Size Matters Secrets of Bones

'Bones...

'they offer structure,

'support, and strength.

'But they have a much bigger story to tell.'

'Vertebrates may look very different on the outside,

'but one crucial thing unites them all...

'..the skeleton.'

'I'm Ben Garrod,

'an evolutionary biologist with a very...unusual passion.'

This is unbelievable!

There are too many skeletons for me to look at all at once.

'As a child, I was fascinated by bones.

'Now, skeletons have become my life.'

'And I put them together

'for museums and universities all over the world.'

'I'm going to explore the natural world

'from the inside out

'to see how the skeleton has enabled animals to move,

'hunt,

'and even sense the world.'

I will take you on a very personal journey

to discover how this one bony blueprint

has shaped such massive diversity across the animal kingdom

and how it has come to dominate life on planet Earth.

'I'll be putting bones to the test...'

Starting to go... There it goes.

I thought I'd been shot!

'..discovering their strengths...'

You can see all these adaptations coming into one very sleek,

fast animal right here.

'..and their limitations.'

'I'll find out things we never knew about animals...'

Oh, wow! That's absolutely amazing.

These bones genuinely are more air than they are bone.

'..and even a few things about myself.'

I'm quite shocked. It's so weird to look at your own skull

whilst you're still alive, I think, really.

'I'm going to reveal the Secrets of Bones.'

'The skeleton.

'More than 60,000 species share the same basic body plan.'

'If you look closely,

'you can tell everything about how an animal lives its life.'

'The way it moves...'

'..what it eats,

'how it survives.

'Every single bone tells a story.'

'Bones have allowed vertebrates to do remarkable things.

'And I'm going to start

'by looking at how they've enabled animals to become massive.'

'My first stop is Paris.'

Wow. I've always wanted to come here.

This is unbelievable!

'Here in the Paris Museum of Natural History,

'there are thousands of specimens from every corner of the globe.

'And, for a bone-lover like me, this is paradise.'

There are animals here perfectly adapted for swimming,

for running, gliding, digging, killing.

But what's overwhelming for me is that,

when you have this many together in one place,

is their sheer diversity in size.

'The smallest skeleton on the planet is found inside a frog

'recently discovered in Papua New Guinea.

'At just over seven millimetres long,

'this animal's skeleton offers strength and support

'on a tiny scale.

'And that's all made possible by one remarkable substance...

'bone.'

'The very same material is also found in the largest animal

'that has ever lived, the blue whale,

'over 200 million times bigger.'

'But what is it about bone that makes it strong enough

'to support enormous animals

'and yet still be light enough to allow a tiny frog to jump?'

We all know that bone...

is very hard, that's a given.

But there's more to bones than that.

They're actually what we call a composite material

made up of two very different types of element that,

when combined, make something very, very unique and very, very special.

The first one is an organic compound.

It's collagen, and this gives bone its flexibility and durability.

The opposite end of the scale here

is something called calcium phosphate.

This is a mineral compound,

and this gives bone its structure and its strength.

Combining the two makes bone the unique material that it is.

'I'm going to do an experiment

'to separate these two key ingredients

'in order to understand the critical role each one plays.'

Now, there's a skull that's been in an oven...for several days.

This has taken out all of the organic material,

leaving just the calcium phosphate,

and if our bones were made of just calcium,

then this is what would happen.

Now, this is absolutely no use at all.

You've lost all this wonderful collagen structure

that gives bone flexibility

and you're left with this structure that's still quite dense

but there's no integrity to the bone, and that's the issue.

Next, we're going to do the exact opposite.

What I want to do is remove all the mineral component,

and this time just leave myself with the organic compound.

So this skull should be entirely collagen.

'It's been soaking away in formic acid for over a month,

'which should have removed all of the calcium phosphate from the bone,

'leaving almost pure collagen.

'And the result is something really surprising.'

This time, without the structure and all the strength...

..you can see you're left with a twisty, squishy,

flexible skull.

Even the teeth are flexible!

This is what surprised me the most.

If I had a skeleton that was entirely made of collagen,

you'd have to scrape me off the floor.

I'd have absolutely no strength or integrity to my bones,

a bit like this thing.

And that highlights just how important it is to have a skeleton

with bones made of this composite material.

This allows bone to be both flexible and durable,

but, more than anything, it allows bone to be strong.

'Strength in your bones is crucial...

'if you want to be big.'

'To see just how the skeleton's perfect blend

'of mineral and organic elements work together,

'I've come to the University of Bath to really put bone to the test.

Professor Richie Gill studies how bone reacts inside the body

'after joint replacements.

'He has a great piece of kit to test its strength

'compared to various other materials.

'Concrete, for instance.'

Obviously, concrete is used for houses and building materials,

so I'm guessing it's going to be kind of strong?

The concrete that we've got here is unreinforced concrete,

so this is really quite representative of the mineral content

part of bone, so what we'll be able to get

is the feel for how well the concrete will do in bending.

It should be interesting.

We'll just start it now.

HE CHUCKLES

Still made me jump, even though I knew it was going to pop.

That was really quite quick, so...how much force was in there?

It went at 1.2 kilonewtons,

so it's approximately 120 kilograms.

That's about 1½ of me, I guess.

'Despite this section of concrete being relatively small,

'its mineral content still offers enough support

'to take 1½ times my body weight.'

'But, as a direct comparison,

'how much weight would a bone with a similar diameter withstand

'under exactly the same sideways force?'

'For the purposes of this test,

'Richie is using the upper leg bone, the femur, of a roe deer.'

-OK, so we'll just set it going.

-Yeah.

The load's building up, 1.3, two kilonewtons,

up to four kilonewtons...

Oh, you can see the movement already.

-CRACKING

-Oh!

-There it goes.

Nice. It really showed that lovely curve and bend in the bone, then.

More than I expected, actually.

What was happening, you heard those little cracks,

there were subcritical fractures taking place,

so it's breaking in stages

and it was cracking and cracking and cracking

and then it reaches a critical threshold

and, boom, the whole thing goes.

And the overall load there was 4.5 kilonewtons,

so equivalent to 450 kilograms.

-If you remember the concrete...

-Yeah.

..broke at about 1.2 kilonewtons, so 120 kilograms.

That's more than three times the amount of force

to break a bone than concrete?

It's phenomenal.

'Although both rigid and hard,

'the concrete's purely mineral composition

'meant it broke under far less force than the bone.

'This is the collagen at work,

'offering up added flexibility to the composite,

'and, therefore, adding strength.

'But, as strong as they are,

'bones aren't really made to take force from the side like this.'

'Most of the load a bone takes is downward.'

'So, Richie sets up a test

'to see how strong another deer femur can be,

'this time under compression, like we see in nature.'

OK, just about to start applying the loading.

1.3, 1.6... Two kilonewtons.

Still increasing.

Five kilonewtons.

'It's quickly passed the load of the earlier lateral test,

'and the bone still isn't showing any sign of breaking.'

Up to nine...still creeping up.

Ten kilonewtons,

11, 12 kilonewtons. Load still increasing.

14 kilonewtons now.

'The femur is now withstanding three times more force

'than when it was on its side.'

16 kilonewtons.

And now 17.

-There's a huge amount of force here.

-There really is.

-Oh, it's...

Something's starting to go now... There it goes.

HE LAUGHS

That was much more impressive than I thought that would be, Richie!

I thought I'd been shot! Wow.

-That's 17 kilonewtons.

-17 kilonewtons?!

That was an incredible amount of force.

There's no two ways about that, that was massively impressive!

In everyday terms, what does 17 kilonewtons translate as?

I can't even think right now, it really has taken me aback.

-It's about 1.7 tonnes.

-Over 1½ tonnes of force

to break a deer bone, a deer femur?

These animals don't weigh much more than a Labrador. That's...

That's kind of too much to understand right now, but basically

it really goes to show just how strong these bones really are.

And the cross-sectional area of this is relatively small,

and if you consider a human femur,

which could be up to three times that diameter,

that can take considerably much more force.

'This ability for bones to be built stronger

'than you may think they need to be can be seen clearly in sprinters.'

STARTING PISTOL FIRES

'At the moment they leave their starting blocks,

'the compressive load on the lower limbs

'is more than 13 times their body weight.

'That's effectively over a tonne of force going through each leg.'

'In the animal kingdom, this safety factor for bone is also built-in.'

'As both predator and prey suddenly switch direction at high speeds,

'the extra force applied to the limbs

'make it essential that bones,

'even in relatively light animals, are made super strong.'

'And when your body is massive,

'strength in your skeleton is even more important.'

'In order for bones to get both big and strong like this,

'they need to do something that may sound obvious,

'they need to be able to grow.'

Most people think of bone as being pure white.

And yeah, it is,

when you're looking at a long-dead animal like this guy here.

But if you took a look inside a living animal -

me, maybe - then you'd see something very different.

'Living bone is actually pink in colour,

'as you can see from this footage of a knee operation.

'The reason is that bone is living tissue

'and is packed full of blood vessels.'

'Although this procedure looks aggressive, bone can take it.

'And that's down to its ability to regenerate.'

Bone cells replenish and replace themselves

almost constantly through our lives.

As an adult, over a ten-year period,

every single bone cell within my skeleton will have been replaced,

and this is even quicker when we're younger.

'At the age of 12 months, I had, in effect,

'a completely different skeleton to the one I was born with.'

'But, as I got older,

'the rate at which my bone cells regenerated began to slow.'

'Even though the rest of me was growing fast,

'the cells in my skeleton were regenerating at a much slower rate,

'and this can vary depending on how active we are.'

'By the time I was in my teens,

'my bones had been replaced about three times.'

Now I'm...early 30s,

and this means that I'm onto skeleton number...five or six.

'If I'm lucky enough to make it to 100,

'I will have worn out and replaced the equivalent

'of around ten complete skeletons.'

'The effects of this ability for bones to grow throughout our lives

'can be found in some surprising places.'

'Henry VIII's flagship, the Mary Rose,

'sunk in Portsmouth Harbour in 1545,

'killing around 400 men on board.'

'It was raised from the depths over 30 years ago

'and, along with its delicate wooden structure,

'divers have brought up the bones from 179 individuals.'

'Nick Owen, a sports scientist from the University of Swansea,

'has been looking closely at these bones.

'He wants to discover more about the lives of these men.'

'Some of the bones had been found close to the remains

'of ancient longbows,

'suggesting the skeletons could belong to archers.'

In here we have two of the bows that the team found,

two of the original ones, almost 500 years old,

and a replica one at the back here,

and one of the many thousands of arrows

that were also found on the ship.

I don't want to touch the old ones because I'm very clumsy,

-but can we look at the replica?

-Of course.

What stands out is that it's just so thick, it's just so big.

I knew it was going to be a long, long bow,

but it's much taller than I am!

It just shows that there must have been a huge amount of force...

Well, these are incredibly rigid,

and you needed 160lbs of pull to pull one of these back,

which is, compared to an Olympic archer

who uses a bow that is 48lbs of pull,

you're talking maybe up to three to four times more draw weight needed

to pull a bow of this sort.

Three or four times more force than an Olympic archer? That's immense.

This doesn't come overnight.

What sort of training's involved to become a longbowman?

They trained in medieval times from the age of about seven.

As they progressed in strength and skill,

they got larger and larger bows

until they ended up working with one of this sort of size and strength.

'But were there any clues in the skeletons to confirm the theory

'that some of these men were experienced archers?'

Here we can see a motion capture of a modern-day archer

using a replica traditional longbow,

where the bow is being drawn right back,

and, at that point there, just before release,

the bow in the left hand is pressing the left-hand side of his body,

whereas the lower arm, the radius, is being stretched on the other side,

so one bone is being compressed,

the other bone is being stretched by the same amount.

'Nick thinks that this repeated force in the radius in the left arm

'over several years

'could actually change the shape of the bone over time.'

'This is something seen in athletes that favour one arm in particular,

'like tennis players.'

'The phenomenon was first identified by 19th-century German anatomist

'Julius Wolff.

'Wolff's Law, as it's now known,

'states it's not just the muscle that can grow

'when we apply repeated force.'

'The bone itself can actually get bigger in order to help cope.'

'So, was there any evidence in these bones of Wolff's Law in action?'

We can see, for example, here,

these are bones from the same person.

They're bones of the lower arm,

and they should be just about the same size, but without any extra

instrumentation we can see here that one is clearly larger than the other.

This one's much larger. Yes, you can see it.

It's like it's from two different people. Really is.

So we measured these down an accuracy of 60 microns,

-which is round about the thickness of the human head.

-So very accurately.

-Very accurate measurements indeed, yes.

-How much bigger do they get?

Well, we've measured differences of up to about 30%

between left and right.

30%? That's huge and that's not normal differences.

I'm right-handed so mine wouldn't be that much bigger than my left hand,

-you're saying?

-We don't think so. I mean, we wouldn't expect to see

that sort of difference in regular people.

-So they really were archers?

-Well, we think so.

Bone is a living tissue that can grow throughout a lifetime.

In some animals, this has been taken to the extreme.

Whales don't begin life as giants.

This Fin whale foetus is just 30cm in length

and weighs around a kilogram.

But its skeleton is already nearly fully formed.

Its bones will need to grow 1,800 times bigger in less than a year.

When fully grown, a Fin whale can dive down to half a kilometre,

and needs a skeleton that can take the pressure.

At these depths,

the force on the bones is 50 times what it would be on the surface.

But impressive as they are, a whale's skeleton has the support

of water, and this reduces the effect of gravity on their bones.

For a life on land,

the skeleton has to hold up a body without the luxury of buoyancy.

And the elephant has come up with some clever solutions.

First up - the legs.

You've got these incredibly long, rigid, straight pillars

just there to support this massive amount of weight.

If you look at the hips, you can see another important factor.

Most land mammals have hips

and especially the socket joint that comes off at an angle to the side,

whereas the elephant here, it's almost facing straight down.

And again this is just to take all of that extra weight

associated with such a large land animal.

Also, and I do love this, they have very weird feet.

Now, there's a gap behind each foot, and this allows for a big

fleshy fatty pad to sit quite nicely underneath.

Now, these act as shock absorbers,

again taking the pressure off all of this heavy extra weight.

And this means that elephants effectively walk on their tip toes.

So you've got an animal that's incredibly big,

that's got pillars for legs, that's got hips that are angled

downwards, and that walks on its tip toes.

Although the elephant skeleton is perfectly adapted for coping

with its enormous size, these adaptations, and especially

the downward-facing hips, leave it unable to move very quickly.

Especially for long periods of time.

Its running style is more akin to a speed walk rather than a gallop,

and there's a reason for this.

When you can run really quickly, the forces on the bones

and joints are huge.

More than ten times an animal's body weight can go through each limb

during every stride.

And for a five-ton elephant whose skeleton isn't built to move

in such a way, these extreme forces would be devastating.

In order to see what it takes to cope with both weight and speed,

you have to look at a very special skeleton indeed.

It's a magnificent beast, which is both massive

and yet can still gallop.

And here it is.

Rhinos can hit between three and four tonnes in weight.

Now, whereas the elephant has evolved and adapted

almost purely to take all of this extra weight of the body,

a rhino, yes, can be large,

but also can be agile and they can reach nearly 50km an hour,

which is twice the speed of an elephant.

This weight at such high speeds puts tremendous force on the skeleton,

and to withstand it the rhino has super-strong bones.

In fact, although much smaller overall,

it can take considerably more force than an elephant skeleton.

And this is largely down to just one single bone.

The femur here is an essential bone for many animals,

and is actually the strongest bone in the body.

What I'd like to do is compare the femur of a rhino

with that of an elephant. Ah, thank you very much, Nigel.

And here we have one. The first thing you can see

when you look at these two very different femurs is not only

that there's a big size difference,

there's also a massive shape difference.

Now, this elephant femur is very long,

slender and quite gracile, it's...

It's more gentle than you'd expect from an elephant, I think.

But then compare this to the rhino.

Now, I absolutely love this femur here. It's so full of character.

It's very short, stocky, robust, heavyset

and it has this amazing flaring

and these beautiful processors down the side of the femur here as well,

which tells me instantly that there's lots of muscle attachment.

So already it's very obvious that this animal is very strong,

very robust and is very well-muscled.

Even though this is a much longer and larger bone,

the femur from the rhino is actually three times stronger.

This is the collagen and the calcium phosphate at work,

combining together to create something remarkable.

And this becomes clear when you apply the same science from earlier.

By taking the cross sectional area of the rhino bone,

and comparing it to that of the deer,

the results are intriguing.

Whereas the tiny deer bone could take 1.7 tonnes

in compressive force,

the rhino femur is capable of withstanding 109 tonnes.

This makes it arguably the strongest single bone

in the animal kingdom.

When it comes to a skeleton adapted perfectly to cope with size,

the rhino has to be my ultimate animal.

So this amazing substance has meant that animals can be

everything from the massive to the absolute minuscule.

That's just the beginning of our journey

into the amazing properties of bone.

It has allowed animals to move in vastly different ways.

And next time,

I'll be exploring how bones have enabled animals to jump,

run, crawl, climb,

dig and slither their way into every single habitat on land.

I'll discover how the horse's skeleton has helped it run so fast.

The limb enables the horse to swing that limb really, really fast.

And how bones can surprise even me.

What you can see instantly is just the weirdness of this bone.

I'll also begin to build a skeleton of my own as I attempt to

transform a lose bunch of bones back into a majestic beast.