THROUGH CUMULATIVE SEGREGATION. 



211 



races, one with good powers of hearing and the other with an 

 increasing liability to deafness. To secure such divergence it is 

 necessary that segregative influences should be introduced, such 

 as have been most amply furnished by the modern system of 

 education for the deaf. Under these influences those endowed 

 with hearing and those without hearing have been separated into 

 two communities, the members of each having but little oppor- 

 tunity 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.* 



Eeasons or A General Character for considering Selection 

 WITHOUT Independent Generation an Unsatisfactory 

 Explanation of Divergent Evolution. 



1. The divergence is often confined to characters which seem 

 to have no possible relations of adaptation either to the environ- 

 ment or to other members of the species, and, therefore, to be 

 independent of botb Natural and Eeflexive Selection. 



2. Divergence relating to adaptive characters successfully 

 propagated involves different kinds rather than different degrees 

 of adaptation and advantage ; and, as Adaptational Selection de- 

 pends on the difference of degrees of advantage, it cannot account 

 for the divergence of forms possessing equal degrees of ad- 

 vantage. 



3. In the very nature of its action, we see that Adaptational 

 Selection unaccompanied by Independent Generation must pro- 

 duce 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. 



5. The general fact that species possessing high powers and 

 large opportunities for migration occupy large areas, while those 



* 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. xxvii. p. 15, entitled " Can Man be Modified by Selection ? " 



