Chap. XIV.] GRADATION OF CHARACTERS. 145 



dition and origin of the ornaments on the wing-feathers 

 of the Argus pheasant. 



From the light reflected by the principle of gradation ; 

 from what we know of the laws of variation; from the 

 changes which have taken place in many of our domesti- 

 cated birds ; and, lastly, from the character (as we shall 

 hereafter more clearly see) of the immature plumage of 

 young birds — we can sometimes indicate, with a certain 

 amount of confidence, the probable steps by which the 

 males have acquired their brilliant plumage and various 

 ornaments ; yet in many cases we are involved in dark- 

 ness. Mr. Gould several years ago pointed out to me a 

 humming-bird, the Urosticte benjamini, remarkable from 

 the curious differences presented by the two sexes. The 

 male, besides a splendid gorget, has greenish-black tail- 

 feathers, with the four central ones tipped with white ; in 

 the female, as with most of the allied species, the three 

 outer tail-feathers on each side are tipped with white, so 

 that the male has the four central, while the female has the 

 six exterior feathers ornamented with white tips. What 

 makes the case curious is that, although the coloring of 

 the tail differs remarkably in both sexes of many kinds 

 of humming-birds, Mr. Gould does not know a single 

 species, besides the Urosticte, in which the male has the 

 four central feathers tipped with white. 



The Duke of Argyll, in commenting on this case, 49 

 passes over sexual selection, and asks, "What explanation 

 does the law of natural selection give of such specific va- 

 rieties as these ? " He answers " none whatever ; " and I 

 quite agree with him. But can this be so confidently 

 said of sexual selection? Seeing in how many ways the 

 tail-feathers of humming-birds differ, why should not the 

 four central feathers have varied in this one species alonQ 



49 ' The Reign of Law,' 1867, p. 247. 

 26 



