South Americans were raising crops at least 10,000 years ago, about 5,000 years earlier than previously thought and nearly contemporary with the emergence of agriculture in the Old World, based on new ages obtained for agricultural samples excavated from the Andes 20 years ago.
"We always thought there was a gap of several thousand years before agriculture began in the New World," said archeologist Jack Rossen of Ithaca College in New York, one of the authors of the report in today's issue of the journal Science. The new find "is bringing it into line with dates from the Old World."
The plant remains found in the 1,500-foot-high Nanchoc Valley on the lower western slopes of the Andes were not native to the region but came from several other sites on the continent. So even though the communities were small and isolated, the residents were involved in some trade over fairly long distances.
That finding correlates well with previous studies showing a trade in obsidian, a naturally occurring glass used to make knives, between the mountains and the coast 10,000 years ago, said archeobotanist Dolores Piperno of the Smithsonian Tropical Research Institute in Panama.
"People were in contact with one another," said Piperno, who was not involved in the research.
For archeologists, the origins of agriculture are important because only when communities developed a stable and adequate supply of food could they devote time and effort to other endeavors, such as statehood, writing, monument building -- and even warfare.
Researchers now know that domestication of crops occurred independently in at least 10 locations around the world, including Africa, southern India and New Guinea.
The Peruvian agricultural samples were excavated two decades ago by Rossen from floors, hearths, storage units, stone hoes, bowls, garden plots and irrigation canals in the small villages along the Nanchoc River.
The sites themselves were accurately radiocarbon dated, "but we could never get the dates [from the agricultural samples] to match up," he said.
After new techniques for preparing the samples were developed, archeologist Tom D. Dillehay of Vanderbilt University decided to have them re-tested.
"The samples turned out perfectly with the dates we expected to get 20 years ago," Rossen said.
They found two separate squash samples dated to 9,240 and 7,800 years ago, a peanut sample dated to 7,700 years ago, a cotton bole dated to 5,400 years ago and two quinoa samples dated to 8,000 and 7,500 years ago. Quinoa is a high-protein grain that can be substituted for rice.
These plants "did not typically grow wild in that area," said Dillehay, the study's lead author. "We believe they must have therefore been domesticated elsewhere first and then brought into this valley by traders or mobile horticulturists."
Piperno said the squash they found was probably domesticated farther north, perhaps in Colombia.
The peanut is thought to have been first grown east of the Andes in a region encompassing southeastern Bolivia, northwestern Argentina, northern Paraguay and western Brazil's Mato Grosso area.
The peanuts Rossen found in the Nanchoc Valley don't look very much like modern peanuts. That indicates that, as in the Old World, people practiced systematic agriculture for a long time before the genetic traits emerged that now characterize crops as domesticated, Piperno said.