Denisovans inhabited Tibetan Plateau 120,000 years before modern humans

Denisovan sample --Optimized
The mandible is so well preserved that it allows for a virtual reconstruction of the two sides of the mandible. Mirrored parts are in grey. — Picture credit: Jean-Jacques Hublin, MPI-EVA, Leipzig.

Contrary to popular belief that high altitudes were inhabited only by modern humans less than 40,000 years ago, fossil remains conclusively prove that Denisovans lived there 160,000 years ago. Denisovans adapted to low-oxygen environment long before modern humans arrived on the plateau.

Analysis of a fossil jawbone containing molars recovered from Baishiya Karst cave in Xiahe, Gansu, China shows Denisovans lived on the Tibetan Plateau some 160,000 years ago. Denisovan is a hominin that was first discovered in 2008 in a Denisova cave in Altai Mountains in Siberia. This is the first time Denisovan has been found outside the Denisova cave. The partial jawbone was so well preserved that it allowed the researchers to virtually reconstruct the two sides of the jawbone.

Contrary to popular belief that high altitudes were inhabited only by modern humans less than 40,000 years ago, fossil remains conclusively prove that Denisovans lived on the Tibetan Plateau at an altitude of 3,280 metres much earlier — 160,000 years ago. The Denisova cave in Siberia is at an altitude of just 700 metres. Results of the study were published in the journal Nature.

Denisovan - 3-Optimized
The opening of the cave is about 5 metre-high and 7 metre-wide. Various Buddhist sacrifices were placed in the immediate entrance of the cave. — Picture credit: Dongju Zhang, Lanzhou University.

Previous genetic studies have found that modern humans living on the Tibetan plateau carry a special gene variant — EPAS1 (Endothelial PAS Domain Protein 1) — that allows them to cope with low-oxygen (hypoxia) environment typical of high altitude. This gene variant has been found in Denisovans.

Since the Denisova cave is at an altitude of just 700 metres, it was not clear why and how the Denisovans possessed this adaptation. The discovery of Denisovan sample on the Tibetan plateau at a high altitude provides the answer. The possible explanation for the presence of this gene variant in the hominin is that Denisovans lived for a long time on the Tibetan Plateau leading to the accumulation of the gene mutation. This mutation has later been passed on to modern humans.

Denisovan - 5-Optimized
A team led by Dongju Zhang (top right in the trench) were excavating in one of the two 2m2 trenches in Baishiya Karst Cave in 2018. —Picture credit: Dongju Zhang, Lanzhou University.

Though the jawbone is well preserved, there is no evidence for the preservation of ancient DNA. So a team led by three researchers extracted proteins from one of the molars and carried out protein analysis. Though the proteins have been highly degraded, protein analysis conclusively proved that the jawbone belonged to Denisovans. The carbonate matrix adhering to the sample was dated using U-Th and the age was determined to be 160,000 years.

“Our protein analysis shows that the Xiahe mandible belonged to a hominin population that was closely related to the Denisovans from Denisova Cave,” Frido Welker from Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany and one of the authors of the paper says in a release.

The research was led by Fahu Chen from the Institute of Tibetan Plateau Research, Chinese Academy of Sciences,  Dongju Zhang from Lanzhou University and Jean-Jacques Hublin from the Max Planck Institute for Evolutionary Anthropology.

Published in The Hindu on May 1, 2019

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