EVERY cook knows there are two main types of rice: the sticky, short-grained stuff used in desserts, sushi and risotto, and the drier, long-grained varieties. Crop scientists call them japonica and indica rice respectively. Both were bred from a wild grass, Oryza rufipogon, some 9000 years ago, but researchers have never been sure whether they came from a single domestication or independent origins.
Now an analysis of the DNA sequences in cultivated rice has shown that japonica and indica rice are genetically more different than previously supposed, and were domesticated in different places at different times. The sticky, short-grained japonica was first bred by Chinese hunter-gatherers, probably along the banks of the Yangtze river, as the world warmed at the end of the last ice age. The long-grained indica was bred independently, from a different gene pool of wild O. rufipogon growing south of the Himalayas, in India, Burma or Thailand (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0603152103).
Asian rice is the world鈥檚 most important food crop, and provides an estimated 20 per cent of all the calories consumed by the human race. Barbara Schaal of Washington University in St Louis, who led the team that made the discovery, says further genetic research into the origins of rice could be a useful way of tracking down genetic resources for improving modern commercial varieties.
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The origins of rice are far more complicated than those of wheat, barley and corn, which each arose from a single domestication. There are an estimated 120,000 local varieties of rice in Asia, and while most of these are descended from the japonica and indica subspecies, some, including basmati rice from India, may have been independently domesticated.
There is also intriguing, though disputed, evidence that rice cultivation may have had at least one false start. Four years ago, Houyuan Lu of the Chinese Academy of Sciences in Beijing reported discovering the remains of domesticated rice grown in southern China almost 14,000 years ago (Boreas, vol 31, p 378), during a warm period towards the end of the last ice age. This breed of rice died out 13,000 years ago during a cold snap known as the Younger Dryas.
Meanwhile, west African farmers cultivated a third, entirely distinct type of rice, Oryza glaberrima. What cooks call 鈥渨ild rice鈥� is from a different genus altogether.
Figs came first
Compared with staples such as rice, the fig seems like little more than an irrelevance. Yet it may deserve a hugely important place in human history, as the plant that started the agricultural age.
Archaeobotanists have discovered that figs were grown by people more than 11,000 years ago, the earliest confirmed date so far for a domesticated crop. Mordechai Kislev and colleagues at Bar-Ilan University in Ramat-Gan, Israel, examined nine carbonised figs and 313 fig fragments that had been collected in the 1970s and 1980s, stored and then forgotten in the Israel Museum in Jerusalem. The figs had been discovered during the excavation of a house in the village of Gilgal in the lower Jordan valley, radiocarbon-dated to be about 11,400 years old (Science, vol 312, p 1372).
Crucially, the figs shared a mutation that made them unable to produce seeds, and would only have survived had people made cuttings of the plants. The finding pushes back the dawn of agriculture by 1000 years.
Rowan Hooper
