As far as positive Eugenics, or the selection of good human stocks for breeding, is concerned, the recent evolution of the movement seems to show that no firm and practicable proposal can yet be formulated. The truth is that the movement is greatly enfeebled by a general reliance on disputed theories of heredity. Some Eugenists rely on Weismann's theory: some on the Mendelist theory. They do not realise that scientific men are by no means agreed upon these theories, and it is a serious mistake to build on either. In England most of our biologists are Weismannists (in a broad sense), but there is more hostility to the theory in Germany and the United States, and both theories have lately had to confront grave difficulties. Any Eugenic proposal which is based on a theory of heredity must be regarded with reserve. The dogmatic statements of Professor Karl Pearson, for instance, in regard to the impossibility of altering by education the innate qualities of a child are entirely unwarranted. Heredity is still a mystery: and the relative importance of heredity and environment (or nature and nurture) is not yet determined. Detaching the element of theory, we have a plain proposal to eradicate tainted stocks from the human garden and promote the growth of the sounder. As I have said, the positive proposal to breed has not yet been put before us in a practicable or discussable form. This is largely because Eugenists fear to alarm the public by pointing out how it affects the position of marriage. There are, however, many other difficulties. The extraordinary diversity among children of the same parents warns us that we cannot count on the result of mating human beings, with their infinitely more complex nervous systems, as we can count on the issue of mating sheep or dogs. The mediocrity of the living children of our ablest men of the last generation, even when the mother was an excellent mate, is another circumstance to be considered. We do not yet know the points to breed for, and there is no constancy of result. Eugenists sometimes refer to the physical or mental superiority of one class of children over another, but in this they do not attempt to distinguish between the effect of environment and the natural endowment. Positive Eugenics is not yet beyond the stage of research. Such research, if conducted without academic prejudice (which is too apparent in many Eugenic papers), is of very great service; and, if ever a firm proposal lies before us, we may trust that rhetorical phrases and clerical prejudices will not be allowed to bar the way.