Baishiya Karst Cave is not easy to call home. It lies on a steep rocky slope on the Tibetan Plateau at an altitude of 10,700 feet, where oxygen is thin and the climate is cold and dry.
But a series of expeditions to the cave in recent years have shown that it was home to one of the most mysterious branches of humanity: a Neanderthal group of people called the Denisovans.
Since 2010, scientists have painted a dark picture of the Denisovans (pronounced De-NEE-so-vans) based on just three teeth, a few bone fragments and traces of DNA. Mystery shrouded much of their existence, especially their behavior.
But researchers who dug several small holes into the Baishyia karst cave uncovered a wealth of clues about the Denisovans. In a paper published Wednesday, they said that for more than 100,000 years, Denisovans on the Tibetan Plateau hunted or scavenged a wide variety of animals, from blue sheep to snow leopards and even golden eagles. The Denisovans not only ate the animals, but probably skinned them for clothing to keep warm in the cold.
The first evidence of the Denisovans appeared about 1,400 miles northwest of this location, in Denisova Cave in Siberia. DNA from a single tooth and pinky bone showed that the group belonged to a lineage distinct from modern humans and Neanderthals.
Millions of living humans carry some Denisovan genes, geneticists later discovered, suggesting that modern humans interbred with them along with Neanderthals before the two groups disappeared.
The Tibetan cave has been a Buddhist shrine for centuries. In 1980, a monk who came to pray there noticed part of the jaw on the ground. The specimen languished in a museum drawer for years until Dongju Zhang, an archaeologist at Lanzhou University, took a closer look.
The jaw appeared human, but lacked some key features, such as a prominent chin. And the two molars, which were still rooted to the bone, were larger than human teeth. Dr. Zhang suspected it might be a Denisovan. So she and her colleagues searched for DNA in the Tibetan jaw, but without success. They had better luck looking for collagen proteins.
The researchers then compared the structure of the proteins to the collagen genes of modern humans, Neanderthals and Denisovans. Denisovan gen was the best match.
In 2016, Dr. Zhang lead an expedition to the cave to learn more. On recent visits, her team dug a pair of six-foot holes into the floor of the cave.
The expeditions revealed that the jaw must have been over 160,000 years old. The sediment also yielded four Denisovan DNA fragments. The oldest comes from a layer that formed about 100,000 years ago, and the youngest from a layer that formed between 48,000 and 32,000 years ago.
If true, it would raise the exciting possibility that modern humans and Denisovans had contact on the Tibetan Plateau. Elsewhere on the plateau, archaeologists have found stone blades at least 30,000 years old and characteristic of modern humans.
As Dr. Zhang and her colleagues dug deeper, the researchers also found thousands of bone fragments in the holes. But they had no idea what kind the battered pieces belonged to.
The researchers ground up the samples and found enough collagen to identify 2,005 bones.
One of them, a rib fragment, contained Denisovan collagen. The rib came from the same layer of sediment that yielded the most recent Denisovan DNA.
Samantha Brown, an anthropologist at the University of Tübingen in Germany who was not involved in the study, said finding both DNA and a rib in the same layer strongly supports the existence of Denisovans in Tibet so recently.
“This is such an exciting discovery,” she said. “Without these multiple lines of evidence, it might be too good to be true.
But Tom Higham, an archaeologist at the University of Vienna, said it was unfortunate that Dr Zhang’s team could not find any DNA in the rib, nor did they find any carbon they could use to accurately determine its age. “It’s a big disappointment for me,” he said.
Dr. Zhang and her colleagues concluded that the 2,004 additional bones mostly belonged to animals brought to the cave by the Denisovans. Many of them show cut marks indicating that they were slaughtered.
The Denisovans seem to have taken a liking to the blue sheep, a species that still lives on the Tibetan Plateau today. But the Denisovans also hunted or scavenged carnivores and birds of prey. They also weren’t above killing marmots, cat-sized rodents that hibernate in the winter.
Frido Welker, molecular anthropologist at the University of Copenhagen and one of the research partners of Dr. Zhang, said evidence in the Baishiya Karst Cave showed that Denisovans successfully adapted to the Tibetan Plateau even during the Ice Age.
“The Denisovans just happened not to be there on a random day,” he said. “They were able to last a lot longer there, which says something about their resilience.”