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