Wheat: History and Origins

Wheat's history is the history of a mutation that would have killed the plant in the wild. A wild wheat plant scatters its seed the moment the grain is ripe — the stalk that holds the ear together snaps, and the seeds fall to the ground where they belong. Every so often a plant is born whose stalk does not snap. In a wild field that plant is a dead end: its seed stays trapped in the ear and never reaches the soil. In a field being harvested by people with sickles, it is the only plant whose seed gets collected, carried home, and sown again next season. That single trait — the tough, non-shattering rachis — is the essence of domestication. It made wheat completely dependent on humans, and it made humans completely dependent on wheat. Roughly ten thousand years later, wheat covers more of the earth's farmland than any other crop.

Table of Contents

  1. The Wild Ancestors
  2. The Mutation That Made Domestication
  3. Karacadağ and the Einkorn Evidence
  4. Emmer and the First Farming Villages
  5. How Bread Wheat Was Made
  6. Grain, Cities and the Invention of Taxes
  7. Rome and the Grain Supply
  8. Medieval Europe and the Prestige Grain
  9. The Columbian Exchange
  10. The Prairie Wheat Belts
  11. Roller Milling and the White Loaf
  12. Vavilov and the Seed Collectors
  13. Norman Borlaug and the Green Revolution
  14. The Fair Criticisms
  15. Reading the Wheat Genome
  16. Legends, Corrections and Things That Are Not True
  17. Research Papers and References
  18. Connections
  19. Featured Videos

The Wild Ancestors

Wheat was not domesticated once. Two different wild grasses, growing in the same region, were brought under cultivation at roughly the same time.

Both still grow wild across the arc of hills running from the Levant through southeastern Turkey and into the Zagros mountains — the region conventionally called the Fertile Crescent. Anyone who has walked through a stand of wild wheat in early summer understands immediately why it was worth harvesting: dense stands, large seeds by grass standards, and all of it ripening within a short window.

What wild wheat is not is convenient. The grain is tightly enclosed in a tough husk, the ears shatter at a touch, and a season's harvest depends on catching the plants in a window of a few days before the seed is on the ground.

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The Mutation That Made Domestication

The rachis is the central axis of the wheat ear, the stalk the individual spikelets attach to. In wild wheat it is brittle: at maturity it develops abscission zones and breaks apart, scattering spikelets. This is the plant's entire reproductive strategy.

A loss-of-function mutation in the genes controlling that brittleness produces a tough rachis. The ear stays whole. In the wild this is fatal — the seed never disperses. In a harvested field it is the winning ticket, because a person cutting ears with a sickle collects disproportionately the plants that have not shattered, and then sows what they collected. The trait selects itself, invisibly, every year, without anyone deciding to breed for it.

The genetic basis was pinned down when the wild emmer genome was sequenced in 2017, identifying the Brittle Rachis genes whose disruption produces the domesticated form. A second key domestication gene, Q, was characterised in 2006: it governs the free-threshing habit — grain that separates cleanly from the husk during threshing instead of staying stubbornly enclosed — along with the squarer, more compact ear shape of modern wheat. Einkorn, emmer, spelt and khorasan are all hulled; bread wheat and durum are free-threshing, which is exactly why they displaced the others commercially.

How fast did it happen? Not fast. Archaeobotanical work counting the proportion of shattering and non-shattering spikelet bases through the layers of Near Eastern sites showed that the non-shattering form took on the order of a thousand years or more to become fixed, not a few generations. A broader survey of Old World crops found the same protracted pattern across species. Domestication was not an invention; it was a very slow drift produced by people doing what they had always done, with sickles.

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Karacadağ and the Einkorn Evidence

In 1997 a team led by Manfred Heun did something that had not been possible before: they DNA-fingerprinted large collections of wild einkorn from across its range and compared them with domesticated einkorn lines. If domestication had happened many times in many places, domesticated einkorn should resemble many different wild populations. It did not. The domesticated lines clustered tightly with wild einkorn from a specific area — the Karacadağ mountains of southeastern Turkey.

Five years later the same approach was applied to tetraploid wheats, using AFLP markers across a large collection. The answer pointed to the same corner of the map: emmer and the hard wheats descended from it were domesticated in southeastern Turkey, in and around the Karacadağ region.

Karacadağ is a volcanic massif a short distance from Göbekli Tepe, the monumental site whose enormous carved pillars were raised by people who were not yet farmers. The proximity is striking, and it has fed a long-running argument about whether large gatherings requiring large amounts of food helped push cereal cultivation forward, or the reverse. The archaeology does not settle it. What the genetics does establish is that this small region is where the wheat lineage that fed the world began.

A later worldwide phylogeographic study of wheat genetic diversity, using a large collection of landraces and modern cultivars, traced how bread wheat radiated out from the Near East across Europe, Asia and Africa — and how much of the diversity accumulated on that journey has been narrowed by twentieth-century breeding.

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Emmer and the First Farming Villages

Einkorn came first, but emmer became the workhorse. It was the principal wheat of the Neolithic villages of the Levant and Anatolia, of Pharaonic Egypt, and of early Mesopotamia, and it stayed dominant for thousands of years.

Emmer built the Egyptian state's food supply. Egyptian bread and beer were emmer products; loaves and grain have been recovered from tombs and settlement sites, and the tax and ration systems of the Old and Middle Kingdoms were denominated in it. Emmer is a hulled wheat, so it had to be parched or pounded to free the grain — an extra step visible in the archaeological record as dedicated processing areas and in tomb paintings as a distinct stage of work.

Wheat farming spread out from the Fertile Crescent along two main routes: westwards through Anatolia into Greece and the Balkans and then up the Danube and along the Mediterranean coast, reaching Britain and Scandinavia by roughly six thousand years ago; and eastwards through Iran into Central Asia, reaching China by around four thousand years ago, where it eventually took its place alongside millet and rice.

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How Bread Wheat Was Made

Bread wheat, Triticum aestivum, does not exist in the wild and never did. It is the product of two hybridisation events, one of them prehistoric and one of them almost certainly accidental, in a farmer's field.

  1. Long before agriculture, a wild diploid A-genome wheat crossed with a wild goatgrass carrying what we call the B genome. The hybrid doubled its chromosomes and became a fertile tetraploid: wild emmer, AABB. Genomic analysis has since shown that the story behind those genomes is older and stranger still — the lineages involved diverged millions of years ago, and the D genome lineage itself appears to have originated from an ancient hybridisation between the ancestors of the A and B genomes.
  2. Around eight to ten thousand years ago, somewhere near the southern shore of the Caspian Sea, cultivated emmer growing at the edge of its range crossed with a scrubby wild goatgrass, Aegilops tauschii, which carried the D genome. The chromosomes doubled again. The result was hexaploid: AABBDD, bread wheat.

The D genome is why you can make a risen loaf. It contributed glutenin subunits that give wheat dough its particular combination of elasticity and extensibility — the ability to stretch into thin gas-holding films and then spring back. No other cereal does this. Rye has some capacity; barley, oats, maize and rice have essentially none. Every risen wheat loaf in the world traces back to a chance cross with a weed that nobody planted.

The D genome also brought cold-hardiness and adaptability, which is why hexaploid wheat could spread into climates emmer could not reach. And it carries most of the gluten sequences that provoke coeliac disease — a point covered in detail on the coeliac, allergy and sensitivity page. Polyploidy also gave wheat something breeders would later exploit heavily: with three copies of most genes, the plant tolerates mutations that would be lethal in a diploid, which is a large part of why wheat has been so adaptable under domestication.

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Grain, Cities and the Invention of Taxes

Wheat has a set of properties that no root crop or fruit shares. It ripens on a predictable schedule, above ground and in plain sight. It can be stored for years if kept dry. It is divisible, countable and standardisable by volume and weight. And it must be harvested within a short window.

Those properties are administratively irresistible. A tax collector can look at a field and estimate the yield before it is cut, arrive on a known date, take a proportion, and store what is taken. None of this is possible with a crop that is harvested continuously or kept underground until needed. The world's earliest writing — the proto-cuneiform tablets from Uruk in southern Mesopotamia, dating to a little before 3000 BCE — is overwhelmingly accounting: quantities of grain, of barley rations, of beer, of livestock, recorded with the names of officials. Writing, so far as the record shows, was invented to keep track of stored cereals.

Grain also underwrote standardised measurement. A grain of wheat or barley was a literal unit of weight, surviving into the English troy system as the grain, which is why apothecaries' weights and the weights of precious metals ultimately reference a cereal seed.

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Rome and the Grain Supply

By the late Republic, Rome had outgrown the capacity of Italy to feed it and depended on imported wheat — from Sicily, from North Africa, and above all from Egypt, which after its annexation became the empire's granary. Fleets sailed on the season, and the whole logistical apparatus of the annona, the grain supply, was a permanent department of state with its own prefect.

The politics of grain were the politics of the city. A subsidised grain ration was introduced in the late second century BCE and made free in 58 BCE; by the early Empire, several hundred thousand residents of Rome held tokens entitling them to a monthly measure of wheat. Emperors invested enormous sums in the infrastructure that guaranteed it — the harbour complex at Portus near Ostia, warehouses, and a state-supported merchant fleet — because a failed harvest or a delayed convoy meant riots.

Romans mostly ate wheat as bread by this period, milled in commercial bakeries and baked in public ovens. Earlier Roman diets had leaned on emmer porridge (puls), and the shift from porridge to leavened bread is one of the clearest dietary transitions visible in Latin literature.

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Medieval Europe and the Prestige Grain

In medieval Europe wheat was the aristocratic grain. It was demanding — it wanted good soil and reasonable weather, and it yielded poorly compared with rye, barley and oats. White wheaten bread was a marker of status; the further down the social scale, the more the loaf was rye, barley, oats, or a mixture stretched with beans and, in bad years, with things that were not food.

Two agricultural changes raised wheat's share. The three-field rotation — winter cereal, spring cereal, fallow — spread through northern Europe and increased the land under crops in any given year while maintaining fertility. And the heavy mouldboard plough, which could turn the wet clay soils of the north, opened land that the light Mediterranean ard could not work.

The grain disease of medieval Europe was not a wheat disease. Ergotism — "St Anthony's fire", with its burning limbs, gangrene and hallucinations — came from the Claviceps purpurea fungus, which principally infects rye. Rye was the poor person's bread across northern Europe, which is why ergotism epidemics map onto rye-eating regions. It is regularly and wrongly attributed to wheat.

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The Columbian Exchange

Wheat crossed the Atlantic almost immediately: Columbus carried seed on his second voyage in 1493, and Spanish colonists planted it wherever they settled. It failed comprehensively in the humid Caribbean lowlands, where heat and fungal disease destroyed it, and succeeded in the cool highlands of Mexico and, later, in Chile, Argentina and the temperate parts of North America.

The motivation was partly culinary and substantially religious — the Catholic Eucharist requires wheaten bread, so establishing a wheat supply was a precondition for the mission system. Wheat travelled with the missions up through Mexico into what is now California and the American Southwest.

The exchange ran both ways, and it is worth being clear about the balance sheet. Europe sent wheat, barley, rye, cattle, sheep and horses; the Americas sent maize, potatoes, tomatoes, beans, squash, chillies, cacao and much else, along with a set of crops that would eventually feed more people than wheat does. Wheat's expansion into the Americas also displaced indigenous agricultural systems and the peoples who maintained them, which is part of the same history and not a footnote to it.

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The Prairie Wheat Belts

The transformation of the North American interior into the world's largest wheat region in the space of a few decades depended on specific varieties, not just on land.

Around those varieties assembled the machinery that made industrial-scale grain farming possible: the steel plough, the mechanical reaper and later the combine harvester, the railways that moved grain to ports, the grain elevator, and the futures exchanges that let a farmer sell a crop before it was grown.

The costs arrived on the same schedule. Ploughing out deep-rooted native prairie sod across the semi-arid southern plains, followed by a run of dry years, produced the Dust Bowl of the 1930s. It remains the clearest demonstration available that wheat's expansion has ecological limits, and it drove the creation of soil-conservation agencies whose descendants still exist.

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Roller Milling and the White Loaf

For most of history, wheat was ground between stones. Stone milling crushes the whole kernel together; the germ's oil smears through the flour, and sifting through cloth can remove much of the bran but never all of the germ. White flour existed, it was laborious, and it was expensive — which is precisely why it signalled status.

The roller mill, refined in Hungary and adopted across Europe and North America through the 1870s and 1880s, changed that completely. Successive pairs of steel rollers running at different speeds shear the kernel open and progressively separate bran, germ and endosperm as distinct streams. The result was cheap, uniform, brilliantly white flour that kept for months instead of weeks, because the oil-bearing germ had been removed.

Within a generation white bread went from a luxury to the default, and the bran and germ went to animal feed. The nutritional consequence was immediate and severe enough that governments eventually legislated: fortification of white flour with thiamine, riboflavin, niacin and iron began in the 1940s in Britain and the United States, and folic acid was added decades later. The consequences of that separation — and what the evidence says about eating the whole kernel instead — are the subject of the whole grain vs refined page.

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Vavilov and the Seed Collectors

The Russian botanist Nikolai Vavilov spent the 1920s and 1930s travelling the world collecting crop seed, and formulated the idea of centres of origin — the regions where a crop's wild relatives and landraces are most diverse, and therefore where its genetic raw material is concentrated. For wheat, his work pointed at the Near East, which the DNA evidence later confirmed.

Vavilov's collection in Leningrad became the world's first great seed bank. He fell foul of Trofim Lysenko, whose rejection of Mendelian genetics had Stalin's backing, was arrested in 1940 and died in prison in 1943. During the 900-day siege of Leningrad, staff at his institute guarded the seed collection through the winter while the city starved; several of them died of starvation surrounded by edible seed they refused to eat, because the collection was irreplaceable and they were keeping it for after the war.

Every wheat breeding programme since has drawn on collections built on that model. When breeders needed disease resistance from a wild goatgrass, or drought tolerance from a Middle Eastern landrace, it was there because someone had collected and kept it.

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Norman Borlaug and the Green Revolution

In 1944 an American plant pathologist named Norman Borlaug went to Mexico on a Rockefeller Foundation programme to work on wheat rust, a fungal disease that was devastating Mexican harvests. He stayed for decades, and what he built there changed the world's food supply.

Three innovations mattered:

  1. Shuttle breeding. Borlaug grew two generations a year by moving material between a highland station near Mexico City and a lowland station in Sonora, at different latitudes and altitudes. Conventional breeding wisdom said this was wrong — selections should be made in the environment where the crop would grow. It halved the time to develop a variety, and it produced an unplanned bonus: lines that performed in both environments turned out to be insensitive to day length, and therefore adaptable across a huge geographic range.
  2. Rust resistance. Systematic crossing and selection produced varieties that held up against stem rust, and Mexico moved from importing wheat to exporting it.
  3. Semi-dwarf stature. This was the decisive one. Traditional tall wheats respond to heavy fertiliser by growing tall and then falling over — lodging — which ruins the crop. Dwarfing genes from the Japanese variety Norin 10, brought to the United States after the war and passed on by the breeder Orville Vogel, produced short, stiff-strawed plants that put their extra growth into grain rather than straw and stood up under fertiliser and irrigation.

Molecular work published in 1999 explained what the dwarfing genes actually do. The Rht ("reduced height") genes encode altered forms of a protein that normally responds to the plant hormone gibberellin. The mutant versions cannot be switched off by gibberellin, so the growth-repressing signal stays on and the stem stays short. It is a change to a hormone signalling switch and to plant architecture — not to grain composition, and not to gluten. That distinction matters, because semi-dwarf wheat is regularly blamed for changes in gluten it did not cause, a claim examined on the coeliac, allergy and sensitivity page.

In the mid-1960s, with India and Pakistan facing catastrophic harvest failures, both countries imported Mexican semi-dwarf seed in enormous quantity. Yields roughly doubled within a few years. India, which had been importing grain on emergency terms, became self-sufficient in cereals within a decade. Borlaug received the Nobel Peace Prize in 1970. Estimates of the number of deaths averted vary widely and are inherently uncertain, but the scale of the yield change is not in doubt.

A careful economic assessment published in Science in 2003 modelled what the world would have looked like without the Green Revolution's improved varieties: substantially lower yields, higher food prices, more childhood malnutrition, and — a point often missed — considerably more land under the plough, because the food would have had to come from somewhere.

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The Fair Criticisms

The Green Revolution is defended and attacked with equal vehemence, and both camps tend to skip the parts that inconvenience them. A review in PNAS in 2012 set out the case with unusual balance, and the substantive criticisms are these:

The honest summary is that the Green Revolution averted famine on a very large scale and did so with real, lasting environmental and social costs, and that saying only one of those things is a form of dishonesty regardless of which one you pick.

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Reading the Wheat Genome

Bread wheat's genome was among the last of the major crop genomes to be sequenced, for a straightforward reason: it is enormous and highly repetitive. Three closely related genomes in one nucleus, roughly five times the size of the human genome, and full of near-identical repeated sequences that defeat assembly software.

An international consortium published a fully annotated reference genome in Science in 2018, covering all 21 chromosomes with more than a hundred thousand genes annotated. It has already made a practical difference — genes for disease resistance, grain quality and heat tolerance can now be located and tracked directly instead of being chased through field trials.

The genome work also confirmed how much plasticity polyploidy gives wheat: with three copies of most genes, mutations that would be lethal in a diploid can be tolerated, and one copy can take on a new function while the others carry on. That is a large part of why wheat has adapted to climates from Norway to Argentina, and why breeders have had so much material to work with.

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Legends, Corrections and Things That Are Not True

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Research Papers and References

  1. Heun M, Schäfer-Pregl R, Klawan D, et al. Site of einkorn wheat domestication identified by DNA fingerprinting. Science. 1997;278(5341):1312-1314. — doi:10.1126/science.278.5341.1312
  2. Özkan H, Brandolini A, Schäfer-Pregl R, Salamini F. AFLP analysis of a collection of tetraploid wheats indicates the origin of emmer and hard wheat domestication in southeast Turkey. Molecular Biology and Evolution. 2002;19(10):1797-1801. — doi:10.1093/oxfordjournals.molbev.a004002
  3. Salamini F, Özkan H, Brandolini A, Schäfer-Pregl R, Martin W. Genetics and geography of wild cereal domestication in the near east. Nature Reviews Genetics. 2002;3(6):429-441. — doi:10.1038/nrg817
  4. Tanno K, Willcox G. How fast was wild wheat domesticated? Science. 2006;311(5769):1886. — doi:10.1126/science.1124635
  5. Fuller DQ. Contrasting patterns in crop domestication and domestication rates: recent archaeobotanical insights from the Old World. Annals of Botany. 2007;100(5):903-924. — doi:10.1093/aob/mcm048
  6. Simons KJ, Fellers JP, Trick HN, et al. Molecular characterization of the major wheat domestication gene Q. Genetics. 2006;172(1):547-555. — doi:10.1534/genetics.105.044727
  7. Avni R, Nave M, Barad O, et al. Wild emmer genome architecture and diversity elucidate wheat evolution and domestication. Science. 2017;357(6346):93-97. — doi:10.1126/science.aan0032
  8. Dubcovsky J, Dvorak J. Genome plasticity a key factor in the success of polyploid wheat under domestication. Science. 2007;316(5833):1862-1866. — doi:10.1126/science.1143986
  9. Marcussen T, Sandve SR, Heier L, et al. Ancient hybridizations among the ancestral genomes of bread wheat. Science. 2014;345(6194):1250092. — doi:10.1126/science.1250092
  10. International Wheat Genome Sequencing Consortium (Appels R, Eversole K, Stein N, et al.). Shifting the limits in wheat research and breeding using a fully annotated reference genome. Science. 2018;361(6403):eaar7191. — doi:10.1126/science.aar7191
  11. Balfourier F, Bouchet S, Robert S, et al. Worldwide phylogeography and history of wheat genetic diversity. Science Advances. 2019;5(5):eaav0536. — doi:10.1126/sciadv.aav0536
  12. Peng J, Richards DE, Hartley NM, et al. "Green revolution" genes encode mutant gibberellin response modulators. Nature. 1999;400(6741):256-261. — doi:10.1038/22307
  13. Hedden P. The genes of the Green Revolution. Trends in Genetics. 2003;19(1):5-9. — doi:10.1016/S0168-9525(02)00009-4
  14. Evenson RE, Gollin D. Assessing the impact of the Green Revolution, 1960 to 2000. Science. 2003;300(5620):758-762. — doi:10.1126/science.1078710
  15. Pingali PL. Green Revolution: impacts, limits, and the path ahead. Proceedings of the National Academy of Sciences. 2012;109(31):12302-12308. — doi:10.1073/pnas.0912953109
  16. Fan MS, Zhao FJ, Fairweather-Tait SJ, Poulton PR, Dunham SJ, McGrath SP. Evidence of decreasing mineral density in wheat grain over the last 160 years. Journal of Trace Elements in Medicine and Biology. 2008;22(4):315-324. — doi:10.1016/j.jtemb.2008.07.002
  17. Kasarda DD. Can an increase in celiac disease be attributed to an increase in the gluten content of wheat as a consequence of wheat breeding? Journal of Agricultural and Food Chemistry. 2013;61(6):1155-1159. — doi:10.1021/jf305122s
  18. Pronin D, Börner A, Weber H, Scherf KA. Wheat (Triticum aestivum L.) breeding from 1891 to 2010 contributed to increasing yield and glutenin contents but decreasing protein and gliadin contents. Journal of Agricultural and Food Chemistry. 2020;68(46):13247-13256. — doi:10.1021/acs.jafc.0c02815

Further reading via topic search: PubMed: wheat domestication in the Fertile Crescent and PubMed: Green Revolution semi-dwarf wheat.

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Connections

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