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no.7
报dormancy这一概念，阅读材料讲到冬眠的涵义：帮助渡过恶劣环境;降低自身生理能耗。
听力材料里professor讲述了一个肺鱼的例子：在河水干涸之后鱼就躲在河床上之前就打好的洞里，这样一方面可以隔热、保湿，另一方面可以降低呼吸、心跳频率。
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 doesn’t 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 p bo of the max planck institute for evolutionary anthropology in leipzig， germany. and that only occurs in exceptional cases， he says.
11. p bo’s team， which has been sequencing neanderthal dna， continually faces these 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 museum specimens are fatally flawed， notes p bo. the neanderthal fossils that were recently sequenced in his own lab， for example， had been part of a museum collection treated in the traditional way. but p bo is keen to see samples of fossils from every major find preserved in line with geigl’s recommendations — just in case.
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