The proofs may, roughly speaking, be grouped under three heads—the extraordinary affinity of bodily structure, the revelations of embryology, and the tale told by the useless rudimentary organs. We will commence with
THE EXTRAORDINARY AFFINITY OF BODILY STRUCTURE.
“It is notorious that man is constructed on the same general type or model with other mammals. All the bones in his skeleton can be compared with corresponding bones in a monkey, bat, or seal. So it is with his muscles, nerves, blood-vessels, and viscera. The brain, the most important of all the organs, follows the same law, as shown by Huxley and other anatomists.”[24] Man’s nearest animal relations are the tailless anthropoid or man-like apes—namely, the gorilla, the chimpanzee, the orang, and the gibbon. “Now that all the details of the human organisation have been studied, and the anatomical structures of man and large monkeys without tails have been compared, bone with bone, and muscle with muscle, a truly astonishing analogy between these organisms is made manifest—an analogy apparent in every detail.”[25] The following are some of the points more particularly calling for notice:—
Dentition.—In the natural history of mammals the teeth play an important part as a means of determining differences and relationships. “Everyone knows the milk teeth and the permanent teeth of man. The anthropoid apes bear in this respect an astonishing likeness to man. The number (thirty-two in the adult), the form and general arrangement of the crown, are identical in man and anthropoid apes. The differences are to be found only in minor details.”[26] “But the fact must not be lost sight of that all these differences are less pronounced than those which exist between the dentition of anthropoid apes and that of all other monkeys.”[27]
The Foot.—Anti-evolutionists have laid great stress on the difference between the foot of a man and that of an anthropoid ape. But it is clearly shown by Huxley that in all essential respects the hinder limb of the gorilla terminates in as true a foot as that of man,[28] and “that, be the differences between the hand and foot of man and those of the gorilla what they may, the differences between those of the gorilla and those of the lower apes are much greater.”[29]
The Sacrum.—“In monkeys, as a whole, the sacrum is composed of three, or rarely four, vertebræ, while in anthropoid apes it contains five—that is to say, just as many as in man.”[30]
The Skull.—Here the differences are more marked; but again we must remind ourselves that, as regards the osteology, Professor Huxley tells us that “for the skull, no less than for the skeleton in general, the proposition holds good that the differences between man and the gorilla are of smaller value than those between the gorilla and some other apes.”[31]
The Brain.—Several distinguished zoologists at one time insisted on the absence in all monkeys of certain parts of the brain peculiarly characteristic of man, but now it is unanimously accepted that the parts of the brain in question are “precisely those structures which are the most marked cerebral characters common to man with the apes. They are among the most distinctly simian peculiarities which the human organism exhibits.”[32]
The difference between the brain of the orang and that of man is a mere difference of degree, and not of kind; and most students of comparative psychology now admit that the intellectual faculties of animals differ from those in man in degree only, not in their essence. Replying to his opponents, Professor Huxley compares the brain of man and that of ape with two watches, one of which will, and the other will not, keep accurate time. He exclaims: “A hair in the balance-wheel, a little rust on a pinion, a bend in a tooth of the escapement, a something so slight that only the practised eye of the watchmaker can discover it, may be the source of all the difference.”[33]