A Bats have a problem: how to find their way around in the dark. A 蝙蝠面临的一大问题是如何在黑暗中辨别方向。 They hunt at night, and cannot use light to help them find prey and avoid obstacles. 它们在夜间捕食，而且无法利用光来找寻猎物和躲避障碍物。 You might say that this is a problem of their own making, one that they could avoid simply by changing their habits and hunting by day. 也许你会说这个问题是它们自找的，只要改变生活习性，在白天出来捕食就可以避免这个问题了。 But the daytime economy is already heavily exploited by other creatures such as birds. 但白天的猎物已经被鸟类等生物瓜分殆尽。 Given that there is a living to be made at night, and given that alternative daytime trades are thoroughly occupied, natural selection has favoured bats that make ago of the night-hunting trade. 鉴于夜间尚可谋生，并且白天的猎物资源已经被全部占用，自然选择最终使蝙蝠们在夜间捕猎行里大显身手。 It is probable that the nocturnal trades go way back in the ancestry of all mammals. 夜间捕猎群体的出现可能要追溯到哺乳动物的先祖。 In the time when the dinosaurs dominated the daytime economy, our mammalian ancestors probably only managed to survive at all because they found ways of scraping a living at night. 在恐龙统治地球白天的时代，我们的哺乳动物祖先只能想方设法在夜间谋生，求得一线生机。 Only after the mysterious mass extinction of the dinosaurs about 65 million years ago were our ancestors able to emerge into the daylight in any substantial numbers. 直到六千五百万年前，恐龙神秘地大规模灭绝之后，我们的祖先才敢成群结队地在大白天出没。

B Bats have an engineering problem: how to find their way and find their prey in the absence of light. B 蝙蝠面临着一个“工程”问题：在没有光线的情况下如何辨识方向并寻找猎物。 Bats are not the only creatures to face this difficulty today. 蝙蝠不是当今世界上唯一面临该问题的物种。 Obviously the night-flying insects that they prey on must find their way about somehow. 显而易见，蝙蝠所捕食的夜间飞行的昆虫肯定能以某种方式在黑暗中找到方向。 Deep-sea fish and whales have little or no light by day or by night. 深海鱼类和鲸无论白天还是黑夜都几乎见不到任何光线。 Fish and dolphins that live in extremely muddy water cannot see because, although there is light, it is obstructed and scattered by the dirt in the water. 生活在极度浑浊的水域中的鱼和海豚也看不见，因为即使有光线，也被水中的淤泥阻挡分散开了。 Plenty of other modern animals make their living in conditions where seeing is difficult or impossible. 现代的许多物种都生活在很难见到光线或者完全黑暗的环境中。

C Given the questions of how to man oeuvre in the dark, what solutions might an engineer consider? C 关于如何在黑暗中巧妙游走这个问题，工程师会给出何种答案呢？ The first one that might occur to him is to manufacture light, to use a lantern or a searchlight. 第一个能想到的办法可能是制造光线，比如用灯笼或者探照灯。 Fireflies and some fish (usually with the help of bacteria) have the power to manufacture their own light, but the process seems to consume a large amount of energy. 萤火虫和某些鱼类可以自己制造光（通常是在细菌的帮助下），但这一过程似乎要耗费很多能量。 Fireflies use their light for attracting mates. 萤火虫用光线吸引配偶. This doesn't require a prohibitive amount of energy: a male's tiny pinprick of light can be seen by a female from some distance on a dark night, since her eyes are exposed directly to the light source itself. 这一过程并不需要很多能量，黑夜中，雌性萤火虫远远地就可以看到雄性萤火虫发出的微弱光芒，因为雌性萤火虫的眼睛直接曝露在光源内。 However; using light to find one's own way around requires vastly more energy, since the eyes have to detect the tiny fraction of the light that bounces off each part of the scene. 然而利用自身的光线寻找方向却要耗费更多的能量，因为此时生物的眼睛需要探测到通过物体反射回来的微弱光芒。 The light source must therefore be immensely brighter if it is to be used as a headlight to illuminate the path, than if it is to be used as a signal to others. 如果要作为灯光来照亮道路的话，就要求光源比作为信号灯时明亮许多。 In any event, whether or not the reason is the energy expense, it seems to be the case that, with the possible exception of some weird deep-sea fish, no animal apart from man uses manufactured light to find its way about. 无论是不是能量消耗的缘故，情况似乎是这样：除了人类以外没有动物使用自己制造的光源探路，一些深海大怪鱼可能例外。

D What else might the engineer think of? D 工程师们还能想到什么呢？ Well, blind humans sometimes seem to have an uncanny sense of obstacles in their path. 喔，盲人，他们好像对路上的障碍物有着不可思议的直觉。 It has been given the name 'facial vision', because blind people have reported that it feels a bit like the sense of touch, on the face. 人们把这叫做“面感视觉”，因为据盲人说，感觉到有障碍物的时候就像脸部被触摸一样。 One report tells of a totally blind boy who could ride his tricycle at good speed round the block near his home, using facial vision. 一则报道称，一位完全失明的男孩能借助面感视觉绕着家附近的街区快速骑三轮车。 Experiments showed that, in fact, facial vision is nothing to do with touch or the front of the face, although the sensation maybe referred to the front of the face, like the referred pain in a phantom limb. 实验表明，面感视觉实际上与“感”和“面”没有任何关系，尽管这种感觉可能被认为源自面部正前方，正如提到的患肢疼痛一样。 The sensation of facial vision, it turns out, really goes in through the ears. 事实上，面感视觉是通过耳朵传输的。 Blind people, without even being aware of the fact, are actually using echoes of their own footsteps and of other sounds, to sense the presence of obstacles. 尽管盲人并没有意识到这一点，但实际生活中他们的确在运用自己的步伐及其他声音的回声来感觉路上障碍物的存在。 Before this was discovered, engineers had already built instruments to exploit the principle, for example to measure the depth of the sea under a ship. 在这个事实被发现之前，其实工程师们已经利用这条原理制造了很多设备，比如用回声来测量船底海洋的深度。 After this technique had been invented, it was only a matter of time before weapons designers adapted it for the detection of submarines. 在这项技术被发明之后，武器制造者很快就将其改良用来侦测潜水艇。 Both sides in the Second World War relied heavily on these devices, under such code names as Asdic (British) and Sonar (American), as well as Radar (American) or RDF (British), which uses radio echoes rather than sound echoes. 二战期间，交战双方都充分运用了这些设备，代号分别为英国的Asdic和美国的Sonar，以及美国的Radar 或是英国的RDF，他们利用的就是雷达回声技术而非声波回声技术。

E The Sonar and Radar pioneers didn't know it then, but all the world now knows that bats, or rather natural selection working on bats, had perfected the system tens of millions of years earlier; and their 'radar' achieves feats of detection and navigation that would strike an engineer dumb with admiration. E 当时的雷达声呐技术先驱们毫不知情，但现在所有人都明白了正是蝙蝠，或者说是自然选择在蝙蝠身上的鬼斧神工，早在几百万年前就已经使这种技术达到了完美的境界，而蝙蝠的“雷达”在探测及导航方面取得的完美成果足以让人类工程师佩服到哑口无言。 It is technically incorrect to talk about bat 'radar', since they do not use radio waves. 从技术角度讲，说蝙蝠有雷达功能是不准确的，因为它们并没有运用无线电波， It is sonar. 而只是运用了声呐系统。 But the underlying mathematical theories of radar and sonar are very similar; and much of our scientific understanding of the details of what bats are doing has come from applying radar theory to them. 但实际上雷达和声呐的基本原理是非常相似的，而且大多数关于蝙蝠细节行为的科学理解都是利用雷达理论完成的。 The American zoologist Donald Griffin, who was largely responsible for the discovery of sonar in bats, coined the term ' echolocation' to cover both sonar and radar, whether used by animals or by human instruments. 美国动物学家Donald Grffin 教授第一个发现蝙蝠的声呐技术，由此，他创造了一个新词汇“回声定位”，这个词涵盖了动物和人类所利用的雷达及声呐系统。