【科学60秒】是什么让猛犸象熬过冰河时期？_英语听力练习mp3下载-科学-沪江听力酷

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【科学60秒】是什么让猛犸象熬过冰河时期？

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A couple million years ago, mammoths migrated north from Africa to colonize Eurasia. Sometime around then a massive ice age ___1___—and it was stay warm or die. So their tails and heat-shedding ears shrunk, and they grew thick coats of oily fur.
But if you're out in the cold all day you also need some biochemical adjustments. Hemoglobin is the protein in red blood cells that delivers oxygen to your tissues. And it doesn't ___2___ oxygen well at low temperatures; it just ___3___ it more tightly. So mammoths solved that problem by evolving hemoglobin that releases oxygen more easily in the cold. That’s according to a study published in the journal Nature Genetics.
Researchers got the DNA that codes for hemoglobin from a 43,000-year-old mammoth. Then they used E. coli bacteria to produce actual mammoth hemoglobin. They compared mammoth hemoglobin to that of their living cousins, Asian elephants, at 37, 25 and 10 degrees Celsius. Due to just a few ___4___, mammoth hemoglobin can release oxygen more readily at cold temperatures. Which was just the thing to help mammoths ___5___.