Chili peppers: an ancient social mixer

For archaeologists trying to unearth the origins of farming, a microscope can be mightier than a spade. Close examination of pollen and silica granules containing plant residues has been instructive. Now botanists are looking at grains of starch that also tell the tale when other evidence of crop cultivation has vanished. Research involving such microfossils reported during the past two weeks shows that agriculture and complex cuisines developed and spread quickly across Central and South America. In some cases, they were established even before their practitioners learned to make pottery.

These discoveries of prehistoric crop dispersion are relevant to our own time. Commenting on research on the spread of chili peppers published Feb. 16 in Science, botanist Sandra Knapp of Britain's Natural History Museum in London notes: "Today's concern over invasive species and their threat to native biodiversity highlights the importance of understanding how human movements and transport have affected distribution of plants and animals."

Linda Perry at the Smithsonian's National Museum of Natural History in Washington and colleagues have opened a new window on the early days of that transport. They have identified distinctive starch grains that unambiguously show the presence of cultivated (not wild) chilies at ancient archaeological sites.

Preservation of other kinds of chili remains is rare. Noting this, Dr. Perry says, "suddenly we are able to gain incredible insight into ancient agriculture, trade, and cuisine by making these plants visible everywhere they occurred."

The team studied seven sites scattered from the Bahamas to Peru and dating from 6,100 to less than 1,000 years old. The chilies were associated with a variety of other foods such as maize, beans, and yams. At some sites, this complex cuisine dates to before the advent of pottery. Perry suggests that "the peppers would have enhanced the flavor of early cultivars such as maize and manioc and may have contributed to their rapid spread after they were domesticated."

Ruth Dickau at Canada's University of Calgary and colleagues have been following the starch grain trail across Panama. Their report Feb. 19 in the Proceedings of the National Academy of Sciences (early edition) documents the early cultivation of maize, manioc, and arrowroot. Starch on stone tools at a central Panama lowland site dates to 7,000 to 7,800 years ago. Starch residues at a forest site in western Panama are 5,600 to 7,400 years old. The scientists note that this latter dating is "several millennia earlier than previously documented."

Again, that's before the early farmers left any evidence of pottery.

Once a plant such as a chili became a cultivated crop, its use apparently spread fast. It wasn't just carried about as early farmers migrated. Dr. Dickau's team says their data suggest "that crop dispersals took place via diffusion or exchange of plant germplasm rather than movement of human populations practicing agriculture."

Perry says their research "shows us that chili peppers are one of the oldest domesticated food sources in the Americas and that people in distant areas ate them." This also suggests contact over a wide area between different human groups.

Plant microfossils contain much useful information. They can uniquely identify ancient crops. They can yield enough material for radiocarbon dating. Their use is revolutionizing the archaeology of agriculture – not just in the Americas, but all over the world.