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138 NATURAL SELECTIONgreater danger to which she is exposed and her greater importanceto the existence of the species and this she ; alwaysacquires, in one way or another, through the action of naturalselection.In his Origin of Species, fourth edition, p. 241, Mr. Darwinrecognises the necessity for protection as sometimes being a1cause of the obscure colours of female birds ;but he does notseem to consider it so very important an agent in modifyingcolour as I am disposed to do. In the same paragraph (p.240) he alludes to the fact of female birds and butterfliesbeing sometimes very plain, sometimes as gay as the males ;but, apparently, considers this mainly due to peculiar laws ofinheritance, which sometimes continue acquired colour in theline of one sex only, sometimes in both. Without denyingthe action of such a law (which Mr. Darwin informs me hehas facts to support), I impute the difference, in the greatmajority of cases, to the greater or less need of protection inthe female sex in these groups of animals.This need was seen to exist a century ago by the Hon.Daines Barrington, who, in the article already quoted (see p.104), after alluding to the fact that singing birds are all small,and suggesting (but I think erroneously) that this may havearisen from the difficulty larger birds would have in concealingthemselves if they called the attention of their enemies byloud notes, goes on thus :" I should rather conceive it is forthe same reason no hen bird sings, because this talent wouldbe still more dangerous during incubation, which may possiblyalso account for the inferiority in point of plumage." This is acurious anticipation of the main idea on which this essay isfounded. It has been unnoticed for near a century, and myattention was only recently called to itby Mr. Darwin himself.ConclusionTo some persons it will perhaps appear that the causes towhich I impute so much of the external aspect of nature aretoo simple, too insignificant, and too unimportant for such amighty Ayork.But I would ask them to consider that thegreat object of all the peculiarities of animal structure is topreserve the life of the individual, and to maintain the exist-1This passage is omitted in the sixth edition.