The squash seeds, for example, matched varieties of a species that people still grow today in northern Colombia. The seeds also had a different color and shape than any wild counterparts.
What's more, Dillehay and colleagues have found no sign that the people of the Ñanchoc Valley were the first to domesticate squashes or peanuts.
"There must be many other sites with early agriculture," Dillehay said.
The squash species found at Ñanchoc might have originated in Colombia, more than 1,000 miles (1,600 kilometers) away.
Likewise, peanuts probably originated in central South America, across the Andes and about 1,500 miles (2,500 kilometers) from the Peruvian sites.
"There must have been pretty wide exchange systems," Dillehay said. "There were probably a lot of ideas, plants, and technologies that were moving around."
Until about a decade ago some researchers thought that New World agriculture got started around 5,000 years ago with a suite of crops that included potatoes, corn, squashes, and chilies.
But in 1997 Bruce Smith of the Smithsonian National Museum of Natural History found seeds of a domesticated squash in a cave in Mexico that dated to nearly 10,000 years ago.
Then in 2003 a study led by Dolores Piperno, also at the National Museum of Natural History, found domesticated squash seeds from a different species in Ecuador that were around the same age.
"The origin of settled, organized communities in the Americas is probably older than we thought and reliance on cultivated plants earlier than we thought," Piperno said.
(Related news: "Ancient Canals in Andes Reveal Early Agriculture" [December 5, 2005].)
Dillehay and colleagues have been studying the sites in Peru for 25 years, so they have been able to get a sense of how the people there gradually settled down over millennia.
In one portion of the valley, "about 10,000 years ago people were building little stone structures and staying in one place for a while," Dillehay said.
"Then about 8,000 years ago, we begin to see larger houses at a greater density," he said. "Around 6,000 to 7,000 years ago, things are really starting to develop."
At that point, people began building simple canals for watering their fields and mounds that may have been sites for public rituals, Dillehay said.
"They were probably moving from gardens outside their houses to communal fields," he said.
The find shows that the origins of agriculture are complex, said Graeme Barker of the University of Cambridge in England.
"The orthodox view about the beginnings of agriculture has tended to focus on a few assumed 'hearths of domestication,'" Barker said.
But "new well-dated finds like these exciting ones from northern Peru are further evidence for the complexity, antiquity, and wide geographical spread of early horticultural systems around the world."
And it makes sense that squashes were part of the origin of agriculture, Piperno added.
"These seeds are very nutritious," Piperno said. "They're high in oil and protein and easy to grow."
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