26 THE THEORY OF EVOLUTION 



of a species and thus we are shut up to the drawing of 

 inferences from what may be learned by comparison 

 and experiment. 



On the other hand, if Darwin's hypothesis be 

 rejected, there is, it must be frankly admitted, no 

 satisfactory alternative to take its place. Granting 

 that de Vries is right in holding that species originate 

 by sudden mutation, the process is not thereby 

 explained and made intelligible and it does not seem 

 likely that such an explanation could ever be found, 

 though it is rash to set a limit to future discovery. 

 In short, while the evolutionary theory is buttressed 

 by such a mass of evidence that nearly all men of 

 science are convinced of its truth, no satisfactory 

 and acceptable explanation of its causation has yet 

 been devised. To repeat Prof. E. B. Wilson's words: 

 "Further discussions concerning the causes of evolu- 

 tion had clearly become futile until a more adequate 

 and critical view of existing genetic phenomena had 

 been attained." 



