206 EEV. J. T. GULTCK ON DIYERGENT EYOLUTION 



advantage depends. The advantage of divergence of character 

 cannot he retained hy those that fail to retain the divergent charac- 

 ter ; a7id divergent character cannot he retained hy those that are 

 constantly crossing with other hinds ; and the prevention of free 

 crossing hetween those that are eg^ually successful is in no way 

 secured hy Natural Selection. 



Natural Selection with Gtreat Difference in External 

 Conditions not sufficient to explain Diyergent Evolution. 



The insufficiency of Natural Selection without Segeneration 

 to account for divergent evolution in an area where the external 

 conditions are nearly uniform may be admitted by some who 

 will claim that the case is quite otherwise when a species ranges 

 freely over an area in which it is subjected to strongly contrasted 

 coiiditions. It may be claimed that Diversity of Natural Selection 

 resulting from a great difference in external nature is sufficient 

 to account for divergent evolution without any Segeneration. 



In the discussion of this subject, important light can be gained 

 by referring to the experience of the breeder. This experience, 

 in as far as it relates to the subject of Separation in the 

 production of divergent breeds, may be arranged under three 

 heads. 1st. Diversity of Selection without Separation. 2nd. 

 Separation without Diversity of Selection. 3rd. Separation more 

 or less complete with Diversity of Selection. 



As the full discussion of these points is impossible here, and as 

 there is probably but little difference of opinion in regard to what 

 the results would be, I shall content myself with a simple state- 

 ment of what I believe the experience of breeders shows. Dif- 

 ference in the standards of Selection without Separation can 

 avail nothing in creating divergence of types ; while Separation 

 without difference in the standards of Selection will avail some- 

 thing, though food and external conditions are kept the same ; 

 but to secure the greatest divergence, in a given time, there must 

 be both Diversity of Selection and complete Separation. In the 

 case of Separation without Diversity of Selection there is room 

 for difference of opinion ; for the examples that some would claim 

 as proving that there is often divergence without Diversity of 

 Selection and without difference in external conditions may be 

 attributed by others to unconscious Selection. It is granted by 

 everyone that no skill in selectiug the animals that possess the 

 desired qualities will have any effect in establishing a new breed, 



