THE PRODUCTION OF DOMESTIC RACES. 15 



Neither change la 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 



