THROUGH CUMULATIVE SEGREGATION. 



207 



unless the selected animals are prevented from breeding with 

 others that are deficient in the desired qualities. We further 

 find that while Separation is an absolutely essential condition for 

 this divergence, Diversity of Selection is not so essential. This 

 is illustrated in the case of the slightly different types that 

 are presented by the wild cattle found in the diff*erent parks of 

 England,* a phenomenon which can hardly be attributed to any 

 diversity in the environment. 



In artificial breeding universal experience teaches that Varia- 

 tion and Selection, without Separation, do not produce diver- 

 gence of races. The separate breeding of diff'erent classes 

 of variation is a necessary condition for the accumulation of 

 divergent variation; and wherever the separate breeding of 

 diff'erent classes of variation is secured, there divergence of 

 character is the result. In other words, Segregate Breeding is 

 necessary to divergent evolution in gamogenetic animals, t 

 Moreover, we have every reason to believe that the same law 

 holds good throughout the whole organic world. The generating 

 together of similars, with the exclusion or separation of dissimi- 

 lars, is the central necessity in all evolution by descent, whether 

 monotypic or polytypic ; and ivhatever causes the separate genera- 

 tion of different classes of variation ivill be the cause of divergent 

 evolution. That is, wherever this condition is added to the per- 

 manent laws of organic life, there divergence will follow. As 

 we have already seen. Natural Selection or the Survival of the 

 Fittest necessarily separates between the survivors and the non- 

 survivors, between the best fitted and the least fitted, and is, 

 therefore, the cause of monotypic transformation ; but it cannot 

 be the cause of separation between the dilFerent families of those 

 that survive, and, therefore, cannot be the cause of divergence 

 of character between these families. But we find that divergence 

 of character often arises between the branches of one stock, 

 and in many cases this divergence increases till well-marked 

 varieties are established. If, therefore, the general principle we 

 have just stated is true, there must be certain causes producing the 



* See Darwin's ' Variation under Domestication,' chapter xv. 2nd page. 



t In a subsequent paper I shall show how it is that Separate Breeding, long 

 continued, inevitably ends in Segregate Breeding. In this chapter I confine my 

 attention more especially to Separate Breeding when combined with Diversity 

 of Selection in the different sections, for it is evident that this will produce 

 Segregate Breeding. 



17* 



