The question of crime offers good illustrations. There are kinds of crime which depend upon defective heredity, because they involve incapacity to acquire normal social functions. It is easier to discriminate these in theory than in practice, but it is well known that a considerable portion of our criminals are feeble-minded or ill balanced. But if a criminal has normal capacity, as the majority have, we must attribute his degeneracy to the fact that he has come under worse social influences rather than better. And the more ability he has, the more pernicious a criminal he makes. The same division may be made in any line of human function; we can never dispense with capacity, but there is no capacity of which we may not make a bad use. While the theory of the matter is not difficult, when one approaches it in this way, the applications are obscure, simply because it is hard to get at the facts. That is, we ordinarily cannot tell with any precision what the original hereditary outfit was, and just how it was developed by social influences. Even if we could study every child at birth it would not help us much, because, although the heredity is there, we have no art to know what it is until it works out in life, and it works out only in social development. Practically the two factors are always found in co-operation, and our knowledge that they are separable is largely derived from the lower forms of life where the social process is absent. It is often possible, however, to reach useful conclusions from indirect evidence. If, for example, hereditary stocks which are not remarkable for crime and vice in one environment rapidly become so in another, we may believe that the environment is the factor most in need of correction. This is the case with the immigrant population in our badly governed cities. On the other hand, if we find that individuals of a certain stock generally turn out ill, no matter in what conditions they may be placed, the argument for bad heredity is strong. This applies to many studies of degenerate lines, for which Dugdale’s work on The Jukes set the example. Where the matter is in doubt, as it must be in most cases, our line of action would seem to be somewhat as follows: If we are trying to better the conduct of living men and women, whose heredity, for better or worse, is already determined, we must proceed on the theory that environment is to blame, and try to better that. But if we are dealing with conditions that affect propagation, we should lean the other way. I mean that, if we find people living in a degeneracy which cannot clearly be ascribed to anything exceptional in the environment, we ought to hold the stock suspect, and prevent its propagation if we can. The cause that we have power over is always the one to emphasize.