138 NATURAL SELECTION VI 
greater danger to which she is exposed and her greater im- 
portance to the existence of the species ; and this she always 
acquires, in one way or another, through the action of natural 
selection. 
In his Origin of Species, fourth edition, p. 241, Mr. Darwin 
recognises the necessity for protection as sometimes being a 
cause of the obscure colours of female birds ;} but he does not 
seem to consider it so very important an agent in modifying 
colour as I am disposed to do. In the same paragraph (p. 
240) he alludes to the fact of female birds and butterflies 
being sometimes very plain, sometimes as gay as the males ; 
but, apparently, considers this mainly due to peculiar laws of 
inheritance, which sometimes continue acquired colour in the 
line of one sex only, sometimes in both. Without denying 
the action of such a law (which Mr. Darwin informs me he 
has facts to support), I impute the difference, in the great 
majority of cases, to the greater or less need of protection in 
the 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 have 
arisen from the difficulty larger birds would have in conceal- 
ing themselves if they called the attention of their enemies by 
loud notes, goes on thus: “I should rather conceive it is for 
the same reason no hen bird sings, because this talent would 
be still more dangerous during incubation, which may possibly 
also account for the inferiority in point of plumage.” This is a 
curious anticipation of the main idea on which this essay is 
founded. It has been unnoticed for near a century, and my 
attention was only recently called to it by Mr. Darwin himself. 
Conclusion 
To some persons it will perhaps appear that the causes to 
which I impute so much of the external aspect of nature are 
too simple, too insignificant, and too unimportant for such a 
mighty work. But I would ask them to consider that the 
great object of all the peculiarities of animal structure is to 
preserve the life of the individual, and to maintain the exist- 
1 This passage is omitted in the sixth edition. 
