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A discovery by researchers at Washington University in St. Louis and Shandong University—together with an international team of scientists working in China, Japan and South Korea—sheds new light on the historical use and domestication of the adzuki bean across East Asia.

Researchers recovered charred adzuki bean remains from the Xiaogao site in Shandong, China, that were dated to 9,000 to 8,000 years ago, during the beginning of the Neolithic age when humans first began to cultivate plants and domesticate animals for food. The findings— in the Proceedings of the National Academy of Sciences on Sept. 22—push the record of this significant legume back by at least 4,000 years in the Yellow River region.

The adzuki bean (Vigna angularis) is a staple crop widely cultivated in East Asia that is prized for both its nutritional value and nitrogen-fixing properties, meaning it also enriches the soil. It holds cultural significance and is featured prominently in various cuisines, even today.

According to the researchers, the new evidence suggests that adzuki beans formed part of an early Neolithic multi-cropping system alongside millet, rice and soybeans, in a well-established agricultural tradition in the Lower Yellow River region.

The discovery was a part of a larger analysis of charred adzuki bean remains from 41 archaeological sites across East Asia, including the Yellow River, Japan, Korea and southern China environment. By combining newly available and previously published data, researchers also discovered significant regional differences in the size and utilization of the bean, providing a comprehensive look at the chronology and evolution of this important legume.

"At the global level, there has been considerable recent momentum in recognizing plant domestication as a protracted and widely dispersed process—one without singular geographical centers," said Xinyi Liu, a professor and associate chair of anthropology in Arts & Sciences at WashU. "Our results align with this perspective by illustrating parallel developments in the Yellow River, Japan and South Korea during the Neolithic.

"The divergent trajectories of adzuki bean size in the Neolithic Yellow River and Jomon-period Japan are particularly revealing, as they demonstrate that culinary and dietary practices played a role in the domestication process as significant as the environmental factors."