It is only right to say here, though the matter should only be touched on, that many Eugenists would contradict this, in so far as to claim that there was a consciously Eugenic reason for the horror of those unions which begin with the celebrated denial to man of the privilege of marrying his grandmother. Dr. S.R. Steinmetz, with that creepy simplicity of mind with which the Eugenists chill the blood, remarks that "we do not yet know quite certainly" what were "the motives for the horror of" that horrible thing which is the agony of Oedipus. With entirely amiable intention, I ask Dr. S.R. Steinmetz to speak for himself. I know the motives for regarding a mother or sister as separate from other women; nor have I reached them by any curious researches. I found them where I found an analogous aversion to eating a baby for breakfast. I found them in a rooted detestation in the human soul to liking a thing in one way, when you already like it in another quite incompatible way. Now it is perfectly true that this aversion may have acted eugenically; and so had a certain ultimate confirmation and basis in the laws of procreation. But there really cannot be any Eugenist quite so dull as not to see that this is not a defence of Eugenics but a direct denial of Eugenics. If something which has been discovered at last by the lamp of learning is something which has been acted on from the first by the light of nature, this (so far as it goes) is plainly not an argument for pestering people, but an argument for letting them alone. If men did not marry their grandmothers when it was, for all they knew, a most hygienic habit; if we know now that they instinctly avoided scientific peril; that, so far as it goes, is a point in favour of letting people marry anyone they like. It is simply the statement that sexual selection, or what Christians call falling in love, is a part of man which in the rough and in the long run can be trusted. And that is the destruction of the whole of this science at a blow.