0:00:05 > 0:00:07'Bones...
0:00:07 > 0:00:09'they offer structure,
0:00:09 > 0:00:13'support, and strength.
0:00:13 > 0:00:16'But they have a much bigger story to tell.'
0:00:22 > 0:00:26'Vertebrates may look very different on the outside,
0:00:26 > 0:00:30'but one crucial thing unites them all...
0:00:30 > 0:00:32'..the skeleton.'
0:00:34 > 0:00:36'I'm Ben Garrod,
0:00:36 > 0:00:41'an evolutionary biologist with a very...unusual passion.'
0:00:41 > 0:00:43This is unbelievable!
0:00:43 > 0:00:46There are too many skeletons for me to look at all at once.
0:00:46 > 0:00:50'As a child, I was fascinated by bones.
0:00:50 > 0:00:54'Now, skeletons have become my life.'
0:00:58 > 0:01:00'And I put them together
0:01:00 > 0:01:03'for museums and universities all over the world.'
0:01:06 > 0:01:09'I'm going to explore the natural world
0:01:09 > 0:01:13'from the inside out
0:01:13 > 0:01:19'to see how the skeleton has enabled animals to move,
0:01:19 > 0:01:20'hunt,
0:01:20 > 0:01:22'and even sense the world.'
0:01:22 > 0:01:25I will take you on a very personal journey
0:01:25 > 0:01:28to discover how this one bony blueprint
0:01:28 > 0:01:32has shaped such massive diversity across the animal kingdom
0:01:32 > 0:01:36and how it has come to dominate life on planet Earth.
0:01:36 > 0:01:39'I'll be putting bones to the test...'
0:01:39 > 0:01:41Starting to go... There it goes.
0:01:41 > 0:01:43I thought I'd been shot!
0:01:43 > 0:01:46'..discovering their strengths...'
0:01:46 > 0:01:49You can see all these adaptations coming into one very sleek,
0:01:49 > 0:01:50fast animal right here.
0:01:50 > 0:01:53'..and their limitations.'
0:01:55 > 0:01:58'I'll find out things we never knew about animals...'
0:01:58 > 0:02:01Oh, wow! That's absolutely amazing.
0:02:01 > 0:02:04These bones genuinely are more air than they are bone.
0:02:04 > 0:02:08'..and even a few things about myself.'
0:02:08 > 0:02:12I'm quite shocked. It's so weird to look at your own skull
0:02:12 > 0:02:14whilst you're still alive, I think, really.
0:02:14 > 0:02:18'I'm going to reveal the Secrets of Bones.'
0:02:27 > 0:02:29'The skeleton.
0:02:29 > 0:02:34'More than 60,000 species share the same basic body plan.'
0:02:36 > 0:02:37'If you look closely,
0:02:37 > 0:02:41'you can tell everything about how an animal lives its life.'
0:02:44 > 0:02:47'The way it moves...'
0:02:48 > 0:02:51'..what it eats,
0:02:51 > 0:02:53'how it survives.
0:02:53 > 0:02:56'Every single bone tells a story.'
0:02:58 > 0:03:03'Bones have allowed vertebrates to do remarkable things.
0:03:03 > 0:03:05'And I'm going to start
0:03:05 > 0:03:10'by looking at how they've enabled animals to become massive.'
0:03:17 > 0:03:20'My first stop is Paris.'
0:03:24 > 0:03:27Wow. I've always wanted to come here.
0:03:27 > 0:03:29This is unbelievable!
0:03:32 > 0:03:35'Here in the Paris Museum of Natural History,
0:03:35 > 0:03:39'there are thousands of specimens from every corner of the globe.
0:03:39 > 0:03:44'And, for a bone-lover like me, this is paradise.'
0:03:56 > 0:03:59There are animals here perfectly adapted for swimming,
0:03:59 > 0:04:02for running, gliding, digging, killing.
0:04:02 > 0:04:05But what's overwhelming for me is that,
0:04:05 > 0:04:08when you have this many together in one place,
0:04:08 > 0:04:12is their sheer diversity in size.
0:04:19 > 0:04:22'The smallest skeleton on the planet is found inside a frog
0:04:22 > 0:04:25'recently discovered in Papua New Guinea.
0:04:25 > 0:04:29'At just over seven millimetres long,
0:04:29 > 0:04:32'this animal's skeleton offers strength and support
0:04:32 > 0:04:35'on a tiny scale.
0:04:35 > 0:04:39'And that's all made possible by one remarkable substance...
0:04:39 > 0:04:41'bone.'
0:04:45 > 0:04:49'The very same material is also found in the largest animal
0:04:49 > 0:04:53'that has ever lived, the blue whale,
0:04:53 > 0:04:56'over 200 million times bigger.'
0:05:04 > 0:05:07'But what is it about bone that makes it strong enough
0:05:07 > 0:05:09'to support enormous animals
0:05:09 > 0:05:14'and yet still be light enough to allow a tiny frog to jump?'
0:05:21 > 0:05:24We all know that bone...
0:05:24 > 0:05:26is very hard, that's a given.
0:05:26 > 0:05:28But there's more to bones than that.
0:05:28 > 0:05:31They're actually what we call a composite material
0:05:31 > 0:05:33made up of two very different types of element that,
0:05:33 > 0:05:38when combined, make something very, very unique and very, very special.
0:05:38 > 0:05:41The first one is an organic compound.
0:05:41 > 0:05:46It's collagen, and this gives bone its flexibility and durability.
0:05:46 > 0:05:47The opposite end of the scale here
0:05:47 > 0:05:50is something called calcium phosphate.
0:05:50 > 0:05:51This is a mineral compound,
0:05:51 > 0:05:54and this gives bone its structure and its strength.
0:05:54 > 0:05:59Combining the two makes bone the unique material that it is.
0:06:00 > 0:06:02'I'm going to do an experiment
0:06:02 > 0:06:05'to separate these two key ingredients
0:06:05 > 0:06:10'in order to understand the critical role each one plays.'
0:06:10 > 0:06:15Now, there's a skull that's been in an oven...for several days.
0:06:15 > 0:06:19This has taken out all of the organic material,
0:06:19 > 0:06:21leaving just the calcium phosphate,
0:06:21 > 0:06:24and if our bones were made of just calcium,
0:06:24 > 0:06:26then this is what would happen.
0:06:29 > 0:06:32Now, this is absolutely no use at all.
0:06:32 > 0:06:36You've lost all this wonderful collagen structure
0:06:36 > 0:06:38that gives bone flexibility
0:06:38 > 0:06:41and you're left with this structure that's still quite dense
0:06:41 > 0:06:45but there's no integrity to the bone, and that's the issue.
0:06:45 > 0:06:48Next, we're going to do the exact opposite.
0:06:48 > 0:06:52What I want to do is remove all the mineral component,
0:06:52 > 0:06:55and this time just leave myself with the organic compound.
0:06:55 > 0:06:59So this skull should be entirely collagen.
0:07:00 > 0:07:04'It's been soaking away in formic acid for over a month,
0:07:04 > 0:07:08'which should have removed all of the calcium phosphate from the bone,
0:07:08 > 0:07:12'leaving almost pure collagen.
0:07:12 > 0:07:15'And the result is something really surprising.'
0:07:15 > 0:07:20This time, without the structure and all the strength...
0:07:21 > 0:07:27..you can see you're left with a twisty, squishy,
0:07:27 > 0:07:29flexible skull.
0:07:29 > 0:07:31Even the teeth are flexible!
0:07:31 > 0:07:34This is what surprised me the most.
0:07:34 > 0:07:37If I had a skeleton that was entirely made of collagen,
0:07:37 > 0:07:39you'd have to scrape me off the floor.
0:07:39 > 0:07:44I'd have absolutely no strength or integrity to my bones,
0:07:44 > 0:07:46a bit like this thing.
0:07:46 > 0:07:50And that highlights just how important it is to have a skeleton
0:07:50 > 0:07:53with bones made of this composite material.
0:07:53 > 0:07:57This allows bone to be both flexible and durable,
0:07:57 > 0:08:00but, more than anything, it allows bone to be strong.
0:08:07 > 0:08:10'Strength in your bones is crucial...
0:08:10 > 0:08:12'if you want to be big.'
0:08:14 > 0:08:17'To see just how the skeleton's perfect blend
0:08:17 > 0:08:20'of mineral and organic elements work together,
0:08:20 > 0:08:26'I've come to the University of Bath to really put bone to the test.
0:08:26 > 0:08:30Professor Richie Gill studies how bone reacts inside the body
0:08:30 > 0:08:33'after joint replacements.
0:08:33 > 0:08:36'He has a great piece of kit to test its strength
0:08:36 > 0:08:39'compared to various other materials.
0:08:39 > 0:08:41'Concrete, for instance.'
0:08:41 > 0:08:44Obviously, concrete is used for houses and building materials,
0:08:44 > 0:08:46so I'm guessing it's going to be kind of strong?
0:08:46 > 0:08:49The concrete that we've got here is unreinforced concrete,
0:08:49 > 0:08:52so this is really quite representative of the mineral content
0:08:52 > 0:08:55part of bone, so what we'll be able to get
0:08:55 > 0:08:58is the feel for how well the concrete will do in bending.
0:08:58 > 0:09:00It should be interesting.
0:09:00 > 0:09:01We'll just start it now.
0:09:03 > 0:09:05HE CHUCKLES
0:09:05 > 0:09:07Still made me jump, even though I knew it was going to pop.
0:09:07 > 0:09:11That was really quite quick, so...how much force was in there?
0:09:11 > 0:09:13It went at 1.2 kilonewtons,
0:09:13 > 0:09:16so it's approximately 120 kilograms.
0:09:16 > 0:09:18That's about 1½ of me, I guess.
0:09:21 > 0:09:24'Despite this section of concrete being relatively small,
0:09:24 > 0:09:28'its mineral content still offers enough support
0:09:28 > 0:09:30'to take 1½ times my body weight.'
0:09:32 > 0:09:34'But, as a direct comparison,
0:09:34 > 0:09:38'how much weight would a bone with a similar diameter withstand
0:09:38 > 0:09:41'under exactly the same sideways force?'
0:09:43 > 0:09:45'For the purposes of this test,
0:09:45 > 0:09:51'Richie is using the upper leg bone, the femur, of a roe deer.'
0:09:51 > 0:09:53- OK, so we'll just set it going.- Yeah.
0:09:53 > 0:09:57The load's building up, 1.3, two kilonewtons,
0:09:57 > 0:10:00up to four kilonewtons...
0:10:00 > 0:10:03Oh, you can see the movement already.
0:10:03 > 0:10:06- CRACKING - Oh!- There it goes.
0:10:06 > 0:10:10Nice. It really showed that lovely curve and bend in the bone, then.
0:10:10 > 0:10:12More than I expected, actually.
0:10:12 > 0:10:14What was happening, you heard those little cracks,
0:10:14 > 0:10:17there were subcritical fractures taking place,
0:10:17 > 0:10:20so it's breaking in stages
0:10:20 > 0:10:23and it was cracking and cracking and cracking
0:10:23 > 0:10:25and then it reaches a critical threshold
0:10:25 > 0:10:27and, boom, the whole thing goes.
0:10:27 > 0:10:30And the overall load there was 4.5 kilonewtons,
0:10:30 > 0:10:33so equivalent to 450 kilograms.
0:10:33 > 0:10:35- If you remember the concrete...- Yeah.
0:10:35 > 0:10:38..broke at about 1.2 kilonewtons, so 120 kilograms.
0:10:38 > 0:10:41That's more than three times the amount of force
0:10:41 > 0:10:43to break a bone than concrete?
0:10:43 > 0:10:45It's phenomenal.
0:10:47 > 0:10:49'Although both rigid and hard,
0:10:49 > 0:10:51'the concrete's purely mineral composition
0:10:51 > 0:10:55'meant it broke under far less force than the bone.
0:10:55 > 0:10:58'This is the collagen at work,
0:10:58 > 0:11:00'offering up added flexibility to the composite,
0:11:00 > 0:11:03'and, therefore, adding strength.
0:11:03 > 0:11:06'But, as strong as they are,
0:11:06 > 0:11:09'bones aren't really made to take force from the side like this.'
0:11:11 > 0:11:15'Most of the load a bone takes is downward.'
0:11:16 > 0:11:18'So, Richie sets up a test
0:11:18 > 0:11:21'to see how strong another deer femur can be,
0:11:21 > 0:11:26'this time under compression, like we see in nature.'
0:11:26 > 0:11:29OK, just about to start applying the loading.
0:11:29 > 0:11:331.3, 1.6... Two kilonewtons.
0:11:33 > 0:11:35Still increasing.
0:11:35 > 0:11:37Five kilonewtons.
0:11:37 > 0:11:41'It's quickly passed the load of the earlier lateral test,
0:11:41 > 0:11:44'and the bone still isn't showing any sign of breaking.'
0:11:44 > 0:11:47Up to nine...still creeping up.
0:11:47 > 0:11:49Ten kilonewtons,
0:11:49 > 0:11:5411, 12 kilonewtons. Load still increasing.
0:11:54 > 0:11:5614 kilonewtons now.
0:11:56 > 0:12:00'The femur is now withstanding three times more force
0:12:00 > 0:12:02'than when it was on its side.'
0:12:05 > 0:12:0716 kilonewtons.
0:12:09 > 0:12:11And now 17.
0:12:11 > 0:12:14- There's a huge amount of force here. - There really is.- Oh, it's...
0:12:14 > 0:12:18Something's starting to go now... There it goes.
0:12:18 > 0:12:19HE LAUGHS
0:12:21 > 0:12:24That was much more impressive than I thought that would be, Richie!
0:12:24 > 0:12:28I thought I'd been shot! Wow.
0:12:28 > 0:12:30- That's 17 kilonewtons. - 17 kilonewtons?!
0:12:30 > 0:12:33That was an incredible amount of force.
0:12:33 > 0:12:37There's no two ways about that, that was massively impressive!
0:12:37 > 0:12:41In everyday terms, what does 17 kilonewtons translate as?
0:12:41 > 0:12:43I can't even think right now, it really has taken me aback.
0:12:43 > 0:12:46- It's about 1.7 tonnes. - Over 1½ tonnes of force
0:12:46 > 0:12:49to break a deer bone, a deer femur?
0:12:49 > 0:12:52These animals don't weigh much more than a Labrador. That's...
0:12:52 > 0:12:56That's kind of too much to understand right now, but basically
0:12:56 > 0:12:59it really goes to show just how strong these bones really are.
0:12:59 > 0:13:02And the cross-sectional area of this is relatively small,
0:13:02 > 0:13:05and if you consider a human femur,
0:13:05 > 0:13:08which could be up to three times that diameter,
0:13:08 > 0:13:11that can take considerably much more force.
0:13:14 > 0:13:17'This ability for bones to be built stronger
0:13:17 > 0:13:21'than you may think they need to be can be seen clearly in sprinters.'
0:13:21 > 0:13:23STARTING PISTOL FIRES
0:13:23 > 0:13:26'At the moment they leave their starting blocks,
0:13:26 > 0:13:28'the compressive load on the lower limbs
0:13:28 > 0:13:32'is more than 13 times their body weight.
0:13:32 > 0:13:36'That's effectively over a tonne of force going through each leg.'
0:13:41 > 0:13:46'In the animal kingdom, this safety factor for bone is also built-in.'
0:13:48 > 0:13:52'As both predator and prey suddenly switch direction at high speeds,
0:13:52 > 0:13:55'the extra force applied to the limbs
0:13:55 > 0:13:57'make it essential that bones,
0:13:57 > 0:14:00'even in relatively light animals, are made super strong.'
0:14:08 > 0:14:11'And when your body is massive,
0:14:11 > 0:14:14'strength in your skeleton is even more important.'
0:14:17 > 0:14:21'In order for bones to get both big and strong like this,
0:14:21 > 0:14:25'they need to do something that may sound obvious,
0:14:25 > 0:14:27'they need to be able to grow.'
0:14:29 > 0:14:32Most people think of bone as being pure white.
0:14:32 > 0:14:33And yeah, it is,
0:14:33 > 0:14:36when you're looking at a long-dead animal like this guy here.
0:14:36 > 0:14:38But if you took a look inside a living animal -
0:14:38 > 0:14:43me, maybe - then you'd see something very different.
0:14:44 > 0:14:47'Living bone is actually pink in colour,
0:14:47 > 0:14:50'as you can see from this footage of a knee operation.
0:14:50 > 0:14:53'The reason is that bone is living tissue
0:14:53 > 0:14:56'and is packed full of blood vessels.'
0:14:58 > 0:15:02'Although this procedure looks aggressive, bone can take it.
0:15:02 > 0:15:06'And that's down to its ability to regenerate.'
0:15:06 > 0:15:09Bone cells replenish and replace themselves
0:15:09 > 0:15:11almost constantly through our lives.
0:15:11 > 0:15:14As an adult, over a ten-year period,
0:15:14 > 0:15:18every single bone cell within my skeleton will have been replaced,
0:15:18 > 0:15:21and this is even quicker when we're younger.
0:15:23 > 0:15:26'At the age of 12 months, I had, in effect,
0:15:26 > 0:15:30'a completely different skeleton to the one I was born with.'
0:15:33 > 0:15:35'But, as I got older,
0:15:35 > 0:15:40'the rate at which my bone cells regenerated began to slow.'
0:15:42 > 0:15:45'Even though the rest of me was growing fast,
0:15:45 > 0:15:49'the cells in my skeleton were regenerating at a much slower rate,
0:15:49 > 0:15:53'and this can vary depending on how active we are.'
0:15:54 > 0:15:56'By the time I was in my teens,
0:15:56 > 0:16:00'my bones had been replaced about three times.'
0:16:02 > 0:16:04Now I'm...early 30s,
0:16:04 > 0:16:09and this means that I'm onto skeleton number...five or six.
0:16:11 > 0:16:14'If I'm lucky enough to make it to 100,
0:16:14 > 0:16:16'I will have worn out and replaced the equivalent
0:16:16 > 0:16:19'of around ten complete skeletons.'
0:16:24 > 0:16:29'The effects of this ability for bones to grow throughout our lives
0:16:29 > 0:16:33'can be found in some surprising places.'
0:16:38 > 0:16:41'Henry VIII's flagship, the Mary Rose,
0:16:41 > 0:16:45'sunk in Portsmouth Harbour in 1545,
0:16:45 > 0:16:48'killing around 400 men on board.'
0:16:50 > 0:16:53'It was raised from the depths over 30 years ago
0:16:53 > 0:16:56'and, along with its delicate wooden structure,
0:16:56 > 0:17:00'divers have brought up the bones from 179 individuals.'
0:17:03 > 0:17:07'Nick Owen, a sports scientist from the University of Swansea,
0:17:07 > 0:17:11'has been looking closely at these bones.
0:17:11 > 0:17:15'He wants to discover more about the lives of these men.'
0:17:16 > 0:17:19'Some of the bones had been found close to the remains
0:17:19 > 0:17:21'of ancient longbows,
0:17:21 > 0:17:25'suggesting the skeletons could belong to archers.'
0:17:26 > 0:17:29In here we have two of the bows that the team found,
0:17:29 > 0:17:32two of the original ones, almost 500 years old,
0:17:32 > 0:17:34and a replica one at the back here,
0:17:34 > 0:17:36and one of the many thousands of arrows
0:17:36 > 0:17:38that were also found on the ship.
0:17:38 > 0:17:40I don't want to touch the old ones because I'm very clumsy,
0:17:40 > 0:17:43- but can we look at the replica? - Of course.
0:17:43 > 0:17:47What stands out is that it's just so thick, it's just so big.
0:17:47 > 0:17:49I knew it was going to be a long, long bow,
0:17:49 > 0:17:51but it's much taller than I am!
0:17:51 > 0:17:54It just shows that there must have been a huge amount of force...
0:17:54 > 0:17:56Well, these are incredibly rigid,
0:17:56 > 0:18:01and you needed 160lbs of pull to pull one of these back,
0:18:01 > 0:18:03which is, compared to an Olympic archer
0:18:03 > 0:18:06who uses a bow that is 48lbs of pull,
0:18:06 > 0:18:11you're talking maybe up to three to four times more draw weight needed
0:18:11 > 0:18:13to pull a bow of this sort.
0:18:13 > 0:18:17Three or four times more force than an Olympic archer? That's immense.
0:18:17 > 0:18:18This doesn't come overnight.
0:18:18 > 0:18:21What sort of training's involved to become a longbowman?
0:18:21 > 0:18:23They trained in medieval times from the age of about seven.
0:18:23 > 0:18:26As they progressed in strength and skill,
0:18:26 > 0:18:28they got larger and larger bows
0:18:28 > 0:18:31until they ended up working with one of this sort of size and strength.
0:18:32 > 0:18:36'But were there any clues in the skeletons to confirm the theory
0:18:36 > 0:18:40'that some of these men were experienced archers?'
0:18:40 > 0:18:44Here we can see a motion capture of a modern-day archer
0:18:44 > 0:18:46using a replica traditional longbow,
0:18:46 > 0:18:49where the bow is being drawn right back,
0:18:49 > 0:18:52and, at that point there, just before release,
0:18:52 > 0:18:56the bow in the left hand is pressing the left-hand side of his body,
0:18:56 > 0:19:01whereas the lower arm, the radius, is being stretched on the other side,
0:19:01 > 0:19:03so one bone is being compressed,
0:19:03 > 0:19:06the other bone is being stretched by the same amount.
0:19:08 > 0:19:12'Nick thinks that this repeated force in the radius in the left arm
0:19:12 > 0:19:13'over several years
0:19:13 > 0:19:17'could actually change the shape of the bone over time.'
0:19:20 > 0:19:24'This is something seen in athletes that favour one arm in particular,
0:19:24 > 0:19:26'like tennis players.'
0:19:27 > 0:19:31'The phenomenon was first identified by 19th-century German anatomist
0:19:31 > 0:19:33'Julius Wolff.
0:19:33 > 0:19:36'Wolff's Law, as it's now known,
0:19:36 > 0:19:39'states it's not just the muscle that can grow
0:19:39 > 0:19:41'when we apply repeated force.'
0:19:44 > 0:19:49'The bone itself can actually get bigger in order to help cope.'
0:19:51 > 0:19:55'So, was there any evidence in these bones of Wolff's Law in action?'
0:19:55 > 0:19:57We can see, for example, here,
0:19:57 > 0:19:59these are bones from the same person.
0:19:59 > 0:20:01They're bones of the lower arm,
0:20:01 > 0:20:04and they should be just about the same size, but without any extra
0:20:04 > 0:20:07instrumentation we can see here that one is clearly larger than the other.
0:20:07 > 0:20:09This one's much larger. Yes, you can see it.
0:20:09 > 0:20:12It's like it's from two different people. Really is.
0:20:12 > 0:20:15So we measured these down an accuracy of 60 microns,
0:20:15 > 0:20:19- which is round about the thickness of the human head.- So very accurately.
0:20:19 > 0:20:23- Very accurate measurements indeed, yes.- How much bigger do they get?
0:20:23 > 0:20:27Well, we've measured differences of up to about 30%
0:20:27 > 0:20:28between left and right.
0:20:28 > 0:20:3130%? That's huge and that's not normal differences.
0:20:31 > 0:20:34I'm right-handed so mine wouldn't be that much bigger than my left hand,
0:20:34 > 0:20:36- you're saying?- We don't think so. I mean, we wouldn't expect to see
0:20:36 > 0:20:38that sort of difference in regular people.
0:20:38 > 0:20:41- So they really were archers? - Well, we think so.
0:20:43 > 0:20:47Bone is a living tissue that can grow throughout a lifetime.
0:20:47 > 0:20:51In some animals, this has been taken to the extreme.
0:20:52 > 0:20:55Whales don't begin life as giants.
0:20:56 > 0:21:01This Fin whale foetus is just 30cm in length
0:21:01 > 0:21:03and weighs around a kilogram.
0:21:03 > 0:21:06But its skeleton is already nearly fully formed.
0:21:09 > 0:21:15Its bones will need to grow 1,800 times bigger in less than a year.
0:21:21 > 0:21:24When fully grown, a Fin whale can dive down to half a kilometre,
0:21:24 > 0:21:27and needs a skeleton that can take the pressure.
0:21:34 > 0:21:35At these depths,
0:21:35 > 0:21:41the force on the bones is 50 times what it would be on the surface.
0:21:41 > 0:21:44But impressive as they are, a whale's skeleton has the support
0:21:44 > 0:21:48of water, and this reduces the effect of gravity on their bones.
0:21:53 > 0:21:55For a life on land,
0:21:56 > 0:22:00the skeleton has to hold up a body without the luxury of buoyancy.
0:22:02 > 0:22:05And the elephant has come up with some clever solutions.
0:22:05 > 0:22:08First up - the legs.
0:22:09 > 0:22:14You've got these incredibly long, rigid, straight pillars
0:22:14 > 0:22:17just there to support this massive amount of weight.
0:22:19 > 0:22:22If you look at the hips, you can see another important factor.
0:22:22 > 0:22:24Most land mammals have hips
0:22:24 > 0:22:28and especially the socket joint that comes off at an angle to the side,
0:22:28 > 0:22:32whereas the elephant here, it's almost facing straight down.
0:22:32 > 0:22:35And again this is just to take all of that extra weight
0:22:35 > 0:22:38associated with such a large land animal.
0:22:38 > 0:22:42Also, and I do love this, they have very weird feet.
0:22:42 > 0:22:47Now, there's a gap behind each foot, and this allows for a big
0:22:47 > 0:22:51fleshy fatty pad to sit quite nicely underneath.
0:22:51 > 0:22:53Now, these act as shock absorbers,
0:22:53 > 0:22:57again taking the pressure off all of this heavy extra weight.
0:22:59 > 0:23:03And this means that elephants effectively walk on their tip toes.
0:23:04 > 0:23:07So you've got an animal that's incredibly big,
0:23:07 > 0:23:11that's got pillars for legs, that's got hips that are angled
0:23:11 > 0:23:13downwards, and that walks on its tip toes.
0:23:16 > 0:23:20Although the elephant skeleton is perfectly adapted for coping
0:23:20 > 0:23:24with its enormous size, these adaptations, and especially
0:23:24 > 0:23:29the downward-facing hips, leave it unable to move very quickly.
0:23:29 > 0:23:31Especially for long periods of time.
0:23:32 > 0:23:36Its running style is more akin to a speed walk rather than a gallop,
0:23:36 > 0:23:38and there's a reason for this.
0:23:39 > 0:23:43When you can run really quickly, the forces on the bones
0:23:43 > 0:23:45and joints are huge.
0:23:45 > 0:23:50More than ten times an animal's body weight can go through each limb
0:23:50 > 0:23:52during every stride.
0:23:52 > 0:23:56And for a five-ton elephant whose skeleton isn't built to move
0:23:56 > 0:23:59in such a way, these extreme forces would be devastating.
0:24:02 > 0:24:06In order to see what it takes to cope with both weight and speed,
0:24:06 > 0:24:09you have to look at a very special skeleton indeed.
0:24:10 > 0:24:14It's a magnificent beast, which is both massive
0:24:14 > 0:24:16and yet can still gallop.
0:24:16 > 0:24:18And here it is.
0:24:18 > 0:24:22Rhinos can hit between three and four tonnes in weight.
0:24:22 > 0:24:24Now, whereas the elephant has evolved and adapted
0:24:24 > 0:24:28almost purely to take all of this extra weight of the body,
0:24:28 > 0:24:30a rhino, yes, can be large,
0:24:30 > 0:24:35but also can be agile and they can reach nearly 50km an hour,
0:24:35 > 0:24:38which is twice the speed of an elephant.
0:24:41 > 0:24:46This weight at such high speeds puts tremendous force on the skeleton,
0:24:46 > 0:24:49and to withstand it the rhino has super-strong bones.
0:24:53 > 0:24:56In fact, although much smaller overall,
0:24:56 > 0:25:00it can take considerably more force than an elephant skeleton.
0:25:03 > 0:25:09And this is largely down to just one single bone.
0:25:10 > 0:25:13The femur here is an essential bone for many animals,
0:25:13 > 0:25:16and is actually the strongest bone in the body.
0:25:16 > 0:25:19What I'd like to do is compare the femur of a rhino
0:25:19 > 0:25:24with that of an elephant. Ah, thank you very much, Nigel.
0:25:24 > 0:25:27And here we have one. The first thing you can see
0:25:27 > 0:25:30when you look at these two very different femurs is not only
0:25:30 > 0:25:31that there's a big size difference,
0:25:31 > 0:25:33there's also a massive shape difference.
0:25:33 > 0:25:36Now, this elephant femur is very long,
0:25:36 > 0:25:39slender and quite gracile, it's...
0:25:39 > 0:25:42It's more gentle than you'd expect from an elephant, I think.
0:25:42 > 0:25:45But then compare this to the rhino.
0:25:45 > 0:25:50Now, I absolutely love this femur here. It's so full of character.
0:25:50 > 0:25:54It's very short, stocky, robust, heavyset
0:25:54 > 0:25:57and it has this amazing flaring
0:25:57 > 0:26:00and these beautiful processors down the side of the femur here as well,
0:26:00 > 0:26:04which tells me instantly that there's lots of muscle attachment.
0:26:04 > 0:26:06So already it's very obvious that this animal is very strong,
0:26:06 > 0:26:09very robust and is very well-muscled.
0:26:10 > 0:26:15Even though this is a much longer and larger bone,
0:26:16 > 0:26:20the femur from the rhino is actually three times stronger.
0:26:24 > 0:26:29This is the collagen and the calcium phosphate at work,
0:26:31 > 0:26:34combining together to create something remarkable.
0:26:36 > 0:26:41And this becomes clear when you apply the same science from earlier.
0:26:45 > 0:26:48By taking the cross sectional area of the rhino bone,
0:26:50 > 0:26:53and comparing it to that of the deer,
0:26:53 > 0:26:55the results are intriguing.
0:26:57 > 0:27:01Whereas the tiny deer bone could take 1.7 tonnes
0:27:01 > 0:27:03in compressive force,
0:27:04 > 0:27:09the rhino femur is capable of withstanding 109 tonnes.
0:27:20 > 0:27:24This makes it arguably the strongest single bone
0:27:24 > 0:27:25in the animal kingdom.
0:27:28 > 0:27:33When it comes to a skeleton adapted perfectly to cope with size,
0:27:33 > 0:27:37the rhino has to be my ultimate animal.
0:27:40 > 0:27:43So this amazing substance has meant that animals can be
0:27:43 > 0:27:47everything from the massive to the absolute minuscule.
0:27:48 > 0:27:50That's just the beginning of our journey
0:27:50 > 0:27:52into the amazing properties of bone.
0:27:52 > 0:27:56It has allowed animals to move in vastly different ways.
0:27:56 > 0:27:58And next time,
0:27:58 > 0:28:02I'll be exploring how bones have enabled animals to jump,
0:28:02 > 0:28:06run, crawl, climb,
0:28:06 > 0:28:10dig and slither their way into every single habitat on land.
0:28:13 > 0:28:18I'll discover how the horse's skeleton has helped it run so fast.
0:28:18 > 0:28:23The limb enables the horse to swing that limb really, really fast.
0:28:23 > 0:28:26And how bones can surprise even me.
0:28:26 > 0:28:30What you can see instantly is just the weirdness of this bone.
0:28:32 > 0:28:36I'll also begin to build a skeleton of my own as I attempt to
0:28:36 > 0:28:42transform a lose bunch of bones back into a majestic beast.