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A new study suggests that Mexican farmers had significantly altered the genetic makeup of maize through selective breeding as much as 4,000 years ago.

An international team of researchers analysed genes from ancient maize, modern maize and teosinte, the wild grassy ancestor of maize. They report in this week's Science that three gene variants common in modern maize also appear frequently in up to 4,000-year-old maize from Mexico.

These variants are not as common in teosinte, suggesting that early farmers bred maize selectively for specific traits.

In an accompanying article in Science, Nina Federoff from Pennsylvania State University, United States, argues that these early "genetic modifications" may have been so beneficial that they were widely adopted, "perhaps causing something of a prehistoric Green Revolution".

She concludes that "the apparent loss of genetic diversity following the introduction of high-yielding Green Revolution wheat and rice varieties in the 1960s and 1970s, and attending the rapid adoption of superior GM [genetically modified] crops today, is far from a new phenomenon".

Link to research paper in Science: Early allelic selection in maize as revealed by ancient DNA
Link to perspectives article in Science by Nina Federoff: Prehistoric GM corn

References: Science 302, 1206 (2003) / Science 302, 1158 (2003)