A tooth unearthed in a remote cave in Laos is helping to unravel an unknown chapter in the story of human evolution.
Researchers believe the tooth belonged to a young woman who lived at least 130,000 years ago and likely belonged to the Denisovans – an enigmatic group of early hominids first identified in 2010.
The lower molar is the earliest fossil evidence that places the Denisovans in Southeast Asia and could help solve a riddle that has long plagued human evolution experts.
The only concrete fossils of Denisovans have been found in North Asia – in the eponymous cave known as Denisova, located in the Altai Mountains of Russia, in the Siberian region. However, genetic evidence has linked early hominids to places much further south – where the Philippines, Papua New Guinea and Australia now exist.
“This proves that the Denisovans probably also existed in Southeast Asia. And it is consistent with the results of geneticists, who claim that the ancestors of modern humans and Denisovans could have interbred in Southeast Asia,” says the author of the study, Clément Zanolli, researcher in paleoanthropology at the CNRS and the University of Bordeaux.
Archaeologists discovered the tooth at a site known as Cobra Cave, 260 kilometers north of Laos’ capital, Vientiane, where excavations began in 2018. The study, published in the journal Nature Communication On Tuesday, he concluded that the molar was between 131,000 and 164,000 years old, based on analysis of cave sediments, the lifespan 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 store a lot of information about their life and biology. They have always been used by paleoanthropologists to describe species or to distinguish between species. So for us, the paleoanthropologists (the teeth) are very useful fossils”said Zanolli.
Comparison with the teeth of early hominids
The researchers compared the ridges and cavities of the tooth with other fossilized teeth belonging to early hominids and found that they did not resemble teeth belonging to the Homo sapiens or homo erectus – the first primitive hominid to walk with an upright posture and whose traces have been found throughout Asia. Findings from the cave determined that it most closely resembles a tooth belonging to a jawbone belonging to the Denisovan group found in the Tibetan Plateau of Xiahe County, Gansu Province, China. The authors noted that it was possible, although less likely, that it could belong to a Neanderthal.
“Think of it (the tooth) as walking through a valley between mountains. And the organization of those mountains and valleys is very species-specific,” Zanolli explained.
Analysis of certain proteins in the tooth’s enamel suggested that it must belong to a woman.
Denisovan’s DNA still exists today in some humans because, since our ancestors Homo sapiens crossed with the Denisovans, the two groups became involved and gave birth to other lives – what geneticists call “genetic mixing”. This means that we can learn more about the history of human evolution by analyzing current genetic data.
This “genetic mixing” occurred more than 50,000 years ago, when the ancestors of modern humans left Africa and likely interbred with Neanderthals and Denisovans. But it has proven difficult to determine exactly where this happened – especially in the case of Denisovan’s hominins.
Any information added to the rare hominid fossil record from Asia is exciting news, said Katerina Douka, assistant professor of archaeological sciences in the department of evolutionary anthropology at the University of Vienna, who did not participated in the research.
Douka said he would have liked to analyze the evidence – “in greater quantity and depth” – that would ensure the tooth belonged unquestionably to the Denisovan hominid group.
“There is a chain of hypotheses that the authors accept to confirm that this is a fossil of a Denisovan,” he said.
“The truth is, we have no way of knowing if this single, poorly preserved molar actually belonged to a Denisovan, a hybrid group, or even an unknown hominin group. It could very well be a Denisovan, and I wish he was, in fact, a Denisovan – how extraordinary would that be? But we need more reliable evidence,” he said.
To consider the tooth found in Laos as belonging to a Denisovan hominin, the researchers in this study used a comparison with the jawbone from Xiahe as a strong reference, Douka said. However, although many believed that the jawbone was Denisovan, this question was not yet settled. No DNA was recovered from the fossilized jawbone, only “faint” protein evidence, he added.
“Anyone who studies this group of hominins, where many important questions remain, wants to add striking new data. The challenge is to reliably identify fossils such as a Denisovan,” she added. . “However, this lack of solid biomolecular data greatly reduces the impact of this new finding and reminds us of how difficult it is to work in the tropics.”
The study authors revealed that they plan to try to extract the ancient DNA from the tooth, which if possible would give them a more definitive answer, but the hot climate makes it possible to achieve the experience a remote possibility. The research team also plans to continue excavating the site after a pandemic-induced hiatus, in hopes that more discoveries can be made about early hominids that may have lived in this area.
“In this type of environment, DNA is not very well preserved, but we will do our best,” said study author Fabrice Demeter, assistant professor at the GeoGenetics Center of the Lundbeck Foundation in Denmark. .