Sexual selection, even when left to random influences, is still not left to chance; it follows definite and ascertainable laws. In that way the play of love, however free it may appear, is really limited in a number of directions. People do not tend to fall in love with those who are in racial respects a contrast to themselves; they do not tend to fall in love with foreigners; they do not tend to be attracted to the ugly, the diseased, the deformed. All these things may happen, but they are the exception and not the rule. These limitations to the roving impulses of love, while very real, to some extent vary at different periods in accordance with the ideals which happen to be fashionable. In more remote ages they have been still more profoundly modified by religious and social ideas; polygamy and polyandry, the custom of marrying only inside one's own caste, or only outside it, all these various and contradictory plans have been easily accepted at some place and some time, and have offered no more conscious obstacle to the free play of love than among ourselves is offered by the prohibition against marriage between near relations.
Those simple-minded people who talk about the blind and irresistible force of passion are themselves blind to very ordinary psychological facts. Passion—when it occurs—requires in normal persons cumulative and prolonged forces to impart to it full momentum.
11 In its early stages it is under the control of many influences, including influences of reason. If it were not so there could be no sexual selection, nor any social organization.
The eugenic ideal which is now developing is thus not an artificial product, but the reasoned manifestation of a natural instinct, which has often been far more severely strained by the arbitrary prohibitions of the past than it is ever likely to be by any eugenic ideals of the future. The new ideal will be absorbed into the conscience of the