12 ARBOREAL MAN 



mand for stability; and others have retained a primitive 

 mobility in, at least, the fore-limb. 



It is the latter which have been successful and have 

 become dominant. The problem we are attempting to 

 solve is : Why have some Mammals retained this primitive 

 feature of mobility of the fore-limb, and why have these 

 same Mammals become more successful in the struggle 

 of evolution ? 



We are here face to face with a fundamental problem, 

 and it is now necessary that we should, as it were, take 

 sides. Man possesses a mobile fore-limb which takes no 

 part in the support or the progression of his body. He 

 is the culmination of a line of ancestors which, on alto- 

 gether different grounds, is distinct enough in general 

 outlines. The question is: Does the stock from which 

 Man arose retain a primitive mobile fore-limb, or has he 

 evolved his present posture and the present freedom of 

 his fore-limb from a previously four-footed or quadru- 

 pedal ancestor ? It may be said with truth that every 

 teaching of modern orthodox anatomy and anthropology 

 would lead us to believe that Man had evolved from a 

 quadrupedal pronograde mammalian stage. With that 

 it is impossible to disagree so long as it is made perfectly 

 clear that the stock from which Man is derived was 

 differentiated so early in the mammalian story, that the 

 primitive mobility of the fore-limb had never been sacri- 

 ficed to the needs of stability. Tliere are two ways of 

 regarding this problem. We may assume that the primi- 

 tive mammal passed into a regular pronograde four- 

 footed stage with four supporting limbs, and from that 

 stage Man evolved into an animal characterized by an 

 orthograde or upright posture. Or we may imagine that 

 the stock from which Man wa derived had never been 

 typically pronograde with four supporting limbs; that in 

 this stock mobility had never become sacrificed to sta- 

 bility in all four limbs. It is in the former view, the 

 assumption of the upright posture from a pronograde 



