Jawbone discovery sheds light on Denisovans

An ancient jawbone found in a Himalayan cave has been identified as being from the mysterious hominin species called the Denisovans — the first fossil evidence of their existence since the original discovery in Siberia was revealed seven years ago.

Scientific analysis of the jawbone found in the cave in the mountains of Tibet showed it contained protein molecules that closely matched those of the Denisovans, whose existence was confirmed in 2012 when German scientists extracted DNA from fossils found in the Denisova cave in Mongolia.

Denisovans — and the Neanderthals identified in the mid-19th century — were different types of ancient humans whose ancestral lineage separated from the ancestors of modern humans, about 500,000 years ago. Scientists disagree whether they should be regarded as a distinct species or a subspecies of Homo sapiens.

Dongju Zhang of Lanzhou University, the project’s senior Chinese scientist, said an unnamed monk found the fossilised jawbone in the cave in 1980 and gave it to his religious leader, the Sixth Gung-Thang Living Buddha, who recognised the potential scientific importance and passed it on to the university.

The Lanzhou team contacted the Max Planck Institute for Evolutionary Biology in Leipzig, whose researchers had identified the original Denisovan bone and two teeth found in Siberia.

“Traces of Denisovan DNA are found in present-day Asian, Australian and Melanesian populations, suggesting that these ancient hominins may have once been widespread,” said Jean-Jacques Hublin, project leader from the Max Planck Institute. “Yet so far the only fossils representing this ancient hominin group were identified at Denisova cave.” The findings were published in Nature magazine.

Though they could not find any trace of DNA in the Tibetan jawbone, the scientific team were able to extract surviving fragments of eight collagen proteins, which make up the body’s connective tissues. The sequence of amino acids in the proteins closely matched the DNA sequence of the corresponding Denisovan genes but not those of Neantherthals or modern humans.

The scientists believe the mandible — robust in shape and with large molar teeth still in place — came from someone who died in late adolescence. They applied a technique called U-series dating to the crust of carbonate mineral attached to the jawbone, concluding that it was at least 160,000 years old.

Denisovans and Neanderthals are believed to have began their evolutionary divergence about 400,000 years ago. Denisovans tended to move eastward through Asia, while Neanderthals spread west through Europe. Genetic evidence shows that different hominin groups occasionally met and interbred with each other — and with ancestral modern humans who arrived later from Africa.

160,000

Approximate age of the Denisovan jawbone found in a cave in the Himalayas

Both Denisovans and Neanderthals are believed to have died out around 40,000 years ago. Whether they were wiped out by invading modern humans or environmental change or both is not clear.

The new discovery also sheds further light on the finding in 2014 that present-day Tibetans have a special gene which enables them to thrive at high altitude by using scarce oxygen more efficiently. This DNA variant was present in the Denisovan genome — and inherited by people living in the Himalayan region — but it does not feature in the genome of other modern humans.

The cave where the jawbone was discovered is about 3,300m above sea level, where winters are harsh today and would have been even more severe in the colder climate 160,000 years ago.

“Until now no one had imagined that archaic humans could have lived in such high-altitude environments,” said Prof Hublin. “If you find the Tibetan plateau challenging today, think of the conditions then. It blows the mind.”

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