Chap. I. DOMESTIC PIGEONS. 37 



tlicy produced a bird of as beautiful a bhie color, with the 

 white loius, double black Aviiif^-bar, and barred and Avliite- 

 ed^cd tail-feathers, as any wild rock-pi2;'eon ! We can under- 

 stand these facts, on the well-known principle of reversion to 

 ancestral characters, if all the domestic breeds are descended 

 from the rock-])igeoii. ]}ut if we deny this, we must make 

 one of the two following; highly improbable suppositions : 

 cither, first, that all the several imagined aboriginal stocks 

 were colored and marked like the rock-pigeon, although no 

 other existing species is thus colored and marked, so that in 

 each separate breed there might be a tendency to revert to 

 the very same colors and markings ; or, secondly, that each 

 breed, even the purest, has within a dozen, or at most with- 

 in a score, of generations, been crossed by the rock-pigeon : 

 I say within a dozen or twenty generations, for no instance 

 is known of crossed descendants reverting to an ancestor 

 of foreign' blood, removed by a greater nmnbcr of genera- 

 tions. In a breed which has been crossed only once, the 

 tendency to revert to any character derived from such a cross 

 will naturall}'^ become less and less, as in each succeeding 

 generation there will be less of the foreign blood ; but when 

 there has been no cross, and there is a tendency in the breed 

 to revert to a character which was lost during some former 

 generation, this tendency, for all that we can see to the contrary, 

 may be transmitted imdiminishcd for an indefinite nunil)er of 

 generations. These two distinct cases of reversion are often 

 confounded together by those who have Avritten on inheritance. 



Lastly, the hybrids or mongrels from between all the 

 domestic breeds of pigeons are perfectly fertile. I can state 

 this from my own oljservationR, purposely made, on the most 

 distinct breeds. Now, it is diflicult, perhaps impossible, to 

 bring forward one case of the hybrid offspring of two animals 

 clenrbj distbict being themselves perfectly fertile. Some 

 authors believe that long-continu(?d domestication eliminates 

 this strong tendency to sterilily: from the histor}' of tlie dog, 

 and of some other domestic animals, there is great probability 

 in this hypothesis, if applied to species closely related to each 

 other, thougli it is imsupported by a single experiment. But 

 A.O extend the h^11otIlesis so far as to suppose that sjx'cies, 

 aboriginally as distinct as carriers, tumblers, pouters, and fan- 

 tails now are, should yield offspring perfectly fertile inter se^ 

 seems to me rash in the extreme. 



From these several reasons, namely, the improbability of 



