0:00:05 > 0:00:08Bones...
0:00:08 > 0:00:10They offer structure...
0:00:10 > 0:00:12support
0:00:12 > 0:00:14and strength.
0:00:14 > 0:00:17But they have a much bigger story to tell.
0:00:23 > 0:00:26Vertebrates may look very different on the outside,
0:00:26 > 0:00:31but one crucial thing unites them all...
0:00:31 > 0:00:32the skeleton.
0:00:36 > 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 > 0:00:48There are too many skeletons for me to look at all at once.
0:00:48 > 0:00:51As a child I was fascinated by bones.
0:00:51 > 0:00:54And now skeletons have become my life.
0:00:58 > 0:01:03And I put them together for museums and universities
0:01:03 > 0:01:04all over the world.
0:01:07 > 0:01:11I'm going to explore the natural world
0:01:11 > 0:01:13from the inside out
0:01:13 > 0:01:18to see how the skeleton has enabled animals to move...
0:01:19 > 0:01:21..hunt
0:01:21 > 0:01:24and even sense the world.
0:01:24 > 0:01:27I will take you on a very personal journey to discover how this
0:01:27 > 0:01:32one bony blueprint has shaped such massive diversity across the
0:01:32 > 0:01:35animal kingdom and how it's come to dominate life on planet Earth
0:01:37 > 0:01:40This time, we'll discover the way the skeleton has
0:01:40 > 0:01:43adapted for vertebrates to move on land.
0:01:43 > 0:01:45For speed on the ground...
0:01:45 > 0:01:48You can see all these adaptations coming into one very sleek,
0:01:48 > 0:01:50fast animal right here.
0:01:50 > 0:01:53Agility in the treetops...
0:01:53 > 0:01:57And for moving underground, driving one animal to evolve, possibly,
0:01:57 > 0:02:00the oddest bone in the natural world.
0:02:00 > 0:02:02What you can see, instantly,
0:02:02 > 0:02:05is just the weirdness of this bone.
0:02:13 > 0:02:16Although bone might seem like an unchanging and hard structure,
0:02:16 > 0:02:17to me it isn't that at all.
0:02:17 > 0:02:20Instead it's a living, flexing,
0:02:20 > 0:02:23ever-changing framework that makes every single species
0:02:23 > 0:02:25just what it is.
0:02:27 > 0:02:31Bones have adapted in an enormous number of ways for movement on land.
0:02:35 > 0:02:38Animals can swing in the highest trees,
0:02:38 > 0:02:43slide on the forest floor, dig through subterranean worlds
0:02:43 > 0:02:46and run at speed across the savannahs.
0:02:47 > 0:02:50This is a story of survival.
0:02:50 > 0:02:54Each bone telling us how animals have evolved for locomotion,
0:02:54 > 0:02:58allowing them to exploit any habitat on the surface of the earth.
0:02:58 > 0:03:00Whenever I build a skeleton, any skeleton,
0:03:00 > 0:03:03I always start with the vertebrae.
0:03:03 > 0:03:06These are the bones of a gorilla which I'm assembling
0:03:06 > 0:03:08to form the whole skeleton.
0:03:08 > 0:03:10The vertebrae themselves go together
0:03:10 > 0:03:13to make up the spine and it's this spinal column which is
0:03:13 > 0:03:15shared by every single vertebrate on earth.
0:03:18 > 0:03:22To really understand movement, the spine is where it all begins.
0:03:23 > 0:03:28It's the central support for the body and it's also flexible.
0:03:28 > 0:03:32That's mainly down to the way these individual bones work together.
0:03:32 > 0:03:35If you look at these ones here,
0:03:35 > 0:03:38You can see that they have an incredible structure,
0:03:38 > 0:03:43allowing each one to perfectly interlock with the one before it.
0:03:43 > 0:03:45More than that, it allows also to interlock, perfectly,
0:03:45 > 0:03:48with the one behind and so on and so on.
0:03:48 > 0:03:53This is what gives the spine, the spinal column, this flexibility.
0:03:55 > 0:03:59And more than that, an incredible range of movement.
0:04:00 > 0:04:04So the spine gives rigidity, flexibility,
0:04:04 > 0:04:07and provides anchor points for muscles.
0:04:07 > 0:04:10It also protects a whole mass of nerves that need to run
0:04:10 > 0:04:12the length of the body.
0:04:12 > 0:04:15But whilst the spine might be the constant in all vertebrates,
0:04:15 > 0:04:19its structure varies significantly between species.
0:04:21 > 0:04:25And it's that change in structure which has had a dramatic
0:04:25 > 0:04:27effect on how those animals are able to move.
0:04:29 > 0:04:32Take the fastest animal on land - the cheetah,
0:04:32 > 0:04:38capable of speeds of nearly 70mph over short bursts.
0:04:38 > 0:04:42The secret to its speed is in the spine.
0:04:44 > 0:04:47Here we have a cheetah which is hunting Thomson's gazelle
0:04:47 > 0:04:50in the Great Rift Plains of East Africa.
0:04:50 > 0:04:53These Thomson's gazelles or tommies, as they're known,
0:04:53 > 0:04:57are incredibly fast and agile animals and can turn
0:04:57 > 0:05:00and change direction, almost in an instant.
0:05:03 > 0:05:06Cheetahs have had to evolve constantly throughout
0:05:06 > 0:05:10the millions of years in order to stand any chance of capturing
0:05:10 > 0:05:12this very agile prey.
0:05:12 > 0:05:16It's an evolutionary arms race with each animal adapting to
0:05:16 > 0:05:19move in ways that give it an advantage.
0:05:19 > 0:05:22A finely balanced fight for survival.
0:05:23 > 0:05:29The cheetah can go from 0 to 60mph in only three seconds.
0:05:29 > 0:05:31Truly phenomenal!
0:05:31 > 0:05:34If I just pause it here, if we look at the tommie here, you can
0:05:34 > 0:05:39see this incredibly flat, straight, inflexible back.
0:05:39 > 0:05:41It's almost horizontal.
0:05:41 > 0:05:43Now compare this to the cheetah.
0:05:43 > 0:05:48This is a beautiful curve there.
0:05:48 > 0:05:52It curves so much that the back legs
0:05:52 > 0:05:56and the front legs overlap to such an extent that it creates
0:05:56 > 0:06:00almost a spring motion and gives the cheetah a seven-metre stride.
0:06:02 > 0:06:05And if I press play again, you can see the spine flexing
0:06:05 > 0:06:10and extending, giving the cheetah that huge stride length.
0:06:10 > 0:06:13And that's how it can reach those extraordinary top speeds.
0:06:15 > 0:06:18The cheetah's spine is so flexible because the joints are simple
0:06:18 > 0:06:22and open, allowing for a wider range of movement.
0:06:26 > 0:06:30And a flexible spine also means the cheetah can change direction,
0:06:30 > 0:06:33suddenly, helping to make it one of the most successful
0:06:33 > 0:06:35hunters of all the big cats.
0:06:43 > 0:06:46In some animals, the vertebrae have adapted to the extreme...
0:06:49 > 0:06:52..and the spine is practically the only thing left
0:06:52 > 0:06:53to generate movement.
0:06:57 > 0:06:59This is a milk snake, and like all snakes,
0:06:59 > 0:07:03it has one of the simplest skeletons in the Animal Kingdom.
0:07:03 > 0:07:05If I put him down now...
0:07:08 > 0:07:11Then if he decides to move!
0:07:11 > 0:07:12Come on.
0:07:14 > 0:07:16Then you can see straight away that beautiful,
0:07:16 > 0:07:20S-curve here as the snake moves.
0:07:23 > 0:07:26Now this is seven-time movement or undulatory locomotion.
0:07:26 > 0:07:29But how is the snake just so flexible?
0:07:30 > 0:07:33Snakes lost their limbs over 100 million years ago
0:07:33 > 0:07:39and now they're essentially one long, very flexible spine with ribs.
0:07:40 > 0:07:44But unlike our vertebrae, which work together to allow movement
0:07:44 > 0:07:48backwards and forwards, the snakes vertebrae have evolved to
0:07:48 > 0:07:50work in a very different way altogether.
0:07:53 > 0:07:56Professor Susan Evans from University College London
0:07:56 > 0:07:57works on snake vertebrae.
0:07:59 > 0:08:03If we look at a couple of vertebrae here, you can see that what
0:08:03 > 0:08:06you've actually got is a ball at one end
0:08:06 > 0:08:07and a cup at the other.
0:08:07 > 0:08:09We've effectively got a ball and a socket joint.
0:08:09 > 0:08:12In the same way that we've got one in our shoulder and our hips?
0:08:12 > 0:08:15- Exactly.- So is this what gives the snake the flexibility?
0:08:15 > 0:08:19You would think so because you can rotate them very well.
0:08:19 > 0:08:23But if the snake did that, with its spinal cord going through
0:08:23 > 0:08:25the middle, it would damage its spinal cord.
0:08:25 > 0:08:28- Not a good idea.- Not a good idea.
0:08:28 > 0:08:32To stop this happening, the snake vertebrae have evolved a double
0:08:32 > 0:08:37set of joints which allow lateral or side-to-side movement,
0:08:37 > 0:08:38but stop the twisting
0:08:38 > 0:08:41so the snake can move with no harm to the spinal cord.
0:08:44 > 0:08:47These individual joints allow for some flexibility
0:08:47 > 0:08:50but not as much as you might imagine when you see a snake move.
0:08:51 > 0:08:54What gives the snake its flexibility
0:08:54 > 0:08:57is not so much the individual joints between the vertebrae,
0:08:57 > 0:09:00but the fact that you've got so many vertebrae.
0:09:00 > 0:09:03If you take a little bit of a snake's spine,
0:09:03 > 0:09:05like this, for example,
0:09:05 > 0:09:07you can see that, although you just get a small amount
0:09:07 > 0:09:10of movement between the individual vertebrae,
0:09:10 > 0:09:14when you multiply that by a length of several vertebrae,
0:09:14 > 0:09:17then you're getting that flexibility.
0:09:17 > 0:09:20The key thing here is the repetition of the vertebrae,
0:09:20 > 0:09:25- the increase in number of vertebrae, up to 500 in a snake.- Mm-hm.
0:09:25 > 0:09:27It's an amazing adaptation.
0:09:27 > 0:09:30It may seem like an obvious, maybe silly question,
0:09:30 > 0:09:33- but why have snakes lost their legs? - It may seem an obvious question
0:09:33 > 0:09:36but it's actually one of the ones that's debated quite a lot.
0:09:36 > 0:09:40It's clearly a very adaptive shape, particularly
0:09:40 > 0:09:44if you're moving in small spaces, in confined spaces,
0:09:44 > 0:09:48or if you want to burrow, you can keep your body size
0:09:48 > 0:09:52relatively large but it's now become very thin
0:09:52 > 0:09:55so that it can get into small spaces, or it can burrow.
0:09:58 > 0:10:01By burrowing, or at least being able to crawl into tight spaces,
0:10:01 > 0:10:03snakes were able to avoid predators
0:10:03 > 0:10:06and exploit new sources of food underground.
0:10:10 > 0:10:14Their spine really is a fantastic adaptation - allowing them
0:10:14 > 0:10:16to travel practically everywhere.
0:10:17 > 0:10:19They can slither up trees...
0:10:21 > 0:10:24..inch themselves along in a straight line...
0:10:25 > 0:10:27..glide.
0:10:27 > 0:10:29One can even jump.
0:10:32 > 0:10:35But being limbless does have its limitations.
0:10:36 > 0:10:38Snakes can't move in the numerous,
0:10:38 > 0:10:42highly specialised ways of vertebrates with arms and legs.
0:10:49 > 0:10:52It's those limbs that really do allow animals to exploit
0:10:52 > 0:10:56every environment on land to its full potential.
0:10:56 > 0:11:00And all vertebrate limbs are based on the same ancestral blueprint.
0:11:02 > 0:11:04You can see here with the gorilla's fore limb, or its arm,
0:11:04 > 0:11:06that it's made up of several parts.
0:11:06 > 0:11:09You've got the one large bone here, the humerus,
0:11:09 > 0:11:12follow down to the two smaller bones, the radius and ulna
0:11:12 > 0:11:15and in the hand you've got a group of bones here, the carpals.
0:11:15 > 0:11:19This then leads down into the five very distinct digits.
0:11:19 > 0:11:22It's called the pentadactyl limb
0:11:22 > 0:11:25because each one ends in five digits.
0:11:25 > 0:11:28And it's the same basic pattern in the hind limb or leg,
0:11:28 > 0:11:32this time it's the femur, the tibia and fibula,
0:11:32 > 0:11:35bones in the feet and five toes.
0:11:35 > 0:11:39Any of my limbs, such as my arm, are exactly the same.
0:11:39 > 0:11:42The one bone, the two bones,
0:11:42 > 0:11:44the collection of little bones and the five digits.
0:11:48 > 0:11:53As animals have evolved to move through every environment on earth,
0:11:53 > 0:11:57so this basic pentadactyl limb has adapted and specialised.
0:12:05 > 0:12:09Up in the trees, one animal has a limb that sets it apart
0:12:09 > 0:12:12from all other canopy dwellers.
0:12:15 > 0:12:19I think this is one of the most spectacular locomotors of them all.
0:12:19 > 0:12:22The gibbon.
0:12:22 > 0:12:23Acrobats of the primate world,
0:12:23 > 0:12:27perfectly adapted to life in the trees.
0:12:27 > 0:12:30First off, they've got these incredibly specialised hands
0:12:30 > 0:12:32with elongated fingers.
0:12:32 > 0:12:34They've got the same sort of thing in their feet
0:12:34 > 0:12:37and this, effectively, makes the hands and feet really long,
0:12:37 > 0:12:41grasping hooks, which is perfect if you're swinging through the canopy.
0:12:43 > 0:12:45They've also got these incredibly long arms.
0:12:45 > 0:12:49They're so long that they are 1.5 times the length of their own legs.
0:12:49 > 0:12:53This is actually not that unusual for an animal which is arboreal.
0:12:53 > 0:12:57What really sets them apart is their special way of moving
0:12:57 > 0:13:01called brachiation, using just their arms to swing through the canopy.
0:13:02 > 0:13:06In this way, they can reach speeds of 35mph.
0:13:06 > 0:13:09One of the reasons the gibbon can do this is
0:13:09 > 0:13:14down to a particular part of the pentadactyl limb, the wrist.
0:13:14 > 0:13:17We can't rotate our hands at the wrist joint at all.
0:13:17 > 0:13:20Any twisting comes from movement in our forearms.
0:13:21 > 0:13:24But the gibbon has a ball and socket-like joint
0:13:24 > 0:13:29allowing it to rotate its hand at the wrist joint by 80 degrees.
0:13:29 > 0:13:32This adaptation means the gibbon can turn its body
0:13:32 > 0:13:36as it swings, building up momentum to propel it through the trees,
0:13:36 > 0:13:38without losing its grip on the branches.
0:13:38 > 0:13:41Having this specialised type of joint allows the gibbon not
0:13:41 > 0:13:45only to save loads of energy, it makes it incredibly flexible
0:13:45 > 0:13:48and ultimately makes it almost limitlessly agile.
0:13:50 > 0:13:52By moving in this fast, efficient way,
0:13:52 > 0:13:55the gibbon can cover a huge territory,
0:13:55 > 0:13:59a great advantage to an animal whose food is usually dispersed
0:13:59 > 0:14:00over a wide area.
0:14:08 > 0:14:12So it's the specialised wrist joint of the gibbon which gives us
0:14:12 > 0:14:15the clue that it's such a remarkable locomotor.
0:14:19 > 0:14:22And every individual bone of the pentadactyl limb,
0:14:22 > 0:14:25its shape, its size, its weight,
0:14:25 > 0:14:28can tell us so much about how that animal
0:14:28 > 0:14:32has evolved and, in particular, how it moves.
0:14:34 > 0:14:37I've got three bones here from three very different animals.
0:14:37 > 0:14:40These are actually all the same bone, they're the humerus,
0:14:40 > 0:14:41the largest home in the upper limb
0:14:41 > 0:14:45and what these bones really tell me is everything about the animals'
0:14:45 > 0:14:48locomotion, so how they move, how they get about.
0:14:48 > 0:14:52The first one is this thing here. This is from a cow.
0:14:52 > 0:14:56As you would expect, it's very large, robust, heavy and stocky.
0:14:56 > 0:15:00Cows can weigh up to 500kg, that's a lot of animal.
0:15:00 > 0:15:02Because you don't see cows gracefully
0:15:02 > 0:15:06running down the street, instead they're heavy, bulky things,
0:15:06 > 0:15:10and they need big, heavyweight bones in order to support this weight.
0:15:10 > 0:15:15On the opposite end of the scale, you've got something like this.
0:15:15 > 0:15:19This is a long, slender, thin, graceful humerus.
0:15:19 > 0:15:23This is actually from a human and fits around here somewhere.
0:15:23 > 0:15:25Unlike the cow, we're not four-legged
0:15:25 > 0:15:28so we don't weight bear on our fore limbs.
0:15:29 > 0:15:31Then we get this little thing.
0:15:31 > 0:15:33This is the humerus of a mole and it doesn't actually
0:15:33 > 0:15:36look like a humerus at all, it looks like a tooth.
0:15:36 > 0:15:40Because it's quite hard to see, I've actually scaled one up.
0:15:40 > 0:15:43I've had a 3D print made which is ten times the size
0:15:43 > 0:15:48of the real mole humerus so that this is now comparable to the human
0:15:48 > 0:15:49and cow bone.
0:15:49 > 0:15:53What you can see instantly is just the weirdness of this bone.
0:15:53 > 0:15:56That's because there are so many special adaptations
0:15:56 > 0:15:58for the underground lifestyle the mole has.
0:15:58 > 0:16:00The bone is very squat, very short,
0:16:00 > 0:16:02very flat, what we call spatulate.
0:16:02 > 0:16:06This allows the whole fore limb to act like a paddle.
0:16:06 > 0:16:09More importantly, you can see these incredible projections here,
0:16:09 > 0:16:11all over the side of the humerus.
0:16:11 > 0:16:13Having a larger surface area,
0:16:13 > 0:16:15and having all these little projections and grooves
0:16:15 > 0:16:20and flanges and holes, really allows for much larger muscle attachment
0:16:20 > 0:16:23and ultimately much stronger muscle attachments, as well.
0:16:23 > 0:16:26This is a perfect adaptation for a mole which spends
0:16:26 > 0:16:29its entire life tunnelling underground.
0:16:35 > 0:16:38This European mole is able to move its own body weight in soil
0:16:38 > 0:16:40every minute,
0:16:40 > 0:16:43searching for worms, beetle larvae and slugs to eat.
0:16:45 > 0:16:47Each mole has its own tunnel network,
0:16:47 > 0:16:49sometimes over 100 metres long.
0:16:51 > 0:16:53They really are super-powered burrowers.
0:16:55 > 0:17:00But their ability to dig isn't just down to their oddly shaped humerus.
0:17:01 > 0:17:03There's an adaptation to the hand of the mole
0:17:03 > 0:17:07which has been puzzling scientists for years.
0:17:07 > 0:17:10I absolutely love mole hands.
0:17:10 > 0:17:11They are very personal to me, actually.
0:17:11 > 0:17:14I was given one when I was about three from my granddad.
0:17:14 > 0:17:16he used to be a mole catcher.
0:17:16 > 0:17:19I kept her with me for ages in a matchbox
0:17:19 > 0:17:24There's something I know now that I didn't know, 30 odd years ago.
0:17:24 > 0:17:29That's that they have something that resembles an extra digit.
0:17:29 > 0:17:31And that's strange because, as far as we know,
0:17:31 > 0:17:35no living species normally has more than the five digits
0:17:35 > 0:17:36of the pentadactyl limb.
0:17:38 > 0:17:41When you look at a X-ray of the mole hand it starts to become
0:17:41 > 0:17:42clear what's going on.
0:17:42 > 0:17:47You can see really clearly they've got these five distinct digits.
0:17:47 > 0:17:51Each one made up of lots of little bones, just like my hand.
0:17:51 > 0:17:55But then stuck on the end, there is this whacking great bone here.
0:17:55 > 0:17:58It's a solid piece of bone that sits on the side of the hand.
0:17:58 > 0:18:02Whereas these five are true digits,
0:18:02 > 0:18:06this thing here looks like an impostor.
0:18:08 > 0:18:11Scientists recently found out that this impostor
0:18:11 > 0:18:14grows from a sesamoid bone in the mole's wrist.
0:18:17 > 0:18:21Sesamoid bones are found where a tendon passes over a joint,
0:18:21 > 0:18:24the kneecap, for instance, is a sesamoid bone.
0:18:25 > 0:18:27They both protect the joint
0:18:27 > 0:18:30and increase tension in the tendon,
0:18:30 > 0:18:34making movement much more effective.
0:18:34 > 0:18:36This sesamoid bone has evolved
0:18:36 > 0:18:40to massively increase the surface area of the mole's hand,
0:18:40 > 0:18:44allowing it to dig through the soil much more effectively.
0:18:47 > 0:18:51The mole is not alone in using a sesamoid bone for other purposes.
0:18:53 > 0:18:57The elephant has also co-opted one to act like an extra
0:18:57 > 0:19:00toe in its foot.
0:19:00 > 0:19:02By studying the fossil evidence,
0:19:02 > 0:19:05scientists have worked out that this evolved when elephants were getting
0:19:05 > 0:19:10larger, becoming more land-based and needing the additional support.
0:19:13 > 0:19:15All these pentadactyl limbs have been
0:19:15 > 0:19:18modified for movement on land,
0:19:18 > 0:19:21but there's one animal which has taken that adaptation
0:19:21 > 0:19:23to the extreme.
0:19:28 > 0:19:31Here we've got a horse's fore limb.
0:19:31 > 0:19:33This equates to being the same series of bones
0:19:33 > 0:19:34that I have in my arm here.
0:19:34 > 0:19:36When you have a look at it, you think, yeah,
0:19:36 > 0:19:39I probably know where most of these bones are.
0:19:39 > 0:19:41It sounds reasonable to say this is the shoulder area.
0:19:41 > 0:19:43It's pretty much there, isn't it?
0:19:43 > 0:19:46Then you look down, this is probably the elbow.
0:19:46 > 0:19:48I guess this must be the wrist.
0:19:48 > 0:19:49But you're wrong.
0:19:49 > 0:19:53If you have a good look, you can see that this is the shoulder area.
0:19:53 > 0:19:55It means this is the elbow
0:19:55 > 0:19:57and this is the wrist.
0:19:57 > 0:19:59That means from here on down,
0:19:59 > 0:20:02this is all hand and digit.
0:20:02 > 0:20:04But the bones haven't just become longer.
0:20:04 > 0:20:08Below the elbow, they've reduced in number as well.
0:20:08 > 0:20:11If you look at an area such as the radius and ulna,
0:20:11 > 0:20:14you can see it has got a very large prominent radius here.
0:20:14 > 0:20:17When you look for the ulna, it's this little projection
0:20:17 > 0:20:19that sticks on the back.
0:20:19 > 0:20:22It's still functional but it actually fuses into the body
0:20:22 > 0:20:23of the radius.
0:20:23 > 0:20:26You've also got the same sort of thing happening in this area here.
0:20:26 > 0:20:28This is the cannon bone,
0:20:28 > 0:20:30which is the equivalent of this little bone
0:20:30 > 0:20:32that sits in the middle of my hand here.
0:20:32 > 0:20:34It's technically called metacarpal number three -
0:20:34 > 0:20:36rolls off the tongue, doesn't it?
0:20:36 > 0:20:37So where are the others?
0:20:37 > 0:20:40Well, metacarpals two and four are here.
0:20:40 > 0:20:43As for metacarpals one and five, they've actually gone
0:20:43 > 0:20:45The horse has evolved to lose these.
0:20:45 > 0:20:48As you follow the cannon bone right to its end,
0:20:48 > 0:20:51you can see the end of the limb itself
0:20:51 > 0:20:53finishes in this one digit. The rest have gone.
0:20:53 > 0:20:59Effectively, the horse is walking around on one toe, or one finger,
0:20:59 > 0:21:03on each leg. All of this reduction in the numbers of bones
0:21:03 > 0:21:08really serves to make the whole horse limb incredibly lightweight.
0:21:08 > 0:21:11Only the horse and its closest relatives,
0:21:11 > 0:21:13including the zebra and the donkey,
0:21:13 > 0:21:17have this adaptation with just one digit at the end of each limb.
0:21:20 > 0:21:23Lengthening and lightening the limb has meant horses can reach
0:21:23 > 0:21:26speeds of over 40mph.
0:21:30 > 0:21:33To really appreciate this wonder of evolution,
0:21:33 > 0:21:37I want to see the horse's limbs in action, close up.
0:21:39 > 0:21:42Here in the Structure and Motion laboratory
0:21:42 > 0:21:44at the Royal Veterinary College outside London,
0:21:44 > 0:21:48Professor John Hutchinson has been studying horse locomotion
0:21:48 > 0:21:52to understand more about how horse bones are adapted for speed.
0:21:57 > 0:22:00Why has a horse evolved to run just so quickly?
0:22:00 > 0:22:03Well, horses evolved as prey animals, and certainly a prey animal
0:22:03 > 0:22:05needs to be fast to escape predators,
0:22:05 > 0:22:08so a horse has just taken that to an extreme.
0:22:11 > 0:22:14You can see all these adaptations coming into one very sleek,
0:22:14 > 0:22:17- fast animal right here. - You absolutely can.
0:22:17 > 0:22:20That leg length is coming into play to lengthen the stride,
0:22:20 > 0:22:24and the lightening in the limb enables the horse to swing that limb
0:22:24 > 0:22:27really fast and achieve a high stride rate.
0:22:28 > 0:22:31An animal's speed is the product of its stride length
0:22:31 > 0:22:34multiplied by its stride rate.
0:22:34 > 0:22:37To run faster you need to increase one or the other.
0:22:40 > 0:22:43In most animals, if one of these elements is increased,
0:22:43 > 0:22:45the other one is compromised.
0:22:46 > 0:22:51The giraffe has a long stride length but not a high stride rate.
0:22:54 > 0:22:59The horse has managed to increase both, with its long and light limbs,
0:22:59 > 0:23:03a combination which is thought to boost speed and efficiency.
0:23:09 > 0:23:13But these elongated limbs also have to cope with immense forces.
0:23:17 > 0:23:20When galloping, a horse often has just one hoof
0:23:20 > 0:23:22in contact with the ground.
0:23:22 > 0:23:28This effectively exerts around 600kg of force on that one digit.
0:23:31 > 0:23:34John has been studying how the bones have adapted
0:23:34 > 0:23:36to deal with such forces.
0:23:38 > 0:23:40If we look inside the foot and look at the bones,
0:23:40 > 0:23:43which we can see here in an X-ray that I've taken,
0:23:43 > 0:23:47you can see how there are lots of little bones that move together
0:23:47 > 0:23:49and give a lot of flexibility,
0:23:49 > 0:23:51and that flexibility allows the bones to move
0:23:51 > 0:23:55with respect to one another and deform and handle a lot of weight,
0:23:55 > 0:23:58so that when the foot hits the ground, like we see here,
0:23:58 > 0:24:00this foot coming down, boom!
0:24:00 > 0:24:04You can see that juddering that provides a lot of shock absorption.
0:24:06 > 0:24:10The adaptations to the horse's pentadactyl limb show us
0:24:10 > 0:24:14what an extraordinary material bone really is.
0:24:14 > 0:24:16How it can be lengthened, lightened,
0:24:16 > 0:24:21moulded by the evolutionary drive for animals to move.
0:24:24 > 0:24:27And every skeleton has adapted to allow each animal
0:24:27 > 0:24:30to move in particular environments.
0:24:35 > 0:24:37If you know what to look for,
0:24:37 > 0:24:40these adaptations can reveal surprising stories.
0:24:44 > 0:24:47And there's no better example than with my mole.
0:24:48 > 0:24:52Dr Nick Crumpton, a mammal expert from Cambridge University,
0:24:52 > 0:24:55has brought a different mole, native to South Africa,
0:24:55 > 0:24:59for comparison with my European version.
0:24:59 > 0:25:03- This is one of my favourite animals, this is a golden mole.- Yeah.
0:25:03 > 0:25:05- It's quite similar to the European mole...- Mm-hm.
0:25:05 > 0:25:08..cos they both live in very similar environments.
0:25:08 > 0:25:12Looking at their skeletons, we can kind of see that they have
0:25:12 > 0:25:14a skeleton adapted to a life under the ground.
0:25:14 > 0:25:18So they're quite small, they have almost like a tubular-shaped body.
0:25:18 > 0:25:23They've got much, much larger fore limbs than hind limbs,
0:25:23 > 0:25:25- exactly the same as your mole right here.- Yep.
0:25:25 > 0:25:28And they also have these huge, elongated scapulae,
0:25:28 > 0:25:29like the shoulder blades.
0:25:30 > 0:25:33Initially they seem similar.
0:25:33 > 0:25:38But a closer look reveals that each one has evolved very differently.
0:25:38 > 0:25:42- On your mole, you have that really strange-shaped humerus.- Yep.
0:25:42 > 0:25:45But on golden moles, it's still fairly strange,
0:25:45 > 0:25:48but it looks not as radically peculiar
0:25:48 > 0:25:50as you find in European moles.
0:25:50 > 0:25:55Instead, we find an ulna, one of these bones in our forearms here,
0:25:55 > 0:25:59- that actually extends a lot further back.- It does, doesn't it?
0:25:59 > 0:26:01- That part there, that's called the olecranon process.- Right.
0:26:01 > 0:26:03We have those as well, that's just like...
0:26:03 > 0:26:06- It's pretty much our elbow. - Elbow isn't it, yeah.
0:26:06 > 0:26:09The muscle attaches to that olecranon process,
0:26:09 > 0:26:11and so if you have a sort of bar coming
0:26:11 > 0:26:14out of the bottom of your arm, and you pull on that with a muscle,
0:26:14 > 0:26:18that's going to whip your arm down really fast and powerfully.
0:26:18 > 0:26:19And that's fascinating because
0:26:19 > 0:26:24that's a completely different way of digging to your European moles.
0:26:24 > 0:26:28It's these variations in the bones between the two species that helped
0:26:28 > 0:26:32scientists make an astonishing discovery about their evolution.
0:26:32 > 0:26:35For hundreds of years, people thought that these guys
0:26:35 > 0:26:37were really closely related.
0:26:37 > 0:26:41But when we started using genetic and molecular techniques,
0:26:41 > 0:26:43in the 1990s, especially,
0:26:43 > 0:26:46we actually found that they're really not closely related at all.
0:26:46 > 0:26:51So whereas the European moles are more closely related to shrews
0:26:51 > 0:26:53- and hedgehogs...- Yep.
0:26:53 > 0:26:58..the golden mole is more closely related to elephants and manatees
0:26:58 > 0:27:02than it is any of those sorts of mammals.
0:27:02 > 0:27:05And this is a fantastic example of convergent evolution.
0:27:05 > 0:27:08So these things are really, remarkably unrelated.
0:27:08 > 0:27:12Natural selection has favoured certain aspects,
0:27:12 > 0:27:14certain shapes of their anatomy,
0:27:14 > 0:27:16and it just so happens that they look so similar
0:27:16 > 0:27:19because looking like this means you can do a really good job
0:27:19 > 0:27:21of digging under the ground.
0:27:22 > 0:27:27So the challenge of moving through the various environments on land
0:27:27 > 0:27:31has meant that some skeletons have adapted in very similar ways,
0:27:31 > 0:27:35even though they have a completely different evolutionary heritage.
0:27:39 > 0:27:43And the way the skeleton, this extraordinary collection of bones,
0:27:43 > 0:27:45has adapted to move on land,
0:27:45 > 0:27:50is just one reason I find bones endlessly fascinating.
0:27:52 > 0:27:55Be that the flexible spine of the cheetah,
0:27:55 > 0:27:58the beautifully elegant limb of the horse
0:27:58 > 0:28:01or the bulky squat frame of the European mole
0:28:01 > 0:28:05with its specially adapted hand.
0:28:05 > 0:28:07It's meant that vertebrates have been able
0:28:07 > 0:28:12to move into the trees, the soil and across the land
0:28:12 > 0:28:15to exploit those environments to their full potential.
0:28:17 > 0:28:18But that's not all.
0:28:18 > 0:28:22Next time we'll look at how bones have also allowed vertebrates
0:28:22 > 0:28:25to make the most remarkable move of all...
0:28:25 > 0:28:26into the air.
0:28:29 > 0:28:31Oh, wow, that's absolutely amazing!
0:28:31 > 0:28:37The biggest pterosaurs had a wingspan of over ten metres.
0:28:37 > 0:28:40This bird can travel for 15,000kms
0:28:40 > 0:28:42from the moment it leaves the ground
0:28:42 > 0:28:45until the moment it lands again.