SEXUAL COLOEATION. 265' 



the males of other dimorphic species. This fact, however, is 

 not necessarily an objection to the theory of sexual selection- 

 It is explained by Darwin as being due to heredity ; the 

 brilliant colours were first of all, it is supposed, acquired by, 

 and limited to, the males, in response to a choice on the part 

 of the female bird. Gradually the effects were handed down to 

 the offspring of both sexes. 



Difficulty of believing in a highly-developed iEsthetic Sense. 



Viewed as a matter of probability or improbability, it is 

 difficult to conceive of so exalted an aesthetic sense in birds. 



It is necessary to assume that the females of many species 

 have a sense of beauty not only equal to, but far surpassing 

 that of the average human being. Merely brightness or un- 

 usual gaudiness in the male bird one could understand, as being 

 in part at least due to " preferential mating," but to put down 

 the delicate browns and greys of the feathers of the Argus 

 pheasant, which is almost the most beautiful of birds, to sexual 

 selection, is to assume a most refined sense of beauty in the 

 bird. Moreover, as Mr. Stolzmann has pointed out in discussing 

 another theory of sexual difi'erences, which will be referred to 

 later, the taste of closely allied birds must diff'er in an immense 

 degree, if this theory be accepted. 



He gives, among other instances, that of two species of the 

 American genus Basileuterus. In B. castaneiceps the coloration 

 is dull ; in B. coronatus the under parts are, in both sexes, a 

 bright yellow; this bright colour would be, on Darwin's theory, 

 first developed in the male and then handed down to the off- 

 spring of both sexes. We must therefore assume that the 

 females of B. coronatus have greatly surpassed the females of 

 the other species, in the development of their aesthetic sense. 

 As the areas of the two species are contiguous, this difference 



