Prehistoric Farming.(origin of maize)

The maize that will soon be piled high on Thanksgiving tables throughout the United States is a thoroughly human invention. It started as teosinte, a wild grass with clusters of puny kernels. From each autumn harvest, ancient Mexicans put aside the biggest kernels for planting in the spring. Each year the crop's kernels got a bit bigger, until--at the hand of humans, rather than natural selection--teosinte gradually "evolved" into the magnificently fat, yellow cobs we now take so much for granted.

Scientists have long assumed that this process took place gradually, perhaps over thousands of years. When geneticist Svante Paabo in Leipzig, Germany, turned the tools of genetic analysis to this ancient question, though, he got a surprise. His study of maize samples from the Balsas River Valley in southern Mexico, published last week in the journal Science, reveals that modern maize appeared on the scene far earlier than scientists had thought--perhaps as early as 9,000 years ago, almost 3,000 years before the earliest archeological evidence. The findings suggest that ancient humans were capable of causing rapid and decisive changes in the genetic makeup of staple crops, even without the tools of modern genetics. And they raise the ...