Inconsistencies of Utilitarianism . 
137 
Why any need of distinctive Recognition Marks for those 
whose 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 their mates from those of other species cannot be 
exaggerated ; but how does it happen that the descendants of 
one stock which had originally but one set of such characters 
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 u Divergent Evolution through Cumulative Segre- 
gation ” (Journ. Linn. Soc., Zoology, vol. xx. pp. 234-238). 
The principles which I have called Sexual and Social Segre- 
gation Mr. Wallace lias mentioned in several places under the 
name u selective association ” or u 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 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 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 u isolation through selective association.” Whatever 
names we give these two principles, they must be important 
factors in divergent evolution. 
