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 com- pared with normal flies. The researchers report in a forthcoming edition of Evolution that although learning ability 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.
(1).Past experiments prove selective breeding can make animals better_______
A.Commanders
B.Competitors
C.survivors
D.learners
参考答案：D
解题思路：
细节题。从文章第二段第一句“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.”可知，实验证明选择性繁殖可以提高 动物的学习能力，故选D。
(2).In this experiment, scientists observed that________
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
参考答案：A
解题思路：
推断题。从文章第三段第五句“Flies that avoided the fruit which had been bitter were deemed to have learned from their experience.”可知，那些果蝇通过学习能力的提升能够避开带有添加剂 的水果，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，故选A。
(3).The forthcoming report says that_______
A.long-lived flies are better at laying eggs
B.long-lived flies are poorer in learning
C.learned flies have a relatively long life
D.learned flies live as long as average ones
参考答案：B
解题思路：
细节题。从文章第四段最后一句“Whereas learned flies had reduced their life spans，the long—lived flies learned less well than even average flies.”可知，长命果蝇的学习能力低于普通果 蝇，故选B。
(4).According to Dr.Kawecki, greater brain activity______
A.reduces oxygen consumption
B.regulates the nervous system
C.speeds up the ageing process
D.stabilizes the ageing process
参考答案：C
解题思路：
推断题。从文章第五段最后一句“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 Call increase oxidation in the body and damage health.”可知，奎克教 授认为这种影响也可能是大脑活动产生活性氧的副作用，活性氧 会增强身体的氧化并损害健康。由此可推断，大量的脑力活动会 加速衰老，故选C。
(5).We learn from the text that_______
A.the research findings need to be tested further
B.biologists are doing similar research on other animals
C.the animal world usually follows the same universal laws
D.biologists are applying their findings to other areas
参考答案：A
解题思路：
推断题。从文章最后一段“N0 0ne knows whether the phenomenon holds true for other animals.So，biologists，at least，still have a lot to learn.”可知，生物学家们目前只对果蝇做了实验，还 不知道其他动物是否有同样效果，他们还要去继续研究，故选A。
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