“People of sense and reflection are most apt to have violent and constant passions,” wrote Mary Wollstonecraft, “and to be preyed on by them." It is that fact which leads to the greater importance of sexual phenomena among the civilized as compared to savages. The conditions of civilization increase the sexual instinct, which consequently tends to be more intimately connected with moral feelings. Morality is bound up with the development of the sexual instinct. The more casual and periodic character of the impulse in animals, since it involves greater sexual indifference, tends to favor a loose tie between the sexes, and hence is not favorable to the development of morals as we understand morals. In man the ever-present impulse of sex, idealizing each sex to the other sex, draws men and women together and holds them together. Foolish and ignorant persons may deplore the full development which the sexual instinct has reached in civilized man; to a finer insight that development is seen to be indissolubly linked with all that is most poignant and most difficult, indeed, but also all that is best, in human life as we know it.
 De Rerum Natura, v, 1016.
 Raciborski (Traite de la Menstruation, p. 43) quotes the observation of an experienced breeder of choice cattle to this effect.
 “The organs which in the feral state,” as Adlerz remarks (Biologisches Centralblatt, No. 4, 1902; quoted in Science, May 16, 1902), “are continually exercised in a severe struggle for existence, do not under domestication compete so closely with one another for the less needed nutriment. Hence, organs like the reproductive glands, which are not so directly implicated in self-preservation, are able to avail themselves of more food.”
 Quarterly Journal of Microscopical Science, vol. xliv, 1900, p. 12, 31, 39.
 “Love,” in Thoughts on the Education of Daughters.
THE DEVELOPMENT OF THE SEXUAL INSTINCT.
It is a very remarkable fact that, although for many years past serious attempts have been made to elucidate the psychology of sexual perversions, little or no endeavor has been made to study the development of the normal sexual emotions. Nearly every writer seems either to take for granted that he and his readers are so familiar with all the facts of normal sex psychology that any detailed statement is altogether uncalled for, or else he is content to write a few fragmentary remarks, mostly made up of miscellaneous extracts from anatomical, philosophical, and historical works.
Yet it is as unreasonable to take normal phenomena for granted here as in any other region of science. A knowledge of such phenomena is as necessary here as physiology is to pathology or anatomy to surgery. So far from the facts of normal sex development, sex emotions, and sex needs being uniform and constant, as is assumed by those who consider their discussion unnecessary, the range of variation within fairly normal limits is immense, and it is impossible to meet with two individuals whose records are nearly identical.