Modern Views.—In 1892 Prof. E. Dubois discovered in the island of Java the fossil remains of a being which answered very well to this hypothetical stage, and named this fossil form of evolving man Pithecanthropus erectus. Haeckel presumed that his pithecanthropi had lived in the Pliocene period ; Prof. Dubois is of opinion that his transitional form of man lived in Java towards the end of the Pliocene period. Discoveries made by Dr.
G. E. Pilgrim of the Geological Survey of India and by members of that survey in the latter part of the 19th century have proved that India, during the Miocene period and the earlier part of the Pliocene, was the home of great anthropoids of many and diverse kinds, several of them belonging to the type of Dryopithecus which Haeckel, at an early period, regarded as a possible ancestor to man. Others of these fossil Indian or Siwalik anthropoids show affinities to the orang, to the chimpanzee and to the gorilla, while still another—Sivapithecus—is regarded by Dr. Pilgrim as an early representative of the human family. Notwithstanding these revelations from India and taking all their bearings into considera tion the majority of modern authorities (Dubois, W. K. Gregory, Elliot Smith, Keith), in constructing diagrams to illustrate the affinities and lines of descent for the higher primates, depict the human stem (fig. 3) as springing from the vicinity of the stem which gave rise to the gorilla and chimpanzee. The conception, first formulated by Haeckel, that a Miocene anthropoid of the type of Dryopithecus (fig. 3) may stand as a common ancestor to man and to the African anthropoids is still regarded as possible.
Doubts Raised by the Occurrence of Parallel Evolution. —There is a line of evidence, accumulating at the present mo ment, which tends to undermine the confidence of those who have drawn up phylogenetic trees of man's descent. All who have en quired into the evolution of horses and elephants, by the study of fossil forms found in widely separated regions of the world, have become impressed by the fact that horses and elephants in Amer ica have passed through evolutionary changes of the same kind and in the same order as have done their representatives in the Old World. This tendency for the descendants of a common an cestry to undergo parallel or even converging evolution, has been very fully expounded in the published works of Dr. Henry Fair
field Osborn (Origin and Evolution of Life, 1918). That parallel evolution has been potent in the order of mammals to which man is assigned there can be no doubt. The monkeys of the New World parted company from those of the Old early in the Eocene period ; it is probable that at the time of their separation they had only reached the stage represented by the Tarsioids, a family of monkey-like primates, which has now only one living representa tive—the Tarsier (Tarsius spectrum) of Borneo and other islands of the Malay Archipelago. Although parted thus early, New and Old World monkeys have acquired corresponding structural modi fications—modifications of a kind which we cannot suppose to have been present in their common ancestor. The brain of the South American spider monkey (Ateles), that of the Old World monkeys of the semnopithek type, and that of the small anthro poid or gibbon, have many common characters which could not have been present in the brain of their Eocene ancestor.
We may legitimately infer, however, that a bias or tendency to produce similar or almost identical modifications was latent in the common ancestor. If parallel evolution has been at work in one section of the order of primates it may have been at work in another, and we must therefore keep in mind the possibility that man and the gorilla may have acquired their many and striking points of structural similarity independently. Cope (1882) and Hubrecht (1897) supposed that human lineage had parted from that of the anthropoids near the base of the primate phylum ; if this were so man would have an independent pedigree of immense length. In more recent times Prof. F. Wood Jones (The Problem of Man's Ancestry, 1918) has put forward the theory that man, because of the number of primitive and generalized features of his structure, is to be traced back to an independent origin from a tarsioid ancestor. In 1927 Dr. Henry Fairfield Osborn also cham pioned the early separation of man's ancestry from the primate phylum. Such a view entails the need of supposing that the mul titude of structural similarities shared by man and the great anthropoids must have been acquired by each independently.