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The introduction of cold-tolerant crops such as barley and wheat may have helped agriculture spread to the roof of the world.

The introduction of cold-tolerant crops such as barley and wheat may have helped agriculture spread to the roof of the world.

Sharada Prasad/Flickr

Barley helped ancient Tibetans climb to 3400 meters

Life above 3000 meters is tough. Not only can the thin air cause gasping and fatigue, but it can also swell brains and fill lungs with fluid, sometimes fatally. Yet people have been living at high altitudes for thousands of years in places like the Andes and the Tibetan Plateau. Now, a group of researchers believes it has identified a key tool that allowed Tibetans to settle at higher and higher elevations: barley.

The Tibetan Plateau, which encompasses the Himalaya Mountains and stretches across 2.5 million square kilometers, seems like a place that would have resisted human settlement. Yet archaeologists know that nomadic hunter-gatherers likely lived there seasonally and possibly year-round by at least 10,000 years ago. How and when agriculture—and the more settled lifestyle it requires—made its way to the higher reaches of the region remained mysterious. To begin to answer the question, a team of Chinese, American, and British researchers reviewed data from past excavations, some of which were conducted as far back as the 1970s. From 53 sites at various elevations and time periods, they managed to collect 63 samples of charred grains suitable for radiocarbon dating.

The new dates yielded an interesting pattern. Before 3600 years ago, farming appears to have been limited to 2500 meters and below. Far and away, the most abundant grain at these sites was millet, which had long been planted across northern China. Then, about 3600 years ago, farmers started climbing higher and higher up on the plateau, reaching as far as 3400 meters above sea level. So what changed?

The researchers think the plateau dwellers got their hands on some barley seeds. Compared with millet, barley is especially tolerant of cold and frost, making it ideal for high-elevation farming in Tibet, as Washington State University archaeologist Jade d’Alpoim Guedes pointed out in previous studies. And at right around 3600 years ago, barley starts showing up all over the Tibetan Plateau, sometimes accompanied by similarly cold-tolerant wheat. At lower elevations, plateau dwellers simply incorporated a bit of barley into their millet-heavy diet, but the high-altitude farmers appear to have abandoned millet altogether and relied almost completely on the new, hardier grain, the team reports online today in Science.

“Barley agriculture could provide people [with] sustained food supplies even during winter,” the three lead authors write in a joint e-mail. “Barley and wheat were first domesticated in [the Fertile Crescent] in West Asia around 10,500 years ago, where the environment is quite different from that in the Tibetan Plateau.” The fact that they thrived in the new, more extreme environment was “a lucky accident.” It’s unclear how and when barley moved from the Fertile Crescent to East Asia.

“It’s a fascinating example of a cultural strategy to tackle a challenging place,” says Kurt Rademaker, an archaeologist at the University of Tübingen in Germany who studies high-elevation settlements in the Andes. Interestingly, the expansion of farming to 3400-plus meters happened just as the climate in Tibet was getting colder—not optimal conditions for settling already chilly higher altitudes. But the barley seems to have made it so that “the climate was no longer a barrier,” Rademaker notes.

Still, agriculture may not have been required for year-round, permanent settlement of the Tibetan Plateau, says Mark Aldenderfer, an archaeologist at the University of California, Merced, who has excavated there for many years. “I think that the 3600-year-ago pulse [of human migration and settlement] is probably one of the very late migrations of people or ideas onto the plateau.” In fact, genetic studies suggest that Tibetans began to exhibit biological adaptions that helped them cope with high-altitude living at least 10,000 years ago, he notes.

But other genetic data suggests that at least one high-elevation gene appeared in Tibetans only between 2750 and 5500 years ago—more in line with the appearance of high-elevation agriculture on the plateau. “With disparate time estimates coming from the genetic studies, we need archaeological data to fix the chronology for when people are present in different places,” Rademaker says. High-elevation sites tend to be particularly difficult to study, so more information about them is “always valuable.”