Tibetan Plateau, as the “Third Pole” on the earth, was reported to be firstly occupied probably by modern humans armed with blade technology as early as 40 ka BP. However, no human fossils representing the specific hominin groups have been previously found or reported on the Tibetan Plateau yet.
A research team led by Fahu Chen, from the Institute of Tibetan Plateau Research, CAS, China, and Dongju Zhang from Lanzhou University, China, and Jean-Jacques Hublin from the Max Planck Institute for Evolutionary Anthropology, Germany, have just reported in Nature their studies on a human mandible found in Xiahe, on the Northeastern Tibetan Plateau. The researchers found that the mandible’s owner belonged to a population that was closely related to the Denisovans first found in Siberia. This population occupied the Tibetan Plateau in the Middle Pleistocene and adapted to this low-oxygen environment long before the arrival of Modern Homo sapiens in the region.
So far Denisovans were only known from a small collection of fossil fragments from Denisova Cave in Siberia. Traces of Denisovan DNA are found in present-day Asian, Australian and Melanesian populations, suggesting that these ancient hominins may have once been widespread. Fahu Chen’s study, for the first time, confirms that Denisovans not only did live in East Asia but also in high-altitude Tibetan Plateau. This study also indicates that the previously found possible introgression of Denisovan DNA (EPAS1) into modern Tibetans and Sherpa, who are mainly living on the high-altitude Tibetan Plateau and surrounding regions today, are probably derived or inherited locally on Tibetan Plateau from Xiahe hominin represented by this Xiahe mandible.
Fieldwork in Baishiya Karst Cave and surrounding regions led by Fahu Chen
The reported Xiahe mandible was found on the Tibetan Plateau in Baishiya Karst Cave in Xiahe, China. The fossil was originally discovered in 1980 by a local monk who donated it to the 6th Gung-Thang Living Buddha who then passed it on to Lanzhou University. Since 2010, researchers Fahu Chen, current director of the Institute of Tibetan Plateau Research, and Dongju Zhang from Lanzhou University, have been studying the area of the discovery and the cave site from where the mandible originated. In 2016, they initiated a collaboration with the Department of Human Evolution at the MPI-EVA and have since been jointly analysing the fossil.
While the researchers could not find any traces of DNA preserved in this fossil, they managed to extract collagen from one of the molars, which they then analysed applying ancient protein analysis. Ancient protein data, analysed by Frido Welker of the MPI-EVA and the University of Copenhagen, and Huan Xia of Lanzhou University, showed that the Xiahe mandible belonged to a hominin population that was closely related to the Denisovans from Denisova Cave.
The robust primitive shape of the mandible and the very large molars still attached to it, analysed by Jean-Jacques Hublin, suggest that this mandible once belonged to a Middle Pleistocene hominin sharing anatomical features with Neandertals and specimens from the Denisova Cave. Attached to the mandible was a heavy carbonate crust, and by applying U-series dating, by Chuan-Chou Shen from the Department of Geosciences at National Taiwan University, to the crust the researchers found that the Xiahe mandible is at least 160,000 years old, representing a minimum age of human presence on the Tibetan Plateau.
The similarities of Xiahe mandible with other Chinese specimens confirm the presence of Denisovans among the current Asian fossil record. Their analyses pave the way towards a better understanding of the evolutionary history of Middle Pleistocene hominins in East Asia. In addition, supported by The Second Tibetan Plateau Comprehensive Scientific Expedition and Research, Fahu Chen’s team and various researchers will carry out wider and deeper studies of prehistoric human activity and high-altitude adaptations in future.