420 STERILITY OP HYBRIDS. 



extinction. This death and extinction may be es- 

 caped, by doing what? — by crossing the varieties ! 

 which is, joining the characters of different varieties, 

 in an individual, the mongrel. This mongrel is fertile 

 and constitutionally vigorous, because it is not diver- 

 gent, — because it has more of the characters of its 

 species, than have the divergent individuals. 



Very great structural differences may mark the varie- 

 ties of a species. The characters of such species may 

 be variedly modified, reduced, suppressed, retained in 

 every stage of degeneration, or every stage of rever- 

 sion, and apportioned among the different varieties, so 

 as to make those varieties most widely divergent and 

 more distinct in character, than are many species, or 

 than are some genera. But, these diversities can sub- 

 sist, within a species, only by impairing a physiologi- 

 cal bond which normally ties together all the positive 

 characters of the species. The further, therefore, any 

 apportionment, or division, of the characters, among 

 different varieties, is carried, the worse impaired be- 

 comes such bond ; the weaker, and less fertile, grow 

 the individuals of the divergent varieties ; until, at last, , 

 that degree of impairment of the bond, is reached, 

 which is incompatible with the function of the repro- 

 ductive element, and with even the existence of the 

 individual. 



How, then, is it possible, for varieties to diverge into 

 distinct species, when Darwin's own facts show demon- 

 stratively, that the only redemption possible, from 

 death and sterility, is in returning to the full and pro- 

 portionate development of all the characters of the 



