Sitting 40 meters (131 feet) above a Chinese riverbed on the Tibetan Plateau is the Baishiya Karst Cave, a famous modern Buddhist pilgrimage destination now decorated with billowing Tibetan prayer flags. But 160,000 years ago, this remote site was home to the first modern humans to ever make their way to the Tibetan Plateau – and they weren’t Neanderthals.
A new analysis of a hominin mandible found in the cave more than three decades ago suggests that the first modern humans to occupy the cave were Denisovan, indicating that the species could have once been widespread and not just limited to the Russian namesake cave we know they once called home.
"Traces of Denisovan DNA are found in present-day Asian, Australian and Melanesian populations, suggesting that these ancient hominins may have once been widespread," said researcher Jean-Jacques Hublin in a statement. “Yet so far the only fossils representing this ancient hominin group were identified at Denisova Cave."
The fossil jawbone was first found in 1980 by a local monk. Since 2010, researchers from Lanzhou University have studied the cave site that it was found at and began a collaboration six years later with the Department of Human Evolution to jointly analyze the jawbone. Publishing their work in Nature, researchers write that although they weren’t able to find any traces of DNA, they were able to analyze ancient proteins extracted from one of the well-preserved molars.
"The ancient proteins in the mandible are highly degraded and clearly distinguishable from modern proteins that may contaminate a sample," said Frido Welker of the MPI-EVA and the University of Copenhagen. "Our protein analysis shows that the Xiahe mandible belonged to a hominin population that was closely related to the Denisovans from Denisova Cave."
The mandible’s robust, primitive shape and large molars are common with Neandertals and specimens found in the Denisova Cave, indicating it likely belonged to a human during the Middle Pleistocene. U-series dating of a heavy carbonate crust attached to the mandible suggests the fossil is at least 160,000 years old – “a minimum age that equals that of the oldest specimens from the Denisova Cave.”
Denisovans are the extinct sister group of Neandertals and their existence is only known directly from fragmented fossils and genomes that have been studied at one Siberian cave site. The species were first revealed in 2010 when researchers sequenced the genome of a fossil finger bone and found that it belonged to a hominin group genetically different from Neandertals.
Until now, their range has neither been well-understood or documented.
Previous genetic studies suggest that present-day Himalayan populations carry a gene that was passed down from Denisovans to help them adapt to the high-altitude, low-oxygen environment of the Tibetan Plateau. The mandible discovery furthers such an idea, adding that Denisovan groups likely adapted to living in this region even before Homo sapiens had arrived.
"Archaic hominins occupied the Tibetan Plateau in the Middle Pleistocene and successfully adapted to high-altitude low-oxygen environments long before the regional arrival of modern Homo sapiens," said Dongju Zhang. "Our analyses pave the way towards a better understanding of the evolutionary history of Middle Pleistocene hominins in East Asia."