Neanderthals in the Family Tree: New Study Confirms Interbreeding

Jul 17, 2011
Robert Adler

Possible Neanderthal Ancestor - Coutesy of Mara/earth light

New genetic research independently confirms what some earlier studies suggested, that early modern humans leaving Africa met and mated with Neanderthals.

In May of 2010, researchers surprised the scientific world by managing to decode most of the Neanderthal genome, and by their finding that contemporary non-Africans shared more genetic markers with Neanderthals than contemporary Africans do. The best explanation for that difference was that early modern humans leaving Africa interbred with Neanderthals, who were already established throughout much of Europe, parts of Asia, and the Middle East.

An independent study by a different research team now finds that the X-chromosomes of people throughout the world, from Australia to the Arctic, carry a specific genetic marker that clearly came from Neanderthals, while current Africans do not.

"This confirms recent findings suggesting that the two populations interbred," says Damian Labuda, at the University of Montreal, and who led the new research effort. He thinks that the most likely meeting place was the Middle East, between 80,000 and 50,000 years ago.

Evolutionary Backgound

Most researchers agree that the human species originated in Africa, and that the Neanderthals who spread across much of Europe and Asia were genetically isolated from human populations evolving in Africa for hundreds of thousands of years.

Until recently, most paleontologists and geneticists thought that although Neanderthal and anatomically modern human populations overlapped in parts of Europe. Asia and the Middle East for perhaps 50,000 years, there was no genetic mixing between the two.

The heavy-boned, low-browed Neanderthals seem to have been gradually out-competed by anatomically modern humans who first appeared in Africa around 200,000 years ago and who started filtering into Europe and Asia around 80,000 years ago.

The last Neanderthals seem to have hung on in Gibraltar until as recently as 25,000 years ago. Modern humans went on to populate Asia, Australia, North and South America, the Pacific and the Arctic.

A Neanderthal Great-great-great-great Grandmother

Labuda and his colleagues were especially interested in a genetic marker called haplotype B006 which is associated with a particular gene on the X-chromosome. They recognized almost a decade ago that it was common in non-African groups throughout the world, but is almost absent in Africa south of the Sahara Desert. That led them to suggest in 2003 that it must have come from "an unknown non-African" population.

When the Neanderthal genome was decoded, in 2010, Labuda's team found that two versions of the B006 marker were found in Neanderthals, in contemporary humans from populations around the world, including Australian aboriginals, but not among sub-Saharan Africans.

"There is little doubt that this haplotype is present because of mating with our ancestors and Neanderthals," says Nick Patterson, at the Broad Institute of Harvard University and MIT.

This independent confirmation closes the case. Our modern human ancestors met, mingled and mated with what we now know to be our Neanderthal kin.