In a study that compared the genes of corn cobs recovered in Mexico and the southwestern United States, researchers found that three key genetic variants were systematically enhanced, probably through selective cultivation, over thousands of years. The technique was not as sophisticated as the methods used for modern genetically modified crops, but experts said that the general effect was the same: genetic traits were amplified or introduced to create plants with improved traits and greater yield.
     The ancestral plant of corn, teosinte, was first domesticated some 6,000 to 9,000 years ago in the Balsas River Valley of southern Mexico, the researchers said. By cultivating plants with desirable characteristics, farmers caused teosinte to morph into an increasingly useful crop. The researchers said by 5,500 years ago the size of the kernels was larger. By 4,400 years ago, all of the gene variants found in modern corn were present in crops grown in Mexico. The plant and its grain were so changed by the directed cultivation that it evolved into a form that could not grow in the wild and was dependent on farmers to survive from generation to generation, the study found.
     Fedoroff, a plant geneticist who was not part of the research team, said the study shows that it is unlikely the changes in corn were by chance. The early farmers, she said, "might have been more sophisticated than we think. The differences between maize (corn) and teosinte come down to just a few genes, but with big effect," said Fedoroff. She also said ancient farmers probably spotted these differences and then planted seeds from those cobs to encourage the improvements to continue.
     "They might have collected the seeds and may have known that if they grew them close together then they could catch (the beneficial changes) in the next generation," she said. "It was like someone found the right combination and it was so much better that people shared it with their friends and relatives and then it got widely propagated."

Sources: MSNBC News, Associated Press (13 November 2003), The Scientist (14 November 2003)