HOW APES BECAME MEN. 299 



Moneron to the Ampliioxus, from this to the Primseval Fish, 

 from the Primaeval Fish to the first Mammal, and again, 

 from the latter to Man, also require for their historical 

 development a succession of periods probably comprising 

 many thousands of millions of years. (Compare vol. i. p. 129.) 



Those processes of development which led to the origin 

 of the most Ape-like Men out of the most Man-like Apes 

 must be looked for in the two adaptational changes which, 

 above all others, are distinctive of Man, namely, upright 

 walk and articulate speech. These two physiological func- 

 tions necessarily originated together with two corresponding 

 morphological transmutations, with which they stand in the 

 closest correlation, namely, the differentiation of the two 

 pairs of limbs and the differentiation of the larynx. The 

 important perfecting of these organs and their functions 

 must have necessarily and powerfully reacted upon the 

 difierentiation of the brain and the mental activities de- 

 pendent upon it, and thus have paved the way for the end- 

 less career in which Man has since progressively developed, 

 and in which he has far outstripped his animal ancestors. 

 (Gen. Morph. ii. p. 430.) 



The first and earliest of these three great processes 

 in the development of the human organism probably was 

 the higher differentiation and the perfecting of the ex- 

 tremities which was efiected by the habit of an upright 

 walk. By the fore feet more and more exclusively adopt- 

 ing and retaining the function of grasping and handling, 

 and the hinder feet more and more exclusively the function 

 of standing and walking, there was developed that contrast 

 between the hand and foot which is indeed not exclusively 

 characteristic of man, but which is much more strongly 



