海角大神

Before Homo sapiens ruled the Earth, other humans also roamed.聽Our famous extinct cousins, Neanderthals, once had cousins even closer to them: Denisovans.

The Denisovans are聽relative newcomers to the archeological family tree, being first identified only in 2008.聽All we know about聽comes from a few fossils unearthed in a single cave in聽southwestern Siberia, all of which so far have been dated about 50,000 years ago.

But a new DNA analysis of two teeth found in the cave suggests that Denisovans may have lived in the region some 60,000 years earlier than that.

The two teeth discovered in the Denisova Cave in Russia's Altai mountains聽are described and details hidden in their genome are revealed in published Monday in the Proceedings of the National Academy of Sciences.聽

鈥淲e got the first glimpse of genetic variation in Denisovans,鈥� Svante P盲盲bo, director of the Max Planck Institute for Evolutionary Anthropology and one of the study's authors, tells 海角大神 in an interview. 鈥淎nd it turns out that they have quite a bit variation, about as much as Neanderthals.鈥�

The teeth came from two distinct individuals, and one is quite a bit older than the other.聽

鈥淲e can sort of see that by detecting missing mutations that one of them is much older than the others, and we see that because it hasn鈥檛 accumulated so many mutations,鈥� explains Dr. P盲盲bo.

鈥淎nd,鈥� he says, 鈥淚t is in fact in the order of 60,000 years older.鈥�

If their residence was continuous between the lives of the two specimens, the Denisovans lived in southern Siberia some 110,000 years ago to around 50,000 years ago. If not, then they moved into the region in the Altai mountains at least twice.

鈥淭his also shows that this enigmatic group, Denisovans, were present over a long time here in the Altai mountains in southern Siberia,鈥� P盲盲bo says.聽

In 2010, scientists sequenced the genome of a finger bone found in the Denisova cave two years earlier, revealing the Denisovans as a unique species for the first time.聽

鈥淣eanderthals and Denisovans share a common ancestor with present day people in the order of 600,000 years,鈥� says P盲盲bo. But Denisovans are more closely related to Neanderthals than to us.

鈥淯sing our best estimates, they share a common ancestor in the order of 400,000 years back with Neanderthals,鈥� he says. 鈥淭ogether, then they are the closest extinct relatives of present-day people.鈥�

鈥淒enisovans are still very enigmatic, since we know so little about them,鈥� says P盲盲bo. 鈥淪o with these two teeth now we have a little bit of feeling for their dental morphology.鈥�

鈥淭hese teeth are very large and they lack specific features that are typical of modern humans and typical of Neanderthals,鈥� he describes.聽

P盲盲bo hopes by describing the teeth in the new paper the researchers will help other scientists identify specimens from other locations as Denisovan. 鈥淲e might find other Denisovans in other places thanks to this,鈥� he says.

Previous research has shown that Denisovans mixed with ancestors of modern day humans living in Asia, particularly populations in the Pacific. Papua New Guineans and other islanders in Oceania have been found to have contributed from these Denisovans, P盲盲bo says.

That suggests that Denisovans lived all over the region, he says, because 鈥渨e don鈥檛 think the ancestors of Papuans were ever in Siberia. Rather we think Denisovans were somewhere in southeast Asia where then Papuan ancestors met them and mixed with them.鈥�

Another study showed Denisovan genetics appearing in another modern population. 聽have a Denisovan trait to help them survive.聽

鈥淭hey carry genetic adaptation to living where there is little oxygen and that adaptation comes from these Denisovans,鈥� P盲盲bo says. 鈥淪o the ancestors of these guys mixed with the Denisovans, picked up this thing that allows them to live at high altitudes, and that is really probably a big contributing factor to why there are such big populations in Tibet today.鈥�

P盲盲bo says his work is about discovering human history. 鈥淭his is finding out things we didn鈥檛 know about our history, about our closest evolutionary relatives, which are now extinct,鈥� he says.聽

鈥淚n a way,鈥� P盲盲bo says of sequencing the Denisovans鈥� genomes, 鈥淚t鈥檚 not so different from making an archeological excavation in a cave. We make sort of an excavation in the genome and find out things about history.鈥�