Today, rice (Oyrza species) feeds more than half the world's population, and accounts for 20 percent of the world's total calorie intake. It grows on every continent in the world except Antartica, and has 21 different wild varieties and two cultivated species: Oryza sativa, domesticated in south Asia at least 10,000 years ago, and Oryza glabberima, domesticated in west Africa between about 1500 and 800 BC.
According to the latest molecular studies, Oryza sativa was domesticated at least twice: O. sativa japonica, developed in south China (probably the Yangtse valley), and O. sativa indica, developed in eastern India or Indonesia. Both of these were domesticated from the original plant called Oryza rufipogon. Rice farming at this early date was dryland cultivation; rice paddies were not developed until about 2500 BC.
The History of Rice in China
The best known evidence for early domestication is japonica. Rice phytoliths (some of which are identifiable to japonica) were identified in the sediment deposits of Diaotonghuan Cave, located near Poyang Lake in the middle Yangtse river valley radiocarbon dated about 10,000-9000 years before the present. Additional soil core testing of the lake sediments revealed rice phytoliths from rice of some sort present in the valley before 12,820 BP (although these were not necessarily domesticated). Shangshan, a Neolithic village in the lower Yangtse valley dated to about 10,000 BP contained ceramic sherds tempered with charred plants, including rice and containing fan-shaped phytoliths. By about 7,000 years ago, japonica is found throughout the Yangtse valley, including large amounts of rice kernels at such sites as TongZian Luojiajiao (7100 BP) and Hemuda (7000 BP).
Earliest Evidence
Four grains of rice were recovered from the Yuchanyan site, a rock shelter in Dao County, Hunan Province in China. They seem to represent very early forms of domestication having characteristics of both japonica and sativa, and are said to be dated between 12,000 and 14,000 years ago, although there is no discussion of what exactly was dated in the very preliminary report.
Sources
This article on the domestication of rice is a part of the About.com Guide to Plant Domestications, and part of the Dictionary of Archaeology. Any mistakes are the responsibility of Kris Hirst.
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