EVOLUTION THE MASTER-KEY 



which therefore tend to diverge more and more from 

 each other in physical characters. Here I cannot 

 doubt that we have a most important factor in 

 organic evolution. 



The factors of organic evolution hitherto named 

 are adaptation with inheritance, natural selection, 

 sexual selection, homogamy, and what De Vries 

 calls mutation. Are any others yet to be dis- 

 covered? The answer to this question depends 

 on our estimate of the adequacy of these factors. 

 Probably most biologists would say that they are 

 completely adequate. There will long remain, 

 however, critics who will attempt to show that 

 these cannot be regarded as adequate for the pro- 

 duction of the multitudinous species that exist 

 to-day and have existed in time past, without aid 

 from a principle of telesis, or design. One author 

 succeeds another 1 in the attempt to show that 

 Darwinism is a half-truth, and that without a 

 principle of "directivity" the facts cannot be ex- 

 plained. But as this belief depends upon an as- 

 sumption of an anthropoid Deity, we may leave it 



to stand or fall therewith. 







1 Such as the Rev. Professor George Henslow, in his Popular 

 Rationalism Critically Examined. 



