1491_ New Revelations of the Americas Before Columbus - Charles C. Mann [114]
More than fifty genetically distinguishable maize “landraces” have been identified in Mexico, of which at least thirty are native to Oaxaca, according to Flavio Aragón Cuevas, a maize researcher at the Oaxaca office of the National Institute for Forestry, Agriculture, and Fisheries Research. A landrace is a family of local varieties, each of which may have scores of “cultivars,” or cultivated varieties. As many as five thousand cultivars may exist in Mesoamerica.
Maize is open pollinated—it scatters pollen far and wide. (Wheat and rice discreetly pollinate themselves.) Because wind frequently blows pollen from one small maize field onto another, varieties are constantly mixing. “Maize is terribly promiscuous,” Hugo Perales, an agronomist at the think tank Ecosur, in Chiapas, told me. Uncontrolled, open pollination would, over time, turn the species into a single, relatively homogeneous entity. But it does not, because farmers carefully sort through the seed they will sow in the next season and generally do not choose obvious hybrids. Thus there is both a steady flow of genes among maize landraces and a force counteracting that flow. “The varieties are not like islands, carefully apart,” Perales explained. “They are more like gentle hills in a landscape—you see them, they are clearly present, but you cannot specify precisely where they start.”
San Juan Chamula, a mountain town in central Chiapas, near the border with Guatemala, is an example. Located outside the colonial city of San Cristóbal de Las Casas, it has a sixteenth-century church with a brilliant blue interior that is a popular tourist destination. But beyond the souvenir kiosks in the cathedral square, most of the 44,000 inhabitants of Chamula scratch a living from the dry mountain slopes outside town. Almost all are Tzotzil, a southwestern branch of the Maya; in 1995, the most recent date for which census data are available, about 28,000 did not speak Spanish. According to a survey by Perales, 85 percent of the farmers plant the same maize landraces as their fathers, varieties that have been passed on and maintained for generations. The crop in the field today is the sum of thousands of individual choices made by community members in the past.
Landrace maize from Oaxaca
Indian farmers grow maize in what is called a milpa. The term means “maize field,” but refers to something considerably more complex. A milpa is a field, usually but not always recently cleared, in which farmers plant a dozen crops at once, including maize, avocados, multiple varieties of squash and bean, melon, tomatoes, chilis, sweet potato, jicama (a tuber), amaranth (a grain-like plant), and mucuna (a tropical legume). In nature, wild beans and squash often grow in the same field as teosinte, the beans using the tall teosinte as a ladder to climb toward the sun; below ground, the beans’ nitrogen-fixing roots provide nutrients needed by teosinte. The milpa is an elaboration of this natural situation, unlike ordinary farms, which involve single-crop expanses of a sort rarely observed in unplowed landscapes.
Milpa crops are nutritionally and environmentally complementary. Maize lacks digestible niacin, the amino acids lysine and tryptophan, necessary to make proteins and diets with too much maize can lead to protein deficiency and pellagra, a disease caused by lack of niacin. Beans have both lysine and tryptophan, but not the amino acids cysteine and methionine, which are provided by maize. As a result, beans and maize make a nutritionally complete meal. Squashes, for their part, provide an array of vitamins; avocados, fats. The milpa, in the estimation of H. Garrison Wilkes, a maize researcher at the University of Massachusetts in Boston, “is one of the most successful human inventions ever created.”
Wilkes was referring to the ecological worries that beset modern