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1 .This is Scientific American 60-Second Science. I'm Cynthia Graber. Got a minute?
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2 .The Tibetan Plateau, at an altitude of some 3000 meters above sea level, is often called the 'roof of the world.'
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3 .Some prehistoric people tried living there starting about 20,000 years ago.
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4 .Remains of cooked animals and small-scale hearths show that a few hardy souls did give the harsh region a go, at least temporarily.
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5 .But they did not stick around.
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6 .Permanent human settlements in the area began about 5,200 years ago.
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7 .So scientists wanted to know. What changed?
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8 .Researchers collected artifacts, animal bones and plant remains from 53 sites.
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9 .The oldest camps only reached altitudes of about 2,500 meters.
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10 .And at these sites, millet makes up 98 percent of dietary grain.
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11 .But about 3,600 years a new kind of barley arrived in the region, after being domesticated in the Fertile Crescent that spread from the Persian Gulf to the Nile.
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12 .The new barley tolerated frost and had a longer growing season.
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13 .Which means it grew above the 3000 meter mark and that people could settle there.
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14 .Diets at those heights became dominated by the new, hardy barley.
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15 .The findings are in the journal Science.
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16 .The researchers say that the cross-cultural grain exchange from the Fertile Crescent thus appears to be what allowed humans to finally reach the roof of the world.
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17 .Thanks for the minute, for Scientific American 60-Second Science. I'm Cynthia Graber.
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