This period of intense social crowding was one of great innovation

From Mapping Human History: Genes, Race, and Our Common Origins by Steve Olson. Page 162.

During the height of the Ice Age, between 20,000 and 16,000 years ago, modern humans gave up on northern Europe, abandoning what is now Britain, northern France, the Low Countries, Germany, and most of Poland. Small groups may have wandered into these areas during the summers, but they left no traces of their visits. Europeans retreated into the warmer areas around the Pyrenees and the Balkans and north of the Black Sea.

This period of intense social crowding was one of great innovation. Artwork flourished among the dense populations of southern Europe. New technologies were developed, such as spear-throwers that allowed hunters to launch projectiles toward their prey wih great force. Groups seem to have heightened their cultural distinctions from each other, as if they were marking off separate territories for themselves.