0:00:02 > 0:00:05We live in a world ablaze with colour...
0:00:06 > 0:00:10..rainbows and rainforests, oceans and humanity.
0:00:12 > 0:00:15Earth is the most colourful place we know of.
0:00:19 > 0:00:22It's easy to take our colourful world for granted.
0:00:22 > 0:00:25Red, yellow and blue are some of the first words we learn.
0:00:28 > 0:00:31But there's a reason why our world looks so vibrant.
0:00:32 > 0:00:34That reason is life.
0:00:40 > 0:00:41I'm Dr Helen Czerski.
0:00:43 > 0:00:47I'm a physicist and when I look at colour, I don't just see beauty,
0:00:47 > 0:00:50I see some of the most intricate processes in nature.
0:00:52 > 0:00:56It's flashing light and it's a new kind of colour.
0:00:57 > 0:01:02The colours of life have exploded across our planet,
0:01:02 > 0:01:06from the palest shades to the most eye-popping, vivid hues.
0:01:09 > 0:01:11And each and every one of them
0:01:11 > 0:01:15has played a part in the spread of life across the Earth.
0:01:18 > 0:01:20This is communication in colour.
0:01:21 > 0:01:25To understand the hidden mechanisms of colour is to uncover
0:01:25 > 0:01:29the fundamental processes at work in every living thing.
0:01:31 > 0:01:35Deep down physiological changes, broadcast in colour.
0:01:36 > 0:01:39In this programme, I'm going in search of the colours
0:01:39 > 0:01:43that have driven the spread of life across the Earth
0:01:43 > 0:01:47and painted our planet in glorious multicolour.
0:02:02 > 0:02:05In its earliest days, the colours of the Earth
0:02:05 > 0:02:08were forged by the forces that shaped the planet.
0:02:09 > 0:02:11Fire and ice,
0:02:11 > 0:02:13water and rock.
0:02:20 > 0:02:24The raw, early Earth had plenty of colour,
0:02:24 > 0:02:27but that was nothing compared with what was going to come next.
0:02:29 > 0:02:33That canvas was about to be painted with a vast, new palette,
0:02:33 > 0:02:36and the source of those colours was life.
0:02:38 > 0:02:41That story begins with one colour,
0:02:41 > 0:02:44without which life as we know it wouldn't exist.
0:02:54 > 0:02:57And to see this vital colour in all its glory,
0:02:57 > 0:02:59I need a bird's eye view.
0:03:08 > 0:03:13From this tower, as far as I can see, the world is green.
0:03:17 > 0:03:19The forest here is alive.
0:03:19 > 0:03:21It's green and healthy
0:03:21 > 0:03:25and green is such an important colour for our planet.
0:03:25 > 0:03:28But there's a question that goes with this familiar view
0:03:28 > 0:03:30and we almost never ask it.
0:03:30 > 0:03:34There are hundreds of species down there, hundreds of plants,
0:03:34 > 0:03:36and they are all green.
0:03:36 > 0:03:38Why is that?
0:03:40 > 0:03:44To answer that, you need to look in a very different environment.
0:03:54 > 0:03:56It's out here that we can shed light
0:03:56 > 0:03:59on why so much of our planet is green.
0:04:04 > 0:04:08With me is Stephanie Henson from the University of Southampton.
0:04:10 > 0:04:13We think that life began in the oceans about 3.5 billion years ago,
0:04:13 > 0:04:15and that's because at the time,
0:04:15 > 0:04:19the land would have just been completely uninhabitable.
0:04:20 > 0:04:23Ultraviolet radiation from the sun was beating down
0:04:23 > 0:04:27and just irradiating everything that tried to come out onto land.
0:04:29 > 0:04:31Back then, there was no ozone layer
0:04:31 > 0:04:34to stop the destructive UV rays reaching Earth.
0:04:37 > 0:04:41So, life evolved in the ocean, where it was protected by water.
0:04:44 > 0:04:46All life needs energy,
0:04:46 > 0:04:50and these earliest life forms used the chemicals
0:04:50 > 0:04:53that seeped through the sea floor at hydrothermal vents.
0:04:54 > 0:04:58But hydrothermal vents aren't everywhere on the sea floor.
0:04:58 > 0:05:01No, that's right. The first organisms to use chemicals
0:05:01 > 0:05:04would have been concentrated just in these little pockets.
0:05:06 > 0:05:09If life was ever to expand beyond these isolated pockets,
0:05:09 > 0:05:12it needed to find a new source of energy.
0:05:17 > 0:05:18And in the ocean today,
0:05:18 > 0:05:21we can find an ancient species that did just that.
0:05:26 > 0:05:29It doesn't look like there's anything in there, does it?
0:05:29 > 0:05:31No, but that'll be full of life.
0:05:31 > 0:05:34Through a small field microscope,
0:05:34 > 0:05:37we can see that what appears to be clear water
0:05:37 > 0:05:40is actually bursting with microscopic creatures.
0:05:43 > 0:05:45Look even closer,
0:05:45 > 0:05:47here magnified many thousand times,
0:05:47 > 0:05:51and their complex and intricate forms are revealed.
0:05:55 > 0:06:00Amongst these bizarre-looking organisms is the ancient life form
0:06:00 > 0:06:03we've been looking for - cyanobacteria.
0:06:05 > 0:06:08Cyanobacteria are still around in very much the same form
0:06:08 > 0:06:11as they first evolved, almost 3.5 billion years ago.
0:06:13 > 0:06:16These tiny organisms evolved a process
0:06:16 > 0:06:19that would dramatically change the colour of the planet,
0:06:19 > 0:06:21and the course of life itself.
0:06:24 > 0:06:28They took sunlight, air, and water,
0:06:28 > 0:06:31and transformed them into sugar, storing the sun's energy.
0:06:33 > 0:06:36Up until that point, organisms had only been able to use chemicals
0:06:36 > 0:06:40as an energy source and suddenly, this new organism appears
0:06:40 > 0:06:42that can use light directly from the sun.
0:06:42 > 0:06:46Cyanobacteria had evolved one of the most enduring
0:06:46 > 0:06:48and vital processes in the living world...
0:06:50 > 0:06:53..photosynthesis.
0:06:55 > 0:06:59At its heart is chlorophyll, a chemical that can capture sunlight.
0:07:03 > 0:07:05It has a very distinctive colour...
0:07:06 > 0:07:08..green.
0:07:16 > 0:07:18And with chlorophyll,
0:07:18 > 0:07:20life was no longer limited to hydrothermal vents.
0:07:22 > 0:07:25It could spread across the oceans,
0:07:25 > 0:07:27creating vast swathes of green.
0:07:35 > 0:07:37But life didn't stop there.
0:07:40 > 0:07:44Because photosynthesis produces a very important by-product.
0:07:47 > 0:07:51The waste product of photosynthesis is oxygen.
0:07:51 > 0:07:54So before these guys evolved, the cyanobacteria,
0:07:54 > 0:07:57there wasn't very much oxygen around on Earth.
0:07:59 > 0:08:01Suddenly, when cyanobacteria evolved,
0:08:01 > 0:08:05a lot of oxygen was being produced as a waste product.
0:08:05 > 0:08:09That oxygen entering the atmosphere started to create an ozone layer.
0:08:10 > 0:08:13And the ozone layer is like sunscreen for the Earth -
0:08:13 > 0:08:15it keeps out the damaging UV.
0:08:15 > 0:08:18That's right. It really allows life as we know it today to evolve.
0:08:22 > 0:08:26With ozone now blocking harmful UV rays,
0:08:26 > 0:08:28life could make a giant leap -
0:08:28 > 0:08:32out of the ocean and onto the land...
0:08:35 > 0:08:37..painting the planet green.
0:08:52 > 0:08:56It's strange to think that all the photosynthesis going on around me
0:08:56 > 0:09:00started with a tiny creature in the ocean.
0:09:00 > 0:09:04Chlorophyll is the key to photosynthesis,
0:09:04 > 0:09:06and the leaves around me are full of it.
0:09:10 > 0:09:14It's what gives them their wonderful green colour.
0:09:14 > 0:09:15And the way it does this
0:09:15 > 0:09:18reveals something essential about all colour.
0:09:24 > 0:09:29To show you, I need to escape the sunlight, so I've set up this hide.
0:09:32 > 0:09:34This light represents the sun.
0:09:36 > 0:09:38And I've got a prism here,
0:09:38 > 0:09:41so I can split white light into all the colours of the spectrum.
0:09:45 > 0:09:49And these fall on leaves, so here's a leaf.
0:09:49 > 0:09:54So, if I add another leaf, and another one...
0:09:54 > 0:09:58Now, what's coming through the leaves looks very, very different -
0:09:58 > 0:10:01and what I can see is that the only light that's getting
0:10:01 > 0:10:04through all the leaves is the green light.
0:10:04 > 0:10:06There's this green stripe along the back here,
0:10:06 > 0:10:09but the red light and the blue light have gone.
0:10:10 > 0:10:13Red light and blue light doesn't pass through.
0:10:13 > 0:10:15It's stopped, it's captured
0:10:15 > 0:10:18and it's used by the leaf to keep itself alive.
0:10:21 > 0:10:23The chlorophyll in the leaf
0:10:23 > 0:10:26is absorbing the red and blue wavelengths of light
0:10:26 > 0:10:29and using their energy to carry out photosynthesis.
0:10:30 > 0:10:33But it doesn't absorb the green wavelengths.
0:10:34 > 0:10:37The green light is actually the waste,
0:10:37 > 0:10:40it's the only bit of the spectrum that they're not using.
0:10:46 > 0:10:49So, this is why we see leaves as green.
0:10:53 > 0:10:56And it tells us something fascinating.
0:11:01 > 0:11:05When we perceive any colour, what we're really seeing is a process.
0:11:08 > 0:11:12Whatever it is we're looking at is absorbing some wavelengths of light
0:11:12 > 0:11:15and reflecting others back into our eyes.
0:11:19 > 0:11:23What we see as colour is the process of light
0:11:23 > 0:11:27interacting with everything around us.
0:11:37 > 0:11:40Green is a potent symbol of how life
0:11:40 > 0:11:43first made its momentous step onto land.
0:11:46 > 0:11:49But there's another colour that tells a different story
0:11:49 > 0:11:52about how life has spread across the planet.
0:11:58 > 0:12:02And this time, it's a colour that exists in each one of us.
0:12:14 > 0:12:15These volunteers give us
0:12:15 > 0:12:19a snapshot of the huge variety of human skin tones.
0:12:22 > 0:12:24Skin colour is such an individual thing.
0:12:26 > 0:12:28Each one of us has our own hue.
0:12:30 > 0:12:32But why are we so varied?
0:12:32 > 0:12:36What's the advantage to our species of this beautiful diversity?
0:12:41 > 0:12:43Nina Jablonski is an anthropologist
0:12:43 > 0:12:46who studies the evolution of skin colour in humans.
0:12:50 > 0:12:53This amazing and beautiful range of skin tones
0:12:53 > 0:12:58is caused by one remarkable pigment called melanin,
0:12:58 > 0:13:02which is found in varying amounts in the people that we have here,
0:13:02 > 0:13:05so the more that you have, the darker that you are.
0:13:07 > 0:13:11The brown pigment melanin is crucial to our survival,
0:13:11 > 0:13:13because of one particular property.
0:13:17 > 0:13:22It has the ability to absorb and scatter ultraviolet radiation.
0:13:22 > 0:13:26You can really think of melanin as nature's sunscreen.
0:13:32 > 0:13:36Too much UV from the sun can damage our DNA
0:13:36 > 0:13:39and destroy a vitamin in our blood called folate, that we need.
0:13:48 > 0:13:50So, we rely on melanin to protect us.
0:13:55 > 0:13:57But we humans aren't all a uniform shade.
0:14:00 > 0:14:03And the differences that exist are key to how our species
0:14:03 > 0:14:05has been able to spread across the globe.
0:14:13 > 0:14:16When early humans first evolved in Africa,
0:14:16 > 0:14:18they needed high levels of melanin
0:14:18 > 0:14:21to protect them from the intense sunlight.
0:14:21 > 0:14:24This gave them very dark brown skin.
0:14:25 > 0:14:28But as our ancestors began to migrate,
0:14:28 > 0:14:31they found themselves in very different environments.
0:14:38 > 0:14:41When modern humans first start to leave Africa,
0:14:41 > 0:14:44we see them beginning to move into areas of the world
0:14:44 > 0:14:48that have remarkably less ultraviolet radiation.
0:14:50 > 0:14:53This map shows how UV varies across the globe.
0:14:56 > 0:14:59Throughout Africa, there are these very high levels,
0:14:59 > 0:15:02but the levels taper off dramatically
0:15:02 > 0:15:05as we begin to get into Western Europe or Eastern Asia.
0:15:06 > 0:15:09And in places with less UV,
0:15:09 > 0:15:11high levels of melanin created a problem.
0:15:15 > 0:15:17There are some wavelengths of UV
0:15:17 > 0:15:20that are actually essential to our health,
0:15:20 > 0:15:24that promote the production of vitamin D in our skin.
0:15:28 > 0:15:31We need vitamin D for a strong immune system and healthy bones.
0:15:35 > 0:15:37But with less exposure to the sun,
0:15:37 > 0:15:40our ancestors couldn't make enough of it.
0:15:44 > 0:15:48To survive in these new lands, our colour had to change.
0:15:52 > 0:15:56Nina has produced a map that shows how human skin colour adapted.
0:15:58 > 0:16:02You see very darkly pigmented people
0:16:02 > 0:16:06that are concentrated in the areas of high UV,
0:16:06 > 0:16:11and then, much more lightly or de-pigmented people,
0:16:11 > 0:16:16as you get closer to the poles under conditions of very low UV.
0:16:16 > 0:16:20So, each population works out a balancing act,
0:16:20 > 0:16:23so they're protected enough that their DNA is OK,
0:16:23 > 0:16:25but they still have enough UV to make vitamin D.
0:16:25 > 0:16:27Precisely.
0:16:29 > 0:16:35This interaction between our skin and the sun is so finely balanced
0:16:35 > 0:16:39that even in a single individual, it can adapt and change.
0:16:42 > 0:16:46To show us, Nina is looking for the people with the biggest
0:16:46 > 0:16:48difference in colour between parts of the body
0:16:48 > 0:16:52that get a lot of sun exposure, and parts that get very little.
0:16:54 > 0:16:56So, let's look here.
0:16:56 > 0:16:58Now, we don't see a lot of difference here
0:16:58 > 0:17:01between your upper inner arm and your forehead.
0:17:01 > 0:17:03They're pretty closely similar.
0:17:03 > 0:17:06And with the two very lightly pigmented people,
0:17:06 > 0:17:08there's very, very little difference.
0:17:08 > 0:17:12And similarly, at the very other end of the line,
0:17:12 > 0:17:15with our most darkly pigmented person,
0:17:15 > 0:17:17there's very little difference.
0:17:17 > 0:17:20But in the middle of the line, things are different.
0:17:22 > 0:17:25So, if we look at some of these individuals,
0:17:25 > 0:17:28the difference is really quite great.
0:17:28 > 0:17:31The unexposed skin versus the exposed skin,
0:17:31 > 0:17:33we can really see a visible difference
0:17:33 > 0:17:38and all of these people have sort of moderately to darkly pigmented skin,
0:17:38 > 0:17:41and they have tremendous abilities to tan.
0:17:44 > 0:17:47Tanning is the solution to living at latitudes
0:17:47 > 0:17:50where sunlight changes dramatically throughout the year.
0:17:52 > 0:17:56In these regions, people produce melanin to protect them in summer
0:17:56 > 0:17:58and then lose it in winter.
0:18:00 > 0:18:02All this suggests a problem,
0:18:02 > 0:18:04because today we jet all over the world.
0:18:04 > 0:18:07We live in countries which we weren't born in.
0:18:07 > 0:18:09Does that cause problems?
0:18:09 > 0:18:11Now, we have to modify our lifestyle.
0:18:11 > 0:18:15We have to think about whether we protect our skin
0:18:15 > 0:18:17from ultraviolet radiation,
0:18:17 > 0:18:20or whether we take vitamin D supplements.
0:18:22 > 0:18:25It's only recently we've been able to take measures like this,
0:18:25 > 0:18:28to help control our relationship with the sun.
0:18:31 > 0:18:34For most of our history, this vital role was played by our own skin.
0:18:39 > 0:18:41The colour of each one of us
0:18:41 > 0:18:44tells a story about the success of our own species.
0:18:44 > 0:18:48Being able to change colour has allowed humans to adapt
0:18:48 > 0:18:51and it's allowed us to colonise our planet.
0:18:51 > 0:18:54This rich diversity of colour has come about
0:18:54 > 0:18:57because we've evolved to suit our environment,
0:18:57 > 0:18:59and to appreciate that,
0:18:59 > 0:19:02we don't need to look any further than our own skin.
0:19:08 > 0:19:12Green and brown are colours with vital functions
0:19:12 > 0:19:14that have enabled life to survive
0:19:14 > 0:19:16and spread across the face of the Earth.
0:19:25 > 0:19:28These two colours, the chlorophyll in the green leaves
0:19:28 > 0:19:31and the melanin in my tanned skin,
0:19:31 > 0:19:34are the workhorses of the world of living colour.
0:19:34 > 0:19:37But they're important for what they do, not what they look like,
0:19:37 > 0:19:41and as long as they're playing their role in the machinery of life,
0:19:41 > 0:19:43their appearance doesn't matter at all.
0:19:47 > 0:19:49But the world isn't just green and brown.
0:19:53 > 0:19:57Life has painted the planet in a kaleidoscope of colours -
0:19:57 > 0:19:59bright, vivid, beautiful.
0:20:01 > 0:20:04These colours exist for an entirely different purpose.
0:20:06 > 0:20:08And their story begins
0:20:08 > 0:20:12with the evolution of one crucial part of animal anatomy.
0:20:15 > 0:20:17Aren't these stunning to look at?
0:20:19 > 0:20:23There is a point where the colours of life really blossomed,
0:20:23 > 0:20:26and it was the evolution of the eye.
0:20:30 > 0:20:34It was a massive step forward, because something that can see you
0:20:34 > 0:20:37is something that you can communicate with.
0:20:44 > 0:20:47Now, colour could take on a new role.
0:20:49 > 0:20:53A colour that can be seen can deliver information,
0:20:53 > 0:20:58and to me, there's one colour more steeped in meaning than any other.
0:21:08 > 0:21:11We humans have got loads of words for red -
0:21:11 > 0:21:15vermillion and ruby, scarlet and crimson.
0:21:16 > 0:21:20And it strikes me that all of those words imply something
0:21:20 > 0:21:22that's bright and deep and rich.
0:21:24 > 0:21:29For us, red is the colour of love and the colour of war.
0:21:35 > 0:21:39It can scare us, and it can worry us, and it can move us.
0:21:44 > 0:21:47But red isn't significant only to us humans.
0:21:49 > 0:21:53It holds a special place across the living world.
0:21:55 > 0:21:58To discover why, I've come to meet Andrew Smith,
0:21:58 > 0:22:01a zoologist at Anglia Ruskin University.
0:22:04 > 0:22:08He's working with New World monkeys, like these marmosets.
0:22:09 > 0:22:13Some individuals in the group can distinguish the colour red.
0:22:13 > 0:22:14Others can't.
0:22:16 > 0:22:20Marmosets have got a slightly strange system of colour vision.
0:22:20 > 0:22:23All of the boys are red/green colour-blind,
0:22:23 > 0:22:26along with about a third of the females,
0:22:26 > 0:22:29and the remaining two-thirds of the females
0:22:29 > 0:22:32see the world in a very similar way to ourselves.
0:22:32 > 0:22:34So, within the same troop of monkeys,
0:22:34 > 0:22:36some have colour vision like ours
0:22:36 > 0:22:39and some have red/green colour blindness type vision,
0:22:39 > 0:22:41- and you can directly compare the difference?- Yes.
0:22:44 > 0:22:46To discover the difference it makes
0:22:46 > 0:22:48if you can distinguish red and green,
0:22:48 > 0:22:51Andrew has set the monkeys a challenge.
0:22:52 > 0:22:54And I'm going to give it a try.
0:22:57 > 0:23:01I've got a pair of glasses which will transform your vision
0:23:01 > 0:23:04from normal colour vision to if you like, colour-blind vision,
0:23:04 > 0:23:06so if you'd like to put them on.
0:23:06 > 0:23:09We put some strawberries in the tree behind you.
0:23:09 > 0:23:11We've got some ripe and some unripe strawberries,
0:23:11 > 0:23:15and I'd like you to find all of the seven ripe strawberries
0:23:15 > 0:23:18- as fast as you can. - Ready to go?- OK. Go.
0:23:19 > 0:23:21The world's gone very green!
0:23:22 > 0:23:26With the goggles on, I see the world as the colour-blind marmosets do.
0:23:29 > 0:23:30There's one.
0:23:32 > 0:23:35The ripe strawberries look very black here, so it's quite hard
0:23:35 > 0:23:39to pick them out against the dark trees and the dark background.
0:23:39 > 0:23:43Under here? Oh, there, right, I was looking too far forward.
0:23:43 > 0:23:46All right, so have I done the job? Seven strawberries.
0:23:46 > 0:23:51Perfect, you found them all and that took you 1 minute, 10 seconds.
0:23:53 > 0:23:56Andrew resets the tree with fresh strawberries
0:23:56 > 0:23:59so that I can try again, but this time, without the goggles.
0:24:00 > 0:24:02OK, go.
0:24:04 > 0:24:07This is much easier. Two, three....
0:24:11 > 0:24:13My natural colour vision is very similar
0:24:13 > 0:24:17to that of the female marmosets that can also see red.
0:24:17 > 0:24:19..six, seven.
0:24:19 > 0:24:22Fantastic. 16 seconds.
0:24:22 > 0:24:24Huge difference!
0:24:24 > 0:24:27So, that's an awful lot faster than the 1 minute 10 that it took you
0:24:27 > 0:24:30when you couldn't tell the difference between red and green.
0:24:32 > 0:24:35Andrew's been carrying out experiments like this on monkeys,
0:24:35 > 0:24:39to see how colour vision effects their ability to find ripe fruit.
0:24:39 > 0:24:43There's one just in the background there, having a bit of a look.
0:24:45 > 0:24:48- Ah, here we go, here we go, here we go.- Yeah, this one's seen it.
0:24:49 > 0:24:52That one is sitting right on top of a ripe strawberry,
0:24:52 > 0:24:54and not noticing it at all.
0:24:56 > 0:25:01After repeating the test hundreds of times, Andrew found a clear pattern.
0:25:01 > 0:25:04What we found is that all of the monkeys could do the task,
0:25:04 > 0:25:08given enough time, but the monkeys with human-like colour vision
0:25:08 > 0:25:10went straight for the ripe fruits.
0:25:13 > 0:25:18In the wild, being the first to find the food gives you a huge advantage.
0:25:18 > 0:25:21It can be the difference between life and death.
0:25:22 > 0:25:26And what's really fascinating is that it's not just the animals
0:25:26 > 0:25:28that can see red who benefit.
0:25:29 > 0:25:34It's also the plants that can turn red to signal their ripeness,
0:25:34 > 0:25:37attracting animals to disperse their seeds.
0:25:40 > 0:25:44The animals come along, eat the fruit, which is full of seeds,
0:25:44 > 0:25:47and then very conveniently deposit them somewhere else,
0:25:47 > 0:25:51in a pile of their own manure - readymade fertiliser.
0:25:51 > 0:25:52It's a brilliant scheme
0:25:52 > 0:25:57and the only condition is that the fruit mustn't be eaten too soon.
0:25:57 > 0:26:01So, when they're growing, the fruits and the seeds are the same colour
0:26:01 > 0:26:03as everything else around them.
0:26:03 > 0:26:07And then, with one very dramatic colour change,
0:26:07 > 0:26:10the signal is sent that the fruit is ready to go.
0:26:14 > 0:26:17It's a wonderful example of the intimate connection
0:26:17 > 0:26:19between colour and life.
0:26:20 > 0:26:24Colours that exist purely to be seen
0:26:24 > 0:26:27and eyes that have evolved to see them.
0:26:31 > 0:26:35It's what makes colour one of the most powerful forms of communication
0:26:35 > 0:26:37in the living world.
0:26:38 > 0:26:41One that can transcend species...
0:26:43 > 0:26:46..and even signal between plants and animals.
0:26:49 > 0:26:52Messages sent, received
0:26:52 > 0:26:54and understood in colour.
0:26:57 > 0:27:00But for animals with a more highly-developed brain,
0:27:00 > 0:27:03colour can also convey a deeper level of meaning.
0:27:09 > 0:27:15To discover how, I've come to meet anthropologist Dr Jo Setchell.
0:27:15 > 0:27:17She studies mandrills,
0:27:17 > 0:27:22a primate species whose males have a distinctive red nose.
0:27:22 > 0:27:24To us, it's really striking.
0:27:24 > 0:27:25When we look at a mandrill,
0:27:25 > 0:27:28the first thing we see is this bright red nose.
0:27:28 > 0:27:32I want to know what it means to a mandrill to see red.
0:27:34 > 0:27:38Today, we're going to investigate the three males living here,
0:27:38 > 0:27:39in Wingham Wildlife Park.
0:27:41 > 0:27:43Malik,
0:27:43 > 0:27:45Kayin
0:27:45 > 0:27:46and Mathias.
0:27:47 > 0:27:52So, what we're after, ideally, is the nose of the animal.
0:27:54 > 0:27:56The intensity of the red colour
0:27:56 > 0:27:58can vary in different members of the group.
0:28:00 > 0:28:02Jo is investigating why.
0:28:03 > 0:28:05CAMERA CLICKS
0:28:05 > 0:28:08First, we take photographs of the three males.
0:28:09 > 0:28:11There you go. CAMERA CLICKS
0:28:13 > 0:28:15He's staying still now.
0:28:16 > 0:28:19Oh, that's nice, almost got them lined up.
0:28:23 > 0:28:26Now, Jo measures the intensity of the red.
0:28:28 > 0:28:31We want to know the red colour of that particular area.
0:28:31 > 0:28:35We're going to chose exactly the same area on each of the three males.
0:28:35 > 0:28:38So, that gives him a red score of 1.37.
0:28:40 > 0:28:43Jo calculates the red score for all three males.
0:28:45 > 0:28:48We've got Mathias, who's the least colourful,
0:28:48 > 0:28:50and his score was 1.4.
0:28:51 > 0:28:56Then, we have Kayin, and his score was 1.7.
0:28:57 > 0:29:01And then finally, we have Malik. His score was 1.9.
0:29:01 > 0:29:03- So, a big difference.- Yes.
0:29:08 > 0:29:11At first, Jo thought this was simply an individual trait,
0:29:11 > 0:29:13like our hair colour.
0:29:16 > 0:29:19But after months of monitoring the mandrills' colour,
0:29:19 > 0:29:21she discovered something unexpected.
0:29:24 > 0:29:27So here, we've got another photo of Malik,
0:29:27 > 0:29:29but this was taken two years ago.
0:29:29 > 0:29:32So, that's the same mandrill as the one over there.
0:29:32 > 0:29:34Yes, you can recognise his face,
0:29:34 > 0:29:37but what you can see is, this colour is completely different.
0:29:37 > 0:29:38That's a huge change.
0:29:38 > 0:29:40Yes, it's marvellous, isn't it?
0:29:42 > 0:29:44Jo had discovered that it was possible
0:29:44 > 0:29:46for the mandrills to change colour.
0:29:46 > 0:29:49She continued to monitor them over time,
0:29:49 > 0:29:52and found a striking correlation.
0:29:58 > 0:30:01They change colour basically with a dominance rank,
0:30:01 > 0:30:04so as a male increases in rank, his colour increases,
0:30:04 > 0:30:07and if he loses his rank, then his colour decreases.
0:30:07 > 0:30:11So, the order of the colours reflects the dominance hierarchy?
0:30:11 > 0:30:14That's right, yes. He's the dominant male.
0:30:18 > 0:30:23The shade of red reflects the strict hierarchy in mandrill societies,
0:30:23 > 0:30:25like this one filmed in Gabon.
0:30:28 > 0:30:30At the top is the dominant male.
0:30:32 > 0:30:36He will have access to the females and first pick of the food.
0:30:37 > 0:30:41He broadcasts his enviable position by having the brightest nose.
0:30:43 > 0:30:45- So, it reflects success? - Yes, basically.
0:30:45 > 0:30:47- It's like a badge that you get.- Yes.
0:30:50 > 0:30:52It's the hormone testosterone
0:30:52 > 0:30:55that keeps the dominant male's nose bright red.
0:30:59 > 0:31:01Jo's work suggests this colour may have
0:31:01 > 0:31:05an important physiological effect on other Mandrills in the group.
0:31:08 > 0:31:12So, subordinate males have lower testosterone than dominant males,
0:31:12 > 0:31:15and that's an effect of being in the presence of a male
0:31:15 > 0:31:17who has bright red colour.
0:31:18 > 0:31:23Having lower testosterone helps keep these mandrills subordinate,
0:31:23 > 0:31:26so each animal knows its place.
0:31:28 > 0:31:31Here, red is a colour that keeps the peace.
0:31:36 > 0:31:41I'm imagining a huge group of these mandrills in a forest in the wild,
0:31:41 > 0:31:44but connected together with these flashes of red,
0:31:44 > 0:31:46coming through the leaves.
0:31:46 > 0:31:50But each glimpse of red doesn't just reflect a public face,
0:31:50 > 0:31:53their position in the hierarchy,
0:31:53 > 0:31:58it also reflects and affects their internal messengers, the hormones.
0:31:59 > 0:32:01Deep down, physiological changes,
0:32:01 > 0:32:03broadcast in colour.
0:32:07 > 0:32:08In the world of the mandrill,
0:32:08 > 0:32:12your colour is a vital part of who you are.
0:32:13 > 0:32:16But they're not the only animals to communicate
0:32:16 > 0:32:18using colour signals in their skin.
0:32:29 > 0:32:31We humans do it too,
0:32:31 > 0:32:34although we're not aware of it.
0:32:37 > 0:32:41David Perrett is a psychologist at the University of St Andrews.
0:32:41 > 0:32:45He's found that we're constantly broadcasting information,
0:32:45 > 0:32:47using one specific hue.
0:32:50 > 0:32:52To see if I can guess which colour that is
0:32:52 > 0:32:55and what it's saying about me, David has a test.
0:32:57 > 0:32:58You can have a look.
0:32:58 > 0:33:00That's definitely me.
0:33:00 > 0:33:02It's definitely you, but if you adjust the picture
0:33:02 > 0:33:06by sliding backwards and forwards, you may be able to see some change.
0:33:06 > 0:33:08So if I scroll this way,
0:33:08 > 0:33:11I can see that the skin colour's changing a little bit.
0:33:11 > 0:33:13Your task is to make it look healthy.
0:33:13 > 0:33:15The healthiest version of me?
0:33:15 > 0:33:18So, the skin colour's changing a bit and on one side,
0:33:18 > 0:33:20that's definitely ill, down there.
0:33:20 > 0:33:24All right. So, I reckon about...there.
0:33:25 > 0:33:29I can't tell what exactly David is changing in my photograph,
0:33:29 > 0:33:32but he's done the same to photographs of many other people
0:33:32 > 0:33:34with different skin colours.
0:33:36 > 0:33:41If you look here, then you can see manipulation of African faces,
0:33:41 > 0:33:43Asian faces and European faces
0:33:43 > 0:33:47And it's very noticeable here, like you definitely pick up
0:33:47 > 0:33:49the bottom row as being the healthy bunch.
0:33:51 > 0:33:54Well, what did you think we'd changed?
0:33:54 > 0:33:57It looks darker, but I'm not sure how.
0:33:57 > 0:34:00I mean, there's lots... So, it could be tanned.
0:34:00 > 0:34:02Well, we didn't make it darker.
0:34:02 > 0:34:04I can't tell, just by looking at them.
0:34:04 > 0:34:07I know this one looks healthy, but I couldn't pick out what's different.
0:34:07 > 0:34:09We made it more yellow.
0:34:09 > 0:34:13A specific type of yellow, or a kind of golden yellow that is...
0:34:15 > 0:34:16It's a unique colour.
0:34:18 > 0:34:22David's research has revealed that across many different cultures,
0:34:22 > 0:34:26people perceive faces with more yellow in them as healthier,
0:34:26 > 0:34:28and more attractive.
0:34:30 > 0:34:32So, why would my skin go yellow?
0:34:32 > 0:34:35Why? Well, it's from what you eat.
0:34:35 > 0:34:39You take in pigments from the fruit and vegetables you eat,
0:34:39 > 0:34:42so we've got here...a pepper.
0:34:42 > 0:34:46Now, that's obviously coloured, but that colours you, when you eat it.
0:34:46 > 0:34:49The pigments get transported in your blood
0:34:49 > 0:34:51and they end up in the skin.
0:34:51 > 0:34:53I mean, there's lots of different colours
0:34:53 > 0:34:55in the fruit and veg we've got.
0:34:55 > 0:34:57We've got carrot, tomatoes...
0:34:57 > 0:34:59But the colours that I'm talking about,
0:34:59 > 0:35:02they're all called carotenoids.
0:35:02 > 0:35:03So, the colour we see in our skin
0:35:03 > 0:35:07is a direct reflection of how much of these pigments we're eating.
0:35:07 > 0:35:10- It is, yeah.- And how much extra would I have to eat,
0:35:10 > 0:35:13for someone to notice a difference in my face?
0:35:13 > 0:35:17In one study, we simply got people to eat one pepper per day extra,
0:35:17 > 0:35:22and some carrot juice. So, a very modest change in the diet.
0:35:23 > 0:35:27Within a few weeks, the person... Everybody seems to look different.
0:35:29 > 0:35:33So, the level of yellow in our skin is a signal of our state of health.
0:35:36 > 0:35:39One that we're constantly communicating to other people
0:35:39 > 0:35:40without even knowing.
0:35:43 > 0:35:46When you were looking at your own image, you chose an image...
0:35:46 > 0:35:48not with your natural diet,
0:35:48 > 0:35:52with the simulation of a diet with increased fruit and veg consumption,
0:35:52 > 0:35:56maybe three or four more portions, per day.
0:35:56 > 0:35:59So, I picked a skin tone that was a little bit higher
0:35:59 > 0:36:02than my natural skin tone, had more carotenoids in it.
0:36:02 > 0:36:03Yeah.
0:36:08 > 0:36:10And we humans aren't the only species
0:36:10 > 0:36:12to signal our health in this way.
0:36:15 > 0:36:19The vivid pink of flamingos comes entirely from carotenoids
0:36:19 > 0:36:22in the algae and crustaceans they eat.
0:36:24 > 0:36:28The more carotenoids, the healthier they'll be, and the brighter.
0:36:30 > 0:36:33So, their colour is an unmistakable signal of their health
0:36:33 > 0:36:35to potential mates.
0:36:39 > 0:36:41When we think about colour,
0:36:41 > 0:36:44we tend to think about aesthetics and its visual appeal.
0:36:44 > 0:36:47But there's so much subtlety in the world of colour
0:36:47 > 0:36:50that it can also carry lots of information.
0:36:50 > 0:36:53All sorts of animal species use it to communicate.
0:36:54 > 0:36:57And so, when you look at a scene like this,
0:36:57 > 0:37:00it's not just a beautiful view of natural history,
0:37:00 > 0:37:03it's also a flood of information.
0:37:09 > 0:37:12But that information isn't always used to communicate.
0:37:15 > 0:37:19Sometimes, colour can do the opposite. It can conceal.
0:37:22 > 0:37:24And there's one particular environment
0:37:24 > 0:37:27where this can be vital for survival.
0:37:42 > 0:37:44The ocean can look uniform from above,
0:37:44 > 0:37:47but it's certainly not like that down below.
0:37:47 > 0:37:50There's a whole, varied, hidden world out there.
0:37:52 > 0:37:54It's a dynamic, changing environment.
0:37:56 > 0:37:58Survival is a challenge
0:37:58 > 0:38:02and everything living out there is potential dinner for something else.
0:38:08 > 0:38:11To stay alive in this dangerous world,
0:38:11 > 0:38:13one type of animal has evolved
0:38:13 > 0:38:16to manipulate colour in an extraordinary way.
0:38:19 > 0:38:22And to see it, I've come to Brighton Sea Life Centre,
0:38:22 > 0:38:25to meet Marine Biologist Kerry Perkins.
0:38:29 > 0:38:30So, what have we got here?
0:38:30 > 0:38:33Well, here we actually have some cuttlefish.
0:38:33 > 0:38:34So, one, two, three, four.
0:38:36 > 0:38:39Cuttlefish are a type of cephalopod,
0:38:39 > 0:38:42a group of marine invertebrates that include squid and octopus.
0:38:43 > 0:38:45They're very soft-bodied creatures,
0:38:45 > 0:38:48so they're very tasty for a lot of animals,
0:38:48 > 0:38:52so you have to think of a strategy, so you don't get eaten all the time.
0:38:54 > 0:38:56When most animals want to hide,
0:38:56 > 0:38:59they seek out an environment that matches their colour.
0:39:01 > 0:39:04But the cephalopods have a different tactic.
0:39:07 > 0:39:11To show me, Kerry puts one of the cuttlefish in her observation tank.
0:39:14 > 0:39:16So, settled down now.
0:39:17 > 0:39:21On the sand, the cuttlefish is a uniform beige colour.
0:39:21 > 0:39:25But let's see what happens when Kerry changes the background.
0:39:28 > 0:39:31Oh, look at that! Completely changed colour.
0:39:33 > 0:39:35There's big, bright spot on his back,
0:39:35 > 0:39:38and another one just behind his eyes.
0:39:38 > 0:39:41He fits in with his new environment, doesn't he?
0:39:42 > 0:39:46Cuttlefish can change the colour of their skin to match the background.
0:39:47 > 0:39:50What the cuttlefish is actually doing,
0:39:50 > 0:39:51it's trying to break up its pattern,
0:39:51 > 0:39:54but obviously, a lot of predators scan for their prey,
0:39:54 > 0:39:57so if you're even one or two metres above this cuttlefish,
0:39:57 > 0:39:59you would think it was just rocks.
0:40:02 > 0:40:05To see just how far it can manipulate its colour,
0:40:05 > 0:40:07Kerry's going to test this cuttlefish
0:40:07 > 0:40:10with an entirely unnatural background.
0:40:12 > 0:40:15So, it's black and white checks. Oh, he's gone white.
0:40:16 > 0:40:18So, he changed straight away,
0:40:18 > 0:40:22and even though this chequerboard isn't something that would
0:40:22 > 0:40:25ever come up in a real ocean situation, he's had a good go at it.
0:40:25 > 0:40:28He has. I mean, it wouldn't come across a chequerboard
0:40:28 > 0:40:31on the seafloor, but obviously, he's still using the same mechanisms
0:40:31 > 0:40:35and same ideas behind seeing the squares and giving it a good try.
0:40:36 > 0:40:39Even with something as foreign as a chequerboard,
0:40:39 > 0:40:44the cuttlefish has changed its colour to try and blend in.
0:40:44 > 0:40:48To achieve this, it manipulates colour in an ingenious way.
0:40:52 > 0:40:55They've got a layer of skin that's actually reflective
0:40:55 > 0:40:59and this is a bit like, if you can imagine, a piece of tin foil
0:40:59 > 0:41:02that'll reflect any colour that is bounced onto it,
0:41:02 > 0:41:05so it has this ability to reflect the colours and its surroundings.
0:41:05 > 0:41:08But what's really interesting - on the top layer of it,
0:41:08 > 0:41:11they have something called chromatophores.
0:41:11 > 0:41:14These are chromatophores, seen under a microscope.
0:41:14 > 0:41:19They're cells containing sacs of different coloured pigments,
0:41:19 > 0:41:22and the cuttlefish can control the shape of each one.
0:41:25 > 0:41:27Here, each of the cocktail umbrellas
0:41:27 > 0:41:29represents a different chromatophore.
0:41:33 > 0:41:37When they're shut, we can't really see what colour the umbrellas are.
0:41:37 > 0:41:39- It's just silver. - It's just sort of silver.
0:41:39 > 0:41:42So, this is what happens when we see the cuttlefish to be uniform,
0:41:42 > 0:41:46so they're just reflecting the colour that's in their environment.
0:41:46 > 0:41:48But once we start opening them...
0:41:48 > 0:41:52So, if you give me a hand, we start seeing the colour of the umbrellas.
0:41:58 > 0:41:59We can create different patterns
0:41:59 > 0:42:03by changing the combination of umbrellas that are open.
0:42:10 > 0:42:12This is how the cuttlefish can change their colour
0:42:12 > 0:42:15to match their immediate environment.
0:42:16 > 0:42:18So, they effectively disappear.
0:42:21 > 0:42:24They're the ocean's masters of disguise.
0:42:35 > 0:42:39The ocean is full of colour and contrast,
0:42:39 > 0:42:43and the cuttlefish can navigate through that world unseen
0:42:43 > 0:42:46by revealing its hidden colours at the right time,
0:42:46 > 0:42:50almost as if it was picking costumes from a portable dressing up box.
0:42:50 > 0:42:55Other animals use toxins or threats or spikes to deter predators,
0:42:55 > 0:42:59but for a cuttlefish, colour is the key to survival.
0:43:10 > 0:43:14So, colour can disguise and protect life,
0:43:14 > 0:43:18but in a world crowded with species competing to survive,
0:43:18 > 0:43:21sometimes you don't need to hide, you need to stand out.
0:43:31 > 0:43:34This is a pollia berry and it's my new favourite fruit.
0:43:34 > 0:43:36Look at it, it's almost metallic.
0:43:36 > 0:43:40Doesn't look like a real fruit at all, but it's flashing light,
0:43:40 > 0:43:41and it's a new kind of colour.
0:43:43 > 0:43:47This is what's known as iridescence -
0:43:47 > 0:43:49a rare and spectacular form of colour
0:43:49 > 0:43:52that only a handful of species on Earth can produce.
0:43:52 > 0:43:56And to discover how they do it, we need to take a closer look.
0:44:02 > 0:44:05A powerful microscope reveals a hidden landscape
0:44:05 > 0:44:09with structures perfectly formed to do something remarkable.
0:44:19 > 0:44:23The secret to all this is to do with shape on tiny, tiny scales.
0:44:25 > 0:44:29Let's imagine this is the shape that the light is hitting.
0:44:29 > 0:44:31So, light waves come in,
0:44:31 > 0:44:35light waves of all different colours come in and hit this structure.
0:44:35 > 0:44:38But they only get reflected back from these bits here.
0:44:38 > 0:44:40Anything that goes down there gets lost.
0:44:43 > 0:44:44The distance between these ridges
0:44:44 > 0:44:47is very close to the wavelength of light itself,
0:44:47 > 0:44:50and this affects how the waves are bounced back.
0:44:53 > 0:44:56So, let's see what happens when light waves are reflected
0:44:56 > 0:44:59away from this surface and we'll start with blue light.
0:45:01 > 0:45:02If we look at the waves together,
0:45:02 > 0:45:05we can see that they both go up at the same time,
0:45:05 > 0:45:08and then down at the same time, and then up at the same time
0:45:08 > 0:45:12and then down at the same time, so they're lined up all the way along.
0:45:14 > 0:45:18The aligned waves reinforce each other, creating a vivid blue.
0:45:22 > 0:45:24But it's not the same for all colours,
0:45:24 > 0:45:26so if we have a look at the red light...
0:45:26 > 0:45:29Red light has a longer wavelength than blue...
0:45:31 > 0:45:34..and these waves are out of alignment.
0:45:34 > 0:45:38They cancel each other out and so from this angle, there's no red -
0:45:38 > 0:45:40just very vivid blue.
0:45:44 > 0:45:48But from this angle, the blue and the red waves line up,
0:45:48 > 0:45:49creating purple.
0:45:52 > 0:45:56And from here, just the red waves line up.
0:45:56 > 0:45:58So, as the point of view changes,
0:45:58 > 0:46:02what the eye perceives are flashes of shimmering colour.
0:46:06 > 0:46:08This is iridescence.
0:46:11 > 0:46:14Until recently, we thought that it only existed
0:46:14 > 0:46:16in a select group of species,
0:46:16 > 0:46:17mainly insects and birds.
0:46:19 > 0:46:22So, plant scientists in Cambridge were surprised
0:46:22 > 0:46:24to find it right under their noses.
0:46:28 > 0:46:31Beverly Glover is head of the botanical gardens.
0:46:32 > 0:46:36Well, at the time, we were interested in patterns of pigment on flowers,
0:46:36 > 0:46:39and so my post-doc, Heather Witney was looking for flowers
0:46:39 > 0:46:41that have different combinations of colour on the petal.
0:46:41 > 0:46:43She found this one in the garden, here.
0:46:43 > 0:46:46She picked it up, brought it back to my office and said,
0:46:46 > 0:46:48"So, how does it make this blue, yellow, green stuff?"
0:46:48 > 0:46:52And we had no idea and that's when we realised that nobody had ever
0:46:52 > 0:46:55noticed iridescence on flowers and it had never been looked at before.
0:46:55 > 0:46:59Beverly wanted to know why these hibiscus flowers were iridescent,
0:46:59 > 0:47:01and to investigate, she needed some help.
0:47:06 > 0:47:09So, this is the bee colony over here.
0:47:09 > 0:47:12Bees are one of the hibiscuses' main pollinators.
0:47:15 > 0:47:17So, Beverly set up an experiment
0:47:17 > 0:47:20to see whether they responded to the iridescent flowers.
0:47:22 > 0:47:25So, we've got a colony of bombus terrestris,
0:47:25 > 0:47:27it's a common British bumblebee,
0:47:27 > 0:47:30and in the wild, they nest in holes in the ground.
0:47:30 > 0:47:34You find them in your garden and in the cracks in the soil and so on.
0:47:34 > 0:47:38The colony is in this cardboard box and they come out through this tube
0:47:38 > 0:47:41and they come out into this box, which we call the flight arena.
0:47:41 > 0:47:45And they're foraging in here for food, mostly nectar
0:47:45 > 0:47:49to take back through the tube, into the colony, to feed to the larvae.
0:47:49 > 0:47:54Within her flight arena, Beverly set up an unlikely-looking meadow.
0:47:55 > 0:47:59And what we've set up in the box are these artificial flowers.
0:47:59 > 0:48:01This iridescent disc
0:48:01 > 0:48:04has sugar solution in the middle to mimic nectar.
0:48:04 > 0:48:07To the bee, it's as good as a flower.
0:48:09 > 0:48:13These then go into the colony, and so, just open the gate,
0:48:13 > 0:48:16and pop the disc in.
0:48:16 > 0:48:20So, the flowers are evenly spaced, they're all iridescent.
0:48:21 > 0:48:24Beverly let a single bee into the flight arena...
0:48:28 > 0:48:32..and then timed how long it took to fly from one flower to the next.
0:48:41 > 0:48:43STOPWATCH BEEPS
0:48:45 > 0:48:48After testing dozens of bees several times each,
0:48:48 > 0:48:51Beverly reset the arena,
0:48:51 > 0:48:54but this time, with non-iridescent flowers.
0:48:57 > 0:49:00She wanted to know whether the iridescence made a difference
0:49:00 > 0:49:03to the time it took the bees to fly between flowers.
0:49:05 > 0:49:07What were the results?
0:49:07 > 0:49:09The iridescent discs are much easier to see.
0:49:09 > 0:49:11The non-iridescent flowers,
0:49:11 > 0:49:13you're looking at three to four seconds to find a flower.
0:49:13 > 0:49:16The iridescent ones, maybe about two seconds to find a flower,
0:49:16 > 0:49:18so it really does make a big difference.
0:49:18 > 0:49:21And that difference really matters, because it's costing the bees energy
0:49:21 > 0:49:24to be in the air and searching. That's expensive time.
0:49:24 > 0:49:27Yep, that's exactly right. They're heavy, compared to most insects
0:49:27 > 0:49:30and so, the fact that this flower is easier to see is good for them,
0:49:30 > 0:49:32it speeds that up, and that gives me an explanation
0:49:32 > 0:49:35for why my hibiscus flowers are making this structure.
0:49:35 > 0:49:38They've figured out that it's a way of attracting the attention -
0:49:38 > 0:49:40the eye, if you like, of a bee - and that means it's more likely
0:49:40 > 0:49:43that they'll get pollinated out there in the wild.
0:49:50 > 0:49:54There's no doubt that hibiscus is a beautiful, elegant flower,
0:49:54 > 0:49:58but even more elegant, I think, is the way that iridescence works.
0:49:58 > 0:50:00It's a solution to a problem.
0:50:01 > 0:50:04The flower can't move, but when something else moves past it,
0:50:04 > 0:50:06it sees strong flashes of colour,
0:50:06 > 0:50:09a beacon advertising the flower's presence.
0:50:19 > 0:50:21Across the Earth,
0:50:21 > 0:50:25life in all its forms has created a spectacular paintbox.
0:50:30 > 0:50:32A stunning array of colours,
0:50:32 > 0:50:36produced by some of the most intricate adaptations in nature.
0:50:39 > 0:50:44But every one of the colours we've seen so far depends on one thing.
0:50:49 > 0:50:50Sunlight.
0:50:51 > 0:50:55Colour is produced by organisms reflecting or manipulating sunlight.
0:50:59 > 0:51:03And so, when the sun goes down, colour goes with it.
0:51:10 > 0:51:13But there are exceptions.
0:51:13 > 0:51:16A rare group of animals have evolved a way to produce colour
0:51:16 > 0:51:19that doesn't depend on light from the sun.
0:51:46 > 0:51:50This is the Great Smokey Mountains National Park in Tennessee.
0:51:50 > 0:51:53It's a pretty bit of forest, but it's not very remarkable.
0:51:53 > 0:51:55There's nothing unusual here,
0:51:55 > 0:51:58but in a couple of hours, that's going to change.
0:52:10 > 0:52:14As darkness descends, the crowds swarm in.
0:52:17 > 0:52:21All of these people are hoping to witness a natural spectacle
0:52:21 > 0:52:24which occurs every year in late May or early June.
0:52:29 > 0:52:32It's all so strange, because normally,
0:52:32 > 0:52:34if you see people lined up along a path,
0:52:34 > 0:52:37they're facing inwards to see what's on the path,
0:52:37 > 0:52:41but out here, everyone's facing out into the forest.
0:52:41 > 0:52:44That's clearly where the spectacle is going to be.
0:52:46 > 0:52:48It's almost as though this is a theatre,
0:52:48 > 0:52:50and that's the stage, out there.
0:52:52 > 0:52:55And it very much feels as though the curtain is about to rise
0:52:55 > 0:52:57and the first act is about to begin.
0:53:10 > 0:53:13Once it's completely dark, the show begins.
0:53:32 > 0:53:35The performers are fireflies.
0:53:35 > 0:53:38A species called photinus carolinus.
0:53:46 > 0:53:50This is it. We're right in the middle of it here,
0:53:50 > 0:53:54and there's these bands of light that are sweeping across the forest.
0:53:57 > 0:53:59And they're lighting up the forest.
0:54:05 > 0:54:07This is their mating display,
0:54:07 > 0:54:09and within it is a hidden code.
0:54:14 > 0:54:19As they fly, each male flashes six times quickly, and then pauses.
0:54:24 > 0:54:28They're trying to catch the attention of the females on the ground.
0:54:29 > 0:54:31It's rippling through the trees.
0:54:34 > 0:54:37The precise pattern of flashes signals their species...
0:54:39 > 0:54:41..a vital way to set themselves apart
0:54:41 > 0:54:44from the 19 other species of firefly that live here.
0:54:46 > 0:54:48And the really amazing thing about this
0:54:48 > 0:54:52is that one single species, all by itself,
0:54:52 > 0:54:55can see all the other ones of its species
0:54:55 > 0:54:57in this section of the forest.
0:55:00 > 0:55:03This is communication in colour.
0:55:12 > 0:55:15These tiny creatures have evolved
0:55:15 > 0:55:18so that a part of their body has become a lantern.
0:55:27 > 0:55:30Inside it, they produce a chemical called luciferin,
0:55:30 > 0:55:32that reacts with oxygen
0:55:32 > 0:55:36to produce these striking flashes of colour that light up the forest.
0:55:49 > 0:55:51For a small insect in a big world,
0:55:51 > 0:55:54this is a fantastic strategy.
0:55:54 > 0:55:58The fireflies bide their time, waiting until
0:55:58 > 0:56:02the bustling multi-coloured riot of the daylight world has gone
0:56:02 > 0:56:06and the forest is black, colourless.
0:56:06 > 0:56:11And then, each tiny insect switches on its own portable colour factory,
0:56:11 > 0:56:14sending a beacon to the rest of its species
0:56:14 > 0:56:18and co-ordinating the start of the next generation.
0:56:18 > 0:56:20Life harnesses light in all kinds of ways,
0:56:20 > 0:56:22but I think it's really lovely
0:56:22 > 0:56:26that this trick of creating colour where there was none before
0:56:26 > 0:56:29has come from one of the smallest species of all.
0:56:42 > 0:56:46Colour has been fundamental to the evolution of the diverse
0:56:46 > 0:56:48and beautiful living world that exists today.
0:56:51 > 0:56:55And in turn, life has painted the Earth in magnificent Technicolor...
0:56:57 > 0:57:00..expanding the palette of the planet
0:57:00 > 0:57:04by manipulating colour and even creating its own.
0:57:07 > 0:57:09But all of these colours
0:57:09 > 0:57:13are still only just the visible part of the spectrum -
0:57:13 > 0:57:16a tiny proportion of all the colours that exist.
0:57:19 > 0:57:23And it's the colours we can't see that are set to shape our future.
0:57:27 > 0:57:30Next time, I'll be looking beyond the rainbow.
0:57:31 > 0:57:35Isn't it fascinating, this view of the world?
0:57:35 > 0:57:37I'll discover the hidden colours
0:57:37 > 0:57:40that can reveal the deepest secrets of the universe.
0:57:40 > 0:57:42This is a picture of the Orion nebula.
0:57:42 > 0:57:45If you look at it in infrared, it completely lights up.
0:57:45 > 0:57:48We're observing the invisible.
0:57:48 > 0:57:50Discover more about the story of the colours of life
0:57:50 > 0:57:52with the Open University.
0:57:52 > 0:57:54Go to...
0:57:56 > 0:57:58..and follow the links to the Open University.