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Wheat Domestication

The Origins of Wheat

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Emmer wheat (Triticum turgidum ssp. dicoccoides)

Emmer wheat (Triticum turgidum ssp. dicoccoides)

Zvi Peleg

Wheat is a grain crop with some 25,000 diffrent cultivars in the world today: most of these forms are varieties of two groups: common wheat and durum wheat. Common or bread wheat Triticum aestivum accounts for some 95% of all the consumed wheat in the world today; the other five percent is durum or hard wheat T. turgidum ssp. durum, used in pasta and semolina products. Bread and durum wheat are both domesticated forms of wild emmer wheat (reported variously as T. araraticum, T. turgidum ssp. dicoccoides, or T. dicocoides). Another early form of wheat called einkorn (T. monococcum), was domesticated at about the same time, but has limited distribution today.

Origins of Wheat

The origins of our modern wheat, according to genetics and archaeological studies, are found in the Karacadag mountain region of what is today southeastern Turkey. There, some 12,000 years ago or so, both einkorn and emmer wheats were domesticated. The earliest collected wheat was wild emmer, at the Ohalo II site, about 23,000 years ago. Emmer was first cultivated in the southern Levant (Netiv Hugdud, Tell Aswad, other PPNA sites); while einkorn is found in the north PPNA sites (Abu Hureyra, Mureybet, Jerf el Ahmar, Göbekli Tepe, other southern PPNA). Spelt (T. spelta) and Timopheev's wheat (T. timopheevii) were ancient forms of emmer wheat developed by the late Neolithic, but neither has much of a market today.

The main differences between the wild forms of wheat and domesticated wheat are that domesticated forms have larger seeds with hulls and a non-shattering rachis. When wild wheat is ripe, the rachis--the stem that keeps the wheat shafts together--shatters so that the seeds can disperse themselves. But that naturally useful brittleness doesn't suit humans, who prefer to wait until the wheat is ripe to harvest it. Of course, if farmers harvest wheat when they believe it is ready, they only get the wheat that remains on the rachis: that wheat is what the farmers plant and in the process selected wheats with rachis that didn't become brittle at harvest time.

Other traits apparently selected for include spike size, growing season, plant height, and grain size.

How Long Did Domestication Take?

One of the ongoing arguments about wheat is the length of time it took for this process to occur. Some scholars argue for a fairly rapid process, of a few centuries; while others argue that the process from cultivation to domestication took up to 5,000 years. These scholars are debating the date of the earliest domestication: all of them agree, and the evidence is abundant, that by ca 10,400 years ago, domesticated wheat was in widespread use throughout the Levant region.

The earliest evidence for both domesticated einkorn and emmer wheats found to date was at the Syrian site of Abu Hureyra, in occupation layers dated to the Late Epipaleolithic period, the beginning of the Younger Dryas, ca 13,000-12,000 cal BP; some scholars (Colledge and Conolly 2010) have argued that the evidence does not show cultivation at this time, although it does indicate a broadening of the diet base to include a reliance on wild grains including the wheats.

Another recent study (Haldorsen and colleagues) focusing on one-grained einkorn (Triticum monococcum ssp. monococcum) agrees with this later timeline and suggests that one-grained einkorn was domesticated in southeastern Turkey after the end of the Younger Dryas (~11,600-10,400 cal BP).

Recent Studies

Domesticated one-grained einkorn wheat has been recovered from the earliest layers at the Pre-Pottery Neolithic B (PPNB: generally considered the first farmers) sites of Nevali Cori and Cafer Hoyuk about 11,600 cal BP, at the end of the Younger Dryas and at the same time as the establishment of the ritual site of Gobekli Tepe. By 10,400 cal BP, einkorn was widespread throughout the region.

Recent studies in wheat origins include a report of a field experiment on the yield potential of the various forms of wheat; a study on the genetic propensity of wheat to dynamically react to bottlenecks by generating new variations; and a genetic study attempting to discriminate the 'new wheat' of the late Neolithic/Bronze Age, T. timopheevii from emmer wheat.

In 2012, a research team (Brenchley and colleagues) reported that they had completed an analysis of the breadwheat genome.

Sources

This article on the domestication of wheat is a part of the About.com Guide to Plant Domestication, and part of the Dictionary of Archaeology.

Asplund L, Hagenblad J, and Leino MW. 2010. Re-evaluating the history of the wheat domestication gene NAM-B1 using historical plant material. Journal of Archaeological Science 37(9):2303-2307.

Boscato P, Carioni C, Brandolini A, Sadori L, and Rottoli M. 2008. Molecular markers for the discrimination of Triticum turgidum L. subsp. dicoccum (Schrank ex Schübl.) Thell. and Triticum timopheevii (Zhuk.) Zhuk. subsp. timopheevii. Journal of Archaeological Science 35(2):239-246.

Brenchley R, Spannagl M, Pfeifer M, Barker GLA, D'Amore R, Allen AM, McKenzie N, Kramer M, Kerhomou A, Bolser D et al. 2012. Analysis of the breadwheat genome using whole-genome shotgun sequencing. Nature 491(703-709).

Colledge S, and Conolly J. 2010. Reassessing the evidence for the cultivation of wild crops during the Younger Dryas at Tell Abu Hureyra, Syria. Environmental Archaeology 15:124-138.

Doebley JF, Gaut BS, and Smith BD. 2006. The Molecular Genetics of Crop Domestication. Cell 127:1309-1321.

Dubcovsky J, and Dvorak J. 2007.Genome plasticity a key factor in the success of polyploid wheat under domestication. Science 316:1862-1866.

Haldorsen S, Akan H, Çelik B, and Heun M. 2011. The climate of the Younger Dryas as a boundary for Einkorn domestication. Vegetation History and Archaeobotany 20(4):305-318.

Heun M, Schäfer-Pregl R, Klawan D, Castagna R, Accerbi M, Borghi B, and Salamini F. 1997. Site of Einkorn Wheat Domestication Identified by DNA Fingerprinting. Science 278:1312-1314.

Miller Rosen A, and Weiner S. 1994. Identifying ancient irrigation: A new method using opaline phytoliths from emmer wheat. Journal of Archaeological Science 21:125-132.

Out WA. 2008. Growing habits? Delayed introduction of crop cultivation at marginal Neolithic wetland sites. Vegetation History and Archaeobotany 17(Supplement 1):131-138.

Özkan H, Willcox G, Graner A, Salamini F, and Kilian B. 2011. Geographic distribution and domestication of wild emmer wheat (Triticum dicoccoides). Genetic Resources and Crop Evolution 58(1):11-53.

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