The first Denisovan remains discovered outside Siberia suggest our extinct cousins lived at extreme altitude in Tibet long before our species made it there
1 May 2019
THE first fossil of our cousins the Denisovans ever to be discovered outside Siberia has been identified in Tibet. It hints that fossils from these extinct humans are more widespread than we thought, and may help settle a long-running debate about our origins.
Denisovans were discovered in 2010, when the DNA from an ancient bone fragment found in Denisova cave in Siberia was sequenced. Since then, a few other fossil fragments have been uncovered in the cave, and genetic analysis has discovered that many people in China and South-East Asia carry a little Denisovan DNA. This reveals that our ancestors must once have lived alongside and interbred with our cousins.
Studies like these also found that people in Tibet carry a specific Denisovan gene that allows red blood cells to cope with low oxygen levels, helping people to live at high altitude.
“It is mind-blowing that they could have lived in such an extreme, low-oxygen environment”
Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, wondered if any human remains previously found in Tibet might really be Denisovan.
He and his colleagues examined a jawbone discovered in 1980 in Baishiya Karst cave, in Tibet’s Jiangla river valley. They found that the shape of the jaw and large size of the teeth are different to those of modern humans.
Radioisotope dating suggested that the fossil is 160,000 years old at least, which is tens of thousands of years before our own species is thought to have reached the Tibetan Plateau.
No DNA could be extracted from the fossil, but analysing collagen protein in its teeth confirmed the jawbone came from a Denisovan, because modern humans and our other extinct cousins the Neanderthals have different genes for collagen (Nature, DOI: 10.1038/s41586-019-1139-x).
The finding could explain the 30,000-year-old stone tools discovered in Tibet last year. It is mind-blowing that hominins could have been living in such an extreme environment, says Hublin. “Even today, Tibet is not an easy place to live. There aren’t many resources and there’s a lack of oxygen.”
The study is the first time that protein analysis has been used as the sole way of identifying an ancient hominin, says team member Frido Welker at Lanzhou University in China.
This technique will prove increasingly useful for fossils without any DNA left, says Murray Cox of Massey University in New Zealand. “As we move away from hominin remains in the cold parts of Eurasia, we simply have to get used to the fact that we often won’t have any ancient DNA to work with.”
Hublin says several previously discovered fossils from sites in China have features that don’t match those of modern humans or Homo erectus, another ancient hominin which is, like the Denisovans and Neanderthals, thought to have left Africa long before we did.
“I predict that most of the Chinese hominin fossil record younger than 350,000 years and older than 50,000 is made of Denisovans,” says Hublin.
“We probably have lots of Denisovan remains sitting in museums all over the world, but they have different names on them,” says Cox.
If Hublin is right, these fossils could help settle the debate over whether our ancestors evolved solely in Africa, or whether important steps took place in Asia too. Previous discoveries of fossils in China have been interpreted by some as intermediate species between H. erectus and modern humans, suggesting that we evolved in eastern Asia. But this idea will lose ground if the fossils turn out to be Denisovan.
However, Sheela Athreya at Texas A&M University says that linking such fossils to Denisovans would be putting the cart before the horse. We know so little about the Denisovans’ physical characteristics and where and when they lived, she says. “We don’t know what ‘Denisovan’ is.”
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