It’s scarcely conceivable that these crests of hair, and the strongly contrasted colours of the fur and pores and skin, can be the results of mere variability without the help of choice; and it’s inconceivable that they can be of use in any ordinary manner to those animals. In these latter instances we’ve motive to imagine that the colours were acquired through sexual selection; and we are naturally led to extend the same view to the foregoing species, although each sexes when adult have their faces coloured in the same method. This is probably carried on in some circumstances by the powerful odours emitted by the males during the breeding-season; the odoriferous glands having been acquired by sexual selection. In most of the species the sexes resemble each other in color, but in some, as we have now seen, the males differ from the females, especially in the color of the bare components of the pores and skin, in the event of the beard, whiskers, and mane. Within the Zoological Society’s Gardens I have typically overheard visitors admiring the beauty of another monkey, deservedly known as Cercopithecus diana (fig. 78); the general color of the fur is gray; the chest and inner surface of the forelegs are white; a large triangular defined space on the hinder part of the again is wealthy chesnut; within the male the inner sides of the thighs and the abdomen are delicate fawn-colored, and the top of the head is black; the face and ears are intensely black, contrasting finely with a white transverse crest over the attention-brows and a protracted white peaked beard, of which the basal portion is black.
The colours of the male in different circumstances may be resulting from simple variation, with out the aid of selection. Various crests, tufts, and mantles of hair, that are both confined to the male, or are more developed in this sex than within the feminine, appear most often to be merely ornamental, though they generally function a defence against rival males. This is surprising, for, because the males generally use their weapons for defence in opposition to enemies of all types, their weapons would have been of service to the females. The legislation of the equal transmission of characters to both sexes, as far as colour and other ornaments are involved, has prevailed far more extensively with mammals than with birds; but weapons, comparable to horns and tusks, have often been transmitted both solely or rather more completely to the males than to the females. As far as we will see, their absence in this sex may be accounted for under by the form of inheritance which has prevailed. Although many kinds of monkeys are far from stunning based on our style, other species are universally admired for their elegant look and bright colours.
With many kinds of deer the young are marked with elegant white spots, of which their mother and father exhibit not a trace. The face of the Cercopithecus petaurista (fig. 77) is black, the whiskers and beard being white, with an outlined, round, white spot on the nostril, coated with brief white hair, which supplies to the animal an almost ludicrous side. The looks of Cercocebus æthiops is grotesque, with its black face, white whiskers and collar, chesnut head, and a big naked white spot over every eyelid. It is often brown or flesh-color, with parts perfectly white, and often as black as that of the most sooty negro. In the hog-deer (Hyelaphus porcinus) the spots are extraordinarily conspicuous during the summer season when the coat is reddish-brown, but fairly disappear through the winter when the coat is brown. The Mantchurian deer (Cervus mantchuricus) is spotted throughout the entire year, but, as I’ve seen within the Zoological Gardens, the spots are a lot plainer during the summer, when the general colour of the coat is lighter, than through the winter, when the overall colour is darker and the horns are totally developed. As to deer, pigs, and tapirs, Fritz Müller has steered to me that these animals, by the removing of their spots or stripes by way of natural selection, would have been less easily seen by their enemies; and that they might have particularly required this protection, as soon because the carnivora elevated in dimension and number in the course of the tertiary periods.