Page:Popular Science Monthly Volume 76.djvu/265

Rh agricultural lands. Wheat and corn are replacing grass on the steppes, especially where irrigation can be practised. Deserts are being reclaimed here and there where water is available. The more civilized man becomes, the denser the population which the different parts of the earth can be made to support. From the wandering hunting and fishing tribes of the African forest or of the borders of the Arctic Sea, through the farming populations of the cleared forest and of the steppe, to the crowded industrial centers of the modern city, there is such a gradation. It is the story of a more complete to a less complete mastery of man by his environment.

But in spite of all that man can do, the larger climatic limitations persist. The Greenland desert of snow and ice, the Saharan desert of sand: these remain, deserts.

Primitive Civilization and the Tropics.—There are reasons for thinking that primitive, prehistoric man, in his earliest stages, when most helpless, was an inhabitant of the tropics; that he lived under the mild, uniform, genial climate of that zone, where food was easily obtained and protection against the inclemencies of the weather least necessary. There has been a belief that southern Asia, with its numerous bays and archipelagoes, was probably the cradle of humanity. Civilized man is believed by many to have appeared first on the delta formed at the head of the Persian Gulf by the Tigris and Euphrates rivers. Ancient civilizations seem to have developed in the drier portions of the tropics, where irrigation was necessary in order to insure abundant and regular crops, and where lived races more energetic and more hardy than those of the damper and rainier portions of the tropics, with more luxuriant vegetation. Within the tropics, the greatest progress later came, not on the damp lowlands, but on the less fertile plateaus of Mexico and Peru, where the Aztecs and the Incas made their marvelous progress in the drier, cooler and somewhat more rigorous climates over 7,000 or 8,000 feet above sea-level.

The Development of the Tropics.—Within the tropics, under the equatorial sun, and where there is abundant moisture, animal and plant life reach a very full development. Here are the lands which are most valuable to the white man because of the wealth of their tropical products. Here are the tropical "spheres of influence" or "colonies" which are among his most coveted possessions. It is in this belt that food is provided for man throughout the year without labor on his part; where shelter and clothing are so easily provided, and often so unnecessary, that life becomes too easy. Nature does too much; there is little left for man to do. The simplicity of life, so far as providing food is concerned, has been emphasized by writers almost without number. Captain Cook put the case very emphatically when he said that a South Sea Islander who plants ten bread-fruit trees does