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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
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LONDON:
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AMEN CORNER, E.C.
_COLUMBIA UNIVERSITY LECTURES_
THE DOCTRINE OF EVOLUTION
ITS BASIS AND ITS SCOPE
BY
HENRY EDWARD CRAMPTON, PH.D.
PROFESSOR OF ZOÖLOGY, COLUMBIA UNIVERSITY
New York
COLUMBIA UNIVERSITY PRESS
1916
_All rights reserved_
COPYRIGHT, 1911,
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
I
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.