Early hominids in the Tibetan plateau were Denisovans

Until now, the Denisovans were known only from a small collection of fossil fragments from the Denisova Cave in Siberia. A research team now describes a 160-year-old Xiahe jaw in China. Using an ancient protein analysis, the researchers found that the owner of the jaw belonged to a population that was closely related to the Denisovans of Siberia. This population occupied the Tibetan plateau in the Middle Pleistocene and was adapted to this low oxygen environment long before Homo Sapiens reached the region.

Denisovans – an extinct sister group of Neanderthals – were discovered in 2010 when a research team led by Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology (MPI-EVA) sequenced the genome of a fossil found in the Denisova cave in Russia. showed that it belonged to a hominin group that was genetically distinct from the Neanderthals. "Traces of Denisovan's DNA are found in Asian, Australian and present-day Melanesian populations, suggesting that these ancient hominins may have been widely diffused," says Jean-Jacques Hublin, director of MPI-EVA's Department of Human Evolution. "However, so far the only fossils representing this ancient hominid group have been identified in the Denisova Cave."

Jaw of the Baishiya Karst Cave

In their new study, researchers now describe a lower hominin jaw that was found on the Tibetan plateau at 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 and Dongju Zhang of Lanzhou University have been studying the area of ​​discovery and the location of the cave where the jaw originated. In 2016, they began a collaboration with the Department of Human Evolution in MPI-EVA and have since jointly analyzed the fossil.

Although the researchers could not find traces of DNA preserved in this fossil, they were able to extract proteins from one of the molars, which they analyzed by applying an ancient protein analysis. "Old jaw proteins are highly degraded and clearly distinguishable from modern proteins that can contaminate a sample," says Frido Welker of MPI-EVA and the University of Copenhagen. "Our protein analysis shows that the Xiahe jaw belonged to a hominin population that was closely related to the Denisovans of the Denisova cave."

Primitive form and large molars

The researchers found that the jaw is well preserved. Its robust primitive form and the very large molars still attached to it suggest that this jaw belonged to a Middle Pleistocene hominid sharing anatomical features with Neanderthals and Denisova Cave specimens. Attached to the jaw was a heavy carbonate crust, and by applying the U series dating from the crust, the researchers found that the Xiahe jaw is at least 160,000 years old. Chuan-Chou Shen of the Department of Geosciences at National Taiwan University, who conducted the dating, says: "This minimum age is the same as the oldest specimens of the Denisova cave."

"The Xiahe jaw probably represents the earliest hominid fossil in the Tibetan plateau," says Fahu Chen, director of the Tibetan Research Institute, CAS. These people had already adapted to live in this low-oxygen environment long before Homo sapiens reached the region. Previous genetic studies have found that current Himalayan populations carry the EPAS1 allele in their genome, transmitted to them by Denisovans, which helps them adapt to their specific environment.

"The archaic hominins occupied the Tibetan plateau in the Middle Pleistocene and successfully adapted to low altitude and oxygen environments long before the modern arrival of modern Homo sapiens," says Dongju Zhang. According to Hublin, similarities with other Chinese specimens confirm the presence of Denisovans among the current Asian fossil record. "Our analysis paves the way for a better understanding of the evolutionary history of Middle Pleistocene hominids in East Asia."

The study is published in Nature.