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2008年雅思阅读模拟试题

　　6.Because the bones had been buried for the same amount of time，and in the same conditions，the conservation method had to be to blame says Geigl. As much DNA was degraded in these 57 years as in the 3，200 years before， she says.

　　Wash in，wash out

　　7.Because many palaeontologists base their work on the shape of fossils alone，their methods of conservation are not designed to preserve 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 contemporary 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 doesnt mean that best practice has become widespread among those who actually find the fossils.

　　10.Getting hold of fossils that have been preserved with their DNA in mind relies on close relationships between lab-based geneticists and the excavators，says palaeogeneticist Svante Pbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig，Germany. And that only occurs in exceptional cases，he says.

　　11.Pbos team，which has been sequencing Neanderthal DNA，continually faces these problems. When you want to study ancient human and Neanderthal remains，theres a big issue of contamination with contemporary human DNA， he says.