The attraction of the Darwinian theory is of course obvious. After having realised the important part which sexual selection plays in the “artistic” activities of animals, one is naturally tempted to apply the same principle to all similar activities in men. The influence of erotic preferences is a biological datum, and, as such, a principle of a more universal order, so to speak, than any one of the social or religious motives.[372] However advantageous it may be to apply this all-embracing explanation to the whole field of art, a descriptive study of the facts must needs compel us to pay attention to the sociological influences which assist or impede the operation of sexual selection. There is no doubt that there are some secondary sexual characters and activities which are developed under all social conditions. And it is no less certain that both sexes are everywhere influenced by individual predilections. But these predilections cannot, of course, be regarded as factors of importance in a society where strictly-fixed marriage customs allow the partners no freedom of choice. They will, on the other hand, produce special and differentiated means of attraction where, either from demoralisation, as in Tahiti, or as the result of institutional polygamy, as in the Mohammedan countries, or owing to free and idyllic conditions of life, as among the various tribes of India, competition for the favour of a male or a female is unrestricted. It is impossible, without transgressing the limits of the present work, to give a complete account of the influences of society on erotic art. An author who should be able to embrace in his treatment all stages of evolution, the latest and most highly developed as well as the earliest, would undoubtedly contribute an interesting chapter to art-philosophy if he were to explain in detail and with examples how, _e.g._, lyric poetry has changed with changed marriage customs. Taking the art of historic nations, the contrast between the literature of polygamous Orientals and that of Europeans, whose notions of love are influenced by marriage institutions at least officially monogamous, would afford an opportunity for most suggestive comparisons. And even within the limits of modern art a comparison perhaps equally instructive may be made between the different classes of society with their varying forms of sexual life. No task could be more interesting than that of finding out to how great an extent the marvellously refined and differentiated expressions of romantic love which characterise some schools of modern poetry are dependent upon the peculiar forms of sexual life prevailing among the upper classes. As social factors of powerful, though never sufficiently recognised influence, the veiled polyandry and polygamy which lie at the bottom of modern society have undoubtedly influenced æsthetic notions as well as artistic activities. By causing a division of the sexual impulses