Xiahe Mandible: A Denisovan Jaw from the Tibetan Plateau

The Xiahe mandible is the right half of a fossil human lower jaw from Baishiya Karst Cave on the north-eastern edge of the Tibetan Plateau in China. Found by a Buddhist monk in 1980 and identified in 2019 from ancient proteins, it was the first Denisovan fossil recognised outside Denisova Cave in Siberia. At least about 160,000 years old, it showed that these archaic humans lived at an altitude of more than 3,000 metres long before our own species reached the region.

The cave and the monk’s find

Baishiya Karst Cave lies at about 3,280 metres above sea level in Xiahe County, Gansu Province, the county that is also home to the famous Labrang Monastery. The cave is a sacred site for local Tibetan Buddhists, who visit it to pray. In 1980 a monk exploring the cave noticed a jaw with large teeth embedded in carbonate crust and took it away.

The jaw was given to the sixth Gungthang Living Buddha, a senior lama of the region, who passed it to Lanzhou University. For three decades it attracted little attention. In 2010 the environmental scientist Fahu Chen and the archaeologist Dongju Zhang of Lanzhou University began to study it, later joined by the palaeoanthropologist Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology in Leipzig and the protein specialist Frido Welker.

Identifying a Denisovan without DNA

At the time the Denisovans were known almost entirely from DNA, from a finger bone and a few teeth found in Denisova Cave. The Xiahe jaw contained no recoverable DNA, so the team used a newer approach: palaeoproteomics, the study of ancient proteins.

Proteins survive longer than DNA, especially in cold settings. The researchers extracted collagen and other proteins from the dentine of one of the molars. Because protein sequences are coded by genes, tiny differences in their building blocks can reveal relationships. The Xiahe proteins carried variants matching the Denisovan genome rather than those of Neanderthals or modern humans.

The results were published in the journal Nature on 1 May 2019. It was one of the first times an archaic human fossil had been identified mainly from ancient proteins.

Dating and anatomy

Uranium-series dating of the carbonate crust that had formed on the jaw gave a minimum age of about 160,000 years. Because the crust grew after the jaw was deposited, the bone itself could be older.

The jaw is robust and primitive. It has no chin, and its molars are very large, similar in size to the Denisovan teeth from Siberia. These features gave researchers a template for recognising Denisovan fossils elsewhere, and later helped link other East Asian finds, such as a molar from Laos and a jaw from the sea floor near Taiwan, to the same group.

Further work at Baishiya Karst Cave

The discovery prompted excavations inside the cave from 2016 onwards. In 2020 the team reported Denisovan mitochondrial DNA preserved in the cave’s sediments, in layers dated from roughly 100,000 to 60,000 years ago, and possibly as recently as about 45,000 years ago. This showed that Denisovans used the cave repeatedly over a long period.

A 2024 study described thousands of animal bones from the cave. The occupants hunted or scavenged blue sheep, wild yaks, wild horses and woolly rhinoceroses, as well as marmots and birds, and broke bones for marrow. A rib fragment from layers dated to roughly 48,000 to 32,000 years ago was also identified as Denisovan from its proteins, extending the group’s presence on the plateau into the later Ice Age.

Denisovans and life at altitude

Living at more than 3,000 metres is hard because the air holds less oxygen. In 2014 geneticists showed that many Tibetans carry a version of the EPAS1 gene that helps them cope with high altitude, and that this variant was inherited from Denisovans through interbreeding.

When that study appeared, it was puzzling that a group known from Siberia had passed on a high-altitude gene. The Xiahe jaw offered an explanation: Denisovans had lived on the Tibetan Plateau for a very long time and may have adapted to its thin air before modern humans arrived and met them. Researchers caution that this link is plausible but not yet proven in detail.

Timeline

• At least c. 160,000 years ago: The Xiahe individual dies and the jaw is left in Baishiya Karst Cave.
• c. 100,000-60,000 years ago: Denisovan DNA accumulates in the cave’s sediments.
• c. 48,000-32,000 years ago: A Denisovan rib fragment is deposited in the cave.
• 1980: A Buddhist monk finds the jaw while visiting the cave.
• 2010: Researchers at Lanzhou University begin studying the jaw.
• 2016-2018: Excavations start inside Baishiya Karst Cave.
• 2019, 1 May: The jaw is published in Nature as the first Denisovan fossil outside Siberia.
• 2020: Denisovan DNA is reported from the cave’s sediments.

Why it matters

The Xiahe mandible turned the Denisovans from a genetic signal into a population with a real geography. It showed that they lived on the roof of the world at least 160,000 years ago, gave researchers a model for recognising Denisovan fossils, and proved that ancient proteins can identify human groups where DNA has not survived. It links directly to the story of Denny and of Neanderthal interbreeding in showing how intertwined ancient human groups were.