OCR Text |
Show 270 THE PRINCIPLES OF PAR'£ II. be polygamous. With the Grallatores, extremely few species differ sexually, but the ruff (Machetes pugnax) affords a strong exception, and this species is believed by Montagu to be a polygamist. Hence it appe~rs that with birds there often exists a close relatiOn between polygamy and the development of stronglymarked sexual differences. On asking Mr. Bartlett, at the Zoological Gardens, who has had such large experience with birds, whether the male tragopan (one of the Gallinacere) was polygamous, I ·was struck by his answering, "I do not know, but should think so from " his splendid colours." It deserves notice that the instinct of pairing with a single female is easily lost under domestication. The wild-duck is strictly monogamous, the domestic-duck highly polygamous. The Rev. W. D. Fox informs me that with some half-tamed wild-ducks, kept on a large pond in his neighbourhood, so many mallards were shot by the gamekeeper that only one was left for every seven or eight females; yet unusually large broods were reared. The guinea-fowl is strictly monogamous; but Mr. Fox finds that his birds succeed best when he keeps one cock to two or three hens.9 Canary-birds pair in a state of nature, but the breeders in England successfully put one male to four or five females; nevertheless the first female, as Mr. Fox has been assured, is alone treated as the wife, she and her young ones being fed by him ; the others are treated as concubines. I have noticed these cases, as it renders it in some degree probable that monogamous species, in a state of nature, might readily become either temporarily or permanently polygamous. 9 The Rev. E. S. Dixon, however, speaks positively ('Ornamental Poultry,' 1848, p. 76) about the eggs of the guinea-fowl being infertile when more than one female is kept with the same male. Cnar. VIII. SEXUAL SELECTION. 271 vVith respect to reptiles and fishes, too little is known of their habits to enable us to speak of their marriage arrangements. The stickle-back Gasterosteus), however, is said to be a polygamist; 10 and the male during the breeding-season differs conspicuously from the female. To sum up on the means through which, as far as we can judge, sexual selection has 1ed to the development ofsecondary sexual characters. It has been shewn that the largest number of vigorous off:3pring will be reared from the pairing of the strongest and best-armed males, which have conquered other males, with the most vigorous and best-nourished females, which are the first to breed in the spring. Such females, if they select the more attractive, and at the same time vigorous, males, will rear a larger number of offspring than the retarded females, which must pair with the less vigorous and less attractive males. So it will be if the more vigorous males select the more attractive and at the same time healthy and vigorous females · and this will especially hold good if the male defend~ the female, and aids i~ providing f<?od for the young. ~he ad.vantage thus gamed by the more vigorous pairs m rearrng a larger number of offspring has apparently sufficed to rend?r sexual selection efficient. But a large preponderance m number of the males over the females would be still more efficient ; whether the preponderance was only occasional and local, or permanent; whether it occurred at birth, or subsequently from the greater destruction of the females ; or whether it indirectly followed from the practice of polygamy. The Male generally more rrwdified than the Female.rrhroughout the animal kingdom, when the sexes differ 10 Noel Humphreys, 'River Gardens,' 1857. |