This scientist watches meat rot to decipher the Neandertal diet

Nitrogen-15 levels in putrefying meat could explain high levels of the isotope in hominid fossils

a composite photo showing steak before and after rotting

HIGH STEAKS  Kimberly Foecke is measuring the biochemical changes of rotting meat, hoping to get a better understanding of Neandertal diets in the process. A fresh steak (left) has turned putrid and black by day 15 (right).

Kimberly Foecke

WASHINGTON — Kimberly Foecke has a great relationship with her local butcher.

Though she buys loads of meat, Foecke is not a chef or the owner of a small zoo. She’s a paleobiologist who studies what Neandertals ate. And that involves, in her words, “experimental putrefaction, which is a fancy way of saying, I rot meat, all day, every day.”

Scientists know Neandertals ate a lot of meat. Fossilized bones from the hominids tend to have high levels of a heavier form of nitrogen, nitrogen-15, compared with the lighter form, nitrogen-14. Nitrogen-15 is least abundant in plants, and becomes more concentrated further up the food chain because it’s harder to break down than nitrogen-14.

But exactly how much meat these hominids ate — and what else was in their diet — is somewhat controversial. Evidence such as tooth scrapings suggests that Neandertals also ate a variety of plants. But the nitrogen-15 measurements point to “an unreasonably huge amount of meat” in the diet, says Foecke, a researcher at George Washington University in Washington, D.C. Those levels tend to be even higher than what’s seen in top carnivores like hyenas, which nosh almost entirely on meat.

a photo of Kimberly Foecke holding a Neandertal skull
SKULL STORY Paleobiologist Kimberly Foecke points out the features of a Neandertal skull. Fossilized bones from the hominids tend to have high levels of a heavier form of nitrogen, nitrogen-15, that suggests a meat-heavy diet. Kimberly Foecke
Foecke thinks those high nitrogen-15 ratios may be explained not just by how much meat Neandertals ate, but also how they got it and prepared it. Perhaps whether meat was eaten fresh or rotten, raw or cooked, could influence the nitrogen-15 signal. That’s why she’s measuring nitrogen in cuts of beef, trying to pin down the biochemical changes that the meat undergoes as it rots.

Grocery store steaks wouldn’t cut it for this experiment. Instead, Foecke calls her butcher in Maryland, who makes sure she receives meat that is fresh and from animals raised as close to Pleistocene-style as is possible in 2018 — after all, no hormones or antibiotics were fed to animals hunted 200,000 years ago. She needs animals raised on organic diets she can sample.

Foecke leaves the steaks to rot for 16 days in a mesh-covered box in her family’s backyard, or sometimes in a greenhouse, and samples nitrogen values daily. She plans future sampling for longer periods.

Her preliminary results suggest that nitrogen-15 ratios do fluctuate as meat rots. In the first week, levels increase. The meat is moist, and there’s lots of microbial activity that breaks down the lighter nitrogen-14 faster than the nitrogen-15, Foecke reported December 14 at the American Geophysical Union meeting. It smells “pretty terrible,” she says — though over time, the stench diminishes as the meat blackens and takes on a more jerkylike consistency.

Foecke’s research so far suggests that eating rotting meat could at least partly explain the high nitrogen-15 signatures in Neandertal fossils. And it makes sense that Neandertals weren’t feasting on fresh grub, particularly when they killed large animals. A carcass from a large animal might last days. Foecke is also measuring what happens biochemically as she cooks or smokes meat — food prep steps that Neandertals might have taken that could also affect nitrogen-15.

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