for National Geographic News
Despite a lack of solid evidence, archeologists have thought for some time that farmers used irrigation canals in agricultural villages in Peru as long as 4,000 years ago.
New discoveries in the Peruvian Andes may push that date back another 2,700 years.
Scientists say they have unearthed evidence of the oldest canals ever found in South America.
The ancient canals were almost certainly designed for irrigation and were built in the Andean foothills in northern Peru's Zaña Valley, about 40 miles (60 kilometers) from the Pacific coast.
Researchers describe their find in the November 22 issue of the journal Proceedings of the National Academy of Sciences.
"This is an important paper with terrific results," said Jonathan Haas, an anthropologist at the Field Museum in Chicago, who was not involved in the research.
"Every day we have a better understanding of the beginnings of agriculture and domesticated economy. But the whole question of irrigation has so far been indirectly inferred based on the existence of the plants," he said.
The new study "has nailed that down very solidly. Irrigation starts remarkably early in the Andes. You're getting agriculture based on irrigation in the Andes as early as anything seen in the rest of the New World," he added. "It is just stunning work."
Researchers found three canals that date to at least 5,400 years ago buried by sediment layering. A fourth possible canal was also found, which special radiocarbon dating techniques revealed to be 6,700 years old.
"Some colleagues in the Andes surmise early canal irrigation based on the presence of crops at 9,000 to 10,000 years ago," said Tom D. Dillehay, an anthropologist at Vanderbilt University in Nashville, Tennessee, who lead the study.
"Yet the actual canal evidence is probably later," he added.
SOURCES AND RELATED WEB SITES