0:00:02 > 0:00:06'The natural world is full of extraordinary animals
0:00:06 > 0:00:09'with amazing life histories.
0:00:09 > 0:00:13'Yet certain stories are more intriguing than most.'
0:00:15 > 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 myth
0:00:26 > 0:00:29and misunderstandings for a very long time.
0:00:29 > 0:00:34And some have only recently revealed their secrets.
0:00:34 > 0:00:38These are the animals that stand out from the crowd -
0:00:38 > 0:00:43the curiosities I find most fascinating of all.
0:00:52 > 0:00:54'The elephant and the mole rat -'
0:00:54 > 0:00:57they're both extremely wrinkled,
0:00:57 > 0:01:00starting their young lives looking ancient,
0:01:00 > 0:01:03and remaining that way into old age.
0:01:03 > 0:01:06Yet they outlive most other animals their size.
0:01:06 > 0:01:08What are their secrets?
0:01:12 > 0:01:15Nature has twisted the task of the narwhal
0:01:15 > 0:01:18and the shells of snails and their relatives.
0:01:18 > 0:01:21But what is the purpose of the twist?
0:01:23 > 0:01:27'Spirals are common in the natural world.
0:01:27 > 0:01:29'We seldom pay attention to them.
0:01:29 > 0:01:32'But in fact, they have remarkable characteristics'
0:01:32 > 0:01:34which many animals exploit.
0:01:35 > 0:01:38And some creatures, having developed a spiral,
0:01:38 > 0:01:42have reworked it in many intriguing and beautiful ways.
0:01:44 > 0:01:47In this programme, I'll try to discover why the spiral
0:01:47 > 0:01:52is so important to two very different kinds of animals.
0:02:06 > 0:02:09Elephants are truly strange creatures,
0:02:09 > 0:02:12both in looks and behaviour.
0:02:12 > 0:02:14Aristotle described them as,
0:02:14 > 0:02:18"The beast that passeth all others in wit and mind."
0:02:18 > 0:02:22But the more we learn about its curious body and behaviour,
0:02:22 > 0:02:24the more remarkable it appears to be.
0:02:24 > 0:02:28The evolution of such a strange-looking creature is no accident.
0:02:28 > 0:02:31Its fascinating body is the key to allowing elephants
0:02:31 > 0:02:34to live a long life.
0:02:34 > 0:02:38For elephants, even young ones, it's an advantage to be wrinkly,
0:02:38 > 0:02:41and not at all a sign of old age.
0:02:43 > 0:02:48Elephants evolved from mammoths over 55 million years ago.
0:02:48 > 0:02:51Today, they're the heaviest land mammals alive,
0:02:51 > 0:02:53and one of the longest lived,
0:02:53 > 0:02:56with a life expectancy of about 70 years.
0:02:58 > 0:03:01Big creatures usually live a long time largely
0:03:01 > 0:03:03because they have slow metabolisms.
0:03:03 > 0:03:06However, elephants have particular characteristics
0:03:06 > 0:03:09that help them reach old age.
0:03:09 > 0:03:11One of the most important, a family structure
0:03:11 > 0:03:16in which the oldest matriarchs pass on vital experience.
0:03:16 > 0:03:19And their bodies have developed some special features
0:03:19 > 0:03:22to deal with the problems of being so big.
0:03:22 > 0:03:25Their trunk is one of them.
0:03:26 > 0:03:28This, surely,
0:03:28 > 0:03:34is the most extraordinary nose possessed by any living creature.
0:03:34 > 0:03:36It can be moved with ease and dexterity,
0:03:36 > 0:03:39to gently caress,
0:03:39 > 0:03:42tear down trees, suck up litres of water.
0:03:42 > 0:03:45The trunk is, in fact, a union between the nose
0:03:45 > 0:03:48and the upper lip, and it's highly sensitive,
0:03:48 > 0:03:52with over 100,000 muscle units in it.
0:03:52 > 0:03:56The end of the trunk can move rather like a hand.
0:03:56 > 0:04:01This mobile tip allows the elephant to feel and pick up
0:04:01 > 0:04:04delicate objects such as a single blade of grass.
0:04:05 > 0:04:09The stretched nose is a masterpiece of evolution,
0:04:09 > 0:04:12and key to how the elephant can survive
0:04:12 > 0:04:15with such a large and curious body.
0:04:16 > 0:04:18ELEPHANT SNORTS
0:04:18 > 0:04:20If they hadn't developed a trunk,
0:04:20 > 0:04:23elephants couldn't have become so big.
0:04:24 > 0:04:27It enables them, in spite of their huge, stocky body,
0:04:27 > 0:04:31to reach down to the ground to collect food and water.
0:04:32 > 0:04:35Fuelling a big body is a full-time job,
0:04:35 > 0:04:39and an elephant has to consume its own weight in food every 20 days.
0:04:41 > 0:04:45One might think this great weight would be a stress on joints
0:04:45 > 0:04:49and teeth, and wear elephants out before old age.
0:04:49 > 0:04:51'But not so.'
0:04:51 > 0:04:55Eating vegetation is of course very tough on the teeth,
0:04:55 > 0:04:59and there are some animals, that when their teeth are worn down,
0:04:59 > 0:05:01simply starve and die.
0:05:01 > 0:05:05But elephants can live to 70 years old,
0:05:05 > 0:05:09and the secret lies in their extraordinary molar teeth.
0:05:09 > 0:05:13They have two pairs - two at the top, two at the bottom -
0:05:13 > 0:05:14and here's one of them.
0:05:14 > 0:05:17This is the grinding surface,
0:05:17 > 0:05:23which is capable of shredding twigs and bark, and even wood,
0:05:23 > 0:05:25and of course, it wears.
0:05:25 > 0:05:27But as it wears down,
0:05:27 > 0:05:31so another tooth is developing within the jaw, which finally emerges
0:05:31 > 0:05:37and pushes this forward until it actually breaks off and is shed.
0:05:39 > 0:05:41Acquiring new teeth in that way
0:05:41 > 0:05:45enables elephants to remain well-fed and healthy into old age.
0:05:46 > 0:05:50In elephant society, the older females are invaluable,
0:05:50 > 0:05:53and pass on the wisdom they've gained during their long lives
0:05:53 > 0:05:56to younger members of the family.
0:05:56 > 0:05:58ELEPHANT GROWLS
0:06:00 > 0:06:03Mature females spend long periods of time
0:06:03 > 0:06:07listening out for vital sounds of danger and warn the group.
0:06:09 > 0:06:13Such sensitivity to sound was the subject
0:06:13 > 0:06:16of one of the very first animal behaviour experiments.
0:06:19 > 0:06:22Someone in France in the early 18th century noted
0:06:22 > 0:06:26that elephants in menageries appeared to react
0:06:26 > 0:06:30to faint, distant sounds outside their enclosures.
0:06:30 > 0:06:34So they tested two elephants - Hans and Parki -
0:06:34 > 0:06:40and engaged a palace orchestra to play love music to them.
0:06:40 > 0:06:44One elephant was very impressed by the French horn player.
0:06:44 > 0:06:48It was reported that, "The animal knelt down before him,
0:06:48 > 0:06:52"caressed him with his trunk and expressed to him in all sorts
0:06:52 > 0:06:58"of pretty ways the pleasure which it had felt in listening to him."
0:07:00 > 0:07:05We now know that the French horn can produce a low-frequency sound
0:07:05 > 0:07:08that's very like the rumble that elephants produce
0:07:08 > 0:07:11using a similar resonating chamber in their heads.
0:07:11 > 0:07:14LOW RUMBLING
0:07:15 > 0:07:20They can also hear very deep sounds beyond our own hearing.
0:07:20 > 0:07:25The oldest, experienced females are experts at interpreting them.
0:07:26 > 0:07:29Such frequencies create vibrations in the ground
0:07:29 > 0:07:31that travel a very long way,
0:07:31 > 0:07:34which the elephants can detect through their feet.
0:07:35 > 0:07:39Their feet, in fact, are not as solid as they might look,
0:07:39 > 0:07:41but have special internal cushioning
0:07:41 > 0:07:44to soften the impact of the animal's weighty footsteps.
0:07:46 > 0:07:50For such a large creature, that can be 40 times our weight,
0:07:50 > 0:07:54this foot seems unfeasibly small.
0:07:54 > 0:07:58Its surface area is little more than twice our own feet,
0:07:58 > 0:08:01but this foot has a surprising structure.
0:08:01 > 0:08:05The elephant walks on five toes,
0:08:05 > 0:08:09and the back part of its foot consists of a highly spongy heel.
0:08:09 > 0:08:14The raised heel can compress and expand to absorb shock,
0:08:14 > 0:08:18and shield the other heavy bones in the body from pressure.
0:08:18 > 0:08:23It's as if the elephant were wearing a high-heeled training shoe.
0:08:23 > 0:08:27When an elephant runs, it bounces on this spongy heel
0:08:27 > 0:08:31and its leg bones act like pogo sticks
0:08:31 > 0:08:33to push the animal upwards.
0:08:35 > 0:08:39This system protects the bones and inner tissues.
0:08:40 > 0:08:42And wild elephants rarely get arthritis.
0:08:45 > 0:08:49Despite their large size, they live active, physical lives
0:08:49 > 0:08:52without too much damage to their bodies.
0:08:54 > 0:08:58Males, as they mature, usually go off to live by themselves.
0:08:58 > 0:09:01But the females stay with the family group
0:09:01 > 0:09:04and play a very important part in guiding the younger ones.
0:09:07 > 0:09:11Young elephants tend to look old even at the start of their lives
0:09:11 > 0:09:13because of their wrinkly skin.
0:09:14 > 0:09:18But, for elephants, wrinkles are not signs of ageing.
0:09:18 > 0:09:21On the contrary, they're extremely important
0:09:21 > 0:09:24for an elephant's very survival.
0:09:24 > 0:09:26The elephant's thick, creased skin
0:09:26 > 0:09:30has been the subject of much debate over the years.
0:09:30 > 0:09:33And early anatomists had some novel ideas about it.
0:09:33 > 0:09:37Many believed that the elephant could actually move its skin
0:09:37 > 0:09:39to crush flies between the wrinkles.
0:09:39 > 0:09:43I may say, that was never witnessed in action.
0:09:43 > 0:09:47But the skin WAS thought to be enormously thick and insensitive.
0:09:47 > 0:09:50But in fact it varies across the elephant's body
0:09:50 > 0:09:52and can be as thick as two or three centimetres
0:09:52 > 0:09:55around the top of its trunk and along the back
0:09:55 > 0:09:58and as thin as paper around the eyes.
0:09:58 > 0:10:02Although the skin looks tough and wrinkly, it's remarkably sensitive.
0:10:02 > 0:10:05An elephant can feel small flies on its body,
0:10:05 > 0:10:08even if it can't crush them between its wrinkles.
0:10:10 > 0:10:15But these wrinkles really do have an important function.
0:10:15 > 0:10:17The patterned crevices hold water,
0:10:17 > 0:10:20which travels along them all over the body.
0:10:20 > 0:10:26Wrinkly skins can contain five to ten times more water than smooth ones.
0:10:26 > 0:10:29So moisture collected during the wallowing
0:10:29 > 0:10:31stops the skin from dehydrating and overheating
0:10:31 > 0:10:34for a long time afterwards.
0:10:35 > 0:10:39Significantly, African elephants, that lived in hotter, drier places,
0:10:39 > 0:10:43have more deeply wrinkled skins than Asian elephants.
0:10:45 > 0:10:50So, wrinkles for the elephant are ways of protecting the skin,
0:10:50 > 0:10:53not the unwanted consequence of old age.
0:10:56 > 0:11:00The elephant was once considered an oddity of nature.
0:11:00 > 0:11:05For centuries, we've been fascinated by their large ears,
0:11:05 > 0:11:06their extraordinary trunks,
0:11:06 > 0:11:09the stocky feet, the wrinkly skins.
0:11:10 > 0:11:14But over the years, we've come to understand their significance.
0:11:14 > 0:11:18The elephant's unique biology is key to its long-term survival
0:11:18 > 0:11:23and its ability to seemingly avoid the rigours of old age.
0:11:29 > 0:11:32Elephants, understandably, live a long time
0:11:32 > 0:11:36because of the slow metabolism of their huge bodies.
0:11:38 > 0:11:41But small, naked mole rats live much longer
0:11:41 > 0:11:44than any other mammal of a comparable size.
0:11:44 > 0:11:45Why?
0:11:47 > 0:11:51Could it be that the body of this bizarre little creature
0:11:51 > 0:11:53holds the secret of eternal youth?
0:11:55 > 0:12:00When a German naturalist, Wilhelm Ruppell,
0:12:00 > 0:12:05discovered a lone, hairless, wrinkled, naked mole rat
0:12:05 > 0:12:08in 1842 in Ethiopia,
0:12:08 > 0:12:11he was convinced that he had stumbled across
0:12:11 > 0:12:13a decrepit, old individual,
0:12:13 > 0:12:16and he gave it the name Heterocephalus glaber,
0:12:16 > 0:12:19which loosely translated means
0:12:19 > 0:12:22a smooth-skinned animal with an oddly shaped head.
0:12:23 > 0:12:27He noted that the form of the body, because of its hairlessness,
0:12:27 > 0:12:30gives an unpleasant impression.
0:12:31 > 0:12:32It does.
0:12:35 > 0:12:37For the next 40 years,
0:12:37 > 0:12:41these bizarre-looking creatures were largely ignored by scientists.
0:12:41 > 0:12:47Then, in 1885, a British zoologist in London's Natural History Museum,
0:12:47 > 0:12:51called Oldfield Thomas decided to examine in detail
0:12:51 > 0:12:55the museum specimens that had been sitting in store for decades.
0:12:58 > 0:13:01Here we can see some of his drawings.
0:13:01 > 0:13:04Thomas declared that the weird animal described by Ruppell
0:13:04 > 0:13:05was in fact normal.
0:13:05 > 0:13:11We now know that all mole rats look like this, whatever their age.
0:13:11 > 0:13:14However, what those early naturalists couldn't have known
0:13:14 > 0:13:17was that they had chanced upon a mammal
0:13:17 > 0:13:22that would fascinate and intrigue scientists for the next 150 years.
0:13:22 > 0:13:25A creature that might even shed light
0:13:25 > 0:13:28on the secrets of ageing and longevity.
0:13:31 > 0:13:35Its body hardly seemed to alter, no matter how long it lived.
0:13:36 > 0:13:41Old mole rats stayed physically young throughout their lives.
0:13:41 > 0:13:45And not only that, the strangest discovery of all
0:13:45 > 0:13:48was that they sometimes lived for almost 30 years.
0:13:52 > 0:13:55The lifespan of animals varies enormously.
0:13:55 > 0:14:01Amongst mammals, a tiny little shrew like this lives just two or so years.
0:14:01 > 0:14:05While a giant whale can reach the age of 100.
0:14:06 > 0:14:11Lifestyle is an important factor in defining lifespan.
0:14:12 > 0:14:15A shrew has a fast and furious life,
0:14:15 > 0:14:18producing many young of which few survive.
0:14:18 > 0:14:22Whales, on the other hand, breed slowly and don't have many predators.
0:14:23 > 0:14:26Generally, big animals live longer.
0:14:26 > 0:14:29So it's very odd indeed
0:14:29 > 0:14:33that mole rats live up to nine times longer
0:14:33 > 0:14:36than any other similar-sized rodent.
0:14:36 > 0:14:38Why?
0:14:38 > 0:14:42In the 1960s, more than 100 years after their discovery,
0:14:42 > 0:14:46scientists started keeping the animals in laboratories
0:14:46 > 0:14:49to try and answer that question.
0:14:49 > 0:14:51The results were confusing.
0:14:51 > 0:14:53The mole rats lived in colonies
0:14:53 > 0:14:56and only a few females ever reproduced.
0:14:57 > 0:14:58Around that time,
0:14:58 > 0:15:02an evolutionary biologist called Richard Alexander was studying
0:15:02 > 0:15:07the way colonial insects, such as termites, organised their colonies.
0:15:07 > 0:15:09They have a single breeding female
0:15:09 > 0:15:13who produces huge numbers of non-breeding workers.
0:15:13 > 0:15:15A system called eusociality.
0:15:15 > 0:15:20He speculated that if there were such things as a eusocial mammal,
0:15:20 > 0:15:24it too, like termites, would live underground in hard soil.
0:15:25 > 0:15:26He was right.
0:15:29 > 0:15:33The naked mole rat perfectly fits Alexander's description
0:15:33 > 0:15:37of what a eusocial animal should be like.
0:15:38 > 0:15:40There it is.
0:15:40 > 0:15:44It lives underground in large social groups
0:15:44 > 0:15:46and digs for tubers
0:15:46 > 0:15:48in exceptionally hard soil.
0:15:49 > 0:15:52Physically, it's evolved for a life below ground.
0:15:52 > 0:15:57It has a long, thin body with short legs that suit life in a tunnel.
0:15:57 > 0:16:00Its enlarged, strong teeth are used for digging,
0:16:00 > 0:16:04its skull is strong, the head quite large.
0:16:04 > 0:16:08Lips close behind its teeth to stop any soil going into its mouth.
0:16:08 > 0:16:14Also, it's almost entirely bald, except for a few sensory hairs.
0:16:14 > 0:16:18Could it be that these extraordinary characteristics
0:16:18 > 0:16:21have something to do with their ability
0:16:21 > 0:16:23to live very, very long lives?
0:16:25 > 0:16:29They are certainly key to the mole rat's unusual life underground.
0:16:31 > 0:16:33The queen is at the heart of the colony.
0:16:33 > 0:16:36She mates with just two or three males
0:16:36 > 0:16:39and produces babies in huge litters,
0:16:39 > 0:16:40sometimes of more than 20.
0:16:42 > 0:16:47The workers feed the queen, care for the young and guard the tunnels.
0:16:47 > 0:16:48Their role is essential -
0:16:48 > 0:16:53the colony would not survive if all its members didn't work together.
0:16:57 > 0:17:02The tubers that they eat are hard to find on the dry African plains,
0:17:02 > 0:17:05and the workers have to dig miles of tunnels in their search for them.
0:17:05 > 0:17:09The fact that they don't breed might seem hard,
0:17:09 > 0:17:11but their mother, the queen, does.
0:17:11 > 0:17:15And her DNA is virtually identical to theirs.
0:17:15 > 0:17:17And by working together,
0:17:17 > 0:17:21the colony can live in places where an individual mole rat could not.
0:17:23 > 0:17:27But this still doesn't explain why these creatures live so long.
0:17:27 > 0:17:32More recently, another adaptation to life underground threw up a clue.
0:17:33 > 0:17:37Fossil records show that mole rats started living underground
0:17:37 > 0:17:39about 24 million years ago.
0:17:39 > 0:17:42Not surprisingly, they are now highly adapted
0:17:42 > 0:17:44to a life in dark and humid tunnels.
0:17:44 > 0:17:48Conditions in a sealed, two-metre-deep tunnel system
0:17:48 > 0:17:51don't fluctuate greatly. And maybe because of this,
0:17:51 > 0:17:55mole rats have lost the ability to regulate their own body temperature.
0:17:55 > 0:17:58So, to prevent getting chilled,
0:17:58 > 0:18:01they huddle together in groups.
0:18:01 > 0:18:03They also, like reptiles, absorb heat
0:18:03 > 0:18:05by basking in the warmer,
0:18:05 > 0:18:07shallow surface tunnels.
0:18:08 > 0:18:10Being hairless might be an advantage
0:18:10 > 0:18:13for an animal that's essentially cold-blooded
0:18:13 > 0:18:15and needs to get some of its heat from its surroundings,
0:18:15 > 0:18:19and that may explain why naked mole rats are virtually bald.
0:18:21 > 0:18:26But why are not other warm-blooded mammals that live underground also bald?
0:18:26 > 0:18:29Badgers, for example, have hairy coats.
0:18:32 > 0:18:36Well, badgers come above ground to feed
0:18:36 > 0:18:39and then they need their hairy coats to keep warm.
0:18:42 > 0:18:46Naked mole rats, on the other hand, never see the light of day.
0:18:46 > 0:18:47Nonetheless, one might think
0:18:47 > 0:18:51that being soft-skinned and bald is a huge disadvantage.
0:18:51 > 0:18:54For mole rats live in stuffy, insanitary conditions.
0:18:56 > 0:18:59Mole rat colonies can contain several hundred individuals,
0:18:59 > 0:19:04and conditions underground are dark and dank and often quite toxic.
0:19:04 > 0:19:08Oxygen levels can be very low and carbon dioxide high,
0:19:08 > 0:19:11yet, mysteriously, mole rats show no discomfort
0:19:11 > 0:19:13and suffer very little from disease.
0:19:14 > 0:19:17This tolerance to such hostile conditions may also be related
0:19:17 > 0:19:21to their strange, wrinkled skin and the cells below it.
0:19:22 > 0:19:28Apparently they lack a key neurotransmitter called substance P,
0:19:28 > 0:19:32that is normally responsible for sending pain signals
0:19:32 > 0:19:34to the central nervous system.
0:19:34 > 0:19:38This may explain their ability to survive the toxic conditions
0:19:38 > 0:19:42underground without stress and damage to their bodies.
0:19:42 > 0:19:46It could also be one of the secrets of their youthful appearance,
0:19:46 > 0:19:49if you can call it that, and even their longevity.
0:19:54 > 0:20:00Most animals react strongly to pain, and this can damage their bodies.
0:20:04 > 0:20:07In mole rats, this effect is eliminated
0:20:07 > 0:20:09by cutting out the pain response.
0:20:11 > 0:20:15Incredibly, no mole rat has ever been found with cancer.
0:20:16 > 0:20:21But even if a normal animal survives disease, it still ages.
0:20:21 > 0:20:25This is largely due to other chemicals in the body
0:20:25 > 0:20:27called oxidising agents.
0:20:27 > 0:20:31They build up with time and break down the body tissues.
0:20:32 > 0:20:35This leads to the tell-tale signs of old age.
0:20:39 > 0:20:44Incredibly, mole rats appear to have no physical reaction
0:20:44 > 0:20:46to high levels of oxidising agents.
0:20:46 > 0:20:51They grow very old, yet they don't physically age.
0:20:52 > 0:20:57In wild mole rats, the queen is the most long-lived.
0:20:57 > 0:20:59And one of them, here,
0:20:59 > 0:21:01is 24 years old.
0:21:01 > 0:21:04Yet she still has the body of a two-year-old.
0:21:04 > 0:21:08No-one is sure how mole rats avoid the symptoms of old age,
0:21:08 > 0:21:12but a unique physiology, evolved in response to the underground life,
0:21:12 > 0:21:15has created an animal that is almost supernatural.
0:21:16 > 0:21:20Here's a creature that's seemingly impervious to pain
0:21:20 > 0:21:22and with an iron constitution.
0:21:22 > 0:21:26It's virtually cold-blooded, with a slow metabolism,
0:21:26 > 0:21:28and has evolved an unusual mix of strategies
0:21:28 > 0:21:31to deal with its challenging lifestyle.
0:21:31 > 0:21:34In the future, these remarkable animals may help us
0:21:34 > 0:21:38solve some of our own problems, such as pain control,
0:21:38 > 0:21:40degenerative disease
0:21:40 > 0:21:43and how we might avoid old age and wrinkly skins.
0:21:44 > 0:21:46Here is a natural curiosity
0:21:46 > 0:21:49that is well worth pursuing.
0:21:51 > 0:21:56Both elephants and mole rats remain much the same as they grow old.
0:21:56 > 0:22:00And surprisingly, the small naked mole rat lives,
0:22:00 > 0:22:03relatively speaking, even longer than the elephant.
0:22:06 > 0:22:09The narwhal lives in the cold waters of the Arctic sea.
0:22:09 > 0:22:14It's rarely seen and little is known about its life, even today.
0:22:14 > 0:22:18But 400 years ago, it was a source of myths and tall tales
0:22:18 > 0:22:22that fooled everyone, including the royal households of Europe.
0:22:24 > 0:22:28These tapestries, hanging in Stirling Castle, are modern,
0:22:28 > 0:22:32but they are accurate copies of medieval originals.
0:22:33 > 0:22:37And they show several images of that most wonderful creature -
0:22:37 > 0:22:39the unicorn.
0:22:39 > 0:22:44In the Middle Ages, the unicorn was thought to be a real animal.
0:22:44 > 0:22:47And what's more, one with magical powers.
0:22:47 > 0:22:51So, the King of Scotland incorporated one in his coat of arms,
0:22:51 > 0:22:56and that in due course was inherited by the British coat of arms
0:22:56 > 0:23:00and is shown sitting opposite the English lion.
0:23:02 > 0:23:05During the Middle Ages, it was believed
0:23:05 > 0:23:09that a unicorn horn could detect poison and neutralise it.
0:23:09 > 0:23:12So it's not surprising that most of the kings of Europe wanted
0:23:12 > 0:23:15one of these wonderful and powerful objects.
0:23:15 > 0:23:18Such treasures, however, weren't easy to come by.
0:23:19 > 0:23:24But in the 16th century, an English seaman accidentally discovered one.
0:23:24 > 0:23:29In 1576, Martin Frobisher sailed across the North Atlantic
0:23:29 > 0:23:34in search of a sea route to connect the Atlantic with the Pacific.
0:23:34 > 0:23:37And when he reached the chilly coast of northern Canada,
0:23:37 > 0:23:41he found, lying on the seashore, a unicorn's horn.
0:23:41 > 0:23:45He brought it back to Britain and soon found a buyer -
0:23:45 > 0:23:47Elizabeth I.
0:23:48 > 0:23:50This is very like the object
0:23:50 > 0:23:54that Sir Martin Frobisher presented to Queen Elizabeth.
0:23:54 > 0:23:57It's said that she paid £10,000 for it.
0:23:57 > 0:24:01In today's money, that's about half a million or more.
0:24:01 > 0:24:07Weight for weight, unicorn horn was worth more than gold.
0:24:07 > 0:24:12But the object was not what Queen Elizabeth supposed it to be.
0:24:12 > 0:24:14It was not the horn of a mythical animal,
0:24:14 > 0:24:20it was the tusk of a kind of whale that swam in the Arctic seas -
0:24:20 > 0:24:21the narwhal.
0:24:21 > 0:24:26The first examples were brought south by the Vikings.
0:24:26 > 0:24:29They almost certainly knew exactly what its origin was,
0:24:29 > 0:24:33but, for 400 years, they maintained the story
0:24:33 > 0:24:36that it came from the mythical unicorn.
0:24:38 > 0:24:41But farther south in Europe, no-one knew about narwhals,
0:24:41 > 0:24:44and scholarly natural history books
0:24:44 > 0:24:48confidently described unicorns in detail, as if they were real.
0:24:48 > 0:24:51Since unicorn horns were hard to come by,
0:24:51 > 0:24:55unscrupulous dealers met the demand by grinding up rhinoceros horn.
0:24:55 > 0:24:58In fact, the horn of a rhino and a narwhal
0:24:58 > 0:25:00could hardly be more different.
0:25:01 > 0:25:03You can see from this narwhal skull,
0:25:03 > 0:25:06the hole where the horn would normally sit.
0:25:06 > 0:25:10It grows outwards through the lip.
0:25:10 > 0:25:13But whereas rhino horn is actually made of keratin -
0:25:13 > 0:25:16the same stuff as our fingernails are made of -
0:25:16 > 0:25:21the narwhal's great horn is actually made largely of dentine.
0:25:21 > 0:25:26It's not a horn at all, it's an enormous canine tooth -
0:25:26 > 0:25:28a tusk.
0:25:29 > 0:25:32Some female narwhals possess tusks,
0:25:32 > 0:25:36but by and large male narwhals grow the long tusks
0:25:36 > 0:25:38which can reach three metres in length.
0:25:38 > 0:25:41It's been described as a cross between
0:25:41 > 0:25:43a corkscrew and a jousting lance.
0:25:43 > 0:25:47But its true purpose has baffled scientists for centuries.
0:25:49 > 0:25:51Very few creatures have tusks.
0:25:51 > 0:25:53The most well-known, of course, are elephants.
0:25:54 > 0:25:58Their tusks are in fact enlarged incisor teeth.
0:25:58 > 0:26:01Both male and female elephants develop them
0:26:01 > 0:26:05and they're used in many ways, but primarily for getting food -
0:26:05 > 0:26:09digging into the ground, ripping up grass or pushing over trees.
0:26:11 > 0:26:14The obvious difference between elephant and narwhal tusks
0:26:14 > 0:26:19is that the narwhal possesses just one, whereas the elephant has two.
0:26:19 > 0:26:22But that may not always have been the case.
0:26:22 > 0:26:24This is a rare curiosity indeed.
0:26:24 > 0:26:28It's the skull of a narwhal with two tusks.
0:26:28 > 0:26:31It's possible that such a rarity offers a window on the past.
0:26:31 > 0:26:36Perhaps the ancient ancestors of the narwhals were once twin-tusked,
0:26:36 > 0:26:38but over time, they lost one.
0:26:39 > 0:26:41But what was it for?
0:26:41 > 0:26:45One early suggestion was that the narwhal used it to spear fish.
0:26:45 > 0:26:48Though how it would manage to transfer its catch
0:26:48 > 0:26:51from the end of its tusk to its mouth was never explained.
0:26:52 > 0:26:56Someone else suggested that the animal used its horn
0:26:56 > 0:26:58to stab holes through the Arctic ice.
0:26:58 > 0:26:59That's not unreasonable,
0:26:59 > 0:27:02since narwhals spend a lot of time under ice,
0:27:02 > 0:27:06and being mammals, they have to get to air in order to breathe.
0:27:06 > 0:27:09But it seems strange that only males have a tusk.
0:27:09 > 0:27:12After all, females need to breathe too.
0:27:12 > 0:27:16Charles Darwin had another explanation.
0:27:16 > 0:27:19He likened the tusk to the antlers carried by male deer -
0:27:19 > 0:27:21stags.
0:27:23 > 0:27:28Antlers help stags to establish hierarchies during the mating season.
0:27:28 > 0:27:31This stag with the biggest antlers asserts his dominance
0:27:31 > 0:27:34by showing them off and occasionally fighting with them.
0:27:39 > 0:27:42Darwin proposed that the long tusk of the narwhal
0:27:42 > 0:27:44functioned in just the same way -
0:27:44 > 0:27:49as a declaration of dominance and, if necessary, as a weapon.
0:27:49 > 0:27:53That would explain why male narwhals possess the long tusks.
0:27:54 > 0:27:56And why, when males meet,
0:27:56 > 0:28:01they sometimes cross tusks in what might be a ritualised form of combat.
0:28:06 > 0:28:08Darwin's theory has long been accepted.
0:28:08 > 0:28:13But recently, scientists have been exploring other possibilities.
0:28:13 > 0:28:16Our teeth are covered with a thick enamel layer
0:28:16 > 0:28:19that protects the softer material beneath.
0:28:19 > 0:28:22If that erodes or is damaged,
0:28:22 > 0:28:24then it exposes the nerves within the tooth
0:28:24 > 0:28:28which can make them extremely sensitive to temperature.
0:28:28 > 0:28:34Narwhal tusks don't possess that external enamel covering.
0:28:34 > 0:28:38And high-magnification photography has revealed something
0:28:38 > 0:28:43very unusual about the exterior surface of this huge elongated tooth.
0:28:44 > 0:28:48The surface of the tusk is cratered with millions of tiny pits
0:28:48 > 0:28:54called tubules. Each tubule contains a fluid, and at its base, a nerve.
0:28:54 > 0:28:58The fluid reacts to the narwhal's environment,
0:28:58 > 0:29:00so the tusk must be highly sensitive.
0:29:03 > 0:29:07Tests on narwhals have shown that they can detect tiny changes
0:29:07 > 0:29:09in the temperature and salinity of water,
0:29:09 > 0:29:12key factors that govern the formation of ice.
0:29:14 > 0:29:17Their migration is tied to the seasonal shrinking
0:29:17 > 0:29:19and expanding of the ice cap.
0:29:19 > 0:29:24So perhaps the tusk plays a role in detecting ice or open water.
0:29:26 > 0:29:29But its sensory powers could be even greater.
0:29:29 > 0:29:34Perhaps the tusk is able to detect movement in the water.
0:29:34 > 0:29:37Or even changes in the fertility of female narwhals.
0:29:37 > 0:29:40These are theories yet to be tested.
0:29:42 > 0:29:44If this is a sensory tool,
0:29:44 > 0:29:48then it would put a very different interpretation on the male jousting.
0:29:48 > 0:29:52Perhaps males enjoy rubbing their tusks together.
0:29:52 > 0:29:57There could be a third explanation, a more practical one.
0:29:57 > 0:30:01Tusks from old narwhals often become coated with algae,
0:30:01 > 0:30:04which might block the pores that lead to the nerves.
0:30:04 > 0:30:09So, perhaps males rub their tusks together to help clean them.
0:30:10 > 0:30:14Could this be not fighting, but cooperative grooming?
0:30:16 > 0:30:20Why mainly male narwhals carry a sensory tool is still unexplained.
0:30:22 > 0:30:23Rather than being a weapon,
0:30:23 > 0:30:28perhaps the highly sensitive tusk helps males to find female partners.
0:30:29 > 0:30:32More than likely, the tusk serves many functions.
0:30:32 > 0:30:34But why should it be twisted?
0:30:36 > 0:30:38The twist increases the surface area,
0:30:38 > 0:30:42so it's possible more nerve endings are exposed.
0:30:42 > 0:30:45And this would increase its sensitivity.
0:30:45 > 0:30:49But there's another theory that suggests that the twist
0:30:49 > 0:30:52actually helps to keep the tusk straight.
0:30:52 > 0:30:54That may sound counterintuitive,
0:30:54 > 0:30:59but tusks of other large animals tend to curve down or up.
0:30:59 > 0:31:03A spiral growth may actually help the tusk to keep pointing forwards,
0:31:03 > 0:31:06and so reduce drag in the water.
0:31:07 > 0:31:11There's another way in which a twist could help in swimming.
0:31:11 > 0:31:15As the animal moves forward, the water around the tusk
0:31:15 > 0:31:19spirals away from it in a way that might reduce drag.
0:31:21 > 0:31:25But at least today we know the true identity of the animals
0:31:25 > 0:31:29that produce these wonderful and spectacular ivory spears.
0:31:34 > 0:31:39The myth that they came from the unicorn was finally exploded in 1638
0:31:39 > 0:31:42by a Danish scientist, Ole Worm,
0:31:42 > 0:31:46who gave a public lecture proving conclusively
0:31:46 > 0:31:48that they came from the narwhal.
0:31:48 > 0:31:51So then, of course, their value plummeted.
0:31:51 > 0:31:55Today, we no longer believe they have magical properties,
0:31:55 > 0:31:59but there's still quite a lot about them we don't fully understand.
0:32:05 > 0:32:08Our second subject belongs to a group of animals
0:32:08 > 0:32:10that have taken the spiral
0:32:10 > 0:32:14and adapted it into a multitude of variations -
0:32:14 > 0:32:15snails.
0:32:21 > 0:32:26When the first snails crawled out of the sea and up onto dry land,
0:32:26 > 0:32:28they carried with them the shells
0:32:28 > 0:32:32that were to be crucial to their survival out of water.
0:32:32 > 0:32:34They themselves were distant relatives
0:32:34 > 0:32:38of other shelled creatures that had dominated the seas
0:32:38 > 0:32:40for millions of years.
0:32:40 > 0:32:42They were the ammonites.
0:32:42 > 0:32:47This is one of them, and this is about 160 million years old.
0:32:47 > 0:32:52Although they experimented in some degree with the shape of the shell,
0:32:52 > 0:32:54nearly all of them are like this -
0:32:54 > 0:32:55flat,
0:32:55 > 0:32:57spiral
0:32:57 > 0:32:59and symmetrical.
0:33:00 > 0:33:05In due course, the ammonites themselves became extinct.
0:33:05 > 0:33:09But since then, other creatures have developed the shell
0:33:09 > 0:33:13into a whole variety of different shapes and sizes.
0:33:17 > 0:33:21This variety shows how successful the spiral can be
0:33:21 > 0:33:24as the basis for a shell's design.
0:33:26 > 0:33:30And how it can be elaborated and decorated.
0:33:35 > 0:33:38Snail shells, like the shells of birds' eggs,
0:33:38 > 0:33:41are made of calcium carbonate.
0:33:41 > 0:33:44They appear at the very beginning of a young snail's life,
0:33:44 > 0:33:49and they are never shed, but simply become enlarged as the animal grows.
0:33:51 > 0:33:55But whatever their shape and size, they are almost always spiralled.
0:33:56 > 0:34:00Spirals have been used by animals for a very long time.
0:34:00 > 0:34:03We can trace them back to a group of sea creatures
0:34:03 > 0:34:07that first appeared around 500 million years ago.
0:34:07 > 0:34:08And some are still around today.
0:34:08 > 0:34:10This is one - the nautilus.
0:34:11 > 0:34:16Today, it's only found in the deep waters of the Indo-Pacific ocean.
0:34:16 > 0:34:20But millions of years ago, animals like it were widespread.
0:34:20 > 0:34:24Its earliest ancestors, however, had a very different shape.
0:34:25 > 0:34:28There's evidence that the nautiloids started out
0:34:28 > 0:34:31more or less straight, like this one,
0:34:31 > 0:34:33just a little curl at the beginning,
0:34:33 > 0:34:35and then running straight like that,
0:34:35 > 0:34:38with the separate chambers running along there.
0:34:38 > 0:34:41But as millions of years passed,
0:34:41 > 0:34:45they began to coil until they became species like this one.
0:34:47 > 0:34:49And then, millions of years later,
0:34:49 > 0:34:52another group adopted the symmetrical coil.
0:34:52 > 0:34:55These were called ammonites.
0:34:56 > 0:34:59But why did these animals coil their shells?
0:35:01 > 0:35:05Well, if their shells remained straight as they increased in size,
0:35:05 > 0:35:08they would inevitably become somewhat cumbersome.
0:35:09 > 0:35:14Coiling them made them more compact and perhaps more mobile.
0:35:16 > 0:35:20Whatever the reason, the change in shell shape was a great success.
0:35:22 > 0:35:26Thousands of new species appeared, all with coiled shells.
0:35:28 > 0:35:30These fossilised shells tell us little
0:35:30 > 0:35:33about the soft-bodied creatures that lived in them,
0:35:33 > 0:35:37but the living nautilus can give us some clues about that.
0:35:40 > 0:35:44At the start of its life, the shell consists of just a few chambers.
0:35:44 > 0:35:46But by the time it's mature,
0:35:46 > 0:35:49there may be as many as 30.
0:35:50 > 0:35:54Richard Owen, the founding director of London's Natural History Museum,
0:35:54 > 0:35:59wrote the first full description of the nautilus.
0:35:59 > 0:36:02This is Owen's own personal copy,
0:36:02 > 0:36:05and it's full of exquisite sketches.
0:36:05 > 0:36:11His drawings show just how the animal is placed inside a shell.
0:36:11 > 0:36:15Almost all the soft tissues - its body and tentacles -
0:36:15 > 0:36:17are held in the outermost chamber.
0:36:17 > 0:36:19And a long tube, called a siphuncle,
0:36:19 > 0:36:22runs through the chambers,
0:36:22 > 0:36:26through which the animal can pump in water or remove it,
0:36:26 > 0:36:29and so regulates its buoyancy.
0:36:30 > 0:36:32So, the nautilus's spiral shell
0:36:32 > 0:36:35not only protects its soft body from enemies,
0:36:35 > 0:36:38but enables it to cruise around.
0:36:38 > 0:36:43And it's so strong that the nautilus can descend as deep as 700 metres,
0:36:43 > 0:36:46where pressure would kill a human being.
0:36:46 > 0:36:48At the peak of their success,
0:36:48 > 0:36:51there were thousands of different kinds of nautiloids.
0:36:51 > 0:36:55But their cousins, the ammonites, were even more varied and diverse.
0:36:57 > 0:37:00Their buoyant shells allowed some of these creatures
0:37:00 > 0:37:03to grow to a huge size.
0:37:08 > 0:37:11Some were as big as a human being.
0:37:11 > 0:37:16But it would be impossible for such a creature to move out of water
0:37:16 > 0:37:20with a shell like this. It would be far too heavy and too cumbersome.
0:37:20 > 0:37:24Nonetheless, something was about to happen to the molluscs
0:37:24 > 0:37:29that would allow them to leave the water and move up onto land.
0:37:31 > 0:37:33The ammonite dynasties were developing
0:37:33 > 0:37:35different shapes to their shells,
0:37:35 > 0:37:38uncoiling them in all sorts of ways.
0:37:39 > 0:37:41Some of these new forms fed on the sea floor
0:37:41 > 0:37:44and therefore had less need to be mobile.
0:37:44 > 0:37:49But other shelled relatives of the ammonites were going even further,
0:37:49 > 0:37:53changing both their shell shape and twisting their soft bodies.
0:37:54 > 0:37:57And these are their descendants -
0:37:57 > 0:37:58snails.
0:38:00 > 0:38:02The problem with a symmetrical shell
0:38:02 > 0:38:05is that each whorl has to grow
0:38:05 > 0:38:07on the outside of the other one,
0:38:07 > 0:38:11so that the shell very quickly becomes very big.
0:38:11 > 0:38:13But by becoming asymmetrical,
0:38:13 > 0:38:16and offsetting each whorl to the side,
0:38:16 > 0:38:19the shell can remain much more compact
0:38:19 > 0:38:22and rounded and easier to manipulate.
0:38:24 > 0:38:28The shift in the snail's symmetry seems to have been triggered
0:38:28 > 0:38:30by the action of a single gene.
0:38:33 > 0:38:36But this change can bring complications.
0:38:38 > 0:38:40Because of their asymmetric shape,
0:38:40 > 0:38:43snails have to position themselves carefully during mating.
0:38:46 > 0:38:48In most snails, this is not a problem,
0:38:48 > 0:38:51as the body plan of snails is usually the same.
0:38:51 > 0:38:53But not all.
0:38:56 > 0:38:59Just like humans, who are either right-handed or left-handed,
0:38:59 > 0:39:01snail shells can twist
0:39:01 > 0:39:04to the left...
0:39:04 > 0:39:05or the right.
0:39:05 > 0:39:09The vast majority of snail shells are right spiralling.
0:39:09 > 0:39:14But in one particular area of Japan, the left-handed form
0:39:14 > 0:39:18of this particular species has a clear advantage.
0:39:19 > 0:39:23That is all because of this creature, a snail-eating snake.
0:39:23 > 0:39:26It's so specialised for eating snails
0:39:26 > 0:39:30that its jaws have evolved to become asymmetrical, just like its prey.
0:39:30 > 0:39:34The right side of its lower jaw has more teeth than the left.
0:39:35 > 0:39:41Recently, scientists in Japan filmed the hunting behaviour of this snake.
0:39:41 > 0:39:45When it attacks a snail with a right spiral shell,
0:39:45 > 0:39:48its row of extra teeth dig into the snail's flesh,
0:39:48 > 0:39:51and by moving its jaws back and forth,
0:39:51 > 0:39:54it separates the snail's body from its shell.
0:39:56 > 0:39:59But attacking a snail with a left-spiralled shell
0:39:59 > 0:40:01is not so straightforward.
0:40:01 > 0:40:05The position of the shell means that the snake can't use
0:40:05 > 0:40:07its specialised jaws so effectively.
0:40:07 > 0:40:09And it gives up.
0:40:14 > 0:40:19Shells help land-living snails to conserve moisture
0:40:19 > 0:40:21and also protect them from their enemies.
0:40:23 > 0:40:27The snails' soft bodies are, of course, welcome meals
0:40:27 > 0:40:31to any predator that can crack their shells.
0:40:35 > 0:40:38Some snails have strengthened their shells.
0:40:40 > 0:40:42Some have protected them with spines.
0:40:45 > 0:40:47Others have become very thick indeed,
0:40:47 > 0:40:49and almost uncrackable.
0:40:51 > 0:40:56Some scientists believe that this could be the golden age of the snail.
0:40:57 > 0:41:00They've never been more diverse, in terms of species
0:41:00 > 0:41:02or indeed the variety of their shells.
0:41:04 > 0:41:07But while the snails are more varied,
0:41:07 > 0:41:09that is not the case with the nautilus.
0:41:09 > 0:41:13The oceans were once dominated by creatures like this,
0:41:13 > 0:41:16and today, just a handful of different types exist.
0:41:18 > 0:41:23While snails have taken the spiral and modified it endlessly,
0:41:23 > 0:41:26the modern nautilus has stuck with a symmetrical spiral
0:41:26 > 0:41:30that's hardly changed for hundreds of millions of years.
0:41:30 > 0:41:32So it's fair to say
0:41:32 > 0:41:36that the nautilus shell is a window on the distant past,
0:41:36 > 0:41:39to a time when the simple, but symmetrical, spiral
0:41:39 > 0:41:41dominated the seas.
0:41:43 > 0:41:47So, both whales and snails have benefited from the twist,
0:41:47 > 0:41:51a design that first appeared 500 million years ago
0:41:51 > 0:41:53and is still widespread today.