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00:00:10,480 --> 00:00:14,280
These are the waters
off Catalina, a tiny island


2
00:00:14,280 --> 00:00:17,520
20 miles off the coast
of Los Angeles, California.


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00:00:22,760 --> 00:00:27,600
These are kelp forests, and they
grow here in tremendous abundance


4
00:00:27,600 --> 00:00:32,760
because the waters here around
Catalina are rich in nutrients.


5
00:00:32,760 --> 00:00:35,280
That's because of
the California currents,


6
00:00:35,280 --> 00:00:37,720
which brings this beautiful, rich,
cold water


7
00:00:37,720 --> 00:00:39,440
up from the depths of the Pacific


8
00:00:39,440 --> 00:00:44,760
and allows this tremendously rich
ecosystem to grow.


9
00:00:47,960 --> 00:00:51,640
This...remarkable place.


10
00:00:56,720 --> 00:00:58,440
Oh, look!


11
00:01:13,920 --> 00:01:18,000
But I'm not here
to marvel at these kelp forests.


12
00:01:18,000 --> 00:01:19,760
Beautiful as they are.


13
00:01:19,760 --> 00:01:25,280
I'm here to search for a little
animal that lives not in this


14
00:01:25,280 --> 00:01:30,480
forest of nutrients, but out there
in the muddy ocean floor.


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00:01:47,960 --> 00:01:49,440
There he is, look!


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00:01:49,440 --> 00:01:50,480
HE LAUGHS


17
00:01:50,480 --> 00:01:52,120
Can you see that?!


18
00:01:55,200 --> 00:01:57,800
Camouflaged in its burrow
on the sea floor,


19
00:01:57,800 --> 00:02:01,480
the mantis shrimp is a seemingly
unremarkable creature.


20
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It's not a real shrimp,
but a type of crustacean,


21
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called a stomatapod.


22
00:02:11,320 --> 00:02:14,000
I've come to see it
because in one way


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00:02:14,000 --> 00:02:17,520
the mantis shrimp is
truly extraordinary -


24
00:02:17,520 --> 00:02:19,800
the way it detects the world.


25
00:02:24,160 --> 00:02:26,280
You see these big...


26
00:02:26,280 --> 00:02:28,520
eyes that they have to see.


27
00:02:30,840 --> 00:02:33,360
These are some of
the most sophisticated eyes


28
00:02:33,360 --> 00:02:34,800
in the natural world.


29
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Each is made up of over
10,000 hexagonal lenses.


30
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And with twice as many
visual pigments as any other animal,


31
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it can see colours and wavelengths
of light that are invisible to me.


32
00:02:57,680 --> 00:02:59,360
These remarkable eyes


33
00:02:59,360 --> 00:03:03,680
give the mantis shrimp
a unique view of the ocean.


34
00:03:03,680 --> 00:03:06,840
And this is just one of the many
finely-tuned senses


35
00:03:06,840 --> 00:03:09,240
that have evolved across the planet.


36
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Sensing, the ability to detect
and to react to the world outside,


37
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is fundamental to life.


38
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Every living thing is able to
respond to its environment.


39
00:03:26,960 --> 00:03:31,000
In this film, I want to show you
how the senses developed,


40
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how the mechanisms
that gather information


41
00:03:33,760 --> 00:03:36,520
about the outside world evolved,


42
00:03:36,520 --> 00:03:39,360
how their emergence
has helped animals


43
00:03:39,360 --> 00:03:41,840
thrive in different environments,


44
00:03:41,840 --> 00:03:45,680
and how the senses
have pushed life in new directions,


45
00:03:45,680 --> 00:03:49,120
and may ultimately have led
to our own curiosity


46
00:03:49,120 --> 00:03:50,640
and intelligence.


47
00:04:06,680 --> 00:04:08,600
ACOUSTIC GUITAR


48
00:04:08,600 --> 00:04:13,920
# If you feel lost


49
00:04:15,840 --> 00:04:19,960
# Lost in the world


50
00:04:22,240 --> 00:04:27,200
# Just like me


51
00:04:29,280 --> 00:04:33,440
# Worlds are lost in me


52
00:04:36,320 --> 00:04:41,000
# Worlds are lost in me. #


53
00:04:44,240 --> 00:04:46,560
These are the woods of Kentucky,


54
00:04:46,560 --> 00:04:49,640
the first stop on a journey
across America


55
00:04:49,640 --> 00:04:52,760
that will take me from the far
west coast to the Atlantic,


56
00:04:52,760 --> 00:04:54,920
through the heart of the country.


57
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It's the animals that I'll find
on the way


58
00:05:02,080 --> 00:05:06,200
that will illuminate
the world of the senses,


59
00:05:06,200 --> 00:05:10,320
and I'm going to start by going deep
underground.


60
00:05:21,560 --> 00:05:24,800
These are
the Mammoth Caves in Kentucky.


61
00:05:24,800 --> 00:05:27,880
With over 300 miles
of mapped passages,


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they're the longest
cave system in the world.


63
00:05:42,320 --> 00:05:46,600
But this is also the place to start
exploring our own senses.


64
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We're normally
dependent on our sight,


65
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but down here in the darkness,
it's a very different world.


66
00:05:54,560 --> 00:05:59,520
I have to rely on my other senses to
build a picture of my environment.


67
00:06:01,280 --> 00:06:06,040
It's...completely dark in this cave.


68
00:06:06,040 --> 00:06:09,880
I can't see anything at all.


69
00:06:09,880 --> 00:06:13,920
You can see me because we're
lighting it with infrared light.


70
00:06:13,920 --> 00:06:17,640
That's at a wavelength that my eyes
are completely insensitive to,


71
00:06:17,640 --> 00:06:21,720
so as far as I'm concerned,
it is pitch black.


72
00:06:23,320 --> 00:06:25,920
And because it's so dark...


73
00:06:28,200 --> 00:06:32,240
..your other senses become
heightened, particularly hearing.


74
00:06:33,400 --> 00:06:36,480
It's virtually silent in here.


75
00:06:39,400 --> 00:06:41,560
But if you listen carefully...


76
00:06:41,560 --> 00:06:44,360
DRIP OF WATER


77
00:06:44,360 --> 00:06:49,400
..you can just hear the faint drop
of water from somewhere


78
00:06:49,400 --> 00:06:51,360
deep in the cave system.


79
00:06:51,360 --> 00:06:55,520
You'd never hear that
if the cave were illuminated.


80
00:06:55,520 --> 00:06:58,880
But you focus on your hearing
when it's as dark as this.


81
00:07:07,280 --> 00:07:09,360
As well as sight and hearing,


82
00:07:09,360 --> 00:07:12,360
we have of course
a range of other senses.


83
00:07:12,360 --> 00:07:15,920
There's touch,
which is a mixture of sensations -


84
00:07:15,920 --> 00:07:19,000
temperature and pressure and pain -


85
00:07:19,000 --> 00:07:21,480
and then there are chemical senses,


86
00:07:21,480 --> 00:07:23,960
so smell and taste,


87
00:07:23,960 --> 00:07:27,880
and we share those senses
with almost every living thing


88
00:07:27,880 --> 00:07:29,400
on the planet today,


89
00:07:29,400 --> 00:07:34,480
because they date back virtually
to the beginning of life on Earth.


90
00:07:47,040 --> 00:07:52,000
And even here, in water that's been
collected from deep within a cave,


91
00:07:52,000 --> 00:07:55,680
there are organisms
that are detecting and responding


92
00:07:55,680 --> 00:07:57,200
to their environment


93
00:07:57,200 --> 00:08:00,320
in the same way
that living things have been doing


94
00:08:00,320 --> 00:08:02,880
for over a billion years.


95
00:08:29,080 --> 00:08:31,280
Ah.


96
00:08:31,280 --> 00:08:33,200
And there it is.


97
00:08:33,200 --> 00:08:35,560
Now that is a paramecium.


98
00:08:35,560 --> 00:08:39,480
It may look like a simple animal,
but in fact


99
00:08:39,480 --> 00:08:42,800
it's a member of a group
of organisms called protists.


100
00:08:42,800 --> 00:08:46,400
You'd have to go back around
two billion years


101
00:08:46,400 --> 00:08:51,320
to find a common ancestor between me
and a paramecium.


102
00:08:55,200 --> 00:08:59,760
Paramecia have probably changed
little in the last billion years.


103
00:09:02,040 --> 00:09:04,360
Although they appear simple,


104
00:09:04,360 --> 00:09:09,000
these tiny creatures display
some remarkably complex behaviour.


105
00:09:11,840 --> 00:09:15,800
You can even see them
responding to their environment.


106
00:09:15,800 --> 00:09:20,320
The cell swims around,
powered by a cohort of cilia,


107
00:09:20,320 --> 00:09:23,720
tiny hairs
embedded in the cell membrane.


108
00:09:28,200 --> 00:09:32,160
If it bumps into something,
the cilia change direction


109
00:09:32,160 --> 00:09:34,000
and it reverses away.


110
00:09:36,840 --> 00:09:40,520
They're clearly demonstrating
a sense of touch.


111
00:09:43,840 --> 00:09:47,560
Even though
they're single-celled organisms,


112
00:09:47,560 --> 00:09:50,280
they have no central nervous system,


113
00:09:50,280 --> 00:09:53,920
they can still do
what all life does.


114
00:09:53,920 --> 00:09:57,920
They can sense their environment
and they can react to it,


115
00:09:57,920 --> 00:10:00,800
and they do that using electricity.


116
00:10:09,320 --> 00:10:13,400
The mechanism that powers
the paramecium's touch response


117
00:10:13,400 --> 00:10:17,720
lies at the heart of all
sensing animals.


118
00:10:17,720 --> 00:10:21,720
It's based on an electrical
phenomenon found throughout nature.


119
00:10:24,640 --> 00:10:28,200
An electric current
is a flow of electric charge,


120
00:10:28,200 --> 00:10:31,280
and for that to happen,
you need an imbalance between


121
00:10:31,280 --> 00:10:33,320
positive and negative charges.


122
00:10:33,320 --> 00:10:37,160
Now, usually in nature,
things are electrically neutral,


123
00:10:37,160 --> 00:10:41,360
the positive and negative charges
exactly balance out,


124
00:10:41,360 --> 00:10:46,080
but there are natural phenomena in
which there is a separation


125
00:10:46,080 --> 00:10:50,000
of electric charge.
A thunderstorm, for example.


126
00:10:51,800 --> 00:10:54,240
As thunder clouds build,


127
00:10:54,240 --> 00:10:57,640
updraughts within them
separate charge.


128
00:10:57,640 --> 00:11:01,160
The lighter ice and water crystals
become positively charged


129
00:11:01,160 --> 00:11:02,520
and are carried upwards,


130
00:11:02,520 --> 00:11:07,240
while the heavier, negatively
charged crystals sink to the bottom.


131
00:11:08,880 --> 00:11:11,520
This can create
a potential difference,


132
00:11:11,520 --> 00:11:14,480
a voltage between the cloud
and the ground


133
00:11:14,480 --> 00:11:17,160
of as much as 100 million volts.


134
00:11:20,200 --> 00:11:24,960
Now, nature abhors a gradient.
It doesn't like an imbalance,


135
00:11:24,960 --> 00:11:29,560
and it tries to correct it
by having an electric current flow.


136
00:11:29,560 --> 00:11:32,920
In the case of a thunderstorm,
that's a bolt of lightning.


137
00:11:52,040 --> 00:11:56,440
And it's the same process that
governs the paramecium's behaviour,


138
00:11:56,440 --> 00:11:59,840
but on a tiny scale.


139
00:11:59,840 --> 00:12:02,480
In common
with virtually all other cells,


140
00:12:02,480 --> 00:12:04,400
and certainly all animal cells,


141
00:12:04,400 --> 00:12:08,200
the paramecium maintains
a potential difference


142
00:12:08,200 --> 00:12:10,040
across its cell membrane.


143
00:12:10,040 --> 00:12:14,840
It does that in common with
a thunderstorm by charge separation.


144
00:12:16,120 --> 00:12:19,200
By manipulating the number
of position ions


145
00:12:19,200 --> 00:12:23,240
inside and outside its membrane,
the paramecium creates


146
00:12:23,240 --> 00:12:27,000
a potential difference of just
40 millivolts.


147
00:12:28,600 --> 00:12:33,280
So when a paramecium is just sat
there, not bumping into anything,


148
00:12:33,280 --> 00:12:37,040
floating in this liquid,
then it's like a little battery.


149
00:12:37,040 --> 00:12:41,440
It's maintaining the potential
difference across its cell membrane,


150
00:12:41,440 --> 00:12:45,120
and it can use that
to sense its surroundings.


151
00:12:46,920 --> 00:12:50,880
When it bumps into something,
its cell membrane deforms,


152
00:12:50,880 --> 00:12:55,040
opening channels that allow
positive ions to flood back


153
00:12:55,040 --> 00:12:56,560
across the membranes.


154
00:12:57,560 --> 00:12:59,800
As the potential difference falls,


155
00:12:59,800 --> 00:13:03,000
it sets off an electrical pulse
that triggers


156
00:13:03,000 --> 00:13:06,080
the cilia to start
beating in the opposite direction.


157
00:13:08,720 --> 00:13:13,320
That electrical pulse spreads
round the whole cell in a wave


158
00:13:13,320 --> 00:13:15,720
called an action potential.


159
00:13:16,800 --> 00:13:20,000
And the paramecium
reverses out of trouble.


160
00:13:22,400 --> 00:13:27,480
This ability to precisely
control flows of electric charge


161
00:13:27,480 --> 00:13:32,360
across a membrane is not unique
to the paramecium.


162
00:13:32,360 --> 00:13:36,480
It actually lies at the heart of all
animal senses.


163
00:13:36,480 --> 00:13:40,080
In fact, every time I sense
anything in the world,


164
00:13:40,080 --> 00:13:43,040
with my eyes, with my ears,
with my fingers,


165
00:13:43,040 --> 00:13:47,480
at some point between that sensation
and my brain,


166
00:13:47,480 --> 00:13:50,920
something very similar
to that will happen.


167
00:14:02,080 --> 00:14:06,720
Although the same electrical
mechanism underpins all sensing,


168
00:14:06,720 --> 00:14:11,400
every animal has a different
suite of sensory capabilities


169
00:14:11,400 --> 00:14:15,240
that is beautifully adapted to
the environment it lives in.


170
00:14:22,560 --> 00:14:24,800
This is the Big Black River,


171
00:14:24,800 --> 00:14:28,840
a tributary of the mighty
Mississippi in America's deep south.


172
00:14:33,640 --> 00:14:39,320
And these dark and murky waters
are home to a ferocious predator.


173
00:14:43,400 --> 00:14:46,760
Even though it's impossible to see
more than a couple of inches


174
00:14:46,760 --> 00:14:48,200
through the water,


175
00:14:48,200 --> 00:14:52,160
this predator has found a way to
track down and catch its prey


176
00:14:52,160 --> 00:14:54,040
with terrifying efficiency.


177
00:15:16,000 --> 00:15:17,360
To help me catch one,


178
00:15:17,360 --> 00:15:21,800
I've enlisted the support of
wildlife biologist Don Jackson.


179
00:15:41,480 --> 00:15:45,720
You go... Wrestle it.
I'll wrestle it now.


180
00:15:47,800 --> 00:15:50,720
He's going over right here. Is he?


181
00:15:57,760 --> 00:15:59,920
There you go.


182
00:15:59,920 --> 00:16:03,520
He can bite. Argh!


183
00:16:03,520 --> 00:16:06,720
I'll show you the mouth
of this thing.


184
00:16:06,720 --> 00:16:11,960
Hang on... So you can see what
the prey sees when he comes.


185
00:16:11,960 --> 00:16:15,160
Anything that'll fit in that mouth,
he'll grab it!


186
00:16:15,160 --> 00:16:19,200
You can hold him if you just want to
put your hand all the way under him.


187
00:16:19,200 --> 00:16:22,960
Come all the way. All the way.
Hold him up close to you. Yeah.


188
00:16:24,840 --> 00:16:27,680
How about that? I've got him. Yeah.


189
00:16:30,040 --> 00:16:32,320
This is the top predator
in this river.


190
00:16:32,320 --> 00:16:37,680
This is a, what?
A 25-pound flathead catfish.


191
00:16:37,680 --> 00:16:40,640
You see those protrusions
from his head?


192
00:16:40,640 --> 00:16:42,240
Those are barbels.


193
00:16:42,240 --> 00:16:45,680
They sense a vibration in the mud,
on the river bed,


194
00:16:45,680 --> 00:16:48,760
but the most interesting thing
about the catfish


195
00:16:48,760 --> 00:16:52,560
is that she really is,
in some ways, one big tongue.


196
00:16:52,560 --> 00:16:57,000
There are taste sensors
covering every part of her body,


197
00:16:57,000 --> 00:17:00,320
and she can build up
a 3D picture of the river


198
00:17:00,320 --> 00:17:04,520
by detecting
the chemical scents of animals.


199
00:17:04,520 --> 00:17:06,120
So, her eyes are not much use.


200
00:17:06,120 --> 00:17:08,640
As you can see,
this river's extremely muddy,


201
00:17:08,640 --> 00:17:11,200
but it's the sense of taste
that does the job of


202
00:17:11,200 --> 00:17:13,720
building up a picture of the world,


203
00:17:13,720 --> 00:17:16,200
and that's how he hunts,
and he weighs a ton.


204
00:17:21,960 --> 00:17:25,280
I can feel those teeth. Ow!


205
00:17:25,280 --> 00:17:27,280
I'm going to let go.


206
00:17:27,280 --> 00:17:29,160
All right, you. Go on.


207
00:17:35,120 --> 00:17:38,320
The sensory world of the catfish
is a remarkable one.


208
00:17:39,680 --> 00:17:43,440
Its map of its universe is built
from the thousands of chemicals


209
00:17:43,440 --> 00:17:44,960
it can detect in the water.


210
00:17:46,200 --> 00:17:50,040
A swirling mix of tastes
and concentrations,


211
00:17:50,040 --> 00:17:53,320
flavours and gradients.


212
00:17:53,320 --> 00:17:55,960
It's a world we can hardly imagine.


213
00:18:00,560 --> 00:18:03,720
There's an interesting almost
philosophical point here


214
00:18:03,720 --> 00:18:07,400
because it's easy to imagine that we
humans perceive the world


215
00:18:07,400 --> 00:18:11,320
in some kind of objective way,
but that's not the case at all.


216
00:18:11,320 --> 00:18:12,760
Think about the catfish.


217
00:18:12,760 --> 00:18:16,720
The catfish sees the world
as a kind of swarm of chemicals


218
00:18:16,720 --> 00:18:19,360
in the river,
or vibrations on the river bed,


219
00:18:19,360 --> 00:18:23,680
whereas we see the world
as reflected light off the forest,


220
00:18:23,680 --> 00:18:26,560
and I can hear the sounds of animals
out there


221
00:18:26,560 --> 00:18:28,440
somewhere in the undergrowth.


222
00:18:28,440 --> 00:18:31,720
The catfish sees the world
completely differently.


223
00:18:31,720 --> 00:18:35,280
So the way you perceive
the world is determined by


224
00:18:35,280 --> 00:18:37,160
your environment,


225
00:18:37,160 --> 00:18:41,240
and no two animals see
the world in the same way.


226
00:18:52,880 --> 00:18:57,880
Like every animal, we have evolved
the senses that enable us to live


227
00:18:57,880 --> 00:18:59,280
in our environment.


228
00:19:05,360 --> 00:19:08,000
But as well as equipping us
for the present,


229
00:19:08,000 --> 00:19:11,320
those senses can also tell us
about our past.


230
00:19:17,960 --> 00:19:21,440
Now we have a sense of touch
like the paramecium,


231
00:19:21,440 --> 00:19:24,800
and we have the chemical senses,
taste and smell,


232
00:19:24,800 --> 00:19:29,240
like the catfish, but for us,
the dominant senses


233
00:19:29,240 --> 00:19:31,560
are hearing and sight,


234
00:19:31,560 --> 00:19:33,360
and to understand them,


235
00:19:33,360 --> 00:19:36,880
we first have to understand
their evolutionary history.


236
00:19:49,560 --> 00:19:53,360
And that's why I'm
in the Mojave Desert in California,


237
00:19:53,360 --> 00:19:56,640
to track down an animal
that can tell us something


238
00:19:56,640 --> 00:19:59,560
about the origins of our own senses.


239
00:20:11,040 --> 00:20:14,440
The creature I'm looking for
is easiest to find in the dark,


240
00:20:14,440 --> 00:20:17,120
using ultra-violet light.


241
00:20:26,960 --> 00:20:28,400
Oh!


242
00:20:28,400 --> 00:20:29,720
HE LAUGHS


243
00:20:29,720 --> 00:20:32,600
Whoa!


244
00:20:32,600 --> 00:20:35,280
Man! Did you see that?


245
00:20:38,960 --> 00:20:41,440
Look at that. Absolutely bizarre.


246
00:20:41,440 --> 00:20:44,160
It's glowing absolutely
bright green.


247
00:20:44,160 --> 00:20:48,200
Nobody has any idea what
evolutionary advantage


248
00:20:48,200 --> 00:20:49,520
that confers.


249
00:20:51,680 --> 00:20:54,720
Although they now live in some
of the driest,


250
00:20:54,720 --> 00:20:57,320
most hostile environments on Earth,


251
00:20:57,320 --> 00:21:02,520
like here in the desert, scorpions
evolved as aquatic predators


252
00:21:02,520 --> 00:21:06,600
before emerging onto the land
about 380 million years ago.


253
00:21:09,280 --> 00:21:13,280
They've adapted to be able
to survive the extreme heat,


254
00:21:13,280 --> 00:21:16,680
and can go for over a year
without food or water.


255
00:21:18,880 --> 00:21:21,280
Despite their fearsome reputation,


256
00:21:21,280 --> 00:21:26,960
98% of scorpion species have a
sting that is no worse than a bee's.


257
00:21:29,760 --> 00:21:32,760
Perhaps the most fascinating
thing about scorpions


258
00:21:32,760 --> 00:21:34,800
from an evolutionary perspective


259
00:21:34,800 --> 00:21:37,920
is the way
that they catch their prey.


260
00:21:37,920 --> 00:21:43,080
You see that he spreads his legs
out on the surface of the sand.


261
00:21:43,080 --> 00:21:47,840
And that's because he uses his legs
to detect vibrations.


262
00:21:52,880 --> 00:21:57,480
Scorpions hunt insects
like this beetle.


263
00:21:57,480 --> 00:22:00,480
It's almost impossible to see them
in the dark,


264
00:22:00,480 --> 00:22:04,720
so the scorpion has evolved
another way to track them down,


265
00:22:04,720 --> 00:22:07,600
by adapting its sense of touch.


266
00:22:12,120 --> 00:22:15,360
As the insect's feet
move across the sand,


267
00:22:15,360 --> 00:22:19,680
they set off tiny waves of vibration
through the ground.


268
00:22:20,680 --> 00:22:24,000
If just a single grain of sand
is disturbed


269
00:22:24,000 --> 00:22:25,880
within range of the scorpion,


270
00:22:25,880 --> 00:22:30,800
it will sense it through
the tips of its legs.


271
00:22:32,240 --> 00:22:38,080
They can detect vibrations that
are around the size of a single atom


272
00:22:38,080 --> 00:22:40,320
as they sweep past.


273
00:22:47,120 --> 00:22:49,200
By measuring the time delay,


274
00:22:49,200 --> 00:22:52,240
between the waves
arriving at each of its feet,


275
00:22:52,240 --> 00:22:56,320
the scorpion can calculate
the precise direction


276
00:22:56,320 --> 00:22:58,400
and distance to its prey.


277
00:23:39,080 --> 00:23:43,000
And that ability to detect
vibrations and use them


278
00:23:43,000 --> 00:23:45,560
to build up a picture
of our surroundings


279
00:23:45,560 --> 00:23:49,640
is something that we share
with scorpions.


280
00:23:53,720 --> 00:23:56,760
While the scorpion has
adapted its sense of touch


281
00:23:56,760 --> 00:24:00,200
to detect vibrations in the ground,


282
00:24:00,200 --> 00:24:04,600
we use a very similar system to
detect the tiny vibrations in air


283
00:24:04,600 --> 00:24:07,120
that we call sound.


284
00:24:08,280 --> 00:24:12,480
And like the scorpions, ours
is a remarkably sensitive system.


285
00:24:14,680 --> 00:24:17,840
Our ears can hear sounds
over a huge range.


286
00:24:22,400 --> 00:24:25,800
We can detect sound waves of very
low frequency


287
00:24:25,800 --> 00:24:28,120
at the bass end of the spectrum.


288
00:24:31,880 --> 00:24:35,600
But we can also hear
much higher-pitched sounds,


289
00:24:35,600 --> 00:24:39,840
sounds with frequencies hundreds
or even a thousand times greater.


290
00:24:43,160 --> 00:24:47,200
And we can detect
huge changes in sound intensity...


291
00:24:50,720 --> 00:24:55,760
..from the delicate buzzing created
by an insect's flapping wings...


292
00:24:59,680 --> 00:25:04,400
..to the roar of an engine, which
can be 100 million times louder.


293
00:25:13,280 --> 00:25:16,880
The story of how
we developed our ability to hear


294
00:25:16,880 --> 00:25:20,560
is one of the great examples
of evolution in action...


295
00:25:22,120 --> 00:25:25,720
..because the first animals to
crawl out of the water onto the land


296
00:25:25,720 --> 00:25:28,760
would have had great difficulty
hearing anything


297
00:25:28,760 --> 00:25:31,040
in their new environment.


298
00:25:39,080 --> 00:25:41,160
These are the Everglades.


299
00:25:45,080 --> 00:25:49,920
A vast area of swamps and wetlands
that has covered the southern tip


300
00:25:49,920 --> 00:25:52,880
of Florida for over 4,000 years.


301
00:26:07,120 --> 00:26:10,000
Through the creatures we find here,


302
00:26:10,000 --> 00:26:14,480
like the American alligator,
a member of the crocodile family,


303
00:26:14,480 --> 00:26:18,200
we can trace the story of how
our hearing developed


304
00:26:18,200 --> 00:26:20,240
as we emerged onto the land.


305
00:26:25,720 --> 00:26:29,840
And it starts below the water,
with the fish.


306
00:26:31,360 --> 00:26:34,600
If you're a fish,
then hearing isn't a problem.


307
00:26:34,600 --> 00:26:37,120
You live in water
and you're made of water,


308
00:26:37,120 --> 00:26:40,400
so sound has no problem at all
travelling from the outside


309
00:26:40,400 --> 00:26:41,960
to the inside,


310
00:26:41,960 --> 00:26:46,440
but when life emerged
from the oceans onto the land,


311
00:26:46,440 --> 00:26:49,760
then hearing became a big problem.


312
00:26:49,760 --> 00:26:53,960
See, sound doesn't travel
well from air into water.


313
00:26:53,960 --> 00:26:55,840
If I make a noise now...


314
00:26:56,960 --> 00:26:59,120
..over 99.9% of the sound


315
00:26:59,120 --> 00:27:03,280
is reflected back off the surface
of the water.


316
00:27:04,680 --> 00:27:07,600
It's because of that reflection
that underwater


317
00:27:07,600 --> 00:27:11,000
you can hear
very little from above the surface.


318
00:27:11,000 --> 00:27:14,800
And it's exactly the same
problem our ears face,


319
00:27:14,800 --> 00:27:17,320
because they too are filled
with fluid.


320
00:27:19,200 --> 00:27:24,000
So, if evolution hadn't found
an ingenious solution to the problem


321
00:27:24,000 --> 00:27:27,520
of getting sound from air
into water,


322
00:27:27,520 --> 00:27:30,200
then I wouldn't be able to hear
anything at all.


323
00:27:33,200 --> 00:27:37,040
And that solution relies on some
of the most delicate moving parts


324
00:27:37,040 --> 00:27:39,080
in the human body.


325
00:27:41,040 --> 00:27:44,720
Have I just dropped them?
Hang on a second.


326
00:27:44,720 --> 00:27:49,520
Oh, I've done it again!
Bloody hell! Idiot!


327
00:27:49,520 --> 00:27:51,120
Just flipped out!


328
00:27:54,920 --> 00:27:58,760
These are the smallest
three bones in the human body,


329
00:27:58,760 --> 00:28:02,120
called the malleus,
the incus and the stapes,


330
00:28:02,120 --> 00:28:08,480
and they sit between the eardrum
and the entrance to your inner ear,


331
00:28:08,480 --> 00:28:12,440
to the place where the fluid sits.


332
00:28:12,440 --> 00:28:17,040
The bones help to channel sound
into the ear through two mechanisms.


333
00:28:19,400 --> 00:28:22,960
First,
they act as a series of levers,


334
00:28:22,960 --> 00:28:26,480
magnifying the movement
of the eardrum.


335
00:28:29,200 --> 00:28:33,400
And second, because the surface
area of the eardrum is 17 times


336
00:28:33,400 --> 00:28:36,280
greater than
the footprint of the stapes,


337
00:28:36,280 --> 00:28:39,280
the vibrations are passed
into the inner ear


338
00:28:39,280 --> 00:28:41,840
with much greater force.


339
00:28:41,840 --> 00:28:45,120
And that has a dramatic effect.


340
00:28:45,120 --> 00:28:50,440
Rather than 99.9% of the sound
energy being reflected away,


341
00:28:50,440 --> 00:28:53,160
it turns out
that with this arrangement,


342
00:28:53,160 --> 00:28:59,280
60% of the sound energy is passed
from the eardrum into the inner ear.


343
00:29:01,120 --> 00:29:04,520
Now, this setup
is so intricate and so efficient,


344
00:29:04,520 --> 00:29:07,880
it almost looks as
if those bones could only ever


345
00:29:07,880 --> 00:29:10,560
have been for this purpose,


346
00:29:10,560 --> 00:29:14,680
but in fact,
you can see their origin if you look


347
00:29:14,680 --> 00:29:17,320
way back
in our evolutionary history.


348
00:29:24,880 --> 00:29:28,720
In order to understand where
that collection of small bones


349
00:29:28,720 --> 00:29:30,760
in our ears came from,


350
00:29:30,760 --> 00:29:33,720
you have to go back
in our evolutionary family tree


351
00:29:33,720 --> 00:29:36,600
way beyond the fish
that we see today.


352
00:29:36,600 --> 00:29:39,840
In fact,
back around 530 million years


353
00:29:39,840 --> 00:29:44,880
to when the oceans were populated
with jawless fish, called agnathans.


354
00:29:44,880 --> 00:29:47,200
They're similar
to the modern lamprey.


355
00:29:47,200 --> 00:29:49,800
Now, they didn't have a jaw,


356
00:29:49,800 --> 00:29:54,000
but they had gills supported
by gill arches.


357
00:29:55,240 --> 00:30:00,800
Now, over a period of 50 million
years, the most forward of those


358
00:30:00,800 --> 00:30:07,680
gill arches migrated forward
in the head to form jaws.


359
00:30:09,400 --> 00:30:11,560
And you see fish like these,


360
00:30:11,560 --> 00:30:14,240
the first jawed fish
in the fossil record,


361
00:30:14,240 --> 00:30:16,480
around 460 million years ago.


362
00:30:16,480 --> 00:30:21,280
And, there, at the back of the jaw,
there is that bone,


363
00:30:21,280 --> 00:30:25,120
the hyomandibular,
supporting the rear of the jaw.


364
00:30:26,360 --> 00:30:30,040
Then, around 400 million years ago,
the first vertebrates


365
00:30:30,040 --> 00:30:33,080
made the journey
from the sea to the land.


366
00:30:33,080 --> 00:30:34,960
Their fins became legs,


367
00:30:34,960 --> 00:30:39,600
but in their skull and throat,
other changes were happening.


368
00:30:39,600 --> 00:30:42,240
The gills were no longer needed


369
00:30:42,240 --> 00:30:45,120
to breathe the oxygen
in the atmosphere,


370
00:30:45,120 --> 00:30:47,000
and so they faded away


371
00:30:47,000 --> 00:30:51,000
and became different structures
in the head and throat,


372
00:30:51,000 --> 00:30:57,120
and that bone, the hyomandibular,
became smaller and smaller,


373
00:30:57,120 --> 00:31:00,880
until its function changed.


374
00:31:00,880 --> 00:31:05,720
It now was responsible for
picking up vibrations in the jaw


375
00:31:05,720 --> 00:31:09,720
and transmitting them to
the inner ear of the reptiles.


376
00:31:09,720 --> 00:31:16,400
And that is still true today
of our friends over there...


377
00:31:17,960 --> 00:31:19,800
the crocodiles.


378
00:31:25,240 --> 00:31:27,120
Once more with alligator.


379
00:31:30,560 --> 00:31:33,360
But even then,
the process continued.


380
00:31:34,760 --> 00:31:39,800
Around 210 million years ago,
the first mammals evolved,


381
00:31:39,800 --> 00:31:43,760
and unlike our friends,
the reptiles here,


382
00:31:43,760 --> 00:31:47,840
mammals have a jaw
that's made of only one bone.


383
00:31:47,840 --> 00:31:52,640
A reptile's jaw is made of
several bones fused together,


384
00:31:52,640 --> 00:31:56,640
so that freed up two bones,


385
00:31:56,640 --> 00:31:58,640
which moved,


386
00:31:58,640 --> 00:32:01,280
and shrank,


387
00:32:01,280 --> 00:32:05,720
and eventually became the malleus,


388
00:32:05,720 --> 00:32:09,800
the incus and stapes.


389
00:32:09,800 --> 00:32:12,760
So this is the origin of
those three tiny bones


390
00:32:12,760 --> 00:32:16,160
that are so important
to mammalian hearing.


391
00:32:21,520 --> 00:32:22,840
He's quite big, isn't he?


392
00:32:52,240 --> 00:32:55,160
I think this is a most wonderful
example of the blind,


393
00:32:55,160 --> 00:32:58,680
undirected ingenuity of evolution,


394
00:32:58,680 --> 00:33:02,160
that it's taken the bones
in gills of fish


395
00:33:02,160 --> 00:33:06,880
and converted them into the
intricate structures inside my ears


396
00:33:06,880 --> 00:33:12,520
that efficiently allow sound to be
transmitted from air into fluid.


397
00:33:12,520 --> 00:33:14,120
It's a remarkable thought


398
00:33:14,120 --> 00:33:17,640
that to fully understand
the form and function of my ears,


399
00:33:17,640 --> 00:33:22,080
you have to understand
my distant evolutionary past


400
00:33:22,080 --> 00:33:24,560
in the oceans of ancient earth.


401
00:33:42,120 --> 00:33:44,480
We're hunting for the mantis shrimp.


402
00:33:46,040 --> 00:33:50,840
'All sensing has evolved to fulfil
one simple function - to provide us


403
00:33:50,840 --> 00:33:54,880
'with the specific information
we need to survive.'


404
00:33:54,880 --> 00:33:56,640
There he is!


405
00:33:59,960 --> 00:34:02,560
I might try and grab him.


406
00:34:02,560 --> 00:34:06,640
'And nowhere is that clearer
than in the sense of vision.'


407
00:34:10,120 --> 00:34:12,680
He's quite tricky to catch!


408
00:34:14,160 --> 00:34:16,000
'Almost all animals can see.'


409
00:34:17,400 --> 00:34:20,360
'96% of animal species have eyes.'


410
00:34:22,040 --> 00:34:25,160
'But what those eyes can see
varies enormously.'


411
00:34:27,400 --> 00:34:31,400
'So with an animal like the mantis
shrimp, you have to ask what it is


412
00:34:31,400 --> 00:34:36,320
'about its way of life that demands
such a complex visual system.'


413
00:34:42,360 --> 00:34:46,960
Got to be very quick
and very careful with this.


414
00:34:46,960 --> 00:34:48,200
Let him out.


415
00:34:51,520 --> 00:34:54,760
The complex structure of
the mantis shrimp's eyes


416
00:34:54,760 --> 00:34:57,800
give it incredibly precise
depth perception.


417
00:34:59,960 --> 00:35:02,400
We have binocular vision.


418
00:35:02,400 --> 00:35:05,440
We look with two eyes from
slightly different angles,


419
00:35:05,440 --> 00:35:09,960
and judge distance by comparing the
differences between the two images.


420
00:35:11,640 --> 00:35:15,520
Each of the mantis shrimp's eyes
has trinocular vision.


421
00:35:17,920 --> 00:35:21,160
Each eye takes three separate images
of the same object.


422
00:35:22,240 --> 00:35:27,720
Comparing all three gives them
exceptionally precise range-finding,


423
00:35:27,720 --> 00:35:31,000
and they need that information
to hunt their prey.


424
00:35:35,120 --> 00:35:37,280
Despite appearances,


425
00:35:37,280 --> 00:35:43,440
it is a dangerous animal. He has one
of the hardest punches in nature.


426
00:35:43,440 --> 00:35:46,240
Those yellow appendages you can see
on the front of his body


427
00:35:46,240 --> 00:35:48,320
are called raptoral appendages.


428
00:35:48,320 --> 00:35:50,920
They're actually
highly evolved from legs,


429
00:35:50,920 --> 00:35:54,440
and they can punch
with tremendous force.


430
00:35:57,760 --> 00:35:59,240
The mantis shrimp's punch


431
00:35:59,240 --> 00:36:01,960
is one of the fastest movements
in the animal world.


432
00:36:05,120 --> 00:36:09,840
Slowed down by over a thousand
times, we can clearly see its power.


433
00:36:11,960 --> 00:36:14,760
It can release its legs
with the force of a bullet.


434
00:36:17,880 --> 00:36:19,160
In the wild,


435
00:36:19,160 --> 00:36:23,560
they use that punch to break through
the shells of their prey.


436
00:36:23,560 --> 00:36:25,640
But it could easily break my finger.


437
00:36:28,240 --> 00:36:31,800
The need to precisely deploy
this formidable weapon


438
00:36:31,800 --> 00:36:34,520
is one of the reasons
the mantis shrimp has developed


439
00:36:34,520 --> 00:36:36,720
its complex range-finding ability.


440
00:36:42,880 --> 00:36:47,040
And that punch can also help explain
their sophisticated colour vision.


441
00:36:48,720 --> 00:36:52,520
Because the coloured flashes on
their body warn other mantis shrimp


442
00:36:52,520 --> 00:36:54,360
that they may be about to attack.


443
00:36:55,720 --> 00:36:58,720
While other colour signals
have a quite different meaning.


444
00:37:01,200 --> 00:37:05,320
Yet reading these signals in the
ocean can be surprisingly difficult.


445
00:37:07,960 --> 00:37:11,760
In the deep ocean,
colours shift from minute to minute,


446
00:37:11,760 --> 00:37:14,440
from hour to hour,
with changing lighting conditions,


447
00:37:14,440 --> 00:37:16,320
changing conditions in the ocean,


448
00:37:16,320 --> 00:37:17,600
but it's thought that


449
00:37:17,600 --> 00:37:20,880
even though the light quality
can change tremendously,


450
00:37:20,880 --> 00:37:25,600
the mantis shrimp can still identify
specific colours very accurately,


451
00:37:25,600 --> 00:37:28,120
because of those sophisticated eyes.


452
00:37:32,760 --> 00:37:36,960
The mantis shrimp's eyes are
beautifully tuned to their needs.


453
00:37:36,960 --> 00:37:40,240
But they're very different
from our eyes.


454
00:37:40,240 --> 00:37:43,480
With their thousands of lenses
and their complex colour vision,


455
00:37:43,480 --> 00:37:46,600
they have a completely different
way of viewing the world.


456
00:37:48,440 --> 00:37:51,960
And yet there's strong evidence
that the mantis shrimp's eyes


457
00:37:51,960 --> 00:37:54,120
and ours share a common origin.


458
00:37:57,720 --> 00:37:59,720
Because on a molecular level,


459
00:37:59,720 --> 00:38:02,800
every eye in the world
works in the same way.


460
00:38:16,360 --> 00:38:18,440
In order to form
an image of the world,


461
00:38:18,440 --> 00:38:22,160
then obviously the first thing
you have to do is detect light,


462
00:38:22,160 --> 00:38:28,640
and I have a sample here
of the molecules that do that,


463
00:38:28,640 --> 00:38:31,320
that detect light in my eye.


464
00:38:31,320 --> 00:38:34,160
It's actually, specifically,
the molecules that's in the black


465
00:38:34,160 --> 00:38:38,280
and white receptor cells in my eyes,
the rods.


466
00:38:38,280 --> 00:38:40,800
It's called rhodopsin.


467
00:38:40,800 --> 00:38:43,120
And the moment
I expose this to light,


468
00:38:43,120 --> 00:38:46,400
you'll see an immediate
physical change.


469
00:38:50,480 --> 00:38:52,040
There you go.


470
00:38:52,040 --> 00:38:54,520
Did you see that? It was very quick.


471
00:38:54,520 --> 00:38:58,680
It came out very pink indeed,
and it immediately went yellow.


472
00:38:58,680 --> 00:39:02,840
This subtle shift in colour is
caused by the rhodopsin molecule


473
00:39:02,840 --> 00:39:05,480
changing shape
as it absorbs the light.


474
00:39:06,480 --> 00:39:08,320
In my eyes, what happens is


475
00:39:08,320 --> 00:39:12,200
that change in structure triggers
an electrical signal


476
00:39:12,200 --> 00:39:15,160
which ultimately goes all the way
to my brain,


477
00:39:15,160 --> 00:39:17,360
which forms an image of the world.


478
00:39:20,400 --> 00:39:21,840
It is this chemical reaction


479
00:39:21,840 --> 00:39:24,600
that's responsible
for all vision on the planet.


480
00:39:27,920 --> 00:39:32,160
Closely related molecules lie
at the heart of every animal eye.


481
00:39:33,880 --> 00:39:37,320
That tells us that this must be
a very ancient mechanism.


482
00:39:42,200 --> 00:39:46,240
To find its origins,
we must find a common ancestor


483
00:39:46,240 --> 00:39:49,480
that links every organism
that uses rhodopsin today.


484
00:39:50,760 --> 00:39:52,960
We know that common ancestor
must have lived


485
00:39:52,960 --> 00:39:56,440
before all animals'
evolutionary lines diverged.


486
00:39:58,240 --> 00:40:00,640
But it may have lived
at any time before then.


487
00:40:03,880 --> 00:40:06,400
So what is that common ancestor?


488
00:40:06,400 --> 00:40:10,240
Well, here's where we approach the
cutting edge of scientific research.


489
00:40:10,240 --> 00:40:13,480
The answer is that
we don't know for sure,


490
00:40:13,480 --> 00:40:17,440
but a clue might be found here,


491
00:40:17,440 --> 00:40:20,160
in these little green blobs,


492
00:40:20,160 --> 00:40:26,120
which are actually colonies
of algae, algae called volvox.


493
00:40:28,440 --> 00:40:31,280
We have very little
in common with algae.


494
00:40:31,280 --> 00:40:35,560
We've been separated in evolutionary
terms for over one billion years.


495
00:40:36,880 --> 00:40:39,560
But we do share
one surprising similarity.


496
00:40:41,120 --> 00:40:45,080
These volvox have light-sensitive
cells that control their movement.


497
00:40:47,000 --> 00:40:49,600
And the active ingredient
of those cells


498
00:40:49,600 --> 00:40:52,280
is a form of rhodopsin
so similar to our own


499
00:40:52,280 --> 00:40:55,480
that it's thought
they may share a common origin.


500
00:41:00,440 --> 00:41:01,600
What does that mean?


501
00:41:03,040 --> 00:41:06,480
Does it mean that we share
a common ancestor with the algae,


502
00:41:06,480 --> 00:41:11,040
and in that common ancestor,
the seeds of vision can be found?


503
00:41:13,880 --> 00:41:18,000
To find a source that may have
passed this ability to detect light


504
00:41:18,000 --> 00:41:19,560
to both us and the algae,


505
00:41:19,560 --> 00:41:23,080
we need to go much further back
down the evolutionary tree.


506
00:41:27,280 --> 00:41:30,040
To organisms like cyanobacteria.


507
00:41:31,040 --> 00:41:35,320
They were among the first living
things to evolve on the planet,


508
00:41:35,320 --> 00:41:38,760
and it's thought that the original
rhodopsins may have developed


509
00:41:38,760 --> 00:41:41,640
in these ancient
photosynthetic cells.


510
00:41:44,480 --> 00:41:48,200
So the origin of my ability to see


511
00:41:48,200 --> 00:41:53,320
may have been well over
a billion years ago,


512
00:41:53,320 --> 00:41:58,440
in an organism as seemingly simple
as a cyanobacteria.


513
00:42:08,160 --> 00:42:09,960
The basic chemistry of vision


514
00:42:09,960 --> 00:42:12,480
may have been established
for a long time,


515
00:42:12,480 --> 00:42:15,320
but it's a long way
from that chemical reaction


516
00:42:15,320 --> 00:42:19,120
to a fully functioning eye that
can create an image of the world.


517
00:42:22,800 --> 00:42:25,680
The eye is a tremendously complex
piece of machinery,


518
00:42:25,680 --> 00:42:28,880
built from lots of
interdependent parts,


519
00:42:28,880 --> 00:42:33,440
and it seems very difficult to
imagine how that could have evolved


520
00:42:33,440 --> 00:42:36,280
in a series of small steps,
but actually,


521
00:42:36,280 --> 00:42:38,600
we understand that process
very well indeed.


522
00:42:39,600 --> 00:42:41,800
I can show you, by building an eye.


523
00:42:53,640 --> 00:42:55,600
The first step
in building an eye


524
00:42:55,600 --> 00:42:59,080
would need to take some kind
of light-sensitive pigment,


525
00:42:59,080 --> 00:43:02,760
rhodopsin, for example,
and build it on to a membrane.


526
00:43:02,760 --> 00:43:07,440
So imagine this is such a membrane,
with the pigment cells attached,


527
00:43:07,440 --> 00:43:10,760
then immediately you have
something that can detect


528
00:43:10,760 --> 00:43:15,400
the difference between
dark and light.


529
00:43:15,400 --> 00:43:17,600
Now, the advantage
of this arrangement


530
00:43:17,600 --> 00:43:19,720
is that it's very sensitive
to light.


531
00:43:19,720 --> 00:43:23,400
There's no paraphernalia in front of
the retina to block light,


532
00:43:23,400 --> 00:43:26,360
but the disadvantage,
as you can see,


533
00:43:26,360 --> 00:43:29,200
is that there is
no image formed at all.


534
00:43:29,200 --> 00:43:33,040
It just allows you to tell the
difference between light and dark.


535
00:43:33,040 --> 00:43:39,680
But you can improve that a lot
by adding an aperture,


536
00:43:39,680 --> 00:43:45,320
a small hole in front of the retina,
so this is a movable aperture,


537
00:43:45,320 --> 00:43:49,000
just like the sort of thing
you've got in your camera,


538
00:43:49,000 --> 00:43:53,800
And now, we see that
the image gets sharper.


539
00:43:56,400 --> 00:43:59,240
But the problem is that
in order to make it sharper,


540
00:43:59,240 --> 00:44:01,560
we have to narrow down the aperture,


541
00:44:01,560 --> 00:44:04,560
and that means that
you get less and less light,


542
00:44:04,560 --> 00:44:07,480
so this eye becomes
less and less sensitive.


543
00:44:08,720 --> 00:44:12,120
So there's one more improvement
that nature made,


544
00:44:12,120 --> 00:44:17,320
which is to replace the pinhole,
the simple aperture...


545
00:44:19,200 --> 00:44:20,520
With a lens.


546
00:44:26,640 --> 00:44:28,000
Look at that.


547
00:44:29,400 --> 00:44:32,520
A beautifully sharp image.


548
00:44:35,240 --> 00:44:38,680
The lens is the crowning glory
of the evolution of the eye.


549
00:44:40,160 --> 00:44:44,880
By bending light onto the retina,
it allows the aperture to be opened,


550
00:44:44,880 --> 00:44:49,760
letting more light into the eye, and
a bright, detailed image is formed.


551
00:45:04,520 --> 00:45:08,520
Our eyes are called camera eyes,
because, like a camera,


552
00:45:08,520 --> 00:45:10,480
they consist of a single lens


553
00:45:10,480 --> 00:45:13,480
that bends the light
onto the photoreceptor


554
00:45:13,480 --> 00:45:16,520
to create a high-quality
image of the world.


555
00:45:19,240 --> 00:45:21,200
But that has a potential drawback,


556
00:45:21,200 --> 00:45:23,840
because to make sense of all
that information,


557
00:45:23,840 --> 00:45:25,640
we need to be able to process it.


558
00:45:27,480 --> 00:45:29,200
Each one of my eyes contains


559
00:45:29,200 --> 00:45:32,480
over 100 million
individual photoreceptor cells.


560
00:45:32,480 --> 00:45:34,640
That's about five or ten
times the number


561
00:45:34,640 --> 00:45:36,680
in the average digital camera.


562
00:45:36,680 --> 00:45:38,560
So if my visual system works


563
00:45:38,560 --> 00:45:43,960
by just taking a series of
individual still images of the world


564
00:45:43,960 --> 00:45:46,320
and transmitting all that
information to my brain,


565
00:45:46,320 --> 00:45:48,040
then my brain would be overwhelmed.


566
00:45:48,040 --> 00:45:52,360
It's just not practical,
so that's NOT what animals do.


567
00:45:52,360 --> 00:45:55,400
Instead, their visual systems
have evolved


568
00:45:55,400 --> 00:45:59,000
to extract only the information
that is necessary.


569
00:46:04,280 --> 00:46:07,080
And this is wonderfully
illustrated in the toad.


570
00:46:10,120 --> 00:46:14,000
The toad has eyes that are
structurally very similar to ours.


571
00:46:15,680 --> 00:46:19,240
But much of the time, it's as
if it isn't seeing anything at all.


572
00:46:21,080 --> 00:46:24,120
It seems completely oblivious
to its surroundings.


573
00:46:26,520 --> 00:46:30,880
Until something, like a mealworm,
takes its interest.


574
00:46:32,400 --> 00:46:35,840
If you think about what's important
to a toad visually,


575
00:46:35,840 --> 00:46:39,800
then it's the approach of
either pray or predators,


576
00:46:39,800 --> 00:46:45,000
so the toad's visual system
is optimised to detect them,


577
00:46:45,000 --> 00:46:51,000
So, there, we've put a worm in front
of the toad, and did you see that?


578
00:46:51,000 --> 00:46:54,320
Incredibly quickly,
the toad ate the worm.


579
00:46:55,400 --> 00:46:58,400
As soon as the mealworm wriggles
in front of the toad,


580
00:46:58,400 --> 00:47:00,680
its eyes lock onto the target.


581
00:47:02,720 --> 00:47:05,720
Then it strikes
in a fraction of a second.


582
00:47:09,640 --> 00:47:11,680
It's an astonishingly precise
reaction,


583
00:47:11,680 --> 00:47:14,920
but it's also a very simple one.


584
00:47:14,920 --> 00:47:19,600
Because the toad is only focusing
on one property of the mealworm -


585
00:47:19,600 --> 00:47:21,400
the way it moves.


586
00:47:28,480 --> 00:47:30,600
These 1970s lab tests


587
00:47:30,600 --> 00:47:35,880
show how a toad will try and eat
anything long and thin.


588
00:47:35,880 --> 00:47:39,080
But only if it moves on its side,
like a worm.


589
00:47:40,680 --> 00:47:44,120
And that's because the toad
has neural circuits in its retina


590
00:47:44,120 --> 00:47:47,640
that only respond
to lengthwise motion.


591
00:47:49,520 --> 00:47:52,480
If, instead, the target is rotated
into an upright position,


592
00:47:52,480 --> 00:47:54,760
the toad doesn't respond at all.


593
00:48:10,040 --> 00:48:13,120
At first sight,
the visual system of the toad


594
00:48:13,120 --> 00:48:16,200
seems a little bit
primitive and imperfect.


595
00:48:16,200 --> 00:48:20,120
It is true that if you put a toad
in a tank full of dead worms,


596
00:48:20,120 --> 00:48:23,280
it'll starve to death,
because they're not moving,


597
00:48:23,280 --> 00:48:26,480
so it doesn't recognise them
as food.


598
00:48:26,480 --> 00:48:30,720
But it doesn't need to see the world
in all the detail that I see it.


599
00:48:30,720 --> 00:48:33,080
What it needs to focus on
is movement,


600
00:48:33,080 --> 00:48:36,600
because if it can see movement
then it can survive,


601
00:48:36,600 --> 00:48:40,440
because it can avoid predators,
and it can eat its prey.


602
00:48:40,440 --> 00:48:44,960
I suppose, in a sense,
if it moves like a worm, in nature,


603
00:48:44,960 --> 00:48:46,600
then it's likely to be a worm.


604
00:48:58,600 --> 00:49:01,560
This ability to simplify
the visual world


605
00:49:01,560 --> 00:49:04,560
into the most relevant bits
of information


606
00:49:04,560 --> 00:49:07,200
is something
that every animal does.


607
00:49:07,200 --> 00:49:09,240
We do it all the time.


608
00:49:09,240 --> 00:49:13,000
We also have visual systems
that detect motion.


609
00:49:13,000 --> 00:49:15,960
Others identify edges and faces.


610
00:49:17,720 --> 00:49:22,280
But extracting more information
takes more processing power.


611
00:49:22,280 --> 00:49:24,000
That requires a bigger brain.


612
00:49:25,600 --> 00:49:28,280
And to see the results
of this evolutionary drive


613
00:49:28,280 --> 00:49:30,320
towards greater processing power,


614
00:49:30,320 --> 00:49:33,040
I've come to the heart
of Metropolitan Florida.


615
00:49:35,320 --> 00:49:38,360
You know, it may not look like it,
but underneath this flyover,


616
00:49:38,360 --> 00:49:40,000
just out in the shallow water,


617
00:49:40,000 --> 00:49:42,080
is one of the best places
in the world


618
00:49:42,080 --> 00:49:44,640
to find a particularly
interesting animal.


619
00:49:46,560 --> 00:49:48,200
It's an animal that's evolved


620
00:49:48,200 --> 00:49:51,360
to make the most of the information
its eyes can provide.


621
00:49:58,880 --> 00:50:03,440
Well, what we're going to do
is find some octopus.


622
00:50:05,640 --> 00:50:09,040
And it's, as you say in physics,
nontrivial.


623
00:50:10,400 --> 00:50:13,160
Because they've developed
a beautiful way


624
00:50:13,160 --> 00:50:15,360
of camouflaging themselves.


625
00:50:19,120 --> 00:50:23,480
They change colour. Their cells
and their skin change colour


626
00:50:23,480 --> 00:50:24,920
to match their surroundings.


627
00:50:24,920 --> 00:50:27,680
It's an ability that
we don't possess, of course.


628
00:50:27,680 --> 00:50:29,560
It makes them difficult to find.


629
00:50:41,600 --> 00:50:44,360
There he is, look.


630
00:50:46,280 --> 00:50:47,840
Ha-ha!


631
00:50:47,840 --> 00:50:49,280
He went flying into there,


632
00:50:49,280 --> 00:50:53,320
and a crab and a load of fish
are flying out, and look at his ink.


633
00:50:53,320 --> 00:50:55,720
A defence mechanism.
I don't know where he is.


634
00:50:55,720 --> 00:50:57,600
He's hiding somewhere in there.


635
00:51:05,600 --> 00:51:06,920
Look at those colours!


636
00:51:07,960 --> 00:51:09,280
What a remarkable creature.


637
00:51:11,800 --> 00:51:15,560
'Although the octopus is a mollusc,
like slugs and snails,


638
00:51:15,560 --> 00:51:19,200
'in many ways,
it seems more similar to us.'


639
00:51:19,200 --> 00:51:20,720
Whoa!


640
00:51:21,920 --> 00:51:25,440
'It's believed to be the most
intelligent invertebrate.'


641
00:51:25,440 --> 00:51:28,320
It's like he's holding his fists up.


642
00:51:28,320 --> 00:51:29,680
Look at that.


643
00:51:29,680 --> 00:51:33,240
'Its brain contains about
500 million nerve cells,


644
00:51:33,240 --> 00:51:35,240
'about the same as a dog's.'


645
00:51:35,240 --> 00:51:36,360
What are you doing?


646
00:51:41,080 --> 00:51:43,720
You know, if you want an example
of an alien intelligence


647
00:51:43,720 --> 00:51:44,760
here on earth..


648
00:51:46,480 --> 00:51:47,800
that must surely be it.


649
00:51:49,120 --> 00:51:54,040
'And it's used that brain to develop
some remarkable abilities.'


650
00:51:56,600 --> 00:51:59,080
'It's become a skilled mimic.'


651
00:51:59,080 --> 00:52:01,760
'It can rapidly change
not only its colour,


652
00:52:01,760 --> 00:52:03,840
'but its shape,
to match the background.'


653
00:52:19,040 --> 00:52:22,080
'Some species even do impressions
of other animals.'


654
00:52:29,760 --> 00:52:34,280
'They become cunning predators,
and adept problem-solvers.'


655
00:52:36,920 --> 00:52:39,400
'They've even been reported
to use tools.'


656
00:52:41,880 --> 00:52:44,800
'All these skills are signs
of great intelligence,


657
00:52:44,800 --> 00:52:48,480
'but they also rely on
an acute sense of vision.'


658
00:52:50,240 --> 00:52:54,440
Look at those big eyes
surveying the surroundings.


659
00:52:55,920 --> 00:52:58,200
Checking us out.


660
00:52:58,200 --> 00:53:03,040
Camera eyes, just like mine,
and they're vitally important


661
00:53:03,040 --> 00:53:06,600
for allowing the octopus
to live the lifestyle it does,


662
00:53:06,600 --> 00:53:11,320
so a visual animal in the same way
that I'm a visual animal.


663
00:53:14,800 --> 00:53:17,440
'The octopus is one of
the only invertebrates


664
00:53:17,440 --> 00:53:19,520
'to have complex camera eyes.'


665
00:53:22,640 --> 00:53:26,400
'Like our eyes, they capture
detailed images of the world.'


666
00:53:27,400 --> 00:53:29,120
'And their brains have evolved


667
00:53:29,120 --> 00:53:32,600
'to be able to extract the most
information from those images.'


668
00:53:36,200 --> 00:53:40,280
'The optic lobes make up about
30% of the octopus' brain.'


669
00:53:41,600 --> 00:53:43,120
'The only other group


670
00:53:43,120 --> 00:53:46,560
'that is known to devote so much of
its brain to visual processing


671
00:53:46,560 --> 00:53:48,560
'is our group.


672
00:53:48,560 --> 00:53:53,080
'The primates - the most
intelligent vertebrates.'


673
00:53:55,560 --> 00:53:57,960
I think it's a fascinating thought


674
00:53:57,960 --> 00:54:00,400
that that intelligence is a result


675
00:54:00,400 --> 00:54:04,120
of the need to process
all the information


676
00:54:04,120 --> 00:54:06,840
from those big, complex eyes.


677
00:54:10,200 --> 00:54:13,400
'What's so compelling
about the octopus' intelligence


678
00:54:13,400 --> 00:54:16,840
'is that it evolved
completely separately to ours.'


679
00:54:19,040 --> 00:54:22,840
'We last shared a common ancestor
600 million years ago.'


680
00:54:23,960 --> 00:54:27,280
'An ancestor that had
neither eyes nor a brain.'


681
00:54:29,400 --> 00:54:32,680
'But we've both evolved
sophisticated camera eyes,


682
00:54:32,680 --> 00:54:35,840
'and large, intelligent brains.'


683
00:54:37,800 --> 00:54:42,400
'It suggests a tantalising link
between sensory processing


684
00:54:42,400 --> 00:54:44,720
'and the evolution of intelligence.'


685
00:54:55,800 --> 00:54:59,760
Sensing has played a key role
in the evolution of life on Earth.


686
00:55:04,720 --> 00:55:05,960
The first organisms


687
00:55:05,960 --> 00:55:09,840
were able to detect and respond
to their immediate environment,


688
00:55:09,840 --> 00:55:11,240
as paramecia do today.


689
00:55:15,280 --> 00:55:19,480
But as animals evolved, and their
environments became more complex,


690
00:55:19,480 --> 00:55:22,000
their senses evolved with them.


691
00:55:23,400 --> 00:55:27,000
Developing the mechanisms
to let them decode vibrations


692
00:55:27,000 --> 00:55:28,440
and detect light.


693
00:55:29,760 --> 00:55:32,880
Allowing them to build
three-dimensional pictures


694
00:55:32,880 --> 00:55:34,320
of their environments,


695
00:55:34,320 --> 00:55:42,400
and stimulating the growth of brains
that could handle all that data.


696
00:55:49,080 --> 00:55:50,400
But for one species,


697
00:55:50,400 --> 00:55:53,880
the desire to gather
more and more sensory information


698
00:55:53,880 --> 00:55:55,600
has become overwhelming.


699
00:56:01,040 --> 00:56:03,520
That species is us.


700
00:56:19,280 --> 00:56:22,320
This is the closest thing
to hallowed ground that exists


701
00:56:22,320 --> 00:56:24,080
in a subject that has no saints,


702
00:56:24,080 --> 00:56:28,080
because that telescope is the one
that Edwin Hubble used


703
00:56:28,080 --> 00:56:30,800
to expand our horizons,
I would argue,


704
00:56:30,800 --> 00:56:34,480
more than anyone else
before or since.


705
00:56:45,680 --> 00:56:50,000
In 1923, Edwin Hubble took this
photograph of the Andromeda galaxy.


706
00:56:50,000 --> 00:56:52,120
You can see his handwriting
on the photograph.


707
00:56:52,120 --> 00:56:56,320
He did it by sitting here
night after night for over a week,


708
00:56:56,320 --> 00:56:58,560
exposing this photographic plate.


709
00:56:58,560 --> 00:56:59,680
Now, at the time,


710
00:56:59,680 --> 00:57:03,080
it was thought that this misty patch
you see in the night sky


711
00:57:03,080 --> 00:57:07,200
was just a cloud, maybe a gas cloud
in our own galaxy,


712
00:57:07,200 --> 00:57:09,880
but Hubble, because of
the power of this telescope,


713
00:57:09,880 --> 00:57:13,800
identified individual stars,
and crucially,


714
00:57:13,800 --> 00:57:18,040
he found that it was
way outside our own galaxy.


715
00:57:18,040 --> 00:57:19,120
In other words,


716
00:57:19,120 --> 00:57:23,920
Hubble had discovered
this is a distant island of stars.


717
00:57:23,920 --> 00:57:26,760
We now know it's over
two million light years away,


718
00:57:26,760 --> 00:57:29,840
composed of a trillion suns
like ours.


719
00:57:37,040 --> 00:57:40,080
Hubble demonstrated that
there's more to the universe


720
00:57:40,080 --> 00:57:41,280
than our own galaxy.


721
00:57:42,320 --> 00:57:46,440
He extended the reach of our senses
further than we could have imagined.


722
00:57:48,120 --> 00:57:49,640
With the help of the telescope,


723
00:57:49,640 --> 00:57:55,960
we could perceive and comprehend
worlds billions of light years away.


724
00:58:02,360 --> 00:58:04,600
There's a wonderful feedback
at work here,


725
00:58:04,600 --> 00:58:08,480
because the increasing amounts
of data delivered by our senses


726
00:58:08,480 --> 00:58:10,760
drove the evolution of our brains,


727
00:58:10,760 --> 00:58:14,720
and those increasingly sophisticated
brains became curious


728
00:58:14,720 --> 00:58:16,800
and demanded more and more data.


729
00:58:18,480 --> 00:58:20,200
And so we built telescopes


730
00:58:20,200 --> 00:58:23,600
that were able to extend our senses
beyond the horizon


731
00:58:23,600 --> 00:58:27,400
and showed us a universe that's
billions of years old


732
00:58:27,400 --> 00:58:30,840
and contains trillions
of stars and galaxies.


733
00:58:32,800 --> 00:58:37,120
Our insatiable quest for information
is the making of us.


734
00:59:02,880 --> 00:59:06,000
Subtitles by Red Bee Media