http://www.sci-news.com/othersciences/anthropology/denisovan-mitochondrial-dna-baishiya-karst-cave-09010.html
A portrait of a juvenile female Denisovan based on a skeletal profile reconstructed from ancient DNA methylation maps.
Image credit: Maayan Harel.
Denisovans are an extinct hominin group initially identified from a genome sequence determined from a fragment of a finger bone found at Denisova Cave in the Altai Mountains in southern Siberia.
Subsequent analyses of the genome have shown that Denisovans diverged from Neanderthals 400,000 years ago and that at least two distinct Denisovan populations mixed with ancestors of present-day Asians.
The only physical remains of Denisovans discovered so far in Siberia are a fragmentary finger bone, three teeth, and a skull fragment, all of which were found at Denisova Cave.
In 2019, the Xiahe mandible from Baishiya Karst Cave — dated to at least 160,000 years ago — was identified to be of Denisovan origin.
However, this identification of the fossil as Denisovan is based on a single amino acid position and is therefore tenuous.
In the new study, a team of scientists from China, Australia, Germany, and the United States found evidence for the long-term presence of Denisovans in Baishiya Karst Cave and described stratigraphic and chronological context for their occupation in the cave.
“When we started developing this project about ten years ago, none of us expected Baishiya Karst Cave to be such a rich site,” said co-author Dr. Charles Perreault, a researcher in the Institute of Human Origins and the School of Human Evolution and Social Change at Arizona State University.
“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.”
The entrance of the Baishiya Karst Cave. Image credit: Zhang et al., doi: 10.1126/science.abb6320.
Dr. Perreault and colleagues extracted genetic material from Baishiya Karst Cave sediments and identified Denisovan mtDNA within them.
The findings indicate that 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.
“Finding Denisovan DNA on the Tibetan Plateau itself is surprising. Evidence of archaic hominins 2,000 m above sea level is unusual,” they said.
“Life this high on the plateau is harsh for many reasons, including its thin air, and humans can develop altitude sickness anywhere above 2,500 m above sea level.”
“This suggests that the Denisovans may have evolved adaptations to high altitude, much like modern Tibetans.”
“The dates of the sediments with mtDNA, along with the older Xiahe mandible, suggest that the Denisovans have been on the Plateau perhaps continuously for tens of thousands of years — more than enough for genetic adaptations to emerge.”
The Denisovan fossil and their mtDNA from Baishiya Karst Cave indicate that early modern humans coexisted in Asia with other archaic hominins, but, unexpectedly, that they interbred with them.
Like Neanderthals, Denisovan populations intermixed with modern humans as they dispersed into Asia.
“Baishiya Karst Cave is an extraordinary site that holds tremendous potential to understand human origins in Asia,” Dr. Perreault said.
“Future work in Baishiya Karst 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.”
The findings were published in the journal Science.
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Dongju Zhang et al. 2020. Denisovan DNA in Late Pleistocene sediments from Baishiya Karst Cave on the Tibetan Plateau. Science 370 (6516): 584-587; doi: 10.1126/science.abb6320
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