As one of the world's most important crops, maize (corn) needs little introduction. What is less well appreciated is the story of its remarkable transformation (Figure 1). Genetic data point to the tropical Balsas river valley in Mexico as the site where maize (Zea mays ssp. mays) was domesticated from teosinte (Zea mays ssp. parviglumis) (Matsuoka et al., 2002; van Heerwaarden et al., 2011). Archeological data support this location and also suggest that squash may have been domesticated at the same time (Piperno et al., 2009). Some think maize was first collected for the fermentable sugars in its stalk (Iltis, 2000; Smalley and Blake, 2003), but more likely it was for the storable starch in its seed.

The word teosinte is derived from ‘teocintli’—‘teotl’ meaning sacred and ‘cintli’ meaning dried ear of corn—from the indigenous Nahuatl language. We use the word teosinte to refer to all the wild species of Zea that are native to Mexico and Central America. Teosinte sows its seeds widely. In addition to dispersing pollen in the wind, the kernels fall from the plant and, if eaten, are carried to other locations in fecal matter, thanks to the indigestible fruitcase (see Box 1 for a glossary of specialist terms used in this article). The domestication of maize kept the wind-born pollen of teosinte, but changed other traits, improving its utility for human consumption (Doebley, 2004). The teosinte fruitcase, full of silica and lignin, became softer (Figure 1C), allowing humans to grind its kernels for food. The branch holding the kernels (cob) grew in girth, increasing the kernel row number from 2 to 20, or more (Figure 1D). Kernels no longer self-dispersed but were held tight on the cob, requiring the intervention of humans to sow seeds. Finally, the long branches shortened, but kept the leaves along the branch. These ‘husk leaves’ keep birds, insects and other pests from eating the kernels.

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