Domestication of maize
A weedy grass with tiny ears becomes the world's top grain
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About 9,000 years ago, farmers in southern Mexico began selecting seeds of teosinte, a wild grass whose ears held only a handful of kernels. Millennia of selection turned it into maize, which fed the Olmec, Maya, Aztecs and Inca. After Columbus it spread worldwide, and today it is the most-harvested grain on Earth.