This does not mean that no differences exist or can be found, only that the method of investigation must be different. It does not seem probable that the minds of races which show variations in their anatomical structure should act in exactly the same manner. Differences of structure must be accompanied by differences of function, physiological as well as psychological; and, as we found clear evidence of difference in structure between the races, so we must anticipate that differences in mental characteristics will be found. Thus, a smaller size or lesser number of nervous elements would probably entail loss of mental energy, and paucity of connections in the central nervous system would produce sluggishness of the mind. As stated before, it seems probable that some slight differences of this character will be found between the white and the negro, for instance, but they have not yet been proved. As all structural differences are quantitative, we must expect to find mental differences to be of the same description; and as we found the variations in structure to overlap, so that many forms are common to individuals of all races, so we may expect that many individuals will not differ in regard to their faculty, while a statistical inquiry embracing whole races would reveal certain differences. Furthermore, as certain anatomical traits are found to be hereditary in certain families, and hence in tribes, and perhaps even in peoples, in the same manner mental traits characterize certain families, and may prevail among tribes. It seems, however, an impossible undertaking to separate in a satisfactory manner the social and the hereditary features. Galton’s attempt to establish the laws of hereditary genius, and later endeavors in the same direction, point out a way of treatment for these questions which will prove useful in so far as it opens a method of determining the influence of heredity upon mental qualities.