18661872] SEXUAL SELECTION 63 



could be sexually selected. We seem to require a series of bold and Letter 431 

 abrupt variations. How can we imagine that an inch in the tail of 

 the peacock, or |-inch in that of the Bird of Paradise, would be noticed 

 and preferred by the female." 



In regard to sexual selection. A girl sees a handsome 

 man, and without observing whether his nose or whiskers are 

 the tenth of an inch longer or shorter than in some other 

 man, admires his appearance and says she will marry him. 

 So, I suppose, with the pea-hen ; and the tail has been 

 increased in length merely by, on the whole, presenting a 

 more gorgeous appearance. J. Jenner Weir, however, has 

 given me some facts showing that birds apparently admire 

 details of plumage. 



To F. Miiller. Letter 432 



March 28th [1868]. 



I am particularly obliged to you for your observations on 

 the stridulation of the two sexes of Lamellicorns. 1 I begin to 

 fear that I am completely in error owing to that common 

 cause, viz. mistaking at first individual variability for sexual 

 difference. 



I go on working at sexual selection, and, though never 

 idle, I am able to do so little work each day that I make very 

 slow progress. I knew from Azara about the young of the 

 tapir being striped, and about young deer being spotted ; 2 I 

 have often reflected on this subject, and know not what to 

 conclude about the loss of the stripes and spots. From the 

 geographical distribution of the striped and unstriped species 

 of Equus there seems to be something very mysterious about 

 the loss of stripes ; and I cannot persuade myself that the 

 common ass has lost its stripes owing to being rendered 

 more conspicuous from having stripes arid thus exposed to 

 danger. 



1 We are unable to find any mention of F. Miiller's observations 

 on this point ; but the reference is clearly to Darwin's observations on 

 Necrophorus and Pelobius, in which the stridulating rasp was bigger in 

 the males in the first individuals examined, but not so in succeeding 

 specimens. Descent of Man, Ed. II., Vol. I., p. 382. 



2 Fritz Miiller's views are discussed in the Descent of Man, Ed. II., 

 Vol. II., p. 305. 



