THE CAUSATION OF DISEASE. 1 89 



the word i: environment;' and what a vast assemblage of 

 diverse conditions it embraces (vide Part I.). Thus, as I have 

 said, the effects of use and disuse are embraced under " the 

 environment" of the individual, and there can be no doubt 

 that species are in this way moulded in a very marked degree. 

 To take a single example from Spencer : the aesthetic sense 

 cannot have attained its present high development through the 

 process of natural selection, since it is one that can only help 

 in a very minor degree in the struggle for existence. It has 

 grown through long cultivation or exercise, from generation to 

 generation — that is to say, through use. Chiefly in this way, 

 too, the moral sense has been evolved. The average civilized 

 child is taught morality from its earliest age ; it finds itself 

 in a society whose very existence depends upon the observance 

 of social law, and such cultivation, assiduously carried on 

 through many generations, has led to the development of an 

 innate moral sense. Thus, the aesthetic and the moral faculty 

 have both been evolved by the continuous operation of an 

 aesthetic and moral E on the human organism, independently 

 of selection, at all events in large measure. 



Herbert Spencer, as I have said, designates this process 

 direct equilibration. It consists, in his language, " of changes 

 of function and structure that are directly consequent on 

 changes in the incident forces — inner changes, by which the 

 outer changes are balanced and equilibrium restored." Even 

 in the lifetime of an individual this process plays an im- 

 portant part, for in this way he tends to become more 

 and more adapted to his E. Let us suppose twin brothers to 

 be as like one another as it is possible for them to be : 

 then, if one be brought up as a peasant and the other as a 

 clerk, a steady divergence in structure will gradually ensue, 

 each individual becoming adapted to his own particular 

 E. We may speak of this individual tissue-alteration as 

 personal to distinguish it from racial adaptation ; and we can 

 see how, by a summation of such personal adaptations 

 through many generations, a race may be very considerably 

 modified. 



A study of this threefold method whereby animal organisms 

 are evolved shows us, therefore, that evolution depends upon 



