288 THE INTERMEDIATE PRIMATES 



Many features in the behavior of the gibbon are noteworthy and raise 

 the animal to a plane somewhat above that of the other intermediate pri- 

 mates. In hylobates the brachiating type of locomotion has replaced the 

 pronograde speciaHzation of lower primates. Swinging from the branches by 

 the long arms has obviously produced a greater erectness of the body in the 

 gibbon than is true of any other intermediate primates. The gibbon also 

 is able to stand, walk and even run in the erect posture. This hylobate 

 erectness therefore appears to be the first step toward the manlike speciali- 

 zations of bipedal locomotion and bimanal differentiation. These facts 

 warrant the recognition of the Proanthropoid Stage as represented by 

 the gibbons. 



