DIVERGENT EVOLUTION THROUGH SEGREGATION. 307 
segregative variations. We must therefore 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 segregative quality of the forms thus endowed will be 
preserved and accumulated through the self-accumulating effect of the 
segregative endowments. 
It is probable that in many of the higher vertebrates sexual instincts 
tend to bring together those of somewhat divergent character, but the 
difference preferred is within 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 difference in the characters of the races rep- 
resented, 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 meansof which the members of any section may discriminate 
between those of their own and other sections. If there are no con- 
stant characteristics there can be no constant aversion between members 
of different groups, no constant preference of those of one’s own group. 
From 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 
segregation 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 perpetu- 
ates the segregation which the initial causes can no longer sustain. 
As long as the groups are held apart by divergent sexual instincts, it 
is evident that divergent forms of sexual selection are almost sure to 
arise, leading to a further accumulation 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 charae- 
ters are gained, the entrance of sexual segregation will be prevented. 
I therefore conclude that the chief influence of this latter factor is 
found in its prolonging and fortifying the separate breeding of varie- 
ties that have arisen under local, social, or industrial segregation, and 
in thus continuing the necessary condition for the development of 
increasingly divergent forms of intensive segregation, under which the 
organism passes by the laws of its own vital activity when dealing with 
a complex environment in groups that never cross. 
12. Germinal segregation is caused by the propagation of the species 
by means of seeds or germs any one of which, when developed, forms 
a community so related that the members breed with each other more 
frequently than with the members of other communities. If the con- 
stitution of any species is such that the ovules produced from one seed 
are more likely to be reached and fertilized by pollen produced from 
