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.