ARUN RATH, HOST:
A story now about scientists who are looking into the distant past. Archaeologists studying a prehistoric site in Sudan have used an ingenious technique to learn about the early human diet. NPR's Rae Ellen Bichell tells us what they found.
RAE ELLEN BICHELL, BYLINE: Karen Hardy is an archaeologist of the Autonomous University of Barcelona. She started to think about dental plaque.
KAREN HARDY: When you eat, you get this kind of film of dental plaque over your teeth. And if you don't clean it off, it mixes up with bits of food, and it gets stuck in this area below the gum. And it can calcify within about two weeks. And once it's calcified, it's very hard.
BICHELL: So hard that it can last thousands of years. Hardy and her colleagues were studying skeletons from a burial site called Al Khiday in central Sudan. It was used between around 2,000 and 9,000 years ago, since before farming. Prehistoric folk were not known for their flossing habits. And because of that, dental plaque scraped from their molars turned out to be archaeological gold.
HARDY: We get all sorts of different things.
BICHELL: Sand, dirt, evidence of carbon from breathing smoke from a fire.
HARDY: Starch granules from carbohydrates.
HARDY: Plant fiber, microfossils.
BICHELL: And to their surprise, they found evidence that people were eating a plant called purple nutsedge or cyperus rotundus. It looks like grass, with a network of routes like little potatoes. Ted Webster is a weed scientist with the USDA. He wrote his PhD on nutsedges, and he ate one, raw.
TED WEBSTER: Not very tasty. It tastes a lot like dirt.
BICHELL: But for a hunter-gatherer, it was great - a starchy pack of energy that grew everywhere. And it contains lysine and amino acid we need to survive. Even when they became farmers, people in the area were still eating it, 7,000 years later. But at some point, it lost its charm. By the 1970s, botanists branded purple nutsedge as the world's worst weed.
WEBSTER: They listed it as being a problem in 92 countries and 52 different crops.
BICHELL: But a weed is just a plant growing in the wrong place at the wrong time. Hardy says, it wasn't just the prehistoric Sudanese who valued did. Ancient Egyptians used it to make perfume. It was a staple for some aboriginal populations. And it may even have prevented tooth decay. In one group of skeletons, Hardy's group found fewer cavities than expected for the time period. Turns out, nutsedge produces antibacterial chemicals.
HARDY: That's why this study was very exciting because we identified a plant that had been forgotten about, but has all these wonderful qualities.
BICHELL: Hardy's team published their work on the healthy prehistoric snacks in the journal "Plos One." Rae Ellen Bichell, NPR News. Transcript provided by NPR, Copyright NPR.