centimeters. That of the American Indian is 1376, and that of the Negro 1344 cubic centimeters. With this difference in size there appears to be a corresponding difference in function. Thus far not enough accurate tests have been made upon Indians to enable us to draw reliable conclusions. The Negro, however, has been tested on an extensive scale. The results seem to leave little doubt that there are real and measurable differences in the mental powers of races, just as we know to be the case among individuals. The matter is so important that we may well dwell on it a moment before turning to the cause of the differences in the three streams of American immigrants. If there is a measurable difference between the inherent brain power of the white race and the black, it is practically certain that there are also measurable differences between the white and the red.

Numerous tests indicate that in the lower mental powers there is no great difference between the black and the white. In physical reactions one is as quick as the other. In the capacity of the senses and in the power to perceive and to discriminate between different kinds of objects there is also practical equality. When it comes to the higher faculties, however, such as judgment, inventiveness, and the power of organization, a difference begins to be apparent. These, as Ferguson * says, are the traits that "divide mankind into the able and the mediocre, the brilliant and the dull, and they determine the progress of civilization more directly than do the simple fundamental powers which man has in common with the lower animals." On the basis of the most exhaustive study yet made, Ferguson believes that, apart from all differences due to home training and environment, the average intellectual power of the colored people of this country is only about three-fourths as great as that of white persons of the same amount of training. He believes it probable, indeed, that this estimate is too high rather than too low. As to the Indian, his past achievements and present condition indicate that intellectually he stands between the white man and the Negro in about the position that would be expected from the capacity of his brain. If this is so, the mental differences in the three streams of migration to America are fully as great as the outward and manifest physical differences and far more important.

Why does the American Indian differ from the Negro, and the European from both? This is a question on which we can only speculate. But we shall find it profitable to study the paths by which these diverse races found their way to America from man's primeval home. According to the now almost universally accepted theory, all the races of mankind had a common origin. But where did man make the change from a four-handed, tree-dwelling little ape to a much larger, upright creature with two hands and two feet? It is a mistake to suppose that because he is hairless he must have originated in a warm climate. In fact quite the opposite seems to be the case, for apparently he lost his hair because he took to wearing the skins of slain beasts in order that he might have not only his own hair but that of other animals as a protection from the cold.

In our search for the starting-place of man's slow migration to America our first step should be to ascertain what responses to physical environment are common to all men. If we find that all men live and thrive best under certain climatic conditions, it is fair to assume that those conditions prevailed in man's original home, and this conclusion will enable us to cast out of the reckoning the regions where they do not prevail. A study of the relations of millions of deaths to weather conditions indicates that the white race is physically at its best when the average temperature for night and day ranges from about 50 to 73 degrees F. and when the air is neither extremely moist nor extremely dry. In addition to these conditions there must be not only seasonal changes but frequent changes from day to day. Such changes are possible only where there is a distinct winter and where storms are of frequent occurrence. The best climate is, therefore, one where the temperature ranges from not much below the freezing-point at night in winter to about 80 degrees F. by day in summer, and where the storms which bring daily changes are frequent at all seasons.

Surprising as it may seem, this study indicates that similar conditions are best for all sorts of races. Finns from the Arctic Circle and Italians of sunny Sicily have the best health and greatest energy under practically the same conditions; so too with Frenchmen, Japanese, and Americans. Most surprising of all, the African black man in the United States is likewise at his best in essentially the same kind of weather that is most favorable for his white fellow-citizens, and for Finns, Italians, and other races. For the red race, no exact figures are available, but general observation of the Indian's health and activity suggests that in this respect he is at one with the rest of mankind.

For the source of any characteristic so widespread and uniform as this adaptation to environment we must go back to the very beginning of the human race. Such a characteristic must have become firmly fixed in the human constitution before primitive man became divided into races, or at least before any of the races had left their original home and started on their long journey to America. On the way to this continent one race took on a dark reddish or brownish hue and its hair grew straight and black; another became black skinned and crinkly-haired, while a third developed a white skin and wavy blonde hair. Yet throughout the thousands of years which brought about these changes, all the races apparently retained the indelible constitutional impress of the climate of their common birthplace. Man's physical adaptation to climate seems to be a deep-seated physiological fact like the uniformity of the temperature of the blood in all races. Just as a change in the temperature of the blood brings distress to the individual, so a change of climate apparently brings distress to a race. Again and again, to be sure, on the way to America, and under many other circumstances, man has passed through the most adverse climates and has survived, but he has flourished and waxed strong only in certain zones.

Curiously enough man's body and his mind appear to differ in their climatic adaptations. Moreover, in this respect the black race, and perhaps the red, appears to be diverse from the white. In America an investigation of the marks of students at West Point and Annapolis indicates that the best mental work is done when the temperature averages not much above 40 degrees F. for night and day together. Tests of school children in Denmark point to a similar conclusion. On the other hand, daily tests of twenty-two Negroes at Hampton Institute for sixteen months suggest that their mental ability may be greatest at a temperature only a little lower than that which is best for the most efficient physical activity. No tests of this sort have ever been made upon Indians, but such facts as the inventiveness of the Eskimo, the artistic development of the people of northern British Columbia and southern Alaska, and the relatively high civilization of the cold regions of the Peruvian plateau suggest that the Indian in this respect is more like the white race than the black. Perhaps man's mental powers underwent their chief evolution after the various races had left the aboriginal home in which the physical characteristics became fixed. Thus the races, though alike in their physical response to climate, may possibly be different in their mental response because they have approached America by different paths.

Before we can understand how man may have been modified on his way from his