By Norman Hammond
Archaeology Correspondent

New evidence from Mexico and Panama has shown that agriculture in the Americas began around 7,000 years ago with the domestication of maize. The process seems to have taken place in the lowland humid tropics, not in the drier highland zone.

When the Spanish arrived in the New World, maize was the sole cereal crop, a staple that supported village societies and civilisations over the vast area of the United States to Chile. It was comparable in its cultural importance to the wheat and barley which underpinned the early civilisations of Mesopotamia and Egypt.

The botanical origins of maize, and hence its initial domestication by humans, were thought to lie in Mexico. Forty years ago, the late Richard “Scotty” MacNeish showed that maize was being grown in the highland valley of Tehuacan at a date he estimated to be around 5,500 BC, but recent radiocarbon dating of his finds had brought that figure down by two millennia, to around 3,600 BC.

Finds form the Gulf Coast of Mexico, near the city of Villahermosa, from the valley of Oaxaca to the Panama Canal, much further east, all now suggest that MacNeish’s date was close to the truth. Farming also seems to have spread through tropical America well before permanent villages were established, let alone the first civilisations, with an informal network of communication which would one day harden into trade routes for minerals and finished goods.

On the Gulf Coast, pollen evidence suggests that forest was being cleared around 5,100 BC, and domesticated maize plants were being grown only a century later, according to Kevin Pope and his colleagues. Speaking at the Society for American Archaeology in New Orleans, Dr Pope said that the San Andres site near the famous Olmec centre of La Venta showed that maize had been introduced and grown in a region of beaches and lagoons.

The combination of fertile soils and easily harvested protein such as fish and water birds made the area attractive, and evidence for the cultivation of cassava (manioc), a carbohydrate- rich root crop, appeared only a few centuries after the first maize. Cassava is thought to have originated in the Amazon-Orinoco region of South America and spread northwards to Mexico.

Coincidentally, new radiocarbon dates from old excavations in the Valley of Oaxaca, 160 miles to the southwest but several thousand feet higher up, show that maize farming spread rapidly into the Mexican highlands. Dolores Piperno and Kent Flannery report in the Proceedings of the National Academy of Sciences that direct dating of corn-cobs excavated by Flannery, at the cave of Guila Naquitz 30 years ago, shows them to date to around 4,300 BC.

This is some 700 years older than the new dates for MacNeish’s early corn in the San Marcos and Coxcatlan Caves, at a still higher altitude in the Tehuacan Valley, and suggests that farming developed in the resource-rich tropical lowlands as part of a mixed economy that included fishing, hunting and gathering. Spreading to the highlands gradually as domesticated maize, one of the most genetically plastic crops, adapted to higher and drier climes.

Movement of maize south-east to Panama and into South America, perhaps along the same routes that took cassava northwest to Mexico, has also been documented by Dr Piperno and her colleagues, by identifying phytoliths, tiny opal crystals that form in the cell tissue of plants, which enable species to be identified.

Phytoliths were identified in sediments at the Aguadulce rock shelter in Panama, and both phytoliths and starch grains from maize were recovered from grinding tools dating 5,000-3,000 BC. In a striking piece of parallel research, maize phytoliths were recovered from tartar deposits on the teeth of skeletons excavated at the Vegas site, near Guayaquil in coastal Ecuador, hundreds of miles to the south on the Pacific coast of South America.

“All the lines of direct, palaeobotanical evidence that can currently be brought to bear indicate that maize was initially dispersed out of Mexico into Central and South America between 5,200 and 3,000 BC,” Dr Piperno and her colleagues conclude.