Episode 10

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0:00:03 > 0:00:06The natural world is full of extraordinary animals with

0:00:06 > 0:00:09amazing life histories.

0:00:09 > 0:00:13Yet certain stories are more intriguing than most.

0:00:16 > 0:00:19The mysteries of a butterfly's life cycle,

0:00:19 > 0:00:23or the strange biology of the emperor penguin.

0:00:23 > 0:00:26Some of these creatures were surrounded by myths

0:00:26 > 0:00:30and misunderstandings for a very long time,

0:00:30 > 0:00:33and some have only recently revealed their secrets.

0:00:35 > 0:00:38These are the animals that stand out from the crowd,

0:00:38 > 0:00:42the curiosities I find most fascinating of all.

0:00:50 > 0:00:54The abilities of some plants and animals are so remarkable

0:00:54 > 0:00:57that they seem to be almost supernatural.

0:00:57 > 0:01:02In this programme, I investigate the shocking power of a fish that

0:01:02 > 0:01:05advanced our understanding of electricity,

0:01:05 > 0:01:09and plants with senses that are surprising modern science.

0:01:11 > 0:01:14But how do these extraordinary powers help the organisms that

0:01:14 > 0:01:16produce them?

0:01:24 > 0:01:27The freshwater eel is surrounded by legends.

0:01:27 > 0:01:31The first Europeans to explore the New World heard amazing

0:01:31 > 0:01:33stories about it.

0:01:33 > 0:01:37And when, in the 18th century, specimens of this strange fish

0:01:37 > 0:01:39reached Europe, they created a sensation.

0:01:41 > 0:01:45In 1776, Captain George Baker,

0:01:45 > 0:01:47an American mariner and whaler,

0:01:47 > 0:01:50made the long and difficult journey from South America across a

0:01:50 > 0:01:56raging Atlantic Ocean to bring five live electric eels to London.

0:01:56 > 0:01:59These are two of his actual eels.

0:02:00 > 0:02:02Captain Baker and his five electric eels,

0:02:02 > 0:02:04or gymnotas as they were known,

0:02:04 > 0:02:08set up shop in the Haymarket and offered two shillings

0:02:08 > 0:02:12and sixpence for a shock, or five shillings for a spark.

0:02:14 > 0:02:17Baker's eels had come all the way from the lower

0:02:17 > 0:02:20reaches of the Amazon and Orinoco rivers,

0:02:20 > 0:02:23where he had heard tales from the locals about

0:02:23 > 0:02:25their astonishing powers.

0:02:25 > 0:02:29They called these fish "trembladores".

0:02:29 > 0:02:33Humboldt, the famous naturalist and explorer, had described how he

0:02:33 > 0:02:37had witnessed horses being killed by the repeated shocks from these fish.

0:02:39 > 0:02:41And he himself accidentally stepped on one

0:02:41 > 0:02:43and vividly described the effect.

0:02:44 > 0:02:48"With each stroke, you feel an internal vibration that lasts

0:02:48 > 0:02:52"two or three seconds, followed by a painful numbness.

0:02:52 > 0:02:56"All day I felt strong pain in my knees and in all my joints."

0:02:59 > 0:03:03I encountered this remarkable fish in its natural environment

0:03:03 > 0:03:07when I filmed at the same rivers that Humboldt explored.

0:03:07 > 0:03:09There was talk of me swimming with the eel,

0:03:09 > 0:03:13but thankfully we had some technical difficulties with the diving

0:03:13 > 0:03:15equipment that I was supposed to wear,

0:03:15 > 0:03:19and so I stayed safely in a canoe and was able to demonstrate

0:03:19 > 0:03:23another subtler, but equally remarkable, side to this fish.

0:03:25 > 0:03:30The eels were constantly producing electric discharges.

0:03:30 > 0:03:34Somehow they were generating a small, nonstop flowing current.

0:03:34 > 0:03:36ELECTRIC DRONE

0:03:36 > 0:03:39They were also able to sense electricity and were

0:03:39 > 0:03:44attracted to electrical pulses emitted from my underwater detector,

0:03:44 > 0:03:49suggesting that electricity plays a key role in their lives.

0:03:50 > 0:03:52But at the time of their discovery,

0:03:52 > 0:03:56no-one knew the full functions of their extraordinary abilities.

0:03:58 > 0:04:02We now know that the shock was caused by electricity,

0:04:02 > 0:04:07and I can demonstrate it by touching the animal with an electrode.

0:04:07 > 0:04:09Watch.

0:04:09 > 0:04:11There. You see?

0:04:11 > 0:04:14The scope and the lights are flashing up and down.

0:04:14 > 0:04:16Extraordinary.

0:04:16 > 0:04:20But this is only a small indication of the real power of this fish.

0:04:20 > 0:04:21If I were to try and pick it up,

0:04:21 > 0:04:25I could get a jolt of an astonishing 600 volts,

0:04:25 > 0:04:27which is quite enough to kill me.

0:04:35 > 0:04:39This 1960s educational film illustrated the shock,

0:04:39 > 0:04:42even though the equipment used prevented

0:04:42 > 0:04:45the volunteers from getting its full power.

0:04:45 > 0:04:48They were to join hands and then connected to a live eel.

0:04:50 > 0:04:53WOMAN SCREAMS

0:04:54 > 0:04:58Firm believers in electric eels. Thank you very much.

0:04:59 > 0:05:02You can imagine how startling Baker's electric eels

0:05:02 > 0:05:04were 200 years ago.

0:05:07 > 0:05:08In the 18th century,

0:05:08 > 0:05:11electricity was becoming one of the most fashionable areas

0:05:11 > 0:05:16of scientific investigation, but it was still very poorly understood.

0:05:16 > 0:05:19Very few advances had been made since its discovery 150 years

0:05:19 > 0:05:23earlier by Elizabeth I's personal physician, William Gilbert.

0:05:23 > 0:05:28Gilbert repeated a trick that had been known about since Greek times.

0:05:28 > 0:05:32Rubbing a piece of amber with cat fur, that allowed the amber

0:05:32 > 0:05:36to attract a small object like a feather. Let's give it a try.

0:05:36 > 0:05:37Here is a bit of amber.

0:05:41 > 0:05:42There.

0:05:42 > 0:05:45It had always been assumed that this amber effect was caused

0:05:45 > 0:05:49by magnetism but Gilbert showed that it was something different.

0:05:49 > 0:05:53He named this new force after the Greek word for amber,

0:05:53 > 0:05:58electron, and so electricity was born.

0:05:59 > 0:06:04Londoners of the time developed a fascination for this magical force.

0:06:04 > 0:06:09Showmen staged bizarre spectacles to demonstrate its properties.

0:06:09 > 0:06:13In one, a young boy attached to a friction generator

0:06:13 > 0:06:15attracted small pieces of paper to his hands.

0:06:15 > 0:06:20In another, a gentleman kissed a lady and was repulsed

0:06:20 > 0:06:23by the charge carried through her whalebone corset.

0:06:24 > 0:06:27No-one knew what to do with electricity

0:06:27 > 0:06:31but a better understanding of its nature was slowly emerging.

0:06:32 > 0:06:34More and more ingenious ways were developed

0:06:34 > 0:06:38to create what we now call static electricity.

0:06:38 > 0:06:42And soon it became something more than just a quirk of rubbing amber,

0:06:42 > 0:06:44it became visible as a spark.

0:06:49 > 0:06:52The ability to produce this characteristic blue spark

0:06:52 > 0:06:55along with its invigorating smell became the signature

0:06:55 > 0:06:59of this new force and it prompted scientists to make

0:06:59 > 0:07:02obvious comparisons with other natural phenomena.

0:07:02 > 0:07:04THUNDER RUMBLES

0:07:06 > 0:07:10In the American colonies, Benjamin Franklin bravely,

0:07:10 > 0:07:14or perhaps foolishly, flew kites into thunderstorms and proved that

0:07:14 > 0:07:18lightning and the electric spark were one and the same.

0:07:19 > 0:07:23But there's another common property of lightning and static electricity.

0:07:23 > 0:07:25That is the ability to shock.

0:07:25 > 0:07:29It wasn't long before a comparison was made between the shock from

0:07:29 > 0:07:33the early generators and the shock that could be delivered by a fish.

0:07:36 > 0:07:38The electric eel wasn't the only kind of fish

0:07:38 > 0:07:41known to give humans a powerful jolt.

0:07:41 > 0:07:45The ancient Egyptians knew that the electric catfish could also

0:07:45 > 0:07:49give shocks and they called it the "Thunderer of the Nile".

0:07:50 > 0:07:55And in the nearby Mediterranean lives the torpedo ray.

0:07:55 > 0:07:57Its muscle batteries make it so bulky

0:07:57 > 0:08:00it can't undulate its body like other rays

0:08:00 > 0:08:04but has to propel itself by waving its tail.

0:08:04 > 0:08:06Like the electric eel,

0:08:06 > 0:08:10it uses its discharge to stun the other fish on which it preys.

0:08:12 > 0:08:16Sadly, the pressure of celebrity and having to produce shocks

0:08:16 > 0:08:20and sparks to order exhausted Baker's long-suffering eels

0:08:20 > 0:08:22and they didn't last the winter.

0:08:22 > 0:08:27But two were preserved and expertly dissected by John Hunter,

0:08:27 > 0:08:30a very distinguished Scottish surgeon of the time

0:08:30 > 0:08:34and he found a great number of striped muscular layers

0:08:34 > 0:08:37that proved to be where the electricity was generated.

0:08:37 > 0:08:41They are now referred to as Hunter's organs.

0:08:42 > 0:08:46He found these muscles along the tail and sides of the eels

0:08:46 > 0:08:48arranged in stacks.

0:08:50 > 0:08:53One scientist called Galvani believed that animals

0:08:53 > 0:08:58had their own natural electricity even without these electric organs

0:08:58 > 0:09:03and he tried to prove this by connecting wires to frogs' legs

0:09:03 > 0:09:05and making them twitch.

0:09:05 > 0:09:09He called this phenomenon animal electricity.

0:09:10 > 0:09:14But another scientist called Volta had other ideas.

0:09:14 > 0:09:18He proved that the frog was merely a conductor for electricity

0:09:18 > 0:09:20with a simple experiment.

0:09:21 > 0:09:26Volta replaced Galvani's frog with discs of cloth

0:09:26 > 0:09:28soaked in saltwater or acid

0:09:28 > 0:09:31and sandwiched them between two different metals.

0:09:31 > 0:09:34I can do the same thing with filter paper,

0:09:34 > 0:09:39copper two-pence pieces and these simple galvanised zinc washers.

0:09:39 > 0:09:40Watch.

0:09:42 > 0:09:44Tuppenny piece.

0:09:45 > 0:09:46Filter.

0:09:46 > 0:09:48And washer.

0:09:52 > 0:09:54There, nearly 0.6 of a volt.

0:09:55 > 0:09:59But the amount of electricity generated was tiny.

0:09:59 > 0:10:03Certainly not enough to make the sparks seen from eels.

0:10:03 > 0:10:06Unlike Galvani, Volta saw no distinction

0:10:06 > 0:10:10between animal electricity and his new electricity from metals

0:10:10 > 0:10:15so he now looked at animals to see how he might amplify his new device.

0:10:18 > 0:10:21Was it significant that the muscles

0:10:21 > 0:10:25producing the electric power in the eels were arranged in stacks?

0:10:27 > 0:10:32Volta decided to add more stacks to his electric pile.

0:10:32 > 0:10:35We call this way of connecting electric cells together

0:10:35 > 0:10:39"in series", and we now know that it increases the voltage.

0:10:39 > 0:10:42But Volta was about to find this out for the first time.

0:10:42 > 0:10:45He piled up his tiny cells like the bands of muscle

0:10:45 > 0:10:46in an electric fish.

0:10:46 > 0:10:49Here I've got ten pairs.

0:10:49 > 0:10:50And just watch.

0:10:53 > 0:10:54Nearly six volts.

0:10:54 > 0:10:56Wonderful.

0:10:56 > 0:11:01Volta could now produce heat, shocks and even sparks

0:11:01 > 0:11:05from electricity in a continuous never-ending stream.

0:11:06 > 0:11:12He had made the first battery, partly inspired by the electric eel.

0:11:12 > 0:11:16The pieces of the puzzle had come together and the eel's example

0:11:16 > 0:11:19had helped to advance our understanding of electricity.

0:11:20 > 0:11:24Eels, in fact, contain natural batteries -

0:11:24 > 0:11:26stacks of special muscles.

0:11:27 > 0:11:30It's amazing to think when electricity is so much

0:11:30 > 0:11:34a part of our lives today that before Volta

0:11:34 > 0:11:37the only source of electricity was lightning,

0:11:37 > 0:11:39a few static generators

0:11:39 > 0:11:43and fish like this incredible electric eel.

0:11:47 > 0:11:51Understanding how electric eels managed to find their way around

0:11:51 > 0:11:56revealed a hitherto unknown animal sense.

0:11:56 > 0:12:00But it's not just animals that have surprised us.

0:12:00 > 0:12:03We're now discovering that plants too

0:12:03 > 0:12:07have intriguing abilities that are still mysterious.

0:12:10 > 0:12:14We think of plants as passive, still and silent,

0:12:14 > 0:12:17but they may have more in common with animals than you might think.

0:12:22 > 0:12:26New research suggests that they have surprising abilities.

0:12:26 > 0:12:29It depends on how you look at them.

0:12:32 > 0:12:35I first started seeing plants in a different light

0:12:35 > 0:12:38when making a series called The Private Life of Plants.

0:12:40 > 0:12:44We used time-lapse photography to reveal the way they move.

0:12:45 > 0:12:49The bramble spreads aggressively - seemingly unstoppable.

0:12:49 > 0:12:53Other plants pulse to the rhythms of day and night,

0:12:53 > 0:12:56and flower buds explode like fireworks.

0:12:59 > 0:13:03So, with speeded-up film, we've been able to translate

0:13:03 > 0:13:05their time into ours

0:13:05 > 0:13:08and to realise that they're constantly on the move.

0:13:15 > 0:13:19200 years ago, one plant that moved very quickly indeed

0:13:19 > 0:13:24attracted the attention of a great scientific mind.

0:13:24 > 0:13:26It appeared to behave like an animal

0:13:26 > 0:13:30and could move fast enough to catch its own food.

0:13:30 > 0:13:35Charles Darwin was fascinated by the Venus flytrap.

0:13:35 > 0:13:38He called it one of the most wonderful plants in the world.

0:13:38 > 0:13:42He recognised that it could move in a very different way

0:13:42 > 0:13:45to that of plant growth.

0:13:45 > 0:13:48This movement was not only fast but also repeatable.

0:13:48 > 0:13:50Darwin experimented and found that the traps

0:13:50 > 0:13:52are not triggered by raindrops

0:13:52 > 0:13:56but only by a very particular stimulation of the leaf hairs,

0:13:56 > 0:13:59such as an insect might make.

0:13:59 > 0:14:04But what intrigued him most was the speed of the reaction.

0:14:04 > 0:14:07He sent one of these flytraps to a friend, Dr Burdon-Sanderson,

0:14:07 > 0:14:11who was performing ground-breaking work on muscles and electricity.

0:14:11 > 0:14:15His tests confirmed that the tiny electrical discharge

0:14:15 > 0:14:20caused by an animal muscle cell contracting was almost identical

0:14:20 > 0:14:23to those signals obtained by attaching electrodes to the flytrap

0:14:23 > 0:14:26when it was shutting.

0:14:26 > 0:14:28Although plants have no muscles,

0:14:28 > 0:14:33electrical stimulation enables them to move in a similar way to animals.

0:14:35 > 0:14:39Electrical signals cause cells to change the pressure of sap

0:14:39 > 0:14:42in their leaves, so creating movement.

0:14:43 > 0:14:46As a result, some plants, like animals,

0:14:46 > 0:14:48can actively catch their prey.

0:14:51 > 0:14:56Recently it's been discovered that other plants use electricity too

0:14:56 > 0:14:59but for a very different purpose.

0:15:00 > 0:15:05Plants are rooted to the ground and have a small negative charge.

0:15:05 > 0:15:09The higher up the plant you go, the greater the electric charge.

0:15:09 > 0:15:12This creates an electric field around the flower.

0:15:12 > 0:15:17We can't see it but these electrodes are picking up the energy

0:15:17 > 0:15:22of this tiny field and converting it into the sound that we can hear.

0:15:22 > 0:15:26Bees, on the other hand, have a positive charge.

0:15:26 > 0:15:28Friction whilst flying causes them

0:15:28 > 0:15:32to lose electrons, leaving them electrically charged.

0:15:32 > 0:15:36As a bee approaches a flower, the charge fields around the flower

0:15:36 > 0:15:39and the bee interact, and the sound changes...

0:15:39 > 0:15:42FALTERING ELECTRONIC BUZZ ..there.

0:15:42 > 0:15:44And when it lands, the positive

0:15:44 > 0:15:48and negative fields immediately cancel each other out.

0:15:48 > 0:15:51As this happens, there are two very surprising consequences.

0:15:51 > 0:15:56Firstly, the plant's negatively charged pollen actually

0:15:56 > 0:16:00jumps across onto the positively charged bee.

0:16:00 > 0:16:04Secondly, the plant has a changed electrical field

0:16:04 > 0:16:08and when another bee comes along, it detects this altered

0:16:08 > 0:16:11electrical signature and avoids the flower.

0:16:11 > 0:16:15The plant is, in effect, telling the bee that it has no nectar

0:16:15 > 0:16:17and to come back later.

0:16:18 > 0:16:22When the flower has refilled its stores of nectar, it creates

0:16:22 > 0:16:27a new electric charge which attracts another passing bee.

0:16:27 > 0:16:32This simple on/off signal benefits both the bee and the flower,

0:16:32 > 0:16:35but it does have its limitations.

0:16:36 > 0:16:38The electrical field is tiny,

0:16:38 > 0:16:41so insects can only detect it at close quarters.

0:16:42 > 0:16:46But flowers can also draw attention to themselves over much

0:16:46 > 0:16:51greater distances and they do this by floating messages in the air.

0:16:53 > 0:16:56The perfume of a flower is not just a pleasant smell,

0:16:56 > 0:17:01it's also the primary way in which plants communicate with insects.

0:17:01 > 0:17:05A rose can contain over 400 chemical compounds and a bee

0:17:05 > 0:17:10can recognise a particular combination from over a mile away.

0:17:10 > 0:17:13The very latest research has discovered

0:17:13 > 0:17:17that 90% of the chemicals made by plants, are also

0:17:17 > 0:17:20produced by insects and that is no coincidence.

0:17:23 > 0:17:29Most flowers produce scent to persuade insects to visit them,

0:17:29 > 0:17:33but others use it in a more sophisticated way...

0:17:33 > 0:17:35for protection.

0:17:35 > 0:17:39Cabbages communicate with each other using smell.

0:17:41 > 0:17:44When the leaves of one plant are being attacked by caterpillars,

0:17:44 > 0:17:48it releases a scent which warns its neighbours.

0:17:48 > 0:17:52They then produce chemicals in their leaves that caterpillars

0:17:52 > 0:17:54don't like and so they avoid being eaten.

0:17:56 > 0:18:00And scent also serves to call in the cavalry.

0:18:00 > 0:18:04Leaves that are under attack give off a chemical alarm signal that

0:18:04 > 0:18:09attracts wasps which obligingly pick off the caterpillar attackers.

0:18:13 > 0:18:17So, vegetables, fruits, leaves and flowers are constantly

0:18:17 > 0:18:23communicating with each other using touch, vision and smell.

0:18:23 > 0:18:29They seem to exploit all the senses, apart, that is, from hearing.

0:18:29 > 0:18:33But there are old stories that one particular plant is able to

0:18:33 > 0:18:37produce a very strange sound.

0:18:37 > 0:18:41Hundreds of years ago, a plant with a root that was thought to

0:18:41 > 0:18:46resemble a human body was said to emit a sound that could kill.

0:18:46 > 0:18:48The root was known to have strong anaesthetic

0:18:48 > 0:18:52and hallucinogenic properties. And in the first century AD,

0:18:52 > 0:18:57it was called a mandragora or mandrake as it's now known.

0:18:57 > 0:19:01It was associated with magic and the supernatural

0:19:01 > 0:19:05and was thought to derive power from a demon that emitted a dreadful

0:19:05 > 0:19:09and fatal shriek if the plant was uprooted.

0:19:09 > 0:19:12Fortunately, there were creative ways of avoiding

0:19:12 > 0:19:14death from the killer sound.

0:19:14 > 0:19:17One account advised plugging one's ears

0:19:17 > 0:19:21and then tying a starving dog to the mandrake plant.

0:19:21 > 0:19:26And then, as the dog lunged for food, the plant would be uprooted.

0:19:26 > 0:19:30The dog would tragically die from the mandrake's shriek

0:19:30 > 0:19:32but the man would survive.

0:19:34 > 0:19:38This particular story may have arisen because drinks made with

0:19:38 > 0:19:41the mandrake root can produce hallucinations.

0:19:45 > 0:19:49But we're just beginning to realise that the sensory abilities

0:19:49 > 0:19:53of a root could be as sophisticated as the rest of the plant.

0:19:58 > 0:20:02Latest research suggests that roots are communicating underground.

0:20:05 > 0:20:09And we now have the technology to eavesdrop on the roots' world.

0:20:12 > 0:20:17Believe it or not, the roots of these corn seedlings can make

0:20:17 > 0:20:19and sense sound.

0:20:19 > 0:20:24The noise is very quiet but we can hear it with this equipment,

0:20:24 > 0:20:29if I place a corn seedling in front of a laser beam Like this.

0:20:33 > 0:20:37Now the sound vibration can be detected

0:20:37 > 0:20:40and we can hear it through a speaker...

0:20:40 > 0:20:42CRACKLING

0:20:42 > 0:20:43..there.

0:20:43 > 0:20:48That strange crackling is the sound of corn roots growing.

0:20:48 > 0:20:51It can be seen as pulses on the screen.

0:20:51 > 0:20:54It's been shown, too, that the corn roots respond to the sound

0:20:54 > 0:20:57when it's played back to them.

0:20:57 > 0:21:00Time-lapse footage shot over just a few hours clearly shows

0:21:00 > 0:21:04the roots growing towards the tiny speakers that emit the sound.

0:21:05 > 0:21:07There is much speculation

0:21:07 > 0:21:10about the purpose of this curious phenomenon.

0:21:10 > 0:21:14Perhaps it helps roots avoid growing into hard objects or being too

0:21:14 > 0:21:17close to competing plants.

0:21:17 > 0:21:20It could act like simple echolocation,

0:21:20 > 0:21:24we just don't know, but it's the first clear evidence that

0:21:24 > 0:21:27plants have a rudimentary form of hearing

0:21:27 > 0:21:31and might even be communicating underground using sound.

0:21:31 > 0:21:35Sensitive equipment is creating a new window into the plant world

0:21:35 > 0:21:38and it seems that, like animals, they have a sophisticated

0:21:38 > 0:21:42sense of their environment and possess abilities that

0:21:42 > 0:21:47not so long ago, we would have thought of as supernatural.