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130 NATURAL SELECTION viout being of any use. From the number of examples aboveadduced of bright colours in the female, this would imply thatcolour-characters acquired by one sex are generally (but notnecessarily) transmitted to the other. If this be the case itwill, I think, enable us to explain the phenomena, even if wedo not admit that the male bird is ever influenced in thechoice of a mate by her more gay or perfect plumage.The female bird, while sitting on her eggs in an uncoverednest, is much exposed to the attacks of enemies, and anymodification of colour which rendered her more conspicuouswould often lead to her destruction and that of her offspring.All variations of colour in this direction in the female wouldtherefore sooner or later be eliminated, while such modificationsas rendered her inconspicuous, by assimilating her to surroundingobjects, as the earth or the foliage, would, on thewhole, survive the longest, and thus lead to the attainmentof those brown or green and inconspicuous tints, which formthe colouring (of the upper surface at least) of the vastmajority of female birds which sit upon open nests.This does not imply, as some have thought, that all femalebirds were once as brilliant as the males. The change hasbeen a very gradual one, generally dating from the origin ofgenera or of larger groups, but there can be no doubt thatthe remote ancestry of birds having great sexual differencesof colour were nearly or quite alike, sometimes (perhaps inmost cases) more nearly resembling the female, but occasionallyperhaps being nearer what the male is now. The youngbirds (which usually resemble the females) will probably givesome idea of this ancestral type, and it is well known thatthe young of allied species and of different sexes are oftenundistinguishable.Colour more variable than Structure or Habits, and thereforetheCharacter which has generally been ModifiedAt the commencement of this essay I have endeavouredto prove that the characteristic differences and the essentialfeatures of birds' nests are dependent on the structure of thespecies and upon the present and past conditions of theirexistence. Both these factors are more important and lessvariable than colour jand we must therefore conclude that in