新知|《苍蝇难拍》：苍蝇的反应速度为啥子能完胜人类？

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新知|《苍蝇难拍》：苍蝇的反应速度为啥子能完胜人类？

原创 2017-09-27 从余启 我与我们的世界

欢迎打开“我与我们的世界”，从此，让我们一起“纵览世界之风云变幻、洞察社会之脉搏律动、感受个体之生活命运、挖掘自然之点滴奥妙”。

我与我们的世界，既是一个“奋斗”的世界，也是一个“思考”的世界。奋而不思则罔，思而不奋则殆。这个世界，你大，它就大；你小，它就小。

欢迎通过上方公众号名称打开公众号“查看历史信息”来挖掘往期文章，因为，每期都能让你“走近”不一样的世界、带给你不一样的精彩。

本期导读：西方谚语云，上帝给你关闭一扇门，一定会给你打开一扇窗。对于不同的物种来说，造物主也不会厚此薄彼，当给某一物种关闭一扇门时，也一定会给它打开一扇窗。

造物主赋予了人类以智慧，让它统领万物，不过，即使是如此智慧的人类，也不是在所有方面都能胜过其他物种的。就拿小小的苍蝇来说吧，它的反应速度之快，地球上的几十亿人中，就没一人能胜过它。

Why is it so hard to swat a fly?

为啥子拍到苍蝇就这么滴难？

Try to swat a fly and it will soon become clear that they're faster than you. Much faster. But how on Earth do these tiny creatures - with their minuscule brains - outwit us so easily?

你拍只苍蝇试试，很快就会发现，苍蝇的反应速度会比你快，而且会快很多。但是，小小苍蝇，脑袋也那么一丁点儿，反应速度竟然完胜我们人类，究竟咋回事儿捏？

You've probably pondered it after chasing a fly around your house and flailing your shoe with repeated, unsuccessful swats. How does it move so fast? Can it read my mind?

很可能，你也有过房间里追着苍蝇到处乱转，抡起鞋子一次又一次狠狠扔向苍蝇，但却难以获胜，然后就纳闷儿，它的反应速度怎么能这么快？它是不是能读懂我的心思？

It was the question put to the BBC World Service CrowdScience team for our most recent episode addressing the apparent super powers of tiny animals. The answer is that, compared with you and me, flies essentially see the world in slow motion.

这个问题，也是我们团队最近在做一期有关体格微小但却具有某种惊人能力的动物的节目时，所关心的问题。答案就是，你我所看到的世界，在苍蝇的眼里，都会变成慢镜头。

To illustrate this, have a look at a clock with a ticking hand. As a human, you see the clock ticking at a particular speed. But for a turtle it would appear to be ticking at twice that speed. For most fly species, each tick would drag by about four times more slowly. In effect, the speed of time differs depending on your species.

要理解这一点，可以找个带有指针的钟表来看看。在我们人类眼里，指针跳动会以某种速度进行。但是，在龟类动物的眼里，指针跳动的速度会快两倍。而对于多数蝇类来说，每次跳动则会变慢四倍。其实，物种不同，时间的速度是不同的。

This happens because animals see the world around them like a continuous video. But in reality, they piece together images sent from the eyes to the brain in distinct flashes a set number of times per second. Humans average 60 flashes per second, turtles 15, and flies 250.

之所以会这样，主要是因为，动物所看到的世界，就像是一个连续性视频。而实际上，每秒间，会有特定频次的不同画面，从眼睛传递给大脑，然后再拼接成连续性视频。每秒钟，人类的平均为60次，龟类为15次，蝇类为250次。

It's all relative

全都具有相对性

The speed at which those images are processed by the brain is called the "flicker fusion rate". In general, the smaller the species, the faster its critical flicker fusion rate - and flies, in particular, put us to shame.

大脑对这些画面的处理速度被称为“画面熔接速度”。一般情况下，物种的体型越小，它的画面熔接速度就越快。而在这方面，特别是苍蝇，完胜我们人类，让我们自愧弗如。

Professor Roger Hardie, from the University of Cambridge, investigates how flies' eyes work, and he has an experiment to determine their flicker fusion rate.

剑桥大学教授罗杰·哈迪就对苍蝇的视觉系统如何运行进行了研究，并通过实验来确定苍蝇的画面熔接速度。

"The flicker fusion rate is simply how fast a light has to be turning on and off before it's perceived or seen as just a continuous light" says Prof Hardie.

哈迪教授介绍说，“画面熔接速度就是指，每闪画面能构成连续性画面一部分被识别或看到之前，该闪画面从出现到结束的速度。”

Roger inserts tiny glass electrodes into the living light sensitive cells of their eyes - photoreceptors - before flashing LED lights at faster and faster speeds. Each flash of the LED produces a tiny electrical current in the photoreceptors that a computer can graph onto a screen. Tests reveal the fastest fly records distinct responses to flickering up to 400 times per second, more than six times faster than our own rate.

罗杰教授在实验动物眼部光感活体细胞中植入微小的玻璃电极，然后从慢到快的速度闪动LED灯，每闪一次，光感细胞中就会产生一次微弱电流，然后经电脑处理形成图形。实验记录显示，蝇类的画面反应速度最高可达每秒钟400次，超过人类的六倍。

The fastest vision of all is found in a species literally called a "killer fly". It's a tiny predatory species found in Europe that catches other flies out of the air with super-fast reactions. In her "fly lab" at Cambridge University, Dr Paloma Gonzales-Bellido demonstrates the killer flies' hunting behaviour by releasing fruit fly prey into a special filming box with a female killer fly.

反应速度最快的蝇类是一种被叫做“杀手蝇”的物种。该物种在欧洲被发现，体型较小，会猎食其他蝇类，能以超快的反应速度捕捉其他蝇类。在剑桥大学的“蝇类实验室”，帕洛玛·冈萨雷斯-贝里多博士就通过在一个特制的摄影箱中释放果蝇让一只雌性杀手蝇捕捉来展示杀手蝇的捕猎行为。

Fly vs fly

蝇蝇大战

With the killer flies and their prey in the filming box, initially the killer fly just sat around motionless, but as one of the fruit flies flew about 7cm above it, there was a flash of movement and suddenly the killer fly was at the bottom of the box chomping into the quivering fruit fly.

摄影箱里的杀手蝇和猎物果蝇，刚开始杀手蝇只是带着一动不动，但当一只果蝇飞到杀手蝇上方7厘米时，一闪间，杀手蝇就突然出现在箱子的底部，已在那里大口大口地撕咬浑身颤抖的果蝇。

Only looking at the slowed-down footage on the computer did it become clear what happened: the killer fly took off, circled the fruit fly three times as it tried to grab it repeatedly, before succeeding in capturing the elusive fruit fly with its front legs.

只有把电脑记录的视频放慢后，才能看清整个过程：杀手蝇飞起来，绕着果蝇飞了三圈，一再努力捉到猎物，然后就用前腿成功捕捉到了很难捉到的果蝇。

The whole behaviour from take-off to landing took just one second. It appears as a flash to our eyes, so conversely, the swatting hand of a human must appear at a snail's pace.

从飞起来出发到捕获猎物落下来整个过程只有一秒钟，在我们人类眼里，只不过就那么一闪，因此，我们人类拍苍蝇时的动作，在蝇类眼里，不过如蜗牛般缓慢。

To enable this incredible speed of the killer fly, which is faster even than other fly species, the light-detecting cells in the killer fly eyes contain many more mitochondria (the "batteries" of biological cells) than are present in the same cells of other flies.

杀手蝇的速度比其他蝇类的都要快，要获得如此之快的速度，杀手蝇眼部的光感细胞就需要比其他蝇类具有更多线粒体（相当于生物细胞的“电池”）。

These are the batteries of the cell, so the speedy vision must take more energy than slow vision, explaining why all eyes aren't just set to the highest flicker fusion rate.

细胞活动需要能量，视觉反应快，就需要更多能量，这或许就可以解释为什么，并不是所有物种的眼睛，都能拥有最高的画面熔接速度。

The carnivorous diet of the killer fly provides the large amounts of energy it needs to power these high-energy cells. But even if we had the same number of mitochondria in the cells or our own eyes, we wouldn't have the same vision speed because flies' light-sensitive cells have a totally different design to those of vertebrates.

杀手蝇所进食的美味大餐，能给它那些高能量细胞提供所需的大量能量。不过，即使我们人类眼睛细胞里有同样多的线粒体，我们也不能拥有同样的视觉反应速度，主要是因为蝇类与脊椎动物的光感细胞，有着完全不同的结构。

Behind the structural differences in the eyes of flies is their evolutionary origin. Arthropods and vertebrates, the groups holding flies and humans, evolved their eyes entirely separately around 700-750 million years ago.

蝇类眼部的细胞结构，有着自己的演化渊源。蝇类和人类，分属节肢动物和脊椎动物，两类物种的眼部早在约70000至75000万年之前就完全分化各自开始演化了。

String theory

弦线理论

Flies' eyes evolved to pick up light with a series of tiny string-like structures that lie horizontal to the path that light travels through the eye. These structures react to light mechanically whereas vertebrates have long tube-like cells facing the light, with chemicals that react to light at the base.

蝇类的眼部经过演化，通过一种与光线穿过眼睛路径平行的弦线式细微结构捕获光线，这些结构对光线的感应是物理性的，而脊椎动物的眼部，则是由朝向光线的细长管状细胞构成，并通过底部的化学成分感应光线。

This structure in the fly eye is something Roger studies in his lab. "It's more sensitive in terms of being able to give a large signal to the tiniest amount of light and it can also respond faster than the rods and cones in the vertebrate eye," he explains.

蝇类眼部的这种结构，正是罗杰教授在实验室的重点研究对象。罗杰教授解释说，“即使对于很微量的光源，这种结构也能产生较大信号量，因此对光线的敏感度更高，而且，与脊椎动物眼部的管杆式或椎体式结构相比，反应速度也更快。”

There are a few reasons for this higher sensitivity, but what Prof Hardie discovered is that they respond mechanically to light, as opposed to chemically as in cones and rods.

对于蝇类敏感度较高这个问题，会牵涉好几个方面的因素。不过，就哈迪教授目前的研究结果来看，弦线式结构对光线的反应，是物理性的，而管杆式或椎体式结构对光线的反应，则是化学性的。

Mechanical responses enable faster neural signals. On top of that, there's a limit to the speed at which neural impulses can travel and the smaller nerve distances from fly eye to fly brain speeds up processing compared to larger vertebrates.

物理性的反应，能产生更快的神经信号。不过，对于神经脉冲的传播速度，也是有极限的，但蝇类从眼部到脑部的神经传输距离较短，因而与脊椎动物相比，神经信号的处理速度也就会更快。

Some vertebrates experience much faster vision than our own. Whether the species is able to fly seems to correlate with faster vision, as does being small. This may be because small flying animals have to react so quickly during flight to avoid approaching obstacles.

有些脊椎动物的视觉反应速度，比人类的要快。而且，那些物种是否会飞，貌似也与视觉反应速度快慢有关，正如体格大小与视觉反应速度相关一样。这或许主要是因为，会飞的小型动物，必须能反应迅速，才能在飞行时避免与其他物体发生撞击。

'Slow motion swats'

“拍蝇之慢动作”

The fastest vision of all is found in species that catch flies in the air.

目前所发现的视觉反应速度最快的物种，是一种能在空中捕捉蝇类的物种。

Back with vertebrates, when investigating the vision of the pied flycatcher, a small perching bird that catches flies in flight, scientists at Uppsala University in Sweden discovered that it was able to identify a light flashing on and off 146 times per second from a continuous light source.

就脊椎动物来说，瑞典乌普萨拉大学的研究人员在对一种能捕捉到飞蝇的小型鸟类的视觉进行研究时发现，该鸟类能识别出每秒钟忽闪146次的光源。

The birds were trained to associate a flashing light source with a tasty treat, and would accurately identify the flashing light up to this rate, placing their flicker fusion rate at 146. That's about twice the rate humans can see but still not as fast as the average fly.

研究人员通过训练，让实验鸟意识到闪光就意味着美味，该类鸟能准确地识别出这种速度的闪光，然后该类鸟的画面熔接速度就定为了146。这样的速度，比人类的要快两倍，但依然没达到蝇类的平均速度。

This means the birds, like flies, experience each tick of the clock more slowly than humans.

这也就意味着，就像蝇类，鸟类所看到的钟表指针跳动速度，也比人类看到的要慢。

There is an evolutionary pressure on the flycatchers to experience the ticking hand of the clock as slowly as possible in order to outwit their speedy prey. Over evolutionary time, birds that experienced 'slower ticking' could react faster to their prey, allowing them to eat more, raise more chicks and pass this speedy vision to future generations.

对于以捕食蝇类卫生的物种，它们有一种进化压力，为了能追上猎物，就不得不尽力提高自己的反应速度。随着进化演变，反应速度快的鸟类就能捕捉到猎物，然后就会食物充足，能繁育更多后代，并能把自己的反应速度遗传给下一代。

The flies that have been chased by the fast-sighted birds will be evolving faster reactions to get away, creating an evolutionary arms race that has gone on longer even than the existence of birds. Prey flies have been evolving faster vision and reactions to escape predatory flies like the killer fly since they evolved flight.

而鸟类的捕猎对象蝇类，则需要进化提高自己的反应速度，才能逃生。这就形成一种进化角力赛，而这种角力赛，自然是发生在鸟类出现之后。自蝇类进化出飞行功能后，猎物类蝇视觉反应速度一直在进化提高，这样才能逃过诸如杀手蝇等猎手类蝇的捕捉。

Next time you try inanely to swat a fly, try not to be so disheartened. Your lumbering, slow motion swats are being thwarted by hundreds of millions of years of natural selection letting the flies watch your attempts in slow motion.

等你下次疯狂地要拍死一只苍蝇时，不要灰心丧气，你动作笨拙缓慢，是因为数百万千万年的自然进化选择，你动作拍的再快，在苍蝇眼里，也都是慢动作。

Between you and the fly, time, it seems, is relative.

看来，人类与蝇类之间，时间具有相对性。

译后记：

与我们日常生活如此紧密的苍蝇，和人类之间竟然有这么奇特的相对性，让人不禁想到，神话故事中人界与仙界之间那奇幻的相对性：天上一天，地上一年。

佛教中有“三界二十八重天”之说，三界即欲界、色界和无色界。其中，欲界有六层天，色界有十八层天，无色界有四层天。道教根据道生万物的宇宙创世理论，将"天"分为三十六层构想出来神仙所处的空间，并为学道成仙提供了教义依据。

《圣经》记载中，公元36年-45年没有提及保罗，这段时期便是保罗的“沉默时期”，在这期间，保罗曾被提到“三层天”去，看见有关“三层天”的异象，保罗叙述他被提去三层天时，在那里“听见隐秘的言语，是人不可说的”。

美国哲学家与心理学家威廉·詹姆士1895年所提出的“多重宇宙论”，在近代已经在科学、哲学和神学等领域激起大量哲思问题，而通俗的科幻小说，也喜欢将平行宇宙的概念用于其中。

由此看来，不同物种、不同宗教、不同领域之间，都有着不同的“世界”。即使是地球上所生存的人类，在不同的个体、民族、国家之间，它们的“世界”也都相差甚巨，“语言”也会有所不通。

往期精彩：

飞掠地球|《提心吊胆》：小行星撞地球，距离我们有多远？

生命之谜|施一公：生命之源或缘于35亿年前的一团量子纠缠，人类认知或囿于自身生命的物质形式局限