Neanderthal DNA Suggests Yet Another Wave of Human Migration out of Africa

The entrance to the cave where the Neanderthal thigh bone was found in 1937. (credit: Wolfgang Adler, © Photo Museum Ulm)

Modern humans and Neanderthals have a confusing genetic relationship. One set of data suggests our two species diverged around 650,000 years ago but other clues point to an ongoing close (that is, sexual) relationship between our ancestors that persisted until around 300,000 years ago. This is made all the more muddled by the fact that Neanderthals look like they were living in Eurasia 300,000 years ago while our own ancestors were still in Africa. And then the two groups clearly intermingled once humans did leave Africa.

One way to account for all this contradictory information is to suggest that another group of humans left Africa sometime between the Neanderthals’ departure and our own. An analysis of Neanderthal DNA, published this week in Nature Communications, adds new weight to this hypothesis.

When people talk about DNA, most often they’re talking about nuclear DNA. That’s the DNA that combines genetic material from a mother and a father and sits in the nucleus of each cell. But the mitochondria – little energy-producing blobs that sit inside cells – have their own DNA, which comes exclusively from the mother. Mitochondrial DNA (mtDNA) is a fantastically useful tool for understanding evolutionary lineages, in part because there’s so much more of it that it’s still detectable in very old samples.

The picture painted by nuclear DNA(nDNA) is that, between 765,000 and 550,000 years ago, our ancestors in Africa diverged into two groups. One group would eventually lead to our own species, although we wouldn’t make an appearance until around 200,000 years ago. The other group would lead to Neanderthals and the closely related Denisovans. This proto-Neanderthal/Denisovan group left Africa for Eurasia at some point; sometime around 430,000 years ago, they diverged into distinct Neanderthals and Denisovans.

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