Watching meat rot helps decode what Neandertals ate

WASHINGTON, D.C. — Kimberly Foecke has a great relationship with her local butcher. She buys lots of organic meat — then lets it rot. Go really bad. What’s she’s learning may help her better understand what Neandertals ate.

Foecke undertakes experimental putrefaction (Pyoo-truh-FACK-shun). That, she explains, is “a fancy way of saying, I rot meat — all day, every day.” Foecke is a paleobiologist at George Washington University in Washington, D.C.

Neandertals (Nee-AN-dur-tals) are an extinct species of hominid that was closely related to humans. They lived in Europe and parts of Asia from about 200,000 years ago until about 28,000 years ago. Scientists have a lot of questions about how they lived, including what they ate.

Researchers know Neandertals ate a lot of meat because much of the nitrogen in the hominids’ fossil bones tends to be a heavy form known as nitrogen-15, or ¹⁵N. ¹⁵N is least abundant in plants. Animals tend to have far more because their enzymes (or those of the food-digesting microbes in their guts) have a preference for breaking down molecules that have nitrogen-14 (or ¹⁴N). So when an animal eats plants with ¹⁵N, the chemical tends to accumulate in them. When that animal becomes the prey of another, the predator takes in even more ¹⁵N. In this way, ¹⁵N becomes more concentrated as nitrogen moves up the food chain.

The more meat an animal — including some hominid — eats, the higher the share of ¹⁵N their bones will tend to have.

But exactly how much meat Neandertals ate is somewhat controversial. So is the question of what else they dined on. Evidence such as tooth scrapings suggests Neandertals ate a variety of plants. But the high ratio of ¹⁵N to ¹⁴N in their bones points to their having eaten “an unreasonably huge amount of meat,” says Foecke. Their levels can exceed what’s seen in top carnivores, such as hyenas. Those critters eat little other than meat.

Foecke thinks the high ¹⁵N levels in their bones may be explained not just by how much meat Neandertals ate, but also how fresh it had been. Whether meat was eaten fresh or rotten, raw or cooked, might influence the ratio of ¹⁵N to ¹⁴N that ends up in bones. That’s why she’s measuring nitrogen in beef. She’s trying to pin down the chemical changes meat undergoes as it rots.

Grocery store steaks wouldn’t cut it for this experiment. Instead, Foecke calls her butcher in Maryland. The butcher makes sure that the steaks she receives are fresh and from animals raised on an organic diet. By that she means those animals must not have had added hormones or antibiotics. She wants those animals to be as close as possible to what Neandertals would have hunted 200,000 years ago.

Foecke places the meat in a mesh-covered box in her family’s backyard, or sometimes in a greenhouse. Then she leaves them to rot for 16 days. She samples nitrogen values in the meat daily. (In future, she plans to sample for even longer periods.)

Her early results suggest that ¹⁵N ratios vary as meat rots. In the first week, the share of nitrogen that’s ¹⁵N tends to increase. The meat is moist, she notes. So the microbes in it are busy breaking down the lighter ¹⁴N faster than the ¹⁵N. This meat smells “pretty terrible,” Foecke admits. Over time, however, the stench diminishes. At the same time, the meat blackens and becomes more jerkylike.

She reported her findings December 14 at the American Geophysical Union meeting, here, in Washington, D.C.

This research suggests that eating rotting meat could at least partly explain the high ¹⁵N levels in Neandertal fossils. And that makes sense, Foecke says. Neandertals weren’t always feasting on fresh grub. Especially after they killed a large animal, its carcass might last many days. Foecke also is measuring what happens chemically as she cooks or smokes meat. These are food-prep steps that Neandertals might have taken that also might affect ¹⁵N.