Siberian cave revealed something absolutely unexpected - a new hominid of the unknown origin. Where did he came from, where did he go? We don't know.
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In the summer of 2008, Russian researchers dug up a fragment of human finger bone from an isolated Siberian cave. The team stored it away for later testing, assuming that the unknown fragment came from one of the Neanderthals who left a welter of tools in the cave between 30,000 and 48,000 years ago. Nothing about the bone shard seemed extraordinary.
Its genetic material told another story. When German researchers extracted and sequenced DNA from the fossil, they found that it did not match that of Neanderthals or of modern humans, which were also living nearby at the time. The genetic data reveal that the bone may belong to a previously unrecognized, extinct human species that migrated out of Africa long before our known relatives.
If further work does support the initial conclusions, the discovery would mark the first time that an extinct human relative had been identified by DNA analysis. It would also suggest that ice-age humans were more diverse than had been thought. Since the late 19th century, researchers have known that two species of Homo — Neanderthals and modern humans — coexisted during the later part of the last ice age.
The Siberian site in the Altai Mountains, called Denisova Cave, is known as a rich source of Mousterian and Levallois artefacts, two styles of tool attributed to Neanderthals. For more than a decade, Russian scientists have been searching for the toolmakers' bones. They discovered several bone specimens, handling each potentially important new find with gloves to prevent contamination with modern human DNA.
The German team extracted the bone's genetic material and sequenced its mitochondrial DNA, the most abundant kind of DNA, and the best bet for getting an undegraded sequence from ancient tissue. After re-reading the mtDNA sequences more than 150 times each to ensure accuracy, the researchers compared them with the mtDNA genomes of 54 modern humans, a 30,000-year-old modern human found in Russia and six Neanderthals.
Surprise! It didn't match neither Neanderthals nor modern human. The differences tells that the Siberian ancestor branched off from the human family tree a million years ago, well before the split between modern humans and Neanderthals. If so, the proposed species must have left Africa in a previously unknown migration, between that of Homo erectus 1.9 million years ago and that of the Neanderthal ancestor Homo heidelbergensis, some 400,000 years ago.
The cave has yielded few clues about the culture of the Siberian hominid, although a fragment of a polished bracelet with a drilled hole was found earlier in the same layer that yielded the bone. ■