SSS 2010-01-29_在线英语听力室_免费在线英语听力学习网站

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Organisms evolved sexual reproduction so they could stay one step ahead of parasites¹. Or so the theory goes. But what about beasties that make babies without sex? How do they escape infection? A study in the journal Science suggests that for bdelloid rotifers, the answer is blowin’ in the wind.

Biologists believe that sex offers an evolutionary² advantage because it promotes genetic⁴ diversity. Coming up with fresh new gene³ combinations should allow organisms to outsmart parasites, which are also continuously evolving. But if that theory is correct then bdelloid rotifers, freshwater invertebrates⁵ that haven’t had sex in at least 30 million years, should have been parasited into extinction⁶ long ago. Yet here they are, alive and well.

To find out why, scientists infected rotifers with a deadly fungus⁷. And they found that bdelloid rotifers can shake the infection by drying out, drifting away and then rehydrating once they land someplace moist but fungus-free. The fungi⁸ don’t survive the desiccation, so the longer the bdelloids stay dry, the better off they be.

So for celibate⁹ rotifers that want to stay clean, a good long dry spell is just what the doctor ordered.

—Karen Hopkin

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1 parasites
寄生物( parasite的名词复数 )；靠他人为生的人；诸虫
参考例句：
These symptoms may be referable to virus infection rather than parasites. 这些症状也许是由病毒感染引起的，而与寄生虫无关。 Kangaroos harbor a vast range of parasites. 袋鼠身上有各种各样的寄生虫。

2 evolutionary
adj.进化的；演化的，演变的；[生]进化论的
参考例句：
Life has its own evolutionary process.生命有其自身的进化过程。 These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。

3 gene
n.遗传因子，基因
参考例句：
A single gene may have many effects.单一基因可能具有很多种效应。 The targeting of gene therapy has been paid close attention.其中基因治疗的靶向性是值得密切关注的问题之一。

4 genetic
adj.遗传的，遗传学的
参考例句：
It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。 Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。

5 invertebrates
n.无脊椎动物( invertebrate的名词复数 )
参考例句：
Insects and worms are all invertebrates. 昆虫和蠕虫都是无脊椎动物。来自辞典例句 In the earthworm and many other invertebrates, these excretory structures are called nephridia. 在蚯蚓和许多其它无脊椎动物中，这些排泄结构称为肾管。来自辞典例句

6 extinction
n.熄灭，消亡，消灭，灭绝，绝种
参考例句：
The plant is now in danger of extinction.这种植物现在有绝种的危险。 The island's way of life is doomed to extinction.这个岛上的生活方式注定要消失。

7 fungus
n.真菌，真菌类植物
参考例句：
Mushrooms are a type of fungus.蘑菇是一种真菌。 This fungus can just be detected by the unaided eye.这种真菌只用肉眼就能检查出。

8 fungi
n.真菌，霉菌
参考例句：
Students practice to apply the study of genetics to multicellular plants and fungi.学生们练习把基因学应用到多细胞植物和真菌中。 The lawn was covered with fungi.草地上到处都是蘑菇。

9 celibate
adj.独身的，独身主义的；n.独身者
参考例句：
He had defended the institution of a celibate priesthood.他捍卫了独身牧师制度。 The instinct of the celibate warned him to hold back.单身汉的本能告诫他回头是岸。