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Show 284 DARWINISM OHAP, sexual characters which may have been produced by ~atural selection. Such are the various sounds and odours whiCh arc pecu l1. ar t o th e rna1 e , an d wh1'ch serve as a call to th.e female or as an m. d1' cat 1' 0n of hi's presence · These are evidently a valuable addition to the means of recognition _o~ the two sexes, and are a further indication that the pa1rmg. seaso~ ~as · d . d the production intensification, and drfferentmt10n arnve , an ' · h' h f of these sounds and odours are clearly w1t m t c power. o natural selection. The same remark will apply to the pecuhar calls of birds, and even to the singing of the males. T_h~sc ell have orio-inatcd merely as a means of recogmt1on may w b • · · f between the two sexes of a species, and as a~ u~v~tat10n rom the male to the female bird. When the md1v1duals of a species are widely s~attere~, . s~h a call must be of great importance in enablmg parrmg to take place as early as possible, and thus the clearness, loudness, and individuality of the song becomes a useful cha:acter, a_nd therefore the .subject of natural selection. Such IS especmlly the case with tho cuckoo and with all solitary birds, and it may have been equall~ important ~t s_om~ per~od of the development of all birds. The act of smgmg IS eVIdently a pleasurable one ; and it probably serves as an outlet for ~uper~bu~dant nervous energy and excitement, just as d_ancmg, s_mg1~g, and field sports do with us. It is suggestive of this VIew that the exercise of the vocal power seems to be complementary to the development of accessory plumes and ornamcu t~, all our finest sino-ino- birds being plainly coloured, and with no crests, ne~k ~r tail plumes to display ; while the gorgeously ornamented birds of tho ~rop~cs have no song, and those which expend much energy m d1splay of plumage, as the turkey, peacocks, birds of paradise, and hummingbirds have comparatively an insignificant development of voice: Some birds have, in the wings or tail, peculiarly developed feathers which produce special sounds. In som~ of the little manakins of Bmzil, two or three of the wmgfeathers are curiously shaped and stiffened in the male, so that the bird is able to produce with thorn a peculiar snapping or cracking sound ; and the tail-feathers of s?v~ral species of snipe are so narrowed as to produce d1st:nct drumming, whistling, or switching sounds when the lmds x COLOUR~ AND ORNAMENTS CHARACTERISTIC OF SEX 285 descend rapidly from a great height. All these are probably recognition and call notes, useful to each species in relation to the most important function of their lives, and thus capable of being developed by the agency of natural selection. Decorative Plumage of Birds and its Display. Mr. Darwin has devoted four chapters of his Descent of Man to the colours of birds, their decorative plumage, and its display at the pairing season ; and it is on this latter circumstance that he founds his theory, that both the plumage and the colours have been developed by the prefer· ence of the females, the more ornamented males becoming the parents of each successive generation. Any one who reads these most interesting chapters will admit, that the fact of the display is demonstrated; and it may al so be admitted, as highly probable, that the female is pleased or excited by the display. But it by no means follows that slight differences in the shape, pattern, or colours of the ornamental plumes are what lead a female to give the preference to one malo over another ; sLill less that all the females of a species, or the great majority of them, over a wide area of country, and for many successive generations, prefer exactly the same modification of the colour or ornament. The evidence on this matter is very scanty, and in most cases not at all to the point. Some peahens preferred an old pied peacock; albino birds in a state of nature have never been seen paired with other birds ; a, Canada goose paired with a Bernicle gander ; a male widgeon preferred a pintail duck to its own species ; a hen canary preferred a male greenfinch to either linnet, goldfinch, siskin, or chaffinch. These cases are evidently exceptional, and are not such as generally occur in nature; and they only prove that the female does exert some choice between very different males, and some observations on birds in a state of nature prove the same thing; but there is no evidence that slight variations in the colour or plumes, in the way of increased intensity or complexity, arc what determines the choice. On the other hand, Mr. Darwin gives much evidence that it is not so determined. He tells us that Messrs. Hewitt, Tegetmeier, and Brent, three of the highest authorities and best observers, "do not believe that |