March 24, 2010 6:45 pm

Gene research reveals fourth human species

A fourth type of hominid, besides Neanderthals, modern humans and the tiny “hobbit”, was living as recently as 40,000 years ago, according to research published in the journal Nature.

The discovery by Svante Pääbo and colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, is based on DNA sequences from a finger bone fragment discovered in a Siberian cave.

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It further enriches the scientific picture of human life in the recent geological past. “Forty thousand years ago the planet was more crowded than we thought,” said Terry Brown, an expert in ancient DNA at Manchester University.

Until recently scientists believed there were just two members of the genus Homo alive at the time: Neanderthals whose ancestors left Africa 400,000 years ago, and modern humans, who left about 50,000 years ago. The picture changed in 2003 when archaeologists found remains of a third species, the tiny “hobbit”, which had survived on the Indonesian island of Flores until 14,000 years ago.

The identification of a fourth species is potentially more significant because it was not an isolated population but lived in the centre of the Eurasian continent, where Neanderthals and Homo Sapiens were also present.

The Leipzig team extracted DNA from a child’s finger bone, which Russian archaeologists discovered with other hominid bone fragments in Denisova Cave, a well known Neanderthal site in Russia’s Altai Mountains.

The site’s exceptional cold helped preserve enough DNA to be read with the latest gene sequencing technology.

The scientists first decoded the “mitochondrial” DNA. It was human but, to their astonishment, very different from Homo Sapiens and Neanderthals.

The differences imply that the ancestors of the still unnamed Siberian hominid diverged from the human family tree about 1m years ago, well before the split between Neanderthals and modern hominids about 500,000 years ago. The results also suggest a previously unsuspected migration out of Africa about 1m years ago, said Prof Pääbo.

He expects within months to decode the hominid’s “nuclear” DNA. That will be compared with the modern human and Neanderthal genomes.

Until more of the new hominid’s DNA has been analysed – or larger pieces of bone discovered – it will not be possible to say much about its physical or cultural characteristics, or how it interacted with other human species.

But one thing is clear: it must have clothed itself in thick furs to withstand the Siberian winter, said Prof Pääbo: “It would have been a bit colder 40,000 years ago than today, and it was -40°C when we went there this January.”

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