As gross as it sounds, samples of the world's oldest known human feces are offering scientists new insight into the gastronomic behavior of our extinct, meat-loving cousins, the Neanderthals.
In a study published Monday in the journal PLOS One, researchers say an analysis of 50,000-year-old coprolites discovered in Spain suggests Neanderthals supplemented their carnivorous diet with a "significant" amount of vegetation.
The study is the latest to argue against the long-held view that Neanderthals ate large, land-roaming herbivores exclusively and ignored plants and fish as food sources.
Last year, another group of researchers examined the tartar on Neanderthal teeth and concluded that the hardened calculus showed evidence of plant consumption.
In this latest study, researchers scraped remnants of poop from the floor of Neanderthal living areas at the El Salt archaeological site near the Mediterranean port of Alicante, and analyzed it for two specific biomarkers.
Using gas chromatography-mass spectrometry, researchers studied the powdered samples for traces of stanols and sterols, lipids that are formed in the intestines when gut bacteria act on plant and animal matter.
The authors said that samples taken from five different areas suggested that Neanderthals predominantly consumed meat, but also had significant plant intake.
"This wasn't a complete surprise," said lead study author Ainara Sistiaga, an organic chemistry and Paleolithic archaeology researcher at MIT. "Neanderthals are primates after all. Our findings are solid evidence of a dietary component — plants — that so far has been missing in the fossil record."
The idea that Neanderthals strayed from a strict meat-eating diet, and were even more sophisticated than we give them credit for, is somewhat controversial.
After authors of the dental calculus study argued that Neanderthals may have cooked foods and used plants as medicinal remedies, other researchers countered that the substances found in Neanderthal teeth were probably just the stomach contents of animals they had consumed.
Sistiaga said it was possible, though unlikely, that the fecal biomarkers she and her colleagues found were solely the result of Neanderthals eating the stomach contents of their prey.
"In any case, this would represent another way to eat plants," she said.
Biomarkers weren't the only things researchers found. They said they also observed objects that resembled nematode eggs. This suggests that the authors of the fecal samples may have suffered from intestinal worms.
After occupying Eurasia for possibly 300,000 years, Neanderthals vanished from the archaeological record about 40,000 years ago — roughly the same time Homo sapiens made their appearance in Europe.
Some researchers have argued that it was because of our eat-anything-you-can-get-your-hands-on attitude that anatomically modern humans prospered, while Neanderthals perished.
Study authors said further examination of coprolite samples will shed more light on this argument.
"Future studies in Middle Paleolithic sites using the fecal biomarker approach will help clarify the nature, role and proportion of the plant component in the Neanderthal diet, and allow us to assess whether our results reflect occasional consumption or can be representative of their staple diet," authors wrote.