You can learn a lot about someone by their smile, and new research has taken that approach to study the true paleo diet. Scientists from the University of Adelaide and the University of Liverpool have analyzed the teeth of Neanderthals found in two European caves, and learned that not only did they chow down on a wide variety of food, but they may have even been the first to discover the pain-killing effects of certain plants and molds.

Teeth from our closest extinct relatives have taught us plenty about them in the past, busting the myth that they were predominantly meat-eaters, and suggesting they may even have cleaned up with toothpicks after a hearty meal. Examining dental calculus, or hardened plaque, is great at filling in these blanks, because it preserves traces of their dinner's DNA, as well as the bacteria that called Neanderthal mouths home.

"Dental plaque traps microorganisms that lived in the mouth and pathogens found in the respiratory and gastrointestinal tract, as well as bits of food stuck in the teeth – preserving the DNA for thousands of years," says Dr Laura Weyrich, lead author of the study. "Genetic analysis of that DNA 'locked-up' in plaque, represents a unique window into Neanderthal lifestyle – revealing new details of what they ate, what their health was like and how the environment impacted their behavior."

The study genetically examined the plaque of four Neanderthal specimens, dating back to between 42,000 and 50,000 years, from two caves in Europe – Spy Cave in Belgium and El Sidrón in Spain. The first group had a taste for woolly rhinoceros and European wild sheep, with a side of mushrooms, while the Spanish cavemen leaned towards a more vegetarian diet of nuts, moss, mushrooms and even tree bark.

These findings line up with the results of other studies of Neanderthal plaque, but a particularly unwell fellow from El Sidrón had a few new things to tell. The researchers spotted a dental abscess on the man's jawbone, as well as signs that he suffered from an intestinal parasite. It's likely he was in a lot of pain, so it makes sense that his teeth also showed traces of poplar – which contains salicylic acid, the active ingredient in aspirin – and Penicillium, an antibiotic mold.

"Apparently, Neanderthals possessed a good knowledge of medicinal plants and their various anti-inflammatory and pain-relieving properties, and seem to be self-medicating," says Alan Cooper, corresponding author of the study. "The use of antibiotics would be very surprising, as this is more than 40,000 years before we developed penicillin. Certainly our findings contrast markedly with the rather simplistic view of our ancient relatives in popular imagination."

From the plaque, the researchers were also able to reconstruct the genome of a microbe called Methanobrevibacter oralis, which lived in the mouths of both humans and Neanderthals. As a result of their different diets, the oral microbial community of the two groups was also drastically different: the Spanish Neanderthals hosted bugs similar to chimpanzees and early humans from Africa, while those in Belgium were closer to early hunter-gatherers, farmers and modern humans.

"Major changes in what we eat have significantly altered the balance of these microbial communities over thousands of years, which in turn continue to have fundamental consequences for our own health and well-being," says Keith Dobney, an author of the study from the University of Liverpool. "This extraordinary window on the past is providing us with new ways to explore and understand our evolutionary history through the microorganisms that lived in us and with us."

The research was published in the journal Nature.

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