1380 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 ; and we must therefore conclude that in 
