Birds can navigate by the Earth's magnetic field.How they do it is still a mystery.Where would people be without magnetic compasses?The short answer is: lost.By giving human beings a sixth sense—an ability to detect the hitherto invisible magneticfield of the Earth—the compass proved one of the most important inventions ever.
鳥類能夠利用地球磁場導(dǎo)航。機(jī)理尚不明確人類沒有指南針會怎樣?很簡單：迷失方向。指南針給了人類第6感，使人能辨別地球無形的磁場，成為最重要的發(fā)明之一。
It let sailors navigate without sight of the night sky.And that led to the voyages of discovery, trade and conquest which created the politicalgeography of the modern world.Imagine, then, what animals which had their own, built-in compasses could achieve.They might spend their summers doingthe English Season in Glyndebourne or Henley, and then overwinter in the warmth of Mombasa. They might strike out, like intrepid pioneers, from Angola to Anchorage.They might even, if truly gripped by wanderlust and a hatred of the darkness, live in near-perpetual daylight by migrating from Pole to Pole.And that is just what some birds do.
海員不用觀察夜空便可以辨識方向。人們用它進(jìn)行海上探索，海上交易，攻城掠地，進(jìn)而開創(chuàng)了現(xiàn)代世界的政治版圖。有些動物有自己內(nèi)嵌的指南系統(tǒng)。可以想象得出這些動物的能力。它們可以在戈林德伯恩或亨利鎮(zhèn)消暑，享受自己的英格蘭夏日。然后在溫暖的蒙巴薩島過冬。它們可以像無畏的開拓者一樣，從安哥拉獨闖安克雷奇。假如它們?yōu)槁眯兴鶢拷O，為黑暗而煩惱，它們會穿梭于兩極之間，過著永遠(yuǎn)有光亮的生活。以上這些只是鳥類能力的一部分。
Swallows travel between Europe and Africa. Northern wheatears fly from Africa to Alaska, andback.Arctic terns each year make the journey from one end of the planet to the other.And they can do it, at least in part, because they do have a magnetic sense denied tohumans.
家燕在歐洲和非洲之間遷徙。石棲鳥在非洲和阿拉斯加之間遷徙。每年，北極燕鷗都會從地球的一端飛到另一端。它們能這么做的原因之一便是鳥類可以感知磁性，而人類不行。
The most familiar avian navigation trick is that pulled off by homing pigeons.As a consequence pigeons have often found themselves at the sharp end of investigationsabout how bird navigation in general, and magnetic sense in particular, actually work.That pigeons have such a sense was shown more than 40 years ago, by William Keeton ofCornell University, in upstate New York, who attached magnets to pigeons to see if they couldstill home.They could not, though birds fitted with non-magnetic dummies managed perfectly well.
人類最為熟知的鳥類導(dǎo)航技巧就是通過研究信鴿而得到的。鴿子便處在了人類研究的尖端。人們用它研究鳥類整體的導(dǎo)航機(jī)能，用它特別研究磁性感應(yīng)機(jī)制。鴿子顯示出此種能力是在40年前。當(dāng)時，紐約州北部康乃爾大學(xué)的William Keeton把磁體系在鴿子身上，觀察它們是否能夠回家。結(jié)果是它們不能，但是那些帶有仿磁體的鴿子卻回家。
Since then, experiments on other species have shown magnetic sensitivity is common amongbirds. What these experiments have not shown, however, is how the birds manage it.See it? Hear it? Smell it?There are two theories.One is that the magnetic sensors are grains of magnetite, a form of iron oxide which, as itsname suggests, is easily magnetised.The other is that the Earth's magnetic field affects a particular chemical reaction in the retinain a way that reaches into the arcane depths of quantum mechanics.
此后的實驗表明，磁性感知能力是鳥類共有的，但并沒有解釋是如何操作的。視覺?聽覺?嗅覺?理論上的說法有兩種。一種是鴿子具有磁感應(yīng)器，這是一種以氧化鐵形式存在的磁鐵礦粒子。顧名思義，這種物質(zhì)極易磁化。另一種說法認(rèn)為，地球磁場能對視網(wǎng)膜里特定的化學(xué)反映產(chǎn)生影響，在某種程序上可以達(dá)到神秘量子力學(xué)的深度。
The magnetite hypothesis concentrates on birds' beaks.Magnetite grains are common in living things, and are known to be involved in magneticsensing in bacteria. In birds they are particularly abundant in the beak.So last year David Keays of the Institute of Molecular Pathology, in Vienna, dissected the beaksof nearly 200 unfortunate pigeons, to find out more.What he discovered was not encouraging.There were, indeed, lots of magnetite grains.But he had expected they would congregate in some sort of specialised sensory cell akin to thetaste buds of the tongue or the hair cells of the ear.Instead, he found that the beak's magnetite is mostly in macrophages.
These are cells whose job is to wander around amoeba-like, chewing up bacteria and debrisfrom other body cells as they go.
磁鐵礦假說的焦點是鳥類的喙。磁鐵礦粒子是生物共有的，廣泛存在于鳥的喙中。去年，維也納分子病理學(xué)研究所的David Keays對將近200只鴿子進(jìn)行了解剖，以期得到更多發(fā)現(xiàn)。但是，他發(fā)現(xiàn)的并不令人鼓舞。大量鐵磁礦粒子確實存在。他原以為鐵磁礦粒子會聚集成為專門的感覺細(xì)胞，類似于舌頭上的味蕾和內(nèi)耳毛細(xì)胞。但是，他發(fā)現(xiàn)，喙部的鐵磁礦主要以巨噬細(xì)胞的形式存在，這些細(xì)胞的職能是以游離細(xì)胞的形式對細(xì)胞殘片及病原體進(jìn)行噬菌。
Not, then, likely candidates as magnetic sensors.Other experiments, though, do suggest the beak is involved.The nerve that connects it to the brain is known as the trigeminal.When Dominik Heyers and Henrik Mouritsen of Oldenburg University, in Germany, cut thetrigeminals of reed warblers the birds' ability to detect which way was north remained intact.They did, however, lose their sense of magnetic dip.Dip indicates latitude, another important part of navigation.To confuse matters further, some people accept Dr Keays's interpretation of what is going onin the beak,but think that the relevant magnetite grains are elsewhere—in the hair cells of the ear, whichare also rich in iron oxide.If they are right, then from the birds' point of view they are probably hearing the magneticsignal.The main alternative to the nasal-magnetite hypothesis, though, is not that birds hearmagnetic fields, but that they see them.
因此，巨噬細(xì)胞不可能具有磁感應(yīng)功能。其它的實驗也包含了對喙的研究。聯(lián)結(jié)喙與腦的神經(jīng)叫三叉神經(jīng)。德國奧爾登堡大學(xué)的Dominik Heyers和Henrik Mouritsena切斷了葦鶯的三叉神經(jīng)，保留了它們辨別北方的能力。然而，這些鳥卻失掉了磁傾角的感應(yīng)力。磁傾角可以指示緯度，是導(dǎo)航的重要組成部分。Keays對鳥喙解釋使情況更加復(fù)雜。但有些人還是接受了他的說法。但是這些人認(rèn)為鳥身體的其它部位也存在磁鐵礦粒子—內(nèi)耳毛細(xì)胞。氧化鐵也富含這種粒子。假如這些人的假定正確，從鳥的角度來看，它們可能聽得到磁信號。鼻腔內(nèi)存在磁鐵礦的假說 并不是鳥類可以聽到磁場，而是能看到磁場。
One line of evidence for this is that part of a bird's brain, called cluster N, which gets its inputdirectly from the eyes, seems to be involved in magnetic sensing.Experiments Dr Mouritsen's team conducted on robins showed that destroying cluster Ndestroys a bird's north-detecting sense, and other experiments, on meadow pipits, show thatcells in cluster N are far more active when the birds are using their magnetic sense than whenthey are not.
關(guān)于此的證明是，鳥大腦中有一部分叫cluster N，可以直接得到眼部輸送的信息，好像跟磁場感應(yīng)有聯(lián)系。博士Mouritsen研究團(tuán)隊對知更鳥進(jìn)行了實驗，得出推斷。實驗顯示破壞知更鳥的cluster N，也就破壞了它們識別北方的能力。研究團(tuán)隊又對草地鷚進(jìn)行了實驗。實驗顯示，鳥類使用磁感應(yīng)能力的時候，cluster N細(xì)胞異�；钴S。
The problem with this idea is that birds' eyes do not have magnetite in them.If they do house magnetism detectors, those detectors must be something else.That something, according to a hypothesis advanced by Klaus Schulten, who works at theUniversity of Illinois at Urbana-Champaign, is a type of retinal protein called a cryptochrome.When hit by light, a cryptochrome produces pairs of molecules called free radicals that areelectrically neutral but have unpaired electrons in them.Electrons are tiny magnets, so they tend to attract each other and pair up in a way thatneutralises their joint magnetic fields.
此種假說的問題在于鳥類的眼部沒有磁鐵礦。假如它們真的起到了磁探測器的作用，那么肯定另有他物。在伊利諾斯大學(xué)香檳分校工作。據(jù)Schulten，這種他物是一種名為cryptochrome的尿視黃醇蛋白。當(dāng)受到光照時，就產(chǎn)生名為自由基的分子對。這種自由基呈電中性，其中含有未配對電子。電子就是微小的磁性體。因此，當(dāng)它們的聯(lián)合磁場中合之時，電子就會相互吸引，就會形成組對。
Unpaired electrons, however, remain magnetic, and thus sensitive to the Earth's field.Moreover, because the unpaired electrons in the free radicals were originally paired in themolecule that split to form the radicals, quantum mechanics dictates that these electronsremain entangled.This means that however far apart they move, what happens to one affects the other'sbehaviour.
但是，那些不成對電子仍具磁性，對地球磁場很敏感。因為自由基中的那些不成對電子最初存在于分 裂成為自由基分子之中，量子力學(xué)規(guī)定這些電子依然是絞纏的。也就是說，無論雙方離得有多遠(yuǎn)，一方的行為會影響另一方。
Calculations suggest the different ways the two radicals feel the Earth's field as they separateis enough to change the way they will react with other chemicals—including ones that triggernerve impulses, and that, via entanglement, they can transmit this information to each other,and thus affect each other's reactions.
此種假設(shè)表明，當(dāng)兩種自由基分離時，它們感知地球磁場的相反作用足夠能夠改變它們與其它化學(xué)物質(zhì)相互反應(yīng)的方式――包括那些能產(chǎn)生神經(jīng)脈沖的化學(xué)物質(zhì)。同時，通過絞纏，它們彼此能互相信息，從而產(chǎn)生相互影響。
This, the calculations indicate, would be enough for a bird's brain to interpret the magneticfield.It would probably see a pattern of spots before its eyes, which would remainstationary as itscanned its head from side to side.And some birds do, indeed, scan their heads this waywhen assessing the direction ofmagnetic north.It is possible, of course, that both hypotheses are right,and that birds have two magneticsenses, with one perhaps concentrated on north detection and theother on detecting dip.But there is something particularly poetic about the idea that even part of thismysterioussixth sense depends on a still-more-mysterious quantum effect—one that Einsteinhimselfdescribed as spooky action at a distance.
此種假設(shè)表明，這足可以讓鳥腦識別磁場。鳥眼可能會看到眼前有某種樣式的斑點圖案，當(dāng)鳥類對其識別之時，眼睛是固定的。其實，當(dāng)鳥類辨別地磁北極之時，確實能夠用此法掃描頭部。當(dāng)然，兩種假說都有正確的可能。鳥類也有可能有兩套磁感應(yīng)能力，一種集中在北方，另一種集中于磁傾角。這種神秘的第六感覺依賴于更加神秘的量子力學(xué)效應(yīng)。對此還有一種詩意般的解釋，即愛因斯坦自己說的鬼魅般的超距作用。
