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Denisovans survived and thrived on the high-altitude plateau of Tibet for more than 100,000 years, according to new research that deepens scientific understanding of the mysterious ancient humans first described in 2010.
Researchers analyzed thousands of animal bone fragments unearthed in the Baishiya Karst Cave, located 3,280 meters above sea level near the city of Xiahe in China’s Gansu Province. The cave is one of only three known sites of extinct human habitation. Their work revealed that Denisovans were able to hunt, butcher and process a variety of large and small animals, including woolly rhinos, blue sheep, wild yaks, marmots and birds.
The team of archaeologists working in the cave also uncovered a rib fragment in a layer of sediment dating back 48,000 to 32,000 years, making it the youngest of a handful of known Denisova fossils and a clue that the species existed more recently than scientists previously thought.
Because of the paucity of fossil evidence, details about how these archaic human ancestors lived are scarce. But the new study reveals that the Denisovans living in Baishiya Karst Cave were incredibly resilient, surviving in one of Earth’s most extreme environments through warmer and colder periods and maximizing the diverse animal resources available on the grazing land.
“We really want to know how the Denisovans lived there for so long in the cave and on this Tibetan plateau. How did they adapt to the environment?” said Dongju Zhang, an archaeologist and professor at Lanzhou University in China and co-lead author of the study published Wednesday in the journal Nature.
“They used all the animals we had, which means their behavior is flexible,” Zhang added.
The rib likely belonged to Denisovans, who lived at a time when modern humans were spreading across the Eurasian continent, said study co-author Frido Welker, an associate professor in the Globe Institute for Biomolecular Paleoanthropology Group at the University of Copenhagen. Future research at the site and in the region could shed light on whether the two groups interacted there, Welker said.
“This puts this fossil and (sedimentary) layer in a context where humans were likely present in the broader region, and that’s interesting,” he said.
The trail of Denisovan clues
Denisovans were first identified in a laboratory a little over a decade ago, using DNA sequences extracted from a small piece of finger bone. Since then, fewer than a dozen Denisovan fossils have been found around the world.
Many of these were found in the Denisova Cave in the Altai Mountains of Siberia, from which the group takes its name. Later genetic analysis has shown that Denisovans, like Neanderthals, once interbred with modern humans. Traces of Denisovan DNA found in modern humans suggest that the ancient species likely once inhabited much of Asia.
However, researchers identified the first Denisova fossil outside the cave from which it takes its name in 2019.
A toothed jawbone found by a monk in the Baishiya Karst Cave, a sacred site for Tibetan Buddhists, was at least 160,000 years old and contained a molecular signature of Denisovans. The discovery of DNA extracted from sediment at the site, published a year later, provided further evidence that Denisovans once called the area home.
In 2022, scientists identified a tooth found in a cave in Laos as Denisovan, a clue that the species first settled in Southeast Asia. As with the jawbone, DNA could not be extracted from the tooth, so researchers instead examined microscopic remains of proteins, which are better preserved than DNA but less informative.
The research, published on Wednesday, examined more than 2,500 animal bone fragments unearthed during excavations at Baishiya cave in 2018 and 2019.
Because many of the pieces are too small to be identified by eye, the researchers turned to a relatively new technique known as Zooarchaeology with Mass Spectrometry (ZooMS), which allows scientists to extract valuable information from samples that might have been overlooked in the past.
ZooMS helped researchers determine which animal species the bones belonged to, based on small differences in the amino acid sequence of collagen preserved within the bone.
Baishiya’s place in Denisovan history
As well as large and small herbivores, the analysis also revealed carnivores such as hyenas. Some animals, such as blue sheep, are still common in the Himalayas today.
Many of the bones had cut marks, indicating that the Denisovans had processed the animals for their skin, meat and marrow. Some bones were also used as tools, according to the study.
The diversity of animal species found suggests that the area around the cave had a grassland landscape with some small forest areas, similar to today’s. Most of the animals living there today are domesticated yaks and goats, Zhang said.
During the painstaking, months-long process of categorizing the bones, the team identified a 2-inch-long rib fragment. But the resolution of the protein information was not clear enough to immediately determine what type of human it belonged to. Further analysis of the preserved ancient proteins, led by Welker, revealed it to be Denisovan.
The rib came from a layer of sediment from which the team had previously extracted Denisovan DNA, and Zhang said the researchers are working to extract DNA from the new sample, a process that could provide more detailed genetic information about the rib’s owner and the broader Denisovan population that once inhabited the area.
Given that so little is known about the Denisovans, “every discovery is of great importance,” and the zooarchaeological analysis conducted by the authors of the new study was “particularly informative,” said archaeological scientist Samantha Brown, Young Group Leader for Paleoproteomics at the University of Tübingen in Germany, who worked on the Denisova Cave remains.
“The young age of the fossil was certainly surprising. We have evidence that modern humans occupied areas as far as Australia during this period. This really opens up conversations about the possibility that these groups interacted as modern humans moved into Asia and the Pacific, but more evidence is probably needed to understand the nature of these interactions,” said Brown, who was not involved in the research.
Work at Baishiya Karst Cave is ongoing and another paleolithic site has been excavated in the area where Denisovans or modern humans who came after them may have lived, Zhang said.
Unlike Denisova Cave, which was occupied by early modern humans and Neanderthals, as well as Denisovans, current evidence suggests that Denisovans were the only human group living in Baishiya Karst Cave, Zhang said. That makes the Tibetan plateau, an area nicknamed the “roof of the world,” a particularly important site in the quest to answer many lingering questions about who the Denisovans were, what they were like, how they disappeared and their place on the human family tree.
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