SEXUAL SELECTION 643 



bave come to differ from each other cWefly through the 

 action of sexual selection, while the females have come to 

 differ chiefly from partaking more or less of the characters 

 thus acquired by the males. The effects, moreover, of the 

 definite action of the conditions of life will not have been 

 masked in the females, as in the males, by the accumula- 

 tion through sexual selection of strongly pronounced colors 

 and other ornaments. The individuals of both sexes, how- 

 ever affected, will have been kept at 'each successive period 

 nearly uniform by the free intercrossing of many individuals. 



With species in which the sexes differ in color it is possi- 

 ble or probable that some of the successive variations often 

 tended to be transmitted equally to both sexes; but that 

 when this occurred the females were prevented from ac- 

 quiring the bright colors ' from the males by the destruc- 

 tion which they suffered during incubation. There is no 

 evidence that it is possible by natural selection tp convert 

 one form of transmission into ,another. But there would 

 not be the least difficulty in rendering a female dull col- 

 ored, the male being still kept bright colored by the se- 

 lection of successive variations, which were from the first 

 limited in their transmission to the same sex. Whether 

 the females of many species have actually been thus modi- 

 fied must at present remain doubtful. When, through the 

 law of the equal transmission of characters to both sexes, 

 the females were- rendered as conspicuously colored as the 

 males, their instincts appear often to have been modified so 

 that they were led to build domed or concealed nests. 



In one small and curious class of cases the characters 

 and habits of the two sexes have been completely trans- 

 posed, for the females are larger, stronger, more vociferous, 

 and brighter colored than the males. They have, also, be- 

 come so quarrelsome that they often fight together for the 

 possession of the males, like the males of other pugnacious 

 species for the possession of the females. If, as seems prob- 

 able, such females habitually drive away their rivals, and by 

 the display of their bright colors or other charms endeavor 



