'X woman' bone from new species

To the trained eye of the palaeontologist, the tiny fragment of fossilised bone can be identified as coming from the little finger of a child who lived about 40,000 years ago in the Altai mountains of southern Siberia.

But in the hands of molecular biologists, the bone has revealed it belonged to a new lineage of human being, an unknown "hominin" who, although human, was not a member of our own species, Homo sapiens.

The finger-bone was unearthed in 2008 from the floor of Denisova Cave, a rock shelter known to have been inhabited by ancient humans for several hundred thousand years.

After exhaustive tests on DNA extracted from the fragment, scientists can reveal that in Siberia at this time there lived a hitherto unknown type of human who was neither Homo sapiens nor Neanderthal, the only other human species living in the area at about this time.

It raises the possibility that in central Asia about 40,000 years ago three species of human were living alongside one another, perhaps for thousands of years.

Nothing is known of how they interacted or whether they interbred but it is clear that only one of the three species survived, anatomically modern humans.

Fossilised bone fragments of woolly mammoth and woolly rhino and ostrich shell, and a polished stone bracelet and bone tools, have also been unearthed at Denisova, a cave consisting of a central chamber and several short galleries overlooking the Anui River which runs through a steppe-like landscape.

Scientists have no other physical remains of this hominin who lived in the Denisova cave except the fragment of finger-bone.

The size of the bone suggests that the finger belonged to a child of 7 or 8, and carbon dating of the sediments surrounding it indicates that he or she lived between 30,000 and 48,000 years ago.

The scientists were able to identify a new lineage of hominin from DNA analysis alone by extracting the DNA of the mitochondria, tiny "organelles" inside the cells of the bone that house their own genetic material. It is unlike the DNA found in the cell nucleus in that it is simpler and always inherited down the maternal line.

The scientists have nicknamed the fossil "X woman" to indicate that it was this maternally inherited mitochondrial DNA that has revealed the existence of another species of human who lived during the last Ice Age.

- INDEPENDENT