SEXUAL SELECTION 581 



count of the danger to which they would have been exposed 

 by attracting the attention of birds or beasts of prey ? This 

 does not seem to me probable, when we think of the multi- 

 tude of birds which with impunity gladden the country with 

 their voices during the spring.' It is a safer conclusion that, 

 as vocal and instrumental organs are of special service only 

 to the males during their courtship, these organs were de- 

 veloped through sexual selection and their constant use in 

 that sex alone — the successive variations and the effects of 

 use having been from the first more or less limited in trans- 

 mission to the male offspring. 



Many analogous cases could be adduced; those, for in- 

 stance, of the plumes on the head being generally longer 

 in the male than in the female, sometimes of equal length in 

 both sexes, and occasionally absent in the female — these 

 several cases occurring in the same group of birds. It 

 would be difficult to account for such a difference between 

 the sexes by the female having been benefited by possessing 

 a slightly shorter crest than the male, and its consequent 

 diminution or complete suppression through natural selec- 

 tion. But I will take a more favorable case,, namely, the 

 length of the tail. The long train of the peacock would 

 have been not only inconvenient but dangerous to the 

 peahen during the period of incubation and while accom- 

 panying her young. Hence there is not the least ct, priori 

 improbability in the development of her tail having been 

 checked through natural selection. But the females of 

 various pheasants, which apparently are exposed on their 

 open nests to as much danger as the peahen, have tails of 

 considerable length. The females as well as the males 

 of the Menura superba have long tails, and they build a 

 domed nest, which is a great anomaly in so large a bird. 

 Naturalists have wondered how the female Menura could 



' DaineB Barrington, however, thought it probable ("Phil. Transact.," 1713, 

 p. 164) that few female birds sing, because the talent would have been danger- 

 ous to them during incubation. He adds, that a similar view may possibly 

 account for the inferiority of the female to the male in plumage. 



