Manchester, United Kingdom--What you eat can reveal a lot about your lifestyle and health. What you excrete can reveal even more. At the 5th International Ancient DNA Conference here 13 July, researchers reported that DNA can lay bare a wealth of hidden information on the diet of hunter-gatherers.
Dry, cool caves were not only a good place to live in prehistoric days--they seem to have offered decent enough environmental conditions to preserve DNA. Still, the hunt for DNA from cave samples of paleofeces proved frustrating until 2 years ago, when Hendrik Poinar and Svante Pääbo of the Max Plank Institute for Evolutionary Anthropology in Leipzig, Germany, pioneered an approach to release DNA trapped inside the 20,000-year-old dung of extinct ground sloths (Science, 17 July 1998, p. 402 ). The secret was a compound called N-phenacylthiazolium bromide (PTB), which cleaves sugar bonds that entangle DNA and prevent its amplification--a particular problem for sugar-rich paleofeces.
Kristin Sobolik, an archaeologist at the University of Maine, Orono, encouraged the team to test human paleofeces from Hinds Cave, a well-studied prehistoric rock-shelter in the Lower Pecos River area of Texas. Thousands of paleofeces, ranging in age from 8500 to 500 years old, have been collected, but only a few analyzed. Poinar's team used PTB to amplify chloroplast DNA that had survived digestion. They found sequences that match buckthorn, acorns, sunflower, ocotillo, and a kind of nightshade, probably wild tobacco. Without DNA analysis, these plants were invisible--Sobolik found no remnants of them when she examined the paleofeces under a microscope.
The paleofeces contain other hints about early human diets as well. Visible bones of packrats and mice, as well as fish scales, were found in some specimens. And using DNA analysis, Poinar also found sequences that match sheep--which came as a surprise since no sheep bones had been found in Hinds Cave. The finding suggests the large game was killed and eaten elsewhere, Poinar says.
"This is really neat," says longtime paleofeces examiner Karl Reinhard, an archaeologist at the University of Nebraska, Lincoln. "It will expand our ability to identify the total diet and use of natural resources." Next the team hopes to track diet over 8000 years by looking at Hinds Cave feces from different millennia. For instance, the researchers might be able to see changes in big game abundance.