How brain parasites change their host's behavior - Jaap de Roode

寄生生物如何改变宿主的行为 - Jaap de Roode

翻译人员: Ruohan Lu 校对人员: Cissy Yun

Which of these entities has evolved the ability

这些家伙中有哪些进化出了

控制体积是他们好多倍的动物的能力呢？

to manipulate an animal many times its size?

The answer is all of them.

答案就是他们都能

These are all parasites,

这些家伙就是寄生生物

organisms that live on or inside another host organism,

一种依赖或者寄生于宿主内部的有机生物

which they harm and sometimes even kill.

他们会伤害甚至有时杀死他们的宿主

Parasite survival depends on transmitting from one host to the next,

寄生生物的存活依赖于在不同宿主间转移，

sometimes through an intermediate species.

有时还需要通过一个中间物种

Our parasites elegantly achieve this by manipulating their host's behavior,

我们的寄生生物微妙 通过控制他们宿主来达到目的

sometimes through direct brain hijacking.

有时会直接向大脑发起进攻

For example, this is the Gordian worm.

例如，这是一个线形虫

One of its hosts, this cricket.

这是它的宿主，一只蟋蟀

The Gordian worm needs water to mate, but the cricket prefers dry land.

线形虫需要水分来交配 但蟋蟀喜欢干燥的陆地

So once it's big enough to reproduce,

所以一旦线形虫长成可以繁殖的大小

the worm produces proteins that garble the cricket's navigational system.

它就会产生某种蛋白质 以干扰蟋蟀的导航系统

The confused cricket jumps around erratically,

这只被迷惑的蟋蟀就稀里糊涂地跳来跳去

moves closer to water,

向水域移动

and eventually leaps in, often drowning in the process.

最终跳进水里，溺死

The worm then wriggles out to mate

之后，线形虫向外蠕动并进行交配

and its eggs get eaten by little water insects

它的卵又被小型水生生物吃掉

that mature,

这些小型水生生物逐渐成熟

colonize land,

聚居于陆地

and are, in turn, eaten by new crickets.

然后又被新的蟋蟀吃掉

And thus, the Gordian worm lives on.

这样，线形虫就活下来了

And here's the rabies virus, another mind-altering parasite.

这是狂犬病毒 又一个干扰思维的寄生生物

This virus infects mammals, often dogs,

这种病毒会感染哺乳动物，通常是狗

and travels up the animal's nerves to its brain

并且顺着动物的神经抵达它们的大脑

where it causes inflammation that eventually kills the host.

引起大脑里发炎， 最终会杀死宿主的炎症

But before it does, it often increases its host's aggressiveness

但在这之前，它通常会增强宿主的攻击性

and ramps up the production of rabies-transmitting saliva,

产生更多会传播狂犬病的唾液

while making it hard to swallow.

并使得宿主很难吞咽

These factors make the host more likely to bite another animal

这些因素提高了宿主撕咬其他动物的可能性

and more likely to pass the virus on when it does.

也更有可能在此过程中传播病毒

And now, meet Ophiocordyceps, also known as the zombie fungus.

现在，来见见侧偏蛇虫草菌，又称僵尸真菌

Its host of choice is tropical ants that normally live in treetops.

它的宿主是住在树梢上的热带蚂蚁

After Ophiocordyceps spores pierce the ant's exoskeleton,

侧偏蛇虫草菌的孢子们会 在蚂蚁的外骨骼上穿孔

they set off convulsions that make the ant fall from the tree.

然后，它们引起蚂蚁痉挛，使蚂蚁从树上掉下来

The fungus changes the ant's behavior, compelling it to wander mindlessly

真菌改变了蚂蚁的行为，强迫蚂蚁无意识地闲逛

until it stumbles onto a plant leaf with the perfect fungal breeding conditions,

直到蚂蚁碰到一片有着完美真菌孕育条件的树叶

which it latches onto.

并牢牢揪住这个树叶

The ant then dies,

然后这只蚂蚁就死了

and the fungus parasitizes its body to build a tall, thin stalk from its neck.

寄生于其身的真菌 会从它的颈部伸出细长柄状物

Within several weeks, the stalk shoots off spores,

几周之内，这个柄状物射出孢子

which turn more ants into six-legged leaf-seeking zombies.

这些孢子把更多蚂蚁变成“六腿寻叶僵尸”

One of humanity's most deadly assailants is a behavior-altering parasite,

其中一个对人类最致命的攻击者 是改变行为的寄生生物

though if it's any consolation,

算得上安慰的是

it's not our brains that are being hijacked.

被攻击的并不是我们的大脑

I'm talking about Plasmodium, which causes malaria.

我说的是疟原虫，它会导致疟疾

This parasite needs mosquitoes to shuttle it between hosts,

这种寄生生物需要蚊子将其传播于宿主之间

so it makes them bite more frequently and for longer.

所以它使得蚊子叮咬得更频繁，时间更长

There's also evidence that humans infected with malaria

也有证据说感染了疟疾人

对于蚊子的吸引力更大

are more attractive to mosquitoes,

蚊子会叮咬他们，并将寄生虫传播得更远

which will bite them and transfer the parasite further.

This multi-species system is so effective,

这个多物种体系是如此有效率

that there are hundreds of millions of malaria cases every year.

以至于每年有数千万疟疾的案例

And finally, there are cats.

最后，说说猫

Don't worry, there probably aren't any cats living in your body

别担心，应该没有猫住在你的身体里

控制你的思想

and controlling your thoughts.

I mean, probably.

我是说，应该是

But there is a microorganism called Toxoplasma

但是有一种微生物叫弓形虫

that needs both cats and rodents to complete its life cycle.

需要猫和啮齿动物两者来完成它的生命周期

When a rat gets infected by eating cat feces,

当老鼠通过食用猫的粪便，感染了寄生虫，

the parasite changes chemical levels in the rat's brain,

这种寄生虫会改变老鼠大脑中的化学成分水平

making it less cautious around the hungry felines,

使它在饥饿的猫科动物身旁疏于谨慎

maybe even attracted to them.

猫科动物甚至会吸引到它们

This makes them easy prey,

这使得猫科动物更易捕食

so these infected rodents get eaten and pass the parasite on.

所以这些感染了的啮齿动物被吃掉 并继续传播寄生虫

Mind control successful.

控制思维就这样成功了

There's even evidence that the parasite affects human behavior.

甚至还有证据证明寄生生物会影响人类的行为

In most cases, we don't completely understand

多数情况下，我们不会完全理解

how these parasites manage their feats of behavior modification.

这些寄生生物是如何管理 它们的操控行为的本领

But from what we do know,

但从我们知道的来看

we can tell that they have a pretty diverse toolbox.

我们可以看出他们确实会耍不少花招

Gordian worms seem to affect crickets' brains directly.

线形虫似乎可以直接影响蟋蟀的大脑

The malaria parasite, on the other hand,

疟疾寄生虫（疟原虫）则可以

blocks an enzyme that helps the mosquitoes feed,

阻碍生产可以帮助蚊子吃东西的酶

forcing them to bite over and over and over again.

强迫蚊子不停地叮咬

The rabies virus may cause that snarling, slobbering behavior

狂犬病病毒会通过让免疫系统“开挂”

by putting the immune system into overdrive.

来引起吼叫和流口水的行为

But whatever the method,

但不管是什么方式

when you think about how effectively

当你想到这些寄生生物

these parasites control the behavior of their hosts,

多么有效地控制着他们宿主的行为

you may wonder how much of human behavior is actually parasites doing the talking.

你就会想知道 有多少人类行为实际是由寄生生物主宰着的

Since more than half of the species on Earth are parasites,

由于地球上超过一半的生物是寄生生物

it could be more than we think.

这种“主宰”恐怕是多于我们所以为的