THE EVOLUTION OF MAN 191 



The anatomy of the man-hkc apes is much Hke that of man 

 (Fig. 113). The apes have stronger jaws and teeth and a relatively 

 low cranial capacity, their mouths are not formed in such a way 

 as to permit articulate speech, their hands and feet alike are grasp- 

 ing appendages, and the skeleton is not sufficiently modificnl to 

 allow a fully erect posture. Within the range of their own group, 

 however, they show nnich greater anatomical differences than are 

 evident between the highest ai^es and man. Man shows all of the 

 modifications incidental to intellectual dcwelojMiient and erectness. 

 These structures and the pro])al)le reasons for their development 

 are treated in the following paragraphs; detailed comparison with 

 the existing apes is unnecessary for these animals are, at the most, 

 merely similar to some of the remote ancestors of man. 



The Arboreal Origin of Man. The fact that man is in so 

 many ways like these great apes, and that they are highly de- 

 veloped arboreal animals, suggests that man himself is derived 

 from arboreal ancestors. In analyzing this possibility it is first 

 necessary to consider how the assumption of arboreal habits 

 might affect the normal quadrupedal form characteristic of the 

 lower vertebrates. With the condition of the arboreal primates 

 established, it is then necessary to inquire into the possibility of 

 return to the ground, and into the effects of such a return upon 

 the arboreal organism. 



Arboreal Quadrupeds. The assumption of arboreal life by 

 quadrupeds is not at all uncommon. Squirrels are a familiar ex- 

 ample. In all of the many mammalian orders represented by 

 such species, however, sharp curved claws are the effective means 

 of locomotion except among the lemurs, the lowest primates. 

 Here the thumb and great toe are opposable, and the animal is 

 able to grasp the limbs of trees instead of merely clinging to them 

 or hanging from them as by a series of hooks. 



Hands versus Claws. The result of opposal)ility is a much more 

 effective appendage for arboreal progress. Claws, if sufficiently 

 long, as in the sloth, are most effective for suspension of the body 

 from branches, but they are a hindrance to any other use of the 

 appendages. If short and sharp, they provide sure footing, but as 

 organs of prehension they are of little or no use, and for suspending 

 the body from branches, of very limited use. A grasping struc- 

 ture, however, as we can determine from personal experience, is use- 

 ful in many ways. It provides sure footing for locomotion above 



