Story of Prehistoric Food Globalization as Told by Tiny Grains, Thousands Of Years Old

First domesticated 10,000 years ago in the Fertile Crescent of the Middle East, wheat and barley took vastly different routes to China, with barley switching from a winter to both a winter and summer crop during a thousand-year detour along the southern Tibetan Plateau, suggests new research from Washington University in St. Louis.

“The eastern dispersals of wheat and barley were distinct in both space and time,” said Xinyi Liu, assistant professor of archaeology in Arts & Sciences, and lead author of this study published in the journal PLOS One.

“Wheat was introduced to central China in the second or third millennium B.C., but barley did not arrive there until the first millennium B.C.,” Liu said. “While previous research suggests wheat cultivation moved east along the northern edge of the Tibetan Plateau, our study calls attention to the possibility of a southern route (via India and Tibet) for barley.”

Based on the radiocarbon analysis of 70 ancient barley grains recovered from archaeological sites in China, India, Kyrgyzstan and Pakistan, together with DNA and ancient textual evidence, the study tackles the mystery of why ancient Chinese farmers would change the seasonality of a barley crop that originated in a latitudinal range similar to their own.

The answer, Liu explains, is that barley changed from a winter to summer crop during its passage to China, a period in which it spent hundreds of years evolving traits that allowed it to thrive during short summer growing seasons in the highlands of Tibet and northern India.

“Barley arrives in central China later than wheat, bringing with it a degree of genetic diversity in relation to flowering time responses,” Liu said. “We infer such diversity reflects preadaptation of barley varieties along that possible southern route to seasonal challenges, particularly the high altitude effect, and that led to the origins of eastern spring barley.”

Liu’s research on the dispersal of wheat and barley cultivation adds a new chapter to our understanding of prehistoric food globalization, a process that began about 5000 B.C. and intensified around 1500 B.C. This ongoing research traces the geographic paths and dispersal times of crops and cultivation systems that expanded across Eurasia and eventually worldwide, from points of origination in North Africa and West, East and South Asia. The eastern expansion of wheat and barley is a key story in this process.Map of Eurasia shows the oldest radiocarbon-measured dates (B.C.) for individual grains of barley recovered from each region. Wheat and barley arrived in South Asia about a millennium before they arrived in East Asia. Free-threshing wheats spread to China along a route to the north of the Tibetan Plateau. Naked barley is likely to have been introduced to China via southern highland routes that remain to be identified. 

Citation: Journey to the east: Diverse routes and variable flowering times for wheat and barley en route to prehistoric China  http://dx.doi.org/10.1371/journal.pone.0187405