=Inefficacy of Laws Which Forbid Marriage of Mental Defectives.--=The utter inefficacy of the first proposition, namely the enactment of laws restricting marriage, at least as regards the socially unfit whose condition is based on impaired mentality, has been demonstrated time and again. If they are forbidden marriage, they merely have children without getting married. Most states have laws to prevent the marriage of such individuals but these laws are almost wholly ineffective in preventing procreation on their part. We might as well recognize once for all that in such cases nothing short of close custodial care or sterilization will accomplish the end desired. As to the second proposition, systems of mating with the purpose of covering up and gradually diluting out defective traits, this has been shown to be possible with certain types of defectives. Whether it is desirable or not is a different question. [Illustration: FIG. 39 Inheritance of ability (chart condensed and incomplete) in three markedly able families (from Kellicott after Whetham): 1, Charles Darwin; 2, his cousin, Francis Galton, founder of the modern eugenic movement.] =Systems of Mating Impracticable in the Main.--=By systems of mating, it should be said, is not meant the arbitrary marrying of two individuals willy-nilly, but rather it is the prevention from marriage of two individuals having similar defects. In general the facts at our command indicate that in the majority of cases the offspring from a marriage of an insane, feeble-minded or epileptic person with a normal individual free from all neuropathic taints are normal or at most show but slight effects of the taint. But what normal individual would knowingly marry into such a stock? With few exceptions such traits where inheritable are apparently negative, that is, not represented by some positive abnormal factor but due to the lack of some element or elements necessary to the proper working of the normal brain. In the offspring of such a union the necessary missing factors are supplied by the normal parent. Or in Mendelian phraseology, the defective traits are recessive and are dominated by the normality of the other parent. Such offspring, however, while apparently normal of body are not normal of germ-plasm, inasmuch as half of their germ-cells will carry the abnormality of the defective parent as earlier explained (page 119) under Mendelism. We have already seen (page 119) how by continually marrying into strong strains the liability to recessive defect can be diluted out until the descendants are no more likely to have defective children than are members of our ordinary population. If, however, as is estimated in Bulletin No. 5 of the _Eugenics Record Office_, about thirty per cent. of our general population already carry recessive neuropathic taints, it certainly is a hazardous proceeding to attempt thus to breed out nervous defects unless one is