英语听力文摘 English Digest 669 高原反应是什么引起的？

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　　Anyone who has vacationed in the higher elevations¹ of Colorado, such as Vail and Estes Park, will tell you altitude sickness can be a real problem. Loss of appetite, nausea², vomiting³, weakness, dizziness, and difficulty sleeping can plague those visiting areas over eight thousand feet.

　　High Up

　　Altitude sickness results from the lack of oxygen at high elevations. At thirteen thousand feet, every lungful of air holds only sixty percent of what it would at sea level. Despite that fact, many indigenous⁴ people live in areas of low oxygen concentration with few adverse⁵ effects. The big question is, how do they survive?

　　The body can adapt to low oxygen levels by making more hemoglobin, an oxygen-carrying molecule⁶ in red blood cells. But too much hemoglobin over a long period of time can put a person at risk of blood clots⁷, stroke, or chronic⁸ mountain sickness.

　　Scientists wondered how mountain people can remain healthy living at high altitudes. To see if genes⁹ contribute, scientists analyzed¹⁰ the genomes of three ethnic¹¹ groups living at altitudes over twelve thousand feet, two from Ethiopia, and Tibetans.

　　Oromo

　　One Ethiopian group, the Oromo, cope the same way lowlanders do, by making more hemoglobin. The Amhara and Tibetans, on the other hand, have hemoglobin levels ten percent lower than the Oromo. Does genetic¹² variation account for this?

　　Scientists found that both the Amhara and Tibetan highlanders possessed¹³ genetic variants¹⁴ associated with low hemoglobin levels.

　　But they were not the same genes. It appears that each group took a different evolutionary¹⁵ path to achieve the same outcome of dampening the usual response of increased hemoglobin.

　　How about all those vacationers in Colorado? They will have to make do with their own lowland genes, for now.

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