The Physical Kinship
The Factors of Organic Evolution
The Evidences of Organic Evolution
‘Like the Roman emperors, who, intoxicated by their power, at length regarded themselves as demigods, so the ruler of the earth believes that the animals subjected to his will have nothing in common with his own nature. Man is not content to be the king of animals. He insists on having it that an impassable gulf separates him from his subjects. The affinity of the ape disturbs and humbles him. And, turning his back upon the earth, he flies, with his threatened majesty, into the cloudy sphere of a special “human kingdom.” But Anatomy, like those slaves who followed the conqueror’s car crying, “Thou art a man,” disturbs him in his self-admiration, and reminds him of those plain and tangible realities which unite him with the animal world.’
— Broca.
I. Man an Animal
It was in the zoology class at college. We had made all the long journey from amoeba to coral, from coral to worm, from worm to mollusk, from mollusk to fish, from fish to reptile, and from reptile to mammal—and there, in the closing pages of faithful old Packard, we found it. ‘A mammal of the order of primates,’ the book said, with that unconcern characteristic of the deliverances of science. I was almost saddened. It was the first intimation I had ever received of that trite but neglected truth that man is an animal.
But the intimation was so weak, and I was at that time so unconscious, that it was not till years later that I began, through reflection, actually to realise the truth here first caught sight of. During these years I knew that man was not a mineral nor a plant—that, indeed, he belonged to the animal kingdom. But, like most men still, I continued to think of him as being altogether different from other animals. I thought of man and the animals, not of man and the other animals. Man was somehow sui generis. He had had, I believed, a unique and miraculous origin; for I had not yet learned of organic evolution. The pre-Darwinian belief that I had come down from the skies, and that non-human creatures of all kinds had been brought into existence as adjuncts of the distinguished species to which I belonged, occupied prominent place in my thinking. Non-human races, so I had been taught, had in themselves no reason for existence. They were accessories. A chasm, too wide for any bridge ever to span, yawned between the human and all other species. Man was celestial, a blue-blood barely escaping divinity. All other beings were little higher than clods. So faithfully and mechanically did I reflect the bias in which I had grown up.
But man is an animal. It was away out there on the prairies, among the green corn rows, one beautiful June morning—a long time ago it seems to me now—that this revelation really came to me. And I repeat it here, as it has grown to seem to me, for the sake of a world which is so wise in many things, but so darkened and wayward regarding this one thing. However averse to accepting it we may be on account of favourite traditions, man is an animal in the most literal and materialistic meaning of the word. Man has not a spark of so-called ‘divinity’ about him. In important respects he is the most highly evolved of animals; but in origin, disposition, and form he is no more ‘divine’ than the dog who laps his sores, the terrapin who waddles over the earth in a carapace, or the unfastidious worm who dines on the dust of his feet. Man is not the pedestalled individual pictured by his imagination—a being glittering with prerogatives, and towering apart from and above all other beings. He is a pain-shunning, pleasure-seeking, death-dreading organism, differing in particulars, but not in kind, from the pain-shunning, pleasure-seeking, death-dreading organisms below and around him. Man is neither a rock, a vegetable, nor a deity. He belongs to the same class of existences, and has been brought into existence by the same evolutional processes, as the horse, the toad that hops in his garden, the firefly that lights its twilight torch, and the bivalve that reluctantly feeds him.
Man’s body is composed fundamentally of the same materials as the bodies of all other animals. The bodies of all animals are composed of clay. They are formed of the same elements as those that murmur in the waters, gallop in the winds, and constitute the substance of the insensate rocks and soils. More than two-thirds of the weight of the human body is made up of oxygen alone, a gas which forms one-fifth of the weight of the air, more than eight-ninths of that of the sea, and forty-seven per cent, of the superficial solids of the earth.
Man’s body is composed of cells. So are the bodies of all other animals. And the cells in the body of a human being are not essentially different in composition or structure from the cells in the body of the sponge. All cells are composed primarily of protoplasm, a compound of carbon, hydrogen, nitrogen, and oxygen. Like all other animals, man is incapable of producing a particle of the essential substance of which his body is made. No animal can produce protoplasm. This is a power of the plant, and the plant only. All that any animal can do is to burn the compounds formed in the sun-lit laboratories of the vegetable world. The human skeleton, like the skeletons of nearly all other animals, is composed chiefly of lime—lime being, in the sea, where life spent so many of its earlier centuries, the most available material for parts whose purpose it is to furnish shape and durability to the organism. Man grows from an egg. So do all creatures of clay. Every animal commences at the same place—in a single, lowly, almost homogeneous cell. A dog, a frog, a philosopher, and a worm cannot for a long time after their embryonic commencement be distinguished from each other. Like the oyster, the ox, the insect, and the fish, like all that live, move, and breathe, man is mortal. He increases in size and complexity through an allotted period of time; then, like all his kindred, wilts back into the indistinguishable flux from which he came. Man inhales oxygen and exhales carbon dioxide. So does every animal that breathes, whether it breathe by lungs, gills, skin, or ectosarc, and whether it breathe the sunless ooze of the sea floor or the ethereal blue of the sky. Animals inhale oxygen because they eat carbon and hydrogen. The energy of all animals is produced mainly by the union of oxygen with the elements of carbon and hydrogen in the tissues of animal bodies, the plentiful and ardent oxygen being the most available supporter of the combustion of these two elements.
Man is, then, an animal, more highly evolved than the most of his fellow-beings, but positively of the same clay, and of the same fundamental make-up, with the same eagerness to exceed and the same destiny, as his less pompous kindred who float and frolic and pass away in the seas and atmospheres, and creep over the land-patches of a common clod.
II. Man a Vertebrate
Man is a vertebrate animal.1 He has (anatomically at least) a backbone. He belongs to that substantial class of organisms possessing an articulating internal skeleton—the family of the fishes, amphibians, reptiles, birds, and mammals. Most animals have some sort of skeleton, some sort of calcareous contrivance, whose business it is to give form and protection to the softer parts of the organism. Some animals, as the starfishes, have plates of lime scattered throughout the surface parts of the body; others, as the corals and sponges secrete plant-like frames, upon and among the branches of which the organisms reside; and still others, as the clams, crustaceans, and insects, have skeletons consisting of a shell or sheath on the outside of, and more or less surrounding, the softer substances of the body. The limbs of insects are tiny tubes on the inside of which are the miniature muscles with which they perform their marvels of locomotion. The skeleton of vertebrates, consisting of levers, beams, columns, and arches, all skilfully joined together and sunk deep within the muscular tissue, forms a conspicuous contrast to the rudimentary frames of other animals. The vertebrate skeleton consists of a hollow axis, divided into segments and extending along the dorsal region of the body, from the ventral side of which articulate, by means of awkwardly-constructed girdles, an anterior and a posterior pair of limbs. This dorsal axis ends in front in a peculiar bulbous arrangement called the head, which contains, among other valuables, the brain and buccal cavern. The thoracic segments of the backbone send off pairs of flat bones, which, arching ventrally, form the chest for the protection of the heart and other vitals. The limbs (except in fishes) consist each of a single long bone, succeeded by two long bones, followed by two transverse rows of short, irregular wrist or ankle bones, ending normally in five branching series of bones called digits. This is essentially the skeleton of all fishes, amphibians, reptiles, birds, and mammals. In short, it is the universal vertebrate type of frame. There are minor modifications to suit the various kinds of environment, adaptations to the necessities of aquatic, terrestrial, and aerial locomotion and life, some parts being specialised, others atrophied, and still others omitted, but there is never anywhere, from fishes to philosophers, any fundamental departure from the established vertebrate type of skeleton.2 The pectoral fins of fishes correspond to the fore-limbs of frogs and reptiles, the wings of birds, and the arms of men. The pelvic fins of fishes are homologous with the hind-limbs of frogs, reptiles, and quadrupeds, and the legs of birds, apes, and men. The foot of the dog and crocodile, the hand of the orang, and the flipper of the dolphin and seal, all have the same general structure as the hand of man; and the wings of the bat and bird, the forelimbs of the lizard and elephant, and the comical shovels of the mole and ornithorhynchus, notwithstanding the great differences in their external appearance and use, contain essentially the same bones and the same arrangement of the bones as do the arms of men and women. The human body has two primary cavities in it. So have the bodies of all vertebrates: a neural cavity containing the brain and spinal cord, and a visceral cavity containing the heart, liver, lungs, and alimentary canal. Invertebrates have only one body cavity—the one corresponding to the visceral cavity of vertebrates—and the main nerve trunk, instead of extending along the back, as among vertebrates, is in invertebrates located ventrally. Vertebrates are the only animals on the earth that have a highly developed circulatory system, a system entirely shut off from the other systems, and containing a heart, arteries, veins, and capillaries. In all invertebrates the digestive and circulatory systems remain to a greater or less extent connected, the blood and food mingling more or less in the general cavity of the body. Worms and insects have pulsating tubes instead of heart and arteries. Crustaceans have hearts with one chamber, and mollusks have two or three chambered hearts, but the blood, instead of returning to the heart after its journey through the arteries, passes into the body cavity. In man and other vertebrates the circulating current is confined strictly to the bloodvessels, no particle of it ever escaping into the general body cavity. The heart of vertebrates is distinguished from that of invertebrates by being located ventrally. The heart of invertebrates is in the back. The blood of vertebrates differs from that of invertebrates in containing both red and white corpuscles. Invertebrates have white corpuscles only. Worms have yellow, red, or bright green blood. The blood of crustaceans is bluish, that of mollusks is white, and that of insects dusky or brown. The blood of all vertebrates, excepting amphioxus, is red. All backboned beings, whether they dwell in seas or cities, and whether they build nests or empires, have two eyes, two ears, nose and mouth, all located in the head, and always occupying the same relative position to each other. Invertebrates may have their brains in their abdomen, as do the mites; hear with their legs or antennae, as many insects do; see with their tunics, like the scallops; and breathe with their skin, as do the worms. The crayfish hears with its ‘feelers,’ the cricket and katydid with their fore-legs, the grasshopper with its abdomen, the clam with its ‘foot,’ and mysis and other low crustaceans have their auditory organs on their tails.
Man is, then, like the fishes, frogs, reptiles, birds, and quadrupeds, a vertebrate animal. Excepting in his infancy, when he is a quadruped going on all fours, he uses his posterior limbs only for locomotion, and his anterior for prehension and the like. His spinal axis is erect instead of horizontal, and his tail is atrophied. But he possesses all of the unmistakable qualities of the vertebrate type of structure—a two-chambered body cavity, a highly developed and dorsally located nerve trunk, vertebrate vitals, a closed circulatory system, a ventral heart, red blood, a head containing sense organs and brain, and a well-ordered internal skeleton, consisting of a vertebral column with skull and ribs and two pairs of limbs, the limbs consisting each of one long bone, two long bones, two transverse rows of irregular bones, and five branches at the end.
1. See ‘Classes of Animals,’ at the end of the chapter. 2. Snakes are limbless, and hind-limbs are lacking in whales and other degenerates; but rudimentary limbs are found in the embryonic stages of these animals. Frogs, it may be said also, have no ribs.
Classes of Animals
III. Man a Mammal
Man is a mammal. He belongs to the most brilliant and influential of the five classes of vertebrates—the class to which belong so many of his associates and victims, the class to which belong the horse, the dog, the deer, the ox, the sheep, the swine, the squirrel, the camel, the unattenuated elephant, and the timid-hearted hare. To this class belong also the lion, the tiger, the kangaroo, the beaver, the bear, the bat, the monkey, the mole, the wolf, the ornithorhynchus, and the whale—in short, all animals that have hair. Fishes and reptiles have scales; birds have feathers; all mammals are covered to a greater or less extent with hair. The aquatic habits of whales render hair of no use to them. Hence, while the unborn of these animals still cling to the structural traditions of their ancestors and are covered with hair, the adults are almost hairless. The sartorial habits of human beings and the selective influences of the sexes have had a similar effect on the hairy covering of the human body. Hair exists all over the human body surface, excepting on the soles of the hands and feet, but in a greatly dwarfed condition. It is only on the scalp and on the faces of males, where it is scientifically assisted for purposes of display, that it grows luxuriantly. It is by no means certain that even the hair on the masculine scalp will last forever. For if the hermetical derby and other deadly devices worn by men continue their devastations as they have in the past, we may expect to have, in the course of generations, men with foreheads reaching regularly to the occiput. Most animals lay eggs. Man does not. Like the dog, the horse, the squirrel, and the bat, man is viviparous, the eggs hatching within the parental body. Human young are born helpless, and are sustained during the period of their infancy by the secretions of the milk glands. So are all the sons and daughters of mammals. Whether they come into the world among the waters or among the desert sands, in the hollow of a tree, in a hole in the earth, or in a palace, the children of mammals are frail and pitiful, and they survive to grow and multiply only because they are the object of the loving and incessant sacrifices of a mother.
Mammals are distinguished from all other animals by the possession of two kinds of skin glands—the sweat glands and the oil glands—and by the development of certain of these glands in the female into organs for the nourishing of the young. Among reptiles and birds the lower jaw is suspended from the skull by a bone called the quadrate bone. Among men and other mammals the lower jaw is joined directly to the skull, the quadrate bone becoming, in the vicissitudes of evolution, the hammer (malleus) of the mammalian ear. Man has a four-chambered heart—two reservoirs which receive, and two pumps which propel, the scarlet waters of the body. Fishes have two-chambered hearts; frogs and most reptiles have three-chambered hearts; all mammals and birds have four-chambered hearts. The red corpuscles in the blood of fishes, frogs, reptiles, and birds, are discs, double-convex, nucleated, and in shape oval or triangular. In man and in all other mammals (except the archaic camel) the red corpuscles are double-concave, non-nucleated, and circular. ‘Man has a diaphragm dividing the body cavity into chest and abdomen, and a shining white bridge of interlacing fibres, called corpus callosum, uniting his cerebral hemispheres. And man is a mammal because, like other mammals, he has, in addition to the qualities already mentioned, these valuable and distinct characteristics.
IV. Man a Primate
Man is a primate. There are four divisions in the order of primates—lemurs, monkeys, apes, and men. But the most interesting and important of these, according to man, is man. Man is a primate because, like other primates, he has arms and hands instead of fore-legs. And these are important characteristics. It was a splendid moment when the tendencies of evolution, pondering the possibilities of structural improvement, decided to rear the vertebrate upon its hind-limbs, and convert its anterior appendages into instruments of manipulation. So long as living creatures were able simply to move through the airs and waters of the earth and over the surface of the solids, they were powerless to modify the universe about them very much. But the moment beings were developed with parts of their bodies fitted to take hold of and move and fashion and compel the universe around them, that moment the life process was endowed with the power of miracles. With the invention of hands and arms commenced seriously that long campaign against the tendencies of inanimate nature which finds its most marvellous achievements in the sustained and triumphant operations of human industry. None of the primates excepting man use their hind-limbs as a sole means of changing their place in the universe, but in all of them the fore-limbs are regularly used as organs of manipulation. Man is a primate because his fingers and toes, like those of other primates (except the tiny marmosets of Brazil), end in nails. Man has neither claws to burrow into the earth, talons with which to hold and rend his victims, nor hoofs to put thunder into his movements. The human stomach, like that of all the other primates, is a bagpipe. The stomach of the carnivora is usually a simple sack, while rodents have, as a rule, two stomachs, and ruminants four. Man is a primate because his milk glands are located on the breast and are two in number. The mammary glands vary in number in the different orders of mammals, from two in the horse and whale to twenty-two in some insectivora. Most ruminating animals have four, swine ten, and carnivora generally six or eight. These glands may be located in the region of the groin, as in the horse and whale; between the forelimbs, as in the elephant and bat; or arranged in pairs extending from the fore to the hind limbs, as in the carnivora and swine. In man and all other primates (except lemurs) the mammary glands are pectoral and two in number. All primates, including man, have also a disc-shaped placenta. The placenta is the organ of nutrition in mammalian embryos. It is found in all young-bearing animals above the marsupials, and consists of a mass of glands between the embryo and the parental body. In some animals it entirely surrounds and encloses the embryo; in others it assumes the form of a girdle; and in still others it is bell-shaped. The primates are the only animals in which this peculiar organ is in the shape of a simple disc.1
The nearest relatives by blood man has in this world are the exceedingly man-like apes—the tailless anthropoids—the gorillas and chimpanzees of Africa, and the orangs and gibbons of southern and insular Asia. The fact that man is an actual relative and descendant of the ape is one of the most disagreeable of the many distasteful truths which the human mind in its evolution has come upon. To a vanity puffed, as is that of human beings, to the splitting, the consanguinity of gorilla and gentleman seems horrible. Man prefers to have arrived on the earth by way of a ladder let down by his imagination from the celestial concave. Within his own memory man has been guilty of many foolish and disgraceful things. But this attempt by him to repudiate his ancestors by surreptitiously fabricating for himself an origin different from, and more glorious than the rest is one of the most absurd and scandalous in the whole list. It is a shallow logic—the logic of those who, without worth of their own, try to shine with a false and stolen lustre. No more masterly rebuke was ever administered to those in the habit of sneering at the truth in this matter than the caustic reply of Huxley to the taunt of the fat-witted Bishop—that he would rather be the descendant of a respectable ape than the descendant of one who not only closed his eyes to the facts around him, but used his official position to persuade others to do likewise. Man’s reluctance to take his anatomical place beside his simian kinspeople has been exceeded only by his selfish and high-handed determination to exclude all other terrestrial beings from his heaven.
Man is a talkative and religious ape. He is an ape, but with a much greater amount of enterprise and with a greater likelihood of being found in every variety of climate. Like the anthropoid, man has a bald face and an obsolete tail. But he is distinguished from his arboreal relative by his arrogant bearing, his skilled larynx, and especially by the satisfaction he experiences in the contemplation of the image which appears when he looks in a mirror.
The man-like apes are from three to six feet tall, and are all of them very strong, the gorilla, who sometimes weighs over three hundred pounds, being about the bravest and most formidable unarmed animal on the planet. They are erect or semi-erect, have loud voices, plantigrade feet, and irritable dispositions—in all of these particulars being strikingly like men. The gorilla, chimpanzee, and gibbon are highlanders, preferring the uplands and mountains. The orang is a lowlander, living phlegmatically among the sylvan swamps of Sumatra and Borneo. The gorilla and chimpanzee are terrestrial, seldom going among the trees except to get food or to sleep. The orang and gibbon are arboreal, seldom coming to the ground except to drink or bathe. They all walk on their hind-limbs, generally in a stooping posture, with their knuckles or fingers touching the ground. But they sometimes walk with their arms hanging down by their sides, and sometimes with their hands clasped back of their heads to give them balance. None of them ever place their palms on the ground when they walk—that is, none of them walk on four feet. The anthropoid races, in the shape of their heads and faces and in the general form and structure of their bodies, and even in their habits of life, resemble in a remarkable manner the lowest races of human beings. This resemblance is recognised by the negro races, who call the gorilla and chimpanzee ‘hairy men,’ and believe them to be descendants of outcast members of their own species.
There are differences in structure between man and the apes, just as there are differences in structure between the Caucasian and the Caffre, or even between individual Caucasians or individual Caffres. There are differences in structure and topography, often very noticeable differences, even among members of the same family. But in all of its essential characters, and extending often to astonishing particulars, the structure of man is identical with that of the anthropoid.2
In external appearances the man-like races differ from men in having a luxuriant covering of natural hair. But anthropoids differ very much among themselves in this particular. The orang, usually covered with long hair, is sometimes almost hairless. There are, too, races of human beings whose bodies are covered with a considerable growth of hair. The Todas (Australians) and Ainus (aborigines of Japan) are noted for the hairiness of their bodies, certain individuals among them being covered with a real fur, especially on the lower limbs.3
Individuals also often appear in every race with a remarkable development of the hair. Adrian and his son Fedor, exhibited years ago over Europe as ‘dog-men,’ are examples. The father was completely covered with a thick growth of fine dirty-yellow hair two or three inches long. Long tufts grew out of his nostrils and ears, giving him a striking resemblance to a Skye terrier. Fedor, and also his sister, were covered with hair like the father, but another son was like ordinary men. The man-like races have also longer arms in proportion to the height of the body than man generally has. But this is also true of human infants and negroes. The gibbon has relatively much longer arms than the other anthropoids. It differs from the chimpanzee in this respect more than the chimpanzee differs from man. When standing upright and reaching down with the middle finger, the gibbon can touch its foot, while the chimpanzee can reach only to the knee. Man ordinarily reaches part way down the thigh, but negroes have been known to have arms reaching to the knee-pan.4
The skeleton of the African races contains many characters recognised by osteologists as ‘pithecoid,’ or ape-like. It is massive, the flat bones are thick, and the pelvis narrow. In the manlike apes the large toe is opposable to the other four, and is used by them much as the thumb is used. But this difference between the two races of beings is just what might be expected from the differences in their modes of life. Man has little need of this opposability on account of his exclusively terrestrial life, while to the ape it is indispensable on account of his arboreal environment and life. ‘But there are,’ says Haeckel, ‘wild tribes of men who can oppose the large toe to the other four just as if it were a thumb, and even new-born infants of the most highly-developed races of men can grasp as easily with their hind-hands as with their forehands. Chinese boatmen row with their feet, and Bengal workmen weave with them. The negro, in whom the big toe is freely movable, seizes hold of the branches of trees with it when climbing, just like the four-handed apes’.5
Many men have lost their arms by accident and have learned to use their feet as hands with wonderful skill. Not many years ago there died in Europe an armless violinist who had during his lifetime played to cultured audiences in most of the capitals of the world. Some of the most accomplished of penmen hold their pen between their toes. The man-like apes live to about the same age as man, and all of them, like man, have beards. The anthropoid beard, too, like the human, appears at the age of sexual maturity. The human beard often differs in colour from the hair of the scalp, and whenever it does it has been observed to be invariably lighter—never darker—than the hair on the scalp. This is true among all races of men. The same rule and the same uniformity exists among anthropoids. The races of mankind are divided into two primary groups depending upon the shape of the head and the character of the hair: the short-headed races (Brachycephali), such as the Malays, Mongols, and Aryans, with round or oval faces, straight hair, and vertical profiles; and the long-headed races (Dolichocephali), with woolly hair and prognathous faces, such as the Papuans and Africa races. The skin of the short-headed races is orange or white, while the skin and hair of the long-headed races are glossy black.
It is, at least, interesting that the orang and gibbon, who live in Asia and its islands, where the brachycephalic races of men supposedly arose, are themselves brachycephalic; and that the gorilla and chimpanzee, who live in Africa, where the dolichocephalic races chiefly live, are dolichocephalic. The gorilla and chimpanzee also have, like the men and women of Africa, black skin and hair; while the hair of the orang is a reddish-brown, and its skin sometimes yellowish-white. The dentition of the anthropoids and men is in all essentials identical. They all have two sets of teeth: a set of milk-teeth, twenty in number, and thirty-two permanent teeth, the permanents consisting of two incisors, one canine, two premolars, and three molars, in each half-jaw. Man has ordinarily twelve pairs of ribs and thirty-two vertebrae. So has the orang. The other anthropoids have thirteen pairs of ribs. But the number of ribs in both human and anthropoid beings is not uniform, man occasionally having thirteen pairs, and the gorilla fourteen. Man has also the same number of caudal vertebrae in his rudimentary tail as the anthropoid has. The hands and feet of anthropoids, bone for bone and muscle for muscle, correspond with those of men, no greater structural differences existing than among different species of men. The human foot has three muscles not found in the human hand—a short flexor muscle, a short extensor muscle, and a long muscle extending from the fibula to the foot. All of these muscles are found in the anthropoid foot just as in the foot of man. There are also the same differences between the arrangement of the bones of the anthropoid wrist and ankle as between the wrist and ankle bones of man. Whatever set of anatomical particulars may be selected, whether it be hands, arms, feet, muscles, skull, viscera, ribs, or dentition, it is found that the anthropoid races and men are in all essentials the same. The differences are such as have arisen as a result of different modes of life, and such as exist between different tribes of either group of animals.
‘The structural differences which separate man from the gorilla and chimpanzee,’ says Huxley, in summing up the conclusion of his brilliant inquiry into ‘Man’s Place in Nature,’ ‘are not so great as those which separate the gorilla from the lower apes.’
‘The body of man and that of the anthropoid are not only peculiarly similar,’ says Haeckel, ‘but they are practically one and the same in every important respect. The same two hundred bones, in the same order and structure, make up our inner skeleton; the same three hundred muscles effect our movements; the same hair clothes our skin; the same four-chambered heart is the central pulsometer in our circulation; the same thirty-two teeth are set in the same order in our jaws; the same salivary, hepatic, and gastric glands compass our digestion; the same reproductive organs insure the maintenance of our race’.6
‘Not being able,’ says Owen in his paper on ‘The Characters of Mammalia,’ ‘to appreciate or conceive of the distinction between the psychical phenomena of a chimpanzee and of a Boschisman or of an Aztec with arrested brain-growth, as being of a nature so essential as to preclude a comparison between them, or as being other than a difference in degree, I cannot shut my eyes to the significance of that all-pervading similitude of structure—every tooth, every bone, strictly homologous—which makes the determination of the difference between Homo and Pithecus the anatomist’s difficulty.’
‘If before the appearance of man on the earth,’ says Ward in his ‘Dynamic Sociology,’ ‘an imaginary painter had visited it, and drawn a portrait embodying the thorax of the gibbon, the hands and feet of the gorilla, the form and skull of the chimpanzee, the brain development of the orang, and the countenance of Semnopithecus, giving to the whole the average stature of all of these apes, the result would have been a being not far removed from our conception of the primitive man, and not widely different from the actual condition of certain low tribes of savages. The brain development would perhaps be too low for the average of any existing tribe, and would correspond better with that of certain microcephalous idiots and cretins, of which the human race furnishes many examples.’
And it is not true, as is commonly supposed, that, after all other resemblances between the human and anthropoid structures have been made out, there still exists somewhere some undistinguishable difference in the organic structure of their brains. All differences in structure from time to time suspected or asserted to exist between the brain of man and that of the man-like apes have been one after another completely swept away. And it is now known to all neurologists that the human and anthropoid brains differ structurally in no particulars whatever, both of them containing the same lobes, the same ventricles and cornua, and the same convolutional outline. Even the posterior lobe, the posterior cornu, and the hippocampus minor, so long triumphantly asserted to be characteristic features of the human brain, have been pitilessly identified in all anthropoids by the profound and terrible Huxley. There is not an important fold or fissure in the brain of man that is not found in the brain of the anthropoid. ‘The surface of the brain of a monkey,’ says Huxley, ‘exhibits a sort of skeleton map of man’s, and in the man-like apes the details become more and more filled in, until it is only in minor characters that the chimpanzee’s or the orang’s brain can be structurally distinguished from man’s’.7
The great difference physically between man and the anthropoids, aside from man’s talented larynx and erect posture, lies in man’s abnormal cranial capacity. The normal human cranium never contains less than 55 cubic inches of space, while the largest gorilla cranium contains only 34½ cubic inches. This is a difference of 20½ cubic inches. And 20½ cubic inches of thinking matter is an alarming amount to be lacking in a single individual. But this cranial gap between gorilla and man is deprived of some of its significance by the fact that human crania sometimes measure 114 cubic inches, making a difference between the smallest and largest human brains of 59 cubic inches. The difference between the gorilla and the savage in cranial capacity is, therefore, only about one-third as great as the cranial chasm between the savage and the sage.
1. The bat and a few other animals have a disc-like placenta, but it develops into the disc shape by a different route from what it does in the primates. 2. Hartmann: Anthropoid Apes; New York, 1901. 3. Quatrefages: The Human Species; New York, 1898. 4. Tyler: Anthropology; New York; 1899. 5. Haeckel: History of Creation, 2 vols.; New York, 1896. 6. Haeckel: The Riddle of the Universe; New York, 1901. 7. Huxley: Man’s Place in Nature; New York, 1883.
V. Recapitulation
The anatomical gulf between men and apes does not exist. There are, in fact, no gulfs anywhere, only gradations. All chasms are completely covered by unmistakable affinities, in spite of the fact that the remains of so many millions of deceased races lie hidden beneath seas or everlastingly locked in the limy bosoms of the continents. There are closer kinships and remoter kinships, but there are kinships everywhere. The more intimate kinships are indicated by more definite and detailed similarities, and the more general relationships by more fundamental resemblances. All creatures are bound to all other creatures by the ties of a varying but undeniable consanguinity.
Man stands unquestionably in the primate order of animals, because he has certain qualities of structure which all primates have, and which all other animals have not: hands and arms and nails, a bagpipe stomach, great subordination of the cerebellum, a disc-like placenta, teeth differentiated into incisors, canines, and molars, and pectoral milk glands.
Man is more closely akin to the anthropoid apes than to the other primates on account of his immense brain, his ape-like face, his vertical spine, and in being a true two-handed biped. The manlike apes and men have the same number and kinds of teeth, the same limb bones and muscles, like ribs and vertebrae, an atrophied tail, the same brain structure, and a suspicious similarity in looks and disposition. Men and anthropoids live about the same number of years, both being toothless and wrinkled in old age. The beard, too, in both classes of animals appears at the same period of life and obeys the same law of variation in colour. Even the hairs on different parts of the bodies of men and anthropoids, as on the arms, incline at a like angle to the body surface. The hair on the upper arm and that on the forearm, in both anthropoids and men, point in opposite directions—toward the elbow. This peculiarity is found nowhere in the animal kingdom excepting in a few American monkeys.
Man’s mammalian affinities are shown in his diaphragm, his hair, his four-chambered heart, his corpus callosum, his non-nucleated blood-corpuscles, and his awkward incubation.
The fishes, frogs, reptiles, birds, and non-human mammals are human in having two body cavities, segmented internal skeletons, two pairs of limbs, skulls and spinal columns, red blood, brains, and dorsal cords; and in possessing two eyes, two ears, nostrils, and mouth opening out of the head. And finally all animals, including man, are related to all other animal forms by the great underlying facts of their origin, structure, composition, and destiny. All creatures, whether they live in the sea, in the heavens, or in subterranean glooms; whether they swim, fly, crawl, or walk; whether their world is a planet or a water-drop; and whether they realise it or not, commence existence in the same way, are composed of the same substances, are nourished by the same matters, follow fundamentally the same occupations, all do under the circumstances the best they can, and all arrive ultimately at the same pitiful end.
VI. The Meaning of Homology
The similarities and homologies of structure existing between man and other animals, and between other animals and still others, are not accidental and causeless. They are not resemblances scattered arbitrarily among the multitudinous forms of life by the capricious levities of chance. That all animals commence existence as an egg and are all made up of cells composed of the same protoplasmic substance, and all inhale oxygen and exhale carbon dioxide, and are all seeking pleasure and seeking to avoid pain, are more than ordinary facts. They are filled with inferences. That vertebrate animals, differing in externals as widely as herring and Englishmen, are all built according to the same fundamental plan, with marrow-filled backbones and exactly two pairs of limbs branching in the same way, is an astonishing coincidence. That the wing of the bird, the foreleg of the dog, the flipper of the whale, and the fore-limb of the toad and crocodile, have essentially the same bones as the human arm has is a fact which may be without significance to blind men, but to no one else. The metamorphosis of the frog from a fish, of the insect from a worm, and of a poet from a senseless cell, are transformations simply marvellous in meaning. And it is not easy, since Darwin, to understand how such lessons could remain long unintelligible, even to stones and simpletons. Not many generations have passed, however, since these revelations, now so distinct and wonderful, fell on the listless minds of men as ineffectually as the glories of the flower fall on the sightless sockets of the blind.
It is hardly two generations since the highest intelligences on the earth conceived that not only the different varieties of men—the black, the white, and the orange—but all the orders and genera of the animal world, and not only animals, but plants, had all been somehow simultaneously and arbitrarily brought into existence in some indistinct antiquity, and that they had from the beginning all existed with practically the same features and in approximately the same conditions as those with which and in which they are found to-day. The universe was conceived to be a fixed and stupid something, born as we see it, incapable of growth, and indulging in nothing but repetitions. There were no necessary coherencies and consanguinities, no cosmical tendencies operating eternally and universally. All was whimsical and arbitrary. It was not known that anything had grown or evolved. All things were believed to have been given beginning and assigned to their respective places in the universe by a potential and all-clever creator. The serpent was limbless because it had officiously allowed Eve to include in her dietary that which had been expressly forbidden. The quadruped walked with its face towards the earth as a structural reminder of its subjection to the biped, who was supposed to be especially skilled in keeping his eyes rolled heavenward. The flowers flung out their colours, not for the benefit of the bugs and bees, and the stars paraded, not because they were moved to do so by their own eternal urgings, but because man had eyes capable of being affected by them. Man was an erect and featherless vertebrate because his hypothetical maker was erect and featherless. (I wonder whether, if a clam should conceive a creator, it would have the magnanimity to make him an insect or a vertebrate, or anything other than a great big clam.)
VII. The Earth an Evolution
The world now knows—at least, the scientific part of it knows—that these things are not true, that they are but the solemn fancies of honest but simple-minded ancients who did the best they could in that twilight age to explain to their inquiring instincts the wilderness of phenomena in which they found themselves. The universe is a process. It is not petrified, but flowing. It is going somewhere. Everything is changing and evolving, and will always continue to do so. The forms of life, of continents and oceans, and of streams and systems, which we perceive as we open our senses upon the world to-day, are not the forms that have always existed, and they are not the forms of the eternal future. There was a time, away in the inconceivable, when there was no life upon the earth, no solids, and no seas. The world was an incandescent lump, lifeless and alone, in the cold solitudes of the spaces. There was a time—there must have been a time—when life appeared for the first time upon the earth, simple cellules without bones or blood, and without a suspicion of their immense and quarrelsome posterity. There was a time when North America was an island, and the Alleghany Mountains were the only mountains of the continent. The time was—in the coal-forming age—when the Mississippi Valley, from the Colorado Islands to the Alleghanies, was a vast marsh or sea, choked with forests of equisetum and fern, and swarming with gigantic reptiles now extinct. There was a time when palms grew in Dakota, and magnolias waved in the semi-tropical climate of Greenland and Spitzbergen. There was a time when there were no Rocky Mountains in existence, no Andes, no Alps, no Pyrenees, and no Himalayas. And that time, compared with the vast stretches of geological duration, was not so very long ago, for these mountains are all young mountains. The time was when Jurassic saurians—those repulsive ruffians of that rude old time—represented the highest intelligence and civilisation of the known universe. There were no men and women in the world, not even savages, when our ape-like forefathers wandered and wondered through the awesome silences of primeval wilds; there were no railroads, steamboats, telegraphs, telephones, typewriters, harvesters, electric lights, nor sewing machines; no billionaires nor bicycles, no socialists nor steam-heat, no ‘watered stock’ nor ‘government by injunction,’ no women’s clubs, captains of industry, labour unions, nor ‘yellow perils’—there was none of these things on the earth a hundred years ago. All things have evolved to be what they are—the continents, oceans, and atmospheres, and the plants and populations that live in and upon them.
There will come a time, too, looking forward into the future, when what we see now will be seen no more. As we go backward into the past, the earth in all of its aspects rapidly changes; the continents dwindle, the mountains melt, and existing races and species disappear one after another. The farther we penetrate into the past, the stranger and the more different from the present does everything become, until finally we come to a world of molten rocks and vapourised seas without a creeping thing upon it. As it has been in the past so will it be in time to come. The present is not everlasting. The minds that perceive upon this planet a thousand centuries in the future will perceive a very different world from that which the minds of this day perceive—different arts, animals, events, ideals, geographies, sciences, and civilisations. The earth seems fixed and changeless because we are so fleeting. We see it but a moment, and are gone. The tossing forest in the wrath of the storm is motionless when looked at by a flash of lightning. The same tendencies that have worked past changes are at work to-day as tirelessly as in the past. By invisible chisels the mountains are being sculptured, ocean floors are lifting, and continents are sinking into the seas. Species, systems, and civilisations are changing, some crumbling and passing away, others rising out of the ruins of the departed. Mighty astronomical tendencies are secretly but relentlessly at work, and immense vicissitudes are in store for this clod of our nativity. The earth is doomed to be frozen to death. In a few million years, according to astronomers, the sun will have shrunken to a fraction of his present size, and will have become correspondingly reduced in heat-giving powers. It is estimated that in twelve or fifteen million years the sun, upon whose mighty dispensations all life and activity on the earth are absolutely dependent, will become so enfeebled that no form of life on the earth will be possible. The partially-cooled earth itself is giving up its internal warmth, and will continue to give it up until it is the same temperature as the surrounding abysms, which is the frightful negative of something like 270 centigrade degrees. These are not very cheerful facts for those who inhabit the earth to contemplate. But they that seek the things that cheer must seek another sphere. No power can stay the emaciation of suns or the thievery of enveloping immensities. Old age is inevitable. It is far off, but it is as certain as human decay, and as mournful. In that dreadful but inevitable time no living being will be left in this world; there will be no cities nor states nor vanities nor creeping things, no flowers, no twilights, no love, only a frozen sphere. The oceans that now rave against the rocky flanks of the continents will be locked in eternal immobility; the atmospheres, which to-day drive their fleecy flocks over the azure meads of heaven and float sweet sounds and feathered forms, will be, in that terrible time, turned to stone; the radiant woods and fields, the home of the myriads and the green play-places of the shadows, will, like all that live, move, and breathe, have rotted into the everlasting lumber of the elements. There will be no Europe then, no pompous philosophies, no hellish rich, and no gods. All will have suffered indescribable refrigeration. The earth will be a fluidless, lifeless, sunless cinder, unimaginably dead and desolate, a decrepit and pitiful old ruin falling endlessly among heartless immensities, the universal tomb of the activities.
The universe is an evolution. Change is as extensive as time and space. The present has come out of that which has been, and will enter into and determine that which is to be. Everything has a biography. Everything has evolved—everything—from the murmur on the lips of the speechless babe to the soul of the poet, and from the molecule to Jehovah.
VIII. The Factors of Organic Evolution
The animal kingdom represents one of the two grand branches of the organic universe. It has been evolved—evolved in a manner as simple and straightforward as it is revolting. It has all been brought about by partiality or selection. Generations of beings have come into existence. The individual members of each generation have differed from each other—differed in size, strength, speed, colour, shape, sagacity, luck, and likelihood of life. No two beings, not even those born from the same womb, are in all respects identical. Hardships have come. They have come from the inanimate universe in the form of floods, fires, frosts, accidents, diseases, droughts, storms, and the like; from other species, who were competitors or enemies; and from unbrotherly members of the same species. Some have survived, but the great majority have perished. Only a fraction, and generally an appallingly small fraction, of each generation of a species have lived to maturity. The lobster lays 10,000 eggs in a season, yet the mortality is such that the number of lobsters do not increase from one year to another. The elephant is the slowest breeder of all animals, yet, if they should all live, the offspring of a single pair in 750 years would, according to Darwin, number nearly 19,000,000. It has been shown that at the normal rate of increase of English sparrows, if none were to die save of old age, it would take but twenty years for a single pair to give one sparrow to every square inch in the State of Indiana.1 A single cyclops (one of the humbler crustaceans) may have 5,000,000 descendants in a season. One aphis will produce 100 young, and these young will reproduce in like manner for ten generations in a season, when, if they should all live, there would be a quintillion of young. A female white ant, when adult, does nothing but lie in a cell and lay eggs. She lays 80,000 eggs a day regularly for several months. An oyster lays 2,000,000 eggs in a season, and if all these eggs came to maturity a few dozen oysters might supply the markets of the world. The tapeworm is said to produce the incredible number of 1,000,000,000 ova, and some of the humbler plants three times this number of spores. If each egg of the codfish should produce an adult, a single pair in twenty-five years would produce a mass of fish larger than the earth. Lower forms of life are even more prolific than the higher. Maupas said that certain microscopic infusorians which he studied multiplied so rapidly that, if they should continue to multiply for thirty-eight days, and all of them should live, any one of them would produce a mass of protoplasm as big as the sun.
Those of each generation that have died have been inferior, or unfitted to the environment in which they found themselves. Those that have survived have been superior, superior in something—bigness, cunning, courage, virtue, vitality, strength, speed, littleness, or ferocity—something that has related them advantageously to surrounding conditions. The surviving remnant of each generation have become the progenitors of the next generation, and have transmitted, or tended to transmit, to their offspring the qualities of their superiority. This winnowing has gone on in each generation of living beings during many millions of years—almost ever since life commenced to be on the earth. Some have continued themselves, and others have died childless. The environment of each species has been an immense sieve, and only the superior have gone through it. Different environments have emphasised different qualities of structure and disposition, and have thus given rise to permanent varieties in survival. These varieties, through the accumulated effects of many generations of selection, have diverged into species; species, after a still longer series of selections, have evolved into genera; genera have evolved into families; families into orders; and so on. In this simple, terrible manner have all the branches of organic beings (thanks to the horrors of a million ages) been brought into existence.
Variation, therefore, which furnishes variety in offspring; Heredity, which tends to perpetuate peculiarities by causing offspring to resemble more or less the characters of their parents; and Environment, which determines the character of the selections, are the three factors, and the only three factors, in organic evolution.
1. Jordan: Footnotes of Evolution; New York, 1898.
IX. The Evidences of Organic Evolution
That the forms of life to-day found on the earth have come into existence by the evolution of the more complex forms from the simpler, and of these simpler forms from still simpler, through the ever-operating law of Selection, is a necessary conclusion from the following facts:
1. The existence in the animal world of all grades of structures, from the humblest possible protozoan, whose body consists of a single simple speck, to the most powerful and complex of mammals. There are estimated to be something like a million species of animals living on the earth to-day. There may be several times this number. These species are linked together by millions of varieties, and are so related to each other that they may be all gathered together into various genera; these genera may be grouped into families, the families into orders, and the orders into seven or eight great primary phyla. By taking existing species and adding to them the extinct species of the rocks, and placing them all according to their structural affinities, it is possible to arrange them in the form of a tree with the various phyla, orders, families, genera, and species, branching and rebranching from the main trunk. The existence of structures, so graduated as to render such an arrangement possible, is in itself suggestive of a common relationship and origin.
2. Evolution is suggested by the similarities and homologies of structure found throughout the animal kingdom. Some of these similarities and homologies have already been mentioned. They are everywhere—remoter and more fundamental, some of them, others closer and more detailed. To the untrained mind, which sees surfaces only, and not even surfaces well, the animal world is an interminable miscellany of forms. But to the biologist, who looks deeper and with immense acumen over the whole field of animal life, there are only seven or eight different types of structure in the entire animal world. These seven or eight types correspond with the primary classes, or phyla, into which animals are divided, viz., protozoa, sponges, celenterates, echinoderms, worms, mollusks, arthropods, and vertebrates. However widely the members of each of these great groups may differ among themselves in colour, size, habits of life, and the like, the members of each group all resemble each other fundamentally. Moles differ from monkeys, bats from men, and birds from crocodiles and toads. They differ enormously. But they are all vertebrates with red blood, double body cavities, backbones, two pairs of limbs, and five fingers on each limb. When they are looked at superficially, there is not much similarity between a water-strider and a butterfly or between a stag-beetle and a gnat. But they are all, in reality, built according to the same plan. Like all other insects, they have six legs, a sheath-like skeleton, and bodies characteristically divided into head, thorax, and abdomen. It is the same with all other great classes of beings. All worms resemble each other; and so do all mollusks, although they may differ in particulars as widely as nautiluses and clams. Echinoderms have a radiate structure, celenterates and sponges are vase-like in shape, and protozoa are one-celled. The differences in structure among the members of a group consist in different modifications of a fundamental type. Among the vertebrates the fore-limb may be an arm, a leg, a wing, a shovel, a flipper, or a fin. But in all cases it is the same organ—that is, the same implement modified to serve different ends. Take the mouth-parts of insects. In the grasshopper and cricket these parts are fitted for grinding; in the moths and butterflies they are fashioned into long tubes for sucking the sweets of flowers; in the mosquito they form an elaborate apparatus for drilling and drinking; and in the mayfly the mouth-parts, though present, are not used at all. In all of these animals these parts are essentially the same, although differing so much in their forms and purposes that the unscientific can scarcely be made to believe they are fundamentally alike. There is no fact more familiar to the biologist or more frequently met with in the fields of animal morphology than the fact that the same general type may be hammered into dozens, or hundreds, or even thousands, of different patterns by the incessant industry of its surroundings, and that the same organic part may be moulded into various implements serving totally different ends by the environmental vicissitudes of time and space. On the hypothesis that the members of each group of animals possessing common characteristics, whether the group be large or small, have sprung from a common ancestry, and that the differences in structure have arisen as a result of differences in environment, the similarities and homologies of structure existing among animals are perfectly intelligible. But on any other supposition they are inexplicable.
3. Evolution is suggested by the remarkable series of phenomena presented by embryology. There are at least four facts in the developmental history of every creature which can hardly be accounted for on any other supposition than that of organic evolution.
First, the fact that every animal, above the lowest, individually passes through an evolution between the beginning of its existence and its maturity. Terrestrial beings are not born, like Minerva, full-grown. They grow. They evolve. They commence close down to the very atoms. And from this lowly genesis they rise, through a series of marvellous changes, to that high state of perfection and greatness from which they descend to dissolution.
If we knew by actual observation as little concerning the evolution of individuals as we do of the evolution of species—if we had always been used to seeing animals, including ourselves, in full bloom—had never watched the tadpole, the pupa, and the babe pass through their wonderful metamorphoses on their way to maturity, it would probably be just as hard for many minds to believe that animals evolve individually to be what they are as it is for them to believe that species have grown to be what they are. In the case of individuals, however, the evolution takes place right before our eyes largely, while the evolution of species goes on so slowly and stretches back so far into the past that it can only be inferred.
Second, the fact that animals, no matter how much they may differ from each other at maturity, all begin existence at the same place. Every animal commences its organic existence as an egg—as a one-celled animal—as an organism identical in structure with the simplest protozoan. The ova of whales ‘are no larger than fern seeds.’ The eggs of the coral, the crab, the ape, and the man are so precisely alike that the highest powers of the microscope cannot distinguish between them.
Third, the fact that the members of the same great group of animals in their individual development pass through similar stages of evolution. The ‘worm’ stage in the development of most insects and the ‘fish’ stage of frogs are well known.
There are no more remarkable instances of individual evolution in the whole range of animal life. The fish, the reptile, the bird, the dog, and the human being—all vertebrates, in short—cannot for some time after their embryonic commencement be distinguished from each other. ‘The feet of lizards and mammals, the wings and feet of birds, and the hands and feet of men,’ says the illustrious Von Baer, as quoted by Darwin, ‘all arise from the same fundamental form’.1a
‘It is quite in the later stages of development,’ says Huxley, ‘that the human being presents marked differences from the ape, while the latter departs as much from the dog in its development as the man does’.2
Not only frogs, but reptiles, birds, and mammals, including man, all have gills at a certain stage in their embryonic development. Nearly all the lower invertebrate animals are hermaphroditic—that is, in the body of each animal is found the two kinds of sex organs which in the higher animals exist in distinct animals. And frogs, birds, and other higher animals, which as adults are unisexual, have, as an inheritance from these primitive forms, hermaphroditic embryos.3a
Fourth, the fact that the structural stages through which animals in embryo pass correspond in a wonderful manner with the permanent structures of those lower forms which extend serially back to the beginnings of life. It is the proudest boast of the embryologist that he is able to know the route through which any species has come to be what it is by a simple study of the individual evolution of its members. Each animal repeats in its individual evolution the evolution of its species. This recapitulation is not always complete—is, in fact, frequently vague, sometimes circuitous, and often broken or abbreviated. Processes requiring originally centuries or thousands of years to accomplish are here telescoped into a few months, or even days. It is not strange that the process is imperfect. But so firmly is the belief in the correspondence of ontogeny and phylogeny fixed in the minds of modern biologists that, in determining the classification and affinities of any particular animal, more reliance is placed on the facts of embryology than on those of adult structure.
The first thing that an animal becomes after it is an egg—unless it is a one-celled animal, in which case it remains always an egg—is two cells; these two cells become four; these four become eight; and so on, until the embryo becomes a many-celled ball, consisting of a single layer of cells surrounding a fluid interior. A dimple forms in the cell layer on one side of this ball, and, by deepening to a hollow, changes the ball into a double-walled sac. This is the gastrula—the permanent structure of the sponges and celenterates, and an (almost) invariable stage in the larval development of all animals above the sponges and celenterates. The gastrula becomes a worm (or an insect or a fish through the worm) by elongation and enlargement, and by the development of the endoderm, which is the inner layer of the cell wall, into organs of nutrition and reproduction, and by the development of the ectoderm, which is the outer cell layer, into organs of motion and sensation.
The embryonic development of a human being is not different in kind from the embryonic development of any other animal. Every human being at the beginning of his organic existence is a protozoan, about 1⁄125 inch in diameter; at another stage of development he is a tiny sac-shaped mass of cells without blood or nerves, the gastrula; at another stage he is a worm, with a pulsating tube instead of a heart, and without head, neck, spinal column, or limbs; at another stage he has, as a backbone, a rod of cartilage extending along the back, and a faint nerve cord, as in amphioxus, the lowest of the vertebrates; at another stage he is a fish with a two-chambered heart, mesonephric kidneys, and gill-slits with gill arteries leading to them, just as in fishes; at another stage he is a reptile with a three-chambered heart, and voiding his excreta through a cloaca like other reptiles; and finally, when he enters upon post-natal sins and actualities, he is a sprawling, squalling, unreasoning quadruped. The human larva from the fifth to the seventh month of development is covered with a thick growth of hair and has a true caudal appendage, like the monkey. At this stage the embryo has in all thirty-eight vertebrae, nine of which are caudal, and the great toe extends at right angles to the other toes, and is not longer than the other toes, but shorter, as in the ape.
These facts are unmistakable. There is a reason for everything, and there is a reason for these transformations through which each generation of living beings journeys. The individual passes through them because the species to which he belongs has passed through them. They represent ancestral wanderings. As if to emphasise the kinship of all of life’s forms and to render incontrovertible the fact of universal evolution, Nature compels every individual to commence existence at the same place, and to recapitulate in his individual evolution the phylogenetic journeyings of his species.
4. That existing forms of life have been evolved from other forms, and that these ancestral forms have been different from those derived from them, is shown by the occasional appearance of antecedent and abandoned types of structure among the offspring of existing species. Occasionally a human child is born strangely unlike its parents, but bearing an unmistakable resemblance in looks and disposition to his great-grandfather or some other remote ancestor. This is atavism, that tendency to revert to ancestral types which is prevalent among all animals. We may think of it figuratively as a flash of indecision when Nature hesitates for a moment whether to adopt a new form of structure or cling to the old and tried. Horses and mules are sometimes born with three toes on each foot, and zebra-like stripes on their legs and shoulders; and domestic pigeons, such as are naturally black, red, or mottled, occasionally produce offspring with blue plumage and two black wing-bars, like the wild rock-dove, from which all domestic breeds have sprung. In man the cheekbone and the frontal bone of the forehead consist normally each of a single bone. But in children and human embryos these bones are always double, as is normally the case in adults among some of the anthropoids and other mammals. Gills appear regularly in the embryos of reptiles, birds, and mammals, and human young are sometimes born with gill-slits on the neck. There are times when, owing to inaccurate or incomplete embryological development, these fish-like characteristics are so perfect at birth as to allow liquids, on being swallowed, to pass out through them and trickle down on the outside of the neck. Many muscles are occasionally developed in man which are normal in the apes and other mammals. As many as seven different muscular variations have been found in a single human being, every one of which were muscles found normally in the structure of the apes.1b
5. Closely akin to atavism, which is the occasional persistence of ancestral types of character, is the regular occurrence of vestigial organs or structures, organs which in ancestral forms have definite functions, but which in existing species, owing to changed conditions, are rudimentary and useless. On the back of each ankle of the horse are two splints, the atrophied remains of the second and fourth toes. Similar vestiges of two obsolete toes are also found just back of the wrists and ankles on all the two-toed ungulates, such as the cow and sheep. In the body of the whale where hind-limbs would naturally be, there are found the anatomical ruins of these organs in the form of a few diminutive bones. The same thing is true in the sirenians. In the Greenland whale there are remnants of both femur and tibia in the region of the atrophied hind-limbs. The snakes are limbless, but the pythons and boas have internal remnants of hind-limbs and sometimes even clawed structures representing toes. The so-called ‘glass-snake’ or ‘joint-snake’ (which is really a limbless lizard) has four complete internal limbs. Young turtles, parrots, and whalebone whales have teeth, but the adults of these animals are toothless. Cows, sheep, deer, and other ruminants, never have as adults any upper incisors, but these teeth are found in the foetal stages of these animals just under the gums. The female frog has rudimentary male reproductive organs, and the male has corresponding vestiges of female organs. Similar remnants of the reproductive structures exist in many other animals. They represent stages in the transition from the hermaphroditism of primitive animals to the unisexuality of the higher forms, the separation of the sex organs into those of male and female having come about through the decay of one set of structures in each individual.
For reasons which it is not necessary to mention here, biologists believe that insects all originated from a common parental form, with two pairs of wings and six legs. Insects all retain their original allowance of legs, but in many species one or the other pair of wings has become more or less degenerated. In the whole order of flies the back pair of wings is represented by a couple of insignificant knobs. In the Strepsiptera, a sub-order of beetles, the front-wings are similarly reduced, being mere twisted filaments. Many parasites, such as fleas and ticks, whose mode of life renders organs of aerial locomotion unnecessary, are entirely wingless. The insects of small isolated islands are also largely without wings, the proportion of wingless species being much larger than among insects inhabiting continents. This is due to their greater liability on small land masses of being carried out to sea and drowned, owing to the feebleness and uncertainty of insect flight. On the island of Madeira, out of the 550 species found there, 220 species no longer have the power of flight.
Air-breathing animals—amphibians, reptiles, birds, and mammals—have normally a pair of lungs—a right one and a left one. But in snakes and snake-like lizards, where the body is very slender and elongated, only one lung, sometimes the right one, and sometimes the left, is fully developed. The right ovary is likewise aborted in all birds, the left one yielding all the eggs. The swifts and frigate birds live almost their whole lives long on the wing, and the legs of these birds have grown so short and weak and rudimentary, as a result of their constant life in the air, that they can scarcely walk. The chimney swift is said never to alight anywhere except on the sooty inner walls of the chimney where its nest is. Its food consists of insects which it gathers in the air, and the few dead twigs used in making its nest are nipped from the tree while the bird continues its flight. The ostriches, cassowaries, and many other birds, have, on the other hand, developed their legs at the expense of their wings. The ostrich is said to be able to outrun the horse, but it has no power of flight, although it has wings and wing muscles, and even the skin-folds covering the wings corresponding to those of birds that fly. But its whole flying apparatus is in ruins. The rudimentary hind-toe of birds is a vestigial organ, and so are the claws which appear on the thumb and first finger of all young birds. So also are the rudiments of eyes in cave crickets, fishes, and other inhabitants of total darkness. The flounder and other so-called flat fishes swim straight up, as ordinary fishes do, when young. But as they grow they incline more and more to one side, and finally swim entirely on their side, the eye on the lower side migrating around, and joining the other on the upper side of the head.
About the first thing a human infant does on coming into the world is to prove its arboreal origin by grasping and spitefully clinging to everything that stimulates its palms. A little peeperless babe an hour old can perform feats of strength with its hands and arms that many men and women cannot equal. It can support the entire weight of its body for several seconds hanging by its hands. Dr. Robinson, an English physician, found as a result of sixty experiments on as many infants, more than half of whom were less than an hour old, that with two exceptions every babe was able to hang to the finger or to a small stick, and sustain the whole weight of the body for at least ten seconds. Twelve of those just born held on for nearly a minute. At the age of two or three weeks, when this power is greatest, several succeeded in sustaining themselves for over a minute and a half, two for over two minutes, and one for two minutes and thirty-five seconds. The young ape for some weeks after birth clings tenaciously to its mother’s neck and hair, and the instinct of the child to cling to objects is probably a survival of the instinct of the young ape. I believe it is Wallace who relates somewhere an incident which illustrates the instinct of the young simian to cling to something. Wallace had captured a young ape, and was carrying it to camp, when the little fellow happened to get its hands on the naturalist’s whiskers, which it mistook, evidently, for the hirsute property of its mother, and, driven by the powerful instinct of self-preservation, it hung on to them so desperately it could scarcely be pulled loose. Many mammals are provided with a well-developed muscular apparatus for the manipulation of their ears. But in man there does not exist the same necessity for auricular detection of enemies, and while these muscles still exist, and are capable of being used to a slight extent by occasional individuals, they are generally so emaciated as to be useless.
Another vestigial organ in the body of man, and one of significance from the standpoint of morphology, is the tail. The tail is an exceedingly unpopular part of the human anatomy, most men and women being unwilling to admit that they have such an appendage. But many a person who has hitherto dozed in ignorance on this matter has learned with considerable dismay, when he has for the first time looked upon the undraped lineaments of the human skeleton, that man actually has a tail. It consists of three or four (sometimes five) small vertebrae, more or less fused, at the posterior end of the spinal column. That this is really a rudimentary tail is proved beyond a doubt by the fact that in the embryo it is highly developed, being longer than the limbs, and is provided with a regular muscular apparatus for wagging it. These caudal muscles are generally represented in grown-up people by bands of fibrous tissue, but cases are known where the actual muscles have persisted through life.4
The nictitating membrane, which in birds and many reptiles consists of a half-transparent curtain acting as a lid to sweep the eye, is in the human eye dwindled to a small membranous remnant, draped at the inner corner. The growth of hair over the human body surface may be regarded, in view of the sartorial habits of man, as a vestigial inheritance from hairy ancestors. One of the most notorious of the vestigial organs of man is the vermiform appendix, a small slender sac opening from the large intestine near where the large intestine is joined by the small intestine. In some animals this organ is large and performs an important part in the process of digestion. But in man it is a mere rudiment, not only of no possible aid in digestion, but the source of frequent disease, and even of death.
There are in all, according to Darwin, about eighty vestigial organs in the human body. But these organs occur everywhere throughout the animal kingdom. There is not an order of animals, nor of plants either, without them. They are necessary facts growing out of evolution. Organic structures are the result of adjustment to surrounding conditions. The continual changes in environment to which all organisms are exposed necessitate corresponding changes in structure. And the vestiges found in the bodies of all animals represent parts which in the previous existence were useful and necessary to a complete adjustment of the organism, but which, owing to a change of emphasis in surroundings, have become useless, and consequently shrunken. They are the obsolete or obsolescent parts of animal structure—parts which have been outgrown and superseded—the ‘silent letters’ of morphology. They sustain the same relation to the individual organism as dead or dwindling species sustain to a fauna. They furnish indisputable proof of the kinship and unity of the animal world.
6. It is only on the supposition that the life of the earth has evolved step by step with the evolution of the land masses, and that the forms of life from which existing forms were evolved were dispersed over the earth at a time when physiographic conditions were very different from what they are now, that it is possible to account for the peculiar manner in which animals are distributed over the earth. The cassowary is a flightless bird of the ostrich order inhabiting Australia and the islands to the north of it. This bird is found nowhere else in the world, and each area has its own particular species. The same things are also true of the kangaroo. It is found over a similar region, with a different species occupying each land mass. Now, on the hypothesis of special creation there is no thinkable reason why these animals should be divided, as they are, into distinct species, and restricted to this particular region. But on the hypothesis of evolution it is perfectly plain. All of these regions at one time were united with one another, and were subsequently submerged in part, forming islands. Each group of animals, being isolated from every other group and subjected to somewhat different conditions, developed a style of departure from the original type of structure different from that of every other group in response to the peculiar conditions operating upon it. This has led, in the course of centuries of selection, to the formation of distinct species such as exist to-day.
Lombock Strait, a narrow neck of water between Bali and Lombock Island, and Macassar Strait, separating Celebes from Borneo, are parts of a continuous passage of water which in remote times separated two continents—an Indo-Malayan continent to which belonged Borneo, Sumatra, Java, and the Malay Peninsula; and an Austro-Malayan continent, now represented by Australia, Celebes, the Moluccas, New Guinea, Solomon’s Islands, etc. Wallace first announced this ancient boundary, and it has been called ‘Wallace’s line.’ He was led to infer its existence by the fact which he observed as he travelled about from island to island, that, while the faunas of these two regions are as wholes very different from each other, the faunas of the various land patches in each area have a wonderful similarity. Australia is a veritable museum of old and obsolete forms of both plants and animals. Its fauna and flora are made up prevailingly of forms such as have on the other continents long been superseded by more specialised species. No true mammals, excepting men and a few rats, lived in Australia when Englishmen first went there. The most powerful animals were the comparatively helpless marsupials. The explanation of these remarkable facts is probably this: The Australian continent, which formerly included New Guinea and other islands to the north, has not been connected with the other land masses for a very long period of time. The development upon the other continents of the more powerful mammals, especially of the ungulates and the carnivora, resulted in the extermination of the more helpless forms from most of the earth’s surface. But Australia, protected by its isolation, has retained to this day its old-fashioned forms of life, neither land animals nor plants having been able to navigate the intervening straits. This supposition is strengthened by the fact that fossil remains of marsupials are to-day found scattered all over the world, while, with the exception of the American opossums, living marsupials are found only in Australia and its islands. There is to-day not a single survivor of these once-numerous races in either Europe, Asia, or Africa. Similar facts of distribution are furnished by the lemurs—those small, monkey-like animals with fox faces, which are sometimes called ‘half-apes,’ since they are supposed to be the link connecting the true apes with lower forms. Fossil lemurs are found in both America and Europe, but lemurs are now extinct in both continents. Those of America were probably exterminated by the carnivora, who are known to be very fond of monkey meat of all kinds. The European lemurs seem to have migrated southward into eastern Africa at a time when Madagascar formed a part of the mainland. ‘There they have been isolated, and have developed in a fashion comparable to that which has occurred in the case of the Australian marsupials. Of fifty living species, thirty are confined to Madagascar, and the lemurs are there exceedingly numerous in individuals. Outside of Madagascar they only maintain a precarious footing in forests or on islands, and are usually few in number’.3b
If the earth were peopled by migrations from Ararat, it would require a good deal of intellectual legerdemain to show why the sloths are confined to South America and the monotremes to Australia and its islands. The reindeer of northern Europe and Asia, and the elk and caribou of Arctic America, are so much alike they must have descended from a common ancestry, and been developed into distinct species since the separation of North America and Eurasia. The same thing is probably also true of the puma and jaguar, who inhabit the middle latitudes of the New World, and the lion, tiger, and leopard, occupying like latitudes of the Old World. They all belong to the cat family, and represent divergences from a common feline type of structure. The camel does not exist normally outside of northern Africa and central and western Asia. And when the camel-like llama of South America first became known to zoologists, it was a problem how this creature could have become separated so far from the apparent origin of the camel family. But since then fossil camels have been found all over both North and South America. And it has even been suspected that perhaps America was the original home of the camel, and that, like the horse, the camel migrated to the eastern hemisphere at a time when the eastern and western land masses were connected. The foxes, hares, and other mammals of the upper Alps, also many Alpine plants, are like those of the Arctic regions. The most probable explanation of these resemblances is that these Alpine species climbed up into these inhospitable altitudes, and were left stranded here on this island of cold, when their relatives, on the return of warmth at the close of the glacial period, retreated back to the ice-bound fastnesses around the pole. It is for a similar reason, probably, that the flora of the upper White Mountains resembles that of Labrador.
7. One of the strongest pieces of evidence bearing on evolution that is furnished by any department of knowledge is that furnished by geology. It is the evidence of the rocks. Geology is, among other things, a history of the earth. This history has been written by the earth itself on laminae of stone. It is from these records that we learn incontestably the order in which the forms of life have made their appearance on the earth.
Three-fourths of the surface of the earth is sea. Over the surface of the remaining fourth, excepting in mountainous places, is a layer of soil, varying from a few feet to a few hundred feet in depth. Beneath this coverlet of soil, extending as far as man has penetrated into the earth, is rock. Excepting in regions overflowed by lava poured out from beneath, or along the backbones of continents where the surface rocks have been upheaved into folds and carried away by denudation, the rocks immediately beneath the soil, to a thickness often of thousands of feet, are in the form of layers, or sheets, arranged one above another. These rocks are called sedimentary rocks, as distinguished from the unlaminated rocks of the interior. They have been formed at the bottom of the sea, and have, hence, all been formed since the condensation of the oceans. They have been formed out of the detritus of continents brought down by the rivers and the accumulated remains of animal and vegetal forms which have slowly settled down through the waters. They are the successive cemeteries of the dead past. Such rocks are now forming over the floors of all oceans—forming just as they have formed throughout the long eons of geological history. Along the axes of ancient mountains and in deep-cut canyons the rock layers are exposed to a thickness of thousands of feet, in some cases thirty or forty thousand feet. Here they lie, piled up, one on top of another, the great, broad pages upon which are written the long, dark story of our planet. It is the mightiest and most everlasting of all annals—the autobiography of a world. It is possible, by studying these rock records, to know not only the kind of life that lived in each age, but a good deal regarding the conditions in which that life lived and passed away. Just as the naturalist is able, from a single bone of an unknown animal, to reconstruct the entire animal and to infer something of its surroundings and habits of life, and as the archeologist, by going back to the graves of deceased races and digging up the dust upon which these races wrought, is able to tell much of their history and characteristics, so the geologist, by studying the bones of those more distant civilisations, the civilisations sandwiched among the fossiliferous rocks, is able to know, not only just the kind of life that lived in each age, but, by comparing the species of successive strata, can construct with astonishing fulness the genealogical outline of the entire life process. The succession of life forms as they appear in the rocks, with a sketch of their probable genealogy, is traced elsewhere in this chapter. It is only necessary to say here that the order in which the forms of life appear in the sedimentary strata is that of a gradually increasing complexity. The invertebrates appear first; then the fishes, the lowest of the vertebrates; after these come the amphibians; following these the reptiles; and finally the birds and mammals.
8. There is another reason for a belief in evolution furnished by geology, but of a somewhat different kind from that just stated. It consists in the fact that there are found in the rocks series or grades of structures, which fit with amazing accuracy on to the structures of existing species. Now, this is precisely what, according to the evolutional hypothesis, is to be expected. For, if evolution is true, existing species represent the tops of things. They are the existing and visible parts of processes which extend indefinitely back into the past, and whose deceased stages may reasonably be expected to be found fossil in the earth. Considering the youth and inexperience of paleontology and the torn and incoherent character of the record, it is surprising that anatomists have been able to accomplish what they have accomplished. In many cases—notably, those of man, the snail, the crocodile, and the horse—antecedent forms of structure have been found in almost unbroken gradations leading back to types differing immensely from their existing representatives. Bones and fossils of men have been found buried beneath the alluvium of rivers, under old lava-beds, and in caves, crusted over by the deposits of percolating waters. Many such fossils are found in quaternary rocks, along with the bones of animals still living and some extinct. Some of these remains indicate unmistakable affinities with the ape. The most celebrated of these discoveries is the fossil of an erect ape-man (Pithecanthropus erectus), found by a Dutch Governor on the island of Java in 1894. This fossil, in the shape and size of the head and in its general structure, strikes about as near as could be the middle between man and ape. That it is the fossil of an ambiguous form is indicated by the fact that, when it was examined by a company of twelve specialists at Berlin soon after its discovery, three of them declared it to be the remains of an individual belonging to a low variety of man; three others thought it was a large anthropoid; while the other six held that it was neither man nor anthropoid, but a genuine connecting link between them. It is discussed at length by Haeckel in ‘The Last Link,’ a paper read before the International Congress of Zoology, at Cambridge, in 1898. ‘It is,’ says the veteran biologist, ‘the much-sought “missing link” supposed to be wanting in the chain of primates which stretches unbroken from the lowest catarhine to the most highly developed man.’ Associated with this fossil ape-man were the fossils of the elephant, hyena, and hippopotamus, none of which any longer exist in that part of the world, also the fossil remains of two orders of animals now extinct. The genealogy of the crocodile has been traced by Huxley, through all intermediate stages, back to the giant reptiles of the early Tertiary.5And the pedigree of the horse has been even more completely worked out by the indefatigable Marsh. In the museum of Yale University may be seen the fossil history of this splendid ungulate, from the time it was a clumsy little quadruped only 14 inches high, and with four or five toes on each foot, down to existing horses. The earliest known ancestor of the horse, the eohippus, lived at the beginning of the Eocene epoch. It had five toes, almost equal, on each front foot (four toes behind), and was about the size of a fox. The orohippus, which lived a little later, had four toes on each front-foot, and three behind. The mesohippus, found in the Miocene, had three toes and one rudimentary toe on each front-foot, and three toes behind. It was about the size of a sheep. The miohippus, which is found later, had three toes on each of its four feet, with the middle toe on each foot larger than the other two. The pliohippus, living in the Pliocene epoch, had one principal toe on each foot, and two secondary toes, the two secondary toes not reaching to the ground. It was about the size of a donkey. Existing horses have one toe on each foot—the digit corresponding to the big middle finger—and the ruins of two others in the form of splints on the back of each ankle. In the embryo of the horse these splints are segmented, each of them, into three phalanges. Fossil remains representing all stages in the development of the horse have been found in the regions about the upper waters of the Missouri River.
It is an important fact that the types of structure forming any series grow more and more generalised as the distance from the present increases, and that different lines of development, when traced back into the past, often converge in types which combine the main characters of various existing groups. The horses, rhinoceroses, and tapirs, great as are the differences among them now, can be traced back step by step through fossil forms, their differences gradually becoming less marked, until ‘the lines ultimately blend together, if not in one common ancestor, at all events into forms so closely alike in all essentials that no reasonable doubt can be held as to their common origin.’ ‘The four chief orders of the higher mammals—the primates, ungulates, carnivora, and rodents—seem to be separated by profound gulfs, when we confine our attention to the representatives of to-day. But these gulfs are completely closed, and the sharp distinctions of the four orders are entirely lost, when we go back and compare their extinct predecessors of the Cenozoic period, who lived at least three million years ago. There we find the great sub-class of the placentals, which to-day comprises more than two thousand five hundred species, represented by only a small number of insignificant pro-placentals, in which the characters of the four divergent orders are so intermingled and toned down that we cannot in reason do other than consider them as the precursors of those features. The oldest primates, the oldest ungulates, the oldest carnivora, and the oldest rodents, all have the same skeletal structure and the same typical dentition (forty-four teeth) as these pro-placentals; all are characterised by the small and imperfect structure of the brain, especially of the cortex, its chief part, and all have short legs and five-toed, flat-soled (plantigrade) feet. In many cases among these oldest placentals it was at first very difficult to say whether they should be classed with the primates, ungulates, carnivora, or rodents, so very closely and confusedly do these four groups, which diverge so widely afterwards, approach each other at that time. Their common origin from a single ancestral group follows incontestably’.6
9. Man is the most powerful and influential of animals. He rules the world—rules it with a sovereignty more despotic and extensive than that hitherto exercised by any other animal. Many races of beings are, and have been for centuries, completely dominated by him. These races, during their long subjection, have been changed and transformed by man in a wonderful manner through his control of their power to breed. All domestic animals have come from wild animals; they have been derived by a process of selective evolution conducted by man himself. By continually choosing as the progenitors of each generation those with qualities best suited to his whims and purposes, man has evolved races as different from each other in appearance and structure, and as different from the original species, as many groups which, in the wild state, constitute distinct species; indeed, man has in some cases created entirely new species, both of plants and animals—species that breed true and are what biologists call ‘good’—by his own selections.
There are something over 150 different varieties of the domestic pigeon. Some of these varieties—as many as a dozen, Mr. Darwin thinks—differ from each other sufficiently to be reckoned, if they are considered solely with reference to their structures, as entirely distinct species. The carrier, for instance, the giant of the pigeons, measures 17 inches from bill-tip to the end of its tail, and has a beak 1 3⁄4 inches long. Around each eye is a large dahlia-like wattle, and another large wattle is on the beak, giving the beak the appearance of having been thrust through the kernel of a walnut. The tumbler is small, squatty, and almost beakless. It has the preposterous habit of rising high in the air and then tumbling heels over head. The roller, one of the many varieties of the tumbler, descends to the ground in a series of back somersaults, executed so rapidly that it looks like a falling ball. The runt is large, weighing sometimes as much as the carrier. The fantail has thirty or forty feathers in its tail, while all other varieties have only twelve or fourteen, the normal number for birds. The trumpeter, so named on account of its peculiar coo, has an umbrella-like hood of feathers covering its head and face, and its feet are so heavily feathered that they look like little wings. In the correct specimens of this variety the feathers have to be clipped from the face before the birds can see to feed themselves. The pouter has the absurd habit of inflating its gullet to a prodigious size, and the Jacobin wears a gigantic ruff. The homing pigeon has such a strong attachment for its cote that it will travel hundreds of miles, sometimes as many as 1,400 miles, in order to reach the home from which it has been separated. But it is not simply in their colour, size, habits, and plumage, that pigeons vary. There are corresponding differences in their structures, in the number of their ribs and vertebrae, in the shape and size of the skull, in the bones of the face, in the development of the breast-bone, and in the length of the neck, legs, and bill. Pigeons also differ in the shape and size of their eggs, and in their dispositions and voice. ‘There is,’ says Huxley in summing up his discussion of the great variety in these birds, ‘hardly a particular of either internal economy or external shape which has not by selective breeding been perpetuated and become the foundation of a new race’.7
All of the 150 different varieties of domestic pigeons have been evolved by human selection during the past three or four thousand years from the blue rock-doves which to-day inhabit the seacoast countries of Europe.
What is true of pigeons is also true largely of most of the other races associated with man—of cats, cattle, horses, sheep, swine, goats, fowls, and the like. All varieties of the domestic chicken—the clumsy Cochin with its feather-duster legs, the tall and stately Spanish, the great-crested Minorca, the Dorking with its matchless; comb and wattle, the almost combless Polish, the blue Andalusian, the gigantic Brahma, the tiny Bantam, the Wyandottes in all colours (black, white, buff, silver, and golden), the magnificent Plymouth Rocks, and the exceedingly pugnacious Game-cock—these and dozens of other varieties, all flightless, have come from the jungle-bird whose morning clarion still greets Aurora from the wilds of distant India. The dog is a civilised wolf, and the wild-boar is the progenitor of the oleaginous swine. The Merino and South Down breeds of sheep have come from the same stock in the last century and a half. In 1790 a lamb was born on the farm of Seth Wright in Massachusetts. It had a long body and short, bowed legs. It was noticed that this lamb could not follow the others over the fences. The owner thought it would be a good thing if all his sheep were like it. So he selected it to breed from. Some of its offspring were like it, and some were like the ordinary sheep. By continual selection of those with long bodies and short legs the ancon breed of sheep was finally produced. In 1770 in a herd of Paraguay cattle a hornless male calf appeared, and from this individual in a similar way came the stock of Muleys. The occasional appearance of horned calves and lambs among the offspring of hornless breeds of cattle and sheep are examples of atavism indicating the presence of a vestigial tendency to breed true to their horned ancestors. The Hereford cattle originated as a distinct variety about 1769 through the careful selections of a certain Englishman by the name of Tompkins. All domesticated quadrupeds, except the elephant, have come from wild species with erect ears, the ears acting as funnels to harvest the sound-waves. But there are few of them in which there is not one or more varieties with drooping ears—cats in China, horses in parts of Russia, sheep in Italy, cattle in India, and pigs, dogs, and rabbits in all long-civilised lands. We are so accustomed to seeing dogs and pigs with pendent ears that we are surprised to know there are varieties with erect ears. The goldfish is a carp, and in its native haunts in the waters of China it has the colour of the carp. The golden hue seen in the occupants of our aquaria has been given to this fish by the Chinese through the continual selection of certain kinds. The goldfish, almost as much as the pigeon, has been the sport of fanciers, and the strangest varieties have resulted. Some have outlandishly long fins, while others have no dorsal fin at all. Some are streaked and splotched with gold and scarlet; others are pure albinos. One of the most monstrous varieties has a three-lobed tail-fin, and its eyeballs, without sockets, are on the outside of its head. All of our common barnyard fowls—turkeys, ducks, geese, and chickens—are flightless, but the varieties from which the domesticated forms have come all have functional wings, two of these varieties crossing continents in their annual migrations.
Not only animals, but plants also, many of them, have been greatly changed by man in his efforts to adapt them to his uses as food, ornamentation, and the like. On the seaside cliffs of Chili and Peru may still be found growing the wild-potato—the small, tough, bitter ancestor of the mammoth Burbank, Peerless, Early Rose, and the nearly two hundred other varieties of this matchless tuber found in the gardens of civilised man. The cabbage, kale, cauliflower, and kohlrabi are all modifications of the same wild species (Brassica oleracea), the cauliflower being the developed flower, kohlrabi the stalk, and kale and cabbage the leaves. The peach and the almond, Darwin thinks, have also come from a common ancestral drupe, the peach being the developed fruit, and the almond the seed. There are nearly 900 different varieties of apples, varying in the most wonderful manner in size, colour, flavour, texture, and shape, but all of them probably derived from the little, sour, inedible Asiatic crab. The many times ‘double’ roses of our gardens have come from the five-petalled wild-rose of the prairies. The cultivated varieties of viburnum and hydrangea have showy corymbs of infertile flowers only, but the wild forms from which the domestic varieties have been derived have only a single marginal row of showy infertile flowers surrounding a mass of inconspicuous fertile flowers. It has been due to their efforts to please men that bananas, pineapples, and oranges have got into the habit of neglecting to produce seeds. There are certain species of grapes that are seedless, also seedless sugar-cane, and a seedless apple has just been announced by horticulturists. The development of domesticated plants is only in its infancy, and it is probably impossible even for the most agile imagination to dream of the miracles the horticulturist is destined to work in the ages to come. There is every reason to believe that seedless varieties of all our common fruits will ultimately be produced, and that in size, flavour, nutrient constituents, and appearance, they will be developed into forms utterly different from existing varieties. Just within the last few years the U.S. Department of Agriculture has developed a cotton-plant immune to the bacterial diseases of the soil, which had completely driven the cotton-raising industry out of large districts of the South. The cultivation of many of the cereals has gone on so long, and has proceeded so far, that their origin is lost in antiquity.
Whether or not it is possible for new varieties and species to be evolved is a question, therefore, which does not need to depend for reply wholly upon theory. It is known to have taken place; and the process by which the different varieties of domestic animals and plants have been evolved—domestic selection—is not different in principle from the process of natural selection, the chief operation by which life in general, both plant and animal, is assumed to have been evolved.
10. There are other reasons for a belief in organic evolution, but the last one I shall mention is the fact that the theory of organic evolution harmonises with the known tendencies of the universe as a whole. The organic kingdoms of the earth—animals and plants—are as truly parts of the terrestrial globe as the inorganic kingdom is; and as such they share in, and are actuated by, the same great tendency or instinct as that which actuates the whole. Nine-tenths of the substance of all animals and plants is oxygen, hydrogen, carbon, and nitrogen—the very elements which make up the entire ocean and air, and enter largely into the composition of the continents. The human body, which has essentially the same chemical composition as the bodies of animals in general, is made up of four solids, five gases, and seven metals—in all, sixteen elements of the something like seventy which constitute the entire planet. ‘In the past, man appeared to be a creature foreign to the earth, and placed upon it as a transitory inhabitant by some incomprehensible power. The more perfect insight of the present day sees man as a being whose development has taken place in accordance with the same laws as those that have governed the development of the earth and its entire organisation—a being not put upon the earth accidentally by an arbitrary act, but produced in harmony with the earth’s nature, and belonging to it as do the flowers and the fruits to the tree which bears them.’ Animals are not outside of, nor distinct from, the universe, as one might suspect who has listened much to the recital of tradition so long accepted as science. They are more or less detached portions of the planet earth which move over its surfaces and through its fluids and multiply, but which in their phenomena obey the same laws of chemistry and physics as those in accordance with which the rest of the universe acts. Animals are moulds through which digressing matters from the soil, sea, and sky pass on rounds of eternal itineracy.
Now, the earth as a planet is in process of evolution. Not many things are more certain than this. The earth has come out of fire. It has grown to be what it is. Its mountains, valleys, plains, seas, shores, islands, lakes, rivers, and continents—these were not always here. They have been evolved. Not only the earth, but the entire family of spheres of which the earth is a member—the solar system—are all evolving. Mr. Spencer never did anything more profound than when he demonstrated in his ‘Law and Cause of Progress’ the universal migration of things from a condition of homogeneity toward a condition of greater and greater heterogeneity. The whole universe, or as much of it as can be examined by terrestrial instruments, has probably evolved out of the same primordial matters. The organic part of the earth has evolved, therefore, and is destined to continue to evolve, because it is a part of a whole whose habit or ambition it is to evolve.
The evidence is overwhelming. The theory of organic evolution is sustained by a mass of facts not less authoritative and convincing than that which supports the Copernican theory of the worlds. Evolution is, in fact, a doctrine so apparent that it only needs to be honestly and intelligently looked into to be accepted unreservedly. It is, indeed, more than a doctrine. It is a known fact. It is a necessary effect of the conditions known to exist among the animals and plants of the earth. If beings vary among themselves generation after generation, if only the fittest of each generation survive and if the survivors tend to transmit to their offspring the qualities of their superiority (and the animals and plants of the earth are known to do continually all of these things), then it follows with mathematical certainty that evolution is going on, and that it will continue to go on as long as these conditions continue. It is inevitable. It could not be otherwise. We would know that evolution were going on among organisms where these conditions existed, even though we had never observed it.
The boldest and most enthusiastic opponents of evolution have always been those with the least information about it. But the evidence is accumulating so rapidly, and is being drawn up in such unanswerable array, that, if it is not already the case, it will not be many years before it will be an intellectual reproach for anyone to discredit, or to be known to have discredited, this splendid and inspiring revelation.
1a. 1b. Darwin: Descent of Man, 2nd edit.; London, 1874.
2. Huxley: Man’s Place in Nature; New York, 1883.
3a. 3b. Thompson: Outlines of Zoology, 3rd edit.; Edinburgh, 1899.
4. Drummond: Ascent of Man; New York, 1894.
5. See table of geological ages, at the end of the chapter.
6. Haeckel: The Riddle of the Universe; New York, 1901.
7. Huxley: On the Origin of Species, lecture iv.
Table of Geological Ages
X. The Genealogy of Animals
Life originated in the sea, and for an immense period of time after it commenced it was confined to the place of its origin. The civilisations of the earth were for many millions of years exclusively aquatic. It has, indeed, been estimated that the time required by the life process in getting out of the water—that is, that the time consumed in elaborating the first species of land animals—was much longer than the time which has elapsed since then. I presume that during a large part of this early period it would have seemed to one living at that time extremely doubtful whether there would ever be on the earth any other kinds of life than the aquatic. And if those who to-day weave the fashionable fabrics of human philosophy, and who know nothing about anything outside the thin edge of the present, had been back there, they would no doubt have declared confidently, as they looked upon the naked continents and the uninhabited air and the sea teeming with its peculiar faunas, that life upon solids or in gases, life anywhere, in fact, except in the sea, where it had always existed, and to which alone it was adapted, was absolutely, and would be forever, impossible; and that feathered fishes and fishes with the power to run and skip, and especially ‘sharks’ competent to walk on one end and jabber with the other, were unthinkable nonsense. Life originated in the sea for the same reason that the first of the series of so-called ‘civilisations’ which have appeared in human history sprang from the alluvium of the Euphrates and the Nile, because the conditions for bringing life into existence were here the most favourable. The atmosphere was incompetent to perform such a task as the inventing of protoplasm and there was no land above the oceans.
The first forms of life were one-celled—simple, jelly-like dots of almost homogeneous plasm—the protozoa. These primitive organisms were the common grandparents of all beings. From them evolved, through infinite travail and suffering, all of the orders, families, species, and varieties of animals that to-day live on the earth, and all those that have in the past lived and passed away. By the multiplication and specialisation of cells, and the formation of cell aggregates, the sponges, celenterates, and flat worms were developed from the protozoa.1 The connecting links between the one-celled and the many-celled animals consist of a series of colonial forms of increasing size and complexity, some of which may be found in every roadside ditch and pool, while others are extinct. The development of these many-celled organisms (metazoa) from one-celled organisms was a perfectly natural process, a process which takes place in the initial evolutions of every embryo. There is no more mystery about it than there is about any other act of association. All association is simply a matter of ‘business.’ Many-celled organisms are colonies, or societies, of more or less closely co-operating one-celled organisms, and they have come into existence in obedience to the same laws of economy and advantage as have those more modern societies of metazoa known as nations, communities, and states, the organised bodies of men, ants, and millionaires.
The sponges are the lowest of the many-celled animals. They consist of irregular masses of loosely associated cells, hopelessly anchored to the sea-floor. They represent the social instinct in embryo. The cells are but slightly specialised, and each cell leads a more or less independent existence. The sponge stands at about that stage of social integration and intelligence represented by those stupendous porifera which cover continents and constitute the ‘social organisms’ of the civilised world. The nutritive system of sponges consists of countless pores opening from the surface into a common canal within, through which ever-waving cilia urge the alimental waters. In the celenterates the cells arrange themselves in the form of a cup with one large opening into and from the vase-like stomach. The unsegmented worms are flat and sac-like, with bilateral symmetry and the power to move about, but not tubular, as are the true worms. They are bloodless, like the celenterates and sponges.
From the flat worms developed the annelid worms, animals perforated by a food canal and possessing a body cavity filled with blood surrounding this canal. The body cavity is the space between the walls of the body and the alimentary canal, the cavity which in the higher animals contains the heart, liver, lungs, kidneys, etc. The worms and all animals above them have this cavity. The worms and all animals above them also have, as an inheritance from the flat worms, bodies with bilateral symmetry—that is, bodies with two halves similar. This peculiarity was probably acquired by the flat worms, and so fastened upon all subsequently evolved species, as a result of pure carelessness. It probably arose out of the habit of using continually, or over and over again, the same parts of the body as fore and aft. It has been facetiously said that if it had not been for this habit, so inadvertently acquired by these humble beings so long, long ago, we would not to-day be able to tell our right hand from our left. In the worm is found the beginning of that wonderful organ of co-ordination, the brain. The brain is a modification of the skin. It may weaken our regard for this imperial organ to know that it is, in its morphology, akin to nails and corns. But it will certainly add to our admiration for the infinite labours of evolution to remember that the magnificent thinking apparatus of modern philosophers was originally a small sensitive plate developed down in the sea a hundred million years ago on the dorsal wall of the mouths of primeval worms.
From the worms developed all of the highest four phyla of the animal kingdom—the echinoderms, the mollusks, the arthropods, and the chordate animals, the last of which were the progenitors of the illustrious vertebrates. The lowest of the mollusks are the snails, and from these humble tenants of our ponds and shores sprang the headless bivalves and the giant jawed cuttles. The mollusks were for a long time after their development the mailed monarchs of the sea, and shared with the worms the dominion of the primordial waters. But after the development of the more active arthropods, especially the crustaceans, the less agile worms and mollusks rapidly declined. Existing worms and mollusks are remnants of once powerful and populous races.
From the worms also developed the arthropods, the water-breathing crustaceans and the air-breathing spiders and insects. The crustaceans came early, away back in the gray of the Silurian period, just about the time North America was born. North America lay, a naked, V-shaped infant, in the regions of Labrador and Canada. The crustaceans rapidly superseded the mollusks as rulers of the sea, attaining, in extreme species, a length of four or five feet. The spiders and Insects came into existence toward the latter part of the Silurian period,2 probably contemporaneous, or nearly so, with the appearance of land vegetation. The spiders and insects were the aborigines of the land and air. They are the only races of living beings, except the original inhabitants of the sea, who ever invaded and settled an unoccupied world. The earliest land fossils so far found are the fossils of scorpions. But the existence of a sting among the structural possessions of these animals indicates that there were already others who contended with them for supremacy in the new world. The first insects were the masticating insects, insects such as cockroaches, crickets, grasshoppers, dragon-flies, and beetles. They are found abundantly in the Devonian and Carboniferous rocks. The licking insects (bees) and the pricking insects (flies and bugs) appeared first in the Mesozoic Era, and the sipping insects (butterflies) in the Cenozoic. The flower-loving insects (the bees and butterflies) came into the world at the same time as did the flowers. The wings of insects may be modifications of the gills used by insect young in respiration during their aquatic existence. They are, hence, very different in origin from the wings of birds, which are the modified fore-legs of reptiles.
The most important class of animals arising out of the worms, on account of their distinguished offspring, were the hypothetical cord animals. The only existing species allied to these animals is the amphioxus, a strange, unpromising-looking creature, half worm and half fish, found in the beach sands of many seas. It has white blood and a tubular heart. It is without either head or limbs, and looks very much like a long semitransparent leaf, tapering at both ends. But it has two unmistakable prophecies of the vertebrate anatomy: a cartilaginous rod, pointed at both ends, extending along the back, and above this, and parallel to it, a cord of nerve matter. These are the same positions occupied by the spinal column and spinal cord in all true vertebrates. That the amphioxus is a genuine relative of the ancestor of the vertebrates is also shown by the fact that these simple forms of column and cord possessed by amphioxus are precisely the forms assumed by the spinal column and spinal cord in the embryos of all vertebrates, including man.
From these quasi-vertebrates developed the fishes—first (after the scaleless, limbless lampreys) the sharks with spiny scales and cartilaginous skeleton, and after these the lung fishes and the bony fishes, with flat, horny scales and skeletons of bone. From the beginning of the Devonian age, when fishes first came into prominence, till the rise of the great reptiles in the Triassic time, fishes were the dominant life of the sea. In the fishes first appeared jaws, a sympathetic nervous system, red blood, backbone, and the characteristic two pairs of limbs of vertebrates.
The lung fishes (Dipneusta), a small order of strange salamander-like creatures which live ingeniously on the borderland between the liquid and the land, may be looked upon as physiological, if not morphological, links between the fishes and the frogs. They combine the characters of both fishes and frogs, and zoologists have been tempted to make a separate class of them, and place them between the two classes to which they are related. They are like fishes in having scales, fins, permanent gills, and a fish-like shape and skeleton. They resemble frogs in having lungs, nostrils, an incipiently three-chambered heart, a pulmonary circulation, and frog-like skin glands. There are three genera with several species. One genus (Neoceratodus) is found in two or three small rivers of Queensland, Australia; another (Protopterus) lives in the Gambia and other rivers of Africa; and the third (Lepidosiren) inhabits the swamps of the Amazon region. They all breathe ordinarily by means of gills, like true fishes, but have the habit of coming frequently to the surface and inhaling air. The air-bladder acts as an incipient lung in supplementing respiration by gills. They all live in regions where a dry season regularly converts the watercourses into beds of sand and mud. During the season of drought these strange animals build for themselves a cocoon or nest of mud and leaves. This cocoon is lined with mucus, and provided with a lid through which air is admitted. Here they lie in this capsule throughout the hot southern summer, from August to December, breathing air by means of their lungs and living upon the stored-up fat of their tails, until the return of the wet season, when they again live in the rivers and breathe water in true piscatorial fashion. These capsules have often been carried to Europe, and opened 3,000 miles from their place of construction without harming the life within.
Here, in these eccentric denizens of the southern world, we find the beginnings of a grand transformation—a transformation in both structure and function, a transformation made necessary by the transition from life in the water to life in the air, a transformation which reaches its maturity in the higher air-breathing vertebrates, where the simple air-sac of the fish becomes a pair of lobed and elaborately sacculated lungs, performing almost exclusively the function of respiration, and the gills change into parts of the ears and lower jaw.
The air-bladder of ordinary fishes, which is used chiefly as a hydrostatic organ to enable the fish to rise and fall in the water, is probably the degenerated lung of the lung fishes.
From the lung fishes or allied forms developed the amphibians, the well-known fish quadrupeds of our bogs and brooks. The amphibians are genuine connectives—living links between the life of the sea and the life of the land. In early life they are fishes, with gills and two-chambered hearts. In later life they are air-breathing quadrupeds, with legs and lungs and three-chambered hearts. Here is evolution, plenty of it, and of the most tangible character. And it takes place right before the eyes. The transformation from the fish to the frog is, however, no more wonderful than the embryonic transformations of other vertebrates. It is simply more apparent, because it can be seen. The lungs of amphibians and the lower reptiles are simple sacks opening by a very short passage into the mouth. Some amphibians, as the axolotl of Mexican lakes, ordinarily retain their gills through life, but may be induced to develop lungs and adapt themselves to terrestrial life by being kept out of the water. Others, as the newts, which ordinarily develop lungs, may be compelled to retain their gills through life by being forced to remain uninterruptedly in the water. The black salamander, inhabiting droughty regions of the Alps, brings forth its young bearing lungs, and only a pair at a time. But if the young are prematurely removed from the body of the mother and placed in the water, they develop gills in the ordinary way. These are remarkable instances of elasticity in the presence of a varying environment.
In the amphibians the characteristic five-toed or five-fingered foot, which normally forms the extremities of the limbs of all vertebrates except fishes, is first met with. It was this pentadactyl peculiarity of the frog, inherited by men and women through the reptiles and mammals, that gave rise to the decimal system of numbers and other unhandy facts in human life. The decimal system arose out of the practice of early men performing their calculations on their fingers. This method of calculating is still used by primitive peoples all over the world. The sum of the digits of the two hands came, in the course of arithmetical evolution, to be used as a unit, and from this simple beginning grew up the complicated system of tens found among civilised peoples. It has all come about as a result of amphibian initiative. Our very arithmetics have been predetermined by the anatomical peculiarities of the frog’s foot. If these unthinking foreordainers of human affairs had had four or six toes on each foot instead of five, man would no doubt have inherited them just as cheerfully as the number he did inherit, and the civilised world would in this case be to-day using in all of its mathematical activities a system of eights or twelves instead of a system of tens. A system of eights or twelves would be much superior in flexibility to the existing system; for eight is a cube, and its half and double are squares; and twelve can be divided by two, three, four, and six, while ten is divisible by two and five only.
How helpless human beings are—in fact, how helpless all beings are! How hopelessly dependent we are upon the past, and how impossible it is to be really original! What the future will be depends upon what the present is, for the future will grow out of, and inherit, the present. What the present is depends upon what the past was, for the present has grown out of, and inherited, the past. And what the past was depends upon a remoter past from which it evolved, and so on. There is no end anywhere of dependence, either forward or backward. Every fact, from an idea to a sun, is a contingent link in an eternal chain.
From the amphibians (probably from extinct forms, not from living) there arose the highest three classes of vertebrates—the true reptiles, the birds, and the mammals—all of whom have lungs and breathe air from the beginning to the end of their days. Gills, as organs of breathing, disappear forever, being changed, as has been said, into parts of the organs of mastication and hearing. In the reptiles first appear those organs which in the highest races overflow on occasions of tenderness and grief, the tear glands. These organs are, however, in our cold-blooded antecedents, organs of ocular lubrication rather than of weeping. There are but four small orders of existing reptiles—snakes, turtles, lizards, and crocodilians. These are the pygmean descendants of a mighty line, the last of a dynasty which during the greater part of the Mesozoic ages was represented by the most immense and powerful monsters that have ever lived upon the earth. Mesozoic civilisation was pre-eminently saurian. Reptiles were supreme everywhere—on sea and land and in the air. Their rulership of the world was not so bloody and masterful as man’s, but quite as remorseless. Imagine an aristocracy made up of pterosaurs (flying reptiles), with teeth, and measuring 20 feet between wing-tips; great plesiosaurs (serpent reptiles) and ichthyosaurs (fish reptiles), enormous bandits of the seas; and dinosaurs and atlantosaurs, giant land lizards, 30 feet high and from 50 to 100 feet in length. A government of demagogs is bad enough, as king-ridden mankind well know, but dragons would be worse, if possible. The atlantosaurs were the largest animals that have ever walked upon the earth. They were huge plant-eaters inhabiting North America. It has been surmised that one of these behemoths ‘may have consumed a whole tree for breakfast.’ It was the mighty saurians of the Mesozoic time who brought into everlasting subordination the piscatorial civilisation of the Devonian and carboniferous ages.
Toward the latter part of the Reptilian Age, and somewhere along about the time of the appearance of hard-wood forests, came the birds, those beautiful and emotional beings who, in spite of human destructiveness, continue to fill our groves and gardens with the miracles of beauty and song. The bird is a ‘glorified reptile.’ How the ‘slow, cold-blooded, scaly saurian ever became transformed into the quick, hot-blooded, feathered bird, the joy of creation,’ is a considerable mystery, yet we know no reason for believing that the transformation did not take place. Although in their external appearance and mode of life birds and reptiles differ so widely from each other, yet, in their internal structure and embryology, they are so much alike that one of the brightest anatomists that has ever lived (Huxley) united them both into a single class under the name Sauropsida. It might naturally be supposed that the birds are descendants of the flying reptiles, the pterosaurs. But this may not be true. The pterosaurs were structurally much further removed from the birds than were certain extinct terrestrial reptiles. The fact that birds and pterosaurs both had wings has really nothing to do with the case. For the wings of reptiles, we almost know, were not homologous with the wings of birds. The bird’s wing is a feathered fore-leg; the wing of the reptile was an expanded skin stretching from the much-elongated last finger backwards to the hind-leg and tail. Wings, it may be remarked in passing, have had at least four different and distinct beginnings in the animal kingdom, represented by the bats, the birds, the reptiles, and the insects. This does not include the parachutes of the so-called flying squirrels, lemurs, lizards, phalangers, and fishes.
The first birds had teeth and vertebrated tails. The archeopteryx, which is the earliest toothed bird whose remains have yet been found, was about the size of a crow. It had thirty-two teeth and twenty caudal vertebrae. Two specimens of it have been found in the Jurassic slates of Bavaria. One of these fossils is in the British Museum, and the other in the Museum of Berlin. Other toothed birds have been found fossil by Dr. Mudge in the cretaceous chalk of North America. These last had short, fan tails like existing birds.
From the toothed birds developed the beaked birds—the keel-breasted birds (the group to which most existing birds belong) and the birds with unkeeled breasts, i.e., the ostrich-like birds. The ostrich-like birds are runners. They have rudimentary wings, and the keel of the breast-bone, which in the keel-breasted birds acts as a stay for the attachment of the wing muscles, is lacking. The ostrich-like birds are probably degenerate flyers, the flying apparatus having become obsolete through disuse. The feathers of birds are generally supposed to be the modified scales of reptiles.
The most brilliant offspring of the reptiles were the mammals, animals capable of a wider distribution over the face of the earth than the cold-blooded reptiles, on account of their hair and their warm blood. Cold-blooded animals of great size are able to inhabit but a small zone of the existing earth’s surface—the torrid belt. They cannot house themselves during the seasons of cold, as men can; nor escape to the tropics on the wings of the wind, as do the birds; nor bury themselves in subaqueous mud, as do the frogs, snakes, and crustaceans. During the Mesozoic period, when cold-blooded reptiles of gigantic size flourished over a wide area of the earth’s surface, the planet was far warmer than now. Animals, therefore, like the mammals (or birds), capable of maintaining a fixed temperature regardless of the thermal fluctuations of the surrounding media, are the only animals of large size and power capable of uninterrupted existence over the greater part of the surface of the existing earth. The pre-eminent life of the Cenozoic time was mammalian. But the decline and fall of the saurian power was not wholly due to the rise of the more dynamic mammals. It was in part due, no doubt, to adverse conditions of climate, and also to the fact that mammals and birds guard their eggs, and saurians do not.
The lowest of the mammals are the monotremes, animals which blend in a marvellous manner the characteristics of birds, reptiles, and mammals. Only two families of these old-fashioned creatures are left, the echidna and the duck-bill (ornithorhynchus), both of them found on or near that museum of biological antiquities, Australia. They are covered with hair and suckle their young like other mammals, but they have only the rudiments of milk glands, and they lay eggs with large yolks from a cloaca, like the reptiles and birds. The duck-bill hides its eggs in the ground, but the echidna hatches its eggs in a small external brooding pouch, periodically developed for this purpose. The young of the monotremes feed on the oily perspiration which exudes from the body of the mother. The monotremes first appear in the fossiliferous rocks of the Triassic Age.
From the monotreme-like mammals developed the marsupial mammals, animals possessing a purse-like pouch on the after part of the abdomen, in which they carry their young. The young of marsupials are born in an extremely immature state, and are carried in this pouch in order to complete their development. The young of the kangaroo, an animal as large as a man, are only about an inch in length when they are born. They are carried for nine months after their birth in the marsupium of the mother, firmly attached to the maternal nipple. The marsupials came into existence during the Jurassic Age, and during the next age, the Cretaceous, they arose to considerable power. During this latter age they were found on every continent. But they have been almost exterminated by their more powerful descendants.
From the marsupials developed the placental mammals, animals so called because their young are developed within the parental body in association with a peculiar nourishing organ called the placenta. From the herbivorous marsupials developed the almost toothless edentates, the rodents, or gnawing animals, the sirenians, the cetaceans, and the hoofed animals, or ungulates. The sirenians are fish-like animals with two flippers, and are often called sea-cows. They resemble whales in many respects, and are sometimes classed with them. They are plant-eaters exclusively, and are found grazing along the bottoms of tropical estuaries and rivers. They have tiny eyes, teeth fitted for grinding (not spike-like as in the whales), and a strong affection for their young, the mother, when pursued, often carrying her little one under her flippers. An immense sirenian, known as Steller’s manatee, was discovered on the Behring Islands, along the Kamschatka coast, in 1741. Twenty-seven years afterwards not one of them was left, all having been murdered by the Russian sailors. The sirenians are probably degenerate forms of land quadrupeds, having lost their hind-limbs and developed the fish-like shape in adapting themselves to aquatic conditions. They appear first in the Eocene Age.
Among the most interesting derivatives of the herbivorous marsupials, because the most aberrant, are the whales. They are true mammals—have warm blood, breathe the air with lungs, and suckle their young like other mammals. But, like the sirenians, they live in the surface of the waters, and have flippers and a fish-like tail and form. They differ from the sirenians, however, in being carnivorous, in having inguinal instead of pectoral milk glands, and in being structurally less like quadrupeds. They probably degenerated from land quadrupeds during the Jurassic period, and, owing to their longer residence in the waters, have become further removed from the quadrupedal type than the sirenians. Whales have two limbs, the hind-limbs having disappeared as a result of the pre-eminent development of the tail. The tails of whales and sirenians are flattened horizontally, not vertically, as in fishes.
Out of generalised forms of hoofed animals now extinct developed the odd-toed and even-toed races of existing ungulates. The original ungulates had five hoofs on each foot, and were highly generalised in their structure. From these original five-toed forms have arisen the variously hoofed and variously structured tribes of existing ungulates: the five-toed elephant, the four-toed tapir and hippopotamus, the three-toed rhinoceros, the two-toed camel, sheep, swine, deer, antelope, giraffe, and ox, and the one-toed horse and zebra.
The carnivorous branch of the placental animals came from the carnivorous branch of the marsupials. From early forms of carnivorous placentals developed the ape-like lemurs and those generalised forms of rapacious animals from which arose the insect-eaters, the bats, and the true carnivora. The seals represent a by-development from the main line of the carnivora, a third defection, and a comparatively recent one, from land faunas. Seals live at the meeting of the land and the waters rather than in or on the waters, as do the cetaceans and sirenians. They have retained their fur and their four limbs, but have almost lost their power of land locomotion by the conversion of their feet into flippers. The two front-limbs of seals are the only ones used as ordinary limbs are used. The hind-limbs in most seals stretch permanently out behind, the webbed digits spreading out fan-shaped on either side of the stumpy tail, and constituting a rowing apparatus functionally homologous with the tail of fishes and whales. According to Jordan, the fur seals and the hair seals are descended from different families of land carnivora, the former probably from the bears, and the latter from the cats.
The lemurs are of especial interest to human beings, because in them are found the first startling approximation in looks and structure to the ‘human form divine.’ The lemurs are monkey-like creatures living in trees, but differ enough from true monkeys to be often placed in an order by themselves. Their milk glands are abdominal instead of pectoral, as in the monkeys, and the second digit of each hand and foot ends in a claw. The most of them live in Madagascar. They are generally nocturnal in their habits, although some species are diurnal. They appear first in the Eocene rocks, and Haeckel thinks they may have developed from opossum-like marsupials in the late Cretaceous or early Eocene Age.
From lemurs or from some other similar sort of semi-apes developed the true apes—the flat-nosed (platyrhine) apes of the New World and the narrow-nosed (catarhine) apes of the Old World. There is considerable difference between the New World apes and those of the Old World. The differences between the two classes is, in fact, so striking that they are thought by some to have developed independently of each other from distinct species of semi-apes. The apes of the New World have flat noses, and the nostrils are far apart and open in front of the nose, never below. The Old World apes have narrow noses, the nostrils being close together and opening downwards as in man. The tail of (nearly) all New World apes is prehensile, being used regularly as a fifth limb, while among Old World apes the tail is never so used. The Old World apes all have the same number and kinds of teeth as man has, while the New World apes (excepting the Brazilian marmosets) have an additional premolar in each half-jaw, making thirty-six in all. The catarhine apes are, therefore, structurally much nearer to man than their platyrhine cousins. All tailed apes probably sprang originally from a single stirp of semi-apes, and spread over the earth at a time when the eastern and western land masses of the southern hemisphere were connected with each other. The earliest remains of apes appear in the Miocene Age.
From the Old World tailed apes were developed the tailless, man-like, or anthropoid apes—the gorillas and chimpanzees of Africa, and the orangs and gibbons of Asia and the East Indies. The anthropoids arose from the tailed apes by the loss of the tail, the thinning of the hairy covering, the enlargement of the fore-brain, and by structural adaptations to a more nearly vertical position. No remains of anthropoids are found earlier than the Pliocene Age.
The man-like apes are the nearest living relatives of the human races. It is not probable that man has been derived directly from any of the existing races of man-like apes. For no one of them in all particulars of its structure stands closer to him than the rest. The orang approaches closest to man in the formation of the brain, the chimpanzee in the shape of the spine and in certain characteristics of the skull, the gorilla in the development of the feet and in size, and the gibbon in the formation of the throat and teeth. The earliest human races probably sprang from man-like races of apes now extinct, who lived in southern Asia or in Africa during the Pliocene Age (possibly as early as the Miocene), and who combined in their structures the various man-like characters possessed by existing anthropoids.
The earliest races of men were speechless—the ape-like ‘Alali’—beings, living wholly upon the ground and walking upon their hind-limbs, but without more than the mere rudiments of language. The vertical position led to a much greater development of the posterior parts, especially of the muscles of the back and the calves of the leg. The great toe, which in the ape is opposable, lost its opposability, or all except traces of it, after the abandonment of arboreal life. It must have been a sight fit to stir the soul of the most leathern, these children of the night, with low brows, stooping gait, and ape-like faces, armed with rude clubs, clothed in natural hair, and wandering about in droves without law, fire, or understanding, hiding in thickets and in the holes of the earth, feeding on roots and fruits, and contending doubtfully with the species around them for food and existence.
From the ‘Alali’—the speechless ape-men—we may imagine the true men to have evolved—talking men, men with erect posture and mature brain and larynx, the woolly-haired ulotrichi and the straight-haired lissotrichi. There are four existing species of woolly-haired men: the Papuans of New Guinea and Melanesia, and the Hottentots, Caffres, and Negroes of southern, equatorial, and north central Africa respectively. They all have long heads, slanting teeth, very dark skin, and black, bushy hair, each individual hair in cross-section being flat or oval in shape. In the straight-haired races the skin is much fairer than in the woolly-haired races, being seldom darker than brown, and each individual hair in cross-section is round like the cross-section of a cylinder. The principal species of straight-haired men are the sea-roving Malays of the East Indies and the Pacific, the round-faced Mongols of eastern and northern Asia, the aboriginal Americans of the western hemisphere, and the incomparable Aryans, including the ancient Greeks and Romans and the modern peoples of India, Persia, and Europe.
Man is to-day the pre-eminent animal of the planet. The successive ascendancies of the Worm, the Mollusk, the Crustacean, the Fish, the Reptile, and the Mammal, are followed triumphantly by the ascendancy of the Children of the Ape.
A large part of the life of the earth has remained steadfastly where it was cradled, beneath the waves. But more restless portions have left the sea and crept forth upon the land, or swarmed into the air. One migration, the most numerous, is represented by the insects. Another, the most enterprising, was the amphibian. After ages of evolution the amphibian branch divided. One branch acquired wings and sailed off into the air. The other divided and subdivided. One of these subdivisions entered the forests, climbed and clambered among the trees, acquired perpendicularity and hands, descended and walked upon the soil, invented agriculture, built cities and states, and imagined itself immortal. Human society is but the van—the hither terminus—of an evolutional process which had its beginning away back in the protoplasm of primeval waters. There is not a form that creeps beneath the sea but can claim kinship with the eagle. The philosopher is the remote posterity of the meek and lowly amoeba.
1. See ‘Genealogy of Animals,’ at the end of the chapter. 2. See table of geological ages, at the end of the previous chapter.
Geneaology of Animals
XI. Conclusion
The resemblances, homologies, and metamorphoses existing everywhere among animal forms are, therefore, evidence of the most logical consanguinities. It is all so perfectly plain. The structures of organic beings have come about as a result of the action and reaction of environment upon these structures. Every being—and not only every being, but every species, the whole organic world—has come to be what it is as a result of the incessant hammerings of its surroundings, the hammerings not only of the present, but of the long-stretching past. By surroundings is meant, of course, the rest of the universe. Those animals belonging to the same stock resemble each other because they have been subjected to the same experiences, the same series of selections. They have lain on the same great anvil, and felt the down-comings of the same sledge. The similarities among animal forms in general indicate relationships, just as the similarities among the races of men indicate racial consanguinities. All men belong to the human species because they are all fundamentally alike. But there are differences in the character of the hair, in the colour of the skin, in the conformation of the skull, and in the structure of the language, among the different varieties of the species, indicating striking variety in relationship and origin. An eminent biologist has said that if Negroes and Caucasians were snails they would be classed as entirely distinct species of animals. Whether, as is thought by some, the woolly-haired races are the descendants of the African anthropoids, and the straight-haired varieties are the posterity of the orangs and gibbons, we may never know positively. But we do know that these two great branches of mankind must have different genealogies, extending to a remote antiquity, and that the varieties belonging to each great group sustain to each other the relations of a common kinship. Englishmen look like each other, act like each other, and speak the same language. So do Frenchmen and Swedes and Chinese. Every people is peculiar. This is not the result of accident or agreement, but the result of law. Mongolians do not all have short heads, yellow faces, slanting eyes, and prominent malars because they have agreed to have them, but as a result of a common pedigree. Similarity of structure implies commonalty of origin, and commonalty of origin means consanguinity.
And this is true whether you contemplate the featural resemblances of brothers and sisters of the same human parent, or those more fundamental characteristics which distinguish species, orders, and sub-kingdoms. All animals are composed of protoplasm, which is a compound of clay, because all animals are descended from the same first parents, protoplasmic organisms evolved out of the elemental ooze. All vertebrates have nerve-filled backbones with two pairs of ventrally branching limbs, because the original ancestors of the vertebrates had nerve-filled backbones with two pairs of ventrally branching limbs. Insects individually evolve from worms because worms are their phylogenetic fathers and mothers. Man has hands and a vertical spine, and walks on his hind-limbs, not because he was fashioned in the image of a god, but because his ancestors lived among the trees. The habit of using the posterior limbs for locomotion, and the anterior for prehension, and the resulting perpendicular, are peculiarities developed by our simian ancestors wholly on account of the incentives to such structure and posture afforded by aboreal life. These peculiarities would not likely have been acquired by quadrupeds living upon and taking their food from a perfectly level and treeless plain. If there had been no forests on the earth, therefore, there would have been no incentive to the perpendicular, and the ‘human form divine’ would have been inconceivably different from what it is to-day. And if fishes had had three serial pairs of limbs instead of two, and their posterity had inherited them, as they certainly would have had the foresight to do if they had had the opportunity, the highest animals on the earth to-day, the ‘paragons of creation,’ would probably be two-handed quadrupeds (centaurs) instead of two-handed bipeds. And much more efficient and ideal individuals they would have been in every way than the rickety, peculiar, unsubstantial plantigrades who, by their talent to talk, have become the masters of the universe, and, by their imaginations, ‘divine.’
Kinship is universal. The orders, families, species, and races of the animal kingdom are the branches of a gigantic arbour. Every individual is a cell, every species is a tissue, and every order is an organ in the great surging, suffering, palpitating process. Man is simply one portion of the immense enterprise. He is as veritably an animal as the insect that drinks its little fill from his veins, the ox he goads, or the wild-fox that flees before his bellowings. Man is not a god, nor in any imminent danger of becoming one. He is not a celestial star-babe dropped down among mundane matters for a time and endowed with wing possibilities and the anatomy of a deity. He is a mammal of the order of primates, not so lamentable when we think of the hyena and the serpent, but an exceedingly discouraging vertebrate compared with what he ought to be. He has come up from the worm and the quadruped. His relatives dwell on the prairies and in the fields, forests, and waves. He shares the honours and partakes of the infirmities of all his kindred. He walks on his hind-limbs like the ape; he eats herbage and suckles his young like the ox; he slays his fellows and fills himself with their blood like the crocodile and the tiger; he grows old and dies, and turns to banqueting worms, like all that come from the elemental loins. He cannot exceed the winds like the hound, nor dissolve his image in the mid-day blue like the eagle. He has not the courage of the gorilla, the magnificence of the steed, nor the plaintive innocence of the ring-dove. Poor, pitiful, glory-hunting hideful! Born into a universe which he creates when he comes into it, and clinging, like all his kindred, to a clod that knows him not, he drives on in the preposterous storm of the atoms, as helpless to fashion his fate as the sleet that pelts him, and lost absolutely in the somnambulism of his own being.