A THEORY OF BIRDS 1 NESTS. 247 



way in which nature works, and give us any insight 

 into the causes which have brought about the marvel- 

 lous variety, and beauty, and harmony of living things? 

 I believe we can answer these questions in the affirm- 

 ative; 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 correspond- 

 ing 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 saxes are rarely armed with equally developed 

 offensive and defensive weapons when not required for 

 individual safety), that the normal action of " sexual 

 selection " 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 



