A new study published in the journal Genetics (Wall et al, 2013) has concluded that East Asians have a higher level of Neanderthal DNA than do Europeans. The result implies that there was more than one episode of interbreeding between modern humans and Neanderthals. After the ancestors of modern Europeans and East Asians separated, the latter population continued to interbreed with Neanderthals.
Given that the Neanderthals are thought to have been a predominantly Western Eurasian species, this result is unexpected. It is becoming clear that the history of interbreeding between modern humans and Neanderthals was rather more complex than was originally thought.
The paper is available open access - see this link on the Genetics website
Wall, J., Yang, M., Jay, F., Kim, S., Durand, E., Stevison, L., Gignoux, C., Woerner, A., Hammer, M., and Slatkin, M. (2013) Higher levels of Neanderthal ancestry in East Asians than in Europeans, Genetics, Early Online