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K. Kris Hirst

Earliest Corn Domestication

By March 24, 2009

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An astonishing discovery in the Rio Balsas region of Mexico has pushed the domestication of corn—or rather, American corn or maize—back to at least 7,000 BC. Maize (Zea mays—and decidedly not teosinte) starch granules and opal phytoliths from squash dated to more than 9,000 years ago have been found in a rockshelter in the Rio Balsas valley of Mexico, where teosinte is believed to have originated. The new findings were reported in the March 23 issue of the Proceedings of the National Academy of Sciences by a team led by Dolores Piperno.

Teosinte at the Jardín Etnobotánico in Oaxaca City, Oaxaca
Teosinte at the Jardín Etnobotánico in Oaxaca City, Oaxaca. Photo by
Jerry Friedman

At a rockshelter site called Xihuatoxtla in the state of Guerrero, five stratified layers contain occupational debris between 1000 and 9000 cal BP, or between about 7000 BC and AD 1000. Each of the layers contain millstones or hand stones and the majority of those stones—including the Archaic and Paleoindian layers—had either starch granules from domesticated maize and/or phytoliths from domesticated squash (cucurbits).

The squash and maize are on stone tools and in the sediment layers of even the lowest layer, which includes a Pedernales point base and another lanceolate point, clearly an Early Archaic or Paleoindian occupation. Before the discoveries at Xihuatoxtla shelter, the earliest maize was noted at Archaic period Guila Naquitz (5400 RCYBP) and Coxcatlan Cave (5960 BC).

What this all means

First of all, its important to note that the starch is from domesticated Zea mays, not the wild form of teosinte (Zea mays spp. parviglumis) thought to be its progenitor. Interestingly enough, teosinte is thought to be native to the Rio Balsas valley—so the Xihuatoxtla rockshelter could well be near the location of the first domestication of corn, which had to have taken place before 9,000 BP.

Further, the discovery of domestic corn and squash in Paleoindian/Early Archaic settings suggests that we need to seriously rethink our ideas of what a "typical" hunter-gatherer lifestyle is. The notion that hunter-gatherers only collect or at most tend to stands of crops is clearly no longer viable with this discovery.

Sources and Further Information

Piperno, Dolores R., et al. 2009 Starch grain and phytolith evidence for early ninth millennium B.P. maize from the Central Balsas River Valley, Mexico. Proceedings of the National Academy of Sciences 106:5019-5024.

Ranere, Anthony J., et al. 2009 The cultural and chronological context of early Holocene maize and squash domestication in the Central Balsas River Valley, Mexico. Proceedings of the National Academy of Sciences 106:5014-5018.

Comments

March 30, 2009 at 7:29 pm
(1) Richard A. Diehl says:

This is not unexpected but is an important discovery. When I wen to school they did not even talk about starch grains.

Dick

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