Evidence that squash was being grown nearly 10,000 years ago, in what is now Peru, is reported in Friday's edition of the journal Science.
A team led by anthropologist Tom D. Dillehay of Vanderbilt University also uncovered remains of peanuts from 7,600 years ago and cotton dated to 5,500 years ago in the floors and hearths of sites in the Nanchoc Valley of northern Peru.
"We believe the development of agriculture by the Nanchoc people served as a catalyst for cultural and social changes that eventually led to intensified agriculture, institutionalized political power and new towns in the Andean highlands and along the coast 4,000 to 5,500 years ago," Dillehay said.
Dolores Piperno, curator for archaeobotany and South American archaeology at the Smithsonian's National Museum of Natural History, said the report "adds to the accumulating data for agriculture in the Americas as old or nearly as old as that in the Old World, provides evidence for the domestication of a major species of squash native to South America, and documents ancient peanuts and quinoa."
Piperno, who was not part of the research team, said other species of squash have been identified at early dates in Mexico and Ecuador.
The earliest evidence of growing wheat, barley and legumes dates to about 10,000 to 12,000 years ago in the Fertile Crescent of the Middle East.
"The plants we found in northern Peru did not typically grow in the wild in that area," Dillehay said. "We believe they must have therefore been domesticated elsewhere first and then brought to this valley by traders or mobile horticulturists.
The Nanchoc Valley is located on the lower western slopes of the Andes.
In addition to the peanuts, squash and cotton the researchers found a quinoa-like grain, manioc and other tubers and fruits at the sites, including in garden plots, irrigation canals, storage structures and on hoes.
In addition to the Middle East and South America, other early agricultural sites include China, southeast Asia and what is now the eastern United States.
"Many scholars, including myself, believe that the profound environmental transitions and associated changes in the distribution and abundance of wild plants and animals that occurred around the world as the ice age was ending 11,000-10,000 years ago was significant in the development of agriculture in several geographically widespread places at this time," Piperno commented.
She said people in various places "made different choices in how to procure their food as plant and animal availability was changing — and in many places, farming was a very good choice."