THROUGH CUMULATIVE SEGREGATION - . 
213 
each other and from the type by their divergent adaptation to 
different kinds of resources, or by any other cause. The per- 
petuation of such variations depends not upon any advantage 
they possess above the type from which they diverge, but upon 
ability to appropriate from the environment sufficient simply to 
maintain existence, and the result is Polytypic Evolution. In 
other w r ords, of the freely crossing forms of any species it is 
only those that are most successful that are perpetuated ; while 
of forms that are neither competing nor crossing , every kind is 
perpetuated that is not fatally deficient in its adaptations. It 
follows that a form that under present conditions maintains 
only a precarious existence may, if kept from crossing, maintain 
its characteristics unimpaired for many generations, and at last, 
through changes in the environment, enter upon a period of 
great prosperity. Such w r ould be the case with a form de- 
pending upon resources at first scarce, and afterwards very 
abundant. 
Again, the individuals of a species that are brought together 
in their attempts to appropriate some new kind of resource, and 
are thus led to breed with each other, and not with the rest of 
the species, become a new Intergenerating Group iu which a new 
and divergent form of natural selection is established, depending 
on divergent adaptations in the orgauism, without any change in 
the environment. The gradual process of gaining full adapta- 
tion to the new resources may extend over many generations, 
and during this long period the divergent form may be at a great 
disadvantage as compared with the typical form ; but after this 
long process of divergence is completed, and full command of the 
new resource is gained, the new race may enter upon a period of 
great prosperity. In such a case, the period of most rapidly 
accumulating divergence is a period when the incipient race is 
suffering the heaviest disadvantage. The transformation from a 
wild to a domestic state affords a complete parallel to this process. 
In the initial and earlier stages, the divergent branch that is 
being domesticated is in constant danger of extermination ; and 
it is only when a good degree of adaptation to the new conditions 
has been gained that it can be said to be as prosperous as the 
wild stock from which it was derived. Darwin has not explained 
how r disadvantageous sexual instincts can be formed ; but, assum- 
ing that there are such instincts, he has shown that they would 
modify the species in a way that is disadvantageous. He believes 
