THROUGH CUMULATIVE SEGREGATION. 
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Selection of evert kind insufficient to account for 
Divergent Evolution. 
Though I have no reason to doubt the importance of Sexual 
Selection in promoting the transformation of many species, I 
think I can show that unless combined with some separative or 
segregative influence, that prevents free intercrossing, it can 
avail nothing in producing a diversity of races from one stock. 
In the nature of its action Sexual Selection is simply exclusive. 
It is the exclusive breeding of those better fitted to the sexual 
instincts of the species, resulting from the failure to breed of the 
less fitted. It therefore indicates a method of separation between 
the better fitted and the less fitted ; but it gives no explanation 
of separation between those that are equally successful in pro- 
pagating. 
I maintain that in a great number of animal species there are 
sexual and social instincts that prevent the free crossing of 
clearly marked races ; but as these segregative instincts are 
rarely the cause of failure to propagate, and since when they are 
the cause of failure the failure is as likely to fall on one kind as 
on another, I conclude that the Segregate Breeding resulting 
from these instincts cannot be classed as either Sexual or Social 
Selection. Beflexive Selection in all its forms is, like Natural 
Selection, the result of success and failure in vital processes 
through which the successful propagate without crossing with 
the unsuccessful ; but it in no way secures the breeding in 
separate groups of those that are successful in propagating. The 
exclusion of certain competitors from breeding is a very different 
process from the separation of the successful competitors into 
different groups that are prevented from intercrossing, and 
whose competition even is often limited to the members of the 
same group. Sexual Selection, like other forms of Beflexive 
Selection, can extend only as far as members of the same species 
act on each other. If the individuals of two groups have 
through difference in their tastes ceased to compete with each 
other in seeking mates, they are already subject to different and 
divergent forms of Sexual Selection ; and is there any reason to 
attribute this difference in their tastes to the fact that, when 
there was but one group and the tastes of all were conformed to 
a single standard, some of the competitors failed of propagating, 
through being crowded aside by those more successful? If the 
