80 HUMAN BIOLOGY 



and not only raised his face toward the sky but encouraged 

 him to use his hands and brains in working out his own 

 salvation. Like all other great discoveries which disturb 

 the complacency and the traditions of mankind, this one 

 has been either neglected, waved aside or ridiculed; but we 

 shall presently see that when the masking effect of man's 

 present hfe habits is taken into account, his very bones 

 testify and his inward parts reveal the signs of his brachiating 

 origin. 



In the present imperfect record of Primate hfe we first 

 come upon the brachiating habit and its anatomical corre- 

 lates in the gibbons of Southeastern Asia. It is true that 

 some feeble attempts at brachiation are occasionally offered 

 by some of the longer-limbed catarrhine monkeys or even 

 by the spider monkeys of the New World series. But these 

 skilled tumblers are mere beginners; their performances, 

 wonderful as they are when considered as feats in balancing 

 and in ballistics, pale in comparison with the dazzling 

 exhibitions of the gibbons, which are the true virtuosi of the 

 upper branches of the jungle. With all the abandon due to 

 perfect mastery of the technical details, they hurl them- 

 selves from the springing bamboo stalks, keeping them- 

 selves upright in the air and catching the next hold on the 

 branches with the greatest ease. 



Some of the gibbons of the genus Hylobates have begun to 

 pay a price for this virtuosity; their arms and hands are 

 excessivel}^ long and their thumbs considerably enfeebled, 

 since Hke a trapeze performer they tend to use the fingers as 

 hooks. But these speciaHzations are less pronounced in the 

 hoolock gibbons, in which the thumb is vigorously developed. 

 Moreover the single known fossil femur from the Miocene 

 of Germany (named Pliohylobates), which appears to 

 belong to a primitive gibbon, is distinctly stouter than that 

 of its modern relatives. It is a reasonable inference therefore 

 that the earhest gibbons were somewhat less slender, less 

 fully specialized for advanced brachiating habits than are 

 their modern descendants, and in view of the various 

 souvenirs of a non-brachiating catarrhine ancestral stock 

 that are retained even in the modern gibbon, such an 

 inference becomes highly probable. Again, the small fossil 



