Luyện tập: Đọc và học từ

Let’s Go Bats

A

Bats have a problem: how to find their way around in the dark. They mammalsfacial visionhuntstrikesăn bắt at night, and cannot use light to help them find prey and avoid obstacles. You might say that this is a problem headlightof their own makingecholocationscatteredlỗi của chính bản thân/tự làm tự chịu, one that they could avoid simply by changing their habits and hunting by day. But the daytime economyprohibitivenavigationnocturnalthị trường (kiếm ăn) is already heavily exploited by other creatures such as birds. Given that there is a living to be made at night, and given that immenselymuddyalternativesubstantialthay thế, khác daytime trades are thoroughly occupied, natural selection has favoured bats that make a go of the night-hunting trade. It is probable that the weirdecholocationnocturnalhabitshoạt động về đêm trades go way back in the ancestry of all mammals. In the time when the dinosaurs dominated the daytime economy, our coinednavigationfavouredmammalianthuộc về giống động vật có vú 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 navigationancestorsnatural selectionmanoeuvretổ tiên able to emerge into the daylight in any substantial numbers.

B

Bats have an facial visionobstaclesnatural selectionengineeringkỹ thuật 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 echoesoccupiedmuddyprohibitivedính bùn, chứa bùn, đầy bùn 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

Given the questions of how to manoeuvreoccupiedscatteredpinprickdi chuyển, dịch chuyển in the dark, what solutions might an engineer consider? The first one that might occur to him is to manufacture light, to use a lanternscraping a livingsensationuncannyđèn lồng 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 underlyingadmirationprohibitiveilluminatequá nhiều, tốn kém 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 một phần nhỏ 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 scraping a livingpreyprincipleheadlightđèn pha 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 coinedweirdilluminateuncannykỳ quặc, lạ lùng deep-sea fish, no animal apart from man uses manufactured light to find its way about.

D

What else might the engineer think of? Well, blind humans sometimes seem to have an kỳ lạ, không tự nhiên sense of obstacles in their path. It has been given the name ‘facial visionoccupiedilluminateprinciplethuật ngữ y học, chỉ khả năng nhận thức chướng ngại vật mà không cần đến thị lực’, 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 xe đạp 3 bánh 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 technicallyechoessensationprinciplecảm giác (khi bị tác động bởi hoàn cảnh bên ngoài) 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 echoesselectioncreaturesscatteredâm thanh dội lại 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 principleexploitedscatteredsonarnguyên tắc, nguyên lý, 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.

E

The Sonar and Radar pioneers didn’t know it then, but all the world now knows that bats, or rather natural selectionnatural selectionpreyancestrysự chọn lựa 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 navigationtheoriesadmirationtechnicallyvề mặt kỹ thuật incorrect to talk about bat ‘radar’, since they do not use radio waves. It is sonar but the natural selectionoccupiedunderlyinghabitscơ bản 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, coinedoccupiedextinctionancestrytạo ra/đặt ra một từ/cách diễn đạt mới the term ‘echolocation’ to cover both sonar and radar, whether used by animals or by human instruments.