Why Black Bears Sleep in Trees

The ancestors of modern North American bears evolved in Asia during the Pleistocene, wandering over to Alaska during several appearances of the Bering land bridge, between the Bering and Kamchatka Peninsulas. Advancing and receding glaciers, fueled by evaporating sea water, caused ocean levels to alternately drop and rise, exposing and resubmerging the Bering Strait. The ancestors of black bears came across half a million years ago, and it is suspected that black bears adapted to climbing tr...