164 Elliot on Hybridism. [April 



to accomplish similar results in their offspring. It is, of course, 

 next to impossible to prove this fact among wild animals, but 

 the fact that a strain of hybrids occupying a district to the ex- 

 clusion of their parent stock, save in one or two very excep- 

 tional instances, has not been observed in a state of nature, 

 would seem to be the best possible proof that a cause does exist 

 which prevents complete hybrids from continuing to exist, and 

 that they either die out from inability to reproduce, or else are 

 swallowed up and extinguished through the interbreeding of 

 incomplete hybrids and pure-blooded races, the influences ex- 

 erted by the latter proving too powerful for the mixed races to 

 overcome. In this fact lies the possibility, and the only one 

 w^here two pure-blooded races are liable to cross, of the con- 

 tinuity of distinct species. 



In this connection it may be suggested by some believer in 

 complete hybrid fertility, that these individuals are the progeni- 

 tors of new species, evolving new characters out of the mixed 

 ones derived from their original sources. I do not think that 

 there is any recorded evidence permitting the belief that such a 

 view is anywise tenable. 



Sterility in hybrids is caused by the disturbance in the repro- 

 ductive organs arising from the union of two distinct forms, thus 

 rendering them inopei'ative ; or the continuance of the race is 

 prevented by the early death of the embryo. (vSee Darwin, Ori- 

 gin of Species, 3d ed. p. 2S6.) 



The principle of reversion also acts as a check to the continua- 

 tion of hybrid and mongrel strains. Thus domesticated pigeons 

 constantly show a tendency to revert to their parent stock, Co- 

 lumba livia^ and fowls in the same way, to their original source, 

 G alius f err ugineus. Darwin relates an instance ('Animals 

 and Plants under Domestication', 1S68, Vol. I, p. 242) where 

 he crossed a black Spanish cock with a white silk hen, and one 

 of the progeny, a cock, closely resembled the wild G. ferr7igin- 

 eus. This was the more extraordinary as the black Spanish 

 has been long known to breed true, and the silk hen, being of 

 most ancient extraction, having been known previous to the year 

 1600, also breeds true. If left entirely to themselves, without 

 the possibility of receiving any fresh blood, it is presumable that 

 in course of time these hybrid and mongrel strains would breed 

 back to their original stock, by means of this inherited tendency 

 to reversion. 



