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Show 222 SEXUAL SELECTION: BIRDS. will not pretend to say; but the case is too remarkable to be passed over without notice. We have now seen in numerous instances under all six classes, that an intimate relation exists between the plumage of the young and that of the adults, ~ither of one sex or both sexes. These relations are fauly well explained on the principle that one sex-this being in the great majority of cases the male-first ac:quired throuO'h variation and sexual selection bright colours 0 • • or other ornaments, and transmitted them m vanous ways, in accordance with the recognised laws of inheritance. Why variations have oceurred at different periods of life, even sometimes with the species of the same group, we do not know ; but with respect to the form of transmission, one important determining cause seems to have been the age at which the varia-tions first appeared. From the principle of inheritance at corresponding ages, and from any variations in colour which occurred in the males at an early age not being then selected, on the contrary being often eliminated as dangerous, whilst similar variations occurring at or near the period of reproduction have been preserved, it follows that the plumage of the young will often have been left unmodified, or but little modified. vVe thus get some insight into the colouring of the progenitors of our existing species. In a vast number of species in five out of our six classes of cases, the adults of one sex or both are brightly coloured, at least during the breeding-season, whilst the young are invariably less brightly coloured than the adults, or are quite dull-coloured; for no instance is known, as far as I can discover, of the young of dull-coloured species displaying bright colours, or CIIAP. XVI. COLOUR AND PROTECTION. 223 of. t~e young of brightly-coloured species being more bnll1antly coloured than their parents. In the fourth class, however, in which the young and the old resemble each o~her, there are many species (though by no means all) bng~tly-coloured~ and as these form whole groups, we. may mfer that their early progenitors were likewise bngh~ly-coloured. With this exception, if we look to the bu·ds of the world, it appears that their beaut has been great!y increased since that pe1·iod, of which we have a partial record in their immature plumage. ~n the Ool?ur of the Plumage in relation to Pr;·otectwn.- It w.Ill have been seen that I cannot follow Mr. Wallace m the belief'that dull colours when confin. ed to the females have been in most cases speciaJly gamed for the sake of protection. There can, however, be no d?ubt, as formerly remarked, that both sexes of many b1rds have had their colours modified for this ~urpose, ~o a_s to escape the notice of their enemies; or, m some. Instances, su as to approach their prey unobserved, m the same manner as owls have had their plumage rendered soft, that their flight may not be o" v.e rheard. Mr. vVallace remarks 50 that " 't · 1 1 . 1 IS on y " m .t 1e tropics, among forests which never lose their fol~age, that we find whole groups of birds whose "ch1 e f co l our 1· s green. " It will be admitted b'y every one, wh? has ever tried, how difficult it is to distinguish parrots m a leaf-covered tree. Nevertheless, we must remember that many parrots are ornamented with crimson blue, and orange tin~s, which can hardly be protective~ Woo.dpeckers are emmently arboreal, but, besides green f?.ecies, there are ~any ~lack, and black-and-white l..mds-all the species bemg apparently exposed to ~0 'Westminster Review,' July, 18G7, p. 5. |