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THE MEANING OF
EVOLUTION
BY
SAMUEL CHRISTIAN SCHMUCKER, PH.D.
PROFESSOR OF BIOLOGICAL SCIENCES IN THE
WEST CHESTER STATE NORMAL SCHOOL
WEST CHESTER, PA.
[Illustration]
The Chautauqua Press
CHAUTAUQUA, NEW YORK
MCMXIII
COPYRIGHT, 1913
BY THE MACMILLAN COMPANY
Set up and electrotyped. Published June, 1913
CONTENTS
CHAPTER PAGE
A FOREWORD 1
I. EVOLUTION BEFORE DARWIN 7
II. DARWIN AND WALLACE 21
III. THE UNDERLYING IDEA 44
IV. ADAPTATION FOR THE INDIVIDUAL 87
V. ADAPTATION FOR THE SPECIES 125
VI. LIFE IN THE PAST 149
VII. HOW THE MAMMALS DEVELOPED 192
VIII. THE STORY OF THE HORSE 220
IX. EVOLUTION SINCE DARWIN 233
X. THE FUTURE EVOLUTION OF MAN 249
XI. SCIENCE AND THE BOOK 274
INDEX 293
APPENDIX 299
A FOREWORD
Before my window lies an enchanting landscape. It embraces a stretch
of open rolling country, beautiful as the eye could wish to rest upon.
The sun with its slanting rays is not giving it heat enough in these
winter months to make it blossom in its radiant beauty, but the mind
goes easily back through the few brown months to the time when the
field not far away was waving with its rich yellow grain so soon to be
food for those who planted it. Beyond this field lies an orchard
where, in regular and orderly rows, stand the apple trees whose bright
blossoms in the spring make the landscape so beautiful and whose fruit
in the fall serves so richly for our enjoyment. A little farther on, a
pasture is filled with sleek-coated cows, feeding quietly and
patiently until the evening when they will return to their stalls to
yield their rich milk. Still farther on lies a tract of forest. The
varied shades of the beeches, the tulip poplars and the chestnuts make
an exquisite contrast and give to the landscape its attractive
background framed in by a distant hill. Behind this hill flows a
mighty river carrying on its breast the ships by which we share the
over-abundance of our own blessings with our brothers on the other
side of the sea, from whom in turn we receive of their overplus.
Beyond this teeming river lies a level stretch of fertile land and
then the mighty ocean. On one side of the scene runs a busy highway.
Along this men pass and repass, some on foot, others drawn by their
patient and submissive horses. Still others are carried by the
new-found power of the sunshine imprisoned beneath the rocks in the
oil that has been forming ever since the sun shone down upon the great
forests of the far distant past.
In a pathway to one side, some children are playing. One of them has
laid upon the ground a rectangle of stones divided into four and her
little mind sees before her the house which is teaching her to get
ready for the work that shall come to her in later life. Meanwhile her
short-haired companion is prancing around astride a stick; he too,
little as he suspects it, is getting ready for life.
It needs little reflection to realize that the scene has not always
been what it is. The underlying ground has surely been there longest,
its age vying only with that of the bounding ocean that beats upon the
shore and works the sand into fantastic stretches. The forest has been
there long and so has the stream; the road perhaps ranks next in age;
then come the orchard trees, and most recent of all the waving grain.
People come and go but form no stable part of this landscape. We know
how the grain came to be there, and we understand the orderly
arrangement of the orchard trees; the road too we can explain. How
came the stream there, and how the forest trees? Have they always been
there, or did they too have a beginning? Was there a time when there
was no ocean? When was this time? How came they there?
When the lisping lips of my young child asked me, "Papa, who made me?"
I told him "God," and he knew enough and was content with his
knowledge. After a while he grew older and his inquisitive spirit
began to puzzle with the question of how God had made him. When his
growing mind was ready for the new knowledge I took him to my side and
told him the great mystery of life. I told him how he owed to his
father and to his mother the beginnings of his life, how God gave him
to us. Now a new era opened in his childish mind. As he grows on to
greater maturity he cannot help wondering how the first man was made,
how the trees, and the world came to be. He is no longer satisfied
with the simple statement that God made them. His eager mind wants to
know, if may be, how God made them.
So, in the distant past, in the childhood of our race, the question
was asked, "Who made us?" and the answer was "God." Men formed their
simple conception at that time of how He did it. As the centuries
rolled by and the children of men have learned from creation the story
of its origin a riper and richer knowledge has given them a broader
and finer conception. No less does the reverent student believe that
God created the earth, but he no longer thinks of God as working, as
man works. He no longer feels that it is impious to attempt to read
God's plan in His work; to see how this work has arisen, to see, if
may be, what there is ahead.
This is one of the tasks to which science is now giving itself. The
answer is uncertain and halting. A few things seem clear; others seem
to be nearly certain; of still others we can only say that for the
present we must be content with the knowledge we have. But if we take
the best we have and work over it thoughtfully and carefully, the
better will slowly come, and in time we shall know far more than we
now suspect. Meanwhile, it is the attempt of this book to give to
people whose training is other than scientific some conception of this
great story of creation. Without dogmatic certainty but without
indecision it tries to tell what modern science thinks as to the great
problems of life. It tries to describe the possible origin of animals
and plants, their slow advance, the length of their steady uplift, the
forces that brought it about. It tries to tell a little of the men
who have helped to develop the great idea of evolution, of the great
men who persuaded the scientific world of its truth, and of the later
minds that are modifying and enlarging the idea of the master
evolutionist. It tries to tell what science perhaps vaguely hopes as
to the future. What are we to be? Can we help the great advance?
The Meaning of Evolution
CHAPTER I
EVOLUTION BEFORE DARWIN
Ever since men have been able to think they must have puzzled out for
themselves some way of accounting for their own beginnings. Every
savage tribe with whom we have any intimate acquaintance has some
story that accounts for the origin of the tribe at least, and often
for the beginning of the world. These stories are handed down from
generation to generation and are scarcely questioned in the thought of
most men. In early Greece there was a succession of men whom the world
calls philosophers. These men thought earnestly and deeply on all
kinds of questions. Their method was not our method. The plan of
making a long series of observations, before coming to any conclusion,
was not the habit of their minds. They reasoned out on general
principles what seemed to them must have been the origin of the world.
It is not strange that among these should come, now and then, some one
who in some passage or other should show that there had come to his
mind at least a glimmer of the thought that was later to develop into
the great idea which the modern world calls evolution.
Among the earliest of these was Anaximander, who lived 600 years
before Christ. He thought that the earth was at first a fluid.
Gradually this fluid began to dry and grow thicker, and here and
there, where it thickened most, dry land appeared. When this dry land
had become firm enough to serve as his home, man came up from the
water in the form of a fish. Slowly and gradually the fish, struggling
about on the land, gained for himself the limbs and members he needed
for his new situation and developed into a man. After him other
animals came up in much the same fashion, then the plants, until the
whole world was clothed with its present inhabitants.
One hundred and fifty years later Empedocles announced a new thought.
He said that in the beginnings there were all sorts of strange,
incomplete, and misjointed monsters which swarmed upon the earth,
having sprung up out of the earth itself. Each was a chaos of the
limbs which afterward were to belong to other animals which needed
them more. Slowly and gradually an interchanging came about by which
appropriate limbs fastened themselves to the proper animals. The last
of these misjointed creatures is the one known as the centaur,
half-man--half-horse. After a while, when all the members had found
their proper places, the animals were complete. In one respect this
opinion foreshadowed our later idea. It suggested that the more
perfect animals had arisen out of the less perfect and that the change
came gradually.
Then came Anaxagoras, who was the first to believe that there was
intelligent design back of the creation of animals and of plants. He
thought there had originally been a slime in which were the germs of
all the later plants, animals, and minerals, mixed in a chaos. Slowly
order arose. Out of the mixture settled first the minerals forming the
earth, with the air floating above it, and above the air was the
ether. Out of the air the germs of plants settled upon the earth, and
vegetation covered the mineral floor. Then from the ether came the
germs of animals and of men. These settled among the plants and sprang
up into the animals of the world, as well as the people.
The greatest scientific thinker of early Greece was Aristotle. He had
lived by the seashore and knew better than any other man of his times
the exquisite seaweeds and the still more beautiful marine animals. He
was the first to think of them as a linked series, the higher
developing out of the lower under the pressure of what he called a
perfecting principle. Out of the inanimate rocks had sprung the marine
plants--the seaweeds. From these had developed first "plant animals"
like the sea anemones and the sponges. These grew attached to the
rocks, as plants do. With higher development came locomotion, with
ever-increasing energy. At last man arose, the crown of all creation.
Presiding over all this advance is the "efficient cause," God.
Aristotle rejected entirely the earlier ideas that any of this work
came about by chance. He was certain of the existence of plan and
purpose in the development.
Just a little before the time of Christ the Latin poet, Lucretius,
wrote a poem on "The Nature of Things." Here he describes how in the
early years the beginnings of things in small, disjointed fashion
moved about among each other at first in utter confusion, each trying
itself with the other. After many trials the proper members came
together. When they had been thus placed the warmth of the sun shining
down upon the earth helped the earth to reproduce the same sort of
creatures. So living things came up and flourished. The poem expresses
many beautiful ideas, but the underlying conceptions lack the unity
and grandeur that marked Aristotle's work, which later was the potent
influence in shaping men's minds. It died out after a while, only to
awake in the Renaissance with marvelous vitality, starting the world
to think afresh great thoughts that would not die, but would grow from
that time on with ever-widening scope.
Among the Jews and early Christians the stately and beautiful account
in Genesis sufficed for all the needs of minds fully occupied with
other questions. With the growth of philosophy among Christian minds
again came the need of a satisfactory solution. St. Augustine was
probably the greatest of the so-called "Fathers" of the church. His
mind was eminently philosophical, and he was learned in the writings
of the older Greeks. He believed the language of Genesis to mean that
in the beginning God planted in chaos the seed that afterward sprang
up into the heavens and the earth. He further says that the six days
of creation were not days of time, but a series of causes, and that,
in the order described as these six days, God planted in chaos the
various beginnings of things. These in the fullness of time sprang up
into the world as we know it now. The problem was not a question about
which the church cared to trouble itself, and with the oncoming of the
Dark Ages the whole matter dropped nearly out of the thoughts of men.
When the times began to lighten we find the schoolmen, among the
greatest of whom was Thomas Aquinas. Referring especially to the
authority of his master, St. Augustine, he says that it would be easy
mistakenly to believe that the author of Genesis meant to convey the
idea that on each of the six days certain acts of creation were
performed. It is quite evident, thinks Aquinas, that in those early
times God only created the germs of things and put into the earth
powers which should later become active. After the Creator had thus
endowed the earth he rested from the work, which proceeded to develop
under the influence of these first germs.
Nearly four hundred years later, when Europe had finally awakened out
of the deep and refreshing sleep in which it had fortunately forgotten
much of the past, a new era dawned and modern thought began.
Immediately men commenced to busy their minds with broader problems
than they had been discussing since the time of the Greek
philosophers. The hand of tradition, however, was heavy on them still.
They dreaded to run counter to authority, and did not dare think
unrestrainedly. Descartes shows us how we can understand things better
if we will imagine a few principles by which it will be easy to
account for things as they are. Then he carefully elaborates these
principles as they occur to him; but he has no sooner done so than he
takes care to add, "Of course, we know the earth was not made in this
way."
A little later the philosopher, Leibnitz, believed in an orderly
creation that had advanced by regular degrees, and that the lower
animals had thus developed into the higher. He adds interestingly that
there are probably on some other planets animals midway between the
ape and man, but that nature has kindly removed such animals from the
earth in order that man's superiority to the apes should be entirely
beyond question.
By the middle of the eighteenth century men had begun to think more
fearlessly. The great Emanuel Kant wrote in his younger and less timid
years, "The General History of Nature and Theory of the Heavens." The
great Newton had by his law of gravitation brought order into the
heavens. Kant looked longingly for a greater Newton, who should find a
similar unity in the animal world. He saw the wonderful likenesses
between animals that the anatomist, Buffon, had recently pointed out.
He believed there must somehow be blood relationship between all
animals. He tried hard to conceive of some underlying natural cause by
which all could have come about. As he grew older and his mind became
more cautious he came to think the matter deeper than the human mind
could ever fathom. He gave up the hope and believed the problem of
animal origin and derivation would forever remain insoluble. He
feared there was not in man the power to conceive his own origin.
If we ever wonder why it took so long before the thought of evolution
should have fully dawned upon the world, the answer is not far to
seek. No student of Natural History in ancient or medieval times had
the faintest conception of the enormous number of animals and of
plants in the world. The old Greek or Roman student of Natural History
gives no evidence of knowing more than a few hundred animals. Men have
named to-day, with systematic Latin names, hundreds of animals for
every one that Pliny ever knew, and he knew more than any other man of
early times of whom record has come to us.
In early days men who traveled into foreign countries brought back
accounts of what they saw. The whole Natural History of ancient times
was filled with the most absurd and ludicrous stories of all sorts of
things to be seen in distant lands. Sir John Mandeville tells tales
almost as imaginative and quite as amusing as those attributed to
Baron Munchausen.
Upon the great awakening of the fifteenth century, with its new study
and its wide-ranging travel, an entire change came over the human
mind. Men who journeyed into far countries brought back with them not
only accounts of what they saw, but, so far as might be, the things
themselves. Collections of plants and of such parts of animals as
could be readily preserved soon began to accumulate in every great
center of Europe. It was only a question of time when such
acquisitions must be arranged and classified, but as yet there was no
system by which this could be done. The great Swedish botanist,
Linnaeus, who lived in the eighteenth century, first taught us to give
to each animal and plant two Latin names, the first of these to be the
name of the group, known as a genus, to which it belongs, the second
to be the name of that sort, or species, of animal. The cat, for
instance, is _Felis catus_, the lion _Felis leo_, the tiger _Felis
tigris_, and so on. Linnaeus then arranged the genera (plural of genus)
into families, and these families into orders and so classified the
animal and plant world as far as he knew it. In his earlier years
Linnaeus thought of each species as being utterly apart and distant
from any other. He believed it had been so from the first, each
species having sprung in its complete form from the creative hand of
God. In later life he came to show some evidence of the belief in
development, but his great work is all built on the idea of the entire
fixity of species.
About this time we find in the writings of Buffon, the French
naturalist, many indications of an idea approaching our modern
conceptions of evolution. He felt sure the pig could not have been a
special creation, because he had four toes, two of which, with all
their bones and their hoofs, are quite useless to him. We now call
these toes "vestigial," and know the pig's ancestors used them,
walking on four toes and not on two, as at present. Buffon believed
there were degenerations as well as developments, and considered the
ape a degenerate man. He conceived these changes to be brought about
by what he called the favors and disfavors of nature. He varied much
in his opinions in various parts of his career and occasionally is
smitten either with conscience or with fear of authority. Then he goes
back and says it is all a mistake and each animal is the product of a
special act on the part of the Creator.
A little later, in England, Erasmus Darwin, the grandfather of Charles
Darwin, who was subsequently to establish the evolution theory, wrote
a long and elaborate poem called the "Temple of Nature." In this we
find a remarkable prevision of many of the principles which were
afterward to be warmly advocated and disputed during the growth of the
idea of evolution.
"Hence without parents by spontaneous growth,
Rise the first specks of animated life.
* * * * * * *
Thus as successive generations bloom
New powers acquire and larger limbs assume."
Erasmus Darwin recognized the struggle for existence, but he saw in it
only a check against overcrowding, and not an active factor in the
development as his grandson Charles came to see it. It is possible the
elder Darwin's views might have been taken more seriously had he not
clothed them with the form of verse. In these days it seems quite
ludicrous to think of giving to the world a new scientific concept or
a new phase of philosophy in verse.
The beginning of the nineteenth century gives us the first really
great contribution to the idea of evolution. Under more favorable
surroundings, this idea would have budded and become the parent stock
of our modern theories. The chill frosts of adverse criticism by those
in authority in science nipped the budding idea and so set it back
that only of late years have men come to realize its strength and
power. The Chevalier de Lamarck, serving in Monaco, was attracted by
its rich flora to the study of botany. Coming later to Paris, he
became acquainted with Buffon and was led by him to publish a Flora of
France, using the Linnaean system of classification. He was appointed
to the chair of zooelogy in the Jardin des Plantes, and was given
especial charge of the invertebrate animals, comprising all the
members of the animal kingdom except those with backbones. After
seventeen years of work over these forms, during which he wrote
several books describing them, he finally published the great work on
which his fame depends. This was the "Philosophie Zooelogique." In this
treatise he taught that the animal kingdom is a unit and that all its
members are blood relations; that the members vary with varying
conditions; that this variation results in continued advance. In all
of these points Lamarck is at one with modern thought. His idea of the
method by which the variation comes about has been accepted and
rejected; modified, reaccepted, and again rejected.
Lamarck's conception of the cause of progress was somewhat as follows:
The desire for any action on the part of an animal leads to efforts to
accomplish that desire. From these efforts came gradually the organ
and its accompanying powers. With every exercise of these powers the
organ and its corresponding function became better developed. Every
gain either in function or in organ was transmitted to those of the
next generation, who were thus enabled to start where their parents
left off. The general environment constantly gave the stimuli that led
to the adaptive changes.
American zooelogists have been especially inclined toward Lamarck's
ideas. Until Weissmann startled the scientific world with his sharp
denial of the possibility of transmitting to offspring any growth
acquired by the parents, all seemed well. There is a tendency now to
insist once more that slowly and gradually, in some perhaps as yet
unexplained way, external factors do influence even egg cells, and
gradually acquired characters do reappear in the offspring.
The blighting setback these views suffered came from the criticisms of
Baron Cuvier. This genuinely remarkable man had built up the study of
comparative anatomy. To him students flocked from all sides. Among
these one of the most brilliant was Agassiz, the Swiss naturalist, who
later came to this country, filled with Cuvier's ideas. This great
teacher believed that species are fixed. He knew better than any man
of his times the wonderful similarity in structure between animals of
a given class. He attributed this not to any real blood relationship
between the animals. They were alike because they had been made by the
same Creator. This great Artificer worked along four main lines, and
hence animals could be divided into four groups. Many who have studied
text books on zooelogy written in this country by Agassiz and his
followers will remember the four classes--Radiates, Articulates,
Mollusks, and Vertebrates. Agassiz was such a wonderful teacher and so
genial and so lovable a man that his opposition to evolution held back
the advance of the Darwinian idea in America as Cuvier's influence
had held back the Lamarckian idea in Europe. For the brilliant Cuvier
simply laughed before his students at each "new folly" of Buffon and
of Lamarck. Under this ridicule the influence of both men withered and
died.
A little later the great poet, Goethe, turned his attention to the
problem of evolution, giving an interesting account of the
metamorphoses of plants. He declared, also, that the human skull is a
continuation of the backbones of the neck, and that these bones have
been transformed into the present skull. But his great genius as a
poet drew his attention into other fields. Haeckel points out that if
Goethe had known Lamarck's work his genius would have gained for the
"Philosophie Zooelogique" the interest and respect of the reading
world. But Cuvier laughed it out of court, and only in comparatively
modern times, since Darwin's work has set the world thinking anew, is
Lamarck's career recognized at its true value. Lamarck should have
been the founder of the evolution theory. But the time was not quite
ripe, and it remained for Charles Darwin to announce his idea,
sustained and fortified by years of careful observation and thoughtful
reflection.