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'The natural world is full of extraordinary animals
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'with amazing life histories.
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'Yet certain stories are more intriguing than most.'
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The mysteries of a butterfly's life cycle,
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or the strange biology of the emperor penguin.
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Some of these creatures were surrounded by myth
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and misunderstandings for a very long time.
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And some have only recently revealed their secrets.
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These are the animals that stand out from the crowd -
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the curiosities I find most fascinating of all.
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'The elephant and the mole rat -'
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they're both extremely wrinkled,
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starting their young lives looking ancient,
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and remaining that way into old age.
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Yet they outlive most other animals their size.
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What are their secrets?
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Nature has twisted the task of the narwhal
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and the shells of snails and their relatives.
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But what is the purpose of the twist?
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'Spirals are common in the natural world.
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'We seldom pay attention to them.
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'But in fact, they have remarkable characteristics'
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which many animals exploit.
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And some creatures, having developed a spiral,
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have reworked it in many intriguing and beautiful ways.
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In this programme, I'll try to discover why the spiral
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is so important to two very different kinds of animals.
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Elephants are truly strange creatures,
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both in looks and behaviour.
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Aristotle described them as,
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"The beast that passeth all others in wit and mind."
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But the more we learn about its curious body and behaviour,
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the more remarkable it appears to be.
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The evolution of such a strange-looking creature is no accident.
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Its fascinating body is the key to allowing elephants
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to live a long life.
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For elephants, even young ones, it's an advantage to be wrinkly,
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and not at all a sign of old age.
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Elephants evolved from mammoths over 55 million years ago.
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Today, they're the heaviest land mammals alive,
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and one of the longest lived,
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with a life expectancy of about 70 years.
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Big creatures usually live a long time largely
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because they have slow metabolisms.
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However, elephants have particular characteristics
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that help them reach old age.
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One of the most important, a family structure
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in which the oldest matriarchs pass on vital experience.
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And their bodies have developed some special features
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to deal with the problems of being so big.
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Their trunk is one of them.
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This, surely,
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is the most extraordinary nose possessed by any living creature.
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It can be moved with ease and dexterity,
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to gently caress,
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tear down trees, suck up litres of water.
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The trunk is, in fact, a union between the nose
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and the upper lip, and it's highly sensitive,
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with over 100,000 muscle units in it.
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The end of the trunk can move rather like a hand.
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This mobile tip allows the elephant to feel and pick up
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delicate objects such as a single blade of grass.
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The stretched nose is a masterpiece of evolution,
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and key to how the elephant can survive
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with such a large and curious body.
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ELEPHANT SNORTS
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If they hadn't developed a trunk,
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elephants couldn't have become so big.
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It enables them, in spite of their huge, stocky body,
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to reach down to the ground to collect food and water.
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Fuelling a big body is a full-time job,
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and an elephant has to consume its own weight in food every 20 days.
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One might think this great weight would be a stress on joints
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and teeth, and wear elephants out before old age.
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'But not so.'
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Eating vegetation is of course very tough on the teeth,
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and there are some animals, that when their teeth are worn down,
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simply starve and die.
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But elephants can live to 70 years old,
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and the secret lies in their extraordinary molar teeth.
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They have two pairs - two at the top, two at the bottom -
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and here's one of them.
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This is the grinding surface,
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which is capable of shredding twigs and bark, and even wood,
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and of course, it wears.
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But as it wears down,
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so another tooth is developing within the jaw, which finally emerges
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and pushes this forward until it actually breaks off and is shed.
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Acquiring new teeth in that way
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enables elephants to remain well-fed and healthy into old age.
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In elephant society, the older females are invaluable,
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and pass on the wisdom they've gained during their long lives
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to younger members of the family.
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ELEPHANT GROWLS
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Mature females spend long periods of time
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listening out for vital sounds of danger and warn the group.
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Such sensitivity to sound was the subject
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of one of the very first animal behaviour experiments.
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Someone in France in the early 18th century noted
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that elephants in menageries appeared to react
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to faint, distant sounds outside their enclosures.
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So they tested two elephants - Hans and Parki -
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and engaged a palace orchestra to play love music to them.
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One elephant was very impressed by the French horn player.
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It was reported that, "The animal knelt down before him,
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"caressed him with his trunk and expressed to him in all sorts
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"of pretty ways the pleasure which it had felt in listening to him."
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We now know that the French horn can produce a low-frequency sound
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that's very like the rumble that elephants produce
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using a similar resonating chamber in their heads.
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LOW RUMBLING
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They can also hear very deep sounds beyond our own hearing.
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The oldest, experienced females are experts at interpreting them.
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Such frequencies create vibrations in the ground
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that travel a very long way,
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which the elephants can detect through their feet.
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Their feet, in fact, are not as solid as they might look,
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but have special internal cushioning
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to soften the impact of the animal's weighty footsteps.
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For such a large creature, that can be 40 times our weight,
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this foot seems unfeasibly small.
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Its surface area is little more than twice our own feet,
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but this foot has a surprising structure.
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The elephant walks on five toes,
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and the back part of its foot consists of a highly spongy heel.
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The raised heel can compress and expand to absorb shock,
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and shield the other heavy bones in the body from pressure.
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It's as if the elephant were wearing a high-heeled training shoe.
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When an elephant runs, it bounces on this spongy heel
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and its leg bones act like pogo sticks
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to push the animal upwards.
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This system protects the bones and inner tissues.
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And wild elephants rarely get arthritis.
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Despite their large size, they live active, physical lives
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without too much damage to their bodies.
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Males, as they mature, usually go off to live by themselves.
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But the females stay with the family group
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and play a very important part in guiding the younger ones.
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Young elephants tend to look old even at the start of their lives
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because of their wrinkly skin.
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But, for elephants, wrinkles are not signs of ageing.
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On the contrary, they're extremely important
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for an elephant's very survival.
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The elephant's thick, creased skin
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has been the subject of much debate over the years.
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And early anatomists had some novel ideas about it.
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Many believed that the elephant could actually move its skin
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to crush flies between the wrinkles.
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I may say, that was never witnessed in action.
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But the skin WAS thought to be enormously thick and insensitive.
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But in fact it varies across the elephant's body
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and can be as thick as two or three centimetres
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around the top of its trunk and along the back
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and as thin as paper around the eyes.
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Although the skin looks tough and wrinkly, it's remarkably sensitive.
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An elephant can feel small flies on its body,
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even if it can't crush them between its wrinkles.
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But these wrinkles really do have an important function.
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The patterned crevices hold water,
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which travels along them all over the body.
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Wrinkly skins can contain five to ten times more water than smooth ones.
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So moisture collected during the wallowing
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stops the skin from dehydrating and overheating
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for a long time afterwards.
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Significantly, African elephants, that lived in hotter, drier places,
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have more deeply wrinkled skins than Asian elephants.
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So, wrinkles for the elephant are ways of protecting the skin,
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not the unwanted consequence of old age.
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The elephant was once considered an oddity of nature.
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For centuries, we've been fascinated by their large ears,
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their extraordinary trunks,
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the stocky feet, the wrinkly skins.
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But over the years, we've come to understand their significance.
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The elephant's unique biology is key to its long-term survival
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and its ability to seemingly avoid the rigours of old age.
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Elephants, understandably, live a long time
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because of the slow metabolism of their huge bodies.
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But small, naked mole rats live much longer
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than any other mammal of a comparable size.
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Why?
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Could it be that the body of this bizarre little creature
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holds the secret of eternal youth?
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When a German naturalist, Wilhelm Ruppell,
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discovered a lone, hairless, wrinkled, naked mole rat
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in 1842 in Ethiopia,
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he was convinced that he had stumbled across
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a decrepit, old individual,
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and he gave it the name Heterocephalus glaber,
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which loosely translated means
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a smooth-skinned animal with an oddly shaped head.
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He noted that the form of the body, because of its hairlessness,
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gives an unpleasant impression.
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It does.
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For the next 40 years,
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these bizarre-looking creatures were largely ignored by scientists.
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Then, in 1885, a British zoologist in London's Natural History Museum,
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called Oldfield Thomas decided to examine in detail
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the museum specimens that had been sitting in store for decades.
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Here we can see some of his drawings.
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Thomas declared that the weird animal described by Ruppell
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was in fact normal.
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We now know that all mole rats look like this, whatever their age.
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However, what those early naturalists couldn't have known
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was that they had chanced upon a mammal
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that would fascinate and intrigue scientists for the next 150 years.
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A creature that might even shed light
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on the secrets of ageing and longevity.
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Its body hardly seemed to alter, no matter how long it lived.
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Old mole rats stayed physically young throughout their lives.
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And not only that, the strangest discovery of all
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was that they sometimes lived for almost 30 years.
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The lifespan of animals varies enormously.
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Amongst mammals, a tiny little shrew like this lives just two or so years.
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While a giant whale can reach the age of 100.
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Lifestyle is an important factor in defining lifespan.
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A shrew has a fast and furious life,
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producing many young of which few survive.
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Whales, on the other hand, breed slowly and don't have many predators.
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Generally, big animals live longer.
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So it's very odd indeed
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that mole rats live up to nine times longer
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than any other similar-sized rodent.
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Why?
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In the 1960s, more than 100 years after their discovery,
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scientists started keeping the animals in laboratories
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to try and answer that question.
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The results were confusing.
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The mole rats lived in colonies
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and only a few females ever reproduced.
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Around that time,
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an evolutionary biologist called Richard Alexander was studying
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the way colonial insects, such as termites, organised their colonies.
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They have a single breeding female
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who produces huge numbers of non-breeding workers.
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A system called eusociality.
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He speculated that if there were such things as a eusocial mammal,
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it too, like termites, would live underground in hard soil.
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He was right.
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The naked mole rat perfectly fits Alexander's description
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of what a eusocial animal should be like.
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There it is.
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It lives underground in large social groups
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and digs for tubers
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in exceptionally hard soil.
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Physically, it's evolved for a life below ground.
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It has a long, thin body with short legs that suit life in a tunnel.
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Its enlarged, strong teeth are used for digging,
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its skull is strong, the head quite large.
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Lips close behind its teeth to stop any soil going into its mouth.
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Also, it's almost entirely bald, except for a few sensory hairs.
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Could it be that these extraordinary characteristics
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have something to do with their ability
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to live very, very long lives?
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They are certainly key to the mole rat's unusual life underground.
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The queen is at the heart of the colony.
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She mates with just two or three males
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00:16:36,280 --> 00:16:39,080
and produces babies in huge litters,
258
00:16:39,080 --> 00:16:40,920
sometimes of more than 20.
259
00:16:42,640 --> 00:16:47,040
The workers feed the queen, care for the young and guard the tunnels.
260
00:16:47,040 --> 00:16:48,800
Their role is essential -
261
00:16:48,800 --> 00:16:53,560
the colony would not survive if all its members didn't work together.
262
00:16:57,320 --> 00:17:02,000
The tubers that they eat are hard to find on the dry African plains,
263
00:17:02,000 --> 00:17:05,920
and the workers have to dig miles of tunnels in their search for them.
264
00:17:05,920 --> 00:17:09,360
The fact that they don't breed might seem hard,
265
00:17:09,360 --> 00:17:11,800
but their mother, the queen, does.
266
00:17:11,800 --> 00:17:15,440
And her DNA is virtually identical to theirs.
267
00:17:15,440 --> 00:17:17,280
And by working together,
268
00:17:17,280 --> 00:17:21,840
the colony can live in places where an individual mole rat could not.
269
00:17:23,720 --> 00:17:27,680
But this still doesn't explain why these creatures live so long.
270
00:17:27,680 --> 00:17:32,240
More recently, another adaptation to life underground threw up a clue.
271
00:17:33,440 --> 00:17:37,160
Fossil records show that mole rats started living underground
272
00:17:37,160 --> 00:17:39,600
about 24 million years ago.
273
00:17:39,600 --> 00:17:42,640
Not surprisingly, they are now highly adapted
274
00:17:42,640 --> 00:17:44,920
to a life in dark and humid tunnels.
275
00:17:44,920 --> 00:17:48,640
Conditions in a sealed, two-metre-deep tunnel system
276
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don't fluctuate greatly. And maybe because of this,
277
00:17:51,720 --> 00:17:55,400
mole rats have lost the ability to regulate their own body temperature.
278
00:17:55,400 --> 00:17:58,240
So, to prevent getting chilled,
279
00:17:58,240 --> 00:18:01,080
they huddle together in groups.
280
00:18:01,080 --> 00:18:03,640
They also, like reptiles, absorb heat
281
00:18:03,640 --> 00:18:05,320
by basking in the warmer,
282
00:18:05,320 --> 00:18:07,120
shallow surface tunnels.
283
00:18:08,240 --> 00:18:10,320
Being hairless might be an advantage
284
00:18:10,320 --> 00:18:13,000
for an animal that's essentially cold-blooded
285
00:18:13,000 --> 00:18:15,600
and needs to get some of its heat from its surroundings,
286
00:18:15,600 --> 00:18:19,320
and that may explain why naked mole rats are virtually bald.
287
00:18:21,280 --> 00:18:26,480
But why are not other warm-blooded mammals that live underground also bald?
288
00:18:26,480 --> 00:18:29,600
Badgers, for example, have hairy coats.
289
00:18:32,960 --> 00:18:36,240
Well, badgers come above ground to feed
290
00:18:36,240 --> 00:18:39,680
and then they need their hairy coats to keep warm.
291
00:18:42,440 --> 00:18:46,040
Naked mole rats, on the other hand, never see the light of day.
292
00:18:46,040 --> 00:18:47,880
Nonetheless, one might think
293
00:18:47,880 --> 00:18:51,440
that being soft-skinned and bald is a huge disadvantage.
294
00:18:51,440 --> 00:18:54,920
For mole rats live in stuffy, insanitary conditions.
295
00:18:56,080 --> 00:18:59,600
Mole rat colonies can contain several hundred individuals,
296
00:18:59,600 --> 00:19:04,200
and conditions underground are dark and dank and often quite toxic.
297
00:19:04,200 --> 00:19:08,120
Oxygen levels can be very low and carbon dioxide high,
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00:19:08,120 --> 00:19:11,160
yet, mysteriously, mole rats show no discomfort
299
00:19:11,160 --> 00:19:13,120
and suffer very little from disease.
300
00:19:14,120 --> 00:19:17,840
This tolerance to such hostile conditions may also be related
301
00:19:17,840 --> 00:19:21,520
to their strange, wrinkled skin and the cells below it.
302
00:19:22,880 --> 00:19:28,760
Apparently they lack a key neurotransmitter called substance P,
303
00:19:28,760 --> 00:19:32,120
that is normally responsible for sending pain signals
304
00:19:32,120 --> 00:19:34,480
to the central nervous system.
305
00:19:34,480 --> 00:19:38,440
This may explain their ability to survive the toxic conditions
306
00:19:38,440 --> 00:19:42,720
underground without stress and damage to their bodies.
307
00:19:42,720 --> 00:19:46,440
It could also be one of the secrets of their youthful appearance,
308
00:19:46,440 --> 00:19:49,920
if you can call it that, and even their longevity.
309
00:19:54,640 --> 00:20:00,080
Most animals react strongly to pain, and this can damage their bodies.
310
00:20:04,280 --> 00:20:07,040
In mole rats, this effect is eliminated
311
00:20:07,040 --> 00:20:09,400
by cutting out the pain response.
312
00:20:11,560 --> 00:20:15,280
Incredibly, no mole rat has ever been found with cancer.
313
00:20:16,800 --> 00:20:21,680
But even if a normal animal survives disease, it still ages.
314
00:20:21,680 --> 00:20:25,160
This is largely due to other chemicals in the body
315
00:20:25,160 --> 00:20:27,120
called oxidising agents.
316
00:20:27,120 --> 00:20:31,040
They build up with time and break down the body tissues.
317
00:20:32,360 --> 00:20:35,880
This leads to the tell-tale signs of old age.
318
00:20:39,800 --> 00:20:44,280
Incredibly, mole rats appear to have no physical reaction
319
00:20:44,280 --> 00:20:46,840
to high levels of oxidising agents.
320
00:20:46,840 --> 00:20:51,000
They grow very old, yet they don't physically age.
321
00:20:52,440 --> 00:20:57,040
In wild mole rats, the queen is the most long-lived.
322
00:20:57,040 --> 00:20:59,400
And one of them, here,
323
00:20:59,400 --> 00:21:01,120
is 24 years old.
324
00:21:01,120 --> 00:21:04,400
Yet she still has the body of a two-year-old.
325
00:21:04,400 --> 00:21:08,400
No-one is sure how mole rats avoid the symptoms of old age,
326
00:21:08,400 --> 00:21:12,520
but a unique physiology, evolved in response to the underground life,
327
00:21:12,520 --> 00:21:15,800
has created an animal that is almost supernatural.
328
00:21:16,880 --> 00:21:20,160
Here's a creature that's seemingly impervious to pain
329
00:21:20,160 --> 00:21:22,720
and with an iron constitution.
330
00:21:22,720 --> 00:21:26,080
It's virtually cold-blooded, with a slow metabolism,
331
00:21:26,080 --> 00:21:28,920
and has evolved an unusual mix of strategies
332
00:21:28,920 --> 00:21:31,360
to deal with its challenging lifestyle.
333
00:21:31,360 --> 00:21:34,520
In the future, these remarkable animals may help us
334
00:21:34,520 --> 00:21:38,080
solve some of our own problems, such as pain control,
335
00:21:38,080 --> 00:21:40,120
degenerative disease
336
00:21:40,120 --> 00:21:43,560
and how we might avoid old age and wrinkly skins.
337
00:21:44,600 --> 00:21:46,560
Here is a natural curiosity
338
00:21:46,560 --> 00:21:49,200
that is well worth pursuing.
339
00:21:51,800 --> 00:21:56,480
Both elephants and mole rats remain much the same as they grow old.
340
00:21:56,480 --> 00:22:00,000
And surprisingly, the small naked mole rat lives,
341
00:22:00,000 --> 00:22:03,920
relatively speaking, even longer than the elephant.
342
00:22:06,640 --> 00:22:09,840
The narwhal lives in the cold waters of the Arctic sea.
343
00:22:09,840 --> 00:22:14,800
It's rarely seen and little is known about its life, even today.
344
00:22:14,800 --> 00:22:18,680
But 400 years ago, it was a source of myths and tall tales
345
00:22:18,680 --> 00:22:22,960
that fooled everyone, including the royal households of Europe.
346
00:22:24,520 --> 00:22:28,480
These tapestries, hanging in Stirling Castle, are modern,
347
00:22:28,480 --> 00:22:32,120
but they are accurate copies of medieval originals.
348
00:22:33,200 --> 00:22:37,840
And they show several images of that most wonderful creature -
349
00:22:37,840 --> 00:22:39,680
the unicorn.
350
00:22:39,680 --> 00:22:44,680
In the Middle Ages, the unicorn was thought to be a real animal.
351
00:22:44,680 --> 00:22:47,800
And what's more, one with magical powers.
352
00:22:47,800 --> 00:22:51,800
So, the King of Scotland incorporated one in his coat of arms,
353
00:22:51,800 --> 00:22:56,520
and that in due course was inherited by the British coat of arms
354
00:22:56,520 --> 00:23:00,080
and is shown sitting opposite the English lion.
355
00:23:02,640 --> 00:23:05,400
During the Middle Ages, it was believed
356
00:23:05,400 --> 00:23:09,080
that a unicorn horn could detect poison and neutralise it.
357
00:23:09,080 --> 00:23:12,440
So it's not surprising that most of the kings of Europe wanted
358
00:23:12,440 --> 00:23:15,440
one of these wonderful and powerful objects.
359
00:23:15,440 --> 00:23:18,600
Such treasures, however, weren't easy to come by.
360
00:23:19,840 --> 00:23:24,440
But in the 16th century, an English seaman accidentally discovered one.
361
00:23:24,440 --> 00:23:29,920
In 1576, Martin Frobisher sailed across the North Atlantic
362
00:23:29,920 --> 00:23:34,200
in search of a sea route to connect the Atlantic with the Pacific.
363
00:23:34,200 --> 00:23:37,040
And when he reached the chilly coast of northern Canada,
364
00:23:37,040 --> 00:23:41,720
he found, lying on the seashore, a unicorn's horn.
365
00:23:41,720 --> 00:23:45,200
He brought it back to Britain and soon found a buyer -
366
00:23:45,200 --> 00:23:47,040
Elizabeth I.
367
00:23:48,800 --> 00:23:50,800
This is very like the object
368
00:23:50,800 --> 00:23:54,000
that Sir Martin Frobisher presented to Queen Elizabeth.
369
00:23:54,000 --> 00:23:57,720
It's said that she paid �10,000 for it.
370
00:23:57,720 --> 00:24:01,480
In today's money, that's about half a million or more.
371
00:24:01,480 --> 00:24:07,480
Weight for weight, unicorn horn was worth more than gold.
372
00:24:07,480 --> 00:24:12,080
But the object was not what Queen Elizabeth supposed it to be.
373
00:24:12,080 --> 00:24:14,880
It was not the horn of a mythical animal,
374
00:24:14,880 --> 00:24:20,200
it was the tusk of a kind of whale that swam in the Arctic seas -
375
00:24:20,200 --> 00:24:21,840
the narwhal.
376
00:24:21,840 --> 00:24:26,320
The first examples were brought south by the Vikings.
377
00:24:26,320 --> 00:24:29,680
They almost certainly knew exactly what its origin was,
378
00:24:29,680 --> 00:24:33,600
but, for 400 years, they maintained the story
379
00:24:33,600 --> 00:24:36,480
that it came from the mythical unicorn.
380
00:24:38,200 --> 00:24:41,640
But farther south in Europe, no-one knew about narwhals,
381
00:24:41,640 --> 00:24:44,040
and scholarly natural history books
382
00:24:44,040 --> 00:24:48,120
confidently described unicorns in detail, as if they were real.
383
00:24:48,120 --> 00:24:51,280
Since unicorn horns were hard to come by,
384
00:24:51,280 --> 00:24:55,800
unscrupulous dealers met the demand by grinding up rhinoceros horn.
385
00:24:55,800 --> 00:24:58,480
In fact, the horn of a rhino and a narwhal
386
00:24:58,480 --> 00:25:00,200
could hardly be more different.
387
00:25:01,200 --> 00:25:03,520
You can see from this narwhal skull,
388
00:25:03,520 --> 00:25:06,920
the hole where the horn would normally sit.
389
00:25:06,920 --> 00:25:10,400
It grows outwards through the lip.
390
00:25:10,400 --> 00:25:13,480
But whereas rhino horn is actually made of keratin -
391
00:25:13,480 --> 00:25:16,440
the same stuff as our fingernails are made of -
392
00:25:16,440 --> 00:25:21,160
the narwhal's great horn is actually made largely of dentine.
393
00:25:21,160 --> 00:25:26,280
It's not a horn at all, it's an enormous canine tooth -
394
00:25:26,280 --> 00:25:28,160
a tusk.
395
00:25:29,560 --> 00:25:32,360
Some female narwhals possess tusks,
396
00:25:32,360 --> 00:25:36,000
but by and large male narwhals grow the long tusks
397
00:25:36,000 --> 00:25:38,560
which can reach three metres in length.
398
00:25:38,560 --> 00:25:41,160
It's been described as a cross between
399
00:25:41,160 --> 00:25:43,720
a corkscrew and a jousting lance.
400
00:25:43,720 --> 00:25:47,520
But its true purpose has baffled scientists for centuries.
401
00:25:49,320 --> 00:25:51,400
Very few creatures have tusks.
402
00:25:51,400 --> 00:25:53,920
The most well-known, of course, are elephants.
403
00:25:54,920 --> 00:25:58,800
Their tusks are in fact enlarged incisor teeth.
404
00:25:58,800 --> 00:26:01,720
Both male and female elephants develop them
405
00:26:01,720 --> 00:26:05,600
and they're used in many ways, but primarily for getting food -
406
00:26:05,600 --> 00:26:09,320
digging into the ground, ripping up grass or pushing over trees.
407
00:26:11,320 --> 00:26:14,680
The obvious difference between elephant and narwhal tusks
408
00:26:14,680 --> 00:26:19,120
is that the narwhal possesses just one, whereas the elephant has two.
409
00:26:19,120 --> 00:26:22,000
But that may not always have been the case.
410
00:26:22,000 --> 00:26:24,560
This is a rare curiosity indeed.
411
00:26:24,560 --> 00:26:28,200
It's the skull of a narwhal with two tusks.
412
00:26:28,200 --> 00:26:31,760
It's possible that such a rarity offers a window on the past.
413
00:26:31,760 --> 00:26:36,520
Perhaps the ancient ancestors of the narwhals were once twin-tusked,
414
00:26:36,520 --> 00:26:38,440
but over time, they lost one.
415
00:26:39,800 --> 00:26:41,440
But what was it for?
416
00:26:41,440 --> 00:26:45,880
One early suggestion was that the narwhal used it to spear fish.
417
00:26:45,880 --> 00:26:48,560
Though how it would manage to transfer its catch
418
00:26:48,560 --> 00:26:51,760
from the end of its tusk to its mouth was never explained.
419
00:26:52,760 --> 00:26:56,040
Someone else suggested that the animal used its horn
420
00:26:56,040 --> 00:26:58,400
to stab holes through the Arctic ice.
421
00:26:58,400 --> 00:26:59,960
That's not unreasonable,
422
00:26:59,960 --> 00:27:02,600
since narwhals spend a lot of time under ice,
423
00:27:02,600 --> 00:27:06,080
and being mammals, they have to get to air in order to breathe.
424
00:27:06,080 --> 00:27:09,560
But it seems strange that only males have a tusk.
425
00:27:09,560 --> 00:27:12,880
After all, females need to breathe too.
426
00:27:12,880 --> 00:27:16,120
Charles Darwin had another explanation.
427
00:27:16,120 --> 00:27:19,760
He likened the tusk to the antlers carried by male deer -
428
00:27:19,760 --> 00:27:21,680
stags.
429
00:27:23,360 --> 00:27:28,240
Antlers help stags to establish hierarchies during the mating season.
430
00:27:28,240 --> 00:27:31,280
This stag with the biggest antlers asserts his dominance
431
00:27:31,280 --> 00:27:34,280
by showing them off and occasionally fighting with them.
432
00:27:39,200 --> 00:27:42,560
Darwin proposed that the long tusk of the narwhal
433
00:27:42,560 --> 00:27:44,680
functioned in just the same way -
434
00:27:44,680 --> 00:27:49,080
as a declaration of dominance and, if necessary, as a weapon.
435
00:27:49,080 --> 00:27:53,120
That would explain why male narwhals possess the long tusks.
436
00:27:54,520 --> 00:27:56,400
And why, when males meet,
437
00:27:56,400 --> 00:28:01,320
they sometimes cross tusks in what might be a ritualised form of combat.
438
00:28:06,000 --> 00:28:08,920
Darwin's theory has long been accepted.
439
00:28:08,920 --> 00:28:13,680
But recently, scientists have been exploring other possibilities.
440
00:28:13,680 --> 00:28:16,880
Our teeth are covered with a thick enamel layer
441
00:28:16,880 --> 00:28:19,920
that protects the softer material beneath.
442
00:28:19,920 --> 00:28:22,040
If that erodes or is damaged,
443
00:28:22,040 --> 00:28:24,840
then it exposes the nerves within the tooth
444
00:28:24,840 --> 00:28:28,840
which can make them extremely sensitive to temperature.
445
00:28:28,840 --> 00:28:34,080
Narwhal tusks don't possess that external enamel covering.
446
00:28:34,080 --> 00:28:38,120
And high-magnification photography has revealed something
447
00:28:38,120 --> 00:28:43,200
very unusual about the exterior surface of this huge elongated tooth.
448
00:28:44,200 --> 00:28:48,720
The surface of the tusk is cratered with millions of tiny pits
449
00:28:48,720 --> 00:28:54,880
called tubules. Each tubule contains a fluid, and at its base, a nerve.
450
00:28:54,880 --> 00:28:58,120
The fluid reacts to the narwhal's environment,
451
00:28:58,120 --> 00:29:00,680
so the tusk must be highly sensitive.
452
00:29:03,240 --> 00:29:07,000
Tests on narwhals have shown that they can detect tiny changes
453
00:29:07,000 --> 00:29:09,400
in the temperature and salinity of water,
454
00:29:09,400 --> 00:29:12,720
key factors that govern the formation of ice.
455
00:29:14,360 --> 00:29:17,200
Their migration is tied to the seasonal shrinking
456
00:29:17,200 --> 00:29:19,560
and expanding of the ice cap.
457
00:29:19,560 --> 00:29:24,280
So perhaps the tusk plays a role in detecting ice or open water.
458
00:29:26,000 --> 00:29:29,720
But its sensory powers could be even greater.
459
00:29:29,720 --> 00:29:34,080
Perhaps the tusk is able to detect movement in the water.
460
00:29:34,080 --> 00:29:37,800
Or even changes in the fertility of female narwhals.
461
00:29:37,800 --> 00:29:40,840
These are theories yet to be tested.
462
00:29:42,200 --> 00:29:44,280
If this is a sensory tool,
463
00:29:44,280 --> 00:29:48,560
then it would put a very different interpretation on the male jousting.
464
00:29:48,560 --> 00:29:52,760
Perhaps males enjoy rubbing their tusks together.
465
00:29:52,760 --> 00:29:57,200
There could be a third explanation, a more practical one.
466
00:29:57,200 --> 00:30:01,120
Tusks from old narwhals often become coated with algae,
467
00:30:01,120 --> 00:30:04,480
which might block the pores that lead to the nerves.
468
00:30:04,480 --> 00:30:09,320
So, perhaps males rub their tusks together to help clean them.
469
00:30:10,600 --> 00:30:14,160
Could this be not fighting, but cooperative grooming?
470
00:30:16,040 --> 00:30:20,680
Why mainly male narwhals carry a sensory tool is still unexplained.
471
00:30:22,000 --> 00:30:23,560
Rather than being a weapon,
472
00:30:23,560 --> 00:30:28,200
perhaps the highly sensitive tusk helps males to find female partners.
473
00:30:29,280 --> 00:30:32,920
More than likely, the tusk serves many functions.
474
00:30:32,920 --> 00:30:34,600
But why should it be twisted?
475
00:30:36,080 --> 00:30:38,960
The twist increases the surface area,
476
00:30:38,960 --> 00:30:42,680
so it's possible more nerve endings are exposed.
477
00:30:42,680 --> 00:30:45,640
And this would increase its sensitivity.
478
00:30:45,640 --> 00:30:49,200
But there's another theory that suggests that the twist
479
00:30:49,200 --> 00:30:52,120
actually helps to keep the tusk straight.
480
00:30:52,120 --> 00:30:54,800
That may sound counterintuitive,
481
00:30:54,800 --> 00:30:59,160
but tusks of other large animals tend to curve down or up.
482
00:30:59,160 --> 00:31:03,760
A spiral growth may actually help the tusk to keep pointing forwards,
483
00:31:03,760 --> 00:31:06,120
and so reduce drag in the water.
484
00:31:07,680 --> 00:31:11,520
There's another way in which a twist could help in swimming.
485
00:31:11,520 --> 00:31:15,360
As the animal moves forward, the water around the tusk
486
00:31:15,360 --> 00:31:19,360
spirals away from it in a way that might reduce drag.
487
00:31:21,440 --> 00:31:25,280
But at least today we know the true identity of the animals
488
00:31:25,280 --> 00:31:29,120
that produce these wonderful and spectacular ivory spears.
489
00:31:34,720 --> 00:31:39,920
The myth that they came from the unicorn was finally exploded in 1638
490
00:31:39,920 --> 00:31:42,640
by a Danish scientist, Ole Worm,
491
00:31:42,640 --> 00:31:46,160
who gave a public lecture proving conclusively
492
00:31:46,160 --> 00:31:48,400
that they came from the narwhal.
493
00:31:48,400 --> 00:31:51,640
So then, of course, their value plummeted.
494
00:31:51,640 --> 00:31:55,400
Today, we no longer believe they have magical properties,
495
00:31:55,400 --> 00:31:59,520
but there's still quite a lot about them we don't fully understand.
496
00:32:05,120 --> 00:32:08,120
Our second subject belongs to a group of animals
497
00:32:08,120 --> 00:32:10,400
that have taken the spiral
498
00:32:10,400 --> 00:32:14,080
and adapted it into a multitude of variations -
499
00:32:14,080 --> 00:32:15,720
snails.
500
00:32:21,280 --> 00:32:26,080
When the first snails crawled out of the sea and up onto dry land,
501
00:32:26,080 --> 00:32:28,440
they carried with them the shells
502
00:32:28,440 --> 00:32:32,280
that were to be crucial to their survival out of water.
503
00:32:32,280 --> 00:32:34,800
They themselves were distant relatives
504
00:32:34,800 --> 00:32:38,080
of other shelled creatures that had dominated the seas
505
00:32:38,080 --> 00:32:40,440
for millions of years.
506
00:32:40,440 --> 00:32:42,400
They were the ammonites.
507
00:32:42,400 --> 00:32:47,360
This is one of them, and this is about 160 million years old.
508
00:32:47,360 --> 00:32:52,000
Although they experimented in some degree with the shape of the shell,
509
00:32:52,000 --> 00:32:54,400
nearly all of them are like this -
510
00:32:54,400 --> 00:32:55,880
flat,
511
00:32:55,880 --> 00:32:57,720
spiral
512
00:32:57,720 --> 00:32:59,400
and symmetrical.
513
00:33:00,520 --> 00:33:05,040
In due course, the ammonites themselves became extinct.
514
00:33:05,040 --> 00:33:09,320
But since then, other creatures have developed the shell
515
00:33:09,320 --> 00:33:13,720
into a whole variety of different shapes and sizes.
516
00:33:17,080 --> 00:33:21,640
This variety shows how successful the spiral can be
517
00:33:21,640 --> 00:33:24,080
as the basis for a shell's design.
518
00:33:26,920 --> 00:33:30,840
And how it can be elaborated and decorated.
519
00:33:35,520 --> 00:33:38,520
Snail shells, like the shells of birds' eggs,
520
00:33:38,520 --> 00:33:41,040
are made of calcium carbonate.
521
00:33:41,040 --> 00:33:44,760
They appear at the very beginning of a young snail's life,
522
00:33:44,760 --> 00:33:49,000
and they are never shed, but simply become enlarged as the animal grows.
523
00:33:51,360 --> 00:33:55,800
But whatever their shape and size, they are almost always spiralled.
524
00:33:56,800 --> 00:34:00,240
Spirals have been used by animals for a very long time.
525
00:34:00,240 --> 00:34:03,560
We can trace them back to a group of sea creatures
526
00:34:03,560 --> 00:34:07,080
that first appeared around 500 million years ago.
527
00:34:07,080 --> 00:34:08,920
And some are still around today.
528
00:34:08,920 --> 00:34:10,920
This is one - the nautilus.
529
00:34:11,920 --> 00:34:16,640
Today, it's only found in the deep waters of the Indo-Pacific ocean.
530
00:34:16,640 --> 00:34:20,640
But millions of years ago, animals like it were widespread.
531
00:34:20,640 --> 00:34:24,440
Its earliest ancestors, however, had a very different shape.
532
00:34:25,600 --> 00:34:28,800
There's evidence that the nautiloids started out
533
00:34:28,800 --> 00:34:31,080
more or less straight, like this one,
534
00:34:31,080 --> 00:34:33,200
just a little curl at the beginning,
535
00:34:33,200 --> 00:34:35,800
and then running straight like that,
536
00:34:35,800 --> 00:34:38,560
with the separate chambers running along there.
537
00:34:38,560 --> 00:34:41,480
But as millions of years passed,
538
00:34:41,480 --> 00:34:45,880
they began to coil until they became species like this one.
539
00:34:47,000 --> 00:34:49,400
And then, millions of years later,
540
00:34:49,400 --> 00:34:52,800
another group adopted the symmetrical coil.
541
00:34:52,800 --> 00:34:55,000
These were called ammonites.
542
00:34:56,960 --> 00:34:59,760
But why did these animals coil their shells?
543
00:35:01,360 --> 00:35:05,360
Well, if their shells remained straight as they increased in size,
544
00:35:05,360 --> 00:35:08,560
they would inevitably become somewhat cumbersome.
545
00:35:09,840 --> 00:35:14,680
Coiling them made them more compact and perhaps more mobile.
546
00:35:16,760 --> 00:35:20,880
Whatever the reason, the change in shell shape was a great success.
547
00:35:22,520 --> 00:35:26,920
Thousands of new species appeared, all with coiled shells.
548
00:35:28,080 --> 00:35:30,680
These fossilised shells tell us little
549
00:35:30,680 --> 00:35:33,760
about the soft-bodied creatures that lived in them,
550
00:35:33,760 --> 00:35:37,240
but the living nautilus can give us some clues about that.
551
00:35:40,040 --> 00:35:44,400
At the start of its life, the shell consists of just a few chambers.
552
00:35:44,400 --> 00:35:46,600
But by the time it's mature,
553
00:35:46,600 --> 00:35:49,440
there may be as many as 30.
554
00:35:50,720 --> 00:35:54,920
Richard Owen, the founding director of London's Natural History Museum,
555
00:35:54,920 --> 00:35:59,480
wrote the first full description of the nautilus.
556
00:35:59,480 --> 00:36:02,840
This is Owen's own personal copy,
557
00:36:02,840 --> 00:36:05,480
and it's full of exquisite sketches.
558
00:36:05,480 --> 00:36:11,280
His drawings show just how the animal is placed inside a shell.
559
00:36:11,280 --> 00:36:15,200
Almost all the soft tissues - its body and tentacles -
560
00:36:15,200 --> 00:36:17,520
are held in the outermost chamber.
561
00:36:17,520 --> 00:36:19,880
And a long tube, called a siphuncle,
562
00:36:19,880 --> 00:36:22,280
runs through the chambers,
563
00:36:22,280 --> 00:36:26,440
through which the animal can pump in water or remove it,
564
00:36:26,440 --> 00:36:29,080
and so regulates its buoyancy.
565
00:36:30,600 --> 00:36:32,720
So, the nautilus's spiral shell
566
00:36:32,720 --> 00:36:35,720
not only protects its soft body from enemies,
567
00:36:35,720 --> 00:36:38,160
but enables it to cruise around.
568
00:36:38,160 --> 00:36:43,520
And it's so strong that the nautilus can descend as deep as 700 metres,
569
00:36:43,520 --> 00:36:46,160
where pressure would kill a human being.
570
00:36:46,160 --> 00:36:48,400
At the peak of their success,
571
00:36:48,400 --> 00:36:51,600
there were thousands of different kinds of nautiloids.
572
00:36:51,600 --> 00:36:55,920
But their cousins, the ammonites, were even more varied and diverse.
573
00:36:57,160 --> 00:37:00,760
Their buoyant shells allowed some of these creatures
574
00:37:00,760 --> 00:37:03,000
to grow to a huge size.
575
00:37:08,640 --> 00:37:11,920
Some were as big as a human being.
576
00:37:11,920 --> 00:37:16,280
But it would be impossible for such a creature to move out of water
577
00:37:16,280 --> 00:37:20,400
with a shell like this. It would be far too heavy and too cumbersome.
578
00:37:20,400 --> 00:37:24,600
Nonetheless, something was about to happen to the molluscs
579
00:37:24,600 --> 00:37:29,520
that would allow them to leave the water and move up onto land.
580
00:37:31,120 --> 00:37:33,600
The ammonite dynasties were developing
581
00:37:33,600 --> 00:37:35,760
different shapes to their shells,
582
00:37:35,760 --> 00:37:38,000
uncoiling them in all sorts of ways.
583
00:37:39,240 --> 00:37:41,920
Some of these new forms fed on the sea floor
584
00:37:41,920 --> 00:37:44,840
and therefore had less need to be mobile.
585
00:37:44,840 --> 00:37:49,440
But other shelled relatives of the ammonites were going even further,
586
00:37:49,440 --> 00:37:53,400
changing both their shell shape and twisting their soft bodies.
587
00:37:54,480 --> 00:37:57,080
And these are their descendants -
588
00:37:57,080 --> 00:37:58,440
snails.
589
00:38:00,040 --> 00:38:02,760
The problem with a symmetrical shell
590
00:38:02,760 --> 00:38:05,000
is that each whorl has to grow
591
00:38:05,000 --> 00:38:07,480
on the outside of the other one,
592
00:38:07,480 --> 00:38:11,480
so that the shell very quickly becomes very big.
593
00:38:11,480 --> 00:38:13,840
But by becoming asymmetrical,
594
00:38:13,840 --> 00:38:16,920
and offsetting each whorl to the side,
595
00:38:16,920 --> 00:38:19,520
the shell can remain much more compact
596
00:38:19,520 --> 00:38:22,680
and rounded and easier to manipulate.
597
00:38:24,920 --> 00:38:28,680
The shift in the snail's symmetry seems to have been triggered
598
00:38:28,680 --> 00:38:30,720
by the action of a single gene.
599
00:38:33,200 --> 00:38:36,080
But this change can bring complications.
600
00:38:38,080 --> 00:38:40,320
Because of their asymmetric shape,
601
00:38:40,320 --> 00:38:43,920
snails have to position themselves carefully during mating.
602
00:38:46,200 --> 00:38:48,720
In most snails, this is not a problem,
603
00:38:48,720 --> 00:38:51,800
as the body plan of snails is usually the same.
604
00:38:51,800 --> 00:38:53,080
But not all.
605
00:38:56,040 --> 00:38:59,640
Just like humans, who are either right-handed or left-handed,
606
00:38:59,640 --> 00:39:01,480
snail shells can twist
607
00:39:01,480 --> 00:39:04,080
to the left...
608
00:39:04,080 --> 00:39:05,760
or the right.
609
00:39:05,760 --> 00:39:09,960
The vast majority of snail shells are right spiralling.
610
00:39:09,960 --> 00:39:14,240
But in one particular area of Japan, the left-handed form
611
00:39:14,240 --> 00:39:18,000
of this particular species has a clear advantage.
612
00:39:19,440 --> 00:39:23,520
That is all because of this creature, a snail-eating snake.
613
00:39:23,520 --> 00:39:26,120
It's so specialised for eating snails
614
00:39:26,120 --> 00:39:30,640
that its jaws have evolved to become asymmetrical, just like its prey.
615
00:39:30,640 --> 00:39:34,200
The right side of its lower jaw has more teeth than the left.
616
00:39:35,880 --> 00:39:41,040
Recently, scientists in Japan filmed the hunting behaviour of this snake.
617
00:39:41,040 --> 00:39:45,080
When it attacks a snail with a right spiral shell,
618
00:39:45,080 --> 00:39:48,640
its row of extra teeth dig into the snail's flesh,
619
00:39:48,640 --> 00:39:51,360
and by moving its jaws back and forth,
620
00:39:51,360 --> 00:39:54,640
it separates the snail's body from its shell.
621
00:39:56,040 --> 00:39:59,600
But attacking a snail with a left-spiralled shell
622
00:39:59,600 --> 00:40:01,200
is not so straightforward.
623
00:40:01,200 --> 00:40:05,040
The position of the shell means that the snake can't use
624
00:40:05,040 --> 00:40:07,440
its specialised jaws so effectively.
625
00:40:07,440 --> 00:40:09,040
And it gives up.
626
00:40:14,920 --> 00:40:19,040
Shells help land-living snails to conserve moisture
627
00:40:19,040 --> 00:40:21,640
and also protect them from their enemies.
628
00:40:23,720 --> 00:40:27,800
The snails' soft bodies are, of course, welcome meals
629
00:40:27,800 --> 00:40:31,000
to any predator that can crack their shells.
630
00:40:35,840 --> 00:40:38,440
Some snails have strengthened their shells.
631
00:40:40,120 --> 00:40:42,480
Some have protected them with spines.
632
00:40:45,160 --> 00:40:47,880
Others have become very thick indeed,
633
00:40:47,880 --> 00:40:49,680
and almost uncrackable.
634
00:40:51,960 --> 00:40:56,560
Some scientists believe that this could be the golden age of the snail.
635
00:40:57,560 --> 00:41:00,440
They've never been more diverse, in terms of species
636
00:41:00,440 --> 00:41:02,680
or indeed the variety of their shells.
637
00:41:04,200 --> 00:41:07,160
But while the snails are more varied,
638
00:41:07,160 --> 00:41:09,720
that is not the case with the nautilus.
639
00:41:09,720 --> 00:41:13,400
The oceans were once dominated by creatures like this,
640
00:41:13,400 --> 00:41:16,800
and today, just a handful of different types exist.
641
00:41:18,680 --> 00:41:23,560
While snails have taken the spiral and modified it endlessly,
642
00:41:23,560 --> 00:41:26,960
the modern nautilus has stuck with a symmetrical spiral
643
00:41:26,960 --> 00:41:30,800
that's hardly changed for hundreds of millions of years.
644
00:41:30,800 --> 00:41:32,200
So it's fair to say
645
00:41:32,200 --> 00:41:36,000
that the nautilus shell is a window on the distant past,
646
00:41:36,000 --> 00:41:39,920
to a time when the simple, but symmetrical, spiral
647
00:41:39,920 --> 00:41:41,880
dominated the seas.
648
00:41:43,440 --> 00:41:47,680
So, both whales and snails have benefited from the twist,
649
00:41:47,680 --> 00:41:51,320
a design that first appeared 500 million years ago
650
00:41:51,320 --> 00:41:53,600
and is still widespread today.
55924
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