26 DOMESTIC PIGEONS. Chap. I. 



that each breed, even the purest, has within a dozen or, 

 at most, within a score of generations, been crossed by 

 the rock-pigeon : I say within a dozen or twenty genera- 

 tions, for we know of no fact countenancing the belief 

 that the child ever reverts to some one ancestor, removed 

 by a greater number of generations. In a breed which 

 has been crossed only once with some distinct breed, the 

 tendency to reversion to any character derived from such 

 cross will naturally become less and less, as in each suc- 

 ceeding generation there will be less of the foreign blood ; 

 but when there has been no cross with a distinct breed, 

 and there is a tendency in both parents to revert to a 

 character, which has been lost during some former gene- 

 ration, this tendency, for all that we can see to the 

 contrary, may be transmitted undiminished for an indefi- 

 nite number of generations. These two distinct cases are 

 often confounded in treatises on inheritance. 



Lastly, the hybrids or mongrels from between all the 

 domestic breeds of pigeons are perfectly fertile. I can 

 state tins from my own observations, purposely made 

 on the most distinct breeds. Now, it is difficult, per- 

 haps impossible, to bring forward one case of the hybrid 

 offspring of two animals clearly distinct being themselves 

 perfectly fertile. Some authors believe that long-con- 

 tinued domestication eliminates this strong tendency to 

 sterility : from the history of the dog I think there is 

 some probability in this hypothesis, if applied to species 

 closely related together, though it is unsupported by a 

 single experiment. But to extend the hypothesis so 

 far as to suppose that species, aboriginally as distinct 

 as earners, tumblers, pouters, and fantails now are, 

 should yield offspring perfectly fertile, inter se, seems to 

 me rash in the extreme. 



From these several reasons, namely, the improbability 

 of man having formerly got seven or eight supposed 



