INTENSIVE SEGREGATION. 377 



the operation of the principles o£ transformation in the isolated 

 sections of the species. This change is often brought about by 

 the difference of the environments to which the organism is exposed 

 in the isolated areas. This one form of Segregation has been 

 clearly pointed out by Darwin, though he did not recognize segre- 

 gation as a necessary condition for divergence. There are, how- 

 ever, many other ways in which nature produces a similar result. 

 Some of these are operative when the organism is distributed in 

 isolated districts but surrounded by the same environment, and 

 some of them have to do with the development of non-adaptative 

 divergences, which cannot come under the cumulative influence 

 of natural selection. 



It thus appears that Independent Generation co-operating with 

 Natural Selection is one I'orm of the wider principle of Segre- 

 gation, which , in its many forms, is the ever present condition 

 preceding cumulative divergence. Whatever divides the repre- 

 sentatives of a species in such a way that those of a kind are 

 made to intergenerate while prevented from intergenerating with 

 other kinds is a cause of Segregation. This is my definition of 

 Segregation ; and my theory is that whatever causes Segregation 

 causes divergence, and without Segregation there is no cumulative 

 divergence. Now, in order to refute the theory it is necessary 

 to show either that Segregation does not take place in nature, or 

 that it is not accompanied by divergence, or that divergence takes 

 place without Segregation. As Mr. Wallace has not attempted to 

 prove any one of these counter propositions, I think his criticism 

 is aside from the main issue. Even if my paper presents " a body 

 of theoretical statements" with "no additional facts," this does 

 not show that the theory is incorrect or the new use of the old 

 facts unimportant in the explanation of divergent evolution. 

 ' The Origin of Species ' was filled with new theories applied to 

 old facts. The importance of Cumulative Divergence through 

 Cumulative Segregation, if a fact, is admitted. Is it a fact ? is 

 then the question that needs to be discussed ; but, if Segregation 

 is supposed to be no more than Isolation, the discussion will be 

 of little avail. 



lu the Journal of the Eoyal Microscopical Society, 1889, part i. 

 pages 33-4, will be found an appreciative, though a very brief 

 review of my theory, closing with the suggestion that fuller 

 elucidation is needed of the alleged tendency in nature to trans- 

 form separation, when long continued, into increasing segregation 



