Neanderthals and Humans Were Hooking Up Way More Than Anyone Thought, by Charles Choi.

Scientists initially thought that interbreeding among the two groups was more isolated to a particular place and time — specifically, when they encountered each other in western Eurasia shortly after modern humans left Africa. This idea stemmed from the fact that the genomes of modern humans from outside Africa are only about 2 percent Neanderthal, on average.

Subsequent research, however, has found that Neanderthal ancestry is 12 to 20 percent higher in modern East Asians compared to modern Europeans. …

The researchers suggested the patterns of Neanderthal DNA inheritance seen in modern humans are best explained by not one, but multiple, independent episodes of interbreeding between Neanderthal and modern humans, first and foremost in the Middle East, but also later in both Europe and East Asia.