THE GEOGRAPHIC BASIS OF HISTORY 381
southern Canada, with the centre of power between latitudes forty and forty-five.
In explanation of the manifest movement of civilization from south to north, it has been commonly said that, for some undefined reason, man's relation to climate has changed. As he has become more civilized, he has also become adapted to colder and moister climatic conditions. To put it more fairly, the civilized man of to-day, being supposedly of a more nervous organization than his predecessor of two or three thousand years ago, finds that his impulses toward activity and toward self-control are most perfectly balanced in a fairly moist and cool climate; whereas the pioneers of civilization found the most favorable conditions in a dry, warm climate. According to a further assumption necessitated by this view, man took the first great step toward civilization, that is, adopted the pursuit of agriculture, in arid regions where irrigation was necessary. It was an easy matter, so it is said, to lead a little water to a patch of seeded ground which otherwise would have been unproductive; far easier, indeed, than to clear and cultivate a similar patch which needed no artificial supply of water, but was sure to be full of a great variety of plants not wanted by the sower. To a certain extent these views are perhaps true, but if our theory of changes of climate is valid, they require profound modification.
According to the climatic hypothesis of history, as we may call it, mankind, since first the race gained the rudiments of civilization, has always made the most rapid progress under essentially the same climatic conditions. The conditions apparently are that the summers shall have a
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