These threaten to modify Galton's law of regression towards mediocrity, and indeed to nullify his ancestral law. Mendelian experiments, however, on human beings have not yet been conspicuously successful. Owing to disturbing and amplifying factors only few normal characters, eye-colour for instance, have been demonstrated to follow Mendelian laws. Abnormal characters can be more easily verified. Deaf-mutism, for instance, acts as a recessive.
Selection implies rejection.
Thus the science is divided into positive eugenics and negative. The one encourages parenthood of the fit or worthy, whilst the other discourages parenthood of the unfit or unworthy. Thus eugenics concerns itself largely with selection in marriage and with the exercise of the marital function. Negative eugenics also seeks to eradicate the racial defects of alcohol, venereal disease, lead poisoning, feeble-mindedness, and consumption. But the Church, too, has a doctrine concerning marriage and its use, and also a doctrine and a method of dealing with racial defects.