490 



THE CHANGING GENERATIONS 



hybridization on a grand scale, resulted in his present racial and indi- 

 vidual diversity. 



The Interglacial Ages. The general distribution of plant and animal life during 

 the interglacials was not unlike that of today, although warmth-loving species at 

 times occurred much farther north. The Arctic tundras were bordered to the 

 south by coniferous forest. The interiors of the continents were chiefly grassland 

 and desert, and the marginal lowlands — China, Europe, and eastern North 

 America — were humid and covered with temperate hardwood forest. Then, as 

 now, the Mediterranean region and Near East were warm and dry, with winter 

 rains, and with scrubby chaparral-type forests. Deer, bison, hairless elephants, 



Fig. 30.2. The musk ox is a northern animal that came as far south as France during the 

 Pleistocene glaciations. (Courtesy Chicago Natural History Museum.) 



and lions lived in France, the hippopotamus reached southern England, and wild 

 asses, gazelles, and horses were abundant around the borders of the Mediterranean 

 sea. 



The Glacial Ages. During the glaciations so much water was frozen in the 

 ice sheets that sea levels fell hundreds of feet, exposing broad coastal plains and 

 uniting islands with mainlands. Tundra stretched along the ice front. Beyond 

 were dry, cold grassy steppes where wind-blown loess accumulated, and forests 

 of spruce and pine. In the Mediterranean region and over much of Africa the 

 glacial ages were cool, rainy periods called pluvials, during which hardwood 

 forests increased and the Sahara desert was partly covered by grassland and 

 scrub forest. Cold climate animals such as reindeer, musk ox, woolly mammoth, 

 and woolly rhinoceros occupied southern Europe, and herds of small northern 

 horses roamed the central European steppes. 



Postglacial Extinction. Many species, especially among the larger mammals, 

 died out both in Europe and in North America toward the end of the Pleistocene 

 epoch. Man's too efficient hunting may have contributed to the disappearance 

 of some of them. Among the Old World forms that vanished were the woolly 

 mammoth, woolly rhinoceros, Irish deer, and cave bear. Among the North 



