Henry Edward Crampton - The Doctrine of Evolution

H >> Henry Edward Crampton >> The Doctrine of Evolution

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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 cooerdinated, 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 haemoglobin 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.

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