>«■ 



422 CONCLUDING REMARKS. Chap. XXVIII 



in the course of time become similarly modified. But a fer 

 commoner result would be, that one bird would vary in one 

 way and another bird in another way ; one would be born with 

 a little longer beak, and another with a shorter beak ; one would 



5 



some black feathe 



ed feathers 



And as these birds would be continually intercrossing, the final 



r 



would be a body of individuals differing from 



y ways, yet far more than did the original 



offspring would tend to revert to the state of the abori 

 rock-pigeon. In the course of time they would probably b 

 not much more heterogeneous in character than in our firs 





when birds of the same breed were confined 



<D 







pigeons. But there would not be the least tendency to the 

 formation of distinct breeds. 



If two separate lots of pigeons were to be treated in the 

 manner just described, one in England and the other in a 

 tropical country, the two lots being supplied with different food, 

 would they, after many generations had passed, differ ? When 

 we reflect on the cases given in the twenty-third chapter, and 

 on such facts as the difference in former times between the 

 breeds of cattle, sheep, &c, in almost every district of Europe, 

 we are strongly inclined to admit that the two lots would be 

 differently modified through the influence of climate and food. 

 But the evidence on the definite action of changed condi- 

 tions is in most cases insufficient ; and, with respect to pi 

 I have had the opportunity of examining a large collection of 

 domesticated birds, sent to me by Sir W. Elliot from India, 

 and they varied in a remarkably similar manner with our 

 European birds. 



If two distinct breeds were to be confined together in equal 

 numbers, there is reason to suspect that they would to a certain 

 extent prefer pairing with their own kind; but they would like- 

 wise intercross. From the greater vigour and fertility of the 

 crossed offspring, the whole body would by this means become 

 interblended sooner than would otherwise have occurred. From 

 certain breeds being prepotent over others, it does not follow 

 that the interblended progeny would be strictly intermediate 

 in character. I have, also, proved that the act of crossing in 

 itself gives a strong tendency to reversion, so that the crossed 



4 



