of the tribes living in various parts of the United
States. Indeed throughout all of North America the basic characteristics
of Indians prove to be strikingly conservative, although in the Eskimo
there are some departures which seem to indicate a closer connection of
these peoples with the Mongols, probably as the result of some more recent
influx from the neighboring and not very distant region of northeastern
Siberia. Extending our survey southward through Central America, the
Aztecs and Mayas are found to possess many of the same characters, though
in some respects they are transitional to the Caribs of the northern edge
of South America and to the Indians of South America. Traveling still
farther southward, we meet the very tall Patagonian, still an Indian in
essential respects, and finally, the Yahgan and Alacaluf of the Fuegian
region, the most degenerate members of the race. The last-mentioned people
are dull and brutish and most degraded in all respects, and stand at the
lowest end of the red Indian series as regards intellectual ability and
cultural attainment.

* * * * *

We now come to the last of the four great divisions of the human species
which includes the races usually spoken of as Africans or Ethiopians. But
these races are by no means restricted to the continent of Africa, for
quite as typical black types are found in far-distant lands such as
Australia and many islands of the Pacific Ocean. The races assigned to
this division group themselves about two subordinate types,--the tall
negro proper and the shorter or dwarf negrito,--and each of these has
representatives both in Africa and in the oceanic territory.

The black slaves of America were all descended from typical negros brought
from the western part of Africa, and they provide us with adequate
illustrations of Ethiopians as a group. In them the stature is above the
average of men in general, specifically about five feet ten inches. The
short jet-black hair is strikingly different from the head covering of the
other great groups of human races; each individual hair is so flat in
cross-section that it curls into a very tight close spiral, and this
brings about a frizzly appearance of the whole head covering. There is
little or no beard, the skin is soft and velvety and of various shades
approaching black in color. The skull is long, the cheek bones are small,
but the most distinctive characteristics of the head are found in the
apelike ridges over the eyes and in the very broad flat nose which
projects only slightly and turns up so that the nostrils open forward to a
marked degree, while in the jaws there is an astonishing divergence from
the Caucasian condition in the great protrusion which causes the angle at
the chin to be about sixty degrees.

The warlike Zulus and other peoples of Southern and Central Africa are
perhaps the most characteristic races in this division. Their relatives
are found to the northward as far as the Sahara desert, along the southern
borders of which they have spread out to the eastward and westward. Fusion
with other races has taken place along this border so that many of these
northern tribes are much lighter than the Zulus in the color of the skin.
But many relatives of the taller African negro are found in other parts of
the world, namely in Australia, and in New Hebrides and New
Caledonia--islands to the north and east of this continent. The Papuan of
New Guinea is a typical negro in all true respects, with strongly marked
Ethiopian characteristics, though there are some differences which are
transitional to the more aberrant natives of Melanesia, which includes
many archipelagos like the Fiji, Bismarck, Marshall, and Solomon islands.
Undoubtedly the most degenerate member of the tall negro division is the
Australian native, the so-called "blackfellow." The bulbous nose and the
well-grown beard mark him off from the typical stock, but his obvious
relationship to this is indicated by the low brain capacity, the prominent
ridges over the eyes, and the heavy projecting jaws.

Taking up the other division of the so-called Ethiopian race, constituting
the Negrito section, we may begin with its Oceanic members. The natives of
the Andaman Islands, the Kalangs and the Sakais of Java and neighboring
regions, and the Aetas of the Philippine Islands agree in a dwarfed
stature of four feet or a little over, in their yellowish brown skin
color, a round head, and woolly reddish-brown hair. They, too, possess
large ridges over the eyes and extremely prominent jaws, and in these
latter characteristics particularly we see evidences of their relationship
to the negro. But perhaps the most characteristic pygmies are found in
Africa. The little Bushmen and Hottentots are low types of the Negrito
stock, and they lead us to the lowest men of all, the Akkas of the West
Congo region. It is difficult for us to realize how utterly degenerate and
apelike these pygmies are. The jaws are disproportionately large as
compared with the cranium or brain-case, and project to a degree which
brings the skull very close to that of the higher apes; while in mental
respects, in the absence of dwellings, and in many other ways they prove
to be the lowest of all mankind,--veritable brutes in form and mode of
life.

* * * * *

Without a full series of photographs before us the foregoing sketch of the
various races of men cannot make us fully acquainted with all the strange
varieties of the human body, but it will suffice to establish two
fundamental results. While all men agree in the possession of certain
features which set them apart from other members of the primate order,
they differ among themselves in such a way as to fall into four
well-marked subdivisions branching out from a common starting-point.
Furthermore, in each of these primary groups the subordinate types arrange
themselves also in the manner of branches arising from a common limb. This
is the relation that we have earlier found to be a universal one
throughout the animal kingdom, and science believes that it indicates
everywhere an evolutionary history--an actual development along different
lines of descent of forms which have a common starting-point and ancestry.

The second principle is perhaps even more significant: when we review the
many races from the Caucasian to the dwarf Negrito, we traverse a downward
path which will bring us inevitably to the higher apes. In our survey of
human races, we have passed from the Caucasian, with the largest brain and
cranium and with straight jaws well underneath the brain-case, to the
pygmy with a relatively small brain, with huge projecting jaws and with
prominent ridges over the eyes; one step more along that path would bring
us to the gorilla or the chimpanzee. The array of lower primates, from the
lemur to the gorilla, gives a series of forms exhibiting a progressive
advance in respect to the size of the brain and cranium, and a gradual
retreat of the jaws to a position underneath the cranium; and one step
further brings us to man. In a word, these two lines join--in fact, they
are directly continuous. There is a far smaller difference between the
lowest man and the highest ape than we have been accustomed to suppose.

Thus in general terms, it can justly be said that process of evolution
which developed the first man from its ape-man progenitor seems to have
continued during subsequent ages. Spreading out in diverging lines of
evolutionary descent no less clearly than they have in geographical
respects, certain races have far surpassed their fellows of a lower order,
which, like the brute pygmy, remain nearer the common structural form from
which all men have sprung.

THE MENTAL EVOLUTION OF MAN

The problems dealing with the make-up of the human mind and with the
evidences of mental evolution bring the student to matters of more vivid
human interest. Mental phenomena are so complex and intricate that it is
well-nigh impossible to analyze their history without a knowledge of the
principles derived from the broad study of evolution as a general
doctrine, where human prejudice is not so large a factor and where his
perspective is less affected by the proximity of the observer to his
facts. For these and other reasons the foregoing treatment of human
evolution has been confined to the purely structural characteristics of
man as a species and of human races as so many varieties of this type.
When the broad comparative methods of biological science are employed for
the elucidation of human anatomical facts, the result in this special
case, like that established through the study of the characteristics of
living things in general, is the proof that evolution gives the most
rational and natural explanation of the observed data. This being true,
the naturalist who turns from purely structural matters to human intellect
and its history, finds well-tried methods of inquiry already available,
and he approaches his further studies with a conviction that evolution,
having proved to be universal so far, in all probability will be found
equally true in the case of psychological phenomena. This expectation is
indeed realized, and the scope of the doctrine is extended over a new
field, when the facts of human psychology are treated as materials for
impersonal comparative study; and this result is not only useful and
valuable in and by itself, but it also provides in the principles of
mental evolution the transition to the field of social relations and
ethical ideas and ideals which are apparently the unique possessions of
men as individuals and as associated groups.

The field of comparative psychology might seem at first sight to be a
foreign territory to the average well-informed layman in science, but the
contrary is really the case. Every one has thought at one time or another
about his own mental make-up, and about the minds of others. No one can
watch a child at play with his toys or at work with his schoolbooks
without being struck by many evidences of marked differences between the
immature and the experienced types of mind. Every one knows also that the
mental "scheme of things" is by no means the same for all nations or races
of mankind existing to-day, while furthermore the fact is entirely
familiar that the intellectual heritage of a present race has changed in
the course of previous ages. Therefore in this field as before we need
only to amplify our knowledge of such representative psychological facts
as these by drawing upon the full stores of the special investigator, in
order to learn that human thought, like the human frame, has undergone a
natural history of transformation to become what it is and what it was
not.

Many who would be ready to accept the evolution of physical
characteristics find it impossible to treat the history of human mentality
as a subject for dispassionate consideration, because above all else the
intellectual powers of mankind seem to be truly distinctive. It is only
after constant use of the methods of science that we can bring ourselves
to see how closely we resemble lower forms in physical make-up; still
greater reluctance must be overcome before we can view our mental
processes as counterparts of those of inferior animals, so essential to
our very humanity do they seem. But our duty to undertake the task is
plain, and its discharge will be greatly facilitated by a clear
realization that mental evolution is but a part of human transformation in
times past, as the latter is only a small fraction of the universal
process of organic evolution in general. While our own nature and
inquisitiveness give us so intense an interest in the teachings of science
that relate to the constitution and history of human faculty, wherefore
these matters gain an undue prominence in perspective, it must never be
forgotten that these teachings do not stand by themselves, for they are
built upon the sure foundations already laid in physical evolution; and
these foundations cannot be disturbed by our failure to use them as a
basis when we construct our own conceptions of human intellect and its
history.

* * * * *

Before passing to the systematic review of the facts and principles of
comparative psychology which demonstrate evolution, there are certain
general aspects of the subject to be considered so as to clear the ground,
as it were, for further progress. When the several organic systems of the
human body were compared with those of the apes and of lower animals,
their evolution was proved as far as the purely physical and material
characteristics were concerned. But we know that there is no part of any
one of these systems which has not its own particular function, even
though this may be a relatively passive one; while furthermore, science
does not know of any physiological activity without some organ or tissue
or cell as its material basis. Therefore the evolution of an organic
system in material respects involves its functional or dynamic evolution
as an inseparable correlate; the two proceed in unity, and they cannot be
regarded as entirely distinct without violating common-sense.

The fin of a fish is used as an organ of locomotion in water; from some
such organ have evolved the walking limbs of amphibia and reptiles,
constructed for progression upon land. Among the mammalia the fore limbs
have become structurally adapted so as to be such diverse organs of
locomotion as the stilt-like leg of a horse, the flipper of a seal, the
whale's paddle, and the bat's wing, while among the birds the wing may
change into a flipper like that of the penguin, or become reduced to a
vestige as in _Apteryx_. We may focus our attention upon the material
likenesses and differences in such a series of locomotory organs, but an
inevitable accompaniment of their physical changes in the transformation
of species has been an evolution in the functional matter of locomotion.
The most complex and differentiated tracts of even the highest animals
have evolved from a simple sac like that of a polyp or jellyfish, as we
know from the independent testimony of comparative anatomy and embryology;
in this case also the evolution of alimentary functions is no less
inseparable from the transformations in structural respects. And again, we
cannot understand the historical development of vision without taking into
account the eyes of various types belonging to lower and higher animals.

So it is with the nervous systems of man and other animals, and with their
functions. The nervous system of the human organism comprises identical
organs with the same arrangements that are found in other primates and in
lower vertebrates as well; the differences in structure are differences in
the degree of the complexity of certain parts, notably of the cerebrum.
Therefore the evolution of human mentality, which depends upon a human
type of brain as a physical basis, is already demonstrated with the proof
that the human brain and nervous system have evolved. It is true that an
invariable and necessary connection between mind and matter is implied in
the foregoing statement, and this is something which demands further
consideration at a later point. But just _how_ the human mind is produced
by or depends upon the brain, is of far less importance for us at this
time than the obvious fact that mental performance requires active nervous
tissues. So far investigation has been unable to discover a valid reason
for a belief in the existence of mental phenomena, as such, apart from
some kind of material basis. And while we may prefer to restrict the use
of the word _mind_ to the series of nervous processes going on in the
human organ of thought, in so far as these processes are carried on by the
peculiar tissues of the nervous system they cannot be finally
distinguished from the functional products or accompaniments of the same
kind of active tissues and organs in lower creatures. Thus the subject of
mental evolution becomes much clarified at the outset by understanding
that nervous processes and nervous systems evolve together.

In the direct treatment of the facts and principles of mental evolution we
can use exactly the same classification and subdivisions of the materials
of study as heretofore, because psychological data are the correlates of
material organic systems, and also because the former, being natural
phenomena, are subject to the methods of analysis which can be employed
for any series of objects that have undergone evolution. Separating the
matter of fact from the question as to the method, and recalling the main
bodies of evidence as to the reality of evolution, we may establish four
sections of the subject before us: these are (1) the anatomy, (2) the
embryology, and (3) "palæontology" of mind, and (4) an inquiry into the
way nature deals with the psychical characteristics of organisms in
accomplishing their evolution. To specify more particularly, it is
possible in the first place to compare the activities belonging to the
category of mental and nervous operations, displayed by man and other
organisms, and the results form the subject of comparative descriptive
psychology; the second division, namely, developmental or genetic
psychology, deals with the sequence of events in the life of a single
individual by which the infantile and adolescent types of mind become
adult intellectuality; in the third place, in speaking of the palæontology
of mind, the phrase is used to refer to the varied and changing mental
abilities of human races in historic and prehistoric times as they may be
demonstrated and determined by the evidences of the culture of such
earlier epochs. In considering the matter of method, the questions are
whether variation, inheritance, and selection are as real in the world of
mental phenomena as they are in the material world, and whether the laws
are the same or similar in the two cases. We shall learn how the results
of such studies prove with convincing clearness, first, that the contents
of the individual mind and of the minds of various human races are truly
the products of natural evolution, and second, that the human mind differs
only in degree from that of lower organisms, and not in kind or
fundamental nature.

* * * * *

When the operations of human mental life are examined, they include what
are called processes of _reason_ as apparently distinctive elements. The
lower mammalia exhibit a simpler order of "mentality" denoted
_intelligence_, while the nervous processes of still simpler forms are
called _instinctive_ and _reflex_ activities. These are the terms of the
comparative array of psychology which are to be separately examined and
classified, and to be brought into an evolutionary sequence if
common-sense directs us to do so.

Let us begin our comparative study with an example of the simplest animals
that consist of only a single cell, such as the little protozoon
_Amoeba_. We have become familiar with this organism as one that carries
on all of the vital functions within the limits of a single structural
unit; it is a mass of protoplasm enclosing a nucleus, and as a biological
individual it must perform all of the eight tasks that are essential for
life. It does not possess a digestive tract, but it does digest; it does
not have breathing organs, but it does respire; and it is particularly
noteworthy that it must coordinate the different activities of its parts,
and maintain definite relations with the environment, even though its
coordination and sensation are not accomplished by any special parts that
would deserve the name of elementary nervous organs. Its many activities
are simple responses to stimuli that reach it from without, and its
reactions to such stimuli are called reflex processes. Should the light
become too strong, it will slowly crawl to a shady place; should the water
in which it lives become warmer, it responds by displaying greater
activity. It exhibits, in a word, the property of _irritability_--that is,
simply the power of receiving and reacting to stimuli; and being only a
single cell this property is held in common by all of its parts.

We come next to a simple many-celled animal like the polyp _Hydra_, or a
jellyfish. In such an animal the body is composed of numerous cells which
are not all alike either in their make-up or in their functions. Some of
them are concerned primarily with digestion, others with protection, while
still others are exempt from these tasks and as sense-cells they devote
all their energies to the reception of stimuli from without, or, beneath
the outer sheet of cells of the two-layered body, they conduct impulses
from one part of the animal to another, and thus serve as coordinating
members of the community. For the first time, then, a nervous system as
such is set apart and specialized to devote itself to the two tasks of
sensation and coordination that are performed by nervous systems
throughout the entire range of organisms higher in the scale. But the
activities of _Hydra_, like those of _Amoeba_, are reflex and
mechanical,--that is to say, _given similar stimuli and similar
physiological states of the animal, the reactions will be the same_. A
little water-crustacean like _Daphnia_ may swim against the tentacles of
_Hydra_; it is stung to death by the minute cell-batteries which the
animal possesses, and then in a mechanical way the tentacles transport the
food to the mouth, through which it is passed inward to the digestive
cavity. There is nothing that can be called "mentality" throughout these
processes, but the series of activities is much more complex than in
_Amoeba_ because the whole organism is constructed more elaborately, and
because the special and peculiar mechanism directing the activities has
advanced to a far higher condition.

Passing to the jointed animals like worms and insects, we find nervous
mechanisms that are still more intricate, and with their advance in
structural respects there is a corresponding and correlated progress in
their functions. Because the whole organism has developed more highly
differentiated groups of organs to perform the several biological tasks,
such as eating and respiring and moving, it is necessary for the nervous
structures concerned with the direction of these actions to become more
efficient. An earthworm avoids the light of day and digs its burrow and
seeks its food by wonderfully coördinated activities of its muscles and
other parts, which are controlled by a double chain of ganglia along its
ventral side, connected with a similar pair of grouped nerve-cells above
the anterior part of the digestive tract. The ganglia of each segment
exercise immediate supervision over the structures of their respective
territory, while they pass on impulses to other ganglia so that movements
involving many segments can be properly adjusted. Everything an earthworm
does is controlled by the cells grouped in these ganglia, or scattered
along the intervening connecting cords. We speak of its acts as
instinctive, employing a term which seems to indicate a different kind of
operation carried on by the nervous system, but a moment's thought will
show that an instinctive act is simply a complex group of reflex acts. The
physical basis and ultimate unit is a cell, and the functional unit is
likewise a cell act; therefore the seeming difference proves to be one
merely of degree and not of kind. The greater complexity of the worm's
nervous system as compared with that of _Hydra_ gives to the whole
mechanism a plasticity that diverts the attention from the mechanical
nature of the entire instinctive act and of its basic cell elements.

The instinct, like the elementary reflex, is determined by heredity.
Because a certain configuration of the cells and fibers making up a
nervous system is inherited as well as the characters of the constituent
elements themselves, a worm or an insect is enabled to act as it does. A
butterfly does not have to learn how to fly, for it flies instinctively.
When it emerges from its chrysalis with its complete adult series of wings
and muscles, it has also the nervous mechanism by which these parts are
mechanically controlled. A ground-wasp deposits its eggs in a small burrow
in which it places also a caterpillar or a grasshopper paralyzed by
stinging, so that when the larva is hatched from an egg it finds an ample
supply of fresh food provided by a complex series of its mother's acts
that seem to be directed by conscious maternal solicitude. When the larva
passes through the later stages of development and makes its way to the
open air as a fully formed adult, it in its turn may go through the same
course of action as its parent, but it is clear that it cannot have any
remembrance of its mother's work or any personal knowledge of the value of
burying its own eggs in a chamber with a living prisoner to serve as food.
It was an egg when its parent did these things; as a parent itself it does
not remain on watch to see how beneficial or fruitless its acts may be. A
mechanism produced by nature's methods, the ground-wasp behaves as it is
capable of working with its inherited structure and its inherited
instinctive powers of coördination and sensation.

The complex lives of communal insects like ants and bees bring us to the
level of mentality where an understanding of causes and effects seems to
be the guide for conduct. Nevertheless the facts do not warrant the
assumption that reason and intelligence play any part in the mental life
of these creatures, as they do in the lives of man and the apes. Because
we ourselves can see the utility of the definite and peculiar behavior of
the queen and the worker, there is no logical necessity for assuming an
identical form of knowledge as a possession of these insects. Many
investigators have dealt with these fascinating subjects, and they are
almost unanimous in the conclusion that the instinct of an insect is a
mechanical and hereditary synthesis of combined reflex acts.

The lower orders of psychological processes play a far larger part in the
lives of the higher animals than we are wont to believe. A pointer and
sheep dog possess different qualifications in the way of instincts that
make them useful to man in different ways. A bulldog or a game-cock does
not reason out its course of action during a contest, but like a mechanism
when the spring is released, it acts promptly and with effect. A ball
flashing past the human eye causes the lids to close unconsciously, and it
is not always possible to inhibit this instinctive mechanical act by the
exercise of the will. An examination of the workings of the human body
reveals manifold activities of an even lower or reflex nature, like the
movements of the viscera and the adjustments in respect to the amount of
supplies of blood sent to different parts of the body as local needs
arise. Directed always by specific portions of the nervous system, such
reflex actions play their part in human life without any effort on the
part of reason and so-called will, and without coming into consciousness
except indirectly and subsequently.

Passing by many interesting members of the psychological series of
intergrading forms, we reach the familiar animals like the cat and dog and
horse which display what is called intelligence. This is the power to
learn by experience, and to improve the quality and promptitude of
reactions to stimuli. In certain respects intelligence seems to differ
from instinct, inasmuch as it involves a response to stimuli that may be
altered and quickened by repeated experience, but in ultimate analysis the
two forms of psychological processes are fundamentally alike. A single
example chosen from Thorndike's extensive investigation will serve to
bring out the primary characteristics of intelligence. A cat was placed in
a latticed cage provided with a door that could be opened from within when
a catch was pressed down, and meat was put in a dish outside the door
where the cat could see it. At first, the animal escaped from the cage by
freeing the door during its aimless scrambling about the catch, but as
trial after trial was made, the time necessary for the cat to make its way
out was shortened, until after seventy-five or one hundred trials, the
animal immediately opened the door and seized the food. In mechanical
terms, the connection between "scrambling about the door" and "freedom to
get the meat" became established by numerous repetitions until the
originally disconnected elements were physiologically associated and made
inseparable. When animals like horses and seals and dogs are trained for
the circus, it is by exactly the same method, for training consists merely
in the establishment of a psychological sequence so that the performance
of one series of acts leads mechanically to others. Thus we learn that the
psychological property called intelligence is the ability to establish
wide relations between numerous activities which are themselves of a more
or less complex nature; and we find also that because these elements are
ultimately nerve-cell and sense-cell reflexes, an intelligent response is
quite as machine-like as any and all of its elements. A difference in
degree of complexity and extent is the only thing that places intelligence
apart from instinct and reflex action, for the units are the same in all
cases,--so far as science knows.

The apes are of the greatest value in providing the transition from the
grade of intelligence to the human level where reason is found. Whether or
not a chimpanzee can reason at all is less important than the fact that
its total "mental" powers are lower than those of man, and higher than
those of inferior mammalia. Apes are far more susceptible to training than
cats and dogs, because their improved nervous mechanism enables them to
establish a psychological sequence with greater facility. If we are to
judge by the facts at hand, these creatures possess a low order of
mentality, like, but by no means equivalent to, that of man.

At the end of the comparative scale, we reach the human mind which is
characterized by its ability to perceive and recognize far wider relations
than those which are involved in intelligence. Human consciousness is the
stream of thoughts and feelings which constitute the immediate contents of
mind. In our own case, we know both the activities we perform and some of
the internal phenomena with which such activities are connected. Then we
are impelled to compare the objective phenomena of action with the
behavior of other men and of lower organisms, and if their behavior does
not coincide with our own we are justified in believing that its direction
lacks some of the elements we know about in our own case. This is the
method of comparative psychology, which establishes the conclusion that
reason is the more complex term of a series to which reflex action,
instinct, and intelligence directly lead.

Were we to study in detail the psychology of adult human beings, we would
find only more truly that instinct and intelligence play a large part in
our everyday mental life, and more certainly that even the highest
reasoning powers we possess are only more complex in nature than the
nervous processes of lower mammals and invertebrates. Just as the nervous
systems advance in physical or structural respects, so must their
activities become more and more complex until the result is human faculty.

* * * * *

We must now briefly consider what may be called the "comparative
anthropology" of mind which deals with the various degrees of mental
ability displayed by different human races; this subject follows
inevitably upon the comparison of the human mind viewed as a single type
with the psychological processes of lower animals. When we reviewed the
diverse characteristics of human races--the protrusion of the jaws,
greater or lesser stature, and the like--it appeared that so-called
"lower" races could be distinguished which differed from the "higher"
races in the direction of the apes; the question immediately arises
whether similar distinctions and relations are discoverable on the basis
of mental traits. But in the present case there are not so many
well-substantiated differentia at the disposal of the student, and it does
not appear so clearly that the "higher" races are furthest from the lower
primates and lower mammalia as regards their mental processes. What facts
there are, however, prove to be highly significant, and they materially
amplify our conception of human faculty as a product of evolution. The
essential point is that the intellectual attainments of various races are
by no means the same. The calculus is a mental product of the white race
only; gunpowder and printing from movable type were independently invented
by the Caucasian and Mongolian races; but the American Indian and the
Negro never originated them. Human faculty, to employ the most general
term for all that distinguishes man from the brutes, proves to be a very
varied thing when we draw comparisons between and among races with
independent lines of ancestry and heredity occupying widely separated
areas. Should we analyze it, we find it to be composed of three
constituents; namely, the physical elements of the brain, the degree to
which the observational or perceptual and higher elements cooperate in
building up the conceptions peculiar to the type, and the materials with
which the physical mechanism deals, in the way of environmental,
educational, and social "grist for the mental mill." Many anthropologists
accord too great an importance to the third constituent of human faculty,
I believe, and they are therefore led to deny that races differ in mental
respects to so large a degree as the thoroughgoing evolutionist would
contend. They hold that differences in such things as powers of
observation are due to training: that, for example, an American Indian or
a South Sea Islander sees certain things in his environment more quickly
than a white man only because these are the things which the experiences
of his earlier life have accustomed him to look for and to find. This may
be granted, and it may also be admitted that children of so-called "lower"
races can be educated side by side with the youth of white races without
noticeably falling behind, up to a certain point when, at the age of
adolescence, in the classic case of the Australian natives, other factors
prove to be obstacles to further progress. We must also recognize that the
character of the environment of a race determines to a large extent the
mode of life of the people; a forest-dwelling Indian of the interior is a
hunter as well as a warrior, while a South Sea Islander is a navigator and
a fisherman.

But the fact remains that the inhabitants of similar countries have
reached markedly different grades of intellectual and cultural life.
Anglo-Saxon dominance must be referred ultimately to Anglo-Saxon heredity
and not to the peculiarities of the land. Although adaptation is no less
necessary for men as individuals and as social groups than it is for all
other living things, I believe that it is to diversity in constitutional
endowments, however these may have arisen, that we must attribute the
superiority of some races over others. The question is not whether a
savage race can or cannot adopt the higher conceptions of a civilized
people; the fact is that they have not actually become civilized by
themselves. Thus, while evolution in mental respects has not resulted in
the loss of plasticity in the case of the brain and the nervous system as
a whole, wherefore the activities of these organs still remain capable of
individual and racial modifications that are impossible in the case of the
skeleton and in the color and shape of the eye, it remains true that races
do differ intellectually, and that their differences are marks of a mental
evolution quite as definite as their physical natural histories of change.

* * * * *

In my own view the strongest and most impressive evidence bearing upon the
great problem before us is provided by the series of transformations by
which the human intellect develops during an individual life. Mind has an
embryology no less significant than that of the skull or of any other
element of the body; and its investigation leads to the evolutionary
interpretation quite as surely as the study of the various grades of adult
psychology constituting the anatomical sequence, which we have reviewed
previously. When in the earlier part of the book we dealt with embryology
in general, we learned how the changes which take place when an organism
develops from an egg demonstrate the actuality of true organic
transformation without the necessity of concluding or inferring that this
process might occur. It is not superfluous to insist again that the
essential fact in evolution is the alteration of one organic
characteristic into another type; must we not recognize at the very outset
that mental transformation is as real as physical development?

In the first instance we might concern ourselves with the physical basis
of mind and its history. In the earliest stages of human embryology no
nervous system whatsoever is present, and it is unreasonable to suppose
that there is anything going on which corresponds to human thought. A
little later a cellular tube is established as a primitive nerve axis,
which at first is nearly uniform throughout its entire length and displays
no differentiation into brain and spinal cord. Before long an enlargement
of the anterior end expands and develops into a primitive three-parted
brain. It is not yet a real brain, however, and it is entirely incapable
of functioning in such a way as to justify the use of the word _mental_
for the results of its operations. We know that it is only in the cerebral
hemisphere of the adult brain that the processes of true human
consciousness go on. But it is not until long after the three-parted stage
that the cerebral hemispheres make their appearance therefore we cannot
speak of mind as present when the cell and tissue basis of mind is not
present. When, now, the cerebral hemispheres do appear, they are small
bean-shaped structures no larger relatively than those of a fish. Later
they enlarge so as to attain the relative size of the cerebral hemispheres
of an amphibian, and still later they are like those of a reptilian brain.
Continuing to enlarge, they begin to fold so that the total surface is
increased without very much addition to their bulk. At this time the
cerebral hemispheres of the brain of the human embryo are like those of an
adult cat or dog. The process of general enlargement and of progressive
convolution are continued, and stages are reached and passed which
correspond with the monkey and ape conditions.

Nothing in human development is more impressive than the origin of the
cerebrum and its development by passing through successive stages which
are counterparts in the main of the adult brains of other and lower
animals. The alteration of a tissue-mechanism constructed in one way into
a tissue-mechanism of a more complex nature, provides the most conclusive
evidence of the reality of brain evolution, because the process of
transformation actually takes place.

But in the present connection we are more interested in the dynamic or
functional aspects of mental evolution, which it must be remembered are
inseparably bound up with the physical structures and their modifications.
After a human infant is born its activities are reflex and mechanical like
those of the adult members of lower groups. As it grows it performs
instinctive acts because its inherited nervous system operates in the
purely mechanical manner of a lower mammal's nervous system. For these
reasons an eminent psychologist has said that the mental ability of an
infant six months old is about that of a well-bred fox terrier. The same
infant at nine months displays an intelligence of a higher order equal to
that of a well-trained chimpanzee; it has become what it was not, and in
so far it has truly evolved in mental respects. At two years of age the
child is incapable of solving problems of the calculus, for its reasoning
powers are elementary and restricted, but these same powers change and
intensify so as to render the older mind quite capable of grasping the
highest of human conceptions and ideas. In my judgment the unbroken
transformation of a child's mind that exhibits only instinct and
intelligence into an adult's mind with its power of reasoning, is far more
conclusive as proof of mental evolution than the inference drawn from the
comparisons we have made above of the adult psychological phenomena of
man, ape, cat, and fish. It is surely natural for such mental
transformations to take place, for they do take place in the vast majority
of human beings; when they do not, in cases where the brain fails to
mature, we speak of unnatural or diseased minds.

The third division of our evidence relating to mental evolution
constitutes what we have called the palæontology of mind. By this term we
mean the study of human minds of the past as we may know them through the
many varied relics and documents which indicate their characters. It is
only too obvious to every one that human knowledge has advanced in the
course of time and that every department of human thought and mental
activity has participated in this progress. No one would have the temerity
to assert that we know nothing more than our ancestors of 5000 or even
1000 years ago. Our common-sense teaches us even before the man of science
produces the full body of evidence at his disposal that human faculties
have evolved. With regard to reasoning powers, which form one of the four
distinguishing characteristics of the human species as contrasted with
other animals, the case has already been reviewed, and we now turn to
speech and language and other departments of human mentality. When we
compare the attainments of present day men with the abilities and ideas of
their ancestors we will do for mental phenomena precisely what was done
when we compared the skeletons of modern animals with those of creatures
belonging to bygone geological ages; in this reason is found the
justification for the phrase employed in the present connection.

Written history furnishes a wealth of material for interpreting the mental
conditions of ancient peoples, but beside documentary evidence the
anthropologist learns to use inscriptions of prehistoric times, the
primitive graphic representations on tombs and monuments, and even the
characteristics of crude implements like axes and arrow-heads. The layman
finds it difficult at first to regard such relics as indications of the
mental stature of the people who made and possessed them; but a little
thought will show that a man who used a rough stone ax in the time of the
ancient Celts could not possibly have had a mind which included the
conception of a finished iron tool or modern mechanism. So in all
departments of human culture, the evolution of material objects may be
justly employed in interpreting and estimating the mental abilities of
ancient peoples.

Language is undoubtedly the most important single intellectual possession
of mankind, for it constitutes, as it were, the very framework of social
organization. Without a ready means of communication the myriad human
units who perform the varied tasks necessary for the economic well-being
of a body-politic would be unable to coordinate their manifold activities
with success, and the structure of civilized societies at least would
collapse. It needs no legend of a Tower of Babel to make this plain. So
fundamental is this truth that although we may not have recognized it
explicitly, we unconsciously form the belief that speech and language are
exclusive properties of the human species, and even more characteristic of
man alone than the power of reason itself. While organized language is
clearly something that as such we do not share with the lower animals,
nevertheless we cannot regard the communication of ideas or states of
feeling by sound as an exclusive property of mankind. All are familiar
with the difference between the whine and the bark of a dog and with the
widely different feelings that are expressed by these contrasted sounds.
And we know too that dogs can understand what many of their master's words
signify, as when a shepherd gives directions to his collie. We could even
go further down in the scale and find in the shrill chirping of the
katydid at the mating season a still more elementary combination of
significant instinctive sound elements. To the comparative student the
speech of man differs from these lower modes of communication only in its
greater complexity, and in its employment of more numerous and varied
sounds,--in a word, only in the higher degree of its evolution. And it is
even more evident that the diverse forms of speech employed by various
races have gradually grown to be what they now are.

At the outset it is well to distinguish between writing, as the
conventional mode of symbolizing words, and spoken language itself; the
two have been more independent in their evolution than we may be wont to
believe. Speech came first in historical development, just as a child now
learns to talk before it can understand and use printed or written
letters. Furthermore, many races still exist who have a well-developed
form of language without any concrete way of recording it. It is true, of
course, that back of the conventions of speech and writing are the ideas
themselves that find expression in the one way or the other, or even by
the still more primitive use of signs and gestures. But it is not with
these ultimate elements of thought that we are now concerned; our task is
to learn, first, what evidences are discoverable which show that the
property of human language in general has originated by evolution, and
then, in the second place, to perceive how this development proves an
evolution of one group of ultimate ideas, namely, human concepts of the
modal value of words and symbols as expressions of ideas themselves.

A simple common-sense treatment of obvious facts will greatly facilitate
our progress. We know very well that the English we speak to-day differs
in many ways from the language of Elizabethan times, and that the former
is a direct descendant of the other. The latter, in turn, was a product of
Norman French and Anglo-Saxon,--a combination of certain elements of both,
but identical with neither of its immediate parents. The Saxon tongue
itself has a history that leads back to King Alfred's time and earlier.
Thus we are already aware of the fact that our speech has truly evolved,
like the physical structure of the men who employ it; and we know, too,
how readily new words are adopted into current English, like _tabu_ from
Polynesia, or _garage_ from the French, showing that language is even now
in process of evolution.

The sounds that make up spoken words can be resolved into a single element
with its modifications; this basic element is the brute-like call or shout
made with the mouth and throat opened wide--a sound we may have heard
uttered by men under the stress of pain or terror. All of the various
vowels are simply modifications of this element by altering the shape of
the mouth cavity and orifice, while the consonants are produced by
interrupting the sound-waves with the palate or lips or tongue. Like the
cell as a unit of structure throughout the organic world, this elemental
utterance proves to be the basic unit of all human languages, which vary
so widely among races of to-day no less than they have in the history of
any single people.

One of the first steps in the making of spoken words was taken by human
beings when they imitated the calls or other sounds produced by living
things, and tacitly agreed to recognize the imitation as a symbol of the
creature making it. Thus the names for the cuckoo and the crow in many
languages besides our own are simply copies of the calls uttered by these
birds; a Tahitian calls a cat _mimi_; the name for a snake almost
invariably includes the hissing attributed to that creature. After a time
words which were at first simply imitations and which referred only to the
things that made these sounds came to refer to certain qualities of the
things imitated, so that the naming of other than natural objects, such as
qualities, began, leading ultimately to the use of words for qualities
belonging to many and different objects in the way of abstractions.

Much light upon the evolution of language is obtained when we treat the
speech of various races as we did the skeletal structures of cats and
seals and whales. When we compare the Italian, Spanish, Portuguese, and
French languages, they reveal the same general structure in thousands of
their words,--a common basis which in these cases is due to their
derivation from the same ancestor, the Latin tongue. The Latin word for
star is _stella_, and the Italian word of to-day is an identical and
unchanged descendant, like a persistent type of shark which lives now in
practically the same form as did its ancestor in the coal ages. The
Spanish word is _estrella_, a modified derivative, but still one that
bears in its structure the marks of its Latin origin; the French word
_étoile_ is a still more altered product of word evolution. Even in the
German _stern_, Norse _stjern_, Danish _starn_, and English _star_ we may
recognize mutual affinities and common ancestral structure. Choosing
illustrations from a different group, the Hebrew salutation "Peace be with
you," _Shalom lachem_, proves to be a blood cousin of the Arabic _Salaam
alaikum_, indicating the common ancestry of these diverse languages. Among
Polynesian peoples the Tahitian calls a house a _fare_, the Maori of New
Zealand uses _whare_, while the Hawaiian employs the word _hale_, and the
Samoan, _fale_. Whenever we classify and compare human languages, we find
similar consistent anatomical evidences of their relationships and
evolution. We can even discern counterparts of the vestigial structures
like the rudimentary limbs of whales. In the English word _night_ certain
letters do not function vocally, though in the German counterpart _Nacht_
their correspondents still play a part. In the word _dough_ as correctly
pronounced the final letters are similarly vestigial, although in the
phonetic relative _tough_ they are still sounded.

The evolution of the art of writing appears with equal clearness when we
compare the texts of modern peoples with inscriptions found on ancient
temples and monuments and tablets. Even races of the present day employ
methods of communicating ideas by writing symbols that are counterparts of
the earliest stages in the historic development of writing. An Eskimo
describes the events of a journey by a series of little pictures
representing himself in the act of doing various things. A simple outline
of a man with one arm pointing to the body and the other pointing away
indicates "I go." A circle denotes the island to which he goes. He sleeps
there one night, and he tells this by drawing a figure with one hand over
the eyes, indicating sleep, while the other hand has one finger upraised
to specify a single night. The next day he goes further and he employs the
first figure again. A second island is indicated, in this case with a dot
in the center of the circle to show a house in which he sleeps two nights,
as his figure with closed eyes and two fingers uplifted shows. He hunts
the walrus, an outline of which is given alongside of his figure waving a
spear in one hand; likewise he hunts with a bow and arrow, which is
demonstrated by the same method. A rude drawing representing a boat with
two upright lines for himself and another man with paddles in their hands
gives a further account of his journey, and the final figure is the circle
denoting the original island to which he returns.

Pictography, as this method of communicating ideas is called, is often
highly developed among the American Indians. For example, a petition from
a tribe of Chippewa Indians to the President of the United States asking
for the possession of certain lakes near their reservation is a series of
pictures of the sacred animals or "totems" which represent the several
subtribes. Lines run from the hearts of the totem animals to the heart of
the chief totem, while similar lines run from the eyes of the subsidiary
totems to the eyes of the chief, and these indicate that all of the
subtribes feel the same way about the matter and view it alike,--the
sentiment is unanimous. From the chief totem run out two lines, one going
to the picture of the desired object, while the other goes to the
President, conveying the petition. Thus pictography, a method of writing
that belongs to the childhood of races, may be made to communicate ideas
of a strikingly complex nature.

The ancient and modern inscriptions of Asia, from the Red Sea to China,
present many significant stages in the development of picture-writing. In
earliest ages the men of Asia made actual drawings of particular objects,
such as the sun, trees, and human figures; subsequently these became
conventionalized to a certain degree, but even as late as 3000 B.C. the
Akkadian script was still largely pictographic. From it originated the
knife-point writing of Babylonian and Chaldean clay tablets, while among
the peoples of Eastern Asia, who continued to draw their symbols, the
transition to conventionalized pictures such as those made by the Chinaman
was slower and less drastic.

In another line of evolution, the hieroglyphics of Egyptian tombs and
monuments illustrate a most interesting intermediate condition of
development. These inscriptions have been deciphered only since the
discovery of the famous Rosetta stone-fragment, which bears portions of
three identical texts written in hieroglyphics, in Greek, and in another
series of symbols. The Egyptian used more or less formalized characters to
represent certain sounds, while in addition to the group of such
characters combined to make a word, the scribe drew a supplementary
picture of the thing or act signified. For instance, _xeftu_ means
enemies, but the Egyptian graver added a picture of a kneeling bowman to
avoid any possible misapprehension as to his meaning. The symbols denoting
"to walk" are followed by a pair of legs; the setting sun is described not
only by a word but also by its outline as it lies on the horizon. Here
again one is struck by the similarity between a stage in the historic
development of racial characteristics and a method employed at the present
time to teach the immature minds of children that certain letters
represent a particular object; in a kindergarten primer the sentence "see
the rat and the cat" is accompanied by pictures of the animals specified,
in true hieroglyphic simplicity.

Just as the child's mind develops so that the aid of the picture can be
dispensed with, and the symbolic characters can be used in increasingly
complex ways, in like manner the minds of men living in successive
centuries have evolved. While an evolution of human conceptual processes
in general is not necessarily implied by the evolution of the forms of
written language, the former process is in part demonstrated by the latter
in so far as the change from the writing of pictures to the use of
conventional symbols involves an advance in human ideas of the
interpretation and value of the symbols in question. A man of ancient
times drew a tree to represent his conception of this object; in the
writing of English we now use four letters to stand for the same object,
and none of these symbols is in any way a replica of the tree. It is
certainly obvious that some change in the mental association of symbol and
object has been brought about, and to this extent there has been mental
evolution.

* * * * *

Passing now to other departments of human culture, we must deal in the
next place with the basic "arts of life"; that is, the modes of conducting
the necessary activities of every day. All men of all times, be they
civilized or savage, are impelled like the brutes by their biological
nature to seek food and to repel their foes. The rough stone club and ax
were fashioned by the first savage men, when diminishing physical prowess
placed them at a disadvantage in the competition with stronger animals.
Smoother and more efficient weapons were made by the hordes of their more
advanced descendants, some of whom remained in the mental and cultural
condition of the stone age like the Fuegian, until the white travelers of
recent centuries brought them newer ideas and implements. In Europe and
elsewhere the period of stone gave place to the bronze and iron ages, and
throughout the changing years human inventiveness improved the missile and
weapon to become the bow and arrow of medieval civilization and recent
African savagery. The artillery and shells of modern warfare are their
still more highly evolved descendants.

So it is with the dwellings of men, and the significance of the changes
displayed by such things. The cave was a natural shelter for primitive man
as well as for the wolf, and it is still used by men to-day. Where it did
not exist, a leafy screen of branches served in its stead; even now there
are human beings, like the African pygmy and the Indian of Brazil, who are
little beyond the orang-outang as regards the character of the shelter
they construct out of vegetation. From such crude beginnings, on a par
with the lairs and nests of lower animals, have evolved the grass huts of
the Zulu, the bamboo dwelling of the Malay, the igloo of the Arctic
tribes, and the mud house of the desert Indians. The modern palace and
apartment are merely more complex and more elaborate in material and
architectural plan, when compared with their primitive antecedents.

Baskets, clay vessels, and other household articles testify in the same
way to an evolution of the mental views of the people making them. The
means of transportation are even more demonstrative. The wagon of the
early Briton was like a rough ox-cart of the present day, evolved from the
simple sledge as a beginning. In its turn it has served as a prototype for
all the conveyances on wheels such as the stage-coach and the modern
Pullman. The history of locomotives, employed in the first chapter to
develop a clear conception of what evolution means, takes its place here
as a demonstration of the way human ideas about traction have themselves
evolved so as to render the construction of such mechanisms possible.

The primitive savage swimming in the sea found that a floating log
supported his weight as he rested from his efforts. By the strokes of his
arms or of a club in his hand, he could propel this log in a desired
direction; thus the dugout canoe arose, to be steadied by the outrigger as
the savage enlarged his experience. A cloth held aloft aided his progress
down or across the wind, and it became an integral element of the sailing
craft, which evolved through the stages of the galley and caravel to the
schooner and frigate of modern times. When the steam-engine was invented
and incorporated in the boat, a new line of evolution was initiated,
leading from the "Clermont" to the "Lusitania" and the battleship.

The history of clothing begins with the employment of an animal's hide or
a branch of leaves to protect the body from the sun's heat or the cold
winds. Other early beginnings of the more elaborate decorative clothing
are discerned by anthropologists in the scars made upon the arms and
breast as in the case of the Australian black man, and in the figured
patterns of tattooing, so remarkably developed by the natives in the
islands of the South Pacific Ocean. A visit to a gallery of ancient and
medieval paintings clearly shows that the conventional modes of clothing
the human body have changed from century to century, while it is equally
plain that they alter even from year to year of the present time,
according to the vagaries of fashion.

A brief review of the "arts of pleasure," including music and sculpture
and painting, demonstrates their evolution also. The earliest cavemen of
Europe left crude drawings of reindeer and bears and wild oxen scratched
upon bits of ivory or upon the stone walls of their shelters; the painting
and sculpture of early historic Europe were more advanced, but they were
far from being what Greece and Rome produced in later centuries. Indeed,
the evolution of Greek sculpture carried this higher art to a point that
is generally conceded to be far beyond that attained by even our modern
sculptors, just as flying reptiles of the Chalk Age developed wings and
learned to fly long before birds and bats came into existence.

In the field of music, the earliest stages can be surmised only by a study
of the actual songs and instruments of primitive peoples now living in
wild places. No doubt the song began as a recitation by a savage of the
events of a battle or a journey in which he had participated. In giving
such a description he lives his battles again, and his simulated moods and
passions alter his voice so that the spoken history becomes a chant. From
this to the choral and oratorio is not very far.

Musical instruments seem to have had a multiple origin. The ram's horn of
the early Briton and the perforated conch-shell of the South Sea Islander
are natural trumpets; when they were copied in brass and other metals they
evolved rapidly to become the varied wind instruments typified to-day by
the cornet and the tuba. In the same way the reed of the Greek shepherd is
the ancestor of the flute and clarionet. Stringed instruments like the
guitar, zither, and violin form another class which begins with the bow
and its twanging string. The power of the note was intensified by holding
a gourd against the bow to serve as a resonance-chamber. When the musician
of early times enlarged this chamber, moved it to the end of the bow, and
multiplied the strings, he constructed the cithara of antiquity,--the
ancestor of a host of modern types, from the harp to the bass-viol and
mandolin.

The dance and the drama find their beginnings in the simple reënactment of
an actual series of events. Among Polynesians of to-day the dances still
retain the rhythmic beat of the war-tread measure, and many of the motions
of the arms are more or less conventionalized imitations of the act of
striking with a club, or hurling a spear, and other acts. To such elements
many other things have been added, but the fact remains that our own
formal dances, as well as the sun-dance of the Indian and the mad whirl of
the Dervish, are modern products which have truly evolved.

* * * * *

When we turn to science and philosophy and other intellectual attainments
of modern civilized peoples, it is easier to see how evolution has been
accomplished, because we possess a wealth of written literature which
explains the way that human ideas have changed from century to century. In
these cases there can be no question that such evidences provide accurate
instruments for estimating the mental abilities of the writers who
produced them. We shall take up the higher conceptions of mankind at a
later juncture, so at this point we need only to note that even these
mental possessions, like household culture and even the physical
structures of a human body, have changed and differentiated to become the
widely different interpretations of the world and supernature that are
held by the civilized, barbarous, and savage races of to-day.

As we look back over the facts that have been cited, and as we contemplate
the large departments of knowledge about human psychology, mental
development, and racial culture which these few details illustrate, we
come to realize how securely founded is the doctrine that even the human
mind with all its varied powers has grown to be what it is. Indeed, it is
solely due to his mental prowess that man has attained a position above
that of any lower animal. And yet every human organ and its function can
be traced to something in the lower world; it is a difference only in
degree and not in category that science discovers. The line connecting
civilized man with the savage leads inevitably through the ape to the
lower mammalia possessing intelligence, and on down to the reflex organic
mechanisms which end with the _Amoeba_. It is a long distance from the
mechanical activities of the protozoön to the processes of human thought;
yet the physical basis of the latter is a cellular mechanism and nothing
more, developed during a single human life in company with all other
organs from a one-celled starting-point--the human egg.

* * * * *

The method by which mental evolution has been accomplished is likewise
demonstrable, because the factors are identical with those which bring
about specific transformation in physical respects. This is to be
expected, for the contention that the structures and the functions of the
several organs constituting any system are inseparable has never been
gainsaid.

Mental variation is real. It needs no scientist to tell us that human
beings differ in intellectual qualifications and attainments, and that no
two people are exactly similar even though they may be brothers or
sisters. The struggle for existence or competition on the basis of mental
ability is equally real, and every day we see the prize awarded to the
more fit, while those who lose are crowded ever closer to the wall. As in
all other fields of endeavor, the goal of success can be attained only by
adaptation, which involves an adjustment to all of the conditions of
existence--to social and ethical as well as to the more expressly material
biological circumstances.

Heredity of mental qualities has also been demonstrated notably by Galton,
Pearson, Woods, and Thorndike, who have also shown that the strength of
inheritance in the case of mental traits is approximately the same as for
physical characteristics like stature and eye-color. Just as a worker-bee
inherits a specific form of nervous system which coöperates with the other
equally determined organic systems, wherefore the animal is forced to
perform "instinctively" its peculiar specialized tasks, so the mental
capacity of a human being is largely determined by congenital factors.
Upon these primarily depends his success or failure. It is quite true that
environment has a high degree of influence, so great indeed that some
speak of a "social heredity"; they mean by this phrase that the mental
equipment of an individual is determined by the things he finds about him,
or learns from others without having to invent or originate them himself.
Thus a Zulu boy acquires the habits of a warrior and a huntsman when he
grows up in his native village, although he would undoubtedly develop
quite different aptitudes if he should be taken as an infant to a city of
white men. Nevertheless his mental machinery itself would be no less
surely determined by heredity, even though the things with which it dealt
would be provided by an alien environment.

Our present knowledge of the nature and history of human mentality enables
us to learn many lessons that have a direct practical value, although it
is impossible under the present limitations to give them the full
discussion they deserve. Starting from the dictum that physical
inheritance provides the mechanism of intellect, education and training of
any kind prove to be effective as agents for developing hereditary
qualities or for suppressing undesirable tendencies. Just as wind-strewn
grains of wheat may fall upon rock and stony soil and loam, to grow well
or poorly or not at all according to their environmental situations, so
children with similar intellectual possibilities would have their growth
fostered or hampered or prevented by the educational systems to which they
were subjected. But the common-sense of science demonstrates that the
mental qualities themselves could not be altered _in nature_ by the
circumstances controlling their development any more than the hereditary
capability of the wheat grains to produce wheat would be altered by the
character of the ground upon which they fell. Education and training thus
find their sphere of usefulness is developing what it is worth while to
bring out, and inhibiting the growth of what is harmful. That heredity in
mental as well as in physical aspects provides the varying materials with
which education must deal is a fundamental biological fact which is too
often disregarded. It would be as futile for an instructor to attempt the
task of forcing the children in a single schoolroom into the same mental
mold, as it would be for a gymnasium master to expect that by a similar
course of exercise he could make all of his students conform to the same
identical stature, the same shape of the skull, or the same color of the
eye and hair.

* * * * *

Before leaving the subject of mental evolution we must return to the
conception of inseparable mind and matter with which the present
discussion began. The whole problem of human mental evolution is solved
when we accept the conclusion that the nervous mechanism and the total
series of its functional operations have evolved together in the
production of the human brain and human faculty. The case regarding the
physical organs rests solidly on the basis of the evidences outlined in a
previous chapter; the special examination of purely mental phenomena has
likewise been made in the foregoing sections. Just here we must pause to
give further attention to the invariable relation between the human mind
and the human brain.

The personality of human consciousness consists of the current of thoughts
and feelings flowing continuously as one of them rises for a time to
dominance only to fade when it leads to and is replaced by another
dominant element of thought. This current is affected by the messages
brought to the brain by nerves from the outer parts of the body where lie
the eye and ear and other sense-organs. In like manner the various
non-nervous parts of the body exert their influences upon consciousness,
but the affective processes, as they are called, are not as well understood
as the impressions passed inwards by the sense-organs along their nervous
roadways to the central organ, the brain. But the brain is the place where
the thinking individual resides; and this is one of the most important
teachings of psychology, for not only does it help us to understand the
evidence that human faculty has evolved, but it also inevitably brings us
to consider certain vital questions of metaphysics, such as the
immortality of the thinking individual after the material person with its
brain ceases to exist. However, the latter question is something which
does not concern us here; now it is most important to realize how
completely mind is connected with the brain.

Many of the facts demonstrating this connection are matters of common
knowledge. In deep and dreamless sleep the essential tissues of the brain
are inactive, and in correspondence with the cessation of material events
the thinking individual actually ceases to exist for a time. Any one who
has ever fainted is subsequently aware of the break in the current of
human consciousness when the blood does not fully supply the brain and
this organ ceases to function properly; a severe blow upon the head
likewise interrupts the normal physical processes, and at the same time
the mind is correspondingly affected. Again, a progressive alteration of
the brain as the result of diseased growth causes the mind to grow dim and
incapable. Sometimes infants are born which are so deficient mentally as
to be idiots, and an examination of the brain in such a case reveals
certain correlated defects in physical organization. These and similar
facts form the basis for the dictum that the development and evolution of
the brain mean the growth and evolution of human intellect.

The further question as to the nature of the connection is interesting,
but it relates to matters of far less consequence to the naturalist than
the central fact of the invariable relation which does exist. Throughout
the centuries many philosophers and naturalists of numerous peoples have
endeavored to explain the connection in question in ways that have been
largely determined by the changing states of knowledge of various periods,
as well as by differences in individual temperament. Three general
conceptions have been developed: first, that the material and mental
phenomena _interact_; second, that they are _parallel_; and third, that
they are _one_.

According to the first view, the individual thoughts and feelings forming
elements in the chain of consecutive consciousness are affected by the
events in the material physiology of the brain as a physical structure;
the latter in turn react upon the psychical or mental elements. Thus there
would be two complete series of phenomena, which are interdependent and
interacting at all times, although each would be in itself a complete
chain of elements.

The second interpretation is that the two series of events--namely, the
physical processes of the brain and the elements of consciousness--are
completely _independent_ but entirely parallel. As one writer has put the
case, it is as though we had two clocks whose machinery worked at the same
rate and whose relationships were such that "one clock would give the
proper number of strokes when the hands of the other pointed to the hour."
But in my opinion this attempted explanation of the relation of mind to
matter evades the whole question, as it does not account for the
dependence of the former upon the latter, but merely assumes the existence
of a more ultimate and unknown group of causes for a parallelism in the
rates of operation of two series of things regarded as disconnected.

The third conception recommends itself to many on account of its greater
simplicity. Formulated as the doctrine of monism, it states that the mind
and its material basis are merely different _aspects_ of one and the same
thing, and that there is only one series of connected elements which are
known to us directly as the current of our thoughts and indirectly as the
physiological processes going on mainly in the cerebrum. Thus mind is
purely subjective, the brain is only mediately objective. It is because
the mental and the material are so intimately related that the monist
believes them to be connected as are the lungs and respiration, the hand
and grasping, or the eye and the reception of visual impressions from
without.

But whichever one of these explanations we choose to adopt as our own, the
basic fact of primary importance is that there is an invariable dependence
of human thought upon a brain comprising a highly developed cerebrum,
whatever may be the ultimate nature of the way mental processes are
determined by physical processes, or _vice versa_. This fact stands
unquestioned and unassailable; human faculty and the brain cannot be
considered apart, even if they may not actually be different aspects of
the same basic "mind-stuff," as Clifford calls the ultimate dual thing.

Like all of the other organs of lesser importance belonging to the nervous
system, the brain is a complex of tissues which in the last analysis are
groups of cell-bodies with their fibrous prolongations. When these
cellular elements are in operation, mental processes go on; the unit of
the mental process therefore is the functioning of a brain-cell. But we
know that the substance of a brain-cell is the wonderful physical basis of
life called protoplasm, that demanded our attention at the outset. The
chemicals that go to make up protoplasm are everywhere carbon, hydrogen,
oxygen, and other substances that are exactly the same outside the body as
inside. It is the combination of these substances in a peculiar way which
makes protoplasm, and it is the combination of their individual properties
which in a real even though unknown manner gives the powers to protoplasm,
even to that of a living brain-cell. Does science teach us, then, that the
ultimate elements of human faculty are carbon-_ness_ and hydrogen-_ness_,
and oxygen-_ness_, which in themselves are not mind, but which when they
are combined, and when such chemical atoms exist in protoplasm, constitute
mental powers? Plain common-sense answers in the affirmative. We need not,
indeed, we must not, attribute mind as such to rock salt or to the water
of a stream, but we do know that salts and water and other dead substances
may enter into the composition of the material brain which is the physical
basis of mind.

In my opinion the individual argument renders the monistic conception of
mind and matter unassailable. The food that we may eat and the water we
may drink are dead, and as such they display absolutely no evidence of
nervous or mental processes. When they enter our bodies, they with other
foods replenish the various tissues, and among these the parts of the
brain. In a material sense they become actual living protoplasm, replacing
the worn-out substances destroyed during our previous thinking; and their
properties are combined to make brain and thought, to play for a time
their part in life, and to pass back into the world of dead, unthinking
things. Every one of us knows that hunger reduces our ability to think
clearly and fully, and every one knows also that mental vigor is renewed
when fresh supplies of nourishment reach the brain. What can be the source
of mentality, if it is not something brought in from the outer world along
with the chemical substances which taken singly are devoid of mind?
Scientific monism frankly replies that it is unable to find another
origin.

We are thus brought to recognize, not only the continuity taught by
organic evolution, but also the uniformity of the materials constituting
the entire sensible world, inasmuch as the ultimate unit of all nervous
phenomena is the reflex act of a protoplasmic mass, which itself is a
synthesis of properties inhering in the chemical elements making up living
matter. Among inorganic things the mind-stuff units are combined in
relatively simple ways, and the "stuff" does not give any outward
evidences of "mind" as such. Living things are almost infinitely complex
as regards their chemical organization, and even in the very lowest of
them we can discern a cell-reflex element which, combined with others like
it, forms the unit of the compounds we call instinct, intelligence, and
reason. Hence through an analysis of mental evolution we are enabled to
form the larger conception of a continuous universe whose ultimate
elements are the same everywhere.

VII

SOCIAL EVOLUTION AS A BIOLOGICAL PROCESS

We now reach a critical juncture in our study of the foundations of
evolutionary doctrine, for we must pass at this point to an inquiry into
the nature and origin of human social relations. In undertaking this task
we may seem to leave the field which is properly that of organic
evolution, and many perhaps will be unwilling to view such aspects of
human life as materials for purely biological analysis, arrangement, and
explanation. But even before the reasons for doing so may be made
apparent, every one must admit that the subject of mental evolution, which
comprises so large a bulk of details expressly social in their character
and value, virtually compels us to scrutinize the history of the economic
and other interrelationships maintained by the human constituents of
civilized, barbarous, and savage communities. Language has been treated as
an individual mental product, and so have the arts of life and of
pleasure; but all of these things find their greatest utility in their
social usage,--in their value as bonds which hold together the few or many
human beings composing groups of lower or higher grade. Without
discovering any other reasons we would be impelled to take up social
evolution, for this process is inextricably bound up with the origin and
development of all departments of human thought and action.

If now this new field is actually to be included within the scope of the
laws controlling the rest of nature's evolution, two general conclusions
must be established. Although no formal order need be followed, it must at
some time be shown that human social relations are biological relations,
to be best explained only through their comparison with the far simpler
modes of association found by the biologist among lower orders of beings;
and in the second place it must be demonstrated that identical biological
laws, uniform in their operation everywhere in the organic world, have
controlled the origin and establishment of even the most complex societies
of men. So far no reason has been discovered by science for believing that
evolution has been discontinuous, holding true only for the merely
physical characteristics of humanity as a whole; and furthermore, the
impersonal student of nature finds ample positive evidences showing that
the basic laws of associations of whatever grade are exactly the same. For
these laws we are to seek.

Heretofore the doctrine of organic evolution has been discussed with
reference to the single individual organism viewed as a natural object
whose history and vital relations require elucidation. Both in the general
arguments of the first few chapters and in the fifth and sixth chapters
dealing with the single case of the human species, the proof has been
given that all of the structural and physiological characters of any and
every organic type fall within the scope of the principles of evolution,
by which alone they can be reasonably interpreted. It has been unjust in a
sense to ignore completely the importance of the organic relations of a
social nature to which we are now to turn, because no individual can exist
without having its life directly influenced, not only by other kinds of
organisms, but even more intimately by other members of its own species.
In a single day's activity we who are citizens of a great metropolis are
forced into contact with almost countless other lives, glancing off from
one and another after influencing them to some degree, and gaining
ourselves some impetus and stimulus from our longer or shorter intercourse
with each of them. Our varied social relations are so many and obvious
that it is quite superfluous to specify them as essential things in human
life. For the very reason that they are so obvious and constitute so large
a part of our daily life, we are in danger of conceiving them to be
exclusively human; we unconsciously regard them as different from anything
to be found elsewhere and quite independent of the biological laws
controlling the human unit.

On the contrary, as we trace the development of social organization from
its earliest rudiments it becomes ever clearer that evolution has been
continuous, and that during later ages there has been no suspension of the
natural laws which earlier produced the human type of organism. The
lessons we have learned are by no means to be ignored from this point
forward; all of our conceptions of human biological history must be kept
in mind, for anything new that we may learn is superadded to the rest,--it
cannot disturb or alter the foundations already laid. It is even more
important to realize that the same scientific method is to be employed
which has been so fruitful heretofore. It has given us interesting facts;
it has indicated the most profitable lines of attack upon one and another
scientific problem; and it has demonstrated the practical value of
accurate knowledge, even of information about the evolutionary process. As
familiarity with the laws of human physiology enables one to lead a more
hygienic and efficient life, and as the results of analyzing the evolution
of mentality make it possible to advance intellectually with greater
sureness, conserving our mental energies for effort along lines
established by hereditary endowment, so now we are justified in expecting
that a clear insight into the origin of our social situation and social
obligations will have a higher usefulness beyond the value of the mere
interest inhering in our new knowledge. Every one is necessarily concerned
with social questions; never before has there been so much world-wide
discussion of topics in this field. And while it is true that much good
may be accomplished in utter ignorance of the past history of human
institutions and of the underlying principles which control the varied
types of organic associations, surely enlightened efforts will be more
effective for good. Therefore every member of a community who is capable
of thinking straight rests under an obligation imposed by nature to learn
how he is related to his fellow-men; he must act in concert with them or
else he forfeits his rights as a social unit. And it is his clear duty to
search among the results of science for aid in ascertaining what he ought
to do, and what reasons are given by evolution for the nature of his vital
duties.

Despite the growing appreciation of the fundamental relation between
biology and sociology, it is still far from universal. That the latter
science is in a sense a division of the former is more often recognized by
the biologist than by the average well-informed student of human social
phenomena. The layman in sociology too often concerns himself solely with
the complexities of the human problems, and he remains unaware of the
manifold products in the way of communal organisms far lower in the scale
of life firmly established as primitive biological associations ages
before the first human beings so advanced in mental stature that tribal
unions were found good. Among insects especially the biologist finds many
types of organized living things, ranging widely from the solitary
individual--a counterpart of something even more primitive than the most
unsocial savage now existing--up to communities that rival human
civilization, as regards the concerted effect of the diversified lives of
the component units. The student of the whole of living nature is favored
still more in that he learns how the make-up of such a simple organism as
a jellyfish displays principles underlying the structure of the whole and
the interplay of the parts that are identical with principles of
organization everywhere else. And all of these things can be dealt with in
a purely impersonal way which is impossible when attention is restricted
to the human case alone. Thus it becomes the biologist's privilege and his
duty as well to place his findings before those who wish to understand the
constitution of human society in order that evils may be lessened and
benefits may be extended. He does this so far as he may be able in full
confidence that the elements and basic principles are discoverable in
lower nature, just as they are in the case of the material make-up and
mental constitution of the single human individual.

A more explicit preliminary statement must now be given of the grounds for
the belief that social evolution is but a part of organic evolution in
general. Some of these reasons are not far to seek, but their cogency can
scarcely be appreciated until we have examined the concrete facts of the
whole biological series. Any human society selected for examination--be it
a tribe, a village community, or a nation--is in last analysis an
aggregate of human units and nothing besides. Its life consists of the
combined activities of such components--and nothing else. Could we
subtract the members one by one, there would be no intangible residuum
after all the people and their lives had been taken away. When these
simple facts are recognized, it is clear at once that the concerted
activities performed by biological units cannot be anything but organic in
their ultimate basis and nature; the evolution of such activities thus
takes its place as a part of organic evolution.

The task of tracing out the history of social organizations of whatever
grade can now be defined in precise terms: in simple words, it is to learn
how the activities of the component biological units making up any
association really differ from the vital performances of biological units
existing by themselves. What is it that distinguishes a savage of
antiquity from an American of to-day? The modern example is just as much
an animal as the earlier type, and his physiology is essentially the same.
It is something added to the common biological qualities of all men, some
relation which does not appear as such in the life of rude tribes, that
makes the distinction. And it is just this superadded relation that
requires explanation, as regards its exact biological value and its
historic development as well.

In undertaking this difficult task, it seems best to begin with the very
simplest organisms that biology knows, working upwards through the scale
to man. By this course the most basic elements of organization can be
discovered without having to look for them among the intricate details of
our own vital situation, where secondary and adventitious elements stand
out in undue prominence, and where the impersonal view is well-nigh
impossible. Step by step we will then work up the scale of social
morphology, approaching in the natural evolutionary order that part of the
subject which interests us most deeply.

Just as the construction of an edifice must begin with the fashioning of
the individual brick and bolt and girder, so the evolution of a biological
association begins with the unitary organisms consisting of single cells,
like _Amoeba_. We have had occasion to discuss this animal many times
in our previous studies of one or another aspect of evolution, and once
again we must return to it in order to reëstablish certain points that are
of fundamental importance for our present purposes. Within the limits of
its simple body, _Amoeba_ performs the several tasks which nature
demands a living thing shall do; it feeds and respires and moves,
continually utilizing matter and energy obtained from the environment for
the reconstruction of its substance and replenishment of its vital powers;
it coördinates the activities of its simple body, and by its reflex
responses to environmental influences it maintains its adjustment to the
external conditions of life. The animal does all of these things with a
purely individual benefit, namely, the prolongation of its own life. While
it is performing these individual tasks, it does not concern itself with
anything else but its own welfare; the interests of other living things
are not involved in any way, excepting in the case of other organisms that
may serve the animal as food. _Amoeba_, like every other living thing,
if it is to exist, must unconsciously obey the first great commandment of
nature,--"_Preserve thyself_."

But its life is incomplete if it stops with the furtherance of aims that
we may call purely selfish. Nature also demands that an _Amoeba_, again
like every other living thing, shall perpetuate its kind. The mode by
which it reproduces is ordinarily quite simple; the animal grows to a
certain bulk and then it divides into two masses of protoplasm, each of
which receives a portion of the mother nucleus. Sometimes by a peculiar
process it breaks up into numerous small fragments called spores, which
also receive portions of the parent nucleus. The most striking feature in
both kinds of reproduction in _Amoeba_ is the complete destruction of
the individual parent that exists before the act and does not afterwards.
It is quite true that every part of the mother animal passes over into one
or another of its products, but it is equally true that no one of these
products is by itself the original individual. So even the simplest animal
we know performs a task that is not only useless to itself, but is
completely destructive of itself, for nature's greater purpose of
preserving the race. We can readily see why this must be so; there is no
place in the world for a species whose members put individual well-being
above the welfare of the race, for which the production of new generations
is essential, even though the satisfaction of this demand should
necessitate the sacrifice of the parent organism. We might hesitate to use
the word "altruistic" in describing the self-destructive reproductive act
of an _Amoeba_, because this word connotes some degree of consciousness
of the existence of other than personal interests, and of the welfare of
different individuals. There is no reason to believe that such conscious
recognition of any natural duties is possible in the case of so low an
organism. But the fact remains that the result worked out by nature is the
same as though there were a definite understanding of real duties. Even
this unitary organism, then, acts mechanically so as to fulfil two primal
obligations, first _to itself_, through activities with individual benefit
as the result, and _to the race_ by the act of reproduction which closes
its individual existence and inaugurates a new generation.

The life of this example, representing the whole series of one-celled
organisms, is almost infinitely simpler than that of a member of a human
community, yet it reveals the beginnings of certain characteristics of the
latter. Here, it is true, the natural obligations in question are not like
those which are ordinarily denoted social, but it is equally true that
even in this most elementary instance a living thing does not live unto
itself alone. It is easy to see the value to the species as a whole of
obedience to the second great law--"_Preserve thy kind_." But a little
further thought makes it plain that even the performance of acts in
compliance with the first mandate--"_preserve thyself_"--are not purely
selfish, although their immediate value is realized as individual benefit.
Surely an organism that failed to live an efficient individual life would
be ineffective in reproduction, so that from one point of view everything
an animal does is tributary to the culminating act performed for the
larger good of the life of the whole species. It is a nice balance that
nature has worked out in _Amoeba_, as well as in all other cases,
between the personal life of the individual, complete only when the final
process of multiplication supervenes, and this process itself, which
demands an efficient performance, even though this is destructive of the
performer.

Before passing to the next members of the series, which reveal additional
principles more truly social in the human sense, let us pause to note that
already we have found certain natural criteria that belong in the
department of ethics. Even in the case of the biological unit like
_Amoeba_, which is entirely solitary and unrelated to other individuals
of its kind excepting in so far as it is a link in the chain of successive
generations, any vital activity can be called good or bad, right or wrong.
Nature judges an act good and right if it tends to preserve the animal and
the species; an act is wrong and evil if it is biologically destructive of
the animal or if it interferes with the perpetuation of its kind. Again it
must be pointed out that these terms are human words, employed for the
complex conceptions that belong alone to retrospective and contemplative
human consciousness to most of us they seem to imply the existence of some
absolute standard or ideal by which a given act may be tested to see if it
is right or the opposite.

If human ethics is truly unrelated to beginnings found in lower nature,
something that has arisen by itself from supernature, then we must not use
the terms in question except by way of analogy. If, however, nature has
been continuous in the working out of every department of human life and
human thought through evolution, then the criteria of the righteousness of
the acts performed even by an _Amoeba_ may be found to be basic and
fundamental for ethical systems of whatever human race or time. This
subject remains to be discussed in the final chapter, but it must be clear
that we cannot survey the evolutionary process by which social systems
have come into being without dealing at the same time with the origin and
growth of ethical conduct as such.

* * * * *

Without leaving the group of one-celled animals typified by _Amoeba_, we
find colonies of the most elementary biological nature, where other
natural obligations are added to the two of greatest importance. Some
species of the bell-animalcule, _Vorticella_, provide characteristic
examples of these primitive compound protozoa. Here the assemblage is made
up of one-celled individuals essentially similar to one another in
structure and in physiological activities; in the latter respect each one
of them is like _Amoeba_ as well. They may remain together for a longer
or shorter period, or during their whole existence until the time of
reproduction. Like the solitary protozoön, each member leads a complete
life in and by itself, equivalent to that of every biological unit. It
obeys the two great laws already laid down, but in addition it seems to be
required to remain with the others for some mutual good. The biological
value of the association which imposes this additional obligation may be
found perhaps in the fact that a large group is not so readily eaten by an
enemy as an individual cell; but it is clearer that the process of
reproduction, which consists of the fusion of small "gametes," or
nucleated fragments produced by diverse or similar parents, must be
greatly facilitated by the occurrence of gamete-forming individuals in one
and the same colony. "_To remain together_" is the new duty imposed by
nature for the good of all and for the welfare of each member of the
group. Some biological advantage accrues to the several components, just
as the banding of wolves enables the pack to accomplish something which
the single wolf is unable to do, although in the latter case it is not so
much a reproductive alliance that is formed as an offensive and defensive
union.

One step higher in the scale stands the plant-form called _Volvox_, near
the border-line between the one-celled and the many-celled organisms. This
aquatic type, about the size of the head of an ordinary pin, is a hollow
spherical colony, with a wall composed of closely set cellular components.
These elements are not all alike, as in the case of colonial protozoa like
_Vorticella_, for they fall into two classes which are distinguished by
certain structural and functional characteristics. Most of them are simple
feeding individuals which absorb nourishment for themselves primarily, but
they pass on their surplus supplies to less favored neighbors if occasion
demands. The other members begin life like the first-named, but later they
become specialized to serve as reproductive individuals solely. Every
member of the colony must obey the first precept of nature, otherwise it
would be unable to play its part in the life of the whole community. But
the discharge of the second natural obligation, namely to preserve the
race, is here assigned to some, and to some only, of the whole group of
cell individuals. It follows therefore that the division of the tasks
necessary for the maintenance of a complete biological individual, and the
differentiation of the members of the group into two kinds, leads to the
establishment of an individuality of a higher order than the cell. Neither
the purely nutritive nor the reproducing member is complete in itself; the
two kinds must be combined to make a perfect organism. The life of any
member can be selfish no longer, for if it is to exist itself, it must
help others for the mutual advantage of all. A clear social relation is
thus established; and the reflex conduct of the units of a _Volvox_ colony
can be justly denoted altruistic, even though in this case, as before,
there can be no conscious recognition of the reasons why mutual interests
are best served by what is actually done.

One of the most interesting and significant aspects of the life-history of
_Volvox_ is the appearance for the first time of biological death. More
elementary organisms are immortal potentially even if not actually, for
every portion of the body is capable of passing over into an animal of a
succeeding generation. But in _Volvox_ a division of labor has been
effected of such a nature that most of the components discharge the tasks
of individual value, and with the performance of these they die. Only the
reproductive members are immortal in the sense that _Amoeba_ is, for
they only have a place in the chain of consecutive generations of _Volvox_
colonies. From the standpoint of the nutritive individual it is better to
be relieved of the reproductive task in order that there may be no
interruption of its specialized activities for the good of all, but the
entailed mortality is certainly disadvantageous to it. It is the higher
interest of the colony as a whole that supersedes the welfare of the parts
taken singly, and this larger welfare is safeguarded by a differentiation
worked out by natural evolution which results in the assignment of
personal and racial duties to different individuals, at the cost
ultimately of the lives of the former.

We now reach the realm of the true many-celled animals, or Metazoa, where
the biological units are combined to form an organic association
displaying many more resemblances to a human society. The freshwater polyp
_Hydra_, like the foregoing illustrations, is one whose structure has
already been discussed in the earlier chapters, but now we may use it for
an analysis of another series of biological phenomena. Its sac-like body
consists of two cell-layers; the outer one is concerned primarily with
offense and defense, while the inner layer is made up of digesting or
nutritive elements. The essential cells concerned solely with reproduction
lie below the outer sheet. Comparing this animal with an association like
_Volvox_, we discover the same differentiation into immortal germ-elements
and mortal cells, concerned respectively with the _Hydra's_ racial
existence and with its individual life; but far-reaching changes have come
about in the biological relationships of the second class of cells. In
describing the new phenomena it is absolutely necessary to employ the
terms of human social organization, because the _Hydra's_ body is a true
colony of diverse cells in exactly the same sense that a nation is a body
of human beings with more or less dissimilar social functions.

To begin with the differentiation into ectoderm and endoderm, the organism
is comparable to a human community made up of military and agricultural
classes. The cells of the former group protect themselves and the feeding
elements also, while the units of the second defenseless type devote
themselves to the task of provisioning the whole community, giving
supplies of food to the defenders in exchange for the protection they
afford; each kind needs the other, and each performs some distinctive task
for the other as well as for itself. But the parallel thus drawn need not
stop here. In the case of the outer layer, the cells are mostly flat
covering elements that are the first to be torn off and injured when the
animal is attacked. Scattered about among them are sense-cells standing
like sentinels with delicate upright processes which receive stimuli from
without the sense-cells transmit impulses to the network of nerve-cells
below, which is a counterpart of the signal corps of an army, keeping all
parts of the whole organization in communication with one another. Most
wonderful of all are the stinging-cells of the outer layer; these produce
a flask-shaped, poisoned bomb which is discharged by the convulsive
contraction of the cell itself so as to stun and injure the enemy or prey.
The bomb-throwing cells die immediately after they have ejected their
missiles; like soldiers participating in a forlorn hope, they sacrifice
their lives in one supreme effort of service to the cell-community of
which they are members.

These and similar facts prove conclusively that _Hydra_ is a true
community even in the human sense, and that the laws of biological
association are established at a point far below the level of the insects.
The individuality of the unit is still maintained, and each cell must
guard its own interests to a certain degree, but the original independence
of the unit has become so altered by differentiation and division of labor
that a close interdependent relation has come about. The complete
individual is now the _whole_ aggregate; it is the entire _Hydra_ itself
which must obey the primary commands of nature to live efficiently and to
perpetuate its kind. True it is that the life of the higher individual is
the sum total of the activities performed by its constituent cells, but no
one of the varied specialized elements is biologically perfect by itself
or equivalent to the whole. And, as we have seen, the welfare of the
complete animal takes precedence over that of any one of its parts, just
as the existence of a nation may be preserved only by the death of
soldiers warring for its honor and life.

If, now, we should pass on to the more complex organisms like worms and
insects and vertebrates, and should disregard the communal relations of
some of these animals, each individual proves to be like _Hydra_ as
regards the principles underlying its make-up and workings. A single bee,
like a man, is a definitely constituted aggregate of cells, differing as a
whole from _Hydra_ only in the _degree of differentiation_ exhibited by
its constituent elements. Instead of a loose network of nerve-cells there
is the far more complex nervous system whose evolution has been outlined
in the sixth chapter. The blood-vascular and respiratory and excretory
systems have become well organized, in response, so to speak, to the
demands on the part of the nervous and alimentary organs that they may be
relieved of the tasks of circulation and respiration and the discharge of
ash-wastes. Therefore the cells which make up an insect and a man are more
diverse, they have more varied interrelationships, and they are far more
interdependent then in the case of the components of _Hydra_. Yet all the
many-celled organisms that we are so accustomed to regard as individuals
are really communities, demonstrating the existence and partial antithesis
of the great laws of egoism and altruism, which are traceable even down to
_Amoeba_ and its like.

So much has been made of the lower kinds of cell-associations because the
mind of the layman is unconsciously imbued with the idea that human
society is a new thing,--an idea which we now see it is necessary to
discard at the outset. Indeed, the cell-association of the _Hydra_ and
insect type is a more compact and a more stable kind of community than any
group of human individuals worked out by nature toward the present end of
the whole scheme of evolution. That is to say, the subordination of
cell-interest to cell-group welfare, while it must not go so far as to
render the unit incapable of doing its work, is sufficiently advanced to
make uncontrolled individualism impossible. Let any class of _Hydra's_
cells, such as the nerve or muscle network, assume to exercise a selfish
preeminence or to conduct a "strike," the other classes, like the feeding
cells, would not be properly served and they would be unable in
consequence to work efficiently for the strikers. The immediate result
would be suicidal, for the selfish nerve-class would inevitably suffer
through the downfall of the whole social fabric. It is a nicely adjusted
equilibrium that is established, where the "equal rights" of all the
diverse cells consist in freedom to play a special part in the life of the
group, serving other individuals in return for their service. The Golden
Rule is a natural law as old as nature; for even in _Hydra's_ life,
unconscious discharge of duties to the race, and hence to others, is
obligatory. And all these low types of organic associations evolved ages
before the rules of human social order were vaguely recognized by the
reflective self-consciousness of man, to be formulated as the science of
ethics.

The evolution of the wonderfully varied societies found among insects
begins with the solitary insect itself, just as this, viewed as a
cell-community, originates from one-celled beginnings like _Amoeba_
through progressive evolution in time. The similarity between social
insects and human associations is clearer than in the case of a comparison
between an example from either group and a cell-community, because the
higher forms lack the organic contact of the components which is so
prominent a feature in the lower instance. The social bonds are looser and
they allow a freer play of the constituents; but nevertheless the same laws
that control the activities of the cells making up what we now take as the
individual element, command obedience on the part of the interrelated
members of an insect community with equal strictness.

A butterfly or a moth is primarily egoistic and unsocial in the ordinary
sense during its entire life-history, until the final reproductive act
which has a value to the species. The caterpillar larva devotes all of its
energies to feeding and growing, unconcerned with the final duties of the
moth with which it is connected just as the indifferent unit of a young
_Volvox_ colony is related to a reproducing member of the full-grown
organism. Now and then, it is true, species like the so-called tent
caterpillar are met with where numerous larvæ spin silken communal nests
to which they retire at night and in which they remain to molt. The pupa,
like the larva, is individualistic and employs its time in producing the
final adult form. The mature individual, however, is constructed almost
solely for the greater purpose of perpetuating the species. Indeed the
larger silkworm moths do not and cannot feed, and their value is only that
of a device for keeping the race established. Adult may-flies live only a
few minutes, just long enough to provide for the fertilization and
deposition of the eggs, although to prepare for these acts the young
individuals must have toiled for months; the preparatory time may amount
to many years in such a case as the seventeen-year locust. But nature is
satisfied, as long as the organic mechanisms obey her double commandment,
"Live and grow so as to multiply." Like an _Amoeba_, the solitary insect
must be egoistic at first, in order to be altruistic in a racial sense in
its last days.

Wasps, bees, and ants provide many familiar examples of colonial
organizations that become all the more marvelous on closer acquaintance,
on account of their resemblances to human associations on the one hand,
and to cell-associations on the other. Their illustrative beauty is
enhanced by their wide variety, for they grade from counterparts of highly
civilized men down to a savage among insects, such as the strictly
solitary digger-wasp, whose instincts served to exemplify the insect type
of "mentality" in the discussions of the preceding chapter.

The true communities founded by wasps and hornets must be assigned to a
low grade in the scale because they originate during a single season and
break up at its end; for this very reason the wasp community is intensely
interesting to the student of comparative social evolution. In the spring
a solitary female emerges from the crevice where she has hibernated and
resumes active life; she feeds for a time to renew her strength and then
she constructs a simple nest of mud or masticated wood-pulp. In the first
few cells of this nest she deposits her eggs, and when they hatch she
herself provides the larvæ with food, but still continues to enlarge the
house and to produce more eggs. Thus during the first few weeks of the
colony's existence this single individual performs a variety of tasks of
racial as well as of purely egoistic value; but as time goes on, a
profound change comes about in her activities and in the life of the whole
community. The members of the first brood do not grow into counterparts of
their mother; they are all sexless "workers" who progressively relieve
their parent of the tasks of nest-building and foraging and nursing, so
that their mother becomes a "queen" who devotes her entire time to the
special reproductive task which she only can perform. We may justly
compare the queen to the reproductive organ of _Hydra_, for the values to
the life of the species are identical in the two cases, while the various
classes of workers are counterparts of such units as the muscle and nerve
and nutritive components of the _Hydra_ or any other cell-community
individual. Another resemblance between the two is found in the death of
all the sexless individuals at the end of the season, when reproducing
males and females are finally formed, of whom the fertile queens only
survive in their winter hiding places; and again we can discover the cause
for biological death in that division of labor which calls upon certain
members of the whole community to perform tasks that have no value when
once provision has been made for perpetuating the species. Finally the
mode by which the colony grows and amplifies is in all respects like the
embryonic development of an egg into a _Hydra_, so that we may add the
phrase "social embryology" to our vocabulary. The original female is an
undifferentiated master of all trades; the small tribe she first
establishes is little better off than a horde of savages; but during its
seasonal existence the community increases in numbers and complexity until
it advances well toward the civilized condition, when each class performs
its special task for the good of all.

The bees take us higher in the scale, although many solitary species
occur, as well as social forms like the bumblebees where colonies are
formed in a single season only to break up with the advent of cold
weather. The honeybees, however, establish permanent communities from
which swarms may set out during the warm months to become new colonies
elsewhere. Many hundreds of bees make up a hive, and they belong to three
classes or castes, which differ in structure and social function. The
queen is a fertile female, the drones are males, and the workers are
stunted and infertile females which take no part in reproduction. In this
case the queen never discharges any menial duties, for these are attended
to by the workers; she devotes her entire time to laying eggs, which are
cared for by her subjects, who act as nurses and guards for the monarch as
well. The young workers serve at first as doorkeepers, and only later do
they take the field in the search for nectar and pollen, and work as
house-builders. Each individual performs its special task for its own
benefit and for the weal of all; each possesses an equal right to share in
the prosperity of the whole community so long as it acts altruistically as
well as egoistically. And just as the welfare of _Hydra_ is superior to
that of any one of its constituent cells, so the well-being of a hive of
bees may be safeguarded only by the actual sacrifice of some of its
members. Should food supplies be inadequate, the superfluous drones are
stung to death,--the victims of legalized murder. But more marvelous still
is the provision that is said to be made by certain individuals for their
own destruction should this become desirable. As every one knows, a
reigning queen may leave the hive with many of her subjects and "swarm" in
a new locality. When she does this, during the warm months, the workers of
the original hive feed some of the female larvæ with richer food, and
place these potential queens or princesses in special roomy cells apart
from the ordinary brood chambers; one of them soon emerges to become a new
sovereign. Let us note in passing how similar this is to the production of
new egg-cells in a _Hydra_, when the mature germs of an earlier generation
are prepared and discharged. When, now, the colder weather sets in, and
the possibility of subsequent swarming is set aside, the reigning queen is
allowed by her attendant guards to visit the royal cells, whose occupants
she stings to death, thus destroying any possible claimant to her place.
And when the royal princess constructs her part of the pupal case, she
leaves an aperture so that if and when it should become necessary for the
queen to kill her, the sovereign would not injure her sting and be unable
to kill the other individuals who might become aspirants for the throne
and so precipitate a civil war! As in the case of the self-destructive act
on the part of a stinging cell in _Hydra_, altruistic subservience to the
interests of the colony can go no farther.

The ants form stable colonies of still higher grades, where the workers
are not all alike in general structure, but become more rigidly
specialized for the performance of restricted tasks. As before, there is
the fundamental differentiation into the sexual "queens" and males, and
the sterile workers concerned with the immediate material life of the
community. In some species the workers serve as herdsmen, caring for the
ant-cattle or aphids, from which they receive minute drops of a sweet
juice for food. The aphids are tended on the leaves of various plants
during the summer, and are carefully reared and stabled and fed below
ground during the winter months. In other species seeds are procured and
stored in underground granaries. The leaf-cutters are forms which grow
food supplies of fungi in subterranean mushroom gardens; the compost
consists of cuttings brought from the leaves of bushes by myriads of
workers, whose processions are guarded by larger-headed soldiers of
several ranks. In the honey-ants of Colorado and tropical America certain
individuals pass their time suspended from the roof of a large
nest-chamber, where they receive the sweet juice brought in by the workers.
They serve as animated preserve jars, distended sometimes to the size of a
grape with the communal stores of food, which they return to the workers
when external sources of food may fail. Finally there are the slaveholding
species which conduct forays upon the nests of other forms, to procure the
young of the latter, which grow up in their captors' nests and serve them
as nurses and masons and foragers. So long has this custom been
established that some slaveholders are entirely unable to feed themselves,
and would die out if their slaves failed to support them.

* * * * *

Let us pause at this point to summarize the results of the foregoing
analysis, in order that we may approach the biological study of human
associations with definite and clear conceptions of the fundamental laws
controlling living communities of all grades.

We have dealt mainly with _Amoeba_, _Hydra_, and the ant-community
which exemplify three somewhat distinct types of organic individuality.
Some of the transitional forms have been specified to show how the second
kind originates from the first, and how in its turn this grows in time
into the third and most complex association; thus _Vorticella_ and
_Volvox_ connect _Amoeba_ with the cell-community individual like
_Hydra_ and a solitary wasp, while the annually established colonies of
social wasps and of bumblebees lead to the permanent colony-individual.
Restricting attention to the three primary examples, and remembering that
the criterion of completeness is the ability to discharge satisfactorily
all of the eight biological tasks, it is clear that the entire _Hydra_ and
the whole ant-community correspond _physiologically_ with _Amoeba_,
although the first-named is _structurally_ a cell-community equivalent to
many protozoa, and the insect colony is composed of many such
cell-communities as elements. In the third type, neither a single queen
nor a single worker is able to carry on all of the biological tasks any
more than a muscle-cell or an unformed egg of _Hydra_ can maintain itself
capably in isolation. Therefore the ant-society as a whole and the _Hydra_
in its entirety are organic individuals on the same physiological plane
with _Amoeba_, and they are equally subject to the same great laws of
nature demanding selfish maintenance and racial perpetuation.

But we must not lose sight of the fundamental value of the unit during the
evolution of a higher from a lower type. The tissue-cell of _Hydra_ must
still obey the mandate to live an efficient personal life, because this is
necessary for the welfare of other cells and of the whole complex. The
original egoistic tasks are not abolished, but new duties are added to
them in ways we have learned to distinguish. In _Vorticella_ the products
of fission do not separate, and certain advantages accrue from the organic
continuity thus maintained. The success of _Hydra_ in its ceaseless
struggle to live depends wholly upon the cooperation of its differentiated
cell-units, now no longer equivalent in function to the all-powerful
_Amoeba_, although each one must be kept alive until its task is done,
or the whole association would have no place in nature. Similarly in the
higher insect community, the superadded duties to fellow-components are
even clearer, for in the competition of colony with colony, involving
terrific battles whose casualties may be numbered by thousands, the
stronger wins; and strength depends upon the concerted efforts of all the
members of the kingdom, that only collectively constitute a complete
biological whole. Mere self-protection demands altruistic conduct: if the
worker ceased to bring in food when its own hunger was satisfied, there
would be no tribal stores for the stay-at-home queens and nurses; and if
the soldier fled from the field of battle to save its own life, its act
would be suicidal ultimately, for to the degree of one unit the defense of
its non-military supporters would be weakened and they would be so much
the less unprotected during their service for the soldiers and all others.
Furthermore, we must admit the reality of natural criteria of ethical
values, established far below mankind in the scale of life. In an
ant-republic, laws are instinctively obeyed quite as implicitly as though
they were intelligibly proclaimed to all of the emmet citizens. Right is
might when community battles with community, for right is that which is
biologically favorable. And what may be correct conduct on the part of the
members of one species may be naturally wrong and evil in another case. To
kill the princesses in order to obviate the possibility of civil war seems
advantageous and therefore right when the queen remains in the persistent
colony of honeybees, ready to do her part the following spring; but it
might result in disaster and evil in the case of the social wasps, where
the community dies as such in the fall, and the continuity of the species
from one year to another requires the production of many queens lest the
severe conditions of the winter's hibernation should kill all fertile
females if only one or two were available. The standards of conduct are
simple indeed; and whether or not it may seem best to separate the
processes of social and ethical evolution culminating in human phenomena,
the fact remains that these processes begin with elements discovered by
the biologist among organisms of the lower levels in the scale.

* * * * *

We come at length to the biological interpretation of human social
evolution, in so far as this may be expounded in a simple and concise
form. The comparative method must be employed in order to discover the
fundamental attributes of savage, barbarous, and civilized communities
which seem to differ so considerably in their complexity of social
structure, and in order also to show that such basic elements are like
those of communities formed by lower animals, and are equally the products
of natural evolution. This whole subject seems to be exceedingly complex,
because in our daily contact with others of our kind and in our occasional
views of foreign races like our own, the smaller details occupy our
attention, diverting it from the great basic principles according to which
every society is organized and operates. But when once the major elements
have been discovered in civilized and more primitive nations, the
secondary and less essential phenomena fall into their proper relations,
and a statement of the whole process of development becomes relatively
simple. So much space has been devoted to lower types of communal
organisms in order to learn what the fundamentals are, and not merely to
provide analogies that may be useful hereafter. It now remains to arrange
the evidences of social progress during the history of mankind itself, and
to bring such human facts into relation with what has been discovered in
lower nature. It is helpful to begin this part of the subject by asking
ourselves what is already part of common knowledge about human history. Do
we know of any civilized nation that is absolutely stable and unvarying in
social structure, or one that has remained unchanged throughout historic
time? The answer must be negative, for in no case does the past disclose
an example of permanence in social or in any other respect; monarchies and
republics are plastic like the human frame itself. The American
Commonwealth is a relatively young social organism, and it is an easy task
to trace its growth from beginnings in the diffuse and uncorrelated
colonies of pre-Revolutionary years. Those colonies that were formed by
English settlers were transplanted outgrowths from a civilized social
parent which in its turn had clearly evolved from the state of King John's
time and the still cruder form it had under King Alfred.

Should we follow back the recorded history of any people now civilized, we
would always find evidence of ceaseless change; and the writings of
ancient historians like Herodotus and Cæsar and Tacitus give a great deal
of information about the barbarous conditions from which civilization
evolved.

But much more is known that materially amplifies the account of human
progress based upon documents alone. The student of existing human races
early learns that social structure is a very varied thing. The natives of
northern Africa now live in a semi-civilized state which is very like that
of medieval England. In Siberia and the American Southwest are tribes that
correspond socially with the barbarians of Europe described by Greek and
Roman writers. The American Indians discovered by the earliest colonists,
the Polynesians of a century ago, and the Fuegians of recent decades
provide counterparts of the ancient stone-wielding people who were the
savage ancestors of European barbarians. Hence the comparative study and
classification of modern races establishes a scale of social grades which
corresponds with the order of their historic succession, just as in a
larger way the complete series of comparative anatomy from _Amoeba_ to
man displays the order of evolution from unicellular beginnings to the
present culminating types. Savagery, barbarism, and civilization are the
three major terms of this social scale, but by no means are they
discontinuous, for many intermediate forms of organization occur which are
transitional from one major type to a higher one.

In human social evolution the starting point is not so simple as the
solitary unit from which insect societies evolved,--that is, an organism
which lives alone and is associated with another of its species only at
the time of mating. The lowest human beings now existing have some form of
family organization, traceable to the more or less continuous unions
formed among certain of the apes and even among many lower animals, and
not a characteristic that belongs to mankind alone. The savage and his
mate constitute the social unit out of which all else is built up; the man
and the woman must perform all of the vital tasks demanded by nature.
Fruits and vegetables must be secured from the wild forest or by
cultivation; the flesh of game animals or of a human victim is no less
essential for food. The savage is his own weapon maker and warrior; he
himself builds the rude shelter for his family and fashions the canoe if
such is required. He is also his own judge, recognizing no control save
the dictates of his wishes and needs, for he does not consciously realize
that he must obey the primal commands of nature to preserve himself and
his family so that the species shall persist. In brief, the elementary
family unit carries on all of the individual biological tasks of foraging,
righting, home-building, and the like, and it also discharges the racial
task of multiplying, quite as instinctively as it provides for its own
maintenance.

By the union of several families, a primitive association arises, like
that of the Veddahs in Ceylon. The primal duties of each family are
unchanged, and their biological activities are identical, as in the
protozoön colony of _Vorticella_ or in a pack of wolves; but certain new
relations are established. A member of such an inchoate tribe must not
treat his confrères as he might a man of another group; robbery and murder
within the limits of the small association are detrimental to communal
interests, though they may remain unchecked if the victims are strangers.
Coöperation for mutual offense and defense makes the group stronger than
its constituent family units taken singly, and every man of such a tribe
gains something by looking out for others as well as for himself. By
natural selection alone the bonds of union would be strengthened in direct
proportion to the subordination of individual interest to group welfare,
and to the amount of altruistic action that in a true sense grows out of
purely selfish conduct.

But when such a primitive biological association forms and grows, an
opportunity arises for increasing the effectiveness of the whole group by
differentiation. Some of the men are stronger in battle and they soon
become the chief warriors; others prove to be more skilful in the hunt or
in the construction of canoes and weapons. Just as among the insects, the
hunter seeks food not only for himself but for the warriors, who in their
turn defend themselves, but do not cease fighting when they have disposed
of their own enemies if foes of their comrades still survive. The
barbarous state of society thus arises, and the division of labor brought
about during its origin makes it possible and indeed essential for many
family units to remain together for mutual good. The union is stable and
efficient, however, only if the individual suppresses his own selfish
inclinations, suspending private quarrels when public wars are toward, and
acting at all times in concert with his fellows. Self-control increases
necessarily, and lines of conduct deemed right by a solitary savage unit
come more and more under the sway of social inhibition, for although the
primitive savages must inhibit individualistic action to some degree, the
barbarian must suppress much more of his purely personal wishes for the
purpose of social solidarity. Thus it comes about that a barbarous
community can number thousands, while a tribe of savages with a higher
degree of individualism and less altruism cannot cohere if it comprises
more than hundreds or scores.

Civilization is a product of evolution by precisely the same natural mode
of development, that is, through further subordination of individual to
communal interests and through progressive dividing up of the tasks
necessary for the life of the group. The final result is so obvious and
familiar that we take it for granted, accepting it as self-sufficient
without realizing how it has come about and how modern is the present
state of affairs. Let us compare the life of an Indian savage living on
Manhattan Island four centuries ago with that of a New Yorker to-day, as
regards so simple a matter as the procuring of fish food. The Indian
emerged from his tepee, built by himself, and walking to the shore,
stepped into a canoe which also he had made with his own hands. Paddling
to the fishing ground, he patiently cast his line until the desired fish
were caught. Does any one of us do all of these things for himself? We
live in houses constructed for us by others who devote their lives to
building; we are very apt to go about the city in conveyances that demand
special and peculiar skill for their invention, manufacture, and
operation. Arriving at a market-place, we obtain such an article of food
as a fish without having to go out upon the water ourselves, for many
other workers have built vessels that we do not know how to make and may
not know how to handle, and hundreds of fishermen devote their lives to
their special task, not for themselves, but for us and all others, such as
the builder, the subway operator, the boat maker, and the manufacturers
who supply their clothing and apparatus.

What has come about then is a higher degree of specialization in the
performance of the fundamental biological tasks, resulting in the
formation of coherent and efficient groups comprising millions as compared
with the thousands of barbarism and the hundreds of savagery. Just so the
communities of insects with the greatest degree of altruism and division
of labor far exceed in numbers the small colonies of the social wasps with
lower social differentiation.

But the great biological functions of an entire complex civilized society
remain the same as those of a primitive savage family unit, of an insect
community, of _Hydra_, and of _Amoeba_. Let any nation fail to maintain
itself in material individual respects, it must inevitably die out; in the
islands of the South Seas many a tragic death-struggle of a people can be
witnessed. If in the second place a nation should concern itself too
greatly with the material benefits of human life without obeying the
natural mandate to propagate itself, its place in the scheme of things
becomes insecure, as in the case of the French Republic. Natural social
laws that go back to _Amoeba_ must be observed, consciously or
unconsciously, or else even the civilized community must fall, like scores
and hundreds of others that lie along the road of historic progress--a
road strewn with the remains of the unfit thrown out by natural selection.

What now are the lessons of social evolution and what guidance does
science give for human endeavor? Although it may seem that the biologist
leaves his field when he considers these questions, his duty would be
unfulfilled if he neglected an opportunity to give his results their
highest utility through their use for the betterment of human life.

The first lesson is that the history of human social organization is far
from unique, and that it is identical with the process by which insect
communities and cell-aggregates have evolved; in a word, the laws of
biological association are uniform throughout the entire organic scale. In
some respects evolution in mankind has yet to equal the heights attained
by some insects, inasmuch as no human society has accomplished so rigid a
specialization of its members that a given individual is foreordained by
its inherited structure to be a particular kind of worker and nothing
else. Furthermore, evolution in human society is still far short of a
state where some and some only are reproductive members of the group while
the others are necessarily sterile; social insects with stable colonies
are so organized that the queens and drones are solely reproductive while
the workers are destined to care for the material wants of the colony. It
is true that the birth-rate is by no means the same in all classes of
society, but the social and other adventitious restrictions that bring
this about are not on the same plane with the hereditary determining
factors which operate among insects. Therefore the scale of human
communities proves to be only a part of the wider range of organic
associations in general--a part which can be definitely placed in such a
wider scheme and so become more intelligible in itself.

In all departments of social evolution, progress is made by the twofold
process of combination and differentiation. We have dealt with detailed
instances, and now it is profitable to treat the process in a larger way,
with a view toward the possibilities of the future. The Thirteen Colonies,
somewhat similar in their earlier economic activities, united for mutual
support much as wolves combine to form a pack. Later, as circumstances
directed, they differentiated into farming or manufacturing or commercial
organs of the body politic, each to some degree freeing itself of the
functions undertaken by others, and becoming thereby more dependent than
before upon those that specialized in different ways. As in the history of
the insects in a growing wasp community and of savages evolving into
barbarians, the original condition of relative independence passed into a
state of interdependence and cooperation. In like manner, if nature
remains the same, as there is every reason to believe it will, nations now
separate will unite to make more complex combinations that will be
veritable empires of world-wide scope. Countries on opposite sides of an
ocean are now more closely connected by lines of communication and means
of travel than were the Carolinas and New England a century ago.
Diplomatic activities give many signs of a growing appreciation of the
value of reciprocal agreements for mutual advantage, and the Hague
Conference is a concrete manifestation of a continuing process of social
evolution that finds its beginnings and its interpretation far below human
history in lower organic nature.

But perhaps the most important result of this whole discussion is the
lesson of social service that it teaches. We are members of a vast
community whose complex total life seems far removed from anything going
on in an ant-colony, and our daily tasks vary greatly in specific
character and degree when compared with those of lower communal organisms.
It seems scarcely credible that any principles of social relationship,
however general, can hold true for us and for them. But when the
rock-bottom foundations are reached, they are simple and instructive
indeed. Being here, we cannot escape our personal obligations as living
things or our equally clear duties as members of our community. These
facts being as they are, what must we do? Self-interest is rightly to be
served, otherwise we would be incapable of discharging our secondary
tasks, namely, those of service to others in ways that are determined by
hereditary endowment and conditional circumstances. The difficulty is to
find the right compromise between the two sets of obligations; but the
right balance must be found, or else the health of the community is
impaired. Should any class demand more than its just dues, others must
suffer through the diversion of what they require, and the well-being of
the selfish class is jeopardized to some degree, so closely interwoven are
the interests of all. Freedom of opportunity within the limits of ability
and efficiency is the right of every one, but freedom of conduct must
never result in trespass upon the equal rights of others to make the most
of their abilities and opportunities.

To summarize, then, social evolution is a continuous process accomplished
through differentiation and division of labor among the components of
biological associations. Although the total form remains the same
everywhere, progress has been made in content through the further
subordination of selfish to altruistic conduct; only by this means does an
individual gain liberty to pursue the social task for which he is best
fitted by nature.

VIII

EVOLUTION AND THE HIGHER HUMAN LIFE

We have now reached the last division of the large subject that has
occupied our thoughts for so long. The present title has been chosen
because the questions now before us relate to the highest human ideas
belonging to the departments of ethics, religion, theology, science, and
philosophy. These matters may seem at first sight to be far removed from
the territory of the naturalist as such, and quite exempt from the control
of laws which determine the nature and history of the human individual in
physical, mental, and social respects. Yet one reason alone would impel us
onward: we cannot close the present examination into the basic facts of
evolution and into the scope of the doctrine without asking to what extent
a belief in its truth may affect our earlier formed conceptions of nature
and supernature. Heretofore these possible effects upon what may be dearly
cherished intellectual possessions have received no attention, so that we
might learn how evolution works in the lower fields of organic life in
general and human life in particular without being disturbed by them. No
doubt, however, the conviction has grown with each step in our progress
that the principles we have learned must cause us to readjust our views of
the highest elements in human thought to a degree that must be inversely
proportional to our previous acquaintance with the laws and processes of
nature. But the seeker after truth is fearless of consequences. He knows
that truth cannot contradict itself; and if those to whom he looks for
authority give him conflicting accounts of nature's history, he knows that
one of these must be less surely grounded than the other. The investigator
soon learns to withhold final judgment, realizing that the primary
conditions for intellectual development are the plasticity and openness of
mind that dogmatism and finality destroy. He knows that while his
researches may be, and indeed must be, iconoclastic, they provide him with
better icons in place of the old.

Let us recall the steps in our progress through one and another field of
knowledge, from which representative facts have been chosen for
classification and summary. We began with the basic principles of organic
structure and workings, and then we examined serially the larger
categories of the evidences relating to evolution as a fact, and to the
mode of its accomplishment by natural factors. Proceeding to the special
case of our own species, we learned that human beings are inevitably a
part of nature and not outside it; in structure, development, and
palæontological history, mankind is subject to the control of the uniform
laws which operate throughout the entire range of living things. Finally,
the mental characters and the social relations of human organisms were
derived from beginnings lower down in the scale, and were proved to be no
more exceptional than the physical constitution of a single human being.

Are we to forget all of these things when we try to put in order our ideas
belonging to the categories of higher thought? Can we hope to find the
truth if we fail to employ the methods of scientific common-sense which
only yield sure results? It is no more justifiable to discard our
hard-earned knowledge than it would be for an advocate to undertake the
conduct of a case in deliberate disregard of what he had learned of the
law, or for a surgeon to leave his knowledge at the door when he entered
the operating room. Too often we are bidden to view the larger conceptions
of nature and supernature as something outside the realm of ordered
knowledge too frequently we are given statements upon authority that takes
no account of reason, and we are asked to accept these views whether or not
they accord with the demonstrated facts of common-sense. But those who
have followed the present description of evolution can readily recognize
their obligation to use for the further analysis of higher human life the
means which have given in that doctrine the most reasonable explanation of
the natural phenomena already investigated.

I need hardly say that we now enter upon the most difficult stage of our
progress. The regions we have traversed were more readily explored because
they were remote from the matters now before us; even in the case of man's
mental and social evolution it was possible to take a partially impersonal
view of certain of the essential elements in human life, which we cannot
do now. For ethics and religion and philosophy are groups of ideas that
are familiar to us as the property of mankind alone. Countless obstacles
are in the way. Much mental inertia must be overcome, for it is far easier
to accept the average and traditional judgments of other men--to let well
enough alone--than it is to win our own way to the heights from which we
may survey knowledge more fully. Human prejudices confront us as a
veritable jungle, hemming us in and obstructing our vision on all sides;
and perhaps much underbrush must be cut away if we are to see widely and
wisely. Nevertheless, to those imbued with a desire to learn truth,
anything and everything gained must surely repay a thousand times all
efforts to obtain clearness of vision and breadth of view. With our
perspective thus rectified by our backward glance, we turn to the three
divisions of human thought now to be examined. The conceptions of ethics
come first for reasons that must be apparent from the classification of
the facts of social evolution; just as mental attributes and communal
organization are inseparable, so rules of conduct arise _pari passu_ with
the origin of a biological association. Religion and theology form the
second division, which takes its origin in part from the first, for these
two groups of ideas are largely concerned with the authority for right
conduct and with human responsibility for taking the right attitude toward
the entire visible and unseen universe. Finally, science and philosophy
are briefly treated as evolved products which include within their scope
all that there is in human knowledge; for this reason they take the
highest place, instead of the position below religion usually assigned to
them. At the last, having reached our final standing ground, we must look
back in order that we may clearly define the lessons and ultimate values
of the whole doctrine of evolution.

* * * * *

Ethics is the science of duty. It is usually restricted to an examination
of purely human obligations, and to a search for the reasons why men
should do certain things and refrain from committing other acts. Like
psychology and sociology, ethics began as a strictly formal and _a priori_
system of dogmas which related to the life of cultured human beings alone.
Again, like the sciences specified, it gradually broadened its scope so as
to include the conventions of races lower in the scale than the civilized
peoples who only were sufficiently advanced intellectually to conceive it.
Thus the comparative method came to be employed, and in direct proportion
to its use, more liberal views have developed regarding the diverse
methods of thought and standards of social life and of conduct among
differently conditioned peoples. Still more important is the demonstration
that human ethics as a whole, like human faculty and civilization, takes
its place at the end of a scale whose beginnings can be found in lower
organic nature.

Those who have followed the account of social evolution given in the
preceding chapter must realize that the basic general principles of
natural ethics, as contrasted with "formal" ethics, have already been
discovered and formulated. A biological association of whatever grade and
degree of complexity is impossible unless biological duties are
discharged. Human ethical conduct differs from insect and protozoön
ethical conduct only in the element of a participation in the process by
the explicit consciousness of man that he has definite obligations to
others; and this distinguishing characteristic is the direct outcome of an
evolution which adds reflection and conceptual thought to a mental
framework derived from prehuman ancestors. The insect hurries about in its
daily life as an animated machine, whose activities are defined by
heredity; its special mode of conduct is just what nature has produced by
selection from among countless other forms of living which have not had
the same degree of biological utility. But man alone recognizes vaguely or
clearly the "why and wherefore" of his acts that are far more instinctive
than he supposes; he only is consciously aware of the bonds of kinship and
economic interdependence. He looks about for the authority which imposes
his duties and fashions his bonds, and conceives this authority as
something superhuman, until the comparative studies of evolutionary
phenomena reveal the true causes in uniform nature itself.

According to biological ethics, the fundamental obligations of all living
things are the same, even though the modes of discharging them may be
various. Every individual must lead an efficient personal life by
procuring food, but animals differ very much in their alimentary
apparatus; among other things they must respire, but some are so simply
organized that they do not need elaborate organs like the tufted gills of
a crustacean or the lungs of higher vertebrates. Every individual of
whatever grade must also provide in some way for the maintenance of the
species, but some, like a conger eel, produce enormous numbers of eggs
which are left uncared for, while others, like birds, bring forth only a
few young, which receive constant attention and protection until they are
able to shift for themselves. Nature has no place for even a human
community unless individual and racial interests are conserved, so that
the greatest duties are definitely formulated--all else is secondary and
less essential. Selfish action on the part of every unit is obligatory,
but it must always be antecedent to endeavor in the wider interests of the
race if the unit is a solitary individual; if it is a member of an
association of any grade, then it must serve its fellows in some way.
Egoism and altruism are natural essential guides to conduct; neither can
safely exclude the other, and their antithesis sets a problem for every
organism, which is to work out the proper compromise that will be most
satisfactory to nature. The Golden Rule is taught by biology because it is
demonstrated empirically, and not because it has any _a priori_ value as
an ideal ethical principle.

But utilitarian or natural ethics need not stop with the statement of
vague generalities like the foregoing. In human society, as in the life of
low animals, the worth and value of any form of conduct and of every
single act can be estimated by definite biological criteria. The
institution of marriage and the conventions of common morality have their
biological value in their provision for the care of children; the
safeguards of property rights enable the industrious--the biologically
efficient--to keep the fruits of their labors; the establishment of formal
civil and criminal laws is biologically valuable in a social way, in so
far as such laws diminish the unsettling effects of personal animosity and
the desire to wreak personal vengeance; the establishment and
differentiation of legislative, executive, and judicial organs of
government lead to greater social solidarity and higher biological
efficiency. Thus unchecked individualism is just as wrong ethically and
biologically among men as it would be in the case of insect communities,
as pointed out in the preceding chapter; no one has a right to expect
service or deference to personal interest from others if he fails to work
for them and for the good of all. It is true that the social structure
will stand a great amount of tension, but if this becomes too great,
either a readjustment is effected, as when King John was forced by the
barons to concede their rights, or else the whole nation suffers, owing to
the selfishness of a few. In the war between Russia and Japan, the latter
won because the individual soldier merged his individuality in the larger
mechanism of the regiment and brigade and army corps, gladly sacrificing
his life for the nation represented by the person of its Emperor. The
single Russian soldier may have been far superior to a Japanese in
muscular strength, and perhaps in arms also, but selfishness and greed on
the part of many who were responsible for the organization and equipment
of the Russian armies rendered the whole fighting machine less coherent
and therefore less efficient than that of the Japanese.

In the evolution of ethics the recognition of ideals of conduct has
followed long after the institution of a particular precept by nature,
which is obeyed instinctively and mechanically by force of inheritance. In
the case of the communities of insects, the results are the same as though
the individual animal fully recognized the value of concerted endeavor. So
among primitive savages of to-day there is only a vague conception of
abstract duty as such, or it may be practically lacking, as in the case of
the Fuegians. So also a growing child is substantially egoistic, and it
must be taught by precept and example that the rights of others can be
safeguarded only by the altruistic correction of personal action, long
before the child can grasp the higher conceptions of ethics. If a human
being never learns to do so, and becomes a criminal through force of
heredity or circumstances, the machinery of the law automatically comes
into operation to conserve the welfare of the community. Such a criminal
may be unable to control his destiny, and may not be responsible for being
what he is, but nevertheless he must pay the penalty for his unsocial
heritage by suffering elimination.

Ethical systems are built around man's vague recognition of certain
natural obligations, and they have thus become more or less complex, and
more or less varied as worked out by different peoples. They must
necessarily be much concerned with social questions, with morals in the
usual sense and the more rigid principles enacted into the spoken and
printed law, but they have also become closely connected with religion and
theological elements. Especially is this true in the ethics of barbarous
and savage peoples, who accredit the "categorical imperative" to some
supernatural power, as we are to see in a later section. The one point
that comes out clearly is that the systems of conduct and duties have
evolved so as to be very different among various races, and that in the
history of any one people, ethics has passed through many varied
conditions. What may be deemed right at one period becomes wrong at
another when conditions may be changed; in medieval England the penalty of
death was prescribed for one who killed a king's deer, as well as for a
highway murderer. The Fijian of a quarter century ago killed his parents
when they became too old to be effective members of their tribe. And so
deeply ingrained was this principle of duty that elderly people would
voluntarily go to a living grave surrounded by their friends; while in
other authentic cases, parents have first killed their sons who failed to
obey the tribal law, and have then committed suicide. We can see how
nature and necessity would institute a law requiring such conduct where a
tribe must carry on almost incessant warfare and where the available food
supplies would be enough for only the most efficient individuals.
Infanticide also has been practised for reasons of biological utility, as
among the Romans, who at first maintained their racial vigor by
deliberately ordering the death of weak babes. But times have changed, and
ethics has become very different with passing decades. Our civilization
has resulted in a development of human sympathy as an emotional outgrowth
of necessary altruism; this motive directs us through charitable
institutions and hospitals to prolong countless lives which are more or
less inefficient, but which do not render the whole body politic
incompetent in its struggle for existence.

Nature then has itself attended to the development and institution of
ethics. As we look back over the long series of stages leading to our own
system of conduct the most striking feature of the history is the
increasing power of self-control or inhibition. As a natural instinct this
tends to prevent the committing of acts which for one reason or another
are naturally harmful to society as a whole. What we call conscience is an
instinct implanted by purely natural factors, and it unconsciously turns
the course of human action in the directions of selfish and altruistic
interests. Conscience, then, without ceasing to have validity and
efficiency, appears on the same plane with all of the other products of
evolution which owe their existence to individual or social utility.

Theology and religion involve intimately related conceptions of the world,
its make-up, and its causes. Strictly speaking, religion is a system of
piety and worship, while theology deals more particularly with the
ultimate and supernatural powers conceived in one way or another as the
God and the gods who have constructed the universe and have subsequently
ordered its happenings. A religion is a group of ideas having the effect
of motives; it is dynamic and directs human conduct. Theology, on the
other hand, is more theoretical and descriptive, and its conceptions,
together with those of other departments of human thought, give the
materials for the formulation of the religious beliefs which determine the
attitudes of men toward all of the great universe in which they play their
part and whose mysteries they attempt to solve.

Defined and distinguished in these ways, these two departments of higher
human life present themselves for comparative study and historic
explanation. They differ much among the varied races of mankind, so much,
indeed, that an investigator who approaches their study with a knowledge
only of Christian religion and theology finds it difficult at first to
recognize that the same fundamental ideas, although of far cruder nature,
enter into the conceptions of an idol-worshiping fanatic living in the
heart of Africa. But, nevertheless, beliefs that fall within the scope of
the definitions adopted above are to be found among all men, and they must
be examined so that their agreements and differences may be demonstrated,
and their common elements may be explained as the natural products of a
process of evolution.

Such a broad comparative study, like that of physical, mental, and social
phenomena discussed heretofore, must be conducted objectively; that is,
each and every particular belief of a religious or theological nature
which can be discovered in any race is entitled to a place in the array of
materials which demand scientific treatment. They must be verified,
classified, and summarized, in order that their total meaning and value
can be discovered. It must be strongly emphasized that for such purposes
the inherent validity and truth or falsity of diverse religions are not
called into question when they are so considered as objects of study; many
still entertain the view that the mere task of conducting an analysis of a
group of religious beliefs of whatever nature must tend to destroy or
alter that system of religion in some way and degree. But whatever the
comparative student may himself believe, the conception of Jehovah in the
Hebrew religion is quite as legitimate an object of study as the
Buddhistic concept of Brahma as the Ultimate Being, or the Polynesian idea
of Tangaroa as the god of the waves. We would naturally be inclined to
exclude the last from our own personal system of piety and worship as the
childish concept of an imaginative, adolescent race; but whatever the
truth may be, the fact of a belief in Tangaroa is as real as the fact of
Christian belief in God. We can no more destroy any one of these ideas by
investigating its nature and origin than we destroy the efficacy of the
human arm when we study its muscles and bones and sinews. The former, like
the latter, take their places among natural phenomena whose history must
be inquired into if there are any reasons for supposing that they fall
within the scope of evolution. I would be the last to lead or to take part
in an attack upon any system of religion, but as a student who is
interested in the universality of organic evolution, I am forced to
scrutinize each and every authentic account of a religion to see if such
systems present objective evidence of the fact of their evolution through
the operation of purely natural causes.

But before passing to a detailed treatment of the analysis, synthesis, and
genesis of religious systems, let us employ our common-sense for a brief
backward glance over the known history of familiar facts. Every one is
aware that the Christian religions of our time and community have not
existed forever; this, indeed, is indicated by the way the passing years
are denominated. We call the present year 1907 Anno Domini, and this whole
expression explicitly refers to the fact that less than two thousand years
ago the Christian systems of piety and worship collectively took their
origin from their Hebrew ancestor. The same parent has produced the
relatively unchanged Judaism of the present day. Judaism itself evolved
under the influence of the Prophets, of Moses, and of Abraham. Turning to
Asia, we learn how Buddhism evolved from Brahmanism. The teachings of
Mohammed at a later time developed into the formulated precepts of the
Koran. Would any one venture to assert that all or any of these systems of
thought have stood firm and immutable from the finite or infinite
beginnings of time? Would any one contend that the creeds of Protestantism
have remained unchanged even during the past twenty years? Like all
departments of human belief and knowledge, religious concepts have
obviously altered in natural adjustment to changing times and to advancing
conditions of human intellect; and the question turns to the mode by which
they have been modified, to see whether natural causes of evolution have
changed them, and have originated their earliest beginnings at the very
outset of human history. It has been stated above that every race of
mankind, however primitive or advanced it may be, holds some form of
religious belief based upon some conception of the supernatural powers
back of the world; and what the universe is conceived to be must largely
determine the particular characteristics of a theology, and through this
the special form of its attendant religion. We have before us a wide array
of types to study and to compare, which vary so greatly, partly for the
reason specified, that an inclusive definition of religion must be couched
in very general terms. If we define it as the attitude and reaction of a
human being conditioned by his knowledge of the immediate materials and
his conception of the ultimate powers of the universe, its scope is so
extended as to include the ideas of the atheists and agnostics as well as
the crude conceptions of lower races and those systems of piety and
worship conventionally regarded as religions by civilized peoples. More
than this: we cannot regard the total reaction of a thinking being as
essentially different in ultimate value from the attitudes toward their
worlds of animals lower than man. The situation of a well-trained sheep
dog is one of pastures and fences and gates, of rain and sunshine, of
sheep, and of a master whose voice is to be obeyed. What the dog may do is
partly determined by what it finds in its world of animate and inanimate
things. Although the animal's "conception" of such things must be far
simpler than a human being's, nevertheless its life is lived in reaction
to all of its surroundings as they are presented to its cerebral apparatus
by the proper organs. So in the human case, conduct is directly affected
by the living and lifeless objects of a total human situation, the only
difference being that reflective consciousness and reasoned interpretation
have their share in determining the assumed attitude in ways that seem to
have no counterparts as such in the mental lives of lower animals. But
whether or not the similarity between human religion and lower organic
reaction be admitted,--and the admission is one that greatly facilitates
an understanding of evolution in this field,--the general resemblance of
all religions in fundamental character at least must be accepted.

Another general feature of religious systems is their complexity. The
essential elements of all of them are few indeed, as we shall see at a
later point; they are beliefs regarding ultimate powers, human
responsibility to such powers, and future existence. These have taken one
specific form or another in various lines of racial evolution, but aside
from their own changes they have gathered about them many other articles
of creed relating to other departments of thought and life. Ethical rules
of conduct are so added, as in the Hebrew religion where the idea of
Jehovah involves God the Ruler and Judge who imposes and administers the
laws of right living. Social customs are almost invariably intertwined
with religious views, among savages as well as among the more advanced
Mohammedans whose rules relating to family organization form an integral
part of the whole cult. The emotional elements play a large part in some
cases, in the fanatical creeds of the Dervish and Mahdist and in the
"revivals" under nearer observation. In Greek cosmology and worship,
aesthetics figured to a large degree. Temperamental and other
psychological characteristics have profound effects upon religions, which
we may illustrate by such extreme examples as the austerities of New
England and Scotch Presbyterianism and the contrasted liberties of the
natural religions of tropical races. But all of these accessory elements
belong to other well-defined departments, some of which have already been
considered, and among the materials of their proper divisions they find
their interpretation and historical explanation in evolution. It is with
the basic elements themselves that we are now concerned.

Only within recent years have systematic attempts been made to classify
religions on the basis of impersonal objective study. Throughout all times
men have instinctively set up their own religion as the only true one,
besides which all others are designated simply as false--a very natural
distinction, but one which is too naïve for science, as well as one that
takes into account subjective or personal values which are not to be
considered in an objective comparison and analysis. The linguistic basis
was first employed by Müller, with the result that religions were placed
in the category of evolutionary accompaniments of the other mental
possessions and of the physical qualities of genetically connected
peoples. Thus the nations of Europe that branched out in all directions
from very nearly the same sources possessed common linguistic characters
and somewhat similar creeds. The Sanskrit-speaking races were the original
Brahmins and Buddhists. Ancestor worship is an accompaniment of the
peculiar languages spoken by eastern Mongolian peoples. And although the
correlation specified is by no means invariable, because a race of one
stock can readily accept the religion of a neighbor or of a conqueror, yet
much is gained through the introduction of the idea of evolutionary
relationships.

A more logical classification frankly adopts the genetic method and
clearly recognizes the direct effects of cultural and intellectual
attainments upon the way a religious system becomes formulated. In such an
arrangement, similar to that of Jastrow, religions can be classed as those
of savagery, of barbarism, of advanced culture, and of civilization. Among
the first named, notably those of Polynesian and African tribes, beliefs
in diversified ghosts and spirits bulk largely, and every moving thing, be
it a river or a cloud or a tree or animal, is held to be animated by an
invisible conscious genius; the spirits reside in everything, as well as
in the great unknown beyond. Above these in the scale are the religions of
so-called primitive cults, more elaborate and formalized in the ancient
beliefs of Egypt and Assyria, but still below those of advanced culture,
which make up a third group. The fourth class includes the religions which
tend to be coextensive with life, and which enjoin the higher harmony of
practical and theoretical conceptions. Taking Christianity as an example,
the contrast with the beliefs of savagery brings out clearly the nature of
progressive development. Here religious thought is no longer esoteric,
confined to a chosen sect like the Levites among the Hebrews or the shaman
and medicine-man among the American Indians; nor is religious observance
restricted to the innermost shrine of the tabernacle or sacred dwelling,
accessible to few or only one. It comes to be regarded as something in
which each and every individual can participate, and a personal possession
that has a direct part in determining all forms of human life and action.
This is another way of saying that the more highly evolved religions owe
their character to the greatly varied and abundant intellectual elements
which are built into them. And this is why religion in the highest form,
more clearly than in the lowest forms, is to be spoken of as an outlook
upon the world which is determined by the total intellectual equipment of
the individual man who thinks about the universe and directs his course of
action by what he finds.

* * * * *

We come now to a closer concrete study of the basic elements of religion;
that is, of those beliefs that are invariably present, in one form or
another, in every system of piety and worship, and that constitute the
innermost framework beneath the secondary creeds added to them. Following
Mallock and others, we may distinguish three such elemental conceptions.
These are, first, the belief in the existence of a supernatural being or
beings, endowed with intelligence like, but superior to, our own; second,
the idea of human responsibility to this or these powers; and, third, the
belief in immortality as an attribute of the supreme powers and of human
individuals also. Let us see how these beliefs appear in characteristic
systems of religion.

In all forms of Christianity the central idea is the conception of a
triple unity personified as God. He is regarded as the Creator who has
made all things and who demands reverence from his subjects. He is the
Author and Finisher of the faith as well as the sole Cause of the universe
itself. Much of this element is directly derived from Judaism, the
progenitor of Christianity; but a difference consists in the triple nature
of the supreme being according to the newer creed. As the original and
supreme being, God is not only the Creator, but the watchful Judge as
well, demanding reverent obedience to the laws of the world in which he
has placed man, and imposing sacrifices and penitential observances when
his mandates have been disobeyed. As the God of Mercy he is incarnated in
the person of Jesus of Nazareth, and offered as a vicarious sacrifice for
sinners who are thus enabled to escape the penalties they would otherwise
have suffered. As the Holy Ghost, God is the vaguely personified ultimate
source of the higher and nobler elements of human thought, aspiration, and
life in general. The second basic tenet of Christianity is that of human
responsibility to God, to whom man is related as the created to a creator,
as a subject to a ruler, and as one saved to his redeemer. The
institutions of sacrifice and ritual are outward signs of human subjection
to God himself and to his laws, according to which the universe is
conceived to operate. Finally, Christianity teaches that just as God in
his single and triune form is eternal, so the soul of man is immortal,
with or without its earthly temple of flesh and blood. The essential
thinking individual is believed to pass to heaven, where rewards for right
living are bestowed, or to hell, in order to suffer punishment for sin
during all eternity, or some part of it, according to different views
regarding the efficacy of Christ's vicarious atonement.

It is true that the manifold sects of Christianity differ somewhat in the
detailed forms of these three essential beliefs, but not to the same
degree as in the case of the secondary additions. God's laws, Christ's
teachings, and the inspiration of the Holy Ghost are the recognized guides
to conduct; but human frailty has been such that the history of Europe
presents a panorama of warring sects in almost unceasing strife about
details of ritual and interpretation, while the great fundamental truths
have been too frequently ignored. The conflicts of Catholics and
Protestants, Puritan and Cavalier, and Northern and Southern
Presbyterianism, have not been waged on account of basic beliefs like the
three outlined above, or about the Golden Rule, but on account of
comparatively trivial details which to the impersonal student have
scarcely more than the value of individual preference.

Judaism, the next great religion, has already been mentioned as the parent
of Christianity, to which it gave the concept of a Supreme Being, as well
as that of a Messiah. It is a purer monotheism than its outgrowth, whose
trinity is more like certain elements of Greek theology. Jehovah is the
one supernatural power, the creator and lawgiver and immediate cause of
all the workings of nature. It is he who shapes the world out of
nothingness and who separates the waters from the dry land; he parts the
waters of the Red Sea to save the Israelites, and brings them together
again to overwhelm the pursuing hosts of Pharaoh. It is his voice that
thunders from Mt. Sinai, and his finger that traces the commandments to
rule the lives of his chosen people upon the tablets of stone intrusted to
Moses the Seer. At the behest of Joshua he holds the sun and the moon in
their courses above the vale of Ajalon so that there will be more time for
the destruction of the Philistines. In brief, Jehovah is the eternal god
of law and power, demanding sacrifice and priestly atonement, and
promising happiness eternal upon the bosom of Abraham to those who
recognize their responsibility to him and obey his precepts. Again, there
are three fundamental beliefs, that differ from those of Christianity as
the Talmud diverges from the New Testament scriptures.

Mohammedanism is another outgrowth from this group of religions. The
teachings of the Koran give the institutional and ritual forms to the same
three elements distinguished above. God is the identical single God; and
Mohammed is His Prophet, as Jesus is the New Prophet of Christendom. The
true believer's responsibility entails active warfare upon the heretics,
that is, those who do not accept the Koran. The immortal state of
Mohammedanism is a very different thing from the heavenly bliss of
Christianity, for the promised rewards are such as would appeal to the
warm-blooded Southern temperament.

Turning now to Asia, we find in Brahmanism and Buddhism two systems of
religion that are related to one another exactly as are Judaism and
Christianity. The analogue of the Old Testament is a group of priestly
hymnal writings known as the Vedas, which date back to about the
fourteenth century before Christ lived. Their objects of worship at first
are numerous invisible beings that actuate the things of the world, as in
Greek theology, but later one of them assumes preëminence as the
all-pervading essence of things,--Brahma. The precepts of Brahmanism
enjoined adoration of the unseen powers and of their works, as well as
practical rules of human conduct, such as those which divided a man's life
into the four periods when he should be successively a student, the head
of a family, a counselor, and a religious mendicant who should renounce
the world of social activities and human desires. In earlier writings, the
immortal state is a kind of heaven, but later it meant simply an
absorption into Brahma, the eternal impersonal being.

Buddha was an orthodox Brahman reformer of the sixth century before our
present era, just as Jesus was an orthodox Hebrew reformer. The essential
creed of Buddha made his religion far more ethical than earlier forms, and
placed it on a plane even above Christianity of later centuries. This
creed relates to the element of human responsibility particularly, the
other two remaining much as they were found by Buddha. According to his
teachings, a man rested under an obligation to live nobly in the truest
sense, and he acquired merit--_karma_--or lost it, in proportion to his
deserts. At death a human soul is reincarnated, in a lower form of animal
or even in a being residing in one of a series of unseen hells, if
punishment is due; if a higher state is merited, progress is made through
thousands of existences until perfection is rewarded by an eternal fusion
with the essence of Brahma. It is because there is no escape from just
punishment that Buddhism in its original form is properly denoted more
ethical than a religion which teaches that sacrifice of any kind will
exempt the sinner from deserved penalties and bring about the bestowal of
unearned rewards.

Polytheism is the name given to a religion such as that of the Greeks or
Romans, who believed in many gods and spirits of greater and lesser power.
These supernatural beings, each in its own sphere, immediately directed
the processes of nature and controlled the lives of men. One of them,
Zeus, was regarded as the supreme "father of gods and men," who delegated
specific duties to others; Ares was the god of battles, Hermes was the
messenger, Athena implanted wisdom in the minds of men, and Poseidon ruled
the sea. The gods were very human to the Greek mind, living in Olympus as
men do upon earth, and even visiting the mortals. Their worship involved
propitiatory sacrifices and rites as well as thanksgiving offerings when
favors were bestowed. But although they were immortal, they did not allow
the immortal souls of human beings to join them in their elysium, but
compelled the disembodied shades to wander unhappily among the tombs and
about their earthly abodes.

Roman theology and religion comprise almost identical forms of the three
fundamental elements. The names are changed, and Zeus becomes Jove, his
wife Hera is Juno, Ares is Mars, and Hermes is called Mercury. In all
other respects, however, the two systems are as much alike as the Greek
and Roman languages and Greek and Roman physique.

The religions of savagery are far less analytical, and much more naïve in
their reference of natural happenings to the direct interposition of
malevolent and benevolent spirits. Their gods are numerous as in Greek
religion, and likewise one of them is usually set up as the superior
deity, to be the Tirawa of the Indian, the greater Atua of Polynesia, and
the Mumbo Jumbo of a West African negro. There is no centralization of the
supernatural powers, as in the Jehovah of Judaism and the still subtler
Brahma of the Asian. Then, too, the gods must be concretely materialized
for purposes of worship and sacrifice; consequently idols are made, to be
regarded as the actual spirits themselves permanently or for the time
being, and not viewed as representations of an ideal, like the statues of
more advanced peoples. The immortal state is described in low religions in
various ways that seem to be determined by what the believer himself most
desires. The spirit of an American Indian goes to the happy
hunting-grounds, where it mounts a spirit pony and forever pursues the
ghosts of bison which it kills with spirit bow and arrows; to provide these
necessaries his earthly possessions are laid beside his dead body. The
Norseman was conducted to Valhalla and, attended by the Valkyrie as
handmaidens, he eternally drank mead from the skull of an enemy and
gloried over his mundane prowess in battle. It is unnecessary to expand
the foregoing list, because the examples sufficiently represent the
various grades of human religions. Regarding them as typical, we can see
how universal are the three fundamental ideas with which we are concerned.
Every race has its own conception of future bliss, as well as its
conception of responsibility to the immortal and supernatural powers of
the universe. Whatever may be the actual reality, and however closely the
conceptions of one or another religion may approximate to the truth, such
reality and approximation are not the subjects of the present discussion.
Nor is it our purpose to bring out more explicitly the genetic
relationship of one religion to another; the evolution of Buddhism from
Brahmanism, the origin of Christianity from Judaism, and the divergent
development of the several creeds of Christendom amply illustrate the
nature of religious history. It is evolution here as elsewhere and
everywhere.

* * * * *

Having distinguished the three general elements of all religions, beyond
which everything else is of minor importance, we now turn to the question
as to the _natural_ origin of these elements. Clearly they cannot arise
independently, for the belief in supernatural and eternal spirits is
closely connected with the conception of an immortal soul.

The first is the conception of infinite personalities that later become
more or less merged into one supreme being. This begins with the idea of
the soul as the human ego, conventionally regarded as something
independent of the material body during life and immortal after death. The
savage goes to sleep, and in his dreams he goes upon journeys and battles
strenuously with other men and with beasts, only to find when he awakes
that his body is not fatigued, and that it has not really taken part in
the activities of his dream life. His companions about the fire also tell
him that this is so, while he is equally sure that his essential self has
been doing many things during the interval of sleep. In his dream life he
finds himself joined by others whom he knows are dead. He sees again even
those whose bodies he may have assisted in eating. His total world very
soon comes to have an unseen region which is the abode of ordinarily
invisible beings having the forms of men, with whom his own dream person
can associate; this unseen sphere is furnished also with ghostly
counterparts of the trees and rocks and waters with which he is familiar
when he is awake. Before long his soul or ghost or spirit is conceived as
something which possesses two qualities: it can be disassociated from his
body and enter the spirit-world where it seems to defy all the laws of
waking life, for with the quickness of thought it visits neighboring
islands as readily as it passes to the next hut; and it possesses
immortality, for it is exactly like the persistent spirit-individualities
of those who have died before him. The other cause for the development of
the conception of gods and God in the mind of the savage is the fact that
things have been made which neither he nor any other man can make. He can
dig a ditch, and make a house, and fashion a canoe, and build ramparts of
earth; but human power has obviously been insufficient to construct rivers
and mountains and forests and their denizens. Mankind itself has certainly
been made in some way, for it exists. Because the savage cannot conceive
of things being made excepting as they are made by the human hand, and
because so much confronts him that is beyond the power of human
construction, he comes to postulate the existence of man-like, but greater
than human, personalities, and as he cannot see them in the light of day,
they belong to the spirit-world to which souls go. Imagination sometimes
gives human outlines to shadows among the moon-lit trees, so that elves
and pixies, nymphs and fairies, become established in the world as the
primitive man conceives it. Larger tasks are discharged by more important
spirits, and everything natural thus becomes animated by supernatural
beings. Thor was the god of thunder; Freia the goddess of spring and
vernal awakening; Athena inspired the minds of men. Venus and Aphrodite
played their special parts, also. But such powers as these, established by
the untutored mind, needed to be accounted for, and so in the more
advanced religions Jove and Jupiter were created as the more ultimate
causes, in response to intellectual demands. By combining all powers into
one, God and Brahma are the results.

Thus in merest outline the conception of the infinite personality works
out its evolution. At all times, among primitive and higher religions, the
powers are clothed with human forms, and gods are pictured as men endowed
with intellects and passions, and motives of vengeance and benignity. Man
cannot shape his postulated deities save in such forms, with the possible
exception of the most philosophical concept of all, Brahma.

The second fundamental belief, namely, in immortality, owes its origin in
greatest measure to the psychological processes described above. Another
potent factor, however, has been the natural desire to continue existence
hereafter, usually in order to reap rewards not bestowed here. This desire
is implanted by nature through the operation of purely biological factors,
and it has the value of an organic instinct. To specify more particularly,
nature has placed every organic individual under the necessity of doing
its utmost to prolong its own life in the interests of itself, of others
of its tribe, and of its species. Extinction is not faced willingly by a
human being endowed with full consciousness any more than it is passively
tolerated by a lower animal which instinctively struggles with its foes
until death. So the desire to continue alive--the "will to live"--is a
natural instinct, which combines with the belief in persistent disembodied
spirits and, no doubt, with many other elements, to develop the basic
conception of some kind of an immortal existence.

The third element, human responsibility to the infinite personality, is
variously recorded in lower and higher religions. Its conception grows
partly out of the feelings of awe and terror inspired by great works of
nature such as the thunder-storm, the cyclone, and the volcano, while the
orderly and regular workings of even everyday nature seem to demonstrate
the direct control of the powers who rule man as well. The savage sees his
crops destroyed by a tempest or drought; he attributes the disaster to the
particular powers concerned with such things whom he must have angered
unwittingly, and whom he must propitiate by sacrifice or penitence. His
individual and tribal acts do not always accomplish the desired ends, and
again the laws of infinite and ultimate powers must have been contravened,
as he interprets the situation. Therefore his whole religious
consciousness was exerted in the direction of finding out what was the
ultimate constitution of nature, with which human activities must
harmonize if they are to be successful. Bound by custom and convention and
biological law, he looks about wonderingly to find the external authority
for his bonds. To his mind this authority must be the host of spirits and
gods who had made him and the things of his world. It is in this way that
so many ethical elements have found places in religious doctrines, to be
viewed as absolute rules of conduct coming from outside of nature, and not
from nature itself, in the way the earlier sections of this chapter have
shown.

Let us now summarize the results of the foregoing brief survey, conducted
by the identical methods employed for the analysis of other bodies of
fact. We have sought for those characteristics which are common to all
religions of whatever time and place and race. Combined with many
secondary and adventitious elements of other fields of thought and action,
such as social, political, ethical, and psychological factors, they have
proved to be the three essential beliefs in God or gods, human
responsibility, and immortality. As a veritable backbone, they underlie
and support the whole body of religious doctrine and organs of thought
formed about them. We have seen, furthermore, that a natural explanation
of the way these elements have originated can be discovered by the
comparative student of religion, who describes also how they have
variously evolved among different peoples. In all of this we have not
questioned at any time the validity or reality of any one of these
concepts; to ask whether or not they correspond actually to the truth is
beyond our purpose, which is simply and solely to inquire whether even
these mental conceptions furnish evidence of their evolution in the course
of time. I believe that such evidence is found, and I believe also that
this discovery must be of the greatest importance to everyone in
formulating a system of religious belief, but the construction of this is
not the task of science as such. Every individual must work out his own
relation to the world on the basis of knowledge as complete as he can make
it, but every individual must accomplish this end for himself. Because no
two men can be exactly alike in temperament, intellect, and social
situation, it is impossible for entire agreement in religious faith to
exist. One's outlook upon the whole universe is and must be an individual
matter; science and evolution are of overwhelming value, not by directing
the mind to adopt this or that attitude toward the unseen, but by
providing the seeker after the truth with definite knowledge about the
things of the world, so that his position may be taken on the sound basis
of reasonable and common-sensible principles.

* * * * *

When we take up science and philosophy, or knowledge as a whole, after
religion, it may seem that we have reversed the proper sequence. There are
many reasons for following this course, inasmuch as "knowledge" is the
all-inclusive category of thought; our world is after all a world of
individual consciousness and ideas. In dealing with religion, ethics,
social organization, and human culture, we have been concerned with the
evolution of so many departments of thought and action; and now we are to
develop a final conception of evolution as a universal process in the
progress of all knowledge.

Let us look back over the history of mathematics. The primitive human
individual did not need to count. He dealt with things as he met them, and
he disposed of them singly and individually. A squirrel does not count the
nuts it gathers; it simply accumulates a store, and it perishes or
survives according to its instinctive ability to do this. Just so was
primitive man. The savage, when he organized the first formed tribes,
learned to count the days of a journey and the numbers engaged on opposite
sides in battle. He employed the "score" of his fingers and toes, and our
use of this very word is a survival of such a primitive method of
counting. The abacus of the Roman and Chinese extended the scope of simple
mathematical operations as it employed more symbolic elements. With the
development of Arabic notation capable of indefinite expansion, the
science progressed rapidly, and in the course of long time it has become
the higher calculus of to-day. The conceptions of geometry have likewise
evolved until to-day mathematicians speak of configurated bodies in fourth
and higher dimensions of space, which are beyond the powers of perception,
even though in a sense they exist conceptually. The behavior of
geometrical examples in one dimension leads to the characteristics of
bodies in two dimensions. Upon these facts are constructed the laws of
three-dimensional space which serve to carry mathematical thought to the
remoter conceptual spaces of which we have spoken. It may seem that we are
recording only one phase of mental evolution, but in fact we are dealing
with a larger matter, namely, with the progressive evolution of knowledge
in the Kantian category of number.

Natural science began with the savage's rough classification of the things
with which he dealt in everyday life. As facts accumulated, lifeless
objects were grouped apart from living organisms, and in time two great
divisions of natural science took form. Physics, chemistry, astronomy,
geology, and the like describe the concrete world of matter and energy,
while the biological sciences deal with the structure, development,
interrelationships, and vital activities of animals and plants. Surely
knowledge has evolved with the advance in all of these subjects from
decade to decade and from year to year. And just as surely must evolution
continue, for the world has not stopped developing, and therefore the
great principles of science must undergo further changes, even though they
are the best summaries that can be formulated at the present time.

Philosophy deals with general conceptions of the universe. When we look
back through the ages we find men picturing the world as an aggregate of
diverse and uncorrelated elements--earth, air, fire, and water. The
synthesis of facts and the construction of general principles down through
Bacon, Newton, and Schopenhauer to modern world conceptions results in the
unification of all--"the choir of heaven and furniture of earth." The
lineal descendant of the long line of ancestral philosophies is the monism
which sees no difference between the living and lifeless worlds save that
of varying combinations of ultimate elements which are conceived as
uniform "mind-stuff" everywhere. Whether or not this universal conception
of totality is true, remains for the future to show. For us the important
truth is that here, as in all other departments of knowledge, evolution
proves to be real.

* * * * *

In closing the present description of the basis, nature, and scope of the
doctrine of evolution, I find great difficulty in choosing the right words
for a concise statement of the larger values and results of this
department of science. So much might be said, and yet it is not fitting
for the investigator to preach unduly. The lessons of the doctrine must be
brought home to each individual through personal conviction. But because I
firmly believe in the truth of the statement made in the opening pages,
namely, that science and its results are of practical human value, it is
in a sense my duty as an advocate of evolution to make this plain.

The method of science is justified of its fruits. At the very beginning we
learned how, and how only, sure knowledge can be obtained and how it
differs from a belief which may or may not correspond with the truth.
Based upon facts of smaller or larger groups, scientific laws are so many
summaries of past experience, and they describe in concise conceptual
shorthand the manifold happenings of nature. Their difference from belief
inheres in their ability to serve as guides for everyday and future
experience. This entire volume is a plea for the employment of
common-sense as we look upon and interpret the world in which we have our
places and in which we must play our rôles. Our search for truth will be
rewarded in so far as we organize our common-sense observations into clear
conceptions of the laws of nature's order.

The doctrine of evolution enjoins us to learn the rules of the great game
of life which we must play, as science reveals them to us. It is well to
remember that a little knowledge is a dangerous thing, but because
evolution is true always and everywhere, an understanding of its workings
in any department of thought and life clears the vision of other realms of
knowledge and action. Perhaps the greatest lesson is at the same time the
most practical one. It is that, however much we may concern ourselves with
ultimate matters, our immediate duties are here and now, and we cannot
escape them without giving up our right to a place in nature. We are
taught by science that we live under the control of certain fundamental
biological, social, and ethical laws; we might well wish that they were
otherwise, but having recognized them we have no recourse save to obey
them. Evolution as a complete doctrine commands every one to live a life
of service as full as hereditary endowments and surrounding circumstances
will permit. Thus we are taught that the immediate problems of life ought
to concern us more than questions as to the ultimate nature of the
universe and of existence.

Every one can find something worth while in the lessons of evolution,
summarized in the foregoing statements. The atheist, who declines to
personify the ultimate powers of the universe, may, nevertheless, find
direction for his life in the principles brought to light by science. The
agnostic, who doubts the validity of many conventional dicta that may not
seem well grounded, can also find something to believe and to obey.
Finally, the orthodox theist of whatever creed may discover cogent reasons
for many of his beliefs like the Golden Rule previously accepted through
convention; and he must surely welcome the fuller knowledge of their sound
basis in the materials and results of comparative analytical study. To
every one, then, science and evolution offer valuable principles of life,
but great as their service has been, their tasks are not yet completed,
and cannot be completed until the end of all knowledge and of time.

INDEX

Achatinellidæ, 103, 104.

Activities, instinctive and reflex, 203, 205, 208;
of familiar animals, 208, 209;
differ from instinct, 209, 210.

Adaptation, universal relation to environment, 15;
principle of, 17;
degenerate forms enlarge our conception of, 50;
results of larval short cuts in development, 71; 109, 213.

Africa, fauna of, 103, 164, 165.

Agassiz, a believer in special creation, 98.

Ages, Palæozoic, 92;
Mesozoic or Secondary, 93, 94;
Cenozoic or Tertiary, 93;
Coal or Carboniferous, 94.

Albumen, of egg, 60.

Alligators, a diverging branch of lizard, 45.

Amoeba, 21, 51, 69;
comparative study of, 203, 205, 231, 247, 251, 254, 257, 258, 259, 265,
266.

Amphibia, frogs, salamanders, a lower class, 45, 62;
order of evolution of, 63;
evolved from fishes, 64;
most primitive backboned animals, 92; 94, 157;
embryos of, 171; 200.

Anatomy, of mind, 202.

Ant-bears, 42.

Anthropoidea, 160.

Anthropology, 177;
methods and results of, 186;
types of, 186, 187;
comparative, of mind, 211.

Anthropometry, 177.

Ants, communities of, 125;
mental life of, 207, 208;
organizations of, 260, 263, 264.

Apes, 158;
susceptible to training, 210;
line from Amoeba, 231.

Appendix, vermiform, 168.

Apteryx, wingless bird of New Zealand, 44, 200.

Arachnida, 49.

Archæopteryx, a famous "link," 99.

Ares, 300.

Armadillo, 42.

"Arts of life," 226-230;
dwellings of men, utensils, 227;
history of clothing, 228;
arts of pleasure, 228-230.

Atom, carbon, 22;
nitrogen, 23;
hydrogen, oxygen, 24;
chemical, 25.

Atua, 301.

Azores, animals of, 103.

Bacteria, amazing production of, 123;
relation of, 127.

Baldwin, 148.

Bandicoot, 42.

Barnacles, really crustacea, 50.

Bats, 41, 94.

"Beagle," 102, 117, 136.

Bear, 38, 39.

Bees, mental life of, 207, 208;
nervous system of, 232, 256, 257;
organizations of, 260, 261, 262;
queen, workers, 262, 263.

Beetles, 67.

Bernier, 183.

Bertillon, 183.

Birds, 44;
have they descended from gill-breathing ancestors? 61;
evolution of, 63;
primitive, 99;
embryos of, 171, 200.

Blastula, 68.

Blumenbach, 183.

Bonnet, 70.

Borneo, 164.

Brachiopods, 95.

Brahma, 299, 304.

Brain, 215, 235-240.

Brontosaurus, 94.

Brown-Séquard, 148.

Buddha, 299.

Buffon, 114, 135.

Butterflies, 67, 206, 207, 259.

Carbohydrate, 23, 24.

Carbon, atom, 22; 25, 27.

Carnivora, 35, 37, 38, 39, 40;
order of, 157.

Caterpillar, larva of, 259.

Cats, Manx, Angora, Persian, 37, 39;
domesticated, 137;
intelligence of, 208, 209.

Cattle, products of human selection, 137;
resemblance, 157.

Cebidæ, true monkeys, 160, 161, 162.

Cells, 19, 20, 21;
sex, 144;
human, composition of, 156;
of ectoderm and endoderm, 255, 256, 257, 258.

Celts, 218.

Cercopithecidæ, 160, 162.

Cerebrum, 215.

Cetacea, 40.

Chemical transformation, 17.

Chick, development of, 60, 61.

Chimpanzee, 163, 164, 195.

Chromatin, 143, 144.

Civilization, a product of evolution, 272.

Classes, 32.

Classification, 32.

Clifford, 238.

Coccyx, 168.

Communities, cell, 258;
insect, 258, 260-264.

Comparative anatomy, 35, 37, 39;
any form will disclose development, 57;
amphibia evolved from fishes, 64;
Law of Recapitulation, 66;
insects arisen from wormlike ancestors, 67;
larvæ of insects, 67;
higher animals evolved from two-layered saccular ancestors, 68; 70, 71;
supplements comparative embryology, 72;
appearance of great classes of vertebrates, 94;
proves order of evolution, 163.

Composition, chemical, 15.

Compounds, organic, 29.

Conger-eel, 123, 124, 127.

Consanguinity, essential likeness, 54.

Conscience, 287.

Consciousness, human, 234, 235.

Crabs, 48, 49, 66;
hermit, 66.

Crustacea, lobsters, crabs, 48, 49;
barnacles, 49, 50; 82.

Cuvier, 158, 78;
a believer in special creation, 79.

Curve of error, 120.

Cyclones, 85.

Cyclostomes, 156.

Daphnia, 205.

Darwin, Charles, 80, 100, 102, 115, 116, 117;
Origin of Species, 116, 124, 130, 132, 135;
Erasmus, 135, 136, 138, 142, 143.

Deer, 42;
fossil, of North America, 97, 98.

Development, 54;
a natural process, 56.

De Vries, 145, 146;
his mutation theory, 147, 148.

Dinosaurs, 94.

Distribution, geographical, 32.

Dogs, 38, 39;
embryo of, 66;
varied forms of, 137;
pointer, sheep-dog, instincts of, 208;
intelligence of, 208, 209.

Dubois, 173.

Ducksbill, or Ornithorhynchus, bottom of mammalian scale, 43.

Ducksworth, 184.

Eagle, 44.

Earthquake, 85.

Echidna, bottom of mammalian scale, 43.

Ectoderm, 255.

Egg, of common fowl, 60;
of frog, 68;
nuclei contains factors of development, 71; 144, 145;
human, 231.

Eimer, 148.

Elements, chemical, 15.

Elephant, 41;
place in zoölogical science, 95; 96, 97;
age of, 124.

Embryo, of frog, 58;
of chick, 60-62, 63, 64, 65;
embryos of carnivora, rodents, hoofed animals alike in earlier
development, 65;
of cat, dog, rat, sheep, rabbit, squirrel, cattle, pig, 65;
of skate, shark, hammerhead, 66;
the human, 168, 170, 171;
of birds, reptiles, amphibia, 171;
human hemispheres of brain like adult cat or dog, 215.

Embryology, 32, 33, 34;
of no form fully understood, 57;
general principles of, 57-67;
embryonic agreement, 65;
of insects, 67;
weight of facts of, 69;
comparative, a distinct division of zoölogy, 70, 71; 76, 94, 100;
evidence of, 170;
of mind, 202, 214;
in early stages of human, no nervous system present, 214;
development of, 215.

English sparrow, 123, 127.

Environment, 111, 112;
influences of, 126;
determines mode of life of a race, 213.

Epoch, Glacial, 86;
Silurian and Devonian, rich array of types, 93;
Cenozoic, 96.

Erosion, 89.

Eskimo, picture-writing, 223.

Ethics, 281;
biological, 283;
natural, 284;
evolution of, 285.

Ethnology, 177.

Evolution, the Doctrine of, 1;
is it a science, 3;
the conception of, 8;
organic, 10-12; 31, 32;
evidence of, 54, 95;
of amphibia, 62;
of birds, 63;
of protozoa, 69;
theory of, supported by palæontology, 76;
cosmic, 84;
biological evidence of, 91;
three important elements of, 109;
adaptation, variation and inheritance, 110;
mechanical, 109;
dynamics of, 109;
second element of, 122;
human, 150-196; 174;
physical, of man, falls into two groups, 153;
of human races, 176;
racial, 177, 178;
mental, 197-240;
human faculty as a product of, 212;
mental as real as physical, 214;
of brain, 214-217;
of art of writing, 223;
method of mental, 231;
social, 241;
of societies of insects, 258;
human, biological interpretation of, 267-274;
of higher human life, 278-311;
of ethics, 285;
final conception of, 307-311.

Factors, primary, secondary, 110;
three kinds, 111;
congenital, 113.

Falls of St. Anthony, 86.

Fishes, lowest among common vertebrates, 46;
trunk-fish, cow-fish, puff-fish, mouse-fish, flounder, 46;
most primitive backboned animals, 92; 94; 157;
embryos of, 171.

Fiske, 139.

Flies, may, 259.

Flounder, a variant of the fish theme, 66.

Fossilization, conditions of, 77-78.

Fossils, 73-105;
remains of, 73;
groups, 77; 78, 79;
order of succession, 91;
oldest rocks devoid of, 92;
forms, 99.

Fowl, game cock, 138;
pigeons, 138.

Frog, 45;
eggs of, larva, development of, 58, 59, 60, 68.

Galapagos Islands, 102, 103, 104.

Galton, 142, 147;
heredity of mental qualities, 232.

Gametes, 252.

Gastrula, 68.

Gemmules, 143.

Genera, 32.

Generation, spontaneous, 78.

Geographical distribution, 32.

Geological agencies, rain, rivers, glaciers, 88;
construction, volcanoes, 88.

Geology, data of, 83, 84.

Germ, Bonnet's idea of, 70;
cells, 144, 146;
plasm, 145, 146.

Gibbon, 163.

Gills, 58, 62.

Gill-slits, bars, clefts, 61, 62, 64;
in embryos of lizards, birds, mammals, 69; 171.

Giraffe, 133.

Glaciers, alterations made by, 87.

Goats, 157.

Gorilla, 163, 165, 195.

Grand Cañon of the Colorado, 85, 90.

Gravitation, 155.

Guinea-pigs, Brown-Séquard's, 148.

Gulick, 103.

Haeckel, 63, 71, 184.

Hæmoglobin, 22.

Hapalidæ, 160.

Harvey, 70.

Hawaiian Islands, 103;
snails of, 104.

Heredity, 142;
a real human process, 175;
instinct determined by, 206;
Anglo-Saxon, 213;
of mental qualities, 232.

Heron, 44.

Hesperornis, 99.

Hippopotamus, 42.

Hominidæ, 160.

Homo sapiens, 183.

Hoofed animals, 95, 96, 97.

Hornets, communities of, larvæ of, 260.

Horse, 41, 42, 65;
place of in zoölogical science, 95, 96;
development of, 97;
perfection of one type of, 136, 157; 167;
intelligence of, 209.

House-fly, eggs of, 67.

Human faculty, 212;
its three constituents, 212.

Huxley, 6, 26, 30, 63, 184.

Hydra, 50, 51, 52, 53, 68, 69;
comparative study of, 204, 205, 206; 254;
cells of, 255; 256, 257, 258, 261, 262, 263, 265, 266.

Hydrogen, 25, 27.

Hyracotherium, 96.

Ichthyornis, 99.

Ichthyosaurus, 94.

Indians, American, pictography of, 223, 224;
of Brazil, 227;
life of, 272.

Individual development, a résumé of history of species, 63.

Inertia, 155.

Infant, human, activities of, 216.

Ingestive structures, 17.

Inheritance, 110, 131;
biological laws of, 142;
paternal and maternal basis of, 144; 145;
Mendelian phenomena of, 146;
Galton's Law of, 147;
laws of, in mental phenomena, 203;
strength of, in mental traits, 232;
physical, provides mechanism of intellect, 233.

Insects, butterflies, beetles, bees, grasshoppers, spiders, scorpions, 49;
66;
eggs of common house-fly, 67; 82;
nervous mechanism of, 205;
communities of, 207, 258-260, 267;
nervous system of, 256, 257.

Instinct, determined by heredity, 206;
of higher animals, 208;
differs from intelligence in degree, 210.

Intelligence, 203;
in mental life of communal insects, 207.

Invertebrates, lower animals devoid of backbone, 47;
structural plan, 48;
branches of, 49;
groups, two layer animals, 50;
hydra, sea-anemones, soft-polyps, 50;
more complicated, 68;
palæontological materials, 82;
evolution of lowest members, 92.

Jaguar, 101.

Jastrow, 294.

Java, 173.

Jellyfish, 81.

Jordan, David Starr, 123.

Kangaroo, 42.

Keane, 185.

Lamarck, 115, 133, 135.

Lampreys, 156.

Language, most important single possession of mankind, 218.

Laplace, 29.

Larvæ, of lobster, 66;
of insects, 67;
of ground wasp, 207;
of caterpillar, 259;
of wasps, 260.

Lavoisier, 29.

Law of Recapitulation, 66;
stated by Von Baer and Haeckel, 71.

Lemurs, 158, 160, 161, 195.

Life, what is it? 27.

Limestone, 89, 90.

Links, 99.

Linnæus, 79, 158, 183.

Lions, 101;
environment of, 112.

Lizard, nearest form to remote ancestor, 45.

Lobsters, 66;
larvæ of, 66.

Lyell, 80, 107, 135, 136.

MacDougal, 148.

Madagascar, 161.

Mallock, 295.

Malthus, 136.

Mammalia,
lower orders of, 42;
their own mode of growing up, 64;
embryos of, 64; 97;
members of class differ, 157, 158; 200;
order of mentality, 203.

Mammals, 40, 43, 157;
embryo of, 171.

Mammoth, 97.

Marmosets, 161.

Marquesas, 103.

Marsupials, 104.

Mastodon, 97.

Mechanism,
organic, 14;
living, 110.

Melanesia, 103.

Mendel, Gregor, 145;
his law, 146; 147, 148.

Mentality, human, 233.

Metazoa, 254.

Mice, 41, 134;
field, 139.

Miller, 293.

Mind,
anatomy of, 202;
human, differs only in degree, 203; 210, 211;
embryology of, 214;
palæontology of, 217;
and matter inseparable, 234-237.

Missing links, 77.

Moeritherium, a significant fossil, 97.

Molecule, protein, 22, 23, 24.

Mollusks, 81, 82;
connecting widely separated ages, 95.

Monkeys, 158.

Morgan, Lloyd, 148.

Morphology, 32.

Moths, 67.

Müller, 293.

Mutation theory, 146.

Naegeli, 143, 148.

Natural Selection,
doctrine of, 116, 117, 118;
the struggle for existence, 124, 125;
simply trial and error, 131;
Darwin recognized it as incomplete, 142;
germ-plasm theory supplements, 145.

Nebula, gaseous, 84.

Nervous systems, 201, 202, 205, 206, 211;
of worker-bee, 232.

Niagara, 85, 86, 89.

Ontogeny, recapitulates phylogeny, 63.

Orang-outang, 163, 164.

Orders, 32.

Organic, 15;
systems, 17;
transformation, analogies of, 43,
a real and natural process, 55, 56, 76;
mechanism, alteration of, 55.

Organisms,
living, 14;
analysis of, 16; 17, 18, 19, 26, 28, 29, 31, 32;
characteristic early stages, 55;
are they adapted by circumstances? 109;
environment, 111;
physical heritage of, 113;
variation of, 119;
difference, 121;
universal conflict of, 127;
change, 130;
human, 32, 156, 159, 165-171;
nervous system of, 201;
psychical characteristics of, 202;
many-celled, 257.

Organs, 16, 17, 28;
of human body, 156.

Origin of Species, 136, 149.

Origination of new parts, 109.

Osborn, 148.

Ostrich, 44.

Over production, 122-124, 129.

Owls, horned, of Arizona, 45; 139.

Palæontology, 32, 34, 73, 74, 76;
evidence of, not complete, 80, 81;
table of facts of, 91; 94;
second division of evidence, 95;
does it throw light on antiquity of man? 155;
of mind, 202, 203, 217.

Paludina, 95.

Partulæ, 103.

Pearson, Karl, 6, 7, 142, 147;
heredity of mental qualities, 232.

Penguin, a counterpart of the seal, 44.

Peoples,
fusion of, 178, 179;
Mexicans, 178, 181;
Anglo-Saxon, 179;
American, 179;
Indians, 181, 183, 185, 191, 192;
Patagonian, 180, 192;
Polynesian, 181, 182, 187;
Moor, 181;
Zulu, 181, 183;
Malay, 181, 183, 190;
Mongolian, 181, 186-190;
Papuan, 182;
Negro, African, Ethiopian, 182, 183, 192-195;
Caucasian, 182, 185-189, 195;
Veddahs, 182, 188;
European, 183;
Asiatic, 183;
Laplander, 183, 190;
Scandinavian types,
Norwegians, Swedes, Danes, Germans--north and south--186, 187;
types of, 186-196;
Persians, 186,
eastern, 187;
Afghans, Hindus, 186;
Welsh, French, Swiss, 187;
Russians, 187-190;
Poles, Armenians, 187;
Mediterranean type,
Spaniard, Italian, Greek, Arab, 187;
subordinate group,
Semitic, Arab, Hebrew, 187;
North African, Berber, Hamites, 187;
relatives of the Mediterranean,
Dravidas, Todas, Veddahs, Ainus, 188;
Manchurian, Chukchi, Buryats, Yukaghir, 189;
Finlander, Bulgar, Magyar, Korean, Japanese, Gurkhas, Burmans, Annams,
Cochin Chinese, Tagals, Bisayans, Hovars, 190;
Pueblos, Eskimos, Aztecs, Mayas, Caribs, 191;
Yahgan, Alacaluf, 191;
Papuan, Australian, 193;
Negrito section,
Adamans, Kalangs, Sakais Ætas, Bushmen, Hottentots, Akkas, 194.

Periods,
Triassic, Jurassic, 94;
Eocene, Miocene, 96.

Phenacodus, 96.

Phyla, 32.

Phylogeny, 63.

Pictography, 223-226;
of Eskimos, of American Indians, 223, 224;
of Asia, 224;
of Egypt, 224, 225.

Pig, 42, 157.

Pithecanthropus, 174.

Plesiosaurus, 94.

Polynesia, 103, 104.

Pouched animals, kangaroo, opossums, 42.

Primates, name given by Linnæus, 158;
eutheria, 158, 159;
order of, 160;
anthropoids, 161;
arrangement of organs, 201.

Processes, psychological, of higher animals, 208, 209.

Prosimii, 160.

Proteins, 22, 23, 24.

Protoplasm, 22-30;
the physical basis of life, 143; 144;
human, 156;
chemicals that make up, 156.

Protozoa, 52, 53, 68, 70;
relations of, 126.

Protozoön, 251.

Psychology,
comparative, 198;
principle of, 199;
descriptive, genetic, 202;
terms of, 203;
human, 210, 211.

Pseudopodia, 52.

Puma, 101.

Pupa, 259.

Pygmy, 195, 196, 227.

Rabbits, 41, 101;
domesticated, 137;
introduced into Australia, 140.

Races, human,
age of, 178;
divisions of, 183-195;
character of:
status, variations of, 180, 181;
color, a criterion of racial relationship, 181, 184;
hair, character of, as means of classification, 181, 182;
cranium, shape of, as means of identification, nose, jaws, 182.

Racoon, 38.

Rats, 41, 134.

Reason, 203;
in mental life of communal insects, 207.

Religions, 288;
Christian, Hebrew, Buddhistic, Tangaroan, 289, 290;
Mohammedan, 290, 298;
Dervish, Mahdist, 293;
linguistic basis of, 293, 294;
of savagery, 294, 300, 301;
barbarism, civilization, 294;
elements of, 295;
forms of Christianity, 296;
sects,
Judaism, 297, 298;
Brahmanism, Buddhism, 298, 299;
Polytheism, Roman, 300.

Reptiles, variations about a central theme, 45;
lizard, typical, 46; 157;
embryos of, 171; 200.

Retention of better invention, 109.

Rhinoceros, 41.

Rivers,
Mississippi, 86, 89;
Hoang-ho, Ganges, Thames, 87;
alterations made by, 87.

Rocks, crystalline or plutonic:
sedimentary, 85;
eruptive, 88;
new, 59;
of Grand Cañon, 90;
testimony of, establishes evolution, 100.

Salamanders, 45, 46.

Salts, of sodium, chlorine, magnesium, potassium, 24.

Samoan Islands, 103.

Sandstone, 90.

Science, what is it? 5, 6;
physiological, 14.

Sea anemones, 68.

Sea elephant, 38.

Seals, 38, 39, 40, 209.

Selection,
natural, doctrine of, 116, 117, 118;
struggle for existence, 124, 125;
simply trial and error, 131, 136,
artificial, 136, 137, 138;
laws of, in mental phenomena, 203.

Sequence, physiological, in training animals, 209; 210.

Series,
sedimentary, 84, 90, 92;
crystalline or plutonic, 85;
Azoic or Archæan, age of, 92.

Shale, 89.

Shark,
common, most fundamental form, 46;
embryo of, hammerhead;
embryos of, 66.

Sheep, 157.

Simiidæ, 160, 163.

Skate, embryos of, 66.

Snails, 45;
shells of, 95;
land snails, 103;
Hawaiian and Polynesian, 104.

Society Islands, 103.

Solar system, origin of, 84.

Solomon Islands, 103.

Species, origin of human, 153.

Spencer, Herbert, 8.

Squirrels,
evolved from terrestrial rodents, 14; 41;
flying, true rodents, 41.

Starch, 24.

Stephenson, 10.

Strata, 88, 89;
arranged according to ages, 89; 90;
time of formation, 92.

Struggle for existence, 124;
intra-specific, 125;
three divisions of, 126-129; 139, 174, 175.

Substances, inorganic, 29.

Sugar, 23, 24.

Survival of the fittest, 129.

Systems,
respiratory, excretory, circulatory, 17;
organic, reproductive, 18;
nervous, 256, 257;
blood-vascular, respiratory and excretory, 257;
ethical, 286;
religious, 288.

Tadpole, 58, 59, 60;
larvæ, 64.

Tapeworm, a relative of simple worms, 50; 123.

Tapir, 41;
Moeritherium, 97.

Thorndike, 209;
heredity of mental qualities, 232.

Tidal waves, 85.

Tigers, 101.

Tirawa, 301.

Tissue-cells, 28.

Torga, 183.

Tortoise, soft shelled, of the Mississippi, 45.

Tower, 148.

Transformation, natural, 170.

Tribes, 32.

Tuberculosis, bacillus of, 127.

Turtles, evolution of, 45.

Ungulates, 65.

Uniformitarianism, Lyell's doctrine, 80.

Urea, 29.

Ussher, Archbishop, 178.

Variation, 110;
causes of, 111;
among individuals, 112, 113;
fact of difference, phenomenon of, 114; 115, 118, 119, 121, 129;
congenital, 138;
human, 174;
racial, 177;
laws of, in mental phenomena, 203; 232.

Vertebrata, 43.

Vertebrates,
backboned animals, fishes the lowest order of, 46;
principles of relationship, families, tribes, 47; 53-59;
great classes originate together, 64;
more complicated, 68;
skeleton remains of, succeed invertebrates, 92;
testimony of the rocks, 93;
largest, 94;
appearance of great classes of, 94; 95;
classes that make up, 156;
lower, arrangement of organs, 201;
nervous system of, 256, 257.

Volcanoes, 88.

Volvox, 252, 254, 259, 265.

Von Baer, law of recapitulation, 71.

Vorticella, 251, 252, 265.

Wagner, 100.

Wallace, Alfred Russel, 117, 100.

Walruses, 38.

Wasps,
ground, 207;
organizations, of digger, 260; 261.

Weismann, 71, 72;
proved nuclei of egg contains, essential factors, 71, 145, 148.

Weisner, 143.

Whales, 40.

Wilson, 146.

Woehler, 29.

Wolf, Tasmanian, a true marsupial, 42.

Wolff, 70.

Wolves, 140.

Wombat, 42.

Wood-frog, 71.

Woods, heredity of mental qualities, 232.

Worms,
blindworm of England, 45; 48, 50, 53, 81;
nervous mechanism of, 205, 206;
nervous system of, 256, 257.

Zebras, 96, 97, 112.

Zoölogy, 34, 75, 78;
geographical distribution, 100.

"Zoönomia," 135.

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