130 NATURAL SELECTION vi 



out being of any use. From the number of examples above 

 adduced of bright colours in the female, this would imply that 

 colour-characters acquired by one sex are generally (but not 

 necessarily) transmitted to the other. If this be the case it 

 will, I think, enable us to explain the phenomena, even if we 

 do not admit that the male bird is ever influenced in the 

 choice of a mate by her more gay or perfect plumage. 



The female bird, while sitting on her eggs in an uncovered 

 nest, is much exposed to the attacks of enemies, and any 

 modification of colour which rendered her more conspicuous 

 would often lead to her destruction and that of her offspring. 

 All variations of colour in this direction in the female would 

 therefore sooner or later be eliminated, while such modifications 

 as rendered her inconspicuous, by assimilating her to sur- 

 rounding objects, as the earth or the foliage, would, on the 

 whole, survive the longest, and thus lead to the attainment 

 of those brown or green and inconspicuous tints, which form 

 the colouring (of the upper surface at least) of the vast 

 majority of female birds which sit upon open nests. 



This does not imply, as some have thought, that all female 

 birds were once as brilliant as the males. The change has 

 been a very gradual one, generally dating from the origin of 

 genera or of larger groups, but there can be no doubt that 

 the remote ancestry of birds having great sexual differences 

 of colour were nearly or quite alike, sometimes (perhaps in 

 most cases) more nearly resembling the female, but occasion- 

 ally perhaps being nearer what the male is now. The young 

 birds (which usually resemble the females) will probably give 

 some idea of this ancestral type, and it is well known that 

 the young of allied species and of different sexes are often 

 undistinguishable. 



Colour more variable than Structure or Habits, and therefore the 



Character which has generally been Modified 

 At the commencement of this essay I have endeavoured 

 to prove that the characteristic differences and the essential 

 features of birds' nests are dependent on the structure of the 

 species and upon the present and past conditions of their 

 existence. Both these factors are more important and less 

 variable than colour j and we must therefore conclude that in 



