科学美国人60秒 SSS 2014-09-02_在线英语听力室

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When you hear the word “mutation¹,” you may think of something destructive, or of Marvel’s X-Men. But some mutations—which are just differences in DNA²—can be historic. Take, for example, a genetic³ sequence found in the vast majority of people from Tibet.

Millions of Tibetans spend their days at average elevations⁴ of nearly 15,000 feet—that’s more than half the height of Mount Everest. Up there, the air is thin—with 40 percent less oxygen than at sea level. That lack of O2 would leave most Westerners struggling for breath, but Tibetans seem to breathe easy.

To find out how these highlanders cope, researchers compared the DNA of 90 Tibetans to that of people who are not altitude adapted. And they discovered a single change that prevents Tibetans’ blood from becoming dangerously clogged⁵ with red blood cells—a response that can be deadly for non-native mountaineers. The finding is described in the journal Nature Genetics.

This mutation appears to have originated just 8,000 years ago. But it’s so advantageous⁶ that today nearly 90 percent of Tibetans have it. While it’s virtually absent in even closely related lowland neighbors.

The finding demonstrates that a really useful mutation will always rise to the top.

— Karen Hopkin

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1 mutation
n.变化，变异，转变
参考例句：
People who have this mutation need less sleep than others.有这种突变的人需要的睡眠比其他人少。 So far the discussion has centered entirely around mutation in the strict sense.到目前为止，严格来讲，讨论完全集中于围绕突变问题上。

2 DNA
(缩)deoxyribonucleic acid 脱氧核糖核酸
参考例句：
DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。 Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

3 genetic
adj.遗传的，遗传学的
参考例句：
It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。 Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。

4 elevations
（水平或数量）提高( elevation的名词复数 )；高地；海拔；提升
参考例句：
Weight of the crust changes as elevations are eroded and materials are deposited elsewhere. 当高地受到侵蚀，物质沉积到别的地方时，地壳的重量就改变。 All deck elevations are on the top of structural beams. 所有甲板标高线均指结构梁顶线。

5 clogged
（使）阻碍( clog的过去式和过去分词 )；淤滞
参考例句：
The narrow streets were clogged with traffic. 狭窄的街道上交通堵塞。 The intake of gasoline was stopped by a clogged fuel line. 汽油的注入由于管道阻塞而停止了。

6 advantageous
adj.有利的；有帮助的
参考例句：
Injections of vitamin C are obviously advantageous.注射维生素C显然是有利的。 You're in a very advantageous position.你处于非常有利的地位。

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科学美国人60秒 SSS 2014-09-02