240 APPENDIX II — INTENSIVE SEGREGATION. 



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 apphed to old facts. 

 The importance of cumulative divergence through cumulative segre- 

 gation, if a fact, is admitted. Is it a fact? is then the question that 

 needs to be discussed. If, however, segregation is assumed to be the 

 isolation of sections of a species possessing exactly the same average 

 character, the assumption will be contrary to the facts that usually 

 exist, even in cases of indiscriminate isolation. 



In the Journal of the Royal Microscopical Society, 1889, part i, 

 pages 33-34, will be found an appreciative, though a very brief 

 review of my theory, closing with the suggestion that fuller elucida- 

 tion is needed of the alleged tendency in nature to transform separa- 

 tion, when long continued, into increasing segregation and divergence. 

 Want of space in my first essay made it necessary to postpone the full 

 discussion of this part of the theory, but in the present paper I 

 have sought to point out some of the more manifest principles on 

 which this general law of intension rests. There are undoubtedly 

 other principles of transformation, which, when combined with 

 separate breeding, inevitably produce divergent instead of parallel 

 evolution ; but the principles pointed out in this paper are sufficient 

 to establish the general tendency and to show that natural selection 

 is by no means the only principle on which the law rests. If we could 

 obtain sections of a species presenting exactly the same average char- 

 acter, and if we could prevent all the principles of transformation 

 from coming in to aid in the process, separate breeding under such 

 conditions would perhaps never produce divergence ; but, as separa- 

 tion never produces exactly equivalent sections, it always tends to 

 introduce transformation, through changed or unbalanced action, 

 and transformation in the separated sections inevitably becomes 

 divergence. We thus gain an explanation of the fact that isolation, 

 even when accompanied by exposure to the same environment, if long 

 continued, always introduces divergent forms of selection. Indepen- 

 'dent generation precedes and determines the possibility of the diver- 

 gence, and if it is segregative it also determines in a measure the form 

 of the divergence ; but even if it is simply separative, it involves the 

 complete cessation of all forms of reflexive selection maintaining 

 compatibility between the isolated sections, and, therefore, opens the 

 way for the gradual entrance of divergent forms, first of reflexive, and 

 then of environal selection. 



