The wild rice consumed by our Neolithic ancestors was very different from the domesticated rice eaten today. Although it is unclear when humans first started farming rice, the oldest paddy fieldsin the lower Yangzi River Valleydate back to 4000 BC. During its long history of cultivation, rice plants with traits that reduce yield or impede harvest (e.g., grain shattering) were weeded out, whereas those with traits that increase yield (e.g., highly branched flowering structures) were selected and propagated. Although the resulting rice plants are super-producers that feed much of the world's population, they rely on human assistance and cannot withstand harsh environmental conditions.