Barley (Hordeum vulgare ssp. vulgare) was one of the first and earliest diffused crops of the Neolithic farming communities of the middle east. The earliest remains of barley have been recovered alongside einkorn and emmer wheat at Neolithic sites in the so-called Fertile Crescent, including Jericho (Palestine) and Abu Hureyra (Syria) about 8500 years BC. In the Zagros Mountains, at sites such as Ali Kosh (Iran) and Jarmo (Iraq), domestic barley has been found at sites dated between 7000 and 8000 BC. Further east, domesticated barley has been found at Mehrgarh (Pakistan) about 7000 BC, and at Jeitun (Turkmenistan) as early as about 6000 years BC.
The natural form of barley grows wild in the mideast and central Asia; the main difference between domestic and wild barley (H. vulgare ssp. spontaneum),is that the domesticated form has non-brittle ears. What that means is that when ripe, the undomesticated form of barley becomes brittle and shatters, allowing a wide dispersion of its seeds. Humans modified the barley, probably by selectively harvesting the barley that did not shatter when ripe.
Recent investigations suggest that genetic evidence exists for at least two separate domestication events, one in the Fertile Crescent and a second in central Asia some 1500-3000 kilometers east.
Barley and DNA
A recent (Jones and colleagues 2012) phylogeographic analysis of barley in the northern fringes of Europe and in the Alpine region found that cold adaptive gene mutations were identifiable in modern barley landraces. The adaptations included one type that was non-responsive to day length (that is, delayed flowering), and is found in northeast Europe and high altitude locations. Alternatively, landraces in the Mediterranean region were predominantly responsive to day length. In central Europe, however, day length is not a trait which (apparently) had been selected for.
Jones and colleagues were unwilling to rule out the actions of possible bottlenecks, but suggest that temporary climate changes might have affected the selection of traits for various regions, delaying the spread of barley or speeding it, depending on the adaptability of the crop to the region.
Badr, A., et al. 2000. On the Origin and Domestication History of Barley (Hordeum vulgare). Molecular Biology and Evolution 17:499-510.
Jones G, Jones H, Charles MP, Jones MK, Colledge S, Leigh FJ, Lister DA, Smith LMJ, Powell W, and Brown TA. 2012. Phylogeographic analysis of barley DNA as evidence for the spread of Neolithic agriculture through Europe. Journal of Archaeological Science 39(10):3230-3238.
Komatsuda, Takao et al. 2007. Six-rowed barley originated from a mutation in a homeodomain-leucine zipper I-class homeobox gene. Proceedings of the National Academy of Sciences 104:1424-1429.
Morrell, Peter L. and Michael T. Clegg 2007 Genetic evidence for a second domestication of barley (Hordeum vulgare) east of the Fertile Crescent. Proceedings of the National Academy of Sciences 104: 3289-3294.
Barley Domestication is a part of the About.com Guide to Plant Domestications.