THEOTJan CITMIJLATIVE SEGBEGATION. 



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Selection of evert kind instifpicient to account for 

 Divergent Evolution. 



Thougli 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. Eeflexive 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 iu 

 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 Heflexive 

 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 diff'erent and 

 divergent forms of Sexual Selection ; and is there any reason to 

 attribute this diff'erence in their tastes to the fact that, when 

 there was but one group and the tastes of all were conformed to 

 u single standard, some of the competitors failed of propagating, 

 through being crowded aside by those more successful F If the 



