At a Glance

The Xiahe mandible was found in a Chinese cave in 1980.It's the first Denisovan fossil identified outside of Siberia.It may help explain how modern Tibetans have adapted to harsh, high-altitude climates.

A fossilized jawbone picked up 40 years ago in a cave on the Tibetan Plateau is the first evidence of an ancient human relative called the Denisovans found outside of Siberia, Russia.

And, it may help explain how modern Tibetans have, according to a study published in Nature.

A Buddhist monk found the jawbone with two teeth in 1980 in Baishiya Karst Cave in China's Gansu province. He passed it along to a Buddhist leader who later gave it to Lanzhou University, where it sat until 2010, the Associated Press reports.

That's when Dongju Zhang, an archaeologist at Lanzhou, began studying the jaw, known as the Xiahe mandible for the county where it was found.

DNA in the jawbone, which is at least 160,000 years old, was too degraded to be useful. Instead, researchers , the New York Times reports. That protein matched DNA from Denisovan fossils found about 1,400 miles away in Siberia.

Until now, Denisova Cave in Siberia's Altai Mountains was the only place Denisovan remains have been found. The species lived about the same time as Neanderthals. Like Neanderthals, Denisovans interbred with the earliest humans.

This undated photo made available by Dr. Dongju Zhang of Lanzhou University in April 2019 shows the Baishiya Karst Cave above the Jiangla riverbed in the Gansu province of China. It is both a locally famous Buddhist cave and a tourist site. According to a report released on Wednesday, May 1, 2019, a jawbone fragment found in the cave is least 160,000 years old, and recovered proteins led scientists to conclude it came from a Denisovan, a relative of Neanderthals.

(Dongju Zhang/Lanzhou University via AP)

The Xiahe mandible explains how Denisovan DNA can be, the National Geographic writes. The Denisovans traveled far beyond that single cave in Siberia.

The jaw also answers the mystery of how the Siberian Denisovan DNA indicated the species had adapted to living at high altitudes even though the cave in Russia is close to sea level, AP reports.

The Chinese cave is at an elevation of 10,800 feet.

"Now we have an explanation," said Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, one of the paper's authors.

This undated photo made available by Dr. Dongju Zhang of Lanzhou University in April 2019 shows the right half of the Xiahe mandible, found in 1980 in the Baishiya Karst Cave in the Gansu province of China. According to a report released on Wednesday, May 1, 2019, it is at least 160,000 years old, and recovered proteins led scientists to conclude the jaw came from a Denisovan, a relative of Neanderthals.

(Qiu Menghan/Dongju Zhang/Lanzhou University via AP)

"It's a big surprise" that any human relative could live in cold thin air atop the Tibetan Plateau more than 100,000 years before our own species showed up there, he told reporters, according to AP.

In 2014, researchers discovered that to the harsh conditions at high altitudes can only be found today in modern Tibetans and a very few Han Chinese.

Emilia Huerta-Sanchez, a population geneticist at Brown University who led the 2014 study, told the New York Times that without DNA from Tibetan Denisovans it's impossible to know in which species the gene first developed.

“We don’t know the order of events,” she said. “But Denisovans are such a mysterious group that anything we learn is exciting.”