vI A THEORY OF BIRDS’ NESTS 129 
natural phenomena? Do they teach us anything of the way 
in which nature works, and give us any insight into the 
causes which have brought about the marvellous variety, and 
beauty, and harmony of living things? I believe we can 
answer these questions in the affirmative ; and I may mention, 
as a sufficient proof that these are not isolated facts, that I 
was first led to see their relation to each other by the study 
of an analogous though distinct set of phenomena among in- 
sects, that of protective resemblance and “ mimicry.” 
On considering this remarkable series of corresponding 
facts, the first thing we are taught by them seems to be, that 
there is no incapacity in the female sex among birds to receive 
the same bright hues and strongly contrasted tints with which 
their partners are so often decorated, since whenever they are 
protected and concealed during the period of incubation they 
are similarly adorned. The fair inference is, that it is chiefly 
due to the absence of protection or concealment during this 
important epoch, that gay and conspicuous tints are withheld 
or left undeveloped. The mode in which this has been effected 
is very intelligible, if we admit the action of natural and 
sexual selection. It would appear from the numerous cases 
in which both sexes are adorned with equally brilliant colours 
(while both sexes are rarely armed with equally developed 
offensive and defensive weapons when not required for indi- 
vidual safety), that the normal action of “sexual selection” or 
of other unknown causes, is to develop colour and beauty in 
both sexes, by the preservation and multiplication of all 
varieties of colour in either sex which are pleasing to the 
other. Several very close observers of the habits of animals 
have assured me that male birds and quadrupeds do often 
take very strong likes and dislikes to individual females, and 
we can hardly believe that the one sex (the female) can have 
a general taste for colour while the other has no such taste. 
However this may be, the fact remains, that in a vast number 
of cases the female acquires as brilliant and as varied colours 
as the male, and therefore most probably acquires them in the 
same way as the male does—that is, either because the 
colour is useful to it, or is correlated with some useful varia- 
tion, or is pleasing to the other sex. The only remaining 
supposition is that it is transmitted from the other sex, with- 
K 
