Chap. VIII.] SEXUAL SELECTION. 2V5 



their masculine plumes and hackles. On the other hand, 

 the diiferences between the sexes may be increased under 

 domestication, as with merino sheep, in which the ewes 

 have lost their horns. Again, characters proper to one 

 sex may suddenly ajDpear in the other sex ; as with those 

 sub-breeds of the fowl in which the hens while young ac- 

 quire spurs ; or, as in certain Polish sub-breeds, in which 

 the females, as there is reason to believe, originally ac- 

 quired a crest, and subsequently transferred it to the 

 males. All these cases are intelligible on the hypothesis 

 of pangenesis ; for they depend on the gemmules of certain 

 units of the body, although .present in both sexes, becoming 

 through the influence of domestication dormant in the one 

 sex ; or, if naturally dormant, becoming developed. 



There is one difficult question which it will be conven- 

 ient to defer to a future chapter ; namely, whether a char- 

 acter, at first developed in both sexes, can be rendered 

 through selection limited in its development to one sex 

 alone. If, for instance, a breeder observed that some of 

 his pigeons (in which species characters are usually trans- 

 ferred in an equal degree to both sexes) varied into pale 

 blue ; could he by long-continued selection make a breed, 

 in which the males alone should be of this tint while the 

 females remained unchanged ? I will here only say that 

 this, though perhaps not impossible, would be extremely 

 difficult ; for the natural result of breeding from the pale- 

 blue males would be to change his whole stock, including 

 both sexes, into this tint. If, hov,^ever, variations of the 

 desired tint appeared, which were from the first limited 

 in their develoi)ment to the male sex, there would not be 

 the least difficulty in making a breed characterized by the 

 two sexes being of a dififerent color, as indeed has been 

 eftected with a Belgian breed, in which the males alone 

 are streaked with black. In a similar manner, if any vari- 

 ation appeared in a female pigeon, which was from the 



