Rice is delicious, nutritious, and the primary staple for about half of the world's population. Most researchers agree that humanity's close relationship with the grain (Oryza sativa) began thousands of years ago in China's Yangtze River valley, but they have sharply debated when prehistoric farmers began domesticating wild rice and how long they took to do it. On page 1607 of this issue, archaeologists argue that rice remains from a 7000-year-old site in the Yangtze delta point to a later and slower domestication than has often been claimed.
What is the evidence?
The new data come from the site of Tianluoshan, just inland from Hangzhou Bay, south of Shanghai. Excavations between 2004 and 2007 revealed the wooden posts of buildings from a prehistoric village, along with boat paddles, stone axes, and thousands of plant remains. A team led by archaeologist Dorian Fuller of University College London and dig director Guo-Ping Sun of the Zhejiang Provincial Institute of Cultural Relics and Archaeology in the city of Hangzhou analyzed some 24,000 plant remains from the site, including about 2600 rice spikelets, which are attached to the stalk and carry the edible grain. In wild rice, the spikelets ripen and then fall to the ground naturally, allowing the plant to reproduce. But domesticated varieties require human action, such as threshing, to tear the spikelets from the stalk. Archaeologists can often tell the difference: The bases of wild spikelets have a smooth scar where they were attached to the plant, whereas domesticated spikelets have uneven scars from being torn off.
The team focused on three archaeological levels spanning 6900 to 6600 years ago, based on radiocarbon dating of rice and other plant remains. (All dates are in calibrated calendar years.) Over that 300-year period, domesticated spikelets increased from 27.4% of the total to 38.8%; over the same time, rice increased from 8% to 24% of the total plant remains, which came from more than 50 species including wild acorns and water chestnuts. Fuller and his colleagues conclude that domestication was a slow process still under way 6600 years ago, and that the villagers of Tianluoshan relied heavily on wild plants--such as wild rice and acorns--at that late date.
Not everyone agrees, and I go on to quote other researchers who think that these conclusions are premature, and who also point to evidence that rice might have been domesticated as early as 10,000 years ago--eg at the site of Shangshan, about 150 kilometers southwest of Tianluoshan.
So think about all this next time you go for sushi--unless, of course, you don't care when rice was domesticated as long as the job got done.