MAN'S RELATIVES: THE PRIMATES 



471 



a history of increasingly perfect adaptation to life in the trees, until the 

 direction of modification was partly reversed among the larger and 

 heavier apes and more completely in man. Although man is not a tree 

 dweller, the arboreal life of his ancestors has left its mark deeply upon 

 him and is perhaps in great measure responsible for his attainment of 

 his present estate. Some of the more important primate characteristics, 

 most of which are related to this arboreal habit, may here be considered. 

 Primate characteristics. The primates fall into three groups — lemurs, 

 tarsioids, and anthropoids, the last being highest in the scale and including 



Fig. 29.1. A Philippine tree shrew, Tupaia. The members of this group are intermediate 

 between insectivores and the more typical primates and are placed at the base of the 

 primate family tree. (Courtesy Zoological Society of Philadelphia.) 



the monkeys, apes, and man. All share the following features: hands and 

 feet prehensile (grasping), or evidently derived from the prehensile type; 

 a clavicle, or collarbone, present; some or all of the fingers and toes with 

 flattened nails instead of claws; breasts as a rule restricted to a single 

 anteriorly situated pair; and brain relatively large, often attaining great 

 size and intricacy of pattern. 



For locomotion in trees, flexibility of the limbs is essential. This is particularly 

 true of the forelimb, which reaches for new holds, grasps and clings, while the 

 hind limbs support the weight of the body. The result has been the differentiation 

 of a more mobile arm with a more prehensile hand, and of a more stable leg with 

 a less supple foot. There has been no restriction of limb movement to one plane 

 and no solidification of the foot into a strong supporting structure as in terrestrial 



