Barley elevated Central Asian farmers to ‘the roof of the world’

A menu shift courtesy of the Fertile Crescent enabled farmers to live year-round at high altitudes on Central Asia’s Tibetan Plateau starting about 3,600 years ago, a new study finds.

Barley and wheat, frost-resistant crops that originated in the Middle East, provided a stable food source for Tibetan farmers in villages located 2,500 to 3,400 meters above sea level, says a team led by geologist Fahu Chen and geoarchaeologist Guanghui Dong, both of Lanzhou University in China.

Tibetan farmers, who also raised cattle and other animals, lived year-round on the plateau — also known as “the roof of the world” — as early as 5,200 years ago. But they did not go any higher than 2,500 meters above sea level for more than a millennium, the researchers report November 20 in Science. Crops at that time consisted mainly of North Chinese broomcorn and foxtail millet, grains unable to withstand extreme cold at higher altitudes, the team concludes.

Villagers sought unsettled ground as high as 2,500 meters above sea level on the Tibetan Plateau as regional populations expanded, Dong suggests. Above that altitude, people face health problems due to thin air and the challenge of storing enough food for brutal winters. Migrations to higher ground continued even as temperatures started cooling around 4,500 years ago.

“But only after 3,600 years ago, when frost-hardy and cold-tolerant barley and wheat, and perhaps sheep too, arrived, could people move to as high as 3,400 meters above sea level,” Dong says.

Barley and wheat reached Tibet after high-altitude farmers elsewhere, possibly in Iran, developed genetic variants of these crops capable of growing over the summer, suggests archaeobotanist Dorian Fuller of University College London. Barley and wheat typically grow in winter, a season that lacks enough heat and sunlight to germinate crops at high altitudes, he says.

Previous discoveries indicate that, at least 15,000 years ago, hunter-gatherers occasionally tracked game on the Tibetan Plateau at altitudes of 4,300 meters above sea level or more. These seasonal hunting forays continued until 5,200 years ago, when agriculture and animal herding made it possible to store enough food for high-altitude winters, Chen proposes.

He and his colleagues studied pottery, plant remains, stone implements, human and nonhuman bones and other material from 53 ancient sites on the northeastern Tibetan Plateau, mostly farming villages along the Yellow River and its tributaries. Radiocarbon analyses of charred grains yielded age estimates for each site.

Ratios of specific forms of carbon in farmers’ bones indicated that, at villages located 2,500 meters above sea level or higher, diets shifted to Middle Eastern crops starting about 3,600 years ago. Barley dominated the plant remains at those sites.

The new study confirms earlier suspicions that high-altitude farming on the Tibetan Plateau began only a few thousand years ago, says archaeologist David Madsen of the University of Texas at Austin. But extended stays at comparable elevations could have occurred earlier, he holds.

By about 8,000 years ago, evidence suggests, extended families of hunter-gatherers lived by a Tibetan Plateau lake at an altitude of 3,200 meters above sea level during summer months. “These families may have lived at lower altitudes during winter, but whether those altitudes were above or below 2,500 meters is unknown,” Madsen says.

It’s also an open question whether yak herders spent all or most of the year roaming above 2,500 meters before farmers arrived, he adds. Limited finds suggest the first farming villages were built almost 1,000 years before domesticated yaks arrived, Dong says.