Cultivation of Corn not as Long Ago as Initially Thought (3/22/2007)

Colored Maize Photo courtesy: www.flickr.com/photos/jbc16/

An LSU researcher and a Mexican colleague have made a groundbreaking discovery about one of the world’s most important crops, corn.

According to findings by LSU Assistant Professor of Geography and Anthropology Andrew Sluyter and Mexican plant ecologist Gabriela Dominguez, cultivation of corn (or, as it is known outside of North America, maize) in Mexico’s Gulf Coast began around 5,000 years ago, rather than the 7,000 years ago that previous research had suggested.

The results of Sluyter and Dominguez’s research were recently published in the Proceedings of the National Academy of Sciences, one of the most widely read and cited multidisciplinary journals.

In order to determine a time frame for the cultivation of corn, Sluyter and Dominguez analyzed pollen grains found in lake sediments near the port of Veracruz, Mexico. Their dating re-establishes the Southern Highland region of Mexico, near Tehuacan and Oaxaca, as home to the oldest known remains of domesticated corn.

Sluyter explained that this information about the crop’s history is important because corn is one of the most widely distributed crops in the world and is used in the manufacturing of a number of products besides food. It’s also important, he said, because its origin is mysterious and has been hotly debated.

“Corn is one of the most important crops in the world, yet, oddly, we don’t really know much about where it came from, compared to other domesticates such as wheat,” he said.

Sluyter added that, while scientists know some of the wild plant “ancestors” of corn and that the crop was first cultivated in Mexico, the exact location and time of its appearance in the country have been difficult to pin down. Years ago, ancient cob remains were found in the Southern Highland region, leading to speculation that the area might have been the “birthplace” of domesticated corn. However, more recent research on pollen found in the Gulf Coast plain of the state of Tabasco suggested that maize there was around 7,000 years old, shifting the search for maize origins to the lowlands.

According to the opening of Sluyter and Dominguez’s paper on their research, “a sedimentary pollen sequence from the coastal plain of Veracruz, Mexico, demonstrates maize cultivation by 5,000 years ago, refining understanding of the geography of early maize cultivation.” The pollen sequence examined by Sluyter and Dominguez is similar to the pollen sequence from Tabasco, but the duo used a newer, more rigorous dating methodology.

Thus, their findings show that “the inception of maize cultivation ... occurred as much as 1,000 to 2,000 years more recently” in the lowlands than the previously claimed 7,000 years ago. This means that the corn cobs found in the highland regions of Mexico remain the oldest known direct evidence of the crop.

Sluyter said that geographers tend to be interested in how people change environments over time, so he first began researching Mexico while investigating how the Gulf Coast lowlands had been altered since the introduction of cattle by Europeans. He eventually wrote a book on that research that won the 2004 CAPE James M. Blaut Award from the Association of American Geographers, and his interest in the area remained strong.

He began working with Dominguez, who, at the time, was at the University of Texas at Austin. Together, they began examining the “natural archives” of the area: sediments found at the bottoms of lakes that contain the layered pollen produced by plants in the surrounding area. This allowed them to “look back in time” at how vegetation has changed over the millennia due to various forms of human impacts, including clearing forests for maize farming beginning 5,000 years ago.

Sluyter said that their research “clarified” how pollen (including corn pollen) from lake beds can be dated. He said that they showed that using radiocarbon dating on tiny grains of pollen from lake beds is more precise than dating associated pieces of wood, as was done in the Tabasco study.

“Dating precision has been overstated in the past,” he said, adding that the best current method is to date the pollen grains themselves, as he and Dominguez did.

Note: This story has been adapted from a news release issued by the Louisiana State University

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