Metamorphosis: The Science of Change

'Imagine you woke one day to find yourself

living in the body of a creature

completely different to what you used to be.

Your shape, your body parts,

your individual cells.

Rearranged by some unknown force into something new.

You have been transformed.

This is what happens to countless creatures.

It is called metamorphosis.

It is how the tadpole is changed into a frog.

How the caterpillar becomes a butterfly.

It is one of nature's most powerful phenomena,

and to me one of nature's most mysterious.'

Metamorphosis is such a spectacularly odd kind of change.

A creature stops itself in its tracks,

seems to tear itself apart

and then rebuilds itself as a completely different kind of creature.

I don't think you can help but be intrigued by that.

'Generations of artists and writers

have been drawn to the idea of metamorphosis.

Imagining creatures that shapeshift,

that turn into something else.

Visions that feed our dreams and nightmares.'

I wonder if our fascination with metamorphosis

is because somewhere written deep in the science of it

there's a half-perceived truth about us.

'So how does nature work, this seeming miracle

of turning one creature into another?

What is the truth behind this extraordinary, beautiful process

that has taken such a hold on our imagination?

And might it even in some way happen to us?

Two thousand years ago,

the Roman poet Ovid wrote an epic poem

retelling tales from Roman and Greek mythology

of a man being turned into a werewolf,

a woman changed into a tree.

The title Ovid chose for his poem

was Metamorphoses,

a word from ancient Greek that means to change form.

And many hundreds of years later,

when scientists began to study the process of real transformation in nature,

they chose to use this same word.'

I've always thought that metamorphosis was weirdly interesting.

Apart from the phenomenon of a creature turning itself into another creature,

what intrigues me is the fact that

metamorphosis as a concept

has two forms, two meanings.

There's the scientific meaning

but there's also a metaphorical meaning

that we find in books and that we use when we talk about ourselves.

And I suppose what interests me

is whether the connection is just metaphorical

or whether there's something deeper going on, a deeper connection.

'I want to begin by understanding more about what metamorphosis means in the natural world.

Most of us think we're familiar with it.

Every child knows that a caterpillar turns into a butterfly

but it seems to me that even this transformation

is rather extraordinary.

Professor Stuart Reynolds is an entomologist

who has studied the intricate sequence of events

that makes up this metamorphosis.'

This here is a chrysalis

and the chrysalis

is a stage intermediate between the caterpillar and the butterfly.

So one of those attaches itself and turns into that?

'Virtually every stage of metamorphosis

seems to have something unexpected about it

and how the caterpillar turns itself into a chrysalis is no exception.'

-These guys live in a kind of suit of armour all the time.

-Yeah.

Their skeleton is on the outside and so if they want to grow,

they have to grow a new skeleton that's a bit bigger

-and we call this moulting.

-Right.

When you moult you split the old skeleton and crawl out

-and then you inflate the new one from inside.

-OK.

Sometimes by swallowing air, for example, blowing themselves up.

Fantastic!

The formation of this chrysalis is just another example of moulting.

There's probably several days

during which it's forming

this rather different shape of creature inside the old caterpillar.

-In, still inside itself?

-Absolutely inside.

Oh, that's weird.

So the demolition job of the caterpillar

and the beginnings of the construction of the new creature

is happening while it's still in that skin?

Yes. While it still looks like a caterpillar,

but actually it's not really.

'The formation of the chrysalis

hidden inside the body of the caterpillar

marks the beginning of the metamorphosis.

But what triggers this in the first place?

What tells the caterpillar that this moult won't be like the others?

That it is time to begin the change into a butterfly.'

When it's a last-stage caterpillar like this one,

it has some clever way of saying,

"Well, actually, this next moult is going to be different, chaps."

-Klaxons start going off!

-Absolutely.

Yeah, it's a real emergency moment

because absolutely every tissue inside the caterpillar

is going to have to be involved in this.

What actually triggers that?

That's a hormone called a juvenile hormone.

And it's a timing signal.

As long as you have the juvenile hormone,

you go on being a caterpillar.

You take it away and then you start to metamorphose.

'As the juvenile hormone leaves the body of the caterpillar,

so a cascade of processes is set in motion.

And the metamorphosis begins.

The caterpillar stops feeding and finds a resting spot.

It makes itself a little pad of silk

and from this hangs upside-down by the tip of its tail.

For the final time, the caterpillar sheds its skeleton

and the chrysalis that has been growing inside emerges.

Where is the creature that was?

And where is the creature that will be?

This X-ray scan is as close as we can get

to seeing the scale of the transformation

that is occurring inside the chrysalis.

The structures highlighted in yellow

make up the respiratory system

that allows the caterpillar to breathe.

Slowly, through the course of metamorphosis,

this is entirely remodelled.

Almost all the other major organs are also changed.

It is a process that can take for some species a few days,

others weeks.

But when it is done, a new creature emerges.

The caterpillar has been replaced by a very different being.

A creature with wings,

with a new brain, eyes and legs.

And most important, the ability to reproduce.

But crucially, remarkably,

it is still the same individual insect.

Its unique genetic code has not changed.

No wonder people have seen something almost magical in this transformation.

According to legend,

it was when the Hindu god Brahma

watched the caterpillars in his garden change into chrysalises

and then into butterflies

that he conceived the idea of reincarnation.

Perfection through rebirth.

The ancient Greeks associated the butterfly with the soul

and used the same word, psyche, to describe both.

But what is the biological meaning behind this metamorphosis?

Why lead two lives in one?'

If you're doing perfectly well as a caterpillar,

why not just stay as a caterpillar?

I mean, what do you think the purpose of the trick is?

Well, the trouble with being a caterpillar

is that it's hard to get around.

And if you see what these caterpillars

-have done to this plant here, there's...

-Yes.

There's not a lot of food left for another generation of caterpillars.

So if I were a caterpillar and I had ambitions to reproduce,

I would like to go somewhere else.

So what do you do? Well, you have some wings.

All right, but are you saying then that the purpose is to do two different jobs?

Yeah.

The really great thing about metamorphosis

is it allows specialisation.

You can have an adult that has wings

that allows you to find mates,

fly around, find the right kind of food plant,

and then you can have a specialised caterpillar form

that does really nothing but eat.

It just enables each stage to do its job in the best way possible.

'And this is the real advantage of metamorphosis.

By dividing the creature's life into two parts,

each life form can perform very different roles.'

I think one of the most interesting things for me talking to Stuart Reynolds

was you have a creature which has lots of legs and trundles about in plants.

It's turning into something that has few legs and flies.

And it's easy, I suppose, to be focused on that

and his point was that that's almost hiding

something more important about metamorphosis,

which is what you're really changing is a creature

that can't move about much and which eats leaves

into one which feeds on nectar and flies.

So the real change isn't a physical transformation, however spectacular it looks,

the real change is in the way of life of the creature.

'If it were only butterflies that used this trick

of living two lives in one,

then metamorphosis would be an oddity,

but it is not.

Of the one million species of insect we know of today,

from beetles

to bees

to flies,

most undergo some form of metamorphosis.

It's a trick insects evolved around 300 million years ago.

Yet metamorphosis is more widespread than just the insects

and more ancient too.

It is in the ocean where metamorphosis first evolved

and where it takes on even more dramatic forms.

These are adult sea urchins.

They live in the depths of the ocean floor

feeding mainly on algae and other plants.

But the sea urchins begin life as very different creatures,

tiny microscopic larvae,

which swim in surface waters and feed off plankton.

Doctor Paola Oliveri is a biologist

who studies the process of development in sea urchins.'

So you can see this is a sea urchin larva.

-Here you can see there is the mouth, stomach.

-Right.

This big round thing.

-Now this one's not metamorphosing yet?

-Not yet.

It's getting ready.

'How this larva is transformed into the juvenile or young adult sea urchin

shows metamorphosis at its most disturbing.

For even before the process is underway,

what this creature will become can be seen growing inside it.'

So what is that?

That is the little juvenile that is growing...

-That...

-Inside the larva.

-This is turning into that?

-Yes. One inside the other.

And in another couple of hours,

-the little juvenile here...

-Yeah.

-..will pop out, literally.

-Pop? Pop out?

Yes, so that first tube feet,

which are this little tiny kind of like flexible structure

that we see in the adults,

the first five tubes will go out.

-Punctures its way through?

-Punctures it.

-It will finish the metamorphosis.

-What about the larval stage?

Well, then it's completely basically reabsorbed and dies.

-Reabsorbed?

-Yeah, reabsorbed.

Is that a polite word for being eaten?

Yes, in a way.

Part of it and part of it really dies by natural death.

'In the metamorphosis of the sea urchin,

the juvenile takes over the body of its larval host

and then eats it.

The last act of the larva is to swim down to the deep ocean

where the juvenile will live.

And once it reaches the seabed, the metamorphosis begins.

This time-lapse footage shows the process unfolding.

The tube feet of the juvenile puncture through the body of the larva

and slowly, one by one, its spines emerge.

The juvenile has literally turned the larva inside out

as if it were a sock

and in the process extinguished its life.

For at the end, what is left is just the one life form

of the juvenile sea urchin.

The creature's body and its way of life

have been completely transformed.'

It does have that slight feeling of the alien popping out from inside.

It's not really anything like the kind of

garden variety metamorphosis that we're used to.

No, it's very different, it's very dramatic.

With the caterpillar butterfly, most of the animal,

the cells and the body plan of the caterpillar

actually is retained after metamorphosis into butterflies.

This case is very different.

The larva will not exist any more.

-Right.

-Will be reabsorbed and die

and will be completely different form.

The completely different form I can cope with

but what's slightly worrying here is the second one has got started

before the first one's stopped.

-Yes.

-Does that not bother you?

-No.

-No, OK, it's just me then!

It's very dramatic change

but if you think about the sea urchins

are actually more related to us

than a caterpillar and a butterfly.

-Really?

-Yes.

They're actually our direct cousin.

Wow, all I can say is I'm glad we changed our way of reproducing and developing

cos I don't really fancy that!

'The metamorphosis of the sea urchin appears alien to us,

but others in the ocean are even more bizarre.

This is the larva of a species of starfish called Luidia sarsi.

Just as with the sea urchin,

the two life forms exist together

for at the end of the larval form

can be seen the juvenile form,

a miniature orange starfish.

This grows attached to the larva until the moment of metamorphosis

when it breaks free.

For a short time, the two forms of the same creature live parallel lives

until the larva dies.

With both the starfish and the sea urchin,

we see the different forms of the creatures overlap in a disturbing way.

Unlike the caterpillar, this is not simply a remodelling job.

Here the juvenile is essentially built from scratch.

But what is common to all these cases

is that the same genetic code, the same genome,

controls both versions of the creature before and after metamorphosis.'

-From the genetic point of view it's the same genome.

-Right.

It's the same creature.

How does the genome work then? They're different sets of genes?

No, actually most of the genes

are going to be used in both life parts.

In the larva and in the juvenile.

Certainly there are genes that they are specific for the larval stages

and genes that they are specific for adult stages.

That's clever as a piece of engineering though.

It's like having a factory that follows a programme

and turns out bicycles

and then the exact same programme turns out hot air balloons.

That's beautiful.

-HE LAUGHS

-That's economic! It's magical.

'In the ocean, many creatures shapeshift,

transforming themselves into something else.

The spiny lobster moults and crawls out of its skeleton

to leave its larval life behind.

The sea squirt larva absorbs its own tail

and consumes its own brain

to allow its juvenile form to take over.

Metamorphosis is even witnessed in certain species of fish.

The flat fish moves its eyes to the same side of its head

so it can better spot predators in its adult life

swimming on the ocean floor.

In each case, the creatures are changing not just how they look,

but how they live.

Is it any wonder that metamorphosis holds such intrigue for us?'

I suppose I did think that metamorphosis was just something

strange that tadpoles and butterflies did

but there are so many branches of life

that benefit from metamorphosis.

Insects, amphibians, marine invertebrates, crustaceans.

It begins to make me wonder

if evolution couldn't have found some way

for us to benefit from the same trick.

'The time when human beings change the most, physically, is in the womb.

So perhaps we should consider the transformations that take place here

and what happens when we are born.'

-Do you see the baby's face just?

-Yes.

-Have you seen this before, Michelle?

-No.

Wow! I'll take a picture. I'll take a picture or two.

That's amazing.

It is, it's beautiful actually.

'Michelle's baby is 27 weeks old

and is being scanned by consultant obstetrician Christoph Lees.'

How many weeks ago would the baby have just been a little tiny ball of cells?

Well, we're 27 weeks now

so about 20 weeks ago at about six, seven weeks,

the baby would be about half a centimetre,

a centimetre long, this long.

'The most obvious type of change that occurs in the womb

is the change in shape.

How from a ball of cells a human form develops,

with a head, eyes and limbs.

It is a slow, gradual process

that occurs in the first 12 weeks of pregnancy,

but it is not the only type of change that the baby goes through.

A transformation far more abrupt and dramatic is yet to happen.'

So you can see the lungs. There's the heart and these are the lungs.

The lungs are full of fluid at the moment.

Within about 30 seconds of the baby being born,

all that fluid is expelled and the lungs suddenly expand.

SOUND OF HEART BEATING

'The physiological change that will occur to this baby at birth

goes well beyond the baby inhaling its first breath of air.

This is when many of its organs

will begin to work properly for the first time,

and even something as fundamental as how blood flows around its heart and lungs

will be transformed.'

Do you see that blue flash there?

-And there's a lot of blood there, isn't there?

-Yes. Seems like it.

And that is going from the right side of the heart into the baby's aorta.

So the blood that goes into the right side of the heart

-that in you and me goes round the lungs...

-Yes, yes.

-Then goes back into the left side of the heart and is pumped round the body.

-Yes.

Instead it bypasses the lungs

and goes straight into the aorta

through that blue tube there.

It's not of course a blue tube, but it's called the ductus arteriosus.

What happens when the baby is born?

When the baby's born, that collapses very very quickly.

-What, like that?

-Within minutes.

Those moments, a few moments before and a few moments after,

the child is changing in how it works in its internal structure,

probably more radically than in any other time in its life.

The first 24 hours of a baby's life,

the most amazing changes are happening.

In the lungs, in the blood vessels,

some shrinking, others opening up,

-so although to you, you look at a baby and...

-It's finished.

Baby looks the same on the day baby's born

perhaps to the day after to the day after.

In that time some truly remarkable things have happened in the baby's circulation

and in the baby's internal organs.

And of course the kidneys start functioning even better.

No wonder babies are slightly preoccupied.

They've got to learn everything in those first few minutes.

I'm amazed they don't cry more than they do!

Because they've got an awful lot to be going on with.

'So in fundamental ways the body of the newborn baby

works quite differently to how it worked in the womb.

Only at birth does the baby's blood begin to circulate as it does in us.

Only then does the baby begin to get oxygen from its lungs

rather than from the placenta.'

The changes that you've described are really, they're profound.

Especially the ones you say happen at birth.

Is it like metamorphosis?

Does it share enough similarities with what we would call metamorphosis, do you think?

I suppose you would be thinking metamorphosis as a change in form

and where you have moths developing from caterpillars.

That of course is clear change in form.

What we're getting with a baby is something much more subtle but no less dramatic.

Certainly an internal change in form, an internal metamorphosis, if you like,

but I don't think we could call it metamorphosis,

metamorphosis as we see in insects.

'The physical changes that occur at birth are remarkable,

but in the view of science are better described as development.

But does this mean that metamorphosis plays no role in our lives?'

You can't get away from the fact that we are the most extraordinarily changeable creatures

so it would still seem strange to me

if metamorphosis didn't happen in our lives,

just not in a simple straightforward way.

'We certainly seem to be afraid that it might happen to us.

Writers and storytellers have long recognised

that something about this type of change

that we see in caterpillars and tadpoles

nevertheless taps into some deep-set fear.'

We have a strong sense of identity.

Our sense of identity is bound up

with our outer appearance with our shape.

We look in the mirror and think, Oh yeah, that's me.

So we don't expect any radical change in that outer appearance.

We would like to be able to determine what shape we are

and what changes are undertaken that affect us.

When we find we can't then of course we lose control.

'Most famously, this anxiety and fear of transformation

was explored by Franz Kafka in his short story The Metamorphosis.

Kafka imagines a man, Gregor Samsa,

who awakes one day to find himself transformed into a beetle.

In his new form the character slowly loses everything he once was.

His place in society, his family and ultimately his life.'

Kafka is using an image of the man

who wakes up as a beetle

in order to explore

somebody's fall out of the social order he was used to

and he was familiar with.

He was used to being in this deadpan terrible job

that had him work him all the hours that God sent

and he hates the job, but it's what he's used to.

He does it all the time

and all of a sudden that is taken away from him.

'Kafka's story isn't the only one

and metamorphosis isn't always something we imagine forced upon us.

When the respectable Dr Jekyll takes a potion to change himself

into the vile Mr Hyde,

the transformation is still frightening but it is self-inflicted.'

So if you think of Jekyll and Hyde,

we have one man who feels

he cannot, in the shape of Dr Jekyll,

live out everything that he would like to live and be,

therefore invents Mr Hyde as his dark alter ego.

Dr Jekyll realised that man is not truly one, but two.

And he felt very much this dual identity.

The person he wanted to be, the good person,

but then he also had instincts and desires

that were not acceptable to society.

I think what the writers who use metamorphosis

as a metaphor for change and transformation are telling us,

is that our attitude towards change is deeply ambivalent.

On the one hand we can all like change,

but on the other hand,

I think we're all aware that change can be something we are swept up in.

'Our relationship with change is very different to how metamorphosis

would appear to work in nature.

Where it seems to be a process that runs like clockwork,

rigid and pre-programmed.

But there is a creature that shows this isn't always the case.

The humble tadpole.

The beauty of the tadpoles' metamorphosis

is that it occurs right in front of our eyes

in our garden and woodland ponds.'

-This looks lovely.

-Yes, it's nice.

'Dr Patrick Walsh is a behavioural ecologist who studies this metamorphosis.'

Did you just decide sometime in your teen years

you weren't going to grow up?

Basically! Yeah, I know, I often phone family and friends

and say I'm getting paid to do the stuff I used to do as a child.

Let's get these guys here.

'As any child who has collected tadpoles will have noticed,

it's often possible to see all the stages of metamorphosis in the same pond.

This simple observation says something profound about the tadpoles' metamorphosis.

The difference between the tadpoles isn't because they were born at different times.'

These would have all been laid nearly at the same time?

Yeah, pretty much at the same time. Within a week of each other.

So then why is one tadpole just a tadpole

and then there are others that have got legs and are well on the way to being frogs?

Why the difference?

Well, so that the amount of time that they spend as a tadpole

and go through metamorphosis will be quicker in one than another.

And so they'll be kind of, in quotations, making decisions

about the environment that they're in

and how favourable it is for them to be in this aquatic environment

and then trying to hedge their bets

about what it's going to be like in the terrestrial environment.

-They don't all make the same decision?

-They don't.

How much variation are we talking about?

It can be huge. The first ones may come out in late June,

but we've actually done some observations of them spending their winters as tadpoles.

So you can have some in the same pond that will develop into frogs,

and they spend the entire winter as a tadpole and come out the following spring.

'Scientists have captured images

which show the complexity of the changes

that must occur inside the tadpole to turn it into a frog.

The tadpole's intestines must transform

to accommodate a new diet,

from a tadpole that eats mainly algae and plants,

to a frog that can eat meat.

The gills that allow the tadpole to breathe underwater

are of no use to the frog and so must be destroyed.

And the tadpole's skull, made of cartilage,

must be replaced by one made of bone and a backbone created.

It is an epic reconstruction project, of amazing complexity.

And yet remarkably it appears that the tadpole can influence

the timing and the speed of this metamorphosis.

One way the tadpole is able to do this

is as simple as where it spends its time in the pond.

In the warm sunlit water near the surface,

the biochemical processes that power metamorphosis will be speeded up.

Whereas in the cooler water at the bottom of the pond,

these processes will go slower.'

Different areas of the pond will have different sunlight exposure,

different amount of food, different predation risks,

so where they choose to be in that pond

will have a huge impact on how long it takes them

to go through the larval period.

You say the tadpoles choose.

Yeah, I don't think that they're thinking about things and saying,

"Oh, it's a really nice day, I think I'll go spend some time up here

and go through metamorphosis quicker."

I don't think it's that kind of sense that we would think of making a decision

about, you know, which restaurant to go to or what not.

But they are making choices.

'And they are choices with different consequences.

By metamorphosing earlier in life and more quickly,

the tadpole will become a smaller frog, more vulnerable to attack,

but if it stays in the pond, it may be eaten.

It's a choice made by the tadpole

based on an awareness of what is happening around it.'

There's actually chemical signals released by tadpoles

-when they're injured or eaten.

-Right.

And so the other tadpoles react to those chemical signals

so they're able to pick up those chemicals and interpret them.

So if, once you start, once they start getting killed

then the amount of that warning chemical builds up in there and that will tell them...

It's a dangerous place. Yeah, and so then they go through an acceleration of development

and they think, Well, this is really risky being here.

I have a better chance on land.

'And the tadpoles are able to read other signals too.'

Having ponds that dry out is a really, really big driver

on how long they spend as tadpoles.

-So they can actually judge the change in depth of water.

-Can they?

So if it seems to be drying out or decreasing in its depth rapidly

-they'll accelerate.

-It triggers something?

It'll accelerate so they'll go through metamorphosis because the trade-off is

I'm an aquatic stage and if I have no water then I'm in a lot of trouble.

And does the opposite happen? If they're in a pond and it's...

There's an abundance of the food that they eat,

they'll just stay at that stage for longer?

Yeah, so they can stay at that stage and the idea would be then

that they'd feed and get larger and larger,

and when they come out onto land they'd be larger frogs.

And they'd have a competitive advantage.

-So we know what happens to tadpoles.

-Yeah.

-But the tadpole decisions...

-Are much less understood.

-It's still a mystery how they decide?

-Mm-hm.

So that's future work.

The mystery of tadpoles.

'The transformation of the tadpole into the frog

shows metamorphosis in a new light.'

I thought one of the most thoughtful things that Patrick said

was the way he was suggesting that the tadpoles were involved

in making the metamorphosis happen to themselves.

It wasn't any longer something which overcame them almost against their will.

They were evolved in how the metamorphosis happened, how quickly.

I thought that was interesting.

It just moves it away from being something entirely pre-programmed.

It makes it part of the life decisions of the creature itself.

'So it seems that metamorphosis in nature

might sometimes be closer

to the sort of change we are familiar with in our lives.

Change that we have a degree of control over.

There are other creatures that change themselves in ways

that suggest even closer parallels.

These two locusts are the Jekyll and Hyde of the insect world.

Through a special transformation, one can turn into the other.

The physical change involved in this transformation

is insignificant compared to the other metamorphoses we have seen.

Yet the change in their way of life is dramatic.

The green locust live a solitary and inconspicuous existence

but transformed into the other locust

it becomes a destructive pest.

Flying in vast swarms that reek devastation on crops.

The change is not one of shape, but in behaviour.

Professor Malcolm Burrows is a neurobiologist who's studying how this happens.'

I would call that a grasshopper. Is that incorrect?

No, that's absolutely correct.

There's something like 4000 species of grasshopper in the world

and only about 13 of them

can show this remarkable change from one state, this state,

to this state, the gregarious phase that forms swarms.

-That turns into that?

-That turns into that.

Blimey.

'The difference between the two is shown by an elegant experiment.

First introduce a green locust into an arena,

which has empty space on one side

and a crowd of locusts on the other.

For a green locust, seeing a crowd of other locusts repels it.

It wants to be alone.

It heads for a quiet corner.

But when a darker coloured locust is introduced, it's a very different story.

This is a gregarious insect. It heads straight for the crowd.

And it is this behaviour that creates swarms.

But what triggers the individual locust to switch from one behaviour to the other?'

In the lab, we can convert this solitary animal into a gregarious animal.

We can change its behaviour.

And the bizarre thing we can do is to tickle their hind legs.

HE LAUGHS

And we can tickle their hind legs for a couple of hours.

How did you discover that?

-Well...

-Were you just idly tickling a grasshopper?

Oh yes, that's the way we pass our time in Cambridge, didn't you know?

Just tickling animals.

And what's that mimicking then? I mean, why are you tickling its rear legs?

When they actually come into contact with other locusts,

the things that they jostle up against each other are the things that stick out.

And the main things that stick out are the tips of the hind legs.

-And that...

-And so...

-That's the stimulus?

-That's the stimulus.

So tickling them for a couple of hours will change their behaviour

from being this solitary animal

that avoids others to ones that actively seeks out other animals.

But when they do, do they look like him?

After several generations

the behaviour leads to changes

in the form and size of the body as well.

But the behaviour first?

But the behaviour is the all-important thing.

Can they, can they go back?

They can go backwards as well.

And then if you keep them isolated for a long time

they will revert back to this sort of colouration.

The family photo album of these creatures must be bizarre!

'This transformation explains

how it is possible for biblical plagues of swarming locusts

to emerge apparently from nowhere.

For much of the time these same creatures that form swarms

live a solitary life unseen and unnoticed by humans.

But living in the desert, the locust is always ready to change its way of life.

Rain brings plentiful food.

But when the rain stops, food becomes scarce

and the solitary locust are forced together

jostling one another as they compete for whatever remains.

And so the transformation occurs and the locust begin to swarm.

Swarms which can number in the millions

as they fly together to find new sources of food.

But how does the locust jostling and tickling one another

lead to this astonishing transformation?

Malcolm's team have found that what produces this change in the locusts' behaviour

appears to be a single chemical hormone

also found in the human brain.

It is called serotonin.'

This is the part of the nervous system that controls the movements of the hind legs.

So this is where it gets all the tickling input

that starts off the whole process.

And the light is showing us the presence of serotonin?

That's showing us the presence of serotonin.

We can follow the changes in these cells

during the process of changing from solitary to gregarious.

-Right at that cellular level?

-Down at that cellular level.

So we can look at animals that are fully solitarious animals.

-Right.

-Then we can look at them

after an hour or after two hours or four hours

of being exposed to stimuli that will make them change into the gregarious phase.

-And do they light up differently?

-They light up differently.

And there's a group of cells here.

Look, there's one here that's shining up very bright at the moment

and that is a cell that we're very interested in at the moment.

-A single cell?

-A single cell.

-When it starts having its hind legs tickled...

-Yes.

That cell reacts by starting to crank out a lot more serotonin...

Than any of the other cells.

And serotonin being a neurotransmitter starts to change how the animal behaves?

That's right.

'So can we consider this transformation a metamorphosis?

Unlike the metamorphosis that turns the caterpillar into a butterfly,

the transformation of the locust

is not an irreversible change from larva to adult.

It is triggered by a change in the locusts' environment

and can be undone.

And in contrast with other metamorphoses,

the physical changes are minor.'

For you, then, what counts as metamorphosis?

Cos when we've looked at caterpillars and butterflies,

and tadpoles and frogs,

metamorphosis is just the change of shape, it's what the word says.

Well, for me it has a much broader definition than that.

It means that the behaviour of an individual animal

that has the same set of genetic instructions inside it,

is to behave in a very different way.

And that allows it to live a different life?

And that allows it to live a completely different lifestyle

from being solitary to now living

in swarms of millions and millions of animals.

So is that behavioural change then kind of...

Is that metamorphosis for you for these fellows?

That's what I would call metamorphosis in these animals, yes.

'If we do consider metamorphosis

to include this remarkable transformation of the locust,

then suddenly its reach extends well beyond the realm of caterpillars and butterflies.

Biological metamorphosis, metamorphosis as it happens in nature,

moves much closer to us.

We change our behaviour

and we change in response to our surroundings.'

When we started this film

and metamorphosis was just something that tadpoles and butterflies did,

something physical,

metamorphosis did seem quite simple.

But now with the locusts it seems to me it's not nearly so clear cut.

And that distance between biological metamorphosis

and the more metaphorical idea that the writers use,

seems to me that gap is shrinking.

'Maybe evolution has found a way for complicated creatures like us

to be able to pull off this trick of changing radically.

Perhaps we just don't do it physically.

If a caterpillar wishes to fly,

it must grow wings and become a butterfly.

-If

-we

-wish to fly,

we do not need to change our bodies, we invent an aircraft.

I believe it is through our minds that we metamorphose.

This is how we change our way of life.'

You see, to my mind,

how we transform ourselves is a radical version of what the locust does.

We both transform our behaviour.

Of course, the key difference is we are the authors of our transformation.

'We invent technologies that force us to live in new ways.

We have ideas that radically alter society.

We dream a better version of ourselves.

Change conceived in our mind that drives our history.'

And once those changes are set in motion,

they become bigger than any of us individually.

They get a hold of us, they can overwhelm us,

and surely that is metamorphosis.

'And this is what Kafka was pointing to in his story.

How collectively we shape the society in which we live,

but then that same society

forces change back upon us as individuals.'

I believe that we metamorphose not just metaphorically,

but in the truest, broadest sense of the word.

Yet I think there will always be that part of us

that fights against it.

For in one fundamental way,

our metamorphosis remains very different

to that of the caterpillar or the tadpole.'

Think of a soldier, someone's who's been living in a world of killing and mayhem,

who then comes back home to a civilian life where nothing's the same.

Now that to me is as profound a metamorphosis

as the caterpillar into a butterfly.

But of course the critical difference

is that there's no butterfly

that looks back with remorse to the caterpillar it used to be.

But we do.

We remember.

We can't help but look back and remember the creature we used to be.

And regret what we might have lost.

'And this for us is the great irony at the heart of metamorphosis.

That the same part of us in which metamorphosis is realised,

our mind, is the same part of us that fears it most.'

We have this deep conflict about wanting to change,

wanting newness, wanting to advance ourselves, develop ourselves, and so on and so forth.

But at the same time we don't want to lose what we were.

And that's what makes me fear, as it were, profound change.

Losing that person that I am.

So we're really the only creatures who were gifted metamorphosis.

But we're the only ones who can see its darker side really.

It seems to me that much of our change is self driven.

And we seek out change actively.

We don't really suffer it, it doesn't just happen.

It isn't enacted organically through our bodies.

We are the one creature that can redefine the nature of life.

We're not constrained by a biological prescription.

We're not like caterpillars that are, as it were,

committed, condemned, fated to become butterflies.

We could become anything.

'At the end of Kafka's story,

the man who has turned into a beetle dies.

He has lost everything because of the change forced upon him.

But there is also a scene shortly before he dies

when he hears his sister playing the violin.

He notices it precisely because the metamorphosis

has forced him out of his old routine,

where he was too busy to notice the over familiar.

And when he hears, really hears the music,

he feels completely alive,

completely human,

perhaps for the first and last time in his life.'

I think one of the things that has come out of this film for me

is that when we started off with caterpillars and butterflies

and tadpoles and frogs,

metamorphosis seemed so clear cut.

You know, nature had invented this very clear thing

where you were one thing and then you were another.

It was very clear and very simple.

And yet when you then apply it to us,

it's as if all that clarity disappears

and we're so ambivalent about it.

It's the thing which we've argued is so important

to who we are both individually and as a species,

and yet we're not happy with it.

It's as if a butterfly was afraid of flying.

Here we are the most changeable, the most metamorphic of creatures,

and we're so troubled by it.

But maybe that's...

Maybe that's what being human is about.

Subtitles by Red Bee Media Ltd