MAN'S ZOOLOGICAL POSITION Zoologists classify animals into families, sub-families, genera and species, according to their degrees of structural likeness; they presume, although fully aware that parallel evolution can and does take place, that two animals, such as the gorilla and chimpanzee, which are so similar in the structural details of their bodies, owe that similarity to their descent from a common ancestry. Darwin urged rightly that in settling the zoological relationship of one group of animals to another, more weight must be attached to the points wherein they agree than to those in which they differ.
Huxley's Views.—In the masterly analysis of man's structural relationships given by Huxley in Man's Place in Nature (1863), more stress was laid on the anatomical differences which separate man from the gorilla than on the points wherein they agree. Hux ley held that differences which separated man from the gorilla were like in kind and similar in degree to those which separated the gorilla from any form of catarhine or platyrhine monkey a critic might choose for comparison. He held that if evolution could produce the structural gap which separates a monkey from the gorilla it could also bring about the abyss which divides the gorilla from man. Huxley's conclusions are still valid ; indeed, the modern anatomist is convinced that the structural hiatus which lies between a baboon or any other form of monkey and the gorilla is much wider than that which lies between the gorilla or chim panzee and man. When tested by modern methods, the blood of
the chimpanzee shows a much closer affinity in its reactions to that of man than to that of any Old World monkey; the blood of monkeys of the New World, when submitted to the same tests, reveals a still more distant affinity (Prof. G. H. Nuttall, Blood Immunity and Blood Relationship, 1904). Huxley included in one family the great anthropoids (gorilla, chimpanzee and orang), the small anthropoids (siamang, gibbon), and the various genera of monkeys of the Old World; if we are to be guided by anatomical considerations we must give to each of these groups the rank of a family. The same rank—that of a primate family—must be given to the section which embraces all the various races and types of mankind, living and extinct. The various genera of New World monkeys make up a fifth family of primates.
The Primate Families.—Thus in that part of the living animal kingdom to which man belongs, there are five families—the human family, that of the great anthropoids, that of the small anthro poids, the family of catarhine or Old World monkeys and the family of platyrhine or New World monkeys. These families are separated by structural gaps of about equal magnitude. From the platyrhine monkeys upwards, these families form an ascending series in the sense that each succeeding family marks a further departure from the ancestral tarsioid type, the point of highest differentiation being reached in the human family.