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Show PART II. 192 SEX~ UAL SELECTION : BIRDS. s have been exposed will cause they will almost ~lwa~ (J' from a widely-spread analog~, them to undergo, JUdgmo t' variability. In this . t f fluctua mg a certam amoun . o h' ·h depends on an element case sexual selectwn, w lC l the taste or admi-eminently liable to cha~Ilgl el-nahma~ ~ew shades of colour ratw. n of t 1l e !.!'e m ale-Wl lave d accumulate ; and as • J!i' to act on an < • or other dwerenc~s l at '''ork it would (judgmg sexual se l cc t1. 011 1s . a wahys lts o'n domestiC· am· ma1 s from wh at we l{ n o.w of t e resu . . "f' , · t tlonal se 1e c t"I on ), be a surpr1smg fact 1 of man s.umn .e~1 se arate districts, which can never animals mhab1tmg Ph . ly acquired characters, h bl nd t e1r new - cross and t us e ffi . t 1 pse of time, differently were. not, after a s:1a~~:~ike~ise apply to the nuptial modified. These re h tl confined to the males or or summer plumage, w e ler common to both sexes. l f the above closely-allied Although the f~mha els .o ung differ hardly at all · t ther wtt t 1ell' yo ' . · speCies, oge h t th males alone can be distm-from each otl~er, so t a etlle females of the species . h d t m most cases gm. s . e t'h y e me genus ob Vl.O U sly differ from each other. w1thm e sa . . . l as reat as between The differen;~~ h;e:e~~~~ :~:a~·~~ei~ theg whole family of the mal~s. . females, for instance, of the comthe Gallmacere . thhe t and especially of the gold and d Japan p easan ' h 'ld mon an heasant-of the silver pheasant and t e \~I Amherst p bl < ch other very closely in colour, W~ll~t fowl-resem e ea · d So 1t IS l differ to an extraordmary egree. . . . th"etl mtha esf emales of mos t of the Cotin(J'idre Frmgilhdre, o ' b Wl 1 e f "}' rrhere can indeed be no clou t d Y other mm 1es. d" athn t man a genera1 rul e, the females have been m.o d1 - a ' as less extent than the males. Some few b~r s, fied to a i!i' • a sin(J'ular and inexplicable exceptiOn ; however, ouer o d p ana £ ales of p aradisea apoda an · papu . tdhifufse r thfreo me mea ch oth er. moi. e than do their respective •CnaP. XVI. THE YOUNG LII\E TilE ADULT FEMALES. 193 males; 7 the female of the latter species having the 1.mder surface pure white, whilst the female P. apoda is deep brown beneath. So, again, as I hear from Professor Newton, the males of two species of Oxynotus (shrikes), which represent each other in the islands of Mauritius and Bourbon,8 differ but little in colour, whilst the females differ much. In the Bourbon species the female appears to have partially retained an immature condition of plumage, for at first sight she "might be taken for "the young of the Mauritian species." These differences may be compared with those which occur, independently of selection by man, and which we cannot explain, in certain sub-breeds of the game-fowl, in which the females are very different, whilst the males can hardly be distinguished. 9 As I account so largely by sexual selection for the differences between the males of allied species, how can the differences between the females be accounted for in all ordinary cases ? We need not here consider the species which belong to distinct genera; for with these, adaptation to different habits of life, and other agencies, will have come into play. In regard to the differences between the females within the same genus, it appears to me almost certain, after looking through various large groups, that the chief agent has been the transference, in a greater or less degree, to the female of the characters acquired by the males through sexual selection. In the several British finches, the two sexes differ either very slightly or considerably; and if we compare the females of the green:finch, chaffinch, goldfinch, bullfinch, crossbil1, sparrow, &c., we shall see that they 1 Wallace,' The Malay Archipelago,' vol. ii. 1869, p. 304. 8 These species are described, with coloured figures, by M. F. Pollen, in 'Ibis,' 1866, p. 275. 0 ' Variation of Animals, &c., under Domestication,' vol. i. p. 251. VOL. II. 0 |