At this very moment, 10 steaks are rotting on a rooftop near the Foggy Bottom Metro in downtown Washington, D. C. The steaks sit in a greenhouse on top of a laboratory building owned by the science and engineering departments of George Washington University. And those steaks belong to anthropologist and doctoral student Kimberly Foecke, who’s been closely monitoring their progress.
“All the experiments are doing great,” Foecke said. They’ve even added bones and organs to the collection, she said.
The rotting meat is part of a study under way by Foecke to better understand one of our closest relatives: the Neanderthal. Foecke suspects that the putrefying meat may hold clues to what Neanderthals ate when they roamed Earth from 400,000 to 40,000 years ago. And what her research shows may call into question a common proxy used widely in dietary reconstruction in paleoanthropology. Foecke will present a poster on the work at AGU’s Fall Meeting this Friday.
A Not-So-Balanced Diet
Past research has suggested that Neanderthals ate inordinate amounts of meat, so much so that they have been labeled a hypercarnivore, meaning they got more than 70% of their diet from meat. This percentage puts them in the ranks of other meat-loving animals like hyenas and polar bears.
But Foecke is skeptical that Neanderthals truly ate so much meat. Neanderthals were quite similar to humans, Foecke told Eos, noting that it would be “impossible for a human to survive on a diet like that.” Research into the plaque on Neanderthal teeth also suggests that they consumed more plants than previously thought.
The portrait of Neanderthals as meat guzzlers comes in part from chemical analysis of their bones. Bone collagen in Neanderthal skeletons reveals the relative ratio of the stable isotopes of nitrogen, 15N and 14N. Certain foods, like meat, carry higher 15N ratios, and researchers use this chemical fingerprint as a way to determine diet. The higher the 15N is in the bones, the theory goes, the more meat was packed into their diets.
Foecke hypothesized that something else may be driving 15N enrichment in Neanderthals’ bones, however. When meat begins to rot, microbes munch on the proteins in the meat, breaking them down. Because the lighter of the stable isotopes of nitrogen weighs slightly less, microbes can break those proteins down more easily, said Foecke, “leaving the rest of the meat with higher ratios of the heavy isotope of nitrogen.”
Something Rotten This Way Comes
To test her theory, Foecke rotted beef from a local butcher in her parents’ backyard in Maryland in autumn of 2017. For 2 weeks, twelve 1-pound steaks lay out in the elements in series of mesh enclosures to keep out animals.
Foecke sampled the meat every day with a copper coring device, popping out little tubes of the meat for analysis. She then measured the 15N levels in the meat with a mass spectrometer in the same way that researchers test Neanderthals’ bones.
She found that the meat went through two phases, each of which had a distinct effect on the nitrogen signature.
“For the first week, it’s pretty bad,” Foecke said. The meat began to give off a foul stench and turn gray. “It starts to act traditionally like rotting meat,” she explained. “You start to see some maggots forming.”
When Foecke ran the isotopic analysis, she saw that the chemical composition of the meat was also changing. “Within the first week or so, the 15N levels are increasing at a statistically significant rate,” she explained.
In the second week, however, the outside of the steaks began to resemble “beef jerky,” the smell of rotting flesh diminished, and 15N levels started to decrease again. Foecke said that it’s unclear why the second phase would cause a decrease, which demands further study.
Taken together, said Foecke, “this work is starting to show that we really don’t fully understand all of the potential inputs and processes going on with generating the 15N signal.”
Hypercarnivores or Just Connoisseurs of Rotten Meat?
Hervé Bocherens, a paleobiologist at the University of Tübingen in Germany who was not involved in the research, said that these results point to just another nuance of nitrogen isotopes as a dietary proxy. The idea that Neanderthals are considered hypercarnivores because of their nitrogen isotope signatures “is just wrong, but unfortunately still widespread,” he said
He said that high 15N ratios could be due to the fact that Neanderthals ate prey higher up the food chain, for example. But none of this would matter, he said, if Neanderthals altered their food by aging, cooking, or some other modification. “So far, only the impact of cooking practices has been tested,” Bocherens said. He is looking forward to seeing the results of the present study in full and hopes to be able to take them into account in future work.
Foecke already has a second batch of steaks putrefying, this time in a greenhouse on top of her campus’s lab building. She’ll watch those for 18 months, mapping out a longer timeline of nitrogen’s ups and downs. Foecke is also investigating how cooking, drying, and other treatments might affect nitrogen signatures in meat.
With many more months of putrefied meat ahead of her, Foecke said that she is unfazed by the work. “Here I am, doing a dissertation that’s possibly the grossest that’s ever come through our department.” Foecke said. And yet, she added, “it actually doesn’t bother me that much. I still enjoy a lovely steak.”
—Jenessa Duncombe (@jenessaduncombe), News Writing and Production Intern