CHAPTER XXVII
THE SKELETON OF APES AND OF MAN

THE upright carriage of man has entailed remarkable changes in the proportions and shapes of parts of his body, as well as leading to special skill in the use of his hands. The vertebral column of man has not the single curve of a bow, as it has (practically) in the higher apes, but as he stands it curves (slightly, it is true, but definitely) forward at the neck, backward at the chest, forward at the loins, and backward again at the hips, an arrangement which appears to protect to some extent the brain from the transmission to it along the vertebral column of the shock caused by the sudden impact of the feet on the ground in jumping. The head is balanced on the top of this slightly elastic curvilinear column, the joint by which the skull rests on the vertebræ being placed beneath the brain-box and near the middle region of the skull. The ligaments which hold the skull in place are smaller than those in monkeys. In the higher apes the skull is not so balanced, but is held by very strong ligaments and muscles braced, as it were, on to the end of the forwardly sloping, nearly straight, backbone, from which it projects, and has further to be held in position by a great ligament attached to it and the dorsal processes of the neck vertebræ. As an adaptation to the upright carriage of man, the shape of his pelvic bones is that of a basin upon which his coiled mass of intestines can rest when he stands erect. The pelvic bones of the higher apes are flat, nearly parallel with the broad plane of the back, and give no such support; the viscera have to rest against the wall of the abdomen in the stooping position assumed by these animals in walking. The abdominal walls are consequently strong and thick, and the abdomen protrudes, as does that of a very young child. One result of man's upright carriage, showing that it is a recent acquirement and one to which he is not completely adapted, is the frequent occurrence in him of "hernia," or protrusion of the intestine through certain spaces in the deep fibrous wall of the abdomen. There would be no excessive pressure upon these spaces (near the groin), and therefore little danger of hernia, were it not for man's newly-acquired habit of erect gait. He is still incompletely adapted to the upright pose.

The arms of man are relatively shorter and his legs much longer than in the man-like apes. The Neandermen were more ape-like in these proportions than are modern races of man, and show also an "ape-like" curvature of the thigh bone which in man is straight. Whilst the arm and hand of man has gradually become a more delicate thing than that of the apes, and capable of much greater variety and efficiency in the movements of its parts, this condition has come about by alteration in proportions and to some extent shape, and not by any great change in construction. Only two muscles exist in connexion with man's hand not found in that of the higher apes. They are small slips adding to the efficiency of the fingers and thumb, whilst in the foot there is in man a small muscle connected with its outer border—"the peroneus tertius"—which helps to keep the sole of the foot turned downwards, and is not present in the apes. The general shape and proportionate size of the muscles of the leg in man give it a very different appearance from that of the ape; but there are no muscles or bones present which are not found in the apes. The beautiful outline and form of the human leg and buttocks are directly the result of the increased size of certain muscles used in maintaining the upright position, and in the peculiarly human swing of the leg in walking and running. Their beauty, like that of the other specially human features which we consider beautiful, depends upon the fact that their development, in due proportion, is a necessary condition of efficiency, activity, and strength in movements and attitudes which have gradually been acquired by man, and distinguish him from the apes. Our admiration for them is a sort of self-love, a worship of an ideal of efficiency and balance which is specifically "human," and is more or less fully realized in every individual. Probably sexual selection has had a large share in thus moulding the human form. The apes do not present the development of the gluteal region characteristic of man, and the muscles of both the arms and legs in them are, though very powerful, less fleshy and more "stringy" than those of man. There is, indeed, a difference of "quality" in the muscles of apes and men, especially civilized men, which needs investigation by the microscopist and experimental physiologist.

Though we necessarily compare man with the highest existing apes, we must not suppose that the man-like ape from which the earliest ape-like men developed was in fact a gorilla or a chimpanzee. The survival of the gorilla and chimpanzee at this day necessarily implies that they were not the actual ancestral forms which became modified and superseded in the course of man's development. Very probably the ape (the creature more ape-like than man-like, of which more anon) from which man took his direct descent had already developed a plantigrade foot—that is a foot of which the sole is placed on the ground for support, as it is in gibbons, baboons, and bears, but not in most apes, nor in cats, dogs, sheep, and horses! And probably the hands of that ancestral ape were already used more dexterously in consequence, and the dog teeth were less needed either in fighting or in breaking up food and so had become smaller.

This reflection brings us to the differences between the teeth of a man and those of apes. The face of apes is drawn forward so as to approach in form the "muzzle" of a dog. It is far less muzzle-like in the more man-like apes than in the dog-faced baboons, and in the least civilized living races of man is much less prominent—what is called "prognathous"—than in the highest existing apes. In civilized living races of man it is markedly reduced, so that in the habitual carriage of the head, with the eyes looking forward over a horizontal plane at right angles to the vertical or upright body, the front border of the jaws, in which the chisel-like incisor teeth are set, usually projects but very little beyond the brow or forehead. In Greek sculpture and other examples regarded by us as types of "beauty," the jaws do not project at all. Such a face is called "orthognathous." This modification of the shape of the face is due to the progressive dwindling in the size of the front part of the jaw and its teeth in the series dog, ape, less-civilized man, highly-civilized man, and is accompanied by an increase in the size of the front part of the brain. The number of the teeth and their arrangement in groups are identical in man and the apes. The most important difference is in the size of the front teeth, and especially in the size of the "corner" teeth (one on each side above and below), also called eye-teeth, dog-teeth, or "canines." In the highest apes, as in all monkeys, the canine teeth are very large, and even tusk-like in the males, projecting above the horizonal line formed by the crowns of the other teeth. This projecting of the canine teeth results in their not meeting one another point to point when the jaws are closed, but necessitates one, the lower, shutting in front of the other, and a space is left in the row of teeth, both in the upper and the lower jaw, for this interlocking of the great canines. It is called a "diastema." Man stands in strong contrast to the apes in this respect. His canines do not project beyond the level of the neighbouring teeth, and there is no "diastema" or gap in either the upper or lower row of his teeth.[9] There is no trace of such a gap nor any excess of size of the canines in any living race of men, and what is more remarkable, the jaws of very ancient prehistoric men which have been found in the Middle Pleistocene—the Neander or Moustierian men as well as the more ancient jaw from Heidelberg (see p. 286)—do not show any difference in this respect from the most advanced European race. On the other hand, it is one of the most remarkable features presented by the recently discovered "Piltdown" lower jaw that it had a larger canine tooth than that of any recent or fossil man, and consequently a gap or "diastema" in the row of teeth (see Chap. XXX). This difference between men and apes is all the more marked since the grinders or cheek teeth (called also molars) of man and the higher apes agree very closely, each to each in order of their position, in the pattern formed by the irregular surface of the crown. There are some slight differences in relative size and in the order of their "cutting" or growth, but these are trivial. The jaws of man show their derivation by gradual dwindling from the larger projecting jaws seen in apes and monkeys, in the close setting (that is to say, "crowding") of the teeth, and also in the dwindling and late "cutting" of the last tooth, in each jaw above and below, which we call the wisdom tooth. The "wisdom teeth" are in the higher races of men on their way to total disappearance. In lower races of men they are larger than in the higher, and in the man-like apes are of full size, and there is plenty of room in the jaw for them.

[9] See Plates VII. and VIII., p. 166, in "Science from an Easy Chair," Second Series, for careful drawings of the complete series of teeth in both the upper and lower jaw of Man and of an Ape.

In the highest apes as well as the lower, the bony lower jaw slopes gradually backwards and downwards from the palisade of front chisel-like teeth or incisors ([see Fig. 23 C, p. 277]). There is no bony projection below the front teeth—in fact, no bony "chin." But in all modern races of men the front part of the semicircle arch of teeth has shrunk or "withdrawn" considerably or more than has the bony jaw in which the teeth are set. Consequently the bone projects in front of the front teeth as the bony chin ([see Fig. 23 A, p. 277,] and also "Science from an Easy Chair," 1910, pp. 404, 405). This is characteristic of modern races of man and occurs in no other animal. The very remarkable fact has recently been established that in the ancient species of man from the Middle and Lower Pleistocene—the Neander man and the Heidelberg man (Homo Neanderthalensis)—this extra or excessive shrinking of the dental arch (the half-circle formed by the complete row of teeth) had not taken place. Though the teeth are placed closely side by side and have the same shape as in modern man, they are a little bigger and form a larger and longer arch—more like a horse-shoe than a semicircle, and have not shrunk back so as to leave a projecting bony chin. The bony jaw recedes in these early races of men from the line of the front teeth as it does in the apes. They have no chin ([see Fig. 25, p. 286]).

Since we are all accustomed to regard a well-marked chin as a necessary feature of a beautiful human face, and to deplore or disapprove the receding or evanescent chin, it is not improbable that sexual selection has favoured the recession of the dental arch with the retention of the original bulk of the lower front margin of the jaw and chin, though why the chin should be thus appreciated is a matter of speculation. It is remarkable that in many of the monkeys the hair grows forward as a projecting beard on the front of the jaw, so as to resemble a chin although no chin is there. It is also the fact that some uncivilized races of men trim the beard and train it in a forward growth so as to suggest the possession of a very prominent chin, when in reality their solid chins of flesh and bone are not especially large.