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Scientists have long assumed that Southeast Asia was once home to Denisovans, those ancient cousins of modern humans about whom much remains to be known. Now, the first physical evidence has emerged and been verified: the wisdom tooth of a child, most likely a girl, discovered in a cave in Laos, where it was likely deposited 1,60,000 to 1,30,000 years ago.
The findings, published in Nature Communications, throw new light on the regions inhabited by Denisovans, and their interbreeding with the ancestors of modern humans.
They lived lakhs of years ago, coexisting with Neanderthals in some regions, and interbreeding with early modern humans in some cases. They were first identified as a separate species in 2010, following the discovery of a fragment of a finger bone and two teeth, dating back to about 40,000 years ago, in the Denisovan Cave in Siberia. In 2019, another fossil — a mandible with a set of teeth — was found on the Tibetan plateau.
Once these samples were analysed and their characteristics identified, traces of Denisovan DNA have been identified in certain indigenous groups in the Philippines and other regions. But further fossil finds remained elusive. “Until we find more Denisovan material, we cannot begin to understand their full genome in the way that we can study Neanderthals,” the Smithsonian Institute said in a post on its website in December 2020.
One reason why Denisovan fossils are so rare is that their population was smaller than that of Neanderthals — “plus the fact that they are certainly a number of fossils attributed to the ‘archaic humans’, a group we put fossils into when we don’t really know where to put them”, Dr Fabrice Demeter, palaeoanthropologist at the University of Copenhagen’s Globe Institute, and one of the senior authors of the study, told The Indian Express by email.
“This is the case for several fossils from China such as Maba or Harbin that are certainly Denisovans. We should also consider that Neanderthals are adapted to Western Eurasia and to cold regions, whereas Denisovans originated from Far East Asia with certainly less favourable climate conditions to preserve the bones,” said.
So, what has been found now?
The team that has reported the Laos finds has been working in the region for over 20 years, and in 2009 found some of the oldest modern humans in Northern Laos. “Then in 2018, we found that new cave, Cobra Cave, about 100 m from the previous one,” Demeter said.
In the cave were skeletal remains of various animals — and the tooth that turned out to be of a Denisovan child.
“We microCT-scanned the tooth, did geometric analysis, we extracted the proteins that could tell us the individual belonged to genus Homo and was female. The morphology of the crown tells us it was a young individual of 5-7 years old… The tooth is closer to Neanderthals and Denisovans. But as Neanderthals are only adapted to Western Europe and to cold regions, the best option is that the tooth is Denisovan,” Demeter said.
The DNA has not been extracted for analysis. “DNA doesn’t preserve well in tropical regions, but we will attempt soon,” he said.
Why is the finding important?
So far, it was known that Denisovans were only found in cold and high-altitude regions such as in Siberia and the Himalayas. “Our discovery proves that they were also adapted to a warm environment. Meaning that they had very large flexibility of adaptation,” Demeter said.
It also confirms recent genetic findings “that some populations (Negrito from Philippines, Papuans and Australian Aborigines) have 3 to 5% of Denisovan genes compared to us with 0.001%. Meaning that at some point, their ancestors interbred with some Denisovans in Southeast Asia. Our discovery can now prove it,” he said.
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