172 APPENDIX I—DIVERGENT EVOLUTION. 
supplemental to the laws of segregation already discussed, simply 
reinforcing by artificiai barriers the segregations that have their orig- 
inal basis in nature. ‘The chief forms to be enumerated are national, 
linguistic, caste, penal, sanitary, and educational segregation.* 
CONCLUDING REMARKS. 
1. Impregnational Segregation a Cause of Divergence in both its Earlier 
and Later Stages. 
The negative forms of segregation would tend to produce extinc- 
tion if they were not associated with the positive forms of segregation. 
But in the case of organisms whose fertilizing elements are dis- 
tributed by wind and water, the qualities that produce these nega- 
tive forms of segregation are usually accompanied by those that 
produce potential segregation, and potential segregation coéperating 
with this free distribution results in positive segregation. But even 
prepotential segregation, when produced by mutual incompatibility 
between a few individuals and a numerous parent stock, depends for 
its continuance and development on some degree of local, germinal, 
or floral segregation, partially securing the intergeneration of the few 
that are mutually compatible. On the one hand, impregnational 
segregation depends on some degree of local, germinal, or floral segre- 
gation which is a constant feature in most species; and, on the other 
hand, not only do these initial forms of positive segregation fail of 
producing any permanent divergence till associated with impreg- 
national segregation, but the more effective forms of positive segrega- 
tion, such as industrial, chronal, fertilizational, sexual, and social 
segregation, often depend on impregnational segregation, inasmuch 
as the divergence of endowments which produces these depends on 
impregnational segregation. Moreover, in all such cases, increasing 
degrees of diversity in the forms of adaptation, and consequently of 
diversity in the forms of natural selection, must also depend upon 
these negative factors, which in their turn depend on the weak, initial 
forms of positive segregation. 
Divergent evolution always depends on some degree of positive 
segregation, but not always on negative segregation. Under positive 

* This completes the classification of the forms of isolation which are here pre- 
sented as forms of demarcational segregation. It is probably correct to say that 
with the exception of transportational and geological isolation, and perhaps some 
cases of migrational isolation, all the forms of isolation so far discovered are, from 
the first, more or less discriminative, and, therefore, segregative. Moreover, if 
transportational or geological action plants an isolated colony of only a few indi- 
viduals, the average type of the original stock is not fully represented in the colony 
and, therefore, the effect is more or less segregative from the beginning. 
