The Meaning of Evolution
by Samuel Christian Schmucker · English · Gutenberg #29422 · 429,485 chars · public domain (US)
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Title: The Meaning of Evolution
Author: Samuel Christian Schmucker
Release date: July 16, 2009 [eBook #29422]
Language: English
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*** START OF THE PROJECT GUTENBERG EBOOK THE MEANING OF EVOLUTION ***
Produced by Juliet Sutherland, Chris Logan and the Online
Distributed Proofreading Team at http://www.pgdp.net
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,
Linnæus, 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. Linnæus 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
Linnæus 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 Linnæan system of classification. He was appointed
to the chair of zoölogy 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 Zoölogique." 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 zoölogists 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 zoölogy 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 Zoölogique" 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.
CHAPTER II
DARWIN AND WALLACE
We have seen in the last chapter that whenever men have actively
thought they have attempted to explain the origin of plants and
animals as well as of themselves. No one who wrote previous to the
time of Charles Darwin had expressed any idea concerning this matter
with force enough to convince any large portion of the thinking world.
If Lamarck had fallen on better times, if the great Cuvier had not
laughed him to scorn, if Goethe had found him out and made him known
to the world, evolution might have come into its own sooner. None of
these conditions arose, and it remained for Charles Darwin to give to
the world in clear and cogent form the thought of evolution. He
gathered so much material before he expressed his opinions, and looked
at the matter from so many sides that, when he published his results,
he had foreseen most of the objections which were subsequently to
arise in opposition to his announcement. Charles Darwin is recognized
to-day as the father of the evolutionary movement.
It has been sometimes said in recent years that Darwinism is dead, and
there is a sense in which this is true. Unmodified and unassisted
natural selection is not to-day considered by most scientists a
sufficient agent for producing evolution. But everyone connected with
the subject acknowledges Darwin as the master, and says that it was
his work which converted the world to a belief in evolution. We can
have no better preparation for an intelligent understanding of this
subject than to consider carefully the life of this remarkable man and
the circumstances under which he came to his epoch-making conclusions.
Evolution has taught us to attempt as far as may be to account for man
on the basis of his heredity or of his environment. It is interesting
to note that both of these factors in Darwin's case were entirely
favorable. In the latter part of the eighteenth century Erasmus Darwin
had given to the world an astonishing poem in which he anticipated not
a little of the thought which his more famous grandson was to make so
widely known. Josiah Wedgwood had learned to make for England her most
famous pottery, no quality of which was more widely recognized than
the sterling patience with which it was made. Erasmus Darwin, with his
scientific proclivities, and Josiah Wedgwood, with his sturdy common
sense and patient workmanship, united to give Charles Darwin his
inherited tastes, for he was a grandson of both. Born in 1809, on the
banks of the Severn in England, Charles Darwin was the delicate son of
a practicing physician of modest but sufficient means. Owing to his
lack of early vigor, Darwin spent much time in the open air, and in
his excursions about his home was chiefly interested in collecting
beetles. This taste, which lasted through all his young manhood, is
the one early indication of the traits that were later to develop. At
first in the day-school and later in the preparatory school Charles
Darwin was anything but a satisfactory student. Even a kindly desire
later to make the most of him makes it impossible to find traces of
any especial fondness for earnest study. He himself believed his
education to have been nearly useless, although he doubtless
under-estimated its value. At the age of sixteen he went to Edinburgh
at his father's desire, to study medicine. The sight of the
dissecting-room nauseated him completely, and he refused to continue
working in it. Later an operation which he witnessed in a clinic at
the hospital sickened him so thoroughly that he declined to attend
further operations. It became evident that the young man was not
adapted to the life of a physician. The next move was to educate him
for the church, and for this purpose, at the age of nineteen, he went
to Cambridge. Here it soon appeared that he was no better adapted to
the ministry than he was to the practice of medicine, and his
university career went on in very desultory fashion. Most of his work
was distinctly neglected, but two of the men he met there were to
influence largely his future life. Henslow, the botanist, was
unusually fond, for a professor in those days, of work in the field.
Charles Darwin's tastes coincided with those of Henslow, with whom he
formed an intimate friendship. He was always welcomed as a companion
on the field trips. Though he studied little of botany in the
classroom or laboratory, he was constantly with Henslow or with
Sedgwick in the field. Sedgwick was the professor of geology, and of
him Darwin was particularly fond, and under him did much the largest
amount of his study. When he came up for graduation he ranked tenth of
those who "did not go in for honors," a not very remarkable class
standing. He was still required to put in two years of residence, and
during this interval he spent most of his time with Sedgwick in the
study of geology in the field. Returning to his home after a
geological trip into Wales, Darwin found awaiting him a letter from
Henslow, offering him an appointment that opened to his ardent mind
the door to a career after his own heart.
The British nation, being the greatest commercial nation of the globe,
has the greatest need for accurate charts of all the seas. Frequently
she has sent out great charting expeditions to various parts of the
world. One of these was to go out in Her Majesty's ship, _Beagle_, for
a voyage around the world. Captain Fitzroy was in command, and he was
especially commissioned to map the coast of South America from La
Plata to Cape Horn and up the western side. In addition to this work,
by carrying a set of accurate chronometers, he was to check up the
longitude of the various ports to be visited in this circumnavigation
of the globe. It was customary on such expeditions to carry a young
man whose duty it was to study the natural history of the countries
visited on the trip. The salary of such a naturalist was so small that
an experienced man could scarcely afford to take the place. Therefore
the appointment usually went to a man rather of promise than of
achievement. Through Henslow's influence, Charles Darwin was offered
this position in 1831. Darwin hastened to obtain his father's
permission, but the elder Darwin at first declined to consider the
matter. He felt that his son had not made such use of his time at the
university as warranted the hope that much could be expected of such a
journey. He believed it necessary that Charles should have some means
of earning an adequate living before he could think of devoting his
time to science. Charles found an efficient advocate in the person of
his uncle, Josiah Wedgwood, Jr. Together they persuaded the father of
the propriety of giving to Charles this opportunity to follow out his
real tastes and ambitions. Accordingly, at the age of twenty-two, we
find him embarked on a journey around the world. In the cabin of the
_Beagle_ he had abundant time, in his long sail across the Atlantic,
to read the two volumes of Lyell's "Elements of Geology," which
Henslow had handed him, with the suggestion that he read it, but on no
account believe it. Filled with the love of geology as Darwin was,
this epoch-making book was exactly the stimulus needed. Lyell had just
begun to persuade the world that to understand the past we must study
the present. In the forces now at work he saw cause enough to account
for all the history of the past of the earth.
There is little doubt that this book was one of the most potent
factors in determining the bent of Darwin's mind. His entire
educational experience had failed to appeal to him. It is fortunate,
we now know, that this was the case. If the university course of the
time had really seized him it would have made but one more student
like hundreds it was turning out each year. For most of us this is the
happy event. Now and then comes the rare spirit to whom all of this
fails to appeal because he is ready for something better. Such was the
spirit of Charles Darwin. He started on his journey with a mind
singularly free from prepossessions. In the long hours of this sailing
voyage across the Atlantic Ocean Darwin had time to read and ponder
Lyell's weighty words. By the time he reached the Brazilian shore he
was filled with Lyell's conception that the present is the child of
the past, developing out of it in orderly sequence. Lyell expressly
denied that this is true of the animal and plant world. He applied it
only to the face of the earth, with its mountains of uplift and its
valleys of erosion. But the underlying principle of an orderly
development under the action of natural causes was there. In Darwin's
mind this at once found acceptance, and was destined to a fruition its
author had expressly disclaimed.
The narrative of this voyage, as subsequently written, describes the
islands visited by the _Beagle_ in crossing the Atlantic Ocean. The
contrast between the simple and general interest in these islands and
the care with which Darwin described the Galapagos and the Keeling
Atoll visited later in the voyage are speaking evidence of the rapid
development going on in the mind of the young naturalist.
Reaching the shore of South America, Darwin first turns to its
geology. But before long the animal life attracts his attention. In
the Brazilian forest Darwin had his first experience of the wealth of
animal and plant life in the tropics, and, like all naturalists, he
was very enthusiastic over it. Among the animals that particularly
attracted his attention was the sloth, a peculiar creature climbing
slowly about the trees, small of size and sluggish of habit. Another
animal that interested him greatly was the little armadillo with its
interesting habit of curling up in its plated skin.
Captain Fitzroy soon finished what work he was required to do in this
neighborhood, and Darwin was called back to the _Beagle_ to continue
his voyage. When they arrived at the mouth of La Plata their most
serious work began. Here there was much tedious charting for Fitzroy,
and Darwin could now leave the vessel for a lengthy trip on shore.
This was doubly welcome. Seasickness was nearly constant with Darwin
while on this entire voyage and every opportunity to work on land was
eagerly seized. This region, too, was rich in objects of interest and
in strange people. While exploring the pampas, beyond Buenos Ayres,
Darwin came across the skeletons of the great mammals some of which
Cuvier had previously described. He studied these bones with much
care, and recognized at once in the megatherium a great similarity in
structure to the sloth he had seen in Brazil. The enormous skeletons
of the glyptodons struck him also as strangely similar to that of the
armadillo. One evening, seated alone in the broad expanse of the
pampas, the idea suddenly swept over him, stimulated, of course, by
his study of Lyell: "Can it be that the little armadillo and the sloth
of to-day are the degenerate descendants of the enormous megatherium
and glyptodon of the past?" But his mind was not yet ready to accept
so bold an idea and he swept it aside.
The people of this wild neighborhood interested Darwin very greatly,
and he describes them with care. In this connection a charming trait
of Darwin's character comes beautifully in evidence. The absolute
purity of his mind, his utter freedom from grossness, shows clearly in
his account of the first really semi-civilized people he had ever
seen.
A little later, while exploring Patagonia, Darwin noticed the
terrace-like formation of that desolate country. A flat near the sea
was succeeded by a rapid rise, then came another flat. Three of these
terraces in succession stretch back toward the Andes. At the base of
the high terraces Darwin found marine shells, largely similar to those
of the ocean beach so many miles to the east. His study of Lyell led
him to suspect at once that this portion of South America had been
raised in successive stages out of the bed of the Pacific. When they
passed around Cape Horn and up the western coast he hunted for
similar beach marks on the sheer western face of the Andes, and found
them without difficulty, confirming his idea of the recent rise of
this end of the Andean chain.
The _Beagle_ continued its voyage up the western coast of South
America until it reached Peru. Once more the abundance of tropical
life is under Darwin's eyes, but now it is the life of an entirely
different section. The dry climate of Peru furnished him with an
environment distinctly unlike that of the moist Brazilian forest. He
collects now with avidity, gathering especially insects and birds.
Then the ship turned its prow westward across the Pacific, only to
stop five hundred miles out at the Galapagos Islands. This little
group he studied intensely, collecting large numbers of insects and
birds. He had not worked over his collection long before he realized
that each island in the group had peculiarities which marked its
animals from those of any other island. Whenever two islands were
close together in the group the differences in their fauna were found
to be comparatively slight. If, however, he examined the animals from
two islands lying at opposite ends of the group, the differences were
always considerably greater. There was, however, a strong general
resemblance among them all and a distant though not so strong
resemblance to the corresponding animals of the Peruvian coast. On
leaving the Galapagos group, Charles Darwin writes in his diary the
suggestive observation that this little group of rocky islands seems
to be one of the greatest centers of creative activity. It was this
interesting resemblance of the animals of these islands to each other
and to those of the Peruvian coast that finally persuaded Darwin that
they were all related and were all descended from those of Peru. For
the rest of his life, with an intensity which increased with each
year, Darwin persisted in a patient search for the possible agencies
by which such change could have been brought about. The problem,
however, was temporarily eclipsed by a pressing geological question
aroused by his visit to the Keeling Atoll. Here his investigation of
coral reef formation absolutely captivated him. In the case of most
coral islands in the Pacific Ocean the reef exists as a circle of
coral enclosing a lagoon of water. In the center of this lagoon stands
commonly a rocky island. It is plain that this is the foundation on
which the coral built. But, in the case of the Atoll, the coral ring
was present and so was the internal lagoon, but there was no rocky
island. The key to the solution came with an interesting discovery.
Darwin began to put down a grappling iron on the outer side of the
reef and to drag up coral. The farther away from the reef he went the
deeper was the water from whose bottom he pulled the coral. What at
first puzzled him was the fact that so long as he dragged up his coral
from depths of a hundred feet or less the coral was alive. Whenever he
went to depths of much more than a hundred feet, his coral was always
dead, though he was evidently pulling it from situations in which it
had grown. Then Darwin remembered the rising Andes, lifting themselves
out of the bed of the Pacific. Here was the correlated movement. The
bottom of the ocean here was sinking. As it sank it dragged down the
corals with it. But the descent was so slow that new corals could
build on top of the others fast enough to keep the reef up to the
surface of the water. At the rate of growth of coral, this would seem
to mean that the bottom could be sinking at a rate of only a few feet
a century. But while the reef could keep up to the surface, the rocky
island must slowly sink. Darwin inferred that there must be a rocky
summit within the lagoon, below the surface of the water. A little
sounding soon discovered this island, and the verification of Darwin's
theory of coral reef formation was at hand. The description of this
Atoll and of his theory of its formation won for Darwin the esteem of
geologists when he later presented it in book form.
The voyage was continued around the Cape of Good Hope. Pursuing the
usual course of sailing vessels, the _Beagle_ touched once more at
Brazil, returning home to England in 1836, after an absence of five
years. Charles Darwin himself believed this trip to have been both his
education and his opportunity. He had started on it a rather careless
and indifferent student. He returned from it the most painstaking and
patient naturalist the world has ever known. His father, who had
hardly consented to his going because he believed him not stable
enough to be intrusted to his own devices for so long a period, was
profoundly moved at the sight of him on his return. Believing in
phrenology, as did many of the physicians of his time, his father
turned to his mother and said, "Look at the shape of his head; it is
quite altered"; which, translated into the language of to-day, would
read, "How wonderfully the young man has developed."
A part of Charles Darwin's duty to the British Government was to write
a narrative of the voyage, and this account of his trip upon the
_Beagle_ is one of the great classics of travel in the English
language. It won the confidence and respect of a wide circle of
readers. In his next book he published his observations made at the
Keeling Atoll and announced his theory of the formation of coral
islands. This was a distinctly scientific investigation, and it won
such immediate favor among geologists as to increase materially the
young man's reputation. No one man is ever widely enough acquainted
with the animal world to classify all the specimens gathered on such
an expedition. In accordance with custom, Darwin began distributing
his collections among specialists. Each of these was to identify and
describe, to name, if necessary, the kind of material he knew best.
Among others, Darwin had a considerable collection of barnacles
gathered from boats and wharves in all parts of the world. As he could
find no one sufficiently acquainted with these creatures to classify
them he decided reluctantly to work them up himself. For about eight
years much of his spare time was given to this painfully exacting
work. He expresses himself as fearing it was a waste of time. Few
systematic workers will agree with him. He did his work so well that
it has been unnecessary for anyone to do it again. In addition it
gained him the esteem of a new circle of scientists and that a
decidedly exclusive circle.
The publication of these books did much for Darwin. His narrative of
the voyage gained the good will of cultured England in general. The
book on coral reefs won the geologists. His "Manual of the
Cirrhipedia" (as the barnacle book was called) secured the attention
of systematic zoölogists. The time was not far distant when he would
need every aid possible toward gaining and keeping the regard of men;
for he was to promulgate a theory that would arouse the bitterest
opposition and the keenest scorn.
All the while Darwin was working on these books his mind was quietly
busying itself with what he called the species question. The more he
studied the material collected on his long tour, the more confident he
became that the animals of the present are the altered descendants of
the animals of the past. He tried patiently to work out every
conceivable hypothesis to see whether he could account for the
alteration. He felt quite sure animals changed, but how they changed,
and why, he could not for a long time conceive. He knew that gardeners
were constantly producing new varieties of plants, and that animals of
various breeds were clearly the descendants of other and familiar
varieties. Accordingly he began to study the methods of animal and
plant breeders, to visit their farms, to open correspondence with them
and read all their trade journals, to undertake experiments in the
breeding of plants. The longer he worked the more confident he became
of the reality of the change; but for a long time no glimmer of the
cause by which it could be brought about came to his mind. In 1838 he
came across a book by Malthus called "An Essay on Population," in
which the author shows that, whereas man increases by a geometric
ratio, he cannot hope to increase his food supply in more than an
arithmetic ratio. That is, while the food might increase like the
series 2-4-6-8-10, the population would increase like the series
2-4-8-16-32. On this basis it is only a question of time when the
earth will be too full of people for it to be possible for the food to
sustain them. Malthus added many observations and suggestions, but
this is as much of the book as interests us in this connection. Here
was the idea that suggested to Darwin his agency for producing the
change of the animals of the past into those of the present.
The number of animals of any particular species remains practically
the same. There may be a few more one year, and a few less another,
but on the average, year by year, the number of toads, the number of
blacksnakes, the number of field mice, remains sensibly the same.
Sometimes the rise of man brings an end to the wild population, and so
in the past animals have dropped out of the race. Yet in the long run
and for a considerable time the number of any species is constant. But
each animal produces offspring in quantities sufficient to far more
than replace himself as he dies out. In other words, animals increase
not by addition but by multiplication. Too many are born for all of
them to live. What becomes of the great mass of them? The answer is
they die; most of them die young. Only a few fortunate individuals,
favored by being a little stronger, a little more cunning, a little
more attractively colored than their mates, survive to carry on the
race.
The skillful gardener, looking over his flowers, finds a plant of more
than ordinary beauty and thrift of growth. When it comes to maturity
he keeps its seeds separate from those of the rest and next year
plants them by themselves. As they come up he weeds out all unthrifty
plants, only allowing the strongest to come to maturity. As they break
into bloom he plucks away all whose flowers do not come up to the high
standard he has set for himself. After a while he has but a few plants
left, but these are the thriftiest and bear the most beautiful
flowers. Again he allows these to mature and selects the seed of the
very finest. Next year the process is repeated. After a few
generations, usually three if the man is skillful enough, he has a
definite strain of flowers that will thereafter come true. This is the
process of artificial selection as carried on by man.
Darwin saw that Nature is constantly carrying on a similar process.
She produces seeds enough on almost any plant to clothe the world in a
few years if all of them could fall into proper ground and thrive like
their parents. A friend of mine found a mullein stalk that bore more
than seven hundred seed pods and averaged more than nine hundred seeds
to the pod, a total of more than six hundred and thirty thousand
seeds. If each of these could find lodgment on a plot eighteen inches
square, produce a similar number of seeds and plant them all, the
result would be overwhelming. The fourth generation would cover land
and sea, from pole to pole, one hundred layers deep. But there is no
such danger. Year by year the mulleins hold their own and no more. Any
particular field may have more or less, but in the long run the
average for a district is about the same. Some of the seeds are poor
and thin. These scarcely sprout. Others spring up into thin-skinned
plants, and the first frost nips them. Still others lack the woolly
coating in its finest abundance, and the browsing animals eat these.
Others lack power to put out a wide-ranging root supply and the first
drought kills these. Still others fail to send up a vigorous stem and
the passing animal knocks them over and they die. Of the few that are
still surviving, some produce such small and inconspicuous blossoms
that the insects scarcely see them, and they go unfertilized. In the
end only the aristocrats of the group are left, aristocrats in the
best sense of the word. These are strong, thrifty, and beautiful, and
are provided with every defense known to the mullein world. From these
the mulleins of the next generation will spring. Again Nature will
select the best of these, by a repetition of the same process. Thus
year by year the stock is improved. Any new feature that is favorable
helps its possessor to survive, and, if happily mated, will show
itself after a while in the entire group. This, in brief, is the
underlying idea of Natural Selection, as Darwin conceived it.
In 1842, at Lyell's suggestion, Darwin wrote a short sketch of his
ideas which he, two years later, expanded into a somewhat larger
account. The manuscript of these early views of the theory was
completely lost and has only been recovered within the last few years.
It was recently published under the editorship of Charles Darwin's
son, Francis. It is astonishing to see how clearly the first short
sketch states the underlying conception which all of Darwin's
subsequent work amplifies. Hooker was constantly urging Darwin to
write out his whole theory in the form of a book, and Darwin had begun
to do so in 1856.
Meanwhile, down in the Moluccas, Alfred Russell Wallace had been lying
sick of a fever contracted during his exploring expedition in that
neighborhood. He had been studying the distribution of the animal life
of the Malay Archipelago. Overcome by sickness, as he lay in bed, he
began to think over a book which he had read not long before, "Malthus
on Population." Wallace had been pondering on the question of the
origin of the animals of the Malay Archipelago. He had not the
faintest knowledge of what Darwin was doing, but was influenced, of
course, like Darwin, by what he read in Malthus. Interesting to
relate, he had come to exactly the same conclusions, writing his
opinions in the form of an essay. By the strangest sort of
coincidence, he sent this essay to Charles Darwin, asking him to read
it, and, if he thought it was not altogether too foolish, to send it
to Lyell for publication by the Linnæan Society. Darwin read with
utter astonishment this essay containing views so absolutely like
those that had come to him from his own long series of observations
and reflections. With uncommon magnanimity his first impulse was to
withhold his own publication entirely, but to this Lyell and Hooker
would not for a moment consent. They were determined that Darwin
should give them his long series of notebooks as evidence of the
independence of his work and that he present to the Linnæan Society,
simultaneously with Wallace's paper, one of his own upon the same
subject. In this manly form both essays were read at the next meeting
of the society. The joint papers provoked instant discussion and
prompt opposition. The world at large scarcely admitted a possible
doubt of the fixity of species. Men generally believed the idea to be
absolutely irreconcilable with their religious faith. Any question of
the fact that the species of to-day exist practically as they had been
handed down to the earth in the beginning by the Creator himself
seemed to most men a direct blow at religion. At this time a very
large number of natural scientists were clergymen, hence the
opposition had abundant and influential support. The storm grew
fiercer and more widespread. The publication in 1859 of Darwin's great
book on "The Origin of Species by Means of Natural Selection or the
Preservation of Favored Races in the Struggle for Life" added fuel to
the flame.
In 1860 the British Association met in Oxford, and Bishop Wilberforce,
the retiring president, in accordance with the custom of the society,
gave a summary of the advance of science, especially during the
preceding year. Everyone knew perfectly that the bishop would deal
with the species question, and that he would handle it severely.
Darwin was prevented by his usual ill health from being present at
this meeting, but Huxley was there to see that their side of the
question received proper attention. The bishop made a lengthy address,
in the major portion of which he brought forward entirely worthy
objections to Darwin's theories. Toward its close his feelings
overmastered him and he departed from his manuscript and unburdened
his mind. The lack of stenographers in those days and the tenseness
of the moment, which made everyone forget to take down what was said,
make it impossible to tell exactly what happened. It seems that Bishop
Wilberforce, appealing to the prejudices of his audience, said, in
language that now seems ludicrous but then was terribly bitter:
"However, any of us might be willing to consider ourselves descended
from an ape upon his father's side, no one would so demean his
mother's memory as to imagine that she could possibly have shared in
this descent." Huxley, who had waited patiently for the close of the
bishop's address, saw immediately the fatal mistake. Turning to his
companion beside him, he said, "The Lord has delivered the Philistine
into my hands," and, rising, he hurled back at the bishop the
indignant reply, "I should far rather owe my origin to an ape than I
would owe it to a man who would use great gifts to obscure the truth."
The bishop had made the mistake, and the struggle was on. Year by year
it raged. One by one the scientists, first of England, and then of
Germany, took their stand by Darwin. Huxley in England and Haeckel in
Germany were the foremost advocates of the Darwinian idea. Long and
fiercely the battle raged; slowly and gradually men began to see that,
instead of undermining religion, the idea of evolution uplifted
creation and made it not a strange happening in the distant past, but
a divine activity through all time. But the battle had by no means
subsided when one day came the sad news that Darwin's heart, so long
feeble, so serious a hindrance to his work, had beaten its last on
April 19, 1882.
His own people wished to bury Darwin quietly at his home in Down, but
Darwin now belonged to the nation. A petition signed by many public
men was sent to the Dean of Westminster, asking that his body might be
granted burial in the Abbey. Probably no greater honor can come to man
to-day, and fortunately Dean Bradbury was broad-minded enough to
acquiesce. So it came to pass that the church that had so long
believed him her enemy, that had first so bitterly fought him, came at
length to see that he added a new dignity and worth to her faith, and
took him to her bosom. Darwin's body lies buried in the Abbey.
In all the glorious company of immortal dead whose earthly frames are
gathered in England's great mausoleum, there is no other one who has
done so much to modify the mind of thinking man.
CHAPTER III
THE UNDERLYING IDEA
We have seen in the preceding chapters how the idea of evolution
worked its way through the minds of men. Man after man got a glimpse
of the idea, even among the ancient philosophers. But no one could
speak convincingly on the subject before modern times, when a wider
acquaintance with the animal world gave a body of facts on which it
was safe to base conclusions. Even then the idea eluded men, until
there came a worker trained by a long voyage around the world in which
he had nothing to do except to study nature. He finally gathered in
his mind material sufficient to convince himself not only of the truth
of evolution but of the process by which this evolution was brought
about. Every scientific principle is simple in its basal idea. In
actual life the action of the principle may be so bound up with others
as to need a skillful mind for its detection. But under all the
complexities and modifications, like a silver thread woven into a
cloth, runs the basal idea. Until a master has detected it the
presence of it may be unsuspected. But once discovered and expounded,
thereafter anyone may follow out its workings. So it is with the
Darwinian idea of selection. It waited long for a discoverer, but,
once found, we cannot but wonder why men did not see it earlier, it is
so simple.
Mr. Darwin's mind, while slow and cautious, had a wonderful
perseverance. When he had finished his work he had not only given a
clear account of the process of evolution, but he had foreseen almost
all the valid objections that were afterward to be brought against his
theory. Some of them he had explained quite fully; of others he
indicated a possible explanation; of still other questions he
confessed that as yet they were not plain. But the whole theory is so
simple in its fundamental ideas that it has completely revolutionized
the whole aspect of modern biology and, indeed, of modern thinking in
many lines.
There are four underlying conceptions, each simple in itself, which
must be clearly perceived before one can understand Mr. Darwin's
theory of "Natural Selection." The first of these is known under the
name of Heredity. It is a matter of common observation that every
animal or plant produces offspring after its own kind. Under no
conditions would we expect a duck to lay an egg from which could hatch
anything but a duck. No Plymouth Rock chicken mated with another of
her own kind will ever lay an egg that will produce a Rhode Island
Red. We may believe that the dog has descended from some form of wolf,
but it is not meant that at any particular time in the past any wolf
mated with a wolf ever produced pups that were anything but wolves.
Why this should be so is one of the most profound problems of biology.
Nothing but the fact that the process has gone on under our eyes for
so long a time could blind us to its marvelous character. To open the
egg of a chicken and examine it by the most refined methods known to
science is to find in it absolutely nothing that could be by the
widest stretch of the imagination considered anything like a chicken.
The biologist who has examined such eggs before and knows them in all
stages of the process may recognize in an egg which had been incubated
for a short time something which his previous experience tells him
will become a chicken. But it has not the faintest resemblance to a
chicken until later in its development. In early spring one may gather
pond snails from any country stream and place them in an aquarium. The
change from the cold water on the outside to the warmer water of the
aquarium and the temperate climate of the room hastens the process
which in the stream would not take place until later. In a short time
one may find fastened to the glass side of the aquarium the little
mass of transparent jelly which surrounds and protects the delicate
eggs of these creatures. Fastened as they are it is easy to direct a
magnifying glass so as to observe the change which goes on within
these transparent eggs. It is even possible to apply a microscope in
such a way as to watch the transformation under the low power of the
glass. At first the eggs are as clear as water, having at the center a
slightly yellowish spot. This central mass divides and subdivides
until the separated sections grow so small and numerous as to lose
individuality. Then the mass begins to press out here and dent in
there. After a little while a double line of fine, hairlike
projections runs around the creature. These hairs wave in such fashion
as to make the embryo snail revolve slowly in its egg. A little later
and swellings become more pronounced over the surface. One side
flattens; the rotary motion stops; eyes appear at the front of the
animal; a hump on the back begins to be covered with a shell, and the
little creatures, pushing from the jelly, start their life journey on
the side of the aquarium. Why did it happen? How did it happen? Here
we have seen creation at work. Here surely the hand of the Creator is
working in the only sense in which the Creator may be properly said to
have a hand. How the history of the substance out of which the egg was
produced provides for the future development of that egg no man has
yet clearly said. This is not to say that we shall never know, still
less is it to say that this can never be known. Ralph Waldo Emerson
has said that there is no question propounded by the order of nature
which the order of nature will not at some time solve. If he is right,
and I believe he is, we shall at some time know how it is that this
egg produces this snail. But, as I said before, nothing but the
frequency with which the process goes on under our eyes could possibly
blind us to the marvel of it.
The regularity with which each animal reproduces its kind is no more
surprising than the faithfulness of that reproduction. Some of our
birds have wonderful markings on their plumage. It is astonishing to
see with what fidelity the feather of a bird may reproduce the
corresponding feather of its parent. It will occur to everyone how, in
the human family to which he belongs, there is some little peculiarity
which, while not appearing in every member of the family, when it does
appear is remarkably uniform. It may be only the droop of an eyelid,
it may be a tendency to lift one side of the lip more than the other,
it may be the peculiar shape of a certain tooth in the set, and yet
when it appears it comes with astonishing similarity in all who
possess it. So much for the principle of Heredity.
The second great underlying idea is known by the name of Variation. We
have just been dwelling on the regularity with which parents produce
offspring like themselves. We must now draw attention to the fact
that, while it is true animals must absolutely belong to the same
genus or species, even to the same variety, none the less no animal is
exactly like his parents. Furthermore, in a group of animals produced
at the same time from the same parent each one will have at least some
small point in which he differs from every other one in the group. Two
animals may look alike at first to the undiscerning eye, but a keen
analysis of the measurements of the various parts of their bodies will
show distinct differences. This is quite as true among lower animals.
A toad may lay a double string of four hundred eggs which may be
fertilized by the same male at the same time. These eggs may develop
into tadpoles in the same pool not over a foot square. Within a few
weeks these little toads may have gained their legs, lost their tails,
and all may have left the water and taken to the ground upon the same
day. Already the careful observer will notice differences among them.
Some are larger than others, having grown more rapidly even though
their surroundings were exactly the same; others are more skillful in
their peculiar method of throwing the tongue at an insect they wish to
catch. Still others will be differently colored. They might be
arranged to show a considerable gradation between the lightest and the
darkest of the group, though there may not be anywhere in the row a
considerable gap. It is variation in animals of the same parentage and
same surroundings which in the mind of Mr. Darwin made evolution
possible. He always favored the idea that it was the continuous
accumulation of these small variations that finally produced the
profound changes which mark the new species. He admitted the
possibility of the occasional appearance of those more distinct leaps
in variation on which the present school of mutationists so strongly
insists; but he believed them to be less influential, in the general
trend of evolution, than the slower but much more frequent variations.
One of the most complicated and perplexing problems in the biology of
to-day is the question of the origin of these variations. It is quite
as hard to understand as is the method by which animals produce their
own kind. No problem is being more earnestly studied. Suppositions we
have in considerable number, and two of these at least may reasonably
be mentioned. We will consider first the less certain theory. There is
nothing in the egg that in the remotest degree resembles its parent.
The old idea that every acorn had in it a miniature oak which only
needed to unfold itself, or that the hen's egg had within it a
miniature chick which only needed the warming process in order to make
it evident, could not possibly survive the invention of the
microscope. We may not, and we certainly do not, know everything that
is in one of these eggs, but we do know most certainly that what is
there has no resemblance to what it will be in time. The biologist
finds in the nucleus or central core of every growing and reproducing
cell certain minute bodies which Weissmann believes do much to
determine the growth of the rest of the cell. He believes also that
there are many more such "determinants" than are necessary for the
reproduction of the cell. Each of these determinants may be fitted to
produce slightly different results, but what decides which of them
shall have its own way is quite uncertain. It may be that one
determinant happens to be more favorably placed than others in the
cell and that it has consequently secured more of the nourishment that
comes to the cell in the blood of its parent. If this is true it would
certainly be favored in the competition. We are becoming quite certain
that whatever variations arise really start in the egg. The simplest
conception as to the cause of variation would seem to be varied
experience. One man trains his brain, another his hand; and in each
case the organ so trained develops. But science is strongly of the
mind that such influence does not reach the next generation.
A musician may have taught his fingers to be nimble; may have given
them speed of motion and precision in their action. No child of his
born after he acquired this wonderful facility of execution is any
more likely to be a skilled musician than a child born before he had
ever practiced enough to be anything more than a crude performer.
Science is nearly certain that his children are just as likely to be
talented along musical lines if he himself never had become a
musician, simply because he had it in him to be a musician. In other
words, they may inherit the talent which he developed, but they
inherited it not because he developed it, but because it was in him to
be developed. This is in accordance with the famous principle that
there is no inheritance of acquired characters. We shall touch this
question a little more fully in a later chapter, in speaking of the
development of the evolution theory since Darwin's time.
If we are right in this matter, and we certainly are nearly right,
variation must take place for the most part in the germ. These
variations may not show until the animal has grown up, but they must
have taken place among the determinants in the germ cell or they would
not reappear in subsequent generations.
There is another process by which new variations may arise and which
is more easily understood. It is the method of double parentage. The
Barred Plymouth Rock chicken had its origin in such a double ancestry.
The one parent was a Black Java whose color has disappeared entirely
in the cross, but whose single comb with its few large points comes
out clearly in the newly produced fowl. The other parent was a Barred
Dominique. It is to this parent that the Plymouth Rock owes the
interesting cross markings on its feathers. The comb on the head of
the Barred Dominique is of the type known as the rose-comb, having
many rows of slight projections. This has completely disappeared from
the Plymouth Rock fowls. I am told that the skilled chicken fancier
can tell, concerning many points in this fowl, to which of the crossed
ancestors each quality is due. To a certain extent it is undoubtedly
true that here we have the secret of the origin of many of those
interesting people whom we are pleased to call geniuses. They may not
possess any qualities not clearly discernible in various of their near
ancestors, but in them we find what we, for the lack of a better
understanding, call chance combination in one individual of the finer
qualities of many ancestors, and this individual is so placed in life
as to have these qualities developed and strengthened.
Charles Darwin, humanly speaking, may be accounted for as the happy
combination of a double heredity and a favorable environment. He
inherited the scientific inclinations of his grandfather, Erasmus
Darwin, and the patient, sturdy honesty of his other grandfather,
Josiah Wedgwood. These developed under the stimulus of the long
five-year voyage, face to face with the world of nature. This happy
complex produced the master biologist. To believe that he came about
purely by chance requires a great stretch of the imagination. "There's
a divinity that shapes our ends."
We have endeavored to make clear two of the basal ideas underlying
evolution. One of these is responsible for the continued production of
animals or plants of the same kind, preventing the world from becoming
a wild kaleidoscopic and fantastic dream. Heredity is the conservative
force of nature. The other idea underlies the development of new
departures which keep the world from being a dull, dead, unending
repetition of the same monotonous material. Variation is the
progressive tendency in nature.
The third basal idea is that of Multiplication. Animals and plants
multiply; they do not simply increase, they increase in a geometrical
ratio. Anyone who has worked out one of these geometrical ratios knows
how wondrously they mount up. There is an old familiar story of the
blacksmith who asked the price at which the stranger would sell the
horse he was shoeing. The owner of the horse replied that, if the
blacksmith would give him one penny for the first nail he drove into
the shoe, two for the second, four for the third, and so on, he might
have the horse. No hundred horses in the world taken together have
ever brought such a price as the blacksmith would have had to pay for
the animal on which he was working. This is no circumstance to the
awful story of what would happen to the earth if any animal could
multiply unrestricted. The usual number of eggs laid by a mother robin
for a single brood is four, and she may produce two broods in one
season. This would mean that the original pair had produced eight
offspring, four times their own number. If we can imagine these mating
the next year and producing their kind in the same proportion; and, if
we further suppose that each robin needs a space one hundred feet
square from which to gather his food, we realize the astonishing fact
that in fifteen years every patch one hundred feet square in
Pennsylvania and New York would each have its resident robin, while
the following season would find a robin on every similar patch from
Maine to the Carolinas. Of course this could never happen, this is
simply what would happen if all the robins could grow to maturity and
reproduce at the normal ratio. But the robin is a comparatively slow
producer.
Our turtles are more prolific. Twenty eggs would probably not be an
unusual number. If we could imagine a turtle to live in the sea and to
produce at this rate; and, if each turtle should need as much room
each way as the robin, and a depth of water equal to its width, before
the robins had spread over New York and Pennsylvania the turtles would
have filled all the seas of the globe. Frogs are even more remarkable
in this respect. Two hundred eggs is not an uncommon number. If each
frog required a space twenty-five feet square on which to subsist, the
entire earth would be more than covered with them within six years. It
is ludicrous to think of such numbers, especially when we realize the
hundreds of thousands of kinds of animals there are in the world, each
of which is also multiplying, and it becomes evident at once that only
an infinitely small proportion of all these creatures can possibly
survive. This, then, is multiplication.
Here comes into play the fourth basal idea in Mr. Darwin's
explanation. This is the part of Selection. When man produces new
varieties of animals he does it by picking out from his flocks or his
herds such as conform most nearly to his idea of what is desirable.
These he mates, and from their progeny he selects the ones that suit
him best. Generation by generation he gets his domesticated animals to
conform more nearly to the standard of his desires. Natural selection
works in exactly similar fashion. Of all the eggs that are produced by
the animals at large in nature an overwhelming proportion never
develop at all. They dry up, are eaten by their enemies, find no
suitable place or time for development and decay, or are overtaken by
some other calamity. Of the animals which emerge from the remainder an
overwhelming majority come to an untimely end within the first few
days of life. Each has countless enemies which prey upon him, and
these have scarcely devoured him before they themselves become the
prey of some stronger creature. Until Mr. Darwin gave us his elemental
idea it was taken for granted that it was a matter of pure accident
which survived and which yielded in the struggle and cares of life. It
was Darwin who showed us that in this tremendous struggle against
those of his own kind in the search for the same food, against the
elements, in securing a mate, any animals possessing a superiority,
however slight, must have some little advantage in the battle.
Certainly, where so many must utterly fail, only those could possibly
succeed who were well fitted to the circumstances in which they must
live. We used to think animals were destroyed by the "accidents" of
life and no one could foretell accidents. Mr. Darwin made clear that
it was not a question of chance. That which might happen to any
individual animal might be what we, not knowing the process, called
accident, and yet there could be no possible doubt that those who
succeeded were better fitted to battle with life than those who
failed, and that their success was due primarily to their being thus
advantaged. Consequently, if generation by generation the so-called
accidents of life are constantly eliminating the unfit in overwhelming
proportions, not only must the positively unfit disappear, but even
the less fit. The more keen the struggle, the fewer could survive and
the fitter they must be to survive at all. This is Selection. These,
then, are Darwin's four great factors of evolution: Heredity,
Variation, Multiplication, Selection.
From these it results that the animals and plants naturally become
better adapted to the situation in which they are placed. When, as is
constantly happening through the history of the earth, a change occurs
in the physical geography of any region, when a plain is lifted to be
a plateau, or a mountain chain is submerged until it becomes a row of
small islands, this alteration will produce uncommon hardships among
animals, even though they were well fitted to the old conditions. Any
animal or any species of animals which meets such a calamity has
before it only three possible outcomes of the struggle. First it may
be plastic enough and it may vary enough in the right direction to
adjust itself to the changed conditions. In this case it and a favored
few like it will occupy the altered territory. The second possibility
is that it may migrate while the actual change is going on, thus
remaining in the sort of situation suited to it and its kind. The
third possibility is the one which overtakes a great majority of
animals--they die. Even the entire line dies out, and the strata of
the rocks are filled with the bones, shells, and teeth of such as have
met this fate. They have become extinct.
Thus far in this chapter we have been considering the influences under
which it is conceivable that animals should advance. There is no
question whatever that there are too many animals born, nor is there
any possible question that a very large proportion of them must
certainly die. There is equally no doubt that every animal produces
after its own kind, and that its offspring, while they resemble it
closely, still vary a little from it and from each other. This fact is
perfectly plain to the most superficial observer who thinks on the
matter at all. It is not so plain, nor is it easily demonstrated, that
all of these acting together do surely, even if slowly, alter the form
and behavior of the animal world. It is difficult to prove that there
is going on under our eyes a steady and real improvement in the
adaptation of the animals and plants around us to the situation in
which they are placed. As far back as man's memory runs they seem to
have been about what they now are; as far even as man's historical
record runs they seem to have suffered no great alteration. The
Egyptian of the old tombs is much like the Egyptian of the same rank
to-day. The African of the tombs has the African features of to-day.
Under such circumstances it is hard to prove that there is a steady
and undoubted advance. For the most part the balance of the animal
world is fairly even, and any species does not ordinarily change
rapidly enough or migrate widely enough to show us its new features.
It is difficult to see the struggle which we are so sure is going on.
The life of animals is so hidden in many of its details that their
joys and sorrows, if such we may call them, scarcely fall under our
observation. Now and then an opportunity comes to see the process of
adaptation work itself out. The struggle for existence begins anew and
is carried on with special vigor, with victory, temporary or
permanent, to one of the participants in the struggle.
The opportunity to observe such a change is presented in the United
States by the introduction of the so-called English sparrow. This
little creature, received at first with such joy, soon became the
object of an almost bitter hatred on the part of very many people.
This is really due to the fact that this bird is one of nature's
darlings and thoroughly succeeds where it has an even chance.
The number of birds of any particular species which a region will
support seems to be fairly definite. If a species is especially
protected until it becomes unusually abundant, the removal of the
protection commonly brings it down promptly to its original numbers.
On the other hand, an accident of severe character or a special
persecution may much diminish the number of the species, and still it
will, within a comparatively few years, return to its previous
abundance.
The inhabitants of Florida who own orange groves will never forget the
winter of '94-5. A bitter cold wave swept along the coast and killed
such large numbers of orange trees as almost to cut Florida out of the
orange market and to open the gate to California, who was eagerly
offering her fruit. This same frost caught the migrating blue birds
and killed them by the thousands. When spring came bird-lovers
throughout the eastern United States found an astonishing scarcity of
these favorites. It was feared that with numbers so small they could
not possibly compete with their enemies and with whatever untoward
circumstances should be their lot. But there is room in this
environment for a definite number of bluebirds. When this number was
suddenly reduced the chances to make a bluebird's living were so
wondrously multiplied that young bluebirds had such an opportunity in
life as their fellows had not had for many long years. Accordingly
they thrived as never before, and, of their progeny, a larger
proportion lived to the following year. It was only a few years before
the number of bluebirds had risen. Now we probably have as many as we
have had for a long time past. I cite this simply to show that a
region can support a certain number of animals of any one particular
kind, and that the animal is likely to multiply, if given a fair
chance, until it has reached such proportions. Now to my story of the
rapid development of a newcomer.
In the year 1850 a resident of Brooklyn came home from a trip to
Europe. He was a lover of birds, and while in Europe had been
particularly attracted, no one now knows quite why, to the common
House Sparrow, as it should be called. It is no more abundant in
England than in many parts of the continent of Europe. A name that has
been used for a long time is very hard to cast aside, and we shall
probably continue to mistakenly call him the English Sparrow to the
end. Our Brooklyn traveler brought home with him from Europe eight of
these interesting little birds and succeeded in inducing his
colleagues in a scientific society to share his interest in them. Not
wishing to commit the newcomers suddenly to the rigors of the American
winter, these men built a large cage for the sparrows, meaning to set
them free in the spring. For some reason or other when the winter was
over the birds were all dead, and this first attempt to introduce the
sparrow into America failed entirely. The little bird had won so many
friends that his success was now sure. Finding a favorable
opportunity, these Brooklyn men dispatched an order to a man in
Europe, asking him to supply them with one hundred English sparrows.
The consignment came in good shape and the birds were liberated on the
edge of Brooklyn. This was the first of a number of introductions. A
little later New York City sent for two hundred and twenty of these
interesting creatures and turned them loose in her parks, while
Rochester, with what was then considered great public spirit,
purchased one hundred for herself. But the most progressive city in
this respect was Philadelphia. She had long been troubled with the
spanworm on her trees. This detestable larva had the unpleasant
fashion of lowering itself by a long silken thread from the shade
trees then so abundant in that beautiful city. The spanworms traveling
around over the clothing of the passersby were so objectionable to
everybody that it was with greatest delight that Philadelphia heard
of the new birds which ate the pest. One wonders why some
ornithologist did not look at the bird long enough to see that it had
the sort of a bill characteristic of birds that eat seeds. It is true
that most birds feed their young on insects, hence there is a time
when any bird is apt to be insectivorous. But the structure of the
sparrow's bill, like that of all finches, should have warned these
bird-lovers that the sparrow was not to be depended upon to earn his
living by catching worms. It is easy, however, to be wise after the
event. Philadelphia believed she was engaging in a particularly
advanced movement when she imported from England one thousand English
sparrows, nearly as many as were liberated by all other cities
together. These birds were turned loose among the shady streets and
wide spreading parks of the City of Brotherly Love.
It is a serious matter lightly to disturb the balance of nature by the
introduction of a new species. It is true that the sparrow did eat
some spanworms and for a while enthusiastic bird-lovers hoped that
here was the solution of the difficulty. Philadelphians will also
remember that, with the spanworm removed from competition, the tussock
moth, whose caterpillar carries on his back a series of yellow, red,
and black paint brushes, at once become the permanent parasite of the
long-suffering shade trees. This caterpillar is covered with bristling
hairs, very closely set. Almost any bird objects to hair in his
victuals; and this particular larva has hair more than ordinarily
objectionable, for it irritates wherever it pricks the sensitive skin.
This coating seems to protect the caterpillar from the sparrow, with
the result that Philadelphia's trees were soon nearly defoliated by
this comparatively new pest, worse than the spanworm. With the paving
of the city's highways and the consequent shutting off of the air from
the roots, the trees have largely disappeared from the streets of
Philadelphia. With them have gone a fair portion of the tussock worms,
but the sparrow holds his own. Here is a new bird in the field, and
the struggle for existence on the part of every other kind of bird is
now more complicated and severe. The sparrow can live where the rest
of the birds have no possible chance. He throve so well in this
country that by 1875 he had spread over five hundred square miles in
the neighborhood of our larger Eastern cities. Thus far almost
everybody was pleased with the new introduction. Within the next five
years he had spread over more than fifteen thousand square miles, and
wise men were beginning to feel doubtful of the virtues of their
aforetime friend. When by 1885 more than five hundred thousand square
miles had been occupied by the enterprising little fellow, there
remained no longer a doubt in the minds of most people that the
sparrow was an unmitigated nuisance and great fears were entertained
that he had multiplied to such an extent as to be a serious menace.
Here, then, is a modern instance under our own eyes of a victory in
the struggle. If the sparrow has multiplied rapidly, while all the
other birds have either only held their own or even have diminished in
numbers, it is quite evident he must be better fitted to the
conditions than they are. What are his fit points? Why does he succeed
while others fail? The thoughtful bird-lover will have little trouble
in understanding at least some of his victory-winning characteristics.
How did he come to be almost the only bird who can live in large
numbers in our great cities, without losing his ability to get along
in less crowded situations?
In the first place this interesting bird is a clannish fellow. He has
lost the ordinary sparrow habit and has come to like to live in
crowded groups. Seclusion is not at all to his taste, and if there are
only a few sparrows in the neighborhood those few will most certainly
be found living near each other. One of the early adaptations of the
sparrow to his city surroundings was the ability to find for himself a
considerable proportion of his food in the undigested seed that could
be picked up from the droppings of the horses. This naturally led the
surplus sparrows out through the many thoroughfares leading from any
large city. Where horses went sparrows could follow. Accordingly along
the great lines of travel this bird found the simple path by which he
could enter new territory. Meanwhile box-cars came into our large
cities with freight. Sometimes they had carried grain, sometimes
cattle. In either case it was not unlikely that a certain amount of
grain should be found scattered over the floor of such cars. The
sparrow visited these cars for the grain, and it must have been no
infrequent accident that a door should be shut upon a group of
sparrows, especially in inclement weather, when they were apt to be
huddled in a dark corner of the car. These prisoners would be carried
to the destination of the car and there liberated, thus producing a
new center of what we are now inclined to call infestation. By such
means the English sparrow has spread over much the larger portion of
the American continent. Few birds are bold enough to visit a railroad
car. Of the few who might be tempted, most are timid enough to fly on
the first approach of man. Hence they fail to gain this chance of
spreading. They must remain in the old crowded home. Meanwhile the
sparrow, thus transported, finds a new home with fewer or no sparrows.
The struggle is less keen. More of his kind can live. His boldness
has been here a fit quality and has helped him in the race.
Man is only slowly coming to be a city-dwelling animal. Although it is
a voluntary process with him, he still usually visits the country with
much enjoyment. He has not as yet learned to adapt himself thoroughly
to the city, for somehow city life kills him. Families that move into
the city gradually have a smaller number of children in each
generation until shortly the family is wiped out. The population of
the city must constantly be replenished from the country. But the
English sparrow is more adaptable than are the people. He has made
himself at home in the heart of the biggest city. The Wall Street
canyon is not deep enough, nor contracted enough, nor free enough of
food to blot out the life of the English sparrow. At the heart of the
deepest gully among the skyscrapers of our biggest cities we find this
little bird hopping between the horses' feet, darting out from under
the wheel of the push-cart, fluttering only a few yards to a place of
safety, to return at once to his scanty meal upon the pavement as soon
as opportunity offers. He is a typical city dweller and has learned to
thrive there. Again in this matter he has distanced other birds to
whom the city is more deadly than it is to people.
Another very important element in his fitness for the struggle of
life lies in the fact that he is unafraid of man. He is wary of man;
by which I mean he will quickly fly up from in front of man's feet. It
is exceedingly difficult to catch a sparrow in one's hand. It is far
easier to lure a pigeon within reach. But the sparrow, when escaping
your hands, comes to rest but a slight distance away, only to elude
you quite as successfully if you try again. If the sparrow is let
severely alone he becomes more and more familiar with men, flies less
promptly, and goes a shorter distance, but any attempt to trap him
renders him shy more quickly than almost any other bird we have. He
soon learns to avoid a trap in which his companions have come to
grief. Those who would poison or trap sparrows must change constantly
the base of their operations. This fearlessness of man is a valuable
asset to the bird, for it is an important defense against other foes.
The most serious enemy the birds at large have, after man himself, is
the bird of prey. Hawks and owls capture a large quantity of our
smaller birds. Now the hawks and owls are for the most part shy of
man. They have gotten a bad reputation, especially if they are of any
size, because of their more or less pronounced proclivities for
seizing our domestic poultry, and consequently many people will fire
upon a hawk or an owl who would probably fire upon no other bird. By
living close to man the sparrow is largely saved from the danger of
capture by these carnivorous creatures, and this is the first and a
very important element of the advantage to the sparrow of living near
man. But there is the additional advantage that man scatters about
him, in one way or another, a very considerable amount of waste food.
I have suggested that the seeds in the droppings of the horse form a
large proportion of the sparrow's food, and horses are to be found
only with men. In the neighborhood of man's home, unless he has become
sanitary to a degree which has only been attained in recent years,
there is usually more or less garbage, kitchen offal of one sort or
another. To this the sparrow has easy access and from it he makes many
a meal. But this fearlessness of man gives him still another advantage
which his competitors fear to use, it provides him with nesting sites.
Man has the faculty of putting up ornamental trimmings on his house,
and there is no spot the sparrow chooses more willingly in which to
build his nest than the ornamental quirks and cornices of man's
architecture. A Corinthian column with comely leaves in its capital
seems especially designed for the comfort of the sparrow, and his
distinctly untidy nest is the familiar disfigurement of almost every
ornate public building. These are the advantages which come to the
sparrow from his willingness to associate with man, and there are
comparatively few birds with whom he must share them. Few birds select
the immediate neighborhood of man's home for their nests. They may
live in the neighboring trees, they may haunt his orchard, but his
house, for the most part, they decline to frequent.
Still another quality which makes for success in this buccaneer is the
willingness with which he will vary his food as occasion requires. It
is a not infrequent characteristic of the bird family that each
species should have its own rather restricted diet. Birds are quite
particular eaters, and many of them will come well nigh to starvation
before they will use unaccustomed food. The sparrow, on the contrary,
like man, eats almost anything he comes across that could reasonably
be considered edible. He belongs to a group of birds which are
structurally adapted to cracking the hard coats of seeds. This group
of birds known as the finches is provided with the sort of bill
familiar in the ordinary canary bird. It is short, heavy at the base,
comes quickly to a point, and is firm and strong. With it the bird
readily breaks through the hard outer coat of most seeds and feeds
upon the rich cotyledons that are enclosed within. Nowhere in its
entire structure does the plant crowd so much nourishment in so little
space as it does in the seeds. It is not by chance that the great
human food is grain. The sparrow belongs to the one bird group that
makes a specialty of such seeds.
Most of the English sparrow's cousins in this finch group confine
themselves rather rigidly to this diet. Here the variability of the
sparrow again gives him the advantage. He may have the family fondness
for seeds, but in their absence he can be content with almost anything
edible. In the early springtime, when the seeds of last year are gone
and those of the new year have not yet been produced, the sparrow is
not averse to eating young buds from the trees. At this time he is not
unlikely to eat our sprouting lettuce and peas. It is easy to be
severe on him in this matter; but for a creature like man, who has the
same tastes, who eats the enormous buds of the cabbage, the
cauliflower, and the brussels sprouts, or the more tender buds which
he calls heads of lettuce, it seems particularly inappropriate that he
should throw stones at this little creature whose tastes are so
similar to his own.
While seeds are more suitable for an elder bird they are altogether
too indigestible to be the food of nestlings. So when the sparrow
finds its nest full we know he must sally forth in search of
nourishment more simple of digestion. Now for a few weeks he searches
assiduously, catching insects and caterpillars of various kinds, and
feeds them to his young. This taste passes as his children grow older,
especially as shortly the seeds begin to ripen. Now is the time for
the sparrow to fatten. Now he is eating the food for which he was
really built. By the time the wheat is ripe there are sparrows enough
about to form quite a flock, and when these settle down in a wheat,
rye, or oats field and feed upon the grain, meanwhile shaking out upon
the ground perhaps as much as they eat, the farmer begins to realize
that the sparrow is not his friend.
When winter comes the struggle for existence among the birds is
intensified, and comparatively few of them dare face it. Most of our
birds betake themselves to less rigorous quarters, leaving to the
sparrow a comparatively small number of competitors for the diminished
supply of food. As long as the snow is off the ground the sparrows can
find sufficient sustenance. They gather themselves into groups and
sally out from the city into the open country. The immediate result is
that great quantities of weed seeds are seized upon by the English
sparrow, as, indeed, by every other finch which is with us in winter.
Perhaps we have not given the little fellow credit for the good he
does at this particular time, for the rest of the account truly does
not help him in our esteem.
There is a further direct advantage in the sparrow's sociability. One
robin may nest in the vines about your porch. If there were room for a
dozen, scarcely more than one would be likely to use it, because he
would drive away any other robin who attempted to share the
neighborhood with him. To the sparrow company is always in order.
While he may quarrel from morning until night with his fellow, it is a
sociable quarrel and neither would willingly forgo it. This union is
strength among birds, as with man. Every animal is safer from his
enemies when he can have the constant presence of others of his own
kind. The deer that stays in the herd is safer from the wolves. It is
only when the latter succeed in cutting out some weaker or less
sagacious animal that these carnivorous creatures succeed in tearing
down their prey. I think the superiority of the sparrow over most of
our common birds, when considered as a city dweller, is scarcely
understood. Because he had won in the race with other birds is no
necessary indication that he warred directly against them. Bird-men
often attribute to him a quarrelsome disposition, as if he actually
drove other birds away. It almost seems like animosity against the
sparrow to speak of him as attacking blackbirds and crows. It is a
cowardly crow who can be driven away by a sparrow, and if the two
cannot live together it seems to me certainly to the discredit of the
crow and not of the sparrow. I believe the truth to be that, while
the sparrow is undoubtedly a quarrelsome fellow, his bickerings are
his form of social converse with those of his own kind. A quarrel
among themselves seems not to indicate animosity, but would appear to
be the sparrow's idea of conviviality. It rarely leads to serious
results. I have never seen a male sparrow trounce any other bird with
half the vigor that I have occasionally seen the mother sparrow evince
when she caught her male companion by the feathers of his head, hung
him over the side of the limb, and vigorously and thoroughly shook him
until he desisted from his annoying and possibly insulting attentions.
The truth of the matter is that a colony of these little birds, with
their continual social chatter, including their quarrels, makes such a
continuous noise that the ordinary bird, which is generally of rather
quiet disposition, is too much annoyed by the unending nuisance to
find the neighborhood at all to his taste. Where a large number of
sparrows have gathered together the conditions are such as would give
a robin or a bluebird nervous prostration, and his only recourse is to
depart to a neighborhood where there is more peace and quiet. But our
English sparrow is not only better fitted for the struggle than the
robins and bluebirds, the orioles and the wrens. He has one important
advantage over even his own sparrow cousins. The males are
handsome--much more so than the females or than their sparrow cousins
in general.
In the song sparrow, field sparrow, chipping sparrow, and the fox
sparrow the male and female are very nearly alike in color. It often
becomes necessary for the bird-man to examine the internal organs of
the bird he is stuffing before he can certainly decide its sex. But
there is no difficulty whatever in telling the male from the female of
the English sparrow. The male is far the more ornate bird. His back is
striped with a richer brown; his head has two splendid dashes of
chestnut over the eyes; his throat and breast are splashed with red
and lustrous black; his bill is a clear fine black. Altogether the
bird is strikingly colored for a sparrow, and this characteristic is
the more remarkable when we see how quiet and somber is his more
modest mate. This brilliancy of male plumage in the presence of the
somber color of his mate would seem to indicate that the English
sparrow is eye-minded rather than ear-minded. It is true among human
beings that most of them are eye-minded. That is to say, they notice
things with their eyes chiefly. Memories they have are memories of
things seen; recollections of their friends bring up the appearance of
their friends. Their language is full of metaphors which imply form
and shape. But occasionally we come across an ear-minded person. He
remembers voices quite as well as he remembers faces. To him music is
an unending delight, and painting and sculpture fall into a distinctly
secondary place. This is ear-mindedness. Now, most of the sparrows
seem to be ear-minded, at least as far as their recognition of their
mates are concerned. In this group beauty of song is developed many
times oftener than is especial ornateness of plumage. The bird-lover
who is himself keen of ear is never tired of listening, when in the
field, for the two low notes with which the vesper sparrow introduces
a song, the rest of which is not at all unlike the one of his
song-sparrow cousin. The field sparrow begins more like the song
sparrow, but ends with an often repeated note, which not a little
resembles in general character the somewhat more monotonous song of
the grasshopper sparrow or of the chippy. In comparison with these
melodious birds the English sparrow makes no showing whatever. His
voice is harsh and querulous, although very occasionally it is
possible for the bird-lover to detect a note or two which would
indicate that, if he were properly educated, his voice might amount to
something. He wins his wife not by his pleasant voice, but by his
attractive appearance and his winning ways. We have every right to
infer from the character of its fellow birds of the sparrow family
that once the female and male sparrow were colored about alike. But
Madam English Sparrow was apparently eye-minded rather than
ear-minded. Whatever pleasant voice a suitor might have seems to have
been to her without attraction, and there was nothing to encourage him
in developing it, nor was she likely to mate with him for it and
transmit it to her male children. On the other hand, let a suitor
appear in whom a more brilliant coloring proclaimed his superior
vigor, and this seems to catch her eye at once. The less accomplished
rival in the tournament of love seems to have been already forgotten.
To their children these successful characteristics were naturally
handed on and led to equal success on their part. If any of these
children possessed this badge of honor in a more than ordinary degree,
he was the more likely to win a mate and thus again the opportunity of
passing on to his offspring his own distinct advantage. Generation by
generation the males have become more beautiful and the females more
discriminating. That the bird is either instinctively or actually
conscious of this advantage would appear from the constant fluffing of
his feathers and spreading of his highly colored wings with which he
evinces his admiration for his ladylove. Even the most hardened
dweller in the city can scarcely have failed to see the sparrow spread
his wings, fluff his feathers, and sink close to the ground, twirling
and gyrating about the object of his affection. It must give him a
shock to see how often she proves temporarily or hypocritically
indifferent to the demonstrative proceedings. Indeed they may
terminate in a thorough trouncing of the male on the part of the lady
of his affections. Now this preference for color over song must have
evidently evolved in connection with the development of social habits
in the English sparrows. His cousins of the fields, our native
sparrows, are much less social, much less likely to be met with in
flocks. To birds who scatter more, beautiful song is a great
advantage. It can be heard at a long distance. But when birds flock
together a much better advantage is that of beautiful clothing, added
to alluring ways.
But we have not nearly exhausted the catalogue of the traits belonging
to our little friend which give him the advantage over other birds in
the struggle for life. His ability to remain with us in winter when
most birds are gone stands him in good stead.
It is readily observed by one who pays the least attention to outdoor
life that winter finds us with comparatively few birds. North of
Maryland and the Ohio River the robin is practically absent in the
winter, except in much diminished numbers close to the border. The
bluebird is similarly absent; the great flocks of blackbirds are gone;
the bobolink is missing entirely; the thrush and the catbird have all
left; the flicker and red-headed woodpecker are also spending their
winter in the South. The great mass of our bird population has left us
until warmer weather shall bring back to us once more our feathered
friends. It is true that we are south to the snowbirds or juncos, and
their little slate-colored bodies, with their light breasts and their
white on each side of the tail, make our bare hedge rows brighter by
their presence. A few of our birds like the song sparrow and the
cardinal are hidden away in the thicket, and have not all joined their
comrades in the south.
The English sparrow was once probably quite as migratory as any of the
rest of these, but a great change has come over his habits. With his
newly acquired fondness for the haunts of men he has suffered a change
in this respect also. Whatever may have been his reason for migrating,
it no longer holds. He now finds himself quite able to stand the cold
of winter. Accordingly he never leaves us, except very temporarily.
When the migrating season comes the sparrows of the neighborhood are
very likely to gather themselves together in a single group and take
to the neighboring country. I believe this flocking on their part at
this time of the year is a remnant of the old migratory habit. Until
snow covers the ground the sparrow is not likely to be seen again in
such numbers in the city. The advantage the sparrow gains over his
competitors by not going south does not appear during winter. When
spring comes, however, his gain is evident. He has his choice of all
the nesting sites in the region. When the migratory birds return every
first-class place is filled by a sparrow's nest. Nothing but second
choice situations remain, and with these the late comers must be
content. When we consider how much the safety of the next generation
depends upon the security of the young while helpless in the nest, we
appreciate what the English sparrow has gained by staying throughout
the year. Often while the season is so inclement that it would seem
there is still danger of frost, the sparrow builds her nest. All sorts
of places are open to her choice. She will find a protected corner
under a roof, above a spout, in the corner of the porch, behind an
open shutter, in the vines against the side of the house, on top of an
old robin's nest in the tree, in the bird boxes which have been put up
for more desirable creatures; anywhere and everywhere this industrious
little mother is liable to build her nest. Her husband will help her
more or less in the task, often bringing material and helping to place
it in the negligent pile of which their nest is composed. But he does
a good deal more fussing and cheering up than he does actual work, and
she seems to depend much upon his cheerful presence for her happiness.
It is hard to discourage Madam Sparrow when once she has set her mind
on home-making. A bird-lover, some time since, reported how a pair of
sparrows had started to build a nest upon his lawn. He, wishing to
interfere with the process, took a small rifle and shot the male bird.
Within twenty minutes the female, who had scouted round the
neighborhood, returned with another mate and resumed her nest-building
process. Again he interjected the tragic note into her life by
shooting her second husband, only to find her start out in pursuit of
a third, with whom she returned in the course of an hour. He felt that
by this time he had interfered with her domestic happiness as much as
he had any right to do, and suffered her to continue her housekeeping
with her third husband without further molestation. I imagine it would
have puzzled both birds to tell who was the father of the nestlings
who appeared two weeks later.
Not only do sparrows nest early, they nest often. I suggested to one
of my students that she locate as early in the season as she could the
nest of a pair of English sparrows, which was sufficiently accessible,
and that she keep it under observation at intervals of a few days
throughout the summer. In the fall she came to me with glowing eyes
and gave me her report. "It is simply great," she said. "I never went
to that nest a single time this summer to find it empty. When I first
got there I found four eggs; after a while these hatched out, and the
young were on the nest until they were old enough to fly; but before
they had left she had slipped a fresh egg among them, ready to start a
new batch. Whenever I saw the nest throughout the entire summer, I
found in it either eggs, or young, or both." Such reproductive energy
as this is hard to beat; compared with this rate of increase, the
ordinary bird is the exponent of race suicide. How can a robin hope to
compete with this family industry? What can a bluebird offer that will
approach such chances of a worthy successor when his work shall be
finished?
These, then, are the most important points in which the English
sparrow has varied from his sparrow cousins and made of himself the
most successful town dweller in the bird world. He has become clannish
and gained the advantages of coöperation. He has used man's highways
and cars by means of which to expand his area. He has cultivated the
presence of man and thus gained protection from his enemies, food from
man's waste, and nesting sites on man's house. He has assumed a varied
diet. The male has become handsome. He has given up migrating, and
thus secured the best nesting sites. He has learned to produce many
offspring. With all his versatility, why should he not succeed?
Thrown into competition with our native birds, he easily beats them
on their own ground. He survives against the competition of birds
which seem to us more estimable in every way. The very fact that he
survives proclaims his superiority over them, and shows that our
criterion is not the one by which nature judges. We like the birds
which serve our purpose. We admire the brilliant plumage of the jay,
cardinal and goldfinch. We love the mellow notes of the woodthrush,
and of the veery, the clear, rollicking outpourings of the bobolink,
the musical love song of the brown thrasher, the cheerful scolding of
the wren. We are fond of the birds who busy themselves taking the
insects out from among our grain and from off our fruit trees. We can
only understand the value of the bird to nature when he is valuable to
us. So, because the English sparrow does little that is to our
advantage and much that is to our annoyance, he is in our estimation a
reprobate and an unending nuisance.
All sensible bird-men must clearly acknowledge that he is a very
undesirable citizen. I write the above sentence to show that I realize
the whole duty of the bird-lover in the matter of the sparrow. This
pestiferous creature should be exterminated by traps, by grain soaked
in alcohol, or strychnia, by fair means or foul. But personally, I am
taking no share in his destruction. Any bird-lover, after reading the
foregoing account, can scarcely have missed the undercurrent of my
affection for the little rascal. He is a thorough optimist; he is
absolutely persistent; no hardship seems to dampen his ardor. His
heart is valiant above that of most birds so that he has dared to make
of man his near neighbor when other birds consider him their worst
enemy. I love him for it. When I am in the midst of a big city with
its cliffs of offices and its gorges of paved streets, it is to me a
cheer and a delight to see this happy little fellow who has adapted
himself to circumstances against which no other bird, excepting the
pigeon, can cope. I confess that it would be with regret that I should
see him disappear from the landscape. I have missed a long line of
spring peas through his ravages, and he has objectionably decorated
many places about my own home. But I have yet the first violent hand
to lay upon the sparrow, and I doubt whether my hand is ever to be
reddened with his blood.
I am going to ask bird-men to forgive me if I say that I believe,
although I speak only from general impression, and not from careful
research, that the sparrow within the past eight years has reached his
equilibrium in the neighborhood of Philadelphia and is growing no more
abundant. Meanwhile another and very desirable state of affairs is
arising. Bird love and bird protection are so active in this
neighborhood that there is growing to be a new race of birds who lack
the fear of man their ancestors justly had. Under these conditions the
wild birds, which for a while we believed to have been completely
driven out by the sparrow, are rapidly returning to our villages and
towns, and we have many more robins and catbirds, wrens and flickers
than we had ten years ago. We have seen the worst of the English
sparrow; he has now found his equilibrium.
CHAPTER IV
ADAPTATION FOR THE INDIVIDUAL
Among the standard books of the classical curriculum in the
denominational college of thirty years ago was a volume which I
suppose has practically disappeared from such courses. It delighted
many of its students for a reason entirely different from that which
the author meant should be its taking feature. It was Paley's "Natural
Theology." The author started with a story of a watch found by a
savage. This child of nature was supposed to examine its mechanism and
to infer that the watch was made for a definite purpose. As I
remember, he was even supposed to discover that its purpose was to
mark time. It was at least to become clear to his savage mind that
this was no chance object, but was the definite product of a designing
mind. Having brought this hypothetical savage to these conclusions,
the author turned himself to savages nearer home who fail to see
design in nature. The book takes up a great many cases of interesting
facts in animals and plants as clearly showing evidences of design as
did the watch our savage picked up. But the inference we were expected
to draw was that the design shown in nature argued clearly for a
Designer above nature; in other words, that nature was unintelligible
without God. Everyone in the class believed in God without this
preliminary, and consequently the book was unnecessary, so far as we
were concerned. We started with the condition of mind which the author
hoped to produce. One effect the book did have; in the absence of any
other reputable course in zoölogy, it gave us an astonishing
collection of interesting facts about animals.
Some of Paley's statements were certainly peculiar. His Malay pig with
its upper teeth wonderfully curved was said to be in the habit of
hanging its head upon a bush while it slept, in order to save the
strain upon its porcine neck. This was too much even for our
credulity. None the less the impression made upon some of us by the
evidence for design in nature has never left us.
Among many scientists to-day it is supposed to be crude to speak of
purpose in nature, and there is reason for their attitude. But the
statement that there is no such plan conveys to the ordinary thinker a
meaning that is far more erroneous than could possibly exist in his
mind should he believe implicitly in design and purpose. As between
design in the universe in the usual sense of the word, and a purely
accidental connection of events in the universe, there can be no
doubt as to the choice. The truth is far better expressed by the word
design than by the chaos which is the alternative idea in the average
mind. In these later years we have come to use a different word. We
now conjure in such connection with the word adaptation. In every
animal and every plant the trained eye sees unending examples of
adaptation; that is, of a fittedness to the work it has to do. The
modern scientist feels sure not only that the animal is fitted to his
work, but that he has been so fitted by the work; that the very use he
makes of his organs has determined their structure. This work has
decided that the structure which he has is the structure that shall
survive and shall produce other structures like itself. Adaptation
therefore does not simply express the idea that the animal is adjusted
to its surroundings, but it further suggests that the animal by
gradual process has become thus adjusted. The word adaptation applies
not simply to the result, but also to the process. The scientist does
not consider the animal a final and complete result. He thinks it
still in a state of flux, and so long as its line lasts it will be in
a state of flux. Change is about it on every side, and it must adapt
itself to this change or it will pass away. It may adjust itself, as
has been previously stated, by moving to another environment in which
it feels more at home, but unless it does this, if there come much
change in its present surroundings, it must either meet the
difficulty by altering itself, or it must give up the struggle. The
alteration is unconscious so far as the animal is concerned. It is
seriously to be doubted whether there is any recognition of the
process on the part of any animal excepting man. But though the
process be unconscious, it is none the less there. Slowly and
gradually the animal and the environment are becoming adjusted to each
other.
While it is exceedingly difficult to lay our hands on any animal which
is at present visibly changing its structure, it is not hard to find
closely related animals. These are nearly alike in structure in most
respects. In a few points, however, they may differ materially, and
these points are often directly concerned with different habits of
life. Considered in this aspect, these adaptations of a single organ
separately examined form an excellent argument in favor of that
gradual alteration of the entire organism which evolution suggests.
The most primitive struggle in which an animal can possibly engage is
the effort to maintain its own life and vigor. This struggle will
result in certain adaptations for the individual, adjustments which
make for the safety of the animal himself. These form the subject
matter of the present chapter.
The farther up the animal kingdom we pass in the study of adaptation,
the more likely we are to find changes which have but little bearing
on the safety of the individual. They work for the good of the entire
species, sometimes to the distinct disadvantage of the individual. The
King Salmon may make its long run to the headwaters of our western
rivers, deposit its eggs, have them fertilized, and then float down to
death. But it does not die before abundant preparation has been made
for the continuance of the race. Such adaptation for the good of the
species will be considered in the next chapter.
The first and most important struggle any animal has to enter is the
never-ending battle for its food. Occasionally there is a similar
straining after the air it breathes. But ordinarily air is
sufficiently abundant, except to animals living in the water, where
the supply is always more or less restricted and easily becomes
exhausted. But food is the constant need of every organism, and most
creatures die for lack of it. In this struggle the animal is pitted
against those of his own kind, rather than against those of other
species. Even his brother is his enemy, for he desires the same food.
In many a nest of birdlings one of them fails to reach its development
simply because the parent either is unable to find or it cannot carry
enough food to satisfy all the hungry mouths in the same nest. Before
the nestlings are ready to take their place in the struggle for life
outside and hunt their own living, one or more of them has succumbed.
After the battle for food comes the struggle for shelter. For most
animals there is no such thing as shelter. They are exposed to the
inclemencies of the weather and to the depredations of their enemies
without the means of retiring into any situation which might protect
them. In the higher animals, especially when they are warmer blooded
and their bodies must be kept at a higher temperature, some form of
covering has come to be almost universal.
Though comparatively few animals are prepared to seek shelter from the
cold, all of them have enemies against whom they must battle. These
foes may wish to eat them or may simply wish to get them out of the
way. In either event this struggle is so persistent and so keen that
after starvation it is probably the source of the largest loss to the
animal kingdom.
Considering first the feeding habits of animals, we find they are
exceedingly varied. Some creatures simply engulf other and more minute
animals, often only microscopic in size, in such quantities as to
satisfy their hunger. Others, feeding upon larger plants or animals,
must have some means of breaking off particles of this food; still
others confine themselves entirely to nutritious fluids, and must have
organs adapted to this particular type of food.
Insects are so common that anyone, who cares to, may easily verify
what is here described. It will take nothing but a clear observant eye
and a little patience to make out what is suggested. Each of our
common insects has one of two clearly defined habits in the matter of
food. Either it eats solid food, which must be made fine before it can
be taken into the mouth, or it feeds upon liquids. These liquids may
be easily accessible like the nectar of flowers, in which case one
sort of mouth will serve; or they may be the juices inside the tissues
of animals and plants, when an entirely different type of mouth must
be employed in their acquisition. Perhaps the most easily found
representative of the biting type of mouth, which breaks up solid
food, will be seen in the common grasshopper. Doubtless each one of my
readers has at some time taken a grasshopper into his hand, and,
holding the tip of his finger against the insect's mouth, has promised
the creature its freedom on condition that it disclosed its
reprehensible habit of chewing tobacco. The grasshopper surely
complied, and I trust the promiser was as good as his word. The
grasshopper's head is so placed that, while it is at the front of its
body, the mouth is directly on the under side of its head, while the
eyes are at the top of the front of its face. Under these
circumstances it cannot see what is going into its mouth, and this
makes an interesting variation of conditions to which it must adapt
itself. The means by which it accomplishes this will be clearer if the
mouth of the grasshopper be compared with our own. Our lips are upper
and lower, but the grasshopper has a front lip and a hind one. The
broad front lip is easily seen at the forward side of the mouth. Just
behind it, serving the purpose of our teeth, is a pair of hard jaws
with horny tips upon them, which serve to break small pieces from its
food. While our jaws and those of all other backboned animals work up
and down, so that we may be said to have an upper and lower jaw, the
grasshopper and all of his insect, crab, or spider relations, which
have jaws at all, have them right and left, and they work from side to
side. Behind these harder mouth parts is found a pair of softer jaws,
each of which has on it a little finger-like feeler. With this pair
the insect holds its food while the hard jaws break it to pieces. The
hind lip follows, and is also provided with short finger-like feelers.
The feelers on the hind lip and on the soft jaw are necessary because
the eyes are so placed as not to be able to see what goes into the
mouth, hence the insect must make up for the loss of sight by the
addition of touch. The same type of mouth as the grasshopper has will
be found among the beetles. Here the males sometimes have the hard
jaws so enormously enlarged that they are known as pinchers and have
given to their owners the name of pinching bugs. All insects with such
jaws as these use them for breaking up solid food.
A glimpse at the mouth of the butterfly captured on an adjoining
flower will show a most remarkable variation from that seen in the
grasshopper. Practically all of the mouth parts mentioned are present
in this insect, and its early ancestors had their organs practically
like those of the grasshopper. Now they are so modified and united
with each other as to be almost unrecognizable. The pair of soft jaws
has become very much elongated, and they lock together in such a way
as to enclose a hollow space between them through which the creature
can suck its fluid food. Not only have these soft jaws joined
together, but, because they have become so much elongated when not in
use, they must be coiled up like a watch spring and laid between two
hairy lip-like processes which correspond in reality to the two
finger-like feelers of the grasshopper's hind lips.
The butterfly, lighting upon the corolla of the flower, uncurls this
long "tongue," and through its hollow center pumps up into its crop
the nectar which the flower has stored in its base. When the butterfly
comes to get the nectar from the flower, it rubs upon its own hairy
body pollen from the stamens of the flower and carries it to the
pistil of the next flower of the same kind which it visits. Most of
us have at some time sucked the nectar from the back of a torn
honeysuckle blossom and approved the taste of the butterfly in this
matter. If the airy creature be watched as it lights upon a flower, it
will not be difficult to see it uncurl this long tongue and probe the
depths of the flower. If the butterfly be taken in the hand and the
tip of a pin inserted in the center of the coiled tongue, it can be
uncoiled without the slightest harm to the butterfly.
Insects which wish to use for their food the juices of other animals
or of plants do not find them so easy to gather. In the mosquito most
of the mouth parts are developed into slender pointed bristles wrapped
in a hind lip. These bristles serve to puncture the skin of the
creature attacked, while the curled lip serves as a tube through which
the blood may be extracted.
If, while sitting on the porch on a warm summer evening, mosquitoes
begin to annoy, let one of them at least serve to show his method of
procedure before he is destroyed. Allow the creature to alight upon
the back of your hand and slowly raise the arm until the eye looking
at near range can see the head of the mosquito, which, by the way, is
sure to be a female. Males in this species are entirely harmless. They
never eat after they have grown up; that is, after they are truly
mosquitoes. But the female is very assiduous. Alternately raising and
lowering her lancets from either side, she pierces, then saws, her way
down through the flesh until she has buried her instruments in her
victim and her head rests against her prey. Now a pumping motion of
the abdomen will be apparent, and this continues its accordion-like
action until it becomes more and more distended. The insect only gives
up its task when the entire abdomen is swollen into a great red ball
of blood. The mosquito will now slowly withdraw its instruments and
retire from the scene, if permitted to do so. If there is any fear of
annoyance from the bite, a drop of ammonia immediately applied will
counteract any irritation which would have been produced by the saliva
of the mosquito. The insect is not intentionally vicious in this
procedure. It is simply gathering its own natural food, though this
does not make it less annoying to us since we are its victims. The
swelling produced after the bite is the result of the action of the
saliva the mosquito injected into the wound. The opening through the
tongue is so small that blood would readily clot inside the tube and
prevent its further usefulness, did not the mosquito inject the
secretion of its salivary glands into the wound. This acts upon the
blood in such a way as to prevent its coagulation.
Anyone who thinks carefully can add numberless specializations for
food getting. For instance, primitive mammals have little pointed
teeth which fit them for feeding on insects. In each of the great
order of mammals a special development of these teeth has occurred.
Among the rodents or gnawing animals the front teeth have become long
and chisel-shaped for nibbling. The horse has formed them for nipping,
and his hind teeth for grinding. In the dog the teeth near the front
have become long for tearing his flesh food, while his hind teeth,
working with the motion of scissors, cut it into pieces.
A second great class of specialization is seen in the changes of habit
that provide the animal with shelter. The home seems so necessary a
part of human life that it is almost impossible to think of an animal
having nothing that in the faintest degree could be called a home. We
at least expect it to have some sheltered place in which it passes
most of its time and to which it returns after its wanderings. The
great majority of all animals have no such home. The place in which we
find them to-day may not be the place in which they will be to-morrow.
All places are alike to them. The ordinary conduct of their daily life
drives them about in the search for food. Their attempt to escape from
their enemies leads them each day into new situations, and they may,
and probably do, have no power to recognize the old location if they
return to it. When we come to the backboned animals there is a little
more tendency to a stationary location. The sun fish may frequent the
same reach of the stream, the trout may haunt the same pool, year
after year, but a great majority of fishes doubtless move
indiscriminately up and down the stream or about the lake or ocean and
are not found two successive days in the same place. The same may be
said of frogs. For a time a particular frog may have a fondness for a
special bend in the stream, but it is only a temporary fondness, I
believe.
Our own need for shelter is the prime motive in leading us to build a
home, and this necessity arises first of all because of our warm
blood. What we are accustomed to call cold-blooded animals are not
truly so. Their blood holds practically the temperature of their
surroundings. As the air or the water in which they live grows warmer
or colder the bodies of these creatures alter with it. Consequently
they are active when the temperature is high and grow more sluggish as
the thermometer falls. When the day grows distinctly cold the animals
may go practically dormant.
Only the birds and mammals have warm blood, and of these the birds are
distinctly the warmer. Whereas the temperature of the mammals runs
from about ninety-eight to a hundred degrees Fahrenheit, that of
birds lies somewhere between one hundred and five degrees and a
hundred and ten. Creatures which are warmer than their surroundings
must have some protection against chilling. Accordingly both mammals
and birds have clothing. In the case of mammals the covering is fur,
in the case of birds feathers. In some of the tropical animals like
the elephant and rhinoceros, or in man, who has learned to protect
himself in cold regions by making clothing for himself, this hair is
very short, and except where serving for ornament is quite scanty, no
longer being of use as a protection. But the great majority of all
mammals are well covered with a dense coat of hair. In many of those
living in the colder regions there is in reality a double coat. The
fur seal of the Alaskan Islands is so provided. A set of long hairs
deeply fastened in the skin forms a covering, which shows on looking
at the seal. Underneath this layer, and set but lightly into the skin,
is a short coat of very much finer hair known as the underpelt. When
the skin is taken from the seal it is split by machinery into a lower
and an upper layer. When so split the deep-seated pits of the long
hairs are cut, and these hairs come out. The fine underpelt thus laid
bare is what is commonly known as sealskin. Fashion has decreed that
this must be dyed a rich brown, although when taken from the animal it
is nearly mouse gray.
The birds have need for better clothing. To begin with, their blood is
much warmer, and hence needs better protection from outside cold. In
addition such of them as fly high must be prepared to stand great
variations in temperature. For these purposes birds need a covering of
the finest type. This clothing, in addition, must be extremely light
because the creature must carry it into the air in flight. All of the
requisite conditions are thoroughly met by the feather, which is the
lightest and warmest clothing known to man. If at night we wish,
regardless of expense, to keep ourselves warm with the lightest and
warmest of covering, we send to the Arctic Sea, and from the breast of
the eider duck we pluck the down which lies between the warm blood of
the duck with its temperature of one hundred and seven degrees and the
water in which the iceberg floats.
Young mammals and birds, before their clothing has well formed, are
naturally susceptible to cold; this leads to the first genuine
approach to a home among animals lower than man. Birds lay their eggs
long before the creatures inside of them are ready to emerge.
Accordingly they have learned to build nests in which to place these
eggs, and to protect them from the outside air; meanwhile the bird
keeps the eggs warm by close contact with its own body. The lowest of
the birds may lay their eggs simply on the ground without any special
protection. As we rise in the scale of the bird world we find nests
provided for the eggs. These nests become increasingly complex and
specialized, until we reach the oriole's home with its wonderfully
woven mass of fiber, which, in spite of its apparent looseness,
supports well the weight of the mother bird and of her eggs. The
robin, not content with making a woven basket, plasters it with clay,
and makes an absolutely impervious nest.
When we remember that both mammals and birds are the modern
descendants of cold and scaly reptiles of an earlier geological time,
it becomes interesting to compare their clothing. Evidently in the
mammals hairs began to come out between the scales. Gradually the
scales became fewer and the hairs more abundant until finally the
scales have all disappeared, except those that remain as the claws on
the toes. The ancestors of the birds, on the other hand, boldly
transformed their scales into feathers.
Another need for shelter arises in connection with the approach of
winter. This problem of withstanding the cold season is complicated by
the presence of two new factors. First and most directly, the cold
itself is a distinct obstacle to the comfort of many of these
creatures; as a secondary result of this cold, the food of many
animals disappears entirely in winter. Most of our birds meet this
difficulty by changing their base of operations. When the north grows
cold these creatures fly to the south. Some of their migrations cover
enormous stretches of country. Our bobolink, so well known and loved
by all watchers of spring migrations, passes twice a year between the
latitude of New York and Rio Janeiro. One of our most careful students
of bird migration says that the Golden Plover makes, twice each year,
the long journey from the Arctic shores of North America to the plains
of La Plata.
Different fur-covered animals have specialized to meet the winter by
any one of three different methods. They may brave it out, hunting for
their food as best they can all winter long. Such a course is pursued
by the rabbit. Again like the squirrel, they may store large
quantities of food during the summer, and on this provender they may
subsist during winter, remaining for most of the time near their
hiding-places, which, however, they may frequently leave upon warm
days. A third method is less common, but very interesting. The
groundhog or woodchuck is the best-known example of the group. It
remains asleep, or, as it is technically known, dormant, during the
winter. This stupor is more profound than ordinary sleep, and from it
these animals awaken with difficulty. It is needless to remark that
the groundhog's behavior on the second of February has no relation
whatever to the weather we are to have later in the season. This is
coming to be pretty generally understood. While the newspapers each
year comment upon the groundhog and his shadow upon that day, year by
year the notice has more of humor in it, and fewer people pay any
attention to it.
As for the backboned animals which are cold-blooded, these must,
unless they are fish, give up the struggle completely, bury themselves
in out-of-the-way places, and go worse than dormant. They often become
absolutely cold and stiff. In the case at least of fish, it is quite
possible for them to be frozen stiff, even to be enclosed in cakes of
ice, and still to recover if the encasement is not too long continued.
But the snakes, the turtles, the toads, the lizards, all are hidden
beneath the ground waiting in absolutely unconscious rest the return
of warmer weather.
After the need for food and shelter comes the continually recurring
necessity on the part of almost every type of animal to escape from
the unwearying persecution of higher creatures which would feed upon
it. The whole creation is a constant network of animals which prey
upon each other. It is the fate of a great majority of all creatures
to fall victim to other animals to whom they serve as food.
Accordingly nature has concocted many devices by which she assists
her favored children in escaping this relentless persecution. Perhaps
the most widespread means which animals have developed in order to
elude their enemies lies in the possession of power to escape their
attention. Two different factors may contribute to this end. The first
of these consists in the practice on the part of many animals of
remaining absolutely quiet in time of danger. This instinct seems to
be nearly universal. The first impulse of most animals upon
discovering danger is to remain absolutely motionless. The eye
detects, with ease, objects in motion. These same objects might
entirely escape attention were they quiet. A mouse could remain in the
corner of a room for a long time without attracting the eyes of the
occupants of the room. Let it but scamper across the corner, and at
once it is discovered. It is quite conceivable that early animals were
divided in the matter; that the impulse of some was to escape from
danger, while others, frightened by the presence of the enemy,
remained absolutely still. Each plan has succeeded. Those which, on
running, ran fast enough to escape became the parents of others like
themselves, led eventually to a line of animals in whose speed lay
their safety. Those, however, which attempted to escape, and failed
because they were not swift enough, had their line cut off, and were
thus less likely to be represented in the following generation. The
constant result of errors along this line would be to destroy the slow
and preserve the swift, and in the course of time it is quite
thinkable that only the swift should remain. As the movements grew
more and more keen, even the slower of these would pass out, thus
tending always to produce the succeeding generation from those who
were most rapid, and hence most likely to transfer to their children a
similar power.
But there is another tendency of animals which leads them when
frightened by their enemies to remain quiet. If this impulse is obeyed
thoroughly enough, it is easy to see how the owner of this habit might
entirely escape detection by his enemy. Any restless animal unable to
restrain his nervous agitation naturally betrays his presence and is
picked off. The result of evolution along this line would be the exact
reverse of the preceding. Those that lay most absolutely quiet would
be the parents of succeeding generations, while those who were slow in
coming to rest, or were indifferent about remaining quiet, were picked
off, and their tendency eliminated from the future of the species. In
this way many animals have come to keep entirely quiet in the presence
of danger. It is not a sign of high intelligence. As a matter of fact,
it is rather a stupid procedure, so far as the animal itself is
concerned, but it is a preserving stupidity, and many animals have it.
The "June Bug" (which is not a bug, but a beetle, and arrives in May)
has this interesting habit of keeping quiet. If in its flight it
strikes the globe of an electric light, it falls at once to the
ground, and remains perfectly quiet for a time. After a short interval
it recovers and starts out to regain its previous activity. But this
recovery is by slow stages, and the whole procedure on its part looks
exceedingly stupid.
The little snake with flattened and expanded head, known as the
blowing viper, or puff adder, is one of the most amusing
representatives of the tendency to "play dead" that could well be
found. If you strike him the faintest blow with the lightest stick, he
at once goes into apparent convulsions, in which he seems to suffer
the greatest agony. Then, throwing himself upon his back, he, to all
appearances, yields up the ghost. If, however, you retire but a slight
distance and keep your eye upon him, you find that his ghost returns
after a comparatively short absence, and he slinks away out of danger.
This is the most effective exhibition of this kind with which I am
acquainted.
As for the habit of "playing 'possum" on the part of our opossum, the
trick would seem to be particularly inane. The truth of the matter is,
what is attributed to an unusual brilliancy on the part of the
creature is positively unusual witlessness. The animal has an
exceedingly small brain, as compared with that of a dog of similar
size, and to anyone who knows brains at all this particular organ
would not be looked upon as furnishing its owner much ability. The
fact is that the opossum has exceedingly small wit, and this little
deserts it in an emergency, as a result of which he grows helpless and
motionless. This is often supposed to indicate great wisdom. There may
be wisdom in it, but it is the wisdom that lies back of all nature. It
certainly is not the wisdom of the opossum.
Man himself possesses to a marked degree this impulse to keep quiet in
danger. The man from the country who is visiting the large city,
suddenly startled by the "honk" of the auto horn, finds his power of
movement promptly arrested, and he is not unlikely to be struck and
injured by the machine from which the city dweller would easily
escape. This is not particularly to the credit of the city dweller,
who, when in the country, may find himself similarly startled by the
sudden appearance of the calf, the pig, or the sheep. The bull, which
a country boy, accustomed to him from childhood, will drive with a
willow switch, is a source of terrified concern to the city man.
While the trick of keeping quiet serves many an animal in time of
danger, there is another device for escaping attention, far more
common and widespread throughout the animal world. The eye does not
easily see an object if it is colored like the background against
which it stands. A host of animals find their main safety in being
indistinguishable in color from the surface on which they live. There
are many biologists who seriously question whether protective
coloration, as Darwin called it, is as effective as he believed it. In
some quarters it is the present fashion to doubt protective coloration
entirely. No one has yet shown any principles which will better
explain the great color scheme of the animal world, and until such
explanation is forthcoming I believe it will not be wise for us to
discard the idea of protective coloration. No doubt it has been
overworked by enthusiastic believers in its efficiency. At the same
time, to overlook it completely, is, I believe, to make a greater
error. I have little doubt that when the broader explanation comes,
which will satisfactorily explain the color scheme of the animal
world, the idea of protective coloration will be found, not so much to
have been wrong, as to have been but partial. It will be included
under the broader principle which takes its place and will not be
supplanted by it.
The idea of protective coloration is that very many animals have
ordinarily come to be colored like the background on which they live.
The process has taken many generations, and is very slow, but is none
the less sure in the end. In most cases the animal is probably
entirely unconscious of this point in its favor, and usually it does
nothing to assist the deception. The result is none the less effective
because the animals themselves are unconscious of the process. The
cabbage worm is green in color like the cabbage. This does not mean
that it got green by eating cabbage or by longing for greennesses.
Through long years the enemies of the cabbage worm have been picking
it off the plants on which it fed. This does not imply that cabbages
as we know them are very old, but cabbage worms doubtless ate the
leaves of the sea-kale long before man had cultivated it into cabbage.
During all these years the enemies of the caterpillars, generally in
the shape of birds, have been assiduously gathering them up.
When we see how much the various members of the same human family may
differ in complexion, how much the various pigs in the same litter may
differ in size and in coloration, it is easy to understand that among
these caterpillars which have eaten the cabbage there must have been
considerable color variations. I do not imagine for a moment that the
birds had any preference for any particular color in their cabbage
worms. They took every caterpillar they saw, but they naturally first
saw those that were least like the background on which they lived.
The only caterpillar which was effectively hidden from his enemy was
the one that was indistinguishable on the leaf. If it escaped in this
way, the probabilities are that it would produce young which would be
at least a little more likely to be green in color than the progeny of
its darker-colored brothers and sisters. By this continued process the
birds steadily weed out the darker-colored specimens. There would
result, in the course of time, a race of caterpillars, whose ancestors
for so many generations back had been light green in color, that there
is little likelihood of any of the older and darker forms turning up
again. In the course of time all dark tendencies will have disappeared
from the family and practically all of the group will be light green.
Any sport or variation in the shape of greater conspicuousness would
fall a quick prey to the enemy and its line be cut off forever.
The same sort of activity has resulted in the peculiar green color of
the katydid. This creature lives chiefly upon the leaves of trees and
shrubs. This insect is so large that, even though it is leaflike in
color, it might still be conspicuous. As a result those katydids whose
wings were most like leaves in form were least likely to be picked up
by the passing bird. This sort of protective appearance is intensified
by exactly the same means as that which brought about protective
coloration. The katydid least leaflike in appearance was eaten first.
Thus those most leaflike remain until the last, and are most likely to
produce young. Again, it was not the fact that they lived among leaves
which made them look leaflike, but it is because they look like leaves
that they escaped being devoured.
The katydid has materially assisted in its own preservation by being
active chiefly at night. In the daytime it keeps comparatively quiet.
Thus seated upon a twig, especially if hidden among the leaves, it is
almost unnoticeable. At night, however, it moves about more freely,
seeking its food and eventually its mate. At such times it becomes
distinctly more conspicuous because its wings are steadily fluttering.
The hind wings are filmy and are very light green. The creature looks
most ghost-like as it flies through the evening air.
A very similar history lies back of the coloring of the ordinary toad.
Though descended from the frog, and originally a creature of the
water, the toad has long since adapted itself to live upon the dry
ground. It still produces its young in the water as it did when a
frog. Whereas the childhood of the frog, that is, its tadpole stage,
is very long and it assumes its adult form comparatively late, just
the reverse is the case of the toad. The young hasten through their
tadpole stage within a few weeks, and assume the shape of the parent
toad when about big enough to cover your little fingernail. Now they
leave the water and seek dry land. Naturally they make the change when
the land is damp, that is, after a warm spring rain. People seeing
these multitudes of little toads hopping around over a bare spot of
ground, and remembering the rain of the night before, insist that it
has rained toads. Of course it never rains down anything which cannot
evaporate up. The stories of showers of toads and of earth worms, with
an occasional fish, or even creatures of larger size, are all pure
myths. There are conceivable tornadoes after which there might be a
shower of such creatures, but at such a time it is likely also to rain
barn roofs and buggies. You may be sure that toads which come down in
the rain are dead after they strike the ground.
The little toads started out, perhaps a hundred at a time, from the
small pool in which their eggs were laid. These creatures find dragons
on every side. The gartersnake comes along and gets his first toll;
the heron follows him and takes such as catch his hungry eye; the
turkey gobbles up his from what are left. By the time the toad-eating
creatures in the neighborhood have taken such as they found, there are
very few remaining. These doubtless have been left for a very good
reason, generally because they were not noticed. This was because they
looked like the ground on which they sat, and because they kept
perfectly quiet while the enemy moved about. This process has gone on
so long that the toad has come to be astonishingly well protected by
its resemblance to the ground. This likeness it intensifies by its
interesting habit not only of keeping entirely quiet, but of dropping
its nose to the ground, instead of sitting high on its front legs, as
it does when not in danger.
I have noticed that if a snake and a toad be placed in the same cage,
when the snake approaches to capture the toad the toad drops into a
squatting position, and is very likely to blow himself up until he is
rounder in outline than he was before. Whether this is a deceptive
trick which makes him the more resemble a stone is more than I can
say. I do not remember having seen our eastern toad do it. I have seen
it happen a number of times in the laboratory of a Colorado
naturalist, and it is quite possible that in the open country more
sparsely covered with vegetation than is our ground in the east this
inflating device may serve the toad more effectually than if it kept
its own outline.
Even among creatures far more active than the toad and the katydid an
inconspicuous color must certainly result in distinctly better
protection. Everyone knows the jay and the cardinal when first he has
seen them, if only he has a slight acquaintance with their pictures.
They are so conspicuous that we recognize them at once. More common in
my region than the jay or the cardinal is the red-eyed vireo. This
creature moves industriously in and out among the leaves of our trees.
It is persistently in motion, is nearly constant in song, and is a
bird of fair size, being larger than our English sparrow, though
smaller than a robin. Many a nature lover will recognize twenty-five
or thirty birds at sight without any difficulty, and not know the
vireo. Yet the vireo is more common than two-thirds of the birds he
knows. There can be but one reason for this; the bird is
inconspicuous. The olive-green of its back, with its light under
parts, serves to hide it completely amid the foliage. Even the
bird-lover learns to find it first by its jerky song, and then by
watching for its movements among the leaves.
One aspect of protective coloration has been brought to our attention
by the artist, Mr. Abbott N. Thayer. He first clearly explained why it
is that animals are usually so much lighter on the under side than
they are upon the upper. Mr. Thayer proves his position by taking some
ordinary cobblestones and painting one of them a uniform color and
placing it upon a board painted the same color. One would think the
stone would be inconspicuous; as a matter of fact, is quite easily
seen. The underside of the stone, turned away from the light, is so
shaded as to mark a distinct boundary between the stone and the board.
Another cobblestone was colored on its upper side like the board, but
the color faded into a lighter and lighter tint until the bottom of
the stone was nearly white. This stone, placed upon the board, was at
a short distance nearly invisible. In other words, although the
pigment was actually lighter on the under side, it was so much less
intensely illuminated, that the result was the same in tint as the
other side under the clear sharp light of the sky.
Many a person, looking down into the water from a bridge, sees nothing
whatever of the fish in the water below, because their backs are
exactly like the bottom of the stream. Suddenly one of the fish, by a
quick movement, turns its lighter under side over in such a way that
it is clearly illuminated from the sky. Immediately a flash as of
silver strikes the eye of the onlooker and makes him aware of the
presence of the fish which had previously been undetected. If rendered
thus suspicious, the observer will carefully examine the bottom of the
water, he may quite likely find dozens of fish which had previously
escaped his attention.
Nature is very versatile. So many of her apparently chance ventures
have proved successful that she has retained many devices by which her
children may be safe. One of these, which is doubtless often quite
effective and may serve to save an animal's life, is that of being
able to emit an odor so nauseating as to offend the enemy's sense of
smell, and doubtless remove the keen edge of his appetite. It is not
uncommon among the group of insects properly known as bugs to possess
an exceedingly unpleasant odor. Anyone who has handled a squash bug
will know exactly what I mean, and there are other members of the
group not so common as the squash bug, which, at least to the human
nose, are distinctly offensive. Some of the beetles also save
themselves by this device.
One of the most interesting developments of this peculiarity is found
in the case of the common skunk. This creature has in each groin a
gland capable of secreting a highly offensive fluid. Ordinarily this
liquid is kept safely within its sac, and for a long time none of it
may escape. When closely cornered, the skunk will turn its tail toward
the enemy and with a quiver and a flip of his tail it can guide the
openings of two little tubes that come out along the root of the tail
in such fashion as to eject the fluid in a fine and foul-smelling
stream against the animal from which the skunk would escape. Once
fairly hit by this fluid, I imagine most animals will drop the skunk.
A dog surely will, and will hate himself for having made the attempt
to capture anything which must be so ignominiously allowed to escape.
If ones clothing is well saturated with it, it is nearly useless to
hope to remove the odor. A dog will carry the smell for several weeks.
For a long time it will be so strong as to make him an unfit denizen
of the house. Even swimming in deep water does not remove it. After
two weeks, although he may seem to be practically free from the odor,
a light rain will bring it all out again and make him nearly as
offensive as before.
Not as prompt in its action, but in the end nearly as effective, is
the protective device which the toad sometimes uses to his distinct
advantage. May I be pardoned a personal account of this particular
feature. It was my good fortune to be for a short time a student in a
class taught by Edward Drinker Cope, one of the most brilliant of our
American biologists. Prof. Cope mentioned in class the fact that the
Batrachians (the group to which the toad belongs) have in many cases
the power to emit from their skin a fluid which is sufficiently
nauseous to deter an animal from eating the creature that secretes it.
Upon such authority as this, I had no hesitancy whatever in repeating
Cope's statement. One morning I had a class in the field studying the
ground ivy, whose dainty blue flowers were lifting themselves out of
the dewy grass. While we were thus engaged, a toad joined the circle.
He came out of his dewy retreat clean and fresh from his morning bath.
I took him in my hands, and made him the subject of an immediate
lesson. I showed to my pupils his eyes and his interesting method of
handling them, his tongue and its strange insertion; showed them how
to look into his mouth and look up his ears to his ear drums, and
pointed out many other interesting facts. Then I told them how Cope
had said that the toad had power to emit from its skin a fluid so
nauseous that many an animal hesitates to eat it. This is the first
peculiarity I had mentioned which I had not myself observed, and a
scientific qualm came over my conscience. Why had I never verified
this statement which I had so frequently repeated? On the impulse of
the moment, with the bright, clean skin of the creature fresh from the
dewy grass, making it less than usually repulsive, I ran my tongue up
its back only to find that it had no taste whatever. I was of course
surprised, but I was not foolish enough to deny, as the result of one
observation, the statement of a good scientist. The observation,
moreover, was one which I naturally did not care to repeat with any
frequency. Of one thing I was sure, toads do not always have an
unpleasant taste.
A year later I had a class down by the side of a neighboring pond. The
pool was not an attractive one, and I had picked from it a more than
commonly unappetizing looking toad, which proved to be a mother which
had not yet laid her eggs. As I held her in my hands and exhibited her
various points to my pupils, I told them of Prof. Cope's statement. I
also told them of my unsuccessful attempt the previous year to verify
the statement. I added, however, that I would not repeat this
experiment on this unappetizing specimen. Hereupon the toad not only
exuded, but squirted, from a gland over her left shoulder blade a
fluid, milky-like in appearance, and forming a jet as thin as a
needle, but ejected with force enough to strike my face, which was at
least fifteen inches away. I moistened my finger on my tongue, lifted
the fluid from my cheek, and tasted it. Cope was right. A toad can
exude a most nauseous fluid. Horsechestnuts extracted and distilled
might possibly provide something as bitter. Why did I not find this in
the preceding case? I have too few observations on which to base a
conclusion, but I have a suspicion as to the reason. In the case of
the toad which spurted the fluid in my face, we had a creature with
whose life were tied up the lives of her many offspring, to be
produced from the eggs she was so soon to lay. Under conditions like
these, nature is more than commonly careful of her children. Whether
this be the reason or not, toads do not always have an unpleasant
taste, but when they do it certainly is most unpleasant.
There remains to be considered the most effective plan yet mentioned
of escaping the enemy, and that is of really escaping. In all the
devices we have considered thus far the enemy is eluded. When the
creature lies quiet, or finds safety in its protective coloration, or
in its bad taste, or unpleasant odor, it still remains in the presence
of the enemy. A more progressive plan altogether is to escape the
enemy by flight. The great advantage of this plan lies in the fact
that the acquisition is valuable for every purpose. The creature then
can escape the enemy, can range widely for food or for a mate. This
gives it an enormous advantage in the struggle for life. The power to
fly, in insects, was doubtless originally gained in the attempt to
escape the enemy. Among many of the lower animals it is nearly the
only purpose that flying serves. Later on it enables the animal to
pass from one food locality to another. In a few creatures it plays an
effective part during the mating season. These last are probably both
derived powers, and the original function was that of escape from the
enemy. The grasshopper has grown its long legs to serve him for
safety, and through them it is helped along, moving about chiefly by
leaps when it wishes to go any material distance. It is only toward
the very end of its life that the grasshopper has wings, and then they
serve probably to aid in the search for a mate. Among the birds flight
began simply in sailing out of the trees, into which the creature,
still half lizard, had crept to escape its enemy. The earliest bird
known to us had comparatively insignificant wings. There was really
more support in its tail than in its wings, and this would distinctly
indicate that it glided more than it flew. It had claws also upon its
wings, and it was probably the case that this creature crept into the
trees, at least in its earliest forms, and sailed down in a manner not
unlike that employed to-day by the flying squirrel. From such simple
beginnings came the wonderful power of flight in the birds.
Among mammals the attempt to escape from the enemy has led to an
interesting development, which will be more fully explained in a later
section when we speak of the history of the horse. The early mammals
walked flat-footed, as we do on our feet and as the raccoon and the
bear do on theirs. Gradually, however, as their enemies became more
fierce and better able to injure the larger mammals, the latter gained
in power of flight, and this gain consisted first in rising from the
toes, lifting the heels completely off the ground. At the same time
the leg and foot were gradually lengthened. Doubtless in this way the
fleet animals, like the deer, the horse and the giraffe, first came by
their long legs. Constant elimination of the short-legged ones, by the
pursuing enemy, resulted in the selection of the long-limbed ones for
breeding purposes, and hence to the ultimate elongation of the legs of
the species.
The method of escape from the enemy involves cowardice. "He who fights
and runs away may live to fight another day," and so it may be the
part of wisdom in the weak creature to escape from his enemy by
flight. It is a far more estimable process, from our standpoint at
least, to stand against the onslaught of the enemy and beat him upon
his own ground. This end is secured in many animals by acquiring horns
or by lengthening certain of the teeth. The horn is a very ancient
instrument of defense. When the reptiles ruled the land horns were not
uncommon. They consisted in those days of hardened scales, which
lengthened and fastened themselves over a core of bone. Such an
old-fashioned instrument, sometimes made of newer materials, still
remains the defense of a number of animals. The rhinoceros has upon
his nose a lengthened projection, which is what might not improperly
be called hair glued into a cone. This enormous horn is a frightful
weapon, both of offense and defense, and, when backed by the terrible
weight of the body of the rhinoceros, it can do as deadly work as
almost any instrument of destruction known to animals below the grade
of man. But, after all, this is an old-fashioned method, and the
rhinoceros is a relic.
Among the carnivorous animals the teeth, which were developed first
chiefly for the tearing of flesh in its consumption, became effective
for their courageous owners. Because these tearing teeth are well
developed in the dog they have come to be known as canine teeth.
Usually where an animal can use its teeth effectively for offense or
defense, it is the canine teeth that are thus modified. The cat has
developed them better than the dog, and one of the cats of a bygone
geological period had canine teeth so magnificently enlarged and so
sharp at the back as to give this frightful creature the name of the
saber-toothed tiger. The long teeth in the upper jaws of the elephant,
commonly known as tusks, are not canine teeth. The elephant has
completely lost his canines. His tusks are his incisors, and they have
developed as have almost no other teeth in the mammals.
These are only a few of the numberless devices nature has evolved for
furthering the success of her children. There are so many others that
to many of us they form almost the chief point of interest in our
study of a new animal, or our closer observation of an old friend.
CHAPTER V
ADAPTATION FOR THE SPECIES
The strife, as we have described it thus far, is a purely selfish
struggle. Every point gained is a point favorable to the welfare of
the individual animal. But nature is uncommonly careless of the
individual unless the advantage gained is also of use to the species
as a whole. Very often the life of an animal ceases when provision has
been made for its young. The male garden spider may have a long and
dangerous courtship, in which the uncertain temper of his ladylove may
lead her to bite off four or five of his eight legs. But her
ingratitude is not yet complete. He may have barely accomplished his
desperate purpose of fertilizing her eggs at all hazards, when she
ends the process by eating him. The male bumblebee fertilizes the
female in the late summer and then dies. She does not lay her eggs
before the next season. So it happens that no bumblebee ever sees its
own father, and no father bumblebee ever sees his own children. In the
honey bee the male, which has been fortunate enough to fertilize the
queen, pays for his honor by death within the hour. Superfluous
bachelors, among the honey bees, when the bridal season has passed,
are driven from the hive to die of starvation.
An animal need not always be successful himself, but it is more
essential that he hand down his successful traits to those who come
after him. It is more important for the future generation that an
animal should have had it in him to do great things, though he himself
really have never done them, than that he should have learned to do
great things on a meager original endowment. Not what an animal
accomplishes is important to his children, but what he has it in him
to accomplish. Accordingly Nature is full of devices by which those
who have proved their original endowment by winning out in the
struggle shall hand on this endowment to a subsequent generation. In
other words, Nature is anxious that they may successfully mate. Here
we are again on distinctly debatable ground. Darwin himself believed
thoroughly in what he called sexual selection. It is the essence of
this idea that the males and females have grown unlike, more
technically have developed secondary sexual characters, through the
choice of the mating pair. It would usually be the more serious loss
if accident should come to the female, for she may carry fertilized
eggs for some time. Hence, if both sexes may not become attractive, it
is usually the male that develops fine colors, ornamental appendages
or a captivating voice.
An interesting reversal of this process has taken place in civilized
man. His more savage ancestor adorned himself more lavishly than he
permitted his mate to do. With the advance of civilization man has
undertaken to defend his own mate most valorously. The result is it is
safe for her to be beautiful. Under these circumstances, however, it
is more necessary to her welfare that her consort be vigorous rather
than that he be handsome. Hence in the human species beauty has become
the prerogative of the woman, and this is increasingly the case the
higher the civilization. Whether woman suffrage and self-support will
reverse this process remains to be seen. There are indications that
point that way.
There are many biologists who are at present expressing serious doubt
as to the validity of sexual selection. As in the previous cases of
protective coloration, I believe it will be wise for us to retain,
even though with an interrogation point behind it, the idea of sexual
selection until such time as those who object to it have furnished us
with another theory which will more nearly account for the observed
facts. While entirely conscious of the possibility that there is a
weak spot in the theory, we will still tentatively hold to sexual
selection. The fact that beauty in women is so intensely attractive
to man, and that vigor and manliness in man are so attractive to
women, leads us to infer that among the lower animals, although of
course in a vastly less degree, vigor and beauty are also attractive.
The weakest point of the position lies in the fact that it probably
presupposes a higher degree of capacity for appreciation on the part
of lower animals than they possess. Those who deny the truth of the
theory laugh at the idea that a butterfly can see clearly enough and
care enough for what it sees to notice whether its mate has wings of
one type or of another. The size, number and position of the spots on
the wings of many butterflies are so nearly constant that they cannot
of themselves have been entirely determined by the choice of the
insect. Yet this may not preclude the possibility of the fact that,
while the spots were produced through some other agency, certain types
of them were selected by sexual preference.
If attractive coloration is effective anywhere in the animal world, it
will possibly be found among the insects, but it is especially likely
to be found among the birds. Very many field workers in these groups
feel quite sure of the value of attractiveness. When butterflies chase
each other up and down, circling and doubling, following each other
for long distances, it would certainly seem as if they were pleased
with each other's appearance. Some naturalists, especially those who
have worked chiefly in the laboratory, insist that it is the odor, not
the color of these insects, which is attractive, and some experiments
which have been made would seem to point in this direction. But the
creatures experimented upon most carefully were night-flying moths,
and it is quite possible that the sense of sight in the night-flying
moths has lost its vigor.
The great difficulty in understanding sexual attraction in insects, as
based upon beauty, lies in the undoubtedly lower development of their
nervous activity; in other words, in the apparent absence of anything
worth calling mind. I think no one imagines that a butterfly, looking
upon two other butterflies who are competing for her affections,
deliberates between them and determines to admit to the circle of her
friendship the more brilliantly colored male. Moths are so
irresistibly attracted to a light as to fly into it without apparent
power to withstand its influence. They repeat the flight again and
again until they are destroyed. If they react so vigorously to the
stimulus of the light, it seems not impossible that they may also act
vigorously to the stimulus of color pattern, and that the male most
beautifully colored, according to the nervous ideal of the female,
should win her unconscious regard. At least it is certain that, in
very many of the butterflies and moths, the attractive coloration is
chiefly displayed when they are moving actively about; and when they
alight and their enemies can the more easily capture them, they
conceal their brilliant colorings. Most butterflies are very brilliant
on the upper surface of the wings and very much duller on the under
surface. Hence in flight they show their colorings exquisitely, but
when they alight, and are thus more likely to be captured, they fold
the brilliant surfaces together in an upright position. In this way
not only is the dull side of the wings placed outward, but the wings
themselves are placed edgewise to the sky, and it is from this
direction that their enemies, the birds, are most likely to see them.
Once upon the wing these creatures display their beauty with much
greater safety because they can escape the birds very readily by use
of their exceedingly jerky flight. The butterfly's motion is as
irregular as any we have except the bat's. This eccentricity is one
great element in their safety, and makes it less dangerous for them to
display their attractive colorations.
One very large group of the night-flying moths have been named the
"underwings," because of the fact that their hind wings are very much
more brilliant than the front, and in lighting they fold the dull pair
back over the bright, completely concealing them. These creatures are
in the habit of resting in the daytime against walls, or stones, or
the bark of trees. The similarity in color between their front wings,
which alone show while sitting, and the background on which they rest,
is most remarkable. One may pass them again and again, although they
are of considerable size, and not notice them at all. Once let them
display their hind wings and the brilliancy of their color always
attracts immediate attention.
It is among birds, however, that brilliant coloration serves its most
effective purpose. The birds are alert, exceedingly quick of sight,
and are much more discriminating than insects in almost every respect.
It is not so impossible that these creatures might even voluntarily
prefer a distinctly more brilliant mate, though the voluntary
character of the process is not essential to its success. Men
certainly are constantly attracted to women for whose charm it would
puzzle them to account. If this is true with regard to men, it is
certainly probable that birds would be largely influenced by phases of
attractiveness, of which they were observant, but unconscious.
Certain it is that in many birds the males are far more beautiful than
the females. Perhaps the commonest illustration, and, at the same
time, one of the best is found in the so-called red-wing or swamp
blackbird. The male of this creature is a brilliant black, excepting
that upon the angle of the wing, spoken of roughly as his shoulder,
though in reality it is equivalent to our wrist, there appears a
splendid orange patch with a border of lemon yellow. When he folds his
wing he pushes this colored angle of the wing so deftly under the
feathers of his shoulder as almost to conceal it. When in flight the
bird is exceedingly conspicuous, showing, with every bend and twist of
his body, his gorgeous epaulets. Meanwhile, the female is likely to
pass unnoticed. She is dull in color and streaked like the grass among
which she lives. During the mating season the male hovers about her,
swaying from side to side in such a way as certainly to make it appear
as if he realized his good points and was bringing them to bear as
effectively as he knew how. After his mate has nested and is rearing
her young, it would appear that the male uses his brilliancy to lure
the observing enemy away from the nest containing his wife and
children.
Another illustration of the remarkable superiority of the male over
the female, in many parts of the bird world, is seen in the case of
the common barnyard fowl. The rooster is so much more gorgeous than
the hen that anyone reasonably acquainted with these birds cannot have
failed to notice the fact. In some of our modern varieties we have by
breeding colored them nearly alike. The original chicken is colored
much like the common Leghorns. Shades of red and yellow decorate his
neck and back, while the flight feathers of his wings and of his tail
and the sickle feathers which ornament the rear of his back and hang
over his tail are lustrous dark green. The hen meanwhile is very much
less brilliant in her contrasts. I shall speak more fully of this in
discussing polygamy.
The attraction of beauty is not the only lure by which a creature may
win its mate. Sound may captivate as effectively as beauty. This is
true of insects as well as of birds. Certain insects at least advise
their mates of their presence by means of a sound which they emit.
This is particularly noticeable among the group of straight-winged
insects to which the grasshopper, katydid and cricket belong. The
grasshopper has a ridge on the angle of his wing and a roughness on
the side of his leg. When these two are rubbed together the result is
sometimes a fiddling, sometimes a snapping or cracking sound,
differing in different grasshoppers. I doubt not these sounds are
pleasing to the female of the species, for they are always made by the
male. The katydid, instead of fiddling in this way, has a sort of drum
on the angle of his one wing, which he can rub over a tooth in the
corresponding angle of his other wing, thus producing the familiar
"katydid" sound. I have never succeeded in making a dead grasshopper
fiddle, but I have long known how to make a dead katydid say "ka."
Quite recently I have added to my accomplishment in this respect and
can make it say "katy." The "did" part of the song still lies beyond
my power. The crickets produce their sharp notes in much the same
fashion as the katydids.
One observer of the chirping of the cricket says that the pitch of the
song varies with the temperature. He has even worked out a formula by
which one can tell the pitch of the chirp, if he knows the
temperature, or, knowing the temperature, can determine the pitch. Of
course this is too mechanical; yet it indicates that there must be
considerable relation between the two; the warmer the cricket the
happier he is.
It is the males among insects that chirp their love songs. The females
never answer them. There is a peculiar notion that the female katydid,
when thus accused of some offense, replies "katy didn't." The truth of
the matter is that no female katydid ever replied to the accusations
of her lover, if accusation it be. She is absolutely dumb, not having
the drum upon her wings with which to reply. She is provided with ears
wherewith to hear, and, strange to say, she keeps them on her elbow,
as does also the cricket, while the grasshopper has his ears upon the
side of his body.
Everyone who lives in the country, or goes into the country in the
summertime, is sure to know the humming of the so-called locust. It is
an unfortunate fact that the word locust may have several meanings. It
is properly applied to one group of the grasshoppers. The creature
most commonly called a locust is a cicada, or harvest fly. When the
weather gets quite warm the cicada starts his love song. He has two
long flaps to his vest, and under each flap he has a vibrating drum
head. This is set shivering by a muscle on its under side. The female
cicada again is silent.
It is among birds that the love song reaches its finest development.
It may consist simply of a little chirp as in the chippy. It may
consist of two notes of a different pitch repeated steadily, as in the
tufted titmouse. It may attain considerable variation, as in the
robin. But in the choir of our best singers, like the catbird,
thrasher, and mocking bird, there is unending variation of notes. It
seems almost impossible to doubt the charming quality of this voice
upon the mate. It certainly is chiefly confined to the mating season,
and is indulged in almost entirely by the males. This does not mean
that a male does not sing excepting when he wishes to charm his mate.
But the time when he is in his most exquisite feather and most
charming mood is the time when he sings most sweetly, and this is the
time when he is taking to himself a mate. The love joy may so
overcrowd his life that he sings much and often, but the increase in
its amount and character during the mating season seems to proclaim
its purpose beyond a doubt.
In addition to the allurements above described there are certain
peculiar behaviors of the animal during the mating season which are
intensely interesting. Sometimes they consist simply of a wild
delirium of joy, which overpowers the animal completely and makes him
do wonderful things. Birds will fly with impetuous leaps in the air,
mount higher and higher, singing wildly, only to turn suddenly at the
top of the flight and drop promptly to the ground. I have seen such
ecstatic flights in the oven bird and in our rollicking gold finch. I
have seen a catbird on his way to a tree turn three somersaults, much
like those performed by a tumbler pigeon, after which he alighted upon
the bough. None of these acts seemed deliberately performed in front
of the females, but I have seen three or four killdeer parading in
most stately and precise manner, spreading their wings and fluffing
their feathers, performing a sublimated cup-and-cake walk amid a
circle of attracted females.
Even our little English sparrow, as I have previously mentioned,
fluffs himself up and spreads his wings and prances around in front of
his presumably adoring ladylove. But the weirdest performance of this
sort I have ever seen is that shown by the male ostrich. When he
becomes excited, swaying his body from side to side, he sinks slowly
upon his knees, until his body touches the ground, his wings spread on
either side and the feathers fluffed up so as to show every exquisite
plume in all its splendid beauty. The long neck is laid back until the
head, which is doubled sharply forward, is pressed almost against the
back, and in this strange position he sways from side to side,
apparently utterly oblivious, for a time, of everything. After about a
minute of this performance, he seems slowly to come to himself and
rise again to his feet. Now he is particularly likely to make vicious
attack upon anything within reach.
It is not only necessary that the animal should be able to attract a
mate. There may be more than one claimant for the damsel's affection.
In many animals we see provisions whereby the male may effectively
deal with his rivals. This is especially likely to be the case if the
animal be a polygamist. In every species there are produced about as
many males as females. If the polygamous habit leads one male to
gather about him a group of females, with whom he mates, it is evident
that he is displacing an equal number of rivals, and they are not
willingly displaced. Accordingly we find that polygamy is usually
accompanied by a belligerent disposition on the part of the males. In
our ordinary barnyard fowl this trait is very evident. The rooster not
only domineers over the hens, not only struts about among them in
stately fashion and gives vent to his feelings by his sonorous voice,
he must also drive away from the neighborhood any rivals for the
affections of his wives. Hence the rooster attacks upon sight the
neighboring rooster, and battles with him to his entire discomfiture
and sometimes to the death.
Among the members of the deer family this particular phase of the
relation between the sexes has produced in the males, and only very
rarely in the females, the magnificent branching horns. These are
intended not so much as a protection against the enemy as for an
offensive weapon in the battle for the mates.
Beautiful and stately as are these magnificent horns, they last only
for a part of the year. We begin to understand their meaning. When the
wolf is hungriest, toward the close of the bitter winter, the deer is
without horns. When the time for mating comes, the deer within a few
weeks grows his horns, which at first are covered with a plushlike
coating, known as velvet. After a while this dries and he rubs his
horns against the trees until they are clean and smooth. Now he is
ready for the battle royal.
In the case of the fur seals polygamy has carried its specialization
of the males to a remarkable extent. The bull seals are several times
as large as the cows, and are provided with terrific canine teeth.
With these they battle with a violence that very often results in the
death of one of the combatants. A successful bull seal who has
gathered about him a cluster of seal cows is seamed and scarred with
the marks of his annual combats.
One more type of adaptation can be profitably considered. Animals have
developed many devices which serve for the protection of their young.
The wonderful silk spun by the spider was evidently primarily intended
to serve as a covering for the eggs. Probably all of our spiders agree
in using the silk for this purpose. Many of them employ it for
practically no other, though there are half a dozen different uses to
which different spiders may put their silk. Under these conditions we
have a right to infer that silk was primarily developed as a coating
for the eggs. In the case of some of our spiders a little fluffy mass
of silk covers the egg, while a firmly woven sheet of silk covers both
egg mass and fluff, holding it flat against a wall or the trunk of a
tree. In some of the higher spiders, notably our bank spiders, the
silken covering becomes an effective cocoon, spherical in shape, with
a little opening at the top like the neck of a small bottle. The egg
cocoon is woven in a mass of tangled silk between the branches of some
tough weed which will be sure to outlast the winter. Into the egg
cocoon the spider may place one thousand or more eggs. Having thus
provided her children with a snug winter home, the spider dies. When
spring comes with the warm rays of the sun, the eggs hatch and the
cocoon becomes a creeping mass of minute spiders. At the time these
spiders appear there is nothing for them to eat. The obvious way out
of this difficulty is taken. At once there begins a progressive party.
Spider fights with spider, and the prize in each conflict is the body
of the victim, which is promptly eaten. The winners in the first round
pair off again, and a little later, as hunger drives them, another set
of combats comes on, resulting in another halving of the number of
spiders in the cocoon. This process continues until not more than
one-tenth of the original number of spiders remains. By this time they
have gained sufficient strength of leg and jaw, and sufficient
dexterity in the use of both, to make it safe for them to venture out
and try their fortunes among the accidents of a strenuous world. There
can be little doubt after this long process has worked its final
results which tenth remains. Chance plays but small part in this
game. It is the fittest that survive. When this procedure goes on
generation after generation, the result must necessarily be that the
spiders grow fitter and fitter for their work. This method is hard on
the little spider, but it makes good spiders.
Most insects die before their eggs hatch; accordingly they can pay no
attention to their own children. Whatever arrangements are provided
for the safety and strength of these offspring must be provided before
they appear. About the only care the majority of insects take in this
direction is to see that the eggs are placed where the young shall
find food as soon as they emerge. Insects' eggs are very small, and as
a consequence the creatures which emerge from them are likewise
exceedingly minute. As a result they cannot be expected to hunt far
for their food. Different insects use different devices by which to
overcome this difficulty. The katydid, for instance, must die with the
approach of fall. Her children will not appear until the following
year. Her food consists of leaves, but to lay the eggs in such a
situation would be a fatal process, because the leaf will drop off
before the eggs hatch. Accordingly, the katydid lays its shield-shaped
eggs in a double row near the end of a young twig. Next year when the
weather is sufficiently warm to hatch katydids, it is also warm enough
to force the buds on the end of the twigs. When the katydids arrive
their jaws are young and tender, but so are the leaves upon which they
are born. Hence there is little difficulty on the part of the young
katydids in finding an abundance of food. By the time the leaves have
grown tougher, the katydid's jaws are stronger, and the leaves will
still serve as food.
Everyone who is at all familiar with country life and gardening is
familiar with what is called the potato or tomato worm. It is a long,
green, smooth, caterpillar, as long and as fat as your finger and
provided with a horn upon his tail. The gardener may not know that
after a while this creature will burrow into the ground, and there
change into an oblong brown mass with a sort of a pitcher handle at
one side. Next year this pupa will split down the back, and from out
of the brown case will come a hawk-moth, which soon will fly with
rapidly quivering wings and feast upon the nectar of our moon flowers
or on that of the "Jimson" weed. Those who have cleaned these pests
from the potato or tomato vines will often have noticed one of them
covered with what look almost like grains of rice. This appearance
reveals an interesting story. Some time earlier an insect that looked
very much like a dainty wasp with a rather long sting in its tail
hovered over the caterpillar. This is the ichneumon fly. Eventually
lighting upon the caterpillar's back, it punctured the skin with its
sting, and deposited eggs within the caterpillar's body. These eggs
soon hatched and the little grubs worked their way through the body of
its host. The infested victim feeds upon leaves and fills itself with
rich food. These parasites eat the food, and, try as it may, the
caterpillar does not succeed in getting fat. After the grubs have
gotten their full growth, each of them eats its way through a little
hole to the outside of the caterpillar's body. Here it spins around
itself a little white case, and looks like a rice grain. As the
caterpillar moves about, these seeming rice grains are rubbed off and
fall to the ground. Next year there will come up new ichneumon flies
to sting fresh caterpillars and repeat the entire process.
Another remarkable provision for the young on the part of insects is
seen in the behavior of the big sphex wasp, known as the cicada
killer. The cicada, it will be remembered, is what is commonly called
a locust. The cicada killer is a magnificent big wasp, whose body is
nearly an inch long, banded with black and yellow, while the wings are
colored a smoky brown. This muscular wasp digs a long tunnel eight or
ten inches deep, which ends in a slightly larger room. Having provided
the location, he now sallies forth in search of the cicada. The heavy
song of the male probably serves as a guide to the wasp in case of
scarcity of cicadas, but the killer has apparently little difficulty
in finding his prey. The wasp pounces upon the insect, and in spite of
its strength and the thrashing of its vigorous wings punctures it with
his sting again and again. The poison of the sting entering into the
nerve centers gradually paralyzes, but usually does not kill, the
cicada. Now the killer carries its prey home, pushes it to the bottom
of the tunnel and deposits upon it a single egg. The wasp closes up
the hole and leaves the place. When the egg hatches and the grub of
the wasp emerges, it finds a big cicada just at hand, upon which it
feeds. By the time the cicada is completely devoured, the wasp grub
has obtained its full growth. After a short period of development a
new sphex wasp is ready to work its way out of the tunnel, find a
mate, dig a hole, and safely provide for its own children.
Still more remarkable adaptations for the care of the young appear
among the birds. Here the eggs are not to be deserted, but are to be
cared for until the young appear. These again must have attention
until such time as they are quite able to take care of themselves. The
birds are warm-blooded animals, and even their young, while they are
developing in the egg, are warm-blooded. Consequently the temperature
of the egg must be maintained evenly and uniformly, or there will be
no development.
The fish may drop its eggs carelessly upon the bottom of the stream. A
frog may deposit them in a mass of jelly and leave them forever. A
turtle may bury its eggs in a sand bank and abandon them to their
fate. The warm blood of the young bird demands more attention than
this. Accordingly, the parent bird has learned to make for itself some
sort of nest, in which the young may be kept properly warm until they
are developed. The ancestral bird, who was to be the progenitor of the
entire bird class, must have had some very simple method of providing
a place in which its eggs might be hatched. As the descendants of this
original bird have passed into new situations, the various lines have
taken upon themselves different shapes until we have the multiform
birds of to-day. The habits of the birds have also varied. Each has
adapted itself to the situation in which it found itself, and no
adaptation has been more varied and effective than the adjustment of
the nesting site. Nests are found upon the ground, in the bushes, on
the lower limbs, in the crotches of the trees, in the trunks of the
trees, upon their very summits, and on the tops of inaccessible crags.
To every sort of situation some bird has been enabled to adapt itself.
This has made it possible for very many more birds to thrive than
could have found a place in the world, had they all lived upon the
same plan.
In the case of the bank swallow his nest may be a very simple
contrivance, consisting only of a tunnel running back into a bank, and
widening at the back. Some material that will soften the bed upon
which eggs are to be laid must be placed in this cavity. The whole
home is a very simple and crude affair. But little better is the
arrangement which the woodpecker calls a home. This has been cut into
the dry wood of a defective tree. No woodpecker can make his home in
absolutely solid sapwood. Hence the first labor of the woodpecker must
consist in finding a place in which it can dig. If there is an old
stump of a limb sticking up, the problem is readily solved. Such wood
has no sap in it, and is brittle enough to be easily dug out. But, if
there be no such stub, the woodpecker will find a suitable place in
most trees. At some time or other almost every tree loses a big limb.
When such accident occurs there will always be in the old trunk a
region through which sap once went to this limb. This region, deprived
of its function, goes completely dry, like the heartwood of the tree,
and it is into such material as this that the woodpecker succeeds in
drilling his well-protected home.
As birds rise higher in the scale the nest-building becomes a more
complicated affair, and after a while we find a well-woven substantial
nest, through which even the air will not chill the eggs enough to
prevent their hatching, while the warmth is supplied by the mother's
body. It is often a matter of surprise to many people that a bird
should contrive to build a nest so exquisitely circular. The trick,
after all, is not quite so difficult as it looks. The robin gathers up
a few sticks and places them as the beginning of the platform. More
and more are brought and woven into each other, making a framework
altogether too big for the nest. Then mud is brought and plastered
inside of this. With the plastering of this mud the careful
circularity of the work begins. Every time a little material has been
added the robin sits down in the nest and revolves her body, in this
way shaping the interior much as the potter shapes a pot. In the case
of the artisan, it is the pot that revolves. In the case of the robin,
the bird itself revolves. The effect is the same in both cases--a
circular vessel is produced. A little lining added to the interior of
the nest softens it for the reception of the eggs. In this exquisite
home the robin lays her eggs, and sits upon them until they are
developed enough to hatch, and then feeds the young until they are old
enough to feed themselves.
Far more remarkable than any of the devices thus far described are the
wonderful developments which have come in the class of animals known
as the mammals. Here the most wonderful protection is made for the
care and feeding of the young. But this is to be the subject of a
separate chapter.
As long as we thought of each sort of animal as being a separate
species shaped in the beginning by the hands of the Creator, each of
these devices seemed to us a new manifestation of the Divine
Providence, whose fertile planning had conceived so many methods of
providing for his children. Unconsciously we thought of God acting as
man acted. Each animal seemed a purely separate invention purposely
designed for an especial place. Now we understand the plan in creation
better, and see that each animal has come from another not quite like
itself, some distance back, and this from still another. Our
admiration for these devices as they arise through evolution is no
less, but takes on another form.
CHAPTER VI
LIFE IN THE PAST
Anyone who earnestly studies plants and animals as they exist in the
world to-day cannot help wondering how the earth began and where it
got its life. This is the true end and aim of geological study. The
history of man seems to run back into a far distant and gloomy past.
Except for the poetical account in Genesis and the traditions of
various peoples throughout the world, real history fades away into an
earlier time of which there are no written records. When the delvers
in the Mesopotamian plain talk to us of kingdoms running back through
seven or eight or nine thousand years, we seem to be getting back to
the beg
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