The final holdout woolly mammoths had large numbers of harmful mutations-which would have given them satiny coats and a weakened sense of smell. Christopher Intagliata reports.

最后坚持下来的长毛猛犸象有大量有害的突变——这带给它们光滑的皮毛和更弱的嗅觉。克里斯托弗·因塔利亚塔报道。

撰文/播音：克里斯托弗·因塔利亚塔（Christopher Intagliata）

翻译：郭鑫鹏

审校：丁可含

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.

长毛猛犸象在它们的全盛时期，覆盖了西伯利亚草原，阿拉斯加和北美大部地区。但是经过10000年时间，温暖的气候让它们生活的草原变为森林。人类也并不是特别友好，一只猛犸象便能令人们饱餐一顿。所以猛犸象们大规模消失。最后只剩下一个坚持下来的群体。它们在北冰洋的一座被称为“弗兰格尔岛”的岛上。这群最后的猛犸象隐藏了超过6000年时间。

“So the pyramids have been built, they’re 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.”

“随着金字塔建立，人们在中国开始种茶叶，文化建立，很长时间中，没有人知道那儿还有一群猛犸象。”北卡罗来纳大学进化进化遗传学家丽贝卡·罗杰斯说。“然后人们在3700年前左右发现了这座岛屿，它们那时已经濒临灭绝。”

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 father 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.

罗杰斯和她的同事蒙哥马利·斯拉特金分析了岛上某个猛犸象牙齿的基因组，它生活在4300年前。他们将其与大陆猛犸象作比较，后者生活在45000年前。他们发现有害的突变在那个时间间隔出现在岛屿猛犸象的基因中。这些突变导致嗅觉感受器和尿蛋白缺失——这样的复合物发挥着社交信号和异性选择的作用。

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. [Rebekah L. Rogers, Montgomery Slatkin: Excess of genomic defects in a woolly mammoth on Wrangel island]

这些动物也进化出了光滑的毛皮，反射着阳光。这是今天宠物饲养者喜欢兔子、豚鼠拥有的某个特征。这些突变的原因是什么呢？罗杰斯说那时在岛上只有少量个体——不超过1000只，最低只有300只——自然选择无法按常规发展。因此存活下来的并不是最适合的。存活下来的个体更出于一种随机选择。这表示它们积累了大量突变。所有这些都不会让它们死亡——但是也不是让它们更加适应。研究发表在期刊《科学公共图书馆&遗传学》上。

Rogers says a similar process could happened 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.”

罗杰斯说同样的情况也会发生在现有地球上的稀有动物身上，比如非洲猎豹、熊猫、大猩猩上。“如果长时间种群只维持在一个很少数量上，就会在基因中积累这样的有害突变。所以我们也能在它们身上看到同样的效应。但是要看到猛犸象上那样明显的特征还需要很长一段时间，所以我们越早对这些生物进行干预，它们能过得更好。”

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.”

那么很早之前在岛上发现这些隐藏猛犸象的那些人类呢？“我们没有直接证据表明他们捕猎了这些猛犸象，但是你会希望他们把这些生物带回来驯养它们。”已经有一个买家对此感兴趣了。“没错，如果你发现了一只，我很想拥有一只作为宠物。小一点能进入的房子就更好了。”

-Christopher Intagliata

https://www.scientificamerican.com/podcast/episode/last-woollies-had-mammoth-mutations/