Scientists have uncovered the most complete remains yet from the mysterious ancient-hominin group known as the Denisovans.
The jawbone, discovered high up on the Tibetan Plateau and dated to more than 160,000 years ago, is also the first Denisovan specimen found outside the Siberian cave in which the hominin was uncovered a decade ago — confirming suspicions that Denisovans were more widespread than the fossil record currently suggests.
Hominins are part of the family, or larger group of primates, called hominids. Hominids include orangutans, gorillas, chimpanzees, and human beings. All hominins are hominids, but very few hominids are hominins.
Analysis of a fossil jawbone containing molars recovered from Baishiya Karst cave in Xiahe, Gansu, China shows Denisovans lived in the Tibetan Plateau some 1,60,000 years ago.
The first evidence for Denisovans or Denisovan hominins was first discovered in 2008 in a cave in the Altai Mountains in Siberia. This is the first time evidence of Denisovan presence has been found outside the Denisovan cave.
The mandible was so well preserved that it allowed for a virtual reconstruction of the two sides of the mandible.
Contrary to popular belief that high altitude regions were inhabited only by modern humans dating back to less than 40,000 years, the fossil remains conclusively prove that Denisovans lived in the Tibetan Plateau at an altitude of 3,280 meters much earlier — 1,60,000 years ago. The Denisovan cave in Siberia is at an altitude of just 700 meters.
Previous genetic studies have found that modern humans living in the Tibetan Plateau carried a special gene variant — EPAS1 (Endothelial PAS Domain Protein 1) — that allowed them to cope with low oxygen (hypoxia) environments typical of high altitude. This gene variant has been found in Denisovans.
Since the Denisovan cave is at an altitude of just 700 meters, it was not clear why and how the Denisovans possessed this adaptation. The discovery of a Denisovan sample in 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 in the plateau leading to the gene mutation. This mutation has later been passed on to modern humans.
Though the jawbone is well preserved, there was no evidence for the preservation of ancient DNA. A team led by three researchers extracted proteins from one of the molars and carried out protein analysis. Though the proteins were highly degraded, protein analysis conclusively proved that the jawbone belonged to Denisovans. The carbonate matrix adhering to the sample was dated using Uranium-Thorium and the age was determined to be 1,60,000 years.
“Our protein analysis shows that the Xiahe mandible belonged to a hominin population that was closely related to the Denisovans from Denisovan Cave,” Frido Welker from Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany and one of the authors of the paper said in a release.