164 DARWINISM AND THE PROBLEMS OF LIFE 



bird's wing, be reduced by natural selection until they 

 were harmless ; but if they were of no consequence 

 either way to the new species, they would remain 

 unchanged in size, because their plus and minus 

 variations would neutralise each other. They would 

 only change their size in the event of the total size 

 of the new species having to be altered. 



The province we have now entered is a very delicate 

 one, because, as I said above, we can never know 

 whether a characteristic of an animal, the use of which 

 is not visible, may not be indispensable all the same. 

 In any case, it is certain that indifferent features do not 

 form the chief criteria of species and classes, as has been 

 said ; nor is it true that the adaptations are not con- 

 cerned in the discrimination of species. It has been 

 justly replied to these writers that it is precisely the 

 adaptations that constitute the species or the class as 

 such. What else is left in the whale if we take away 

 its adaptation to aquatic life ? What becomes of the 

 bird, which, as we saw above, consists entirely of 

 adaptations to aerial life ? I f we look at species in 

 this way, we feel inclined to say that there is nothing 

 indifferent in an animal. 



Hence we see the rise of new species especially 

 in the selection of new adaptations. In this, in- 

 different organs may be taken over ; in fact, it is 

 possible for them to appear for the first time. Darwin 

 himself established a law that he called the law of 

 correlation. According to this, the various parts of 

 the animal body mutually affect each other in growth. 

 Everybody knows, as a matter of fact, that organs that 



