All language subtitles for 18CC59B71F004C868859281EDE698A7F_eng

These are the waters
off Catalina, a tiny island

20 miles off the coast
of Los Angeles, California.

These are kelp forests, and they
grow here in tremendous abundance

because the waters here around
Catalina are rich in nutrients.

That's because of
the California currents,

which brings this beautiful, rich,
cold water

up from the depths of the Pacific

and allows this tremendously rich
ecosystem to grow.

This... 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!

HE LAUGHS

Can you see that?!

Camouflaged in its burrow
on the sea floor,

the mantis shrimp is a seemingly
unremarkable creature.

It's not a real shrimp,
but a type of crustacean,

called a stomatapod.

I've come to see it
because in one way

the mantis shrimp is
truly extraordinary -

the way it detects the world.

You see these big...

eyes that they have to see.

These are some of
the most sophisticated eyes

in the natural world.

Each is made up of over
10,000 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 unique view of the ocean.

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, I 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 led
to our own curiosity

and intelligence.

ACOUSTIC GUITAR

♪ If you feel lost

♪ Lost in the world

♪ Just like me

♪ Worlds are lost in me

♪ Worlds are lost in me. ♪

These 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 I'll find
on the way

that will illuminate
the world of the senses,

and I'm going to start by going 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 sight,

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

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

It's... completely dark in this cave.

I can't see anything at all.

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

That's at a wavelength that my eyes
are completely insensitive to,

so as far as I'm concerned,
it is pitch black.

And because it's so dark...

..your other senses become
heightened, particularly hearing.

It's virtually silent in here.

But if you listen carefully...

DRIP OF WATER

..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.

As well as sight and hearing,

we have of course
a range of other senses.

There's touch,
which is 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.

And there it is.

Now that is a paramecium.

It may look like a simple animal,
but in fact

it's a member of a group
of organisms called protists.

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.

Although they appear simple,

these tiny creatures display
some remarkably 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.

If 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 animals.

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 imbalance 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.

As thunder clouds build,

updraughts 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,

a voltage between the cloud
and the ground

of as much as 100 million volts.

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
governs 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.

It does that in common with
a thunderstorm by charge separation.

By manipulating the number
of position 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 liquid,
then it's like a little battery.

It'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 membranes.

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
round the whole cell in a wave

called an action potential.

And the paramecium
reverses out of trouble.

This ability to precisely
control flows of electric charge

across a membrane is not unique
to the paramecium.

It 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,
with my fingers,

at some point between that sensation
and my brain,

something very similar
to that will happen.

Although the 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.

You go... Wrestle it.
I'll wrestle it now.

He's going over right here. Is he?

There you go.

He can bite. Argh!

I'll show you the mouth
of this thing.

Hang on... So you can see what
the prey sees when he comes.

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

You can hold him if you just want to
put your hand all the way under him.

Come all the way. All the way.
Hold him up close to you. Yeah.

How about that? I've got him. Yeah.

This is the top predator
in this river.

This is a, what?
A 25-pound flathead catfish.

You see those protrusions
from his head?

Those are barbels.

They sense a vibration in the mud,
on the river bed,

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 part of her body,

and she can build up
a 3D 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.

I can feel those teeth. Ow!

I'm going to let go.

All right, you. Go on.

The sensory world of the catfish
is a remarkable one.

Its map of its universe is built
from the thousands of chemicals

it can detect in the water.

A swirling mix of tastes
and concentrations,

flavours and gradients.

It's a world we can hardly 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 at all.

Think about the catfish.

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

in the river,
or vibrations on the river bed,

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 equipping 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 I'm looking for
is easiest to find in the dark,

using ultra-violet light.

Oh!

HE LAUGHS

Whoa!

Man! Did you see that?

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 Earth,

like here in the desert, scorpions
evolved as aquatic predators

before emerging onto 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.

Despite their fearsome reputation,

98% of scorpion species have a
sting that is no worse than a bee's.

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.

And that ability to detect
vibrations and use them

to build up a picture
of our surroundings

is something that we share
with scorpions.

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 scorpions, ours
is a remarkably sensitive system.

Our ears can hear sounds
over a huge range.

We can detect sound waves of very
low frequency

at the bass end of the spectrum.

But we can also hear
much higher-pitched sounds,

sounds with frequencies hundreds
or even a thousand times greater.

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 100 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 onto 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.

Through 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 onto 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 onto the land,

then hearing became a big problem.

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

If I make a noise now...

..over 99.9% 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 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,

called the malleus,
the incus and the stapes,

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

to 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 movement
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 99.9% of the sound
energy being reflected away,

it turns out
that with this arrangement,

60% of the sound energy is passed
from the eardrum into the inner ear.

Now, this setup
is so intricate and so efficient,

it almost looks as
if those 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 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 hyomandibular,
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 hyomandibular,
became smaller and smaller,

until its function changed.

It 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.

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 jaw
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 quite big, isn't he?

I think 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.

It'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.

We're hunting for the mantis shrimp.

'All sensing has evolved to fulfil
one simple function - to provide us

'with the specific information
we need to survive.'

There he is!

I might try and grab him.

'And nowhere is that clearer
than in the sense of vision.'

He's quite tricky to catch!

'Almost all animals can see.'

'96% of animal species have eyes.'

'But what those eyes can see
varies 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 quick
and very careful with this.

Let him out.

The complex structure of
the mantis shrimp's eyes

give it incredibly 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.

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

Each 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,

it is 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 raptoral appendages.

They're actually
highly evolved from legs,

and they can punch
with tremendous force.

The mantis shrimp's punch

is one of the fastest movements
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 other mantis shrimp

that they may be about to attack.

While other colour signals
have a quite different meaning.

Yet reading these signals in the
ocean 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 quality
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 their 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 origin.

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.

It's actually, specifically,
the molecules that's in the black

and white receptor cells in my eyes,
the rods.

It's called rhodopsin.

And the moment
I expose this to light,

you'll see an immediate
physical change.

There you go.

Did you see that? It was very quick.

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

This subtle shift in colour is
caused by the rhodopsin molecule

changing shape
as it absorbs the light.

In 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 is this chemical reaction

that's responsible
for all vision on the planet.

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

That tells 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 common with algae.

We've been separated in evolutionary
terms for over one billion years.

But we do share
one surprising similarity.

These volvox have light-sensitive
cells that control their movement.

And the active ingredient
of those cells

is a form of rhodopsin
so similar to our own

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

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 among 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 cyanobacteria.

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 need to take some kind
of light-sensitive pigment,

rhodopsin, for example,
and build it on to 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 is
no image formed at all.

It 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, we see that
the image gets sharper.

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

we 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 one more improvement
that nature made,

which is to replace the pinhole,
the simple aperture...

With a lens.

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 light 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-quality
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 100 million
individual photoreceptor cells.

That's about five or ten
times the number

in the average digital camera.

So if my visual system works

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.

It's just not practical,
so that's NOT what animals do.

Instead, their visual systems
have evolved

to extract only the information
that is 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 it isn't seeing anything at all.

It 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 pray or predators,

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

So, there, we've put a worm in front
of the toad, and did you see that?

Incredibly quickly,
the toad ate the worm.

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

its eyes lock onto the target.

Then it strikes
in a fraction of a second.

It's an astonishingly precise
reaction,

but it's also a very simple one.

Because the toad is only focusing
on one 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 neural circuits in its retina

that only respond
to lengthwise motion.

If, 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.

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 it.

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 requires 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.

It's an animal that's evolved

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

Well, what we're going to do
is find some octopus.

And it's, as you say in physics,
nontrivial.

Because they've developed
a beautiful way

of camouflaging themselves.

They change colour. Their cells
and their skin change colour

to match their surroundings.

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

It makes them difficult to find.

There he is, look.

Ha-ha!

He went flying into there,

and a crab and a load of fish
are flying out, and look at his ink.

A defence mechanism.
I don't know where he is.

He's hiding somewhere in there.

Look at those colours!

What a remarkable creature.

'Although the octopus is a mollusc,
like slugs and snails,

'in many ways,
it seems more similar to us.'

Whoa!

'It's believed to be the most
intelligent invertebrate.'

It's like he's holding his fists up.

Look at that.

'Its brain contains about
500 million nerve cells,

'about the same as a dog's.'

What are you doing?

You know, if you want an example
of an alien intelligence

here on earth..

That must surely be it.

'And it's used that brain to develop
some remarkable abilities.'

'It's become a skilled mimic.'

'It can rapidly change
not only its colour,

'but its shape,
to match the background.'

'Some species even do impressions
of other animals.'

'They 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.'

Look 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.

'The 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
30% of the octopus' 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.'

I think it's a fascinating thought

that that intelligence is a result

of the need to process
all the information

from those big, complex eyes.

'What's so compelling
about the octopus' 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've both evolved
sophisticated camera eyes,

'and large, intelligent brains.'

'It suggests a tantalising link
between sensory processing

'and the evolution of intelligence.'

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

The first organisms

were able to detect and respond
to their immediate environment,

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 the 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 just 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 galaxies.

Our insatiable quest for information
is the making of us.