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科学美国人60秒 SSS Last Woollies Had Mammoth Mutations

时间:2017-03-15 02:58:17

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In their heyday1, woolly mammoths blanketed the Siberian steppe, Alaska and large parts of North America. But by 10,000 years ago, warming climates had turned many of the grasslands3 they grazed into forest. And humans, well they weren't so friendly either—one mammoth2 provides quite a feast. So the mammoths largely disappeared. Except there's this one holdout population. On an island in the Arctic Ocean, called Wrangel Island. Where the last mammoths hid out…for more than 6,000 years. 

"So the pyramids have been built, they've started to grow tea in China, and civilization had formed, and here are these mammoths no one knew was there, for the longest period of time." Rebekah Rogers, an evolutionary4 geneticist at the University of North Carolina. "And then people finally found this island around 3,700 years ago, around the time they went extinct."

Rogers and her colleague Montgomery Slatkin analyzed5 the genome from the tooth of one of those island mammoths, which lived 4,300 years ago. They compared it to the genome of a mainland mammoth, from much farther back, 45,000 years. And they found that harmful mutations had polluted the island mammoth's genome in that time interval6. Mutations that led to the loss of smell receptors, and urine proteins—compounds they probably needed for social signaling and mate choice.

The animals also developed this satiny coat, that shines in the light. A trait that's actually popular for pet breeders today, for rabbits and guinea pigs. And the reason for all these mutations? Rogers says there just weren't enough individuals on the island—1,000 at the most, 300 at their lowest—to allow natural selection to run its course. So it wasn't survival of the fittest. It was survival of… whoever randomly7 survived. Which meant they accumulated a lot of mutations. None of which made them drop dead—but they weren't all that fit, either. The study is in the journal PLoS Genetics. [Rebekah L. Rogers, Montgomery Slatkin: Excess of genomic defects in a woolly mammoth on Wrangel island]

Rogers says a similar process could happen for rare animals on Earth today, like cheetahs8, pandas, gorillas9. "If you have a very small population for a very long time you can get this accumulation of bad mutations in their genomes. And so we'd expect to see the same effect for them. It does take a long time period to get a signal as big as what we saw in the mammoths, so the earlier we can intervene for those species, the better off they'll be."

As for those humans who, long ago, found this last holdout of mammoths on Wrangel Island? "We don't have direct evidence they hunted them, but you kind of wish that they had taken them back and domesticated10 them." There's already one interested buyer. "Oh yes, if you can find one I would like to have one as a pet. Preferably a little smaller so it fits in my house."

—Christopher Intagliata


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点击收听单词发音收听单词发音  

1 heyday CdTxI     
n.全盛时期,青春期
参考例句:
  • The 19th century was the heyday of steam railways.19世纪是蒸汽机车鼎盛的时代。
  • She was a great singer in her heyday.她在自己的黄金时代是个了不起的歌唱家。
2 mammoth u2wy8     
n.长毛象;adj.长毛象似的,巨大的
参考例句:
  • You can only undertake mammoth changes if the finances are there.资金到位的情况下方可进行重大变革。
  • Building the new railroad will be a mammoth job.修建那条新铁路将是一项巨大工程。
3 grasslands 72179cad53224d2f605476ff67a1d94c     
n.草原,牧场( grassland的名词复数 )
参考例句:
  • Songs were heard ringing loud and clear over the grasslands. 草原上扬起清亮激越的歌声。 来自《现代汉英综合大词典》
  • Grasslands have been broken and planted to wheat. 草原已经开垦出来,种上了小麦。 来自《简明英汉词典》
4 evolutionary Ctqz7m     
adj.进化的;演化的,演变的;[生]进化论的
参考例句:
  • Life has its own evolutionary process.生命有其自身的进化过程。
  • These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。
5 analyzed 483f1acae53789fbee273a644fdcda80     
v.分析( analyze的过去式和过去分词 );分解;解释;对…进行心理分析
参考例句:
  • The doctors analyzed the blood sample for anemia. 医生们分析了贫血的血样。 来自《简明英汉词典》
  • The young man did not analyze the process of his captivation and enrapturement, for love to him was a mystery and could not be analyzed. 这年轻人没有分析自己蛊惑著迷的过程,因为对他来说,爱是个不可分析的迷。 来自《简明英汉词典》
6 interval 85kxY     
n.间隔,间距;幕间休息,中场休息
参考例句:
  • The interval between the two trees measures 40 feet.这两棵树的间隔是40英尺。
  • There was a long interval before he anwsered the telephone.隔了好久他才回了电话。
7 randomly cktzBM     
adv.随便地,未加计划地
参考例句:
  • Within the hot gas chamber, molecules are moving randomly in all directions. 在灼热的气体燃烧室内,分子在各个方向上作无规运动。 来自辞典例句
  • Transformed cells are loosely attached, rounded and randomly oriented. 转化细胞则不大贴壁、圆缩并呈杂乱分布。 来自辞典例句
8 cheetahs 49fe48184ec612a4c6ab48e2544552ef     
n.(奔跑极快的)非洲猎豹( cheetah的名词复数 )
参考例句:
  • Unlike lions or cheetahs, leopards are secretive, solitary cats. 花豹不像狮子或印度豹,是属于较神秘而隐居的大猫。 来自互联网
  • Among this lot are cheetahs, lions, leopards, rhinoceroses, spotted hyenas and elephants. 印度豹、狮子、花豹、犀牛、斑点土狼、大象等,都是此地的居民。 来自互联网
9 gorillas a04bd21e2b9b42b0d71bbb65c0c6d365     
n.大猩猩( gorilla的名词复数 );暴徒,打手
参考例句:
  • the similitude between humans and gorillas 人类和大猩猩的相像
  • Each family of gorillas is led by a great silverbacked patriarch. 每个大星星家族都由一个魁梧的、长着银色被毛的族长带领着。 来自《简明英汉词典》
10 domesticated Lu2zBm     
adj.喜欢家庭生活的;(指动物)被驯养了的v.驯化( domesticate的过去式和过去分词 )
参考例句:
  • He is thoroughly domesticated and cooks a delicious chicken casserole. 他精于家务,烹制的砂锅炖小鸡非常可口。 来自《简明英汉词典》
  • The donkey is a domesticated form of the African wild ass. 驴是非洲野驴的一种已驯化的品种。 来自《简明英汉词典》

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