DIVERGENT EVOLUTION THROUGH SEGREGATION. 289 
process of gaining full adaptation 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 com- 
mand 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 domes- 
tic 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. Dar- 
win has not explained how disadvantageous sexual instincts can be 
formed; but, assuming that there are such instincts, he has shown that 
they would modify the species in a way that is disadvantageous. He 
believes the progenitors of man were deprived of their hairy coat by 
sexual selection that was, in its earlier stages, disadvantageous. 
It is therefore evident that the simple fact of divergence in any case 
is not a sufficient ground for assuming that the divergent form has an 
advantage over the type from which it diverges. We may however 
be sure that there is some cause or combination of causes that facili- 
tates the intergenerating of those similarly endowed, and hinders their 
crossing with other kinds; and if we can discover the cause of this 
segregate generation we shall have an explanation of one part of the 
process by which the forms thus endowed are becoming a distinct race. 
SEPARATION AND SEGREGATION WITH THE PRINCIPLE OF INTENSION. 
It will contribute to clearness in our discussion if we can gain definite 
conceptions of the conditions that are necessarily involved in separate 
and segregate breeding. 
Separate generation, which for convenience I call separation, implies: 
First. The indiscriminate separation of the members of a species into 
different sections that are prevented from freely crossing with each 
other. 
Second. The ager 
their being brought 
their freely crossing. 
Third. The integration of the members of each section into one inter- 
generating group, through the operation of functional adaptations by 
which the members of each section freely cross with each other. This 
analysis of the process shows that it may depend upon a great variety 
of causes, working together in a very complex way. We shall here- 
after find that the causes of separation may operate in such a way 
that no aggregation or propagation takes place among the members 
that are separated from the old stock; but in such cases there is no 
H. Mis. 334, pt. 1——19 
egation of the members of one section; that is, 
into conditions of time and place that allow of 
