Western mountain climbers are fortunate that there are Sherpas to guide them up Mount Everest. While Westerners can train for years and still not make the summit—although they may still get headlines—Sherpas do it repeatedly, with little fanfare, and while carrying food, packs, and oxygen for their clients. Anthropologists have long been wondering how any humans ever managed to start living up at the Roof of the World in the first place. New work suggests that one of the keys is very, very mundane—nothing like their having superpowers or anything like that. No, the key is... barley.

The northeastern Tibetan Plateau is at an inhospitable elevation, approximately 3,000-4,000 meters above sea level. Yet there are traces of human life there dating back at least 20,000 years BP (Before Present, Present being defined as January 1, 1950, as used in radiocarbon dating). And indications are that at least some aspects of altitude tolerance had evolved long before then (see sidebar).

Handprints, footprints, small hearths, and stone tools have been found from this early period, but these artifacts are probably evidence of temporary hunting camps, each used perhaps only once when parties ventured onto the plateau seeking game. These types of objects do not imply any kind of permanent human habitation up there.

Neolithic and Bronze Age remains of agricultural settlements start showing up around 5,500 years BP. In order to figure out exactly when and how humans moved up onto the plateau, researchers collected animal and plant remains from fifty-three different sites for a comparative analysis. Their results were recently published in Science.

Millet, newly popular as an alternative, gluten-free grain, was the cereal of choice 3,000-5,000 years BP, when it was grown along the Yellow River. But millet is sensitive to frost; its charred remains were found primarily at relatively lower altitudes on the Plateau, only around 2,500 meters above sea level. At higher altitudes—4,700 meters above sea level—barley predominates.

Barley requires about six months between planting and harvesting, so its presence suggests that it was planted in association with sustained, permanent human residence. But barley didn't appear in the region until around 3,000-4,000 years BP, when the typical Chinese millet crop was supplanted by barley that had arrived from the Fertile Crescent. Critically, this Western import is frost resistant and was likely to be what allowed people to first set up sustainable homes and communities way up on the Tibetan Plateau.

It is around this same time that wheat was introduced into China, in the 'Trans-Eurasian Exchange’ that also transferred metallurgical technologies, the use of horses and other animals, and, less helpfully, diseases. These exchanges lay the foundations for the legendary overland routes that would eventually become the Silk Road.

But the cold-tolerant barley was a key transplant. Not only did it enable ancient groups of people to settle the upper reaches of the northeastern Tibetan Plateau, it allowed them to brew beer.

Science, 2014. DOI: 10.1126/science.1259172 (About DOIs).