Neanderthals seem stuck with unflattering reputations. The entire species of early human ancestors has long been reduced to a pejorative for describing someone who isn’t very bright, despite growing evidence of the sophistication of Homo neanderthalensis. And recent research suggests another overlooked mark of their ingenuity: they made the first glues in the form of tar.

Archaeologists first found tar-covered stones and black lumps at Neanderthal sites across Europe about two decades ago. The tar was distilled from the bark of birch trees some 200,000 years ago, and seemed to have been used for hafting, or attaching handles to stone tools and weapons. But scientists did not know how Neanderthals produced the dark, sticky substance, more than 100,000 years before Homo sapiens in Africa used tree resin and ocher adhesives.

Now, in a study published last Thursday in the journal Scientific Reports, a team of archaeologists has used materials available during prehistoric times to demonstrate three possible ways Neanderthals could have deliberately made tar. While the study does not prove that Neanderthals used any of these methods, it aims to demonstrate that they had access to the ingredients and means to produce tar.