The history of humans in Asia may have to be rewritten. A fossilized jawbone discovered on the Tibetan Plateau has been found to belong to a Denisovan, an enigmatic early human species closely related to Neanderthals. Its age suggests that Denisovans were the first hominins to occupy the area, long before the arrival of modern humans.
Denisovans were only added to the family tree relatively recently, when DNA analysis conducted on a finger bone found it to be related to, but distinct from, Neanderthals. Since then many other bones have been linked to the species, all from the same place – Denisova Cave in Siberia.
That makes this new discovery the first Denisovan bone to be found outside of their namesake location. The mandible was originally found in Baishiya Karst Cave in Xiahe, China in 1980, before being passed onto Lanzhou University. But what species it came from remained a mystery until now, after the researchers examined it more closely. The bone turned up no traces of DNA, but the identity of its owner was found by analyzing proteins extracted from one of its teeth.
"The ancient proteins in the mandible are highly degraded and clearly distinguishable from modern proteins that may contaminate a sample," says Frido Welker, an author of the study. "Our protein analysis shows that the Xiahe mandible belonged to a hominin population that was closely related to the Denisovans from Denisova Cave."
To determine its age, the researchers focused on a carbonate crust that had formed on the outside of the jawbone over the millennia. U-series dating revealed it to be 160,000 years old – meaning, obviously, that the bone itself had to have been even older than that. Interestingly, that minimum age is the same as the oldest specimens found so far in Denisova Cave.
The discovery of a Denisovan bone in China helps to fill some gaps in the fossil record. Since all early human species moved out of Africa into the Middle East, Europe, Asia and onto the rest of the world, the Denisovans should have left traces somewhere along the line before they reached Siberia. It also fits the story that this Chinese bone is older than the Siberian ones.
But there are other traces of Denisovans in the world today besides fossils. Their DNA can be found in the genomes of modern-day humans, particularly in Asian, Melanesian and indigenous Australian populations. And perhaps most importantly, modern Himalayan people. In fact, previous studies have found that a gene called EPAS1 helps the locals thrive in this high altitude environment – a trait passed down to them by the Denisovans.
"Archaic hominins occupied the Tibetan Plateau in the Middle Pleistocene and successfully adapted to high-altitude low-oxygen environments long before the regional arrival of modern Homo sapiens," says Dongju Zhang, co-lead author of the study. "Our analyses pave the way towards a better understanding of the evolutionary history of Middle Pleistocene hominins in East Asia."
The research was published in the journal Nature.
Source: Max Planck Institute
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