SEXUAL SELECTION. 195 



Among domestic pigeons the character of the different 

 breeds is often most strongly manifested in the male 

 birds ; the wattles of the carriers and the eye- wattles of 

 the barbs are largest in the males, and male pouters dis- 

 tend their crops to a much greater extent than do the 

 females, while the cock fantails often have a greater num- 

 ber of tail-feathers than the females. There are also 

 some varieties of pigeons of which the males are striped 

 or spotted with black while the females are never so 

 spotted (Animals and Plants under Domestication, I. 

 161) ; yet in the parent stock of these pigeons there are 

 no differences between the sexes either of plumage or 

 colour, and artificial selection has not been applied to 

 produce them. 



The greater intensity of coloration in the male 

 which may be termed the normal sexual difference, 

 would be further developed by the combats of the males 

 for the possession of the females. The most vigorous 

 and energetic usually being able to rear most offspring, 

 intensity of colour, if dependent on, or correlated with 

 vigour, would tend to increase. But as differences of 

 colour depend upon minute chemical or structural dif- 

 ferences in the organism, increasing vigour acting un- 

 equally on different portions of the integument, and often 

 producing at the same time abnormal developments of 

 hair, horns, scales, feathers, &c., would almost necessarily 

 lead also to variable distribution of colour, and thus to 

 the production of new tints and markings. These 

 acquired colours would, as Mr. Darwin has shown, be 

 transmitted to both sexes or to one only, according as 

 they first appeared at an early age, or in adults of one 

 sex ; and thus we may account for some of the most 



o 2 



