0:00:06 > 0:00:08Bones.
0:00:08 > 0:00:12They offer structure, support
0:00:12 > 0:00:17and strength, but they have a much bigger story to tell.
0:00:21 > 0:00:27Vertebrates may look very different on the outside,
0:00:27 > 0:00:30but one crucial thing unites them all.
0:00:30 > 0:00:32The skeleton.
0:00:35 > 0:00:39I'm Ben Garrod, an evolutionary biologist
0:00:39 > 0:00:42with a very unusual passion.
0:00:42 > 0:00:44This is unbelievable!
0:00:44 > 0:00:47There are too many skeletons for me to look at all at once.
0:00:47 > 0:00:51As a child I was fascinated by bones.
0:00:51 > 0:00:55Now, skeletons have become my life.
0:00:59 > 0:01:04And I put them together for museums and universities all over the world.
0:01:06 > 0:01:12I'm going to explore the natural world from the inside out.
0:01:14 > 0:01:18To see how the skeleton has enabled animals to move...
0:01:19 > 0:01:21..hunt...
0:01:21 > 0:01:23and even sense the world.
0:01:23 > 0:01:27I will take you on a very personal journey, to discover
0:01:27 > 0:01:31how this one bony blueprint has shaped such massive diversity
0:01:31 > 0:01:35across the animal kingdom, and how it has come to dominate
0:01:35 > 0:01:37life on Planet Earth.
0:01:37 > 0:01:41This time, we'll see how bones
0:01:41 > 0:01:46have helped vertebrates to capture and devour
0:01:46 > 0:01:51practically every type of food on the planet.
0:01:53 > 0:01:55We'll look at extreme jaws...
0:01:55 > 0:01:58bizarre teeth...
0:01:58 > 0:02:01It really is a bonkers adaptation.
0:02:01 > 0:02:04..highly specialised bony tools,
0:02:04 > 0:02:09and one small appendage that has had an immense impact.
0:02:09 > 0:02:11It may not look much,
0:02:11 > 0:02:15but it changed the course of our evolutionary history.
0:02:15 > 0:02:20I'm going to reveal the Secrets of Bones.
0:02:36 > 0:02:41This is the jaw of the largest living toothed predator on the planet.
0:02:41 > 0:02:43At five metres long,
0:02:43 > 0:02:47it's from a sperm whale that was nearly 30 metres in length.
0:02:49 > 0:02:52The teeth can be 20cm long,
0:02:52 > 0:02:55and they're all roughly the same in terms of their shape.
0:02:55 > 0:02:59This makes them perfectly adapted for grabbing and killing.
0:02:59 > 0:03:03Now teeth and jaws absolutely fascinate me because they reveal
0:03:03 > 0:03:07so many of the secrets behind an animal's life and their success.
0:03:08 > 0:03:11Sperm whales may have a spectacular set of jaws
0:03:11 > 0:03:14but there are more than 60,000 species of vertebrate
0:03:14 > 0:03:18and each has evolved its own special way of feeding.
0:03:18 > 0:03:24Jaws first appeared around 420 million years ago.
0:03:25 > 0:03:29Important tools for catching and consuming food,
0:03:29 > 0:03:34their shape and size adapted to exploit whatever was available.
0:03:34 > 0:03:39This evolutionary change can take place surprisingly quickly.
0:03:45 > 0:03:48To understand the story of rapid jaw evolution,
0:03:48 > 0:03:53I need to get an MRI scan of my skull.
0:03:53 > 0:03:57The information is processed to create a model in plastic.
0:04:08 > 0:04:11I'm more than a little curious to see what my own skull looks like.
0:04:13 > 0:04:17I've been working with bones for 20 years
0:04:17 > 0:04:19but this is a first.
0:04:22 > 0:04:24I'm quite shocked.
0:04:24 > 0:04:28It's so weird to look at your own skull,
0:04:28 > 0:04:31whilst you're still alive, I think, really.
0:04:34 > 0:04:37Even though I study bones, you look in a mirror
0:04:37 > 0:04:40and you don't see all these little lumps or this massive brow ridge
0:04:40 > 0:04:44that I apparently have, or this quite large jutting jaw.
0:04:52 > 0:04:53Weird!
0:04:55 > 0:04:58I'm taking my skull to Dr Carolyn Rando,
0:04:58 > 0:05:01an archaeologist at University College London,
0:05:01 > 0:05:04who's been conducting some fascinating research
0:05:04 > 0:05:08into how human jaws are adapting to our ever-changing diet.
0:05:12 > 0:05:15You've got an impressive array of skulls here, Carolyn.
0:05:15 > 0:05:18What can they tell us about the evolution of our jaws?
0:05:18 > 0:05:21Well, what we have here is we have a selection of skulls
0:05:21 > 0:05:24going all the way back from Neanderthal man to Cro-Magnon,
0:05:24 > 0:05:26and medieval London and post-medieval London here.
0:05:26 > 0:05:30And so while these give us a cross section of essentially human
0:05:30 > 0:05:35evolutionary history, my main interest is with these two here.
0:05:35 > 0:05:39What I found out through my research is that jaws have got
0:05:39 > 0:05:42significantly smaller since the medieval period,
0:05:42 > 0:05:44up until the modern period.
0:05:44 > 0:05:46We're talking just several hundred years, aren't we?
0:05:46 > 0:05:49Absolutely. So the medieval period ends in 1550
0:05:49 > 0:05:53and post-medieval were talking 17-1800s, 1900s.
0:05:53 > 0:05:55When you say the jaws are changing, how?
0:05:55 > 0:05:59Well, what's happening is that for one, in this individual,
0:05:59 > 0:06:01we have what we call an edge to edge bite,
0:06:01 > 0:06:04which means that his front teeth line up perfectly.
0:06:04 > 0:06:06so real nice top and bottom together.
0:06:06 > 0:06:07And what we have here is his top teeth
0:06:07 > 0:06:10and bottom teeth, they don't fit together at all.
0:06:10 > 0:06:14That's massive, that. I'm closing mine now, mine do the same.
0:06:14 > 0:06:17- Is that typical of modern man now? - Absolutely.
0:06:17 > 0:06:22And in this individual here they fit together so poorly that I can put
0:06:22 > 0:06:26an entire finger in between his upper and lower teeth.
0:06:26 > 0:06:29How would my diet make my jaw become smaller?
0:06:29 > 0:06:32Throughout human evolution, we've had a very specific type of diet
0:06:32 > 0:06:35which is lots of rough, hard food.
0:06:35 > 0:06:38- Tough and fibrous, isn't it? - Exactly.
0:06:38 > 0:06:41Yeah, we really have to chew hard to make our food work for us,
0:06:41 > 0:06:46and all of that work is stimulating our jaws to grow.
0:06:46 > 0:06:48It stimulates our teeth, which stimulates the jaws,
0:06:48 > 0:06:51and then the whole face responds in kind to these things.
0:06:51 > 0:06:54And so what happened then is we switched from a very
0:06:54 > 0:06:59traditional agriculturalist diet, to one that was soft and sticky
0:06:59 > 0:07:03and very sweet, and something that's almost identical to what we have now.
0:07:03 > 0:07:05- Processed foods, I guess. - Absolutely.
0:07:05 > 0:07:08We don't have that same type of interaction
0:07:08 > 0:07:10between the food and the jaws any more,
0:07:10 > 0:07:14they just tend to become smaller through inactivity.
0:07:15 > 0:07:18Although the trend is towards an increasing overbite,
0:07:18 > 0:07:21the severity differs between individuals.
0:07:21 > 0:07:25And this is largely down to their particular eating habits.
0:07:25 > 0:07:28So where does that leave me?
0:07:28 > 0:07:30Now I have another skull for you.
0:07:30 > 0:07:33I just happen to have it in my bag, as I often do.
0:07:33 > 0:07:37Now I want to see what you make of this one.
0:07:37 > 0:07:40And if it looks familiar, it's because it's mine.
0:07:40 > 0:07:45- Ah, Ben, that's amazing! It looks just like you.- Thank you!
0:07:46 > 0:07:48We're very attached.
0:07:48 > 0:07:52This is a skull I've had printed off from a 3D image,
0:07:52 > 0:07:56but where does this fit with the jaw story?
0:07:56 > 0:08:00Well, if we compare it to our two gentlemen here,
0:08:00 > 0:08:04what we can see is that while you are not quite as bad
0:08:04 > 0:08:06as our modern individual over here,
0:08:06 > 0:08:09you still do have quite a bit of an overbite here.
0:08:09 > 0:08:12So I think you're going more towards modern,
0:08:12 > 0:08:14but not quite as bad as this gentleman here.
0:08:14 > 0:08:16It's reassuring.
0:08:16 > 0:08:19Can we predict what will happen to humans in the future?
0:08:19 > 0:08:21Will this carry on, will they get smaller?
0:08:21 > 0:08:25I think it's a bit hard to say, because who knows what our diet
0:08:25 > 0:08:28will be like 50 or 100 or 200 years from now.
0:08:28 > 0:08:32We could have a liquid-based diet, or maybe something that's pill-based,
0:08:32 > 0:08:36instead of actually chewing our food, and then I imagine that our jaws
0:08:36 > 0:08:38would start getting smaller yet again.
0:08:38 > 0:08:42I love this, because it really emphasises yet again
0:08:42 > 0:08:45just how malleable, changeable, adaptable, not only the skull,
0:08:45 > 0:08:48but bones and skeletons in general really are.
0:08:48 > 0:08:53Dr Rando believes that due to the lack of tough, fibrous foods in our diet,
0:08:53 > 0:08:57there's no longer a need for large, powerful jaws.
0:08:57 > 0:09:01This is evolution in action, and it is happening to us.
0:09:01 > 0:09:04We are not outside of our environment, we are still evolving
0:09:04 > 0:09:07and adapting to everything around us.
0:09:10 > 0:09:14Diet has shaped the vertebrate jaw.
0:09:14 > 0:09:17In some cases, to the extreme.
0:09:19 > 0:09:24Snakes' flexible mandibles allow them to consume enormous prey.
0:09:27 > 0:09:31Some species can open their jaws 180 degrees,
0:09:31 > 0:09:38stretching so wide they can eat prey five times larger than their own heads!
0:09:47 > 0:09:49So just how do they do this?
0:09:49 > 0:09:53Well, the old idea that they dislocate their jaws,
0:09:53 > 0:09:55that's a load of rubbish.
0:09:55 > 0:09:58What they actually do is far more interesting.
0:09:58 > 0:10:01You can see here that each side of the lower jaw is made up
0:10:01 > 0:10:04of different bones that are connected together,
0:10:04 > 0:10:09and both lower jaws aren't even attached to one another.
0:10:09 > 0:10:12This all goes together to make a very flexible lower jaw
0:10:12 > 0:10:16and it's connected through a whole network of very tight
0:10:16 > 0:10:19but elastic-like ligaments.
0:10:19 > 0:10:23Imagine that my two arms are the lower jaw bones
0:10:23 > 0:10:27or mandibles of the snake, and these two elastic bands
0:10:27 > 0:10:32are the ligaments that hold the jaws together.
0:10:32 > 0:10:34When the snake is trying to eat something,
0:10:34 > 0:10:39these ligaments stretch allowing the jaw bones to spread massively.
0:10:39 > 0:10:43This is how a snake can eat something much larger
0:10:43 > 0:10:45than you might expect.
0:10:45 > 0:10:48It's very simple but effective.
0:10:51 > 0:10:55Snakes are the ultimate binge eaters.
0:10:55 > 0:10:57They're ectothermic,
0:10:57 > 0:10:59relying on the environment to warm their bodies,
0:10:59 > 0:11:03and so need to conserve energy wherever possible.
0:11:03 > 0:11:07By eating huge meals every few weeks,
0:11:07 > 0:11:09snakes can maximum food intake
0:11:09 > 0:11:11whilst minimising energy expenditure.
0:11:14 > 0:11:18To achieve this, their bones have had to adapt spectacularly.
0:11:21 > 0:11:23Once they've secured their prey,
0:11:23 > 0:11:28they move one mandible forward at a time to swallow it.
0:11:28 > 0:11:31It can then take several days for their food to be dissolved
0:11:31 > 0:11:34by strong acids in their stomach.
0:11:37 > 0:11:41The African egg-eating snake has found a more immediate
0:11:41 > 0:11:43bony solution to breaking up its prey.
0:11:43 > 0:11:48It feed exclusively on bird's eggs.
0:11:52 > 0:11:56Its skeletal secret is revealed by this video X-ray.
0:11:57 > 0:12:00With a superbly flexible jaw,
0:12:00 > 0:12:04it can consume an egg many times bigger than its head.
0:12:06 > 0:12:09Knife-like bony spikes in its vertebrae
0:12:09 > 0:12:12protrude into the body cavity.
0:12:13 > 0:12:17When the egg reaches the part of the backbone
0:12:17 > 0:12:21with downward pointing spines, the snake arches and squeezes.
0:12:21 > 0:12:26The spikes first pierce the shell and then slit the membrane inside,
0:12:26 > 0:12:29releasing a highly nutritious meal.
0:12:32 > 0:12:35A backbone that can break up your food
0:12:35 > 0:12:38is an ingenious skeletal adaptation.
0:12:43 > 0:12:46But most vertebrates use a more conventional method,
0:12:46 > 0:12:48teeth.
0:12:52 > 0:12:55They're mostly made up of enamel and dentine,
0:12:55 > 0:12:58and are similar in composition to bone.
0:12:58 > 0:13:03But as they contain little or no collagen, they're much harder.
0:13:03 > 0:13:06Teeth do different jobs
0:13:06 > 0:13:09from biting and ripping
0:13:09 > 0:13:13to crushing and nibbling.
0:13:14 > 0:13:18A wide variety of foods has led to a diverse range
0:13:18 > 0:13:21of tooth shape and size.
0:13:22 > 0:13:25Carnivores have particularly impressive teeth.
0:13:27 > 0:13:29They use their canines for puncturing,
0:13:29 > 0:13:31carnassials for shearing
0:13:31 > 0:13:34and incisors for tearing flesh.
0:13:38 > 0:13:41However, it's a herbivore that holds the record
0:13:41 > 0:13:45when it comes to tooth size.
0:13:45 > 0:13:50The animal with the largest teeth on the planet is the elephant.
0:13:51 > 0:13:54First up, teeth for chewing.
0:13:54 > 0:13:59They're massive! Each one of these molars can be 30cm in length
0:13:59 > 0:14:02and can weigh up to five kilograms.
0:14:02 > 0:14:06Their flattened surface is ideal for grinding.
0:14:06 > 0:14:08They're also heavily ridged on the top,
0:14:08 > 0:14:12and this is a perfect adaptation for a vegetation diet
0:14:12 > 0:14:14which is really tough and fibrous.
0:14:17 > 0:14:20An elephant gets six sets of these teeth throughout its lifetime.
0:14:20 > 0:14:24As each one is worn down, new ones are pushed forward
0:14:24 > 0:14:27from the back of the mouth, a bit like a conveyor belt.
0:14:27 > 0:14:31As the last one is worn down and is finally lost, the elephant
0:14:31 > 0:14:35can no longer eat and this marks the end of the animal's life.
0:14:37 > 0:14:40The elephant's biggest teeth are its tusks.
0:14:40 > 0:14:44They can grow to more than 3m long.
0:14:45 > 0:14:47They're actually modified incisors
0:14:47 > 0:14:50like the front teeth in humans.
0:14:50 > 0:14:56Like ours, they keep growing, as much as 17cm a year.
0:14:56 > 0:15:00Made from ivory, a kind of dentine,
0:15:00 > 0:15:04tusks are important for display and defence,
0:15:04 > 0:15:08and as tools for helping elephants collect their food.
0:15:08 > 0:15:13There's a marine mammal that has independently evolved tusks
0:15:13 > 0:15:16that aren't used for feeding at all.
0:15:19 > 0:15:22The walrus has these enormous tusks.
0:15:22 > 0:15:24These are actually specialised canine teeth
0:15:24 > 0:15:26which erupt from the upper jaw here
0:15:26 > 0:15:30and these tusks can be over one metre in length.
0:15:30 > 0:15:33Their scientific name "odobenus" means "tooth walker."
0:15:33 > 0:15:37And walruses use their teeth to haul their one tonne bodies
0:15:37 > 0:15:39out of the icy water and on to ice floes.
0:15:44 > 0:15:48The tusks are also used for duelling
0:15:48 > 0:15:50and defence.
0:15:54 > 0:15:58If they're not used for eating, how do they feed?
0:16:01 > 0:16:05Walruses produce jets of water to uncover clams
0:16:05 > 0:16:07hidden in the silt on the sea bed.
0:16:10 > 0:16:16They can consume 6,000 in one feeding session.
0:16:18 > 0:16:21Exactly how they were able to prise open the shells
0:16:21 > 0:16:22puzzled researchers for years.
0:16:28 > 0:16:33Looking at the jaws, they noticed that the teeth were very worn.
0:16:33 > 0:16:36Now this you might expect from an animal that is eating
0:16:36 > 0:16:39and chewing and crushing lots of shellfish.
0:16:39 > 0:16:42But when scientists looked in the stomachs of walruses,
0:16:42 > 0:16:47they found they can have up to 70 kilograms of shellfish meat
0:16:47 > 0:16:49and not a single shell.
0:16:51 > 0:16:54What researchers discovered is that walruses are able
0:16:54 > 0:16:59to turn their mouths into powerful suction devices.
0:16:59 > 0:17:04And they do this through some very specific skeletal adaptations.
0:17:04 > 0:17:06The first of which is in the roof of the mouth.
0:17:06 > 0:17:09Now you can see here it's highly arched and domed,
0:17:09 > 0:17:12and this allows them to put their thick, muscular tongue
0:17:12 > 0:17:15right at the front of their mouths.
0:17:15 > 0:17:16They grind their jaws together
0:17:16 > 0:17:20so tightly that this is what wears the teeth down.
0:17:20 > 0:17:23So they've got the shellfish at the front of their mouths and lips,
0:17:23 > 0:17:25their teeth are held together very tightly
0:17:25 > 0:17:28and this tongue is pushed forward.
0:17:28 > 0:17:31They'll pull this back so quickly that it forms a vacuum,
0:17:31 > 0:17:34and the vacuum power is so strong
0:17:34 > 0:17:38that it sucks the meat clean out of the shellfish.
0:17:38 > 0:17:41In captivity, walruses have been seen to suck a hole
0:17:41 > 0:17:44through plywood board!
0:17:46 > 0:17:49Vertebrates have evolved many novel ways
0:17:49 > 0:17:52of using their mouths to feed.
0:17:52 > 0:17:55But there is one specialist feeder
0:17:55 > 0:17:59with the most bizarre-looking teeth I have ever seen,
0:17:59 > 0:18:04and a specimen is kept in the stores of Dublin's Natural History Museum.
0:18:08 > 0:18:10A close relative of the walrus,
0:18:10 > 0:18:13it's one of the most abundant large mammals on earth.
0:18:15 > 0:18:17It's the crabeater seal.
0:18:18 > 0:18:24There are estimated to be 15 million of them found in Antarctic waters.
0:18:24 > 0:18:28As they primarily live on free-floating pack ice
0:18:28 > 0:18:30in remote and inhospitable locations,
0:18:30 > 0:18:33they are rarely seen and little studied.
0:18:33 > 0:18:36Much of their lives still remain a mystery.
0:18:36 > 0:18:41The crabeater seal you assume would eat crabs
0:18:41 > 0:18:44and even the scientific name, "Lobodon carcinophaga,"
0:18:44 > 0:18:46means "lobed tooth crab eater."
0:18:48 > 0:18:52But more than 95% of their diet is made up of Antarctic krill,
0:18:52 > 0:18:55a shrimp-like crustacean,
0:18:55 > 0:18:59and they can consume 20 kilograms of them a day!
0:19:02 > 0:19:06It's said to have the most complex teeth of any carnivore!
0:19:08 > 0:19:12Like the walrus, the crabeater seal uses suction to feed,
0:19:12 > 0:19:14but in a very different way.
0:19:14 > 0:19:19As it swims, it sucks water and krill into its mouth,
0:19:19 > 0:19:23then filters the tiny crustaceans through its teeth.
0:19:25 > 0:19:29I genuinely love these teeth. They fit together perfectly.
0:19:29 > 0:19:33And by being shaped with all these little lobes and nooks and crannies,
0:19:33 > 0:19:37the teeth can fit together and form an amazing sieve.
0:19:38 > 0:19:41It really is a bonkers adaptation
0:19:41 > 0:19:45and these teeth are perfectly adapted feeding tools.
0:19:53 > 0:19:56Using a mouth to capture and manipulate food
0:19:56 > 0:19:58works for most vertebrates.
0:20:00 > 0:20:05Sometimes, however, jaws and teeth just aren't enough...
0:20:07 > 0:20:12..and more sophisticated bony tools are needed to secure a meal.
0:20:14 > 0:20:17Particularly when you live in a challenging environment
0:20:17 > 0:20:20where food can be hard to come by.
0:20:20 > 0:20:24The monkfish is one of the ultimate ambush predators.
0:20:24 > 0:20:26It's the stuff of nightmares, it really is.
0:20:26 > 0:20:28It's more alien than it is animal,
0:20:28 > 0:20:33and it's one massive killing machine head with a little tail attached to the back of it.
0:20:33 > 0:20:38This hefty beast of a fish sits on the sea bed where it's dark
0:20:38 > 0:20:41and murky for long periods of time.
0:20:41 > 0:20:48It has a set of skeletal adaptations that really help maximise
0:20:48 > 0:20:51any chance of getting some grub.
0:20:52 > 0:20:55The most peculiar of which is a lure.
0:20:57 > 0:21:01The monkfish is a species of angler fish.
0:21:03 > 0:21:06The lures of angler fish come in a variety of cunning shapes
0:21:06 > 0:21:09to entice prey within jaw's reach.
0:21:09 > 0:21:14Some deep sea species even have ones that glow in the dark.
0:21:16 > 0:21:19On the monkfish, the lure is a specialised dorsal filament
0:21:19 > 0:21:22on its head made of bone.
0:21:22 > 0:21:25And its success, I think, is almost entirely down
0:21:25 > 0:21:28to this one little bony appendage.
0:21:28 > 0:21:32Now fish are quite inquisitive, so something will swim past,
0:21:32 > 0:21:35it'll have a good look and then that's the start of the end.
0:21:39 > 0:21:44The monkfish has a clever strategy to bring food...
0:21:44 > 0:21:46straight to its mouth.
0:21:48 > 0:21:51There are other vertebrates that have evolved even more
0:21:51 > 0:21:53sophisticated ways to gather food,
0:21:53 > 0:21:57and the most advanced example of this is in the human body.
0:21:59 > 0:22:03It's a bony feature that has totally revolutionised
0:22:03 > 0:22:08the way we collect our food, and is found in the skeletons
0:22:08 > 0:22:13of most primates, including this gorilla.
0:22:19 > 0:22:23When you compare my hands to those of the gorilla here,
0:22:23 > 0:22:25you can see they are similar.
0:22:25 > 0:22:28Not only the shape of the bones, but the orientation,
0:22:28 > 0:22:31the number of bones, everything.
0:22:31 > 0:22:34But more than that, we share this wonderful,
0:22:34 > 0:22:37unassuming opposable thumb.
0:22:37 > 0:22:38It may not look much
0:22:38 > 0:22:42but it changed the course of our evolutionary history.
0:22:46 > 0:22:50An opposable digit enabled primates to move their thumb freely
0:22:50 > 0:22:57and independently, giving them a precision grip to grasp branches,
0:22:57 > 0:23:02pick leaves and use tools to attain food normally out of reach.
0:23:02 > 0:23:05Around 3.5 million years ago,
0:23:05 > 0:23:09something happened in our evolutionary history that set us
0:23:09 > 0:23:12apart from our primate cousins.
0:23:14 > 0:23:16Primates mainly walk on all fours,
0:23:16 > 0:23:21but when our early human ancestors started walking upright on two legs,
0:23:21 > 0:23:25it freed up their hands allowing them to use their opposable thumbs
0:23:25 > 0:23:28to carry and manipulate tools,
0:23:28 > 0:23:31including weapons for hunting.
0:23:32 > 0:23:36With arms freed up, they became skilled at throwing,
0:23:36 > 0:23:39helping them hunt big game at a distance,
0:23:39 > 0:23:43enabled by a set of skeletal adaptations.
0:23:46 > 0:23:50The human shoulder has an amazing ability to release stored energy
0:23:50 > 0:23:53from a huge crisscrossing network of tendons
0:23:53 > 0:23:55and ligaments right across this area.
0:23:55 > 0:23:59It acts like a slingshot and this allows us to be such good throwers.
0:23:59 > 0:24:03Today, top class baseball pitchers can throw accurately
0:24:03 > 0:24:07at speeds of over 100 miles an hour.
0:24:11 > 0:24:14There are three key skeletal adaptations,
0:24:14 > 0:24:18the first of which is having a really high and mobile waist,
0:24:18 > 0:24:21and this allows a lot of torsion in the torso.
0:24:21 > 0:24:24Secondly and really importantly is the very low position
0:24:24 > 0:24:27of the shoulder blade up on the body.
0:24:29 > 0:24:31Our humerus, our upper arm bone here,
0:24:31 > 0:24:34has the ability to twist and turn, as well.
0:24:34 > 0:24:37This all happened about two million years ago,
0:24:37 > 0:24:40way before we existed as homo sapien,
0:24:40 > 0:24:43back in the day when homo erectus roamed the earth.
0:24:50 > 0:24:56Our ability to throw and our success as hunters is an important part
0:24:56 > 0:24:59of why we have thrived as a species.
0:25:11 > 0:25:15But there's one primate that stands out as having
0:25:15 > 0:25:17the most highly specialised hands
0:25:17 > 0:25:20that it uses in an unparalleled way.
0:25:27 > 0:25:32This lemur from Madagascar is the world's largest nocturnal primate.
0:25:32 > 0:25:36It's the aye-aye.
0:25:36 > 0:25:40Feeding on insects and larvae hidden deep inside tree trunks,
0:25:40 > 0:25:44it needs very specialised digits to extract them.
0:25:45 > 0:25:49Now, like most primates, it has this wonderful opposable thumb
0:25:49 > 0:25:52allowing it to grasp and manipulate objects.
0:25:53 > 0:25:59But unique to the aye-aye, it has a very, very specialised finger.
0:25:59 > 0:26:03So you can see this wonderful third digit, which is a very long
0:26:03 > 0:26:07needle-like structure with this great little hook claw on the end.
0:26:07 > 0:26:12To try to find where the grubs are hiding, the aye-aye
0:26:12 > 0:26:17uses its highly sensitive bony finger to sound them out by tapping.
0:26:18 > 0:26:21It'll tap up to ten times a second.
0:26:21 > 0:26:23Much faster than I can do.
0:26:23 > 0:26:26This is called percussive foraging.
0:26:28 > 0:26:32The aye-aye uses its large ears to listen for the echo
0:26:32 > 0:26:36produced from the tapping to locate where the grubs are hiding.
0:26:36 > 0:26:40It's the only primate to use echolocation.
0:26:43 > 0:26:48Once it's pin-pointed a grub, it gnaws a hole in the wood
0:26:48 > 0:26:50with its chisel-like teeth
0:26:50 > 0:26:54and uses its spiky long finger to search for it.
0:26:58 > 0:27:01This finger has a ball and socket joint
0:27:01 > 0:27:03which is unique in the primate world.
0:27:03 > 0:27:07Now I've got one in my hip, but nothing else has one in its fingers.
0:27:07 > 0:27:11And it gives the aye-aye's finger great flexibility
0:27:11 > 0:27:13to explore inside wood cavities.
0:27:13 > 0:27:18Once it's found the little grub, it'll use its third finger again,
0:27:18 > 0:27:22drag it out, eat it.
0:27:28 > 0:27:30With its sophisticated and specialised hands,
0:27:30 > 0:27:33the aye-aye is, in my opinion,
0:27:33 > 0:27:36the most extraordinary predator on Planet Earth!
0:27:40 > 0:27:42The skeleton has allowed vertebrates to capture
0:27:42 > 0:27:48and devour practically every type of food on the planet,
0:27:48 > 0:27:52using a diverse range of jaws, teeth
0:27:52 > 0:27:55and other sophisticated bony tools.
0:28:00 > 0:28:04Next time, I'll be investigating what role bones play
0:28:04 > 0:28:08in the three crucial things needed for reproduction.
0:28:08 > 0:28:10Flirting,
0:28:10 > 0:28:11fighting
0:28:11 > 0:28:14and mating.
0:28:14 > 0:28:16It's the largest penis bone on earth.