0:00:02 > 0:00:06The natural world is full of extraordinary animals,
0:00:06 > 0:00:09with amazing life histories.
0:00:09 > 0:00:12Yet certain stories are more intriguing than most.
0:00:16 > 0:00:19The mysteries of a butterfly's life cycle,
0:00:19 > 0:00:22or 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.
0:00:30 > 0:00:33And some have only recently revealed their secrets.
0:00:35 > 0:00:39These are the animals that stand out from the crowd.
0:00:39 > 0:00:42The curiosities I find most fascinating of all.
0:00:51 > 0:00:55Orang-utans have an extraordinary ability to use tools.
0:00:55 > 0:01:00But the full extent of their skills remained undiscovered for centuries.
0:01:01 > 0:01:04Surprisingly, crows also make tools.
0:01:07 > 0:01:10How and why have these two very different animals
0:01:10 > 0:01:12become so inventive?
0:01:18 > 0:01:20And also, in this programme,
0:01:20 > 0:01:24salamanders can regenerate entire legs and tails
0:01:24 > 0:01:26to replace ones that they lose.
0:01:29 > 0:01:34And moose can regrow their enormous antlers every year.
0:01:36 > 0:01:40How do these animals regenerate entire body parts,
0:01:40 > 0:01:43and why isn't it possible for all animals to do the same?
0:01:55 > 0:01:59When I first saw orang-utans that have been raised in captivity
0:01:59 > 0:02:02using tools, I was truly astonished.
0:02:03 > 0:02:07They were extraordinarily skilful at imitating the things we do.
0:02:12 > 0:02:15But, at the time, some skills had never been observed
0:02:15 > 0:02:17among wild orang-utans.
0:02:20 > 0:02:24So, are these apes just clever mimics?
0:02:24 > 0:02:26Or do they ever make and use tools in the wild?
0:02:28 > 0:02:32We didn't know the answers to such questions until quite recently.
0:02:34 > 0:02:38This dramatic sculpture, by the French artist
0:02:38 > 0:02:39Emmanuel Fremiet,
0:02:39 > 0:02:44entitled 'An Orang-utan Strangling A Borneo Native',
0:02:44 > 0:02:48represents the image people have of this formidable giant ape.
0:02:48 > 0:02:51It's pretty accurate, as Fremiet studied live orangs
0:02:51 > 0:02:53at the Jardin des Plantes in Paris,
0:02:53 > 0:02:56and you can see why orangs are so-called.
0:02:56 > 0:02:59The name, in Malay, means all 'orang' - people,
0:02:59 > 0:03:01and 'hutan' - of the forest.
0:03:04 > 0:03:07At first, orang-utans were feared and misunderstood.
0:03:09 > 0:03:12Early explorers thought that these long-armed, tree-living apes
0:03:12 > 0:03:14were degenerate human beings,
0:03:14 > 0:03:16and for centuries their true nature
0:03:16 > 0:03:19and behaviour in the wild was largely unknown.
0:03:23 > 0:03:27Orang-utans are only found in the rainforests of Indonesia.
0:03:27 > 0:03:29One population in Borneo,
0:03:29 > 0:03:31and another slightly different one
0:03:31 > 0:03:34in the island of Sumatra, to the west.
0:03:36 > 0:03:39They have strong, dextrous hands and feet,
0:03:39 > 0:03:42and a very mobile mouth, that enable them to break open
0:03:42 > 0:03:46and eat the fruits on which they depend.
0:03:46 > 0:03:48But although they're clearly very intelligent,
0:03:48 > 0:03:51the only tools they seemed to use were sticks,
0:03:51 > 0:03:54which they wielded in a very simple way.
0:03:56 > 0:04:01Yet, in Africa, chimpanzees had been seen using tools
0:04:01 > 0:04:02in a rather more complex fashion.
0:04:05 > 0:04:08Back in 1871, Darwin had reported
0:04:08 > 0:04:11wild chimpanzees cracking open
0:04:11 > 0:04:13walnut-like fruits with stones.
0:04:15 > 0:04:19And in the 1960s, they were even seen the modifying sticks
0:04:19 > 0:04:21with which they fished for termites.
0:04:23 > 0:04:25It seemed strange that,
0:04:25 > 0:04:29while wild chimps used tools in a quite complicated way,
0:04:29 > 0:04:31orang-utans apparently did not.
0:04:35 > 0:04:39Orangs, unlike chimps, are not very sociable.
0:04:39 > 0:04:41Individuals are largely solitary.
0:04:42 > 0:04:45The males have large, individual territories,
0:04:45 > 0:04:48within which several females have their own home ranges.
0:04:52 > 0:04:56This more solitary way of life affects the way orangs
0:04:56 > 0:04:59share their knowledge and develop their skills.
0:05:01 > 0:05:03The most social time of an orang-utan's life
0:05:03 > 0:05:05is when it's a baby.
0:05:05 > 0:05:06And in the wild,
0:05:06 > 0:05:08youngsters stay with their mothers
0:05:08 > 0:05:11for the first six years of their lives.
0:05:11 > 0:05:14During this time, they learn the skills needed to
0:05:14 > 0:05:16survive in the forest alone.
0:05:16 > 0:05:19The need to know how to climb, build nests,
0:05:19 > 0:05:23and how to solve problems such as breaking into tough food.
0:05:23 > 0:05:27And their large brains certainly help them to master these tasks.
0:05:31 > 0:05:34So, a young orang behaves like its mother,
0:05:34 > 0:05:38and copies the way she searches for food and prepares it to eat.
0:05:40 > 0:05:44In captivity, they readily make tools to reach food,
0:05:44 > 0:05:46or to escape from their enclosures.
0:05:46 > 0:05:48They're clearly very inventive
0:05:48 > 0:05:52and good at developing ways to solve particular problems.
0:05:53 > 0:05:58So, it was a puzzle as to why such bright and capable apes
0:05:58 > 0:06:01were apparently not behaving in a similar way in the wild.
0:06:05 > 0:06:08Orangs are clever and physically dextrous.
0:06:08 > 0:06:12They've very strong jaws and mobile hands and feet,
0:06:12 > 0:06:16and in the wild they can reach and prise open most food.
0:06:16 > 0:06:19It was assumed for many years that, even though they used
0:06:19 > 0:06:23tools in captivity, they didn't perhaps need to do so in the wild.
0:06:25 > 0:06:29It seems that, strangely, these great apes have more skills
0:06:29 > 0:06:32than they normally need for their lives in the wild.
0:06:35 > 0:06:39It wasn't until 1964 that orangs were studied in detail.
0:06:40 > 0:06:44A Lithuanian scientist from Canada called Birute Galdikas
0:06:44 > 0:06:47settled in Borneo to live alongside these great apes.
0:06:48 > 0:06:52For over 30 years, she watched both tame orangs
0:06:52 > 0:06:54and wholly wild ones in the forests.
0:06:56 > 0:06:59In her camp, she found that the tame ones quickly discovered how
0:06:59 > 0:07:04to use tools in a relatively sophisticated way.
0:07:04 > 0:07:07But in the wild she only saw them build nests
0:07:07 > 0:07:09and use sticks in a simple fashion.
0:07:12 > 0:07:14That picture of the character
0:07:14 > 0:07:18and abilities of orangs remained unchanged for long time.
0:07:21 > 0:07:26Then, in 1994, our understanding of orangs changed radically.
0:07:28 > 0:07:32A group of Swiss scientists observed some orangs that were
0:07:32 > 0:07:34behaving very differently.
0:07:36 > 0:07:40They lived several hundred miles away from their Borneo cousins,
0:07:40 > 0:07:43in swampy rainforests on the island of Sumatra.
0:07:47 > 0:07:50The orangs' diet is about 90% fruit.
0:07:50 > 0:07:52And this is one of their favourites.
0:07:52 > 0:07:55It's a durian and it's well known...
0:07:55 > 0:07:58for its pungent smell.
0:07:58 > 0:08:01As you can see, it's got a very spiky case.
0:08:01 > 0:08:04But orangs are able to break it open and reach the soft,
0:08:04 > 0:08:06pulpy flesh inside.
0:08:07 > 0:08:12But it's when they tackle another similar spiky fruit called neesia,
0:08:12 > 0:08:14which is more difficult to open,
0:08:14 > 0:08:19that scientists got their first glimpse of orangs making tools.
0:08:19 > 0:08:22Neesia presents an extra challenge because inside,
0:08:22 > 0:08:25it contains rich, nutritious seeds
0:08:25 > 0:08:29which are embedded in a mass of sharp, needlelike hairs.
0:08:31 > 0:08:34To avoid touching these irritating hairs,
0:08:34 > 0:08:39the swamp-living orangs slid sticks into cracks in the food husks.
0:08:39 > 0:08:42Then they push them up and down to flick out the hairs
0:08:42 > 0:08:43and free the seeds.
0:08:45 > 0:08:47They also modified sticks
0:08:47 > 0:08:50so that they fitted different sized cracks in the fruits.
0:08:53 > 0:08:57The particular fruit that grew in these wet forests had stimulated
0:08:57 > 0:09:00the Sumatran orangs to make and use special tools.
0:09:05 > 0:09:07Unusually, for such solitary creatures,
0:09:07 > 0:09:10they gathered at these rich feeding areas in a group,
0:09:10 > 0:09:14and feeding close to one another, they shared their skills.
0:09:16 > 0:09:20So now it was realised that orangs were not just mimics.
0:09:20 > 0:09:22They were able to invent their own ways of making
0:09:22 > 0:09:25and using tools, just like chimps.
0:09:31 > 0:09:34We have long known that captive orangs can quickly work out
0:09:34 > 0:09:37ways to solve problems.
0:09:37 > 0:09:40And now, it was clear that wild orangs are no different.
0:09:44 > 0:09:46In recent years, they've been seen
0:09:46 > 0:09:49using sticks to fish for termites and honey
0:09:49 > 0:09:52in much the same way as individuals do in captivity.
0:09:56 > 0:09:57In the flooded forests,
0:09:57 > 0:10:01many insects are forced above ground to live in tree holes.
0:10:01 > 0:10:04So the orangs use sticks to extract them.
0:10:06 > 0:10:09It seems incredible that tool use in wild orangs
0:10:09 > 0:10:11took hundreds of years to discover.
0:10:14 > 0:10:16In fact, it had been happening all the time,
0:10:16 > 0:10:18just hidden away from view.
0:10:20 > 0:10:23These red men and women of the forest
0:10:23 > 0:10:26have very dextrous hands and feet,
0:10:26 > 0:10:29strong jaws and a large brain.
0:10:29 > 0:10:33In the wild, they have little need for complex tools,
0:10:33 > 0:10:36and being solitary means that tool use
0:10:36 > 0:10:38is not usually shared or spread.
0:10:38 > 0:10:42But even as loners, they are inventive
0:10:42 > 0:10:44and can work out how to solve problems.
0:10:44 > 0:10:49Here is a creature that could be one of the greatest tool users
0:10:49 > 0:10:51in the animal kingdom.
0:10:53 > 0:10:56Orang-utan tool use was not discovered for many years.
0:10:58 > 0:11:02Next, meet the clever crow that also makes tools.
0:11:03 > 0:11:08How have crows' curious minds helped them become so inventive?
0:11:16 > 0:11:20The most famous members of the crow family in Britain
0:11:20 > 0:11:24are the ravens that live here in the Tower of London.
0:11:24 > 0:11:27By tradition, they protect the Crown.
0:11:27 > 0:11:29And they are recruited
0:11:29 > 0:11:33and indeed dismissed from the British Army, just like soldiers.
0:11:34 > 0:11:37In 1986, one of them, called George,
0:11:37 > 0:11:41had to be exiled to Wales for persistent bad behaviour
0:11:41 > 0:11:45in destroying the television aerials around here.
0:11:45 > 0:11:47And more recently, another one,
0:11:47 > 0:11:49noticing that one of its fellows had died
0:11:49 > 0:11:52and was attracting a great deal of attention,
0:11:52 > 0:11:54also lay down on the ground feigning death.
0:11:54 > 0:11:58And when the raven master came over to see what the matter was,
0:11:58 > 0:11:59he got a sharp peck.
0:12:00 > 0:12:04Well, stories like those suggest that members of the crow family
0:12:04 > 0:12:08have minds rather different from other birds.
0:12:12 > 0:12:17Ravens are cheeky, self-aware and socially intelligent.
0:12:21 > 0:12:24They're part of the big crow family that, in Britain, includes
0:12:24 > 0:12:28hooded and carrion crows, jackdaws, jays, chuffs and magpies.
0:12:33 > 0:12:36Their brains are twice as large as other birds'
0:12:36 > 0:12:39and, relative to body size, comparable to a chimpanzee's.
0:12:42 > 0:12:45This extra brain capacity has helped them
0:12:45 > 0:12:47become very good at solving problems.
0:12:55 > 0:12:57Here is Bran the raven,
0:12:57 > 0:13:01and I've put a screen in front of his cage,
0:13:01 > 0:13:03so he can't see what is going on.
0:13:03 > 0:13:07And this is Bran's stone.
0:13:07 > 0:13:10He's had it since he was a chick,
0:13:10 > 0:13:15and he can recognise it amongst a whole pile of other pebbles.
0:13:15 > 0:13:19Now, I've put a few of a similar size on this grid,
0:13:19 > 0:13:22and I'll put his stone just there.
0:13:22 > 0:13:25And now, we'll see whether he can find it.
0:13:28 > 0:13:30Bran, where's your stone?
0:13:35 > 0:13:37Immediately. Well done!
0:13:39 > 0:13:41The only explanation of this
0:13:41 > 0:13:46is that he has an extremely acute visual memory.
0:13:46 > 0:13:48Indeed he has.
0:13:52 > 0:13:56You could say that by putting stones on a gridded square like that,
0:13:56 > 0:14:00that makes each one very obvious. All right.
0:14:00 > 0:14:02Well, let's make things a little more difficult.
0:14:02 > 0:14:07This is his stone and I'll put it in this pile of stones
0:14:07 > 0:14:10so that he can only see just a little tip of it.
0:14:12 > 0:14:15Now, Bran. Where's your stone?
0:14:17 > 0:14:18Oh, come on.
0:14:18 > 0:14:22HE LAUGHS
0:14:22 > 0:14:24Fantastic. Thank you very much.
0:14:27 > 0:14:32And this ability to recognise a little small detail
0:14:32 > 0:14:36is used by these birds when they cache food.
0:14:36 > 0:14:39In the good times, they will hide hundreds of different
0:14:39 > 0:14:44pieces of food and conceal them, and remember every one.
0:14:44 > 0:14:48And come back to it in the hard times to pick up that piece of food.
0:14:48 > 0:14:51Extraordinary. You're an amazing bird, Bran.
0:14:53 > 0:14:56Another species of crow, Clark's Nutcracker,
0:14:56 > 0:14:59is a champion at caching food.
0:15:00 > 0:15:05It collects and hides up to 33,000 seeds every season,
0:15:05 > 0:15:09and remembers where each one is put for up to nine months.
0:15:10 > 0:15:12It can even find them under snow.
0:15:15 > 0:15:19Crows also remember the kind of food that they have hidden.
0:15:19 > 0:15:22Freshly buried grubs perish quickly
0:15:22 > 0:15:25so need to be recovered sooner than seeds.
0:15:27 > 0:15:28The ability to think ahead
0:15:28 > 0:15:34and anticipate future events can also help in other situations.
0:15:34 > 0:15:37Other birds will steal buried food if they can find it,
0:15:37 > 0:15:40but some kinds of crows are able to recognise these thieves
0:15:40 > 0:15:42and outwit them.
0:15:44 > 0:15:47Recent research at Cambridge has revealed that scrub jays
0:15:47 > 0:15:51take great care in how they hide their food.
0:15:53 > 0:15:57One jay is given the choice of two locations in which to cache food.
0:15:57 > 0:16:01Under stones which make a noise if they are moved,
0:16:01 > 0:16:05or soil which can be cleared away quietly.
0:16:05 > 0:16:09In the cage next door, another scrub jay watches.
0:16:09 > 0:16:11He is a potential thief.
0:16:14 > 0:16:18When the caching jay knows that its neighbour can see,
0:16:18 > 0:16:20it buries its food under stones.
0:16:22 > 0:16:26If the jay next door attempts to steal that buried food,
0:16:26 > 0:16:29the noisy stones will act like a burglar alarm.
0:16:31 > 0:16:33But when the screen is added,
0:16:33 > 0:16:36so that the neighbouring jay can only hear what's happening,
0:16:36 > 0:16:39the caching jay changes its plan.
0:16:39 > 0:16:42This time it decides to bury its food under soil,
0:16:42 > 0:16:44which makes hardly any noise,
0:16:44 > 0:16:48so its location remains unknown to the jay next door.
0:16:54 > 0:16:56For centuries, members of the crow family
0:16:56 > 0:16:59have been recognised to be unusual birds.
0:17:01 > 0:17:05Their noisy gatherings gave them a sinister reputation.
0:17:05 > 0:17:07But their intelligence was legendary.
0:17:11 > 0:17:14In one of Aesop's Fables, a clever crow
0:17:14 > 0:17:16drops pebbles into a jug of water
0:17:16 > 0:17:19to raise the level high enough so that it can drink.
0:17:19 > 0:17:22This is perhaps one of the first recorded examples
0:17:22 > 0:17:24of a crow using a tool.
0:17:26 > 0:17:30Here, once again, is Bran the raven.
0:17:30 > 0:17:35And like the crow in Aesop's fable, he is extremely intelligent
0:17:35 > 0:17:37and clever at collecting food.
0:17:37 > 0:17:40I'm going to set him a problem, which he has seen before,
0:17:40 > 0:17:44and for which he produced his own solution.
0:17:44 > 0:17:47I'm going to take a little bit of meat,
0:17:47 > 0:17:51put it in this plastic bottle and then just to make it
0:17:51 > 0:17:56difficult for him, I'm going to crush the bottle.
0:17:58 > 0:18:01So that it won't come out just by shaking it.
0:18:01 > 0:18:03Now, then, Bran.
0:18:03 > 0:18:05How are you going to get that out?
0:18:16 > 0:18:21HE LAUGHS
0:18:21 > 0:18:23What he did was to take this bottle,
0:18:23 > 0:18:25put it in the water,
0:18:25 > 0:18:28and use the water to swill it out and collect the bit.
0:18:28 > 0:18:30And he did that in about 10 seconds flat.
0:18:36 > 0:18:39Bran, in effect, used the water as a tool.
0:18:41 > 0:18:44And he is very quick to understand the potential of any object
0:18:44 > 0:18:48and work out how it might help solve one of his problems.
0:18:51 > 0:18:55All crows, it seems, have extraordinary memories,
0:18:55 > 0:18:59acute vision and great ingenuity in devising tools.
0:19:03 > 0:19:07In New Caledonia, a tropical island east of Australia,
0:19:07 > 0:19:11wild crows use tools just as expertly and inventively as apes.
0:19:16 > 0:19:19They fashion sticks to tease grubs out from places
0:19:19 > 0:19:21they would otherwise find impossible to reach.
0:19:26 > 0:19:29More recently, scientists discovered
0:19:29 > 0:19:35and filmed crows that had taken their tool making a stage further.
0:19:35 > 0:19:37They were creating hooks,
0:19:37 > 0:19:42by carefully modifying the thick ends of twigs.
0:19:42 > 0:19:44This seemed extraordinary.
0:19:45 > 0:19:48But there were more surprises.
0:19:48 > 0:19:51On the nearby island of Grand Terre,
0:19:51 > 0:19:55the crows were making even more sophisticated implements.
0:19:59 > 0:20:03These are the actual tools made by New Caledonian crows.
0:20:03 > 0:20:06They are constructed from the leaves of the pandanus tree,
0:20:06 > 0:20:10which have lines of sharp spikes along their margins.
0:20:10 > 0:20:14And the crows use them to winkle insects out of crevices.
0:20:14 > 0:20:19But each population of these crows makes the tool in their own way.
0:20:20 > 0:20:24This one is a broad strip,
0:20:24 > 0:20:28this one a very thin strip,
0:20:28 > 0:20:32and these two, which come from the north of the island,
0:20:32 > 0:20:34are used by two different populations.
0:20:34 > 0:20:39One makes a two-step tool, thin at the end.
0:20:39 > 0:20:43And this one makes a one, two, three-step tool.
0:20:46 > 0:20:47In this rare footage,
0:20:47 > 0:20:50the crow strips off the serrated edge of a leaf.
0:20:53 > 0:20:57The series of small spines are better than just a single hook,
0:20:57 > 0:21:00because they can snag an insect along all its length.
0:21:07 > 0:21:11Each population of the crows have their own design,
0:21:11 > 0:21:14which they pass on to the next generation.
0:21:14 > 0:21:18So just like us, these New Caledonian crows
0:21:18 > 0:21:23have their own cultures, their own inquisitive, curious minds.
0:21:23 > 0:21:26Which is pretty unusual for a bird.
0:21:28 > 0:21:32Orang-utans, in the wild, make very simple tools.
0:21:32 > 0:21:36But surprisingly, it's the smart crows that take the prize
0:21:36 > 0:21:40for making the most sophisticated tools used by any animal.
0:21:40 > 0:21:41Very clever.
0:21:43 > 0:21:45Are we finished now?
0:21:45 > 0:21:47Where's my lunch?
0:21:53 > 0:21:59When I was a boy, my father gave me one of these for my eighth birthday.
0:21:59 > 0:22:01It's a fire salamander.
0:22:01 > 0:22:06They may look like lizards but in fact they're not reptiles,
0:22:06 > 0:22:09they're amphibians with moist skins.
0:22:09 > 0:22:13For centuries, mythical stories surrounded these creatures.
0:22:13 > 0:22:17It was believed that they were icy cold animals that could
0:22:17 > 0:22:21dwell within fires, unharmed by the heat.
0:22:21 > 0:22:24Although their fire-surviving powers may be untrue,
0:22:24 > 0:22:29the salamander nonetheless possesses a real natural ability,
0:22:29 > 0:22:31that is just as extraordinary.
0:22:31 > 0:22:36They're able to regrow damaged tails, legs
0:22:36 > 0:22:41and other parts of the body through a process called regeneration.
0:22:44 > 0:22:47There are more than 600 different species of salamander.
0:22:49 > 0:22:52They range in size from just a couple of centimetres,
0:22:52 > 0:22:58up to the world's largest amphibian, the Chinese giant salamander,
0:22:58 > 0:23:01that can grow to over a metre and a half in length
0:23:04 > 0:23:09Salamanders are predators and many hunt for small invertebrates
0:23:09 > 0:23:10such as slugs and worms.
0:23:16 > 0:23:22But sometimes, they hunt each other with dramatic consequences.
0:23:25 > 0:23:28This tiny North American red-backed salamander
0:23:28 > 0:23:32is on the menu of the much bigger seal salamander.
0:23:42 > 0:23:43Time to make a retreat.
0:23:48 > 0:23:53This may look shocking, but the red-back isn't badly injured.
0:23:53 > 0:23:57A weak point in its skin allows its tail to break off easily.
0:24:01 > 0:24:06Incredibly, it will regrow a new tale in just a matter of weeks.
0:24:09 > 0:24:12This ability to replace an entire body part
0:24:12 > 0:24:16is unusual among adult vertebrates, and seems almost magical.
0:24:18 > 0:24:21Regeneration is a subject that fascinates us.
0:24:22 > 0:24:25Modern medicine has spent a lot of money and time
0:24:25 > 0:24:29studying the ways our own bodies can regenerate tissue.
0:24:29 > 0:24:31All living creatures, including humans,
0:24:31 > 0:24:34have the ability to repair damaged parts of the body
0:24:34 > 0:24:38but the extent of that repair varies considerably.
0:24:38 > 0:24:41As small infants, we have the ability to
0:24:41 > 0:24:44regrow the tips of our fingers if they're severed,
0:24:44 > 0:24:46but we lose this ability as we age.
0:24:47 > 0:24:50So animals, like salamanders,
0:24:50 > 0:24:52with their super-regenerative powers,
0:24:52 > 0:24:54seem intriguing to us.
0:24:58 > 0:25:02Regeneration had been known about since ancient times.
0:25:02 > 0:25:05But for a long time, no-one understood how it happened.
0:25:07 > 0:25:09In the 17th and 18th century,
0:25:09 > 0:25:13there was a new wave of scientific discovery.
0:25:13 > 0:25:18A brilliant Italian scientist named Lazzaro Spallanzani
0:25:18 > 0:25:22made meticulous observations into regeneration
0:25:22 > 0:25:24across many different species,
0:25:24 > 0:25:27and shared his ideas in detailed letters.
0:25:29 > 0:25:34In November, 1765, he wrote to the eminent scientist Charles Bonnet,
0:25:34 > 0:25:36whom he regularly corresponded with,
0:25:36 > 0:25:41to announce that he had discovered tail regeneration in salamanders.
0:25:41 > 0:25:45Throughout the following year, he followed up his initial observations
0:25:45 > 0:25:47with numerous experiments to try to understand
0:25:47 > 0:25:51how the salamander could regrow a tail just like the original.
0:25:51 > 0:25:54He found that all species of salamander that he tested
0:25:54 > 0:25:57could regrow their tails when injured,
0:25:57 > 0:26:01and that they did so more rapidly in summer than in winter.
0:26:01 > 0:26:05And retained this incredible ability throughout their lives.
0:26:05 > 0:26:09Spallanzani advocated a radical theory.
0:26:09 > 0:26:12He thought that salamanders already possessed
0:26:12 > 0:26:16a number of miniature spare parts at the base of each limb,
0:26:16 > 0:26:19that could grow in size to replace a lost or damaged one.
0:26:22 > 0:26:26He was unable to prove this theory but he didn't give up.
0:26:26 > 0:26:29He studied salamander tadpoles,
0:26:29 > 0:26:32and came up with another, even more interesting idea.
0:26:33 > 0:26:35A year after his initial letter,
0:26:35 > 0:26:38Spallanzani once again wrote to Charles Bonnet.
0:26:38 > 0:26:41This time with detailed descriptions of further
0:26:41 > 0:26:44experiments into tail regeneration.
0:26:44 > 0:26:46Most notably, in this description, he wrote,
0:26:46 > 0:26:52'I am almost led to believe that the tail regenerates in tadpoles
0:26:52 > 0:26:55'are more of an elongation of the old parts
0:26:55 > 0:26:58'than a development from the germ.'
0:26:58 > 0:27:02This suggests that Spallanzani was on the right track.
0:27:02 > 0:27:04But the idea that a salamander could regrow a new tail
0:27:04 > 0:27:07from seemingly nothing was not well supported,
0:27:07 > 0:27:12and Spallanzani was therefore never willing to pursue the idea further.
0:27:13 > 0:27:15However, there's no doubt that his research helped
0:27:15 > 0:27:17to lead other scientists closer
0:27:17 > 0:27:22towards proving what really happens when a salamander regrows its tail.
0:27:25 > 0:27:29In fact, Spallanzani's rough sketches did make sense.
0:27:29 > 0:27:33And they were the first to describe some of the vital processes in
0:27:33 > 0:27:38the remarkable growth of new limbs that we understand better today.
0:27:38 > 0:27:42When a limb is lost, the exposed blood vessels
0:27:42 > 0:27:46and tissue contract to quickly stop any bleeding.
0:27:46 > 0:27:50Then, skin from the edges begins to grow across the damaged area
0:27:50 > 0:27:52to protect the body from infection.
0:27:54 > 0:27:58Now, cells that were once dormant begin dividing
0:27:58 > 0:28:00and multiplying to create new ones.
0:28:04 > 0:28:09Each cell retains a kind of memory of the type of tissue it used to be,
0:28:09 > 0:28:12so a new cell that regrows from damaged muscle will
0:28:12 > 0:28:13always become muscle.
0:28:15 > 0:28:18Within weeks, the salamander has a full-grown leg
0:28:18 > 0:28:20almost identical to the original.
0:28:22 > 0:28:24Although we now know the steps
0:28:24 > 0:28:27that take place during the regeneration of the body parts,
0:28:27 > 0:28:30we still don't fully understand what triggers this kind of response.
0:28:30 > 0:28:33But it seems the answer may lie
0:28:33 > 0:28:36in how the salamander's body responds to injury.
0:28:37 > 0:28:40In humans, if an arm is severed, the cells die,
0:28:40 > 0:28:43alerting the immune system to the problem.
0:28:43 > 0:28:47In response, the area becomes swollen and is covered over
0:28:47 > 0:28:52with scar tissue, preventing any new growth occurring.
0:28:52 > 0:28:56But in salamanders, the immune system responds differently.
0:28:56 > 0:29:00And instead of forming a scar, it triggers regeneration.
0:29:03 > 0:29:06Another rather unusual-looking salamander
0:29:06 > 0:29:08that lives in the fresh waters of Mexico,
0:29:08 > 0:29:11sheds new light on how this happens.
0:29:13 > 0:29:17Axolotls among the best regenerators in the natural world.
0:29:17 > 0:29:22And scientists wondered if their blood played a role in the process.
0:29:22 > 0:29:26Like us, they have special white blood cells that consume
0:29:26 > 0:29:31invading bacteria and damaged tissue around injuries and wounds.
0:29:33 > 0:29:36Researchers removed them and the results were surprising.
0:29:36 > 0:29:40The axolotl was unable to regrow new limbs.
0:29:42 > 0:29:46So white blood cells were part of the secret of their powers
0:29:46 > 0:29:48of regeneration.
0:29:48 > 0:29:51Understanding the role of the salamander's blood cells
0:29:51 > 0:29:55in regrowing limbs could be a step towards discovering why
0:29:55 > 0:29:59they can regenerate body parts and we can't.
0:30:00 > 0:30:04All amphibians have tadpoles which develop limbs
0:30:04 > 0:30:07and enable them to move onto land.
0:30:07 > 0:30:11But salamanders are able to re-trigger that remarkable process.
0:30:13 > 0:30:17We, too, undergo extraordinary development in the womb.
0:30:17 > 0:30:20Maybe, like the salamander, there is a way of us
0:30:20 > 0:30:24retaining this ability into our adult lives as well.
0:30:25 > 0:30:28The salamander has a truly amazing ability
0:30:28 > 0:30:31to regrow complex body parts
0:30:31 > 0:30:34to enhance its chances of survival.
0:30:34 > 0:30:37While we don't yet know all the answers,
0:30:37 > 0:30:39it's likely that this incredible creature
0:30:39 > 0:30:42could revolutionise modern medicine,
0:30:42 > 0:30:44and the way we treat injuries.
0:30:49 > 0:30:52Next, we uncover the secret behind how moose
0:30:52 > 0:30:56and other deer regrow their enormous new antlers every year.
0:30:58 > 0:31:01And discover what happens when regeneration goes wrong.
0:31:12 > 0:31:16This impressive skeleton belonged to one of the biggest deer
0:31:16 > 0:31:18to ever live on the planet.
0:31:18 > 0:31:20It's an Irish elk.
0:31:20 > 0:31:25Its antlers are enormous. They're almost 4 metres, 12 feet, across.
0:31:25 > 0:31:27And they weigh 40 kilos.
0:31:27 > 0:31:30An Irishman named Dr Molyneux
0:31:30 > 0:31:34first scientifically described the elk in 1697,
0:31:34 > 0:31:37from specimens taken out of an Irish peat bog.
0:31:39 > 0:31:43Some believed that this elk was a large moose, and were convinced
0:31:43 > 0:31:47living specimens could be found elsewhere across Europe and Russia.
0:31:47 > 0:31:49But not everyone agreed.
0:31:49 > 0:31:52And a debate about the life of this creature would continue
0:31:52 > 0:31:54for more than 100 years.
0:31:57 > 0:32:02The skeleton of an Irish elk looks very similar to that of a moose.
0:32:06 > 0:32:10So it's easy to see why many believed them to be the same animal.
0:32:12 > 0:32:15Both have very impressive antlers.
0:32:18 > 0:32:22Antlers are only found in the deer family and are made of bone.
0:32:24 > 0:32:27Unlike horns, which are permanent structures,
0:32:27 > 0:32:30they are shed and replaced every year.
0:32:31 > 0:32:35But how can deer regrow huge chunks of bone?
0:32:35 > 0:32:37Something no other mammal can do.
0:32:41 > 0:32:45Moose, like this young bull behind me, start growing their new antlers
0:32:45 > 0:32:48immediately after they shed their old ones.
0:32:48 > 0:32:53The antlers first appear on little bumps on either side of the head,
0:32:53 > 0:32:54known as pedicles.
0:32:54 > 0:32:58And they have a soft, furry covering, called velvet.
0:32:58 > 0:33:01This is vital to their amazing powers of regeneration.
0:33:04 > 0:33:07Blood vessels at the base start the growth.
0:33:07 > 0:33:11But as the antler gets longer, this blood supply is cut off.
0:33:12 > 0:33:15Then, blood vessels within the velvet take over
0:33:15 > 0:33:19and transport nutrients and growth hormones to the growing tips.
0:33:22 > 0:33:28In older males, the antlers can grow at a rate of two centimetres a day.
0:33:28 > 0:33:31Making it the fastest-growing bone of any animal.
0:33:37 > 0:33:39Once at full size, the velvet is shed.
0:33:42 > 0:33:44The animal rubs its head against the tree
0:33:44 > 0:33:47to encourage the thin velvet to fall off.
0:33:53 > 0:33:55It may look gruesome,
0:33:55 > 0:33:57but it's a natural part of the animal's cycle
0:33:57 > 0:33:59and does the animal no harm.
0:34:04 > 0:34:08But why should a huge set of antlers be regrown every year?
0:34:10 > 0:34:14It's a question that baffled early naturalists.
0:34:14 > 0:34:17Until Charles Darwin suggested it may be to do with
0:34:17 > 0:34:19attracting the opposite sex.
0:34:21 > 0:34:25In the first few years of adulthood, the anglers are small,
0:34:25 > 0:34:29and as a result, young males remain subordinate to the larger bulls.
0:34:29 > 0:34:33But as they get older, and their body size increases,
0:34:33 > 0:34:35so the antlers will also increase.
0:34:35 > 0:34:38Eventually becoming impressive ornaments with which to
0:34:38 > 0:34:40compete for females.
0:34:48 > 0:34:51Those with the biggest answers are certainly more
0:34:51 > 0:34:52attractive to the females.
0:34:54 > 0:34:57Maybe they are an indicator of fitness and strength.
0:35:00 > 0:35:04And it's no coincidence that antlers are at their full size
0:35:04 > 0:35:06during the breeding season.
0:35:14 > 0:35:17This is a time when a bull must protect his harem,
0:35:17 > 0:35:19and see off competitors.
0:35:26 > 0:35:29Competing males tilt their heads to show off their antlers
0:35:29 > 0:35:31to their best advantage.
0:35:36 > 0:35:40But if the bulls are equally matched, then the competitors fight.
0:35:58 > 0:36:02The winner then gains access to the females.
0:36:05 > 0:36:08The benefits of such a victory are huge.
0:36:09 > 0:36:11But to get to that point,
0:36:11 > 0:36:16every young bull must, for many years, grow and regrow antlers.
0:36:17 > 0:36:22It's a big investment, draining the body of vital resources.
0:36:23 > 0:36:27And no investment was bigger than that of the Irish elk.
0:36:29 > 0:36:33The sheer size of these antlers have led some to argue that they
0:36:33 > 0:36:36were unlikely to have been used in physical combat.
0:36:36 > 0:36:40Unlike other deer, the antlers of the Irish elk grew with a large
0:36:40 > 0:36:43flat palm-like plain facing forwards.
0:36:43 > 0:36:45So that if a bull looked straight ahead,
0:36:45 > 0:36:49it would be at its biggest and most impressive.
0:36:49 > 0:36:52In this way, they may been able to intimidate rivals
0:36:52 > 0:36:55and attract females without actually fighting.
0:36:58 > 0:37:01So although the Irish elk was armed with what appeared to be
0:37:01 > 0:37:06enormous weapons, it seems they were mostly for show.
0:37:06 > 0:37:11But this strategy might have been an advantage for the large elk.
0:37:12 > 0:37:14Fighting is always a risky business
0:37:14 > 0:37:17and will often result in serious injuries.
0:37:21 > 0:37:25After the breeding season, the antlers are discarded.
0:37:25 > 0:37:27Moose shed theirs in the winter,
0:37:27 > 0:37:31whereas smaller deer keep theirs until the next spring.
0:37:31 > 0:37:34This may be because the moose antlers are such a heavy load
0:37:34 > 0:37:37to carry throughout the winter.
0:37:39 > 0:37:42But why are antlers shed at all?
0:37:42 > 0:37:46Antlers are made of dead bone and can't be repaired.
0:37:47 > 0:37:50If a moose damages an antler during a fight,
0:37:50 > 0:37:53it will lose its chance of mating for that season.
0:37:55 > 0:37:58By shedding and regrowing their antlers each year,
0:37:58 > 0:38:01bulls ensure that they stay in the mating game.
0:38:04 > 0:38:06Just before antlers are shed,
0:38:06 > 0:38:10minerals within them are reabsorbed from the base,
0:38:10 > 0:38:13weakening the structure so that they eventually fall off.
0:38:16 > 0:38:20The flesh underneath is exposed, but not for long,
0:38:20 > 0:38:22as new skin soon covers the wound.
0:38:24 > 0:38:28Experiments have shown that the skin lesion that forms over
0:38:28 > 0:38:31the open wound creates a connection with the underlying tissue,
0:38:31 > 0:38:34that is crucial to regeneration.
0:38:36 > 0:38:40If this connection isn't made, the production of velvet will be
0:38:40 > 0:38:44interrupted and the antlers will either not grow at all,
0:38:44 > 0:38:46or develop into strange shapes.
0:38:50 > 0:38:53So, what about the Irish elk?
0:38:54 > 0:38:57Could the problems of regenerating such gigantic antlers
0:38:57 > 0:38:59have determined its fate?
0:39:00 > 0:39:04The French scientist George Cuvier was keen to demonstrate
0:39:04 > 0:39:09that the Irish elk was a unique species that had become extinct.
0:39:09 > 0:39:11To prove this point,
0:39:11 > 0:39:15Cuvier undertook a detailed examination of Irish elk fossils.
0:39:15 > 0:39:20He was able to show that it was indeed a distinct type of deer,
0:39:20 > 0:39:23that could no longer be found alive.
0:39:23 > 0:39:26And so the Irish elk was one of the first animals to be
0:39:26 > 0:39:29recognised as being extinct.
0:39:31 > 0:39:35George Cuvier had solved the question of whether or not
0:39:35 > 0:39:39the Irish elk and moose were one and the same creature.
0:39:39 > 0:39:41But why did the Irish elk die out?
0:39:42 > 0:39:45Cuvier suggested that evolution has set it
0:39:45 > 0:39:48on a course of ever-increasing growth.
0:39:48 > 0:39:51And that eventually, the antlers became
0:39:51 > 0:39:54so large that the poor animal could not even lift its neck.
0:39:56 > 0:39:59He may not have been that far from the truth.
0:40:01 > 0:40:05It's now thought that the annual growth of the Irish elk antlers
0:40:05 > 0:40:07put a strain on their bodies.
0:40:07 > 0:40:11A significant proportion of minerals within their bones
0:40:11 > 0:40:15were extracted and moved into their growing antlers.
0:40:15 > 0:40:21This led to a seasonal osteoporosis, with their bones weakening.
0:40:21 > 0:40:25They were, in effect, robbing one part of their body to boost another.
0:40:28 > 0:40:31It was a gamble that worked for thousands of years.
0:40:32 > 0:40:36But around 10,000 years ago, the climate began to warm.
0:40:38 > 0:40:43The nutrient-rich grasses that the elk relied upon began to disappear.
0:40:45 > 0:40:49Growing massive antlers may now have been too much of a drain,
0:40:49 > 0:40:51and permanently weakened the skeleton.
0:40:53 > 0:40:57The change in diet may also have affected their ability to breed,
0:40:57 > 0:41:01with females no longer able to produce young every year.
0:41:04 > 0:41:08Whatever the reason, the Irish elk, with its magnificent antlers,
0:41:08 > 0:41:10finally vanished from the landscape.
0:41:11 > 0:41:12And in its place,
0:41:12 > 0:41:16the moose has become the largest deer on earth today.
0:41:20 > 0:41:23So, while regeneration can give the salamander
0:41:23 > 0:41:26a second chance to a full life,
0:41:26 > 0:41:29the yearly regeneration of antlers
0:41:29 > 0:41:32in male moose is a risky strategy.
0:41:32 > 0:41:37But one with huge rewards for those with the best antlers.