1892.1 Elliot on Hybridism. 1 6 "2 



blood, may also be fertile ; and these incomplete hybrids may 

 thus transmit the characters of the separate stocks to which they 

 owe their existence, through numerous generations, and spi^ead 

 over a wide extent of country, but it is the constant infusion of 

 fresh blood that makes this fact possible, and not the ability of 

 complete hybrids to produce offspring indefinitely, breeding 

 inter se. Without the accession of pure blood constantly in- 

 troduced into the hybrid stock, there appears to be no recorded 

 evidence of the continued fertility of complete hybrids. Under 

 this hypothesis an explanation is obtained of the occurrence of 

 Cola pies hybridns. already mentioned, over an extent of coun- 

 try about one thousand miles in length with a varying width of 

 from three to five hundred miles. (See Allen, Bull. Amer. 

 Mus. Nat. Hist. IV, pp. 39-33.) The two species dwelling on 

 either side of this tract encroach probably upon it to a certain 

 degree, breeding with the incomplete hybrids within the bor- 

 ders, thus introducing a constant stream of fresh blood, and these 

 incomplete hybrids breeding again, if even only through their 

 first generation, would easily produce the almost limitless diver- 

 sity of characters pertaining originally to the pure-blooded 

 C auratus and C. cafer which are met with throughout the 

 district in which these crosses are mainly dispersed. 



It has been urged as a proof of the unlimited fertility of 

 hybrids, at all events among mammals, that the wild bison 

 {Bison americanus) can be crossed with domestic cattle, and 

 that their progeny is fertile. This, however, cannot be con- 

 sidered a proper criterion for the reason that domestic cattle are 

 artificial breeds that either have never been wild, or, if the 

 present generations of any of them can be traced back to a 

 wild ancestor, it is only through such a lapse of time that their 

 descendants are practically, if not completely, domesticated ani- 

 mals, and therefore through artificial selection have acquired 

 the power of fertility. Their offspring are mongrels, i. e. off- 

 spring of varieties, not hybrids, which are offspring of species. 

 The influences of domestication have dominated and super- 

 seded those pertaining to the animals in a state of nature, and 

 it is hazardous to argue that, because wild animals crossed with 

 those in captivity can produce offspring that are fertile and 

 which transmit their power of fertility to their descendants in- 

 definitely, two wild animals in a state of nature would be able 



