我真幸福作文2019年雅思考试模考巩固试题及答案四
1. Washing， brushing and varnishing fossils — all standard conrvation treatments ud by many fossil hunters and muum curators alike — vastly reduces the chances of recovering ancient DNA.
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2. Instead， excavators should be handling at least some of their bounty with gloves， and freezing samples as they are found， dirt and all， concludes a paper in the Proceedings of the National Academy of Sciences today.
3. Although many palaeontologists know anecdotally that this is the best way to up the odds of extracting good DNA， Eva-Maria Geigl of the Jacques Monod Institute in Paris， France， and her colleagues have now shown just how important conrvation practices can be. This information， they say， needs to be hammered home among the people who are actually out in the field digging up bones.
4. Geigl and her colleagues looked at 3，200-year-old fossil bones belonging to a single
individual of an extinct cattle species， called an aurochs. The fossils were dug up at a site in France at two different times — either in 1947， and stored in a muum collection， or in 2004， and conrved in sterile conditions at -20 oC.
5. The team’s attempts to extract DNA from the 1947 bones all failed. The newly excavated fossils， however， all yielded DNA.
6. Becau the bones had been buried for the same amount of time， and in the same conditions， the conrvation method had to be to blame says Geigl. “As much DNA was degraded in the 57 years as in the 3，200 years before，” she says.
Wash in， wash out
7. Becau many palaeontologists ba their work on the shape of fossils alone， their methods of conrvation are not designed to prerve DNA， Geigl explains.
8. The biggest problem is how they are cleaned. Fossils are often washed together on-site in a large bath， which can allow water — and contaminants in the form of contempo
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rary DNA — to permeate into the porous bones. “Not only is the authentic DNA getting washed out， but contamination is getting washed in，” says Geigl.
9. Most ancient DNA specialists know this already， says Hendrik Poinar， an evolutionary geneticist at McMaster University in Ontario， Canada. But that doesn’t mean that best practice has become widespread among tho who actually find the fossils.
10. Getting hold of fossils that have been prerved with their DNA in mind relies on clo relationships between lab-bad geneticists and the excavators， says palaeogeneticist Svante P bo of the Max Planck Institute for Evolutionary Anthropology in Leipzig， Germany. And that only occurs in exceptional cas， he says.
11. P bo’s team， which has been quencing Neanderthal DNA， continually faces the problems. “When you want to study ancient human and Neanderthal remains， there’s a big issue of contamination with contemporary human DNA，” he says.
12. This doesn’t mean that all muum specimens are fatally flawed， notes P bo. The Neanderthal fossils that were recently quenced in his own lab， for example， had been part of a muum collection treated in the traditional way. But P bo is keen to e samples of fossils from every major find prerved in line with Geigl’s recommendations — just in ca.
Warm and wet
13. Geigl herlf believes that， with cooperation between bench and field rearchers， prerving fossils properly could open up avenues of discovery that have long been assumed clod.
14. Much human cultural development took place in temperate regions. DNA does not survive well in warm environments in the first place， and can vanish when fossils are washed and treated. For this reason， Geigl says， most ancient DNA studies have been done on permafrost samples， such as the woolly mammoth， or on remains sheltered from the elements in cold caves — including cave bear and Neanderthal fossils.
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15. Better conrvation methods， and a focus on fresh fossils， could boost DNA extraction from more delicate specimens， says Geigl. And that could shed more light on the story of human evolution.
婚礼音乐 (640 words nature )
大阿卡那牌 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。朱自清背影读后感
Permafrost (地理)永冻层
Questions 1-6
Answer the following questions by using NO MORE THAN THREE WORDS for each an
swer.
1. How did people traditionally treat fossils?
2. What suggestions do Geigl and her colleagues give on what should be done when fossils are found?
3. What problems may be pod if fossil bones are washed on-site? Name ONE.
4. What characteristic do fossil bones have to make them susceptible to be contaminated with contemporary DNA when they are washed?
5. What could be better understood when conrvation treatments are improved?
