"The reader who grasps that a thousand years is but a small period in the evolution of man, and yet realises how diverse were morality and customs in matters of sex in the period which this essay treats of" (_i.e._ _Mother-Age Civilisation_), "will hardly approach modern social problems with the notion that there is a rigid and unchangeable code of right and wrong. He will mark, in the first place, a continuous flux in all social institutions and moral standards; but in the next place, if he be a real historical student, he will appreciate the slowness of this steady secular change; he will perceive how almost insensible it is in the lifetime of individuals, and although he may work for social reforms, he will refrain from constructing social Utopias."--Professor KARL PEARSON. Our study of the sexual associations among animals has brought us to understand how large a part the gratification of the sex-instincts plays in animal life, equalling and, indeed, overmastering and directing the hunger instinct for food. If we now turn to man we find the same domination of sex-needs, but under different conditions of expression.[97] Man not only loves, but he knows that he loves; a new factor is added, and sex itself is lifted to a plane of clear self-consciousness. Pathways are opened up to great heights, but also to great depths. We must not, therefore, expect to take up our study of primitive human sexual and familial associations at the point where those of the mammals and birds leave off.[98] We have with man to some extent to begin again, so that it may appear, on a superficial view, that the first steps now taken in love's evolution were in a backward direction. But the fact is that the increased powers of recollection and heightened complexity of nervous organisation among men, led to different habits and social customs, separating man radically in his love from the animals. Man's instincts are very vague when compared, for instance, with the beautiful love-habits of birds; he is necessarily guided by conflicting forces, inborn and acquired. Thus precisely by means of his added qualities he took a new and personal, rather than an instinctive, interest in sex; and this after a time, even if not at first, aroused a state of consciousness in love which made sex uninterruptedly interesting in contrast with the fixed pairing season among animals. Hence arose also a human and different need for sexual variety, much stronger than can ever have been experienced by the animals, which resulted in a constant tendency towards sexual licence, of a more or less pronounced promiscuity, in group marriage and other forms of sexual association which developed from it.