82 



HUMAN BIOLOGY 



jaw from the Lower Oligocene of Egypt, to which the name 

 PropHopithecus has been appHed and which appears to be 

 in the Hne of ascent to the gibbons also, retains all or nearly 

 all the characters which might be predicated of the jaw 

 of the common stem form of all the anthropoid series, 

 including man. The lower teeth in this jaw are each more 

 primitive, that is, more hke those of still older primates, 

 than are the corresponding parts in modern gibbons. Hence 

 the palaeontological evidence, slender as it is, lends support 

 to the conclusion based on comparative studies of the 

 teeth, skull and many parts of the anatomy of the recent 

 Primates, namely, that the later specializations of brachia- 

 tion seen in the gibbons had not been assumed by the direct 

 ancestors of the higher anthropoid group. 



Nevertheless, repeated consideration of the subject must 

 also support the view that the gibbons on the whole retain 

 the basic features of the earher stages of brachiation, namely, 

 the maintenance of an upright posture at right angles to the 

 general plane of forward motion, that was also prerequisite 

 for the emergence of man. The relative nearness of the 

 oibbons on the one hand to the ancestral stock of the anthro- 

 poid-man series, and on the other hand to the older catar- 

 rhine stock, has been recognized by all authorities. The 

 gibbons are definitely more primitive (that is, more like the 

 lower Primates) than any of the great apes or man in many 

 characters of the dentition, of the skull, vertebral column, 

 pelvis, etc., as well as in the brain and in many features of 

 the viscera (Keith). Their pelvis is remarkably primitive; 

 it retains clear traces of the ischial expansions characteristic 

 of the Old World monkeys, while the blade of the ilium is 

 but little expanded transversely. 



When the brachiating gibbon comes down on the ground, 

 he does not run on all fours like a monkey, he does not 

 swing on his long forearms as crutches like an orang, he 

 does not walk on all fours with bent knuckles as do the 

 chimpanzee and the gorilla; on the contrary, he walks or 

 runs upright like a man, with his femora overextended, so 

 as to be nearly vertical and parallel with his backbone. 

 His gait on the ground diflers from that of man in that the 

 arms are held upward, the knees turned outward and the 



