从最古老DNA中瞥见郁郁葱葱的北极(下)

在此过程中，研究人员调整了从古代样本中提取DNA的方法，并升级了用来对其测序的机器。

双语精读

Along the way, the researchers tweaked their methods for extracting DNA from ancient samples and upgraded the machines they used to sequence it.

在此过程中，研究人员调整了从古代样本中提取DNA的方法，并升级了用来对其测序的机器。

As they became better at fishing for genes, they would take out more of the Kap Kobenhavn samples for another shot. But for years they failed, again and again.

随着他们在寻找基因方面更得心应手，他们取出更多的Kap Kobenhavn样本进行另一次尝试。但多年来，他们失败了一次又一次。

From time to time they were tantalized by what looked like short bits of DNA, which are called reads.

有很多次，他们被看起来像短小DNA片段的物质所戏弄，这些物质叫读长。

The researchers couldn't rule out the possibility that bits of young DNA in Greenland, or even in their lab, had contaminated the reads.

研究人员不能排除来自格陵兰岛，甚至是来自他们实验室的晚期DNA片段已经污染了读长的可能性。

Finally, after a major upgrade in their technology, they found DNA in the samples in 2017. The permafrost turned out to be loaded with genetic material. Before long they had collected millions of DNA fragments.

最后，在他们的技术进行了一次重大升级后，2017年他们在样本中发现了DNA。这些永久冻土中原来含有大量遗传物质。不久，他们就收集了数百万个DNA片段。

"It was a breakthrough," Dr. Willerslev said. "It was going from nothing or very little that you don't know is real, to suddenly: It's there."

"这是一个突破，"威勒斯列夫博士说，"从什么都没有或者只有很少难辨真假的东西，突然变成了：它就摆在你面前。"

The researchers lined up the fragments with DNA sequences of living species to figure out where they belonged on the evolutionary tree.

研究人员将这些片段与现存物种的DNA序列比对，以确定它们在进化树上的位置。

They found 102 different kinds of plants--including 78 that had previously been identified from fossils and 24 new ones. The plant DNA painted a picture of forests dominated by poplar and birch trees.

他们发现了102种不同的植物，其中包括78种以前从化石中发现的植物和24种新的植物。植物DNA描绘了一幅以白杨树和白桦树为主的森林图景。

Other sequences come from land animals, including caribou, hares, mastodons, geese, lemmings and ants. The researchers also found marine species, such as horseshoe crabs, corals and algae.

其他序列来自陆地动物，包括驯鹿、野兔、乳齿象、鹅、旅鼠和蚂蚁。研究人员还发现了海洋物种，如马蹄蟹、珊瑚和藻类。

"It superseded everything we imagined," Dr. Kjaer said.

"它取代了我们之前想象的一切。"克亚博士说。

The researchers also searched the permafrost for new clues to the age of the fossils. They found layers in the sediment in which the minerals revealed that the Earth's magnetic field had flipped.

研究人员还在永久冻土中寻找化石年代的新线索。他们在沉积物中发现了几层矿物质，揭示地球磁场曾经发生了翻转。

The age of those reversals helped the researchers determine that Kap Kobenhavn was at least two million years old, but they could not establish a clear upper limit. "My gut feeling as a geoscientist is that it's older," Dr. Kjaer said.

这些逆转发生的年代帮助研究人员确定，Kap Kobenhavn至少有200万岁，但他们无法确定一个明确的上限。"作为一名地球科学家，我的直觉是它还要更加古老。"克亚博士说。

The researchers ruled out the possibility that the DNA came from younger species that contaminated the older permafrost.

研究人员排除了这些DNA来自较晚期的物种，而这些物种污染了较古老的永久冻土的可能性。

The DNA of the birch trees lacked many of the mutations that living species have, indicating that they were ancient. The DNA also had a distinct pattern of damage that occurs only when the molecules have been sitting in sediment for geological stretches of time.

白桦树的DNA缺乏许多现存物种所具有的突变，这表明它们是古老的。这些DNA也有一种明显的损伤模式，只有当分子在沉积物中停留几段地质时期才会发生。

"It really helps show that this really is old DNA," said Tyler Murchie, a postdoctoral researcher at McMaster University who was not involved in the new study.

没有参与这项新研究的麦克马斯特大学博士后研究员泰勒·默奇说："这真的有助于证明这确实是古老的DNA。"

词汇预习

• species [高考]

  美[ˈspiːʃiːz] | 英[ˈspiːʃiːz]

  n. 种类；（单复同）物种

• magnetic [高考]

  美[mæɡˈnetɪk] | 英[mæɡˈnetɪk]

  adj. 有磁性的；有吸引力的；催眠术的 n. 磁体，磁性物质

• previously [高考]

  美[ˈpriːviəsli] | 英[ˈpriːviəsli]

  adv. 先前；在此之前

• marine [高考]

  美[məˈriːn] | 英[məˈriːn]

  adj. 海的；海事的；海生的；航海的 n. 海运业；船舶；水兵

• evolutionary [高考]

  美[ˌiːvəˈluːʃəneri] | 英[ˌiːvəˈluːʃənri]

  adj. 进化的；发展的；演变的

• distinct [高考]

  美[dɪˈstɪŋkt] | 英[dɪˈstɪŋkt]

  adj. 明显的；清晰的；不同的；独特的

• upgrade [高考]

  美[ˌʌpˈɡreɪd , ˈʌpɡreɪd] | 英[ˌʌpˈɡreɪd , ˈʌpɡreɪd]

  vt. 升级；提高；改善 adv. 向上地 n. 升级；上坡

• determine [高考]

  美[dɪˈtɜːrmɪn] | 英[dɪˈtɜːmɪn]

  v. 决定；决心；确定；测定

• figure [高考]

  美[ˈfɪɡjər] | 英[ˈfɪɡə(r)]

  n. 图形；人物；身材；体形 v. 认为；是重要部分；是…的部分；计算（数量或成本）

• possibility [高考]

  美[ˌpɑːsəˈbɪləti] | 英[ˌpɒsəˈbɪləti]

  n. 可能；可能性；可能的事情；潜在的价值

• upper [高考]

  美[ˈʌpər] | 英[ˈʌpə(r)]

  adj. 较高的；上面的；上部的 n. 鞋帮；上铺 n. 兴奋剂；令人兴奋的经历

• breakthrough [高考]

  美[ˈbreɪkθruː] | 英[ˈbreɪkθruː]

  n. 突破，突破性进展；关键问题的解决

• figure out [高考]

  美[ˈfɪɡjər aʊt] | 英[ˈfɪɡə(r) aʊt]

  vt. 算出；想出；解决；理解；断定

• living [高考]

  美[ˈlɪvɪŋ] | 英[ˈlɪvɪŋ]

  adj. 活着的；生动的 n. 生活；生计

• sequence [高考]

  美[ˈsiːkwəns] | 英[ˈsiːkwəns]

  n. 顺序；连续；次序；一系列 vt. 按顺序排好

• shot [高考]

  美[ ʃɑːt] | 英[ʃɒt]

  n. 注射；投篮；发射；拍摄；开枪；子弹 adj. (织物)闪色的；精疲力尽的；完了的

• where [高考]

  美[wer] | 英[weə(r)]

  adv. 在哪里；在那个地方 conj. 在 ... 地方

• would [高考]

  美[wʊd , wəd] | 英[wʊd , wəd]

  aux. 将；可能；大概；总会；愿意；will的过去式

• gut [四级]

  美[ɡʌt] | 英[ɡʌt]

  n. 内脏；肠子；勇气，胆量；直觉，本能；(用于制网球拍、琴弦等的) 肠线 vt. 取出内脏；摧毁（内部） adj. 本能的；（问题等）根本的

• birch [四级]

  美[bɜrtʃ] | 英[bɜ:tʃ]

  n. 桦树；桦木；用桦条抽打 v. 用桦条抽打

• involved in [四级]

  美 | 英

  涉及； 包含在 ... 中

• rule out [四级]

  美[rʊl aʊt] | 英[ruːl aʊt]

  消除； 排除； 划线隔开

• involved [四级]

  美[ɪnˈvɑlvd] | 英[ɪnˈvɒlvd]

  adj. 涉及的；牵连的；复杂的；感情投入的；有密切关系的

• poplar [专八]

  美[ˈpɑplə(r)] | 英[ˈpɒplə(r)]

  n. 白杨；白杨木

• horseshoe [专八]

  美[ˈhɔːrʃʃuː] | 英[ˈhɔːsʃuː]

  n. 马蹄铁；U形物；马蹄形 v. 装马蹄铁

• geological [考研]

  美[ˌdʒiːəˈlɑːdʒɪkl] | 英[ˌdʒiːəˈlɒdʒɪkl]

  adj. 地质学的

• caribou [托福]

  美[ˈkærəˌbu] | 英[ˈkærɪbu:]

  n. 北美驯鹿

• don [托福]

  美[dɑn] | 英[dɒn]

  n. 先生（西班牙用语）；(牛津、剑桥大学的)指导教师 v. 穿上

重点讲解

Along the way, the researchers tweaked their methods for extracting DNA from ancient samples and upgraded the machines they used to sequence it.

在此过程中，研究人员调整了从古代样本中提取DNA的方法，并升级了用来对其测序的机器。

tweak  v. & n.

1. 作动词

（1）扭；拧

【例】tweak one's ear  拧某人的耳朵

（2）稍稍调整（机器、系统等）

【例】You just need to tweak the last paragraph and then it's done.

只需要微调一下最后一段，然后就完事了。

2. 作名词

（1）扭；拧

【例】give one's ear a tweak 拧一下某人的耳朵

（2）（对机器、系统等的）轻微调整

【例】Experts say the system could be improved with a few tweaks.

专家说做点微调可以改进这个系统。

As they became better at fishing for genes, they would take out more of the Kap Kobenhavn samples for another shot. But for years they failed, again and again.

随着他们在寻找基因方面更得心应手，他们取出更多的Kap Kobenhavn样本进行另一次尝试。但多年来，他们失败了一次又一次。

fish for  

1. 钓鱼

【例】fish for trout  钓鳟鱼

2. 旁敲侧击地打听；转弯抹角地谋取

（英文释义：to try to get sth, or to find out sth, although you are pretending not to）

【例】to fish for compliments/information 转弯抹角地谋取恭维╱旁敲侧击打听情况

3. 摸索着寻找

【搭配】fish around/in...for sth

【例】She fished around in her bag for her keys. 

她在包里摸索着找钥匙。

【拓展】fish sth out of  （从……中）取出，拿出

【例】He fished an envelope out of his pocket. 

他从口袋里掏出一个信封。

shot   n. 尝试；努力

【例】I've never produced a play before but I'll have a shot at it/give it a shot. 

我从来没有制作过一出戏剧，不过我要尝试一下。

【拓展】a long shot  成功希望不大的尝试

【例】It's a long shot, but it just might work. 

没有什么把握，但也许行得通。

From time to time they were tantalized by what looked like short bits of DNA, which are called reads.

有很多次，他们被看起来像短小DNA片段的物质所戏弄，这些物质叫读长。

tantalize   v. （以可望而不可即之物）逗引，招惹

【例】He tantalized the puppy with a bone. 

他拿一根骨头逗引那小狗。

【拓展】tantalizing  adj. 诱人的；挑逗性的

【例】a tantalizing aroma of coffee  咖啡诱人的香味

The researchers couldn't rule out the possibility that bits of young DNA in Greenland, or even in their lab, had contaminated the reads.

研究人员不能排除来自格陵兰岛，甚至是来自他们实验室的晚期DNA片段已经污染了读长的可能性。

rule out   排除

【例】The proposed solution was ruled out as too expensive. 

提出的解决方案被认为花钱太多而被排除。

【近义词】exclude  v. 排除

【例】The police have excluded theft as a motive for the murder. 

警方已排除这起谋杀案中有偷窃的动机。

Finally, after a major upgrade in their technology, they found DNA in the samples in 2017. The permafrost turned out to be loaded with genetic material. Before long they had collected millions of DNA fragments.

最后，在他们的技术进行了一次重大升级后，2017年他们在样本中发现了DNA。这些永久冻土中原来含有大量遗传物质。不久，他们就收集了数百万个DNA片段。

be loaded with  充满……的

（英文释义：full of a particular thing, quality or meaning）

【例】a cup of bubble tea loaded with calories 一杯高热量的奶茶

【拓展】load sb (down) with...  给某人加以重负

【例】The city council loaded the community (down) with taxes. 

市政会把沉重的赋税压在市民身上。

"It was a breakthrough," Dr. Willerslev said. "It was going from nothing or very little that you don't know is real, to suddenly: It's there."

"这是一个突破，"威勒斯列夫博士说，"从什么都没有或者只有很少难辨真假的东西，突然变成了：它就摆在你面前。"

be loaded with  充满……的

（英文释义：full of a particular thing, quality or meaning）

【例】a cup of bubble tea loaded with calories 一杯高热量的奶茶

【拓展】load sb (down) with...  给某人加以重负

【例】The city council loaded the community (down) with taxes. 

市政会把沉重的赋税压在市民身上。

The researchers lined up the fragments with DNA sequences of living species to figure out where they belonged on the evolutionary tree.

研究人员将这些片段与现存物种的DNA序列比对，以确定它们在进化树上的位置。

line up 

1. 使……（与相关的另一物）排齐；使……对齐

【搭配】line up sth with

【例】You have to line the car up with the ones beside you.

你必须让车和旁边的车对齐。

2. 组织，安排（活动）

【例】Mark had a job lined up when he left college. 

马克大学毕业时，工作已经安排好了。

They**** found 102 different kinds of**** plants****--including**** 78**** that**** had previously**** been**** identified**** from**** fossils and 24**** new ones****.**** The plant DNA painted a picture of**** forests dominated by**** poplar**** and birch trees.****

他们发现了102种不同的植物，其中包括78种以前从化石中发现的植物和24种新的植物。植物DNA描绘了一幅以白杨树和白桦树为主的森林图景。

Other sequences come**** from**** land**** animals,**** including caribou,**** hares,**** mastodons,**** geese,**** lemmings**** and ants****.**** The researchers also**** found marine**** species,**** such**** as**** horseshoe crabs,**** corals**** and algae.****

其他序列来自陆地动物，包括驯鹿、野兔、乳齿象、鹅、旅鼠和蚂蚁。研究人员还发现了海洋物种，如马蹄蟹、珊瑚和藻类。

"It superseded everything we imagined," Dr. Kjaer said.

"它取代了我们之前想象的一切。"克亚博士说。

supersede   v. 取代，替代（已非最佳选择或已过时的事物）

【例】The theory has been superseded by more recent research. 

这一理论已为新近的研究所取代。

【拓展】displace/replace/take the place of  代替；替换

The researchers also searched the permafrost for new clues to the age of the fossils. They found layers in the sediment in which the minerals revealed that the Earth's magnetic field had flipped.

研究人员还在永久冻土中寻找化石年代的新线索。他们在沉积物中发现了几层矿物质，揭示地球磁场曾经发生了翻转。

flip   v. & n. & adj.

1. 作动词

（1）翻转；快速翻动

【例】The plane flipped and crashed. 飞机猛地翻转，然后撞毁了。

She felt her heart flip. 她感到心潮澎湃。

（2）按（开关）

【例】to flip a switch  按开关

（3）（用手指）轻抛

【例】to flip a coin  抛硬币

2. 作名词：翻转；抛掷

【例】a flip of a coin/heart   抛硬币/心里咯噔一下

3. 作形容词：轻浮的

【例】Don't be flip with me. 

不要对我油腔滑舌。

The age of those reversals helped the researchers determine that Kap Kobenhavn was at least two million years old, but they could not establish a clear upper limit. "My gut feeling as a geoscientist is that it's older," Dr. Kjaer said.

这些逆转发生的年代帮助研究人员确定，Kap Kobenhavn至少有200万岁，但他们无法确定一个明确的上限。"作为一名地球科学家，我的直觉是它还要更加古老。"克亚博士说。

gut   n. & v. & adj.

1. 作名词

（1）肠道；（动物的）内脏；大肚子

【例】to remove the guts of the fish/a beer gut  掏出鱼的内脏/啤酒肚

（2）勇气；胆量

【例】have the guts to do sth  有胆量做某事

（3）内心

【例】I had a feeling in my guts that something was wrong. 

我内里感到出了事。

2. 作动词：取出内脏；摧毁（房屋）内部

【例】a factory gutted by fire 内部被火烧毁的工厂

3. 作形容词：非理性的；本能的

【例】a gut reaction/instinct   本能反应/直觉

The researchers ruled out the possibility that the DNA came from younger species that contaminated the older permafrost.

研究人员排除了这些DNA来自较晚期的物种，而这些物种污染了较古老的永久冻土的可能性。

distinct   adj.

1. 清晰的；明显的；确切的

【例】There was a distinct smell of gas. 

有一股明显的煤气味。

2. 截然不同的

【例】Rural areas are distinct from major cities.

农村地区和大城市截然不同。

The DNA of the birch trees lacked many of the mutations that living species have, indicating that they were ancient. The DNA also had a distinct pattern of damage that occurs only when the molecules have been sitting in sediment for geological stretches of time.

白桦树的DNA缺乏许多现存物种所具有的突变，这表明它们是古老的。这些DNA也有一种明显的损伤模式，只有当分子在沉积物中停留几段地质时期才会发生。

distinct   adj.

1. 清晰的；明显的；确切的

【例】There was a distinct smell of gas. 

有一股明显的煤气味。

2. 截然不同的

【例】Rural areas are distinct from major cities.

农村地区和大城市截然不同。

"It really**** helps show**** that**** this**** really**** is**** old DNA," said**** Tyler Murchie,**** a postdoctoral**** researcher**** at**** McMaster**** University**** who was not involved**** in**** the new study.****

没有参与这项新研究的麦克马斯特大学博士后研究员泰勒·默奇说："这真的有助于证明这确实是古老的DNA。"

课后练习

• The researchers thought that the reads in the Kap Kobenhavn samples____.

  A. could not be detected even by advanced technology

  B. would solve a mystery in the history of science

  C. were difficult to distinguish from genetic materials

  D. might come from younger DNA in other samples

• The process of discovering the oldest known DNA is ____.

  A. smooth and successful

  B. time-consuming and disappointing

  C. tortuous and complicated

  D. accidental and unexpected

• The DNA fragments gave information about ____.

  A. the genetic characteristics of the living species

  B. the biological composition of the ancient ecosystem

  C. the development of the Earth’s magnetic field

  D. the approximate age of Kap Kobenhavn

• The pattern of damage in the DNA proved that ____.

  A. ancient birch trees lacked important mutations

  B. molecules could be well preserved in sediments

  C. the DNA did not belong to younger species

  D. the old permafrost had been contaminated