A mysterious 40,000-year-old hip bone suggests human ancestors and Neanderthals shared a cave — and perhaps a culture

• A 40,000-year-old newborn's hip bone was found in a French cave.
• The bone could mean modern humans shared the cave with Neanderthals.

A tiny 40,000-year-old human hip bone found in a French cave could overhaul what we know about how humans interacted with Neanderthals.

The early human bone was found in a cave at the center of a debate about Neanderthal culture.

"It is the first time that we have the association in a single year of two different human lineages: Neanderthals and anatomically modern humans," expert Bruno Maureille told Insider.

Maureille is an author of the study about the hip bone, and an archaeologist from the University of Bordeaux.

The finding suggests that early humans and Neanderthals may have shared the cave at the same time — and possibly lived together, said Maureille.

This raises a controversial hypothesis: that modern humans and Neanderthals shared the mysterious Châtelperronien culture, which has long baffled scientists.

Who is responsible for the Châtelperronien culture?

The Grotte du Renne cave in Arcy-sur-Cure, southwestern France, is a particularly important site for our burgeoning understanding of Neanderthal culture.

Most of us were taught Neanderthals were thick-headed brutes. But recent studies have challenged that idea.

Evidence now suggests Neanderthals used bone tools, produced pigments, maybe buried their dead, and likely even interbred with humans.

Some think the Grotte du Renne may have been the last bastion of Neanderthal culture in western Europe.

There is evidence of a mysterious culture in this cave, called the Châtelpererronian culture, found only in Spain and France. At that time, palm-sized scrapers and knives, typically associated with Neanderthal culture, were replaced with more sophisticated tools like slender rock blades.

That culture emerged at a seminal date, around 42,000 years ago when Neanderthals started disappearing and modern humans started moving up to Europe.

Whether or not these two groups overlapped has been a point of contention. That's in part because 42,000 years ago, the Earth's magnetic poles flipped.

Not only is this important because it may have brought on a global climate crisis that could have helped edge out Neanderthals, but the flip may also have supercharged the carbon-14 isotope in the atmosphere, which has made carbon dating around that time particularly tricky to interpret, Science Magazine previously reported.

That's why the Châtelperronian culture is so important. Some believe Neanderthals were the artisans of this culture. Others think modern humans brought the tools with them, and Neanderthals had nothing to do with it.

This new finding offers weight to another hypothesis: early modern humans and Neanderthals may have cooked it up together.

A modern human baby bone among the Neanderthals

It all comes down to one bone fragment, a hip bone from a newborn baby that had gone unnoticed among Neanderthal fossils collected from the cave in 2019.

These fossils were found in a layer of dirt dated between about 40,799 to 42,300 years ago, which puts them in that controversial period.

Maureille and his colleagues were intrigued by this one hip bone. It was slender and looked closer to the anatomy of a modern human.

The scientists did a wide-ranging analysis comparing the hip bone to that of two contemporary Neanderthal babies and that of 32 modern-day human babies.

With this work, they were able to confirm their inkling: this particular hip bone was not from a Neanderthal but likely came from an early modern human lineage. The findings were published in the peer-reviewed journal Scientific Reports on August 4.

"They are the most ancient ilea that we know for all the history of humanity," said Maureille, using the scientific name for a hip bone.

The question then is: what is this human bone doing mixed in with Neanderthal remains?

For some, it proves that humans were indeed there all along, and they were the ones who originated the Châtelperronian culture. For others, the human bone was simply misplaced among the Neanderthal remains when it was collected and stored.

Still, Maureille thinks the "simplest" explanation is that humans and Neanderthals were either mixed together or lived side-by-side.

This would be in line with another recent finding uncovered about 3,000 miles away in the mountains of Siberia. Research there suggests modern humans shared a cave with Neanderthals and Denisovans about 45,000 years ago.

And because both were able to understand the industry of the other, Maureille thinks it would make sense that Neanderthals and humans would likely have shared the Châtelperronian culture.