Denisova Cave, in the Altai mountains of Siberia, was a hot property in the past – at least for ancient humans who called it home for more than 200,000 years.
This is according to researchers who dated artifacts, fossils and sediments excavated in wells on the floor of the cave to gather a record of housing.
In a couple of papers in Nature today, they report that Denisovans – an extinct species of humans whose genome was reported in 2011 – occupied the cave from about 287,000 to 50,000 years ago.
This coincided with the Neanderthals, who also resided there, but for a shorter period: between about 193 thousand and 91 thousand years ago.
Until the timeline was set up, archaeologists did not know when Denisovans arrived in the cave, said Bert Roberts, a geochronologist at Wollongong University and co-author of the two works.
"They could have been there a million years ago or 100,000 years ago," Roberts said.
We do not know if Denisovans and Neanderthals were housemates living in the cave at the same time.
But more recent studies "suggest that both groups lived in the region, met and – from time to time – crossed over about 150,000 years," the researchers reported.
Not much is known about the mysterious Denisovans.
His remains were found only in one place – Denisova Cave, hence his nickname – and yet fossils comprise a finger bone and some teeth of four distinct individuals and a hybrid child.
"We know very little about them," said Professor Roberts.
"We do not even know what they were like."
This is because they were first identified not by a skeleton or skull, but by their DNA, scraped from the precious finger of a girl's finger.
The use of genetic material is possible because the cave, being in the mountains of Siberia, is like a large freezer, preserving the DNA that would normally disintegrate in warmer and humid climates.
Russian scientists have known and excavated the floor of the cave for 40 years, finding bones and artifacts such as tools and pendants.
But to rebuild a time line of housing, they had to date the sediment.
Dirt layers act as a file of what was happening in the cave the moment they were laid.
The idea is that the more you dig, the more back in time you see.
And because the sediments in the cave stretch for at least 300,000 years, the researchers of an article needed to use a number of dating techniques.
They included radiocarbon dating, which is good for about 50,000 years, and optically stimulated luminescence, which measures when the quartz and feldspar minerals were last exposed to sunlight.
Optically stimulated luminescence, coupled with some cool modeling, can bring archaeologists back to about 300,000 years, said Zenobia Jacobs of Wollongong University and co-author of the articles.
In a separate article, the researchers used radiocarbon dating to determine the age of the Denisovan fossils, along with the remains of three Neanderthals and the hybrid child.
They estimated that the oldest and youngest fossils of Denisovan were 194,400 years and 51,600 years, respectively.
Neanderthals were between 90,900 and 147,300 years old, and the Neanderthal / Denisovana child ranged between 79,300 and 118,100 years, largely within the dates determined by sediment analysis.
The issue of artifacts
Among the Denisova caves were pendants carved from teeth and bone spearheads, dating from 43,000 to 49,000 years old.
So they were made by Denisovans?
The idea was launched by researchers, but Darren Curnoe, a paleoanthropologist at the University of New South Wales who was not involved in the work, is not convinced.
Even though there are still no signs that modern humans – Homo sapiens – lived in the cave of Denisova until much later, "they were not too distant at the same time," he said.
Complex behaviors such as sculpting jewelry are typical of modern humans.
"And now we have claims in southern China that there are modern humans for over 100,000 years," Curnoe said.
"If this is correct, then modern humans were already in the vicinity [of Siberia] for 50,000 years or more. "
Professor Jacobs said that assigning the artifacts to the Denisovans would undoubtedly be controversial.
"As Western scientists, we immediately assume, looking at artifacts such as these, that they can be made by Homo sapiens.
"But we have collaborators who strongly feel that the evidence for Homo sapiens is not in the cave, there are no fossils or DNA except in much later periods."
DNA from Denisovan in Australia
Australian Indigenous and Papua New Guinea populations have a relatively high percentage of Denisovan DNA, which their ancestors captured in Asia prior to their arrival in Australia.
Recent genetic analyzes have suggested that the crossing occurred after the Altai Denisovans evacuated the cave, said João Teixeira, a population geneticist at the University of Adelaide who was not involved in recent work.
Thus, although there are no traces of Denisovans after about 50,000 years ago in the cave – or anywhere else by the way – it is highly unlikely that a particular population was the last of its kind.
"Not only is geographic distribution more widespread than Altai … but also the nature of Denisovan's DNA seems to point to different populations of Denisovan, probably reflecting geographic isolation, which would lead to small accumulations of genetic differences," he said Teixeira.