It鈥檚 known as the roof of the world. At altitudes of over 2.5聽kilometres, the north-eastern Tibetan plateau proved daunting but irresistible terrain to ancient human societies. But it wasn鈥檛 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聽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鈥檛 until 3600 years ago that humans permanently settled at heights above 2.5聽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聽archaeological sites across the north-eastern plateau.
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Cereal gains
Millet made up 98聽per cent of the cereal grains recovered from earlier sites, none of which were any higher than 2.5聽kilometres above sea-level. But 3600 years ago, agricultural settlements reached new heights, some as high as 3.4聽kilometres, as barley became the crop of choice.
鈥淚t鈥檚 taking a novel crop and using it in a different way 鈥� exploring these high altitudes in a way that wasn鈥檛 possible before,鈥� says of the University of Cambridge, a member of the team that did the analysis.
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.
鈥淧eople spread almost everywhere as hunter-gatherers, but they were mostly few and far between, and mobile, especially in places like Tibet,鈥� says of University College London, who wasn鈥檛 involved in the study. 鈥淎griculture allowed populations to settle into [new] environments and grow in numbers.鈥�
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.
鈥淚t鈥檚 a global phenomenon of farmers taking on exotic crops,鈥� says Jones. 鈥淚t鈥檚 basically an expansionist period where people were looking for new options in new, extreme environments.鈥�
This spreading of crops reflects the opening-up of the first Central Asian trade routes between 4500 and 4000 years ago, says Jones. 鈥淭he 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,鈥� he says.
By about 2500 to 2000 years ago, these routes had become the famous silk road network that linked China and the Mediterranean.
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