SPECIFIC CHARACTERS HIGHLY VARIABLE 169 



birds with two black bars on the wings, white loins, a bar 

 at the end of the tail, with the outer feathers externally 

 edged near their basis with white. As all these marks are 

 characteristic of the parent rock-pigeon, I presume that no 

 one will doubt that this is a case of reversion, and not of a 

 new yet analogous variation appearing in the several breeds. 

 We may, I think, confidently come to this conclusion, be- 

 cause, as we have seen, these coloured marks are eminently 

 liable to appear in the crossed offspring of two distinct and 

 differently coloured breeds; and in this case there is nothing 

 in the external conditions of life to cause the reappearance 

 of the slaty-blue, with the several marks, beyond the influ- 

 ence of the mere act of crossing on the laws of inheritance. 

 No doubt it is a very surprising fact that characters should 

 reappear after having been lost for many, probably for hun- 

 dreds of generations. But when a breed has been crossed 

 only once by some other breed, the offspring occasionally 

 show for many generations a tendency to revert in character 

 to the foreign breed — some say, for a dozen or even a score 

 of generations. After twelve generations, the proportion of 

 blood, to use a common expression, from one ancestor, is 

 only I in 2048; and yet, as we see, it is generally believed 

 that a tendency to reversion is retained by this remnant of 

 foreign blood. In a breed which has not been crossed but 

 in which both parents have lost some character which their 

 progenitor possessed, the tendency, whether strong or weak, 

 to reproduce the lost character might, as was formerly re- 

 marked, for all that we can see to the contrary, be trans- 

 mitted for almost any number of generations. When a 

 character which has been lost in a breed, reappears after a 

 great number of generations, the most probable hypothesis 

 is, not that one individual suddenly takes after an ancestor 

 removed by some hundred generations, but that in each suc- 

 cessive generation the character in question has been lying 

 latent, and at last, under unkno\\ai favourable conditions, is 

 developed. With the barb-pigeon, for instance, which very 

 rarely produces a blue bird, it is probable that there is a 

 latent tendency in each generation to produce blue plumage. 

 The abstract improbability of such a tendency being trans- 

 mitted through a vast number of generations, is not greater 



