Inside Nature's Giants (2009) s01e04 Episode Script
The Giraffe
Hidden inside every giant animal on Earth is a remarkable story of survival.
Tonight, an extraordinary event is about to take place.
A team of leading experts are going to carefully dissect this giraffe to uncover some of the secrets of its evolutionary success.
This is natural history as you've never seen it before, from the inside out.
Richard Dawkins will guide us through one of nature's most bizarre creations.
Engineers have the freedom to go back to the drawing board, evolution doesn't have that freedom.
Biologist Simon Watt will find out how his body measures up against the giraffe's extreme anatomy.
And I'll travel to Africa to see these majestic animals in the wild.
When they're moving, it almost seems like they're running in slow motion.
And we'll try to unravel the mystery of the giraffe's very, very long neck.
Welcome to the Royal Veterinary College where we're about to go under the skin of the world's tallest animal.
In front of me is a young male Rothschild giraffe and despite being almost ten feet tall, it's only about two and half years old, which, for a giraffe, is adolescent.
Sadly, it died recently at a British wildlife park and tonight as well as trying to find out the cause of its unexpected fatal paralysis, we'll also be celebrating a life that's evolved over millions of years by uncovering some of its truly unique anatomy and physiology.
Here in the post-mortem room our dissection will be led by giraffe expert Graham Mitchell and anatomist Joy Reidenberg.
Graham, "specialised" is the word that absolutely comes to mind when you talk about giraffes.
Yes.
The first thing is to step back and say it is truly a remarkable creature.
And when people look at it, what do you see? And everyone sees an extraordinary shape, a relatively narrow and short body, narrow this way, short that way, enormously long legs and an enormously long neck.
And you have to say to yourself, "Why did a creature evolve "and end up in this way? "What were the advantages of having a shape like this?" And that's what strikes you, I think, when you first see it.
But in terms of how it gets through its day, how it survives, how it works, it is the neck that is the main part that we need to understand.
And I think that we should perhaps start by taking off the skin and having a look and see underneath there.
OK, well the team's ready.
Shall we crack on? Just behind the ears there, I think, Richard.
Yes, and then go down the bottom there.
And Joy if you can go along underneath there.
The giraffe is surely one of the most graceful animals to inhabit the African bush.
Yet it's lived through the violent reality of natural selection, where only the fittest survive.
A single blow from its leg can shatter a lion's skull.
To stay alive in this dangerous environment, giraffes have evolved some unusual features.
And the first one we'll explore is its neck.
Richard, can I just let you have that just to put aside for us? So, in terms of the anatomy that we expose straight away in the neck, obviouslyhuge amounts of muscle.
Yes.
I think if we start at the top of this neck and look at this bit of tissue, which runs from way down here as you can see it, all the way up here, it gets a bit thinner up at the top This is definitely perhaps the most important ligament in the giraffe.
You can see that it's yellow.
It's got a very nice yellow look to it.
That means it is almost completely elastic tissue.
Its idea is to elevate the neck.
And you'll see the natural position for a giraffe is about 55 degrees to the vertical.
And that is a perfect balance between the tension in that ligament and the weight of the head, which is forcing down on all of the rest of the neck.
So when the giraffe is holding its head like that, absolutely no effort whatsoever to do so.
But when it wants to drink, then it contracts all of these muscles and has to bend that ligament.
Now, that is impressive.
If we try to bend that head - now, grab it, Mark, and see if you can pull it towards Joy and see how far you manage to get it.
Keep pulling I'm coming your way.
I've got it.
Got to go a lot further if you're going to get it on Whoops.
And then let it go.
You can't move that.
Let it go and see where it goes.
Whoa! Exactly.
That is amazing.
And that's exactly what happens.
And when it stops drinking, that is two seconds for the head to swing through a four-metre arc, and it's all dependent on the tension in that ligament.
Surprisingly, it's not holding its head high, but bending down that requires muscle.
The elastic ligament effortlessly returns the neck to its default position.
But how did the giraffe come to have such a long neck in the first place? The story about how the giraffe got its neck is that sort of classic evolutionary chestnut, because whenever one's introduced, the story had been the giraffe stretched its neck, like that, to try to get to the tops of the trees.
And that simply lengthened the neck and then its children inherited.
That, of course, doesn't happen, acquired characteristics are not inherited.
It's done by Darwinian means, which is that there's variation, genetic variation, and those individuals who survive best are the ones who passed on the genes.
Biologists are still arguing about why the giraffe's neck grew so long.
I've come to South Africa to explore the different theories.
Most of us think that giraffes have long necks so they can reach leaves at the top of trees.
This may seem like an obvious idea, but giraffes use their neck in more ways than you might think.
Is that good? Yes, that's perfect.
So is this the kind of reach of your average giraffe? Yes, it's lovely.
And what I'm doing here is I'm measuring the amount of forage that's available for a giraffe bite.
Remarkably, the old idea that the neck evolved for feeding was only scientifically tested recently by ecologist Elissa Cameron.
Her research shows that giraffes do enjoy more leaves per mouthful by eating above the heads of competing animals.
But giraffes don't just feed up high, they also use their neck to reach low bushes and deep inside trees.
By being able to reach food that competing animals can't, the giraffe has a significant advantage.
This might be one of the reasons why it evolved such a long neck in the first place.
Later, we'll be exploring other reasons why a long neck might have unexpected benefits in the wild.
We've seen how giraffes use their necks to reach food.
Now we want to investigate how they eat and digest it.
As a boy, growing up in South Africa, Graham Mitchell was often mesmerised by the unlikely contortions a giraffe's tongue could perform in its never-ending search for the perfect acacia leaf.
This is the organ that goes out there and collects the food.
When you look at the tongue, firstly, it is exceptionally long.
And in this one, I would guess it's probably all of15 inches from front to back.
But it's not that so much, it's how long and thin and delicate it is.
What this animal feeds on is leaves.
That is what it has to get hold of.
It is not a grass eater.
It is highly selective.
It just doesn't take any old bush with big leaves or small leaves, it takes the acacia predominantly.
And the acacias have got long thorns on them, so it's got to have a structure which allows it to get access to food that is guarded by thorns.
And the head itself is, you can see, a peculiar shape.
It's got a big back end and a long, thin front end that goes in amongst the trees at the top, sticks out this tongue, takes them off very delicately.
And also those lower teeth against the top palette, if they just take some leaves and put them in there and then move their heads back, then they just strip that entire branch.
And all of those leaves then end up in the mouth.
So in terms of its teeth, can we have a look at those in more detail? Because the way it gets its nutrition out of these nutritious acacia leaves, is just by grinding and chewing, grinding and grinding, mixing with its saliva, swallowing it and bringing it back up again to do the same.
So its teeth are absolutely critical to it getting the best out of its food.
And the upper and lower teeth have to fit perfectly.
We can see that better on these skulls, which is quitegood So this is a big male.
A big adult.
A big adult male, old male.
So this is upper jaw obviously, and these are these grinding surfaces.
And they're incredibly sharp, aren't they? They are, they cut as much as they grind, of course.
These little ridges, these crescent shaped ridges on the top cut the leaf and then once the leaf is in that little hollow in between there, it gets crushed.
And how many hours a day would it be eating and grinding up its food and chewing the cud? A lot (LAUGHS) It would probably be, I would think, half the day that she's spending out there.
That's of 24 hours, probably 12 hours a day it is nibbling away, trying to get this food into its Wow, that is amazing.
Here we go.
Now we're seeing the guts for the first time.
The giraffe is a mega herbivore.
Like hippos and elephants, it consumes huge amounts of vegetation, but confines itself to small leaves.
Although it's a large animal, the guts for processing this food are surprisingly compact.
We've got all the digestive system now here on the dissecting table.
This end, the big bit, is the stomach, well, the four stomachs, which flows out into the intestines which Richard's working on at the moment.
If we get a little bit of this here Joy, I don't know whether you can grab a bit of this as well, but If I pass that one over there Here we go.
So we have got an incredibly long small intestine.
Compare this to the guts of the elephant.
Can you stand back, please? In this animal we see the consequence of a junk food diet, compared to the more discerning gourmet diet of a giraffe.
Giraffes' intestines are much longer and thinner because they digest more slowly, extracting every last bit of goodness from their food.
What it's going to produce at the end are these very small pellets, we can squeeze one out of here, here we go.
A fresh one! So this passes out but the other good stuff has already been absorbed.
All the water has been reclaimed.
These animals are living in a very arid environment so they can't afford to lose water.
So they have a very efficient way of reclaiming all of that water so they can then send it back as saliva and start the process all over again.
So, out of the giraffe, we've taken out its digestive system, its four big stomachs are still on the table here.
But we're going to move on from this to go deeper inside the animal to look at its vital organs.
This is where the stomach was and most of the space of this chest was taken up by the stomach.
So there's not much space for heart and lungs.
And the problem is that a big animal like this needs a lot of air to provide the oxygen.
Compared to us, we take in about half a litre per breath, this animal has to take about 30 times that, up to 15 litres of breath.
And it's got another complication which is this long tube down which all the air has to come before it will reach the lung.
That adds another three litres of volume that it has to breathe before it gets anything into the chest.
Maybe we should try and do that and see whether we can get it to blow up.
We've got the air? We're all set.
Excellent.
OK, brilliant.
OK, so we've got this in and we're ready to go.
WHIRRING Whoa! Look at that Look at that.
That's dramatic.
Wow.
That is truly spectacular.
This would've been the dome where the diaphragm was and the stomach.
Keep going, a little bit more.
We're going to hit the sharp edges of the ribs, Graham.
That's OK.
And the ribs would've been like that and so you can see the lung bulges up into where the ribs would've been and it fills this whole space every single time it breathes, that's what it has to do.
So that's the shape of the diaphragm.
Yes, that's exactly right.
That is extraordinary.
And then when he breathes out, this stuff is full of elastic tissue.
So when you let the air out, you will see that the lung just collapses, we're not sucking air out of it now, it just collapses on itself as the elastic tissue that we stretched contracts down and expels all of that air.
That's so amazing.
What about when it's running, though? This is at rest, you've got this huge animal that must require masses of energy to be able to run, to shift such a giant.
It's going to breathe faster, but is this an animal that tires really quickly? It does tire.
It's just simply not an athlete.
But how does it take in more and to expel it more quickly? It's a kind of mystery because these ribs are very stiff, it's not as if they can lift their ribs the same way as we can, and it's probably related to movement of the intestines up and down against the diaphragm as they gallop.
So when they gallop and put their front feet on the ground, when the front feet hit the ground all of these intestines hit against the diaphragm and that pushes the air out.
And then when they rock onto their back legs, then the intestines move back, and, of course, then the diaphragm can contract quite easily.
This is a piston, beautifully done.
Couldn't be more beautifully designed Evolved.
LAUGHTER We get used to the idea that evolution is so good at producing beautiful, elegant animals that look as though they've been designed.
We forget that sometimes they're not perfect and there are imperfections.
The imperfections are very revealing because they're exactly the kind of imperfections you'd expect from the accidents of history if there were no designer.
There's a nerve called the recurrent laryngeal which runs from the brain and its end organ is the larynx.
You would think it would just go straight there.
But in a human it goes down into the chest, loops around one of the main arteries in the chest and then goes straight back up again.
Obviously a ridiculous detour.
No engineer would ever make a mistake like that.
In our bodies the laryngeal nerve takes a circuitous route, but what happens in an animal with a neck as long as this? It's one of the great evolutionary enigmas that Richard Dawkins is keen to resolve in the flesh.
Interestingly, it's never been dissected out, or only once before has it ever been dissected out in its full length, and that was in 1838.
Don't cut it at this crucial moment.
I won't.
I'm too good an anatomist for that.
You have to trust me now.
What I'm actually holding here is the beginning of that nerve.
It actually starts out not as a separate nerve, but as a branch coming off of a bigger nerve called the vagus nerve.
This keeps running all the way down the body so you'll see it again over here, all the way down the neck on both sides.
So you can see it again right there.
And this is going to wrap around the great vessels coming out of the heart.
So here it is wrapping around that, and then it continues, right there.
So here's the vagus going down and here's the vagus continuing.
And right over here there's a branch, right there, so it's looping and it's coming back, doing a U-turn.
All the way down here.
It's travelled that entire distance to make a U-turn to go all the way back up again.
And so now we can follow it going back up again, so we follow this branch and if we look, we see it again over here.
There it is, like that.
And here you see it going up.
This is the voice box, the larynx, and you can see it going into the back of the larynx here.
And as it innervates this area it controls the muscles that then control making sounds, but also coordinating breathing and swallowing in this area.
So this is a very important nerve.
Interestingly, where it ends is pretty close to where it started.
It started here, coming out of the brain.
It only needed to go about two inches Yes, amazing.
.
.
but it went all the way down and it came all the way back.
That's a beautiful example of historical legacy as opposed to design.
Exactly.
This is not an intelligent design.
An intelligent design would be to go from here to here.
It does beg the question, though, that even in an animal that might've been many millions of years ago with its head down here, why the route around the blood vessels, unless there was a reason that they were there to innervate something else? Well, that was in earlier ancestors.
Then it was the most direct routein fish.
So this is just inherited.
It's a historical legacy.
Fish really don't have much of a neck so there isn't any extension to worry about in fish, it just goes directly there.
Once you introduce a mammalian neck, you start to get a longer neck, now the heart is displaced down lower.
It turns out the laryngeal nerve first evolved in fish-like creatures as a direct link from the brain to gills near the heart.
Over millions of generations this nerve gradually lengthened, each small step always simpler than a major rewiring to a more direct route.
Remember that a designer, an engineer, can go back to the drawing board, throw away the old design, start afresh with what looks more sensible.
A designer has foresight.
Evolution can't go back to the drawing board, evolution has no foresight.
The question of how the giraffe got its long and perfectly engineered neck has been the subject of African folk tales and children's stories.
But the most famous author to really address the question was Charles Darwin.
Darwin realised that over time, species change.
If these changes are useful, then they're passed onto the next generation.
Over time, you get a very different animal, a different species even.
We can trace the incredible history of an animal by looking at the bones surviving from its ancestors.
In the case of a giraffe, we have to go back 60 million years to just after the time when the dinosaurs died out.
At this point, the mammals were small, rodent-like creatures that lived in thick, humid tropical forests.
Fast forward 28 million years and we come to their descendents.
Their legs had extended and they'd started walking on two toes.
Their long snouts were specialised for browsing and choosing the best parts of a plant to eat.
Five million years later lived the sivatheres.
These cousins of modern-day giraffes were as big as elephants and had thick, stocky necks and incredible horns.
Seven million years ago we come to Bohlinia, an animal of a giraffe-like shape that stood six feet tall.
Its fossilised bones were found in what is now Greece and from there it spread out into China, Asia and Africa, and diversified into at least ten different giraffe species.
Those in Asia became extinct.
Of the five in Africa only one survived, growing gradually over five million years to the height and size of modern giraffes.
And that's where the story ends for the time being.
Over 60 million years, they've evolved from rabbit-sized omnivores to 20 foot herbivores, the giraffe.
As the giraffe's neck evolved to belonger and longer, the rest of its organs had to keep up.
Getting blood to a brain so high off the ground requires a heart of incredible power.
Not since the dinosaurs has ananimal faced such a formidablechallenge.
The heart of the giraffeis an extraordinary story in itself, it's got a big problem to deal with, it's got to pump blood all the way up that neck to the head to keep it conscious, to make the whole animal work.
You could solve that problem by having a huge, great colossal heart, but you haven't got the space to do it.
That's right, if you haven't got a big space for a big heart, you have to design the heart slightly differently.
And we can show that very easily by taking this out and cutting through the heart and showing that bit of muscle.
What we're going to do first is to cut through this outer sac of the heart which is called the pericardium.
Quite a strong, fibrous sac.
And it's important that the heart has this because this provides the lubrication, which allows the muscle to contract and relax without drying out or getting friction.
This side of the heart is the right side.
This is the part that is pumping the blood to the lungs.
And you can see that the wall here is perhaps a centimetre and a half, maybe two centimetres thick.
On the other side, pumping the blood to the brain, it's got to go against gravity and in this animal, nearly a metre and a half or more.
And to do that it has to generate a very high pressure.
It does that by thickening the walls of the chamber that is doing the pumping.
And what you're seeing here is just a mass of muscle with a small volume into which the blood is pushed, and then this muscle contracts around it and squirts it out.
Is there any other animal that you know, as a mammal, that has this kind of degree of thickening of its heart? No, because this is determined by the blood pressure.
And this is the animal on the planet with the highest known blood pressure.
And this muscle wall is related almost directly to the length of the neck.
For every 15 centimetres of neck length, this wall gets another half a centimetre thicker.
So this is quite a small thickness, in fact.
I've seen hearts that are nearly three inches thick, in other words another inch of wall.
So, it really is a spectacular bit of machinery that this animal has evolved in order to get the blood up to its head.
Anatomists aren't the only people fascinated by giraffes.
NASA-funded scientist, Jim Hicks, studied them to prepare astronauts for space.
Two things the giraffe has to do.
First it has to pump blood up to the head, and then that blood is returned back to the heart.
At the same time, blood is being pumped out to the rest of the body, down into the legs.
Now there's a real problem associated with being big and tall and long.
Jim is interested in how giraffes cope with gravity.
In particular, how they deal with the weight of blood pressing down into their legs.
Perhaps this physiology could be applied to astronauts.
The result of this research has been this, the Space Cycle.
And I'm gonna give it a spin.
Let's see if I've got the right stuff.
This is really weird.
I'm feeling a real pull into my legs.
I can feel a sort of pins and needles kind of effect.
It's kind of like the feeling you get if you go up a lift really quickly, actually.
You also get a slightly head-rusheffect, you know, as if you're standing up too quickly and all the blood's leaving your brain.
It's kind of exhilarating.
Right now the rate that they're spinning, it's about close to three G's.
Now, the person that's powering the bike is cycling, he's actually getting benefit of skeletal muscle pumps that are driving blood back to the heart.
But for Simon, who's just standing in the cage, under these conditions of increased G-forces, he'll start to feel a bit light-headed as that blood is pooling in the lower legs and his heart has a more difficult time re-establishing blood flow back to his head.
He is getting a little bit green.
Yeah, he's getting actually a lot green.
Bring her down.
I'm OK, I'm OK.
Thank you.
Just relax.
He's going to throw up.
I'm fine, I'm fine, I'm fine, I'm fine.
Welcome to space.
Yeah, man.
Well, that's an example of extreme blood pooling into the lower extremities.
The cardiovascular system was not able to compensate and keep blood profusion up to his brain and he got a bit faint, a bit nauseous.
But once we lay him out horizontally he'll re-establish blood flow.
His colour is slowly coming back.
You'll feel lousy for the rest of the day.
I wouldn't be having these problems if I was a giraffe.
In fact, if we were to put tight fitting pants or spandex pants around your legs, what that'll do is put pressure on the outside of your legs, it would compress your veins, it would prevent your veins from expanding with the increased gravitational stress and therefore blood would not pool to your lower extremities.
So I'm not going to be an astronaut, am I? Not today, you're not going to be an astronaut.
So, Richard, if you're going toopen that up for us, and this is the front leg obviously taken offour giraffe.
So, Graham, how do giraffes avoid the problem of blood pooling in their legs? What this animal has done is to develop a very thick skin, which just is so stiff and strong that nothing inside there can expand and push blood out of that there.
The vessels can't expand.
The pressure inside the vessel is counteracted almost perfectly by the external pressure created by the skin.
So essentially the skin is likea surgical stocking that is just literally clamping everything, so that when there's high pressure you can't end up with fluid coming out of your blood vessels because simply it's confined and restrained.
And as the animal gets older and older, the skin gets thicker and the blood vessel wall gets thicker as well.
It's an adaptive process protecting it from increasing pressure as the leg gets longer and the neck gets taller.
So a built inG-suit prevents a severe case of swollen ankles.
But there's another conundrum.
Why doesn't an animal with the highest blood pressure on the planet blow its brains out every time it bends down for a drink? Now, the question is how does it protect its brain from damage? And not only its brain but it's got a tongue in here, it's got cheek muscles, it's got eyes, it's got skin, etc, all of that has to be protected from this combination of high pressure and gravity.
It's got a really important little structure that lies at the base of the brain.
It's just a great network of vessels, which can't expand, and so the blood pressure is reduced by having to go through many hundreds of rivers rather than just one major river.
So we've got a damping mechanism within the brain that, when your head's on the ground, you're protected from the very high pressure from our big, powerful pump.
But, presumably when its head isdown, gravity will act on the blood that's trying to return to the heart by making it flow back into the brain, which is exactly what you don't want.
Yes, and this is the vessel that we're talking about, this is the jugular vein which normally carries blood from the head all the way back up to the heart.
It's running along here with my fingers.
Now, it has got a whole series of valves in it that prevent blood going from this end of it all the way down to the brain.
And you'll see that there comes a point where the vessel bulges, and there you can see there's a bulge just above my finger, but just beyond that point the vessel is small.
And that shows that we've got a valve at that point preventing blood moving back up this jugular and into the head.
So can we open the jugular up and actually see these valves? Yes, it's very easy to do that.
I'm putting a pair of scissors into the top end of the jugular and I'm just splitting the jugular from one end to the other.
And when we've opened up the jugular, you'll be able to see these flimsy looking little valves that protect the brain from blood running back up.
There's one over there.
So when the blood's trying to flow backwards it goes into there And gets trapped.
And gets trapped.
Incredibly simple and effective way of doing it, but amazingly delicate looking valve.
Wow, that is incredible.
The giraffe has evolved ingenious ways of managing its high pressure blood supply.
The bones of this animal have also undergone radical transformation.
At first glance, the front leg may seem like a gangly version of our limbs, but it couldn't be more different.
So we're looking at the giraffe fore-limb, and it's the right fore-limb, so it's lying as if I were lying like this on the ground.
And what you're seeing at the top is the shoulder which is right here.
This is the shoulder blade or scapula, coming to this joint which is the equivalent of our shoulder.
This bone over here is the equivalent of our arm, the humerus going from the shoulder to the elbow.
So this is an elbow on a giraffe.
And even though this might look like a knee, this is not a knee.
This is in fact the wrist.
So this part over here is the equivalent of our forearm.
And then as we turn the corner, this is the wrist and all of this is the equivalent of a hand.
What you see as this part here is this part here.
And it's extremely elongated in the giraffe.
And then we get down to the actual foot of the giraffe, which is really just these fingers.
And these are animals that started out evolutionarily a long time ago as five-toed animals, eventually lost the outside toes and now walk on just these two toes.
And so that's what we see here in the hoof, two toes right at the end.
If we cut through here and look at the bone inside, what we see is a very, very thick bone.
Here's that thick skin we were talking about before.
Notice how thick the bone itself is.
It's incredibly thick to hold all the weight of this animal.
Also it gives the animal strength if it's going to kick and attack a lion.
That's the equivalent of these two fingers in the human.
If this animal's walking on just those two fingers, you've got two bones in here that are fused together in the adult to make it look like it's one.
So as it's standing, it's standing on two toes, just like that.
These elongated limbs may at first seem strange and unnecessary, but in the context of a giraffe's huge homerange, long legs make perfect sense.
In certain parts of South Africa, giraffe roam over vast areas and the very bestway to see them is from the air.
Giraffe have two basic gaits or ways in which they move around.
When they're walking, it's a kind ofpacing gait, as it's called, where the legs on one side move together in a really coordinated way.
But as soon as they want to movefaster, they have to move into a gallop in which their hind legs move together and their front legs move together.
And they can get up to speeds of around 30 mph, which is pretty staggering, that's much faster than us and, perhaps more importantly, faster than a lion.
You'd think with their markings and their colourings they would really standout but they truly are camouflaged.
There are some down here look, this is amazing, a small group of them galloping.
When you've got giraffe in a small group, you'll have different aged animals andobviously they're different sizes.
But if they're moving together they've got to be able to keep up.
And you can see brilliantly here, we've got a young one with its mother and it's able to keep up because it's got such staggeringly long legs for a young animal.
And it moves pretty much in unison with its mum.
Young giraffes face a precarious early life.
This calf died shortly after it was born at a zoo.
It's been brought to the Royal Veterinary College for post-mortem examination.
Giraffe calves spend 15 months growing in the womb.
They then drop into the world from a dizzying height.
They master their stilt-like legs quickly.
Within 30 minutes they're able to stagger about.
But this is when they're most at risk.
Over half of all newborns die in their first six months.
Most are lost to lions.
The most obvious thing straight away is just how incredibly big it is.
When they're wrapped up as it would be in the uterus in here, it's a fairly, relatively, small package.
When it's born, it's out And if it was standing upright, you can see just how long it really is.
This one is just over six feet long, in fact.
So it's a really big little animal.
Its legs are disproportionately long compared to the size of its body.
Yes.
This one is about one and a half metres long.
And in an adult giraffe, it may be two metres.
So this leg has only got another half a metre to grow.
But compare that to the length of the neck.
The neck is 70% of that length.
And this is going to be longer than the legs when it's mature.
All this has to be long enough is to get to the udder and the milk supply.
And long legs and a short neck is an adaptation that suits it for that particular activity.
But it's got some other things.
When it's coming out, it's got to have hooves that are protected, and you can see that there's a very soft covering over the sharp parts of that hoof, which protect the uterus from damage when the animal is being born.
And, of course, they're born with horns.
But this horn, you'll see, is completely loose and not attached to the skull.
So as it slips through the birth canal, that's streamlined, horns are flat on the head, and then shortly after birth they stand up and then start the long process of fusing to the skull to form what you see as an adult head.
Of course, why it is born with a horn at all, because no other animal is born with a horn, is another little mystery.
Perfectly useless bit of material for a newborn baby giraffe.
A mother won't risk lying down to feed her calf.
Lowering her body to the ground would make her an easy target.
This delicately balanced beast spends as little time as possible bending to drink or lying down to sleep.
In fact, they can get by on as little as ten minutes sleep a day.
This long and heavy neck seems to cause more problems than it solves.
Drinking, breathing, pumping blood to the head, simplystanding up, it's all difficult.
Does the benefit of reaching a few more leaves really outweigh all the costs? Or could there be something else going on? Is there another less obvious advantage to having a long neck? We're in the final stages of our giraffe dissection.
With the neck bones exposed, pathologist Alun Williams can begin his detective work, hunting for clues that may reveal the cause of this animal's mysterious death.
Once all the muscles have been taken off, you end up with seeing the vertebrae underneath and the most obvious thing, a lot of people think there must be loads and loads of bones in the neck of a giraffe.
There aren't.
Just the same number that we have.
There are two up here.
One, two, three, four, five, six.
And there's number seven.
OK, so same number of bones as in us.
It's just that each these has tremendously elongated during evolution and growth.
Still a bit more work to go on there.
But, Alun, obviously we know this animal died from an acute, unexplained paralysis.
Any clues here from having a look at the neck in detail? Yes, we have.
We've discovered a number of things in our dissection.
And if I start around the head, if we look at this muscle here, instead of looking like this nice normal colour, it's become much darker, this bleeding in the muscle, suggesting that there's been some impact onto the lower part of the head.
Almost as if the head has hit the floor.
So, your next step? To take the neck apart even further or not? Yes, I think what we'll do is just take one of these vertebrae out so we can actually see inside.
Richard, can you do that for us? I mean, what it begs a question of is obviously being tall brings certain very distinct disadvantages.
and one of them may be, if you stumble, you fall, the taller you are the harder you fall.
It's serious.
Even though falls can be fatal, giraffes are far from fragile.
When British couple Kathy and Steve Auckland filmed these gentle-looking giants on safari in Tanzania, the last thing they expected to see was this.
No, I haven't seen this on the telly either.
In head-to-head battles like these, males with the largest necks dominate.
They'll win access to the most females and are likely to pass their big neck genes to the next generation.
This could well be a factor in the evolution of the neck.
But there's another theory that involves the beautiful skin patterns of giraffes across Africa.
They all share a hidden secret.
These patches are for camouflage, first and foremost.
But underneath the patch is a really sophisticated little blood system.
Around each patch runs quite a big blood vessel.
And that blood vessel gives off smaller branches into the middle of the patch.
And what a giraffe is able to do is to send blood, when it needs to lose heat, through these little branches into the middle of the patch.
Then the heat is given off through that patch to the environment.
When viewed through a thermal camera, the remarkable properties of the patches become clear.
Each one acts as a thermal window, switching on to release body heat.
You can see the patterns here.
A thermal imaging camera is showing up how these are glowing brightly.
There's a lot of heat coming from those.
And the longer the neck, the more surface area available for these heat-losing patches.
If you want to keep yourself cool in somewhere like Africa, having a long, thin body is a good way of doing it.
It increases your surface area dramatically.
It's much, much better than being, say, fat and squat.
By lengthening themselves out they're able to cool down.
This means they don't have to hide in the shade all day.
Instead, they can keep feeding any time they want.
The evolution of a body shape that stays cool under the African sun could well be an important reason for the giraffe's extraordinary neck.
While looking for clues to the cause of death, Alun discovered bruising around the lower jaw of our giraffe.
Now he wants to go deeper and examine the spinal cord.
If we just take a knife here, and see if we can If we just look here, we have areas that are just slightly discoloured here and here.
It's very difficult to see with the naked eye.
But they are not the colour they should be, which suggests to me there's bleeding into the spinal cord itself, damaging the nerves that spread messages to control limbs.
So, this is all supporting the idea that this giraffe has lost its footing and the degree of impact, as its neck and head hit the floor, has caused bleeding, and the nerves to stop working properly.
The ultimate cause of our giraffe's death was a simple fall.
It highlights just how costly this elongated body and neck can be.
So, will there be another chapter in the remarkable evolutionary story of the giraffe? At the back of everyone's mind, you're saying this is a creature that's living right on the edge.
It won't take much for the disadvantages to outweigh the advantages and then the species will crash, just like all species do when they've come to the end of a suitable environment.
And that's what I think this animal is doing right now.
It's right on the edge of what an animal can do.
We get used to the idea that evolution produces almost perfect design, the illusion of design.
It looks exactly as an engineer might've done it.
But what's very revealing are those imperfections which we sometimes find, imperfections which no designer would ever have perpetrated, but which are exactly what you'd expect if living creatures were the legacy of history.
Red Bee Media Ltd
Tonight, an extraordinary event is about to take place.
A team of leading experts are going to carefully dissect this giraffe to uncover some of the secrets of its evolutionary success.
This is natural history as you've never seen it before, from the inside out.
Richard Dawkins will guide us through one of nature's most bizarre creations.
Engineers have the freedom to go back to the drawing board, evolution doesn't have that freedom.
Biologist Simon Watt will find out how his body measures up against the giraffe's extreme anatomy.
And I'll travel to Africa to see these majestic animals in the wild.
When they're moving, it almost seems like they're running in slow motion.
And we'll try to unravel the mystery of the giraffe's very, very long neck.
Welcome to the Royal Veterinary College where we're about to go under the skin of the world's tallest animal.
In front of me is a young male Rothschild giraffe and despite being almost ten feet tall, it's only about two and half years old, which, for a giraffe, is adolescent.
Sadly, it died recently at a British wildlife park and tonight as well as trying to find out the cause of its unexpected fatal paralysis, we'll also be celebrating a life that's evolved over millions of years by uncovering some of its truly unique anatomy and physiology.
Here in the post-mortem room our dissection will be led by giraffe expert Graham Mitchell and anatomist Joy Reidenberg.
Graham, "specialised" is the word that absolutely comes to mind when you talk about giraffes.
Yes.
The first thing is to step back and say it is truly a remarkable creature.
And when people look at it, what do you see? And everyone sees an extraordinary shape, a relatively narrow and short body, narrow this way, short that way, enormously long legs and an enormously long neck.
And you have to say to yourself, "Why did a creature evolve "and end up in this way? "What were the advantages of having a shape like this?" And that's what strikes you, I think, when you first see it.
But in terms of how it gets through its day, how it survives, how it works, it is the neck that is the main part that we need to understand.
And I think that we should perhaps start by taking off the skin and having a look and see underneath there.
OK, well the team's ready.
Shall we crack on? Just behind the ears there, I think, Richard.
Yes, and then go down the bottom there.
And Joy if you can go along underneath there.
The giraffe is surely one of the most graceful animals to inhabit the African bush.
Yet it's lived through the violent reality of natural selection, where only the fittest survive.
A single blow from its leg can shatter a lion's skull.
To stay alive in this dangerous environment, giraffes have evolved some unusual features.
And the first one we'll explore is its neck.
Richard, can I just let you have that just to put aside for us? So, in terms of the anatomy that we expose straight away in the neck, obviouslyhuge amounts of muscle.
Yes.
I think if we start at the top of this neck and look at this bit of tissue, which runs from way down here as you can see it, all the way up here, it gets a bit thinner up at the top This is definitely perhaps the most important ligament in the giraffe.
You can see that it's yellow.
It's got a very nice yellow look to it.
That means it is almost completely elastic tissue.
Its idea is to elevate the neck.
And you'll see the natural position for a giraffe is about 55 degrees to the vertical.
And that is a perfect balance between the tension in that ligament and the weight of the head, which is forcing down on all of the rest of the neck.
So when the giraffe is holding its head like that, absolutely no effort whatsoever to do so.
But when it wants to drink, then it contracts all of these muscles and has to bend that ligament.
Now, that is impressive.
If we try to bend that head - now, grab it, Mark, and see if you can pull it towards Joy and see how far you manage to get it.
Keep pulling I'm coming your way.
I've got it.
Got to go a lot further if you're going to get it on Whoops.
And then let it go.
You can't move that.
Let it go and see where it goes.
Whoa! Exactly.
That is amazing.
And that's exactly what happens.
And when it stops drinking, that is two seconds for the head to swing through a four-metre arc, and it's all dependent on the tension in that ligament.
Surprisingly, it's not holding its head high, but bending down that requires muscle.
The elastic ligament effortlessly returns the neck to its default position.
But how did the giraffe come to have such a long neck in the first place? The story about how the giraffe got its neck is that sort of classic evolutionary chestnut, because whenever one's introduced, the story had been the giraffe stretched its neck, like that, to try to get to the tops of the trees.
And that simply lengthened the neck and then its children inherited.
That, of course, doesn't happen, acquired characteristics are not inherited.
It's done by Darwinian means, which is that there's variation, genetic variation, and those individuals who survive best are the ones who passed on the genes.
Biologists are still arguing about why the giraffe's neck grew so long.
I've come to South Africa to explore the different theories.
Most of us think that giraffes have long necks so they can reach leaves at the top of trees.
This may seem like an obvious idea, but giraffes use their neck in more ways than you might think.
Is that good? Yes, that's perfect.
So is this the kind of reach of your average giraffe? Yes, it's lovely.
And what I'm doing here is I'm measuring the amount of forage that's available for a giraffe bite.
Remarkably, the old idea that the neck evolved for feeding was only scientifically tested recently by ecologist Elissa Cameron.
Her research shows that giraffes do enjoy more leaves per mouthful by eating above the heads of competing animals.
But giraffes don't just feed up high, they also use their neck to reach low bushes and deep inside trees.
By being able to reach food that competing animals can't, the giraffe has a significant advantage.
This might be one of the reasons why it evolved such a long neck in the first place.
Later, we'll be exploring other reasons why a long neck might have unexpected benefits in the wild.
We've seen how giraffes use their necks to reach food.
Now we want to investigate how they eat and digest it.
As a boy, growing up in South Africa, Graham Mitchell was often mesmerised by the unlikely contortions a giraffe's tongue could perform in its never-ending search for the perfect acacia leaf.
This is the organ that goes out there and collects the food.
When you look at the tongue, firstly, it is exceptionally long.
And in this one, I would guess it's probably all of15 inches from front to back.
But it's not that so much, it's how long and thin and delicate it is.
What this animal feeds on is leaves.
That is what it has to get hold of.
It is not a grass eater.
It is highly selective.
It just doesn't take any old bush with big leaves or small leaves, it takes the acacia predominantly.
And the acacias have got long thorns on them, so it's got to have a structure which allows it to get access to food that is guarded by thorns.
And the head itself is, you can see, a peculiar shape.
It's got a big back end and a long, thin front end that goes in amongst the trees at the top, sticks out this tongue, takes them off very delicately.
And also those lower teeth against the top palette, if they just take some leaves and put them in there and then move their heads back, then they just strip that entire branch.
And all of those leaves then end up in the mouth.
So in terms of its teeth, can we have a look at those in more detail? Because the way it gets its nutrition out of these nutritious acacia leaves, is just by grinding and chewing, grinding and grinding, mixing with its saliva, swallowing it and bringing it back up again to do the same.
So its teeth are absolutely critical to it getting the best out of its food.
And the upper and lower teeth have to fit perfectly.
We can see that better on these skulls, which is quitegood So this is a big male.
A big adult.
A big adult male, old male.
So this is upper jaw obviously, and these are these grinding surfaces.
And they're incredibly sharp, aren't they? They are, they cut as much as they grind, of course.
These little ridges, these crescent shaped ridges on the top cut the leaf and then once the leaf is in that little hollow in between there, it gets crushed.
And how many hours a day would it be eating and grinding up its food and chewing the cud? A lot (LAUGHS) It would probably be, I would think, half the day that she's spending out there.
That's of 24 hours, probably 12 hours a day it is nibbling away, trying to get this food into its Wow, that is amazing.
Here we go.
Now we're seeing the guts for the first time.
The giraffe is a mega herbivore.
Like hippos and elephants, it consumes huge amounts of vegetation, but confines itself to small leaves.
Although it's a large animal, the guts for processing this food are surprisingly compact.
We've got all the digestive system now here on the dissecting table.
This end, the big bit, is the stomach, well, the four stomachs, which flows out into the intestines which Richard's working on at the moment.
If we get a little bit of this here Joy, I don't know whether you can grab a bit of this as well, but If I pass that one over there Here we go.
So we have got an incredibly long small intestine.
Compare this to the guts of the elephant.
Can you stand back, please? In this animal we see the consequence of a junk food diet, compared to the more discerning gourmet diet of a giraffe.
Giraffes' intestines are much longer and thinner because they digest more slowly, extracting every last bit of goodness from their food.
What it's going to produce at the end are these very small pellets, we can squeeze one out of here, here we go.
A fresh one! So this passes out but the other good stuff has already been absorbed.
All the water has been reclaimed.
These animals are living in a very arid environment so they can't afford to lose water.
So they have a very efficient way of reclaiming all of that water so they can then send it back as saliva and start the process all over again.
So, out of the giraffe, we've taken out its digestive system, its four big stomachs are still on the table here.
But we're going to move on from this to go deeper inside the animal to look at its vital organs.
This is where the stomach was and most of the space of this chest was taken up by the stomach.
So there's not much space for heart and lungs.
And the problem is that a big animal like this needs a lot of air to provide the oxygen.
Compared to us, we take in about half a litre per breath, this animal has to take about 30 times that, up to 15 litres of breath.
And it's got another complication which is this long tube down which all the air has to come before it will reach the lung.
That adds another three litres of volume that it has to breathe before it gets anything into the chest.
Maybe we should try and do that and see whether we can get it to blow up.
We've got the air? We're all set.
Excellent.
OK, brilliant.
OK, so we've got this in and we're ready to go.
WHIRRING Whoa! Look at that Look at that.
That's dramatic.
Wow.
That is truly spectacular.
This would've been the dome where the diaphragm was and the stomach.
Keep going, a little bit more.
We're going to hit the sharp edges of the ribs, Graham.
That's OK.
And the ribs would've been like that and so you can see the lung bulges up into where the ribs would've been and it fills this whole space every single time it breathes, that's what it has to do.
So that's the shape of the diaphragm.
Yes, that's exactly right.
That is extraordinary.
And then when he breathes out, this stuff is full of elastic tissue.
So when you let the air out, you will see that the lung just collapses, we're not sucking air out of it now, it just collapses on itself as the elastic tissue that we stretched contracts down and expels all of that air.
That's so amazing.
What about when it's running, though? This is at rest, you've got this huge animal that must require masses of energy to be able to run, to shift such a giant.
It's going to breathe faster, but is this an animal that tires really quickly? It does tire.
It's just simply not an athlete.
But how does it take in more and to expel it more quickly? It's a kind of mystery because these ribs are very stiff, it's not as if they can lift their ribs the same way as we can, and it's probably related to movement of the intestines up and down against the diaphragm as they gallop.
So when they gallop and put their front feet on the ground, when the front feet hit the ground all of these intestines hit against the diaphragm and that pushes the air out.
And then when they rock onto their back legs, then the intestines move back, and, of course, then the diaphragm can contract quite easily.
This is a piston, beautifully done.
Couldn't be more beautifully designed Evolved.
LAUGHTER We get used to the idea that evolution is so good at producing beautiful, elegant animals that look as though they've been designed.
We forget that sometimes they're not perfect and there are imperfections.
The imperfections are very revealing because they're exactly the kind of imperfections you'd expect from the accidents of history if there were no designer.
There's a nerve called the recurrent laryngeal which runs from the brain and its end organ is the larynx.
You would think it would just go straight there.
But in a human it goes down into the chest, loops around one of the main arteries in the chest and then goes straight back up again.
Obviously a ridiculous detour.
No engineer would ever make a mistake like that.
In our bodies the laryngeal nerve takes a circuitous route, but what happens in an animal with a neck as long as this? It's one of the great evolutionary enigmas that Richard Dawkins is keen to resolve in the flesh.
Interestingly, it's never been dissected out, or only once before has it ever been dissected out in its full length, and that was in 1838.
Don't cut it at this crucial moment.
I won't.
I'm too good an anatomist for that.
You have to trust me now.
What I'm actually holding here is the beginning of that nerve.
It actually starts out not as a separate nerve, but as a branch coming off of a bigger nerve called the vagus nerve.
This keeps running all the way down the body so you'll see it again over here, all the way down the neck on both sides.
So you can see it again right there.
And this is going to wrap around the great vessels coming out of the heart.
So here it is wrapping around that, and then it continues, right there.
So here's the vagus going down and here's the vagus continuing.
And right over here there's a branch, right there, so it's looping and it's coming back, doing a U-turn.
All the way down here.
It's travelled that entire distance to make a U-turn to go all the way back up again.
And so now we can follow it going back up again, so we follow this branch and if we look, we see it again over here.
There it is, like that.
And here you see it going up.
This is the voice box, the larynx, and you can see it going into the back of the larynx here.
And as it innervates this area it controls the muscles that then control making sounds, but also coordinating breathing and swallowing in this area.
So this is a very important nerve.
Interestingly, where it ends is pretty close to where it started.
It started here, coming out of the brain.
It only needed to go about two inches Yes, amazing.
.
.
but it went all the way down and it came all the way back.
That's a beautiful example of historical legacy as opposed to design.
Exactly.
This is not an intelligent design.
An intelligent design would be to go from here to here.
It does beg the question, though, that even in an animal that might've been many millions of years ago with its head down here, why the route around the blood vessels, unless there was a reason that they were there to innervate something else? Well, that was in earlier ancestors.
Then it was the most direct routein fish.
So this is just inherited.
It's a historical legacy.
Fish really don't have much of a neck so there isn't any extension to worry about in fish, it just goes directly there.
Once you introduce a mammalian neck, you start to get a longer neck, now the heart is displaced down lower.
It turns out the laryngeal nerve first evolved in fish-like creatures as a direct link from the brain to gills near the heart.
Over millions of generations this nerve gradually lengthened, each small step always simpler than a major rewiring to a more direct route.
Remember that a designer, an engineer, can go back to the drawing board, throw away the old design, start afresh with what looks more sensible.
A designer has foresight.
Evolution can't go back to the drawing board, evolution has no foresight.
The question of how the giraffe got its long and perfectly engineered neck has been the subject of African folk tales and children's stories.
But the most famous author to really address the question was Charles Darwin.
Darwin realised that over time, species change.
If these changes are useful, then they're passed onto the next generation.
Over time, you get a very different animal, a different species even.
We can trace the incredible history of an animal by looking at the bones surviving from its ancestors.
In the case of a giraffe, we have to go back 60 million years to just after the time when the dinosaurs died out.
At this point, the mammals were small, rodent-like creatures that lived in thick, humid tropical forests.
Fast forward 28 million years and we come to their descendents.
Their legs had extended and they'd started walking on two toes.
Their long snouts were specialised for browsing and choosing the best parts of a plant to eat.
Five million years later lived the sivatheres.
These cousins of modern-day giraffes were as big as elephants and had thick, stocky necks and incredible horns.
Seven million years ago we come to Bohlinia, an animal of a giraffe-like shape that stood six feet tall.
Its fossilised bones were found in what is now Greece and from there it spread out into China, Asia and Africa, and diversified into at least ten different giraffe species.
Those in Asia became extinct.
Of the five in Africa only one survived, growing gradually over five million years to the height and size of modern giraffes.
And that's where the story ends for the time being.
Over 60 million years, they've evolved from rabbit-sized omnivores to 20 foot herbivores, the giraffe.
As the giraffe's neck evolved to belonger and longer, the rest of its organs had to keep up.
Getting blood to a brain so high off the ground requires a heart of incredible power.
Not since the dinosaurs has ananimal faced such a formidablechallenge.
The heart of the giraffeis an extraordinary story in itself, it's got a big problem to deal with, it's got to pump blood all the way up that neck to the head to keep it conscious, to make the whole animal work.
You could solve that problem by having a huge, great colossal heart, but you haven't got the space to do it.
That's right, if you haven't got a big space for a big heart, you have to design the heart slightly differently.
And we can show that very easily by taking this out and cutting through the heart and showing that bit of muscle.
What we're going to do first is to cut through this outer sac of the heart which is called the pericardium.
Quite a strong, fibrous sac.
And it's important that the heart has this because this provides the lubrication, which allows the muscle to contract and relax without drying out or getting friction.
This side of the heart is the right side.
This is the part that is pumping the blood to the lungs.
And you can see that the wall here is perhaps a centimetre and a half, maybe two centimetres thick.
On the other side, pumping the blood to the brain, it's got to go against gravity and in this animal, nearly a metre and a half or more.
And to do that it has to generate a very high pressure.
It does that by thickening the walls of the chamber that is doing the pumping.
And what you're seeing here is just a mass of muscle with a small volume into which the blood is pushed, and then this muscle contracts around it and squirts it out.
Is there any other animal that you know, as a mammal, that has this kind of degree of thickening of its heart? No, because this is determined by the blood pressure.
And this is the animal on the planet with the highest known blood pressure.
And this muscle wall is related almost directly to the length of the neck.
For every 15 centimetres of neck length, this wall gets another half a centimetre thicker.
So this is quite a small thickness, in fact.
I've seen hearts that are nearly three inches thick, in other words another inch of wall.
So, it really is a spectacular bit of machinery that this animal has evolved in order to get the blood up to its head.
Anatomists aren't the only people fascinated by giraffes.
NASA-funded scientist, Jim Hicks, studied them to prepare astronauts for space.
Two things the giraffe has to do.
First it has to pump blood up to the head, and then that blood is returned back to the heart.
At the same time, blood is being pumped out to the rest of the body, down into the legs.
Now there's a real problem associated with being big and tall and long.
Jim is interested in how giraffes cope with gravity.
In particular, how they deal with the weight of blood pressing down into their legs.
Perhaps this physiology could be applied to astronauts.
The result of this research has been this, the Space Cycle.
And I'm gonna give it a spin.
Let's see if I've got the right stuff.
This is really weird.
I'm feeling a real pull into my legs.
I can feel a sort of pins and needles kind of effect.
It's kind of like the feeling you get if you go up a lift really quickly, actually.
You also get a slightly head-rusheffect, you know, as if you're standing up too quickly and all the blood's leaving your brain.
It's kind of exhilarating.
Right now the rate that they're spinning, it's about close to three G's.
Now, the person that's powering the bike is cycling, he's actually getting benefit of skeletal muscle pumps that are driving blood back to the heart.
But for Simon, who's just standing in the cage, under these conditions of increased G-forces, he'll start to feel a bit light-headed as that blood is pooling in the lower legs and his heart has a more difficult time re-establishing blood flow back to his head.
He is getting a little bit green.
Yeah, he's getting actually a lot green.
Bring her down.
I'm OK, I'm OK.
Thank you.
Just relax.
He's going to throw up.
I'm fine, I'm fine, I'm fine, I'm fine.
Welcome to space.
Yeah, man.
Well, that's an example of extreme blood pooling into the lower extremities.
The cardiovascular system was not able to compensate and keep blood profusion up to his brain and he got a bit faint, a bit nauseous.
But once we lay him out horizontally he'll re-establish blood flow.
His colour is slowly coming back.
You'll feel lousy for the rest of the day.
I wouldn't be having these problems if I was a giraffe.
In fact, if we were to put tight fitting pants or spandex pants around your legs, what that'll do is put pressure on the outside of your legs, it would compress your veins, it would prevent your veins from expanding with the increased gravitational stress and therefore blood would not pool to your lower extremities.
So I'm not going to be an astronaut, am I? Not today, you're not going to be an astronaut.
So, Richard, if you're going toopen that up for us, and this is the front leg obviously taken offour giraffe.
So, Graham, how do giraffes avoid the problem of blood pooling in their legs? What this animal has done is to develop a very thick skin, which just is so stiff and strong that nothing inside there can expand and push blood out of that there.
The vessels can't expand.
The pressure inside the vessel is counteracted almost perfectly by the external pressure created by the skin.
So essentially the skin is likea surgical stocking that is just literally clamping everything, so that when there's high pressure you can't end up with fluid coming out of your blood vessels because simply it's confined and restrained.
And as the animal gets older and older, the skin gets thicker and the blood vessel wall gets thicker as well.
It's an adaptive process protecting it from increasing pressure as the leg gets longer and the neck gets taller.
So a built inG-suit prevents a severe case of swollen ankles.
But there's another conundrum.
Why doesn't an animal with the highest blood pressure on the planet blow its brains out every time it bends down for a drink? Now, the question is how does it protect its brain from damage? And not only its brain but it's got a tongue in here, it's got cheek muscles, it's got eyes, it's got skin, etc, all of that has to be protected from this combination of high pressure and gravity.
It's got a really important little structure that lies at the base of the brain.
It's just a great network of vessels, which can't expand, and so the blood pressure is reduced by having to go through many hundreds of rivers rather than just one major river.
So we've got a damping mechanism within the brain that, when your head's on the ground, you're protected from the very high pressure from our big, powerful pump.
But, presumably when its head isdown, gravity will act on the blood that's trying to return to the heart by making it flow back into the brain, which is exactly what you don't want.
Yes, and this is the vessel that we're talking about, this is the jugular vein which normally carries blood from the head all the way back up to the heart.
It's running along here with my fingers.
Now, it has got a whole series of valves in it that prevent blood going from this end of it all the way down to the brain.
And you'll see that there comes a point where the vessel bulges, and there you can see there's a bulge just above my finger, but just beyond that point the vessel is small.
And that shows that we've got a valve at that point preventing blood moving back up this jugular and into the head.
So can we open the jugular up and actually see these valves? Yes, it's very easy to do that.
I'm putting a pair of scissors into the top end of the jugular and I'm just splitting the jugular from one end to the other.
And when we've opened up the jugular, you'll be able to see these flimsy looking little valves that protect the brain from blood running back up.
There's one over there.
So when the blood's trying to flow backwards it goes into there And gets trapped.
And gets trapped.
Incredibly simple and effective way of doing it, but amazingly delicate looking valve.
Wow, that is incredible.
The giraffe has evolved ingenious ways of managing its high pressure blood supply.
The bones of this animal have also undergone radical transformation.
At first glance, the front leg may seem like a gangly version of our limbs, but it couldn't be more different.
So we're looking at the giraffe fore-limb, and it's the right fore-limb, so it's lying as if I were lying like this on the ground.
And what you're seeing at the top is the shoulder which is right here.
This is the shoulder blade or scapula, coming to this joint which is the equivalent of our shoulder.
This bone over here is the equivalent of our arm, the humerus going from the shoulder to the elbow.
So this is an elbow on a giraffe.
And even though this might look like a knee, this is not a knee.
This is in fact the wrist.
So this part over here is the equivalent of our forearm.
And then as we turn the corner, this is the wrist and all of this is the equivalent of a hand.
What you see as this part here is this part here.
And it's extremely elongated in the giraffe.
And then we get down to the actual foot of the giraffe, which is really just these fingers.
And these are animals that started out evolutionarily a long time ago as five-toed animals, eventually lost the outside toes and now walk on just these two toes.
And so that's what we see here in the hoof, two toes right at the end.
If we cut through here and look at the bone inside, what we see is a very, very thick bone.
Here's that thick skin we were talking about before.
Notice how thick the bone itself is.
It's incredibly thick to hold all the weight of this animal.
Also it gives the animal strength if it's going to kick and attack a lion.
That's the equivalent of these two fingers in the human.
If this animal's walking on just those two fingers, you've got two bones in here that are fused together in the adult to make it look like it's one.
So as it's standing, it's standing on two toes, just like that.
These elongated limbs may at first seem strange and unnecessary, but in the context of a giraffe's huge homerange, long legs make perfect sense.
In certain parts of South Africa, giraffe roam over vast areas and the very bestway to see them is from the air.
Giraffe have two basic gaits or ways in which they move around.
When they're walking, it's a kind ofpacing gait, as it's called, where the legs on one side move together in a really coordinated way.
But as soon as they want to movefaster, they have to move into a gallop in which their hind legs move together and their front legs move together.
And they can get up to speeds of around 30 mph, which is pretty staggering, that's much faster than us and, perhaps more importantly, faster than a lion.
You'd think with their markings and their colourings they would really standout but they truly are camouflaged.
There are some down here look, this is amazing, a small group of them galloping.
When you've got giraffe in a small group, you'll have different aged animals andobviously they're different sizes.
But if they're moving together they've got to be able to keep up.
And you can see brilliantly here, we've got a young one with its mother and it's able to keep up because it's got such staggeringly long legs for a young animal.
And it moves pretty much in unison with its mum.
Young giraffes face a precarious early life.
This calf died shortly after it was born at a zoo.
It's been brought to the Royal Veterinary College for post-mortem examination.
Giraffe calves spend 15 months growing in the womb.
They then drop into the world from a dizzying height.
They master their stilt-like legs quickly.
Within 30 minutes they're able to stagger about.
But this is when they're most at risk.
Over half of all newborns die in their first six months.
Most are lost to lions.
The most obvious thing straight away is just how incredibly big it is.
When they're wrapped up as it would be in the uterus in here, it's a fairly, relatively, small package.
When it's born, it's out And if it was standing upright, you can see just how long it really is.
This one is just over six feet long, in fact.
So it's a really big little animal.
Its legs are disproportionately long compared to the size of its body.
Yes.
This one is about one and a half metres long.
And in an adult giraffe, it may be two metres.
So this leg has only got another half a metre to grow.
But compare that to the length of the neck.
The neck is 70% of that length.
And this is going to be longer than the legs when it's mature.
All this has to be long enough is to get to the udder and the milk supply.
And long legs and a short neck is an adaptation that suits it for that particular activity.
But it's got some other things.
When it's coming out, it's got to have hooves that are protected, and you can see that there's a very soft covering over the sharp parts of that hoof, which protect the uterus from damage when the animal is being born.
And, of course, they're born with horns.
But this horn, you'll see, is completely loose and not attached to the skull.
So as it slips through the birth canal, that's streamlined, horns are flat on the head, and then shortly after birth they stand up and then start the long process of fusing to the skull to form what you see as an adult head.
Of course, why it is born with a horn at all, because no other animal is born with a horn, is another little mystery.
Perfectly useless bit of material for a newborn baby giraffe.
A mother won't risk lying down to feed her calf.
Lowering her body to the ground would make her an easy target.
This delicately balanced beast spends as little time as possible bending to drink or lying down to sleep.
In fact, they can get by on as little as ten minutes sleep a day.
This long and heavy neck seems to cause more problems than it solves.
Drinking, breathing, pumping blood to the head, simplystanding up, it's all difficult.
Does the benefit of reaching a few more leaves really outweigh all the costs? Or could there be something else going on? Is there another less obvious advantage to having a long neck? We're in the final stages of our giraffe dissection.
With the neck bones exposed, pathologist Alun Williams can begin his detective work, hunting for clues that may reveal the cause of this animal's mysterious death.
Once all the muscles have been taken off, you end up with seeing the vertebrae underneath and the most obvious thing, a lot of people think there must be loads and loads of bones in the neck of a giraffe.
There aren't.
Just the same number that we have.
There are two up here.
One, two, three, four, five, six.
And there's number seven.
OK, so same number of bones as in us.
It's just that each these has tremendously elongated during evolution and growth.
Still a bit more work to go on there.
But, Alun, obviously we know this animal died from an acute, unexplained paralysis.
Any clues here from having a look at the neck in detail? Yes, we have.
We've discovered a number of things in our dissection.
And if I start around the head, if we look at this muscle here, instead of looking like this nice normal colour, it's become much darker, this bleeding in the muscle, suggesting that there's been some impact onto the lower part of the head.
Almost as if the head has hit the floor.
So, your next step? To take the neck apart even further or not? Yes, I think what we'll do is just take one of these vertebrae out so we can actually see inside.
Richard, can you do that for us? I mean, what it begs a question of is obviously being tall brings certain very distinct disadvantages.
and one of them may be, if you stumble, you fall, the taller you are the harder you fall.
It's serious.
Even though falls can be fatal, giraffes are far from fragile.
When British couple Kathy and Steve Auckland filmed these gentle-looking giants on safari in Tanzania, the last thing they expected to see was this.
No, I haven't seen this on the telly either.
In head-to-head battles like these, males with the largest necks dominate.
They'll win access to the most females and are likely to pass their big neck genes to the next generation.
This could well be a factor in the evolution of the neck.
But there's another theory that involves the beautiful skin patterns of giraffes across Africa.
They all share a hidden secret.
These patches are for camouflage, first and foremost.
But underneath the patch is a really sophisticated little blood system.
Around each patch runs quite a big blood vessel.
And that blood vessel gives off smaller branches into the middle of the patch.
And what a giraffe is able to do is to send blood, when it needs to lose heat, through these little branches into the middle of the patch.
Then the heat is given off through that patch to the environment.
When viewed through a thermal camera, the remarkable properties of the patches become clear.
Each one acts as a thermal window, switching on to release body heat.
You can see the patterns here.
A thermal imaging camera is showing up how these are glowing brightly.
There's a lot of heat coming from those.
And the longer the neck, the more surface area available for these heat-losing patches.
If you want to keep yourself cool in somewhere like Africa, having a long, thin body is a good way of doing it.
It increases your surface area dramatically.
It's much, much better than being, say, fat and squat.
By lengthening themselves out they're able to cool down.
This means they don't have to hide in the shade all day.
Instead, they can keep feeding any time they want.
The evolution of a body shape that stays cool under the African sun could well be an important reason for the giraffe's extraordinary neck.
While looking for clues to the cause of death, Alun discovered bruising around the lower jaw of our giraffe.
Now he wants to go deeper and examine the spinal cord.
If we just take a knife here, and see if we can If we just look here, we have areas that are just slightly discoloured here and here.
It's very difficult to see with the naked eye.
But they are not the colour they should be, which suggests to me there's bleeding into the spinal cord itself, damaging the nerves that spread messages to control limbs.
So, this is all supporting the idea that this giraffe has lost its footing and the degree of impact, as its neck and head hit the floor, has caused bleeding, and the nerves to stop working properly.
The ultimate cause of our giraffe's death was a simple fall.
It highlights just how costly this elongated body and neck can be.
So, will there be another chapter in the remarkable evolutionary story of the giraffe? At the back of everyone's mind, you're saying this is a creature that's living right on the edge.
It won't take much for the disadvantages to outweigh the advantages and then the species will crash, just like all species do when they've come to the end of a suitable environment.
And that's what I think this animal is doing right now.
It's right on the edge of what an animal can do.
We get used to the idea that evolution produces almost perfect design, the illusion of design.
It looks exactly as an engineer might've done it.
But what's very revealing are those imperfections which we sometimes find, imperfections which no designer would ever have perpetrated, but which are exactly what you'd expect if living creatures were the legacy of history.
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