206 
HEY. J. T. GULTCK ON DIVERGENT EVOLUTION 
advantage depends. The advantage of divergence of character 
cannot he retained hg those that fail to retain the divergent charac- 
ter ; and divergent character cannot he retained hy those that are 
constantly crossing with other kinds ; and the prevention of free 
crossing between those that are equally successful is in no way 
secured hy Natural Selection. 
Natural Selection with G-reat Dieeerence in External 
Conditions not sueeicient to explain Divergent 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 
conditions. 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 selecting the animals that possess the 
desired qualities will have any effect in establishing a new breed, 
