Maize (Zea mays) is a plant of enormous modern-day economic importance as foodstuff and alternative energy source. Scholars agree that maize was domesticated from the plant teosinte (Zea mays spp. parviglumis) in central America at least as early 9,000 years ago. In the Americas, maize is called corn, somewhat confusingly for the rest of the English-speaking world, where 'corn' refers to the seeds of any grain, including barley, wheat or rye.

The process of maize domestication radically changed it from its origins. The seeds of wild teosinte are encased in hard shells and arranged on a spike with five to seven rows that shatter when ripe to disperse its seed. Modern maize has hundreds of exposed kernels attached to a cob which is completely covered by husks and cannot reproduce on its own. The morphological change is among the most divergent of speciation known on the planet, and it is only recent genetic studies that have proven the connection.

The earliest undisputed domesticated maize cobs are from Guila Naquitz cave in Guerrero, Mexico, dated about 4280-4210 cal BC. Starch grains from domesticated maize have been found in the Xihuatoxtla Shelter, in the Rio Balsas valley of Guerrero, dated to ~9,000 cal BP.

Theories of Maize Domestication

Scientists have put forward two main theories about the rise of maize. The teosinte model argues that maize is a genetic mutation direct from teosinte in the lowlands of Guatemala. The hybrid origin model states that maize originated in the Mexican highlands as a hybrid of diploid perennial teosinte and early-stage domesticated maize.

Eubanks has suggested a parallel development within the Mesoamerican interaction sphere between lowland and highland. Recently starch grain evidence has been discovered in Panama suggesting the use of maize there by 7800-7000 cal BP, and the discovery of wild teosinte growing in the Balsas river region of Mexico has lent support to that model.

The Xihuatoxtla rockshelter in the Balsas river region has been discovered to contain domesticated maize starch granules in occupation levels dated to the Paleoindian period, more than 8990 cal BP. That suggests that maize may have been domesticated by hunter-gatherers thousands of years before it became a staple of people's diets.

• See the Earliest Corn Domestication for more information on this startling news.

The Spread of Maize

Eventually, maize spread out from Mexico, probably by the diffusion of seeds along trade networks rather than migration of people. It was used in the southwestern United States by about 3200 years ago, and in eastern United States beginning about 2100 years ago. By 700 AD, maize was well established up into the Canadian shield. DNA studies suggest that purposeful selection for various traits continued throughout this period, leading to the wide variety of species today. For example, 35 different races of maize have been identified in precolumbian Peru, including popcorns, flint varieties, and varieties for specific uses, such as chicha beer, textile dyes, and flour.

As maize was spread outside of its roots in central America, it became part of already existing agricultural traditions, such as the Eastern Agricultural complex, which included pumpkin (Cucurbita sp), chenopodium and sunflower (Helianthropus).

The earliest direct-dated maize in the northeast is the 399–208 cal BC, in the Finger Lakes region of New York, at the Vinette site. Other early appearances are are Meadowcroft Rockshelter and the Thorp site in the Upper Ohio River valley of Pennsylvania (~109--372 BC); and the Schultz and 20SA1276 sites in the Saginaw River valley in Michigan (~146 BC-AD 19).

Archaeological Sites

Archaeological sites of importance to the discussion of maize domestication include

• Central America:  Xihuatoxtla Shelter (Guerrero, Mexico), Guila Naquitz (Oaxaca, Mexico) and Coxcatlan Cave (Tehuacan, Mexico)
• Southwest USA: Bat Cave (New Mexico), Gatecliff Shelter (Nevada)
• Midwest USA: Newt Kash Hollow (Tennesee)
• Northeast USA: Vinette (New York), Schultz (Michigan), Meadowcroft (Pennsylvania)

Sources

This glossary entry is a part of the About.com Guide to Plant Domestications, and part of the Dictionary of Archaeology.

A brief bibliography of the domestication of maize has been created for this project.