剑桥雅思10Test4阅读Passage3阅读原文+答案解析

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　　先来了解剑桥雅思10Test4阅读Passage3阅读原文：

　　You should spend about 20 minutes on Questions 27-40, which are based on Reading Passage 3 below.

　　When evolution runs backwards

　　Evolution isn’t supposed to run backwards — yet an increasing number of examples show that it does and that it can sometimes represent the future of a species

　　The description of any animal as an ‘evolutionary throwback’ is controversial. For the better part of a century, most biologists have been reluctant to use those words, mindful of a principle of evolution that says ‘evolution cannot run backwards’. But as more and more examples come to light and modern genetics enters the scene, that principle is having to be rewritten. Not only are evolutionary throwbacks possible, they sometimes play an important role in the forward march of evolution.

　　The technical term for an evolutionary throwback is an ‘atavism’, from the Latin atavus, meaning forefather. The word has ugly connotations thanks largely to Cesare Lombroso, a 19th-century Italian medic who argued that criminals were born not made and could be identified by certain physical features that were throwbacks to a primitive, sub-human state.

　　While Lombroso was measuring criminals, a Belgian palaeontologist called Louis Dollo was studying fossil records and coming to the opposite conclusion. In 1890 he proposed that evolution was irreversible: that ‘an organism is unable to return, even partially, to a previous stage already realised in the ranks of its ancestors’. Early 20th-century biologists came to a similar conclusion, though they qualified it in terms of probability, stating that there is no reason why evolution cannot run backwards — it is just very unlikely. And so the idea of irreversibility in evolution stuck and came to be known as ‘Dollo’s law’.

　　If Dollo’s law is right, atavisms should occur only very rarely, if at all. Yet almost since the idea took root, exceptions have been cropping up. In 1919, for example, a humpback whale with a pair of leg-like appendages over a metre long, complete with a full set of limb bones, was caught off Vancouver Island in Canada. Explorer Roy Chapman Andrews argued at the time that the whale must be a throwback to a land-living ancestor. ‘I can see no other explanation,’ he wrote in 1921.

　　Since then, so many other examples have been discovered that it no longer makes sense to say that evolution is as good as irreversible. And this poses a puzzle: how can characteristics that disappeared millions of years ago suddenly reappear? In 1994, Rudolf Raff and colleagues at Indiana University in the USA decided to use genetics to put a number on the probability of evolution going into reverse. They reasoned that while some evolutionary changes involve the loss of genes and are therefore irreversible, others may be the result of genes being switched off. If these silent genes are somehow switched back on, they argued, long-lost traits could reappear.

　　Raff’s team went on to calculate the likelihood of it happening. Silent genes accumulate random mutations, they reasoned, eventually rendering them useless. So how long can a gene survive in a species if it is no longer used? The team calculated that there is a good chance of silent genes surviving for up to 6 million years in at least a few individuals in a population, and that some might survive as long as 10 million years. In other words, throwbacks are possible, but only to the relatively recent evolutionary past.

　　As a possible example, the team pointed to the mole salamanders of Mexico and California. Like most amphibians these begin life in a juvenile ‘tadpole’ state, then metamorphose into the adult form — except for one species, the axolotl, which famously lives its entire life as a juvenile. The simplest explanation for this is that the axolotl lineage alone lost the ability to metamorphose, while others retained it. From a detailed analysis of the salamanders’ family tree, however, it is clear that the other lineages evolved from an ancestor that itself had lost the ability to metamorphose. In other words, metamorphosis in mole salamanders is an atavism. The salamander example fits with Raff’s 10-million-year time frame.

　　More recently, however, examples have been reported that break the time limit, suggesting that silent genes may not be the whole story. In a paper published last year, biologist Gunter Wagner of Yale University reported some work on the evolutionary history of a group of South American lizards called Bachia. Many of these have minuscule limbs; some look more like snakes than lizards and a few have completely lost the toes on their hind limbs. Other species, however, sport up to four toes on their hind legs. The simplest explanation is that the toed lineages never lost their toes, but Wagner begs to differ. According to his analysis of the Bachia family tree, the toed species re-evolved toes from toeless ancestors and, what is more, digit loss and gain has occurred on more than one occasion over tens of millions of years.

　　So what’s going on? One possibility is that these traits are lost and then simply reappear, in much the same way that similar structures can independently arise in unrelated species, such as the dorsal fins of sharks and killer whales. Another more intriguing possibility is that the genetic information needed to make toes somehow survived for tens or perhaps hundreds of millions of years in the lizards and was reactivated. These atavistic traits provided an advantage and spread through the population, effectively reversing evolution.

　　But if silent genes degrade within 6 to 10 million years, how can long-lost traits be reactivated over longer timescales? The answer may lie in the womb. Early embryos of many species develop ancestral features. Snake embryos, for example, sprout hind limb buds. Later in development these features disappear thanks to developmental programs that say ‘lose the leg’. If for any reason this does not happen, the ancestral feature may not disappear, leading to an atavism.

　　Questions 27-31

　　Choose the correct letter, A, B, C or D.

　　Write the correct letter in boxes 27-31 on your answer sheet.

　　27 When discussing the theory developed by Louis Dollo, the writer says that

　　A it was immediately referred to as Dollo’s law.

　　B it supported the possibility of evolutionary throwbacks.

　　C it was modified by biologists in the early twentieth century.

　　D it was based on many years of research.

　　28 The humpback whale caught off Vancouver Island is mentioned because of

　　A the exceptional size of its body.

　　B the way it exemplifies Dollo’s law.

　　C the amount of local controversy it caused.

　　D the reason given for its unusual features.

　　29 What is said about ‘silent genes’?

　　A Their numbers vary according to species.

　　B Raff disagreed with the use of the term.

　　C They could lead to the re-emergence of certain characteristics.

　　D They can have an unlimited life span.

　　30 The writer mentions the mole salamander because

　　A it exemplifies what happens in the development of most amphibians.

　　B it suggests that Raff’s theory is correct.

　　C it has lost and regained more than one ability.

　　D its ancestors have become the subject of extensive research.

　　31 Which of the following does Wagner claim?

　　A Members of the Bachia lizard family have lost and regained certain features several times.

　　B Evidence shows that the evolution of the Bachia lizard is due to the environment.

　　C His research into South American lizards supports Raff’s assertions.

　　D His findings will apply to other species of South American lizards.

　　Questions 32-36

　　Complete each sentence with the correct ending, A-G, below.

　　Write the correct letter, A-G, in boxes 32-36 on your answer sheet.

　　32 For a long time biologists rejected

　　33 Opposing views on evolutionary throwbacks are represented by

　　34 Examples of evolutionary throwbacks have led to

　　35 The shark and killer whale are mentioned to exemplify

　　36 One explanation for the findings of Wagner’s research is

　　A the question of how certain long-lost traits could reappear.

　　B the occurrence of a particular feature in different species.

　　C parallels drawn between behaviour and appearance.

　　D the continued existence of certain genetic information.

　　E the doubts felt about evolutionary throwbacks.

　　F the possibility of evolution being reversible.

　　G Dollo’s findings and the convictions held by Lombroso.

　　Questions 37-40

　　Do the following statements agree with the claims of the writer in Reading Passage 3?

　　In boxes 37-40 on your answer sheet, write

　　YES if the statement agrees with the claims of the writer

　　NO if the statement contradicts the claims of the writer

　　NOT GIVEN if it is impossible to say what the writer thinks about this

　　37 Wagner was the first person to do research on South American lizards.

　　38 Wagner believes that Bachia lizards with toes had toeless ancestors.

　　39 The temporary occurrence of long-lost traits in embryos is rare.

　　40 Evolutionary throwbacks might be caused by developmental problems in the womb.

　　以上是关于剑桥雅思10Test4阅读Passage3阅读原文的介绍，大家在练习结束后可以参照以下答案进行分析，一起来了解一下。

　　Question 27

　　参考译文： 当讨论Louis Dollo的理论时,作者说____

　　难度及答案：难度中等;答案为C。

　　关键词： Louis Dollo

　　定位原文： 第3段第2, 3句“In 1890...”在1890年，他提出进化是不可以逆转的：“一个有机体不能够回转到之前它的祖先已经实现了的阶段，哪怕只是一部分。” 在20世纪早期，生物学家得出一个相似的结论，即尽管他们认同返祖现象的可能性，并表示没有理由证明为什么进化不能被反向运行，但他们就是认为发生的可能性极小。

　　解题思路： 根据关键词Louis Dollo定位至第3段，得知他提出进化是不可逆转的，可是20世纪的时候，生物学家认为没有原因不可逆转，也就是进化是可逆转的。所 以是答案C。

　　Question 28

　　参考译文： 文中提到在Vancouver岛附近捉到的座头鲸，因为_____。

　　难度及答案： 难度低;答案为D

　　关键词： humpback whale、vancouver

　　定位原文： 第4段前4句“If Dollo’s...”如果多洛氏法则是正确的，返祖现象就算真的有， 应该也很少发生。然而，几乎自这种想法产生起，就已经出现特例了。比如， 在1919年，一头座头鲸在加拿大温哥华岛被捕获，它带有一双长达1米、像脚的附肢，且有着一套完整的肢骨。探险家Roy Chapman Andrews在那时表明这头鲸鱼一定是某种陆地生活的祖先动物的反向进化结果。

　　解题思路： 原文中对于座头鲸的特征有详细的描述，为什么长成这个样子也做出了解释，说是一种反向进化的结果。所以选择D。

　　Question 29

　　参考译文： 关于“休眠基因”有何描述?

　　难度及答案： 难度低;答案为C

　　关键词： silent genes

　　定位原文： 第5段最后一句“If these...”如果这些休眠基因在以某种方式再次激活，他们表示，生物长时间丢失的特征可以重现。

　　解题思路： 关键词silent genes 在原文中重现。long-lost traits 替换了 certain characteristics，原文中的 reappear替换了 re-emergence。

　　Question 30

　　参考译文： 作者提到鼹钝口螈，因为_____

　　难度及答案： 难度中等;答案为B

　　关键词： mole salamander

　　定位原文： 第7段第1句及最后—句“As a possible example...”作为一个有可能例证的事件， 团队列举了墨西哥和加利福尼亜的鼹钝口螈。鼹钝口螈的例子与Raff的1000万年的学说框架相符合。

　　解题思路： 找到mole salamander这个例子并不难，难度在于解题点在这段的最后一句话， 距离有点远而已。原文最后一句fits With与选项B中的correct属于同义替换c。证明Raff的理论是正确的。

　　Question 31

　　参考译文： 下面哪一个是Wagner的理论?

　　难度及答案：难度低;答案为A

　　关键词： Wagner

　　定位原文： 第8段第2句到段尾“In a paper...”在一个去年发表的文章中，耶鲁大学的生物学家Gunter Wagner汇报了一些关于南美蜥蜴Bachia进化史研究的工作。 它们中的一些拥有非常小的肢节;有一些看起来更像蛇而非蜥錫;有一些完全失去了后肢的趾头。然而，其他的则彰显出了后肢的四个趾头。 最简单的解释就是这些有趾的蜥蜴品种从没有失去过趾头，但Wagner并不认同。根据他对 Bachia的族谱的区别，有趾的物种从它们无趾的祖先进化而成，更有甚者，脚趾的消失和产生在过去的数百万年间发生过不止一次。

　　解题思路： 根据关键词Wagner定位至第8段。最后一句中的re-evolved、loss and gain和 occurred on more than one occasion 与选项 A 中的 lost and regained several times属于同义替换。

　　Question 32

　　参考译文： 很长一段时间，生物学家都拒绝____。

　　难度及答案： 难度低;答案为F

　　关键词： for a long time、biologist、rejected

　　定位原文：第1段第2句“For the better part…”在一个世纪的大部分时间里，大多数生物学家不愿意用反向进化等这些词，他们铭记着一个进化原则即“进化是不可以反向运行的”。

　　解题思路： 这个題不难，原文中for the better part of a century替换了 for a long time，原文中reluctant 替换了 rejected。

　　Question 33

　　参考译文： 对于返祖进化持有相对立的观点代表有_____。

　　难度及答案： 难度低;答案为G

　　关键词： opposing views

　　定位原文： 第3段第1句“While Lombroso...”当Lombroso在观测犯人时，一位比利时的古生物学家Louis Dollo正在研究化石记录并得出了相反的结论。

　　解题思路： 根据关键词opposing views定位到第3句opposite condusion，句话里的两个人的意见是相反的。

　　Question 34

　　参考译文： 反向进化的例子导致了____。

　　难度及答案： 难度中等;答案为A

　　关键词： examples 、 led to

　　定位原文： 第5段前两句“Since then...”自从那时起，很多其他的例子已被发现，所以进化是不可逆转的这种观点再也无法成立了。这同时产生了困惑：消失了几千万年的特征是如何能重新出现的?

　　解题思路： 关键词examples中原文中重现。原文中propose与题目中led to属于同义替换， 原文中 characteristics that disappeared millions of years ago 与选项 A 中 long?est traits 也属于同义替换。

　　Question 35

　　参考译文： 提到鲨鱼和虎鲸是为了_____.

　　难度及答案： 难度低;答案为B

　　关键词： shark、killer whale

　　定位原文： 倒数第2段第2句“One possibility is…”其中一个可能性就是这三种特性只是失去了，之后又简单地重现。这就像相似的结构可以独立地产生在没有血缘关系的物种中，就像鲨鱼和虎鲸的背部的鳍一样。

　　解题思路： 根据关键词定位至倒数第2段。原文中similar structures替换了选项B中的particular feature，原文中 unrelated species 替换了选项 B 中的 different species。

　　Question 36

　　参考译文：Wabner 的研究成果的解释之一是____.

　　难度及答案： 难度低;答案为D.

　　关键词： explanation finding、Wagner

　　定位原文： 倒数第2段第3句‘Another more...” 另一种更加有吸引力的可能性是那些用来生长趾头的基因信息在蜥蜴上存活了几百或者是几千万年，并且这种基因信息被重新激活了。

　　解题思路： 倒数第2段讲了 Wagner的发现。原文中的possibility与题目中的explanation 属于同义替换。原文中survive与选项D中continued existence属于同义替换。

　　Question 37

　　参考译文： Wagner是第一个做南美洲蜥蜴研究的人。

　　答案及难度： 难度低;答案为NOT GIVEN .

　　关键词： Wagner 、south American lizards

　　定位原文： 第8段第2 句 “In a paper...” 在一个去年发表的文章中，耶鲁大学的生物学家 Gunter Wagner汇报了一些关于南美蜥蜴Bachia进化史研究的工作。

　　解题思路： 在文中并没有提到Wagner是否是第一人，所以未提及。

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　　Question 38

　　参考译文： Wagner相信有趾头的Bachia撕锡，其祖先并没有趾头。

　　难度及答案: 难度低; 答案为YES

　　关键词： Bachia lizards，toeless、ancestors

　　定位原文： 第8段最后两句“The simplest.,”最简单的解释就是这些有趾的蜥蜴品种从没有失去过趾头， 但Wagner并不认同。根据他对Bachia的族谱的区别，有趾的物种从它们无趾的祖先进化而成，更有甚者，脚趾的消失和产生在过去的数百万年间发生过不止一次。

　　解题思路：关键词Bachia和toeless在文中重现，根锯Wagner的调查.它们是从toeless ancestors进化来的;文中内容与题目一致。

　　Question 39

　　参考译文： 胚胎时期，短暂出现了消失很久的特点的这种情况是非常少见的。

　　难度及答案： 难度低;答案为NO。

　　关键词： embryos

　　定位原文： 最后1段第3句话 “Early embryos...”许多物种早期的胚胎发展出了祖先的特性。

　　解题思路： 关键词embryos在文中重现。原文中说这种现象存在于许多物种中(many species),可是题目说这个现象非常少见(rare)，所以很明显矛盾。其中，原文中ancestral features与题目中long-lost trails 属于同义替换。

　　Question 40

　　参考译文： 反向进化可能是由于子宫内的发展问题

　　难度及答案： 难度低;答案为YES

　　关键词： womb、developmental

　　定位原文： 最后1段最后两句“Later in development...”这些特性在后期发展中由于某些进化程式消失了，该程式可能导致“腿部的消失”。如果因为任何原因这些事情没有发生，祖先的种种特性也许就不会消失，导致返祖现象。

　　解题思路： 根据关键间womb和developmental定位至最后一段。 原文中thanks to 中caused by属于同义替换。最后一句说，如果发展的过程没有进行的话，那么就会造成返祖现象，与题目一致，所以答案为YES。