DNA belonging to Denisovans – the ancient human ancestor – discovered in a Tibetan cave may be only 45,000 years old, scientists say.
The ancient Denisovan mitochondrial DNA was recovered in sediments from Baishiya Karst Cave, a limestone cave at the northeast margin of the Tibetan Plateau, 3,280 meters above sea level.
Samples indicate Denisovans occupied the high-altitude cave as early as 100,000 years ago, and possibly as recently as 45,000 years ago, as well as at a point in-between.
If the DNA is indeed only 45,000 years old, the species would have lived alongside modern humans in northeast central Asia.
Site of Baishiya Karst Cave, a Tibetan Buddhist sanctuary and a high-altitude paleoanthropological site for researchers
Denisovans, a group of extinct hominins that diverged from Neanderthals about 400,000 years ago, may have more widely inhabited northeast central Asia than scientists previously thought.
Samples of sediments were analysed by an international team including Charles Perreault at Arizona State University.
‘When we started developing this project about 10 years ago, none of us expected Baishya Cave to be such a rich site,’ he said
‘We’ve barely scratched the surface – three small excavation units have yielded hundreds of stone tools, fauna and ancient DNA. There’s a lot that remains to be done.’
‘Future work in Baishiya Cave may give us a truly unique access to Denisovan behavior and solidifies the picture that is emerging, which is that Denisovans, like Neanderthals, were not mere offshoots of the human family tree.
‘They were part of a web of now-extinct populations that contributed to the current human gene pool and shaped the evolution of our species in ways that we are only beginning to understand.’
By examining the sediment of Baishiya Karst Cave located on a high plateau in Tibet, researchers identified ancient mitochondrial DNA from Denisovans, indicating their presence possibly 45,000 years ago
A mandible fossil (the ‘Xiahe mandible’) from the same cave, which was dated to 160,000, had been previously identified as Denisovan, based on a single amino acid position.
This new study of the DNA dispels any doubt left that the Denisovans occupied the cave, according to the researchers.
Evidence of archaic hominins this far above sea level is unusual due to the severity of the conditions at high altitude.
Life on the plateau is harsh due to its thin air, and humans can develop altitude sickness anywhere above 2,500 meters above sea level.
Presence of the DNA suggests the Denisovans may have evolved adaptations to high altitude, much like modern Tibetans.
The dates of the sediments with mitochondrial DNA, along with the older 160,000-year-old Xiahe mandible, suggest that the Denisovans have been on the Plateau continuously for tens of thousands of years.
Pictured, the Xiahe mandible remains. The Denisovan jawbone was originally discovered in 1980 by a local monk
This would have been more than long enough for genetic adaptations to emerge in Denisovans to help them survive adverse effects of high altitude.
This discovery in Baishiya Karst Cave is the first time Denisovan DNA has been recovered from a location that is outside Denisova Cave in Siberia, Russia.
This Siberian cave was previously the single location in the world where a handful of DNA-bearing Denisovan fossil bones have been discovered.
In 2010, a fingerbone belonging to a previously unknown hominin species was found buried in Denisova Cave in the Russian Altai Mountains.
Evidence of this new species forced anthropologists to revise their model of human evolution outside of Africa.
Scientists had thought that modern humans left Africa about 60,000 years ago and, as they colonized Western Eurasia, found a world empty of any other archaic hominin species.
But this assumption stemmed in part from the fact that the prehistory of Asia is poorly known compared to that of Africa and Europe.
Researchers suspected that Denisovans were widespread in Asia, based on the widespread Denisovan genomic signal among present-day Asians.
The new study has been published in the journal Science.
It is thought that the shared ancestors of Denisovans and Neanderthals, which are unknown in the fossil record, likely split from the ancestors of modern humans around 800,000 years ago
WHO WERE THE DENISOVANS?
The Denisovans are an extinct species of human that appear to have lived in Siberia and even down as far as southeast Asia.
Although remains of these mysterious early humans have only been discovered at one site – the Denisova Cave in the Altai Mountains in Siberia, DNA analysis has shown they were widespread.
DNA from these early humans has been found in the genomes of modern humans over a wide area of Asia, suggesting they once covered a vast range.
DNA analysis of a fragment of pinky finger bone in 2010, (pictured) which belonged to a young girl, revealed the Denisovans were a species related to, but different from, Neanderthals.
They are thought to have been a sister species of the Neanderthals, who lived in western Asia and Europe at around the same time.
The two species appear to have separated from a common ancestor around 200,000 years ago, while they split from the modern human Homo sapien lineage around 600,000 years ago.
Bone and ivory beads found in the Denisova Cave were discovered in the same sediment layers as the Denisovan fossils, leading to suggestions they had sophisticated tools and jewellery.
DNA analysis of a fragment of a fifth digit finger bone in 2010, which belonged to a young girl, revealed they were a species related to, but different from, Neanderthals.
Later genetic studies suggested that the ancient human species split away from the Neanderthals sometime between 470,000 and 190,000 years ago.
Anthropologists have since puzzled over whether the cave had been a temporary shelter for a group of these Denisovans or it had formed a more permanent settlement.
DNA from molar teeth belonging to two other individuals, one adult male and one young female, showed they died in the cave at least 65,000 years earlier.
Other tests have suggested the tooth of the young female could be as old as 170,000 years.
A third molar is thought to have belonged to an adult male who died around 7,500 years before the girl whose pinky was discovered.