[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.45,0:00:09.21,Default,,0000,0000,0000,,Which of these entities \Nhas evolved the ability
Dialogue: 0,0:00:09.21,0:00:13.48,Default,,0000,0000,0000,,to manipulate an animal\Nmany times its size?
Dialogue: 0,0:00:13.48,0:00:15.89,Default,,0000,0000,0000,,The answer is all of them.
Dialogue: 0,0:00:15.89,0:00:17.50,Default,,0000,0000,0000,,These are all parasites,
Dialogue: 0,0:00:17.50,0:00:21.92,Default,,0000,0000,0000,,organisms that live on \Nor inside another host organism,
Dialogue: 0,0:00:21.92,0:00:25.59,Default,,0000,0000,0000,,which they harm and sometimes even kill.
Dialogue: 0,0:00:25.59,0:00:30.45,Default,,0000,0000,0000,,Parasite survival depends on transmitting\Nfrom one host to the next,
Dialogue: 0,0:00:30.45,0:00:33.53,Default,,0000,0000,0000,,sometimes through \Nan intermediate species.
Dialogue: 0,0:00:33.53,0:00:38.57,Default,,0000,0000,0000,,Our parasites elegantly achieve this\Nby manipulating their host's behavior,
Dialogue: 0,0:00:38.57,0:00:42.01,Default,,0000,0000,0000,,sometimes through direct brain hijacking.
Dialogue: 0,0:00:42.01,0:00:45.16,Default,,0000,0000,0000,,For example, this is the Gordian worm.
Dialogue: 0,0:00:45.16,0:00:47.50,Default,,0000,0000,0000,,One of its hosts, this cricket.
Dialogue: 0,0:00:47.50,0:00:52.03,Default,,0000,0000,0000,,The Gordian worm needs water to mate,\Nbut the cricket prefers dry land.
Dialogue: 0,0:00:52.03,0:00:54.64,Default,,0000,0000,0000,,So once it's big enough to reproduce,
Dialogue: 0,0:00:54.64,0:00:59.68,Default,,0000,0000,0000,,the worm produces proteins that garble\Nthe cricket's navigational system.
Dialogue: 0,0:00:59.68,0:01:02.88,Default,,0000,0000,0000,,The confused cricket \Njumps around erratically,
Dialogue: 0,0:01:02.88,0:01:04.35,Default,,0000,0000,0000,,moves closer to water,
Dialogue: 0,0:01:04.35,0:01:08.60,Default,,0000,0000,0000,,and eventually leaps in,\Noften drowning in the process.
Dialogue: 0,0:01:08.60,0:01:10.98,Default,,0000,0000,0000,,The worm then wriggles out to mate
Dialogue: 0,0:01:10.98,0:01:13.35,Default,,0000,0000,0000,,and its eggs get eaten \Nby little water insects
Dialogue: 0,0:01:13.35,0:01:14.70,Default,,0000,0000,0000,,that mature,
Dialogue: 0,0:01:14.70,0:01:16.08,Default,,0000,0000,0000,,colonize land,
Dialogue: 0,0:01:16.08,0:01:19.17,Default,,0000,0000,0000,,and are, in turn, eaten by new crickets.
Dialogue: 0,0:01:19.17,0:01:22.44,Default,,0000,0000,0000,,And thus, the Gordian worm lives on.
Dialogue: 0,0:01:22.44,0:01:26.30,Default,,0000,0000,0000,,And here's the rabies virus,\Nanother mind-altering parasite.
Dialogue: 0,0:01:26.30,0:01:28.99,Default,,0000,0000,0000,,This virus infects mammals, often dogs,
Dialogue: 0,0:01:28.99,0:01:32.59,Default,,0000,0000,0000,,and travels up the animal's \Nnerves to its brain
Dialogue: 0,0:01:32.59,0:01:36.26,Default,,0000,0000,0000,,where it causes inflammation \Nthat eventually kills the host.
Dialogue: 0,0:01:36.26,0:01:40.37,Default,,0000,0000,0000,,But before it does, it often increases\Nits host's aggressiveness
Dialogue: 0,0:01:40.37,0:01:45.25,Default,,0000,0000,0000,,and ramps up the production\Nof rabies-transmitting saliva,
Dialogue: 0,0:01:45.25,0:01:47.44,Default,,0000,0000,0000,,while making it hard to swallow.
Dialogue: 0,0:01:47.44,0:01:51.12,Default,,0000,0000,0000,,These factors make the host \Nmore likely to bite another animal
Dialogue: 0,0:01:51.12,0:01:55.33,Default,,0000,0000,0000,,and more likely to pass \Nthe virus on when it does.
Dialogue: 0,0:01:55.33,0:02:01.02,Default,,0000,0000,0000,,And now, meet Ophiocordyceps,\Nalso known as the zombie fungus.
Dialogue: 0,0:02:01.02,0:02:05.84,Default,,0000,0000,0000,,Its host of choice is tropical ants\Nthat normally live in treetops.
Dialogue: 0,0:02:05.84,0:02:10.86,Default,,0000,0000,0000,,After Ophiocordyceps spores \Npierce the ant's exoskeleton,
Dialogue: 0,0:02:10.86,0:02:15.48,Default,,0000,0000,0000,,they set off convulsions \Nthat make the ant fall from the tree.
Dialogue: 0,0:02:15.48,0:02:20.33,Default,,0000,0000,0000,,The fungus changes the ant's behavior,\Ncompelling it to wander mindlessly
Dialogue: 0,0:02:20.33,0:02:24.83,Default,,0000,0000,0000,,until it stumbles onto a plant leaf with\Nthe perfect fungal breeding conditions,
Dialogue: 0,0:02:24.83,0:02:26.98,Default,,0000,0000,0000,,which it latches onto.
Dialogue: 0,0:02:26.98,0:02:28.43,Default,,0000,0000,0000,,The ant then dies,
Dialogue: 0,0:02:28.43,0:02:34.98,Default,,0000,0000,0000,,and the fungus parasitizes its body\Nto build a tall, thin stalk from its neck.
Dialogue: 0,0:02:34.98,0:02:37.93,Default,,0000,0000,0000,,Within several weeks, \Nthe stalk shoots off spores,
Dialogue: 0,0:02:37.93,0:02:43.59,Default,,0000,0000,0000,,which turn more ants \Ninto six-legged leaf-seeking zombies.
Dialogue: 0,0:02:43.59,0:02:48.86,Default,,0000,0000,0000,,One of humanity's most deadly assailants\Nis a behavior-altering parasite,
Dialogue: 0,0:02:48.86,0:02:50.85,Default,,0000,0000,0000,,though if it's any consolation,
Dialogue: 0,0:02:50.85,0:02:54.02,Default,,0000,0000,0000,,it's not our brains \Nthat are being hijacked.
Dialogue: 0,0:02:54.02,0:02:57.97,Default,,0000,0000,0000,,I'm talking about Plasmodium,\Nwhich causes malaria.
Dialogue: 0,0:02:57.97,0:03:02.08,Default,,0000,0000,0000,,This parasite needs mosquitoes\Nto shuttle it between hosts,
Dialogue: 0,0:03:02.08,0:03:05.91,Default,,0000,0000,0000,,so it makes them bite more frequently\Nand for longer.
Dialogue: 0,0:03:05.91,0:03:09.02,Default,,0000,0000,0000,,There's also evidence \Nthat humans infected with malaria
Dialogue: 0,0:03:09.02,0:03:11.02,Default,,0000,0000,0000,,are more attractive to mosquitoes,
Dialogue: 0,0:03:11.02,0:03:14.68,Default,,0000,0000,0000,,which will bite them \Nand transfer the parasite further.
Dialogue: 0,0:03:14.68,0:03:17.74,Default,,0000,0000,0000,,This multi-species system is so effective,
Dialogue: 0,0:03:17.74,0:03:22.43,Default,,0000,0000,0000,,that there are hundreds of millions\Nof malaria cases every year.
Dialogue: 0,0:03:22.43,0:03:24.74,Default,,0000,0000,0000,,And finally, there are cats.
Dialogue: 0,0:03:24.74,0:03:28.38,Default,,0000,0000,0000,,Don't worry, there probably \Naren't any cats living in your body
Dialogue: 0,0:03:28.38,0:03:29.85,Default,,0000,0000,0000,,and controlling your thoughts.
Dialogue: 0,0:03:29.85,0:03:31.55,Default,,0000,0000,0000,,I mean, probably.
Dialogue: 0,0:03:31.55,0:03:35.30,Default,,0000,0000,0000,,But there is a microorganism\Ncalled Toxoplasma
Dialogue: 0,0:03:35.30,0:03:39.73,Default,,0000,0000,0000,,that needs both cats and rodents\Nto complete its life cycle.
Dialogue: 0,0:03:39.73,0:03:43.08,Default,,0000,0000,0000,,When a rat gets infected\Nby eating cat feces,
Dialogue: 0,0:03:43.08,0:03:47.06,Default,,0000,0000,0000,,the parasite changes chemical levels\Nin the rat's brain,
Dialogue: 0,0:03:47.06,0:03:50.50,Default,,0000,0000,0000,,making it less cautious\Naround the hungry felines,
Dialogue: 0,0:03:50.50,0:03:52.75,Default,,0000,0000,0000,,maybe even attracted to them.
Dialogue: 0,0:03:52.75,0:03:54.52,Default,,0000,0000,0000,,This makes them easy prey,
Dialogue: 0,0:03:54.52,0:03:59.49,Default,,0000,0000,0000,,so these infected rodents\Nget eaten and pass the parasite on.
Dialogue: 0,0:03:59.49,0:04:01.77,Default,,0000,0000,0000,,Mind control successful.
Dialogue: 0,0:04:01.77,0:04:06.21,Default,,0000,0000,0000,,There's even evidence that the parasite\Naffects human behavior.
Dialogue: 0,0:04:06.21,0:04:08.68,Default,,0000,0000,0000,,In most cases, \Nwe don't completely understand
Dialogue: 0,0:04:08.68,0:04:12.99,Default,,0000,0000,0000,,how these parasites manage \Ntheir feats of behavior modification.
Dialogue: 0,0:04:12.99,0:04:14.53,Default,,0000,0000,0000,,But from what we do know,
Dialogue: 0,0:04:14.53,0:04:17.00,Default,,0000,0000,0000,,we can tell that they have \Na pretty diverse toolbox.
Dialogue: 0,0:04:17.00,0:04:21.43,Default,,0000,0000,0000,,Gordian worms seem to affect\Ncrickets' brains directly.
Dialogue: 0,0:04:21.43,0:04:23.65,Default,,0000,0000,0000,,The malaria parasite, on the other hand,
Dialogue: 0,0:04:23.65,0:04:26.90,Default,,0000,0000,0000,,blocks an enzyme \Nthat helps the mosquitoes feed,
Dialogue: 0,0:04:26.90,0:04:30.82,Default,,0000,0000,0000,,forcing them to bite over \Nand over and over again.
Dialogue: 0,0:04:30.82,0:04:34.51,Default,,0000,0000,0000,,The rabies virus may cause \Nthat snarling, slobbering behavior
Dialogue: 0,0:04:34.51,0:04:37.97,Default,,0000,0000,0000,,by putting the immune system\Ninto overdrive.
Dialogue: 0,0:04:37.97,0:04:39.33,Default,,0000,0000,0000,,But whatever the method,
Dialogue: 0,0:04:39.33,0:04:41.00,Default,,0000,0000,0000,,when you think about how effectively
Dialogue: 0,0:04:41.00,0:04:44.44,Default,,0000,0000,0000,,these parasites control \Nthe behavior of their hosts,
Dialogue: 0,0:04:44.44,0:04:51.37,Default,,0000,0000,0000,,you may wonder how much of human behavior\Nis actually parasites doing the talking.
Dialogue: 0,0:04:51.37,0:04:55.04,Default,,0000,0000,0000,,Since more than half of the species\Non Earth are parasites,
Dialogue: 0,0:04:55.04,0:04:58.06,Default,,0000,0000,0000,,it could be more than we think.