David Attenborough's Natural Curiosities (2013) s03e06 Episode Script
Remarkable Regeneration
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.
Salamanders can regenerate entire legs and tails, to replace ones that they loose.
And moose, can regrow their enormous antlers every year.
How do these animals regenerate entire body parts? And why isn't it possible, for all animals, to do the same? When I was a boy, my father gave me one of these, for my 8th birthday.
It's a fire salamander.
They may look like lizards, but in fact they're not reptiles.
They're amphibians, with moist skins.
For centuries, mythical stories surrounded these creatures.
It was believed, that they were icy cold animals, and could dwell within fires, unharmed by the heat.
Although their fire surviving powers may be untrue, the salamander, nonetheless, possesses a real natural ability, that is just as extraordinary.
They're able to regrow, damaged tails, legs, and other parts of the body, through a process called, regeneration.
There are more than 600 different species of salamander.
They range in size, from just a couple of centimeters, up to the world's largest amphibian, The Chinese giant salamander, that can grow to over a meter and a half in length.
Salamanders are predators, and many hunt for small invertebrates, such as slugs and worms.
But sometimes, they hunt each other.
with dramatic consequences.
This tiny, North American red back salamander is on the menu of the, much bigger, seal salamander.
Time to make a retreat.
This may look shocking, but the red back isn't badly injured.
A weak point in its skin, allows its tail, to break off easily.
Incredibly, it will regrow a new tail, in just a matter of weeks.
This ability, to replace an entire body part, is unusual among adult vertebrates, and seems almost magical.
Regeneration is a subject, that fascinates us.
Modern medicine has spent a lot of money and time, studying the ways, our own bodies can regenerate tissue.
All living creatures, including humans, have the ability to repair damaged parts of the body, but the extend of that repair, varies considerably.
As small infants, we have the ability to regrow the tips of our fingers if they're severed, but we loose this ability, as we age.
So, animals, like salamanders, with their super regenerative powers, seem intriguing to us.
Regeneration had been known about, since ancient times.
But for a long time, no one understood, how it happened.
In the 17th and 18th century, there was a new wave of scientific discovery.
A brilliant Italian scientist, named Lazzaro Spallanzani, made meticulous observations into regeneration, across many different species.
And shared his ideas, in detailed letters.
In November 1765, he wrote to the eminent scientist Charles Bonnet, whom he regularly corresponded with, to announce, that he had discovered tail regeneration in salamanders.
Throughout the following year, he followed up his initial observations, with numerous experiments, to try to understand, how the salamander could regrow a tail, just like the original.
He found, that all species of salamander he tested, could regrow their tails, when injured, and they did so, more rapidly in summer, than in winter, and retain this incredible ability throughout their lives.
Spallanzani advocated a radical theory.
He thought, that salamanders already possessed a number of miniature spare parts, at the base of each limb, that could grow in size, to replace a lost or damaged one.
He was unable to prove this, but he didn't give up.
He studied salamander tadpoles, and came up with another, even more interesting idea.
A year after his initial letter, Spallanzani once again wrote to Charles Bonnet.
This time with detailed descriptions of further experiments into tail regeneration.
Most notably, in this description, he wrote: I am almost lead to believe, that the tail regenerates, in tadpoles, are more of an elongation of the old parts, than a development from a germ.
This suggests, that Spallanzani was on the right track.
But the idea, that the salamander could regrow a new tail, from seemingly nothing, was not well supported.
And Spallanzani was therefore never willing to pursue the idea further.
However, there's no doubt, that his research helped to lead other scientists closer towards proving what really happens, when a salamander regrows its tail.
In fact, Spallanzani's rough sketches did make sense.
For they were the first to describe, some of the vital processes, in the remarkable growth of new limbs, that we understand better today.
When a limb is lost, the exposed blood vessels and tissue, contract, to quickly stop any bleeding.
Then, skin from the edges, begins to grow across the damaged area, to protect the body from infection.
Now, cells that were once dormant, begin dividing and multiplying, to create new ones.
Each cell retains a kind of memory, of the type of tissue it used to be, So, a new cell that regrows from damaged muscle, will always become muscle.
Within weeks, the salamander has a full-grown leg, almost identical to the original.
Although we now know the steps, that take place during the regeneration of body parts, we still don't fully understand, what triggers this kind of response.
But it seems, the answer may lie in how the salamander's body responds to injury.
In humans, if an arm is severed, the cells die, alerting the immune system to the problem.
In response, the area becomes swollen, and is covered over with scar tissue, preventing any new growth occurring.
But in salamanders, the immune system responds differently.
And instead of forming a scar, it triggers regeneration.
Another, rather unusual looking salamander, that lives in the fresh waters of Mexico, sheds new light, on how this happens.
Axolotls are among the best re-generators in the natural world.
And scientists wondered, if their blood played a role, in the process.
Like us, they have special white blood cells, that consume invading bacteria and damaged tissue around injuries and wounds.
Researchers removed them, and the results were surprising.
The axolotl was unable, to regrow new limbs.
So white blood cells, were part of the secret of their powers of regeneration Understanding the role of the salamander's blood cells in regrowing limbs, could be a step towards discovering why they can regenerate body parts, and we can't.
All amphibians have tadpoles, which develop limbs and enable them, to move onto land.
But salamanders are able to re-trigger that remarkable process.
We too, undergo extraordinary development in the womb.
Maybe, like the salamander, there is a way of us, retaining this ability, into our adult lives as well.
The salamander has a truly amazing ability, to regrow complex body parts, to enhance its chances of survival.
While we donât yet know all the answers, it's likely, that this incredible creature, could revolutionize modern medicine, and the way we treat injuries.
Next, we uncover the secret behind how the moose regrows its enormous new antlers every year.
and discover what happens, when regeneration goes wrong.
The salamander's ability to re-grow entire limbs, is truly remarkable.
But moose and other deer, possess huge antlers, that are shed and re-grown, each season.
How can they regenerate such large body parts, every single year? This impressive skeleton, belongs to one of the biggest deer, to ever live on the planet.
It's an Irish Elk.
His antlers were enormous, they're almost 4 meters, 12 feet across, and they weigh 40 kilos.
An Irishman, named Dr.
Molyneux, first scientifically described the elk, in 1697, from specimens, taken out of an Irish peat bog.
Some believed, that this elk, was a large moose, and were convinced, living specimens could be found elsewhere, across Europe and Russia.
But not everyone agreed.
And the debate, about the life of this creature, would continue for more than 100 years.
The skeleton of an Irish elk, looked very similar, to that of a moose.
So, it's easy to see, why many believed them to be the same animal.
Both have very impressive antlers.
Antlers are only found in the deer family, and are made of bone.
Unlike horns, which are permanent structures, they are shed and replaced, every year.
But how can deer re-grow huge chunks of bone? Something, no other mammal can do.
Moose, like this young bull behind me, start growing their new antlers immediately after they shed their old ones.
The antlers first appear on little bumps, on either side of the head, known as pedicles.
And they have a soft furry covering, called velvet.
This is vital to their amazing powers of regeneration.
Blood vessels at the base, start the growth.
But as the antler gets longer, this blood supply is cut off.
Then, blood vessels within the velvet take over, and transport nutrients and growth hormones to the growing tips.
In older males, the antlers can grow at a rate of 2 cm a day, making it the fastest growing bone of any animal.
Once at full size, the velvet is shed.
The animal rubs its head against a tree, to encourage the thin velvet, to fall off.
It may look gruesome, but it's a natural part of the annual cycle, and does the animal no harm.
But why should a huge set of antlers be regrown every year? It's a question, that baffled early naturalists.
Until Charles Darwin suggested, it may be to do with attracting the opposite sex.
In the first few years of adulthood, the antlers are small.
And as a result, young males remain subordinate to the larger bulls.
But as they get older, their body size increases, so, the antlers will also increase, eventually becoming impressive ornaments with which to compete for females.
Those with the biggest antlers, are certainly more attractive to the females.
Maybe, they are an indicator of fitness and strength.
And it's no coincidence, that antlers are at their full size, during the breeding season.
This is a time, when a bull must protect his harem, and see off competitors.
Competing males tilt their heads, to show off their antlers, to their best advantage.
But if the bulls are equally matched, then, the competitors fight.
The winner, then gains access to the females.
The benefits of such a victory are huge.
But to get to that point, every young bull must, for many years, grow and regrow antlers.
It's a big investment, draining the body of vital resources.
And no investment was bigger, than that, of the Irish Elk.
The sheer size of these antlers, had let some to argue, that they were unlikely to have been used in physical combat.
Unlike other deer, the antlers of the Irish elk, grew with a large flat, palm-like plane, facing forward.
So then, if a bull looked straight ahead, it would be at its biggest and most impressive.
In this way, they may have been able to intimidate rivals and attract females, without actually fighting.
So, although the Irish elk was armed with what appeared to be enormous weapons, it seems, they were mostly for show.
Now, this strategy, may have been an advantage for the large elk.
Fighting is always a risky business, and will often result in serious injuries.
After the breeding season, the antlers are discarded.
Moose shed theirs in the winter, whereas smaller deer, keep theirs until the next spring.
This maybe, because the moose antlers, are such a heavy load to carry, throughout the winter.
But why are antlers shed at all? Antlers are made of dead bone, and can't be repaired.
If a moose damages an antler during a fight, it will loose its chance of mating, for that season.
By shedding and regrowing their antlers each year, bulls ensure, that they stay in the mating game.
Just before antlers are shed, minerals within them, are reabsorbed from the base, weakening the structure, so that they eventually fall off.
The flesh underneath is exposed, but not for long, as new skin soon covers the wound.
Experiments have shown, that the skin lesion that forms over the open wound, creates a connection with the underlying tissue, that is crucial to regeneration.
If this connection isn't laid, the production of velvet will be interrupted, and the antlers will either not grow at all, or develop into strange shapes.
So, what about the Irish elk? Could the problems of regenerating such gigantic antlers, have determined its faith? The French scientist Georges Cuvier, was keen to demonstrate, that the Irish elk was a unique species, that had become extinct.
To prove his point, Cuvier undertook a detailed examination of Irish elk fossils.
He was able to show, that it was indeed a distinct type of deer, that could no longer be found alive.
And so, the Irish elk, was one of the first animals we recognized, as being extinct.
Georges Cuvier had solved the question, of whether or not, the Irish elk and moose, were one and the same creature.
But why did the Irish elk die out? Cuvier suggested, that evolution had set it on a course of ever increasing growth.
And that eventually, the antlers became so large, that the poor animal could not even lift its neck.
He may not have been that far from the truth.
It is now thought, that the annual growth of the Irish elk antlers, put a strain on their bodies.
A significant proportion of minerals, within their bones, were extracted and moved into their growing antlers.
This led to a seasonal osteoporosis, with their bones weakening.
They were, in effect, robbing one part of their body, to boost another.
It was a gamble, that worked for thousands of years.
But around 10,000 years ago, the climate began to warm.
The nutrient-rich grasses, that the elk relied upon, began to disappear.
Growing massive antlers, may now have been too much of a drain, and permanently weakened the skeleton.
The change in diet, may also have effected their ability to breed, with females no longer able to produce young every year.
Whatever the reason, the Irish elk, with its magnificent antlers, finally vanished from the landscape.
And in its place, the moose has become the largest deer on earth, today.
So, while regeneration can give the salamander a second chance, to a full life, the yearly regeneration of antlers in male moose, is a risky strategy.
But one, with huge rewards for those with the best antlers.
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.
Salamanders can regenerate entire legs and tails, to replace ones that they loose.
And moose, can regrow their enormous antlers every year.
How do these animals regenerate entire body parts? And why isn't it possible, for all animals, to do the same? When I was a boy, my father gave me one of these, for my 8th birthday.
It's a fire salamander.
They may look like lizards, but in fact they're not reptiles.
They're amphibians, with moist skins.
For centuries, mythical stories surrounded these creatures.
It was believed, that they were icy cold animals, and could dwell within fires, unharmed by the heat.
Although their fire surviving powers may be untrue, the salamander, nonetheless, possesses a real natural ability, that is just as extraordinary.
They're able to regrow, damaged tails, legs, and other parts of the body, through a process called, regeneration.
There are more than 600 different species of salamander.
They range in size, from just a couple of centimeters, up to the world's largest amphibian, The Chinese giant salamander, that can grow to over a meter and a half in length.
Salamanders are predators, and many hunt for small invertebrates, such as slugs and worms.
But sometimes, they hunt each other.
with dramatic consequences.
This tiny, North American red back salamander is on the menu of the, much bigger, seal salamander.
Time to make a retreat.
This may look shocking, but the red back isn't badly injured.
A weak point in its skin, allows its tail, to break off easily.
Incredibly, it will regrow a new tail, in just a matter of weeks.
This ability, to replace an entire body part, is unusual among adult vertebrates, and seems almost magical.
Regeneration is a subject, that fascinates us.
Modern medicine has spent a lot of money and time, studying the ways, our own bodies can regenerate tissue.
All living creatures, including humans, have the ability to repair damaged parts of the body, but the extend of that repair, varies considerably.
As small infants, we have the ability to regrow the tips of our fingers if they're severed, but we loose this ability, as we age.
So, animals, like salamanders, with their super regenerative powers, seem intriguing to us.
Regeneration had been known about, since ancient times.
But for a long time, no one understood, how it happened.
In the 17th and 18th century, there was a new wave of scientific discovery.
A brilliant Italian scientist, named Lazzaro Spallanzani, made meticulous observations into regeneration, across many different species.
And shared his ideas, in detailed letters.
In November 1765, he wrote to the eminent scientist Charles Bonnet, whom he regularly corresponded with, to announce, that he had discovered tail regeneration in salamanders.
Throughout the following year, he followed up his initial observations, with numerous experiments, to try to understand, how the salamander could regrow a tail, just like the original.
He found, that all species of salamander he tested, could regrow their tails, when injured, and they did so, more rapidly in summer, than in winter, and retain this incredible ability throughout their lives.
Spallanzani advocated a radical theory.
He thought, that salamanders already possessed a number of miniature spare parts, at the base of each limb, that could grow in size, to replace a lost or damaged one.
He was unable to prove this, but he didn't give up.
He studied salamander tadpoles, and came up with another, even more interesting idea.
A year after his initial letter, Spallanzani once again wrote to Charles Bonnet.
This time with detailed descriptions of further experiments into tail regeneration.
Most notably, in this description, he wrote: I am almost lead to believe, that the tail regenerates, in tadpoles, are more of an elongation of the old parts, than a development from a germ.
This suggests, that Spallanzani was on the right track.
But the idea, that the salamander could regrow a new tail, from seemingly nothing, was not well supported.
And Spallanzani was therefore never willing to pursue the idea further.
However, there's no doubt, that his research helped to lead other scientists closer towards proving what really happens, when a salamander regrows its tail.
In fact, Spallanzani's rough sketches did make sense.
For they were the first to describe, some of the vital processes, in the remarkable growth of new limbs, that we understand better today.
When a limb is lost, the exposed blood vessels and tissue, contract, to quickly stop any bleeding.
Then, skin from the edges, begins to grow across the damaged area, to protect the body from infection.
Now, cells that were once dormant, begin dividing and multiplying, to create new ones.
Each cell retains a kind of memory, of the type of tissue it used to be, So, a new cell that regrows from damaged muscle, will always become muscle.
Within weeks, the salamander has a full-grown leg, almost identical to the original.
Although we now know the steps, that take place during the regeneration of body parts, we still don't fully understand, what triggers this kind of response.
But it seems, the answer may lie in how the salamander's body responds to injury.
In humans, if an arm is severed, the cells die, alerting the immune system to the problem.
In response, the area becomes swollen, and is covered over with scar tissue, preventing any new growth occurring.
But in salamanders, the immune system responds differently.
And instead of forming a scar, it triggers regeneration.
Another, rather unusual looking salamander, that lives in the fresh waters of Mexico, sheds new light, on how this happens.
Axolotls are among the best re-generators in the natural world.
And scientists wondered, if their blood played a role, in the process.
Like us, they have special white blood cells, that consume invading bacteria and damaged tissue around injuries and wounds.
Researchers removed them, and the results were surprising.
The axolotl was unable, to regrow new limbs.
So white blood cells, were part of the secret of their powers of regeneration Understanding the role of the salamander's blood cells in regrowing limbs, could be a step towards discovering why they can regenerate body parts, and we can't.
All amphibians have tadpoles, which develop limbs and enable them, to move onto land.
But salamanders are able to re-trigger that remarkable process.
We too, undergo extraordinary development in the womb.
Maybe, like the salamander, there is a way of us, retaining this ability, into our adult lives as well.
The salamander has a truly amazing ability, to regrow complex body parts, to enhance its chances of survival.
While we donât yet know all the answers, it's likely, that this incredible creature, could revolutionize modern medicine, and the way we treat injuries.
Next, we uncover the secret behind how the moose regrows its enormous new antlers every year.
and discover what happens, when regeneration goes wrong.
The salamander's ability to re-grow entire limbs, is truly remarkable.
But moose and other deer, possess huge antlers, that are shed and re-grown, each season.
How can they regenerate such large body parts, every single year? This impressive skeleton, belongs to one of the biggest deer, to ever live on the planet.
It's an Irish Elk.
His antlers were enormous, they're almost 4 meters, 12 feet across, and they weigh 40 kilos.
An Irishman, named Dr.
Molyneux, first scientifically described the elk, in 1697, from specimens, taken out of an Irish peat bog.
Some believed, that this elk, was a large moose, and were convinced, living specimens could be found elsewhere, across Europe and Russia.
But not everyone agreed.
And the debate, about the life of this creature, would continue for more than 100 years.
The skeleton of an Irish elk, looked very similar, to that of a moose.
So, it's easy to see, why many believed them to be the same animal.
Both have very impressive antlers.
Antlers are only found in the deer family, and are made of bone.
Unlike horns, which are permanent structures, they are shed and replaced, every year.
But how can deer re-grow huge chunks of bone? Something, no other mammal can do.
Moose, like this young bull behind me, start growing their new antlers immediately after they shed their old ones.
The antlers first appear on little bumps, on either side of the head, known as pedicles.
And they have a soft furry covering, called velvet.
This is vital to their amazing powers of regeneration.
Blood vessels at the base, start the growth.
But as the antler gets longer, this blood supply is cut off.
Then, blood vessels within the velvet take over, and transport nutrients and growth hormones to the growing tips.
In older males, the antlers can grow at a rate of 2 cm a day, making it the fastest growing bone of any animal.
Once at full size, the velvet is shed.
The animal rubs its head against a tree, to encourage the thin velvet, to fall off.
It may look gruesome, but it's a natural part of the annual cycle, and does the animal no harm.
But why should a huge set of antlers be regrown every year? It's a question, that baffled early naturalists.
Until Charles Darwin suggested, it may be to do with attracting the opposite sex.
In the first few years of adulthood, the antlers are small.
And as a result, young males remain subordinate to the larger bulls.
But as they get older, their body size increases, so, the antlers will also increase, eventually becoming impressive ornaments with which to compete for females.
Those with the biggest antlers, are certainly more attractive to the females.
Maybe, they are an indicator of fitness and strength.
And it's no coincidence, that antlers are at their full size, during the breeding season.
This is a time, when a bull must protect his harem, and see off competitors.
Competing males tilt their heads, to show off their antlers, to their best advantage.
But if the bulls are equally matched, then, the competitors fight.
The winner, then gains access to the females.
The benefits of such a victory are huge.
But to get to that point, every young bull must, for many years, grow and regrow antlers.
It's a big investment, draining the body of vital resources.
And no investment was bigger, than that, of the Irish Elk.
The sheer size of these antlers, had let some to argue, that they were unlikely to have been used in physical combat.
Unlike other deer, the antlers of the Irish elk, grew with a large flat, palm-like plane, facing forward.
So then, if a bull looked straight ahead, it would be at its biggest and most impressive.
In this way, they may have been able to intimidate rivals and attract females, without actually fighting.
So, although the Irish elk was armed with what appeared to be enormous weapons, it seems, they were mostly for show.
Now, this strategy, may have been an advantage for the large elk.
Fighting is always a risky business, and will often result in serious injuries.
After the breeding season, the antlers are discarded.
Moose shed theirs in the winter, whereas smaller deer, keep theirs until the next spring.
This maybe, because the moose antlers, are such a heavy load to carry, throughout the winter.
But why are antlers shed at all? Antlers are made of dead bone, and can't be repaired.
If a moose damages an antler during a fight, it will loose its chance of mating, for that season.
By shedding and regrowing their antlers each year, bulls ensure, that they stay in the mating game.
Just before antlers are shed, minerals within them, are reabsorbed from the base, weakening the structure, so that they eventually fall off.
The flesh underneath is exposed, but not for long, as new skin soon covers the wound.
Experiments have shown, that the skin lesion that forms over the open wound, creates a connection with the underlying tissue, that is crucial to regeneration.
If this connection isn't laid, the production of velvet will be interrupted, and the antlers will either not grow at all, or develop into strange shapes.
So, what about the Irish elk? Could the problems of regenerating such gigantic antlers, have determined its faith? The French scientist Georges Cuvier, was keen to demonstrate, that the Irish elk was a unique species, that had become extinct.
To prove his point, Cuvier undertook a detailed examination of Irish elk fossils.
He was able to show, that it was indeed a distinct type of deer, that could no longer be found alive.
And so, the Irish elk, was one of the first animals we recognized, as being extinct.
Georges Cuvier had solved the question, of whether or not, the Irish elk and moose, were one and the same creature.
But why did the Irish elk die out? Cuvier suggested, that evolution had set it on a course of ever increasing growth.
And that eventually, the antlers became so large, that the poor animal could not even lift its neck.
He may not have been that far from the truth.
It is now thought, that the annual growth of the Irish elk antlers, put a strain on their bodies.
A significant proportion of minerals, within their bones, were extracted and moved into their growing antlers.
This led to a seasonal osteoporosis, with their bones weakening.
They were, in effect, robbing one part of their body, to boost another.
It was a gamble, that worked for thousands of years.
But around 10,000 years ago, the climate began to warm.
The nutrient-rich grasses, that the elk relied upon, began to disappear.
Growing massive antlers, may now have been too much of a drain, and permanently weakened the skeleton.
The change in diet, may also have effected their ability to breed, with females no longer able to produce young every year.
Whatever the reason, the Irish elk, with its magnificent antlers, finally vanished from the landscape.
And in its place, the moose has become the largest deer on earth, today.
So, while regeneration can give the salamander a second chance, to a full life, the yearly regeneration of antlers in male moose, is a risky strategy.
But one, with huge rewards for those with the best antlers.