APPENDIX A. (p. 5)
Since the first few pages of this book were in print an important memoir on the "Phylogeny of Recent and Extinct Anthropoids with Special Reference to the Origin of Man" has been published by W. K. Gregory (Bull. Am. Mus. Nat. Hist. Vol. XXXV., Article XIX, pp. 258 ff., New York, 1916). As Gregory's lucid statement of the problems involved is based on a prolonged examination of very varied and abundant material we have considered it advisable to present his summary. The chief conclusions, which appear to be of a conservative character, are as follows (p. 341).
The Origin of Man.
1. Comparative anatomical (including embryological) evidence alone has shown that man and the anthropoids have been derived from a primitive anthropoid stock and that man's existing relatives are the chimpanzee and the gorilla.
2. The chimpanzee and gorilla have retained, with only minor changes, the ancestral habits and habitus in brain, dentition, skull and limbs, while the forerunners of the Hominidæ, through a profound change in function, lost the primitive anthropoid habitus, gave up arboreal frugivorous adaptations and early became terrestrial, bipedal and predatory, using crude flints to cut up and smash the varied food.
3. The ancestral chimpanzee-gorilla-man stock appears to be represented by the Upper Miocene genera Sivapithecus and Dryopithecus, the former more closely allied to, or directly ancestral to, the Hominidæ, the latter to the chimpanzee and gorilla.
4. Many of the differences that separate man from anthropoids of the Sivapithecus type are retrogressive changes, following the profound change in food habits above noted. Here belong the retraction of the face and dental arch, the reduction in size of the canines, the reduction of the jaw muscles, the loss of the prehensile character of the hallux. Many other differences are secondary adjustments in relative proportions, connected with the change from semi-arboreal, semi-erect and semi-quadrupedal progression to fully terrestrial bipedal progression. The earliest anthropoids being of small size doubtless had slender limbs; later semi-terrestrial semi-erect forms were probably not unlike a very young gorilla, with fairly short legs and not excessively elongate arms. The long legs and short arms of man are due, I believe, to a secondary readjustment of proportions. The very short legs and very long arms of old male gorillas may well be a specialization.
5. At present I know no good evidence for believing that the separation of the Hominidæ from the Simiidæ took place any earlier than the Miocene, and probably the Upper Miocene. The change in structure during this vast interval (two or more million years) is much greater in the Hominidæ than in the conservative anthropoids, but it is not unlikely that during a profound change of life habits evolution sometimes proceeds more rapidly than in the more familiar cases where uninterrupted adaptations proceed in a single direction.
6. Homo heidelbergensis appears to be directly ancestral to all the later Hominidæ.