DIVERGENT EVOLUTION THROUGH SEGREGATION. 39D 
enforcing by artificial barriers the segregations that have their original 
basis in nature. The chief forms that should be enumerated are na- 
tional, linguistic, caste, penal, sanitary, and educational segregation; 
and if we had not already considered industrial segregation in the pre- 
vious chapter, that might be added. 
CONCLUDING REMARKS. 
Besides artificial and institutional segregation, which depend on the 
rational purpose of man, we have now considered numerous forms of 
segregation, resting on no less than 18 groups of purely natural causes. 
Owing to the length of this paper I deem it wise to bring it to a close 
without discussing the laws that co-operate in intensifying the effects 
directly produced by the segregative causes already considered. AsI 
have shown in Chapter II, segregation is not simply the independent 
generation of the different sections of a species, but the independent 
generation of sections that differ; and though no one will believe that 
any two sections of a species are ever exactly equivalent, it is evident 
that the degrees of difference may be greater or less, and that what- 
ever causes a greater difference in two sections that are prevented from 
intergenerating will also be a cause of increased segregation. 
It has been observed that some of the causes enumereted in this and 
the previous chapter are primarily separative, and that no one of those 
that are primarily segregative is at any one time segregative in regard 
to many classes of characters. As several forms of segregation may 
co-operate in securing a given division of a species and one form is 
super-imposed upon another the aggregate effect must be incalculably 
great; but we easily perceive that it may be indefinitely enhanced by 
causes producing increased divergence in the segregated branches. 
The causes which produce monotypic evolution when associated with 
inter-generation must be equally effective in producing polytipic evolu- 
tion when associated with se-generation, whether in its separative or 
segregative forms. But the discussion of intensive segregation must 
be reserved for another occasion. 
Believing that the study of cumulative segregation in its relations to 
the other factors of evolution will throw light on the origin of species 
far beyond what I have been able to elicit, I trust the subject will 
secure the attention of those who enjoy better opportunities than I do 
for carrying forward such investigations. 
