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　　为什么鳄鱼睁一只眼睡觉?

　　While for humans the expression "sleep with one eyeopen" is just a metaphor to keep alert, for someanimals it is a way of life. Called unihemispheric sleep,it is the ability to snooze with one eye open and thecorresponding half of the brain awake, while theother half rests.

　　对人类来说，“睡觉睁一只眼”只是对要“提高警惕”的一个比喻;但是对某些动物来说却是一种习性。一半大脑处于休息状态，另一半大脑时刻保持警惕，这种现象被称为“半脑睡眠”。

　　Researchers believe that this talent that has been observed in marine mammals like dolphinsand seals as well as numerous bird species, serves many purposes. Birds use it to keep aneye out (literally) for predators while dolphins do it to keep track of their pods and young ones.Many social animals are also believed to use the technique to keep track of any interestingactivities going on around them.

　　科学家相信，这种在海豚海狮等海洋哺乳动物和多数鸟类身上存在的天赋，实际上有很多用途。鸟儿睡眠时一只眼保持警惕是为了免受捕食者伤害，海豚却是为了看护自己的幼崽。很多群居动物也用此技能来保持对身边任何有趣活动的关注。

　　Now researchers from Australia's La Trobe University have discovered that crocodiles may havealso evolved this capability. The scientists began by placing three juvenile saltwater crocodilesinside a large enclosure at the University's aquarium and filming their behavior. They noticedthat when left undisturbed, the reptiles spent less than an hour with one eye open. Thecrocodiles instead seemed to prefer snoozing with both eyes shut just like the rest of us.

　　澳大利亚La Trobe大学的研究者发现，鳄鱼似乎也进化了出此技能。他们在大学水族馆腾出地方，圈禁了3条幼年咸水鳄并监控它们的表现。他们发现，在无外界打扰的情况下，这些爬行动物只有不到一小时睁一只眼闭一只眼。似乎大多数时间里，它们跟人类一样，是紧闭双眼睡觉的。

　　However, things changed drastically when the researchers introduced an external stimulus.They began by bringing a new young crocodile to the enclosure. Though it was one of theirown, the other reptiles immediately appeared to perk up. The researchers noticed that thecrocodiles slept with one open eye directly aimed at the newcomer, for longer amounts of time.

　　然而，当研究者们加入了干扰，情况立刻转变了。他们加了一只新鳄鱼进入围栏。虽然都是同类，其他鳄鱼还是立刻进入警戒状态。它们开始针对这个新来的鳄鱼，更久地保持一只眼睁着。

　　If the tests are positive, it would indicate that birds, mammals and reptiles all display thisbehavior. The only ones that don't? Land-based animals and humans that need to fully shutdown the brain and eyes for a snooze. Lesku says that while we have always called the one-eyed napping animals odd it may be that they are perfectly normal!

　　如果实验有效，我们可能会获得鸟类、哺乳动物和爬行动物都有此行为的结论。什么动物例外呢?陆地动物和人类睡觉时，才需要双眼紧闭。Lesku表示，虽然我们认为睁一只眼闭一只眼睡觉的动物奇怪，但其实这种行为才最正常不过。

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