It is only owing to the custom of wearing clothes that nudity provokes the sexual appetite. This custom develops artificially a sentiment of modesty with regard to nudity, which increases progressively in intensity and is especially marked in aged women. It is not so much habit, as to the feeling of progressive deterioration of their charms, which leads the latter to cover themselves as they grow older, and is part of the instinctive æsthetic sentiment of woman.
At the orgies and fêtes held among savages the women cover their sexual organs with certain objects, as a means to excite the men. Complete nudity is found more often in savage women than in the men.
Later on when it became the custom to wear clothes, nudity became attractive and was considered shameful. This is why the Chinese feel shame at exposing their feet, the Mahometans their faces, and some savages even the ends of their fingers.
Certain customs, like circumcision among the Jews, Polynesians and Australians; the artificial elongation of the lips of the vulva in Hottentots, Malays, and North American Indians, originated, according to Westermark, in the intention of exciting the sexual appetite, or of introducing variety into its satisfaction. Later on routine, which sanctions everything, transferred these customs into religious cult. It is possible, however, that among the Jews, who are a practical race, the hygienic advantage of circumcision took a part in its transformation into a rite.
To resume, everything derogatory to established custom excites the sentiment of shame or modesty, not only in sexual matters but in others. Most children are ashamed of not behaving exactly as their comrades or their brothers and sisters, and are very uncomfortable if they are obliged to behave otherwise. All sentiments of morality and modesty rest on conventionalities. The savage women burst into laughter when the naked companions of Livingstone turned their backs from modesty. The sentiment of modesty or shame thus depends only on exceptional violation of an old custom. This is why unconventional ways in one of the sexes (especially in woman) tend to offend the sentiments of modesty, and usually excite the sexual appetite of the other sex.