It’s long been an insult to be called a Neanderthal. But the more these elusive, vanished people have been studied, the more respect they’ve gained among scientists.

On Thursday, a team of researchers offered compelling evidence that Neanderthals bore one of the chief hallmarks of mental sophistication: they could paint cave art. That talent suggests that Neanderthals could think in symbols and may have achieved other milestones not preserved in the fossil record.

“When you have symbols, then you have language,” said João Zilhão, an archaeologist at the University of Barcelona and co-author of the new study.

When Neanderthal fossils first came to light in the mid-1800s, researchers were struck by the low, thick brow ridge on their skulls. Later discoveries showed Neanderthals to have brains as big as our own, but bodies that were shorter and stockier.