最新一期英国《自然》杂志刊登研究报告说，对俄罗斯西伯利亚一个山洞里发现的古人类化石进行基因检测显示，它不同于现代人和任何已知的古人种，很可能是一种前所未知的古人种。
报告说，俄罗斯研究人员早在2008年就在该山洞中发掘出这块指骨化石，但起初认为它是已研究较多的古人种尼安德特人留下的。后来，这块化石被送到德国进行基因检测，对其线粒体DNA的分析结果显示，它不属于现代人和任何已知的古人种。
尼安德特人生活在大约12万年到3万年前。据介绍，在线粒体DNA对比上，尼安德特人与现代人有202处差异，而这块化石与现代人有385处差异，研究人员因此推断它所属人种的生存年代比尼安德特人更早，应该大约在100万年前。
有专家认为，单凭线粒体DNA还不能确认这就是一种未知的古人种。为此，研究人员尚未为其命名，且计划对这块化石进行基因组测序。如果完整基因组测序显示它真属于一个未知的古人种，这将是首次通过基因手段确认人种，也将是迄今完成的对最古老人类的基因组测序。（生物谷Bioon.com）
生物谷推荐原文：
Nature doi:10.1038/464472a
Fossil finger points to new human species
Rex Dalton
In the summer of 2008, Russian researchers dug up a sliver of human finger bone from an isolated Siberian cave. The team stored it away for later testing, assuming that the nondescript 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.
A finger bone found in Denisova Cave in Siberia could add a branch to the human family tree.B. VIOLAIts 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, published online in Nature1, reveal that the bone may belong to a previously unrecognized, extinct human species that migrated out of Africa long before our known relatives.
"This really surpassed our hopes," says Svante P??bo, senior author on the international study and director of evolutionary genetics at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. "I almost could not believe it. It sounded too fantastic to be true."
Researchers not involved in the work applauded the findings but cautioned against drawing too many conclusions from a single study. "With the data in hand, you cannot claim the discovery of a new species," says Eske Willerslev, an evolutionary biologist and director of the Centre for GeoGenetics at the University of Copenhagen.
“I almost could not believe it. It sounded too fantastic to be true.”
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 nineteenth century, researchers have known that two species of Homo — Neanderthals and modern humans — coexisted during the later part of the last ice age. In 2003, a third species, Homo floresiensis, was discovered on the island of Flores in Indonesia, but there has been no sign of this tiny 'hobbit' elsewhere. The relative identified in Siberia, however, raises the possibility that several Homo species ranged across Europe and Asia, overlapping with the direct ancestors of modern people.
The Siberian site in the Altai Mountains, called Denisova Cave, was already known as a rich source of Mousterian and Levallois artefacts, two styles of tool attributed to Neanderthals. For more than a decade, Russian scientists from the Institute of Archaeology and Ethnology in Novosibirsk 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 bones' own DNA could then be extracted and analysed.
When the finger bone was discovered, "we didn't pay special attention to it", says archaeologist Michael Shunkov of the Novosibirsk institute. But P??bo had established a relationship with the Russian team years before to gather material for genetic testing from ice-age humans. After obtaining the bone, the German team extracted the bone's genetic material and sequenced its mitochondrial DNA (mtDNA) — the most abundant kind of DNA and the best bet for getting an undegraded sequence from ancient tissue.
