David Attenborough's Natural Curiosities (2013) s01e01 Episode Script

DAVID ATTENBOROUGH: The natural world is full of extraordinarily shaped creatures, but how have the stretched bodies of some given them an edge? I have had the fortune to meet some of the planet's most enchanting creatures, but some stand out more than others, because of their intriguing biology.
Our knowledge of some of these creatures extends back centuries.
Others we have discovered more recently.
In this series, I share their stories and reveal why they are considered natural curiosities.
In this programme, I investigate two creatures that have taken the ordinary and made it extraordinary, the chameleon that has an extra-long tongue to catch prey and the giraffe with a neck so long it can reach the top of trees.
How and why have these animals stretched nature to the limit? The chameleon is a truly bizarre creature, both in its behaviour and its appearance unlike anything else on earth.
So, not surprisingly, it's given rise to all kinds of legends and myths.
This is The History Of The Four-Footed Beasts by Edward Topsell, written in the 17th century, and he calls the chameleon "a fraudulent, ravening and gluttonous beast, "impure and unclean by the law of God.
" Some believed it was constructed by the devil from parts of other animals, the tail of a monkey, the skin of a crocodile, the tongue of a toad, the horns of a rhinoceros, and the eyes of who knows what.
It was a creature sent to the world to spy for a demon master.
When I first came face to face with a chameleon, more than 50 years ago, I was struck not only by its beauty but intrigued by its strange body, particularly by its tongue.
The outlandish appearance of the chameleon made it much sought after by curiosity hunters.
But scientists and naturalists, too, were greatly puzzled by its extraordinary behaviour and anatomy.
It looked and behaved like no other reptile.
Even today, we are still discovering new things about its unique eyes, its astonishing tongue and its ability to change its appearance.
Chameleons are notoriously hard to find, partly because they move so slowly, but also because they match their surroundings in terms of colour so very well.
This one in front of me is a dwarf chameleon from Natal in South Africa.
If that's threatened by a snake, it doesn't bother to change its colour very much, because a snake's colour vision is not very good, but if it's threatened by a bird, it does camouflage itself very well indeed.
Some species of chameleon, and there are 85 different species in the family, can even fine-tune their camouflage.
If they detect a snake approaching from below, they become lighter in colour and so less noticeable against the sky.
On the other hand, if the threat comes from a bird, they become darker to match the background beneath them.
A chameleon's colour is affected not only by its surroundings, but by the temperature and the light and its emotional state.
Behind this screen, there's a rival male.
Let's see what happens if I remove the screen and let them see one another.
This highly coloured male is dominant, and he immediately adds bright, aggressive colours to his display.
The other male remains dark and too frightened to change colour and fight back.
It's clear who is the boss.
Chameleons are emotional creatures.
Darker colouration signals anger.
This female, on the right, is not in the mood to accept the approaches of this brightly coloured and hopeful male.
Exactly how chameleons achieved such dramatic colour changes greatly puzzled early naturalists.
An Englishman named Barrow, who travelled in Africa in the 19th century, thought the change in colour was caused by something to do with air.
He wrote, "Previous to the chameleon assuming a change in colour, "it makes a long inspiration, "the body swelling out to twice its usual size, "and as this inflation subsides, the change of colour gradually takes place.
" Well, that's an accurate observation of what happens when a chameleon gets angry, and then its anger subsides, but actually the change of colour has nothing to do with air.
A French biologist, Milne-Edwards, soon after that got it about right.
He wrote, "There exist two layers of membranous pigment "placed one above the other "but disposed in such a way to appear simultaneously under the cuticle "and sometimes in such a manner that one may hide the other," which is indeed so.
Today we know that the chameleon's skin has three layers of expandable pigmented cells called chromatophores.
They contain red, yellow, blue and white pigments with a deeper layer of darker melanin which controls the reflection of light.
The chameleons use colour change not only to camouflage themselves, but also to communicate with one another.
Anyone who looks closely at a chameleon is bound to be fascinated by its eyes.
They protrude on either side of its head as though they were mounted on turrets, and, in fact, their eyelids are fused together, except for one tiny spot right in the middle.
But the most extraordinary thing about them is that they move independently.
So, that means the chameleon, at one and the same time, can be viewing above it and below it.
So, any insect that lands nearby is going to be spotted almost immediately.
It seems that its brain receives separate messages from each eye and views them and receives them, alternately, very fast, but independent to one another.
They are not integrated.
But the advantage of that is that it does give this all-round, three-dimensional view, which is unrivalled.
This extraordinary vision is an essential element in the way that the chameleon uses its most astonishing feature, its hugely elongated tongue.
How this tongue worked, and its construction, greatly intrigued early naturalists, and understandably.
This remarkable preserved specimen shows us in detail the impressive elongated tongue of a chameleon.
The physical structure of the chameleon's tongue was easy enough to explain, although it proved to be a somewhat complicated organ, a hollow tube with a tapered, cartilaginous rod at its base.
The pad at the end was thought to be rough and sticky, so that it could snag its prey.
But the mystery of how a contraption like this could be lengthened and projected out of the mouth took a little longer to fully explain.
Perhaps the way a frigate bird inflates the balloon under its beak, or how a calling frog blows up its throat sac could give clues.
Both do it with air.
Or maybe the tentacles that carry a snail's eyes.
It projects them by using its blood as a hydraulic fluid.
But none of them fitted the bill.
It's a much more complex process.
The tongue is a muscular tube that, when relaxed, sits on a rod of cartilage.
When the chameleon is ready to strike, muscles at the back of the tongue push it into launch position.
When the prey is lined up and the distance calculated, super-fast muscles contract and propel the tongue forward at lightning speed.
As the tongue shoots off the end of the cartilage, an extra wave of energy drives it forward to its target.
Then, like a stretched elastic band, its elasticity pulls it back into the chameleon's mouth.
Recently, high-speed images revealed a new detail.
The tip of the tongue, once thought to be sticky, is covered in microscopic protrusions that generate suction and secures its prey.
Chameleons really are the most extraordinary creatures and they hold surprises for us even today.
Only this year, a scientist working in Madagascar discovered a tiny little chameleon, only 29mm long.
It's the smallest known vertebrate in the world.
It's astounding to realise that all the organs of a vertebrate's body could be fitted into such a tiny little creature, including that extraordinary tongue.
Next is the story of another amazing elongated structure, not a tongue but a neck.
The giraffe is an animal that can't fail to impress.
Up to 6m, or 19 feet, in height, it's hugely imposing, intriguing in appearance and mysterious in its biology.
Our attraction to this unusual creature goes back centuries, and one feature, in particular, has piqued our curiosity, its elongated neck.
Such a structure seemed an impossibility of nature, but now we better understand the complex biology behind the giraffe's bizarre body.
Our growing knowledge of this creature can be traced back to three very special giraffes and the story of a royal fascination for the exotic.
In the 19th century, a giraffe named Zarafa, Arabic for "Charming One", made a big impact on Europe, socially and scientifically.
She was one of three captured in 1826 at the order of the Viceroy of Egypt, who wanted to use them as gifts to curry favour with France, Austria and England.
Zarafa, the strongest of the three, was given to the French, seen here in a painting by Jacques Raymond Brascassat.
She travelled from Egypt to Marseille by ship.
On reaching France, her keepers felt it was too risky to continue by boat so the decision was made to walk Zarafa from Marseille in the south all the way to Paris, an overland journey of more than 550 miles.
To some, this looked like a journey doomed to failure, but careful planning and the unique biology of the giraffe were in its favour.
Very wisely, a forward-thinking and eminent French scientist called Geoffroy Saint-Hilaire was put in charge of the giraffe.
But there was something very significant about Zarafa that would be key to the success of her long journey.
It was her age.
She was a youngster, just eight months old.
Baby giraffes are very robust and can stand up and run within an hour of being born.
They have particularly long legs in relation to their bodies, only half a metre shorter than those of an adult.
Such long legs help them keep up with their mothers, so young Zarafa was well equipped for walking.
Crucial, too, was the fuel for Zarafa's journey.
Young giraffe suckle for up to a year, and Zarafa was bottle-fed.
Throughout the journey she drank up to 25 litres of milk a day, supplied by three milking cows.
She marched on at a steady pace with her trusty entourage.
After nearly 200 miles, Zarafa reached Lyon and Saint-Hilaire broke the walk.
He hoped to put Zarafa onto a boat to go downriver for the rest of the journey.
As they waited, 30,000 people flocked to see Zarafa.
To the public, she was a strange and exotic creature, and they were intrigued why such a long neck should exist and curious about how an animal could support its weight.
In those early days, giraffe were seen as freaks, strange, horned camels, whose humps had been flattened by the stretching of their necks.
But this was exactly what attracted Saint-Hilaire to Zarafa.
He was fascinated by genetic exaggerations and how they came to be.
Clearly, the giraffe's long neck enables them to feed on leaves beyond the reach of other browsers.
But how could they physically hold up such a long neck, vertically? Ha-ha! Studies of giraffe anatomy have revealed just how the neck is supported.
A long, thick ligament, like a cable, runs the whole length of the neck.
This counterbalances the weight of the head and the neck, and in its relaxed position it's tight.
So, keeping the neck straight and the head up involves very little muscular effort.
Bending the neck to reach down is more difficult, because the tough ligament has to be stretched.
But was the ability to feed from tall trees the only reason for having a long neck? As the habits of the giraffe in the wild became better known, people discovered that rival males fought one another by jousting with their necks.
Was that the reason that they had developed long necks? But then someone pointed out that the females had long necks too, so that suggestion was discarded.
In truth, there isn't a neat single answer, but access to high food, better vigilance and temperature regulation may all have shaped the giraffe's long neck.
As she walked on, Zarafa continued to attract inquisitive onlookers.
Few had set eyes on such a creature.
She appeared a natural impossibility.
How could a giraffe pump the blood up such a long neck to its brain? And why didn't the blood rush back down into its feet? The giraffe's neck may be very tall, but, in fact, it contains exactly the same number of bones as our own, that is to say, seven, but its blood pressure is twice as high as ours.
In fact, it's higher than any other known animal.
The pump that produces this pressure, the heart, surprisingly, is not particularly big, but it is hugely powerful.
This is the left ventricle that has been cut through and you can see how thick the muscle is, getting on for about 8cm.
This great pump produces blood, squirts it up the artery to the head, and then, when it comes down through the jugular vein, there are pocket-shaped valves which prevent the blood from flowing backwards into the head if the animal lowers its head in order to have a drink.
Giraffes find it very awkward to drink from the ground and, in fact, they rarely do so.
They get most of their water from leaves and shoots.
The only way to get their mouths down to the water is to splay their forelegs, or bend them at the wrist joint.
The giraffe, in fact, has a relatively short neck, compared to its legs.
Antelope and zebra can reach down to the ground without bending their legs.
Only the giraffe and its rain forest relative, the okapi, have necks that are so short, relative to their legs, that they must splay or bend them.
So, perhaps the most remarkable feature of the giraffe is the length of its legs.
They certainly were key to Zarafa's success.
At Lyon, there was a plan to rest her legs from walking and to finish the journey to Paris by boat.
But all didn't go according to plan.
The boat didn't appear in Lyon so she walked on and finally got to Paris.
It took her a total of 41 days to complete the journey of 550 miles to Paris.
Saint-Hilaire, her trusty companion, was exhausted, but the giraffe was very fit.
He wrote, "She gained weight and much more strength from the exercise.
"Her muscles were more defined, "her coat smoother and glossier upon her arrival than they were in Marseille.
" Zarafa was presented to King Charles X and temporarily installed in a greenhouse in the grounds of the Jardin des Plantes.
She was a true animal ambassador and 60,000 people saw her in the first three weeks in Paris.
In the early 19th century, giraffes were a novelty and their biology and lives in the wild were still a mystery.
Zarafa's success was due to a unique interplay of the giraffe's unusual characteristics and good timing.
Her youth, long legs and a diet with milk powered her journey right across France.
A body that was first considered bizarre was revealed to be perfectly evolved.
Our story began with three giraffe that were given to Europe.
Zarafa was the most robust of them and she lived a further 18 years.
The Austrian one lasted just a year, and the one sent to King George IV of England died after two.
Saint-Hilaire learnt much from Zarafa and he became a key figure in the blossoming zoological research in France.
The giraffe brought to England triggered a surge of interest in animal research that shifted the centre of zoological gravity from France to England.
So, we can thank Zarafa for her early role in unravelling the biological mysteries of the giraffe's extraordinary body and stretched neck.
Creatures like the outlandish giraffe and chameleon continue to reveal their biological secrets.
They really are true natural curiosities.