The “necklaces” are tiny: beads of animal teeth, shells, and ivory no more than a centimeter long. But they provoked an outsized debate that has raged for decades. Found in the Grotte du Renne cave at Arcy-sur-Cure in central France, they accompanied delicate bone tools and were found in the same layers as fossils from Neandertals—our archaic cousins. Some archaeologists credited the artifacts—the so-called Châtelperronian culture—to Neandertals. But others argued that Neandertals were incapable of the kind of symbolic expression reflected in the jewelry and insisted that modern humans must have been the creators.

Now, a study uses a new method that relies on ancient proteins to identify and directly date Neandertal bone fragments from Grotte du Renne and finds that the connection between the archaic humans and the artifacts is real. Ross Macphee, a paleontologist at the American Museum of Natural History in New York City, who has worked with ancient proteins in other studies, calls it “a landmark study” in the burgeoning field of paleoproteomics. And others say it shores up the picture of Neandertals as smart, symbolic humans.

Unearthed between 1949 and 1963, the controversial artifacts were made during a transitional time, when modern humans were sweeping across Europe and the Neandertals who had lived there for hundreds of thousands of years were dying out. Although the artifacts were reportedly from the same layer as Neandertal fossils, many researchers suspected that artifacts and bones from different layers got mixed up in the investigation, as dating expert Thomas Higham of the University of Oxford in the United Kingdom suggested in 2010.

Matthew Collins, a bioarchaeologist at the University of York in the United Kingdom, has been an early pioneer in the study of ancient proteins, and decided to turn the new method on some of the unidentified bones associated with the Grotte du Renne cultural artifacts. But the fragments were so small that he couldn’t even tell what species they came from. DNA, increasingly used to identify fossils, was scarce in the fragments, so Collins and his colleagues turned to proteins.

When the protein analysis came back, it left little room for doubt: The bone was human. But was it an archaic human, like a Neandertal, or a modern human? Which species was really associated with the artifacts? Had the earlier discovery of Neandertal fossils in the Châtelperronian layer been an illusion based on sloppy digging and compromised evidence?

To answer that question, Collins and his team compared the chemical composition of the collagen in the fragments with the collagen produced by modern and archaic humans. Modern human collagen contains high amounts of an amino acid called aspartic acid, but the ancient collagen was once rich in a different amino acid, asparagine—and previously sequenced Neandertal DNA includes a collagen-producing gene that likely resulted in an asparagine-rich version. To double-check their finding, they sequenced the fragments’ mitochondrial DNA as well, finding that the bones came from individuals with Neandertal ancestry on their mothers’ side. “[The bone fragments] weren’t useful 10 years ago, but now we realize they’re a great molecular record,” Collins says.

In addition to being archaic, the collagen was a form found only in bone that is still growing. The bone fragment also contained a high proportion of certain nitrogen isotopes, which is associated with children who are breast-feeding. Those two lines of evidences led the researchers to conclude that at least some of the bone fragments likely came from the skull of a Neandertal infant. Direct radiocarbon dating of the sample shows that it’s about 42,000 years old—just when the Châtelperronian beads and tools were made. The team published its results online today in the Proceedings of the National Academy of Sciences .

“You can invent all sorts of stories. But the simplest explanation is that this assemblage was made at least in part by Neandertals,” says co-author Jean-Jacques Hublin, a paeloanthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. He believes that Neandertals likely picked up the ideas behind the tools and the ornaments from their new modern human neighbors but fashioned the artifacts themselves. Chris Stringer, an anthropologist at the Natural History Museum in London, wonders whether modern humans could have had a genetic influence on the last Neandertals as well. Because scientists know Neandertals and modern humans mated with each other, “is it possible that the ‘modern’ DNA these late Neandertal groups picked up included genes for enhanced cognitive abilities?” he wonders. But other researchers who have long argued that Neandertals had sophisticated cognitive abilities, including João Zilhão at the University of Barcelona in Spain, doubt that they had any help, genetic or otherwise, from the new arrivals.

Higham, who led the study that cast doubt on the integrity of the Grotte du Renne layers, is convinced by the new work. “This paper is the first time that a Neandertal bone has been dated from this key site, and it … provides additional data to support a Châtelperronian-Neandertal link,” he says. “I think it is quite possible that Neandertals were capable of making and using personal ornaments.”