In the case of young boys the habit is so common that, according to Christian,[113] “very few are able to say that they have avoided it completely.” The same writer asks the question: “If it be remembered that onanism among certain peoples, at certain times, has been recognised as an ordinary event, it is difficult to avoid asking if there be not a latent vice, hidden in the depths of human nature, and ready to be provoked into activity by very small causes?” The answer is sufficiently plain. The cause of onanism, this “vice” or “crime,” as Tissot and other authors have called it, undoubtedly is the result of a natural disharmony in the human constitution, of a premature development of sexual sensation. Among the most civilised races and the lowest savages the mode of satisfying the premature demand is equally common. It is to be noticed that onanism is more common and earlier developed in the male sex. The development of sexual irritability in the female occurs very irregularly. In some races onanism is so much a custom among little girls that no attempt is made to conceal the practice. This occurs, for instance, among certain Hottentot tribes, and is referred to openly in talk and legends.[114] Similar instances occur elsewhere, but in most races the practice is thought wrong, and is concealed as much as possible. Among girls,[115] onanism is less frequent than in the case of boys, a circumstance in relation with the fact that sexual sensation usually appears much later in the female sex. It is almost a general rule that girls who have arrived at sexual maturity have not acquired sexual irritability, while to many it comes only gradually after marriage. Sometimes it does not occur until after the first child has been born. On the other hand, love begins very early in young girls, although it long retains a platonic character and is not associated with sexual sensation until much later. The maturity of the spermatozoa in the male comes long after the development of sexual irritability and of love. None the less, it comes before the organism of the male is actually ready. It happens, in consequence, especially among the highly civilised peoples, that marriage and regular unions are impossible at the right time. The youth has his education to finish, his profession to choose, and he must be ready to support children before he is able to marry. As civilisation advances, the age of marriage becomes later and later. In the case of Europeans, sexual maturity occurs in the male at the age of twelve to fourteen years, while the average age at the first marriage is shown in the following table:— _Table of Age at First Marriage._[116]