Rare tooth find could help solve a puzzle that has haunted human evolution experts

A tooth unearthed in a remote cave in Laos helps outline an unknown chapter in the human story.

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

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The lower molar is the first fossil evidence that Denisovans have been placed in Southeast Asia and may help unravel a puzzle that has long tormented experts in human evolution.

The only definitive Denisova fossils have been found in a cave in northern Asia named after the group – the Denisova Cave in the Siberian Altai Mountains in Russia.

genetic evidencehowever, has most closely associated the Archaic people with places much further south — in what are now the Philippines, Papua New Guinea, and Australia.

“This shows that the Denisovans were probably also present in South Asia,” said study author and paleoanthropology researcher at CNRS, the French National Center for Scientific Research and the University of Bordeaux Clément Zanolli.

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

Archaeologists have uncovered the tooth at a site known as Cobra Cave, 260 km north of Laos’ capital, Vientiane, where excavations began in 2018.

Archaeologists have uncovered the tooth at a site 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 on Tuesday, the molar estimated between 131,000 and 164,000 years old.

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

“Teeth are like an individual’s black box. They keep a lot of information about their life and biology. They’ve always been used by paleoanthropologists, you know, to describe species or to differentiate between species,” Zanolli said.

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

Comparison with Archaic Human Teeth

The researchers compared the ridges and pits on the tooth with other fossilized teeth from archaic humans.

It did not resemble the teeth of Homo sapiens or Homo erectus – an archaic human who was the first to walk with an upright gait, the remains of which have been found throughout Asia.

The cave find most resembled a tooth found in a Denisovan jawbone found on the Tibetan plateau in Xiahe Province, Gansu Province, China.

The authors said it could possibly, though less likely, belong to a Neanderthal.

“Think about (the tooth) as if you were traveling to (a) valley between mountains. And the organization of these mountains and valleys is very typical of a species,” explains Zanolli.

The researchers compared the ridges and pits on the tooth with other fossilized teeth from archaic humans.
The researchers compared the ridges and pits on the tooth with other fossilized teeth from archaic humans. Credit: Fabrice Demeter

Analysis of a protein in the tooth’s enamel suggested it belonged to a woman.

Denisovan DNA lives on in some people today because, when our Homo sapiens ancestors met the Denisovans, they had sex with them and gave birth to babies — something geneticists call mixing.

This means we can look back into human history by analyzing contemporary genetic data.

The “mixing” was thought to have happened more than 50,000 years ago, when modern humans left Africa and likely crossed paths with both Neanderthals and Denisovans.

But pinpointing exactly where it happened has proven difficult, especially in the case of Denisovans.

Absolutely Denisovan?

Any addition to Asia’s meager hominin fossil record is exciting news, Assistant Professor of Archaeological Sciences at the University of Vienna in the Department of Evolutionary Anthropology Katerina Douka.

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

“There is a series of assumptions the authors accept to confirm that this is a Denisovan fossil,” she said.

“The reality is that we cannot know whether this single and poorly preserved molar indeed belonged to a Denisovan, a hybrid or even an unknown hominin group.

“It could very well be a Denisovan, and I’d love to be a Denisovan, because how cool would that be? But more reliable evidence is needed.”

The study authors said they planned 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 planned 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

When considering the Laos tooth Denisovan, the researchers in this study relied heavily on a comparison with the Xiahe jawbone, Douka said.

However, the jawbone, although considered by many to be Denisovan, was not an open and closed case. No DNA had been recovered from the fossilized jawbone, only “thin” protein evidence, she added.

“Everyone working on this group of hominids, where there are still a lot of big questions, wants to add new dots on the map. The difficulty is reliably identifying fossils as those of a Denisovan,” she said.

“However, this lack of robust biomolecular data significantly reduces the impact of this new find and it reminds us of how difficult it is to work in the tropics.”

The study authors said they planned to extract ancient DNA from the tooth, which, if possible, would provide a more definitive answer, but the warm climate means that could go a long way.

The research team also plans to continue excavating the site after a pandemic-induced hiatus in hopes of more discoveries of ancient people who lived in the area.

“In these kinds of environments, DNA doesn’t hold up well at all, but we’ll do our best,” said study co-author Lundbeck Foundation GeoGenetics Center assistant professor Fabrice Demeter.

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