First evidence of Denisovans in the tropics

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First evidence of the presence of Denisovans in the tropics

Tooth discovered in Laos provides first evidence of Denisovan presence in a tropical climate.

A child's tooth aged at least Less than 130,000 years old discovered in a cave in Laos testifies to the presence of the Denisovans in the tropical climate of Southeast Asia, lifting part of the veil on the mystery of this extinct species, according to a study.

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Very little is known about the Denisovans, an archaic human cousin of Neanderthals, who were first identified in 2010 in a cave in Siberia. From a simple piece of phalanx, paleontologists were able to sequence a complete genome.

Denisovan phalanx fragment and its position in the hand

Then, in 2019, they found a mandible with large teeth on the Tibetan plateau, proving that the species had also lived in this part of China.

The jawbone of a Denisovan man discovered on the Tibetan plateau, more than 3000 meters above sea level

Apart from these rare fossils, the Denisovans had left no trace of their passage… Except in the genes, since before disappearing, this so-called archaic species interbred with Homo sapiens, bequeathing part of its DNA to present-day populations of Southeast Asia and Oceania: Negritos of the Philippines, Papuans of New Guinea and Aborigines of Australia hold a large proportion of the Denisovan genome – until ;to 5%.

Geneticists have deduced that the modern ancestors of these populations hybridized with Denisovans in Southeast Asia, explains to the ;AFP paleoanthropologist Clément Zanolli, co-author of the study published Tuesday in Nature Communications.

But there was no physical proof of their presence in this part of the Asian continent, far from the cold mountains of Siberia or Tibet, adds this CNRS researcher.

Until a team of scientists set out to excavate Cobra Cave in northeastern Laos.

The cavity, located on a massif, was discovered in 2018 by speleologists near the site of Tam Pa Ling, known to have already delivered very ancient human remains. The sediments preserved in the walls of the cave contained bone fragments of animals, as well as a molar.

A Denisovan molar discovered in a cave in Laos.

The tooth had d& #x27;from the outset a typically human morphology, says Clément Zanolli. It must have belonged to a child between the ages of 3 and 8, as it was still growing in the jaw, the study states.

But from what period, what species? The tooth was too old for carbon-14 dating, and its DNA was poorly preserved due to the hot and humid climate, said co-author paleoanthropologist Fabrice Demeter.

The researchers therefore circumvented the obstacle by dating the sediments containing the tooth and the faunal remains, then the upper layer, to obtain a range of 160,000 to 130,000 years.

They then studied the inside of the tooth – temporarily exported to Denmark – using different methods such as X-ray microtomography and paleoproteomics (protein analysis).

The proteins allowed us to identify the sex, female, and to affirm its belonging to the genus Homo, details Fabrice Demeter, researcher at the University of Copenhagen affiliated with the National Museum of Natural History of Paris.

And, surprisingly, the internal structure of the tooth was found to be close to that of the molars of the Denisovan specimen from Tibet. I was really expecting a Homo erectus! recalls the paleoanthropologist.

But no doubt, the molar was easy to distinguish from this ancient species, as well as other extinct groups endemic to the Philippines and the Philippines. Indonesia, Homo floresiensis and Homo luzonensis. And of course the modern human.

Only problem: it shared characteristics with Neanderthals, genetically close to Denisovans – the two species would have diverged about 350,000 years ago.

But we leaned for a Denisovan, because we have never found the trace of the passage of Neanderthals also to the east, specifies Clément Zanolli.

The Denisovans therefore indeed occupied this part of Asia, a sign of adaptation to a wide range of environments, from cold altitudes to tropical climates, concludes the study. A versatility that their Neanderthal cousins, more specialized in the cold regions of the West, did not seem to possess, explains Fabrice Demeter.

It is in the tropics that the later Denisovans could have encountered – and interbred with – local modern human groups of the Pleistocene epoch, who transmitted their genetic heritage to present-day Southeast Asian populations.

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