Corn: History and Origins

Table of Contents

1. The Plant That Should Not Have Become Corn
2. The Balsas River Valley, About 9,000 Years Ago
3. How the Argument Was Settled: tb1 and the Genetics of Maize
4. Spread Through the Americas
5. The Three Sisters
6. Nixtamalization: The Technique That Made Maize Liveable
7. Maize Crosses the Atlantic — Without the Lime
8. Pellagra: A Disease of Missing Knowledge
9. Joseph Goldberger and the Filth Parties
10. Hybrid Corn and the Yield Revolution
11. Feed, Sweeteners and Fuel
12. Corn Today: Scale, Landraces and What Was Nearly Lost
13. Research Papers and References
14. Connections
15. Featured Videos

The Plant That Should Not Have Become Corn

Put an ear of sweet corn next to a seed head of teosinte and the first reaction is disbelief. The corn ear is eight inches long, wrapped in husks, and carries perhaps 500 to 800 soft kernels in neat rows on a thick central cob. The teosinte "ear" is a slender spike about two inches long carrying five to twelve grains in a single alternating rank, and each of those grains is sealed inside a woody, triangular case called a fruitcase or cupulate fruitcase. You cannot chew it. You cannot easily grind it. Left alone, the spike shatters at maturity and scatters its cases so the seeds disperse — exactly what a wild grass ought to do, and exactly what a farmer does not want.

The whole-plant differences are just as large. Teosinte (Zea mays ssp. parviglumis) grows as a bushy, many-branched plant, each branch tipped with its own small seed spike, a form that suits a wild annual competing in a seasonal Mexican thicket. Maize grows as one dominant stalk with short lateral branches that terminate not in more foliage but in the ears themselves. In botanical terms, maize lost its branching and gained apical dominance — the main stem suppresses the side shoots — and its lateral structures were converted into food-bearing organs that cannot disperse their own seed.

That last point is worth pausing on, because it is the deepest thing about corn. Maize cannot reproduce without people. Drop a whole ear on the ground and hundreds of seedlings sprout in a clump a few inches across, choke each other, and mostly die. Every kernel is held to the cob and wrapped in husks that do not open on their own. There is no wild maize anywhere in the world and there never has been, because the plant as we know it is a human artifact that has been kept alive by continuous human planting for something like nine thousand consecutive years. The relationship runs both ways — maize made large settled populations possible in the Americas, and those populations are the only reason maize exists.

Because teosinte and maize look so unalike, the ancestry was genuinely disputed. Through the mid-twentieth century a prominent school held that maize descended from a now-extinct wild maize, with teosinte being a hybrid derivative of maize rather than its parent. The geneticist George Beadle — who shared a Nobel Prize for entirely different work on genes and enzymes — spent decades arguing the opposite, that teosinte was simply the ancestor and that a handful of genetic changes separated the two plants. He crossed the two, found the hybrids fertile, and estimated that a small number of loci accounted for most of the difference. He even parched teosinte grains until they popped, to demonstrate that the wild plant was edible enough to be worth collecting in the first place. He was right, and modern genetics has vindicated him in detail.

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The Balsas River Valley, About 9,000 Years Ago

Two independent lines of evidence converge on where and when this happened.

The genetic line came first in modern form. A 2002 study genotyped 99 microsatellite markers across a large collection of maize landraces and wild teosinte populations, and found that all maize traces back to a single domestication event from Zea mays ssp. parviglumis, with the closest wild populations living in the seasonally dry tropical forests of the central Balsas River drainage in the modern Mexican states of Guerrero and México. The estimated date landed around 9,000 years ago. Later work using far denser genomic data confirmed the same origin while adding nuance about later gene flow, particularly introgression from the highland teosinte Zea mays ssp. mexicana as maize moved up into cooler country.

The archaeological line followed. Excavations at the Xihuatoxtla rock shelter in the central Balsas valley recovered maize starch grains and phytoliths — microscopic silica bodies that form in plant tissue and survive when the tissue does not — on stone grinding tools in layers dated to roughly 8,700 years ago. Starch grains from domesticated maize differ in size and shape from teosinte's, and phytoliths from maize cobs are distinguishable from teosinte's fruitcases, so these are diagnostic rather than suggestive. The same deposits carried squash, which had been domesticated in the region even earlier. This was the first archaeological maize found in the genetically predicted homeland, and its date sat squarely on top of the genetic estimate.

Slightly younger and more famous are the tiny cobs from Guilá Naquitz cave in the Oaxaca highlands, directly dated by accelerator mass spectrometry to about 6,250 years ago. They are barely an inch long and carry two ranks of a handful of kernels each — unmistakably domesticated, unmistakably primitive. Looking at those cobs beside a modern ear is the fastest way to feel how much work the following millennia did.

An extraordinary complementary result came from ancient DNA. Researchers extracted and sequenced DNA from archaeological maize cobs 4,400 to 2,000 years old and looked directly at the domestication genes. The alleles associated with modern maize's plant architecture and storage-protein profile were already fixed or nearly so in the oldest samples, showing that selection at those loci was substantially complete very early, while other traits kept changing for thousands of years afterwards. Domestication was not a single moment; it was a long, uneven process with some traits locking in fast and others drifting for millennia.

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How the Argument Was Settled: tb1 and the Genetics of Maize

The decisive work came from John Doebley and colleagues, who did what Beadle had proposed: crossed maize with teosinte, grew out large segregating populations, and mapped which chromosome regions carried the differences. The answer was that a surprisingly small number of regions carried most of the effect — roughly five genomic regions accounted for the bulk of the morphological gap, which is why a plant that looks like a different genus can in fact be a subspecies of the same one.

The most celebrated of those genes is teosinte branched1, universally abbreviated tb1. It encodes a transcription factor that suppresses the growth of lateral branches. In teosinte the gene is expressed weakly and the plant branches freely; in maize a regulatory change drives much higher expression, the side branches are repressed into short shanks, and those shanks terminate in ears. One gene, one change in how much of a protein gets made, and the whole architecture of the plant flips from bushy grass to single-stalk crop.

The mechanism turned out to be even more specific. The maize tb1 allele carries a transposable element insertion — a Hopscotch retrotransposon — roughly 60 kilobases upstream of the coding sequence, acting as an enhancer that boosts expression. Population data indicate the insertion predates domestication, meaning the variant was already segregating at low frequency in wild teosinte and early farmers selected an existing variant rather than waiting for a new mutation. Standing variation, not a lucky accident.

A second key gene, teosinte glume architecture1 (tga1), governs the hard casing. In teosinte the glume hardens into that stony fruitcase; the maize allele leaves the glume soft and short, so the kernel sits naked on the cob and can be eaten or ground directly. Between tb1 and tga1 you have most of what a person actually notices: one stalk instead of many, and edible naked kernels instead of armoured seeds.

The botanist Hugh Iltis proposed in 1983 that a relatively sudden developmental change — the conversion of a male tassel branch into a female ear, what he called a "catastrophic sexual transmutation" — could have produced the maize ear in a short evolutionary window. The specific mechanism he proposed is not the current consensus, and the gradual-selection picture supported by the mapping work has largely prevailed, but the paper is worth knowing because it framed the central puzzle clearly: the maize ear is not a modified teosinte ear so much as a structure without a straightforward wild counterpart.

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Spread Through the Americas

From the Balsas, maize travelled. It reached the Oaxaca highlands by around 6,300 years ago, appears in the archaeological record of Panama and northern South America within the following millennium or two, and turns up in the southwestern United States by roughly 4,000 years ago. It arrived in the Eastern Woodlands of North America considerably later and did not become a staple there until well into the first millennium CE, after which the great maize-based societies of the Mississippi valley took shape.

The South American story turned out to be more complicated than a single wave. Genomic analysis of ancient and modern samples indicates that maize entered South America as a partially domesticated population that then continued to be improved locally — the crop was still evolving when it arrived, and separate lineages in different regions each finished the job. The Amazon basin emerges as a secondary centre of improvement, not merely a place maize passed through.

The result of thousands of years of dispersal and local selection is an astonishing library of landraces: several hundred recognised in Mexico alone, adapted to elevations from sea level to over 3,000 metres, to short and long growing seasons, to drought and to flood. They include the giant-kernelled Cusco corn of Peru, the blue and red maizes of the Mexican highlands, popcorns, flour corns soft enough to grind by hand, and flint corns hard enough to store for years. Studies of DNA microsatellite diversity across the New World races show clear geographic structure — the crop carries a readable map of its own migration.

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The Three Sisters

Maize was rarely grown alone. Across much of the Americas it was planted with beans and squash in the intercrop known in English as the Three Sisters — a term from Haudenosaunee (Iroquois) tradition, where the three plants are described as sisters who grow and thrive together. The arrangement is not folklore dressing on ordinary farming. It is a genuinely sophisticated polyculture, and it works for reasons that are agronomic and nutritional at once.

Agronomically, each plant does something the others need:

1. Maize provides structure. The stalk is a living trellis, so the climbing bean does not need poles.
2. Beans provide nitrogen. Like other legumes, beans host Rhizobium bacteria in root nodules that fix atmospheric nitrogen into forms plants can use. Maize is a heavy nitrogen feeder; growing it beside a nitrogen fixer partially closes the loop that monoculture leaves open.
3. Squash provides ground cover. Broad squash leaves shade the soil, suppressing weeds, slowing evaporation and moderating soil temperature. The prickly vines were also traditionally credited with discouraging animals.

There is a fourth mechanism that is less obvious and has been measured directly: the three species forage at different soil depths. A study of root architecture in the polyculture found that the crops occupy complementary root niches, and that this below-ground complementarity — not just the above-ground trellis effect — contributes to the yield advantage of the mixture over the same species grown separately. The plants are not merely tolerating each other; they are dividing the resource.

The nutritional logic is the part that matters most for a reader thinking about food. Maize protein is low in two essential amino acids, lysine and tryptophan. Beans are relatively rich in lysine and are limited instead in the sulphur amino acids, which maize supplies adequately. Eaten together, the two foods complement each other into a protein profile far better than either alone. Tryptophan matters twice over, because the body can convert tryptophan into niacin (vitamin B3) — so a maize diet that includes beans is protected against niacin deficiency from two directions at once. A study quantifying the yields and nutrient output of a Haudenosaunee-style Three Sisters plot found that the system produced more food energy and more usable protein per unit of land than the same crops in monoculture. The people who built this system were not guessing.

Maize breeders eventually rediscovered the amino-acid problem from the other end. Quality Protein Maize (QPM), developed from the opaque-2 mutation, carries substantially more lysine and tryptophan than conventional maize while avoiding the soft, chalky kernels that made early opaque-2 lines unmarketable. A meta-analysis of community-based studies in populations where maize is the dominant staple found that children fed QPM instead of conventional maize showed improved growth. It is a genuine achievement — and it is also, in effect, a plant-breeding solution to a problem the Three Sisters had already solved agriculturally.

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Nixtamalization: The Technique That Made Maize Liveable

This is the centrepiece of maize's history, and it is a genuinely startling piece of traditional food technology.

Somewhere before 1500 BCE, Mesoamerican cooks began boiling and steeping dried maize kernels in an alkaline solution — slaked lime (calcium hydroxide) made by burning limestone or shells, or wood ash lye where limestone was scarce — then rinsing and hulling them. The resulting kernels are called nixtamal, from the Nahuatl nextli (ashes) and tamalli (dough), and grinding them produces masa, the dough behind tortillas, tamales, pozole, arepas and a hundred other foods. The technique spread with maize across Mesoamerica and into parts of North and South America, in each place using whatever alkali was locally available.

What it does, in order of importance:

1. It liberates bound niacin. This is the crucial one. Most of the niacin in maize is not free vitamin but niacytin — niacin esterified to complex carbohydrates in the aleurone layer, in a form the human gut largely cannot release or absorb. Alkaline treatment hydrolyses those bonds and converts a nutritionally near-useless pool into available vitamin. Maize can carry a respectable niacin figure on a nutrition label and still leave you deficient, because the analytical method liberates the vitamin that your digestion does not. The same phenomenon has been demonstrated for bound niacin in wheat bran, where controlled human studies confirmed that the bound form is poorly available and that alkali treatment improves it.
2. It improves protein quality. Alkaline cooking alters the balance of protein fractions in the kernel and improves the ratio of available lysine and tryptophan relative to leucine. Excess leucine is itself part of the problem in maize diets, because a high leucine load interferes with the conversion of tryptophan to niacin — so shifting that ratio helps twice.
3. It adds calcium, substantially. Kernels take up calcium from the lime. Tortilla-based diets can derive a meaningful share of daily calcium from the processing water alone, in populations with limited dairy intake.
4. It makes the dough work. Alkali softens and removes the pericarp (the tough seed coat) and partially gelatinises the starch, which is what allows ground nixtamal to form a cohesive, elastic dough. Plain cornmeal will not do this. Every tortilla in the world is a physical demonstration of the chemistry.
5. It reduces mycotoxin load. Alkaline processing degrades a substantial fraction of fumonisins and aflatoxins present in the grain, and the washing step carries more away. This is a real and measurable food-safety benefit, discussed further on the safety deep-dive.

The landmark modern analysis was published in Science in 1974 by Solomon Katz and colleagues, who surveyed traditional maize-processing techniques across the New World and showed that alkali processing tracked maize dependence: the more heavily a society relied on maize, the more likely it was to process it with alkali. That is a strong ethnographic argument that the practice was maintained because it worked, whether or not anyone could have explained why in biochemical terms.

It is worth saying plainly what this means. Nixtamalization is a piece of nutritional technology, developed without any concept of vitamins, that solved a deficiency disease three thousand years before that disease was named. It has no equivalent in the European grain tradition. And it was the part that did not travel.

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Maize Crosses the Atlantic — Without the Lime

Columbus encountered maize in the Caribbean in 1492 and carried it back to Spain. Within a few decades it was growing across southern Europe; within a century it had spread through the Ottoman lands, along the Nile, into West Africa, across India and into southern China. It was an extraordinarily successful transplant, for entirely rational reasons: maize yields more calories per unit of land and labour than most of the small grains it competed with, it tolerates a range of soils, and it matures fast enough to fit into gaps in an existing rotation.

Regional names still record confusion about where it came from. In much of Europe it was called some version of "Turkish wheat" — gran turco in Italy, türkischer Weizen in German-speaking lands — because it arrived via Mediterranean trade routes. In parts of the Middle East it was named after Egypt or Syria. Almost nowhere outside the Americas was it named after the Americas.

What did not cross the Atlantic was the alkali. European and African adopters took the seed, the planting knowledge and the basic cooking — grinding, porridge, bread — and left behind the one processing step that made maize nutritionally sufficient as a staple. Polenta, mämligă, mămăligă, grits, mush, sadza, ugali, nshima: all of them are maize cooked without alkali. Where maize was one grain among many and the diet also carried meat, dairy, eggs, beans or vegetables, this cost nothing. Where poverty or a plantation economy narrowed the diet to maize and little else, the consequences were severe and, in hindsight, entirely predictable.

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Pellagra: A Disease of Missing Knowledge

Pellagra was first described in Spain in 1735 by Gaspar Casal, who called it mal de la rosa for the rash on the neck — still known as Casal's necklace. The Italian name that stuck, pelle agra, means "rough skin". It followed maize wherever maize became a monotonous staple: northern Italy, Spain, southwestern France, Romania, Egypt, parts of southern Africa, and, most consequentially for the historical record, the American South.

The clinical picture is remembered as the four Ds: dermatitis, diarrhoea, dementia and death. The dermatitis is distinctive — a symmetrical, sharply bordered, sunburn-like eruption strictly confined to sun-exposed skin, which is why it draws that collar across the neck and cuffs around the wrists. The diarrhoea reflects atrophy of the gut lining. The neuropsychiatric stage runs from apathy and irritability through confusion to frank psychosis and dementia; nineteenth-century asylums in maize-dependent regions held large numbers of pellagrins. Untreated, advanced pellagra kills.

The underlying deficiency is of niacin (vitamin B3) or of its precursor tryptophan; the body can make niacin from tryptophan at roughly 60 milligrams of tryptophan to 1 milligram of niacin, so either can carry the diet. Maize is poor in available niacin because of the bound niacytin problem, poor in tryptophan, and comparatively rich in leucine, which interferes with the tryptophan-to-niacin conversion. It is a nearly perfect deficiency machine when eaten alone — and a perfectly good food when it is not. The full clinical picture is covered on this site's Pellagra page.

In the United States, pellagra exploded in the first decades of the twentieth century, concentrated in the cotton South. The proximate cause was the three-M diet of tenant farming and mill work — meal, meat (fatback, which is nearly pure fat) and molasses — imposed on households with no land for a garden, wages paid in company scrip, and a cotton monoculture that had displaced food crops. Cases ran into the hundreds of thousands per year at the peak, with tens of thousands of deaths, and the disease was heavily concentrated in mill villages, orphanages, asylums and prisons: institutions where a single cheap menu was served to everyone.

The prevailing explanations were wrong in a way that mattered. Most authorities held that pellagra was an infectious disease, perhaps spread by an insect vector by analogy with malaria; others held that it was hereditary, or caused by a toxin in spoiled maize. Each theory pointed away from the diet, and each was comfortable for those who benefited from the economic arrangements that produced the diet.

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Joseph Goldberger and the Filth Parties

Joseph Goldberger was a US Public Health Service physician, a Hungarian-born immigrant with a record of hard infectious-disease fieldwork, who was assigned to the pellagra problem in 1914. He solved it, essentially, by looking.

His first observation was epidemiological and devastatingly simple. In institutions where pellagra was rampant among inmates, the staff did not get it — nurses, attendants and guards who lived in the same buildings, breathed the same air and handled the sick daily. No infectious disease behaves like that. What separated staff from inmates was not exposure. It was the food.

He then ran a series of studies of increasing rigour:

1. Feeding studies in orphanages and an asylum. Goldberger added milk, eggs, meat and legumes to the institutional diet and pellagra disappeared from the treated groups while continuing in comparison groups. When funding lapsed and the diet reverted, the disease returned — an unintentional but powerful natural experiment.
2. The Rankin Farm experiment (1915). With the Mississippi governor's cooperation, eleven volunteer prisoners at Rankin Prison Farm were offered pardons in exchange for eating a restricted diet modelled on the poor Southern diet. Within months, several had developed the characteristic rash and other signs. Goldberger had produced pellagra deliberately, in previously healthy men, by diet alone. (The ethics of this study are not defensible by modern standards — prisoners offered freedom cannot consent freely — and it is honest to say so while acknowledging what it demonstrated.)
3. The "filth parties" (1916). Sceptics answered that the prisoners had merely been exposed to an infection. So Goldberger set out to prove non-contagion on his own body. He, his wife Mary, and volunteer colleagues injected themselves with blood drawn from pellagra patients, swabbed patients' nasal and throat secretions into their own noses and throats, and swallowed capsules containing scrapings of patients' skin lesions together with their urine and faeces. Sixteen people took part across several rounds. Not one developed pellagra. It is one of the more extraordinary self-experiments in the history of medicine, and it was undertaken because the professional consensus would not move for argument alone.

Even this did not settle the matter immediately. Goldberger's conclusion carried an unwelcome political implication — that pellagra was a disease of poverty, produced by the tenant-farming and mill economy of the South — and it was resisted on those grounds as much as scientific ones. When he and the statistician Edgar Sydenstricker surveyed South Carolina mill villages and demonstrated that pellagra incidence tracked household income and food availability with precision, some Southern officials and newspapers attacked the finding as a slander on the region. Working with the economics rather than around it, Goldberger also argued for agricultural diversification away from cotton.

He identified the protective factor in his diets as a heat-stable substance he called P-P factor, for pellagra-preventive, and found it concentrated in brewer's yeast — cheap enough to distribute during the Mississippi flood relief of 1927. He did not live to see it named: Goldberger died of cancer in 1929, and it was Conrad Elvehjem's group at Wisconsin who identified nicotinic acid as the pellagra-preventive factor in 1937, curing canine black tongue with it. Enrichment of flour and cornmeal with niacin, which began in the United States in the early 1940s, ended endemic pellagra in the country within a few years.

The episode deserves its reputation. It is a clean case of a correct dietary explanation defeating an entrenched infectious one, of field epidemiology beating laboratory prestige, and of a scientist recognising that a social arrangement, not a microbe, was the cause of a mass disease. It is also a warning that is still live: pellagra remains present today in populations dependent on unprocessed maize and among people with alcoholism, malabsorption or eating disorders, and it appears in refugee populations fed maize rations without complementary foods.

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Hybrid Corn and the Yield Revolution

The second transformation of maize was genetic and took about a century.

The groundwork was laid around 1908 by George Shull and Edward East, working independently. Both observed that repeatedly self-pollinating maize produces weak, uniform inbred lines — and that crossing two different inbred lines produces an F1 hybrid that is dramatically more vigorous and productive than either parent, or than the open-pollinated population they came from. This is heterosis, or hybrid vigour. Shull laid out the scheme that the modern seed industry still uses.

The practical obstacle was that inbred lines are, by definition, feeble, so seed produced on them was expensive. Donald Jones solved this in 1918 with the double cross: cross inbred A with inbred B and inbred C with inbred D, then cross the two vigorous single-cross hybrids to produce commercial seed. Seed could now be produced on a vigorous plant, and hybrid maize became economically viable. Henry A. Wallace — later US Secretary of Agriculture and Vice President — founded the company that became Pioneer Hi-Bred to sell it.

Adoption in the US Corn Belt was rapid, running from almost nothing in the early 1930s to nearly universal by the mid-1940s. Its spread became one of the most-studied cases in the sociology of innovation. And yields, which had been essentially flat at roughly 20–30 bushels per acre for the whole preceding recorded history of American maize farming, began a steady climb that has continued for eighty years.

It is important to attribute that climb honestly, and the best analysis of it comes from Donald Duvick, who spent a career as a maize breeder and then studied his own field's contribution. Comparing hybrids from successive eras grown side by side in the same environments, he concluded that roughly half of the yield gain came from genetic improvement and roughly half from changed agronomy — nitrogen fertiliser, herbicides, higher planting densities, better machinery, earlier planting. The two are not independent: much of the genetic gain consists of stress tolerance, particularly tolerance of crowding, which is precisely what allows the higher planting densities that deliver the agronomic half. Modern hybrids are not bigger plants; they are plants that keep working shoulder to shoulder at four times the population density that would have flattened a 1930s variety.

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Feed, Sweeteners and Fuel

The consequence of eight decades of rising yields is that maize became abundant in a way no staple had been before, and the uses expanded to absorb it. Most maize grown today is not eaten by people as maize.

The largest share by far is animal feed. Field corn (dent corn) is the overwhelming majority of the crop, and the majority of that goes to cattle, pigs and poultry, either as grain or as whole-plant silage. When a nutrition discussion treats "corn" as a food category it is usually talking about a small slice of the harvest.

The second major stream is wet milling, which separates the kernel into starch, germ (for corn oil), gluten and fibre. Corn starch is then converted enzymatically into glucose syrups and, since the late 1960s and commercially at scale from the 1970s, into high-fructose corn syrup via glucose isomerase. HFCS displaced sucrose in American soft drinks and processed foods over roughly a decade. Whether HFCS is metabolically worse than sucrose at equal doses is genuinely contested — the two are compositionally similar — but the influential argument, made by Bray, Nielsen and Popkin in 2004, is that its arrival coincided with and enabled a large increase in total caloric sweetener consumption, and it is the total that matters. This site treats HFCS as a refined sweetener to minimise, which is the same advice it gives for cane sugar.

The third stream is fuel ethanol, which since the mid-2000s has consumed a very large share of the United States maize crop, driven by renewable-fuel policy. This is an agricultural and energy-policy question rather than a nutritional one, but it explains a great deal about why so much land grows so much corn.

Smaller streams are still enormous in absolute terms: dry milling for cornmeal, grits, masa flour and breakfast cereals; sweet corn for fresh, frozen and canned eating; popcorn as its own distinct type; corn oil; bioplastics; and the long list of derived ingredients — maltodextrin, dextrose, citric acid, xanthan gum, modified starches — that make corn ubiquitous in an ingredient list without appearing under its own name.

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Corn Today: Scale, Landraces and What Was Nearly Lost

By tonnage, maize is the largest crop in the world, ahead of wheat and rice. It is grown on every inhabited continent, and it is the principal dietary staple for hundreds of millions of people in eastern and southern Africa, Central America and parts of South America — where the nutritional issues on this page are not history but current practice. Reviews of global maize production and utilisation describe a crop whose sheer scale makes small nutritional decisions consequential: how it is stored, whether it is nixtamalised, whether it is fortified, and what else is on the plate beside it.

Two developments are worth ending on.

The first is fortification. Niacin enrichment of cornmeal ended American pellagra. More recently, the United States authorised the addition of folic acid to corn masa flour, closing a gap that had left populations relying on masa rather than wheat flour without the folate fortification that reduces neural-tube defects. It is a small regulatory act with a direct line back to the arguments on this page.

The second is diversity. The commercial crop rests on a narrow genetic base: a large fraction of US hybrids trace to a small number of founder inbred lines. The insurance against that narrowness is the landraces — the hundreds of traditional maize varieties still grown by smallholder farmers, overwhelmingly in Mexico and Central America, which hold the genetic variation that future breeding will need for new diseases and a changing climate. They persist because farmers keep planting them, often for culinary and cultural reasons that have nothing to do with yield: a particular blue maize makes the right tortillas, a particular flour corn grinds properly by hand. The plant that cannot reproduce without people is still, nine thousand years on, entirely dependent on what people choose to keep growing.

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Research Papers and References

Domestication and Genetics

1. Matsuoka Y, Vigouroux Y, Goodman MM, Sánchez GJ, Buckler E, Doebley J. A single domestication for maize shown by multilocus microsatellite genotyping. Proceedings of the National Academy of Sciences. 2002;99(9):6080-6084. — doi:10.1073/pnas.052125199
2. Piperno DR, Ranere AJ, Holst I, Iriarte J, Dickau R. Starch grain and phytolith evidence for early ninth millennium B.P. maize from the Central Balsas River Valley, Mexico. Proceedings of the National Academy of Sciences. 2009;106(13):5019-5024. — doi:10.1073/pnas.0812525106
3. Ranere AJ, Piperno DR, Holst I, Dickau R, Iriarte J. The cultural and chronological context of early Holocene maize and squash domestication in the Central Balsas River Valley, Mexico. Proceedings of the National Academy of Sciences. 2009;106(13):5014-5018. — doi:10.1073/pnas.0812590106
4. Piperno DR, Flannery KV. The earliest archaeological maize (Zea mays L.) from highland Mexico: new accelerator mass spectrometry dates and their implications. Proceedings of the National Academy of Sciences. 2001;98(4):2101-2103. — doi:10.1073/pnas.98.4.2101
5. Doebley J. The genetics of maize evolution. Annual Review of Genetics. 2004;38:37-59. — doi:10.1146/annurev.genet.38.072902.092425
6. Doebley J, Stec A, Gustus C. teosinte branched1 and the origin of maize: evidence for epistasis and the evolution of dominance. Genetics. 1995;141(1):333-346. — doi:10.1093/genetics/141.1.333
7. Doebley J, Stec A, Hubbard L. The evolution of apical dominance in maize. Nature. 1997;386(6624):485-488. — doi:10.1038/386485a0
8. Studer A, Zhao Q, Ross-Ibarra J, Doebley J. Identification of a functional transposon insertion in the maize domestication gene tb1. Nature Genetics. 2011;43(11):1160-1163. — doi:10.1038/ng.942
9. Wang RL, Stec A, Hey J, Lukens L, Doebley J. The limits of selection during maize domestication. Nature. 1999;398(6724):236-239. — doi:10.1038/18435
10. Jaenicke-Després V, Buckler ES, Smith BD, et al. Early allelic selection in maize as revealed by ancient DNA. Science. 2003;302(5648):1206-1208. — doi:10.1126/science.1089056
11. Hufford MB, Xu X, van Heerwaarden J, et al. Comparative population genomics of maize domestication and improvement. Nature Genetics. 2012;44(7):808-811. — doi:10.1038/ng.2309
12. Beadle GW. The ancestry of corn. Scientific American. 1980;242(1):112-119. — doi:10.1038/scientificamerican0180-112
13. Iltis HH. From teosinte to maize: the catastrophic sexual transmutation. Science. 1983;222(4626):886-894. (A hypothesis that framed the problem; not the current consensus mechanism.) — doi:10.1126/science.222.4626.886

Spread, Landraces and the Three Sisters

1. Kistler L, Maezumi SY, Gregorio de Souza J, et al. Multiproxy evidence highlights a complex evolutionary legacy of maize in South America. Science. 2018;362(6420):1309-1313. — doi:10.1126/science.aav0207
2. van Heerwaarden J, Doebley J, Briggs WH, et al. Genetic signals of origin, spread, and introgression in a large sample of maize landraces. Proceedings of the National Academy of Sciences. 2011;108(3):1088-1092. — doi:10.1073/pnas.1013011108
3. Vigouroux Y, Glaubitz JC, Matsuoka Y, Goodman MM, Sánchez GJ, Doebley J. Population structure and genetic diversity of New World maize races assessed by DNA microsatellites. American Journal of Botany. 2008;95(10):1240-1253. — doi:10.3732/ajb.0800097
4. Zhang C, Postma JA, York LM, Lynch JP. Root foraging elicits niche complementarity-dependent yield advantage in the ancient "three sisters" (maize/bean/squash) polyculture. Annals of Botany. 2014;114(8):1719-1733. — doi:10.1093/aob/mcu191
5. Mt. Pleasant J. Food yields and nutrient analyses of the Three Sisters: a Haudenosaunee cropping system. Ethnobiology Letters. 2016;7(1):87-98. — doi:10.14237/ebl.7.1.2016.721
6. Gunaratna NS, De Groote H, Nestel P, Pixley KV, McCabe GP. A meta-analysis of community-based studies on quality protein maize. Food Policy. 2010;35(3):202-210. — doi:10.1016/j.foodpol.2009.11.003

Nixtamalization, Niacin and Pellagra

1. Katz SH, Hediger ML, Valleroy LA. Traditional maize processing techniques in the New World. Science. 1974;184(4138):765-773. — doi:10.1126/science.184.4138.765
2. Carter EG, Carpenter KJ. The bioavailability for humans of bound niacin from wheat bran. American Journal of Clinical Nutrition. 1982;36(5):855-861. — doi:10.1093/ajcn/36.5.855
3. Gwirtz JA, Garcia-Casal MN. Processing maize flour and corn meal food products. Annals of the New York Academy of Sciences. 2014;1312:66-75. — doi:10.1111/nyas.12299
4. Nuss ET, Tanumihardjo SA. Maize: a paramount staple crop in the context of global nutrition. Comprehensive Reviews in Food Science and Food Safety. 2010;9(4):417-436. — doi:10.1111/j.1541-4337.2010.00117.x
5. Elmore JG, Feinstein AR. Joseph Goldberger: an unsung hero of American clinical epidemiology. Annals of Internal Medicine. 1994;121(5):372-375. — doi:10.7326/0003-4819-121-5-199409010-00010
6. Rajakumar K. Pellagra in the United States: a historical perspective. Southern Medical Journal. 2000;93(3):272-277. — doi:10.1097/00007611-200093030-00005
7. Marks HM. Epidemiologists explain pellagra: gender, race, and political economy in the work of Edgar Sydenstricker. Journal of the History of Medicine and Allied Sciences. 2003;58(1):34-55. — doi:10.1093/jhmas/58.1.34
8. Chemical changes in maize during nixtamalization and tortilla preparation — the classic Bressani and Scrimshaw line of work. A specific digital identifier could not be verified for the 1958 paper, so it is given here as a topic search. — PubMed: nixtamalization and niacin availability
9. Goldberger J. The etiology of pellagra: the significance of certain epidemiological observations with respect thereto. Public Health Reports. 1914;29(26):1683-1686. (Reprinted in Public Health Reports and widely anthologised; no modern digital identifier.)

Hybrid Maize, Yields and the Modern Crop

1. Crow JF. 90 years ago: the beginning of hybrid maize. Genetics. 1998;148(3):923-928. — doi:10.1093/genetics/148.3.923
2. Duvick DN. The contribution of breeding to yield advances in maize (Zea mays L.). Advances in Agronomy. 2005;86:83-145. — doi:10.1016/S0065-2113(05)86002-X
3. Ranum P, Peña-Rosas JP, Garcia-Casal MN. Global maize production, utilization, and consumption. Annals of the New York Academy of Sciences. 2014;1312:105-112. — doi:10.1111/nyas.12396
4. Bray GA, Nielsen SJ, Popkin BM. Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity. American Journal of Clinical Nutrition. 2004;79(4):537-543. — doi:10.1093/ajcn/79.4.537
5. Lao F, Sigurdson GT, Giusti MM. Health benefits of purple corn (Zea mays L.) phenolic compounds. Comprehensive Reviews in Food Science and Food Safety. 2017;16(2):234-246. — doi:10.1111/1541-4337.12249

Live PubMed Searches

1. PubMed: maize domestication teosinte
2. PubMed: nixtamalization maize
3. PubMed: pellagra niacin history
4. PubMed: Goldberger pellagra
5. PubMed: quality protein maize
6. PubMed: maize landrace diversity

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Connections

• Corn — the main topic page
• Corn — Benefits Deep Dive
• Corn — Nutrients
• Corn Safety: Mycotoxins, Pellagra and GMOs
• Whole-Grain Corn vs Refined Corn Products
• Pellagra and Niacin Deficiency
• Vitamin B3 (Niacin)
• Tryptophan
• Lysine
• Beans — the second Sister
• Brown Rice
• Barley
• Oats
• Quinoa
• Resistant Starches
• Ferulic Acid
• Magnesium
• Mold and Mycotoxins
• All Food topics

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