During times when the great masses of ice shrank back to the polar regions, European environments changed accordingly. The climate was much less dry and generally warmer, with temperatures even reaching today's levels during the warmest periods, when much of Europe became forested. Animals such as horses and mammoths, which had previously thrive on dry grasslands, could not cope with the new forests, and their numbers were diminished. These animals were replaced by such animals as red deer (Cervus elaphus) and wild boar (Sus scrofa), which flourish in wet, heavily forested conditions.
The picture of the past 100,000 years in Europe that emerges, then, is one of near-continuous climatic oscillation, sometimes rendering parts of northern Europe uninhabitable. In any given region, there were several periods over that time span during which humans would have been required to readapt to changing environmental conditions by altering their diet, their hunting and gathering strategies, their technology, and their knowledge of the world around them.