182 GENERAL DISCUSSION [ch. xiv 



Nothing but sudden mutation can account for such differences, 

 and natural selection has probably nothing to do with it. It 

 sorts the products of evolution into their most suitable places. It 

 is as if the evolutionary train dropped a passenger or two at 

 every station, who has then to make good in the particular 

 conditions that there obtain, in the society or community in 

 which he happens to find himself, and with the equipment for 

 the task that he happens to carry with him. 



But if differentiation or divergent mutation be the more correct 

 explanation, it is clear that evolution moved in a direction the 

 opposite of that in which it would move under natural selection. 

 The latter works upward /rom the small variety, which is assumed 

 to be an incipient species, whilst the former works downward to 

 the variety. The latter, under differentiation, represents the last 

 ripple of the disturbance which gave rise to the family, not the 

 first ripple which is to give rise to a disturbance becoming ever 

 greater and greater. Natural selection kills out the ancestor and 

 the transitional forms, differentiation does not kill the ancestor, 

 nor expect transitions. 



The question as to which explanation is nearer to the truth, 

 therefore, may be settled by an answer to the question as to 

 which was the direction in which evolution moved. To obtain 

 this answer, the author has devised some thirty-four test cases, 

 given in Chaps, x-xiii, and as all of them give good, and a number 

 give very strong, if not convincing, evidence in favour of the 

 direction required by divergent mutation, it becomes in a high 

 degree probable that this is the more correct explanation, and 

 that natural selection had little or nothing to do with the fact 

 that evolution went on. 



There is some other law behind the latter, which at present we 

 do not understand, though probably when we learn what is the 

 driving force in cell-division, we shall be nearer to the goal. My 

 friend Dr Charles Balfour Stewart suggests that the law is 

 probably electrical, and that perhaps the development of a new 

 form may have some relation to the transfer of energy in some 

 way. The divergence of mutation may perhaps become a little 

 less unintelligible by some explanation of this kind. 



To commence with the Numerical test cases (chap, x), it is 

 shown in case i (p. 90) that selection would have great difficulty, 

 as its very name suggests, in causing the evolution of vast and 

 increasing numbers of plants, whilst under differentiation this is 

 automatic, and follows the rule of the hollow curve. In case ii 



