The discovery of a rare tooth may help solve a riddle that has irked human evolution experts

A tooth unearthed from a remote cave in Laos contributes to outline an unknown chapter of human history.

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

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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.

The only definitive Denisovan fossils have been found in a cave in North Asia named after the group – the Denisova Cave in the Altai Mountains of Siberia in Russia.

Genetic evidencehowever, tied 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 South Asia,” said Clément Zanolli, study author and researcher in paleoanthropology at the CNRS, the National Center for Scientific Research and the University of Bordeaux.

“And that supports the findings of geneticists who say modern humans and Denisovans could have met in Southeast Asia.”

Archaeologists discovered the tooth in a place known as Cobra Cave, 260 km north of Laos’ capital, Vientiane, where excavations began in 2018.

Archaeologists discovered the tooth in a place known as Cobra Cave, 260 km north of Laos’ capital, Vientiane, where excavations began in 2018. Credit: Fabrice Demeter

The study, published in the journal Nature Communications Tuesday, estimated the molar to be between 131,000 and 164,000 years old.

Their estimate was based on analysis of cave sediments, the dating of three animal bones found in the same layer, and the age of the rock covering the fossil.

“Teeth are like an individual’s black box. 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,” said said Zanolli.

“So for us paleoanthropologists (the teeth) are very useful fossils.”

Comparison with archaic human teeth

The researchers compared the ridges and valleys of the tooth with other fossilized teeth belonging to archaic humans.

It didn’t look like teeth belonging to Homo sapiens or Homo erectus – an archaic human who was the first to walk with an upright gait whose remains have been found across Asia.

The find in the cave 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.

“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.

The researchers compared the ridges and valleys of the tooth with other fossilized teeth belonging to archaic humans.
The researchers compared the ridges and valleys of the tooth with other fossilized teeth belonging to archaic humans. Credit: Fabrice Demeter

Analysis of certain proteins in the tooth’s enamel suggested that 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’ was thought to have occurred more than 50,000 years ago, when modern humans left Africa and likely intersected with Neanderthals and Denisovans.

But figuring out exactly where this happened has proven difficult – 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 at the University of Vienna in the department of evolutionary anthropology.

She was not involved in the search, but said she would have liked to see “more and more complete evidence” that the tooth was definitely Denisovan.

“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 might just be a Denisovan, and I would love it to be a Denisovan, because that would be cool? But more reliable evidence is needed.

The study authors said they plan to try to extract ancient DNA from the tooth, which, if possible, would provide a more definitive answer as to whether the fossil is actually Denisovan.
The study authors said they plan to try to extract ancient DNA from the tooth, which, if possible, would provide a more definitive answer as to whether the fossil is actually Denisovan. Credit: Fabrice Demeter

In judging the Laos Denisovan tooth, the researchers in this study relied heavily on a comparison with the Xiahe jaw bone, 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 jaw bone, 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 difficulty is to reliably identify all the fossils as being those of a Denisovan,” she said.

“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 type 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. .

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