Secrets of Bones episode 1

GreatBritish1

6/14/2025

Transcript

00:00Bones. They offer structure, support, and strength. But they have a much bigger story to tell.

00:17Vertebrates may look very different on the outside, but one crucial thing unites them all. The skeleton.

00:35I'm Ben Garrett, an evolutionary biologist with a very unusual passion.

00:42This is unbelievable. There are too many skeletons for me to look at all at once.

00:46As a child, I was fascinated by bones. Now, skeletons have become my life.

00:58And I put them together for museums and universities all over the world.

01:06I'm going to explore the natural world from the inside out

01:12to see how the skeleton has enabled animals to move, hunt, and even sense the world.

01:22I will take you on a very personal journey to discover how this one bony blueprint has shaped such massive diversity across the animal kingdom.

01:32And how it has come to dominate life on planet Earth.

01:37I'll be putting bones to the test.

01:39Something sounds a go now. There we go.

01:42I thought I'd been shot.

01:44Discovering their strengths.

01:46You can see all these adaptations coming into one very sleek, fast animal right here.

01:50And their limitations.

01:55I'll find out things we never knew about animals.

01:59Oh, wow. That's absolutely amazing.

02:02These bones genuinely are more air than they are bone.

02:05And even a few things about myself.

02:09I'm quite shocked. It's so weird to look at your own skull whilst it's still alive, I think, really.

02:13I'm going to reveal the secrets of bones.

02:28The skeleton.

02:30More than 60,000 species share the same basic body plan.

02:36If you look closely, you can tell everything about how an animal lives its life.

02:44The way it moves.

02:49What it eats.

02:51How it survives.

02:53Every single bone tells a story.

02:59Bones have allowed vertebrates to do remarkable things.

03:03And I'm going to start by looking at how they've enabled animals to become massive.

03:13My first stop is Paris.

03:25Wow. I've always wanted to come here.

03:28This is unbelievable.

03:29Here, in the Paris Museum of Natural History, there are thousands of specimens from every corner of the globe.

03:40And for a bone lover like me, this is paradise.

03:44There are animals here perfectly adapted for swimming, for running, gliding, digging, killing.

04:02But what's overwhelming for me is that when you have this many together in one place, is their sheer diversity in size.

04:11The smallest skeleton on the planet is found inside a frog, recently discovered in Papua New Guinea.

04:25At just over seven millimeters long, this animal's skeleton offers strength and support on a tiny scale.

04:35And that's all made possible by one remarkable substance.

04:40Bone.

04:41The very same material is also found in the largest animal that has ever lived.

04:52The blue whale.

04:54Over 200 million times bigger.

04:56But 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?

05:14We all know that bone is very hard. That's a given.

05:27But there's more to bones than that.

05:29They're actually what we call a composite material, made up of two very different types of elements,

05:34that when combined, make something very, very unique and very, very special.

05:38The first one is an organic compound. It's collagen, and this gives bone its flexibility and durability.

05:46The opposite end of the scale here is something called calcium phosphate.

05:50Now this is a mineral compound, and this gives bone its structure and its strength.

05:55Combining the two makes bone the unique material that it is.

06:00I'm going to do an experiment to separate these two key ingredients

06:05in order to understand the critical role each one plays.

06:11Now there's a skull that's been in an oven for several days.

06:16Now this has taken out all the organic material, leaving just the calcium phosphate.

06:22And if our bones were made of just calcium, then this is what would happen.

06:30Now this is absolutely no use at all.

06:32You've lost all this wonderful collagen structure that gives bone flexibility,

06:39and you're left with this structure that's still quite dense,

06:42but there's no integrity to the bone, and that's the issue.

06:45Next, we're going to do the exact opposite.

06:49What I want to do is remove all the mineral component,

06:52and this time just leave myself with the organic compound.

06:56So this skull should be entirely collagen.

06:59It's been soaking away in formic acid for over a month,

07:05which should have removed all of the calcium phosphate from the bone,

07:09leaving almost pure collagen.

07:12And the result is something really surprising.

07:15This time, without the structure and all the strength,

07:20you can see you're left with a twisty, squishy, flexible skull.

07:29Even the teeth are flexible. This is what surprised me the most.

07:33So if I had a skeleton that was entirely made of collagen,

07:37you'd have to scrape me off the floor.

07:40I'd have absolutely no strength or integrity to my bones.

07:44A bit like this thing.

07:46And that highlights just how important it is to have a skeleton with bones

07:51made of this composite material.

07:52This allows bone to be both flexible and durable, but more than anything,

07:59it allows bone to be strong.

08:00Strength in your bones is crucial if you want to be big.

08:13To see just how the skeleton's perfect blend of mineral and organic elements work together,

08:19I've come to the University of Bath to really put bone to the test.

08:26Professor Richie Gill studies how bone reacts inside the body after joint replacements.

08:33He has a great piece of kit to test its strength compared to various other materials.

08:39Concrete, for instance.

08:41Now, obviously, concrete is used for houses and building materials,

08:44so I'm guessing it's going to be kind of strong.

08:46The concrete that we've got here is unreinforced concrete.

08:50So this is really quite representative of the mineral content part of bone.

08:55So what we'll be able to get is the feel for how well the concrete will do in bending.

08:59It should be interesting.

09:01We'll just start it now.

09:05Still made me jump even though I knew it was going to pop then.

09:08That was really quite quick. So how much force was in there?

09:12It went at a 1.2 kilonewtons, so it's approximately 120 kilonewtons.

09:16That's about one and a half of me, I guess.

09:21Despite this section of concrete being relatively small,

09:25its mineral content still offers enough support to take one and a half times my body weight.

09:30But, as a direct comparison, how much weight would a bone with a similar diameter withstand under exactly the same sideways force?

09:44For the purposes of this test, Richie is using the upper leg bone, the femur, of a roe deer.

09:50OK, so we'll just let it go.

09:53Yeah.

09:55So the load's building up. 1.3, 2 kilonewtons, up to 4 kilonewtons.

10:00Oh, you can see the movement already.

10:03Oh!

10:05There it goes.

10:07Nice.

10:08It really showed that lovely curve and bend in the bone then, more than I expected actually.

10:12What was happening, you heard those little cracks that were going on, there were sub-critical fractures taking place.

10:17So it's breaking in sort of stages, and it was cracking, and then cracking, and then cracking, and then it reaches a certain critical threshold, and boom, the whole thing goes.

10:27And the overall load there was 4.5 kilonewtons, so equivalent to 450 kilograms.

10:34And if you remember, the concrete broke at about 1.2 kilonewtons, so 120 kilograms.

10:39That's more than three times the amount of force to break a bone than it did concrete. It's phenomenal.

10:44Although both rigid and hard, the concrete's purely mineral composition meant it broke under far less force from the bone.

10:55This is the collagen at work, offering up added flexibility to the composite, and therefore adding strength.

11:03But, as strong as they are, bones aren't really made to take force from the side like this.

11:09Most of the load a bone takes is downward.

11:15So, Richie sets up a test to see how strong another deer femur can be, this time under compression, like we see in nature.

11:25OK, we're just about to start applying the loading.

11:301.3, 1.6, 2 kilonewtons, still increasing.

11:36We've got 5 kilonewtons.

11:38It's quickly passed the load of the earlier lateral test, and the bone still isn't showing any sign of braking.

11:44Up to 9, still creeping up, 10 kilonewtons, 11, 12 kilonewtons, load still increasing, 14 kilonewtons now.

11:57The femur is now withstanding three times more force than when it was on its side.

12:0216 kilonewtons, and now 17.

12:11There's a huge amount of force here. It really is.

12:15Something's starting to go next. There it goes.

12:21That was much more impressive than I thought that would be, Richie.

12:24I thought I'd been shot.

12:27Wow.

12:2817 kilonewtons.

12:2917 kilonewtons!

12:30That was an incredible amount of force, and there's no two ways about that.

12:35That was massively impressive.

12:38In everyday terms, what does 17 kilonewtons translate as?

12:41I can't even think right now, because it really has taken me back.

12:43That's about 1.7 tonnes.

12:45Over 1.5 tonnes of force to break a deer bone, a deer femur.

12:49These animals don't weigh much more than the Labrador.

12:51That's kind of too much to understand right now.

12:55But basically, it really goes to show just how strong these bones really are.

13:00And the cross-sectional area of this is relatively small.

13:03And if you consider a human femur, which could be up to three times that diameter,

13:09I can take it considerably with much more force.

13:15This ability for bones to be built stronger than you may think they need to be

13:19can be seen clearly in sprinters.

13:24At the moment they leave their starting blocks, the compressive load in the lower limbs

13:28is more than 13 times their body weight.

13:32That's effectively over a ton of force going through each leg.

13:36In the animal kingdom, this safety factor for bone is also built in.

13:48As both predator and prey suddenly switch direction at high speeds,

13:53the extra force applied to the limbs make it essential that bones,

13:56even in relatively light animals, are made super strong.

14:08And when your body is massive, strengthen your skeleton is even more important.

14:14In order for bones to get both big and strong like this,

14:21they need to do something that may sound obvious.

14:25They need to be able to grow.

14:27Most people think of bone as being pure white.

14:32And yeah, it is, when you're looking at a long dead animal like this guy here.

14:36But if you took a look inside a living animal, me maybe,

14:40then you'd see something very different.

14:42Living bone is actually pink in colour, as you can see from this footage of a knee operation.

14:50The reason is that bone is living tissue and is packed full of blood vessels.

14:59Although this procedure looks aggressive, bone can take it.

15:03And that's down to its ability to regenerate.

15:07Bone cells replenish and replace themselves almost constantly through our lives.

15:11As an adult, over a 10-year period, every single bone cell within my skeleton will have been replaced.

15:19And this is even quicker when we're younger.

15:23At the age of 12 months, I had in effect a completely different skeleton to the one I was born with.

15:34But as I got older, the rate at which my bone cells regenerated began to slow.

15:39Even though the rest of me was growing fast, the cells in my skeleton were regenerating at a much slower rate.

15:49And this can vary depending on how active we are.

15:52By the time I was in my teens, my bones had been replaced about three times.

16:03Now I'm early 30s, and this means that I'm onto skeleton number five or six.

16:08If I'm lucky enough to make it to a hundred, I will have worn out and replaced the equivalent of around ten complete skeletons.

16:20The effects of this ability for bones to grow throughout our lives can be found in some surprising places.

16:33Henry VIII's flagship, the Mary Rose, sunk in Portsmouth Harbour in 1545, killing around 400 men on board.

16:48It 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.

17:01Nick Owen, a sports scientist from the University of Swansea, has been looking closely at these bones.

17:11He wants to discover more about the lives of these men.

17:14Some of the bones had been found close to the remains of ancient longbows, suggesting the skeletons could belong to archers.

17:27In 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,

17:35and one of the many thousands of arrows that were also found on the ship.

17:39I don't want to touch the old ones because I'm very clumsy, but can we have a look at the replica?

17:42Of course.

17:44What stands out is that it's just so thick, first of all, but it's just so big.

17:47I know it's going to be a long, long bow, but that's much taller than I am.

17:52It just shows that there must have been a huge amount of force involved in one of these things.

17:56Well, these are incredibly rigid, and you needed 160 pounds of pull to pull one of these back,

18:02which is, compared to an Olympic archer who uses a bow that is 48 pounds pull,

18:07so we're talking about maybe up to three to four times more draw weight needed to pull a bow of this sort.

18:12So even three or four times more force than the Olympic archer, that's immense.

18:17This doesn't come overnight, does it? What sort of training is involved to become a long bowman?

18:20That's right. They trained in medieval times from the age of about seven.

18:23As 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.

18:31But were there any clues in the skeletons to confirm the theory that some of these men were experienced archers?

18:39Here we can see a motion capture of a modern day archer using a replica traditional long bow,

18:47where the bow being drawn right back, and at that point there, just before release,

18:53the bow in the left hand is pressing the left hand side of his body,

18:57whereas the lower arm, or the radius, is being stretched on the other side.

19:01So one bone is being compressed, the other bone is being stretched by the same amount.

19:08Nick thinks that this repeated force in the radius in the left arm over several years

19:14could actually change the shape of the bone over time.

19:20This is something seen in athletes that favour one arm in particular, like tennis players.

19:25The phenomenon was first identified by 19th century German anatomist Julius Wolf.

19:33Wolf's law, as it's now known, states it's not just the muscle that can grow when we apply repeated force.

19:45The bone itself can actually get bigger in order to help cope.

19:50So, was there any evidence in these bones of Wolf's law in action?

19:56We can see, for example, here, these are bones from the same person, the bones of the lower arm.

20:01And they should be just about the same size, but without any extra instrumentation,

20:05we can see here that one is clearly larger than the other.

20:08This one is much larger than this, you can see it. It's huge, isn't it?

20:10Yeah, it's like it's from two different people, it really is.

20:13So we measured these down to an accuracy of 60 microns,

20:15which is round about the thickness of human hair.

20:19So very accurately measured?

20:20Very accurate measurements indeed, yes.

20:22How much bigger did they get?

20:24Well, we've measured differences of up to about 30% between left and right.

20:2830%, that's huge, and that's not normal differences.

20:31I mean, I'm right-handed, so mine wouldn't be that much bigger than my left hand, you're saying?

20:35We don't think so. I mean, we wouldn't expect to see that sort of difference in regular people.

20:39So they really were archers?

20:40Well, we think so.

20:41Bone is a living tissue that can grow throughout a lifetime.

20:48In some animals, this has been taken to the extreme.

20:52Whales don't begin life as giants.

20:56This fin whale foetus is just 30 centimetres in length and weighs around a kilogram.

21:03But its skeleton is already nearly fully formed.

21:06Its bones will need to grow 1,800 times bigger in less than a year.

21:21When fully grown, a fin whale can dive down to half a kilometre,

21:24and needs a skeleton that can take the pressure.

21:34At these depths, the force on the bones is 50 times what it would be on the surface.

21:40But impressive as they are, a whale's skeleton has the support of water.

21:46And this reduces the effect of gravity on their bones.

21:53For a life on land, the skeleton has to hold up a body without the luxury of buoyancy.

22:00And the elephant has come up with some clever solutions.

22:06First up, the legs.

22:09You've got these incredibly long, rigid, straight pillars just there to support this massive amount of weight.

22:17If you look at the hips, you can see another important factor.

22:23Most land mammals have hips, and especially the socket joint, that comes off at an angle to the side.

22:29Whereas the elephant here, it's almost facing straight down.

22:33And again, this is just to take all of that extra weight associated with such a large land animal.

22:39Also, and I do love this, they have very weird feet.

22:42Now, there's a gap behind each foot.

22:46And this allows for a big, fleshy, fatty pad to sit quite nicely underneath.

22:51Now, these act as shock absorbers, again taking the pressure of all of this heavy extra weight.

22:59And this means that elephants effectively walk on their tiptoes.

23:04So you've got an animal that's incredibly big, that's got pillars for legs,

23:09that's got hips that are angled downwards, and that walks on its tiptoes.

23:16Although the elephant skeleton is perfectly adapted for coping with its enormous size,

23:22these adaptations, and especially the downward facing hips, leave it unable to move very quickly,

23:29especially for long periods of time.

23:32Its running style is more akin to a speed walk rather than a gallop,

23:36and there's a reason for this.

23:39When you can run really quickly, the forces on the bones and joints are huge.

23:45More than ten times an animal's body weight can go through each limb during every stride.

23:52And for a five-ton elephant, whose skeleton isn't built to move in such a way,

23:57these extreme forces would be devastating.

24:00In order to see what it takes to cope with both weight and speed,

24:06you have to look at a very special skeleton indeed.

24:10It's a magnificent beast, which is both massive and yet can still gallop.

24:16And here it is.

24:17Rhinos can hit between three and four tons in weight.

24:22Now, whereas the elephant has evolved and adapted almost purely to take all of this extra weight of the body,

24:28a rhino, yes, can be large, but also can be agile, and they can reach nearly 50 kilometers an hour,

24:36which is twice the speed of an elephant.

24:38This weight at such high speeds puts tremendous force on the skeleton,

24:46and to withstand it, the rhino has super-strong bones.

24:53In fact, although much smaller overall, it can take considerably more force than an elephant skeleton.

25:00And this is largely down to just one single bone.

25:10The femur here is an essential bone for many animals, and is actually the strongest bone in the body.

25:16What I'd like to do is compare the femur of a rhino with that of an elephant.

25:21Ah, thank you very much, Nigel.

25:24And here we have one.

25:25The first thing you can see when you look at these two very different femurs is not only that there's a big size difference,

25:32there's also a massive shape difference.

25:34Now, this elephant femur is very long, slender, and quite gracile.

25:39It's more gentle than you'd expect from an elephant, I think.

25:43But then compare this to the rhino.

25:45Now, I absolutely love this femur here.

25:48It's so full of character.

25:49It's very short, stocky, robust, heavy set, and it has this amazing flaring and these beautiful processes down the side of the femur here as well,

26:01which tells me instantly that there's lots of muscle attachment.

26:04So, already, it's very obvious that this animal is very strong, very robust, and is very well muscled.

26:09Even though this is a much longer and larger bone, the femur from the rhino is actually three times stronger.

26:21This is the collagen and the calcium phosphate at work.

26:30Combining together to create something remarkable.

26:35And this becomes clear when you apply the same science from earlier.

26:40By taking the cross-sectional area of the rhino bone and comparing it to that of the deer, the results are intriguing.

26:56Whereas the tiny deer bone could take 1.7 tons in compressive force,

27:02the rhino femur is capable of withstanding 109 tons.

27:20This makes it arguably the strongest single bone in the animal kingdom.

27:25When it comes to a skeleton adapted perfectly to cope with size, the rhino has to be my ultimate animal.

27:40So this amazing substance has meant that animals can be everything from the massive to the absolute minuscule.

27:48That's just the beginning of our journey into the amazing properties of bone.

27:52It has allowed animals to move in vastly different ways.

27:56And 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.