4^44 "^^^^ Descent of Man. Pa.bt 11, 



CHAPTEE XV. 



BIRDS — continued. 



Discission at ii why the males alone of some species, and both se^es cf 

 others, are oiightly coloured — Oq sexually-limittid inheritance, as applied 

 to various structures and to brightly-coloured plumage — Nidification in 

 relation to colour — Loss of nuptial plumage during the winter. 



We have in this chapter to consider, why the females of many 

 birds have not acquired the same ornaments as the male ; and 

 wliy, on the other hand, both axes of many other birds are 

 equally, or almost equally, ornamented ? In the following 

 chapter we shall consider the few cases in which the female is 

 more conspicuously coloured than the male. 



In my ' Origin of Species " I briefly suggested that the long 

 tail of the peacock would be inconvenient, and the conspicuous 

 black colour of the male capercailzie dangerous, to the female 

 during the period of incubation ; and consequently that the 

 transmission of these characters from the male to the female 

 offspring had been checked through natural selection. I still 

 think that this may have occurred in some few instances : but 

 after mature reflection on all the facts which 1 have been able to 

 collect, I am now inclined to believe that when the sexes difler, 

 the successive variations have generally heen from the first 

 limited in their ti'ansmitsion to the same sex in which they first 

 arose. Since my remarks appeared, the subject of sexual 

 coloration has been discussed in some very interesting papers 

 by Mr. "Wallace,^ who believes that in almost all cases the 

 successive variations tended at first to be transmitted equally 

 to both sexes; but that the female was saved, through natural 

 selection, from acquiring the conspicuous colours 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 

 »t first inherii;ed by both sexes, can be subsequently limited in 

 Kb transmission to one sex alone by means of natural selection. 

 We must bear in mind, as shewn in the preliminary chapter on 

 Boxual selection, that characters which are limited in their 

 development to one sex are always latent in the other. k\\ 



' Fourth edition, 1866, p. 241. 1867. ' Journal of Tiavel,' vol. i 



• ' Westminster Keview,' July, 1868, p. 7.'). 



