NEW YORK – Nearly 40 years after it was found by a monk in a Chinese cave, a fossilized chunk of jawbone has been revealed as coming from a mysterious relative of the Neanderthals.
Contemporaries of the Neanderthals — and like them, possibly wiped out by anatomically modern man, Homo sapiens — the Denisovans first came to light a decade ago.
Their existence was determined through a piece of finger bone and two molars unearthed at the Denisova Cave in southern Siberia’s Altai Mountains and dated to some 80,000 years ago.
Until now, the only known remains of these Denisovans were the few scraps of bone and teeth recovered in the Siberian cave. DNA from those fossils showed kinship with Neanderthals. But the remains disclosed little else.
The new discovery was made roughly 2,300 kilometers (1,400 miles) to the southeast in China’s Gansu province. The right half of a jawbone with teeth is at least 160,000 years old, scientists reported Wednesday in the journal Nature. No DNA could be found, but scientists recovered protein fragments that they compared to the Siberian DNA. That showed the fossil came from a Denisovan.
The find addresses several mysteries. One was why the Siberian DNA indicated Denisovans were adapted to living at high altitudes when the Siberian cave is relatively close to sea level. The Chinese cave, by contrast, is on the high-altitude Tibetan Plateau, about 3,280 meters (10,800 feet) high.
In 2015 researchers found that ethnic Tibetans and Han Chinese living at altitude had buried in their genetic code an unusual variant of a gene, EPAS1, that regulates hemoglobin, the molecule that hauls oxygen around the blood.
At high altitude, common variants of the gene overproduce hemoglobin and red blood cells, causing the blood to become thick and sludgy — a cause of hypertension, low birth weight and infant mortality.
But the variant found in Tibetans increases production by much less, thus averting the hypoxia problems experienced by many people who relocate to places above 4,000 meters in altitude.
The mutation is nearly identical to that found in the DNA of Denisovans discovered in Siberia — at an altitude of less than 700 meters.
“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.
In fact, “it’s a big surprise” that any human relative could live in the cold climate and thin air of the plateau at that time, more than 100,000 years before our species showed up there, he told reporters.
Previous research had indicated that Denisovans must have lived somewhere other than Siberia, because traces of their DNA can be found in several present-day populations of Asia and Australia whose ancestors probably didn’t pass through that region. The new finding expands their known range, although Hublin said it is still not clear where Denisovans first appeared.
The new work was a long time in coming. The monk who found the fossil in 1980 gave it to a Buddhist leader, who passed it along to Lanzhou University in China. Study of it began in 2010.
The discovery also provides new anatomical details that can be compared to other fossils from China, some of which are “good candidates for being Chinese Denisovans,” Hublin said.
Experts unconnected to the research agreed the fossil could help identify other remains as Denisovan.
“We always assumed … that Denisovans were distributed all across Asia,” said Bence Viola of the University of Toronto.
The Nature paper points out similarities to a fossil jaw reported in 2015 that had been dredged by a fishing net off the coast of Taiwan. So maybe the Denisovan range can be extended that far south, he said.
Such linking of fossils might eventually reveal Denisovan body shape and size, he said. From the scant known remains “I assume they were large guys, but it’s kind of hard to prove,” Viola said.
In addition to the anatomy, the study’s approach of using protein from the bone or teeth could also be used on fossils to look for evidence of Denisovan identity, said Eric Delson of Lehman College in New York. Even if a fossil is found not to be Denisovan, the analysis could reveal details of how it fits on the evolutionary tree, he said.
“The method potentially tells us a whole new way of looking at fossils,” he said.
Katerina Harvati of the University of Tuebingen in Germany said the ability of Denisovans to adapt to the inhospitable climate of the Tibetan Plateau is remarkable. It adds to growing evidence that our ancient relatives were more capable than scientists had thought, she said.
IN FIVE EASY PIECES WITH TAKE 5