Humans may have driven weeds to evolve to resemble crop plants—And they even became edible

thailands rice farmers
Credit: Siebe Baarda
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Nikolai Vavilov’s story has stuck with Longjiang Fan ever since he learned about the Soviet plant biologist during his undergraduate studies in China in the 1980s. Vavilov’s scientific ideas were both important and novel, explains Fan, now a crop scientist at Zhejiang University.

Based on his observations of domesticated oats and rye, as well as of their wild relatives, Vavilov proposed that the crops’ ancestors were weeds that, over generations, came to resemble domesticated wheat because wheat-like characteristics helped them avoid being weeded out by farmers. It was only after this transformation, Vavilov conjectured, that people began to purposely cultivate and eat these interlopers.

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…. [W]ith genome sequencing becoming ever faster and cheaper, Fan thought the time had come to see whether genetic analysis of apparent weedy mimics would support Vavilov’s idea.

The mimic and non-mimic varieties [of barnyard grass] diverged from each other about 1,000 years ago …. The timeline …. coincides with intensified rice cultivation in the Yangtze basin during China’s Song dynasty.

The results are consistent with the idea that humans, through hand weeding, provided the selective pressure that drove the evolution of the rice-imitating variety.

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