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Show 220 SEXUAL RELECTION: 13IRDS. l'AHT II. ocked with brown.48 So that the very same feath rs whlch in the young blackbird assume their .mature character and beeomo black after the others, m those two species assume this character and beco.me bl~o before the others. The most probable view w1th reference to these cases is that the males, differently from what occurs in Class I., have trausmitted their colours to their male offspring at an earlier age than ~hat at whic:h they themselves first acquired them; for rf they had varied whilst quite young, they woul~ proba?ly have transmitted all their characters to thou offsprmg .of both sexes.49 In Aithurus polytmus (one of the humming-birds) the male is splendidly coloured black and green, and two of the tail-feathers are immensely lengthened; the female has an ordinary tail and inconspicuous colours; now the young males, instead of resembling the adu.lt female in accordance with the common rule, begm from ;he first to assume the colours proper to their sex and their tail-·feathers soon become elongated. I ~we this information to Mr. Gould, who has given me tho following more striking and as yet unpublished case. rrwo humming-birds belonging to the genus Eustephanus, both beautifully coloured, inhabit the small island of Juan Fernandez, and have always been ranked as specifically distinct. But it bas lately been ascertained that the one, which is of a rich ches- 4R Mr. C. A. Wright, in' Ibis,' vol. vi. 186·.1:, p. 65. Jordon,' Birds of India,' vol. i. p. 515. . 49 The following additional cases may be mcnt10ned: the young males of Tanagra ru1n·a can be distinguished from the y~u~g f~males (Audubon, 'Ornith. Biography,' vol. iv. p. 392), a~cl ~o 1t ~s wtth the nestlings of a blue nuthatch, Dendrophila j1·ontahs of Iud1a (Jordon, 'Birds of India,' vol. i. p. 389). Mr. Blyth also informs me that the srxrs of the stoncchat, Saxicola rubicola, arc distinguishable at a very -early age, Cn. XVI. THE YOUNG LIKE ADULTS OF SAME SEX. 221 nu~-brown colour with a golden-reel head, is the male, whilst the otl~er, ~hich is elegantly variegated with green and wh1te with a metallic-green head, is the female.. Now tho young from the first resemble to a c01·tam extent tho adults of the corresponding sex, the resemblance gradually becoming more and more complete. In considering this last case, if as before we take the plumage of the young as our guide, it would appr.ar that ~oth sexes have been independently rendered boauttf~l; and not that the one sex has partially transfen ·ecl Its. beau~y to. the other. The male apparently h.as ~cqmred his br1ght colours through sexual selectiOn m the same manner as, for instance, the peacock or pheasant in our first class of cases; and the female in ~he same manner as the female Rhynchma or Turnix m our second class of cases. But there is much difficulty in understanding how this could have been effected a~ the same time with the two sexes of the same .species. Mr. Salvin states, as we have seen in the e1ghth chapter, that with certain bummino--birds th.e males greatly exceed in number the females, 0 whiJst w1th other species inhabiting the same country the females greatly exceed the males. If, then, we might assume t.hat during some former lengthened period the males of the Juan Fernandez species had greatly exceeded the females in number, but that durino· another lengthened period the females had greatly 0 exceedecl t~1e males, we could understand how the males at one t1me, and the fe~ales at another time, might have been rendered. be.a~ttful by the selection of the brightercoloured md1v1dua1s of either sex; both sexes transmitting their characters to their young at a rather earlier age than usual. Whether this is the true explanation I |