152 SEXUAL SELECTION: BIRDS. [Pakt II. 



be a sexually-limited character, otherwise it would prevent 

 the comb of the female from lopping over. 



From the foregoing illustrations, we see that, even with 

 almost unlimited time at command, it would be an ex 

 tremely difficult and complex process, though perhaps.not 

 impossible, to change through selection one form of trans- 

 mission into the other. Therefore, without distinct evi- 

 dence in each case, I am unwilling to admit that this has of- 

 ten been effected with natural species. On the other hand, 

 by means of successive variations, which were from the 

 first sexually limited in their transmission, there would not 

 be the least difficulty in rendering a male bird widely differ- 

 ent in color or in any other character from the female ; the 

 latter being left unaltered, or slightly altered, or specially 

 modified, for the sake of protection. 



As bright colors are of service to the males in their 

 rivalry with other males, such colors would be selected, 

 whether or not they were transmitted exclusively to the 

 same sex. Consequently the females might be expected 

 often to partake of the brightness of the males to a greater 

 or less degree ; and this occurs with a host of species. If 

 all the successive variations were transmitted equally, to 

 both sexes, the females would be undistinguishable from the 

 males ; and this likewise occurs with many birds. If, how- 

 ever, dull colors were of high importance for the safety of 

 the female during incubation, as with many ground birds, 

 the females which varied in brightness, or which received 

 through inheritance from the males any marked accession 

 of brightness, would sooner or later be destroyed. But the 

 tendency in the males to continue for an indefinite period 

 transmitting to their female offspring their own bright- 

 ness, would have to be eliminated by a change in the form 

 of inheritance ; and this, as shown by our previous illus- 

 tration, would be extremely difficult. The more probable 

 result of the long-continued destruction of the more bright- 



