1 8 BIONOMIC LAWS. 



ing group than between them and the members of some other group 

 with which free crossing has been interrupted, there segregate breed- 

 ing or segregation exists. If it were possible to divide the 600 bison 

 into two completely equivalent groups, the isolation of these two 

 groups would not involve segregation ; but the indiscriminate division 

 of any intergenerating group into two or more isolated groups 

 usually involves more or less difference in the groups, and, therefore, 

 more or less segregation. 



If we carefully consider the process by which the different domestic 

 races of any species have been produced, we shall find that the isola- 

 tion of each race from every other race has, in every case, been a 

 prime factor. Until modern times the hostility of different tribes of 

 men and the want of free commerce between nations have secured the 

 isolated breeding of the domestic races under the care of different 

 tribes and peoples. Now, according to the principle I have just 

 pointed out, the initial differences between those portions make them 

 more or less segregated groups whenever free crossing between the 

 portions is cut off. But this initial segregation is soon intensified by 

 the transforming influences to which the different portions are sub- 

 jected. As each portion is subjected to the care of a separate tribe 

 of men who preserve such individuals of the offspring as best suit 

 their purposes or fancies, and as the individuals thus preserved sel- 

 dom represent the average form of the wild species, transformation 

 is soon produced. Each isolated group, if it survives under its new 

 conditions, must produce forms increasingly adapted to meet the 

 desires of those who care for them ; and even when those on whom they 

 depend have no idea of developing new characteristics by selection, 

 unconscious selection usually takes place. If the selected form is not 

 the average form, transformation necessarily follows. But as we are 

 now considering the process by which divergent evolution has been 

 produced in domestic races, the important point is, not that trans- 

 formation is usually produced by domestication, but that, when this 

 cause of transformation modifies continuously isolated portions of 

 the same species, the result is always divergent and not parallel. Ac- 

 count for it as we may, when a domestic breed has been transformed 

 during isolation, the transformed portions are always found to be 

 more or less unlike ; and this is so even when the physical conditions 

 are the same, and when the persons on whom the selection has devolved 

 are representatives of the same race. 



I think it will be found that independent transformation (that is, 

 transformation during isolation), is always divergent and never com- 

 pletely parallel ; and I believe this to be so whether the transf orma- 



