THE DESCENT OF MAN 



nal selection, which depends on an element liable to change 

 — the taste or admiration of the female — will have had new 

 shades of color or other differences to act on and accumu- 

 late; and as sexual selection is always at work, it would 

 (from what we know of the results on domestic animals of 

 man's unintentional selection) be surprising if animals in- 

 habiting separate districts, which can never cross and thus 

 blend their newly acquired characters, were not, after a 

 sufficient lapse of time, differently modified. These re- 

 marks likewise apply to the nuptial or summer plumage, 

 whether confined to the males or common to both sexes. 

 Although the females of the above closely allied or rep- 

 resentative species, together with their young, differ hardly 

 at all from one another, so that the males alone can be dis- 

 tinguished, yet the females of most species within the same 

 genus obviously differ from each other. The difference, 

 however, are rarely as great as between the males. We 

 see this clearly in the whole family of the Gallinaceae: the 

 females, for instance, of the common and Japan pheasant, 

 and especially of the Gold and Amherst pheasant — of the 

 silver pheasant and the wild fowl — resemble one another 

 very closely in color, while the males differ to an extraordi- 

 nary degree. So it is with the females of most of the Co- 

 tingidse, Fringillidse, and many other families. There can 

 indeed be no doubt that, as a general rule, the females have 

 been less modified than the males. Some few birds, how- 

 ever, offer a singular and inexplicable exception; thus the 

 females of Paradisea apoda and P. papuana differ from each 

 other more than do their respective males;' the female of th« 

 latter species having the under surface pure white, while the 

 female P. apoda is deep brown beneath. So again, as I hear 

 from Prof. Newton, the males of two species of Oxynotus 

 (shrikes), which represent each other in the islands of Mau- 

 ritius and Bourbon," differ but little in color, while the 



' Wallace, "The Malay Archipelago," vol. ii., 1869, p. 394. 

 * These species are described with colored figures, by M. P. FoUen, in 

 "Ibis," 1866, p. 275. 



