The relentless force of nature’s uniting will shows itself not only in the way love brings together contradictions in marriage, but also in the rupture of marriage. A good wife, married to a good husband, loving and loved, is thus seized by a passion, incomprehensible to herself, for another man. Without reflection she gives herself up to her passion, to return again to the husband she has not ceased to love, but who never inspired in her the overmastering emotion whose purpose—according to the will of nature and of the woman herself—ought to have been a child. The same will of nature manifests itself in a number of phenomena, incomprehensible to others. An intellectual man or woman is seized by a passion for a person far inferior. How often has not a “good-looking fellow” vanquished the most high-souled man in the affections of such a woman; how often have not thoughtless beauty and empty gaiety won from a superior man what the personality of an exceptional woman could not secure! The whole secret was nature’s will to counterbalance cerebral and nervous genius by healthy, sensuous strength, to the advantage of the race. As sexual love has its origin in the fact that the sexual characters, which biologically are favourable to the race, are the most attractive, this general attraction constantly operates side by side with the individual; and it operates most strongly precisely in that kind of love which is rightly called “blind passion,” the kind which thus brings together to their misfortune conflicting contradictions. But there is no reason to doubt that love’s selection in this case will be able to retain its instinctive sureness, although love is continually widening its instincts of psychical sympathy also. The consequence of this is that the number of contradictions which may attract will become less, but on the other hand the fewer possibilities will be more finely adapted; that the selection among contradictions will thus become more and more difficult but at the same time more and more valuable. Love’s selection now not infrequently has for its result that, of two contradictions, irresistibly united by the affinity of souls, one or both does not offer the best physical conditions for children. But to make up for this the selection may turn out excellently for the enhancement of a particular disposition, the formation of a harmonious temperament, or the fostering of a great spiritual quality. It is not only by avoirdupois and yard-measure that the advance of the race must be tested.