An unappetizing dish has been discovered in the diet of our prehistoric ancestors

However, the chemical composition of Neanderthal remains, which suggests they ate meat in greater quantities than was seen in large predators such as lions and wolves, has puzzled researchers for decades. Now, a new study points to an unexpected Stone Age food.

A study published Friday in the journal Science Advances suggests that fly larvae, which hatch from and feed on decaying animal tissue, may also have been a staple diet of prehistoric humans.

Lead study author Melanie Beasley, an assistant professor of biological anthropology at Purdue University in West Lafayette, Indiana, found that a predilection for maggots could explain distinctive chemical signatures found in the bones of prehistoric humans, including Homo sapiens and Neanderthals, species that went extinct 40,000 years ago.

The findings support a hypothesis advanced by Beasley's co-author John Speth, a University of Michigan anthropologist who has argued for nearly a decade that rotting meat and fish were a key part of prehistoric humans' diets. His work was based on ethnographic descriptions of the diets of indigenous peoples, who he said considered rotting meat and maggots acceptable foods, CNN notes.

“Not many people paid attention to it because it was such an unusual idea. And there was no data,” says Melanie Beasley, who heard Speth speak in 2017 and subsequently decided to test his hypothesis.

To understand past diets and an animal's place in the ancient food chain, scientists study the chemical composition of different isotopes, or varieties of elements such as nitrogen or carbon, that remain in teeth and bones for thousands of years.

In the 1990s, researchers first discovered that fossilized Neanderthal bones found in northern Europe contained particularly high levels of the isotope nitrogen-15, a chemical signature that suggests they ate meat on par with supercarnivores like lions or wolves.

“The grass will have one nitrogen value, but then the deer that eats the grass will have a higher value, and the carnivore that eats the deer will have an even higher value,” Beasley explains. “So you can track the nitrogen content through that trophic food web.” The Neanderthal remains had even higher nitrogen content than the carnivores, she says.

But this was puzzling because modern humans, unlike wolves and lions, cannot digest large amounts of lean meat, CNN points out. Eating too much lean meat can lead to a potentially fatal problem in which the liver is unable to break down protein and remove excess nitrogen from the body.

Known today as protein poisoning, the disease was more common among European explorers of North America. Archaeologists believe that Neanderthals understood the importance of the nutrients in fats and, at least in one site in what is now Germany, processed animal bones on a large scale to extract fat.

Speth's research has shown that rotten meat can contain more nitrogen than fresh tissue, and this may have been the reason for the increased nitrogen levels in Neanderthal bones.

Soon after she heard Speth speak, Beasley, who was previously a research associate at the University of Tennessee at Knoxville, where she conducted research at the Center for Forensic Anthropology, decided to investigate. The research center, sometimes called a "body farm," was created to study how the human body decomposes.

There, she analyzed nitrogen levels in rotting tissue from donor human cadavers left in the open air and fly larvae that had formed in muscle tissue. The work, which took two years, required a strong stomach, she says.

Beasley found that nitrogen levels in human tissues increased slightly over time. However, she observed much higher levels of nitrogen in fly larvae, suggesting that Neanderthals and early modern humans likely regularly consumed animal meat laced with maggots.

“I started restoring the nitrogen levels, and they were just astronomically high,” Beasley recalls. “John Speth and I started talking about what if it wasn’t just the rotting meat, but the fact that they could never stop the flies from coming and landing on the meat, and so the fly larvae were just becoming part of the delicacy.”

Her findings not only provide insight into the diet of Neanderthals, but also serve as a basis for modern forensic science: the nitrogen levels in the larvae that form in human corpses help scientists accurately determine the time that has passed since death, she noted.

It was "no big deal" that Neanderthals ate grubs, says Karen Hardy, professor of prehistoric archaeology at the University of Glasgow in Scotland.

Hardy comments that the authors present “a strong case for larval consumption,” although such behavior is unlikely to be conclusively proven because larval remains have not been preserved in the archaeological record. “The element of surprise has more to do with our Western view of what is edible and what is not,” she added.

The Food and Agriculture Organization of the United Nations estimates that at least 2 billion people worldwide today eat insects as part of their traditional diet.

The study also notes that historical accounts show that many indigenous peoples, such as the Inuit, “regarded thoroughly rotten, maggot-infested animal food as a highly desirable food rather than a starvation ration.” Many such groups, according to the study, “regularly, often intentionally, allowed animal products to decompose to the point that they became maggot-infested, or in some cases even liquefied, and inevitably produced a stench so overpowering that early European explorers, fur trappers, and missionaries became nauseated by it.”

Knud Rasmussen, a polar explorer from Greenland, described the following culinary experience, cited in a study, in his 1931 book, The Netsilik Eskimos: Social Life and Spiritual Culture.

“The meat was green with age, and when we cut it, it seemed ready to burst, so full was it of large white maggots. To my horror, my companions scooped up handfuls of these crawling creatures and ate them with evident pleasure. I criticized their taste, but they quite logically replied: “You yourself like caribou meat, and what are these maggots if not living caribou meat? They taste just like the meat, and pleasantly refresh the mouth.”

The study also notes that maggots are not unknown in Western culinary traditions, and the Sardinian cheese casu marzu is teeming with cheese fly larvae, CNN reports.

Beasley said people in northern latitudes still process these foods and eat them safely if they are prepared using traditional methods.