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GRE双语阅读材料：鸟类磁性感知能力新发现

2018-04-12 14:54:00来源：网络

　　鸽子显示出此种能力是在40年前。当时，纽约州北部康乃尔大学的William Keeton把磁体系在鸽子身上，观察它们是否能够回家。

　　They could not, though birds fitted with non-magnetic dummies managed perfectly well.

　　结果是它们不能，但是那些带有仿磁体的鸽子却回家。

　　Since then, experiments on other species have shown magnetic sensitivity is common among birds. What these experiments have not shown, however, is how the birds manage it.

　　此后的实验表明，磁性感知能力是鸟类共有的，但并没有解释是如何操作的。

　　See it? Hear it? Smell it?

　　视觉?听觉?嗅觉?

　　There are two theories.

　　理论上的说法有两种。

　　One is that the magnetic sensors are grains of magnetite, a form of iron oxide which, as its name suggests, is easily magnetised.

　　一种是鸽子具有磁感应器，这是一种以氧化铁形式存在的磁铁矿粒子。顾名思义，这种物质极易磁化。

　　The other is that the Earth's magnetic field affects a particular chemical reaction in the retina in a way that reaches into the arcane depths of quantum mechanics.

　　另一种说法认为，地球磁场能对视网膜里特定的化学反映产生影响，在某种程序上可以达到神秘量子力学的深度。

　　The magnetite hypothesis concentrates on birds' beaks.

　　磁铁矿假说的焦点是鸟类的喙。

　　Magnetite grains are common in living things, and are known to be involved in magnetic sensing in bacteria. In birds they are particularly abundant in the beak.

　　磁铁矿粒子是生物共有的，广泛存在于鸟的喙中。

　　So last year David Keays of the Institute of Molecular Pathology, in Vienna, dissected the beaks of nearly 200 unfortunate pigeons, to find out more.

　　去年，维也纳分子病理学研究所的David Keays对将近200只鸽子进行了解剖，以期得到更多发现。

　　What he discovered was not encouraging.

　　但是，他发现的并不令人鼓舞。

　　There were, indeed, lots of magnetite grains.

　　大量铁磁矿粒子确实存在。

　　But he had expected they would congregate in some sort of specialised sensory cell akin to the taste buds of the tongue or the hair cells of the ear.

　　他原以为铁磁矿粒子会聚集成为专门的感觉细胞，类似于舌头上的味蕾和内耳毛细胞。

　　Instead, he found that the beak's magnetite is mostly in macrophages.

　　但是，他发现，喙部的铁磁矿主要以巨噬细胞的形式存在，

　　These are cells whose job is to wander around amoeba-like, chewing up bacteria and debris from other body cells as they go.

　　这些细胞的职能是以游离细胞的形式对细胞残片及病原体进行噬菌。

　　Not, then, likely candidates as magnetic sensors.

　　因此，巨噬细胞不可能具有磁感应功能。

　　Other experiments, though, do suggest the beak is involved.

　　其它的实验也包含了对喙的研究。

　　The nerve that connects it to the brain is known as the trigeminal.

　　联结喙与脑的神经叫三叉神经。

　　When Dominik Heyers and Henrik Mouritsen of Oldenburg University, in Germany, cut the trigeminals of reed warblers the birds' ability to detect which way was north remained intact.

　　德国奥尔登堡大学的Dominik Heyers和Henrik Mouritsena切断了苇莺的三叉神经，保留了它们辨别北方的能力。

　　They did, however, lose their sense of magnetic dip.

　　然而，这些鸟却失掉了磁倾角的感应力。

　　Dip indicates latitude, another important part of navigation.

　　磁倾角可以指示纬度，是导航的重要组成部分。

　　To confuse matters further, some people accept Dr Keays's interpretation of what is going on in the beak,

　　Keays对鸟喙解释使情况更加复杂。但有些人还是接受了他的说法。

　　but think that the relevant magnetite grains are elsewhere—in the hair cells of the ear, which are also rich in iron oxide.

　　但是这些人认为鸟身体的其它部位也存在磁铁矿粒子—内耳毛细胞。氧化铁也富含这种粒子。

　　If they are right, then from the birds' point of view they are probably hearing the magnetic signal.

　　假如这些人的假定正确，从鸟的角度来看，它们可能听得到磁信号。

　　The main alternative to the nasal-magnetite hypothesis, though, is not that birds hear magnetic fields, but that they see them.

　　鼻腔内存在磁铁矿的假说 并不是鸟类可以听到磁场，而是能看到磁场。

　　One line of evidence for this is that part of a bird's brain, called cluster N, which gets its input directly from the eyes, seems to be involved in magnetic sensing.

　　关于此的证明是，鸟大脑中有一部分叫cluster N，可以直接得到眼部输送的信息，好像跟磁场感应有联系。

　　Experiments Dr Mouritsen's team conducted on robins showed that destroying cluster N destroys a bird's north-detecting sense, and other experiments, on meadow pipits, show that cells in cluster N are far more active when the birds are using their magnetic sense than when they are not.

　　博士Mouritsen研究团队对知更鸟进行了实验，得出推断。实验显示破坏知更鸟的cluster N，也就破坏了它们识别北方的能力。研究团队又对草地鹨进行了实验。实验显示，鸟类使用磁感应能力的时候，cluster N细胞异常活跃。

　　The problem with this idea is that birds' eyes do not have magnetite in them.

　　此种假说的问题在于鸟类的眼部没有磁铁矿。

　　If they do house magnetism detectors, those detectors must be something else.

　　假如它们真的起到了磁探测器的作用，那么肯定另有他物。

　　That something, according to a hypothesis advanced by Klaus Schulten, who works at the University of Illinois at Urbana-Champaign, is a type of retinal protein called a cryptochrome.

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