THE PRODUCTION OF DOMESTIC RACES. / 17 
selection,” in a very interesting chapter of his volume entitled ‘‘The 
Chances of Death and Other Studies in Evolution.” I fully agree 
with this author in the emphasis he puts on the importance of a care- 
ful statistical investigation of the subject; but I think the term he 
has chosen would naturally apply to sexual and impregnational selec- 
tion as well as to this form of selection which is dependent on degrees 
of fertility. If these are all to be called forms of selection, I would 
suggest that the special principle under consideration might be desig- 
nated fecundal selection, and its effect on the group might be called 
fecundal transformation. 
3. The Divergence of Races. 
In order to produce two or more divergent breeds from one breed, 
it is necessary, first, that the original stock should be divided into 
separate portions that are prevented from crossing (this is conven- 
iently called isolation) ; and, second, that there should be some cause 
transforming one or more of these separated portions. Now, the 
cause producing transformation in a separated portion may be the 
incapacity of a given small fragment of a race or species to perpetuate 
the original average character of that race or species; or, after sepa- 
ration, the portion may be subjected to some form of unbalanced 
selection. 
Returning, for illustration, to the 600 bison, we may suppose them 
to be indiscriminately divided into two isolated herds of 300 each, in 
which case the average character of each herd would probably be 
nearly the same as that of the other herd, and the descendants of the 
two herds, if not subjected to different kinds of selection, would prob- 
ably present no important differences, at least for many generations. 
If, however, the whole herd were broken up into pairs, the offspring 
of the pairs forming 300 isolated groups, each of which was never 
allowed to cross with any other group, we should probably find that 
perceptible divergences would soon present themselves in some of 
the groups, even if they were not subjected to unlike selection. 
Another form of isolation, still more effective in producing diver- 
gence, would be gained if the individuals presenting the highest de- 
gree of some special kind of variation were brought together in one 
group that was prevented from crossing with the others. The 
division of organisms which have descended from one original inter- 
generating group into two or more groups that do not possess the 
same average character, and that lack either the capacity, inclination, 
or opportunity for intergenerating, I call segregation. Whenever 
there is a closer resemblance between the members of an intergenerat- 
