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WHAT EVOLUTION IS
LONDON : HUMPHREY MILFORD
OXFORD UNIVERSITY PRESS
(T
WHAT EVOLUTION IS
BY
GEORGE HOWARD PARKER
Professor of Zoology and Director of the Zoological
Laboratory, Harvard University
CAMBRIDGE
HARVARD UNIVERSITY PRESS
1925
COPYRIGHT, 1925,
BY HARVARD UNrVTRSITY PRESS
PRINTED IN THE
UNITED STATES OF AMERICA
PREFACE
The growing popular interest in evo-
lution calls for a simple statement
concerning this doctrine. Such a
statement should be as brief as is con-
sistent with right understanding, and
should be to the point. In view of the
animated and heated discussions that
have been excited by the present situ-
ation, this statement should be free
from prejudice and partiality. It is
from this standpoint that the follow-
ing pages have been written.
No fundamental doctrine such as
that of evolution can be rightly con-
sidered without taking into account
its full bearings on the whole of or-
ganic nature. Plants and animals,
with all their intricate interrelations,
afford the materials for this theme.
Man as the most complex of animals
vi PREFACE
must find his nature elucidated
through evolution if this doctrine is
to maintain itself. What its value is
in this respect must be judged by
each reader.
That the illustrative examples and
other like materials in the present vol-
ume are chiefly from zoological
sources is due to the fact that the
writer is a zoologist. It is scarcely
necessary to add that botanical ma-
terials afford the same kind of evi-
dence as that given in the body of
this text and might have been utilized
in the same way that the zoological
examples have been.
It is the object of this volume to
present a brief, readable account of
the main facts of evolution, that the
ordinary reader may acquaint him-
self with what may be called the ele-
ments of the subject. That so large a
topic as evolution can be adequately
PREFACE vii
treated in a volume of the size of the
present one is quite inconceivable,
and yet such an account as that which
follows may at least outline the sub-
ject and in this way prepare the
reader for further inquiry.
CONTENTS
I. Introductory i
11. Historical 9
III. Evidence on Evolution . . 19
1. From Comparative Anat-
omy 21
2. From Embryology ... 29
3. From Geology .... 38
4. From Zoogeography . . 47
5. From Rudimentary Or-
gans 53
6. Conclusion 60
IV. Factors in Evolution ... 65
1. Prefatory 67
2. Lamarckism 72
3. Lamarckism criticized . 80
4. Darwinism 100
5. Darwinism criticized . . 113
6. The Mutation Theory . .124
V. Human Applications . . . 145
VI. Reading References .... 175
... / MSS^ \o\
fu
INTRODUCTORY
INTRODUCTORY
Evolution is a term that has been
used in a great variety of ways. We
speak of the evolution of the stars,
meaning thereby the process by which
stars have grown from gaseous masses
to incandescent bodies, such as our
sun, and finally to the cold inert con-
ditions of stellar death. We speak of
the evolution of the earth, in that we
picture the growth of that body as a
part of the solar system whose central
element, the sun, yields the energy by
which the earth is moulded. Under
the varying heat of this luminary our
atmosphere is made to move as wind,
water is evaporated and condensed,
continents are eroded and dissected,
materials are disintegrated, trans-
ported, and deposited — in short, the
surface of the earth is put under con-
4 WHAT EVOLUTION IS
tinual flux and change. Thus the
present configuration of oceans and
of continents, of mountains and of
abysses, is looked upon, not as some-
thing stationary, but as due to opera-
tions whose titanic energies have been
exerting themselves through untold
ages in the past and will continue so
to act far into the future. These
happenings, and such as occur among
the stars, constitute what may be
called cosmic evolution, a body of
change which in the nature of things
preceded life and was, in a certain
sense, preparatory to it. It is the
plan of this book, not to deal with
this type of evolution, notwithstand-
ing the fact that cosmic evolution is
intimately bound up with the origin
of living things, but to consider ex-
clusively the kind of evolution that
has to do with organisms, with plants
and animals. Such a type of evolu-
WHAT EVOLUTION IS 5
tion may be called organic, as con-
trasted with what has just been
spoken of as cosmic.
Organic evolution, dealing as it
does with living organisms, has a set
of problems quite its own. Although
the body of a plant or of an animal
contains no chemical element not
found in the earth, and the energy in
such living bodies is subject to the
same laws that govern the inorganic,
plants and animals have superim-
posed upon their fundamental cosmic
properties, other properties more or
less peculiar to themselves. Thus all
plants and animals, like other bodies
about us, are subject to the law of
gravitation and to other laws of a
purely physical and chemical nature;
yet these plants and animals grow,
reproduce, react, and respond in ways
which are not entirely consonant
with the chemistry and physics of the
6 WHAT EVOLUTION IS
strictly inorganic. They have, in ad-
dition to the chemistry and physics
of lifeless nature, a chemistry and
physics more or less their own. It is
in this way that organic evolution
differs from simple cosmic evolution,
for organic evolution is a general op-
eration among plants and animals
some aspects of which are not to be
met with in the inorganic.
Organic evolution, though a well-
unified field in biology, can be profit-
ably treated under two heads. The
first of these has to do with the doc-
trine of descent with modification —
the belief that plants and animals of
particular kinds have descended by
gradual modification from preexist-
ing plants and animals of very dif-
ferent kinds. This belief, which is
often spoken of as if it were the
whole of evolution, is supplemented
by what may be treated under a sec-
WHAT EVOLUTION IS 7
ond heading, a group of doctrines
that have to do with the way in which
descent with modification has been
accompHshed. Granting that plants
and animals have arisen by the modi-
fication of earlier forms, what have
been the driving forces in nature that
have induced this modification? This
is a newer and much less certain field
of work than that which deals with
the simple fact of change or trans-
mutation in organisms. It includes
a consideration of Lamarckism, of
Darwinism or the theory of natural
selection and such subordinate theo-
ries as sexual selection, of orthogene-
sis, of the mutation theory, and of a
host of other views which from time
to time have been advanced as ex-
planations of descent with modifica-
tion. In the following pages, after
some brief historical comment, the
subject matter will be dealt with
8 WHAT EVOLUTION IS
under the two general headings just
mentioned: evolution as descent with
modification, and the explanations
that have been offered for this
process.
II
HISTORICAL
HISTORICAL
The idea of evolution is often looked
upon as a comparatively modern one.
As a matter of fact, it reaches back
into remote antiquity. Most races of
primitive man believed in some vague
way that they had kinship with the
lower animals. Many of the clans of
American Indians used animals as
their totems. Among the Indians of
the northwest coast the bear, the
raven, and the beaver were used in
this way, and in New England the
wildcat, the wolf, the muskrat, the
squirrel, the porcupine, and the frog
were similarly employed. Although
these totems were primarily signs of
the clan and were used as such, par-
ticularly in religious observances,
they were in many instances invested
with an ancestral aura, and the clan
12 WHAT EVOLUTION IS
was supposed in some vague way to
have descended from the animal con-
cerned. Most primitive human be-
ings seem to have had some such
traditions as these about animals, but,
of course, in no case could these views
be said to have more than remotely-
implied an evolutionary conception.
They merely show that in primitive
man kinship with animals was not an
unknown idea.
To certain Greeks organic evolu-
tion in the modern sense came nearer
to being a reality. Thus the great
physical philosopher of the Ionian
School, Anaximander (611-547 B.C.),
is credited with having held to a
form of general evolution in which
man was especially involved. Anaxi-
mander was apparently impressed
with the inability of man in his early
stages of life to care for himself, and
was thereby led to conclude that
WHAT EVOLUTION IS 13
human beings in the beginning must
have been very different from what
they are at present. He is even be-
lieved to have assumed for them an
aquatic ancestry, perhaps fish-Hke
in character. Anaximander's views
were often quoted, and thus classical
antiquity must have had some idea of
the evolutionary doctrine.
But the serious advances in this
body of opinion date from the last
two centuries. Throughout the early
part of this period uncertain rumors
of an evolutionary kind were contin-
ually heard; and as time went on,
these rumors became more and more
distinct. With this growth in defi-
niteness opposition took on a more
final shape. Thus Linnaeus (1707-
1778), who may be said to have es-
tablished systematics by publishing
in his " Systema Naturae '^ a classifi-
cation and description of all plants
14 WHAT EVOLUTION IS
and animals known in his time, be-
lieved firmly in the immutability of
species and declared in favor of the
biblical account of special creation.
According to him there are as many
different species of plants and of an-
imals on the earth as there were dif-
ferent forms created by the Supreme
Being in the beginning. This view,
based upon the account in Genesis,
was thus set in strong contrast with
that of the origin of species through
descent with modification.
The first radical exponent of mod-
ern organic evolution w^as Lamarck
(1744-1829) who published in 1809
his "Philosophic Zoologique." In
this volume Lamarck set forth a plea
that the plants and animals of to-day
had arisen by the modification of pre-
existing forms, and he further ad-
vanced an hypothesis as to the way
in w^hich this change had come about.
WHAT EVOLUTION IS 15
His views were ably seconded by a
number of the most distinguished
savants of his time, among whom
may be numbered the great Goethe.
Of Lamarck's confreres Geoffroy
Saint-Hilaire took up the subject in
pubHc discussion with Cuvier, per-
haps the greatest naturaHst of his
day. Cuvier, whose opinions were
anti-evolutionary, resisted with all his
strength and authority the rising tide
of new opinion and succeeded in
checking its flow, for it w^as generally
concluded at the end of the contest
that descent with modification must
be permanently abandoned.
For some decades the storm sub-
sided, for the appearance of the little
volume entitled '' Vestiges of the Nat-
ural History of Creation," published
by Robert Chambers in 1844, w^as
only a ripple on the surface. Then
in 1859, with the publication of Dar-
i6 WHAT EVOLUTION IS
win's '^ Origin of Species," the storm
broke afresh, this time not to be
turned aside till it had swept the
shores clear of the wreckage of old
ideas.
Everyone knows the great public
upheaval that followed the appearance
of the "Origin of Species." The
scientific world had been prepared for
it by a paper on the theory of natural
selection, published by Darwin and
Wallace in the preceding year; but
considering the long period of rela-
tive quiescence that had preceded
1859, even scientists must have been
startled at the uproar that broke
forth. Darwin and his able coadju-
tor, Huxley, had the double task of
showing to the world that, in contrast
with special creation, descent with
modification had taken place, and that
natural selection was the driving
force behind this process. In the
WHAT EVOLUTION IS 17
days of Lamarck the chief question
was on the modifiabihty of species,
and on this first Hne of attack the
forces of evolution received for the
time being a serious setback. But
under Darwin and Huxley a new of-
fensive was launched, and after a
vigorous campaign both objectives
were attained. It is to the credit of
Charles Darwin, and his body of able
supporters, that the scientific world
was finally brought to accept the prin-
ciple of descent with modification,
and natural selection as the means
whereby it was accomplished.
The evidence that convinced the
world in Darwin's day that descent
with modification, and not special
creation, was the means of peopling
the present globe with its variety of
living forms was meager in the ex-
treme as compared with what might
be drawn upon to-day, but it never-
i8 WHAT EVOLUTION IS
theless covered the ground and may
be profitably looked into now, since
it still affords the real support on
which the doctrine of evolution rests.
This body of evidence comes from five
important fields in biology : compara-
tive anatomy, embryology, the study
of fossils, zoogeography, and the
nature of rudimentary organs.
Ill
EVIDENCE ON EVOLUTION
EVIDENCE ON EVOLUTION
I. FROM COMPARATIVE
ANATOMY
An important body of evidence that
bears on the evolutionary problem
comes from the field of comparative
anatomy. A little over a century ago
the school of comparative anatomy
was founded by Cuvier (i 769-1 832),
who, though an anti-evolutionist,
showed that animals in their structure
were not immensely diverse, but con-
formed to general plans or types of
organization. From this standpoint
each animal could be said to represent
its type, subject to such modifications
as its special mode of life called for.
Thus under the enormous diversity
of animal forms there was in reality
a more or less hidden uniformity.
This principle of type organization
22 WHAT EVOLUTION IS
is abundantly illustrated by many
sets of organs. For instance, the
human arm is composed of parts that
recur in the corresponding organs in
other animals. The arm of man, as
shown on page 23, contains four sets
of bones : the single bone of the upper
arm, the pair of bones in the forearm,
the group of small wrist bones, and
the series of elongated bones in the
five digits. All these groups of bones
recur with great regularity in the
foreleg of the cat, of the turtle, and
of even so lowly organized an animal
as the frog. The wing of a bat, when
it is examined, is found not to be con-
structed upon a plan peculiar to itself,
but to be a modification of the type of
structure already described for man,
in that the single bone of the upper
arm is present, as are the pair of
forearm bones, the wrist bones, and,
enormously elongated to carry the
WHAT EVOLUTION IS 23
Man Bat Bird
WHAT EVOLUTION IS 25
web of the wing, the finger bones. In
the bird, unlike the bat, the expansion
of the wing is due to feathers but the
skeletal axis that supports the feath-
ers is formed from a set of bones
such as occur in the human arm, ex-
cept that the fingers are reduced in
number and bound together to serve
as a supporting axis for the larger
plumes. The flipper of a whale or
of a porpoise, superficially so unlike
the human arm, nevertheless shows
closely compacted within it the bone
of the upper arm, the two forearm
bones, wrist bones, and finger bones.
In the foreleg of the horse the bone
corresponding to that in the upper
arm of man is hidden in the flesh of
the animal. This bone is followed,
however, by the two bones of the
forearm, fused together, by the wrist
bones, which are situated at what is
popularly called the knee of the horse.
26 WHAT EVOLUTION IS
and by a row of bones which repre-
sent the middle finger of man. These
bones in man are four in number,
counting the deep-seated long bone
in the palm, and this number is ex-
actly reproduced in the horse, in which
the last member of the series carries
the hoof corresponding to the human
nail. The front leg of the horse not
only rests on what is equivalent to
the enormously enlarged middle fin-
ger of man, but it contains, on either
side of this digit, relatively inconspic-
uous splint bones which represent our
index and our ring fingers.
By the comparative method it is
thus possible to demonstrate that
such apparently diverse organs as the
arm of a man, the wing of a bat, and
the foreleg of a horse are similarly
organized and are merely modifica-
tions of one type of structure.
Animals and plants abound on
WHAT EVOLUTION IS 2-]
every hand with series of parts in
which the elements are related, as in
the examples just described, and it is
one of the achievements of the com-
parative method that it has thus
yielded incomparably rich and signifi-
cant material for philosophical bi-
ology. By its means anatomy has
been lifted from a discipline of dead
description to a science rich in prob-
lems and resources.
This advance in method had an
immediate and decisive bearing on
the evolutionary question. If organ-
isms were separately created there
would be every reason to expect that
they would be constructed upon indi-
vidual plans, and not the least ground
to anticipate in them an underlying
common type of structure. If, how-
ever, they have evolved from a
common ancestry, precisely such un-
derlying similarities might be ex-
28 WHAT EVOLUTION IS
pected. The human arm, the foreleg
of a quadruped, the wing of a bird, and
the flipper of a whale have a common
plan of organization because these
animals have had a common ancestry.
Thus the science of comparative an-
atomy yields results that support
most completely the evolutionary
idea, and that give no ground for the
assumption of special creation. It is
a remarkable fact that Cuvier, who,
as already observed, was a strong
anti-evolutionist, should have been
instrumental in founding and in
partly developing a school that in the
end yielded such important evidence
in favor of descent with modification.
WHAT EVOLUTION IS 29
2. FROM EMBRYOLOGY
The science of embryology deals
with the growth of animals from the
tgg to the adult, and this science,
though of comparatively recent ori-
gin, has had an important bearing on
evolutionary problems. It is a com-
monplace that, in the development of
any animal, the creature does not
start life as a miniature of what it is
finally to be and then slowly enlarge
until it reaches adult proportions, but
it begins life in a state very unlike its
adult condition and only gradually
assumes an outline that is associated
with its final form going through a
series of changes, often very pro-
found, till it finally arrives at its ma-
ture state.
Most common animals afford ex-
amples of this kind of growth.
30 WHAT EVOLUTION IS
Frogs, for instance, lay eggs and
from these are hatched, not frogs,
but tadpoles which eventually, through
a series of rather complicated bodily
changes, reach the condition of an
adult frog.
The remarkable peculiarity of this
kind of growth is that, during the
steps in its progress, the young ani-
mal often shows striking resem-
blances to other animals. Thus, in
the instance just given, the tadpole of
the frog has unquestionably fish-like
characteristics. Instead of having
front and hind legs for locomotion as
in the adult frog, the tadpole moves
about by means of a flattened tail in
a way similar to that of a fish. More-
over, the tadpole has in its neck a
system of gills by which it breathes
precisely as a fish does. As develop-
ment goes on, these gills are gradu-
ally absorbed and are replaced by
WHAT EVOLUTION IS 31
lungs when the tadpole approximates
the state of the frog. But before this
metamorphosis has taken place the
tadpole, in structure and in activities,
recalls in many important particulars
the state of a fish.
Examples of this kind may also be
found in the course of human develop-
ment. When the human embryo is a
small fraction of an inch in length a
definite number of narrow transverse
clefts appear on its neck as shown
in the uppermost figure on page ^2>-
These clefts lead into the throat and
correspond in position to the gill open-
ings of fishes. Moreover the sup-
ports between the clefts, the arches,
which are numbered in the figure,
carry large arteries resulting from
the division of the main blood-vessel
that emerges from the embryonic
heart, just as the gill arches of fishes
are supplied by large vessels from the
32 WHAT EVOLUTION IS
heart of the fish. These embryonic
organs in man never serve for breath-
ing as the corresponding parts do in
fishes, but in gross structure the
human gill arches recall in a most
striking way the gill system of fishes.
As the development of the human
embryo proceeds, the gill clefts are
obliterated, excepting the first one
v^hich is retained in forming the aper-
ture of the external ear.
Thus the frog and man and in fact
all the higher vertebrates show in a
temporary way gill clefts and gill
arches, both of which are the perma-
nent possessions of the fishes.
That higher animals should, in the
course of their individual develop-
ment, exhibit temporarily features
that are permanent in lower animals,
seems to be a rule of organic growth.
It certainly is abundantly exempli-
fied in many forms. Thus in all
WHAT EVOLUTION IS 33
Man
WHAT EVOLUTION IS 35
true backboned animals a notochord,
or supporting rod, precedes in devel-
opment the real backbone of these
forms and is replaced by this bone,
except in the very lowest fishes where
the notocord is the permanent and
only organ of support. Another ex-
ample may be found in the embryonic
human being where small ribs occur
attached to the neck vertebrae. As
development advances these ribs fuse
with the vertebrae and are thus lost
to view, but in lower animals, like the
alligator, neck or cervical ribs are
persistent throughout life. Again
all animals that reproduce sexually
pass through an tgg stage in which
they are, for the time being, a single
cell. This state is a permanent condi-
tion in the simplest animals, the pro-
tozoans, which are very usually only
single cells. Innumerable examples
such as these might easily be given.
36 WHAT EVOLUTION IS
The peculiarity of development,
that higher animals pass in a tempo-
rary way through stages that are per-
manent in lower forms, has long been
recognized as a characteristic feature
of general growth. It has sometimes
been dignified as a law of develop-
ment and has been designated, in
honor of the father of modern em-
bryology, von Baer's law. As such it
was strongly advocated by Louis
Agassiz. In a more descriptive way
it has been spoken of as the law of
recapitulation, for the reason that
such features in the development of
an animal as those already alluded to
recapitulate, in a rough way, the ra-
cial history of the animal concerned.
Thus the presence of gill slits in the
embryo of the human being indicates
that a gill-breathing animal is to be
included in our remote ancestry. As
Huxley facetiously remarked in dis-
WHAT EVOLUTION IS 37
cussing this question years ago, each
animal in its development climbs its
own ancestral tree.
The facts associated with the law
of recapitulation are quite meaning-
less from the standpoint of special
creation, but from that of descent
with modification they receive a simple
and adequate interpretation. A de-
veloping animal shows temporary re-
semblances to lower forms, because
these forms represent steps in its
ow^n racial history.
38 WHAT EVOLUTION IS
3. FROM GEOLOGY
The evidence on the evolutionary
problem to be drawn from geology
turns largely on the question of fos-
sils. A fossil is anything dug from
the earth. Specifically fossils are
bones, shells, or even delicate struc-
tures such as ferns and the like, that
have been more or less converted into
stone and have been exhumed from
their hiding places in the rocks.
The ancients were acquainted with
fossils, but they regarded them in a
light very different from that in
which the modern naturalist looks
upon them. Fossils were believed by
the ancients to have had something
to do w^th nature's formative proc-
esses. These early observers were,
for the most part, believers in spon-
taneous generation. They accepted
WHAT EVOLUTION IS 39
the view that new organisms, plants
and animals, were being continually
produced by nature, that fish, frogs,
worms, and the like were being
formed continually from the mud
and slime in the bottoms of ponds,
that maggots were being generated
spontaneously in decomposing meat,
and that parasitic worms were being
produced in the interior of the ani-
mals whose bodies they inhabit; in
short that the process of spontaneous
generation pervaded nature gener-
ally. They were not conversant with
the modern idea, arrived at after
long experimentation, that all living
things come from preexisting living
things and that none are formed de
novo. They held that mother earth
was continually producing new life
from her own substance.
With this doctrine in mind, their
interpretation of fossils _^as very
40 WHAT EVOLUTION IS
different from that given by the mod-
ern naturahst. When they discov-
ered the impressions of shells in the
rocks of the mountainside they recog-
nized at once the inappropriateness
of the situation, and they believed
that they had before them evidence
of nature's unsuccessful effort to
produce new life. She, in her prod-
igality of productiveness, had started
the formation of an aquatic animal
on a mountainside and, in conse-
cjuence of the unfavorableness of
the site, the process had failed of
completion and a mere trace of its
beginning was thus left stranded in
inhospitable surroundings.
This general view of the nature of
fossils was current for many gener-
ations, but as early as the fifteenth
century, Leonardo da Vinci (1452-
15 19) recognized that shore lines
shifted, that the earth's crust was ele-
WHAT EVOLUTION IS 41
vated and depressed, and that what
was once sea bottom, with its myriads
of marine plants and animals, might
well become mountainside with its
contained fossils. Gradually the
opinion grew that all fossils were the
remains of once living organisms,
and this doctrine, advanced through
the efforts of such workers as Fra-
castoro, Steno, Hooke, and others,
had gained complete acceptance in
the days when Lamarck (1744- 1829)
and Cuvier (i 769-1 832) were found-
ing modern paleontology.
Concurrent with the growth of the
new ideas about fossils came the con-
ceptions of stratigraphic geology.
Rocks not only contain the fossil re-
mains of once living organisms, but
the underlying rocks hold remains of
an older date than do those above
them. Such a sequence of fossils, as
is implied by this view, was advocated
42 WHAT EVOLUTION IS
by Woodward (1665-1728), Valis-
nieri (1661-1730), Smith (1769-
1829), and especially by Cuvier
(1769H1832). Cuvier further rec-
ognized that the older rocks con-
tained fossils of a simpler type than
the more recent ones did, and he ex-
plained this difference by assuming
that periods of cataclysmic destruc-
tion alternated with periods of special
creation. This doctrine was carried
to an extreme by d'Orbigny (1802-
1857) who claimed for the past some
twenty-seven such alternations. But
the idea of cataclysmic alternations
was defeated by the school of uni-
formitarians, whose advocates, like
Lyell ( 1 797-1 875), saw in the present
forces of nature an explanation of
the past and supported the idea of
continuity, not interruption, in the
organic series. By these steps the
modern conception of fossils and
WHAT EVOLUTION IS 43
their significance was reached; they
are the remains of once living organ-
isms, and they disclose a continuous and
real history of plant and animal life.
When this history is looked into,
it is found to have, as might be ex-
pected, a profound bearing on evolu-
tionary matters. It is by no means
easy to determine hov^ long living
things have existed on the earth.
Estimates vary from a hundred-mil-
lion to two thousand-million years.
But from an evolutionary standpoint
such enormous periods, and even
such differences in the estimates, are
not so significant as the kinds of or-
ganisms that are shown to be present
at different periods in the earth's
history and the sequences that this
history discloses. Sketched very
broadly, it may be said that during
about the first two-thirds of the period
in which life has been on the globe
44 WHAT EVOLUTION IS
only invertebrates were present.
These include sponges, corals, star-
fish, worms, crustaceans, insects,
brachiopods, snails, clams, and other
shellfish. Vertebrates, or backboned
animals, first arose about the begin-
ning of the last third of the period
of life on the globe, and the earliest
fossil representatives of this group
were the fishes. These were followed,
near the opening of the last quarter, by
the amphibians which were succeeded
by the reptiles, the mammals, and the
birds in the order named. Man has
been present on the globe during some-
what less than the last hundredth of
the total period of living things.
When this sequence is reviewed it
is seen at once to present a reasonable
plan. Invertebrates precede verte-
brates, fishes antedate amphibians
and these in turn come before reptiles,
mammals, and birds. Man appears
WHAT EVOLUTION IS 45
only near the very end, long after the
group of which he is a member, the
mammals, had established itself.
The sequence of forms that is here
portrayed is an orderly one and the
order is such as would be expected on
evolutionary grounds. Had special
creation been the rule of nature there
would have been no reason for inver-
tebrates to have preceded vertebrates
in their time of appearance, or for
fishes to have come before amphibians
and the like. But this order of ap-
pearance being such as it is, one must
conclude that this aspect of the fossil
series gives unequivocal support to
the evolutionary view.
Facts of the kind that have just
been narrated were well known in
Darwin's day. Since that time the
study of fossils, and particularly of
vertebrate fossils, has enormously
expanded. Huxley in his time was
46 WHAT EVOLUTION IS
much interested in the fossil series
illustrating the evolution of the horse.
As is well known, this animal can be
shown to have descended from a small
multi-toed creature of the approxi-
mate size of a fox. In the early days
of the evolutionary controversy this
was the one series of developing forms
that the paleontologist could point to
with assurance. To-day scores of
such series are known not only in the
vertebrates but in the invertebrates.
Even with man the call for the miss-
ing link seems to have subsided, for the
sequence in so many of the fossil series
is so nearly complete that it seems to
be only a matter of diligence and time
till the fossil record of any important
line can be brought to light. The imper-
fections in the fossil series are no longer
interpreted as real and significant
breaks but as interruptions sooner or
later to be filled as science advances.
WHAT EVOLUTION IS 47
4. FROM ZOOGEOGRAPHY
The past and present distribution of
animals on the surface of the globe
has important bearings on the evolu-
tionary problem. Animals are not
scattered in a haphazard fashion over
the earth, but show a marked regular-
ity in their occurrence. This can be
well illustrated by what is known of
the mammals. The group of mam-
mals is made up chiefly of the common
beasts of the field and forest, but it
includes also such exceptional forms
as the bats, among aerial creatures,
and the whales and porpoises of the
sea. Mammals have warm blood,
they produce milk with which they
nourish their young, and they are pro-
vided with more or less hair.
Almost all the mammals bring forth
their young in a highly developed,
48 WHAT EVOLUTION IS
active state. Two of them, however,
the Australian porcupine and the
duckbill, lay eggs. These two mam-
mals, in addition to the habit of
laying eggs, have many primitive char-
acteristics. They constitute the low-
est group of this class of animals.
They are commonly designated as
monotremes. The remarkable feature
about them, from the standpoint of
the present discussion, is that they are
not found broadcast over the earth
but are limited to a very distinct zoo-
geographical area, the Australian
region. Thus the total representation
of this striking group of forms is re-
stricted to a small part of the globe.
The Australian region is not only
the habitation of the monotremes; it
is also the home of the marsupials.
These are mammals, such as the pha-
langers, the wombats, and the kan-
garoos, the females of which are
WHAT EVOLUTION IS 49
commonly characterized by the pres-
ence of a pouch on the abdomen. This
pouch, which contains the milk glands,
serves as a receptacle for the young
after their birth. Most persons have
seen in our zoological gardens the
female kangaroo with her offspring
and have noticed how the young, when
alarmed, run to the pouch, enter it,
and are carried oft' by the mother.
The marsupials, like the monotremes,
are very primitive mammals. Ex-
cepting the American opossums and
one other pouched mammal in South
America, all marsupials are limited
to the Australian region. No mar-
supial occurs in Eur-Asia or in Africa.
Thus the marsupials, like the mono-
tremes, illustrate a common peculiar-
ity of animal distribution, namely, that
many large and important groups are
limited to well circumscribed and often
relativelv small areas of the earth.
50 WHAT EVOLUTION IS
This topic is still better illustrated
if we take into consideration the
distribution of fossil, as well as of
living forms. Again the mammals
may serve as illustrations. Sloths and
armadillos constitute a group of mam-
mals very striking in their distribu-
tion.
The modern sloths are arboreal
creatures of moderate size; they feed
upon the succulent stems and leaves
of tropical trees. By means of their
curved claws, they hook themselves
through the tangle of branches in the
forest jungle. They are almost in-
capable of locomotion on the ground
and when by accident they fall, they
move about in a most awkward fash-
ion in regaining their haunts.
The modern armadillo is a burrow-
ing animal chiefly active at night. Its
covering of segmented shelly pieces
gives it more the appearance of a
WHAT EVOLUTION IS 51
reptile than of a mammal, but its
warm blood, its mammary glands, and
the hair that projects outward be-
tween the segments of its shell pro-
claim it a true mammal.
Modern sloths and armadillos are
limited to the new world particularly
to South and Central America though
the armadillos extend northward
through Mexico into the southern
borders of the United States. None
of these forms occur in the old world
or in fact elsewhere than in the region
just described.
Fossil sloths and armadillos are
known in considerable numbers. Some
of these are of huge size. Fossil
ground sloths have been discovered
whose skeletons justify the belief that
the living animal must have been as
large as a rhinoceros. Armadillo-
like animals, the glyptodons, have been
found whose skeletons are almost as
52 WHAT EVOLUTION IS
large as those of oxen. The fossil re-
mains of all these sloths and armadil-
los are found exclusively in the new
world and in that part south of the
central United States. It is a remark-
able fact that, notwithstanding the
great difference between these fossil
sloths and armadillos and their mod-
ern representatives, the living and the
fossil forms should agree almost
exactly in the regions where they
occur. One is forced to conclude from
facts of this kind, as well as from the
circumstance, that most well-defined
groups of modern animals, like the
monotremes and the marsupials, oc-
cupy definitely restricted areas, that
members of the same great group have
had a common origin, for had they
been specially created their distribu-
tion on the earth's surface would have
called for no particular regularity.
WHAT EVOLUTION IS 53
5. FROM RUDIMENTARY
ORGANS
The last biological topic to be con-
sidered in the present account as bear-
ing on the problem of evolution has
to do with rudimentary organs. Rudi-
mentary organs are those organs that
are without use or function. They
are like the buttons on the sleeve of a
man's coat; they are essentially use-
less and sometimes worse than useless.
A well-known rudimentary organ,
from the human body, is the vermi-
form appendix of the large intestine.
This organ is a blind tube several
inches in length and attached to the
large intestine near its beginning. It
is shown to the right in the figure on
P^^^ 55- It is easily subject to in-
flammation and forms a danger center
in the intestinal tract. In diseased
states it is regularly removed by the
54 WHAT EVOLUTION IS
surgeon and even in normal condi-
tions it is frequently excised as a pre-
cautionary measure. No one is known
to suffer anv inconvenience from its
loss ; in fact a person is commonly re-
garded as better off without it than
with it. In consequence of its com-
plete lack of function, it is a thor-
oughly good example of a rudimentary
organ.
The condition of the vermiform
appendix in man is by no means
typical of this organ in other mam-
mals. Cats show no sign of it, but in
rabbits it is a highly developed struc-
ture and is intimately concerned in this
animal with the regular activities of
the large intestine.
Other rudimentary organs in man
are easily pointed out. The external
ear of the human being has attached
to it three thin muscles, one above the
ear, a second behind that organ, and a
WHAT EVOLUTION IS 55
Cat
Man
Rabbit
WHAT EVOLUTION IS 57
third in front of it. Most persons
have no power of motion in these
muscles and, in such instances, the
muscles may be looked upon as purely
rudimentary, but occasionally an in-
dividual will be found who can con-
trol them to a slight degree and who
can thereby move his external ear.
Even in such instances, however, the
amount of motion is extremely slight
compared with that seen in such
animals as the horse and the dog,
where the tube of the outer ear is
directed with great freedom in a
variety of ways and is used as a means
of discovering the direction of sound.
From the standpoint of actual useful-
ness, the three muscles attached to the
human ear are quite as rudimentary
as is the human vermiform appendix.
Well within the angle of the human
eye next the nose is a slight fold of
whitish membrane, the so-called plica
58 WHAT EVOLUTION IS
semilunaris. No use is known for this
organ in man but in the cat, as one can
readily see by direct inspection, in
place of this fold there is a nictitating
membrane, or third eyelid, which by
its free movement back and forth
across the eyeball serves as a means
of protecting and cleansing that or-
gan. The plica semilunaris in man
is a completely useless remnant of this
third eyelid.
In an enumeration of the rudimen-
tary organs in man made some years
ago by Wiedersheim approximately
ninety such parts were noted. This
seems like a considerable list for one
species, but it is probably by no means
exhaustive. Most higher animals, like
man, abound in a great variety of such
useless parts.
From the standpoint of special
creation, it is by no means easy to
explain the presence of such function-
WHx\T EVOLUTION IS 59
less organs. If animals were spe-
cially created why should they contain
scores of parts that are without use
and that in some instances, like the
vermiform appendix, are positively
deleterious? A satisfactory answer
to this question has never been given.
From the standpoint of evolution,
however, rudimentary organs are
structures in process of disappear-
ance, organs that are just dropping
below the horizon of serviceableness.
Their presence in a given form in-
dicates that they were functional in
some ancestor of that form, and that
as evolution proceeded and the species
changed, it dropped this particular
part from the level of functional sig-
nificance to that of uselessness. Such
an explanation of the presence of these
organs accords completely wath what
is known of them from all points of
view.
6o WHAT EVOLUTION IS
6. CONCLUSION
We have now completed a brief sur-
vey of some of the more important
fields of evidence concerning descent
with modification. We have examined
this question in the light of compara-
tive anatomy, of embryology, of geol-
ogy, of zoogeography, and of the study
of rudimentary organs. In none of
these aspects of the problem has there
appeared reason for assuming that
special creation has been the method
by which the diversity of plants and
of animals at present on the globe has
been produced and in all of them there
has been shown either strong evidence
in favor of descent with modification
or a state of affairs open to ready in-
terpretation from this standpoint.
The several lines of evidence that
have been considered in this connec-
WHAT EVOLUTION IS 6i
tion could scarcely be said to have
been available in the time of Lamarck,
for most of them have been the result
of the scientific endeavor of the last
hundred years. It is therefore not
surprising that in his day evolution
received a serious setback, for at that
time not enough was known to give
the question a fair hearing.
Even when Darwin wrote, knowl-
edge on many important points was
very incomplete compared with what
it is to-day. It is, however, a sig-
nificant fact that practically all the
lines of evidence cited by Darwin as
confirmatory of evolution are signifi-
cant to-day and much more exten-
sively supported than they were in his
time. The confirmation thus received
is the result of the discovery and im-
partial accumulation of new facts on
lines that bear on the question at hand.
If to the naturalist of Darwin's time
62 WHAT EVOLUTION IS
the evidence in favor of evolution
seemed persuasive, that which can be
brought forward now would have been
overpowering. It is this strength of
the modern position that has placed
every biologist of any standing what-
soever on the side of evolution. In
other w^ords, practically all biologists
to-day accept without any reserva-
tions descent with modification as a
process of nature. They no longer
question this view. This statement
cannot be emphasized too strongly.
At the same time that these biolo-
gists accept descent with modification
as an actual occurrence in nature, they
are most skeptical and reserved about
what may be called the driving force
behind descent. What is there in
nature that has kept in motion this
incredible capacity to produce new
species? How is it that from age to
age large and ever larger floods of
WHAT EVOLUTION IS 63
new forms have burst forth? To this
question no biologist has a clear and
unequivocal answer. It is this uncer-
tainty that has been seized upon by a
few thoughtless critics who have at-
tempted to discredit in the eyes of the
general public the well established fact
of descent with modification by con-
fusing it with the explanations of de-
scent. This confusion, commonly due
to ignorance, is the source of most of
the contentions now met with in evo-
lutionary controversies. It does not
characterize the clear thinker. Be-
cause biologists have not as yet dis-
covered how evolution takes place is
no reason for denying evolution itself.
The explanations of the evolution-
ary process thus far offered are large
in number. They include, to mention
only some of the most important,
Lamarck's hypothesis, Darwin's nat-
ural selection, Naegeli's idioplasmic
64 WHAT EVOLUTION IS
hypothesis, Eimer's orthogenesis, De
Vries's mutation theory and the Hke.
In so brief a survey as this volume
offers it will be profitable to consider
only the more noteworthy of these
views and in conformity with this plan
the next chapter will contain brief
critical accounts of Lamarck's hypoth-
esis, of Darwinism or the theory of
natural selection, and of the mutation
theory of De Vries.
IV
FACTORS IN EVOLUTION
FACTORS IN EVOLUTION
I. PREFATORY
In the early discussions on evolution
it soon became apparent that, com-
pared with the biblical account of
creation, descent with modification re-
quired a relatively enormous length
of time. This contrast between the
two views was used by Cuvier in his
opposition to Lamarck. Cuvier had
careful measurements made of the
skeletons of mummified Egyptian
animals and of their recent represen-
tatives. No significant differences
could be detected on comparing these
two sets of measurements and Cuvier,
therefore, concluded that if no meas-
ureable changes had overtaken ani-
mals in the three thousand years that
separated the mummified from the
modern forms, it was useless to con-
68 WHAT EVOLUTION IS
sider the possibilities of a process
which, if it occurred at all, was almost
inconceivably slow. Although Cuvier
has since been shown to be wrong in
his general deductions, the results of
such speculations as this led trans-
formists in the early days to assume a
very long period for the evolution of
life on the earth, a conception quite in
line with the growing uniformitarian
geology of the day. The assumption
of a relatively great age for the earth
and its inhabitants has been entirely
justified by subsequent scientific in-
quiry, but in the days of Cuvier and
Lamarck and even in the time of Dar-
win it was based on much less con-
vincing evidence than at present.
To-day it is beyond dispute that the
age of the earth as the abode of life is
to be reckoned in hundreds if not
thousands of millions of years.
In consequence of these growing
WHAT EVOLUTION IS 69
opinions, there arose a belief among
naturalists of the transformist school
that evolution was so slow and grad-
ual a process that no direct observa-
tion of it could ever be made. The
life of man was not long enough to
admit of even a glimpse at evolution-
ary change. This view was current
in Darwin's day and prevailed more
or less to the end of the nineteenth
century. It served as a most unfor-
tunate deterrent to scientific research,
for it discouraged investigators from
attempting any direct study of a proc-
ess whose operations seemed to be so
infinitely slow.
With the advent of the twentieth
century a new phase in evolutionary
investigation appeared. Through the
work of Tschermak, of Correns, and
particularly of De Vries the subject
passed from the observational and
speculative stage to the experimental
70 WHAT EVOLUTION IS
one, and instead of looking upon evo-
lution as a process so slow as to be
imperceptible, it was soon believed, as
a result of experimental test, to be
relatively rapid at least in particular
instances. In fact it was declared
that species might be created almost
over night. Such a radical change of
view had a profound effect on the
growth of the subject and though the
new programme may not have real-
ized all that was expected of it, it
brought the science into a vastly more
wholesome state and led to positive
growth of a most encouraging kind.
In this revival of activity all the
older explanations of evolution were
brought to the test with the result that
such ideas as Elmer's orthogenesis,
in which variation was supposed to
occur in definite and predetermined
directions, and Naegeli's idioplasm
theory, in which an internal perfect-
WHAT EVOLUTION IS 71
ing principle was assumed, lost ground
and the field was left almost ex-
clusively to Lamarckism, Darwinism
and the mutation theory. A consid-
eration of these views will now follow.
y2 WHAT EVOLUTION IS
2. LAMARCKISM
Lamarck's hypothesis as to the means
by which evolution has been accom-
plished is best stated in his '' Philos-
ophic Zoologique" published in 1809,
a year which is noteworthy as the
birth year of Charles Darwin. La-
marck's explanatory views excited
very little attention at the time of their
publication, for, so far as the scientific
world took any interest in evolution
at all, it was concerned with the ques-
tion of the validity of this doctrine
rather than with its explanation. Fifty
years later when Darwin advanced
natural selection the explanatory as-
pects of this question came much more
to the front. Then a contrast be-
tween Darwin's views and Lamarck's
views could be drawn.
WHAT EVOLUTION IS n
The explanation offered by La-
marck turned chiefly on the effect
upon organisms of the surroundings
or environment. Lamarck noted that
marsh plants, such as the aquatic
Ranunculus, which grew partly sub-
merged and partly out of water, had
leaves of different shapes in the two
situations. Under water the leaves
were finely divided, but in the air they
were simply lobed. This difference
he rightly conceived to be due to the
environment, one situation producing
the first type of leaf and the other the
second. He looked upon this as a
direct effect of the surroundings and
regarded it of great importance par-
ticularly with plants. A special plant
being thus directly dependent upon its
surroundings for its peculiar form, any
change in these surroundings would
be likely to be followed by a change
in the form of the plant, that is, an-
74 WHAT EVOLUTION IS
other form would arise and evolution
could be said to have taken place.
Lamarck conceived the effect of en-
vironmental change on animals to be
carried out in a rather more complex
way than on plants. He illustrated
this by several examples such as the
webbed foot of water birds and the
long neck of the giraffe.
Lamarck rightly believed that land
birds were the ancestors of water
birds, and in thinking of the transi-
tion, he pictured land birds coming
more and more to frequent the shore,
to pass much of their time in shallow
water and to seek their food there.
Such newcomers would from time to
time get into deep water and naturally
attempt to propel themselves by kick-
ing with their legs. The muscular
exercise of kicking would induce an
extra flow of blood to the legs whose
bones, muscles, skin, and the like
WHAT EVOLUTION IS 75
would respond by extra growth. In
this way the skin between the toes
would become firmer, tougher, and
more extensively developed. These
effects would be increased in the de-
scendent stock, and as they accu-
mulated generation after generation,
the passage would be accomplished
from the webless foot of the land
bird to the webbed foot of the water
bird.
Lamarck conceived that the gi-
raffe's neck, to take another of his
examples, was lengthened by a similar
process. These animals were sup-
posed to browse among the branches
of trees. In their endeavors to reach
the leafy food, they would naturally
exert the muscles of the neck and this
activity would induce an extra flow of
blood to that region. In consequence
the muscles, bones, and other parts of
the neck would increase in size, just
76 WHAT EVOLUTION IS
as the arm of a man increases under
exercise. As a result of this activity
continued through generation after
generation, the neck of the giraffe
would lengthen and eventually reach
the extreme condition seen to-day.
Both these instances involve a proc-
ess more complex than that in the
partly submerged plant, but in both
of them the environment is the fun-
damental factor. With the bird the
change from inland surroundings to
a shore environment is the important
element, and with the giraffe the
change from a region where browsing
was low to one where it was among
trees. Thus as with the plant, en-
vironmental differences play the chief
part in the evolution of these animals.
Put briefly, the Lamarckian scheme,
as applied to animals, is as follows:
a change in the environment is fol-
lowed by a change in habit, and a
WHAT EVOLUTION IS ^y
change in habit is followed by a
change in structure. Thus the condi-
tion of the animal is modified and
evolution is the result.
Such an application of the La-
marckian principle, as is involved in
the last two examples, requires what
may be called the indirect influence of
the environment in contrast wath the
direct influence as seen in most plants,
but in both direct and indirect influ-
ences, the environment and its changes
are the paramount elements.
In addition to the general principle
that has just been illustrated, La-
marck also called attention to certain
subordinate principles that he believed
to be significant in evolution. First
of these was the principle of use and
disuse. Organs that are exercised
tend to increase in size, and organs
that are not exercised tend to shrink.
This is so obvious a matter in every-
78 WHAT EVOLUTION IS
day life that it needs no special illus-
tration and no one denies it.
Another principle that Lamarck
advanced was the principle of effort,
that in order to accomplish an end an
animal must make an effort, must
exert itself. If it did not so do its
effective powers would diminish. This
is an element of a psychological na-
ture; it has a certain vague and in-
tangible side not involved in the
principle of use and disuse, for in-
stance. It nevertheless plays no un-
important part in Lamarck's general
hypothesis.
The scheme advanced by Lamarck,
and briefly outlined in the preceding
paragraphs, carries with it the im-
pression of great naturalness. Every-
one knows that activity or lack of
activity modifies an organ and, grant-
ing that the changes thus produced
are handed on generation after gen-
WHAT EVOLUTION IS 79
eration and emphasized, evolution
seems to be a natural consequence. Is
not this precisely the method by which
plants and animals are moulded to
their surroundings; is not this, in
other words, the driving force that
lies behind evolution ? On the surface
it seems as though Lamarck's hy-
pothesis must indeed offer the true
explanation.
8o WHAT EVOLUTION IS
3. LAMARCKISM CRITICIZED
Notwithstanding the ease with
which Lamarckism appears to pro-
vide the necessary machinery for the
evolutionary process, this hypothesis
is not free from serious defects. Dar-
win considered it as a possible factor
in evolution but did not lay much
stress upon it. It was not until after
Darwin's time that Lamarckism came
into prominence in consequence of the
contrast between it and natural selec-
tion. Half a century ago a new
school, chiefly paleontological, arose
which, under the name of neo-La-
marckian, attempted to establish and
expand the principles of Lamarck.
This school was opposed by the neo-
Darwinians who, under the leader-
ship of Weismann, made a vigorous
onslaught against Lamarckism and
WHAT EVOLUTION IS 8i
claimed natural selection as the all-
sufficient factor in evolution.
The objections that were raised
against Lamarckism by its opponents
were first of all as to its limitations.
As a process effective in evolution it
applies to those changes that are in-
duced either directly by the environ-
ment or indirectly through exercise,
lack of exercise, and the like.
Some conditions seen in organisms
do not easily fall under any of these
heads. The protective coloration of
insects is an example of this kind.
Many insects exhibit colors, forms,
and activities that make them easily
mistaken for other objects in their
environment. Moths resemble the
bark of the trees on which they rest,
butterflies, on closing their wings, be-
come indistinguishable from leaves
or the earth and the walking-stick
insect gets its name from its resem-
82 WHAT EVOLUTION IS
blance to twigs. Anyone who has
taken the trouble to acquaint himself
with examples of this kind must have
been struck with the perfection of the
resemblances and with the evident
protection that the creature enjoys
through being mistaken by its foes
for something other than it is. It
was this principle that toward the end
of the Great War led to the camou-
flaging of vessels, of artillery, and
even of men. The insects that are
camouflaged do not acquire this state
through individual activity, but are
hatched out in this condition. They
receive their protective markings
fully formed, in the nature of birth-
rights as it were, and no efforts on
their part make the camouflage more
or less complete. In this respect, the
insects are quite unlike the fishes,
the frogs and toads, and especially the
chameleons where the colors of the
WHAT EVOLUTION IS 83
skin are under nervous control, with
the result, that the animals can mo-
mentarily change colors and patterns
and thus, so to speak, exercise this
system as muscles may be exercised.
In the insect the condition is fixed
once for all and the individual is in-
capable of modifying it. Fixed con-
ditions of this kind are beyond the
reach of the Lamarckian principles
and form a body of material the evo-
lutionary explanation of which must
be sought for in other directions.
Thus, granting the validity of La-
marck's hypothesis, it, nevertheless,
falls short of an explanation of all
the evolutionary aspects of organic
nature and must be supplemented by
other factors to reach completion.
But not only does Lamarckism fail
to apply to all classes of instances
under organic evolution, it also in-
volves, as one of its essentials, the
84 WHAT EVOLUTION IS
assumption of the inheritance of ac-
quired characters. Acquired charac-
ters are those pecuHarities that are
gained during the Hfetime of an in-
dividual as contrasted with his inborn
traits. That Lamarckism shall be
effective, it is necessary that precisely
these characters be inherited. For a
long time biologists have attempted
to show that such characters are in-
herited, but thus far they have been
unable to get any conclusive evidence
that such is the case.
The chief opponent of the inherit-
ance of acquired characters was
Weismann (1834-1914) who pointed
out that the bodies of the higher ani-
mals were composed of two catego-
ries of cells, the body cells proper
such as muscle cells, nerve cells, skin
cells, and the like, and the reproduc-
tive cells, the egg cells and sperm
cells. He also showed that acquired
WHAT EVOLUTION IS 85
characters were changes in the body
cells — muscle, nerve, skin and so
forth — and that there was no known
mechanism whereby the changes reg-
istered in these cells could be trans-
ferred to the reproductive cells in
order that such changes might be
handed on to the offspring. If a black-
smith through exercise increases the
muscles of his arm, how are these
muscles to modify his reproductive
cells that his offspring may have larger
arm muscles than they otherwise would
have had? This theoretic objection
to the inheritance of acquired char-
acters seems to many to be an insuper-
able one. It is, however, an objection
based on ignorance and may at any
time be set aside by new discovery.
Many of the older advocates of the
neo-Lamarckian school pointed to the
inheritance of mutilations as evidence
in favor of Lamarck's views, and it
86 WHAT EVOLUTION IS
was this that led Weismann and
others to experiment in this direction.
Colonies of mice and of rats were
subjected to mutilation and were
then used for breeding with the view
of ascertaining whether such mu-
tilations were heritable. Thus the
lengths of the tails of a number of
adult white mice were measured, their
tails were then cut off, and they were
used as breeding individuals for a
new generation. When the second
generation had matured, their tails
were in turn measured and cut off
and a third generation was produced
from them. After the breeding of
approximately twenty such genera-
tions, all of which had been subjected
to the amputation of the tails at an
appropriate stage, the tails in the final
generation were found to be as long
as those in the first generation. Such
mutilations, then, gave no evidence
WHAT EVOLUTION IS 87
of being inherited and this conclusion
was to have been expected at the out-
set, for it is well known that the
innumerable deformations of the hu-
man body as practiced by primitive
races whereby the ears, the lips, the
nose, and even the head become mis-
shapen, have had no inborn effect
upon the stocks concerned. The an-
cient religious rite of circumcision,
though practiced for very many gen-
erations by the Hebrews, has had no
effect in shortening the foreskin of
Hebrew male infants. If mutilations
were inherited man would be a mere
fragment of what he is as a result of
handing on from one generation to
another the injuries received from
wars and accidents. Mutilations evi-
dently are not inherited and the so-
called examples of this kind seem to
be nothing but old-wives tales or
coincidences.
88 WHAT EVOLUTION IS
But even though mutilations have
no effective influence on the germ
cells of the animals suffering from
such defects, may not bodily activi-
ties, more normal in character than
mutilations, influence the germinal
elements? May not a normal but
novel and unusual condition of the
body cells influence the contained
germ cells? To test this Castle and
Phillips attempted the very ingenious
experiment of transferring germ cells
from one individual, with a given set
of bodily traits, to another individual,
with very different traits, and of test-
ing the results of such a transfer by
breeding. They proceeded in the fol-
lowing way. The ovaries W'Cre re-
moved from a young guinea pig of
pure white stock and in their place
were set the ovaries from a pure
black individual. After recoverv
from the operation, this white female
WHAT EVOLUTION IS 89
with '^ black" ovaries was paired
with a pure white male with the
result that between six to twelve
months after the operation she bore
two litters of young. These consisted
in all of six offspring every one of
which was black exactly as though a
black female had been paired with
the white male. This test shows that
after almost a year of residence in
the foster white body the ovaries
from the black female still retained
in full force their original potentiali-
ties and gave no evidence that the
new foster body had influenced them
in the least. This experiment sup-
ports Weismann's contention that the
germ cells are essentially independent
of the body in which they reside.
But again it may be maintained
that the period over which such trials
extended was much too short for a
real test of the question and that, if
90 WHAT EVOLUTION IS
experiments could be devised that
would of necessity last over a number
of generations, results of a very dif-
ferent kind might be obtained.
To try out this aspect of the prob-
lem numerous investigations have
been made or are still in progress.
Few workers have done more in this
direction than the Viennese experi-
mentalist, Kammerer. Of his num-
erous studies one may be chosen as
an example. The European spotted
salamander deposits either numerous
eggs or young that have been hatched
in the mother's body in ponds and
pools in damp woods. All the young,
irrespective of their condition of
birth, are provided with gills and
live for several months in the water
after which they lose their gills and
become inhabitants of the land. The
European black salamander gives
birth only to active young, usually
WHAT EVOLUTION IS 91
two in number, and these are born
without gills and in full readiness
for terrestrial life. By keeping the
spotted salamander away from water,
Kammerer attempted to change its
breeding habits in the direction of
those of the black salamander. Such
artificially restrained salamanders re-
tained their young in their bodies till
the young had lost their gills and
were in a condition for life on the
land. The young of such parents
were reduced in number, as compared
with the normal number produced,
and were mostly black. In both these
respects the stock approached the
European black salamander. Spotted
salamanders, whose parents had thus
been modified in habit by experimen-
tal conditions, on arriving at sexual
maturity were, during their breeding
season, given access to water. They
deposited their young in the water at
92 WHAT EVOLUTION IS
an advanced stage of groWth, and
these young remained in the water
only a few days instead of several
months. Thus the reproductive hab-
its of the spotted salamander, by a
change in the environment, were
modified in the direction of the black
salamander, and this modification
persisted more or less in their de-
scendants, even after these descend-
ants had been allowed to return to
the original environment.
Several lines of experimentation
such as the one described in the pre-
ceding paragraph have been carried
out by Kammerer within the last few
years and point to the inheritance of
acquired characters. How sound the
experimental evidence is in all such
cases remains to be seen. Is it not
possible that the peculiarities that
Kammerer believed he originated in
the spotted salamander, to take this
WHAT EVOLUTION IS 93
as an instance, may have been inborn
traits in this animal which were
simply called into evidence by the
changed environment rather than
produced by it? Certainly such as-
pects of the problem should be tested
before a final conclusion can be ar-
rived at, and in so crucial an experi-
ment as the one described, it is
extremely desirable that independent
evidence on the same point from
other investigators should be at hand
before a final decision is reached.
Other students of this general
problem have also carried out ex-
tended series of experimental studies
reaching over many generations.
Thus the Americans Guyer and Smith
have advanced evidence to show
that eye defects produced in one
generation of rabbits are inherited
by the descendent stock. But here
the defects produced and those as-
94 WHAT EVOLUTION IS
sumed to be inherited are often quite
different and the question, therefore,
of real inheritance remains open.
The same general criticism applies
to Griffith's studies on the inheritance
of defects in the internal ear of the
rat. Both these lines of investiga-
tion, and especially those of Guyer
and Smith, are, however, extremely
near the point and are very sugges-
tive.
A novel and very remarkable test
of the inheritance of acquired char-
acters is one that has been advanced
by the celebrated Russian physiolo-
gist Pawlow. It is well known that
mice can be trained easily to come to
a particular place for food. If, dur-
ing this training, a bell is sounded
each time that the animals are fed,
they will learn after a while to come
for food at the sound of the bell even
when no other signal for the presence
WHAT EVOLUTION IS 95
of the food is given. This kind of
response where a second form of
stimulus, such as the sound of a bell,
replaces the primary stimulus is called
by Pawlow a conditioned reflex. To
induce this state in untrained mice
required, according to him about
300 lessons. The descendants of this
trained stock, however, acquired this
capacity after only 100 lessons, the
third generation after 30 lessons, the
fourth after 10, and the fifth after 5
lessons. Pawlow expressed the hope
that in time a generation of mice
might be produced in which this con-
ditioned reflex would occur immedi-
ately and, so far as that generation
itself was concerned, without train-
ing at all. These statements were
published in a preliminary way in
1923 and, though in certain respects
they are very precise and final, it is
hardly possible to comment on them
96 WHAT EVOLUTION IS
till the complete report is published.
They are nevertheless full of signifi-
cance.
The whole problem of the inherit-
ance of acquired characters has ar-
rived at a stage where the results are
coming to be of the first importance,
and it must be admitted even by those
who oppose Lamarckism that the re-
cent tests have come much nearer
yielding conclusive results than those
attempted in the early stages of the
controversy. Nevertheless it is gen-
erally agreed by almost everyone
concerned that up to the present time
no entirely convincing instance of
the inheritance of acquired characters
has come to light and that from this
standpoint Lamarckism must be ad-
mitted to be without direct support.
There are, however, those like Samuel
Butler and, more recently, George
Bernard Shaw, as disclosed in his
WHAT EVOLUTION IS 97
preface in "Back to Methuselah,"
who cry out for Lamarckism, but
their cry is far-fetched and aUhough
the Lamarckian doctrine may eventu-
ally prove true, the proof of it will
come from other sources than literary
intuition.
The conclusion that Lamarckism is
a possible but unproved factor in evo-
lution is a statement that represents,
I believe, the opinion of the majority
of modern biologists. That the criti-
cism upon which this statement rests
applies to animals only in so far as
they exhibit sexual reproduction is, I
suspect, generally appreciated though
not so commonly stated. In organ-
isms that reproduce in this way, as
Weismann clearly showed, the cells
that make up the creature are divisi-
ble into the two classes of body cells
and reproductive cells and, as already
noted, it is extremely difficult, if not
98 WHAT EVOLUTION IS
impossible, to show how under such
circumstances the inheritance of ac-
quired characters can take place. In
those forms in which non-sexual re-
production is found the inheritance
of acquired characters must be a reg-
ular occurrence, for, in this method
of reproduction, the whole body of
the organism divides into two or
more masses, and the body cells of
the parent, with all the peculiarities
that the environment may have im-
pressed upon them, become the body
cells of the offspring. Here the
method of reproduction is as clearly
in favor of the inheritance of ac-
quired traits as in the other instance
it is opposed to this process. It must
be kept in mind, however, that non-
sexual reproduction is a characteris-
tic of the plants and the lower
animals and is absent from the higher
forms. It occurs on the animal side
WHAT EVOLUTION IS 99
among protozoans, sponges, corals,
starfish, moss-animals, worms, and
the group of sea-squirts or tunicates,
but it is not known among snails,
clams, crustaceans, insects, or the ver-
tebrates. If, therefore, the inherit-
ance of acquired characters is a
feature of non-sexual reproduction
and the Lamarckian principles may
apply where this occurs, it is after
all a limited application and illus-
trates again what has already been
pointed out that Lamarckism at best
cannot be regarded as an all-inclusive
factor in evolution. From what has
been said it appears to be at best a
possible element in this process.
100 WHAT EVOLUTION IS
4. DARWINISM
Darwinism, or as it is often called
natural selection, is an explanation of
evolution that originated independ-
ently in the minds of Darwin and
of Wallace. It is best stated in Dar-
win's memorable work ''The Origin
of Species" (1859), without doubt
the most significant single publication
of the nineteenth century. As a re-
sult of the discussion called forth by
the appearance of this work, two
great steps in the progress of biology
were accomplished; first, the accept-
ance of descent with modification,
instead of special creation as the
order of organic nature, and, sec-
ondly, the establishment of natural
selection as a driving force in evolu-
tion. The first of these has already
WHAT EVOLUTION IS loi
been taken up; the second remains to
be considered.
In seeking a clue as to the way in
which evolution takes place Darwin
first turned his attention to plant
and animal breeding. Domesticated
plants and animals, notwithstanding
their great diversity and variety, are
the products of comparatively few
wild species. Thus all the various
races of domesticated pigeons have
descended from the European rock-
pigeon. The original wild stock of
this bird is fairly well represented by
the common domesticated individuals
of slaty color, with two dark bars on
the wings and with a white rump. In
addition to this stock there are over
150 named varieties of pigeons that
breed true. These include such un-
usual forms as pouters, carriers, fan-
tails, tumblers, jacobins, trumpeters,
and a host of others whose forms and
I02 WHAT EVOLUTION IS
habits are most diverse. Were these
met with in nature, the zoologist
would unhesitatingly assign many of
them to separate species or even
distinct genera. What is true of
pigeons is also true of other domesti-
cated animals such as dogs, horses,
swine, cattle, and the like.
In considering evolution Darwin
first set for himself the task of ac-
counting for the origin of domesti-
cated stocks. He found that when
the breeder wished to develop a par-
ticular feature, such as an excessive
covering of feathers on the leg and
foot of a pigeon, he watched his stock
closely and chose for breeding pur-
poses those individuals that showed
evidences of the trait he sought. By
this method of selection applied to
one generation after another, he
gradually arrived at a stock in which
the given feature was as pronounced
WHAT EVOLUTION IS 103
as he wished and thus attained his
end. Darwin called this process arti-
ficial selection and believed it to be
the method by which man had pro-
duced from comparatively few wild
sources the great variety of domesti-
cated forms with which he was sur-
rounded.
Darwin then raised the question,
Is there not a similar process going
on in nature as a means of producing
the limitless variety of life in the
open? This he believed to be so and,
in contrast with artificial selection,
he designated this process as natural
selection. The grounds for his belief
in natural selection as an actual proc-
ess in nature may be briefly stated in
the following way.
More organisms are produced than
can possibly continue to exist because
of the limitations of food, space, and
other essentials. This comes about
104 WHAT EVOLUTION IS
from the fact that each individual or
pair of individuals gives rise to sev-
eral offspring and often to many. It
is not always appreciated what this
method of increase means.
If a single plant produces at the
end of its life two seeds and these
grow to mature plants the next year
and produce each two seeds and so
on, in the twenty-first year the orig-
inal plant will be represented by over
a million descendants. Even an ani-
mal, such as the elephant which
breeds with extreme slowness, will
nevertheless in time populate the
globe, if all its progeny live and re-
produce. When rapidly reproducing
forms such as the insects are con-
sidered, the increase in numbers is
bound to be quickly prodigious so
that the swarms of locusts described
in the past seem as nothing to what
might have happened. All organisms
WHAT EVOLUTION IS 105
are endowed with such powers of in-
crease that even the slowest would in
time overrun the earth.
Darwin further recognized the
fact that the offspring of all animals
and plants are more or less diverse,
and that no two are ever exactly
alike. This is apparent to everyone.
In a litter of puppies the individuals
are quickly and easily distinguished
by size, markings, vigor, disposition,
and the like, and we name them and
treat them as we do separate persons.
These slight individual differences
are, according to Darwin, either fa-
vorable or unfavorable for the con-
tinued life of the given organism and,
since more individuals come into the
world than can possibly survive, those
with unfavorable traits are less likely
to reach maturity and leave offspring
than those with favorable traits. In
this way there is a continual elimi-
io6 WHAT EVOLUTION IS
nation of the less fit with the result
that the fittest survive, leave off-
spring, and thus hand on to future
generations their peculiar qualities,
for the individual differences noted by
Darwin are the inborn traits of each
individual. Thus a form of natural
selection is continually in operation
ever moulding plants and animals
with great nicety to their fluctu-
ating surroundings. This, according
to Darwin, is the mainspring that
keeps evolution continually moving.
Survival of the fittest, struggle for
existence, and other like expressions
have been used as figures of speech
with which to make clear what is
meant by natural selection. And
these expressions do indicate what at
times occurs in nature, but anyone
who looks upon the world of plant
and animal life will not see a field of
battle, an arena of combat, with each
WHAT EVOLUTION IS 107
living thing ranged against its neigh-
bor. In fact when we seek a figura-
tive expression for peace and quiet,
we are very Hkely to turn to that very
nature which, according to these
phrases, should be in deadly turmoil.
Nevertheless, natural selection is
probably running at full speed in
every quiet countryside. Four seeds
from a given plant fall on a small
plot of ground. All germinate and
produce growing plants, one a little
in advance of the other three. The
early one shades the others, reaches
maturity first and sets its seeds. Au-
tumn comes and the other three have
not yet flowered and in consequence
they fail to produce fruit. Natural
selection has taken place. The early
plant leaves offspring for the next
year; the other three are unrepre-
sented. All may have lived what is
essentially the same length of time
io8 WHAT EVOLUTION IS
and all in perfect peace; there has
been no struggle, no conflict, but
natural selection has nevertheless
occurred. The essential act of re-
production has been completed by
only one and that one has thereby
handed on its inborn peculiarities to
the next generation. The same oper-
ation is true of animals. Any crea-
ture that fails to leave offspring
suffers elimination from the stand-
point of natural selection, yet such an
animal or plant may live individually
as long or even longer than many
another whose progeny will reach
into future generations. Hence na-
tural selection is not necessarily con-
cerned with the destruction of the
individual, as is often inferred by
the figurative expressions already al-
luded to, but is a process that has to
do with the way in which plants and
animals succeed or fail in leaving off-
WHAT EVOLUTION IS 109
spring. In most instances it is a
quiet, unobtrusive natural phenome-
non that permeates nature in every
direction and is more truthfully rep-
resented by the quiet countryside than
by the turmoil of battle.
Having reached some idea of what
is meant by natural selection or Dar-
winism and having seen how it may
be an active force in moulding plants
and animals, we may pause a moment
to compare it with what Lamarck be-
lieved to be the energizing factor in
evolution. Natural selection first of
all does not suffer from limitations
to the extent that Lamarckism does.
Natural selection not only applies to
all that Lamarckism reaches but it
meets with success such conditions as
the protective coloration of insects,
which, it will be remembered, were
hardly within the range of Lamarck's
principle. Insects, that have only an
no WHAT EVOLUTION IS
imperfect resemblance to the bark of
the tree on which they rest, are much
more Hkely to be espied and carried
off as prey, than those that have a
closer resemblance. Natural selec-
tion may in this case be expected
to act with full efficiency whereas
Lamarck's principle, as already indi-
cated, is apparently entirely inappli-
cable. From this standpoint, natural
selection is not subject to the limita-
tions that characterize Lamarck's
hypothesis.
Further, natural selection is not
concerned with the inheritance of ac-
quired characters. The slight indi-
vidual differences, upon which it is
believed to act, are not differences
due to the action of the environment
on the given organism but are inborn
traits which in consequence may be
handed on through the germ cells to
descendent offspring. In these two
WHAT EVOLUTION IS in
particulars natural selection has' a
great advantage over Lamarckism.
It is of wider application and it
avoids the difficulty concerning the
inheritance of acquired characters.
It may not be amiss if at this point
we compare Lamarckism and Dar-
winism by attempting to show how
each may be made to apply to the
same example, and as an instance to
to be so treated, we may take the
webbed foot of the water fowl origin-
ally discussed by Lamarck. Accord-
ing to his hypothesis this structure
arose by the accumulation, in the
course of generations, of acquired
modifications which resulted from a
change of habit in consequence of the
bird's removal from purely terrestrial
surroundings to an aquatic environ-
ment. From Darwin's standpoint the
webbed foot resulted from selection,
among a diverse offspring, whereby
112 WHAT EVOLUTION IS
those with favorable inborn traits
would be preserved and have off-
spring as contrasted with those whose
conditions were less favorable. Thus
Lamarckism deals with difference in-
duced by the environment, acquired
characters, and Darwinism with in-
born native differences.
Before leaving this comparison of
the two views it should be pointed out
that they are in no sense mutually ex-
clusive. It is sometimes implied that
if Darwinism could be shown to be
true Lamarckism must be false and
vice versa. It must be evident, how-
ever, that such is not the case. There
is not the least reason to assume that
one view is in any way incompatible
with the other. It is entirely possible
that both Lamarckism and Darwin-
ism may be acting at once and in per-
fect accord as mutually efficient
factors in evolution.
WHAT EVOLUTION IS 113
5. DARWINISM CRITICIZED
In discussing Darwinism or natural
selection from a critical standpoint
we may begin by inquiring w^hether
there is any evidence that this process
is an actual occurrence in nature. To
answer such a question, one would
naturally turn to conditions where
organisms are subjected to severe
and unusual strain. Some years ago
Bumpus studied the effects of a
severe winter storm on sparrows.
As a result of a heavy sleet many
birds were brought close to death. A
large number of these spent birds
were collected, and of the total col-
lection, 64 died and J2 revived. Do
the members of these two groups
thus naturally established dift'er, or
are they essentially the same? A
statistical study of the two sets of
114 WHAT EVOLUTION IS
birds showed that the survivors were
less variable than those that perished.
The birds that died were, in many
cases, extreme individuals. For in-
stance, they more frequently had
large bodies combined with small
wings, or the reverse, than the sur-
vivors had. Hence they represented
conditions in which it might be said
that there was too much power or too
little power for the wing surface and
the like. This disadvantageous ten-
dency was in general the cause of
their death. One may therefore con-
clude that, under the severe circum-
stances mentioned, elimination was
not haphazard but rather, as would
be expected, that the least fitted birds
succumbed and the best fitted sur-
vived. In this rather crude way, evi-
dence of a selective capacity in nature
has been obtained, and from instances
of this kind, it is fair to conclude that
WHAT EVOLUTION IS 115
natural selection is a process that is in
actual operation in the world about us.
Natural selection, however, is not
without its limitations. It is an op-
eration that at best can lift organ-
isms only to the level of positive needs.
Nature, with a certain prodigality,
often goes much beyond this limit.
Examples are abundant enough.
Many crustaceans have the curious
habit of casting injured legs and
other appendages. When a crab loses
a part of one of its legs, it recovers
by a new growth, but this new growth
does not replace simply the lost part;
the old stump is thrown off from a
so-called casting joint at the base of
the leg and a wholly new leg is
formed. Most crabs, picked up on
the shore at random, are undergoing
this process on some one of their nu-
merous appendages.
Hermit crabs live with the pos-
ii6 WHAT EVOLUTION IS
terior parts of their bodies tucked
away in some dead snail-shell appro-
priated by the crab for this purpose.
Their hind appendages are therefore
protected and, according to Morgan,
who recorded this case, these append-
ages are never found suffering from
injury as their front legs are. Never-
theless, if by experimental steps the
hind appendages are injured, they are
cast and recovered as the exposed
appendages are. Here then is an in-
stance where nature has stepped be-
yond the actually necessary, and
where it would be difficult to offer for
the condition an explanation based
purely upon natural selection.
Another instance of the same kind
occurs among certain almost micro-
scopic crustaceans, the copepods.
These small creatures are abundantly
represented in the surface waters of the
sea. Copepods of different sexes are, as
WHAT EVOLUTION IS 117
a rule, strikingly unlike. The females
are relatively inconspicuous and sim-
ple in their dress. The males, on the
other hand, are gaudy and ornamen-
tal in the extreme. In their colors
they are veritable microscopic pea-
cocks. In fact the comparison with
birds is quite appropriate, for just as
the male bird often has a conspicuous
plumage so is the male copepod com-
monly highly decked out, and one
would suppose for the same reason,
namely, to attract the females at the
breeding time. But the female cope-
pod, unlike the female bird, has eyes
that are quite incapable of taking in
all this beauty, and we meet again a
condition in which nature seems to
have gone so far in excess of what is
necessary that natural selection can-
not be offered as a means of explaining
the condition. This kind of excess,
which is an example of what has been
ii8 WHAT EVOLUTION IS
called hyper tely, is a common occur-
rence in nature and is beyond the
reach of natural selection.
The most serious objection that
has been raised against natural selec-
tion is its apparent inability to launch
any real change. When we consider
how very slight and insignificant the
individual differences are in any
group of plants or of animals, it is
almost inconceivable that these dif*
ferences can afford sufficient grip for
what natural selection is supposed to
do in producing a new species. Once
well established, it is easy to see how
a new and advantageous trait can be
fostered and developed by this proc-
ess, but at the inception, it would
seem impossible that natural selec-
tion could start a new feature forward
from such small beginnings. Indi-
vidual differences are not sufficiently
life and death differences to enable
WHAT EVOLUTION IS 119
natural selection to obtain an initial
hold. From the time of Darwin this
has been the great obstacle to his
theory, and no Darwinist has thus
far successfully met this objection.
When we view the face of organic
nature, we see such an array of mar-
velous adaptations and such a bewil-
derment of plant and animal species,
many of which are separated one
from another by differences of a very
slight kind, that we are forced to
admit that it is inconceivable that
natural selection, as understood by
Darwin at least, could have produced
what is before us. This conviction
has so impressed itself upon the minds
of most modern evolutionists, that
they have one by one come to the con-
clusion that natural selection, which
in Weismann's time was declared to
be all-sufficient in evolution, may
after all be of little real significance.
120 WHAT EVOLUTION IS
Opinions of this kind have been
frankly expressed by such eminent
authorities as Bateson in England
and Morgan in America, and they
reflect the view of the majority of
biologists the world over.
Although the statements of these,
and other authorities on this subject,
have been made with perfect clear-
ness and in full knowledge of what
the words imply, they have been
seized upon by many thoughtless per-
sons as evidence that biologists are
abandoning the doctrine of evolution.
What is really meant by these decla-
rations, as must be evident to any-
one who has read thus far, is that
descent with modification, or evolu-
tion, is not questioned, but that the
particular explanation of it, known
as natural selection, or Darwinism, is
seriously doubted. One often sees in
current literature lists of noted biolo-
WHAT EVOLUTION IS 121
gists who are said by anti-evolution-
ists to be opposed to evolution, but,
vv^hen the ground for these statements
is scrutinized, it is commonly found
that the authority named questions
natural selection (Darwinism), but
not descent with modification, or evo-
lution, in the ordinary sense of the
word. In a recent newspaper a prom-
inent Boston pastor names "some
scientists who at least call in question
the loudly asserted proof of evolu-
tion/* These names include those of
J. P. Lotsy and William Emerson
Ritter both of whom have criticized
Darwinism but, to the best of my
knowledge, are firm believers in
evolution. If by Paul Kamerer is
meant Paul Kammerer and by E. B.
McBride, E. W. McBride, the same
statement applies to these zoologists
as to the other two scholars named.
Hence this list includes several well
122 WHAT EVOLUTION IS
reputed evolutionists. The confusion
whereby these names have been in-
cluded has probably arisen through
failure to distinguish Darwinism from
evolution. It is unclear thinking of
this kind that is responsible for many
of the present contentions.
In the opening portion of this sec-
tion, it was pointed out that natural
selection was without doubt a real
occurrence in nature, and as the dis-
cussion progressed, it was made clear
that this process, at least as under-
stood by Darwin, fell short, and per-
haps far short, of accomplishing
what it was originally believed to do.
This, in general, seems to be the
modern opinion concerning it. That
it is a real factor in evolution, there
is not the least doubt; but that it is a
subordinate factor, and perhaps even
a very subordinate one, is likewise
true. Biologists know that one spe-
WHAT EVOLUTION IS 123
cies comes from another, but how this
is accomplished no one apparently
can yet explain. As a contributing
factor, natural selection doubtless had
a hand in this operation, but it is in
the rough-hewing of the species, and
not in the polishing of the final prod-
uct that it is concerned. The polishing,
which after all is perhaps the most
essential aspect of the process, seems
still to be hidden from scientific gaze.
124 WHAT EVOLUTION IS
6. THE MUTATION THEORY
For almost forty years after the pro-
mulgation of natural selection, biolo-
gists were content to speculate on the
way in which plants and animals
might be changed through this prin-
ciple. Only as the methods of zo-
ology and of botany changed, from
the more purely observational to the
experimental, did evolutionary inves-
tigation receive a new impulse. This
change in evolutionary work may be
said to have been initiated, about the
beginning of the present century, in
the studies on heredity, carried out
more or less independently by Tscher-
mak, by Correns, and especially by
de Vries. One of the results of these
studies was the unearthing of the
long-neglected but highly important
publications of Mendel which had
WHAT EVOLUTION IS 125
appeared some thirty years previ-
ously. The principles, contained in
Mendel's writings, were at once
made the basis of an extensive and
thorough-going experimental pro-
gramme and served, at the same time,
as ground on which de Vries erected
his mutation theory.
Those portions of Mendel's work
that are directly concerned with
the mutation theory are easily and
quickly grasped. They can be illus-
trated by what occurs in animals as
well as in plants. If we breed a pure
black guinea pig to a pure white one,
the offspring are always black and if
these offspring are bred amongst
themselves, they produce young one-
fourth of which are pure white and
three-fourths are black. On testing
the black individuals, one-third of
them, or one-fourth of the total, can
be shown to be pure black and the
126 WHAT EVOLUTION IS
other two-thirds, or one-half of the
total, can be shown to be mixed, in
that, like their parents, they will
when bred together produce both
black individuals and white individ-
uals. The remarkable feature of
such breeding series is the regularity
with which the proportions, just
stated, occur. The occasion of these
remarkable Mendelian proportions
can be seen when such a series, as
that described, is analyzed.
When opposing characters, such as
white and black, are combined in
breeding, as in the case of the guinea
pigs mentioned in the preceding para-
graph, only one of these characters
appears in the first generation of off-
spring, namely, in the particular in-
stance under consideration, black.
All guinea pigs in the first generation
after the cross white-black are black.
But these black individuals carry
WHAT EVOLUTION IS 127
hidden in their bodies the white trait,
for, when they are bred amongst
themselves, one-fourth of their off-
spring are w^hite. Black, then, in
some way overcomes white; not that
it obliterates the white, but it holds
this trait in abeyance. In the language
of the modern breeder black is said,
in a case such as the guinea pig, to be
dominant over white and white is
said to be recessive to black. This
state of affairs, though not universal,
is common to many such pairs of
breeding characters. As a generali-
zation, it is often referred to as the
principle of dominance and was one
of the discoveries of Mendel.
A second and very much more im-
portant principle, that is illustrated
by the example under consideration,
is, what may be called, the principle
of the purity of the germ. It is
briefly this: a given germ cell, be it
128 WHAT EVOLUTION IS
sperm or egg^ can carry the exciter
or gene of only one of two opposing
characters, such for instance as white
and black. No germ cell can carry a
gene for white and a gene for black
at the same time. In any pair of op-
posing traits, the gene of only one
can be present in any germ cell. In
other words the germ cells are in this
respect always individually pure.
This principle of the purity of the
germ cell makes clear the remarkable
proportions, already pointed out, in
the second generation of offspring.
It will be recalled in the example of
the guinea pigs that, in the second
descendent generation, there were one-
quarter or twenty-five per cent pure
whites, another quarter or twenty-
five per cent pure blacks, and a half
or fifty per cent black individuals
which, however, were really mixed,
for, on being bred amongst them-
WHAT EVOLUTION IS 129
selves, they, like their parents, pro-
duced whites as well as blacks.
If, now, we examine the whole
breeding series from the standpoint
of the purity of the germ, we shall
find reason for the occurrence of the
proportions given. This can be done
best by reference to the diagram on
page 131. Here it will be seen that
the source of the descendent stock
is the pair of guinea pigs, one white
and the other black, represented in
outline at the top of the page. Which
of the two is male and which female
makes no difference so far as the final
outcome is concerned. The white one
is supposed to have been derived
from a pure white stock, that is,
from a stock which in all its pairings,
within its own bounds, produced
nothing but white individuals. Hence
the white pig must be assumed to
have come from an tgg containing a
I30 WHAT EVOLUTION IS
white gene, fertilized by a sperm also
containing a white gene. This is rep-
resented in the diagram by the two
white circles above the white pig, one
for the egg and the other for the
sperm. Such an individual can pro-
duce only one class of germ cells,
namely those with white genes. As-
suming in this particular instance
that the white pig is the female, she
may then be described as an individ-
ual producing eggs all of which carry
the white gene. If the white member
of the pair is the female, the black one
must be the male and what has been
said of the white pig may be said of
her black mate, except that black gene
is to be used in place of white gene
and sperm cell in place of tgg cell.
In the first descendent generation
all offspring, in the present instance,
would be the product of a white tgg
fertilized by a black sperm. This is
WHAT EVOLUTION IS 131
Guinea-pig
• • 00
JR
• • ^o
Four -o'clock
• • 00
t f
00
n
o
n
t
• o ^o 00
f
WHAT EVOLUTION IS 133
indicated by the white circle and the
black circle in the diagram over the
representative of this generation. In
consequence of the dominance of
black over white, all individuals, in
this generation, will have black coats.
But since they arise from a germinal
mixture, each of these individuals
will be able to produce two kinds of
germ cells, the males white sperm and
black sperm, and the females white
eggs and black eggs. If, now, we
assume that the two kinds of eggs
are produced in equal numbers and
that the same is true of the sperm and
that the union of egg and of sperm is
purely fortuitous, the kinds of guinea
pigs and their proportionate num-
bers, as already stated for the second
descendent generation, will be ex-
actly realized. For with two kinds of
sperms and two kinds of eggs, there
will be four possible combinations in
134 WHAT EVOLUTION IS
fertilization. Once in four chances
a white sperm will fertilize a white
egg, a process which will yield the
twenty-five per cent pure white guinea
pigs. Once in four a black sperm
will fertilize a black tgg and thus will
arise the twenty-five per cent pure
black guinea pigs. Once in four a
white sperm will fertilize a black egg
and once in four a black sperm will
fertilize a white egg and these two
classes taken together will yield the
fifty per cent mixed stock which, like
their parents, can produce either
white or black offspring. Thus the
assumption of the purity of the germ
leads to a simple and illuminating
understanding of the proportionate
numbers of young in the several Men-
delian classes.
This assumption has been tested by
geneticists in many ways and has been
found to hold good. In fact, the
WHAT EVOLUTION IS 135
whole set of ^lendelian principles has
proved in the hands of the experi-
mentalist little short of marvelous in
their application. Exceptional cases
often occur, but when these are
worked out, they are commonly found
to be in essential agreement with the
general principles. Thus when the
red-flowered variety of the common
garden four o'clock is crossed with
the white-flowered form, as shown
on the lower half of page 131, the off-
spring are neither red-flowered nor
white-flowered but have flowers of an
intermediate tint, pink. If now these
offspring are bred amongst them-
selves three classes result: twenty-
five per cent pure whites, twenty-five
per cent pure reds, and fifty per cent
pinks, a state of affairs that may be
described as parallel to that of the
guinea pigs, so far at least as purity
of the germ is concerned but without
136 WHAT EVOLUTION IS
dominance. In this way particular
examples may show individual dif-
ferences and thus illustrate the extent
to which the general principles are
open to readjustment.
De Vries, having discovered inde-
pendently much that was afterwards
found in the writings of Mendel and
having come to many of the same
conclusions that this writer had ar-
rived at, turned to the problem of
evolution in the hope that the new
ideas on heredity would be helpful in
understanding descent with modifi-
cation. In 1901 he published the first
general account of his mutation
theory. According to this theory, the
characters by which we distinguish
different plants and animals are made
up of units which are sharply sep-
arated from one another and are
without intergrades. They are repre-
sented by such features as black and
WHAT EVOLUTION IS 137
white in the guinea pig's coat. These
opposing traits were called unit or
elementary characters by de Vries
and, in describing them as elementary,
he meant that they partook in their
separateness of the nature of the
chemical elements. Every organism
is marked by a great array of these
unit characters. In the guinea pig,
for instance, there are coat colors,
white, black, piebald and the like, dif-
ferences in hair, long, short, rosetted,
or smooth, and a host of other features
all of which are inherited in accord-
ance with Mendelian principles.
Thus the pairs of traits in Mendelian
inheritance are the unit characters of
the mutation theory.
According to de Vries a real species,
or as he called it an elementary species,
is to be described from its unit char-
acters and any new combination of
unit characters is a new species. A
138 WHAT EVOLUTION IS
black guinea pig differs from a white
guinea pig in one unit character, and
yet this is sufficient to place these two
individuals in different elementary
species. This is certainly a novel
conception, for it implies that two
brothers may be of diverse species
provided they show a unit character
difference. In evolution, however,
we are not so much concerned with
this aspect of the subject as with
another.
As already stated, the unit char-
acters, by which elementary species
may be distinguished, show no inter-
grades; they are fixed characters.
Hence the difference between one ele-
mentary species and another is an
abrupt difference. These abrupt dif-
ferences are what de Vries calls muta-
tions, and he contrasts them with
the very slight individual differences
which are seen between members of
WHAT EVOLUTION IS 139
the same species and which are com-
monly designated as variations. Vari-
ations, according to de Vries, are
always very slight and insignificant.
They never even approximate the
magnitude of a mutation. Mutations
on the other hand are striking differ-
ences such as black or white in the
coat of a guinea pig and represent,
in this sense, considerable jumps or
breaks. Variations are like the slight
movements that a cube may be made
to execute when it is wabbled about
on one of its faces. Mutations are
like the changes that arise when
the cube is turned from one face to
another.
The mutation theory is to the effect
that evolution takes place not through
small differences or variations, as Dar-
win believed, but through large and
sudden changes, mutations. Just as
the cube does not progress when it
I40 WHAT EVOLUTION IS
merely wabbles back and forth on one
side, so evolution makes no progress
through variations. Only when mu-
tations occur, when the cube rolls over
on to a new face, is evolution taking
place. Darwin recognized mutations
as conditions in nature and used for
them the breeder's common name of
sport. He was doubtful, however,
whether they had any significance in
evolution. To de Vries they are
the only real factor in evolutionary
progress.
No one can have bred plants or an-
imals for any length of time without
having noticed the frequency with
which mutations occur. Morgan, in
his exhaustive study of inheritance in
the fruit fly, has recorded many scores
of mutations, and there is no reason
to suppose that they do not occur as
frequently in open nature as in the
laboratory.
WHAT EVOLUTION IS 141
Whether a mutation persists or not
depends upon its nature. If it is in
a favorable direction, the individual
possessing it is likely to be preserved
and find a mate. As such changes are
handed down undiminished by Men-
delian inheritance, the mutation would
be expected to reappear in many of
the descendants in full vigor. In this
way, it could establish itself in the
stock and help to modify that stock so
as to form a new species. As de Vries
rightly states, this process of preser-
vation involves natural selection, for
the retention of such a character de-
pends upon this principle. All muta-
tions must run the gantlet of natural
selection. In this sense, the mutation
theory and natural selection are
mutually dependent. The mutation
theory yields the grain for the natural
selection hopper.
It must be evident that the muta-
142 WHAT EVOLUTION IS
tion theory presents a means of avoid-
ing the chief difficulty with which
Darwinian natural selection has to
contend. That difficulty, it will be
remembered, had to do with the first
steps in the origin of favorable traits.
These steps are not necessary in the
origin of mutations, for mutations
appear fully formed and are not built
up by slow degrees. This is the great
advantage that the mutation idea has
over Darwin's view of the way in
which new traits are supposed to be
ushered in. As mutations they enter
fully formed.
Difficulties with the mutation the-
ory can be easily found. First of
all this theory depends upon Men-
delian inheritance and what that kind
of inheritance implies as to the sep-
arateness of characters. But char-
acters often blend, in fact there may
be such a condition as blended in-
WHAT EVOLUTION IS 143
heritance, and such a condition, if at
all general, would be very restricting
to the mutation view.
Mutations further give the impres-
sion of laboratory and of garden
products, rather than of products of
the land and sea. Mutations certainly
occur in nature, witness albino ani-
mals, but the experimental product
seems to be far removed from what
is demanded by open nature. Many
workers have been so impressed with
this aspect of the question, that they
have come to look upon the great
biological advance of the last two
decades as illuminating, from the
standpoint of heredity, but as having
very little real bearing on the evolu-
tion problem. The truth is that the
mutation idea, and all its intricate
connections, are somewhat too novel
to admit of final judgment.
What the factors of evolution are.
144 WHAT EVOLUTION IS
what the moving forces behind this
great natural process are, no one is
in a position to state. Lamarckism
may be one of these. Darwinism
alone, or supplemented by the muta-
tion idea, seems quite clearly another
though perhaps a subordinate one.
Others still are probably to be dis-
covered, for it is unlikely that a proc-
ess so intricate, so many-sided, and
so far-reaching as organic evolution
should depend for its energizing on
only one source.
V
HUMAN APPLICATIONS
HUMAN APPLICATIONS
Man as an animal is a product of evo-
lution and is subject to its laws as all
other animals are. Such a statement,
however, does not mean that man with
all his complexities is at once under-
stood the moment this position is as-
sumed. The evolutionary standpoint,
like a mountain top, is a commanding
situation for a general survey, but it
does not do away with the intricacies
in the field of vision, it merely brings
them into more truthful relations with
the whole.
The derivation of civilized man
from a primitive human stock is a
subject that has grown so enormously,
in the last few decades, that its treat-
ment merits a volume. The new in-
formation on the subject, that has
come to us since Darwin's time, is
148 WHAT EVOLUTION IS
simply overwhelming in amount. Man
appears to have been on the earth for
nearly half a million years. His old-
est known representative is from Java,
the Trinil man or Pithecanthropus,
a restoration of whose head has been
made by McGregor. This is shown in
an outline sketch at the top of page 149.
For the use of this sketch and the
other outlines of heads on this page,
I am indebted to Professor R. S. Lull
and to the Yale University Press.
Pithecanthropus flourished about
500,000 years ago and is believed to
have made use of fire and simple flint
implements.
Of later date is the dawn-man,
Eoanthropus, of Piltdown, England,
who lived about 250,000 years ago.
His bones seem to be the most ancient
remains of man in England and occur,
associated with crude stone imple-
ments and the remains of several
WHAT EVOLUTION IS 149
Trinil man
PiltdoLun man
Neandertal man Cro-Maonon man
WHAT EVOLUTION IS 151
animals long since extinct. Another
ancient type of man is the Neandertal,
or Mousterian man, evidences of
whom have been found in many Euro-
pean localities. These remains date
from about 100,000 vears or more
ago. Of still later time is the Cro-
Magnon man, believed to be of the
same species as ourselves. His period
may be set at some 25,000 years ago,
and his blood mav still flow in the
veins of certain European peoples.
He was remarkable for his great
height, being commonly over six feet
tall. His stone implements were of
good workmanship, and his engrav-
ing, painting, and sculpture show him
possessed of aesthetic traits and of
unusual powers of expression. His
remains have been found in Wales,
France, and Spain. These few ex-
amples show how rich and numerous
are the traces of primitive man.
152 WHAT EVOLUTION IS
That man has descended from an
ape-like stock no reasonable person
can doubt. He shows this affiliation
in his body and in his activities in a
thousand ways, and yet more than
most animals, he has peculiarities of
his own. When we look at civiliza-
tion as represented in the complex life
of cities and of nations with all their
commercial interrelations, with their
humane institutions such as asylums
and hospitals, and with their oppor-
tunities for intellectual, aesthetic, and
spiritual growth, it seems as if an
attempt to base this enormous struc-
ture on an evolutionary foundation,
with Lamarckism, Darwinism, and
the like as driving forces, is futility
in the extreme. Who for a moment
would attempt to account for the
Divine Comedy as a product of evolu-
tion? And yet, if evolution means
anything, it means exactly this. Some-
WHAT EVOLUTION IS 153
where in the scope of its totaHty evo-
lution must find a place for the highest
achievements of the human soul, or the
general conception crumbles. Every
thorough-going evolutionist believes
this and looks to the natural history of
man, when viewed in its all-inclusive
light, as the real history of man.
But how is it that man holds such
an exceptional place in the world?
We are quite sure that never before
in the history of the earth has there
arisen an organism that has probed
the universe as man has, that has
developed art, poetry, religion, and
science as the human species has done
and is doing to-day. Not that these
accomplishments are in any sense
final or ultimate, for no one can tell
what the future has in store, but com-
pared with the efforts of the long
geologic past they are stupendous.
We look with admiration on the bee
154 WHAT EVOLUTION IS
and the ant, and we are astounded at
the instinctive capabilities of many
animals, but, when wx examine our-
selves closely, we find most of these
potentialities within us and a host
more of capacities of which no lower
creature seems ever to have dreamed.
In what respects has man lifted
himself so much above his neighbors?
Man is first of all a social organism.
He is banded together in families,
clans, and nations and, as thus organ-
ized, he resists the vicissitudes of life
vastly more successfully than he pos-
sibly could single handed. As an
organization, human society is in
many respects unique. Social life was
tried eons ago by the simpler animals
in a thousand dififerent ways; proto-
zoan colonies out of which sexuality
grew, sponge colonies and coral col-
onies which have had a hand in mould-
ing the earth's surface, insect colonies
WHAT EVOLUTION IS 155
such as the ant hill and the bee swarm,
all these preceded human society by
untold ages. Wheeler informs us
that in the insects alone social states
have arisen no fewer than twenty-
four different times in as many dif-
ferent groups of these animals. Yet
none of these societies accomplished
what man, as a social organism, has
achieved.
They almost all differ from human
society in two fundamental aspects.
First of all, the members of most
animal societies are close-blood rela-
tives. In the ant hill the individuals
are commonly the offspring of one
queen; they are all sisters in one
household. In almost all animal col-
onies, except the human, this close-
blood relationship holds. Second,
among the colonies of lower animals
the division of labor is relatively
slight. In human society occupations
156 WHAT EVOLUTION IS
mount into the tens of thousands at
the very least. Among the other co-
lonial animals the classes of perform-
ance are to be counted at most in
scores. In the beehive, the drones
have as their one duty the fertiliza-
tion of the queen, the queen is service-
able only in that she lays eggs, and
finally the worker performs the ordi-
nary duties of caring for the young,
procuring food, cleaning the hive and
the like. Compare for a moment the
relative simplicity of even so complex
a situation as that in the beehive with
the enormous intricacies of human
life and civilization, where blood-
relationship is most diverse and per-
formance is specialized to an almost
incredible degree. These aspects of
human society set it in strong contrast
with the social organizations of all
other animals.
Another feature, in which man
WHAT EVOLUTION IS 157
differs from most animals, is in his
striking ability to use the environment
to his advantage. The primitive ac-
quisition of fire made available to
him such gigantic forces as we see in
steam, electricity, and their endless
applications. Who would have sus-
pected that the unclad savage, as he
warmed himself over the dying em-
bers, was nursing a form of energy
that was to do for man all that modern
machinery has done! Little do we
think as we look at a watch face that
shines in the dark that the changes
going on there foreshadow, in germ,
possible sources of energy for future
man that may be as much superior to
fire as fire was to ancient brawn. But
this may be so, and it is precisely this
capacity to discover and utilize to the
utmost such environmental changes
that makes man different from almost
all other organisms.
158 WHAT EVOLUTION IS
In harnessing the energies of nature
man has discovered and perfected
tools. Few other animals use tools.
Monkeys and apes have their sticks
and stones, but it took man to fash-
ion them into serviceable shapes,
to discover metals, to build engines,
steamships, and airplanes. Man's
tools were amongst his first posses-
sions and not till he acquired the habit
of preserving them and passing them
on to future generations did society
progress. The race that buries with
the primitive artisan the choice ob-
jects of his life's work never goes
forward. Even the rude tools of one
generation must be put in the hands
of the next, if real progress is to be
made. In this sense the inheritance
of property separates man from most
other animals.
Another trait in which man is pe-
culiar is in the possession of a com-
WHAT EVOLUTION IS 159
plex language. The lower creatures
have their cries as outlets for emo-
tional states, and these cries form
a simple kind of organic language.
Everyone knows the difference be-
tween the hum of a complacent and of
an angry bee. How diverse and in-
forming are the vocal sounds of a
dog. All these are types of primitive
language, but they are almost end-
lessly remote from human speech
which, as represented in written form,
is not only a means of communica-
tion between distant individuals but
the stabilizer of all past events, the
vehicle of history. From this stand-
point the simple organic language
of the lower animals fades into in-
significance.
Finally, though not last, for there
are many other points of contrast be-
tween man and other animals, the
human species has acquired the habit
i6o WHAT EVOLUTION IS
of teaching, of passing on to a new
generation the practices and the wis-
dom of the older generations. This
is largely a human institution, for few
animals other than man possess the
least trace of it. Very many animals
learn. Beasts, birds, frogs, and fishes
learn; even an earthworm can learn
to find its way out of a simple maze.
Such animals learn by individual ex-
perience; they do not learn by ex-
ample. To learn by example is to have
a model and this is at once the worth
and the artificiality of the teacher.
Man learns not only by experience as
the lower animals do, but also by
being taught and the profession of
teacher is almost exclusively a human
profession. Contrary to the belief of
the commonalty, animals, other than
man, do very little teaching. In a
beehive worker bees, that have never
seen a queen reared, will make queen
WHAT EVOLUTION IS i6i
cells and hatch queens with as much
skill as the best. Their operations are
largely instinctive. Such perform-
ances are not taught, though bees like
most animals of their grade can learn.
Thus, man, though an animal, is
preeminent in a multitude of ways as
compared with his neighbors. He has
the most intricate and complicated
form of social life of which we have
any knowledge. He controls his en-
vironment, devises and uses tools, and
acquiresproperty as no other organism
has ever done. He has developed a
most complex spoken and written lan-
guage which serves him for com-
munication and record, and he teaches
as well as learns. No wonder with all
these exceptional traits that he ap-
pears so strikingly unlike other ani-
mals. It is therefore to be expected
that his evolutionary relations will be
far from usual.
i62 WHAT EVOLUTION IS
When we ask ourselves how im-
portant natural selection is in human
affairs, and whether man's life pro-
gresses with no show of the inheritance
of acquired characters, we pass im-
imediately into a situation where every-
thing that the biologist has taught
seems to be contradicted. At every
step human society seems to have
gone forward by the inheritance of
daily acquisitions and all our humane
institutions, charities, and the like cry
out against such an ideal as natural
selection. This reversal of affairs is,
however, merely apparent.
Every scheme in evolution, whether
it be Lamarckian or Darwinian in its
tendencies, turns on the transmission
of traits, on heredity, and when we
inquire what and how man inherits,
we find him as peculiar in this respect
as he is in others. A child may in-
herit, for instance, a book from its
WHAT EVOLUTION IS 163
parent which means that this partic-
ular book is passed from the parent
dead to the child living. This is the
literal significance of the term inherit.
But less tangible things than a book
may be inherited; the child may in-
herit the parent's habits of thrift and
frugality or of poor table-manners.
Such an inheritance involves learning
through example and applies to an
enormous number of social customs.
Finally the child may inherit the color
of the parent's eyes or his stature or
the like, and this form of inheritance,
which involves a rather figurative use
of the term, we know to be germinal.
The eyes, unlike the book, are not
handed on from parent to child, but a
tendency is transmitted whereby the
child's eyes develop the color of those
in the parent. This tendency, as we
know, is passed on by the tgg or the
sperm. ^Almost no other animal than
i64 WHAT EVOLUTION IS
man inherits as we inherit a book, and
few animals inherit as we do thrift or
table-manners, but all animals inherit
as we inherit eye-colors and the like.
This type of inheritance has been
called germinal, or organic, and may
be contrasted with the other types of
inheritance which have been called
social, for they depend primarily on
man's social condition. Human in-
heritance, then, like other human
capacities, is more complex than in-
heritance in lower animals, for it in-
cludes in addition to their type of
inheritance, social inheritance.
Organic or germinal inheritance
involves the physical traits of our
bodies, hair-color, eye-color, size,
tendencies and resistances to disease
and, less physical in character, tem-
perament and the like. Many of these
peculiarities are inherited in accord-
ance with Mendelian principles; they
WHAT EVOLUTION IS 165
are subject to mutational change and
to natural selection. The part La-
marckism plays in their moulding is
as little known in man as in other
animals.
Social inheritance includes our so-
cial customs, our language and the
way we use it, our daily habits of
honesty or dishonesty, frugality or
wastefulness, and such minutiae as
eating food with a knife or using a
napkin. All these features are learned
either through experience or from a
teacher. None of them comes to us
through the sperm or the tgg. Lan-
guage, one of the most fundamental,
never reaches us as a germinal con-
tribution, but must be learned by each
generation as it matures. To these
traits natural selection has no applica-
tion except in a figurative way, for
though an individual may gain a mate
and offspring in consequence of his
1 66 WHAT EVOLUTION IS
table-manners, there is no certainty
that any of his descendants will show
these traits as they may his eye-color
or hair-color. Social inheritance is
accomplished on what may be de-
scribed as a Lamarckian model, for
the habits of one generation are modi-
fied and, as such, are handed on to the
next. But this, of course, is through
what one individual learns from an-
other and not through the germ, so
that when we speak of it as La-
marckian we are using that term in
a figurative way.
The methods of social inheritance,
then, are very different from those of
germinal inheritance. They have a
superficial resemblance to the La-
marckian conception, and probably it
is this resemblance coupled with our
great familiarity with them in daily
life that predisposes us to the La-
marckian doctrine. It is a strange
WHAT EVOLUTION IS 167
fact, but nevertheless true, that in the
estimation of character or in the for-
mation of friendships we are more
Hkely to be influenced by social than
by germinal inheritances. The color
of the hair or the color of the eye is
under such circumstances of less im-
portance to us than the speech or table-
manners. Thus human inheritance
and in consequence human evolution
extend over a wider field than the
corresponding operations in lower an-
imals and man's uniqueness again re-
asserts itself.
But though we are in this respect
above the rest of creation, we are still
subject to the common law. Not an
epidemic sweeps through a commu-
nity without leaving behind it, in the
young members of the population, a
selected race whose partial immunity
will have its effect on the coming gen-
eration. This is especially noticeable
i68 WHAT EVOLUTION IS
in the arrival of a new disease. The
first coming of Europeans to America
is said to have brought to the native
Indian a variety of entirely novel mal-
adies. Among these was smallpox.
This disease is said to have run like
wildfire among the natives and to have
reduced their numbers to an almost
incredible level. Measles is another
disorder of the same kind. To the
Aleut Indians, of the extreme North-
west, this is a disease of great severity
and has been known to have exter-
minated whole villages. Yet to Eu-
ropeans it is a mere bagatelle due
doubtless to the long exposure of this
race to it and to the partial immu-
nity acquired in the course of time
through selection.
The social habits of man have not
only had their influence on the kinds
of inheritance that he has developed,
but they have impressed his nature
WHAT EVOLUTION IS 169
and in fact that of every other social
organism, in a way too often over-
looked. All such organisms are of
necessity cooperative. It is inconceiv-
able that a social state should exist
otherwise; in every sound state there
must be cooperation between its mem-
bers. In fact the so-called solitary
animals show more or less coopera-
tion, and it is this primitive condition
that reaches a much higher level
of development in all social forms.
Wheeler has very justly emphasized
this feature in the life of the insects.
It is commonly overlooked that, among
most animals, cooperation is as usual
a form of response as competition,
and in social organisms, it is of neces-
sity a primary form of response.
In consequence of his social pro-
clivities, we find, in the evolution of
man, a large body of permanent al-
truistic action which in the form of
I70 WHAT EVOLUTION IS
benevolent acts, charities, and the Hke,
is intended to extend the Hf e of those
who otherwise might meet a speedy
end. Viewed from what might be
regarded as a biological level this
practice at first sight would seem to
demand condemnation. Why not fol-
low the example of the ant and destroy
all defectives ? Surely this would give
added resources to those who are most
able to use them. But a wholesome
human society could not exist under
such circumstances. Such an act as
the destruction of the weak would be
so subversive of the cooperative prin-
ciple, not to mention the higher vir-
tues, that a state endorsing such a
practice would disintegrate and fall..
This principle is so clearly recognized
that civilized man has always striven,
and rightly striven, to succor the un-
fortunate.
Yet if one takes the trouble to look
WHAT EVOLUTION IS 171
through any group of public hospitals
or asylums, he cannot help but be im-
pressed with the heavy burden of
wreckage there represented. In a
harsh world natural selection would
have removed much of this, but the
hand of public benevolence has inter-
vened and warded off the stroke.
Nevertheless, every one must see that
if such a weight as this be sufficiently
increased, society may be crushed by
it. The situation is not an academic
one, but has already begun to bear
heavily on legislatures and through
them on the public. What may be
done to meet, in a humane way, such
a situation ? That the state should ar-
range for those who, in their weak-
ness, come upon it as public wards to
live the length of life that nature
allots them is indisputable. But that
such individuals should be restrained
from perpetuating their kind is like-
172 WHAT EVOLUTION IS
wise reasonable. It will probably soon
come to be a recognized function of
the state to guard against offspring
from those of its wards who, because
of serious heritable incapacity, are on
its hands. How this is to be accom-
plished— through segregation, steril-
ization, or some other effective means
— is a practical question that com-
munities may sooner or later be called
upon to settle. In the performance of
this duty society, like natural selec-
tion, will concern itself not so much
with the life of the individual as with
what that life may transmit to future
generations.
Thus man's nature though in many
respects apparently contradictory to
that of the animals below him is after
all grounded on the same basic prin-
ciples. He has evolved far beyond
the vast majority of creatures and
though he has reached a level where
WHAT EVOLUTION IS 173
conduct is directed in new ways and
under novel conditions, he is never-
theless still subject to the old laws.
There is after all only one kind of life
in the universe.
VI
READING REFERENCES
READING REFERENCES
Darwin, C.
The Origin of Species, 1859.
Many subsequent editions.
De Vries, H.
Die Mutationstheorie, 1901-1903.
De Vries^ H.
Species and Varieties. Their Origin
by Mutation, 1905.
Lamarck, J. B.
Philosophic Zoologique, 1809.
Lamarck, J. B.
Zoological Philosophy. Translated by
H. Elliot, 1914.
Castle, W. E.
Genetics and Eugenics, 1924.
CONKLIN, E. G.
Heredity and Environment, 1919.
Lull, R. S., H. B. Ferris and others.
The Evolution of Man, 1922.
Morgan, T. H.
A Critique of the Theory of Evolution,
1916.
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