DIFFERENCE IN USE AND USEFUL DIFFERENCE. 259 



nance and propagation of those better adapted to maintain life under 

 the conditions surrounding the species? 



3. Divergence through Reflexive Selection often Non-advantageous. 



I maintain that this reflexive segregation through the sexual and 

 social instincts of the divergent sections of the species is the first in a 

 series of divergent characters which may become a great advantage to 

 both sections of the species by enabling them to become adapted to 

 different kinds of resources, requiring incompatible adaptations ; but 

 it can not be claimed that the usefulness to which this segregative 

 character may attain in the future, or may have already attained, was 

 the cause of the divergence which was steadily perpetuated, being in- 

 tensified by sexual and social selection, and so completed while as yet 

 this character was of no service to the species. The segregative char- 

 acter is preserved by its segregativeness, though at the lime it arises, and jor 

 many subsequent generations, it may not be of any advantage to its pos- 

 sessors. .In most such cases, I believe, the initial divergence is gained 

 by a local variety in some measure protected by local segregation ; 

 but having gained a character which secures segregation, even when 

 commingled with the other section of the original species, it is no longer 

 liable to be swamped by crossing. It seems to me that such cases are 

 examples of divergence, produced by segregate breeding, brought 

 about by sexual and social segregation, reinforced and strengthened 

 by sexual and social selection, and not by diversity in the action of 

 natural selection. 



4. Different Methods oi Using the Same Resources not Necessarily Advantageous. 



Another fundamental distinction which needs to be kept in mind is 

 that diversity in the action of environal selection on segregated sec- 

 tions of a species may be due to three classes of causes, which are the 

 real causes of the divergence, which results in the production of dif- 

 ferent species. 



(1) Different life-supporting and life-endangering conditions exist- 

 ing in the different districts in which the different sections of the spe- 

 cies are distributed. 



(2) Different hiethods of using resources and escaping dangers 

 adopted by the different sections, though occupying the same district. 



(3) Different methods of using resources and escaping dangers 

 adopted by the different sections of the species occupying isolated 

 districts, whose resources and dangers are alike. 



If the members of the original species are brought under the influence 

 of the first class of causes, the divergence is due to diversity in the en- 

 vironments to which migration introduces them ; if under the second 



