Neanderthals and Humans Agreed About One Thing: This Cave

Tens of thousands of years ago, the hottest real estate in Europe was a rock shelter in southern France. Grotte Mandrin had everything a hominin could want. A rocky overhang that offered shelter from the rain. Sweeping views of a valley and the bison and deer roaming below. A prime location in the Rhône Valley, an important natural corridor linking the Mediterranean Basin with northern lands.

The prehistoric pad was so desirable that about a year after the shelter was occupied by Neanderthals, a group of Homo sapiens moved in. They were followed by several Neanderthal tenants, then yet another settlement of modern humans. Scientists presented these findings in a paper published on Wednesday in the journal Science Advances.

More than showing how Neanderthals and modern humans were co-tenants of the European landmass over time, this new discovery pushes back the timeline for the earliest modern human settlements in Europe. The scientists say that the first modern human occupants at Mandrin were there about 54,000 years ago — a time when Europe was thought to be primarily Neanderthal stomping grounds.

That’s 10,000 years earlier than previously thought (with the notable exception of an even earlier site in Greece that dates to 210,000 years ago). The paper describes the human settlement based on a modern human baby tooth, as well as stone tools that appear to have been made by Homo sapiens.

“This is really interesting and exciting,” Katerina Harvati, a paleoanthropologist at the University of Tübingen in Germany who was not involved in the research, wrote in an email. “It shows the complexity of the modern human dispersal in the European continent and eventual replacement of Neanderthals,” which occurred about 40,000 years ago.

Naomi Martisius, a Paleolithic archaeologist at the University of Tulsa who was not involved with the research, called the discovery of the alternating occupations “extremely intriguing.” But she cautions more evidence is needed to confirm modern humans, or even a hybrid species, made those tools.

Ludovic Slimak, a paleoanthropologist at the University of Toulouse in France and an author on the paper, has spent decades excavating Grotte Mandrin. The cavern opens to the north, where a cold and powerful wind known as the mistral breathes dust under the rock shelter.

“This wind over millennia brings the sand from the Rhône River and deposits it in the cave,” Dr. Slimak said. “It is kind of like Pompeii, with no catastrophic events.” These conditions have preserved the cave exceptionally, giving Dr. Slimak the feeling that artifacts from “55,000 years ago were just left five minutes ago,” he said.

The sands of Grotte Mandrin were littered with stone tools, many of which were clearly made by Neanderthals, the researchers argue. “I read a flint like you can read a book,” Dr. Slimak said. Whereas Neanderthal flints are largely unique, with differing textures and morphology, Homo sapiens crafted more standardized flints, Dr. Slimak said.

By this logic, the flints excavated from certain layers of Grotte Mandrin seemed to have come from humans, not Neanderthals, Dr. Slimak concluded.

The few human remains in the shelter revealed themselves slowly. “We find one tooth every 10 months,” Dr. Slimak said. Once the researchers had excavated nine teeth, Dr. Slimak sent the fossils to Clément Zanolli, a paleoanthropologist at the University of Bordeaux in France and an author on the paper.

“Some of the teeth were a bit strange,” Dr. Zanolli said. “Some were typically Neanderthal, but there was one tooth that was probably not Neanderthal.” When Dr. Zanolli scanned the teeth with micro tomography to examine the internal structure, he found eight teeth belonged to Neanderthals and one tooth was unequivocally from a modern human.

Together, the teeth and the tools make “a convincing argument,” Dr. Harvati said.

The researchers decided not to extract DNA from the human tooth after an unsuccessful attempt to extract DNA from fossil horse teeth also found at the shelter.

Sahra Talamo, a researcher at the University of Bologna in Italy who was not involved with the research, said she expected the new paper to spur debates until that tooth’s genetic material is sampled. Dr. Talamo said she understands why the authors could be worried about partially destroying a unique human remain. But, she emphasized, “the only way to avoid speculations and create false scenarios is to directly date the specimen.”

Although the researchers found only one modern human tooth, they said the presence of alternating layers of modern human tools suggested multiple settlements of Homo sapiens in the shelter. Ségolène Vandevelde, an archaeologist at the University of Paris-Saclay and author on the paper, analyzed the soot deposits from the cave roof to determine when fires were set in the cave. The amount of soot led to their finding that only one year passed between the time a group of Neanderthals moved out and the first modern humans moved in.

Those humans lasted at Grotte Mandrin for about 40 years before leaving the shelter for reasons unknown. Neanderthals then eventually swooped in once more for the next 12,000 years, before again being succeeded by Homo sapiens who spent a few hundred years there.

The new paper adds to scientists’ growing understanding that modern humans’ migration into Europe was a staggered, complex process that often ended in local extinction, Dr. Harvati said. “Modern humans were not always the ‘winners’ in this process,” she wrote.

Dr. Martisius hopes future publications can illuminate the lives of the early toolmakers in Grotte Mandrin. “Who were they? How long were they in Western Europe?” she asked. “Where did they go?”

The researchers plan to publish more papers on their excavations in Grotte Mandrin, taking their place as the latest in a long line of hominins who found refuge in the cave.