Ancient East Asians mixed and mingled multiple times with Neandertals

East Asians got a double dose of Neandertal ancestry. That’s the conclusion of two new studies seeking to explain why East Asians inherited 15 to 30 percent more Neandertal DNA than Europeans did. The results appear in the March 5 American Journal of Human Genetics.

Recent research has suggested that Neandertal DNA is slightly detrimental to modern humans, making some people more prone to certain diseases, for example (SN: 3/8/14, p.12).

Natural selection should weed out the harmful stuff, but selection may have been less efficient at jettisoning Neandertal DNA from East Asians because they had a smaller founding population than Europeans did, one hypothesis suggests. Smaller founding populations make it more likely that genes, even harmful ones, might be inherited by chance.

An alternative idea holds that European ancestors bred more often with Africans, who largely lack Neandertal ancestry, diluting the amount of Neandertal DNA in present-day Europeans. Or East Asian ancestors may have interbred multiple times with Neandertals, upping the percentage of the extinct hominid’s DNA that survives in people today.

Two pairs of researchers — Benjamin Vernot and Joshua Akey of the University of Washington in Seattle and Bernard Kim and Kirk Lohmueller of UCLA — did computer simulations to test these different possibilities. Both groups independently concluded that the most likely explanation is that East Asians’ ancestors interbred with Neandertals more than once.