What was the real paleo diet? Prehistoric plaque reveals what Neanderthals ate.

Neanderthals probably weren't the simple, club-wielding, meat-gnawing brutes of cartoon lore. Clues like cave art, tombs, and complex constructed structures all point to the extinct human species being more culturally advanced than classically thought.

Now the evidence is mounting from a new place: plaque preserved on Neanderthals' teeth.

Examining the contents of the calcified plaque of five Neanderthal specimens that range from 42,000 to 50,000 years old, researchers who study ancient DNA were able to determine their diet. And, it turns out, not all Neanderthals ate alike. 

Some dined on a lot of meat, eating the flesh of animals like woolly rhinoceros and wild sheep. But others may have been complete vegetarians, according to a paper published Wednesday in the journal Nature. In the plaque of these Neanderthal vegetarians, researchers found no evidence of any meat. Instead, they say these individuals dined on mushrooms, pine nuts, and moss.

It's unlikely that these diets reflected any sort of moral or sociopolitical statement. "We really think that these are just reflective of the particular environments that the Neanderthals were in at the time," study lead author Laura Weyrich, a paleomicrobiologist at the Australian Centre for Ancient DNA at the University of Adelaide, tells The Christian Science Monitor.

The meat-munching Neanderthal teeth were unearthed at Spy Cave in Belgium, a region that researchers think was more of a steppe environment, with big, rolling, grassy hills or small mountains, when Neanderthals lived there. The moss-munching Neanderthal specimens are from El Sidrón Cave in Spain, which was probably densely forested at the time. 

"It's easy to understand how a big woolly rhino could have been wandering through a grassy field," Dr. Weyrich says. But "it's very difficult to picture that big beastly animal trying to squeeze its way through a densely forested area. It's much easier to eat pine nuts that are all over the ground."

This suggests that "they weren't maybe as different from us as a lot of people think," Shara Bailey, a paleoanthropologist at New York University who was not involved in the research, tells the Monitor. "They did what any human would do. They ate what was available to them." 

Debbie Guatelli-Steinberg, an anthropologist at Ohio State University who also was not involved in the research, agrees in an email to the Monitor. "Traditionally Neanderthal diets have been considered less variable than those of the anatomically modern humans they coexisted with. On this basis, Neanderthals were assumed to have been less adaptable than anatomically modern humans." 

But, she writes, "Together with other recent work, this study adds further evidence to the conclusion that Neanderthal diets were quite variable." 

Studies of the isotopic composition of some Neanderthal bones published a decade ago suggested that the extinct humans were top-level carnivores. With a diet as meat-heavy as a polar bear, this was hailed as evidence that Neanderthals hunted for many of their meals.

But more recent research looking at wear on Neanderthal teeth from plant roughage and microfossils of plants in their plaque started to paint a more nuanced picture of the Neanderthal diet and foraging habits.

Erik Trinkaus, a paleoanthropologist at Washington University in St. Louis and an author on a 2009 study examining the isotopes in Neanderthal bones, calls this new work "a nice supporting analysis of the inferences concerning Neanderthal diet from faunal remains, starch grains in calculus, and stable isotopes," in an email to the Monitor.

Their regular diet wasn't the only hint as to how Neanderthals benefited from their environments. One of the individuals from El Sidrón displayed evidence of being ill, and the researchers found that he had been eating poplar, which is known to be a natural source of the active ingredient in common painkillers used in modern medicine.

"It's not these individuals that were toting clubs and grunting and running around in caves," Weyrich says. Instead, she says, they led "a very nuanced lifestyle."

How do you determine diet from plaque?

Weyrich and her team weren't looking at fossilized chunks of food in the Neanderthals' dental plaque (although that has been done). Instead, they used a technique called metagenomics and sequenced all the DNA preserved in this built-up, calcified tooth gunk. Once they had all the pieces of DNA, they had to assemble them like puzzle pieces to reconstruct the genomes of organisms preserved on the prehistoric teeth.

This plaque isn't quite the same as modern humans scrub off their teeth every night and morning with a toothbrush (or at least tell their dentists they do). The stuff Weyrich and her colleagues looked at is calcified plaque, called calculus, that forms when plaque has built up over a long period of time.

Because plaque traps microorganisms that live in the mouth and bits of food that get stuck there, calculus is a treasure-trove of insights for geneticists like Weyrich, particularly in people who didn't brush their teeth.

"In an ancient individual that didn't have modern dentistry, we have to assume that these calculus samples likely represent a lifelong record of the microorganisms and things that were present in their mouth," Weyrich explains. 

It is possible that the calculus might not be a complete record of all the plaque and food that has ever been in an individual's mouth in their lifetime, she admits. That's because there are many factors that go into how much calculus might form and how much food debris might get caught there. 

But, Weyrich points out, "because our results matched the isotopes [and other previous research], we really do think we're looking at long-term trends rather than just their last meal that happens to randomly be stuck in there."

"We have to keep in mind that these are individuals," Dr. Bailey cautions. And individuals may not represent the whole group that they live in, so it may be too much of a leap to generalize one population as vegetarians and one as carnivores.

Still, "The kinds of advances that we've been able to make in assessing Neanderthals from such obscure data like dental calculus I think is pretty amazing. The technology blows me away," Bailey says. And, she jokes, thanks to modern dentistry, "the archaeologists of the future are going to be upset that we don't have any of this on our teeth."

Were Neanderthals and Homo sapiens kissing cousins?

Because Weyrich and her team sequenced all the DNA in the Neanderthal plaque, they saw more than just plant and meat matter. 

One detail the researchers extracted from one of the El Sidrón Neanderthals' plaque was a nearly complete genome of a microbe, Methanobrevibacter oralis, a strain of which is found today in H. sapiens' microbiome. Weyrich and her team were able to determine that the Neanderthal strain and the modern human one diverged between 112,000 to 143,000 years ago – long after Neanderthals and H. sapiens diverged from their last common ancestor.

This, Weyrich and her colleagues say, suggests that the mouth-inhabiting microbe was being passed between the two species. 

The two human species are known to have interbred, but "those interactions of interbreeding were always described as something that was very brash and brutal," Weyrich says. "But if they're swapping spit and they're sharing oral microorganisms, that means that there's something much more friendly, or certainly something much more intimate going on with those interactions."

Bailey isn't sure that that's the only explanation. "Maybe, maybe not," she says. It's possible that the divergence date could be shifted due to other factors, like ongoing selection in the microbe, she explains. "I wouldn't want anybody to read too much into that thinking that this is evidence of Neanderthals and modern humans making out."

Regardless, Weyrich maintains that the overall revelation about Neanderthals from her work is that they "were very capable, very intelligent, probably very friendly beings," she says. "We really need to rewrite the history books as far as how we see them and how we view their lifestyle."