All language subtitles for BBC.Colour.The.Spectrum.Of.Science.2of3.Colours.Of.Life.720p.HDTV.x264.AAC.MVGroup.org.eng

We live in a world ablaze with colour...

..rainbows and rainforests, oceans and humanity.

Earth is the most colourful place we know of.

It's easy to take our colourful world for granted.

Red, yellow and blue are some of the first words we learn.

But there's a reason why our world looks so vibrant.

That reason is life.

I'm Dr Helen Czerski.

I'm a physicist and when I look at colour, I don't just see beauty,

I see some of the most intricate processes in nature.

It's flashing light and it's a new kind of colour.

The colours of life have exploded across our planet,

from the palest shades to the most eye-popping, vivid hues.

And each and every one of them

has played a part in the spread of life across the Earth.

This is communication in colour.

To understand the hidden mechanisms of colour is to uncover

the fundamental processes at work in every living thing.

Deep down physiological changes, broadcast in colour.

In this programme, I'm going in search of the colours

that have driven the spread of life across the Earth

and painted our planet in glorious multicolour.

In its earliest days, the colours of the Earth

were forged by the forces that shaped the planet.

Fire and ice,

water and rock.

The raw, early Earth had plenty of colour,

but that was nothing compared with what was going to come next.

That canvas was about to be painted with a vast, new palette,

and the source of those colours was life.

That story begins with one colour,

without which life as we know it wouldn't exist.

And to see this vital colour in all its glory,

I need a bird's eye view.

From this tower, as far as I can see, the world is green.

The forest here is alive.

It's green and healthy

and green is such an important colour for our planet.

But there's a question that goes with this familiar view

and we almost never ask it.

There are hundreds of species down there, hundreds of plants,

and they are all green.

Why is that?

To answer that, you need to look in a very different environment.

It's out here that we can shed light

on why so much of our planet is green.

With me is Stephanie Henson from the University of Southampton.

We think that life began in the oceans about 3.5 billion years ago,

and that's because at the time,

the land would have just been completely uninhabitable.

Ultraviolet radiation from the sun was beating down

and just irradiating everything that tried to come out onto land.

Back then, there was no ozone layer

to stop the destructive UV rays reaching Earth.

So, life evolved in the ocean, where it was protected by water.

All life needs energy,

and these earliest life forms used the chemicals

that seeped through the sea floor at hydrothermal vents.

But hydrothermal vents aren't everywhere on the sea floor.

No, that's right. The first organisms to use chemicals

would have been concentrated just in these little pockets.

If life was ever to expand beyond these isolated pockets,

it needed to find a new source of energy.

And in the ocean today,

we can find an ancient species that did just that.

It doesn't look like there's anything in there, does it?

No, but that'll be full of life.

Through a small field microscope,

we can see that what appears to be clear water

is actually bursting with microscopic creatures.

Look even closer,

here magnified many thousand times,

and their complex and intricate forms are revealed.

Amongst these bizarre-looking organisms is the ancient life form

we've been looking for - cyanobacteria.

Cyanobacteria are still around in very much the same form

as they first evolved, almost 3.5 billion years ago.

These tiny organisms evolved a process

that would dramatically change the colour of the planet,

and the course of life itself.

They took sunlight, air, and water,

and transformed them into sugar, storing the sun's energy.

Up until that point, organisms had only been able to use chemicals

as an energy source and suddenly, this new organism appears

that can use light directly from the sun.

Cyanobacteria had evolved one of the most enduring

and vital processes in the living world...

..photosynthesis.

At its heart is chlorophyll, a chemical that can capture sunlight.

It has a very distinctive colour...

..green.

And with chlorophyll,

life was no longer limited to hydrothermal vents.

It could spread across the oceans,

creating vast swathes of green.

But life didn't stop there.

Because photosynthesis produces a very important by-product.

The waste product of photosynthesis is oxygen.

So before these guys evolved, the cyanobacteria,

there wasn't very much oxygen around on Earth.

Suddenly, when cyanobacteria evolved,

a lot of oxygen was being produced as a waste product.

That oxygen entering the atmosphere started to create an ozone layer.

And the ozone layer is like sunscreen for the Earth -

it keeps out the damaging UV.

That's right. It really allows life as we know it today to evolve.

With ozone now blocking harmful UV rays,

life could make a giant leap -

out of the ocean and onto the land...

..painting the planet green.

It's strange to think that all the photosynthesis going on around me

started with a tiny creature in the ocean.

Chlorophyll is the key to photosynthesis,

and the leaves around me are full of it.

It's what gives them their wonderful green colour.

And the way it does this

reveals something essential about all colour.

To show you, I need to escape the sunlight, so I've set up this hide.

This light represents the sun.

And I've got a prism here,

so I can split white light into all the colours of the spectrum.

And these fall on leaves, so here's a leaf.

So, if I add another leaf, and another one...

Now, what's coming through the leaves looks very, very different -

and what I can see is that the only light that's getting

through all the leaves is the green light.

There's this green stripe along the back here,

but the red light and the blue light have gone.

Red light and blue light doesn't pass through.

It's stopped, it's captured

and it's used by the leaf to keep itself alive.

The chlorophyll in the leaf

is absorbing the red and blue wavelengths of light

and using their energy to carry out photosynthesis.

But it doesn't absorb the green wavelengths.

The green light is actually the waste,

it's the only bit of the spectrum that they're not using.

So, this is why we see leaves as green.

And it tells us something fascinating.

When we perceive any colour, what we're really seeing is a process.

Whatever it is we're looking at is absorbing some wavelengths of light

and reflecting others back into our eyes.

What we see as colour is the process of light

interacting with everything around us.

Green is a potent symbol of how life

first made its momentous step onto land.

But there's another colour that tells a different story

about how life has spread across the planet.

And this time, it's a colour that exists in each one of us.

These volunteers give us

a snapshot of the huge variety of human skin tones.

Skin colour is such an individual thing.

Each one of us has our own hue.

But why are we so varied?

What's the advantage to our species of this beautiful diversity?

Nina Jablonski is an anthropologist

who studies the evolution of skin colour in humans.

This amazing and beautiful range of skin tones

is caused by one remarkable pigment called melanin,

which is found in varying amounts in the people that we have here,

so the more that you have, the darker that you are.

The brown pigment melanin is crucial to our survival,

because of one particular property.

It has the ability to absorb and scatter ultraviolet radiation.

You can really think of melanin as nature's sunscreen.

Too much UV from the sun can damage our DNA

and destroy a vitamin in our blood called folate, that we need.

So, we rely on melanin to protect us.

But we humans aren't all a uniform shade.

And the differences that exist are key to how our species

has been able to spread across the globe.

When early humans first evolved in Africa,

they needed high levels of melanin

to protect them from the intense sunlight.

This gave them very dark brown skin.

But as our ancestors began to migrate,

they found themselves in very different environments.

When modern humans first start to leave Africa,

we see them beginning to move into areas of the world

that have remarkably less ultraviolet radiation.

This map shows how UV varies across the globe.

Throughout Africa, there are these very high levels,

but the levels taper off dramatically

as we begin to get into Western Europe or Eastern Asia.

And in places with less UV,

high levels of melanin created a problem.

There are some wavelengths of UV

that are actually essential to our health,

that promote the production of vitamin D in our skin.

We need vitamin D for a strong immune system and healthy bones.

But with less exposure to the sun,

our ancestors couldn't make enough of it.

To survive in these new lands, our colour had to change.

Nina has produced a map that shows how human skin colour adapted.

You see very darkly pigmented people

that are concentrated in the areas of high UV,

and then, much more lightly or de-pigmented people,

as you get closer to the poles under conditions of very low UV.

So, each population works out a balancing act,

so they're protected enough that their DNA is OK,

but they still have enough UV to make vitamin D.

Precisely.

This interaction between our skin and the sun is so finely balanced

that even in a single individual, it can adapt and change.

To show us, Nina is looking for the people with the biggest

difference in colour between parts of the body

that get a lot of sun exposure, and parts that get very little.

So, let's look here.

Now, we don't see a lot of difference here

between your upper inner arm and your forehead.

They're pretty closely similar.

And with the two very lightly pigmented people,

there's very, very little difference.

And similarly, at the very other end of the line,

with our most darkly pigmented person,

there's very little difference.

But in the middle of the line, things are different.

So, if we look at some of these individuals,

the difference is really quite great.

The unexposed skin versus the exposed skin,

we can really see a visible difference

and all of these people have sort of moderately to darkly pigmented skin,

and they have tremendous abilities to tan.

Tanning is the solution to living at latitudes

where sunlight changes dramatically throughout the year.

In these regions, people produce melanin to protect them in summer

and then lose it in winter.

All this suggests a problem,

because today we jet all over the world.

We live in countries which we weren't born in.

Does that cause problems?

Now, we have to modify our lifestyle.

We have to think about whether we protect our skin

from ultraviolet radiation,

or whether we take vitamin D supplements.

It's only recently we've been able to take measures like this,

to help control our relationship with the sun.

For most of our history, this vital role was played by our own skin.

The colour of each one of us

tells a story about the success of our own species.

Being able to change colour has allowed humans to adapt

and it's allowed us to colonise our planet.

This rich diversity of colour has come about

because we've evolved to suit our environment,

and to appreciate that,

we don't need to look any further than our own skin.

Green and brown are colours with vital functions

that have enabled life to survive

and spread across the face of the Earth.

These two colours, the chlorophyll in the green leaves

and the melanin in my tanned skin,

are the workhorses of the world of living colour.

But they're important for what they do, not what they look like,

and as long as they're playing their role in the machinery of life,

their appearance doesn't matter at all.

But the world isn't just green and brown.

Life has painted the planet in a kaleidoscope of colours -

bright, vivid, beautiful.

These colours exist for an entirely different purpose.

And their story begins

with the evolution of one crucial part of animal anatomy.

Aren't these stunning to look at?

There is a point where the colours of life really blossomed,

and it was the evolution of the eye.

It was a massive step forward, because something that can see you

is something that you can communicate with.

Now, colour could take on a new role.

A colour that can be seen can deliver information,

and to me, there's one colour more steeped in meaning than any other.

We humans have got loads of words for red -

vermillion and ruby, scarlet and crimson.

And it strikes me that all of those words imply something

that's bright and deep and rich.

For us, red is the colour of love and the colour of war.

It can scare us, and it can worry us, and it can move us.

But red isn't significant only to us humans.

It holds a special place across the living world.

To discover why, I've come to meet Andrew Smith,

a zoologist at Anglia Ruskin University.

He's working with New World monkeys, like these marmosets.

Some individuals in the group can distinguish the colour red.

Others can't.

Marmosets have got a slightly strange system of colour vision.

All of the boys are red/green colour-blind,

along with about a third of the females,

and the remaining two-thirds of the females

see the world in a very similar way to ourselves.

So, within the same troop of monkeys,

some have colour vision like ours

and some have red/green colour blindness type vision,

and you can directly compare the difference? Yes.

To discover the difference it makes

if you can distinguish red and green,

Andrew has set the monkeys a challenge.

And I'm going to give it a try.

I've got a pair of glasses which will transform your vision

from normal colour vision to if you like, colour-blind vision,

so if you'd like to put them on.

We put some strawberries in the tree behind you.

We've got some ripe and some unripe strawberries,

and I'd like you to find all of the seven ripe strawberries

as fast as you can. Ready to go? OK. Go.

The world's gone very green!

With the goggles on, I see the world as the colour-blind marmosets do.

There's one.

The ripe strawberries look very black here, so it's quite hard

to pick them out against the dark trees and the dark background.

Under here? Oh, there, right, I was looking too far forward.

All right, so have I done the job? Seven strawberries.

Perfect, you found them all and that took you 1 minute, 10 seconds.

Andrew resets the tree with fresh strawberries

so that I can try again, but this time, without the goggles.

OK, go.

This is much easier. Two, three....

My natural colour vision is very similar

to that of the female marmosets that can also see red.

..six, seven.

Fantastic. 16 seconds.

Huge difference!

So, that's an awful lot faster than the 1 minute 10 that it took you

when you couldn't tell the difference between red and green.

Andrew's been carrying out experiments like this on monkeys,

to see how colour vision effects their ability to find ripe fruit.

There's one just in the background there, having a bit of a look.

Ah, here we go, here we go, here we go. Yeah, this one's seen it.

That one is sitting right on top of a ripe strawberry,

and not noticing it at all.

After repeating the test hundreds of times, Andrew found a clear pattern.

What we found is that all of the monkeys could do the task,

given enough time, but the monkeys with human-like colour vision

went straight for the ripe fruits.

In the wild, being the first to find the food gives you a huge advantage.

It can be the difference between life and death.

And what's really fascinating is that it's not just the animals

that can see red who benefit.

It's also the plants that can turn red to signal their ripeness,

attracting animals to disperse their seeds.

The animals come along, eat the fruit, which is full of seeds,

and then very conveniently deposit them somewhere else,

in a pile of their own manure - readymade fertiliser.

It's a brilliant scheme

and the only condition is that the fruit mustn't be eaten too soon.

So, when they're growing, the fruits and the seeds are the same colour

as everything else around them.

And then, with one very dramatic colour change,

the signal is sent that the fruit is ready to go.

It's a wonderful example of the intimate connection

between colour and life.

Colours that exist purely to be seen

and eyes that have evolved to see them.

It's what makes colour one of the most powerful forms of communication

in the living world.

One that can transcend species...

..and even signal between plants and animals.

Messages sent, received

and understood in colour.

But for animals with a more highly-developed brain,

colour can also convey a deeper level of meaning.

To discover how, I've come to meet anthropologist Dr Jo Setchell.

She studies mandrills,

a primate species whose males have a distinctive red nose.

To us, it's really striking.

When we look at a mandrill,

the first thing we see is this bright red nose.

I want to know what it means to a mandrill to see red.

Today, we're going to investigate the three males living here,

in Wingham Wildlife Park.

Malik,

Kayin

and Mathias.

So, what we're after, ideally, is the nose of the animal.

The intensity of the red colour

can vary in different members of the group.

Jo is investigating why.

CAMERA CLICKS

First, we take photographs of the three males.

There you go. CAMERA CLICKS

He's staying still now.

Oh, that's nice, almost got them lined up.

Now, Jo measures the intensity of the red.

We want to know the red colour of that particular area.

We're going to chose exactly the same area on each of the three males.

So, that gives him a red score of 1.37.

Jo calculates the red score for all three males.

We've got Mathias, who's the least colourful,

and his score was 1.4.

Then, we have Kayin, and his score was 1.7.

And then finally, we have Malik. His score was 1.9.

So, a big difference. Yes.

At first, Jo thought this was simply an individual trait,

like our hair colour.

But after months of monitoring the mandrills' colour,

she discovered something unexpected.

So here, we've got another photo of Malik,

but this was taken two years ago.

So, that's the same mandrill as the one over there.

Yes, you can recognise his face,

but what you can see is, this colour is completely different.

That's a huge change.

Yes, it's marvellous, isn't it?

Jo had discovered that it was possible

for the mandrills to change colour.

She continued to monitor them over time,

and found a striking correlation.

They change colour basically with a dominance rank,

so as a male increases in rank, his colour increases,

and if he loses his rank, then his colour decreases.

So, the order of the colours reflects the dominance hierarchy?

That's right, yes. He's the dominant male.

The shade of red reflects the strict hierarchy in mandrill societies,

like this one filmed in Gabon.

At the top is the dominant male.

He will have access to the females and first pick of the food.

He broadcasts his enviable position by having the brightest nose.

So, it reflects success? Yes, basically.

It's like a badge that you get. Yes.

It's the hormone testosterone

that keeps the dominant male's nose bright red.

Jo's work suggests this colour may have

an important physiological effect on other Mandrills in the group.

So, subordinate males have lower testosterone than dominant males,

and that's an effect of being in the presence of a male

who has bright red colour.

Having lower testosterone helps keep these mandrills subordinate,

so each animal knows its place.

Here, red is a colour that keeps the peace.

I'm imagining a huge group of these mandrills in a forest in the wild,

but connected together with these flashes of red,

coming through the leaves.

But each glimpse of red doesn't just reflect a public face,

their position in the hierarchy,

it also reflects and affects their internal messengers, the hormones.

Deep down, physiological changes,

broadcast in colour.

In the world of the mandrill,

your colour is a vital part of who you are.

But they're not the only animals to communicate

using colour signals in their skin.

We humans do it too,

although we're not aware of it.

David Perrett is a psychologist at the University of St Andrews.

He's found that we're constantly broadcasting information,

using one specific hue.

To see if I can guess which colour that is

and what it's saying about me, David has a test.

You can have a look.

That's definitely me.

It's definitely you, but if you adjust the picture

by sliding backwards and forwards, you may be able to see some change.

So if I scroll this way,

I can see that the skin colour's changing a little bit.

Your task is to make it look healthy.

The healthiest version of me?

So, the skin colour's changing a bit and on one side,

that's definitely ill, down there.

All right. So, I reckon about...there.

I can't tell what exactly David is changing in my photograph,

but he's done the same to photographs of many other people

with different skin colours.

If you look here, then you can see manipulation of African faces,

Asian faces and European faces

And it's very noticeable here, like you definitely pick up

the bottom row as being the healthy bunch.

Well, what did you think we'd changed?

It looks darker, but I'm not sure how.

I mean, there's lots... So, it could be tanned.

Well, we didn't make it darker.

I can't tell, just by looking at them.

I know this one looks healthy, but I couldn't pick out what's different.

We made it more yellow.

A specific type of yellow, or a kind of golden yellow that is...

It's a unique colour.

David's research has revealed that across many different cultures,

people perceive faces with more yellow in them as healthier,

and more attractive.

So, why would my skin go yellow?

Why? Well, it's from what you eat.

You take in pigments from the fruit and vegetables you eat,

so we've got here...a pepper.

Now, that's obviously coloured, but that colours you, when you eat it.

The pigments get transported in your blood

and they end up in the skin.

I mean, there's lots of different colours

in the fruit and veg we've got.

We've got carrot, tomatoes...

But the colours that I'm talking about,

they're all called carotenoids.

So, the colour we see in our skin

is a direct reflection of how much of these pigments we're eating.

It is, yeah. And how much extra would I have to eat,

for someone to notice a difference in my face?

In one study, we simply got people to eat one pepper per day extra,

and some carrot juice. So, a very modest change in the diet.

Within a few weeks, the person... Everybody seems to look different.

So, the level of yellow in our skin is a signal of our state of health.

One that we're constantly communicating to other people

without even knowing.

When you were looking at your own image, you chose an image...

not with your natural diet,

with the simulation of a diet with increased fruit and veg consumption,

maybe three or four more portions, per day.

So, I picked a skin tone that was a little bit higher

than my natural skin tone, had more carotenoids in it.

Yeah.

And we humans aren't the only species

to signal our health in this way.

The vivid pink of flamingos comes entirely from carotenoids

in the algae and crustaceans they eat.

The more carotenoids, the healthier they'll be, and the brighter.

So, their colour is an unmistakable signal of their health

to potential mates.

When we think about colour,

we tend to think about aesthetics and its visual appeal.

But there's so much subtlety in the world of colour

that it can also carry lots of information.

All sorts of animal species use it to communicate.

And so, when you look at a scene like this,

it's not just a beautiful view of natural history,

it's also a flood of information.

But that information isn't always used to communicate.

Sometimes, colour can do the opposite. It can conceal.

And there's one particular environment

where this can be vital for survival.

The ocean can look uniform from above,

but it's certainly not like that down below.

There's a whole, varied, hidden world out there.

It's a dynamic, changing environment.

Survival is a challenge

and everything living out there is potential dinner for something else.

To stay alive in this dangerous world,

one type of animal has evolved

to manipulate colour in an extraordinary way.

And to see it, I've come to Brighton Sea Life Centre,

to meet Marine Biologist Kerry Perkins.

So, what have we got here?

Well, here we actually have some cuttlefish.

So, one, two, three, four.

Cuttlefish are a type of cephalopod,

a group of marine invertebrates that include squid and octopus.

They're very soft-bodied creatures,

so they're very tasty for a lot of animals,

so you have to think of a strategy, so you don't get eaten all the time.

When most animals want to hide,

they seek out an environment that matches their colour.

But the cephalopods have a different tactic.

To show me, Kerry puts one of the cuttlefish in her observation tank.

So, settled down now.

On the sand, the cuttlefish is a uniform beige colour.

But let's see what happens when Kerry changes the background.

Oh, look at that! Completely changed colour.

There's big, bright spot on his back,

and another one just behind his eyes.

He fits in with his new environment, doesn't he?

Cuttlefish can change the colour of their skin to match the background.

What the cuttlefish is actually doing,

it's trying to break up its pattern,

but obviously, a lot of predators scan for their prey,

so if you're even one or two metres above this cuttlefish,

you would think it was just rocks.

To see just how far it can manipulate its colour,

Kerry's going to test this cuttlefish

with an entirely unnatural background.

So, it's black and white checks. Oh, he's gone white.

So, he changed straight away,

and even though this chequerboard isn't something that would

ever come up in a real ocean situation, he's had a good go at it.

He has. I mean, it wouldn't come across a chequerboard

He has. I mean, it wouldn't come across a chequerboard

on the seafloor, but obviously, he's still using the same mechanisms

and same ideas behind seeing the squares and giving it a good try.

Even with something as foreign as a chequerboard,

the cuttlefish has changed its colour to try and blend in.

To achieve this, it manipulates colour in an ingenious way.

They've got a layer of skin that's actually reflective

and this is a bit like, if you can imagine, a piece of tin foil

that'll reflect any colour that is bounced onto it,

so it has this ability to reflect the colours and its surroundings.

But what's really interesting - on the top layer of it,

they have something called chromatophores.

These are chromatophores, seen under a microscope.

They're cells containing sacs of different coloured pigments,

and the cuttlefish can control the shape of each one.

Here, each of the cocktail umbrellas

represents a different chromatophore.

When they're shut, we can't really see what colour the umbrellas are.

It's just silver. It's just sort of silver.

So, this is what happens when we see the cuttlefish to be uniform,

so they're just reflecting the colour that's in their environment.

But once we start opening them...

So, if you give me a hand, we start seeing the colour of the umbrellas.

We can create different patterns

by changing the combination of umbrellas that are open.

This is how the cuttlefish can change their colour

to match their immediate environment.

So, they effectively disappear.

They're the ocean's masters of disguise.

The ocean is full of colour and contrast,

and the cuttlefish can navigate through that world unseen

by revealing its hidden colours at the right time,

almost as if it was picking costumes from a portable dressing up box.

Other animals use toxins or threats or spikes to deter predators,

but for a cuttlefish, colour is the key to survival.

So, colour can disguise and protect life,

but in a world crowded with species competing to survive,

sometimes you don't need to hide, you need to stand out.

This is a pollia berry and it's my new favourite fruit.

Look at it, it's almost metallic.

Doesn't look like a real fruit at all, but it's flashing light,

and it's a new kind of colour.

This is what's known as iridescence -

a rare and spectacular form of colour

that only a handful of species on Earth can produce.

And to discover how they do it, we need to take a closer look.

A powerful microscope reveals a hidden landscape

with structures perfectly formed to do something remarkable.

The secret to all this is to do with shape on tiny, tiny scales.

Let's imagine this is the shape that the light is hitting.

So, light waves come in,

light waves of all different colours come in and hit this structure.

But they only get reflected back from these bits here.

Anything that goes down there gets lost.

The distance between these ridges

is very close to the wavelength of light itself,

and this affects how the waves are bounced back.

So, let's see what happens when light waves are reflected

away from this surface and we'll start with blue light.

If we look at the waves together,

we can see that they both go up at the same time,

and then down at the same time, and then up at the same time

and then down at the same time, so they're lined up all the way along.

The aligned waves reinforce each other, creating a vivid blue.

But it's not the same for all colours,

so if we have a look at the red light...

Red light has a longer wavelength than blue...

..and these waves are out of alignment.

They cancel each other out and so from this angle, there's no red -

just very vivid blue.

But from this angle, the blue and the red waves line up,

creating purple.

And from here, just the red waves line up.

So, as the point of view changes,

what the eye perceives are flashes of shimmering colour.

This is iridescence.

Until recently, we thought that it only existed

in a select group of species,

mainly insects and birds.

So, plant scientists in Cambridge were surprised

to find it right under their noses.

Beverly Glover is head of the botanical gardens.

Well, at the time, we were interested in patterns of pigment on flowers,

and so my post-doc, Heather Witney was looking for flowers

that have different combinations of colour on the petal.

She found this one in the garden, here.

She picked it up, brought it back to my office and said,

"So, how does it make this blue, yellow, green stuff?"

And we had no idea and that's when we realised that nobody had ever

noticed iridescence on flowers and it had never been looked at before.

Beverly wanted to know why these hibiscus flowers were iridescent,

and to investigate, she needed some help.

So, this is the bee colony over here.

Bees are one of the hibiscuses' main pollinators.

So, Beverly set up an experiment

to see whether they responded to the iridescent flowers.

So, we've got a colony of bombus terrestris,

it's a common British bumblebee,

and in the wild, they nest in holes in the ground.

You find them in your garden and in the cracks in the soil and so on.

The colony is in this cardboard box and they come out through this tube

and they come out into this box, which we call the flight arena.

And they're foraging in here for food, mostly nectar

to take back through the tube, into the colony, to feed to the larvae.

Within her flight arena, Beverly set up an unlikely-looking meadow.

And what we've set up in the box are these artificial flowers.

This iridescent disc

has sugar solution in the middle to mimic nectar.

To the bee, it's as good as a flower.

These then go into the colony, and so, just open the gate,

and pop the disc in.

So, the flowers are evenly spaced, they're all iridescent.

Beverly let a single bee into the flight arena...

..and then timed how long it took to fly from one flower to the next.

STOPWATCH BEEPS

After testing dozens of bees several times each,

Beverly reset the arena,

but this time, with non-iridescent flowers.

She wanted to know whether the iridescence made a difference

to the time it took the bees to fly between flowers.

What were the results?

The iridescent discs are much easier to see.

The non-iridescent flowers,

you're looking at three to four seconds to find a flower.

The iridescent ones, maybe about two seconds to find a flower,

so it really does make a big difference.

And that difference really matters, because it's costing the bees energy

to be in the air and searching. That's expensive time.

Yep, that's exactly right. They're heavy, compared to most insects

and so, the fact that this flower is easier to see is good for them,

it speeds that up, and that gives me an explanation

for why my hibiscus flowers are making this structure.

They've figured out that it's a way of attracting the attention -

the eye, if you like, of a bee - and that means it's more likely

that they'll get pollinated out there in the wild.

There's no doubt that hibiscus is a beautiful, elegant flower,

but even more elegant, I think, is the way that iridescence works.

It's a solution to a problem.

The flower can't move, but when something else moves past it,

it sees strong flashes of colour,

a beacon advertising the flower's presence.

Across the Earth,

life in all its forms has created a spectacular paintbox.

A stunning array of colours,

produced by some of the most intricate adaptations in nature.

But every one of the colours we've seen so far depends on one thing.

Sunlight.

Colour is produced by organisms reflecting or manipulating sunlight.

And so, when the sun goes down, colour goes with it.

But there are exceptions.

A rare group of animals have evolved a way to produce colour

that doesn't depend on light from the sun.

This is the Great Smokey Mountains National Park in Tennessee.

It's a pretty bit of forest, but it's not very remarkable.

There's nothing unusual here,

but in a couple of hours, that's going to change.

As darkness descends, the crowds swarm in.

All of these people are hoping to witness a natural spectacle

which occurs every year in late May or early June.

It's all so strange, because normally,

if you see people lined up along a path,

they're facing inwards to see what's on the path,

but out here, everyone's facing out into the forest.

That's clearly where the spectacle is going to be.

It's almost as though this is a theatre,

and that's the stage, out there.

And it very much feels as though the curtain is about to rise

and the first act is about to begin.

Once it's completely dark, the show begins.

The performers are fireflies.

A species called photinus carolinus.

This is it. We're right in the middle of it here,

and there's these bands of light that are sweeping across the forest.

And they're lighting up the forest.

This is their mating display,

and within it is a hidden code.

As they fly, each male flashes six times quickly, and then pauses.

They're trying to catch the attention of the females on the ground.

It's rippling through the trees.

The precise pattern of flashes signals their species...

..a vital way to set themselves apart

from the 19 other species of firefly that live here.

And the really amazing thing about this

is that one single species, all by itself,

can see all the other ones of its species

in this section of the forest.

This is communication in colour.

These tiny creatures have evolved

so that a part of their body has become a lantern.

Inside it, they produce a chemical called luciferin,

that reacts with oxygen

to produce these striking flashes of colour that light up the forest.

For a small insect in a big world,

this is a fantastic strategy.

The fireflies bide their time, waiting until

the bustling multi-coloured riot of the daylight world has gone

and the forest is black, colourless.

And then, each tiny insect switches on its own portable colour factory,

sending a beacon to the rest of its species

and co-ordinating the start of the next generation.

Life harnesses light in all kinds of ways,

but I think it's really lovely

that this trick of creating colour where there was none before

has come from one of the smallest species of all.

Colour has been fundamental to the evolution of the diverse

and beautiful living world that exists today.

And in turn, life has painted the Earth in magnificent Technicolor...

..expanding the palette of the planet

by manipulating colour and even creating its own.

But all of these colours

are still only just the visible part of the spectrum -

a tiny proportion of all the colours that exist.

And it's the colours we can't see that are set to shape our future.

Next time, I'll be looking beyond the rainbow.

Isn't it fascinating, this view of the world?

I'll discover the hidden colours

that can reveal the deepest secrets of the universe.

This is a picture of the Orion nebula.

If you look at it in infrared, it completely lights up.

We're observing the invisible.

Discover more about the story of the colours of life

with the Open University.

Go to...

..and follow the links to the Open University.