HOW APES BECAME MEN, 299 
Moneron to the Amphioxus, from this to the Primeval Fish, 
from the Primeval 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, wpright 
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 
differentiation 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. i. 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- 
trenities which was effected 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 
