J. T. Gulick — Inconsistencies of Utilitarianism. 13 



fuller exposition of this subject I would refer to my paper on 

 " Divergent Evolution through Cumulative Segregation " 

 (Linn. Soc. Jour. Zoology, vol. xx, pp. 234-8). The principles 

 which I have called Sexual and Social Segregation, Mr. Wal- 

 lace has mentioned in several places under the name " selective 

 association," or " selective isolation," but he does not recognize 

 the fact that, whenever this principle segregates forms whose 

 immediate ancestors were not segregated, it must be the direct 

 cause of divergence ; and that, when divergent forms that 

 have arisen under Industrial and Local Segregation are brought 

 together through increase of numbers, this principle is often 

 the one cause preserving varieties that would otherwise be ob- 

 literated. With plants whose pollen is distributed by the wind, 

 and probably with both vegetable and animal forms whose 

 fertilizing elements are distributed by water, Prepotential 

 Segregation plays the same role as the segregative instincts of 

 higher animals. As this principle depends on the greater 

 rapidity with which the male and female elements of the same 

 variety or species combine, as contrasted with the elements of 

 different varieties and species, we might call it isolation through 

 selective impregnation, just as Mr. Wallace has called the in- 

 stinctive segregation, " isolation through selective association." 

 Whatever names we give these two principles, they must be 

 important factors in divergent evolution. 



Segregation produces Domestic Races, why not Sj>ecies ? 



Mr. Wallace seems to be opposed to the idea that some form 

 of isolation is essential to divergence ; but in his argument he 

 yields so much that I cannot but think his opposition is largely 

 due to his misinterpreting the theory. Mr. Romanes has men- 

 tioned eight or ten forms of isolation ; and Mr. Wallace says 

 I have discussed thirty-eight forms ; but neither of us claim 

 that these are the only possible forms ; nor do we claim that 

 any form of this principle is essential to the transformation of 

 one species into another when the original one disappears in 

 the process. The phrase " new species " as used by Mr. 

 Wallace in the following passage is ambiguous ; but the second 

 sentence seems to indicate that he is here discussing diver- 

 gence as well as simple transformation. He says : " Most 

 writers consider the isolation of a portion of a species a very 

 important factor in the formation of new species, while others 

 maintain it to be absolutely essential. This latter view has 

 arisen from an exaggerated opinion as to the power of inter- 

 crossing to keep down any variety or incipient species and 

 merge it in the parent stock. But it is evident that this can 

 only occur with varieties that are not useful, or which, if 



