506 THE DESCENT OF MAN. 



through natural selection, from acquiring the conspicuous 

 colors of the male, owing to the danger which she would 

 thus have incurred during incubation. 



This view necessitates a tedious discussion on a difficult 

 point, namely, whether the transmission of a character 

 which is at first inherited by both sexes can be subsequently 

 limited in its transmission to one sex alone by means of 

 natural selection. We must bear in mind, as shown in the 

 preliminary chapter on sexual selection, that characters 

 which are limited in their development to one sex are 

 always latent in the other. An imaginary illustration vill 

 best aid us in seeing the difficulty of the case; we may sup- 

 pose that a fancier wished to make a breed of pigeons, in 

 which the males alone should be colored of a pale blue, 

 while the females retained their former slaty tint. As with 

 pigeons characters of all kinds are usually transmitted to 

 both sexes equally, the fancier would have to try to convert 

 this latter form of inheritance into sexually limited trans- 

 mission. All that he could do would be to persevere in 

 selecting every male pigeon which was in the least degree 

 of a paler blue; and the natural result of this process, if 

 steadily carried on for a long time, and if the pale varia- 

 tions were strongly inherited or often recurred, would be 

 to make his whole stock of a lighter blue. But our fancier 

 would be compelled to match, generation after generation, 

 his pale-blue males with slaty females, for he wishes to keep 

 the latter of this color. The result would generally be the 

 production either of a mongrel piebald lot, or more prob- 

 ably the speedy and complete loss of the pale-blue tint; for 

 the primordial slaty color would be transmitted with pre- 

 potent force. Supposing, however, that some pale-blue 

 males and slaty females were produced during each succes- 

 sive generation, and were always crossed together, then the 

 slaty females would have, if I may use the expression, much 

 blue blood in their veins, for their fathers, grandfathers, 

 etc., will all have been blue birds. Under these circum- 

 stances it is conceivable (though I know of no distinct facts 

 rendering it probable) that the slaty females might acquire 

 so strong a latent tendency to pale-blueness that they would 

 not destroy this color in their male offspring, their female 

 offspring still inheriting the slaty tint. If so, the desired 

 end of making a breed with the two sexes permanently dif- 

 ferent in color might be gained. 



