Croatia’s scenic Vindija Cave was thought to be a potential trysting site for Neandertals and early modern humans some 32,000 years ago. Now, a new study questions that idea, using a more exacting form of radiocarbon dating to suggest instead that Neandertals used the cave 40,000 years ago—some 8000 years before modern humans lived in that part of Europe. If true, the find casts doubt on the long-held assumption by some that the two hominids overlapped in the region.
“Many of us have long suspected [this],” writes Erik Trinkaus, a biological anthropologist at Washington University in St. Louis who wasn’t involved in the work, in an email. He points out that the dating of sites across Europe have generally put the Neandertal’s demise there about 40,000 years ago. “This article puts to rest an anomalous occurrence of late Neandertals in this region, and allows us to move on from it.”
In the late 1990s, researchers dated the Neandertal remains from the cave, which included fragments of skulls, thighs, and other assorted bones, using radiocarbon dating, which measures an isotope known as carbon-14 that decays over time at a fixed rate. By seeing how much carbon-14 is left, scientists can get a roughly accurate idea of when the Neandertal lived. Using the carbon-14 in bone collagen from skull fragments and other bones found inside the cave, the original studies returned an estimated age of 29,000 to 34,000 years old. That was about the same time that early modern humans moved into Europe—as evidenced by modern human remains and tools also found in the cave—raising the specter that the two groups met, competed, and even mated with one another.
Earlier this year, a team led by archaeologists Thibaut Devièse and Thomas Higham at the University of Oxford in the United Kingdom turned to a more refined method of radiocarbon dating. Instead of measuring the carbon-14 in bone collagen—a gelatinous mixture that can easily be contaminated by sediment and microorganisms from the environment—the researchers zeroed in on a particular amino acid inside the collagen called hydroxyproline.
Dating the isolated hydroxyproline revealed that the remains were likely to be about 40,000 years old, the researchers report today in the Proceedings of the National Academy of Sciences. That’s 8000 years older than previous research had suggested and before modern humans appear in the region.
Archaeologist João Zilhão of the University of Bristol in the United Kingdom, who wasn’t involved in the study, said testing a specific amino acid is a good way to avoid contamination issues when radiocarbon dating a bone sample. But he adds that the technique will have to be replicated by other laboratories before he’s confident the results are reliable.
Geoffrey Clark, an anthropologist at Arizona State University in Tempe, says the new technique is a big improvement over standard bone collagen dating, and he is looking forward to seeing it applied to previously dated Neandertal remains from other sites. "Whether they will get the same results isn’t known yet, but it looks promising," he says.
Shared genes between modern humans and Neandertals make it clear that at some time and place in the past, the two species did meet and interbreed—just not at Vindija Cave, Devièse says. “DNA studies have demonstrated that anatomically modern humans and Neandertals interbred,” he says. “There is no question about this … although the two groups for the most part were not living side-by-side, it would seem. With this dating work, we are continuing our work to understand where and for how long the two species coexisted.”