6 THE SCIENTIFIC EVIDENCES OF 



geographical areas), it follows that the process of 

 natural selection need never reach a terminal 

 phase. And forasmuch as natural selection may 

 thus continue, ad infinitum, slowly to alter a 

 specific type in adaptation to a gradually chang- 

 ing environment, if in any case the alteration 

 thus effected is sufficient in amount to lead 

 naturalists to denote the specific type by some 

 different name, it follows that natural selection 

 has transmuted one specific type into another. 

 And so the process is supposed to go on over 

 all the countless species of plants and animals 

 simultaneously — the world of organic types being 

 thus regarded as in a state of perpetual, though 

 gradual, flux. 



Such, then, is the theory of natural selection, 

 or survival of the fittest ; and the first thing we 

 have to notice with regard to it is, that it offers 

 to our acceptance a scientific explanation of the 

 numberless cases of apparent design which we 



