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Show 210 SEXUAL SELECTION : BIRDS. d. I may remark that under the Before procee mg, s;s of cases the facts arc so present and two nextc~~:~ons so doubtful, that any one complex, and the c?nl . terest in the subject had bettor who feels no especia m pass them over. h · 1 charac- The briUiant or conspicuous colours w IC l ' 1 t : any birds in the present class, can r~re y euse m, . . th m as a protectiOn ; ot· never be of serviCe to e . h 1 that they have probably been gained by t e ma es :~rough sexual selection, and then transferre~lto t~~ females and the young. It is, however, possi .e a the males may have selected the mo:·e attractive fe-les . and if these transmitted theu characters to mthae ir o' ffsprm. g of b ot h sexes, tl 1e same results wou· ld follow as from the selection of the more. attractive males by the females. But there is some evid~nce that this contiugency has rarely, if ever, oceurred m an\ff those groups of birds, in which the se~es are. g.enera y alike; for if even a few of the successive vanatwns bad £ 'led to be transmitted to both sexes, the females ,:~uld have exceeded to a slight degree the males m. b eau t y. Exactly the reverse occurs u. nhd erh Ilature; for in almost every large group, in whw . t e sexes O'enerally resemble each other, the males of some few ~pecies are in a slight degree mo.re brightly coloured · than the females. It is again possible that the females may have selected the more beautiful males, these males having reciprocally selected the more beautiful females; but it is doubtful whether this double process of selection would be likely to occur, owing to the great~r eacrerness of one sex than the other, and whethei: Jt w;uld be more etlicient than selection on ~ne side alone. It is, therefore, the most probable view tha~ sexual selection has acted, in the present class, as far as ornamental characters are. concerned, in accordance «' HAP. XH TilE YOUNG LIKE BOTH .ADULTS. 2ll with the general rule throughout the animal kingdom, that is, on the males; and that these have transmitted their gradually-acquired colours, either equally or almost equally, to their offspring of both sexes. Another point is more doubtful, namely, whether the successive variations first appeared in the males after they had become nearly mature, or whilst quite young. In either case sexual selection mnst have acted on the male when he had to compete with rivals for the possession of the female; and in both cases the characters thus acquired have been transmitted to both sexes and all ages. But these characters, if acquired by the males when adult, may have been transmitted at first to the adult - alone, and at some subsequent peL"iod transferred to the young. For it is known that when the law of inheritance at corresponding ages fails, the offspring often inherit characters at an earlier age than that at which they first appeared in their parents.3° Cases apparently of this kind have been observed with birds in a state of nature. For instance Mr. Blyth has seen specimens of Lanius 'rufus and of Colymbus glacialis which had assumed whilst young, in a quite anomalous manner·, tho adult plumage of their parents.31 Again, the young of the ·ommon swan (Cygnus olo'r) do not cast off their dark feathers and become white until eighteen months or two years old; but Dr. I?. FOI'el has described the case of three vigorous young birds, out of a brood of four, which were born pure white. These young birds were not albinoes, as shewn by the eolour of their beaks :lo 'Variation of Animals and Plants under Domestication,' vol. ii. J). 7D. 31 Chal'lesworth, 'Mag. of Nat. Hist.' vol. i. 1837, p. 305, 306. p 2 |