It’s known as the roof of the world. At altitudes of over 2.5 kilometres, the north-eastern Tibetan plateau proved daunting but irresistible terrain to ancient human societies. But it wasn’t until they got their hands on frost-resistant barley that they could permanently settle these heady heights.
Archaeological evidence, including handprints and footprints found at 4.2 kilometres above sea level, suggests humans had an intermittent presence on the Tibetan Plateau as long as 20,000 years ago. By 5200 years ago, villages began to appear at lower altitudes, but it wasn’t until 3600 years ago that humans permanently settled at heights above 2.5 kilometres.
The move to year-round lofty living coincided with a shift from farming frost-sensitive millet to frost-resistant barley, according to a study of plant remains, animal bones and artefacts from 53 archaeological sites across the north-eastern plateau.
Cereal gains
Millet made up 98 per cent of the cereal grains recovered from earlier sites, none of which were any higher than 2.5 kilometres above sea-level. But 3600 years ago, agricultural settlements reached new heights, some as high as 3.4 kilometres, as barley became the crop of choice.
“It’s taking a novel crop and using it in a different way – exploring these high altitudes in a way that wasn’t possible before,” says Martin Jones of the University of Cambridge, a member of the team that did the analysis.
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He says the barley is likely to have originated in the fertile crescent region of the Middle East, and moved east by being passed from neighbour to neighbour.
“People spread almost everywhere as hunter-gatherers, but they were mostly few and far between, and mobile, especially in places like Tibet,” says Dorian Fuller of University College London, who wasn’t involved in the study. “Agriculture allowed populations to settle into [new] environments and grow in numbers.”
Crop-swapping
This shift to barley coincides with a global period of intensive crop-swapping, particularly in Asia. As barley and wheat moved eastwards, African crops were reaching India, and rice farming was spreading too.
“It’s a global phenomenon of farmers taking on exotic crops,” says Jones. “It’s basically an expansionist period where people were looking for new options in new, extreme environments.”
This spreading of crops reflects the opening-up of the first Central Asian trade routes between 4500 and 4000 years ago, says Jones. “The arrival of barley and wheat in China happened around the same time that Chinese millets, peaches, apricots and genotypes of rice reached Central Asia and the Indus valley,” he says.
By about 2500 to 2000 years ago, these routes had become the famous silk road network that linked China and the Mediterranean.