David Attenborough's Natural Curiosities (2013) s02e06 Episode Script

ATTENBOROUGH: The natural world is full of extraordinary animals with amazing life histories.
Yet certain stories are more intriguing than most.
The mysteries of a butterfly's life cycle or the strange biology of the emperor penguin.
some of these creatures were surrounded by myths and misunderstandings for a very long time.
And some have only recently revealed their secrets.
These are the animals that stand out from the crowd.
The curiosities 1 find most fascinating of all.
ATTENBOROUGH: The abilities of some plants and animals are so remarkable that they seem to be almost supernatural.
1n this programme, 1 investigate the shocking power of a fish that advanced our understanding of electricity.
And plants with senses that are surprising modern science.
But how did these extraordinary powers help the organisms that produce them? The freshwater eel is surrounded by legends.
The first Europeans to explore the New World heard amazing stories about it.
And when, in the 1 8th century, specimens of this strange fish reached Europe, they created a sensation.
In 1 776, Captain George Baker, an American mariner and whaler, made the long and difficult journey from South America, across a raging Atlantic Ocean, to bring five, live electric eels to London.
These are two of his actual eels.
Captain Baker and his five electric eels, or Gymnotus, as they were known, set up shop in the Haymarket and offered two shillings and sixpence for a shock or five shillings for a spark.
Baker's eels had come all the way from the lower reaches of the Amazon and Orinoco rivers where he had heard tales from the locals about their astonishing powers.
They called these fish ''trembladores''.
Humboldt, the famous naturalist and explorer, had described how he had witnessed horses being killed by the repeated shocks from these fish.
And he himself accidentally stepped on one and vividly described the effect.
''With each stroke you feel an internal vibration ''that lasts two or three seconds followed by a painful numbness.
''All day, 1 felt strong pain in my knees and in all my joints.
'' I encountered this remarkable fish in its natural environment where I filmed at the same rivers that Humboldt explored.
There was talk of me swimming with the eel, but, thankfully, we had some technical difficulties with the diving equipment that I was supposed to wear.
And so I stayed safely in the canoe and was able to demonstrate another subtler but equally remarkable side to this fish.
The eels were constantly producing electric discharges.
somehow, they were generating a small, nonstop flowing current.
(DEVICE BUZZING) They were also able to sense electricity and were attracted to electrical pulses emitted from my underwater detector, suggesting that electricity plays a key role in their lives.
But at the time of their discovery, no one knew the full functions of their extraordinary abilities.
We know now that the shock was caused by electricity.
And I can demonstrate it by touching the animal with an electrode.
Watch.
There, you see? The scope in the lights are flashing up and down.
Extraordinary.
But this is only a small indication of the real power of this fish.
If I were to try and pick it up, I could get a jolt of an astonishing 600 volts, which is quite enough to kill me.
This 1 960s educational film illustrated the shock even though the equipment used prevented the volunteers from getting its full power.
They were to join hands and then connected to a live eel.
(VOLUNTEERS EXCLAIM IN SURPRISE) Ah.
Firm believers in electric eels.
Thank you very much.
You can imagine how startling Baker's electric eels were 200 years ago.
In the 1 8th century, electricity was becoming one of the most fashionable areas of scientific investigation, but it was still very poorly understood.
Very few advances had been made since its discovery 1 50 years earlier by Elizabeth I's personal physician, William Gilbert.
Gilbert repeated a trick that had been known about since Greek times.
Rubbing a piece of amber with cat fur that allowed the amber to attract a small object, like a feather.
Let's give it a try.
Here's a bit of amber.
There.
It has always been assumed that this amber effect was caused by magnetism, but Gilbert showed that it was something different.
He named this new force after the Greek word for amber, electron, and so electricity was born.
Londoners of the time developed a fascination for this magical force.
showmen staged bizarre spectacles to demonstrate its properties.
1n one, a young boy attached to a friction generator attracted small pieces of paper to his hands.
1n another, a gentleman kissed a lady and was repulsed by the charge carried through her whalebone corset.
No one knew what to do with electricity, but a better understanding of its nature was slowly emerging.
More and more ingenious ways were developed to create what we now call ''static electricity''.
And soon, it became something more than just a quirk of rubbing amber, it became visible as a spark.
-(ZAPPING) -Ooh.
(CHUCKLES) The ability to produce this characteristic blue spark, along with its invigorating smell, became the signature of this new force.
And it prompted scientists to make obvious comparisons with other natural phenomena.
(THUNDER RUMBLING) 1n the American colonies, Benjamin Franklin bravely, or perhaps foolishly, flew kites into thunderstorms and proved that lightning and the electric spark were one and the same.
But there's another common property of lightning and static electricity, that is the ability to shock.
It wasn't long before a comparison was made between the shock from the early generators and the shock that could be delivered by a fish.
The electric eel wasn't the only kind of fish known to give humans a powerful jolt.
The ancient Egyptians knew that the electric catfish could also give shocks and they called it the ''Thunderer of the Nile''.
And in the nearby Mediterranean lives the torpedo ray.
1ts muscle batteries make it so bulky, it can't undulate its body like other rays, but has to propel itself by waving its tail.
Like the electric eel, it uses its discharge to stun the other fish on which it preys.
Sadly, the pressure of celebrity and having to produce shocks and sparks to order exhausted Baker's long-suffering eels and they didn't last the winter.
But two were preserved and expertly dissected by john Hunter, a very distinguished Scottish surgeon of the time.
And he found a great number of striped muscular layers that proved to be where the electricity was generated.
They're now referred to as ''Hunter's organs''.
He found these muscles along the tail and sides of the eels arranged in stacks.
One scientist called Galvani believed that animals had their own natural electricity even without these electric organs.
And he tried to prove this by connecting wires to frogs' legs and making them twitch.
He called this phenomenon ''animal electricity''.
But another scientist called Volta had other ideas.
He proved that the frog was merely a conductor for electricity with a simple experiment.
Volta replaced Galvani's frog with discs of cloth soaked in saltwater or acid and sandwiched them between two different metals.
I can do the same thing with filter paper, copper two pence pieces and these simple galvanised zinc washers.
Watch.
Tuppenny piece, filter, and washer.
There.
Nearly 0.
6 of a volt.
But the amount of electricity he generated was tiny, certainly not enough to make the spark seen from eels.
Unlike Galvani, Volta saw no distinction between animal electricity and his new electricity from metals.
So, he now looked to animals to see how he might amplify his new device.
Was it significant that the muscles producing the electric power in the eels were arranged in stacks? Volta decided to add more stacks to his electric pile.
We call this way of connecting electric cells together ''in series'' and we now know that it increases the voltage.
But Volta was about to find this out for the first time.
He piled up his tiny cells like the bands of muscle in an electric fish.
Here, I've got 1 0 pairs and just watch.
Nearly six volts.
Wonderful.
Volta could now produce heat, shocks, and even sparks from electricity in a continuous, never-ending stream.
He had made the first battery, partly inspired by the electric eel.
The pieces of the puzzle had come together and the eel's example had helped to advance our understanding of electricity.
Eels, in fact, contain natural batteries, stacks of special muscles.
It's amazing to think when electricity is so much a part of our lives today that, before Volta, the only source of electricity was lightning, a few static generators and fish like this incredible electric eel.
Understanding how electric eels manage to find their way around revealed a hitherto unknown animal sense.
But it's not just animals that have surprised us.
We're now discovering that plants, too, have intriguing abilities that are still mysterious.
We think of plants as passive, still, and silent, but they may have more in common with animals than you might think.
New research suggests that they have surprising abilities.
It depends on how you look at them.
1 first started seeing plants in a different light when making a series called The Private Life of Plants.
We used time-lapse photography to reveal the way they move.
The bramble spreads aggressively, seemingly unstoppable.
Other plants pulse to the rhythms of day and night and flower buds explode like fireworks.
so with speeded-up film, we've been able to translate their time into ours, and to realise that they're constantly on their move.
Two hundred years ago, one plant that moved very quickly indeed attracted the attention of a great scientific mind.
1t appeared to behave like an animal and could move fast enough to catch its own food.
Charles Darwin was fascinated by the Venus flytrap.
He called it ''one of the most wonderful plants in the world''.
He recognised that it could move in a very different way to that of plant growth.
This movement was not only fast but also repeatable.
Darwin experimented and found that the traps were not triggered by raindrops, but only by a very particular stimulation of the leaf hairs, such as an insect might make.
But what intrigued him most was the speed of the reaction.
He sent one of these flytraps to a friend, Dr Burdon-Sanderson, who was performing groundbreaking work on muscles and electricity.
His tests confirmed that the tiny, electrical discharge caused by an animal muscle cell contracting was almost identical to those signals obtained by attaching electrodes to the flytrap when it was shutting.
Although plants have no muscles, electrical stimulation enables them to move in a similar way to animals.
Electrical signals cause cells to change the pressure of sap in their leaves, so creating movement.
As a result, some plants, like animals, can actively catch their prey.
Recently, it's been discovered that other plants use electricity too, but for a very different purpose.
Plants are rooted to the ground and have a small, negative charge.
The higher up the plant you go, the greater the electric charge.
This creates an electric field around the flower.
We can't see it, but these electrodes are picking up -(DEVICE HUMMING) -The energy of this tiny field and converting it into the sound that we can hear.
Bees, on the other hand, have a positive charge.
Friction whilst flying causes them to lose electrons, leaving them electrically charged.
As a bee approaches a flower, the charge fields around the flower -and the bee interact -(WHINING CHANGES FREQUENCY) And the sound changes.
There.
And when it lands, the positive and negative fields immediately cancel each other out.
As this happens, there are two very surprising consequences.
Firstly, the plant's negatively-charged pollen actually jumps across onto the positively-charged bee.
Secondly, the plant has a changed electrical field.
And when another bee comes along, it detects this altered electrical signature and avoids the flower.
The plant is, in effect, telling the bee that it has no nectar and to come back later.
When the flower has refilled its stores of nectar, it creates a new electric charge which attracts another passing bee.
This simple on/off signal benefits both the bee and the flower, but it does have its limitations.
The electrical field is tiny so insects can only detect it at close quarters.
But flowers can also draw attention to themselves over much greater distances and they do this by floating messages in the air.
The perfume of a flower is not just a pleasant smell, it's also the primary way in which plants communicate with insects.
A rose can contain over 400 chemical compounds and the bee can recognise a particular combination from over a mile away.
Very latest research has discovered that 90% of the chemicals made by plants are also produced by insects.
And that is no coincidence.
Most flowers produce scent to persuade insects to visit them, but others use it in a more sophisticated way.
For protection.
Cabbages communicate with each other using smell.
When the leaves of one plant are being attacked by caterpillars, it releases a scent which warns its neighbours.
They then produce chemicals in their leaves that caterpillars don't like and so they avoid being eaten.
And scent also serves to call in the cavalry.
Leaves that are under attack give off a chemical alarm signal that attracts wasps, which obligingly pick off the caterpillar attackers.
so, vegetables, fruits, leaves and flowers are constantly communicating with each other using touch, vision and smell.
They seem to exploit all the senses apart, that is, from hearing.
But there are old stories that one particular plant is able to produce a very strange sound.
Hundreds of years ago, a plant with a root that was thought to resemble a human body was said to emit a sound that could kill.
The root was known to have strong anaesthetic and hallucinogenic properties and, in the 1 st century AD, it was called a ''mandroga'' or ''mandrake'' as it's now known.
It was associated with magic and the supernatural and was thought to derive power from a demon that emitted a dreadful and fatal shriek if the plant was uprooted.
Fortunately, there were creative ways of avoiding death from the killer sound.
One account advised plugging one's ears and then tying a starving dog to the mandrake plant.
And then, as the dog lunged for food, the plant would be uprooted.
The dog would tragically die from the mandrake's shriek, but the man would survive.
This particular story may have arisen because drinks made with the mandrake root can produce hallucinations.
But we're just beginning to realise that the sensory abilities of a root could be as sophisticated as the rest of the plant.
Latest research suggests that roots are communicating underground.
And we now have the technology to eavesdrop on the roots' world.
Believe it or not, the roots of these corn seedlings can make and sense sound.
The noise is very quiet, but we can hear it with this equipment.
If I place a corn seedling in front of a laser beam like this.
Now, the sound vibration can be detected and we can hear it through a speaker.
(CRACKLING) There.
That strange crackling is the sound of corn roots growing.
It can be seen as pulses on the screen.
It's been shown, too, that the corn roots respond to the sound when it's played back to them.
Time-lapse footage shot over just a few hours clearly shows the roots growing towards the tiny speakers that emit the sound.
There's much speculation about the purpose of this curious phenomenon.
Perhaps, it helps roots avoid growing into hard objects or being too close to competing plants.
It could act like simple echolocation.
We just don't know, but it's the first clear evidence that plants have a rudimentary form of hearing and might even be communicating underground using sound.
Sensitive equipment is creating a new window into the plant world and it seems that, like animals, they have a sophisticated sense of their environment and possessed abilities that not so long ago, we would have thought of as supernatural.