The Story of Corn
Corn, also called maize (Zea mays mays), is a crop plant that originated in America. It is one of the approximately 10,000 members of the grass family (Poaceae), but it differs from the other cereal grasses in the extent to which the process of domestication altered it. These differences are so great that at one time botanists believed that the wild ancestor of maize had long been extinct. With the other cereals—wheat, barley, rye, oats, and rice—there are wild plants that closely resemble the domesticated crop plants. Indeed, wild oats (Avena fatua), which closely resemble cultivated oats (A. sativa) in appearance, are a troublesome weed of cereal crops. Corn is different. Its wild ancestor still thrives, but it looks so different from cultivated corn that botanists formerly placed the two plants in different genera.
Corn is the domesticated form of teosinte, a name derived from teocintli, which means “grain of the gods” in the language of the Nahuatl people of Central America. There are five species of teosinte grasses found in Mexico and Guatemala, some of them annual and others perennial—an annual plant completes its life cycle, from germination to releasing seeds, in a single year; a perennial plant lives for more than two years and flowers annually after an initial period during which it may not flower at all. Corn is descended from one of the annual species, Zea mays parviglumis.
Teosinte produces ears with between five and 12 kernels. The kernels are small and enclosed within hardened coatings that protect them from animals that might eat them. When the kernels ripen, the plant sheds them and the protective coatings disappear. Domestication began about 9,000 years ago in the Balsas River Valley in southern Mexico. People began cultivating teosinte, selecting the plants with the biggest ears, tough rachises, and tastiest kernels, and in time a number of mutations occurred that made the mutated plants still more attractive, so those were the ones that were grown. The wild and cultivated forms continued to interbreed—and cultivated corn and wild teosinte are still capable of interbreeding—but the changes continued to accumulate. Modern corn has an ear with several hundred kernels that lack any protective outer coating or any means of releasing and dispersing the seeds. The crop is wholly dependent on humans for its survival.
From Mexico, corn cultivation spread by several routes into North and South America. One route led from the Mexican uplands across the highlands of Panama and into the Andes on the western side of South America. Another began in the Central American lowlands, spread into the coastal regions of northeastern South America, and spread from there into the continental interior along the river valleys. People were growing corn in northern South America about 4,500 years ago, but it was not until about 1,500 years ago that farming became established in Chile. Farming also expanded northward, reaching the southwestern region of North America between about 2,500 and 2,000 years ago. Once established there, the cultivation of corn provided the dietary and economic stability that led to the development of the Pueblo cultures of the Southwest.
- The Story of Rice
- The Story of Wheat
- The Origins of Agriculture
- Carl Skottsberg and the Plants of Southern South America
- August Grisebach and Floral Provinces
- Edward Forbes and the Significance of Ice Ages
- Alphonse de Candolle and Why Plants Grow Where They Do
- Franz Meyen and Vegetation Regions
- Karl Ludwig von Willdenow and the Start of Scientific Plant Geography