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  3. You do not usually get something for nothing. Now, a new study reveals that the evolution of an improved learning ability could

You do not usually get something for nothing. Now, a new study reveals that the evolution of an improved learning ability could

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问题    You do not usually get something for nothing. Now, a new study reveals that the evolution of an improved learning ability could come at a particularly high price: an earlier death.
   Past experiments have demonstrated that it is relatively easy through selective breeding to make rats, honey bees and—that great favourite of researchers—fruit flies a lot better at learning. Animals that are better learners should be competitive and, thus, over time, come to dominate a population by natural selection. But improved learning ability does not get selected amongst these animals in the wild. No one really understands why.
   Tadeusz Kawecki and his colleagues at the University of Fribourg in Switzerland have measured the effects of improved learning on the lives of fruit flies. The flies were given two different fruits as egg-laying sites. One of these was laced with a bitter additive that could be detected only on contact. The flies were then given the same fruit but without an additive. Flies that avoided the fruit which had been bitter were deemed to have learned from their experience. Their children were reared and the experiment was run again.
   After repeating the experiment for 30 generations, the children of the learned flies were compared with normal flies. The researchers report in a forthcoming edition of Evolution that although learning a-bility could be bred into a population of fruit flies, it shortened their lives by 15%. When the researchers compared their learned flies to colonies selectively bred to live long lives, they found even greater differences. Whereas learned flies had reduced their life spans, the long-lived flies learned less well than even average flies.
   The authors suggest that evolving an improved learning ability may require a greater investment in the nervous system which takes resources away from processes that delay ageing. However, Dr. Kawecki thinks the effect could also be a by-product of greater brain activity increasing the production of Reactive Oxygen Species(ROS), which can increase oxidation in the body and damage health.
   No one knows whether the phenomenon holds true for other animals. So, biologists, at least, still have a lot to learn.
In this experiment, scientists observed that_________.
选项 A、some flies avoided the fruit without an addictive
B、some flies preferred the fruit with an addictive
C、the eggs of the flies were not damaged
D、the impact on the flies did not last long
答案A
解析 推断题。根据文章第三段第五句“Flies that avoided the fruit which had been bitter were deemed to have learned from their experience．”可知，会避开苦味添加剂水果的果蝇被认为通过经历提高了学习能力。由此可以推断，果蝇已经有经验，看见同种水果也会避开，所以果蝇也会避开没有添加剂的同种水果，故A选项符合题意，为正确答案。
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