A human jawbone found in a cave on the Tibetan plateau has revealed new details about the appearance and lifestyle of a mysterious ancient species called Denisovans.
The 160,000-year-old fossil, comprising a powerful jaw and unusually large teeth, suggests these early relatives would have looked something like the most primitive of the Neanderthals. The discovery also shows that Denisovans lived at extremely high altitude and, through interbreeding, may have passed on gene adaptations for this lifestyle to modern-day Sherpas in the region.
Jean-Jacques Hublin, the director of the department of human evolution at the Max Planck Institute for Evolutionary Anthropology in Leipzig and senior author of the find, described this element as “spectacular”. He said: “Until today, nobody imagined that archaic humans could be able to dwell in such an environment.”
Denisovans are a sister species to Homo sapiens and Neanderthals, but far less has been known about them, including what they might have looked like.
Their existence was revealed by a DNA analysis of a finger bone found in the Denisova cave in Siberia. This showed that the fossil belonged to a new species that, along with the Neanderthals, split from our own lineage about 700,000 years ago.
Soon after this split, the Denisovans and Neanderthals went their separate ways – although not definitively. There is clear evidence of interbreeding between the two extinct species as well as with modern humans.
About 3% to 5% of the DNA of Melanesians and Aboriginal Australians and about 6% in Papuans appears to derive from Denisovans. These genetic comparisons suggest that Denisovans must once have been widespread.
Since the Siberian fossils amount to just a few chunks of bone and teeth, a crucial piece of the puzzle has been trying to match up DNA evidence with more complete fossils found at other site, including in China, to get a better picture of what our ancient cousins looked like and how they lived.
The dating of the mandible suggests temperatures on the plateau would have been even harsher than today, when temperatures can plunge to -30C (-22F). “It’s a time period colder than now which … blows my mind,” said Hublin. “If you find it a challenging environment today, I recommend you try it [then].”
Previously, the only known Denisovan fossils came from a cave in Siberia, and amounted to a finger fragment, some teeth and a few jagged pieces of bone. Crucially, scientists were able to extract DNA from inside the bone and by comparing this with other ancient DNA and present-day populations they learned that the species must once have been widespread across Europe and Asia.
The latest fossil represents a crucial link between the Siberian specimens and other Chinese fossils, from which scientists had previously failed to extract DNA, but which show remarkable anatomical similarities to the Tibetan specimen.
Prof Chris Stringer, the head of human origins research at the Natural History Museum who was not involved in the research, described it as a landmark paper.
The fossil was discovered by a monk in Baishiya Karst Cave on the Tibetan plateau in China’s Gansu province. After finding the jaw in the 1980s, the monk passed it on to a living Buddha, who passed it to one of the scientists behind the latest analysis.
The scientists were not able to obtain DNA from the sample, but managed to extract proteins from one of the molars. Proteins, like DNA, could be sequenced and the analysis placed the fossil firmly on the Denisovan branch of the evolutionary tree.
The discovery indicates that Denisovans adapted to high-altitude, low-oxygen environments much earlier than the regional arrival of modern humans about 40,000 years ago.
It also helps explain how present-day Sherpas and some Tibetan populations came to carry a gene of Denisovan origin – presumably acquired through ancient interbreeding – that allows these populations to cope with hypoxia. “This has been quite puzzling because the [Siberian] cave was not at high altitude,” said Hublin.
Previously scientists had assumed the gene most probably served a different purpose in Denisovans, such as helping them cope with intense physical activity, and that it was later coopted for a different purpose. Stringer said: “Now it seems more likely that it originated in high altitude-adapted Denisovans, and could have been passed on directly in the region.” Scientists could not be certain of this, though, because they were unable to extract a genome from the new specimen.
The paper, published in Nature, is one of the first to use protein analysis to determine an ancient human species and the technique is seen as hugely promising because protein tends to be preserved better than DNA. The team said they were hopeful that further fossils in China would be able to be tested using the method.
