EVOLUTION OF MAN 227 



izations for brachiation are elongation of the forelimbs, reduction of the 

 thumb so that the other fingers of the hand function as a sort of hook on 

 the branches of trees, and shortening of the hind hmbs (Figs. 11.1 and 

 1 1.3 ). Many correlated changes in muscles, muscle 

 attachments, and joint structure are also entailed. 

 If the body is heavy, great enlargement of the mus- 

 culature of the shoulders and arms is necessitated. 



Man is not a brachiator. Is he descended from 

 ancestors who were? Relative to trunk height both 

 modern apes and man have long arms (Washburn, 

 1950). Man differs from modern apes, however, 

 in that his legs are longer than his arms; in this 

 respect, as in some others, man resembles Old 

 World monkeys more than he does the modern 

 apes (Straus, 1949). In this connection it is of 

 great interest that Miocene apes such as Proconsul 

 also had forelimbs shorter than hind limbs (Simons, 

 1960). Since this was true of Pliopithecus as well, 

 the fact suggests that elongation of the arms was a 

 later acquisition in lines leading to modern apes 

 specialized for brachiation, and that in the lines 

 leading to man the primitive relationship of shorter 

 arms than legs was retained. 



Authorities diflfer as to whether Proconsul itself 

 should be regarded as ancestral to man. If it was a 

 brachiator it was not a highly specialized one. In 

 fact, its arms possessed a sufficiently generalized 

 structure (Fig. 1 1.4) so that both the arm structure 

 of man and that of the specialized brachiators 

 among later apes might have been derived from it 

 (see Napier and Davis, 1959; Le Gros Clark, 

 1960). On the other hand, its teeth were somewhat 

 specialized, suggestive of the teeth of its descend- 

 ants, the chimpanzee and gorilla. But if it was not 

 ancestral to man, some other members of the 

 Dryopithecinae may have been. Future discoveries 

 will doubtless afford much interesting information 

 on this point. 



Great interest has been aroused recently by 

 studies of a fossil primate known as Oreopithecus 



FIG. 11.4. Arm skele- 

 ton of Proconsul (cf. 

 Fig. 3.2). Based on a 

 reconstruction by J. R. 

 Napier and P. R. Davis. 

 (From Le Gros Clark, 

 The Antecedents of 

 Man, Edinburgh Uni- 

 versity Press, 1959, p. 

 216.) 



