ABats have a problem: how to find their way around in the dark. They hunt at night, and cannot use light to help them find prey and avoid obstacles. 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. But the daytime economy is already heavily exploited by other creatures such as birds. 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 a go of the night-hunting trade. It is probable that the nocturnal trades go way back in the ancestry of all mammals. 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. 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.

A 在黑暗中如何找到方向是蝙蛹面临的一大问题。它们在夜间捕食，而且无法利用光搜寻猎物或躲避障碍物。也许你会说它们天生就是这样的，只要改变生活习性在白天出来捕食就可以了。但事实上白天的猎物已经被鸟类开发殆尽。鉴于有些生物要在夜间谋生，并且白天的猎物资源都已经被占用，自然选择最终使蝙蝠们在夜间捕猎行当里大显身手。夜间狩猎群体的出现可能要追溯到哺乳动物的先祖。在恐龙统治地球白昼的时代，我们的哺乳动物祷告只能想方设法在夜间求得一线生机。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 蝙蝠面临着一个“工程”万面的问题：那就是在没有光线的情况下如何辨识方向并寻找猎物。蝙蝠不是当今世界上唯一面临此问题的物种。显而易见，蝙蝠所捕食的夜间昆虫肯定能以某种方式在黑暗中找到方向。深海鱼类、鲸等物种无论是白天还是黑夜都几乎见不到任何光线。生活在浑浊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。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。

BBats have an engineering problem: how to find their way and find their prey in the absence of light. Bats are not the only creatures to face this difficulty today. Obviously the night-flying insects that they prey on must find their way about somehow. Deep-sea fish and whales have little or no light by day or by night. 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. Plenty of other modern animals make their living in conditions where seeing is difficult or impossible.

C 关于如何在黑暗中巧妙移动这个问题，工程师们会给出怎样的答案呢?第一个能想到的办法可能就是要制造光线了，比如用灯笼或者探照灯。萤火虫和某些鱼类可以自己制造光亮(通常是在细菌的帮助下)，但这一过程要耗费很多能量。萤火虫用光线吸引配偶，而这一过程并不需要很多能量。暗夜中，雌性萤火虫远远地就可以看见雄性萤火虫微小的光芒，因为雌性的眼睛就直接暴露在光源内。然而利用自身的光线寻找方向却要耗费更多能量，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。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。无论是不是能位消耗的缘故，事实是，除了一些深海大怪鱼之外，绝没有其他任何一种生物像人类这样自己制造光源来找寻方向。

D 工程师们还能想到什么呢?比如盲人，他们好像对路上的障碍有着不可思议的直觉。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。一则报道称一位完全失明的男孩能凭借面感视觉绕着附近街区快速骑三轮车。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，正如幻肢中的牵涉性痛感一样。事实上，面感视觉是通过耳朵传输的。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以及其他声音的回声来感觉路上障碍物的存在。在这个事实没有被发现之前，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。在这项技术发明之后，武器制造者很快就将其改良来侦测潜水艇。二战期间，交战双方都充分运用了这些设备，代号分别是英国的Asdic和美国Sonar以及美国的Radar或是英国的 RDF，后两者使用了雷达回声技术而非声波回声技术。

CGiven the questions of how to manoeuvre in the dark, what solutions might an engineer consider? The first one that might occur to him is to manufacture light, to use a lantern or a searchlight. 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. Fireflies use their light for attracting mates. 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. 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. 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. 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.

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完美境界，而蝙蛹的“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。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，而只是运用声呐系统。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行为细节的科学理解都是利用雷达理论完成的。美国动物学家Donald Griffin教授第一个发现蝙蝠利用声呐技术，由此，他创造出了一个新的词汇：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。

DWhat else might the engineer think of? well, blind humans sometimes seem to have an uncanny sense of obstacles in their path. 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. 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. Experiments showed that, in fact, facial vision is nothing to do with touch or the front of the face, although the sensation may be referred to the front of the face, like the referred pain in a phantom limb. The sensation of facial vision, it turns out, really goes in through the ears. 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. 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. After this technique had been invented, it was only a matter of time before weapons designers adapted it for the detection of submarines. Both sides in the Second world war relied heavily on these devices, under such codenames as Asdic (British) and Sonar (American), as well as Radar (American) or RDF (British), which uses radio echoes rather than sound echoes.

EThe 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. It is technically incorrect to talk about bat 'radar', since they do not use radio waves. It is sonar. 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. 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.