262 THE DESCENT OF MAN. 



which the characters are usually transferred 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 the whole stock of both sexes to this tint. If, 

 however, variations of the desired tint appeared, which 

 were from the first limited in their development to the 

 male sex, there would not be the least difficulty in making 

 a breed with the two sexes of a different color, as indeed 

 has been effected with a Belgian breed, in which the males 

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

 variation appeared in a female pigeon, which was from the 

 first sexually limited in its development to the females, it 

 would be easy to make a breed with the females alone thus 

 characterized; but if the variation was not thus originally 

 limited the process would be extremely difficult, perhaps 

 impossible.* 



On the Relation Between the Period of Development of a 

 Character and Its Transmission to One Sex or to Both 

 Sexes. Why certain characters should be inherited by both 

 sexes and other characters by one sex alone, namely, by that 

 sex in which the character first appeared, is in most cases 

 quite unknown. We cannot even conjecture why with cer- 

 tain sub-breeds of the pigeon black striae, though trans- 

 mitted through the female, should be developed in the 

 male alone, while every other character is equally trans- 

 ferred to both sexes. Why, again, with cats, the tortoise- 

 shell color should, with rare exceptions, be developed in 

 the female alone. The very same character, such as defi- 

 cient or supernumerary digits, color-blindness, etc., may 



* Since the publication of the first edition of this work, it has been 

 highly satisfactory to me to find the following remarks (the " Field," 

 Sept., 1872) from so experienced a breeder as Mr. Tegetmeier. 

 After describing some curious cases in pigeons, of the transmission ol 

 color by one sex alone, and the formation of a sub-breed with this 

 character, he says : " It is- a singular circumstance that Mr. Darwin 

 should have suggested the possibility of modifying the sexual colors 

 of birds by a course of artificial selection. When he did so, he was 

 in ignorance of these facts that I have related ; but it is remarkable 

 bow very closely he suggested the right method of procedure." 



