April. 1929 



EVOLUTION 



Page Three 



The Origin of Man from the Anthropoid Stem 



When and Where? 



(From Bicentenary Number of American Philosophical Society's Proceedings, Vol. LXVI, 1927) 



By WILLIAM K. GREGORY 



nPHE reduction of the thumb in apes is cited by 

 Professor Osborn as ruHng them out from the Hne 

 of human ascent. But the remarkable feature is, not 

 that apes should have the thumb reduced, but that they 

 should have a thumb at all. No one can doubt, after 

 inspection, that the Chimpanzee has a true hand and 

 not a mere forefoot like that of four-footed animals. 

 (See Figure 1, January EVOLUTION.) Who can 

 now doubt that the thumb of man has not only in- 

 creased the size but also improved its ability to oppose 

 the other fingers. Professor Schultz states : "In early 



Hand Bones of Man and Chimpanzee 



fetal life the free thumb branches from the palm im- 

 mediately at the base of the index finger. In the course 



of growth this place of branching shifts to a 



place nearer the wrist This movement of the 



thumb, away from the other fingers has greatly 



facilitated the opposability of the thumb The op- 



. posability of the thumb, which was ... of greatest im- 

 portance for the evolution of man, was not yet a feat- 

 ure of the original primate hand. It is significant, but 

 not surprising, therefore, to find that this condition is 

 still lacking in the human embryo. Not only does the 

 embryonic thumb branch at a place unfavorable for ef- 

 fective opposability, but it is not yet rotated around its 

 longitudinal axis to face the other digits." 



While the human thumb passed from a stage where 

 it was more nearly parallel to the other fingers to a 

 stage where it can oppose them, the great toe developed 

 in the opposite direction from a stage where it tended 

 to face other toes to a stage in which it parallels them. 



It may well be true that apes have ape minds and 

 ape brains, adapted to life in the forest, whereas the 

 Dawn Men (of Java, Piltdown, etc.) had definitely 

 human minds and brains which for thousands of gen- 

 erations had adapted them for life on the plains. But 

 this only estal)lishes the fact that apes and men are 

 different and have been different for a very long period 

 of time. It does not throw any light on the questions 



whether or not man is an offshoot from the ape stem, 

 what that stem was like, and during what geologic 

 epoch the separation occurred. If we hold with the 

 anti-evolutionists that the human mind has not evolved 

 out of any animal mind, then the labors of the com- 

 parative psychologists and neurologists are in vain. 

 But if we accept man as a member of the order 

 Primates and a derivative of some form of pre-human 

 primate, then the evidence of comparative psychology 

 must be taken into account. 



What then is the testimony of these comparative 

 sciences? From the labors of Koehler, Kohts and 

 Yerkes it may be asserted that, although far below 

 man in mental ability, the apes are unquestionably 

 much nearer to man than are any of the lower animals 

 of which the mentality has been carefully tested. In- 

 deed. Yerkes, a mo?" cautious and conscientious in- 

 vestigator, finds in the apes more than the rudiments 

 of human thinking. And on the side of the "Dawn 

 Men," Dubois, Elliot Smith, Hunter, Tilney, McGre- 

 gor, point out the distinctly inferior development of the 

 Pithecanthropus (Java man) brain as compared with 

 the brain of modern man. in respect to the filling out 

 of the critical areas which, from clinical research and 

 other lines of evidence, are believed to be the seat of 

 the higher mental faculties. The Pithecanthropus men- 

 tality then, while coming within the limits of the human 

 family, was, so far as the brain cast indicates, by no 

 means lacking in lowly traits. 



Opponents of the Darwinian view should never re- 

 fer to the comparison of the brains of apes and man, 

 for there is nothing that so fully testifies to the rela- 

 tively close k'nship of man to the gorilla and chim- 

 panzee, as the field of comparative neurology. The 

 utmost efforts of anti-evolutionists have only brought 

 into clearer relief the basic correspondence in all parts, 

 not only of the brain surface, but of the brain stem 

 of gorilla and man. The ape brain, according to the 

 well-seasoned conclusions of Elliot Smith and Tilney, 

 carries the line of evolution from the lower primates 

 to a definitely sub-human stage. Doubtless the orang 

 is a side specialization in some features, but the gorilla 

 brain stands especially near to the primitive human 

 brain. 



All this is in full accord with the evidence from other 

 sources, that the human stock derived a rich heritage 

 from tree-dwelling ancestors, which, while fully erect 

 in posture, avoided the extreme specializations of the 

 existing apes and abandoned the trees before the thunib 

 was greatly reduced or before the body was as heavy 

 as that of the gorilla. 



If man is not derived from the primitive ape stock, 

 and yet is to be classed in the order Primates, from 

 what other group did he spring? The tailed monkeys 



