Inconsistencies of Utilitarianism. 137 



Why any need of distinctive Recognition Marhs for those 

 ivhose Ancestors had hut one set of Marks? 



An example of one of the effects of divergence being 

 treated as if it were the primary cause of divergence is found 

 on pages 217-228 and 284, where the need of distinctive 

 characters for easy recognition is given as the chief cause of 

 divergence in calls, odours, and colours. The importance of 

 distinctive characters by which the members of a species may 

 distinguish tlieir mates from those of other species cannot be 

 exaggerated ; but how does it liappen that the descendants of 

 one stock which had originally but one set of such cliaracters 

 have become segregated into groups, needing distinctive marks? 

 By confounding the problem of successive monotypic adapta- 

 tion with that of coexistent polytypic adaptation the real 

 causes of divergence have been obscured and misapprehended. 

 The diversity of Sexual and Social Selection, which Mr. 

 Wallace in these passages speaks of as natural selection, is 

 due to diversity of sexual and social instincts, which in their 

 turn have been produced by different forms of segregation. 

 For a fuller exposition of this subject I would refer to my 

 paper on " Divergent Evolution through Cumulative Segre- 

 gation " (Journ. Linn. Soc, Zoology, vol. xx. pp. 234-2H8). 

 The principles which I have called Sexual and Social Segre- 

 gation Mr. Wallace 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 segre- 

 gated, 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 obliterated. 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 ro/e 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 com- 

 bine, as contrasted with the elements of different varieties and 

 species, we might call it isolation through selective impreg- 

 nation, just as Mr. Wallace has called the instinctive segre- 

 gation " isolation through selective association." Whatever 

 names we give these two principles, they must be important 

 factors in diveroent evolution. 



