Extinct human relatives hid a mouthful of surprises
It seems modern humans aren’t the only ones to have had regional cuisine. According to the plaque on their teeth, Neanderthals had striking differences in their diets, depending on where they lived — and they may have also used plants and mold to treat illness and pain.
The findings, described in the journal Nature, mark the first and oldest dental plaque to be genetically analyzed, shed light on the relationship between humans and their closest extinct relatives, and hint at the complexity and diversity of Neanderthal life across Europe.
“The typical view of a Neanderthal is a club-toting beast who grunts at people and lives in a cave,” said lead author Laura Weyrich, a paleomicrobiologist at the University of Adelaide in Australia. “But this research, as well as years of other research, suggests that these were very capable and intelligent individuals that could pass down information from generation to generation and likely lived in friendly contact with humans at some point.”
When scientists look to understand a creature’s diet, they can look to its teeth — specifically, the layers of hardened dental plaque on the surface of the teeth, known as calculus. This mineralized muck contains the DNA of food particles as well as the microbes that inhabited the mouth.
“Dental calculus is calcified during the life of the individual, so it really locks in those bacteria and preserves it quite well,” Weyrich said.
Scientists have studied the information contained in tooth plaque for decades. But now, with high-throughput genetic sequencing and other recent technological breakthroughs, she and her colleagues were able to pick out the genetics of what they ate and of the microbes in their bodies.
The international team of researchers looked at Neanderthal samples from one individual taken from Spy cave in Belgium (around 36,000 years old) and two individuals from El Sidron cave in Spain (around 48,000 years old). The hominins ate very differently, depending on their region: The calculus from presentday Belgium was full of meat such as woolly rhinoceros and wild sheep, which were available on the wide open grasses of the steppe. The diet in Spain, on the other hand, had plenty of mushrooms, pine nuts and moss — the kind of menu you’d have in dense forest — and no detectable meat.
The Spanish Neanderthals, whether by necessity or by choice, may have been vegetarians. Those dietary differences seem to have influenced the microbial communities in the Neanderthals’ mouths, Weyrich said.
“It really looks like meat is kind of a new idea for hominids,” she added.
It’s unclear if the calculus preserved years of accumulated foodstuff or simply recorded a “last meal” of sorts. Still, it’s interesting that there were no squirrels or other small tree-dwelling animals in the calculus of the Neanderthals from Spain. Whether that was intentional or not remains to be seen, she said.
Incidentally, the vegetarian Neanderthals apparently met a nasty fate, according to earlier studies of their remains.
“Somebody definitely filleted them back in the day,” Weyrich said.
Cut marks on their bones show they were probably eaten by other people — though whether by humans or Neanderthals remains unclear.
“There are all sorts of wild stories, but the bottom line is we just don’t know,” she said. “We don’t have a time machine to go back; we just have these little pieces we can try to assemble.”
One of the Neanderthals at the Spanish site had a dental abscess, which was probably quite painful, as well as a gastrointestinal bug (Enterocytozoon bieneusi), which likely caused vomiting or diarrhea (or perhaps both). In his ancient plaque, scientists discovered evidence of poplar, whose bark contains salicylic acid (the active ingredient in the painkiller aspirin); they also found signs of a natural antibiotic mold, Penicillium rubens, that wasn’t found in the teeth of the other individuals.
The scientists suspect that this individual did not specifically seek out that exact mold, because he seemed to have consumed a wide range of molds found on plant material. But it does suggest that they may have known that eating mold somehow made them feel better, the scientist added.
“When you had a stomachache, maybe you ate moldy grain as a way to try to treat bacterial infections,” Weyrich said.
The scientists also managed to sequence the oldest microbial genome yet — a bug called Methanobrevibacter oralis that has been linked to gum disease. By looking at the number of mutations in the genome, the scientists determined it was introduced to Neanderthals around 120,000 years ago — near the edge of the time period when humans and Neanderthals were interbreeding, Weyrich said.
There are a few ways to swap this microbe between species, she pointed out: by sharing food, through parental care, or through kissing.
“We really think that this suggests that Neanderthals and humans may have had a much friendlier relationship than anyone imagined,” Weyrich said. “Certainly if they’re swapping oral microorganisms — or swapping spit — it’s not these brute, rash-type encounters that people were suspecting happened during interbreeding. It’s really kind of friendly interactions.”
Ultimately, she said, this study served as a proof-of-concept of what scientists can learn from sequencing the DNA preserved in ancient plaque.
“This really was a test of how far we could push this method and really (forced) us to develop the methods, develop the means, to try to look at more ancient specimens as well as ancient hominids,” Weyrich said. “The sky’s the limit for this.”
By using this technique on preserved specimens around the globe, scientists can start to understand how the human microbiome evolved over time, in response to changes in their diets and other factors. The discoveries they make could inform researchers trying to understand microbiome-related diseases in modern humans, and thus help advance the field of personalized medicine.
“Ancient humans are the perfect model system,” she said. “In modern humans we have a really difficult time trying to understand how to change the microbiome or what lifestyle alterations might change these bacteria. But in ancient humans, they already did it for us. The experiment’s already been run. We really just need to go back in time and look at it.”