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Species of corn found in the American Southwest.

Fire, not corn was key to prehistoric survival in the arid Southwest USA

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Conventional wisdom holds that prehistoric villagers planted corn, and lots of it, to survive the dry and hostile conditions of the American Southwest.

But University of Cincinnati archaeology professor Alan Sullivan is challenging that long-standing idea, arguing instead that people routinely burned the understory of forests to grow wild crops 1,000 years ago.

"There has been this orthodoxy about the importance of corn," said Sullivan, director of graduate studies in UC's Department of Anthropology in the McMicken College of Arts and Sciences. "It's been widely considered that prehistoric peoples of Arizona between A.D. 900 to 1200 were dependent on it.

"But if corn is lurking out there in the Grand Canyon, it's hiding successfully because we've looked all over and haven't found it."

UC archaeologist Alan Sullivan examines sherds of pottery from sites outside Arizona’s Grand Canyon National Park (Image: Joseph Fuqua II/UC Creative Services)

UC archaeologist Alan Sullivan examines sherds of pottery from sites outside Arizona’s Grand Canyon National Park (Image: Joseph Fuqua II/UC Creative Services)

The Fruitless Search For Corn

Sullivan has published a dozen papers outlining the scarce evidence of corn agriculture at more than 2,000 sites where they have found pottery sherds and other artifacts of prehistoric human settlement. He summarized his findings in a presentation last month at Boston University.

Sullivan has spent more than two decades leading archaeological field research to Grand Canyon National Park and the region's Upper Basin, home to the 1.6-million-acre Kaibab National Forest.

When you think of the Grand Canyon, you might picture rocky cliffs and desert vistas. But the Upper Basin, where Sullivan and his students work, is home to mature forests of juniper and pinyon trees stretching as far as you can see, he said.

"When you look down into the Grand Canyon, you don't see any forest. But on either rim there are deep, dense forests," he said.

The rim of the Grand Canyon is filled with forests

The rim of the Grand Canyon is filled with forests (Image: Alan Sullivan )

Forest Dwellers

On these high-elevation plateaus, Sullivan and his students have unearthed ceramic jugs adorned with corrugated patterns and other evidence of prehistoric life. Sullivan is particularly interested in the cultural and social practices of growing, sharing and eating food, also called a ‘foodway.’

"What would constitute evidence of a corn-based foodway?" he asked. "And if experts agree it should look like this but we don't find evidence of it, that would seem to be a problem for that model."

Like a detective, Sullivan has pieced together clues firsthand and from scientific analysis to make a persuasive argument that people used fire to promote the growth of edible leaves, seeds and nuts of plants such as amaranth and chenopodium, wild relatives of quinoa. These plants are called "ruderals," which are the first to grow in a forest disturbed by fire or clear-cutting.

"It's definitely a paradigm-threatening opinion," Sullivan said. "It's not based on wild speculation. It's evidence-based theorizing. It has taken us about 30 years to get to the point where we can confidently conclude this."

UC students work at many archaeological sites outside Grand Canyon National Park where they have found evidence of prehistoric civilization.

UC students work at many archaeological sites outside Grand Canyon National Park where they have found evidence of prehistoric civilization. (Image: Alan Sullivan )

Evidence from the Lab

Lab analysis identified ancient pollen from dirt inside clay pots that were used 1,000 years ago before Sullivan and his students found them.

"They've identified 6,000 or 7,000 pollen grains and only six [grains] were corn. Everything else is dominated by these ruderals," Sullivan said.

The corn itself looked nothing like the hearty ears of sweet corn people enjoy at barbecues today. The ears were puny, about one-third the size of a typical cob, with tiny, hard kernels, Sullivan said.

So if prehistoric people were not growing corn, what were they eating? Sullivan found clues around his excavation sites that people set fires big enough to burn away the understory of grasses and weeds but small enough not to harm the pinyon and juniper trees, important sources of calorie-rich nuts and berries.

Evidence for this theory was found in ancient trees. Raging wildfires leave burn scars in growth rings of surviving trees. In the absence of frequent small fires, forests would accumulate vast amounts of underbrush and fallen timber to create conditions ripe for an inferno sparked by a lightning strike. But examinations of ancient juniper and ponderosa pine trees found no burn scars, suggesting big fires are a relatively new phenomenon in Arizona.

"To me that confirms there weren't massive fires back then," Sullivan said.

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