The Descent of Man – Day 131 of 151

In the Indian black-buck (A. bezoartica), which belongs to another tribe of antelopes, the male is very dark, almost black; whilst the hornless female is fawn-coloured. We meet in this species, as Mr. Blyth informs me, with an exactly similar series of facts, as in the Portax picta, namely, in the male periodically changing colour during the breeding-season, in the effects of emasculation on this change, and in the young of both sexes being indistinguishable from each other. In the Antilope niger the male is black, the female, as well as the young of both sexes, being brown; in A. sing-sing the male is much brighter coloured than the hornless female, and his chest and belly are blacker; in the male A. caama, the marks and lines which occur on various parts of the body are black, instead of brown as in the female; in the brindled gnu (A. gorgon) “the colours of the male are nearly the same as those of the female, only deeper and of a brighter hue.” (26. On the Ant. niger, see ‘Proc. Zool. Soc.’ 1850, p. 133. With respect to an allied species, in which there is an equal sexual difference in colour, see Sir S. Baker, ‘The Albert Nyanza,’ 1866, vol. ii. p. 627. For the A. sing-sing, Gray, ‘Cat. B. Mus.’ p. 100. Desmarest, ‘Mammalogie,’ p. 468, on the A. caama. Andrew Smith, ‘Zoology of S. Africa,’ on the Gnu.) Other analogous cases could be added.

The Banteng bull (Bos sondaicus) of the Malayan Archipelago is almost black, with white legs and buttocks; the cow is of a bright dun, as are the young males until about the age of three years, when they rapidly change colour. The emasculated bull reverts to the colour of the female. The female Kemas goat is paler, and both it and the female Capra aegagrus are said to be more uniformly tinted than their males. Deer rarely present any sexual differences in colour. Judge Caton, however, informs me that in the males of the wapiti deer (Cervus canadensis) the neck, belly, and legs are much darker than in the female; but during the winter the darker tints gradually fade away and disappear. I may here mention that Judge Caton has in his park three races of the Virginian deer, which differ slightly in colour, but the differences are almost exclusively confined to the blue winter or breeding-coat; so that this case may be compared with those given in a previous chapter of closely-allied or representative species of birds, which differ from each other only in their breeding plumage. (27. ‘Ottawa Academy of Sciences,’ May 21, 1868, pp. 3, 5.) The females of Cervus paludosus of S. America, as well as the young of both sexes, do not possess the black stripes on the nose and the blackish-brown line on the breast, which are characteristic of the adult males. (28. S. Muller, on the Banteng, ‘Zoog. Indischen Archipel.’ 1839-1844, tab. 35; see also Raffles, as quoted by Mr. Blyth, in ‘Land and Water,’ 1867, p. 476. On goats, Dr. Gray, ‘Catalogue of the British Museum,’ p. 146; Desmarest, ‘Mammalogie,’ p. 482. On the Cervus paludosus, Rengger, ibid. s. 345.) Lastly, as I am informed by Mr. Blyth, the mature male of the beautifully coloured and spotted axis deer is considerably darker than the female: and this hue the castrated male never acquires.

The last Order which we need consider is that of the Primates. The male of the Lemur macaco is generally coal-black, whilst the female is brown. (29. Sclater, ‘Proc. Zool. Soc.’ 1866, p. i. The same fact has also been fully ascertained by MM. Pollen and van Dam. See, also, Dr. Gray in ‘Annals and Magazine of Natural History,’ May 1871, p. 340.) Of the Quadrumana of the New World, the females and young of Mycetes caraya are greyish-yellow and like each other; in the second year the young male becomes reddish-brown; in the third, black, excepting the stomach, which, however, becomes quite black in the fourth or fifth year. There is also a strongly-marked difference in colour between the sexes of Mycetes seniculus and Cebus capucinus; the young of the former, and I believe of the latter species, resembling the females. With Pithecia leucocephala the young likewise resemble the females, which are brownish-black above and light rusty-red beneath, the adult males being black. The ruff of hair round the face of Ateles marginatus is tinted yellow in the male and white in the female. Turning to the Old World, the males of Hylobates hoolock are always black, with the exception of a white band over the brows; the females vary from whity-brown to a dark tint mixed with black, but are never wholly black. (30. On Mycetes, Rengger, ibid. s. 14; and Brehm, ‘Thierleben,’ B. i. s. 96, 107. On Ateles Desmarest, ‘Mammalogie,’ p. 75. On Hylobates, Blyth, ‘Land and Water,’ 1867, p. 135. On the Semnopithecus, S. Muller, ‘Zoog. Indischen Archipel.’ tab. x.) In the beautiful Cercopithecus diana, the head of the adult male is of an intense black, whilst that of the female is dark grey; in the former the fur between the thighs is of an elegant fawn-colour, in the latter it is paler. In the beautiful and curious moustache monkey (Cercopithecus cephus) the only difference between the sexes is that the tail of the male is chestnut and that of the female grey; but Mr. Bartlett informs me that all the hues become more pronounced in the male when adult, whilst in the female they remain as they were during youth. According to the coloured figures given by Solomon Muller, the male of Semnopithecus chrysomelas is nearly black, the female being pale brown. In the Cercopithecus cynosurus and griseo-viridis one part of the body, which is confined to the male sex, is of the most brilliant blue or green, and contrasts strikingly with the naked skin on the hinder part of the body, which is vivid red.

Head of male Mandrill (from Gervais, 'Hist. Nat. des Mammiferes').

Figure 69: Head of male Mandrill (from Gervais, ‘Hist. Nat. des Mammiferes’).

Lastly, in the baboon family, the adult male of Cynocephalus hamadryas differs from the female not only by his immense mane, but slightly in the colour of the hair and of the naked callosities. In the drill (C. leucophaeus) the females and young are much paler-coloured, with less green, than the adult males. No other member in the whole class of mammals is coloured in so extraordinary a manner as the adult male mandrill (C. mormon). The face at this age becomes of a fine blue, with the ridge and tip of the nose of the most brilliant red. According to some authors, the face is also marked with whitish stripes, and is shaded in parts with black, but the colours appear to be variable. On the forehead there is a crest of hair, and on the chin a yellow beard. “Toutes les parties superieures de leurs cuisses et le grand espace nu de leurs fesses sont egalement colores du rouge le plus vif, avec un melange de bleu qui ne manque reellement pas d’elegance.” (31. Gervais, ‘Hist. Nat. des Mammiferes,’ 1854, p. 103. Figures are given of the skull of the male. Also Desmarest, ‘Mammalogie,’ p. 70. Geoffroy St.-Hilaire and F. Cuvier, ‘Hist. Nat. des Mammiferes,’ 1824, tom. i.) When the animal is excited all the naked parts become much more vividly tinted. Several authors have used the strongest expressions in describing these resplendent colours, which they compare with those of the most brilliant birds. Another remarkable peculiarity is that when the great canine teeth are fully developed, immense protuberances of bone are formed on each cheek, which are deeply furrowed longitudinally, and the naked skin over them is brilliantly-coloured, as just-described. (Fig. 69.) In the adult females and in the young of both sexes these protuberances are scarcely perceptible; and the naked parts are much less bright coloured, the face being almost black, tinged with blue. In the adult female, however, the nose at certain regular intervals of time becomes tinted with red.

In all the cases hitherto given the male is more strongly or brighter coloured than the female, and differs from the young of both sexes. But as with some few birds it is the female which is brighter coloured than the male, so with the Rhesus monkey (Macacus rhesus), the female has a large surface of naked skin round the tail, of a brilliant carmine red, which, as I was assured by the keepers in the Zoological Gardens, periodically becomes even yet more vivid, and her face also is pale red. On the other hand, in the adult male and in the young of both sexes (as I saw in the Gardens), neither the naked skin at the posterior end of the body, nor the face, shew a trace of red. It appears, however, from some published accounts, that the male does occasionally, or during certain seasons, exhibit some traces of the red. Although he is thus less ornamented than the female, yet in the larger size of his body larger canine teeth, more developed whiskers, more prominent superciliary ridges, he follows the common rule of the male excelling the female.

I have now given all the cases known to me of a difference in colour between the sexes of mammals. Some of these may be the result of variations confined to one sex and transmitted to the same sex, without any good being gained, and therefore without the aid of selection. We have instances of this with our domesticated animals, as in the males of certain cats being rusty-red, whilst the females are tortoise-shell coloured. Analogous cases occur in nature: Mr. Bartlett has seen many black varieties of the jaguar, leopard, vulpine phalanger, and wombat; and he is certain that all, or nearly all these animals, were males. On the other hand, with wolves, foxes, and apparently American squirrels, both sexes are occasionally born black. Hence it is quite possible that with some mammals a difference in colour between the sexes, especially when this is congenital, may simply be the result, without the aid of selection, of the occurrence of one or more variations, which from the first were sexually limited in their transmission. Nevertheless it is improbable that the diversified, vivid, and contrasted colours of certain quadrupeds, for instance, of the above monkeys and antelopes, can thus be accounted for. We should bear in mind that these colours do not appear in the male at birth, but only at or near maturity; and that unlike ordinary variations, they are lost if the male be emasculated. It is on the whole probable that the strongly-marked colours and other ornamental characters of male quadrupeds are beneficial to them in their rivalry with other males, and have consequently been acquired through sexual selection. This view is strengthened by the differences in colour between the sexes occurring almost exclusively, as may be collected from the previous details, in those groups and sub-groups of mammals which present other and strongly-marked secondary sexual characters; these being likewise due to sexual selection.

Quadrupeds manifestly take notice of colour. Sir S. Baker repeatedly observed that the African elephant and rhinoceros attacked white or grey horses with special fury. I have elsewhere shewn (32. The ‘Variation of Animals and Plants under Domestication,’ 1868, vol. ii. pp. 102, 103.) that half-wild horses apparently prefer to pair with those of the same colour, and that herds of fallow-deer of different colours, though living together, have long kept distinct. It is a more significant fact that a female zebra would not admit the addresses of a male ass until he was painted so as to resemble a zebra, and then, as John Hunter remarks, “she received him very readily. In this curious fact, we have instinct excited by mere colour, which had so strong an effect as to get the better of everything else. But the male did not require this, the female being an animal somewhat similar to himself, was sufficient to rouse him.” (33. ‘Essays and Observations,’ by J. Hunter, edited by Owen, 1861, vol. i. p. 194.)

In an earlier chapter we have seen that the mental powers of the higher animals do not differ in kind, though greatly in degree, from the corresponding powers of man, especially of the lower and barbarous races; and it would appear that even their taste for the beautiful is not widely different from that of the Quadrumana. As the negro of Africa raises the flesh on his face into parallel ridges “or cicatrices, high above the natural surface, which unsightly deformities are considered great personal attractions” (34. Sir S. Baker, ‘The Nile Tributaries of Abyssinia,’ 1867.);–as negroes and savages in many parts of the world paint their faces with red, blue, white, or black bars,–so the male mandrill of Africa appears to have acquired his deeply-furrowed and gaudily-coloured face from having been thus rendered attractive to the female. No doubt it is to us a most grotesque notion that the posterior end of the body should be coloured for the sake of ornament even more brilliantly than the face; but this is not more strange than that the tails of many birds should be especially decorated.

With mammals we do not at present possess any evidence that the males take pains to display their charms before the female; and the elaborate manner in which this is performed by male birds and other animals is the strongest argument in favour of the belief that the females admire, or are excited by, the ornaments and colours displayed before them. There is, however, a striking parallelism between mammals and birds in all their secondary sexual characters, namely in their weapons for fighting with rival males, in their ornamental appendages, and in their colours. In both classes, when the male differs from the female, the young of both sexes almost always resemble each other, and in a large majority of cases resemble the adult female. In both classes the male assumes the characters proper to his sex shortly before the age of reproduction; and if emasculated at an early period, loses them. In both classes the change of colour is sometimes seasonal, and the tints of the naked parts sometimes become more vivid during the act of courtship. In both classes the male is almost always more vividly or strongly coloured than the female, and is ornamented with larger crests of hair or feathers, or other such appendages. In a few exceptional cases the female in both classes is more highly ornamented than the male. With many mammals, and at least in the case of one bird, the male is more odoriferous than the female. In both classes the voice of the male is more powerful than that of the female. Considering this parallelism, there can be little doubt that the same cause, whatever it may be, has acted on mammals and birds; and the result, as far as ornamental characters are concerned, may be attributed, as it appears to me, to the long-continued preference of the individuals of one sex for certain individuals of the opposite sex, combined with their success in leaving a larger number of offspring to inherit their superior attractions.

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