Neanderthal-Type Species Once Roamed Africa, DNA Shows

Brian Vastag, Washington Post, July 26, 2012

The human family tree just got another—mysterious—branch, an African “sister species” to the heavy-browed Neanderthals that once roamed Europe.

While no fossilized bones have been found from these enigmatic people, they did leave a calling card in present-day Africans: snippets of foreign DNA.

There’s only one way that genetic material could have made it into modern human populations.

“Geneticists like euphemisms, but we’re talking about sex,” said Joshua Akey of the University of Washington in Seattle, whose lab identified the mystery DNA in three groups of modern Africans.

These genetic leftovers do not resemble DNA from any modern-day humans. The foreign DNA also does not resemble Neanderthal DNA, which shows up in the DNA of some modern-day Europeans, Akey said. That means the newly identified DNA came from an unknown group.

“We’re calling this a Neanderthal sibling species in Africa,” Akey said. He added that the interbreeding probably occurred 20,000 to 50,000 years ago, long after some modern humans had walked out of Africa to colonize Asia and Europe, and around the same time Neanderthals were waning in Europe.

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Another mysterious group of extinct people recently identified from a 30,000-year-old finger bone in Siberia—known as the Denisovans—also left some of their DNA in modern-day Pacific Islanders.

And while modern humans and the newly found “archaic” Africans might be classified as distinct species, they produced viable offspring. Likewise, donkeys and horses, lions and tigers.

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Still, without a definitive fossil, it’s impossible to say what these people looked like. But one thing is clear: This enigmatic group left its DNA all across Africa. The researchers found it in the forest-dwelling pygmies of central Africa and in two groups of hunter-gatherers on the other side of the continent—the Hadza and Sandawe people of Tanzania.

Starting a decade ago, a team led by Sarah Tishkoff and Joseph Lachance of the University of Pennsylvania drew blood from five individuals in each of the three groups. Using the latest genetic technology, Tishkoff spent $150,000 to read, or sequence, the DNA of these 15 people. The research was reported Wednesday in the journal Cell.

In addition to finding evidence of the now-extinct humans, the team discovered a huge range of genetic diversity between the three groups. The human genome contains about 3 billion letters, or base pairs, of DNA. Before this study, scientists had found that about 40 million of these letters vary across human populations.

But in the 15 Africans, Tishkoff and Lachance found 3 million more genetic variants—a huge treasure trove of human diversity. Among this stunning variety, Tishkoff says they have pinpointed some of the genes responsible for the short stature of the pygmies, who average less than 5 feet in height. {snip}

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