THE PRODUCTION OF DOMESTIC RACES. Tey 
Neither change 14 the relative numbers in which we choose to raise 
two species, nor diversity of success in raising those that are equally 
. desired, can be the cause of transformation of species, as long as the 
proportions in the variations of the intergenerating forms of each 
species remain unchanged. Diminution and extinction on the one 
hand, or increase and unprecedented multiplication on the other, 
are alike without effect in changing the character of a race, or a 
species, as long as the proportionate propagation of the different inter- 
generating forms or variations that constitute the race or species 
remains unchanged. 
In other words, the selection that produces transformation is not 
the selection of one segregated race or species to the exclusion of 
another, but the selection, from the offspring of one intergenerating 
race, of certain forms that do not represent the average character of the 
race, and giving to them either exaggerated or exclusive opportunity 
to propagate the race. Failure to recognize this distinction has been 
a source of confusion in the reasoning of certain writers on evolution. 
Briefly stated, the process on which breeders chiefly rely for trans- 
forming a domestic race, without dividing it into divergent races, is 
unbalanced propagation through exclusive breeding from individ- 
uals whose average endowment, in some chosen character, is above 
the average endowment of the whole race. This is often secured by 
destroying the least acceptable individuals before they propagate. 
Of the American bison there are supposed to be about 600 surviving 
individuals. If these were all brought together in one park, and if 
in each successive generation all those that ranked above the average 
of their generation in length of horns were slaughtered before they 
came to maturity, there can be no doubt that after many generations 
the whole species would be transformed into one possessing shorter 
horns than those that now characterize the species. 
This process would be one method of securing what is usually 
called selection in the breeding of animals; and selection is regarded 
as the chief means by which the different races of domestic animals 
have been produced. It should, however, be noted that the success 
of this process of transforming the species depends on certain condi- 
tions that are not secured by the process of selecting. It is neces- 
sary that there should be in each generation such a difference in the 
length of the horns that it is possible to tell with certainty which are 
above and which below the average. Again, there must be such a 
degree of fertility and such success in attaining maturity that there 
shall be a considerable surplus of individuals of both sexes that may 
be slaughtered without gradually exterminating the race. Again, it 
