Around 50,000 years ago in Spain, a Neanderthal had a toothache and popped the botanical version of an aspirin. Maybe. Although it's far from clear-cut, there’s evidence from old teeth that hints at the possibility.

It's part of a study of Neanderthal diet, courtesy of their poor dental hygiene. Published in Nature, an analysis of preserved dental plaque from three different Neanderthals provides an intriguing glimpse into what they put in their mouths. According to the authors, the analysis points to regionally varied diets and suggests possible medicinal plant use.

But some of the DNA evidence is a little strange, suggesting evidence of species where they really shouldn’t have been 50,000 years ago. There are some good explanations for why this could happen, but, like most exciting results, drawing conclusions from the evidence demands a little caution.

Foraging Neanderthals

The stereotypical picture of Neanderthals paints them as hunting the woolly mammoth. There’s evidence to back up a Neanderthal diet “as carnivorous as polar bears or wolves,” write the researchers: archaeological and chemical data suggest meals heavy in large herbivores like reindeer, woolly mammoth, and woolly rhinoceros.

But Neanderthal teeth tell a more nuanced story. Previous research has found that the wear patterns on their teeth suggest a varied diet with regional differences. And dental plaque has been used before to analyze the starches and proteins that were preserved in the plaque. These analyses suggest that Neanderthals were eating many plants, possibly including medicinal ones.

But dental plaque can preserve more than simple chemicals; genetic material from the food can be encased in it. This allowed a team of researchers, led by Laura Weyrich at the University of Adelaide, to get an incredibly detailed look at what plant and animal species three individual Neanderthals had been eating. Two were from El Sidrón Cave in Spain, including the potential aspirin-popper, while one was from Spy Cave in Belgium.

The results add to previous evidence suggesting that the “Neanderthal diet” was actually many different things, depending on where the Neanderthals in question lived. The Belgian followed the meat-heavy pattern, with genetic material from woolly rhinoceros, mushrooms, and wild sheep showing up in the dental plaque. Mammoth, reindeer, rhinoceros and horse bones in the cave tell the same story as the dental plaque: these were hunters.

The Spanish Neanderthals, on the other hand, seemed to eat largely mushrooms, pine nuts, and moss—the kinds of food you’d get from foraging in a forest. One of them had a dental abscess, and this individual’s teeth came up with the genome of a poplar tree that has high levels of salicylic acid, aspirin’s active ingredient.

Ocean-hopping trees?

Here’s where it gets a little slippery. The species identified, Populus trichocarpa, is actually native to North America. It wouldn’t have been present in Europe 50,000 years ago, says Quentin Cronk, a botanist with an interest in the poplar genome, who wasn’t an author on this paper. But it does have a pretty close relative in Europe, Populus nigra.

What’s going on here, says ancient DNA researcher Hannes Schroeder, could be one of two things. The first possibility is contamination. The authors were watching out for this, though, and eliminated the data from two other Neanderthals because there was evidence of contamination. The DNA they ended up analyzing showed all the signs of being properly ancient. The other possibility is that, because ancient DNA is degraded and it’s possible to analyze only short strands of it, the strands left in the dental plaque matched more than one poplar species.

As it happens, Populus trichocarpa has the best genome data available among the poplars. All the other species of tree and mushroom identified—including another oddity, the Korean pine—have good genome-sequencing data available, too. This suggests that the little bits of DNA matched up with the genomes available in genetic databases and just locked onto the species that happened to be in the databases because they didn’t have enough data in them to differentiate between different species.

“The most likely explanation of this issue is that the reads come from a European species of Populus that is not adequately represented in current sequence databases,” says Daniel Huson, one of the authors of the paper. Cronk agrees that this is likely, as does Schroeder.

It’s a bit strange for the authors to have pinpointed a single, impossible species, rather than identifying the genetic remains as belonging to the Populus genus. It doesn’t cause too much of a problem for the evidence of what Neanderthals were eating, though—mushrooms are mushrooms. A difference in species doesn’t really change the evidence that these people were eating like vegans rather than Texans.

As for the medicinal claim, there’s also some evidence of Populus nigra having medicinal properties. Whether or not the Neanderthal knew what these properties were while chowing down on poplar is a different, and possibly unanswerable, question. Some other primate species seem to do this, so it might not be as far-fetched as it seems.

For Schroeder, the evidence doesn't seem like especially solid ground for a big claim like medicinal use. But Keith Dobney, one of the authors on the paper, thinks it all lines up so well that it invites the interpretation of medicinal use. The abscessed individual also had bacteria associated with diarrhea, as well as evidence of the antibiotic Penicillium mould, and “it just seems a bit of a strange coincidence that we have one individual with all these things,” he says.

Rapid change in human diets

With different diets come different oral bacterial cultures. You eat a lot of meat, you get a lot of meat-digesting bacteria in your mouth. Weyrich and her team compared the Neanderthal oral bacteria to a modern human and a group of ancient humans from different cultures.

They found that there were different groupings of oral microbiomes: the Spanish Neanderthals grouped with chimpanzees and ancient African gatherers, in what the researchers called a “forager-gatherer” group with a largely vegetarian diet. The Belgian Neanderthal grouped more closely with the typical meat-heavy hunter-gatherer diet. A modern human and early agriculturalist human also had different profiles.

The result helps us understand modern human oral microbiomes in context, says Dobney. Our current food-related health problems, like obesity, didn’t happen in a vacuum: “it hasn’t happened overnight; it’s part of the journey that we’ve been on for thousands of years. Major cultural changes like the beginnings of agriculture are still impacting our health today.”

As for Neanderthals, he hopes evidence of their important place in our own history—in terms of behavior, genome, and microbiome—can help end the common perception of them as “these knuckle-dragging cavemen able to do not much more than bring down the odd bison here and there.” The evidence is pointing toward varied behavior across the Neanderthals, and we’re starting to be able to get closer to inferences about the sophistication of their behavior and culture.

Nature, 2016. DOI: doi:10.1038/nature21674 (About DOIs).