Evidence of Mans Descent

EVIDENCE OF MAN'S DESCENT Anatomical.—The members of these five families of pri mates have a common structural substratum—an inheritance from the ancestral stock from which they have all descended. Each family in the course of evolution has come by anatomical features which are peculiar to itself. A full analysis of the structural de tails of man's body shows that about 3o% of them are peculiar to himself. The corresponding characters of the gorilla number 16%; the gibbon has about the same proportion of features peculiar to its own family (Keith, Rivista di Antropologia, vol. xx., p. i, 1916). As examples of man's peculiar characters we may cite his nude skin, his projecting nose with well marked wings, the size of his brain, the strength of his thigh, the form of his leg, the shape of his foot.

Common Characters.

Further analysis reveals in man's body a series of characters which he shares with only two other living animals—namely, the gorilla and chimpanzee. These amount to nearly 9% of the total points selected for comparison, but if we include in this group features which man shares with the gorilla alone or with the chimpanzee alone, then man has in his body about 26% of characters which he shares with gorilla and chim panzee or with gorilla alone or chimpanzee alone. Such charac ters, we presume, are derived from a common ancestor which gave birth to man and to the great anthropoids of Africa. As examples of characters common to the three we may cite the air chambers which branch off from the nasal cavity. These have the same arrangement and are of the same number in man, gorilla and chimpanzee. Another example is to be found in the small bones of the wrist. Of the higher primates, only in these three has the os centrale disappeared as a separate unit from the carpus; yet in a foetal stage this bone is present in all three; and as a separate element in adults of all the other higher primates.

Descending still lower in the strata of human anatomy we en counter a group of characters which man shares with the three great anthropoids. We may speak of man and these three as the giant primates, for compared with the earlier types they are giants, or we may apply to this group Haeckel's convenient name —Lipotyla. Man shares with the other giant primates of

similarities of structural detail; to this we may add 5% which he shares with the orang and with the orang only, characters which the chimpanzee and gorilla have apparently lost or perhaps never possessed. Going still lower in our analysis, we find over 8% of characters which are common to the gibbon as well as to the great anthropoids. With the gibbon, man shares 8% of struc tural features which are not to be seen in the bodies of the great anthropoids. In this case, again, we have to suppose that man and the gibbon came by those characters long after they separated from a common ancestor, or that the great anthropoids have lost them in the course of evolution while man and the gibbon have retained them.

Lower in the scale of our analysis we come upon features in man's body which he has apparently retained from a catarhine ancestry; at least, to find their counterparts we have to go to the bodies of Old World monkeys. In man's body there are 5% of such catarhine features; in the gorilla's body such features are three times as numerous. It is remarkable that platyrhine char acters, features to be seen in the bodies of the New World mon keys, should be as numerous as catarhine in man's body.

There is a small residue of anatomical details in human anat omy attributable to a still more distant past, a heritage from a tarsioid or lemuroid ancestry. From the details revealed by ana tomical analysis it is plain that evolution has not proceeded in an orderly or simple manner in shaping the bodies of the higher primates; characters are curiously scattered. Yet to explain the distribution of characters in the various families we must suppose that man's ancestry is linked closely to that of the African anthropoids—the gorilla and chimpanzee. In some instances we obtain help in explaining the distribution of characters by calling in the aid of collateral or paiallel evolution ; in other cases Men del's discoveries in heredity assist us; further, we see that the body of man and of ape is a great mosaic work of structural ele ments and that progressive changes may occur in one set of units while retrograde changes affect another set.