Ancient Agriculture: Maize
By Keith Weller, USDA - This image was released by the Agricultural Research Service, the research agency of the United States Department of Agriculture, with the ID K7743-13 (next)., Public Domain, https://commons.wikimedia.org/w/index.php?curid=185217
Maize, or corn, is a type of annual grass from the New World that has a single stem with long, narrow leaves that grow from joints in the stem. While it is part of the Poaceae family, along with wheat and rice, it is not in the same clade, being in the PACMAD clade rather than the BOP clade. It has separate male and female flowers that grow at different parts on the same stem, with the male flowers being at the top of the stem and the female flowers, which resembles silk strands, being lower down, and the pollen is carried by the wind. The kernels are firmly connected to the ear, enveloped by a leafy husk. The kernels are typically yellow or white in modern varieties, but older varieties can be orange, red, brown, purple, blue, or even black, and are arranged in from 8 to 32 rows and a cob can hold up to 1200 grains. It is a short-day flowering plant, so it tends to be ready to harvest in the autumn, though modern cultivars also allow it to be grown in the tropics, where the days don't change length as much as in higher latitudes, though these don't perform well at higher latitudes.
By John Doebley - Genetically Modified Corn— Environmental Benefits and Risks Gewin V PLoS Biology Vol. 1, No. 1, e8 doi:10.1371/journal.pbio.0000008 Jornual Pbio, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=2509509
Maize was domesticated in southern Mexico about 9000 years ago, with the oldest evidence being in the Mexican highlands. It was developed from a form of teosinte that grew wild in the area, which dropped its kernels, with those that didn't release their kernels. These earliest plants only grew a single, small ear per plant, but gradually was bread to produce larger and more ears per stalk.
By Juan Carlos Fonseca Mata - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=81224187
It spread into the lowlands and then all over the Americas from the Balsas River basin. It likely reached the highlands of modern day Ecuador about 8000 years ago and the lowlands of Central America about 7600 years ago. Pollen was found in an Olmec site known as San Andres, Tabasco on the Caribbean coast of Mexico. The oldest ears were found in the Coxcatlan Cave near Tehuacán, Puebla, Mexico, which date to about 4700 years ago. These cobs were between 'halfway between maize and teosinte—corncobs the size of a cigarette filter' and represents 'Balsas teosinte', the predecessor to modern day maize.
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Among the Aztec, a process known as nixtamalization was used to process maize and other grains. In this process, maize is soaked, or cooked in and alkali limewater, then washed and the husk removed. This improves the nutritional value by making niacin and tryptophan, aroma, flavor, while reducing mycotoxins from molds that might be on the maize. The tryptophan in maize is unavailable to humans without nixtamalization and it is critical for the creation of niacin in the human body. Maize and beans were often cultivated together and nutritionally, these two foods provide all the amino acids that humans need to avoid diseases like pellagra from niacin deficiency or kwashiorkor from protein deficiency. It also makes it easier to grind the dried grains into a flour that will create a dough when water is added, unlike cornmeal from untreated maize. It's uncertain when this technique was developed, but the earliest evidence dates back to about 1500 BCE along Guatamala's southern coast.
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Current theories suggest that the technique was developed from the technique of using stones that had been placed in a fire and then were placed in a pot of water to boil it known as a pot boiler or cooking stone for cooking vessels that were unable to be either suspended over or placed in fires. This would have brought some ashes into the water as well as likely heated limestone, which would make the water alkaline.
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Around 4500 years ago, maize began to move north with it be in cultivated in modern day New Mexico and Arizona around 4100 years ago. It took until the first millennium CE for it to spread more widely through North America with large scale agriculture beginning around 900 CE. At this time, there was a decline in fresh water mussels in the southeastern United States. Forests and grasslands were cleared for maize cultivation, perhaps as a replacement for muscles.
