The Mongoloid peoples seem to have passed along the northern front of the Central Asiatic plateau into Siberia, China, and Japan, and to have sent off the great American branch. Even before the Mongols had started on their eastward journey the Caucasians may have turned westward, following the old Negroid route. There was probably also more or less of an eastern dispersal, but we cannot consider the problem of these Oriental Caucasic remnants and traces. The great body went westward. The Hamitic peoples distributed themselves along the southern shore of the Mediterranean, and many may well have occupied a large part of the Sahara region, then a land of watercourses capable of supporting a large population. Behind them came the Semitic folk. Judging from their languages the Hamitic and Semitic peoples seem to have been in contact over a wide area, and for a long space of time. The Semites found a new and permanent home in Arabia, on whose plateaus and surrounding grasslands they increased and multiplied, and sent off fresh waves of migration and conquest in all directions.

We have already noticed that our classification of races is based upon a study of recent and still surviving peoples. The very earliest inhabitants of Europe would find no place in it. Probably they long antedated the Hamites. African Negroids and Caucasians came from a common home, and journeyed for a time over a common road, though probably at far different times. It would be strange if the earliest inhabitants of Europe showed no traces of this common home and ancestry. Since the remote period which we are considering Negroes and Caucasians have become widely different, and their racial characters have become clear and sharp. This may not have been altogether the case with the first peoples to arrive in Europe. But attempts to relate the Neanderthal crania with those of modern Australians or Tasmanians, or any existing race, have met with no great success. In regard to these questions we are still in the dark.

Beside the African routes into Europe, along the south shore of the Mediterranean and over the Sicilian and Gibraltar land bridges, while they lasted, two others must be noticed. One of these extended through Asia Minor and across the land bridge at the Dardanelles, while the second led westward along the northern border of the Caspian and Black Seas and the Caucasus Mountains. The most southerly of these four routes through Africa were probably the first to be travelled, the most northerly last of all. We shall have to study these routes more closely in a later chapter.

It was at some time during the Glacial period, the Great Ice Age, when a vast ice-cap covered northern Europe with glaciers extending far southward and advancing or retreating according to climatic conditions, that man arrived in Europe. During the first Glacial Epoch the advance of the ice covered the most northern part of Great Britain and the Rhine valley almost as far south as Cologne; Scandinavia was completely buried, like central Greenland to-day, and North Germany probably to the Harz Mountains. Eastward the southern edge of the ice sheet ran nearly along the line of 50° N. lat. across Russia. In Siberia the effects were less marked and the limits were much farther northward. Between the parallel of 50° and the northern edge of the Alpine glaciers a zone was left ice-free, but three-fifths of Germany was overwhelmed. Southern England and France, not yet separated by the English Channel, formed one great habitable province, and but a small part of France was glaciated. The climate was tempered by proximity to the sea.[17] The average yearly temperature of northern Europe was probably not more than 4°-6° Cent. (39°-43° Fahr.), which is colder than at present. But the formation of these enormous masses of ice demanded heavy snowfall and a moist or very damp climate. Hence the edge of the great ice sheet advanced or retreated according to climatic conditions.

There were four periods of advance before the final retreat of the ice, not counting minor oscillations.[18] These are known as the Gunz, Mindel, Riss, and Wurm Glacial Epochs. Alternating with these were the interglacial epochs of ice retreat—the Gunz-Mindel, Mindel-Riss, and Riss-Wurm; while the final retreat is usually termed post-glacial. During the first and second interglacial epochs the climate appears to have been warmer than at present. But at times dryness may have contributed to the retreat of the ice even more than warmth, and then the climate would have been continental, harsh, and extreme.

Even during epochs of glacial advance conditions in France and in the German zone must have been better than we should expect. Some kind of grazing or browsing pasturage must have been rich and abundant to support large animals like the reindeer or even the woolly mammoths characteristic of the second and third glacial epochs, which furnished abundant food for prehistoric hunters. Farther south the glacial epochs may well have been times of heavy rainfall, transforming the Sahara desert and the dryer steppes and plateaus of Asia into veritable gardens.

The retreating ice left behind it a land covered with rocks, clays, gravels, and sands brought by the glaciers and their streams. Here and there basins had been gouged out where lakes or ponds long remained—as in Maine and Minnesota to-day—to be later drained, or, if shallow, to be overgrown with sphagnum and changed into great bogs. Scattered thickets of shrubs and stunted hardy trees, poplars, willows, and others occurred. In sheltered and well-drained valleys and mountainsides the trees grew larger and even forests began to appear. This tundra landscape still characterizes wide areas of northern Canada and Siberia.[19]

The tundra was followed by steppe conditions, where elevation of land to the north and northwest had cut off the tempering oceanic winds. The climate was harsh, dry, continental, with cold winters and hot summers. The winds carried great storms of dust and piled it up in drifts in valleys and on suitably situated mountainsides in the form of loess, so important to the future agricultural development of Europe, though its most massive accumulation is seen in China, which received and held the driftings from the great elevated plains of central Asia. As the climate became moister, if the temperature did not fall too low, steppe finally gave way to the meadow and forest of modern Europe. Tundra, steppe, and forest had each its special types of animal as well as plant life. The characteristic tundra animal is the reindeer, though musk-ox, woolly mammoth, and others were wide-spread at this time. The peculiar steppe animal is the horse. The characteristic forest and meadow animals are the deer and their allies; the wolf and bear; the wild boar and cattle seem to be at home in forest and glade and along the streams.

In France, where there was far less glaciation, the succession of tundra, steppe, and forest is less apparent. Here we find a mingling of varied forms which have come in from very different regions, driven from their original homes by change of climate or drawn by favorable conditions.