Two problems may be distinguished here which have too often been confounded in discussions of the mental characteristics of civilized man and of primitive man. The one relates to the distinctions between races; the other, to distinctions between the social strata of the same race. According to the meaning of the terms “civilized” and “primitive,” it is perfectly conceivable that there may be civilized groups belonging to different races (like the Chinese and Europeans), and civilized as well as primitive groups, both belonging to the same race (like the Yukaghir of Siberia and the Chinese, or like the group of educated negroes in the United States and the primitive tribes of the coasts of Africa). The problems presented by the differences between the various races of man, and by the differences between social groups in the same races, are, of course, entirely distinct, and each requires separate treatment. There is one peculiarity common to both problems, which must be described before we can properly take up their treatment. When we compare the individuals comprising any one racial or social type, we find that they are not by any means uniform, but exhibit considerable variation. When we try to think of a Norwegian and of a negro, two entirely distinct types will be present to our minds,—the Norwegian, tall, with blond and somewhat wavy hair, blue eyes, light complexion, delicate face and nose; the negro, of medium stature, with black and frizzly hair, dark eyes, dark skin, projecting jaw, and heavy flat nose. Still, these pictures are only abstractions of what we think we have noticed most commonly in each type. When we compare the Norwegians among themselves, or the negroes among themselves, we find that each individual in each series has his peculiarities, which the others do not share. There are tall and short Norwegians; their hair is blond or dark, straight or wavy; their eyes vary from brown to blue; their complexion is light or dark, their faces more or less delicate. And so with the negroes. The degree of blackness, the amount of projection of the chin, the flatness of the nose,—all show very considerable variations. Experience has demonstrated that in all cases of this kind, one certain type, one certain combination of features, is most common; and that deviations in either direction from this type become the rarer, the greater their amount. Thus the Norwegians show a prevalence of a certain blond color. Individuals with a color of hair much lighter than the most common color are the rarer, the greater the difference of their hair-color from the most common one; and in the same way individuals with a color of hair much darker than the most common color are the rarer, the greater the deviation of their color of hair from the common one. The extent to which such variations occur is not always the same. In some cases the individuals constituting the group show a remarkable