DIVERGENT EVOLUTION THROUGH SEGREGATION. 287 
ing and those without hearing have been separated into two communi- 
ties, the members of each having but little opportunity for acquaintance 
beyond the limits of that community, each community having separate 
schools, separate newspapers, and to some extent a separate language. 
As the result of this segregation marriages between the two classes 
have been greatly diminished; and little by little two races are arising, 
the hearing race and the deaf race.* 
REASONS OF A GENERAL CHARACTER FOR CONSIDERING SELECTION 
WITHOUT INDEPENDENT GENERATION AN UNSATISFACTORY EX- 
PLANATION OF DIVERGENT EVOLUTION. 
1. The divergence is often confined to characters which seem to have 
no possible relations of adaptation either to the environment or to 
other members of the species, and, therefore, to be independent of both 
natural and reflexive selection. 
2. Divergence relating to adaptive characters successfully propa- 
gated involves different kinds rather than different degrees of adapta- 
tion and advantage; and, as adaptational selection depends on the 
difference of degrees of advantage, it can not account for the diver- 
gence of forms possessing equal degrees of advantage. 
3. In the very nature of its action we see that adaptational selection 
unaccompanied by independent generation must produce essentially 
monotypic transformation. 
4. In artificial breeding, independent generation is found to be an 
essential condition for the production of divergent races; and there is 
no reason to doubt that the same law holds good in the divergence of 
natural forms. 
+. The general fact that species possessing high powers and large 
opportunities for migration occupy large areas, while those possessing 
low powers and small opportunities for migration divide the same area, 
or an area no larger, between many representative species, shows that 
independent generation 1s an important element in their divergence. 
CHAPTER IT. 
CUMULATIVE DIVERGENCE THROUGH CUMULATIVE SEGREGATION 
Local separation in dissimilar environments is the only cause of 
segregation that has been clearly pointed out by Darwin. I shall 
however endeavor to show that there are other causes producing 
segregation, and that, without any change of environment or change 
in the environment, they may produce all the phenomena of divergent 
*See paper by Alexander Graham Bell, read before the National Academy of 
Sciences, November 13, 1883, upon the ‘‘ Formation of a Deaf Variety of the Human 
Race;” also a review of the same in The Popular Science Monthly, vol. Xxvu, p. 15, 
entitled ‘“‘Can Man be Modified by Selection?” 
