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ANCESTRY OF THE ANTHROPOID APES—PLIOCENE CLIMATE, FORESTS, AND LIFE OF WESTERN EUROPE—TRANSITION TO THE PLEISTOCENE, OR AGE OF MAN—THE FIRST GLACIATION, ITS EFFECTS ON CLIMATE, FORESTS, AND ANIMAL LIFE—THE PREHUMAN TRINIL RACE OF JAVA—THE EOLITHS OR PRIMITIVE FLINTS—THE SECOND GLACIATION—THE HEIDELBERG, EARLIEST KNOWN HUMAN RACE—THE THIRD GLACIATION

The partly known ancestors of the anthropoid apes and the unknown ancestors of man probably originated among the forests and flood-plains of southern Asia and early began to migrate westward into northern Africa and western Europe.

As early as Oligocene times a forerunner of the great apes (Propliopithecus), most nearly resembling the gibbons, appears in the desert bordering the Fayum in northern Egypt. Early in Miocene times true tree-living gibbons found their way into Europe and continued throughout the Pliocene in the forms known as Pliopithecus and Pliohylobates, the latter being a true gibbon in its proportions; it ranged northward into the present region of Germany. Another ape which early reached Europe is the Dryopithecus; it is found in Miocene times in southern France; the grinding-teeth suggest those of the orang, the jaw is deep and in some ways resembles that of the Piltdown man. A third ape (Neopithecus) occurs in the Lower Pliocene near Eppelsheim, in Germany, and is known only from a single lower molar tooth, which recalls the dentition of Dryopithecus and more remotely that of Homo. In the Pliocene of the Siwalik hills of Asia is found Palæopithecus, a generalized form which is believed to be related to the chimpanzee, the gorilla, and the gibbon; the upper premolars resemble those of man.

None of these fossil anthropoids either of Europe or of Asia can be regarded as ancestral to man, although both Neopithecus and Dryopithecus have been placed in or near the line of human ancestry by such high authorities as Branco and Gaudry. When Dryopithecus was first discovered by Lartet, Gaudry(1) considered it to be by far the most manlike of all the apes, even attributing to it sufficient intelligence for the working of flints, but fuller knowledge of this animal has shown that some of the living anthropoids are more manlike than Dryopithecus. This animal is closely related to the ancestral stock of the chimpanzee, gorilla, and orang. The jaw, it is true, resembles that of the Piltdown man (Eoanthropus), but the grinding-teeth are much more primitive and there is little reason to think that it is ancestral to any human type.[N]

Fig. 16. The gibbon is primitive in its skull and dentition, but extremely specialized in the adaptation of its limbs to arboreal life. Photograph from the New York Zoological Park.

Among these fossil anthropoids, as well as among the four living forms, we discover no evidence of direct relationship to man but very strong evidence of descent from the same ancestral stock. These proofs of common ancestry, which have already been observed in the existing races of man, become far more conspicuous in the ancient Palæolithic races; in fact, we cannot interpret the anatomy of the men of the Old Stone Age without a survey of the principal characters of the existing anthropoid apes, the gibbon, the orang, the chimpanzee, and the gorilla.

Fig. 17. The orang has a high rounded skull and long face.

Photograph from the New York Zoological Park.

The gibbon is the most primitive of living apes in its skull and dentition, but the most specialized in the length of its arms and its other extreme adaptations to arboreal life. As in the other anthropoids, the face is abbreviated, the narial region is narrow, i. e., catarrhine, and the brain-case is widened, but the top of the skull is smooth, and the forehead lacks the prominent ridges above the orbits; thus the profile of the skull of the gibbon (Fig. 16) is more human than that of the other anthropoid apes. When on the ground the gibbon walks erect and is thus afforded the free use of its arms and independent movements of its fingers. In the brain there is a striking development of the centres of sight, touch, and hearing. It is these characteristics of the modern gibbon which preserve with relatively slight changes the type of the original ancestor of man, as noted by Elliot Smith.(2)

Fig. 18. The chimpanzee. This figure illustrates the walking powers of the chimpanzee, the great length of the arms, and the abbreviation of the legs. Photograph from the New York Zoological Park.

The limbs of the orang are less elongated and less extremely specialized for arboreal life than those of the gibbon but more so than those of the chimpanzee and the gorilla. The skull is rounded and of great vertical height, with broad, bony ridges above the orbits and a great median crest on top of the skull in old males. The lower jaw of the orang is stout and deep, and, although used as a fighting weapon, the canine tusks are much less prominent than in either the gibbon, chimpanzee, or gorilla. Of all anthropoids this jaw most nearly resembles that of the Piltdown man.

Fig. 19. The Chimpanzee. This figure shows certain facial characteristics which are preserved in the Neanderthal race of men. Note also the shortening of the thumb and the enlargement of the big toe. Photograph from the New York Zoological Park.

In the chimpanzee we observe the very prominent bony ridges above the eyes, like those in the Trinil and Neanderthal races of men. The prognathous or protruding tooth rows and receding chin suggest those in the Heidelberg, Piltdown, and Neanderthal races. When the chimpanzee is walking (Fig. 18) the arms reach down below the level of the knees, whereas in the higher races of man they reach only half-way down the thighs. Thus, the fore limb, although much shorter than that of the gibbon, is relatively longer than that of any human race, recent or ancient. We observe also in the walking chimpanzee (Fig. 18) that the upper part of the leg, the thigh-bone, or femur, is relatively long, while the lower part, the shin-bone, or tibia, is relatively short. Indeed, both in the arm and in the leg the upper bones are relatively long and the lower bones are relatively short. These proportions, which are inheritances of arboreal life, are in very marked contrast to those observed in the arms and legs of the Neanderthal race of men, in which the limbs are of the terrestrial or walking type.

ANCESTRAL TREE OF THE ANTHROPOID APES AND OF MAN

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From the unknown and ancestral stock of the anthropoid apes and man the GIBBON was the first to branch off in Oligocene times; the ORANG then branched off in a widely different direction. The stem of the CHIMPANZEE and of the GORILLA branched off at a more recent date and is more nearly allied to that of man. Five early human races have been found in Europe in Glacial or Pleistocene times, but no traces of other primates except the macaques, which are related to the lower division of the baboons, have been found in Europe in Pleistocene times. Modified after Gregory. (For latest discovery see Appendix, Note VII.)

Fig. 20. The Gorilla. An immature female, about three years of age, showing none of the adult male characteristics. Photograph from the New York Zoological Park.

We observe also in the chimpanzee a contrast between the grasping power of the big toe, which is a kind of thumb, and the lack of that power in the hand, in which the thumb is nearly useless; in all apes this function is characteristic of the foot, in man of the hand alone. The opposable thumb, with its power of bringing the thumb against each of the fingers, is the one character which is lacking in every one of the anthropoid apes and which was early developed among the ancestors of man.

The skull of the chimpanzee is longer than that of the orang, the most prominent feature in the top view being the extreme protuberance of the orbits, which are surrounded by a supraorbital and circumorbital bony ridge, which is also strongly developed in the Neanderthal skull as well as in the Pithecanthropus or Trinil skull but, so far as we know, is entirely lacking in that of Piltdown. As in the orang and the gorilla, a crest develops along the middle of the top of the skull for the insertion of the powerful muscles of the jaws, a crest which is wholly wanting in the gibbon and probably wanting in all the true ancestors of man.

Fig. 21. Contrast of the projecting face (prognathism), retreating forehead, and small brain-case of a young gorilla, as compared with the vertical face, prominent nose, high forehead, and large brain-case of a high race of man. After Klaatsch.

The gorilla illustrates in the extreme the specializations which are begun in the chimpanzee, and which are attributable to a life partly arboreal, partly terrestrial, with the skull and jaws used as powerful fighting organs. The head is lengthened by the forward growth of the muzzle into an extreme prognathism. The limbs and body of the gorilla show a departure from the primitive, slender-limbed, arboreal type of apes and are partly adapted to a bipedal, ground-dwelling habit.

As regards psychic evolution,(3) Elliot Smith observes that the arboreal mode of life of the early ancestors of man developed quick, alert, and agile movements which stimulated the progressive development of the posterior and lateral portions of the brain. The sense of smell had been well developed in a previous terrestrial life, but once these creatures left the earth and took to the trees, guidance by the olfactory sense was less essential, for life amidst the branches of the trees is most favorable to the high development of the senses of vision, touch, and hearing. Moreover, it demands an agility and quickness of movement that necessitate efficient motor centres in the brain to co-ordinate and control such actions as tree life calls for. The specialization of sight awakens curiosity to examine objects with greater minuteness and guides the hands to more precise and skilled movements.