50 THE ORIGIN OF SPECIES 



o; species, as he would call tlioin, cculd be shouD 

 hiiu. 



Great as are the differences between the breeds of the 

 pigeon, I am full}'^ convinced that the common opinion of 

 naturalists is correct; namely, that all are descended from 

 the rock-pigeon (Oolumba livia), including under this 

 term several geographical races or sub-species, which 

 differ from each other in the most trifling respects. As 

 several of the reasons which have led me to this belief 

 are in some degree applicable in other cases, I will here 

 briefly give them. If the several breeds are not varieties, 

 and have not proceeded from the rock-pigeon, they must 

 have descended from at least seven or eight aboriginal 

 stocks; for it is impossible to make the present domestic 

 breeds by the crossing of any lesser number: how, for 

 instance, could a pouter be produced by crossing two 

 breeds unless one of the parent-stocks possessed the 

 characteristic enormous crop? The supposed aboriginal 

 stocks must all have been rock- pigeons, that is, they did 

 not breed or willingly perch on trees. But besides C. 

 livia, with its geographical sub-species, only two or three 

 other species of rock-pigeons are known; and these have 

 not any of the characters of the domestic breeds. Hence 

 the supposed aboriginal stocks must either still exist in 

 the countries where they were originally domesticated, 

 and yet be unknown to ornithologists; and this, consider- 

 ing their size, habits, and remarkable characters, seems 

 improbable; or they must have become extinct in the wild 

 state. But birds breeding on precipices, and good fliers, 

 are unlikely to be exterminated; and the common rock- 

 pigeon, which has the same habits with the .-domestic 

 breeds, has not been exterminated even on several of the 



