David Attenborough's Natural Curiosities (2013) s03e03 Episode Script
Expandable Bodies
1 The natural world is full of extraordinary animals, with amazing life histories.
Yet, certain stories are more intriguing than most.
The mysteries of a butterfly's life cycle, or the strange biology of the Emperor penguin.
Some of these creatures were surrounded by myth and misunderstandings, for a very long time.
And some, have only recently revealed their secrets.
These are the animals, that stand out from the crowd, The curiosities, I find particularly fascinating.
The bodies of some animals, stretch and shrink in extraordinary ways.
Constrictor snakes, can swallow prey, twice their own size.
While the camel's hump can almost double in weight, giving it the energy to travel huge distances across deserts.
What is the secret behind such expandable bodies ? We've long been fascinated, by the camel's Places where, during summer, temperatures can sore, up to 50 degrees Celsius, while in winter, they can drop, to 30 degrees below freezing.
With little in the way of food or water, camels can sometimes go without eating or drinking, for over a week.
Most other animals, couldn't survive conditions like this.
How does the camel do it ? The camel's secret, was thought, to lie in its hump.
In a healthy camel, it can be big and firm, like this one, and can weigh as much as 30 kilos, which is the weight of a 10-yo child.
But if the camel goes without food, and particularly water, for any length of time, then the hump can get floppy and even droop over on one side, as that one has done.
So people used to think, that the camel stored water in its hump.
In fact, there are two different kinds of camel.
The one-humped, or Dromedary and the two-humped, or Bactrian.
Nearly all camels alive today, are the domesticated descendants of one or the other.
The wild Dromedary almost certainly, doesn't exist.
And only a few Bactrian camels remain, roaming the deserts of Central Asia.
A camel is a very tough animal, but in the wild today, it's rarer than the Giant Panda.
It's hard to say, where the idea of a water-storing hump came from.
The ancient Romans, were the first to suggest, that the camel may have a built-in water reservoir.
And then, later on, people got the idea, that it had two stomachs.
One for food, and one for water.
In the 18th century, an eminent anatomist, John Hunter, decided to investigate the truth behind these assertions, and he dissected a camel.
He found, that the stomach consisted of 3 or 4 compartments, similar to those of a cow or a sheep.
But inside one of those compartments, he discovered these pocket-like structures, which are not found, in any other large mammal.
Hunter didn't know what the pockets were for, but others after him, proposed that they were special, water-storing cells.
And then, despite any kind of evidence to prove that this was true, for another 250 years, books on natural history, like this one, featured illustrations of water-storing cells, in the camel's stomach.
We now know, that that's not true, even though, we don't know exactly, what the strange pockets are for.
But, the camel's hump is certainly not filled with water.
It's made entirely of fatty tissue.
It is, in fact, an energy reserve, for times when food is scarce.
And it can expand to such a degree, that it makes up 80 percent of the camel's body-fat.
This enables a camel to go for two weeks without feeding, if necessary.
But there's a twist to the story.
When fat is broken down in the body, it produces not just energy, but also water.
In fact, each gram of fat broken down during metabolism, produces one gram of water.
So, could the camel's hump provide it with extra water, after all? A fatty hump, that contains both food and water would seem to be just what a desert animal needs.
But, it's not as simple as that.
To consume its fat, an animal needs more oxygen, so, it has to breathe more.
So, when living on the fat in its hump, the camel actually looses more water through its airways, then it gains.
So the camel doesn't have a secret store of water.
How then, can it survive in a waterless desert? Camels can go without drinking, for more than a week, because they have an extraordinary ability, to retain the body moisture.
We ourselves, loose over a liter of water a day, through our moister-laden breath.
But the camel has nostrils, which he can shut tight.
And that, not only keeps out the sand, but retains the breath, within the nose.
And there, the moisture can be reabsorbed by the linings of the nostrils.
Most mammals also loose a lot of water, when they cool their bodies, by sweating.
But camels can endure a rise in body temperature, that would kill most other mammals.
Without sweating.
If our temperature goes up, by as little as one degree, it's a sign of illness.
While 3 degrees causes vital organ damage, and eventually death.
The camel can cope with as much as 6 degrees rise, with no ill effect.
This means, that camels don't have to sweat, until conditions get very hot, indeed.
And, if necessary, they tolerate loosing more of their body water, than other mammals.
When animals become dehydrated, their blood becomes thicker, and more difficult to pump through the body.
If we loose 10 percent of our body water, we start to go dizzy and blind.
And at 15 percent, our internal organs start to fail.
Camels however, can loose a third of their body water, with no ill effect.
Something that would kill most other animals.
How do they do it? Well, some of the answers may lie in the shape of their blood cells.
These are the red blood cells from a human being, which are disc-shaped, like that of most mammals.
These, on the other hand, are from a camel, and are slimmer and more oval in shape.
It may be, that the oval, streamlined shape, makes it easier for the blood to flow, when the animal is dehydrated.
Certainly, the camel's blood is less thick and sticky than ours.
The cells also have particularly strong walls.
This prevents them from rupturing, when the animal suddenly drinks large amounts of water.
And when they do find water, camels have the ability, to drink it very quickly.
A single camel, can take the contents of all these bottles, (that's 100 liters), in a mere ten minutes.
For any other animal to do that, it would be extremely dangerous.
But the camel has the ability,to hold the water in the stomach, and only release it into the blood stream, very slowly, in a way that does no damage.
We now understand, how camels can survive harsh desert conditions.
And yet, surprisingly, new research suggests, that they may first have evolved, to live in the cold Arctic.
Scientists, have recently discovered the fossil bones of giant, shaggy camels, that roamed the forests of the Canadian Arctic, something of a half million years ago.
The arctic camel was a third larger, than the modern Bactrian but otherwise looked very similar.
And that may be no coincidence.
The wide, flat feet, that stop the camel from sinking into desert sand, could also have helped its ancestors, walk in deep snow.
And a fatty hump, provided the food reserve the camel would need, to survive long, cold winters.
We may never fully understand the mysteries of the camel's hump, but it evolved first, as a way of keeping warm, or staying cool.
But we have unraveled many other mysteries, of the animal's body, that enable it to endure conditions, that few other animals would be able to withstand.
The camel's hump can change dramatically in shape and size.
And in part two, we meet another creature that can stretch its body, in a most extraordinary way.
The camel can go for days, without water.
Our second curiosity, can fast for months on end, and then devour prey, many times its own size.
This is a green Anaconda.
One of the largest snakes in the world.
It's about 4 meters long, and weighs 70 kilos.
And it's only half grown.
They can grow to a length of 6 meters, and weigh twice as much as this one.
But it's their ability to be able to swallow enormous prey, that's really grabbed our imagination.
Could one of these really bite a man, and swallow him whole, and alive? In the 16th century, European explorers, venturing into the Amazon jungle, were fascinated by tales of a huge river monster.
It was said to devour cattle and deer and to spit out water, like shot from a canon knocking animals out of trees.
These fantastic stories, led people to go in search of this marvelous beast.
In 1907, a British explorer, Colonel Percy Fawcett, claimed to have encountered an enormous snake, on the Amazon river.
"A huge head", he said, rose up from the water, dangerously close to his canoe, and a colossal anaconda emerged.
Greatly alarmed, he shot the snake dead.
He claimed, that when measured, it proved to be nearly 19 meters, over 60 feet long.
But Fawcett's account was met with disbelief.
And he never provided convincing proof, because soon after that, he vanished into the Brazilian jungle, and was never seen again.
The creature that Fawcett encountered, was almost certainly a green anaconda.
Despite their massive proportions, these huge snakes are seldom seen, because they spend most of their time in water, waiting in ambush for their prey.
In this murky world, they're certainly well camouflaged, and so, some people believed, that somewhere another real monster might still be lurking, unseen.
In the 1960's a snake was brought to the Museum of Zoology, at University College London.
This is it.
It had lived in London Zoo for some years, before it died, and it was 5 meters long.
A lot of work went into preparing the skeleton.
It had to be carried out, onto the flat roof of the museum, and it was finally displayed, in this rather unusual way.
Wrapped around the branch of a tree.
For years the museum displayed it as an anaconda.
But in 2012, a member of the public saw an old photo of the snake on the museumâs website and pointed out, that it looked like an African rock python, and not an anaconda.
Itâs unclear, how the mistake came about.
The markings on the two snakes, are quite different.
But both are giants.
And thereâs much controversy, as to which species, is the largest snake of all.
Anacondas, pythons and boas, like this one donât kill with venom.
Theyâre constrictors.
They squeeze their prey to death.
And their coils can exert a very strong pressure indeed, as I can feel, with this one on my arm.
But a big anaconda, can squeeze with a force of around 4,000 kilos.
Thatâs like having a bus on your chest.
And that can certainly crush the spine of a deer, or a capibara.
And yet, constrictor snakes, donât usually crush their prey.
In most cases, they simply squeeze it so hard, that the animal canât breathe.
Every time itâs prey tries to inhale, the snakeâs powerful muscles squeeze harder.
The unfortunate victim then, either dies because itâs blood can no longer circulate, or suffocates.
An anaconda, or a python, can kill prey that is not only twice it's own body size, but many times bigger than it's head.
So, how does it manage to swallow itâs victim whole? Popular folklore has it, that anacondas and pythons, unhinge, or dislocate their jaws to swallow large prey.
That is not true.
They do however, have the ability to open their mouths wider, than most animals.
Pythons and anacondas, have this additional bone, attached to the back of their jaws.
This provides a double hinge, at the joint, and allows them, to open their jaws extremely wide, both downwards and sideways.
In addition, the two sides of the lower jaw, are not fused together, but joined by an elastic ligament.
This gives the jaws a lot of stretch, and they can even move apart, when the snake is swallowing a large prey.
It also allows each side of the jaw, to move independently of the other.
When eating a meal, particularly, one that is much larger than itself, the snake can alternatively move it's jaws on either side of it's head, and walk it's prey into it's mouth, even while it's victim is still alive.
As the jaws open wide, the snake's elastic skin stretches.
But the mobility of the skull, comes with a price.
Many of the joints, that in other snakes are solid, have been replaced by mobile ones.
So the skull has less crushing power.
As a consequence, the snake has to use its entire body, to overpower its prey.
Getting large prey into the mouth, is one problem.
But how does a snake push it all the way down the length of its body, into its stomach? This is a Burmese python, and it hasn't fed for a long time.
So, I'm hoping to give it a little breakfast, with a dead rat.
Saliva from the salivary glands in the mouth, has moistened the prey, so it's easier to swallow.
And now, it's moving its jaws, drawing the rat farther down it's throat until eventually, the muscles of the flanks take over, squeezing the prey and pushing against the ribs, so that, it looks, as though the snake is as it were, crawling around the rat.
And that will continue for some time, as the prey is worked down into the snake's body, until eventually, it reaches the stomach, which is around the middle, here.
Equally remarkable is, what happens inside the snake.
After months of fasting, it has to restart its digestive system quickly.
Within a day, some of the internal organs double in size.
The heart expands, pumping greater volumes of blood around the body.
And special cells in the lining of the stomach, produce powerful enzymes, that break down flesh and bones.
And when the prey is entirely digested, the python's organs return to normal again.
Anacondas and pythons are able to take in enormous meals, in a single mouthful.
But how do they then survive fasting for months on end? Like all cold-blooded animals, snakes get much of their heat from the sun.
So they need less food to fuel their bodies, and most of what they eat, is converted directly into body mass.
Snakes continue to grow throughout their lives, and anacondas get bigger than any other species, because they live mostly in water.
Their massive bodies, supported by its buoyancy.
So, it's certainly possible, that an anaconda could grow, to an enormous size.
But how large can a snake really get? In 2009, further light was shed on this question with the discovery of the fossils of a super snake.
It was given the name "Titanoboa" and it suggests that snakes can get very large, indeed.
Titanoboa was nearly 13 meters long, the length of a bus, and must have weighed over a ton.
It lived around 60 million years ago, shortly after the extinction of the dinosaurs.
We don't know for sure, but it may be, that the warmer climate of the earth at the time, allowed cold-blooded snakes, to grow much larger in size.
What is certain, is that for at least 10 million years, Titanoboa was the largest predator on the planet.
Both the camel and the anaconda can withstand extreme periods of fasting.
But it's only by looking inside the camel's hump, and the anaconda's stomach, that we have discovered the truth behind their amazing expandable bodies.
Yet, certain stories are more intriguing than most.
The mysteries of a butterfly's life cycle, or the strange biology of the Emperor penguin.
Some of these creatures were surrounded by myth and misunderstandings, for a very long time.
And some, have only recently revealed their secrets.
These are the animals, that stand out from the crowd, The curiosities, I find particularly fascinating.
The bodies of some animals, stretch and shrink in extraordinary ways.
Constrictor snakes, can swallow prey, twice their own size.
While the camel's hump can almost double in weight, giving it the energy to travel huge distances across deserts.
What is the secret behind such expandable bodies ? We've long been fascinated, by the camel's Places where, during summer, temperatures can sore, up to 50 degrees Celsius, while in winter, they can drop, to 30 degrees below freezing.
With little in the way of food or water, camels can sometimes go without eating or drinking, for over a week.
Most other animals, couldn't survive conditions like this.
How does the camel do it ? The camel's secret, was thought, to lie in its hump.
In a healthy camel, it can be big and firm, like this one, and can weigh as much as 30 kilos, which is the weight of a 10-yo child.
But if the camel goes without food, and particularly water, for any length of time, then the hump can get floppy and even droop over on one side, as that one has done.
So people used to think, that the camel stored water in its hump.
In fact, there are two different kinds of camel.
The one-humped, or Dromedary and the two-humped, or Bactrian.
Nearly all camels alive today, are the domesticated descendants of one or the other.
The wild Dromedary almost certainly, doesn't exist.
And only a few Bactrian camels remain, roaming the deserts of Central Asia.
A camel is a very tough animal, but in the wild today, it's rarer than the Giant Panda.
It's hard to say, where the idea of a water-storing hump came from.
The ancient Romans, were the first to suggest, that the camel may have a built-in water reservoir.
And then, later on, people got the idea, that it had two stomachs.
One for food, and one for water.
In the 18th century, an eminent anatomist, John Hunter, decided to investigate the truth behind these assertions, and he dissected a camel.
He found, that the stomach consisted of 3 or 4 compartments, similar to those of a cow or a sheep.
But inside one of those compartments, he discovered these pocket-like structures, which are not found, in any other large mammal.
Hunter didn't know what the pockets were for, but others after him, proposed that they were special, water-storing cells.
And then, despite any kind of evidence to prove that this was true, for another 250 years, books on natural history, like this one, featured illustrations of water-storing cells, in the camel's stomach.
We now know, that that's not true, even though, we don't know exactly, what the strange pockets are for.
But, the camel's hump is certainly not filled with water.
It's made entirely of fatty tissue.
It is, in fact, an energy reserve, for times when food is scarce.
And it can expand to such a degree, that it makes up 80 percent of the camel's body-fat.
This enables a camel to go for two weeks without feeding, if necessary.
But there's a twist to the story.
When fat is broken down in the body, it produces not just energy, but also water.
In fact, each gram of fat broken down during metabolism, produces one gram of water.
So, could the camel's hump provide it with extra water, after all? A fatty hump, that contains both food and water would seem to be just what a desert animal needs.
But, it's not as simple as that.
To consume its fat, an animal needs more oxygen, so, it has to breathe more.
So, when living on the fat in its hump, the camel actually looses more water through its airways, then it gains.
So the camel doesn't have a secret store of water.
How then, can it survive in a waterless desert? Camels can go without drinking, for more than a week, because they have an extraordinary ability, to retain the body moisture.
We ourselves, loose over a liter of water a day, through our moister-laden breath.
But the camel has nostrils, which he can shut tight.
And that, not only keeps out the sand, but retains the breath, within the nose.
And there, the moisture can be reabsorbed by the linings of the nostrils.
Most mammals also loose a lot of water, when they cool their bodies, by sweating.
But camels can endure a rise in body temperature, that would kill most other mammals.
Without sweating.
If our temperature goes up, by as little as one degree, it's a sign of illness.
While 3 degrees causes vital organ damage, and eventually death.
The camel can cope with as much as 6 degrees rise, with no ill effect.
This means, that camels don't have to sweat, until conditions get very hot, indeed.
And, if necessary, they tolerate loosing more of their body water, than other mammals.
When animals become dehydrated, their blood becomes thicker, and more difficult to pump through the body.
If we loose 10 percent of our body water, we start to go dizzy and blind.
And at 15 percent, our internal organs start to fail.
Camels however, can loose a third of their body water, with no ill effect.
Something that would kill most other animals.
How do they do it? Well, some of the answers may lie in the shape of their blood cells.
These are the red blood cells from a human being, which are disc-shaped, like that of most mammals.
These, on the other hand, are from a camel, and are slimmer and more oval in shape.
It may be, that the oval, streamlined shape, makes it easier for the blood to flow, when the animal is dehydrated.
Certainly, the camel's blood is less thick and sticky than ours.
The cells also have particularly strong walls.
This prevents them from rupturing, when the animal suddenly drinks large amounts of water.
And when they do find water, camels have the ability, to drink it very quickly.
A single camel, can take the contents of all these bottles, (that's 100 liters), in a mere ten minutes.
For any other animal to do that, it would be extremely dangerous.
But the camel has the ability,to hold the water in the stomach, and only release it into the blood stream, very slowly, in a way that does no damage.
We now understand, how camels can survive harsh desert conditions.
And yet, surprisingly, new research suggests, that they may first have evolved, to live in the cold Arctic.
Scientists, have recently discovered the fossil bones of giant, shaggy camels, that roamed the forests of the Canadian Arctic, something of a half million years ago.
The arctic camel was a third larger, than the modern Bactrian but otherwise looked very similar.
And that may be no coincidence.
The wide, flat feet, that stop the camel from sinking into desert sand, could also have helped its ancestors, walk in deep snow.
And a fatty hump, provided the food reserve the camel would need, to survive long, cold winters.
We may never fully understand the mysteries of the camel's hump, but it evolved first, as a way of keeping warm, or staying cool.
But we have unraveled many other mysteries, of the animal's body, that enable it to endure conditions, that few other animals would be able to withstand.
The camel's hump can change dramatically in shape and size.
And in part two, we meet another creature that can stretch its body, in a most extraordinary way.
The camel can go for days, without water.
Our second curiosity, can fast for months on end, and then devour prey, many times its own size.
This is a green Anaconda.
One of the largest snakes in the world.
It's about 4 meters long, and weighs 70 kilos.
And it's only half grown.
They can grow to a length of 6 meters, and weigh twice as much as this one.
But it's their ability to be able to swallow enormous prey, that's really grabbed our imagination.
Could one of these really bite a man, and swallow him whole, and alive? In the 16th century, European explorers, venturing into the Amazon jungle, were fascinated by tales of a huge river monster.
It was said to devour cattle and deer and to spit out water, like shot from a canon knocking animals out of trees.
These fantastic stories, led people to go in search of this marvelous beast.
In 1907, a British explorer, Colonel Percy Fawcett, claimed to have encountered an enormous snake, on the Amazon river.
"A huge head", he said, rose up from the water, dangerously close to his canoe, and a colossal anaconda emerged.
Greatly alarmed, he shot the snake dead.
He claimed, that when measured, it proved to be nearly 19 meters, over 60 feet long.
But Fawcett's account was met with disbelief.
And he never provided convincing proof, because soon after that, he vanished into the Brazilian jungle, and was never seen again.
The creature that Fawcett encountered, was almost certainly a green anaconda.
Despite their massive proportions, these huge snakes are seldom seen, because they spend most of their time in water, waiting in ambush for their prey.
In this murky world, they're certainly well camouflaged, and so, some people believed, that somewhere another real monster might still be lurking, unseen.
In the 1960's a snake was brought to the Museum of Zoology, at University College London.
This is it.
It had lived in London Zoo for some years, before it died, and it was 5 meters long.
A lot of work went into preparing the skeleton.
It had to be carried out, onto the flat roof of the museum, and it was finally displayed, in this rather unusual way.
Wrapped around the branch of a tree.
For years the museum displayed it as an anaconda.
But in 2012, a member of the public saw an old photo of the snake on the museumâs website and pointed out, that it looked like an African rock python, and not an anaconda.
Itâs unclear, how the mistake came about.
The markings on the two snakes, are quite different.
But both are giants.
And thereâs much controversy, as to which species, is the largest snake of all.
Anacondas, pythons and boas, like this one donât kill with venom.
Theyâre constrictors.
They squeeze their prey to death.
And their coils can exert a very strong pressure indeed, as I can feel, with this one on my arm.
But a big anaconda, can squeeze with a force of around 4,000 kilos.
Thatâs like having a bus on your chest.
And that can certainly crush the spine of a deer, or a capibara.
And yet, constrictor snakes, donât usually crush their prey.
In most cases, they simply squeeze it so hard, that the animal canât breathe.
Every time itâs prey tries to inhale, the snakeâs powerful muscles squeeze harder.
The unfortunate victim then, either dies because itâs blood can no longer circulate, or suffocates.
An anaconda, or a python, can kill prey that is not only twice it's own body size, but many times bigger than it's head.
So, how does it manage to swallow itâs victim whole? Popular folklore has it, that anacondas and pythons, unhinge, or dislocate their jaws to swallow large prey.
That is not true.
They do however, have the ability to open their mouths wider, than most animals.
Pythons and anacondas, have this additional bone, attached to the back of their jaws.
This provides a double hinge, at the joint, and allows them, to open their jaws extremely wide, both downwards and sideways.
In addition, the two sides of the lower jaw, are not fused together, but joined by an elastic ligament.
This gives the jaws a lot of stretch, and they can even move apart, when the snake is swallowing a large prey.
It also allows each side of the jaw, to move independently of the other.
When eating a meal, particularly, one that is much larger than itself, the snake can alternatively move it's jaws on either side of it's head, and walk it's prey into it's mouth, even while it's victim is still alive.
As the jaws open wide, the snake's elastic skin stretches.
But the mobility of the skull, comes with a price.
Many of the joints, that in other snakes are solid, have been replaced by mobile ones.
So the skull has less crushing power.
As a consequence, the snake has to use its entire body, to overpower its prey.
Getting large prey into the mouth, is one problem.
But how does a snake push it all the way down the length of its body, into its stomach? This is a Burmese python, and it hasn't fed for a long time.
So, I'm hoping to give it a little breakfast, with a dead rat.
Saliva from the salivary glands in the mouth, has moistened the prey, so it's easier to swallow.
And now, it's moving its jaws, drawing the rat farther down it's throat until eventually, the muscles of the flanks take over, squeezing the prey and pushing against the ribs, so that, it looks, as though the snake is as it were, crawling around the rat.
And that will continue for some time, as the prey is worked down into the snake's body, until eventually, it reaches the stomach, which is around the middle, here.
Equally remarkable is, what happens inside the snake.
After months of fasting, it has to restart its digestive system quickly.
Within a day, some of the internal organs double in size.
The heart expands, pumping greater volumes of blood around the body.
And special cells in the lining of the stomach, produce powerful enzymes, that break down flesh and bones.
And when the prey is entirely digested, the python's organs return to normal again.
Anacondas and pythons are able to take in enormous meals, in a single mouthful.
But how do they then survive fasting for months on end? Like all cold-blooded animals, snakes get much of their heat from the sun.
So they need less food to fuel their bodies, and most of what they eat, is converted directly into body mass.
Snakes continue to grow throughout their lives, and anacondas get bigger than any other species, because they live mostly in water.
Their massive bodies, supported by its buoyancy.
So, it's certainly possible, that an anaconda could grow, to an enormous size.
But how large can a snake really get? In 2009, further light was shed on this question with the discovery of the fossils of a super snake.
It was given the name "Titanoboa" and it suggests that snakes can get very large, indeed.
Titanoboa was nearly 13 meters long, the length of a bus, and must have weighed over a ton.
It lived around 60 million years ago, shortly after the extinction of the dinosaurs.
We don't know for sure, but it may be, that the warmer climate of the earth at the time, allowed cold-blooded snakes, to grow much larger in size.
What is certain, is that for at least 10 million years, Titanoboa was the largest predator on the planet.
Both the camel and the anaconda can withstand extreme periods of fasting.
But it's only by looking inside the camel's hump, and the anaconda's stomach, that we have discovered the truth behind their amazing expandable bodies.