(2) Climate and the Food Supply.—The effect of climate on man's material needs can best be illustrated by considering the food supply, for materials for clothing and shelter vary from place to place in the same way as food. Climate, more than anything else, m the nature and abundance of vegetation and hence of man's food supply. People who have spent their lives among the forests and meadows of a moist temperate climate such as prevails in the eastern United States often feel as if such vegetation prevailed everywhere. Similarly a person who has always lived in a dry climate is likely to think that all parts of the world consist of thriving irrigated orchards and fields surrounded by barren land with only a few scraggly bushes and tufts of dry grass. The man who lives among the forests and meadows may raise cattle, oats, turnips, and potatoes. The man in the dry climate may raise grapes, oranges, wheat, and celeg.1 These examples illustrate how greatly food may vary in response to the climate.
Variations in the food supply in their turn have much to do with people's habits. Since the Eskimo, for instance, lives in a climate which almost forbids the growth of vegetation upon the land, but not in the sea, he must catch sea animals for food. Therefore he is a good hunter and a bold fisherman, and wanders far and wide upon the water. He is as much at home in his kayak as upon the land. The Fiji Islander, on the other hand, lives in a climate where a few bread fruit trees or cocoanut palms furnish food for himself and his family without work. That is one reason why he is lazy and effeminate and spends most of his time sitting idly at home.
(3) Climate in Relation to Health and Energy.—Man's health and energy are influenced by climate both directly and indirectly. In the temperate zone everyone knows that some days the air is invigorating and on others depressing. Most people work slowly on hot, muggy days, for if they work fast the result is unusual weariness. On a clear bracing day in the autumn, on the contrary, we often feel as if we could do anything no matter how hard. Still later, on a cold winter day, we sometimes run to keep warm, but in the house we feel a little dull and stupid. Thus in many ways our activity of mind and body is influenced directly by climate. That is one chief reason why l: tropical races have never made much progress. Their climate is too warm. On the other hand, such people as the Chukjees of northern Asia are made stupid and their progress is retarded because their climate is too cold. .
Climate also influences the body indirectly, especially through diseases. When negroes or other tropical races change their climate by coming to the North they are liable to suffer from consumption, pneumonia, and similar diseases of the lungs. In tropical countries the diseases encouraged by the climate are far worse. There the
climatic conditions favor many disease-bearing insects such as the anopheles mosquito, which carries malaria, and the stegamaria mos quito, which carries yellow fever. How bad the tropical diseases are may be judged from the account of a recent traveler in the Amazon Basin. He speaks of the change in some of his comrades after only two weeks in the steaming, insect-infested forest. "Several of them were already suffering from violent attacks of malaria, and their faces were colorless and sallow; others who had been in the region longer stared at our boat with sunken, lusterless eyes in which not even a vestige of interest in our visit or of hope was evident; a few had apparently reached the stage where the sight of the twelve newly made graves on the hill-top no longer aroused feelings of dread or appre hension, but rather of indifference tempered with longing for a wel come release." The Varying Nature of Climate.—Among the five great elements of physical environment climate is by far the most variable. The location of a place cannot vary; the land forms and water bodies do not change perceptibly during many generations; and neither the soil nor minerals change appreciably except where man intervenes. Climatic conditions, on the contrary, are constantly changing. In the temperate zone a downpour of rain is followed by cloudless skies to-morrow; a warm, muggy day by one that is crisp and bracing.
Some winters are long and so cold that much snow accumulates; others are short and open. One year may be warm and wet, and the crops abundant; while the next year is so dry that the farmers can scarcely raise enough to make a living. Even in tropical and polar regions there are marked differences between different years, although the variability is not so great as in the temperate zone.
Climatic variations last through long periods as well as short. Perhaps twenty-five or thirty thousand years ago occurred the cli max of the last glacial epoch. Ice several thousand feet thick covered much of northwestern Europe and most of North America north of the Missouri and Ohio Rivers. Since that time the climate has changed so that most of the ice has melted and some of the places which it covered have become the most progressive parts of the world. The change, however, has been irregular, for sometimes the climate has for a time tended to go back to the former glacial conditions, and then has become even more mild than at present. Altogether we may say that climate is the variable factor in geographic environ ment. With every climatic variation, whether it be a great change lasting thousands of years or a little seasonal variation from one year to another, or from month to month, there is a corresponding change in vegetation, in animals, and in man.