Maize

Before there was maize there was teosinte, a bushy wild grass with many long branches, each tipped by a tassel.62,4 One kind, Balsas teosinte, grows on the Pacific slope of Mexico from Nayarit to Oaxaca, between 150 and 1,950 meters above the sea.63

Its ear is a slender spike of 5 to 12 kernels, each locked inside a hard, stony case. When the ear ripens it shatters and the cases scatter.3,4 Little about it looks like food. Yet every maize plant on Earth descends from this grass.1,2

About 9,000 years ago, Indigenous people in what is now southern Mexico began turning teosinte into a crop. The DNA of living maize traces back to a single domestication, and the wild populations closest to maize still grow here, in the central Balsas valley. 11,9

The oldest physical trace is microscopic. At Xihuatoxtla, a rock shelter near Iguala, stone grinding tools carry maize starch grains and phytoliths (tiny silica bodies that form inside plants) in layers about 8,700 years old.19,20 The phytoliths come from cobs, not stalks. People were already after the ear.19

Turning teosinte into maize meant rebuilding it. Many branches became one stalk. Two ranks of single kernels became many rows of paired ones. A spike that shattered became a cob that holds its grain. 62,44,8

Two genes did much of this. One, tb1, holds back side branches, and maize carries a version about twice as active as teosinte's.65,62 The other, tga1, differs by a single amino acid, enough to open the hard case and leave the kernel bare.3,66

Neither was a lucky new mutation. Both variants already existed, rarely, in wild teosinte long before farming, and farmers made them universal. 6267

Maize left Mexico before it was finished. Starch on stone tools puts it in Panama by 7,800 to 7,000 years ago, and it entered South America between about 7,000 and 6,500 years ago. 25,2626,55

On the coast of Peru, small eight-rowed cobs are dated to about 6,700 years ago. In the Bolivian Amazon, cob phytoliths are just as old. 3031 This early maize was still only partly domesticated. South American farmers finished the work themselves, perhaps around southwestern Amazonia, and their maize later flowed back north. 26,552655

It became a staple food on the Peruvian coast by 5,000 to 4,500 years ago, and in the Maya lowlands by 4,000 years ago. 7028

The oldest maize cobs yet dated directly were left in Guilá Naquitz, a cave in the highlands of Oaxaca, about 6,250 years ago.21,8 (The Peruvian cobs of the last chapter take their older date from a husk found with them, not from a cob.) They are about 2.5 centimeters long, with two or four rows of grain. But the cob is rigid. These ears did not shatter, so someone had to pull off the grain and plant it. 21,84,7,8

Older layers of the cave hold no maize at all. The crop was domesticated somewhere else and carried here.21

Cobs about 5,300 years old from San Marcos cave, in the Tehuacán Valley, have yielded DNA. It shows a plant caught mid-change, with some key genes already in their maize form and others still wild. 22,23,2424,23

As maize climbed into the cool highlands of central Mexico it met another teosinte, subspecies mexicana, which grows wild above about 1,500 meters. The two crossed, and highland maize still carries about a fifth of its ancestry from that wild cousin. 639,71

For years this looked like a local detail. Then a 2023 study of more than a thousand genomes found highland teosinte in every modern maize it tested: 15 to 25% of the genome, about 18% on average.10 The mixing happened roughly 6,000 to 4,000 years ago, and the mixed maize then spread across the Americas.10

Maize still began once, in the Balsas valley. But it has two wild ancestors, and the second helped shape the ear. 1,910

Maize had reached what is now Arizona and New Mexico by about 2100 BCE.33,34 Ancient DNA points to a route through the western highlands, with coastal maize mixing in later, though the archaeology cannot yet settle the path.34 It then took some 2,000 more years to adapt to the short summers farther north.35

Eastern maize descends from this southwestern stock, but when it arrived is disputed. Microscopic residues on pottery suggest New York by about 2,300 years ago. Re-dated kernels suggest nothing before about 900 CE. 1,5537,38,39,40 What is clear is that around 900 CE maize farming took off along the Mississippi and fed the rise of the city of Cahokia.36

Growing maize was only half the knowledge. Across the Americas, Indigenous cooks learned to simmer the grain with lime or wood ash. The process, nixtamalization, adds calcium and makes maize a food people can live on.43,74 Maya pottery suggests it was in use by 1000 to 800 BCE.75

When maize later traveled the world without that knowledge, the disease pellagra followed it, from Spain in the 1700s to the American South in the 1900s.76,43,77

The plant runs as deep in belief as in diet. In the Popol Vuh of the K'iche' Maya, the first true people are shaped from yellow and white maize.78 And domestication has never stopped. Mexico has 59 native races of maize, kept alive and still changing in the fields of smallholder farmers. 16,1717

In November 1492, men sent inland by Columbus in Cuba came back describing fields of an unfamiliar grain.79 It was not new there. Starch on stone tools hints at maize in the Antilles as early as 3000 BCE.80 A year later a letter by the scholar Peter Martyr gave Europe its name, borrowed from the Taíno: maiz. 44,4512 By 1498 Columbus could write that much of it was growing in Castile.45,46,47

It moved fast, and its origin was quickly forgotten. Painted ears hang among the fruit on the walls of a Roman villa by 1519.48,47 In 1542 the botanist Leonhart Fuchs printed the plant's portrait and called it Turkish grain, sure it came from Asia. 49,4646 Europe in fact received it at least twice, from the Caribbean and from eastern North America.47,56

By the mid-1500s it was growing on the coast of West Africa, and written records place it in Iraq, India and China before 1600. 45,50,5145,52

For seventy years, American corn yields did not move. From 1866 to 1936 they averaged about 26 bushels an acre.82,83 The change began in 1908, when George Shull showed that crossing two inbred lines gives vigorous, uniform offspring. A cheaper method, the double cross, followed in 1917–18.83,54

Henry A. Wallace sold the first commercial hybrid seed in the mid-1920s.83,54 Adoption, when it came, was abrupt. In Iowa, hybrids covered 6% of corn land in 1935 and 90% in 1940.53,54

Yields have climbed ever since, to a record 186.5 bushels an acre in 2025, about seven times the old average.82,83 The dent corn these hybrids were bred from was itself young: a 19th-century cross of southern dents and northern flints.47

In 1939 two theories of maize's origin went into print. The geneticist George Beadle argued that maize is domesticated teosinte, changed by four or five major genes.84,2,85 Paul Mangelsdorf and Robert Reeves argued that its ancestor was a wild maize, since vanished, and that teosinte was only a hybrid.84,86

The second theory held the textbooks for decades, though it never won over the geneticists.84 After retiring in 1968, Beadle returned to the question. He grew some 50,000 hybrid plants and found that about 1 in 500 looked like each parent, as his idea predicted.84,2,4

DNA settled it. Since the 1980s molecular studies have pointed to teosinte, and in 2002 one traced all maize to a single domestication of the Balsas subspecies. 84,871,2

The world grew 1.22 billion metric tons of maize in 2024, more than any other cereal.5,6 Two countries, the United States and China, grew more than half of it.5,6

Most of it is not eaten by people. Worldwide, 56% is fed to animals and 13% is food, and in the United States about 40% of the crop becomes fuel. 66 In Africa more than half is eaten directly, and white maize is the daily staple of eastern and southern Africa and of Central America. 688

All of it still rests on choices first made in the Balsas valley. A maize ear cannot scatter its own seed. The plant that feeds much of the world exists only as long as people keep planting it.4,7,8