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雅思阅读模拟真题系列4
Don’t wash those fossils
Standard museum practice can wash away DNA. 1. Washing, brushingand varnishing fossils — all standard conservation treatments used by manyfossil hunters and museum curators alike — vastly reduces the chances of recoveringancient DNA.
2. Instead,excavators should be handling at least some of their bounty with gloves, andfreezing samples as they are found, dirt and all, concludes a paper in theProceedings of the National Academy of Sciences today.
3. Although manypalaeontologists know anecdotally that this is the best way to up the odds ofextracting good DNA, Eva-Maria Geigl of the Jacques Monod Institute in Paris,France, and her colleagues have now shown just how important conservationpractices can be. This information, they say, needs to be hammered home amongthe people who are actually out in the field digging up bones.
4. Geigl and hercolleagues looked at 3,200-year-old fossil bones belonging to a singleindividual of an extinct cattle species, called an aurochs. The fossils weredug up at a site in France at two different times — either in 1947, and storedin a museum collection, or in 2004, and conserved in sterile conditions at -200C.
5. The team'sattempts to extract DNA from the 1947 bones all failed. The newly excavatedfossils, however, all yielded DNA.
6. Because the boneshad been buried for the same amount of time, and in the same conditions, theconservation method had to be to blame says Geigl. "As much DNA wasdegraded in these 57 years as in the 3,200 years before," she says.
Wash in, wash out 7. Because manypalaeontologists base their work on the shape of fossils alone, their methodsof conservation are not designed to preserve DNA, Geigl explains.
8. The biggestproblem is how they are cleaned. Fossils are often washed together on-site in alarge bath, which can allow water — and contaminants in the form ofcontemporary DNA — to permeate into the porous bones. "Not only is theauthentic DNA getting washed out, but contamination is getting washed in,"says Geigl.
9. Most ancient DNAspecialists know this already, says HendrikPoinar, an evolutionary geneticistat McMaster University in Ontario, Canada. But that doesn't mean that bestpractice has become widespread among those who actually find the fossils.
10.Getting hold offossils that have been preserved with their DNA in mind relies on closerelationships between lab-based geneticists and the excavators, sayspalaeogeneticistSvante P bo of the Max Planck Institute for Evolutionary Anthropologyin Leipzig, Germany. And that only occurs in exceptional cases, he says.
11.P bo's team, whichhas been sequencing Neanderthal DNA, continually faces these problems."When you want to study ancient human and Neanderthal remains, there's abig issue of contamination with contemporary human DNA," he says.
12.This doesn't meanthat all museum specimens are fatally flawed, notes P bo. The Neanderthalfossils that were recently sequenced in his own lab, for example, had been partof a museum collection treated in the traditional way. But P bo is keen to seesamples of fossils from every major find preserved in line with Geigl'srecommendations — just in case.
Warm and wet 13.Geigl herselfbelieves that, with cooperation between bench and field researchers, preservingfossils properly could open up avenues of discovery that have long been assumedclosed.
14.Much humancultural development took place in temperate regions. DNA does not survive wellin warm environments in the first place, and can vanish when fossils are washedand treated. For this reason, Geigl says, most ancient DNA studies have beendone on permafrost samples, such as the woolly mammoth, or on remains shelteredfrom the elements in cold caves — including cave bear and Neanderthal fossils.
15.Betterconservation methods, and a focus on fresh fossils, could boost DNA extractionfrom more delicate specimens, says Geigl. And that could shed more light on thestory of human evolution.
(640 words)
Glossary Palaeontologists 古生物学家 Aurochs 欧洲野牛 Neanderthal (人类学)尼安德特人，旧石器时代的古人类。 Permafrost (地理)永冻层
Questions 1-6 Answer the following questions by using NO MORE THAN THREE WORDS for eachanswer.
1. How did peopletraditionally treat fossils? 2. What suggestionsdo Geigl and her colleagues give on what should be done when fossils are found? 3. What problems maybe posed if fossil bones are washed on-site? Name ONE. 4. Whatcharacteristic do fossil bones have to make them susceptible to be contaminatedwith contemporary DNA when they are washed? 5. What could bebetter understood when conservation treatments are improved? 6. The passagementioned several animal species studied by researchers. How many of them arementioned?
Questions 7-11 Do the following statements agree with the information given in thepassage? Please write TRUE if thestatement agrees with the writer； FALSE ifthe statement does not agree with the writer； NOT GIVEN ifthere is no information about this in the passage 7. In their paperpublished in the Proceedings of the National Academy of Sciences, Geigl and hercolleagues have shown what conservation practices should be followed topreserve ancient DNA. 8. The fossil bonesthat Geigl and her colleagues studied are all from the same aurochs. 9. Geneticists do nothave to work on site. 10.Only newlyexcavated fossil bones using new conservation methods suggested by Geigl andher colleagues contain ancient DNA. 11.Pbo is stillworried about the potential problems caused by treatments of fossils intraditional way.
Questions 12-13 Complete the following the statements by choosing letter A-D for eachanswer.
12.“This information”in paragraph 3 indicates: A. It is critical tofollow proper practices in preserving ancient DNA. B. The best way ofgetting good DNA is to handle fossils with gloves. C. Fossil huntersshould wear home-made hammers while digging up bones. D. Many palaeontologistsknow how one should do in treating fossils.
13.The studyconducted by Geigl and her colleagues suggests: A. The fact thatancient DNA cannot be recovered from fossil bones excavated in the past. B. The correlation betweenthe amount of burying time and that of the recovered DNA. C. The pace at whichDNA degrades. D. The correlationbetween conservation practices and degradation of DNA.
Suggested answers andexplanations
1. washing, brushing,varnishing 见第一段。 2. handling with gloves / freezing samples ( any one of the two ) 见第二段。 3. losing authentic DNA / being contaminated / contamination ( any one ofthe three) 见第八段“Not only is the authentic DNAgetting washed out, but contamination is getting washed in”(答being contaminated或 contamination比较保险) 4. they are porous, porous 的意思是多孔的。见第八段“... which can allow water — and contaminants in the form ofcontemporary DNA — to permeate into the porous bones.” 5. human evolution 见第十五段。其中“shedlight on sth”的意思是使某事显得非常清楚，使人了解某事。 6. 4, 分别为第四段的“an extinct cattle species,called an aurochs”，即欧洲野牛，已经绝迹;第十一段“Neanderthal”，是人类学用语，尼安德特人，旧石器时代的古人类;第十四段“woolly mammoth”和“cave bear”，其中mammoth是猛犸，一种古哺乳动物。 7. T 见第二段。 8. T 见第四段“Geigl and her colleagues lookedat 3,200-year-old fossil bones belonging to a single individual of an extinctcattle species, called an aurochs.”即他们研究的骨化石是一头欧洲野牛身上的。 9. NG 10. F 见第十二段第一、二句话。 11. T 见第十二段末句“But P bo is keen to seesamples of fossils from every major find preserved in line with Geigl'srecommendations — just in case.”意即为保险起见，Pbo还是非常希望见到用Geigl建议的方法保存的化石样本。“just in case” 的意思是以防万一，就是Pbo对用传统保存处理的化石不放心的意思。 12. A 见第三段。This information就是前一句中“... just how important conservation practices can be”(to preservegood DNA)。“be hammered”之中hammer一词的意思是不断重复强调。 13. D，需要理解文章各处关于Geigl和她的同事所作的研究。
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