Neanderthals, who first arrived in Europe from Africa around 300,000 years ago, have long been considered the brutish cousin to early modern humans. But a new study linking Neanderthals to markings found inside a cave overlooking the Mediterranean Sea in Gibraltar suggests that they may have been more intelligent and creative than we gave them credit for.

The British overseas territory of Gibraltar sits on a narrow peninsula of Spain’s southern coast. Just south of “the Rock,” as it is known, is the Strait of Gibraltar, the only passage between the Atlantic Ocean and the Mediterranean Sea. The ancient markings at the center of the new study were first discovered in July 2012 inside Gorham’s Cave on the southeast face of Gibraltar, overlooking the Mediterranean. Now, researchers from 11 European institutions argue that the markings—a series of criss-crossing lines somewhat resembling a game of tic-tac-toe—are the first known examples of Neanderthal rock art. If true, this would mean that humans and Neanderthals shared the capacity for abstract expression, a major cognitive step in human evolution.

Scientists have greeted other examples of possible Neanderthal art with skepticism. Past candidates have included motifs found on cave walls in northern and southern Spain, possible jewelry at a site in central France and a bone instrument found at Divje Babe in Slovenia. But the markings in Gorham’s Cave were found buried underneath layers of sediment in which archaeologists previously uncovered nearly 300 stone tools, made in what has been identified as the signature Neanderthal style. Using standard dating techniques, the tools were dated back to some 39,000 years ago, around the time that Neanderthals went extinct, suggesting that the carvings must be even older.

Rock engraving found inside Gorham's Cave (Credit: Stewart Finlayson)
Rock engraving found inside Gorham's Cave (Credit: Stewart Finlayson)

In the paper outlining their findings, published in the journal Proceedings of the National Academy of Sciences earlier this week, the researchers went to great lengths to prove that the markings were made intentionally. Using different types of tools and cutting techniques, they made markings on blocks of dolomite rock similar to that found in Gorham’s Cave. In the method that best matched the engraving found on the cave walls, a pointed tool or cutting edge was carefully and repeatedly passed along in the same direction along an existing groove. This suggests that the markings were unlikely to be the accidental result of another action, such as cutting meat or fur on top of the stone.

Francesco d’Errico, the director of research at the French Centre National de la Recherche Scientifique (CNRS) in Bordeaux, oversaw the experiments. As he told BBC News, “[Dolomite] is a very hard rock, so it requires a lot of effort to produce the lines.” He estimates it would have taken 200-300 cutting strokes to make the markings they found, and at least an hour’s work. Moreover, the rock bearing the crosshatched markings is located in a very visible spot in the cave, where any visitors would have seen it clearly. Though the researchers deliberately declined to speculate in their paper as to what the markings may mean, d’Errico says: “It’s in a fixed location so, for example, it could be something to indicate to other Neanderthals visiting the cave that somebody was already using it, or that there was a group that owned that cave.”

Professor Clive Finlayson, the director of the Gibraltar Museum and a co-author of the new study, says his team’s discovery “brings the Neanderthals closer to us, yet again.” Paul Taçon, an expert in rock art at Australia’s Griffith University, was not involved in the study, but told the Associated Press: It is the last nail in the coffin for the hypothesis that Neanderthals were cognitively inferior to modern humans.”

Other researchers in the field remain unconvinced, and point out that Neanderthals may have been imitating the behavior of early modern humans they’d come into contact with, or that humans could have done the cave art themselves. Another recent study found that Neanderthals overlapped with early modern humans in Europe for as many as 5,000 years before they went extinct, making attribution of the Gibraltar carvings an even more complicated task than previously thought.