Chap. XXVIII. 



CONCLUDING REMARKS. 



421 



kind ; and afterwards to consider the results when selection is 

 brought into play. Lot us suppose that 500 wild rock-pigeons were 

 confined in their native land in an aviary, and fed in the same 

 manner as pigeons usually are ; and that they were not allowed 

 to increase in number. As pigeons propagate so rapidly, I sup- 

 pose that a thousand or fifteen hundred birds would have to be 

 annually killed by mere chance. After several generations had 

 been thus reared, we may feel sure that some of the youno- 

 birds would vary, and the variations would tend to be inhe- 

 rited; for at the present day slight deviations of structure often 

 occur, but, as most breeds are already well established, these 

 modifications are rejected as blemishes. It would be tedious 

 even to enumerate the multitude of points which still go on 

 varying or have recently varied. Many variations would occur 

 in correlation, as the length of the wing and tail feathers — the 

 number of the primary wing-feathers, as well as the number and 

 breadth of the ribs, in correlation with the size and form of the 



body— the number of the scutellee, with the size of the feet 



the length of the tongue, with the length of the beak— the size 

 of the nostrils and eyelids and the form of lower jaw in 

 correlation with the development of wattle — the nakedness of 

 the young with the future colour of the plumage — the size 

 of the feet and beak, and other such points. Lastly, as our 

 birds are supposed to be confined in an aviary, they would use 

 their wings and legs but little, and certain parts of the ske- 

 leton, such as the sternum and scapulae and the feet, would in 

 consequence become slightly reduced in size. 



As in our assumed case many birds have to be indiscrimi- 

 nately killed every year, the chances are against any new 

 variety surviving long enough to breed. And as the variations 

 which arise are of an extremely diversified nature, the chances 

 are very great against two birds pairing which have varied in 

 the same manner ; nevertheless, a varying bird even when not 

 thus paired would occasionally transmit its character to its young ; 

 and these would not only be exposed to the same conditions which 

 first caused the variation in question to appear, but would in addi- 

 tion inherit from their one modified parent a tendency again to 

 vary in the same manner. So that, if the conditions decidedly 

 tended to induce some particular variation, all the birds might 



