2009年新人教版高二英語上閱讀理解題7

　　7

　　Suppose we built a robot to explore the planet Mars. We provide the robot with seeing detectors(探測器) to keep it away from danger. It is powered entirely by the sun. Should we program the robot to be equally active at all the times? No. The robot would be using up energy at a time when it was not receiving any. So we would probably program it to stop its activity at night and to make up at dawn the next morning.

　　According to the evolutionary(進化的) theory of sleep, evolutionary equipped us with a regular pattern of sleeping and walking for the same reason. Theory does not deny(否認) That sleep provides some important restorative functions(恢復功能). It merely says that evolutionary has programmed us to perform those functions at a time when activity would be inefficient (無效的)and possibly dangerious. However, sleep protects us only from the sort of trouble we might walk into; it does not protect us from trouble that comes looking for us. So we sleep well when we are in a familiar, safe place, but we sleep lightly, if at all, when we fear that bears will nose into the tent.

　　The evolutionary theory explains the differences in sleep among creatures. Why do cats, for example, sleep so much, while horses sleep so little? Surely cats do not need five times as much repair and restoration as horse do. But cats can afford to have long periods of inactivity because they spend little time eating and are unlikely to be attacked while they sleep. Horse must spend over, they cannot afford to sleep to long or too deeply, because their survival(生存) depends on　

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