Neanderthals in Spain weren't just meat eaters, suggests the first direct evidence of their omnivorous diet. An analysis of 50,000-year-old feces -- likely the oldest known human poop -- suggest they ate tubers, berries and nuts as well as meat.

Researchers from MIT and the University of La Laguna say we've probably overemphasized the role of meat in the Neanderthal diet based on traces of plant matter found in samples from a site in El Salt, Spain.

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Previous research showed what sorts of prey Neanderthals consumed -- pigs vs. cows, for example -- and depicted Neanderthals as exclusively carnivorous. Later studies found plant remains in the teeth of Neanderthals, but that might also be misleading.

"Sometimes in prehistoric societies, they used their teeth as tools, biting plants, among other things," said Ainara Sistiaga, a graduate student at the University of La Laguna who led the study as a visiting student at MIT, in a statement. "We can't assume they were actually eating the plants based on finding microfossils in their teeth."

So the researchers decided to take a more direct approach.

"This study represents the first approach to Neanderthal diet through the analysis of fecal markers" found in soil, Sistiaga said.

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The research shows Neanderthals ate meat as their primary food source, but the discovery of a compound from plant sources called 5β-stigmastanol shows that plants added variety to their diet that was previously unproven. Every sample studied showed signs of meat consumption, and some samples showed signs of plant matter.

"It's important to understand all aspects of why humanity has come to dominate the planet the way it does," said co-author Roger Summons, a professor of geobiology at MIT. "A lot of that has to do with improved nutrition over time."

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