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And
only
Norte Chico. For the next four thousand years, Andean civilization was influenced by only one major import from the world outside: maize. A few other minor crops made the trip later, including tobacco, domesticated in Amazonia, then exported north to become the favorite vice of Indians from Mesoamerica to Maine. But it is a mark of maize’s social, cultural, and even political centrality that it was the first—and for centuries the only—phenomenon to pass from Mexico to the Andes. The next major import, alas, was smallpox.

TINY COBS

Although it was just after dawn, several people were already waiting outside the small store. When the metal grating rolled up, I followed them inside. The shop was in a middle-class neighborhood of Oaxaca city, in southern Mexico. Behind the low counter, half a dozen women hovered over waist-high stoves made of concrete block. Recessed into the dome-shaped top of each stove were two shallow clay dishes that served as burners. With expert motions the women slipped tortillas—thin discs of cream-colored flour perhaps nine inches in diameter—onto the hot burners. In seconds the tortilla dried and puffed up like a soufflé. And from the storefront floated the aroma of toasting maize, which has permeated Mexico and Central America for thousands of years.

Established in 2001, the tortilla store is an innovative attempt to preserve one of earth’s greatest cultural and biological assets: the many local varieties of maize in the narrow “waist” of southern Mexico. The isthmus is a medley of mountains, beaches, wet tropical forests, and dry savannas, and is the most ecologically diverse area in Mesoamerica. “Some parts of Oaxaca go up nine thousand feet,” T. Boone Hallberg, a botanist at the Oaxaca Institute of Technology, told me. “Other parts are at sea level. Sometimes the soil is very acid, sometimes it’s quite basic—all within a few hundred feet. You can go on either side of a highway, and the climate will be different on the east side than on the west side.” The area’s human geography is equally diverse: it is the home of more than a dozen major Indian groups, who have a long and fractious history. Despite the strife among them, all of them played a role in the region’s greatest achievement, the development of Mesoamerican agriculture, arguably the world’s most ecologically savvy form of farming, and of its centerpiece,
Zea mays,
the crop known to agronomists as maize.

I was visiting Amado Ramírez Leyva, the entrepreneur behind the tortilla store. Born in Oaxaca and trained as an agronomist, Ramírez Leyva had established a consortium of traditional farmers, Indians like himself (Ramírez Leyva is Ñudzahui [Mixtec], the second most numerous Indian group in the region). The farmers supply eight different varieties of dried maize to his shop, Itanoní, where the kernels are carefully ground, hand-pressed into tortillas, and cooked fresh for customers. Itanoní means “maize flower” in Ñudzahui, and refers to a flower that blooms in maize fields. It is one of the few tortillerías in Mexico—perhaps even the only one—to sell what might be described as “estate” tortillas: proudly labeled as being made from maize of one variety, from one area.

“Everyone in Mexico knows the rules for making a true tortilla,” Ramírez Leyva told me. “But you can’t get them that way now, except maybe in your grandmother’s kitchen.” First soak the dried maize kernels in a bath of lime and water to remove their thin, translucent skins (a process with its own special verb,
nixtamalizar
). Then stone-grind the kernels into
masa,
a light, slightly sticky paste with a distinct maize fragrance. Made without salt, spices, leavening, or preservatives,
masa
must be cooked within a few hours of being ground, and the tortilla should be eaten soon after it is cooked. Hot is best, perhaps folded over with mushrooms or cheese in a
tlacoyo.
Like a glass of wine, he said, a tortilla should carry the flavor of its native place. “You want to try some?”

 

A gourmet tortilla shop in Oaxaca, Itanoní is an attempt to preserve southern Mexico’s hundreds of varieties of maize, a Mesoamerican tradition that has survived for thousands of years.

 

I did. The smells in the shop—dry-toasted maize, melting farm cheese, squash flowers sautéing in home-pressed oil—were causing my stomach to direct urgent messages to my brain.

Ramírez Leyva gave me a plateful of
tlacoyos.
“This is exactly what you would have eaten here ten thousand years ago,” he said.

In his enthusiasm, he was overstating, but not by much. Indians didn’t have cheese, for one thing. And they didn’t eat tortillas ten thousand years ago, though tortillas are indeed ancient. It is known that 11,500 years ago paleo-Indians were hunting from caves in what is now Puebla, the state northwest of Oaxaca. These were not mastodon and mammoth hunters—both species were already extinct. Instead they preyed on deer, horse, antelope, jackrabbit, and, now and then, giant turtle, as well as several species of rodent. Within the next two thousand years all of these animals except deer vanished, too, done in either by a local variant of overkill, the onset of hotter, drier conditions that shrank the available grassland, or both. Responding to the lack of game, people in Oaxaca and Puebla focused more on gathering. Shifting among productive locations, individual families, living on their own, ate seeds and fruit during the spring and fall and hunted during the winter. During the summer they joined together in bands of twenty-five to thirty—cactus leaves, a local favorite, were plentiful enough in that season to support larger groups.

All the while their store of knowledge about the environment increased. People learned how to make agave plants edible (roast them), how to remove the tannic acid from acorns (grind them to a powder, then soak), how to make tongs to pick spiny cactus fruit, how to find wild squash flowers in the undergrowth, and other useful things. Along the way, perhaps, they noticed that seeds thrown in the garbage one year would sprout spontaneously in the next. The sum of these questions led to full-fledged agriculture—not just in the Tehuacán Valley, but in many places in southern Mexico. Squashes, gourds, peppers, and chupandilla plums were among the initial crops. The first cereal was probably millet—not the millet eaten today, which originated in Africa, but a cousin species, knotweed bristle-grass, which is no longer farmed. And then came maize.

At the DNA level, all the major cereals—wheat, rice, maize, millet, barley, and so on—are surprisingly alike. But despite their genetic similarity, maize looks and acts different from the rest. It is like the one redheaded early riser in a family of dark-haired night owls. Left untended, other cereals are capable of propagating themselves. Because maize kernels are wrapped inside a tough husk, human beings must sow the species—it essentially cannot reproduce on its own. The uncultivated ancestors of other cereals resemble their domesticated descendants. People can and do eat their grain; in the Middle East, for example, the wild barley harvest from a small piece of land can feed a family. By contrast, no wild maize ancestor has ever been found, despite decades of search. Maize’s closest relative is a mountain grass called teosinte that looks nothing like it (teosinte splits into many thin stems, whereas maize has a single thick stalk). And teosinte, unlike wild wheat and rice, is not a practical food source; its “ears” are scarcely an inch long and consist of seven to twelve hard, woody seeds. An entire ear of teosinte has less nutritional value than a single kernel of modern maize.

The grain in wild grasses develops near the top of the stem. As it matures, the stem slowly breaks up—shatters, in the jargon—letting the seed dribble to the ground. In wild wheat and barley, a common single-gene mutation blocks shattering. For the plant the change is highly disadvantageous, but it facilitates harvest by humans—the grain waits on the stem to be collected. The discovery and planting of nonshattering grain is thought to have precipitated the Neolithic revolution in the Middle East. Like other grasses, teosinte shatters, but there is no known nonshattering variant. (At least sixteen genes control teosinte and maize shattering, a situation so complex that geneticists have effectively thrown up their hands after trying to explain how a nonshattering type might have appeared spontaneously.) No known wild ancestor, no obvious natural way to evolve a nonshattering variant, no way to propagate itself—little wonder that the Mexican National Museum of Culture claimed in a 1982 exhibition that maize “was not domesticated, but
created
”—almost from scratch.

In the 1960s Richard S. MacNeish, of Phillips Academy, in Andover, Massachusetts, led an archaeological team that meticulously combed Puebla’s Tehuacán Valley for signs of early agriculture. Like the Peruvian littoral, the Tehuacán Valley lies in a double rain shadow, sandwiched between two mountain ranges. The aridity similarly helps preserve archaeological evidence. MacNeish’s team sifted through fifty caves before they found anything. In site No. 50, a rockshelter near the village of Coxcatlán, the team found maize cobs the size of a cigarette butt.

Ultimately, MacNeish’s team found 23,607 whole or partial maize cobs in five caves in the Tehuacán Valley. This ancient refuse became ammunition in a long-running academic battle between Harvard botanist Paul C. Mangelsdorf and George Beadle, a geneticist who worked at Stanford, Caltech, and the University of Chicago. In the late 1930s both men proposed theories about the origin of maize. Mangelsdorf said that it descended from the mix of a now-vanished wild ancestor of maize and wild grasses from the genus
Tripsacum.
Teosinte, he said, played no role in its development. Beadle had a simpler theory: maize was directly descended from teosinte. Mangelsdorf treated this idea with disbelieving scorn. By now the reader will not be surprised to learn that an apparently arcane debate about the distant past could become vehemently personal. Relations between the two men became cold, then bitter, then explosive. Botanists chose sides and wrote caustic letters about each other.

Mangelsdorf worked with MacNeish and classified the 23,607 ancient maize cobs. The smallest and oldest, he proclaimed, were maize’s true wild ancestor, which Indians had then crossed with
Tripsacum
to make modern maize. So powerful did the evidence of Mangelsdorf’s tiny cobs seem that in the 1960s it buried the teosinte hypothesis, even though the latter’s champion, Beadle, had for other research won a Nobel Prize. Beadle’s ideas were taken up in revamped form by University of Wisconsin botanist Hugh Iltis in 1970. Maize originated, Iltis postulated, in a strange, wholesale mutation of teosinte, to which Indians added and subtracted features through intensive breeding. Mangelsdorf’s side found itself on the defensive; Iltis had gleefully pointed out that the “wild maize” cobs from the Tehuacán Valley were identical to those of an unusual, fully domesticated variety of popcorn from Argentina. By then the dispute over the origin of maize had filled almost as much paper—and became as acrimonious—as the battle over Clovis.

In 1997 Mary W. Eubanks, a Duke University biologist, resuscitated the hybridization theory in a new variant. Maize, she suggested, might have been created by repeatedly crossing
Zea diploperennis,
a rare maize relative, and another cousin species, Eastern gamagrass. When species from different genera hybridize, the result can be what the biologist Barbara McClintock called “genomic shock,” a wholesale reordering of DNA in which “new species can arise quite suddenly.” In Eubanks’s theory, Indians came upon a chance combination of
Zea diploperennis
and gamagrass and realized that by mixing these two species they could shape an entirely new biological entity. As proof, she announced the creation of a
Zea diploperennis–
gamagrass hybrid in the laboratory that displayed the attributes of ancient maize.

The teosinte faction remained skeptical. A consortium of twelve maize scientists harshly attacked Eubanks’s work in 2001 for, in their view, failing to demonstrate that her hybrid was actually a
Zea diploperennis–
gamagrass mix and not an accidental blend of
Zea diploperennis
and modern maize. (Such errors are a constant threat; in a busy lab, it is all too easy for biologists to use the wrong pollen, mislabel a tray, or mistake one analysis for another.) Meanwhile other geneticists pinpointed teosinte mutations that could have led to modern maize, including
sugary 1,
a variant gene that alters maize starch in a way that gives tortillas the light, flaky texture celebrated at Itanoní.

Because maize is many steps removed from teosinte, these scientists argued that the modern species had to have been consciously developed by a small group of breeders who hunted through teosinte stands for plants with desired traits. Geneticists from Rutgers University, in New Brunswick, New Jersey, estimated in 1998 that determined, aggressive, knowledgeable plant breeders—which Indians certainly were—might have been able to breed maize in as little as a decade by seeking the right teosinte mutations.