It was here in the Deinsova Cave in 2008 that Siberian scientists discovered a finger bone fragment of 'X woman', a juvenile female. Picture: Max Planck Institute

It has been called the cave that holds the key to man's origins, and it keeps producing more surprises. It was here in the Deinsova Cave in 2008 that Siberian scientists discovered a finger bone fragment of 'X woman', a juvenile female believed to have lived around 41,000 years ago. Analysis showed she was genetically distinct from Neanderthals and modern humans.

In 2010 analysis on an upper molar from a young adult, found in the cave ten years previously, was also from a Denisovan. As we reported previously: 'Traces in the 'cultural layer' of the Denisova Cave show the human habitat reaching back 282,000 years.' The richness of the cave's prehistoric contents means scientists from around the world are co-operating in seeking to solve its riddles.

The Denisova Cave is located in the Bashelaksky Range of the north-western Altai Mountains, close to the border of today's Altai Region and the Altai Republic. Picture: The Siberian Times

Now a new report by the news site of journal Science states that analysis on the Denisovan finger bone and molars as well as cave material shows these little-known ancient people 'occupied the cave surprisingly early and came back repeatedly'.

The young female 'lived at least 50,000 years ago and that two other Denisovan individuals died in the cave at least 110,000 years ago and perhaps as early as 170,000 years ago'.

The report cites scientific talks given to a meeting of the European Society for the study of Human Evolution. It cautions about a wide margin or error in the estimates over dates, but quotes paleoanthropologist Fred Spoor of University College London the findings provide 'really convincing evidence of multiple occupations of the cave', and that the Denisovans should be seen as a 'valid species'.

In 2010 analysis on an upper molar from a young adult, found in the cave ten years previously, was also from a Denisovan. Picture: Max Planck Institute

When researchers first dated animal bones and artifacts in the cave's layer 11, they were said to be between 30,000 and 50,000 years old. 'So Siberian researchers invited geochronologist Tom Higham of the University of Oxford in the United Kingdom to re-date the sequence,' reported news.sciencemag.org

Sediments holding the finger bone, at the bottom of layer 11, came out right at the limit of radiocarbon dating, and are likely older than 48,000 to 50,000 years, reported archaeologist Katerina Douka, of Oxford, it was reported.

'Researchers sequenced nuclear DNA from three molars from layer 11 and a child's molar from a deeper layer, 22, according to a talk by graduate student Viviane Slon, who works in the lab of paleogeneticist Svante Paabo at the Max Planck Institute for Evolutionary Anthropology.' They succeeded in analysing 'a significant amount of nuclear DNA from three teeth that turned out to be Denisovan'.

The girl with the pinky finger was in the cave roughly 65,000 years after the oldest Denisovan, who was there at least 110,000 years ago and possibly earlier'. Pictures: Vera Salnitskaya

This showed that 'the Denisovan inhabitants in that one cave were not closely related. They had more genetic variation among them than all the Neanderthals so far sequenced, although Neanderthals are known to be similar genetically'.

The team sequenced 'their entire mitochondrial DNA (mtDNA) genomes and placed them on a family tree. Then they counted the number of mtDNA differences between individuals and used the modern human mutation rate to estimate how long it might have taken those mutations to appear. They concluded that the girl with the pinky finger was in the cave roughly 65,000 years after the oldest Denisovan, who was there at least 110,000 years ago and possibly earlier'.