Ancient Cultivation Harnessed Pre‑Existing Genetic Variation to Domesticate Rice, Corn, and Beans

More than 8,000 years ago, people in the Lower Yangtze Valley began cultivating the wild grass Oryza rufipogon. By selecting rare plants that failed to shatter seeds, stood upright, and were easier to harvest, they gradually assembled a suite of traits that distinguish modern Asian rice (Oryza sativa japonica) from its wild ancestor. Genomic studies now show that key domestication mutations—such as those in SH4 and qSH3 that prevent seed shattering—were already present at low frequencies in wild populations long before cultivation began. Similar patterns emerged in corn, where the tga1 mutation dates back over 40,000 years, and in adzuki beans, where seed‑coat and pod‑shattering mutations rose in frequency thousands of years before domestication. These findings reveal that early farmers shaped crop evolution by exploiting existing genetic diversity, a process that underpins the rapid adaptation and spread of staple foods worldwide.