Dried-up bits of food lurking on dinnerware make diners cringe, but they are like gold for an archaeo-botanist.

Hot on a new trail of microscopic crumbs, researchers led by Linda Perry of Smithsonian's National Museum of Natural History have revealed that domesticated chili peppers originated in the Americas earlier than previously thought, even before people started making pottery.

Until now, scientists had a hazy and disjointed record of the spread of domesticated chili peppers (Capsicum)--considered one of the most prevalent of the plants cultivated in the Americas.

The food residues were found on 6,000-year-old cooking utensils unearthed from various sites in Central and South America.

Hardy starches

Perry and her colleagues studied particles of food starch found on the utensils, because the substance is hardy and less resistant to degradation than other residues. But thousands of years can wreak havoc on even the sturdiest crumb. Perry suggested that the crevices of ancient tools provided safe havens for the starch grains, sealing them from degradation by micro-organisms.

"It's like tiny rock shelters, little-bitty caves, microscopic caves that are protecting these things," Perry told LiveScience.

Perry discovered the first food-encrusted utensils for this study during a dig in Venezuela. She knew the flecks must be starches but had no idea of their exact food source. Unlike most starch bits, samples of this one appeared under the microscope as a flattened disk with a central depression--like a tiny jelly doughnut with the center squished.???

Microscope observations also showed the starch grains have distinct shapes and other physical details, depending on whether they came from wild or domestic chili peppers.

Pepper puzzle

Scientists previously were unaware that peppers contained starches. "It was something that everybody was finding but nobody knew what it was," Perry said.

Perry had heard that chili peppers cause intestinal problems, which she thought was odd since undigested starches are usually the culprit of such stomach problems. The light bulb went off: Perhaps chili peppers do contain starches. In her lab, Perry compared a sample from the encrusted utensils with archived chili-pepper specimens and found a match.

Other scientists had also unearthed these "microscopic doughnuts" [image] from various sites, including places in Peru, Ecuador, Venezuela, Panama and the Bahamas.

"When I was able to identify it, we put all the data sets together and realized that we had a long and widespread record of chili pepper use in the Americas," Perry said

Ancient starch

The oldest starch grains unearthed, dating back to 6,100 years, came from Ecuador. Past research has established that peppers were not initially domesticated in this area.

"So that means the domestication must have occurred earlier than even than 6,100 years, after which people would have migrated or traded them into this region," Perry explained.

The scientists also found maize alongside the chili-pepper grains at many of the sites. This suggests that maize and chili peppers could form a Neotropical crop grouping analogous to the "three sisters,"? a trio of agricultural crops--maize, beans and squash--frequently grown together in North America.

"We think what we're seeing is the first documented Neotropical plant food complex," Perry said.

The study is published in the Feb. 16 issue of the journal Science.