Chapter II: Part 2

The evolution of animal life was paralleled by the rise of an equal diversity of forms in the vegetable world. From the Monera—organisms so lowly that it cannot be determined whether they are plant or animal—life diverged in opposite directions, producing, on the one hand, the plant, on the other, the animal. Organisms that could feed on inorganic matter assumed a stationary character and became the ancestors of the plants. Creatures that required organic food developed powers of locomotion to facilitate the search for sustenance, and of these were born the varied forms of earth’s animal population. From the first microscopic plants, vegetable life proceeded to seaweed, to mosses, to ferns, to the pine and the yew, to the vines, the fruit-bearing and flowering plants that crowd the forests and beautify the gardens of the world.

The truth of this wonderful story of evolution, of the progressive improvement of living forms with the advance of time, is proved by several lines of evidence. One of these lines of evidence is found in the fossil remains of the life of earlier times. Fossils are relics of forms that lived in the long ago. Dying, they were buried in sediment by the hand of time, and to-day they are found in rock formations, where they have been preserved from the destructive power of the ages. Now, if living things have developed in an increasing variety of forms as time has gone on, and if the stratified rocks of the earth’s crust, as they have grown from age to age, have kept a record of these living things, these testimonies of the rocks must prove the gradual unfoldment of the world’s life. Such precisely is the case. The earlier rocks are poor in fossils, because in the earlier ages the world was poor in life; but in the succeeding rocks, there is a larger deposit of fossils; and the rocks of every progressively later age show an ever increasing wealth of fossil remains.

(_Pithecanthropus Erectus._)

Restored by Dr. Eugene Dubois, and the skull of a modern European.]

The earlier rocks contain fossils of the lower forms of life, like seaweed and simple creatures in shells; in succeeding rocks come the fishes—the first living things with a backbone—primitive forms being followed by more elaborate types; in later strata are found the fossil remains of the amphibians; following these, in rocks higher up, are the relics of the reptiles; then come the reptile-birds, and in still later rocks appear the primitive mammals; onward and upward rises the spiral of life, and in yet later rocks occur placental mammals—early horses, marmosets and lemurs; higher still, the strata imprison fossil cats, pigs, elephants, antelopes and apes; and over the fossil remains of all other creatures, in the rock-crust of the earth, as is required by the facts of biological unfoldment, lie the fossilized forms of man-like apes and men. Thus geology confirms the conclusions of biology.

This picture is a retouched photograph taken of a model made by Guernsey Mitchell according to instructions of Prof. Henry A. Ward of Chicago. Reprinted with the permission of The Open Court Publishing Co.]

In Fig. 32 we have a series of fossil heads from different periods in the ascending geological order, illustrating the gradual development of the elephant’s tusks and trunk. See how the tusk, beginning as an upper tooth in the Eocene period when the elephant was no larger than a rabbit, gradually lengthens as the periods pass, until we get, after millions of years, the great curved tusk of the elephant of to-day. The growth of the trunk kept pace, of course, with the extension of the tusks. On the left side may be seen the gradual and corresponding modification of the elephant’s teeth.

The horse, the noblest of the quadrupeds, has been evolved from a small five-toed animal. The Eohippus, the “dawn horse,” whose fossil remains have been found in the lower Eocene rocks, was no bigger than a small fox (Fig. 33). It had four toes and a splint on each front foot, and three toes and two splints on each hind foot—which proves that its ancestors had five toes on each foot. The “dawn horse” was a browsing animal. Restorations of this little horse, and of the larger three-toed horse that followed him, are now familiar figures in natural history museums. Evolution, you see, is not a figment of somebody’s imagination; it is, rather, the compelling, common sense interpretation of the facts of nature.

On the right, a series of skulls; on the left, last lower molar. Reprinted with the permission of the author and publishers from Prof. William B. Scott’s “A History of Land Mammals in the Western Hemisphere.” The Macmillan Co., New York.]

All modern horned animals have been evolved from ancestors that were without horns. The progenitors of the deer, the elk, the caribou, the moose, before the Miocene period, were entirely destitute of horns. Then the first horns appeared, each as a simple prong. As the succeeding ages passed away, the horns gradually increased in size and took on more prongs. The fossil antlers, found in the successive rock formations from the Miocene period onward, show the gradual evolution of the horns that adorn the heads of living animals (Fig. 34).

But this is only half the story. The history of an individual creature is called ontogeny. The history of a race of creatures is called phylogeny. Now, it is a biological law that ontogeny is always a recapitulation of phylogeny; that is to say, that every creature in the course of its development, especially before birth, passes through the various stages permanently occupied by its ancestors. We see this law beautifully illustrated in the growth of the antlers of one living deer (Fig. 35). During the first year, or thereabout, the deer develops one plain horn, and each year thereafter another prong is added, until after a series of years, the antlers are full grown and full-pronged. In other words, each and every deer, in the development of his horns, repeats the long experience of his race in acquiring horns.

Restored from a skeleton in the American Museum of Natural History, New York. Reprinted with the permission of the author and publishers from Prof. William B. Scott’s “A History of Land Mammals in the Western Hemisphere.” The Macmillan Co., New York.]

Now, this process of recapitulation applies to man as well as to all other creatures. This brings us to another line of evidence which proves the truth of evolution—embryology, or development before birth. Dogs, cattle, sheep, elephants, horses, apes, men and all other mammals had the same origin. Therefore, the early stages in the evolutionary process were the same for all these creatures. That is to say, the course of life’s development, before diverging toward these respective forms, followed for a time a general line of advance.

The truth of this is strikingly illustrated in Fig. 36. Here we have the embryos of four mammals in different stages of development—the dog, the bat, the rabbit and man. These embryos prove that all these creatures have come through the same line of development; that they all had the same remote ancestors. The distant ancestors of all these creatures were fishes in the sea, and here, in the embryo of the dog, the bat, the rabbit and man, we have, still persisting, the gill-clefts of the fish (top row). These gill-slits, which all mammals, before birth, still inherit from the fishes through which ascending life passed in the morning of the world, occasionally persist in man throughout the embryonic period and appear in the child’s neck as fissures pointing towards the throat, through which milk, when swallowed, passes to the outside of the neck. Only on the theory that all mammalian life, including man, has evolved through the fish stage does the persistence of these gill-clefts become intelligible.

The embryonic development of man and the other mammals demonstrates their remote relationship and their gradual evolution. The dog, the sheep, the ox, the horse, the ape and man and every other mammal begins life as a single cell. That cell grows and divides into two; the two enlarge and divide into four; the four divide into eight. Dividing in this way, the cells come to form a cluster resembling a mulberry. This is the morula stage. The cells now form a hollow sphere, one cell in thickness, and the sphere fills with fluid—the blastula. Now the sphere, like a punctured India rubber ball, falls in upon itself, assuming a cup shape with double walls. This is the gastrula stage, when the embryo resembles a worm in the figure of a horseshoe. A third layer of cells is now formed between the other two, and from these three layers of cells are gradually unfolded all the complex parts of the body. From the outer cells arise the skin, the hair, the lenses of the eyes, the nervous system, the membranes of the mouth and nose, and the enamel of the teeth; from the inner cells arise the lining of the larynx, the trachea and the lungs, the intestines, the liver and the thyroid glands; from the middle layer of cells are formed the skeleton, the inner structure of the teeth, the muscles, the blood-vessels and the blood itself, the membranes of the heart and lungs, the kidneys and the reproductive organs.

For a time the human embryo is a simple trunk, without skull or spine, without arms or legs, with only a pulsating tube for a heart. Then the rod of the amphioxus appears running down the back; then the growing embryo resembles a fish, with gill-slits in its neck and with a two-chambered fish heart; then comes the reptile stage when the babe has a three-chambered heart and other features of his reptilian ancestors; then the heart becomes four-chambered and the babe, passing through other transformations, reaches the finished human form.

In all these details of growth, the development of man is paralleled by the development of every other mammal. And certainly only one conclusion may be drawn from the fact that for a time in the embryonic life of the rabbit, the sheep, the pig, the dog, the ape and man, these creatures are formed and look so nearly alike that even the man of science, unaware of their identity, cannot distinguish one from the other.

The significant structural similarity of nearly all living creatures points unmistakably to evolution. For example, the limbs of amphibians, reptiles, birds and mammals consists of one long bone above, then two shorter bones below, then two transverse rows of bones forming the ankle, with the foot ending in five toes. In the foot of the crocodile, in the flipper of the seal, in the paddle of the whale and in the foot of the dog may be seen the general plan of the human hand. So the wing of the bat or bird, the forelimb of the lizard or elephant and the little shovel-like leg and foot of the mole present the same number of bones in essentially the same structural arrangement as do the arm and hand of man. It is the different uses to which these organs have been put that have determined their various developments.

Dog, Bat, Rabbit, Man—at Three Different Stages of Development.]

Comparative anatomy traces the arms and legs of man through various land forms back to the limbs of fishes. And the human heart and lungs, the liver, kidneys and stomach, the eyes and ears, the nose and mouth, have been fashioned from the organs of primitive creatures through successive modifications during countless ages. The larynx, which makes possible the human voice, appears in diverse stages of development in the Amphibia.

Man’s remote ape-like progenitors had tails, and for a time in its embryonic development, the human babe has a tail longer than his legs (Fig. 36, middle row). Moreover, in the annals of medical science, there are records of many otherwise well-formed children born with tails. Professor Haeckel, in his “Evolution of Man,” shows photographs of a six-months-old tailed boy (Fig. 37). The presence of this tail is another rare instance of the vaulting power of heredity—a case in which Nature recalls a phase of her distant life.

Removed by Operation by Dr. Granville Harrison, in 1901. “A great number of such cases,” says Haeckel, “are given by Max Bartells in his essay on ‘Tailed Men,’ 1884.”]

Every human being carries the rudiment of an ancestral tail, the coccyx, at the base of his spine. In the human embryo, the very muscles for wagging this tail are still found. In adult man, these muscles are represented, as a rule, by bands of fibrous tissue. Occasionally, however, the dissecting surgeon finds these muscles well developed in the body of a man or woman. Science says that evolution alone can explain this lingering relic of a tail, with its attendant muscles, in the human body.

This brings us to another line of evidence, which proves the truth of evolution—the presence of rudimentary organs. Fig. 38 shows the vermiform appendix in the orang, in man, and in the babe before birth. It is much larger in the ape than in man. Man has inherited it from his ape-like ancestors, and while it serves no purpose in his body, its infection is the source of the frequently fatal disease, appendicitis.

Then there are the rudimentary muscles of the ear (Fig. 39). In our remote progenitors these muscles were developed, and with them they could move their ears. Monkeys move their ears, though not with the facility characteristic of horses and dogs. Occasionally a man is found who can move his ears as we move the skin of the forehead. But in the anthropoid apes and in most men these muscles are inoperative. Through disuse they have become rudimentary. When the ancestors of these apes and men began to assume the erect posture, they also began to turn their heads, instead of their ears, in the direction of sound. As the erect posture was improved, the turning head answered with increasing loyalty the call of the sound waves, and after innumerable ages of comparative rest and disuse, the ear muscles dwindled into their present impotence. Here, again, evolution alone explains the facts.

Moreover, the whole external ear is a rudimentary organ—a structure that has outlived its function. The male breasts point to a time when the father as well as the mother suckled the young. In some men the breasts are as well developed as in women and supplied with milk, and in many known instances babes have been suckled at these male breasts. Again, in some women and occasionally in men, two or more pairs of breasts appear—a fact which plainly shows that man has descended through humbler forms of life. Still another rudimentary organ is the nictitating membrane—the little fleshy pad at the inner corner of the eye—the relic of a third eyelid that our ancestors in the dim past flashed across the eyeball as the turtle and the eagle do to-day.

Man has evolved from creatures that went on all fours and lived in trees, and in consequence of his upright posture and changed habits of life, some structures which are active in the apes are rudimentary in the human body. A shoulder muscle that is a source of strength to the apes in climbing, lingers in man as a mere fibrous remnant that has dwindled through disuse. Another muscle which runs through the wrist into the palm of the hand, another which extends from the calf of the leg to the sole of the foot, another which passes from the shoulder to the neck and was once used to lift the collar bone—these muscles, which are well developed in the true apes, and less developed in the anthropoids, are rudimentary in man. These rudimentary organs and muscles are links in the chain of man’s descent and they point unerringly to the source of his origin.

The long heel and the poorly developed calf of the anthropoid ape remind us that he has but recently, so to speak, acquired the upright posture. In the negroid races also the long heel and diminutive calf are notable characteristics; while in the white and yellow races the heel is short and the calf well formed and muscular. Once more, the obvious conclusion is that the black man’s long heel and slender calf represent a more primitive development; while the leg and heel of the white man and the Mongolian show the work of evolution farther advanced.

Three months before birth, the human babe is covered with a luxuriant growth of soft, brown hair, called the “lanugo,” precisely the same as the ape baby. And throughout life the body of every human being is covered with a rudimentary growth of hair. But this it not all. It is as suggestive as it is interesting that in man and in the anthropoid apes the hair on the upper arm and the hair on the lower arm always grows towards the elbow (Fig. 40)—a phenomenon which occurs nowhere else in the animal world except in a few American monkeys. In a primitive Australian race, the Ainos of Japan, and the pygmies of the Upper Nile, the extreme hairiness of the body is a notable characteristic. And the photograph of Julia Pastrana, a Siamese (Fig. 41), shows that this lady was not only bearded like a man, but that her entire body was plentifully clothed with hair. Some chimpanzees, on the other hand, are remarkably hairless. One variety is, in fact, almost entirely bald.

If any organ in the human body could distinguish man as a creature standing apart, and argue that he has not been evolved from ape-like ancestors, that organ should be the brain. But the brain yields surprising evidence of man’s kinship with these creatures. Fig. 42 is introduced to show the remarkable similarity in the brains of the anthropoid apes and men. The lower four are the brains of apes; the upper one to the right is the brain of a Bushman, and the one at the upper left is the brain of an European. Mark that while the brains of the apes differ from one another, there is also a striking difference between the brain of the savage and that of the civilized man. Observe, too, how wonderfully these ape brains resemble the human brains, not alone in general form, but also in the number and depth of their convolutions. In fact, the brains of man-like apes and men consist of the same parts—the cerebrum, the cerebellum, the corpus callosum, and the hippocampus minor—and in both anthropoid and man the cortex of the brain is folded in essentially the same convolutions.

If any thoughtful person is still unconvinced of man’s rise from ape-like ancestors, let him compare his mental image of some human beings he has seen with Fig. 43.

Consul II, a chimpanzee from Borneo, now in England, sits at the table, tucks his napkin under his chin, uses a knife and fork, drinks his tea from a cup, and has excellent table manners. After dinner, he sits back, lights his pipe, and enjoys a smoke. He washes himself with soap and water, dresses himself, shines shoes carefully, and, like a hotel waiter, expects a tip for his service. Another, and far more remarkable anthropoid, is Snooky, the educated chimpanzee who frequently appears in the “movies” in the Chester Comedies. Dressed like a man, this ape smokes a cigar, pretends to read a paper, poses as a chauffeur, rides a tricycle, takes care of children, performs capers with boys, and takes various parts with men and women. So intelligent and humorous is the acting of this chimpanzee, so clever and human-like are its numerous performances, that it is justly advertised as the “humanzee.”

(From a photograph by Hintze).]

In considering the relation between the anthropoid apes and men, we must not suppose that apes or ape-like creatures underwent a sudden transformation into human beings. The highest existing apes represent a development that preceded the appearance of man, some authorities think, by some two or three million years. The difference between these creatures and man is therefore the measure of life’s upward rise by slow steps during that inconceivable time.

Man is related to the apes not alone in the structure of his body and brain, but also in the blood stream that courses through his veins. This has been conclusively proved by the remarkable series of blood tests conducted by Professor G. H. F. Nuttall at Cambridge University. By these tests, it was shown that man and the chimpanzee are blood relations; that the gorilla is a more distant relative, and the orang a relative more distant still. Below the anthropoids, the blood relationship is represented with diminishing force in the baboons and monkeys. These blood tests confirm the conclusions of zoology and prove the truth of evolution.

Fig. 44 is a picture of Haeckel’s genealogical tree of humanity. It enables us to visualize in its main outline the history of the evolution of life. At the bottom of the tree are the monera and the amœbæ—tiny creatures consisting of a single cell. As growing life assumes diverse forms, the foremost creatures are represented by higher and higher positions on the trunk of the tree, or by diverging branches in the ascending order. Life is seen to progress from the simple to the complex, past the sponges, the molluscs and the fishes, through the amphibians, the reptiles, the marsupials, rising higher and higher in the scale of being, through lemurs, apes and anthropoids, until, at the topmost summit of the tree appears man.

And what has been the secret, the driving force back of this process of evolution? To understand the causes of evolution, it is necessary to understand the four fundamental laws of life. First, that while creatures resemble their parents through heredity, they nevertheless differ more or less from their parents—this is the law of variation. Secondly, that more creatures are born than can survive—this is the law of surplus population. Thirdly, that among living creatures, and owing largely to over-population, there is continually going on a struggle for existence—this is the law of struggle. And fourthly, that out of this struggle there results the survival of the fittest. Variation, surplus population, struggle, spell the survival of the fittest. In the struggle for existence, those creatures possessing the best bodies and the keenest minds, those that could best protect themselves from their enemies and obtain their food—in a word, those that were best adapted to their environment—survived, while the others perished. Those whose variations were unfavorable, the weak, the inferior, died. But those whose variations were an advantage, the strong, the superior, survived. In consequence of the survival of the fittest, Nature, throughout the unfolding ages, kept breeding from the best. And this practice could have but one result—the gradual improvement of every race of creatures.

It will be well to elucidate somewhat the principles thus summarily stated. First, then, as to variation. The offspring is never exactly like its parents, and no two creatures are ever quite alike. The stems, the leaves, the blossoms of the plants of any species, the size and contour of their fruits, vary greatly. No two blades of grass, or ears of corn, or grains of wheat are alike. Every tree has an individuality of form. The young of dogs, cattle, horses, sheep, of fowls and birds, invariably differ from their parents in size and form, in coloring and character.

G-Gibbon. H-Chimpanzee. I-Orang. K-Gorilla. L-Bushman. M-Teuton. From Haeckel’s “Evolution of Man.”]

So, too, in a large assemblage of people, you will see noses and ears of numerous shapes and sizes, eyes displaying a variety of coloration and expressiveness; you will observe that some foreheads are low and others high, some heads flat and others pointed, some round and others square; some men have long arms and legs, some the reverse; some have long bodies and short limbs, some the opposite; some have one ear, or shoulder, or hip, higher than the other, or are otherwise disproportioned. Moreover, great differences may be observed in the features of almost any family. The black haired mother has red haired daughters; the father’s features are bequeathed to his sons except, perhaps, for the eyes of one or the nose of another. Variation is a basic law of life.

Secondly, as to the multiplication of creatures beyond the power of Nature to sustain them. Darwin, in the “Origin of Species” says: “There is no exception to the rule that every organic being naturally increases at so high a rate, that, if not destroyed, the earth would soon be covered by the progeny of a single pair. Even slow-breeding man has doubled in twenty-five years, and at this rate, in less than a thousand years, there would literally not be standing-room for his progeny.”

On the fertility of the elephant, Darwin remarks: “The elephant is reckoned the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase; it will be safest to assume that it begins breeding when thirty years old, and goes on breeding till ninety years old, bringing forth six young in the interval, and surviving till one hundred years old; if this be true, after a period of from 740 to 750 years there would be nearly nineteen million elephants alive descended from the first pair.”

An illustration from the opposite extreme of the animal world will show that the breeding propensities of the largest existing animal are rivalled by those of the smallest. “The aphis or plant louse,” says Dr. D. Kerfoot Shute in “A First Book in Organic Evolution,” “is so very prolific that it has been estimated that the tenth brood of one female alone would contain more ponderable matter than all the population of China,—estimating this population at five hundred millions.”

The rabbits introduced into Australia, where they found conditions ideally favorable to their increase, have multiplied so exceedingly that they have become a veritable pest. In a brief period, the progeny of a few rabbits has multiplied into millions, and these creatures have become so destructive of agriculture that rabbit-killing parties are organized from time to time and tens of thousands of the animals are killed with sticks and stones, in open places, the object being to exterminate as many rabbits as possible in the interest of the farmers’ crops.

In 1850, some enterprising citizens of Brooklyn imported a hundred English sparrows and gave them to the free city air. A little later, New York City imported two hundred and twenty of the noisy birds and liberated them in the parks of the metropolis. Rochester imported one hundred of the birds, and Philadelphia, with generous public spirit, opened the bosom of brotherly love to one thousand of the little strangers whose perpetual chatter formed a striking contrast to the worshipful quiet dear to the heart of the Quaker City. In the parks, among the trees, and in the streets of these cities, the sparrows—at home everywhere—twittered and quarreled in their friendly way, and multiplied. In twenty-five years the children of these birds had spread over five hundred square miles. Ten years later they had flung their domain over fifteen thousand square miles, and men were beginning to doubt the wisdom of those who had invited them to our shores. Since then the ubiquitous sparrow has about completed the conquest of the continent. Darting like an arrow amongst horses’ feet, or dodging hurrying automobiles, his legions are familiar sights among the traffic of busy streets. He builds his rude nest under the eaves of houses, and in the architectural pockets around the roofs of public buildings, and thrives and multiplies through his wary association with man. The phenomenal increase in the number of sparrows in North America during a period of seventy years has been due to the gregarious habit of these birds and to the favorable character of the environment.

A Chimpanzee couple of Edward’s Zoological Exhibition. From Dr. Paul Carus’s “The Rise of Man.” Courtesy of The Open Court Publishing Co.]

Some animals tend to multiply ten fold in a generation; some would multiply to a hundred fold, and others to ten thousand fold. Not only could the progeny of any land animal, if given the right of way, soon crowd the earth, but the fishes, under favorable conditions, would, in a short time, literally fill the sea. A million eggs are spawned by the cod-fish in order that two cod-fish may reach maturity. The eel also spawns millions of ova that a few eels may reach the spawning age. It is clear, therefore, that if all these eggs produced fishes, and if these reached maturity and in their turn multiplied with such lavish prodigality, a few generations would suffice to transform the ocean into a solid mass.

The same phenomenon obtains in the plant world. Every plant gives its seeds to the soil as Autumn’s spendthrift hand gives its withered leaves to the wind, but of the millions of seeds thus scattered, comparatively few take root and mature and reproduce their kind.

Notwithstanding Nature’s tremendous efforts to overwhelm the earth with the creatures of every species, the checks upon over-population are so numerous and so effective that, speaking generally, the number of animals and plants in any given area where the conditions are unchanging remains fairly constant. This relatively rigid limitation of the number of creatures that shall survive in any environment is due to the operation of Nature’s efficient machinery whose grim function is the destruction of life.

Millions of creatures live only by devouring other creatures. The carnivorous animals eat the flesh and drink the blood of the herbivorous. The larger carnivores feed upon the smaller. That the badger may make a meal, a whole nest of bees must be destroyed. The ant-eater swallows a tongue load of ants at a single gulp. The eagle and the hawk dine on doves and other birds. To the appetite of smaller birds are sacrificed worms, insects and larvae. Big fishes eat the little ones; bigger fishes eat the eaters and in turn are eaten. On land, in the air, and in the sea the incalculable sacrifice of life proceeds without cessation. Pursuit and flight, capture and death—a tragedy on which the curtain never falls!

This is the struggle for existence. In this struggle which, in a sense, is a constant test of skill, the most highly qualified creatures are the ones best adapted to catch their prey or to escape their enemies. Differing from their parents and from one another in numerous variations, some animals excel others in important respects—in having stronger legs with which to run, better eyes with which to see, a keener sense of smell, hearing more acute, and teeth and claws better fitted to hold and rend their prey. To the animal that would obtain food or avoid being eaten, some or all of these characters are prime essentials. In the struggle for existence the animals possessing these attributes in superior form will survive while those in which they are less developed must perish.

Harmless creatures, no less than harmful, survive through favorable characters—some by the wit with which they elude the pursuer, some by flight, some by protective coloration; like the hare whose summer coat resembles the ground and whose winter garment rivals the whiteness of the snow, and the gorgeous butterfly, whose folded wings are a perfect simulation of the form and color of a dead leaf.

Where the herbivorous food was insufficient for the mouths that would feed upon it, and where animals devoured one another, it was inevitable that the weak, the stupid, the ill-favored, the incompetent, should fail in the struggle for existence, and that the strong, the cunning, the efficient should survive and hand their superior qualities to their offspring. And this survival of the fittest by right of might that has been the supreme law of the animal world since life appeared upon this globe, was bound to result in the accumulation of favorable variations, in the consequent production of an ever increasing wealth of species, and in the development of ever higher forms of life.

The fitness of the present forms has been moulded by the death dealing teeth of the past.

Though not by this means alone. Another potent factor that has wrought tremendously for evolution has been the changing environment. We may briefly consider the character of its work. For millions of years before the close of the Carboniferous period, some ten million years ago, the whole earth enjoyed a perpetual summer. During the last million years or more of that vast era, while the dense Carboniferous forests, overwhelmed again and again by the growing soil, were forming the coal deposits of the earth, many kinds of amphibians and low reptiles wandered over the marshes and among the trees.

Then in the succeeding period—the Permian—the climate began to be colder. For a hundred thousand years or thereby the cold increased. At last the summit of an ice age was reached, and some four million square miles of the earth’s surface lay beneath a thick mantle of ice and snow. That ice sheet covered a continent that then extended from India to Australia, on the one hand, and to Africa on the other. The ice age, which was due, probably, to the gradual elevation of the land, wrought fearful havoc among the land animals, and with a ruthless hand pushed evolution forward. It compelled animals—and plants also—to change or die.

In the warm climate that preceded the ice age, all animals were cold-blooded,—warm blood was not needed—and amphibians and reptiles left their eggs on the earth to be incubated by the genial air. But in the awful cold that followed warm blood was required, and, as the cold destroyed their eggs, it was necessary for animals to develop means of wooing their young to life within their bodies. Another required change was that the cold reptile covering be abandoned for a warm coat of hair.

Only a few animals could make these adjustments. Accordingly, as calculations based upon the fossils prevalent before and after the ice age have shown, “thirty-nine out of every forty of all the species of animals and plants on the earth during the coal forest age were destroyed.” Of the animals that survived, some were saved by migrating to favorable regions, and some by adapting themselves to the rigors of the environment. These developed four-chambered hearts to keep their blood warm; they developed coats of hair or fur to retain the heat of their bodies; they made such changes in their internal economy as enabled the young to develop in the body of the mother.

To produce these changes, Nature preserved the favorable variations that appeared in different animals. From age to age these variations along advantageous lines were accumulated, and so, in time, the new creatures were evolved. The result was obtained through natural selection of the fittest. In this manner arose the mammals, and, through a variant line of development, the birds; for birds, like mammals, have four-chambered hearts, and feathers, like hair, are but a modification of primitive scales; while the bird hatches her eggs with the warmth of her body. So we may thank that early ice age for the gift of all mammalian and bird life. The originals of those animals whose development culminated in man, and of our feathered friends of the air, were fashioned by that incomparable sculptor—environment.

With the gradual passing of the Permian ice age, through the lowering of the land, the long backward spring slowly merged into another universal summer that continued for several million years. In this mild period, when Europe was, for the most part, a group of scattered islands, when a continent extended from America to Scotland, a new garment of multiformed vegetation appeared upon the low-lying earth; huge sharks and reptiles dominated the sea; while on the land, weird and prodigious monsters basked in the brilliant sun. It was the age when the giant reptiles,—some with sail-like wings, and all with frightful teeth—and ponderous vegetarians held the earth their own and led in the struggle for existence.

Then came another cold period, less drastic than the former, but severe enough to give a signal forward urge to the work of evolution. The great reptiles disappeared forever. And now the primitive birds and mammals whose evolution had been retarded by their numerous enemies and by the climate in the warm reptilian age, entered upon a period of more rapid development. The bracing cold that required movement served as a stimulant to accelerate their evolution into various forms.

Since that remote time there have been several glacial periods—periods when great ice caps covered vast areas of the earth—periods whose tremendous cold was followed by ages when the climate was temperate and benign. These major changes in the environment, and the numberless other changes of less striking character, have been among the leading factors in the work of evolution.

Among the lesser, though important, environmental changes, may be mentioned the gradual submergence of land beneath the water, occasioning animal migrations which resulted in the mixing of stocks; the drying up of swampy regions bringing new plant life; changes in the food supply transforming animals into vegetarians or carnivores, or otherwise modifying their habits, and in consequence, their structure.

In these changes that have succeeded one another in the lapse of the innumerable ages, countless species of animals and plants have been exterminated altogether; of others, only a few hardy or otherwise adapted specimens have survived; from these have been bred the animals and plants of the succeeding ages, which, in turn, have had to adapt themselves to their environment or disappear; and everywhere the struggle, whether with the environment or with other living things, has resulted in the survival of the fittest and the slow improvement of the fauna and the flora of the world.

The process of selecting the fittest to breed from, as it is carried on by Nature in her blind way, is called natural selection; and when men, in breeding stock, select the specimens possessing the most desirable variations to breed from, the process is named artificial selection.

The great variety of our domestic animals and plants we owe to artificial selection. Note, for example, the two pigs shown in Fig. 45. The grizzly one, the wild boar, is the remote ancestor of the other, the modern, favorite domestic porker. By breeding for many generations from pigs possessing the most desirable details of form, the legs and snout of the animal have been shortened, his body has been made more shapely and greatly enlarged, and his commercial value enormously increased.

Fig. 46 partially illustrates the diversity of dogs. The dog is a civilized wolf. And the pugs and poodles, the spaniels and setters, the hairless dogs and hounds, the terriers and mastiffs, the faithful collies, the noble St. Bernards, and all the other dogs of every size and form, have been developed by selecting parents with approved variations and breeding for desirable results along chosen lines.

In like manner, the barnyard fowls have been developed by selective breeding. The Leghorns and Minorcas, with their beautiful combs and wattles, the Golden Spangled and the Silver Spangled Crested Hamburgs, with their crowning hoods, the noble Plymouth Rocks, with their barred bodies, the magnificent Light Brahmas and Buff Cochins, arrayed with wing-like feathery growths to their very toes, the game fowls of the various varieties—those sleek, trim birds that would rather fight than eat—and the little Bantams of every sort, proud and beautiful in their bearing—all these are the children of the rude jungle fowls whose male birds still shriek a welcome to the morning sun from the wilds of India and the Malay Islands.

Likewise, the hundred and fifty varieties of our pigeons—the graceful Modena, the large Runt, the tall Carrier, the Trumpeter with his strange coo, his hooded head, his winged legs, the Frill-back with his feathers curling towards his head, the Pouter, with his tall, slender body, and throat inflated as though a feathered football were pinched between his beak and breast, the compact Fantail, leaning back with pride in his beautiful tail that rises above his head like a screen, the Tumbler, that from a lofty height tumbles with utter abandon through the air—all these pigeons, whatever their size, their form, their markings, their habits, have been developed during the last few centuries from the modest blue rock pigeons of the European coast (Fig. 47).

Reading from the top downwards: St. Bernard, Bloodhound, Greyhound, English Setter, Irish Spaniel, Dalmatian, Pug, Skye Terrier.]

Such is the story that rounds the vast circumference of life. All life is one, and by the same means its varied ends have been attained. By breeding from those creatures whose qualifications enabled them to survive in their environment, Nature, without knowing why, selected the fittest to become the parents of the creatures that were to follow. Thus, of necessity, the life of the world, ever branching into an increasing diversity of species, gradually improved in form, function and intelligence. And with millions of ages in which to try every experiment, to test every detail, to destroy her failures and seek success along other lines, Nature was bound to reach our day with an array of living creatures of finer development than those that perished in the struggles of the vanished years.

The laws in accordance with which the humbler creatures have been developed from still lower forms have presided over the evolution of man from the beast; and, never pausing in their action, these forces have slowly fashioned the glories of civilization from the dark crudity of savage thought. The story of man but continues in another form the story of life before man appeared.

Modena 10, Runt 19, Carrier 1, Trumpeter 4, Frill-back 37, Pouter 2, Fantail 6, Tumbler 15. Rock Doves in Centre.]

The plant creations of Luther Burbank are renowned throughout the world. The Burbank potato, the Burbank rose, the new walnut trees, the varieties of plums and prunes, the pineapple quince, the spineless cactus, the everlasting flower, the beautiful lilies—the many new species of vegetables, plants, fruits and flowers which Burbank has created by crossing inferior forms and breeding from the best resulting specimens—these experimental triumphs in the plant world are indubitable proofs of the truth of evolution. Mr. Burbank has shown that plant life is not fixed in form, but plastic and ever-changing, and that by breeding and selecting in accordance with Nature’s laws, man can cover the earth with new vegetables, fruits and flowers and vines and trees and grasses, more luxuriant and more wonderful than any found in an uncultivated condition.

Life, like clay, is malleable. Slowly, under the urge of Nature, rapidly in the hands of man, it shapes itself into new moulds. A problem in mathematics is known to be solved when it can be proved. In like manner, evolution is known to be certainly true, since, by following its laws, man now brings into the world new species of animals and plants that did not exist before.

A wonderful panorama is the story of evolution. From nebula to crusted earth, to life’s first spark in the primal sea, to the myriad forms that fought with teeth and claws in forest wilds, to the fierce-browed creature that earth first knew as human, to the warmth of love and the glow of thought in the heart and brain of finished man, the forces of Nature have shaped existence and crowned it with the power of the human brain. Man the builder, so long the victim of ignorance and fear, may now shape his destinies in a world fashioned to his choice. The desert has been made to blossom like the rose; cities of solid masonry have arisen from the noisome swamp; industries supplying a thousand human wants now occupy the sites where wild beasts once filled the jungle with their savage roars; the ocean, earth and air have yielded to the conquering power of thought; invention, art, discovery, have tapped exhaustless stores of wealth and culture; literature, the press, schools, disseminate intelligence; and, rising above earth, man now solves the secrets of the stars and calculates with precision their changing movements. Man, Nature’s gifted son, is Nature’s conqueror! Let him then learn the means by which to further improve his life. Let him equip his mind with truth. Let him solve his problems in the light of knowledge and enjoy a rational existence in a well ordered world.