We need to watch this fighting-line and take care of the wounded—see to it, that is, that those who fall into misery are given a chance to recover, if they are capable of it, and at any rate are not allowed to extend their condition to whole neighborhoods and form infectious misery environments. Unless we can abolish the struggle altogether, which seems neither possible nor desirable, I do not see how we can expect to avoid sporadic misery as a by-product of it; but what we _can_ do is so to standardize the conditions of the struggle and the care of those who fail as to prevent the growth of a self-perpetuating misery class. Scientific _a priori_ tests of fitness to propagate, such as may be developed by the aid of family records or medical and psychological examinations, will probably be found of increasing value in eliminating the definitely degenerate by segregation or sterilization. It is not probable, however, that they can ever meet the more general need of a competitive standard of biological competence. There are two fundamental and possibly permanent reasons why we cannot select our hereditary types artificially: first, because we are not likely to agree as to just what types are desirable, and, second, because if we did agree there is no practicable method of ascertaining the individuals belonging to these types and controlling their propagation. Selective breeding is a comparatively simple matter with domestic animals, where what we seek is a definite and easily ascertained trait like length or fineness of wool in sheep, weight in hogs or beef-cattle, speed or strength in horses, laying capacity in fowls, and so on. But in the case of man we do not know just what we want, and probably never shall. We should not dare to set up a standard of physical vigor, for fear of excluding psychical powers of more value; and the social and moral traits which we might desire to increase do not manifest themselves with certainty until rather late in life. Moreover, it is clear that the desirable thing in human life is not one good type but many, a diversity of types corresponding to multifarious and unforeseeable functions. It is most unlikely that we shall ever assume to define these types in advance. These difficulties seem so insuperable that it is hardly necessary to go on and show that, owing to the great share which environment has in producing desirable types of character, it is difficult to see how we could be sure what individuals lacked the requisite hereditary capacity. Galton’s view that success is a fair test has little following, and no other test is at hand. I conclude, then, that the sphere of a scientific eugenics, which shall deliberately select some types for propagation and reject others, should probably not extend much beyond the suppression of clearly marked kinds of degeneracy.