Some ideas need time to take root. A new analysis suggests it took up to 12,000 years for people in what is now China to go from eating wild plants to farming them. Agriculture elsewhere also took time to flower.
Li Liu of Stanford University and colleagues studied three grinding stones from China's Yellow River region. They bear residues showing that they were used to process millet and other grains, as well as yams, beans and roots.
The stones date from 23,000 to 19,500 years ago, late in the last ice age. But the earliest archaeological evidence for crop cultivation in China is 11,000 years old, suggesting that farming was slow to emerge from ancient traditions of plant use.
That fits with a wider pattern, says Robin Allaby of the University of Warwick, UK. In the Middle East "we also have evidence of cereals at that 23,000-year point", he says ? which is long before people were farming them. "Although this period is around the late glacial maximum, there is a blip at 23,000 years during which time it was milder." Millet and the other food plants could have flourished in the warmth, tempting people to start exploiting them.
Some of the plants, like the snakegourd root, are still used in traditional medicines. Karen Hardy at the Catalan Institution for Research and Advanced Studies in Barcelona, Spain, says she would not be surprised if ancient peoples "knew how to select plant food that benefited their health". Last year she reported evidence that Neanderthals used medicinal plants.
"We can never know for certain why a plant was ingested, but I think these early people probably had a detailed knowledge of the plants they selected and used," Hardy says. "This is likely to have included their medicinal as well as their nutritional qualities."
Journal reference: PNAS, DOI: 10.1073/pnas.1217864110
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