Original subtitles

PROFESSOR BRIAN COX: These are the waters off Catalina,

a tiny island 20 miles off the coast of Llos Angeles, California.

(OVER RADIO) 7hese are kelp forests.

They grow here in tremendous abundance because the waters here around Catalina

are extremely rich in nutrients.

That's because of the California Current

which brings this beautiful rich, cold Water up from the depths of the Pacific

and allows this tremendously rich ecosystem to grow.

İt's a remarkable place.

Oh, look!

But I'm not here to marvel at these kelp forests,

beautiful as they are.

I'm here to search for a little animal

that lives not in this

forest of nutrients,

but out there in the muddy ocean floor.

There he is, look. (LAUGHS)

Do you see that? (LAUGHS)

BRIAN: Camouflaged in its burrow on the sea floor,

the mantis shrimp is a seemingly unremarkable creature.

İt's not a real shrimp,

but a itype of crustacean called a stomatopod.

I've come to see it because,

in one way, the mantis shrimp is truly extraordinary -

the way it detecis the world.

(OVER RADIO) You see those big...

eyes surveying the sea.

(NARRATING) Buf these are some of the most sophisticated eyes

in the natural world.

Fach is made up of over 10, 900 hexagonal lenses.

And with twice as many visual pigments as any other animal,

it can see colours and wavelengths of light that are invisible to me.

These remarkable eyes give the mantis shrimp

a unigğue view of the oöcean.

And this is just one of the many finely-tuned senses

that have evolved across the planet.

Sensing, the ability to detect and to react to the world outside,

is fundamental to life.

Every living thing is able to respond to its environment.

In this film, 1 want to show you how the senses developed,

how the mechanisms that gather information

about the outside world evolved,

how their emergence has helped animals thrive in different environments.

And how the senses have pushed life in new directions

and may ultimately have lead to our own curlosity and intelligence.

(7HE WOODS BY CLEM SNIDE PLAYING)

BRIAN: 7hese are the woods of Kentucky.

The first stop on a journey across America

that will take me from the far west coast to the Atlantic

through the heart of the country.

It's the animals that Til find on the way

that will illuminate the world of the senses.

And I'm gorng to start by golrng deep underground.

These are the Mammoth Caves in Kentucky, with over 300 miles of mapped passages,

they're the longest cave system in the world.

But this is also the place to start exploring our own senses.

We're normally dependent on our sigğht.

But down here, in the darkness, it's a very different world

and I have to rely on my other senses to bulild a picture of my environment.

Oh, it's completely dark in this cave.

I can't see anythingatall.

You can see me because we're lighting it with infrared light,

and that's at a wavelength that my eyes are completely insensitive to.

So, as far as I am concerned, it is pitch-black.

And because it's so dark...

your other senses become heightened, particularly hearing.

İt is virtually silent in here.

But if you listen carefully...

you can just hear the faint drop

of water from somewhere deep in the cave system.

You'd never hear that if the cave were illuminated.

But you focus on your hearing when it's as dark as this.

Now, as well as sight and hearing

we have, of course, a range of other senses.

There's touch, which is really a mixture of sensations,

temperature and pressure and pain.

And then there are chemical senses.

So smell and taste.

And we share those senses with almost every living thing on the planet today

because they date back virtually to the beginning of life on Earth.

And even here, in water that's been collected from deep within a cave,

there are organisms that are detecting and responding to their environment

in the same way that living things have been doing for over a billion years.

Ah.

There İit is.

Now that is a paramecium.

It may look like a simple animal

but, in fact, it isa member of a group of organisms called protists.

And you'd have to go back around two billion years

to find a common ancestor between me and a paramecium.

Paramecia have probably changed little in the last billion years.

And although they appear simple,

these tiny creatures display some remarkabiy complex behaviour.

You can even see them responding to their environment.

The cell swims around,

powered by a cohort of cilia -

tiny hairs embedded in the cell membrane.

F it bumps into something,

the cilia change direction and it reverses away.

They're clearly demonstrating a sense of touch.

Even though they're single-celled organisms,

they have no central nervous system.

They can still do what all life does.

They can sense their environment and they can react to it,

and they do that using electricity.

The mechanism that powers the paramecium's touch response

lies at the heart of all sensing in animals.

And it's based on an electrical phenomenon found throughout nature.

An electric current is a flow of electric charge,

and for that to happen

you need an İmbalance between positive and negative charges.

Now, usually in nature, things are electrically neutral -

the positive and negative charges exactly balance out -

but there are natural phenomena

in which there is a separation of electric charge.

A thunderstorm, for example.

(THUNDER RUMBLING)

As thunder clouds build, up-draughts within them separate charge.

The lighter ice and water crystals become positively-charged

and are carried upwards,

while the heavier negatively-charged crystals sink to the bottom.

This can create a potential difference of voltage

between the cloud and the ground of as much as a 100 million volts.

(THUNDER RUMBLING)

Now, nature abhors a gradient.

It doesn't like an imbalance,

and it tries to correct it by having an electric current flow.

In the case of a thunderstorm, that's a bolt of lightning.

And it's the same process that göverns the paramecium's behaviour,

but on a tiny scale.

In common with virtually all other cells, and certainly all animal cells,

the paramecium maintains a potential difference across its cell membrane

and it does that, in common with the thunderstorm,

by charge separation.

By manipulating the number of positive ions

inside and outside its membrane,

the paramecium creates a potential difference

of just 40 millivolts.

So when a paramecium is just sat there,

not bumping into anything, floating in this liguid,

then it's like a little battery.

İt's maintaining the potential difference across its cell membrane,

and it can use that to sense its surroundings.

When it bumps into something, its cell membrane deforms,

opening channels that allow positive ions to flood back across the membrane.

As the potential difference falls, it sets off an electrical pulse

that triggers the cilia to start beating

in the opposite direction.

That electrical pulse spreads around the whole cell in a wave

called an action potential.

And the paramecium reverses out of trouble.

Now, this ability to precisely control flows of electric charge

across a membrane is not unigue to the paramecium.

İt actually lies at the heart of all animal senses.

In fact, every time I sense anything in the world

with my eyes, with my ears or with my fingers,

at some point between that sensation and my brain

something very similar to that will happen.

Althougğh this same electrical mechanism underpins all sensing,

every animal has a different suite of sensory capabilities

that is beautifully adapted to the environment it lives in.

This is the Big Black River,

a tributary of the mighty Mississippi in America's deep south.

And these dark and murky waters are home to a ferocious predator.

Even though it's impossible to see more than a couple of inches

through the water,

this predator has found a way to track down and catch its prey

With terrifying efficiency.

To help me catch one,

I've enlisted the support of wildlife biologist Don Jackson.

That's big.

Look at those teeth.

-So, you gonna wrestle it a bit? -İ'm wrestling now.

Let's move him over right here. SCUusi.

There you go. But he can bite.

Argh!

IT'll show you the mouth of this thing, head-on,

so you can see what the prey sees when he comes.

Anything that'll fit in that mouth, he'll grab it.

(LAUGHS)

You can hold him. If you just want to put your hands all the way under him.

Come all the way. ALI the way, hold him up close to you.

Yeah.

-How about that? -T've got him.

BRIAN: Yeah.

This is the top predator in this river.

This is a... What? ...a 2b-pound flathead catfish.

You see those protrusions from his head?

Those are barbels. They sense vibration in the mud on the riverbed.

But the most interesting thing about the catfish

is that she really is, in some ways, one big tongue.

There are taste sensors covering every...

every part of her body.

And she can build up a three-dimensional picture of the river

by detecting the chemical scents of animals.

So her eyes are not much use.

As you can see, this river's extremely muddy.

But it's the sense of taste that does the job

of building up a picture of the world, and that's how he hunts.

And he weighs a ton!

Oh, I can feel those teeth. Ow!

I'm gonna let go.

ALI right, you, go on.

There she goes. Wow.

The sensory world of the catfish is a remarkable one.

İIts map of its universe

is bullt from the thousands of chemicals it can detect in the water.

A swirling mix of tastes and concentrations, flavours and gradients.

İIt's a world we can hardiy imagine.

There's an interesting, almost philosophical point here,

because it's easy to imagine

that we humans perceive the world in some kind of objective way,

but that's not the case atall.

Think about the catfish.

The catfish sees the world as a kind of swarm of chemicals in the river

or vibrations on the riverbed,

whereas we see the world as reflected light off the forest,

and I can hear the sounds of animals out there

somewhere in the undergrowth.

The catfish sees the world completely differently.

So the way you perceive the world is determined by your environment,

and no two animals see the world in the same way.

Like every animal,

we have evolved the senses that enable us to live in our environment.

But, as well as egğuvipping us for the present,

those senses can also tell us about our past.

Now we have a sense of touch, like the paramecium,

and we have the chemical senses, taste and smell, like the catfish.

But, for us, the dominant senses are hearing and sight

and to understand them,

we first have to understand their evolutionary history.

And that's why I'm in the Mojave Desert in California,

to track down an animal

that can tell us something about the origins of our own senses.

The creature l am looking for iİs easiest to find in the dark,

using ultraviolet light.

(SHUDDERS)

(LAUGHS)

Whoa!

Man!

Do you see that? (LAUGHS)

Look at that, absolutely bizarre.

It's glowing absolutely bright green.

Nobody has any idea what evolutionary advantage that confers.

Although they now live in some of the driest

most hostile environments on Farth,

like here in the desert,

scorplons evolved as ağuatic predators

before emerging on to the land about 380 million years ago.

They've adapted to be able to survive the extreme heat,

and can go for over a year without food or water.

And despite their fearsome reputation,

9826 of scorpion species have a sting that is no worse than a bee's,

But perhaps the most fascinating thing about scorpions,

from an evolutionary perspective, is the way that they catch their prey.

You see that he spreads his legs out on the surface of the sand.

And that's because he uses his legs to detect vibrations.

Scorpions hunt insects like this beetle.

It's almost impossible to see them in the dark,

so the scorpion has evolved another way to track them down.

By adapting its sense of touch.

As the insect's feet move across the sand,

they set off tiny waves of vibration through the ground.

If just a single grain of sand is disturbed

within range of the scorpion,

it will sense it through the tips of its legs.

They can detect vibrations that are around the size of a single atom

as they sweep past.

By measuring the time delay between the waves arriving at each of its feet,

the scorpion can calculate

the precise direction and distance to its prey.

Now that ability to detect vibrations

and use them to build up a picture of our surroundings

is something that we share with scorplons.

While the scorpion has adapted its sense of touch

to detect vibrations in the ground,

we use a very similar system to detect the tiny vibrations in air

that we call sound.

And like the scorpion's, Ours is a remarkabiy sensitive system.

Our ears can hear sounds oöver a huge range.

(GUTTURAL GRUNT)

We can detect sound waves of very low freguency,

at the bass end of the spectrum.

But we can also hear much higher-pitched sounds,

sounds with freguencies hundreds or even a thousand times greater.

-(BIRDS TWITTERIİNG) -(ENGİNE ROARS)

And we can detect huge changes in sound intensity.

From the delicate buzzing created by an insect's flapping wings...

to the roar of an engine, which can be a hundred million times louder.

The story of how we developed our ability to hear

is one of the great examples of evolution in action.

Because the first animals to crawl out of the water on to the land

Would have had great difficulty hearing anything in their new environment.

These are the Everglades.

A vast area of swamps and wetlands

that has covered the southern tip of Florida for over 4,000 years.

Ihrough the creatures we find here,

like the American Alligator -

a member of the crocodile family -

we can trace the story

of how our hearing developed as We emerged on to the land.

And it starts below the water, with the fish.

If you're a fish, then hearing isn't a problem.

You live in water, and you're made of water,

so sound has no problem at all

travelling from the outside to the inside.

But when life emerged from the oceans on to the land,

then hearing became a big problem.

See, sound doesn't travel well from air into water.

Ifl make a noise now...

then over 99.996 of the sound

is reflected back off the surface of the water.

It's because of that reflection

that, underwater, you can hear very little from above the surface.

And it's exactly the same problem that our ears face,

because they too are filled with fluid.

So, if evolution hadn't found an ingenious solution

to the problem of getting sound from air into water,

then I wouldn't be able to hear anything at all.

And that solution

relies on some of the most delicate moving parts in the human body.

Have I just dropped them?

Hang on a second.

Oh, I've done it again. Bloody hell!

Idiot.

Just flipped out.

These are the smallest three bones in the human body.

They're called the malleus, the incus and the stapes,

and they sit between the eardrum and the entrance to your İnner ear,

so the place where the fluid sits.

The bones help to channel sound into the ear through two mechanisms.

First, they act as a series of levers magnifying the movements of the eardrum.

And second, because the surface area of the eardrum

is 17 times greater than the footprint of the stapes,

the vibrations are passed into the inner ear with much greater force.

And that has a dramatic effect.

Rather than 99.996 of the sound energy being reflected away,

it turns out that, with this arrangement,

6096 of the sound energy is passed from the eardrum into the inner ear.

Now, this set-up İs so intricate and so efficient,

that it almost looks as İf these bones

could only ever have been for this purpose.

But, in fact, you can see their origin

if you look way back in our evolutionary history.

In order to understand

where that collection of small bones in our ears came from,

you have to go back in our evolutionary family tree

way beyond the fish that we see today.

In fact, back around 530 million years,

to when the oceans were populated with jawless fish called agnathans.

They're similar to the modern lamprey.

Now, they didn't have a jaw,

but they had gills supported by gill arches.

Now, over a period of around 50 million years,

the most forward of those gill arches migrated forward in the head

to form jaws.

And you see fish like these, the first jawed fish,

in the fossil record around 460 million years ago.

And there, at the back of the jaw,

there is that bone, the hyomandibula, supporting the rear of the jaw.

Then, around 400 million years ago,

the first vertebrates made the journey from the sea to the land.

Their fins became legs.

But in their skull and throat, other changes were happening.

The gills were no longer needed to breathe the oxygen in the atmosphere,

and so they faded away

and became different structures in the head and throat.

And that bone, the hyomandibula, became smaller and smaller

until its function changed.

İt now was responsible for picking up vibrations in the jaw,

and transmitting them to the inner ear of the reptiles.

And that is still true today of our friends over there,

the crocodiles.

DIRECTOR: Once more, with "alligator".

But, even then, the process continued.

Around 210 million years ago the first mammals evolved.

And unlike our friends the reptiles here,

mammals have a Jjaw that's made of only one bone.

A reptile's jaw is made of several bones fused together.

So, that freed up two bones,

which moved and shrank...

and eventually became the malleus,

the incus and stapes.

So this is the origin of those three tiny bones

that are so important to mammalian hearing.

He's guite big, isn't he?

Ithink this is a most wonderful example

of the blind, undirected ingenuity of evolution.

That it's taken the bones in gills of fish

and converted them into the intricate structures inside my ears

that efficiently allow sound to be transmitted from air into fluid.

İt's a remarkable thought

that to fully understand the form and function of my ears,

you have to understand my distant evolutionary past

in the oceans of ancient Earth.

(OVER RADIO) We're hunting for a mantis shrimp.

(NARRATING) AZ/ sensing has evolved to fulfil one simple function -

to provide us with the specific information we need to survive.

(OVER RADIO) 7here he is.

I miğght try and grab him.

(NARRATING) Arıd nowhere is that clearer than in the sense of vision.

(OVER RADIO) /?'s guite tricky to catch.

(NARRATING) Almost all animals can see.

9626 of animal species have eyes.

But what those eyes see varles enormously.

So with an animal like the mantis shrimp,

you have to ask what it is about its way of life

that demands such a complex visual system.

Got to be very guick and very careful with this.

Let him out.

The complex structure of the mantis shrimp's eyes

give it incredibiy precise depth perception.

We have binocular vision.

We look with two eyes from slightly different angles,

and judge distance by comparing the differences between the two images.

Fach of the mantis shrimp's eyes has trinocular vision.

Fach eye takes three separate images of the same object.

Comparing all three gives them exceptionally precise range-finding.

And they need that information to hunt their prey.

Despite appearances,

he's a dangerous animal.

He has one of the hardest punches in nature.

Those yellow appendages you can see on the front of his body

are called raptorial appendages.

They're actually highly-evolved front legs,

and they can punch with tremendous force.

The mantis shrimp's punch

is one of the fastest movemenits in the animal world.

Slowed down by over a thousand times, we can clearly see its power.

It can release its legs with the force of a bullet.

In the wild, they use that punch to break through the shells of their prey.

But it could easily break my finger.

The need to precisely deploy this formidable weapon

is one of the reasons

the mantis shrimp has developed its complex range-finding ability.

And that punch can also help explain their sophisticated colour vision.

Because the coloured flashes on their body

warn öother mantis shrimp that they may be about to attack.

While other colour signals

have a guülrte different meaning.

And yet reading these signals in the öocean can be surprisingly difficult.

In the deep ocean, colours shift from minute to minute, from hour to hour

with changing lighting conditions, changing conditions in the ocean.

But it's thought that, even though the light guality can change tremendously,

the mantis shrimp can still identify specific colours very accurately

because of those sophisticated eyes.

The mantis shrimp's eyes are beautifully tuned to their needs.

But they're very different from our eyes.

With their thousands of lenses and complex colour vision,

they have a completely different way of viewing the world.

And yet there's strong evidence

that the mantis shrimp's eyes and ours share a common origğin.

Because, on a molecular level,

every eye in the world works in the same way.

In order to form an image of the world,

then obviously the first thing you have to do is detect light.

And I have a sample here of the molecules that do that,

that detect light in my eye.

İt's actually specifically the molecule

that's in the black and white receptor cells in my eyes, the rods.

İt's called rhodopsin.

And the moment I expose this to light, you'll see an immediate physical change.

(LAUGHING) There you go.

Did you see that? It was very guick.

İt came out very pink indeed, and it immediately went yellow.

Ihis subtle shift in colour

is caused by the rhodopsin molecule changing shape as it absorbs the light.

İn my eyes, what happens is

that change in structure triggers an electrical signal

which ultimately goes all the way to my brain,

which forms an image of the world.

It's this chemical reaction

that's responsible for all vision on the planet.

Closely-related molecules lie at the heart of every animal eye.

And that telis us that this must be a very ancient mechanism.

To find its origins, we must find a common ancestor

that links every organism that uses rhodopsin today.

We know that common ancestor must have lived

before all animals' evolutionary lines diverged.

But it may have lived at any time before then.

So what is that common ancestor?

Well, here's where we approach the cutting edge of scientific research.

The answer is that we don't know for sure.

But a clue might be found here,

in these little green blobs which are actually colonies of algae,

algae called Volvox.

We have very little in cemmon With algae.

We've been separated, in evolutionary terms,

for over a billion years.

But we do share öne surprising similarity.

These Volvox have light-sensitive celis that control their movement.

And the active ingredient of those celis is a form of rhodopsin

so similar to our own

that it's thought they may share a common origğin.

What does that mean?

Does it mean that we share a common ancestor with the algae,

and in that common ancestor the seeds of vision can be found?

To find a source that may have passed this ability to detect light

to both us and the algae,

we need to go much further back down the evolutionary tree.

To organisms like cyanobacteria.

They were amongst the first living things to evolve on the planet.

And it's thought that the original rhodopsins

may have developed in these ancient photosynthetic cells.

So, the origin of my ability to see

may have been well over a billion years ago

in an organism as seemingly simple

as a cyanobacterium.

The basic chemistry of vision may have been established for a long time,

but it's a long way from that chemical reaction

to a fully-functioning eye that can create an image of the world.

The eye is a tremendously complex piece of machinery

built from lots of interdependent parts,

and it seems very difficult to imagine

how that could have evolved in a series of small steps.

But, actually, we understand that process very well indeed.

I can show you by building an eye.

The first step in building an eye

would be to take some kind of light-sensitive pigment,

so rhodopsin, for example, and build it onto a membrane.

So, imagine this is such a membrane with the pigment cells attached.

Then immediately you have something that can detect the difference between dark

and light.

Now, the advantage of this arrangement is that it's very sensitive to light.

There's no paraphernalia in front of the retina to block light.

But the disadvantage, as you can see,

is that there's no image formed atall.

İt just allows you to tell the difference between light and dark.

But you can improve that a lot

by adding an aperture, a small hole in front of the retina.

So this is a movable aperture,

just like the sort of thing you've got in your camera.

And now you'll see

that the image gets sharper.

But the problem is that, in order to make it sharper,

you have to narrow down the aperture,

and that means that you get less and less light.

So, this eye becomes less and less sensitive.

So, there's öne more improvement that nature made,

which is to replace the pinhole, the simple aperture,

with a lens.

(CHUCKLES)

Look at that.

A beautifully sharp image.

The lens is the crowning glory of the evolution of the eye.

By bending light onto the retina it allows the aperture to be opened,

letting more liğght into the eye, and a bright, detailed image is formed.

Our eyes are called camera eyes,

because, like a camera,

they consist of a single lens

that bends the light onto the photoreceptor

to create a high-guality image of the world.

But that has a potential drawback,

because to make sense of all that information,

we need to be able to process it.

Each one of my eyes

contains over a hundred million individual photoreceptor cells.

I mean, that's about five or ten times the number

in the average digital camera.

So, if my visual system worked

by just taking a series of individual still images of the world

and transmitting all that information to my brain,

then my brain would be overwhelmed.

İt's just not practical.

So that's not what animals do.

Instead, their visual systems have evolved

to extract only the information that's necessary.

And this is wonderfully illustrated in the toad.

The toad has eyes that are structurally very similar to ours.

But much of the time it's as if itisn't seeing anything at all.

İt seems completely oblivious to its surroundings

until something, like a mealworm, takes its interest.

If you think about what's important to a toad, visually,

then it's the approach of either prey or predators.

So, the toad's visual system is optimised to detect them.

So, there, we put a worm in front of the toad...

And did you see that?

Incredibly guickly, the toad ate the worm.

As soon as the mealworm wriggles in front of the toad,

its eyes lock onto its target.

Then it strikes in a fraction of a second.

İt's an astonishingly precise reaction, but it's also a very simple one.

Because the toad is only focussing on öone property of the mealworm,

the way it moves.

These 1970s lab tests

show how a toad will try and eat anything long and thin,

but only if it moves on its side, like a worm.

And that's because the toad has nevral circuits in its retina

that only respond to length-wise motion.

F instead, the target is rotated into an upright position,

the toad doesn't respond at all.

At first sight,

the visual system of the toad seems a little bit primitive and imperfect.

And it is true that if you put a toad in a tank full of dead worms,

it'll starve to death,

because they're not moving, so it doesn't recognise them as food.

But it doesn't need to see the world in all the detail that I see İt.

What it needs to focus on is movement,

because if it can see movement, then it can survive,

because it can avoid predators and it can eat its prey.

I suppose, in a sense,

if it moves like a worm, in nature, then it's likely to be a worm.

This ability to simplify the visual world

into the most relevant bits of information

is something that every animal does.

We do it all the time.

We also have visual systems that detect motion.

Others identify edges and faces.

But extracting more information takes more processing power.

That regğuires a bigger brain.

And to see the results of this evolutionary drive

towards greater processing power,

I've come to the heart of metropolitan Florida.

You know, it may not look like it,

but underneath this flyover, Just out in the shallow water,

is one of the best places in the world

to find a particularly interesting animal.

İt's an animal that's evolved

to make the most of the information its eyes can provide.

(OVER RADIO) Well,

what we're gonna do is try and hunt for some octopus.

And it's, um, as you say in physics, non-trivial

because they've developed a beautiful way

of camouflaging themselves.

They change colour.

They have cells in their skin that change colour

to match their surroundings.

İt's an ability that we don't possess, of course.

It makes them difficult to find.

Ihere he is. Llook.

(LAUGHING)

He went flying into there and a crab and a load of fish went fiying out.

Look at his ink.

Their defence mechanism.

I don't know where he is. He's hiding somewhere in there.

Ah.

There. Look at those colours.

What a remarkable creature.

(NARRATING) Although the octopus is a mollusc, like slugs and snails,

in many ways it seems more similar to us.

(OVER RADIO) Whoa!

(NARRATING) /?'s believed to be the most intelligent invertebrate.

(OVER RADIO) It's like he's holding his fists up.

Look at that!

(NARRATING) Zfs brain contains about 500 million nerve celis,

about the same as a dog's.

(OVER RADIO) What are you doing?

You know, if you do want an example of an alien intelligence here on Farth,

that must surely be it.

(NARRATING) Arnd it's used that brain to develop some remarkable abilities.

It's become a skilled mimic.

İt can rapidiy change not only its colour,

but its shape to match the background.

Some species even do impressions of other animals.

They've become cunning predators

and adept problem-solvers.

They've even been reported to use tools.

All these skills are signs of great intelligence.

But they also rely on an acute sense of vision.

(OVER RADIO) Zook at those big eyes surveying the surroundings.

Checking us out.

Camera eyes, just like mine.

And they're vitally important

for allowing the octopus to live the lifestyle it does.

So a visual animal, in the same way that I'm a visual animal.

(NARRATING) 7/re octopus is one of the only invertebrates

to have complex camera eyes.

Like our eyes, they capture detailed images of the world.

And their brains have evolved

to be able to extract the most information from those images.

The optic lobes make up about 3026 of the octopus's brain.

The only other group that is known

to devote so much of its brain to visual processing is our group,

the primates, the most intelligent vertebrates.

(OVER RADIO) I think it's a fascinating thought

that intelligence is a result of the need to process

all the information

from those big, complex eyes.

(NARRATING) What's so compelling about the octopus's intelligence

is that it evolved completely separately to ours.

We last shared a common ancestor 600 million years ago.

An ancestor that had neither eyes nor a brain.

But we both evolved sophisticated camera eyes

and large intelligent brains.

İt suggests a tantalising link

between sensory processing and the evolution of intelligence.

Sensing has played a key role in the evolution of life on Farth.

The first organisms were able to detect and respond

to their immediate environmenkt as paramecia do today.

But as animals evolved

and their environments became more complex,

their senses evolved with them.

Developing the mechanisms to let them decode vibrations

and detect light

allowing them to build three-dimensional pictures of their environments,

and stimulating the growth of brains that could handle all that data.

But for one species,

the desire to gather more and more sensory information

has become overwhelming.

That species is us.

This is closest thing to hallowed ground

that exists in a subject that has no saints,

because that telescope is the one that Edwin Hubble used

to expand our horizons, I would argue, more than anyone else before or since.

In 1923, Edwin Hubble took this photograph

of the Andromeda Galaxy.

You can see his handwriting on the photograph.

He did it by sitting here night after night for over a week

exposing this photographic plate.

Now, at the time,

it was thought that this misty patch you see in the night sky

was jJust a cloud, maybe a gas cloud in our own galaxy.

But Hubble, because of the power of this telescope,

identified individual stars,

and, crucially, he found that it was way outside our own galaxy.

In other words, Hubble had discovered this is a distant island of stars.

We now know it's over two million light years away,

composed of a trillion suns like ours.

Hubble demonstrated that there's more to the universe than our own galaxy.

He extended the reach of our senses further than we could have imagined.

With the help of the telescope,

we could perceive and comprehend worlds billions of light years away.

There's a wonderful feedback at work here,

because the increasing amounts of data delivered by our senses

drove the evolution of our brains.

And those increasingly sophisticated brains became curious

and demanded more and more data.

And so we built telescopes

that were able to extend our senses beyond the horizon

and showed us a universe that's billions of years old

and contains trillions of stars and galaxles.

Our insatiable guest for information

is the making of us.