PLEISTOCENE WHITE MEN

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2. Pleistocene climate

It is not easy to overemphasize the importance of climate in human history, particularly in the earliest times when man was merely a numer­ically unimportant parasite in the total fauna. With changes in climate, he was forced to migrate with the animals and plants on which he lived, and at the hunting and gathering of which he was adept. The only alternative was to stay on and adapt his culture to a new food supply, which would need new implements and new methods. On the whole, it was easier to move, even if some of the oscillations were, like those in recent times, rather rapid.

The ponderous ebb and flow of the glaciers caused climatic changes which affected the entire world. With the gathering of vast quantities of ice near the poles, zones of climate shrank inward, converging on the equator. At times of maximum glaciation, wide belts of land bordering the glaciers became treeless, frozen tundras, like the northern rims of Siberia and North America today. During the last glaciation, such a zone included the whole of Europe north of the Alps and Pyrenees, and much of Siberia. Below this stretched temperate forests, with zones of willow and birch, of pine, and of hardwood, and beyond these, temperate, grassy plains, watered by cyclonic rain belts. Still farther away, near the equator, stood tropical forests. The present deserts had shrunk to narrow patches between the grasslands or had disappeared.

As the glaciers retreated, the zones of tundra followed, constantly shrinking as the ice cap thinned. The forest encroached on the tundra belt, and the grasslands likewise moved inward; at the same time the tropical forest shrank, and the land in between two belts of grassland became desert. What had once been the optimum home for food gather­ing man now became bare and sterile, and remained virtually unoccupied until the rise of pastoral nomadism, with ass and camel, once more made it habitable.

The centers of Pleistocene glaciation were not located exactly on the poles. In the northern hemisphere, the center was in the north Atlantic, with land nuclei in Scandinavia, northern Britain, and Greenland, so that northwestern Europe and northeastern America were covered, while territories of higher latitudes, in eastern Europe and Siberia, and in western North America, were left bare. In Europe, the ice covered, at its maximum, all of the British Isles but the southwestern tip of Great Britain; most of Belgium, Holland, northern Germany, the Baltic States, and Finland, as well, of course, as Scandinavia. Secondary centers of glaciation, based on altitude rather than latitude, lay in the Alps, Pyre­nees, and Caucasus, in the Himalayas and Pamirs, in the mountain skele­ton of Siberia, and in the Atlas mountains of North Africa.