Note 49 — Chapter II · —Classes Of Geographic Influences

Most of these problems are only secondarily grist for the geographer's mill. For instance, when the Aryans descended to the enervating lowlands of tropical India, and in that debilitating climate lost the qualities which first gave them supremacy, the change which they underwent was primarily a physiological one. It can be scientifically described and explained therefore only by physiologists and physico-chemists; and upon their investigations the geographer must wait before he approaches the problem from the standpoint of geographical distribution. Into this sub-class of physical effects come all questions of acclimatization.49 These are important to the anthropo-geographer, just as they are to colonial governments like England or France, because they affect the power of national or racial expansion, and fix the historical fate of tropical lands. The present populations of the earth represent physical adaptation to their environments. The intense heat and humidity of most tropical lands prevent any permanent occupation by a native-born population of pure whites. The catarrhal zone north of the fortieth parallel in America soon exterminates the negroes.50