From a consideration of these differences in degree and difference in kind we may see that there is no course of training or treatment, no method of instruction, no trick for the mother or for the teacher that will be usable for all children under all circumstances, to make them all come up to some preconceived uniform standard. On the other hand, if we consider the differences as worth developing, and even emphasizing, it must be obvious that the training and the treatment should be adapted to the individual child so far as possible. Starting out with essentially different human beings, uniform treatment will not make them all alike, nor will _any_ treatment make them all alike. But starting out with a particular human being, we can learn to treat him in such a way as to make him develop into a more desirable person than he would become if he were neglected or if he were treated differently. And that is the main problem, after all.
The relation between heredity and environment may perhaps be made clear by an extreme illustration from the physical side. Here are two full-grown men, both five feet and four inches tall. We observe that they are both short. Now, the shortness of one of them turns out to be the result of heredity,--that is, he belongs to a strain of short people. No amount of feeding or of exercise or of special régime could have made him more than a quarter or half an inch taller. The other man, however, belongs to a race of rather taller men and women: his shortness of stature may be traced to undernutrition, or to overwork, or to sickness during his childhood. It is quite certain that a different kind of environment would have resulted in his being as tall as his brothers and sisters.
Now, the problem of training concerns itself practically not so much with the person who is particularly "long" by nature, nor so much with the person who is unusually "short" by nature--and we may apply "long" and "short" to every other trait as well as to stature. The problem with these extremes is simply to keep the child in good health. The special efforts of the teacher and of the parent are devoted to giving the child who appears somewhat below the average in some particular those special stimulations and exercises and feedings that will bring him up to the average. We find the extremely short too discouraging, and the extremely long do not clamor for our attention; but it is those near the middle-point that we want to help over to the other side of the dividing line. And this is just as true of an undesirable character as it is of a desirable one. We take no trouble to teach honesty to the child that seems instinctively honest; and we give up in despair with the child that convinces us of his utter lack of a moral sense: we concentrate our efforts upon the delinquents whom we catch early, or upon those who are in danger of sliding down if they are not helped along.