2021年经济学人 史前动物猛犸象有望复活(2)

To date a specimen¹, fragments of its DNA² are compared to corresponding chunks³ from known descendants. Armed with a few evolutionary⁴ rules-of-thumb, scientists can calculate how long it would have taken for the observed mutations to arise. Analysis of this sort revealed that the youngest molar, found near a village called Chukochya, was between 500,000 and 800,000 years old. A tooth found near the Adycha river was from an animal that had died between 1m and 1.2m years ago. A third, found near another village called Krestovka, was dated at between 1.1m and 1.2m years. The previous record had been held by a set of horse DNA thought to be as much as 780,000 years old.

确定一个标本的年代要将其DNA片段与其已知后代的相应片段进行比较。科学家们借助一些进化经验法则可以计算出观察到的突变产生所需的时间。此类分析表明，在一个名叫楚科奇的村庄附近发现的最年轻的臼齿年龄在50万至80万岁之间。在阿德恰河附近发现的一颗牙齿属于一种死于100万至120万年前的动物。第三个是在另一个叫做克列斯托夫卡的村庄附近发现的，它的年代在110万到120万年之间。此前的记录是由一组马的DNA保持的，这组DNA据有78万年的历史。

The teeth held other surprises. The Krestovka mammoth⁵ belongs to a previously⁶ unknown branch of the mammoth family tree, an ancestor of the Columbian mammoth which roamed North America 1.5m years ago. The Adycha mammoth was an ancestor of the iconic woolly mammoth. It appeared to possess many of its descendant's features half a million years earlier, suggesting the woolly mammoth's distinctive⁷ physiology⁸ evolved more slowly than had been thought.

这些牙齿还包含着其他惊喜。克雷斯托夫卡猛犸象属于猛犸象家族的一个未知分支，该分支是150万年前生活在北美的哥伦比亚猛犸象的祖先。阿德恰猛犸象是长毛猛犸象的祖先。它拥有其后代在50万年前的许多特征，这表明长毛象独特的生理进化速度比人们想象的要慢。

These are the sorts of insights into the slow workings of evolution that very ancient DNA can offer. And, it seems, prospects⁹ for collecting more such ultra-old samples are good. Permafrost has existed on Earth for the past 2.6m years. That puts an upper limit on the age of sequenceable DNA, but one that still leaves a million years more headroom. "I'm sure that in the permafrost there are going to be samples that have survived longer," says Patricia Pecnerova of the Swedish Museum of Natural History, and a co-author on the study. Records, after all, are made to be broken.

这些都是非常古老的DNA所能提供的关于缓慢进化过程的洞见。而且，收集更多这种超古老样本的前景似乎很好。多年冻土在地球上已经存在了260万年。这就给可测序DNA的年龄设定了上限，但仍留有100万年的空间。瑞典自然历史博物馆的帕特里夏·佩涅洛娃是这项研究的合著者之一，她说：“我敢肯定永久冻土层中会有存活时间更长的样本。”毕竟，记录就是用来被打破的。

1 specimen   

n.样本，标本

参考例句：

• You'll need tweezers to hold up the specimen.你要用镊子来夹这标本。
• This specimen is richly variegated in colour.这件标本上有很多颜色。

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 chunks   

厚厚的一块( chunk的名词复数 )； （某物）相当大的数量或部分

参考例句：

• a tin of pineapple chunks 一罐菠萝块
• Those chunks of meat are rather large—could you chop them up a bIt'smaller? 这些肉块相当大，还能再切小一点吗？

4 evolutionary   

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 mammoth   

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。

6 previously   

adv.以前，先前（地）

参考例句：

• The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
• Let me digress for a moment and explain what had happened previously.让我岔开一会儿，解释原先发生了什么。

7 distinctive   

adj.特别的，有特色的，与众不同的

参考例句：

• She has a very distinctive way of walking.她走路的样子与别人很不相同。
• This bird has several distinctive features.这个鸟具有几种突出的特征。

8 physiology   

n.生理学，生理机能

参考例句：

• He bought a book about physiology.他买了一本生理学方面的书。
• He was awarded the Nobel Prize for achievements in physiology.他因生理学方面的建树而被授予诺贝尔奖。

9 prospects   

n.希望，前途(恒为复数)

参考例句：

• There is a mood of pessimism in the company about future job prospects. 公司中有一种对工作前景悲观的情绪。
• They are less sanguine about the company's long-term prospects. 他们对公司的远景不那么乐观。