?2 DARWINIANA. 



Some suppose that races cannot be perpetuated 

 indefinitely even by keeping up the conditions under 

 which they were fixed j but the high antiquity of 

 several, and the actual fixity of many of them, nega- 

 tive this assumption. " To assert that we could not 

 breed our cart and race horses, long and short horned 

 cattle, and poultry of various breeds, for almost an 

 infinite number of generations, would be opposed to 

 all experience." 



Why varieties develop so readily and deviate so 

 widely under domestication, while they are apparently 

 so rare or so transient in free Nature, may easily be 

 shown. In Nature, even with hermaphrodite plants, 

 there is a vast amount of cross-fertilization among 

 various individuals of the same species. The inevi- 

 table result of this (as was long ago explained in this 

 Journal ') is to repress variation, to keep the mass of 

 a species comparatively homogeneous over any area 

 in which it abounds in individuals. Starting from a 

 suggestion of the late Mr. Knight, now so familiar, 

 that close interbreeding diminishes vigor and fertili- 

 ty ; " and perceiving that bisexuality is ever aimed at 

 in Nature being attained physiologically in numer- 

 ous cases where it is not structurally Mr. Darwin 

 has worked out the subject in detail, and shown how 

 general is the concurrence, either habitual or occasional, 

 of two hermaphrodite individuals in the reproduction 

 of their -kind; and has drawn the philosophical infcr- 



i Volume xvii. (2), 1854, p. 13. 



1 We suspect that this is not an ultimate fact, but a natural conse- 

 quence of inheritance the inheritance of disease or of tendency to dis- 

 ease, which close interbreeding perpetuates and accumulates, but wide 

 breeding may neutralize or eliminate. 



