Soybean adoption began 5,500 years earlier than thought

Archaeologists have claimed that domestication of soybeans started much before it was previously thought.

Human domestication of soybeans is thought to have first occurred in central China some 3,000 years ago, but archaeologists now suggest that cultures in even earlier times and in other locations adopted the legume (Glycine max).

In the study they compared 949 charred soybean samples from 22 sites in northern China, Japan and South Korea - found in ancient households including hearths, flooring and dumping pits - with 180 modern charred and unburned samples.

The findings add a new view to long-running assumptions about soybean domestication that had been based on genetic and historical records, said lead author Gyoung-Ah Lee, an archaeologist at the University of Oregon.

“Preserved beans have been carbonised, and that distorts the sizes,” Lee said.

“So we experimented with modern soybeans, charring them to compare them with historical samples. All the different sizes and shapes of soybeans may indicate different efforts in different times by different cultural groups in different areas,” he stated.

Experts argue that larger beans reflect domestication, but the transition zone between smaller wild-type soybeans and larger hybridised versions is not understood, Lee said.

Small-seeded soybeans indicating wild-type soybeans date to 9,000 years ago. Historical evidence to date shows a close relationship between soybeans and use in China during the Zhou Dynasty, about 2,000 years ago.

The new study moves domestication back to perhaps 5,500 years ago.   

The new archaeological evidence, Lee says, should be a springboard for archaeologists, crop scientists and plant geneticists to collaborate on understanding cultural contributions, which may lead them to better soybean characteristics.

The finding was reported in the Nov. 4 edition of the online journal PLoS ONE, a publication of the Public Library of Science.