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Show 282 DARWINISM CIIAJ•. of colour in the male, but rarely a decide~ diffcr~nco. The female of the great reel kangaroo, however, JS a delicate .gr~y ; while in the Lemur macaco of Madagascar the male lS JOtblack and the female brown. In many monkeys also there arc some differences of colour, especially on th? face. The sexual ·weapons and ornaments of malo mammaha., as horns, crests, manes, and dewlaps, arc well known, and .arc very numerous and remarkable. Having thus briefly revwwcd th~ facts,. we will now consider the theories to which they have g1ven n sc. Sexu.al Selection by the Struggles of Males. Amonrr tho hirrhcr animals it is a very general fact that the malesb firrht tob rrcthor for the possessi.O n of t h e females. This leads, i~ poly;amous animals especially, to the stronger or better armed males becoming the parents of the next generation, which inherits the peculiarities of the p~ren ts; and thus vigour and offensive weapons arc contmually increased in tho males, resulting in the strength and horns of the bull, the tusks of the boar, the antlers of the stag, and the spurs and fighting instinct of the gamecock .But a.lmost all male animals fight together, though not specmlly armed; even hares, moles, squirrels, and beavers fight to the death, anfl. are often found to be scarred and wounded. The s ~unc rule applies to almost all male birds ; and these battles have been observed in such different groups as hummingbirds, finches, goatsuckcrs, woodpeckers, ducks, and waders. Among reptiles, battles of the males arc known to occur in the cases of crocodiles, lizards, and tortoises ; among fishcf', in those of salmon and sticklebats. Even among insects the same law prevails; and male spiders, beetles of many groupR, crickets, and butterflies often fight together. From this very general phenomenon there necessarily results a form of natural selection which increases the vigonr and fighting power of the male animal, since, in every ca se, tho weaker are either killed, wounded, or driven away. This selection would be more powerful if males were always in excess of females, hut after much research Mr. Darwin could not obtain any satisfactory evidence that this was the case. The same effect, however, is produced in some cases by constitution or habits ; thus male insects usually emerge first from x COLOUR8 AND ORNAMENTS CHARACTERISTIC OF SEX 283 the pupa, and among migrating birds the males arrive first both in this country and in North America. Tho struggle is thus intensifi ed, and the most vigorous males arc the first to have offspring. This in all probability is a great advantage, as the early breeders have the start in securing food, and the young arc strong enough to protect themselves while the later broods arc being produced. It is to this form of male rivn.Iry that Mr. Darwin fir. t applied the term "sexual selection." It is evidently a real power in nature; and to it we must impute the development of the exceptional strength, size, and activity of the malo, together with the possession of special offensive and defensive weapons, and of all other characters which arise from the development of these or are correlated with them. But he has extended the principle into a totally different field of action, which has none of that character of constancy and of inevitable result that attaches to natural selection, including male rivalry ; for by far the larger portion of the phenomena, which he endeavours to explain by the direct action of sexual selection, can only be so explained on the hypothesis that the immediate agency is female choice or preference. It is to this that he imputes the origin of all secondary sexual characters other than weapons of offence and defence, of all the ornamental crests and accessory plumes of birds, the stridulating sounds of insects, the crests and beards of monkeys and other mammals, and the brilliant colours and patterns of male birds and butterflies. He even goes further, and imputes to it a large portion of the brilliant colour that occurs in both sexes, on the principle that variations occurring in one sex aro sometimes transmitted to the same sex only, sometimes to both, owing to peculiarities in the laws of inhcritn. ncc. In this extension of sexual selection to include the action of female choice or preference, and in the attempt to give to that choice such wide-reaching effects, I am unahlo to follow him more than a very little way; and I will now state some of the reasons why I think his views arc unsound. Sexual Characters due to N at?.wal Selection. Besides tho acquisition of weapons by the malo for the purpose of fi~hting with other males, there are some other |
