Professor Thorndike undertook experiments with groups of school children of high and of low initial ability respectively to determine whether equal opportunity or equal special training would produce an equalizing effect in easily alterable traits such as rapidity in addition and the like. Without exception he found that at the end of such experiments, although both groups had improved, the superior individuals were farther ahead than ever, that equality of opportunity and training had widened rather than narrowed the gap between the two classes. Others who have made special studies on the causes of individual differences have come to the same conclusion; namely, that individuals differ widely by original nature and that similarity in conditions of nurture and training will not avail in deleting these differences. Galton and others, from extensive studies based on English sources, have shown that notable achievements have run in certain families to a degree that is inexplicable on the basis of opportunity alone; it can be fully accounted for only by attributing much to superior inborn capacity. Doctor Woods has shown much the same thing for certain families in America. Schuster and Elderton have proved that there is a high degree of similarity in scholastic standing between fathers and sons in Oxford. Professor Pearson's measurements of mental characters in brothers and sisters while at school show a high degree of innate resemblance in many cases and certain cases of decided contrast. Where contrasts exist in certain families they remain unreduced in spite of the similarity of environment, thus proving that environment is less operative in the final intellectual establishment of such individuals than are their inborn aptitudes. Even in twins, as both Galton and Thorndike have shown, there is no tendency for similar education, home life and the like to render those originally different any more similar with advancing years. Professor Karl Pearson has done more perhaps than any other individual toward attempting actually to measure the relative strength of heredity and environment. Numerous statistical measurements lead him to conclude that it is a conservative estimate to regard heredity as at least five or ten times as important as environment in the development of the individual. A vigorous defense by him of this position will be found in _Biometrika_ for April, 1914.