236 



EEV. J. T. GULTCK ON DIYERGENT EVOLUTION 



vast and complex environment ; and the former is secured by the 

 advantage over rivals possessed by the variations that favour 

 crossing, and the latter by the better escape from the swamping 

 effect, and sometimes from the competition of certain rivals, 

 secured by the more segregative variations. We must there- 

 fore believe that, whenever in the history of an organism there 

 arise segregative variations which are able to secure sufficient 

 sustentation and propagation to continue the species, the segre- 

 gative quality of the forms thus endowed will be preserved and 

 accumulated through the self-accumulating effect of the segre- 

 gative endowmants. 



It is probable that in many of the higher vertebrates sexual 

 instincts tend to briug together those of somewhat divergent 

 character, but the difference preferred is wnthin very narrow 

 limits ; and beyond those limits, it may be said that the general 

 law for sexual attraction is, that it varies inversely as the dif- 

 ference in the characters of the races represented, if not inversely 

 as some power of such difference. The action of such a law 

 is necessarily segregative, whenever the divergence has, through 

 other causes, passed beyond the limit of higher attraction. Before 

 Sexual Segregation can arise, there must arise distinctive charac- 

 teristics by means of which the members of any section may 

 discriminate between those of their own and other sections. If 

 there are no constant characteristics, there can be no constant 

 aversion between members of different groups, no constant pre- 

 ference of those of one's own grouj). Prom this it follows, that 

 before Sexual Segregation can arise, some form of Segregation 

 that is not dependent on accumulated divergence of character 

 must have produced the divergence on which the Sexual Segre- 

 gation depends. Such forms are Local, Social, and some kinds of 

 Industrial Segregation. "When varieties have arisen through 

 these causes, it often happens that Sexual Segregation comes in 

 and perpetuates the Segregation which the initial causes can no 

 longer sustain. As long as the groups are held apart by diver- 

 gent sexual instincts, it is evident that divergent forms of Sexual 

 Selection are almost sure to arise, leading to a further accumu- 

 lation of the divergence initiated by the previous causes. 



If there is any persistent cause by which local and social 

 groups are broken up and promiscuously intermingled before 

 recognizable characters are gained, the entrance of Sexual Segre- 

 gation will be prevented. I therefore conclude that the chief 



