THE SIGNIFICANCE OF CENTRAL ASIA 15
the west to China Proper on the east. Other evidence, which has not as yet been investigated in detail, indicates that the parallelism applies to all the historic lands of the Old World and possibly to the New. As we look back into the past, we are forced to the conclusion that whatever the motive power of history may be, one of the chief factors in determining its course has been geography; and among geographic forces, changes of climate have been the most potent for both good and bad.
In the last chapter of this book I shall consider this conclusion in its broader outlines as part of the philosophy of history. For the most part, however, I shall confine myself to a statement of the phenomena which have led to its adoption. Briefly restated, the fundamental idea of this volume is that geography is the basis of history. The physical features of the earth's surface limit the organic inhabitants of a given region to certain species of plants and animals, including man, which live together in mutual dependence. The world is naturally divided into geographic provinces characterized by definite organic and inorganic forms. Among primitive men the nature of the province which a tribe happens to inhabit determines its mode of life, industries, and habits ; and these in turn give rise to various moral and mental traits, both good and bad. Thus definite characteristics are acquired, and are passed on by inheritance or training to future generations. If it be proved that the climate of any region has changed during historic times, it follows that the nature of the geographic provinces concerned must have been altered more or less. For example, among the human inhabitants of Central
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