A tooth found in a cave in Laos reveals more about the mysterious Denisovans

Researchers believe the tooth belonged to a young woman who lived at least 130,000 years ago and was likely Denisovan – an enigmatic group of early humans first identified in 2010.

The lower molar is the earliest fossil evidence placing the Denisovans in Southeast Asia and may help unravel a puzzle that has long vexed experts on human evolution.

Denisovan’s only definitive fossils have been found in North Asia – in the eponymous Denisova Cave in the Altai Mountains of Siberia in Russia. Genetic evidence, however, has linked archaic humans most closely to places much further south – in what is now the Philippines, Papua New Guinea and Australia.

“This demonstrates that the Denisovans were probably also present in Southeast Asia. And it supports the results of geneticists who say that modern humans and Denisovans could have met in Southeast Asia,” said the author. he study Clément Zanolli, researcher in paleoanthropology at the CNRS, the National Center for Scientific Research and University of Bordeaux.

Archaeologists discovered the tooth in a location known as Cobra Cave, 260 kilometers north of Laos’ capital, Vientiane, where excavations began in 2018. The study, published Tuesday in the journal Nature Communications, estimated the molar to be between 131,000 and 164,000 years old, based on analysis of a cave sediment, dating of three animal bones found in the same layer, and the age of the rock covering the fossil.

“Teeth are like the black box of an individual. They hold a lot of information about their life and their biology. They’ve always been used by paleoanthropologists, you know, to describe species or to tell species apart. So for us paleoanthropologists (teeth) are very useful fossils,” Zanolli said.

Comparison with archaic human teeth

The researchers compared the ridges and valleys of the tooth with other fossilized teeth belonging to archaic humans and found that they did not resemble teeth belonging to Homo sapiens or Homo erectus – an archaic human who was the first to walk with a straight gait whose remains have been found throughout Asia. The cave find most closely resembled a tooth found in a Denisovan jawbone found on the Tibetan Plateau in Xiahe County, Gansu Province, China. The authors said it was possible, although less likely, that it could belong to a Neanderthal.
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“Think of it (the tooth) as if you are traveling in (a) valley between the mountains. And the organization of these mountains and valleys is very typical of a species,” Zanolli explained.

Analyse of a protein in the enamel of the tooth suggested it belonged to a woman.

Denisovan DNA still lives on in some humans today because once our Homo sapiens ancestors encountered the Denisovans, they had sex with them and gave birth to babies – what geneticists call the mixed. This means we can look back on human history by analyzing current genetic data.

The “mixing” is believed to have occurred more than 50,000 years ago, as modern humans left Africa and likely intersected with Neanderthals and Denisovans. But it has proven difficult to determine exactly where this happened, especially in the case of the Denisovans.

Definitely Denisovan?

Any addition to Asia’s meager hominid fossil record is exciting news, said Katerina Douka, assistant professor of archaeological sciences in the University of Vienna’s department of evolutionary anthropology. She did not participate in the research.

She said she would have liked to see “more and more complete evidence” that the tooth was definitely Denisovan.

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“There is a chain of hypotheses that the authors accept in order to confirm that this is a Denisovan fossil,” she said.

“The reality is that we cannot know if this single, poorly preserved molar really belonged to a Denisovan, a hybrid, or even an unknown hominin group. It could well be a Denisovan, and I wish it was a Denisovan, because that’s cool would it be? But more reliable evidence is needed,” she said.

When considering the Laos Denisovan tooth, researchers in this study relied heavily on a comparison with the Xiahe jawbone, Douka said. However, the jawbone, although believed by many to belong to Denisovan, was not an open and closed case. No DNA was recovered from the fossilized jawbone, only evidence of “thin” proteins, she added.

“Anyone working on this hominin group, where many major questions remain, wants to add new points to the map. The challenge is to reliably identify any fossil as a Denisovan,” she said. declared. “This lack of robust biomolecular data, however, greatly reduces the impact of this new finding and serves as a reminder of how difficult it is to work in the tropics.”

The study authors said they plan to try to extract ancient DNA from the tooth, which if possible would provide a more definitive answer, but the hot climate means this could be time consuming. The research team also plans to continue excavation of the site after a pandemic-induced hiatus in hopes of uncovering more ancient humans who lived in the area.

“In this kind of environment, DNA doesn’t store well at all, but we’ll do our best,” said study co-author Fabrice Demeter, assistant professor at the Lundbeck Foundation Center for Geogenetics. in Denmark.


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