Which of these entities has evolved the ability to manipulate an animal many times its size?
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？
The answer is all of them.
答案就是他们都能。
These are all parasites, organisms that live on or inside another host organism, which they harm and sometimes even kill.
这些家伙就是寄生生物，一种依赖或者寄生于宿主内部的有机生物，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, sometimes through an intermediate species.
寄生生物的存活依赖于在不同宿主间转移，有时还需要通过一个中间物种。
Our parasites elegantly achieve this by manipulating their host's behavior, sometimes through direct brain hijacking.
我们的寄生生物巧妙地通过控制他们宿主来达到该目的，有时会直接向大脑发起进攻。
For example, this is the Gordian worm. One of its hosts, this cricket.
例如，这是一个线形虫。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, the worm produces proteins that garble the cricket's navigational system.
所以一旦线形虫长成可以繁殖的大小，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, moves closer to water, and eventually leaps in, often drowning in the process.
这只被迷惑的蟋蟀就稀里糊涂地跳来跳去，向水域移动，最终跳进水里，溺死。
The worm then wriggles out to mate and its eggs get eaten by little water insects
之后，线形虫向外蠕动并进行交配，它的卵又被小型水生生物吃掉，
that mature, colonize land, and are, in turn, eaten by new crickets.
这些小型水生生物逐渐成熟，聚居于陆地，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 where it causes inflammation that eventually kills the host.
并且顺着动物的神经抵达它们的大脑，引起大脑里发炎，最终会杀死宿主。
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, while making it hard to swallow.
产生更多会传播狂犬病的唾液，并使得宿主很难吞咽。
These factors make the host more likely to bite another animal and more likely to pass the virus on when it does.
这些因素提高了宿主撕咬其他动物的可能性，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, they set off convulsions that make the ant fall from the tree.
侧偏蛇虫草菌的孢子们会在蚂蚁的外骨骼上穿孔，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, which it latches onto.
直到蚂蚁碰到一片有着完美真菌孕育条件的树叶，并牢牢揪住这个树叶。
The ant then dies, and the fungus parasitizes its body to build a tall, thin stalk from its neck.
然后这只蚂蚁就死了，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, which turn more ants into six-legged leaf-seeking zombies.
几周之内，这个柄状物射出孢子，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, it's not our brains that are being hijacked.
如果能安慰你的话，那就是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, so it makes them bite more frequently and for longer.
这种寄生生物需要蚊子将其传播于宿主之间，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 are more attractive to mosquitoes,
也有证据表明，感染了疟疾的人，对于蚊子的吸引力更大，
which will bite them and transfer the parasite further.
蚊子会叮咬他们，并将寄生虫传播得更远。
This multi-species system is so effective, that there are hundreds of millions of malaria cases every year.
这个多物种体系是如此有效率，以至于每年有数千万疟疾的案例。
And finally, there are cats.
最后，来说一说猫。
Don't worry, there probably aren't any cats living in your body and controlling your thoughts. I mean, probably.
别担心，应该没有猫住在你的身体里，控制你的思想。我是说，应该是。
But there is a microorganism called Toxoplasma that needs both cats and rodents to complete its life cycle.
但是有一种微生物叫弓形虫，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, the parasite changes chemical levels in the rat's brain,
当老鼠通过食用猫的粪便感染了寄生虫，这种寄生虫就会改变老鼠大脑中的化学成分水平，
making it less cautious around the hungry felines, maybe even attracted to them.
使它在饥饿的猫科动物身旁疏于谨慎，猫科动物甚至会吸引到它们。
This makes them easy prey, so these infected rodents get eaten and pass the parasite on. Mind control successful.
这使得猫科动物更易捕食，所以这些感染了的啮齿动物被吃掉，并继续传播寄生虫。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 how these parasites manage their feats of behavior modification.
多数情况下，我们不会完全理解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, we can tell that they have a pretty diverse toolbox.
但从我们知道的来看，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, blocks an enzyme that helps the mosquitoes feed,
疟疾寄生虫（疟原虫）则可以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 by putting the immune system into overdrive.
狂犬病病毒会通过让免疫系统“开挂”来引起吼叫和流口水的行为。
But whatever the method, when you think about how effectively these parasites control the behavior of their hosts,
但不管是什么方式，当你想到这些寄生生物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, it could be more than we think.
由于地球上超过一半的生物是寄生生物，这种“主宰”恐怕是多于我们所以为的。