The redundant population of crowded western and southern Europe also seek these sparsely inhabited Tropics, but they come heavily handicapped by the necessity of acclimatization. They leave their homes from Trondhjem and Stockholm in the north to the Mediterranean in the south, where the mean annual temperatures vary from 5° to 17° C, (41° to 63° F.), to seek the Torrid Zone which averages 25° C. or 77° F. over most of its territory. The effects of a tropical climate are due to intense heat, to its long duration without the respite conferred by a bracing winter season, and its combination with the high degree of humidity prevailing over most of the Torrid Zone. These are conditions advantageous to plant life, but hardly favorable to human development. They produce certain derangements in the physiological functions of heart, liver, kidneys and organs of reproduction. Bodily temperature rises, while susceptibility to disease and rate of mortality show an increase ominous for white colonization. The general effect is intense enervation; this starts a craving for stimulants and induces habits of alcoholism which are accountable for many bodily ills usually attributed to direct climatic influences. Transfer to the Tropics tends to relax the mental and moral fiber, induces indolence, self-indulgences and various excesses which lower the physical tone.[1435] The social control of public opinion in the new environment is weak, while temptation, due to both climatic and social causes, is peculiarly strong. The presence of an inferior, more or less servile native population, relaxes both conscience and physical energy just when both need a tonic. The result is general enervation, deterioration both as economic and political agents.
Historical significance of deterioration
This is the effect of climate which has had the most far-reaching and persistent historical consequences. Our study of the historical movements of peoples in the northern hemisphere revealed a steady influx from colder into tropical and sub-tropical lands, followed always by enervation and loss of national efficiency, due partly to the debilitating heat of the new habitat, partly to its easier conditions of living, whether the intruders came as conquerors and appropriated the fat of the land, or as immigrant colonists who dropped into slack methods of agriculture, because rain and sun and soil made their reluctant labor scarcely necessary. Everywhere in the Tropics the enervating effects of heat, moisture, and abundance make not only the natives averse to steady work, but start the energetic European immigrant down the same easy descent to Avernus. Passing over the deterioration of the Aryans in India, the Persians in Mesopotamia, and the Vandals in Africa, we find that modern instances show the transformation to be very rapid. The French who since 1715 have occupied the islands of Réunion and Mauritius have lost much of their thrift and energy, though their new homes lie just within the southern tropic, and are blessed with an oceanic climate. Yet the volunteer troops sent by Réunion to aid in the recent subjugation of the Hovas in Madagascar proved to be utterly useless.[1436] The Spaniards who come to-day to Mexico have great energy, born of their former hard conditions of life in Spain. But their children are reared in a country whose mean annual temperature, even on the plateau, exceeds that of Spain by 10°C. (or 18°F.), a difference equal to that between Mobile and New York, or Madrid and Christiania. Hence they are less energetic and vigorous, while the third generation are typical Mexicans in their easy-going way of life.[1437] The Germans who recently have colonized southern Brazil in great numbers show a similar deterioration under similar increase of mean annual temperature, combined with somewhat greater humidity, which intensifies the debilitating effects of the heat. An investigation made in 1900 by the International Harvester Company of America revealed the fact that the German farmer in the State of Santa Catharina rarely cultivated over one acre of grain.[1438] Much of the iron in the blood and conscience of the New England missionary stock which went to Hawaii two generations ago has been dissolved out by the warm rain and balmy air of the islands.
The problem of acclimatization.
In all these instances the white race has been successfully transplanted. It has domiciled itself on the borders of the Tropics and has propagated its kind, though it has abated some of the vigorous qualities which characterized it in its temperate fatherland. In the real Tropics like India, Cochin China, the Malay Archipelago, and Central Africa, the whole perplexing and urgent problem of European colonization turns on the difficulty or impossibility of acclimatization; and this in turn affects the whole economic, ethnic and political destiny of present colonial holdings. If acclimatization is impossible, the alternative is an imported ruling class, constantly invalided and as constantly renewed, aided by a similar commercial body acting as superintendents of labor; the whole machine of government and economic exploitation is supported by a permanent servile native population, doing the preeminently tropical work of agriculture, which is so fatal to the white man in a torrid climate. This means that the conquering white race of the Temperate Zone is to be excluded by adverse climatic conditions from the productive but undeveloped Tropics, unless it consents to hybridization, like the Spaniards and Portuguese of tropical America. In that national struggle for existence which is a struggle for space, it means an added advantage for the Mediterranean peoples, that they are more tolerant of a torrid climate than the blond Teutons, whose disability in this regard is pronounced; it means that the aptitude of the Chinese for a wide range of climatic accommodation, from the Arctic circle to the equator, lends color to "the yellow peril."
Historical importance of the temperate zones.
In contrast to the monotonous extremes of climate in the hot and cold zones, temperate lands are characterized by the intermediate degrees of annual temperature and marked seasonal diversity which are so favorable to human development. In Arctic lands labor is paralyzed by cold as it is by heat in the enervating and overproductive Tropics. In one, the growing season is too short and ill-favored; in the other, too long to stimulate man to sustained industry. Hence the Temperate Zones, whose climate avoids both these extremes and abounds in contrasts, whose summers are productive enough to supply food for the winter, and whose winters give both motive and energy for the summer's work, are richer in cultural possibilities and hence in historical importance.