_Correlation of Physical Traits to Vital Powers._--The physical traits are correlated to the physiological functions in such a manner as profoundly to influence the destiny of nations. They enable or disable man with reference to the climatic and other conditions of his surroundings. For instance, certain races can support given temperature better than others. The intense heat and humidity of Central Africa or Southern India are destructive to the pure whites, while the climate north of the fortieth parallel soon exterminates the blacks. The food on which the Australian thrives destroys the digestive powers of the European. Exemption and liability to diseases differ noticeably in races. The white race is more liable to yellow fever, malarial diseases, syphilis, scarlet fever and sunstroke; the colored races to measles, tuberculosis, leprosy, elephantiasis, and pneumonia.
Indeed, from the physical point of view, the pure white is weaker than the dark races, worse prepared for the combat of life, with inferior viability. This has been shown by the careful researches of statisticians.[16] But in the white this is more than compensated by the development of the nervous system and the intellectual power. He can bear greater mental strain than any other race, and the activity of his mind supplies him with means to overcome the inferiority of his body, and thus places him at the head of the whole species.
The _tolerance of disease_ is an obscure but momentous element in the comparison of races. It is almost a proverb among the Spanish-American physicians that “when an Indian falls sick, he dies.” The greater longevity of the European peoples is due to their ability to support disease long and frequently, without succumbing to it. On the other hand, surgical injuries, wounds and cuts, appear to heal more rapidly among savage peoples.[17] It is clear that in civilized conditions this is less important than tolerance.
_The Causes of the Fixation of Ethnic Traits._--These causes are mainly related to climate and the food-supply. The former embraces the questions of temperature, humidity, atmospheric pressure (altitude), malarial or zymotic poisons, and the like. All these bear directly upon the relative activity of the great physiological organs, the lungs, heart, liver, skin and kidneys, and to their action we must undoubtedly turn for the origin of the traits I have named. On the food-supply, liquid and solid, whether mainly animal, fish or vegetable, whether abundant or scanty, whether rich in phosphates and nitrogenous constituents or the reverse, depend the condition of the digestive organs, the nutrition of the individual, and the development of numerous physical idiosyncrasies. Nutrition controls the direction of organic development, and it is essentially on arrested or imperfect, in contrast to completed development, that the differences of races depend.