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Although man does not cause variability and cannot even prevent it, he can select, preserve, and accumulate the variations given to him by the hand of nature almost in any way that he chooses; and thus he can certainly produce a great result.

Charles Darwin (1868b)

With its meager ear containing only 2 entwined rows of well-armored kernels, teosinte grows on Mexican hillsides. This grass might easily have been overlooked were it not for its abundant variation, a gift not lost on early agriculturists. Within the last 10,000 years, early Native Americans were able to transform teosinte into a plant whose ears would feed the world. It was a transformation so striking and so complex that some researchers did not believe it was possible, leading to years of competing theories and intense debate. But as Darwin himself recognized, when the desires of humans meet the diversity of nature the result can indeed be astounding.

The molecular revolution of the last 2 decades has provided compelling evidence that teosinte is the progenitor of modern maize. Here, we discuss the rich genetic diversity at the source of this morphological conversion and examine how human selection has impacted this diversity. One key question concerning maize domestication remains to be resolved: Was maize domestication the result of selection on a small number of loci with large effects, a large number of loci with small effects, or both? Recent genetic evidence has provided clues about the relative contributions of large-effect and small-effect loci. We discuss how future studies will help unravel the mysteries surrounding maize domestication and how this information is key to future improvements of maize.


Maize (Poaceae) is a member of the world’s most successful family of agricultural crops, including wheat, rice, oats, sorghum, barley, and sugarcane. Maize belongs to the genus Zea, a group of annual and perennial grasses native to Mexico and Central America. The genus Zea includes wild taxa known collectively as teosinte (Zea mays ssp. parviglumis) and domesticated corn or maize (Z. mays ssp. mays).

For many years, relationships within the genus Zea were the subject of much controversy. The central difficulty in the taxonomy of maize and the identification of its closest relatives was the absence of a coblike pistillate inflorescence, or “ear,” in any other known plant. Whereas teosinte produces only 6–12 kernels in 2 interleaved rows protected by a hard outer covering (Fig. 6.1), modern maize boasts a cob consisting of as

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