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 ina 
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- 
acteris preserved by vts segregativeness, though at the time tt arises, and for 
many subsequent generations, 7t 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 of 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 methods 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 
