今日主題：Last Woollies Had Mammoth Mutations / 長毛象滅絕的真正原因是……
洪欣老師推薦：托福聽力最好的課外教材：60-Second Science
康康精選托福會考的主題，堅持每天精聽一定會進步的哦!!
建議方法：
1. 先聽兩三遍 (不看文稿)
2. 再一句一句聽寫 (每句都要聽寫數遍，直到寫出85%以上的字)
3. 最後check文稿，看哪聽不出來，單字沒背過，還是發音不熟。
4. 堅持天天聽，就能每天進步哦。
MP3音檔 (按右鍵可下載聽)：喜歡的同學，幫忙推或按讚哦~~
http://online1.tingclass.net/voas…/2017/20170629sa_earth.mp3
只有音檔怎夠，聽不懂地方，不用怕，
康康幫你準備好中英文稿了：
中英文稿：
In their heyday, 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 grasslands they grazed into forest. And humans, well they weren't so friendly either—one mammoth 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.
長毛猛獁象在全盛時期遍佈了西伯利亞大草原、阿拉斯加和北美大部分地區。但在一萬年前，氣候變暖導致許多它們放牧的草原變成了森林。而人類也不是那麼友好——一個猛獁象能為人類提供一頓豐盛的大餐。所以後來猛獁象基本上消失了。除了一個仍在頑強生存的“部落”。在北冰洋的一個名為“弗蘭格爾島”的島上。世上最後一批猛獁象在此躲藏了……超過6000年。
"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 evolutionary 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."
“所以金字塔已建成了，中國已開始種植茶葉，文明也形成了，然而如此長的一段時間裡，卻沒有人知道這些猛獁象生活在那裡。”瑞貝卡•羅傑斯，北卡羅萊納大學的一名進化遺傳學家。“後來人們終於在大約3700年前發現了這個島，那時他們也已經滅絕了。
Rogers and her colleague Montgomery Slatkin analyzed 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 interval. Mutations that led to the loss of smell receptors, and urine proteins—compounds they probably needed for social signaling and mate choice.
羅傑斯和她的同事蒙哥馬利•斯拉金分析了4300年前生活在該島上的一隻猛獁象牙齒上的基因組。他們將其與大陸上的猛獁象的基因組進行了比較——而大陸上的猛獁象則來源於更早的4.5萬年前。他們發現，有害的基因突變在這段時間內污染了島上猛獁象的基因組。這種突變導致了猛獁象嗅覺受體喪失和尿蛋白——它們可能需要用來打信號和選擇配偶的化合物。
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 randomly 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.
這裡的猛獁象還長出了有光澤的皮毛。而這種特性在今天的寵物飼養中很普遍，比如兔子和豚鼠。所有這些突變的原因是什麼?羅傑斯表示，島上沒有足夠的猛獁象居民——最多1000只，最少可能只有300只——來允許自然選擇按照常規發展。所以這並不是適者生存的選擇。而是隨機的……誰都有可能倖存下來。這意味著它們積累了大量的突變。這些突變沒有導致它們死亡，但它們也並沒有多麼健康。這項研究發表在《公共科學圖書館•遺傳學》雜誌上。
Rogers says a similar process could happen for rare animals on Earth today, like cheetahs, pandas, gorillas. "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.
羅傑斯說，現今地球上的稀有動物也有可能會經歷類似的過程，比如獵豹、熊貓、大猩猩。“如果一種動物在很長一段時間中種群數量都非常小，那在它們的基因組中可能就會積累這些不良突變。因此，我們可能會看到同樣的效果。不過，我們需要很長一段時間才能得到，像我們在猛獁象中看到的那樣明顯的信號。所以我們越早對這些物種進行干預，結局對它們來說可能就會變得越好。
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 domesticated 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."
至於那些在很久以前就在弗蘭格爾島上發現最後一批猛獁象的人類?“我們沒有直接的證據，證明他們曾獵殺它們，但我們多希望他們曾把它們帶回家並馴養他們。”現在已經有一個感興趣的買家了。“嗯，是的，如果你能找到一隻（猛獁象），那麼會我想養一隻作為寵物。最好稍微小一點，這樣它就比較適合在我的房子裡生活了。”
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