276 COMTE TO BENJAMIN KIDD CHAP. 



and more familiar case of slavery. Yet this differentia- 

 tion, gross and excessive as it is, belongs to another 

 region of things from animal differentiation. The 

 many castes or the slaves and the oppressors con- 

 stitute together one society. The potential unity of 

 the race, implied in reason, has already that notable 

 consequence. Accordingly, the marked physiological 

 differentiation of the various races of mankind does 

 not seem to have taken place in a society having 

 relations even of neighbourhood between its several 

 parts. It has been guessed that race differentiation 

 was due to natural selection in different regions of the 

 world, those naturally superior to cold surviving within 

 the Arctic circle, and those who enjoyed immunity 

 from fever surviving in the tropics. At any rate, the 

 differentiating process came first. While man was 

 mainly an animal or (what is nearly the same thing) 

 while men were divided from their fellows by geo- 

 graphical barriers they diverged physiologically ; and 

 no doubt they also diverged socially. But, as soon 

 as reason began to assert itself and make its way, the 

 tendency to differentiation was held in check by a 

 tendency to unity a growing unity of culture and 

 custom pointing to an ultimate far-off unity of the 

 whole race. The different branches of the human 

 stock can borrow from each other as kindred tribes of 

 animals cannot do. Even if, for a time, the aristocratic 

 few have no mind to help the ignorant many, yet the 

 ignorant many are eager to copy the envied few. 

 Simple survival of the fittest and neglect of the unfit 

 is never long the rule in human affairs. Levelling up 

 is one of the earliest manifestations of reason, when set 

 free to do its work. 



In the first instance, as between different societies, 



