Zombie roaches and other parasite tales
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0:01 - 0:03A herd of wildebeests, a shoal of fish,
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0:03 - 0:05a flock of birds.
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0:05 - 0:07Many animals gather in large groups
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0:07 - 0:09that are among the most wonderful spectacles
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0:09 - 0:11in the natural world.
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0:11 - 0:13But why do these groups form?
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0:13 - 0:15The common answers include things like
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0:15 - 0:18seeking safety in numbers or hunting in packs
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0:18 - 0:20or gathering to mate or breed,
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0:20 - 0:22and all of these explanations,
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0:22 - 0:23while often true,
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0:23 - 0:26make a huge assumption about animal behavior,
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0:26 - 0:30that the animals are in control of their own actions,
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0:30 - 0:32that they are in charge of their bodies.
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0:32 - 0:35And that is often not the case.
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0:35 - 0:38This is Artemia, a brine shrimp.
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0:38 - 0:41You probably know it better as a sea monkey.
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0:41 - 0:43It's small, and it typically lives alone,
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0:43 - 0:46but it can gather in these large red swarms
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0:46 - 0:48that span for meters,
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0:48 - 0:51and these form because of a parasite.
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0:51 - 0:54These shrimp are infected with a tapeworm.
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0:54 - 0:56A tapeworm is effectively a long, living gut
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0:56 - 0:59with genitals at one end and
a hooked mouth at the other. -
0:59 - 1:02As a freelance journalist, I sympathize.
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1:02 - 1:04(Laughter)
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1:04 - 1:07The tapeworm drains nutrients from Artemia's body,
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1:07 - 1:09but it also does other things.
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1:09 - 1:10It castrates them,
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1:10 - 1:15it changes their color from transparent to bright red,
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1:15 - 1:17it makes them live longer,
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1:17 - 1:19and as biologist Nicolas Rode has found,
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1:19 - 1:22it makes them swim in groups.
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1:22 - 1:26Why? Because the tapeworm,
like many other parasites, -
1:26 - 1:27has a complicated life cycle
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1:27 - 1:30involving many different hosts.
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1:30 - 1:32The shrimp are just one step on its journey.
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1:32 - 1:35Its ultimate destination is this,
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1:35 - 1:37the greater flamingo.
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1:37 - 1:40Only in a flamingo can the tapeworm reproduce,
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1:40 - 1:43so to get there, it manipulates its shrimp hosts
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1:43 - 1:46into forming these conspicuous colored swarms
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1:46 - 1:49that are easier for a flamingo to spot
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1:49 - 1:50and to devour,
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1:50 - 1:53and that is the secret of the Artemia swarm.
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1:53 - 1:55They aren't sociable through their own volition,
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1:55 - 1:58but because they are being controlled.
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1:58 - 1:59It's not safety in numbers.
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1:59 - 2:01It's actually the exact opposite.
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2:01 - 2:04The tapeworm hijacks their brains and their bodies,
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2:04 - 2:05turning them into vehicles
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2:05 - 2:09for getting itself into a flamingo.
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2:09 - 2:11And here is another example
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2:11 - 2:13of a parasitic manipulation.
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2:13 - 2:16This is a suicidal cricket.
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2:16 - 2:20This cricket swallowed the
larvae of a Gordian worm, -
2:20 - 2:22or horsehair worm.
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2:22 - 2:24The worm grew to adult size within it,
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2:24 - 2:27but it needs to get into water in order to mate,
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2:27 - 2:29and it does that by releasing proteins
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2:29 - 2:31that addle the cricket's brain,
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2:31 - 2:33causing it to behave erratically.
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2:33 - 2:35When the cricket nears a body of water,
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2:35 - 2:37such as this swimming pool,
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2:37 - 2:39it jumps in and drowns,
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2:39 - 2:41and the worm wriggles out
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2:41 - 2:45of its suicidal corpse.
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2:45 - 2:48Crickets are really roomy. Who knew?
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2:48 - 2:52The tapeworm and the Gordian worm are not alone.
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2:52 - 2:53They are part of an entire cavalcade
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2:53 - 2:55of mind-controlling parasites,
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2:55 - 2:59of fungi, viruses, and worms and insects and more
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2:59 - 3:02that all specialize in subverting and overriding
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3:02 - 3:04the wills of their hosts.
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3:04 - 3:06Now, I first learned about this way of life
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3:06 - 3:08through David Attenborough's "Trials of Life"
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3:08 - 3:10about 20 years ago,
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3:10 - 3:12and then later through a wonderful book called
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3:12 - 3:14"Parasite Rex" by my friend Carl Zimmer.
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3:14 - 3:17And I've been writing about
these creatures ever since. -
3:17 - 3:19Few topics in biology enthrall me more.
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3:19 - 3:23It's like the parasites have subverted my own brain.
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3:23 - 3:26Because after all, they are always compelling
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3:26 - 3:27and they are delightfully macabre.
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3:27 - 3:28When you write about parasites,
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3:28 - 3:30your lexicon swells with phrases like
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3:30 - 3:34"devoured alive" and "bursts out of its body."
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3:34 - 3:35(Laughter)
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3:35 - 3:36But there's more to it than that.
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3:36 - 3:38I'm a writer, and fellow writers in the audience
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3:38 - 3:41will know that we love stories.
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3:41 - 3:44Parasites invite us to resist the allure
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3:44 - 3:45of obvious stories.
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3:45 - 3:48Their world is one of plot twists
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3:48 - 3:51and unexpected explanations.
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3:51 - 3:53Why, for example,
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3:53 - 3:55does this caterpillar
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3:55 - 3:57start violently thrashing about
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3:57 - 3:59when another insect gets close to it
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3:59 - 4:01and those white cocoons that it seems
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4:01 - 4:02to be standing guard over?
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4:02 - 4:05Is it maybe protecting its siblings?
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4:05 - 4:07No.
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4:07 - 4:08This caterpillar was attacked
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4:08 - 4:11by a parasitic wasp which laid eggs inside it.
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4:11 - 4:13The eggs hatched and the young wasps
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4:13 - 4:14devoured the caterpillar alive
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4:14 - 4:16before bursting out of its body.
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4:16 - 4:18See what I mean?
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4:18 - 4:21Now, the caterpillar didn't die.
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4:21 - 4:24Some of the wasps seemed to stay behind
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4:24 - 4:27and controlled it into defending their siblings
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4:27 - 4:29which are metamorphosing
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4:29 - 4:31into adults within those cocoons.
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4:31 - 4:34This caterpillar is a head-banging
zombie bodyguard -
4:34 - 4:35defending the offspring
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4:35 - 4:38of the creature that killed it.
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4:38 - 4:42(Applause)
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4:42 - 4:46We have a lot to get through.
I only have 13 minutes. (Laughter) -
4:46 - 4:48Now, some of you are probably just
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4:48 - 4:50desperately clawing for some solace
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4:50 - 4:52in the idea that these things are oddities
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4:52 - 4:54of the natural world, that they are outliers,
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4:54 - 4:56and that point of view is understandable,
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4:56 - 4:58because by their nature, parasites are quite small
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4:58 - 5:00and they spend a lot of their time
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5:00 - 5:03inside the bodies of other things.
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5:03 - 5:04They're easy to overlook,
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5:04 - 5:07but that doesn't mean that they aren't important.
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5:07 - 5:09A few years back, a man called Kevin Lafferty
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5:09 - 5:12took a group of scientists
into three Californian estuaries -
5:12 - 5:14and they pretty much weighed and dissected
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5:14 - 5:16and recorded everything they could find,
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5:16 - 5:17and what they found
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5:17 - 5:21were parasites in extreme abundance.
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5:21 - 5:23Especially common were trematodes,
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5:23 - 5:25tiny worms that specialize in castrating their hosts
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5:25 - 5:28like this unfortunate snail.
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5:28 - 5:31Now, a single trematode is tiny, microscopic,
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5:31 - 5:33but collectively they weighed as much
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5:33 - 5:35as all the fish in the estuaries
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5:35 - 5:38and three to nine times more than all the birds.
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5:38 - 5:40And remember the Gordian worm that I showed you,
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5:40 - 5:42the cricket thing?
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5:42 - 5:44One Japanese scientist called Takuya Sato
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5:44 - 5:46found that in one stream,
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5:46 - 5:48these things drive so many crickets
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5:48 - 5:49and grasshoppers into the water
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5:49 - 5:51that the drowned insects
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5:51 - 5:55make up some 60 percent of the diet of local trout.
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5:55 - 5:58Manipulation is not an oddity.
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5:58 - 6:00It is a critical and common part
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6:00 - 6:02of the world around us,
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6:02 - 6:03and scientists have now found
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6:03 - 6:06hundreds of examples of such manipulators,
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6:06 - 6:08and more excitingly, they're starting to understand
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6:08 - 6:12exactly how these creatures control their hosts.
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6:12 - 6:15And this is one of my favorite examples.
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6:15 - 6:17This is Ampulex compressa,
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6:17 - 6:20the emerald cockroach wasp,
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6:20 - 6:22and it is a truth universally acknowledged
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6:22 - 6:24that an emerald cockroach wasp in possession
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6:24 - 6:25of some fertilized eggs
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6:25 - 6:28must be in want of a cockroach.
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6:28 - 6:29When she finds one,
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6:29 - 6:31she stabs it with a stinger
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6:31 - 6:33that is also a sense organ.
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6:33 - 6:35This discovery came out three weeks ago.
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6:35 - 6:38She stabs it with a stinger that is a sense organ
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6:38 - 6:39equipped with small sensory bumps
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6:39 - 6:42that allow her to feel the distinctive texture
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6:42 - 6:44of a roach's brain.
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6:44 - 6:47So like a person blindly rooting about in a bag,
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6:47 - 6:50she finds the brain, and she injects it with venom
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6:50 - 6:54into two very specific clusters of neurons.
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6:54 - 6:57Israeli scientists Frederic Libersat and Ram Gal
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6:57 - 7:01found that the venom is a
very specific chemical weapon. -
7:01 - 7:03It doesn't kill the roach, nor does it sedate it.
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7:03 - 7:05The roach could walk away
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7:05 - 7:08or fly or run if it chose to,
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7:08 - 7:10but it doesn't choose to,
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7:10 - 7:14because the venom nixes its motivation to walk,
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7:14 - 7:15and only that.
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7:15 - 7:18The wasp basically un-checks
the escape-from-danger box -
7:18 - 7:20in the roach's operating system,
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7:20 - 7:24allowing her to lead her helpless victim
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7:24 - 7:26back to her lair by its antennae
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7:26 - 7:28like a person walking a dog.
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7:28 - 7:30And once there, she lays an egg on it,
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7:30 - 7:32egg hatches, devoured alive, bursts out of body,
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7:32 - 7:34yadda yadda yadda, you know the drill.
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7:34 - 7:38(Laughter) (Applause)
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7:38 - 7:41Now I would argue that, once stung,
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7:41 - 7:43the cockroach isn't a roach anymore.
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7:43 - 7:45It's more of an extension of the wasp,
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7:45 - 7:48just like the cricket was an
extension of the Gordian worm. -
7:48 - 7:51These hosts won't get to survive or reproduce.
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7:51 - 7:52They have as much control over their own fates
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7:52 - 7:54as my car.
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7:54 - 7:56Once the parasites get in,
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7:56 - 7:58the hosts don't get a say.
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7:58 - 7:59Now humans, of course,
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7:59 - 8:02are no stranger to manipulation.
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8:02 - 8:04We take drugs to shift the chemistries of our brains
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8:04 - 8:05and to change our moods,
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8:05 - 8:09and what are arguments or advertising or big ideas
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8:09 - 8:13if not an attempt to influence someone else's mind?
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8:13 - 8:14But our attempts at doing this
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8:14 - 8:16are crude and blundering compared
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8:16 - 8:19to the fine-grained specificity of the parasites.
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8:19 - 8:22Don Draper only wishes he was as elegant
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8:22 - 8:26and precise as the emerald cockroach wasp.
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8:26 - 8:30Now, I think this is part of what makes parasites
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8:30 - 8:33so sinister and so compelling.
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8:33 - 8:36We place such a premium on our free will
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8:36 - 8:37and our independence
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8:37 - 8:38that the prospect of losing those qualities
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8:38 - 8:40to forces unseen
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8:40 - 8:43informs many of our deepest societal fears.
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8:43 - 8:45Orwellian dystopias and shadowy cabals
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8:45 - 8:47and mind-controlling supervillains --
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8:47 - 8:50these are tropes that fill our darkest fiction,
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8:50 - 8:55but in nature, they happen all the time.
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8:55 - 8:58Which leads me to an obvious
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8:58 - 9:00and disquieting question:
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9:00 - 9:02Are there dark, sinister parasites
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9:02 - 9:04that are influencing our behavior
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9:04 - 9:05without us knowing about it,
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9:05 - 9:08besides the NSA?
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9:08 - 9:09If there are any —
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9:09 - 9:13(Laughter) (Applause)
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9:13 - 9:16I've got a red dot on my forehead now, don't I?
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9:16 - 9:18(Laughter)
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9:18 - 9:21If there are any, this is a good candidate for them.
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9:21 - 9:24This is Toxoplasma gondii, or Toxo, for short,
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9:24 - 9:26because the terrifying creature
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9:26 - 9:28always deserves a cute nickname.
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9:28 - 9:30Toxo infects mammals,
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9:30 - 9:32a wide variety of mammals,
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9:32 - 9:35but it can only sexually reproduce in a cat.
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9:35 - 9:38And scientists like Joanne Webster have shown that
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9:38 - 9:40if Toxo gets into a rat or a mouse,
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9:40 - 9:43it turns the rodent into a cat-seeking missile.
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9:43 - 9:47If the infected rat smells the delightful odor
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9:47 - 9:48of cat piss,
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9:48 - 9:50it runs towards the source of the smell
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9:50 - 9:54rather than the more sensible direction of away.
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9:54 - 9:57The cat eats the rat. Toxo gets to have sex.
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9:57 - 10:00It's a classic tale of Eat, Prey, Love.
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10:00 - 10:04(Laughter) (Applause)
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10:08 - 10:11You're very charitable, generous people.
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10:11 - 10:13Hi, Elizabeth, I loved your talk.
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10:13 - 10:17How does the parasite control its host
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10:17 - 10:18in this way?
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10:18 - 10:19We don't really know.
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10:19 - 10:21We know that Toxo releases an enzyme
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10:21 - 10:23that makes dopamine, a substance involved
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10:23 - 10:25in reward and motivation.
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10:25 - 10:27We know it targets certain parts of a rodent's brain,
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10:27 - 10:30including those involved in sexual arousal.
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10:30 - 10:32But how those puzzle pieces fit together
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10:32 - 10:34is not immediately clear.
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10:34 - 10:36What is clear is that this thing
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10:36 - 10:37is a single cell.
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10:37 - 10:39This has no nervous system.
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10:39 - 10:40It has no consciousness.
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10:40 - 10:41It doesn't even have a body.
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10:41 - 10:44But it's manipulating a mammal?
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10:44 - 10:45We are mammals.
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10:45 - 10:48We are more intelligent than a mere rat, to be sure,
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10:48 - 10:50but our brains have the same basic structure,
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10:50 - 10:52the same types of cells,
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10:52 - 10:53the same chemicals running through them,
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10:53 - 10:55and the same parasites.
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10:55 - 10:58Estimates vary a lot, but some figures suggest
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10:58 - 11:00that one in three people around the world
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11:00 - 11:02have Toxo in their brains.
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11:02 - 11:05Now typically, this doesn't lead to any overt illness.
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11:05 - 11:07The parasite holds up in a dormant state
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11:07 - 11:09for a long period of time.
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11:09 - 11:11But there's some evidence that those people
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11:11 - 11:14who are carriers score slightly differently
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11:14 - 11:17on personality questionnaires than other people,
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11:17 - 11:20that they have a slightly
higher risk of car accidents, -
11:20 - 11:22and there's some evidence
that people with schizophrenia -
11:22 - 11:25are more likely to be infected.
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11:25 - 11:27Now, I think this evidence is still inconclusive,
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11:27 - 11:29and even among Toxo researchers,
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11:29 - 11:31opinion is divided as to whether the parasite
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11:31 - 11:34is truly influencing our behavior.
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11:34 - 11:36But given the widespread
nature of such manipulations, -
11:36 - 11:38it would be completely implausible
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11:38 - 11:40for humans to be the only species
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11:40 - 11:43that weren't similarly affected.
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11:43 - 11:47And I think that this capacity to constantly
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11:47 - 11:50subvert our way of thinking about the world
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11:50 - 11:52makes parasites amazing.
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11:52 - 11:55They're constantly inviting us to
look at the natural world sideways, -
11:55 - 11:57and to ask if the behaviors we're seeing,
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11:57 - 11:59whether they're simple and obvious
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11:59 - 12:00or baffling and puzzling,
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12:00 - 12:02are not the results of individuals
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12:02 - 12:04acting through their own accord
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12:04 - 12:06but because they are being bent
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12:06 - 12:08to the control of something else.
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12:08 - 12:11And while that idea may be disquieting,
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12:11 - 12:13and while parasites' habits may be very grisly,
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12:13 - 12:15I think that ability to surprise us
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12:15 - 12:18makes them as wonderful and as charismatic
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12:18 - 12:22as any panda or butterfly or dolphin.
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12:22 - 12:24At the end of "On the Origin of Species,"
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12:24 - 12:27Charles Darwin writes about the grandeur of life,
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12:27 - 12:30and of endless forms most beautiful
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12:30 - 12:31and most wonderful,
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12:31 - 12:34and I like to think he could easily have been talking
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12:34 - 12:37about a tapeworm that makes shrimp sociable
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12:37 - 12:40or a wasp that takes cockroaches for walks.
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12:40 - 12:43But perhaps, that's just a parasite talking.
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12:43 - 12:45Thank you.
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12:45 - 12:49(Applause)
- Title:
- Zombie roaches and other parasite tales
- Speaker:
- Ed Yong
- Description:
-
We humans set a premium on our own free will and independence ... and yet there's a shadowy influence we might not be considering. As science writer Ed Yong explains in this fascinating, hilarious and disturbing talk, parasites have perfected the art of manipulation to an incredible degree. So are they influencing us? It's more than likely.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TEDTalks
- Duration:
- 13:14
Brian Greene edited English subtitles for Zombie roaches and other parasite tales | ||
Morton Bast approved English subtitles for Zombie roaches and other parasite tales | ||
Morton Bast edited English subtitles for Zombie roaches and other parasite tales | ||
Morton Bast edited English subtitles for Zombie roaches and other parasite tales | ||
Madeleine Aronson accepted English subtitles for Zombie roaches and other parasite tales | ||
Madeleine Aronson edited English subtitles for Zombie roaches and other parasite tales | ||
Joseph Geni edited English subtitles for Zombie roaches and other parasite tales | ||
Amara Bot edited English subtitles for Zombie roaches and other parasite tales |