Earlier this week a team of researchers from the United Kingdom, Italy and Spain published a paper in the journal PLOS ONE with new details about the diets of ancient people who lived in what is now Sudan. They are by no means the first researchers to try and piece together the culinary habits of early humans, but their study drew evidence from an interesting source: dental plaque.
If you’ve been to the dentist for a teeth cleaning recently, you’re probably intimately familiar with the various picks, hooks, and other metal tools used to scrape plaque from around the gum line. Dentists use those tools because plaque is hard — hard enough, it turns out, to persist for thousands of years on the teeth of ancient skeletal remains.
When the team of researchers scraped off and analyzed the chemical composition of the ancient plaque, they found tiny fossils, pollen, traces of smoke from cooking, and starch molecules from a plant called purple nut sedge (Cyperus rotundus). Purple nut sedge is known as “the world’s most expensive weed” and is a highly invasive species throughout tropical regions, where it frequently interferes with agriculture. This choice of snack was a surprising discovery for this region, and one that would not have surfaced without the creative use of chemistry.
Other researchers have use chemical analysis in interesting ways to reveal insights into human diets and habits — both past and present.
Earlier this summer, for example, researchers from the United States and Spain discovered a 50,000-year-old sample of human feces — the oldest on record. When they ground up the fossilized feces and analyzed its chemical composition, they found two important biomarkers. A biomarker is a sort of biological clue. It’s a substance found in an organism that points to a specific biological process, such as the digestion of a particular food, exposure to a particular toxin, or the presence of an infection.
In the case of this ancient feces, the researchers found a high proportion of coprostanol, a substance produced when an organism digests foods, such as red meats, that contain cholesterol. They also found a significant amount of 5B-stigmastanol, a byproduct of digesting plant materials. These biomarkers support a hypothesis that Neanderthals may have been omnivores who ate a wide variety of foods, rather than highly-focused hunters with only a few species of prey.
Scientists also use chemical analysis to understand the diets of modern humans and cultures. Researchers in the lab of environmental scientist Stephen Macko at the University of Virginia use human hair as their window into dietary habits. In the early 1990s, Macko began analyzing the isotopes in hair samples from his students. Isotopes are two atoms of the same element (such as carbon or nitrogen) that contain different numbers of neutrons.
Different foods contain different isotopes. Sulfur-34, for example is common in seafood, nitrogen-15 is common in red meat, and carbon-13 is more prevalent in corn than in other grains. The isotopes contained in a person’s food choices are incorporated into an organism’s hair as it grows. Looking at the isotopic composition of hair samples, Macko was able to determine things like which of his students were vegetarians and who ate lots of fish. Macko and colleagues have put this technique to work studying the hair of people as wide ranging as 4,000-year-old Egyptian mummies and “Oetzi the iceman” found frozen in a glacier in the Alps.
One of Macko’s most talked-about findings is that corn (reflected in high levels of carbon-13) is extremely common in the diets of modern Americans. In most cases, this isn’t because people are eating large amounts of fresh corn; it’s due to eating corn-based additives in foods, such as corn syrup, and meat from animals fed with a corn-based diet.
Food, and the methods by which we procure it, are an important part of any culture. Using chemistry to better understand human diets past and present can give us important insights into cultural norms and our impact on the planet over time.
Learn more about isotopes in our module Atomic Theory II: Ions, Isotopes, and Electron Shells
See how scientists use isotopes in a wide range of other research — from biology to earth science — in our modules The History of Earth’s Atmosphere I: The Origin of the Modern Atmosphere and DNA I: The Genetic Material
Listen to researchers describe their work using dental plaque in the NPR story This Dirty Little Weed May Have Cleaned Up Ancient Teeth
Read more about the research of Stephen Macko in The Hair Detective
Written by Christine Hoekenga
Christine is a freelance writer, editor, and content strategist, specializing in science and nature. She holds an Bachelor's degree in Environmental Science and Media Studies and a Master's of Science Writing. She has been working in science communication and education for nearly a decade as a journalist, an organizer for conservation groups, and a museum educator. Before joining the Visionlearning team, she served as the New Media and Online Community Manager for the Webby award-winning Smithsonian Ocean Portal. Christine is assisting Visionlearning with developing new modules and glossary terms, managing the blog, and outreach through social media.