Corn's deep roots (3/29/2008)

PhD student Sonia Zarrillo (left) and archaeology professor Scott Raymond report that a new technique for examining ancient cooking pots has produced the earliest directly dated examples of domesticated corn (maize) being consumed on the South American continent. - Photo Courtesy (Grady Semmens)

Earliest signs of maize as staple food found after spreading south from Mexican homeland

Corn has long been known as the primary food crop in prehistoric North and Central America. Now it appears it may have been an important part of the South American diet for much longer than previously thought, according to new research by University of Calgary archaeologists who are cobbling together the ancient history of plant domestication in the New World.

In a paper published today in the advanced online edition of the Proceedings of the National Academy of Sciences (PNAS), U of C PhD student Sonia Zarrillo and archaeology professor Dr. Scott Raymond report that a new technique for examining ancient cooking pots has produced the earliest directly dated examples of domesticated corn (maize) being consumed on the South American continent. Their discovery shows the spread of maize out of Mexico more than 9,000 years ago occurred much faster than previously believed and provides evidence that corn was likely a vital food crop for villages in tropical Ecuador at least 5,000 years ago.

"The domestication and dispersal of maize has been a hot topic in archaeology for decades and these are the earliest indisputable dates for its presence in South America," Raymond said. "It has long been thought that maize may have been used south of Panama at this time for ritual purposes but this shows it was also being consumed as food."

Raymond led the excavation of tropical village sites in western Ecuador in the early 1980s, which are the oldest known villages in the Americas. Using pottery fragments recovered from the sites, Zarrillo obtained the charred remnants of prehistoric meals and found they contained starch granules from domesticated corn.

"Plant material typically does not preserve very well in tropical sites but it turns out that microscopic starch grains do survive very well over the years and can be used to identify exact species of plants," Zarrillo said. "Analyzing starch from charred food residues is a new technique in archaeology and it is exciting because it will stimulate research around the world when people realize they can recover starch from cooking pots and use it to date and identify what people were using as food."

Starch analysis was also used by Zarrillo and Raymond for a study published in Science last year that traced the domestication and spread of chili peppers throughout South America, Central America and the Caribbean more than 6,000 years ago.

The paper "Directly dated starch residues document early formative maize (Zea mays L.) in tropical Ecuador" by Sonia Zarrillo, Deborah M. Pearsall (University of Missouri), J. Scott Raymond, Mary Ann Tisdale (Canadian Heritage, Government of Canada) and Dugane Quon (Canadian Food Inspection Agency) will be available in the March 24 online early edition of the Proceedings of the National Academy of Sciences at 3 pm (MDT).

Note: This story has been adapted from a news release issued by the University of Calgary

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