The earliest introduction of rice into the human diet occurred in the Pearl River valley region of China between 10,000 and 14,000 years ago with the cultivation of Oryza rufipogon, a species of wild grass. Both of the main subspecies of rice, indica and japonica, originated in the same time period. The domestication of subspecies O. glaberrima occurred in West Africa between 1,500 and 800 B.C.
The practice of turning soil into muddy patches and transplanting seedlings led to the full domestication of rice in early Chinese civilization. Archaeologists found the earliest rice farming implements, dating back about 8,000 years ago, in the regions of the Chinese Yangtze and Huai Rivers. Cultivation of this rice species spread throughout the region over the proceeding 2,000 years.
The domestication of rice later spread from China to nearby countries such as Sri Lanka and India around 1,000 B.C. The introduction of rice to ancient Greek civilization traces back to the expeditions of Alexander the Great around 340 B.C. Afterwards, rice spread throughout southern Europe and northern Africa.
Rice spread to the Americas via early European explorations of the New World. The Portuguese brought it to Brazil, while the Spanish brought it to Central America. The first rice crops in North America date back to 1685 in what is now South Carolina. Historians believe that slaves from West Africa brought the agricultural methods for growing the crops in this region.