Rewriting the history of agriculture in the Americas, researchers have discovered a surprisingly large farming village in northwestern Mexico that was inhabited at least 3,000 years ago--2,000 years earlier than any other site of such scale in the region--the scientists announced Thursday.
The archeological evidence from the site, called Cerro Juanaquena, supports a new view of how humans first adopted farming as a way of life in Central and North America, experts said.
The research, published today in Science, strongly suggests that these ancient people of the Southwest had settled into large, well-constructed communities to till a variety of crops, at a time when scholars previously had thought that only small roving bands of hunters held sway in the region.
Moreover, it appears that these prehistoric people pursued farming well before the introduction of maize or squash, which were key crops in the ancient Americas.
Bruce D. Smith, an authority on early agriculture at the Smithsonian's National Museum of Natural History, called it "the latest in a decade-long string of surprises" about prehistoric farming in Mexico and the southwestern United States.
"The thing that stands out the most is the scale of the settlement," he said. "More than resolving questions, it opens up a whole new area for agricultural research."
Researchers are especially interested in the different ways that farming developed around the world, because the emergence of agriculture is considered the major turning point in the development of a modern, settled society.
In their quest for the roots of civilization, archeologists have traced some of the world's earliest crops--some 10,000 years ago--to remote Turkish highlands, reconstructed the prehistoric millet fields of ancient China and tracked down the brightly colored ancestors of the potato in the high Andes.
"Agriculture is the foundation of growth and development of societies around the world," said archeologist Robert J. Hard at the University of Texas, San Antonio. "This village is indicating the beginning of that process in the American Southwest." Hard excavated the site in June with John R. Roney of the Bureau of Land Management in Albuquerque, N.M.
The site, which at one time may have been home to as many as 1,000 people, is called Cerro Juanaquena. Located at the crest of a forbidding hilltop overlooking the Rio Casa Grandes just south of the U.S.-Mexico border, the 25-acre complex encompasses 468 graded terraces and housing platforms encircled by almost five miles of stone walls.
"It is the oldest settled village of its size in northwest Mexico or the American Southwest," Hard said.
"The key thing is the dating. The site would not be important if it was not so old. There are lots of terraced hilltop villages, but they are 2,000 years younger."
The team is investigating three other large sites in the region that may prove to be of equal antiquity.
Although the transition from foraging to farming in the Southwest may have happened earlier than experts believed, it also may have taken much longer than in other parts of the world.
Experts said it may have taken as long as 6,000 years in Mexico and the Southwest to go from the first appearance of domesticated plants to the widespread adoption of farming, compared to about 4,000 years in eastern North America and about 3,000 years in the Near East.
"In spite of continuing attempts at simple global explanations for the development of agriculture--such as climatic change, population pressure, El Nino or the need for feasting foods--it is increasingly evident that societies in different world areas followed diverse developmental pathways leading toward agriculture," said Smith at the Museum of Natural History.
Archeologists first mapped the site in the 1960s, but assumed that like many other villages in the Southwest, it was of relatively recent vintage.
It was not until decades later, when Roney hiked the steep hill overlooking the flood plain of the Rio Casa Grandes in search of prehistoric roads, that anyone realized its significance.
"I was astounded by what I saw," Roney said.
Spreading around him was a complex of 468 arc-shaped terraces, known as trincheras, constructed of black basalt cobbles piled into berms 20 feet wide and 4 feet high. There were an additional 100 rock rings. In all, the site's inhabitants had moved about 20,000 metric tons of stone, taking about 16 man-years of effort--a construction task equal to building a 141-room pueblo.
Amid the tumbled boulders, Roney found hundreds of spear points, basalt bowls, stone pipes and utensils that indicated that the site was dramatically older than anyone had suspected. The presence of almost 600 grinding tools was evidence that the milling of grain and seeds was a major activity. Among the crops grown was amaranth, or "pig weed."
Indeed, when Roney first raised the question of the site's age at professional meetings, "he was met with disbelief, including from me," Hard recalled.
Subsequent excavation and sophisticated radiocarbon dating carried out by experts at the University of Colorado confirmed Roney's initial judgment. That data led to today's publication in Science.
"It is rare in your career that you find something totally unexpected and that is what this was," Roney said, "something completely outside your preconceptions."