53 MENTAL EVOLUTION IN ANIMALS 



the ultimate nervous mechanisms which play down upon the 

 muscular mechanisms; we only see a mazy mexus of cells 

 and fibres, the very function of which, much less their inti- 

 mate mechanism, could not be guessed, were it not that we 

 have the grosser mechanisms of the muscular system whereby 

 to study the effects of these finer mechanisms. 



Muscular co-ordinations, then, are so many indices, " writ 

 large," of corresponding co-ordinations taking place in the 

 nervous system. Now we have seen that mental processes 

 may be regarded as indices in precisely the same way, and 

 indeed that, like muscular movements, they are the only 

 indices we have of the operations of the nervous mechanisms 

 with which they are connected. Moreover, we have seen 

 that when this new set of indices has reached a certain level 

 of development, marking of course a corresponding level 

 of development in the nervous system, it begins unmistake- 

 ably to show that the functions of receptive discrimination 

 and of adaptive movement are taking yet another point of 

 departure in the upward course of their development — that 

 the nervous system is beginning to discriminate between 

 novel and enormously complex stimuli, having reference not 

 only to immediate results, but also to remote contingencies ; 

 we see in short that the nervous mechanism is beginning to 

 develope those higher functions of discriminative and adaptive 

 ability which on their subjective side we know as rational. 



Therefore it is clear that these two faculties not only do 

 but must proceed together. Every advance in the power of 

 discrimination will be followed, in the life of the individual 

 and in that of the species, by efforts towards the movements 

 of needful adaptation, and in all cases where such movements 

 require an advance on the previous power of co-ordination, 

 such advance will be favoured 'by natural selection. Thus 

 every advance in the power of discrimination favours an 

 advance of the power of co-ordination. And, conversely, we 

 may now remark that every advance in the power of co- 

 ordination favours an advance of the power of discrimina- 

 tion. For, as a greater power of co-ordinated movement 

 implies the bringing of nerve-centres into new and more 

 varied relations with the outer world, there is thus afforded 

 to the nerve-centres a proportionately increased opportunity 

 of discrimination— an opportunity which will sooner or later 

 be sure to be utilized by natural selection. 



