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Skin.

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We all have it.

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And so does every vertebrate
on the planet.

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It keeps the outside out
and the inside in.

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Animals may look very
different on the surface,

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but we all share the same
basic skin blueprint.

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I'm Ben Garrod, Professor
of Evolutionary Biology,

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and I'm fascinated by this
often-overlooked wonder of nature.

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It's not just the case
that it's hairless,

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the skin's totally different.

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Now, ground-breaking new science...

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This is really quite remarkable.

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It should be a game changer for
so many people.

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RATTLING
That sound!

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Oh, it makes the hairs on the back
of your neck go up, doesn't it?

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..is revealing skin's mysteries.

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It really transforms our
understanding of dinosaurs.

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I'm going to explore the natural
history of the body's largest organ,

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to see how skin has allowed animals
to conquer every habitat,

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disappear into their surroundings
and develop extra sensory abilities.

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We're even discovering the complex
ecosystem living on our skin.

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Jim, that's awful.

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It really is.

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In this episode, I'll reveal
how skin's amazing versatility

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helps frigatebirds attract a mate...

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..means frogs don't have to rely
on their lungs to breathe...

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..and lets microscopic animals
live on our faces.

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Animals that could change
the story of our evolution.

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I'll explore how skin's uniquely
adaptable structure

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allows vertebrates to overcome some
of life's greatest challenges.

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I'm going to reveal the secrets
of skin.

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There are more than 66,000
species of vertebrates

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alive on the planet today.

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They've conquered the water,
land and air.

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And have evolved into a dazzling
array of shapes, sizes and colours.

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And in my opinion, it's skin,
the largest organ in any animal,

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that holds the key to this
diversity and success.

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Over 500 million years of vertebrate
evolution, skin's incredible

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adaptability has enabled
it to become tough...

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..flexible...

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..sensitive...

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..and colourful.

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It can grow feathers, scales,
hair...

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..and even teeth.

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But that's just the tip
of the iceberg.

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The key to this incredible
versatility is a remarkable

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blueprint that forms the basis
of vertebrate skin.

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Fish, reptiles,
amphibians, mammals and birds

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all share the same basic
skin structure.

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On the surface, the epidermis,

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made of a few thin
layers of protective cells.

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Beneath that, the dermis, rich
in glands, nerves and blood vessels,

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where hair, feathers and
scales arise.

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And then finally, the
subcutaneous fat layer,

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a bed of fatty tissue
that helps insulate the body.

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Adaptations in the form and function
of these three basic layers

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have led to the dazzling range
of skin types

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exhibited by vertebrates today.

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And the story starts with
the outermost layer - the epidermis.

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The epidermis is the
final, thin barrier

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between an animal and its
environment.

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On my body, it varies

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between one millimetre thick on the
soles of my feet

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to just 30 micrometres
here on my eyelids.

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On my little friend here,
it can be even thinner,

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between 50
and 12 micrometres.

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It's estimated that the average
human epidermis

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contains up to 180 billion cells.

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Its main function is to protect us
from the outside world.

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And it is constantly
replacing itself.

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I'm losing 20 million epidermal
cells every single hour.

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And in roughly a month's
time, my entire epidermis

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will effectively be brand-new.

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This means mammal skin is a little
bit like a flaky conveyor belt.

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This endless cycle of epidermal
renewal has two benefits.

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Damaged skin falls away to
be replaced by new, healthy cells.

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And because our epidermis
is constantly renewing,

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it can grow with us.

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But this isn't the case
for all vertebrates,

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particularly reptiles, because they
have a problem.

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Reptiles' outer layer of skin
doesn't grow with them,

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so they have to shed their entire
epidermis in one go.

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It's simply replaced by a bigger
version growing underneath.

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A snake's simpler body shape makes
this process much easier.

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Adult snakes do this up to four
times a year,

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although young, fast-growing
individuals

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can shed every two weeks.

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This snake has just shed.

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Her skin came off like one big sock

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and every single bit of her

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was replaced in one go, including
the scales over her eyes.

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Lizards and snakes shed
like this because reptile skin

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is toughened by large amounts
of a fibre made in the epidermis.

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Keratin - a complex of twisted
proteins.

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It's one of the toughest natural
materials in existence.

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Found in all vertebrates' skin,
it's incredibly versatile.

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But just how tough is it?

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One place keratin is found
in high concentrations

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is the hard outer wall of
a horse's hoof.

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Wild stallions use their hooves
as weapons

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in violent battles over mares.

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They're capable of delivering a kick
with a force of up to a tonne,

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with bone shattering results.

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With this in mind, I need a safe way
to see those tough hooves close up.

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So I've come to Hill Livery Stables
near Bristol,

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to meet farrier Dan Downton.

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Who have we got here?
This is Jasper.

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He's come in for a new
set of shoes.

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I'm really interested to see
how it's done.

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Shall we get on with it, then?
Yeah, let's give a go.

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So, first of all, we're going to
take the shoe off. Yeah.

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Dan, that looks quite brutal, but
Jasper's not feeling that, is he?

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No, he's got quite a lot
of foot there,

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and we're not touching
any sensitive structures.

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So it's fine.

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And that's the nail we can
see there, isn't it? Yeah.

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So that's the hoof wall, this
is the sole.

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And this is the frog. OK.

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A horse's hoof evolved from a single
toenail, like one of ours.

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And its dense wall of keratin
grows out of the epidermis

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in a similar way.

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The keratin in an unshod hoof
has to withstand incredible forces.

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A galloping horse can generate 1000
kilograms through each foot.

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Give that a rasp. He hasn't got a
lot of foot on it.

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Once the old shoe's off,
Dan trims the hoof.

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So this is like a big nail file?

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So you've basically given Jasper
a huge manicure right now?

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That's it.

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Just like our nails,
a horse's hooves

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don't contain nerves
or blood vessels.

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The keratin wall grows from the skin

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at around six millimetres a month,
an evolutionary response

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to the constant wear
and tear hooves experience.

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Hooves are so important to the
survival and wellbeing of a horse

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that, for at least 2,000 years,

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we've enhanced keratin's
toughness with iron,

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shoeing domesticated
horses to maintain

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the vital integrity of their hooves.

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It's not just horses that rely
on keratin's durability.

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Many other animals have exploited
its amazing attributes.

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Pangolins, like this one
here, are covered

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in overlapping keratin scales.

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They grow out of the epidermis
and form this tough but flexible

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suit of armour.

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If the pangolin is attacked,
it curls into a ball

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to protect itself.

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And even a lion's teeth and claws
can't get through

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those two millimetre thick scales.

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Keratin isn't just produced
for protection, vertebrates use it

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in a huge range of
skin-based structures.

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It's a key component in all hair
and quills...

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..all feathers and scales...

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...and claws and fingernails.

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There are 30 different forms
of keratin in mammals alone.

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At its most chemically complex
and tough,

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it turns a rhino horn
into a battering ram.

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While the main function
of the epidermis is protection,

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the layer below, the dermis,
combines intense biological activity

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with some extraordinary
physical attributes.

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This is a male great frigatebird
from the Galapagos Islands.

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He's just won a hotly contested
patch of ground to nest on.

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Now he needs a mate.

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Female frigatebirds are gliding
overhead.

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Somehow, he must attract
their attention without abandoning

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his hard won bit of turf.

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His solution is this huge inflated
balloon of skin on his throat.

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Called a gular sac, it's almost
as tall as he is and clearly visible

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to the circling females. He adds
to the dramatic effect by shaking

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it from side to side
and clacking his beak.

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Eventually, his lonely hearts
ad does the trick

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and a female joins him
at the nest site.

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Job done.

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His gular sac deflates
and all but disappears.

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The key to a male frigatebird's
amazingly stretchy skin

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is down to a fibrous protein
that's found in the dermis

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of all vertebrates.

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It's called elastin. Named
for its elastic properties

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and looking and behaving like a mesh
of tightly coiled microscopic

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springs, elastin pulls
stretched skin back into shape.

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Human elastin production
slows down as we get older.

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And this means our skin not only
gets less stretchy, but starts

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to develop wrinkles.

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The impressive elasticity
of the dermis has led to some

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extraordinary adaptations
across the vertebrate world,

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from kangaroo pouches to bat wings.

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And none more so than frogs.

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During the breeding season, male
frogs' vocal sacs combine elastin

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and very thin skin to amplify
their mating calls.

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The amphibian dermis is remarkable
for another reason.

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More than any other vertebrate,

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they rely on their skin
for the uptake of oxygen.

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Amphibians, like this African
bullfrog, use their thin permeable

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skin effectively to breathe
in water as well as on land.

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Their skin has evolved to let
oxygen pass through the cells

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of the epidermis and dermis
and into the bloodstream.

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They can get as much as 20%
of their oxygen through their skin.

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One frog has taken
this to the extreme.

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The Titicaca frog, found in
rivers and lakes high in the Andes,

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is covered in folds of extra skin.

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A dense network of capillaries
in the dermis of these folds allows

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the frog to absorb all the oxygen
it needs from the water, meaning

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it never has to surface to breathe.

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But there are drawbacks
to this type of respiration.

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In order to survive, amphibians
need to live in damp places,

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where their skin remains moist.

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If it dries out, it means
that gases can't diffuse

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across it and they suffocate.

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Alongside its impressive physical
attributes, the dermis is also

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a hive of biological activity.

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Specialised glands produce a huge
array of natural compounds

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which further enhance the skin's
versatility.

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And I've got a neat, low tech
way to demonstrate this.

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These are camphor boats,

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and a tiny camphor crystal on
the back of each one has them

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00:14:28,260 --> 00:14:32,340
shooting across the surface
of the water like magic.

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00:14:32,340 --> 00:14:35,060
Of course, it's not magic.

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Camphor is a pungent chemical
harvested from camphor trees.

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00:14:39,140 --> 00:14:42,780
It dissolves in water, altering
the surface tension and pushing

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the little boats forward.

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00:14:45,540 --> 00:14:50,540
All it takes to stop them is a thin
layer of grease on the water,

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and I know just where to find some.

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In common with most mammals, my skin
is coated in a thin layer of oil.

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This is a waxy substance called
sebum that helps lubricate

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and waterproof my skin.

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It's produced by sebaceous glands
in the dermis of all mammals.

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These are often found next
to hair follicles,

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which is why our hair gets greasy.
While we have an estimated

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two million sebaceous glands
all over our skin,

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it's still a mystery why
they're most abundant

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on our scalp and faces.

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Mammals aren't the only
vertebrates producing natural oils

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in the dermis.

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Birds have sebaceous glands too.

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But instead of lots of small glands
all over the skin, they've evolved

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00:15:47,340 --> 00:15:49,220
one big one.

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00:15:49,220 --> 00:15:52,900
And if we're really careful,
we can look at this conure's...

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00:15:54,140 --> 00:15:56,020
SQUAWKS
..because... Hello!

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00:15:56,020 --> 00:16:02,260
..just at the top of the tail, you
can see a little patch that looks

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like it's a bunch of soggy feathers.

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00:16:05,100 --> 00:16:06,460
That's the preen gland.

241
00:16:07,740 --> 00:16:11,500
And it's this that produces oil
which the bird then spreads

242
00:16:11,500 --> 00:16:15,500
around its body using its beak
and head.

243
00:16:18,500 --> 00:16:22,380
Birds use this dermis-produced oil
for lots of different reasons...

244
00:16:24,860 --> 00:16:30,500
..keeping feathers supple
for flying, sending odour-based
chemical messages

245
00:16:30,500 --> 00:16:32,620
to potential mates or rivals.

246
00:16:33,980 --> 00:16:36,700
It also helps to keep feather
colours vivid.

247
00:16:39,900 --> 00:16:44,940
Many diving birds have large preen
glands, which suggests it also plays

248
00:16:44,940 --> 00:16:48,060
a vital role in waterproofing
their feathers,

249
00:16:48,060 --> 00:16:52,420
although biologists are
unsure of exactly how.

250
00:16:52,420 --> 00:16:57,460
Preen oil is an impressive but
mysterious multi-purpose substance.

251
00:16:59,140 --> 00:17:02,660
And the dermis still has more
surprises in store.

252
00:17:07,140 --> 00:17:12,420
In ancient mammal ancestors living
more than 250 million years ago,

253
00:17:12,420 --> 00:17:16,100
scientists believe the dermis
evolved to secrete something

254
00:17:16,100 --> 00:17:18,500
extraordinary - milk.

255
00:17:20,420 --> 00:17:24,540
There are four different types
of gland in the mammalian dermis,

256
00:17:24,540 --> 00:17:28,540
and it's thought an adaptation
of one, the sweat gland, led

257
00:17:28,540 --> 00:17:31,100
to this vital step in mammal
evolution.

258
00:17:32,980 --> 00:17:36,980
We have a rough idea of how
that might have worked from platypus

259
00:17:36,980 --> 00:17:40,580
and echidnas, like this little
guy here from Australia.

260
00:17:40,580 --> 00:17:44,140
These are unusual mammals
in that they lay eggs,

261
00:17:44,140 --> 00:17:47,500
and they feed their offspring
from milk that's secreted

262
00:17:47,500 --> 00:17:51,740
to the surface of the skin
by collections of pores.

263
00:17:51,740 --> 00:17:55,500
This might have been an early step
into the development of dedicated

264
00:17:55,500 --> 00:17:58,300
nipples and mammary glands
as we see in most

265
00:17:58,300 --> 00:17:59,780
mammals alive today.

266
00:18:01,940 --> 00:18:05,540
The versatility of the dermis allows
it to make an array of unique

267
00:18:05,540 --> 00:18:09,580
compounds that have shaped
vertebrate evolution.

268
00:18:09,580 --> 00:18:14,300
And there is one more - collagen,
a protein with incredible tensile

269
00:18:14,300 --> 00:18:18,900
strength which is found
in every vertebrate dermis.

270
00:18:18,900 --> 00:18:22,340
Only now are we understanding
the far-reaching effect

271
00:18:22,340 --> 00:18:24,300
it could have on our lives.

272
00:18:26,340 --> 00:18:30,420
I'm going to see bio engineer
Dr Claire Higgins.

273
00:18:30,420 --> 00:18:34,940
She's testing a disc of human foot
skin to see how it responds to a bit

274
00:18:34,940 --> 00:18:36,300
of wear and tear.

275
00:18:36,300 --> 00:18:40,380
So the machine compresses the piece
of skin, and we measure the amount

276
00:18:40,380 --> 00:18:43,340
of deformation in the tissue,
so how much the tissue

277
00:18:43,340 --> 00:18:44,460
is changing shape.

278
00:18:45,860 --> 00:18:49,620
The disc of foot skin is repeatedly
squashed up and down and side

279
00:18:49,620 --> 00:18:53,540
to side, mimicking the forces
produced by walking.

280
00:18:53,540 --> 00:18:55,140
And what have the results
shown so far?

281
00:18:55,140 --> 00:19:00,820
So with compression
foot skin deforms by about
15% whereas body skin

282
00:19:00,820 --> 00:19:03,220
changes shape by about 25%.

283
00:19:03,220 --> 00:19:06,620
And then, when we look at shear
forces, foot skin deforms

284
00:19:06,620 --> 00:19:12,700
by about 40% while leg skin actually
deforms by as much as 150%.

285
00:19:12,700 --> 00:19:16,700
Claire's tests reveal that, when it
comes to dealing with wear and tear,

286
00:19:16,700 --> 00:19:20,740
the skin on our feet significantly
outperforms the skin on the rest

287
00:19:20,740 --> 00:19:21,780
of our bodies.

288
00:19:22,820 --> 00:19:28,940
To find out what makes foot skin
so resilient, Claire's using
laser microscopy.

289
00:19:28,940 --> 00:19:31,340
So we're actually
imaging collagen fibres,

290
00:19:31,340 --> 00:19:34,340
and we're interested in collagen
because it makes up about 90%

291
00:19:34,340 --> 00:19:36,980
of the skin dermis
and it's really the structural

292
00:19:36,980 --> 00:19:40,780
protein that contributes
to the integrity of the skin.

293
00:19:40,780 --> 00:19:43,260
Fibres of collagen running
through the dermis

294
00:19:43,260 --> 00:19:46,780
are what give vertebrate
skin its tensile strength.

295
00:19:46,780 --> 00:19:51,220
So you can see, in this image here,
this is collagen in foot skin.
Mm-hm.

296
00:19:51,220 --> 00:19:54,420
And this image on the right
is collagen in leg skin.

297
00:19:54,420 --> 00:19:57,700
The foot skin owes its impressive
toughness to this dense

298
00:19:57,700 --> 00:19:59,420
network of collagen.

299
00:19:59,420 --> 00:20:03,300
The images show that the collagen
fibres in foot skin are much

300
00:20:03,300 --> 00:20:05,980
thicker than the ones in leg skin.

301
00:20:05,980 --> 00:20:10,260
They're also about four times
brighter, which is significant.

302
00:20:10,260 --> 00:20:14,820
That brightness actually
is an indication of tensile state.

303
00:20:14,820 --> 00:20:18,660
The fibres in foot skin are
pretensed, almost.

304
00:20:18,660 --> 00:20:22,940
So basically these are ever ready
little bundles of collagen

305
00:20:22,940 --> 00:20:26,940
in anticipation for this heavy wear
and tear that we're not seeing

306
00:20:26,940 --> 00:20:28,100
elsewhere in the body?

307
00:20:30,380 --> 00:20:34,060
Claire's ground-breaking research
has revealed that our skin structure

308
00:20:34,060 --> 00:20:37,260
varies with the job it has to do.

309
00:20:37,260 --> 00:20:41,540
Her ultimate aim is to replicate
the durability of foot skin in skin

310
00:20:41,540 --> 00:20:46,260
on other parts of the body,
changing lives in the process.

311
00:20:46,260 --> 00:20:49,500
There are some circumstances, such
as after amputation, that skin

312
00:20:49,500 --> 00:20:53,060
on a stump is required to be
load-bearing, but it's not

313
00:20:53,060 --> 00:20:54,180
designed to be.

314
00:20:54,180 --> 00:20:59,140
So we're hoping that we can try to
reengineer skin, such as stump skin,

315
00:20:59,140 --> 00:21:02,580
to make it stronger and make
it capable of being load-bearing.

316
00:21:02,580 --> 00:21:06,380
So you're talking about
developing skin on people
with disabilities or injuries here?

317
00:21:06,380 --> 00:21:09,100
Yeah, re-engineering skin
on the stump, essentially.

318
00:21:09,100 --> 00:21:12,180
This is really quite remarkable,
and it should be a game changer

319
00:21:12,180 --> 00:21:13,500
for so many people.

320
00:21:13,500 --> 00:21:16,100
We hope so. Yeah, absolutely.

321
00:21:16,100 --> 00:21:19,980
Claire's discoveries are shedding
new light, not just on the potential

322
00:21:19,980 --> 00:21:24,620
of human skin, but the versatility
of skin itself.

323
00:21:24,620 --> 00:21:28,780
It's also a clear demonstration
of just how much we still

324
00:21:28,780 --> 00:21:29,820
have to learn.

325
00:21:32,660 --> 00:21:36,180
Another remarkable discovery
about human skin could change our

326
00:21:36,180 --> 00:21:37,220
view of evolution.

327
00:21:39,220 --> 00:21:45,420
It involves looking for an animal
that lives on and in our skin.

328
00:21:45,420 --> 00:21:50,220
They're so small that you can't feel
them or see them with the naked eye,

329
00:21:50,220 --> 00:21:52,620
but most of us do have them.

330
00:21:52,620 --> 00:21:57,220
So I'm off to see whether I can find
mine. They're skin mites.

331
00:21:57,220 --> 00:22:01,060
And I've come to meet Dr Dave
Patton, who's going to help me

332
00:22:01,060 --> 00:22:02,260
track mine down.

333
00:22:02,260 --> 00:22:04,380
Hi, Dave. Hello.

334
00:22:04,380 --> 00:22:06,900
So we're going to look for mites
on my face, are we? Yeah.

335
00:22:06,900 --> 00:22:09,780
We're going to use an interesting
technique involving

336
00:22:09,780 --> 00:22:12,940
supergluing your head
to a glass slide.

337
00:22:12,940 --> 00:22:15,300
You say it like it's
such a common thing!

338
00:22:15,300 --> 00:22:18,780
OK. So we've literally got a
glass slide and some superglue!

339
00:22:18,780 --> 00:22:20,860
Yes. OK. Right.

340
00:22:20,860 --> 00:22:24,540
So all we do is put some
glue on the slide and then press it

341
00:22:24,540 --> 00:22:26,780
onto your forehead for a minute.

342
00:22:26,780 --> 00:22:29,900
Then it'll remove some
of your forehead and, hopefully,

343
00:22:29,900 --> 00:22:32,540
some skin mites. Not much of
my forehead, though, right?

344
00:22:32,540 --> 00:22:34,300
Um... A millimetre.

345
00:22:36,580 --> 00:22:41,020
Mites live in greater concentrations
on our faces than anywhere else,

346
00:22:41,020 --> 00:22:44,060
particularly on our cheeks
and foreheads.

347
00:22:44,060 --> 00:22:45,700
You ready? I think so.

348
00:22:45,700 --> 00:22:46,740
Right, OK.

349
00:22:47,820 --> 00:22:49,540
OK. Can you hold that in place?

350
00:22:49,540 --> 00:22:51,100
Yeah.

351
00:22:51,100 --> 00:22:55,300
While the 60 seconds count down,
I want to check something.

352
00:22:55,300 --> 00:22:57,580
Have you done this to yourself?
Yes. Yes.

353
00:22:57,580 --> 00:22:59,540
Have you found any?

354
00:22:59,540 --> 00:23:00,860
We have found one.

355
00:23:02,300 --> 00:23:04,820
That's not a very high hit rate.

356
00:23:04,820 --> 00:23:08,620
So, to be on the safe side,
we'll need some backup samples.

357
00:23:08,620 --> 00:23:12,660
I think, in that case, then,
what I might do is to get slides

358
00:23:12,660 --> 00:23:15,380
and samples from all the crew
as well.

359
00:23:15,380 --> 00:23:17,220
Why not? Come on, guys!

360
00:23:19,220 --> 00:23:23,660
And so the crew bravely submits
to the superglue treatment.

361
00:23:23,660 --> 00:23:25,180
Just press that on. Thank you.

362
00:23:26,540 --> 00:23:27,580
Thank you.

363
00:23:31,500 --> 00:23:33,580
Argh! Sorry. It didn't hurt.

364
00:23:34,700 --> 00:23:39,540
We have got a nice variety
of peeled skin on there right now.

365
00:23:39,540 --> 00:23:42,300
So now we've put those under
a microscope and we see

366
00:23:42,300 --> 00:23:45,700
whether we can find these little
face mites stuck on the superglue?

367
00:23:45,700 --> 00:23:47,140
Yeah. That's the plan.

368
00:23:47,140 --> 00:23:49,700
Let's see if we can find some.
Good luck, team.

369
00:23:55,620 --> 00:23:59,100
Dave puts my sample in a scanning
electron microscope

370
00:23:59,100 --> 00:24:02,780
and, within minutes, I'm looking
at the inside of my skin

371
00:24:02,780 --> 00:24:05,660
magnified 200 times.

372
00:24:05,660 --> 00:24:08,860
It's like a really horrible
treasure trail cos

373
00:24:08,860 --> 00:24:10,620
I don't want to find what's hiding!

374
00:24:12,660 --> 00:24:16,980
So, to search, I'm just
going to move one screen at a time.
And we're looking

375
00:24:16,980 --> 00:24:21,020
for a little head that's popping out
next to the hair itself, aren't we?

376
00:24:21,020 --> 00:24:24,700
Yeah, in the same pore, so parallel
to the hair, looking

377
00:24:24,700 --> 00:24:26,340
very similar to the hair.

378
00:24:26,340 --> 00:24:30,540
But however hard we search, we just
don't find any signs of life.

379
00:24:32,220 --> 00:24:36,660
So what I think we should do
is have a look at some of the other

380
00:24:36,660 --> 00:24:40,460
film crew members to see
what their skin's like.

381
00:24:40,460 --> 00:24:43,260
So who have we got here, then, Dave?
Andy, the sound man.

382
00:24:45,060 --> 00:24:47,220
There's a pore there
with hair coming

383
00:24:47,220 --> 00:24:51,780
out of it. It's probably just
a big bit of follicle there
belonging to this hair.

384
00:24:54,580 --> 00:24:58,140
Dave looks even closer, and bingo!

385
00:24:58,140 --> 00:25:04,860
Look, look at that. There appear
to be one, two, three Demodex.

386
00:25:04,860 --> 00:25:07,140
Andy not only has mites -

387
00:25:07,140 --> 00:25:08,700
he's got loads of them!

388
00:25:08,700 --> 00:25:12,260
So you've got evidence of three
little mites on one hair strand

389
00:25:12,260 --> 00:25:13,820
from Andy's sample here?

390
00:25:13,820 --> 00:25:15,420
It looks like it.

391
00:25:15,420 --> 00:25:20,780
What we've found are Demodex mites -
tiny, harmless arachnids that live

392
00:25:20,780 --> 00:25:24,460
on my, your and Andy
the soundman's skin.

393
00:25:25,500 --> 00:25:30,460
Their long, thin bodies help them
slide inside our hair follicles,

394
00:25:30,460 --> 00:25:33,820
where they cling on with eight
stumpy claws.

395
00:25:33,820 --> 00:25:38,860
They spend their time hidden away,
feeding on oils made in the dermis

396
00:25:38,860 --> 00:25:41,660
and all those dead epidermal cells.

397
00:25:41,660 --> 00:25:45,700
If that wasn't bad enough,
these little animals are light

398
00:25:45,700 --> 00:25:50,380
sensitive and only come out
at night, when they mate...

399
00:25:50,380 --> 00:25:51,420
..on our faces.

400
00:25:54,540 --> 00:25:57,780
The only time we don't have
Demodex mites

401
00:25:57,780 --> 00:25:59,700
is when we're in the womb.

402
00:25:59,700 --> 00:26:03,220
Once you're born, a few
snuggles from your mum or dad,

403
00:26:03,220 --> 00:26:04,820
and you've probably got mites.

404
00:26:09,100 --> 00:26:13,460
While this is both fascinating
and disturbing, it just goes to show

405
00:26:13,460 --> 00:26:18,540
that our skin isn't just an organ -
it's an entire ecosystem.

406
00:26:20,060 --> 00:26:24,700
This discovery has opened up a whole
new line of scientific inquiry.

407
00:26:24,700 --> 00:26:27,540
By testing mite DNA
from around the globe,

408
00:26:27,540 --> 00:26:32,620
scientists revealed in 2015
that different human populations

409
00:26:32,620 --> 00:26:37,580
have different mite populations,
handed down through the generations.

410
00:26:37,580 --> 00:26:40,420
This means we can map
which continent a person's

411
00:26:40,420 --> 00:26:42,060
ancestors came from

412
00:26:42,060 --> 00:26:48,260
by studying the mites on their skin.
We may even be able to trace ancient

413
00:26:48,260 --> 00:26:50,460
human migration patterns by studying

414
00:26:50,460 --> 00:26:54,980
mite DNA, shedding new light
on our evolution.

415
00:26:54,980 --> 00:26:59,100
And the extraordinary story
doesn't end there.

416
00:26:59,100 --> 00:27:03,820
Every mammal species tested so far
has its own familial Demodex

417
00:27:03,820 --> 00:27:07,620
mites - proof that skin
still has its secrets.

418
00:27:10,260 --> 00:27:13,980
When it comes to helping vertebrates
thrive in an unpredictable world,

419
00:27:13,980 --> 00:27:18,740
skin, which is both resourceful
and adaptable, is the ultimate

420
00:27:18,740 --> 00:27:23,420
multi-purpose tool. And it's
still full of surprises.

421
00:27:24,620 --> 00:27:26,260
Over the rest of this series,

422
00:27:26,260 --> 00:27:30,020
I'll be unpacking the fascinating
ways skin has evolved to make

423
00:27:30,020 --> 00:27:33,340
vertebrate life on Earth possible

424
00:27:33,340 --> 00:27:38,740
by helping animals defend
themselves, disguise themselves,

425
00:27:38,740 --> 00:27:40,620
and even communicate.

426
00:27:40,620 --> 00:27:41,900
BARKS

427
00:27:43,660 --> 00:27:44,900
In the next episode,

428
00:27:44,900 --> 00:27:48,700
I discover why shark skin
is covered in thousands

429
00:27:48,700 --> 00:27:49,860
of tiny teeth...

430
00:27:49,860 --> 00:27:52,780
I'm not about to give this one
a stroke!

431
00:27:52,780 --> 00:27:57,220
..how gecko skin allows them
to defy the laws of gravity...

432
00:27:57,220 --> 00:28:02,420
He's able to cling onto this piece
of vertical smooth glass with ease.

433
00:28:02,420 --> 00:28:07,620
..and I find out why loose skin
is the ideal adaptation to life

434
00:28:07,620 --> 00:28:12,780
underground as I explore
the way skin has evolved

435
00:28:12,780 --> 00:28:14,460
to help animals move.

436
00:28:51,220 --> 00:28:52,500
Skin.

437
00:28:52,500 --> 00:28:54,220
We all have it.

438
00:28:54,220 --> 00:28:57,100
And so does every vertebrate
on the planet.

439
00:28:58,300 --> 00:29:00,860
It keeps the outside out...

440
00:29:00,860 --> 00:29:03,060
..and the inside in.

441
00:29:04,500 --> 00:29:08,180
Animals may look very different
on the surface, but we all share

442
00:29:08,180 --> 00:29:10,660
the same basic skin blueprint.

443
00:29:12,540 --> 00:29:16,620
I'm Ben Garrod, professor
of evolutionary biology,

444
00:29:16,620 --> 00:29:20,340
and I'm fascinated by this often
overlooked wonder of nature.

445
00:29:20,340 --> 00:29:22,740
It's not just a case that
he's hairless,

446
00:29:22,740 --> 00:29:24,780
the skin's totally different.

447
00:29:24,780 --> 00:29:27,300
Now, ground-breaking new science...

448
00:29:27,300 --> 00:29:29,020
This is really quite remarkable.

449
00:29:29,020 --> 00:29:31,340
It shouldn't be a game changer
for so many people.

450
00:29:31,340 --> 00:29:32,700
RATTLESNAKE TAIL RATTLES

451
00:29:32,700 --> 00:29:35,220
That sound, it makes the hair on
the back of your neck go up,

452
00:29:35,220 --> 00:29:36,300
doesn't it?

453
00:29:36,300 --> 00:29:38,980
..is revealing skin's mysteries.

454
00:29:38,980 --> 00:29:43,780
It really transforms our
understanding of dinosaurs.

455
00:29:43,780 --> 00:29:47,900
I'm going to explore the natural
history of the body's largest organ,

456
00:29:47,900 --> 00:29:52,900
to see how skin has allowed animals
to conquer every habitat,

457
00:29:52,900 --> 00:29:58,460
disappear into their surroundings
and develop extra sensory abilities.

458
00:30:00,180 --> 00:30:05,020
We're even discovering the complex
ecosystem living on our skin.

459
00:30:05,020 --> 00:30:06,660
Oh, Jim, that's awful.

460
00:30:06,660 --> 00:30:08,700
It really is.

461
00:30:08,700 --> 00:30:12,100
In this episode, I'll find out
why shark skin is covered

462
00:30:12,100 --> 00:30:14,180
in thousands of tiny teeth.

463
00:30:14,180 --> 00:30:19,020
Now, I love sharks, but I'm not
about to give this one a stroke.

464
00:30:19,020 --> 00:30:22,020
How birds have adapted their skin
to rule the sky.

465
00:30:22,020 --> 00:30:23,260
Ooh! Oh.

466
00:30:23,260 --> 00:30:24,820
And down he goes.

467
00:30:24,820 --> 00:30:29,020
And how a gecko's skin allows it
to defy the laws of gravity.

468
00:30:29,020 --> 00:30:34,140
He's able to cling onto this piece
of vertical, smooth glass with ease.

469
00:30:34,140 --> 00:30:37,860
As I explore how animals
use their skin to move

470
00:30:37,860 --> 00:30:40,580
through the world around them.

471
00:30:40,580 --> 00:30:43,500
I'm going to reveal
the secrets of skin.

472
00:30:46,780 --> 00:30:50,700
Movement is critical for
the survival of animals.

473
00:30:50,700 --> 00:30:52,820
Fish swim.

474
00:30:52,820 --> 00:30:54,900
Moles dig.

475
00:30:54,900 --> 00:30:58,940
Sugar gliders leap
and hummingbirds hover.

476
00:30:58,940 --> 00:31:02,660
Muscles and bones might do
a lot of the heavy lifting,

477
00:31:02,660 --> 00:31:06,260
but it's adaptations to their skin
which have allowed these animals

478
00:31:06,260 --> 00:31:08,860
to move in the ways that they do.

479
00:31:08,860 --> 00:31:14,620
As we'll discover, skin is essential
for all types of movement.

480
00:31:20,820 --> 00:31:24,020
Fish are shaped the way they are
because they need to be

481
00:31:24,020 --> 00:31:27,060
streamline enough to move through
the water while using

482
00:31:27,060 --> 00:31:29,380
the least amount of energy.

483
00:31:33,100 --> 00:31:37,740
But one group of fish have taken
streamlining to the next level,

484
00:31:37,740 --> 00:31:41,220
with a super hydrodynamic surface
to their skin.

485
00:31:44,180 --> 00:31:48,300
Sharks, some of the most
formidable hunters in the oceans.

486
00:31:51,220 --> 00:31:54,820
The mako shark hunts some of
the fastest fish in the sea,

487
00:31:54,820 --> 00:31:57,620
such as tuna and swordfish.

488
00:31:59,260 --> 00:32:03,020
So has evolved to be incredibly
quick, reaching top speeds

489
00:32:03,020 --> 00:32:06,180
of over 64kph.

490
00:32:06,180 --> 00:32:09,740
And as with all sharks, their skin
plays a crucial role

491
00:32:09,740 --> 00:32:11,420
in helping them do this.

492
00:32:14,700 --> 00:32:15,900
OK. We good?

493
00:32:18,420 --> 00:32:20,740
I'm at Blue Planet Aquarium
in Chester,

494
00:32:20,740 --> 00:32:24,660
where I'm about to get
very close to these predators.

495
00:32:24,660 --> 00:32:29,380
In this tank in front of me, there
are five different species of shark.

496
00:32:30,980 --> 00:32:34,820
All of which are infinitely
more suited to moving

497
00:32:34,820 --> 00:32:37,100
through the water than I am.

498
00:32:38,220 --> 00:32:41,980
Anyone who's been in a pool will
know that moving through water

499
00:32:41,980 --> 00:32:44,780
is a lot harder than moving
through air.

500
00:32:44,780 --> 00:32:49,100
When I move through the water
like this,

501
00:32:49,100 --> 00:32:53,460
my body is creating a huge
amount of resistance.

502
00:32:53,460 --> 00:32:55,780
And this really slows me down.

503
00:32:56,900 --> 00:33:00,260
And it's because of this resistance
that I can't move

504
00:33:00,260 --> 00:33:02,420
through the water very fast.

505
00:33:04,460 --> 00:33:08,740
But shark skin is perfectly adapted
to reduce the resistance created

506
00:33:08,740 --> 00:33:12,020
as they swim, and so they can slip
through the water

507
00:33:12,020 --> 00:33:13,420
with relative ease.

508
00:33:14,740 --> 00:33:19,540
Now, I love sharks, but I'm not
about to give this one a stroke.

509
00:33:19,540 --> 00:33:24,060
But if I did, I would feel
that from the head to the tail

510
00:33:24,060 --> 00:33:26,340
is very smooth.

511
00:33:26,340 --> 00:33:30,740
But from the tail to the head
is actually very rough.

512
00:33:30,740 --> 00:33:34,780
And that's because if you look
at the skin of a shark

513
00:33:34,780 --> 00:33:37,180
in microscopic detail,

514
00:33:37,180 --> 00:33:40,780
you'll see their skin
are effectively covered

515
00:33:40,780 --> 00:33:43,940
in millions and millions
of tiny teeth.

516
00:33:46,180 --> 00:33:49,900
These dermal denticles
grow out through the top layer

517
00:33:49,900 --> 00:33:52,140
of skin, the epidermis.

518
00:33:52,140 --> 00:33:55,180
They are made from a hard mineral
called vitrodentine

519
00:33:55,180 --> 00:33:59,500
on the outside, and softer
dentine on the inside.

520
00:33:59,500 --> 00:34:03,380
It's incredibly similar to the
material human teeth are made from.

521
00:34:05,220 --> 00:34:08,140
Denticles form a regular pattern
all over the skin

522
00:34:08,140 --> 00:34:10,220
of every shark in the oceans.

523
00:34:10,220 --> 00:34:15,020
With each species having different
shaped denticles unique to them.

524
00:34:19,820 --> 00:34:24,500
These dermal denticles have
evolved to allow the sharks to slip

525
00:34:24,500 --> 00:34:26,780
seamlessly through the water.

526
00:34:26,780 --> 00:34:30,780
It makes them more streamline
and it reduces resistance.

527
00:34:30,780 --> 00:34:36,140
And this allows sharks to swim
not only fast and stealthily,

528
00:34:36,140 --> 00:34:38,540
but by saving so much energy,

529
00:34:38,540 --> 00:34:43,180
they can cover huge
distances across oceans.

530
00:34:46,420 --> 00:34:51,620
All of these things have helped turn
sharks into very efficient hunters.

531
00:34:54,860 --> 00:34:59,500
These incredible images
are CT scans of baby sharks,

532
00:34:59,500 --> 00:35:02,740
produced at the Natural History
Museum in London.

533
00:35:02,740 --> 00:35:06,980
The sharks in these images are only
a few weeks old, but you can already

534
00:35:06,980 --> 00:35:11,420
clearly see the regular arrangements
that denticles form in the skin.

535
00:35:13,140 --> 00:35:16,140
Dr Tom Fletcher,
from Leicester University,

536
00:35:16,140 --> 00:35:19,220
is an expert on
shark hydrodynamics.

537
00:35:19,220 --> 00:35:22,260
I've seen some amazing sharks
recently and one thing

538
00:35:22,260 --> 00:35:25,580
that really throws me is obviously
they're covered in denticles,

539
00:35:25,580 --> 00:35:28,140
but I don't fully get how those
denticles help them move

540
00:35:28,140 --> 00:35:29,980
through the water with such ease.

541
00:35:29,980 --> 00:35:34,140
Scientists for years were perplexed
by the roughness of these sharks

542
00:35:34,140 --> 00:35:36,700
and how they were managing
to reduce drag so effectively.

543
00:35:36,700 --> 00:35:38,700
Not only are the denticles
quite rough,

544
00:35:38,700 --> 00:35:41,580
because there are lots of them,
all jutting up next to each other,

545
00:35:41,580 --> 00:35:43,100
like we have here,

546
00:35:43,100 --> 00:35:45,460
but they're also very rough
on the surface as well.

547
00:35:45,460 --> 00:35:48,100
Obviously, these aren't actual
denticles, you've had these

548
00:35:48,100 --> 00:35:51,100
3D printed and they're much larger
than real life, yeah?

549
00:35:51,100 --> 00:35:53,980
Yes, they're about 1,000 times
bigger than they should be.

550
00:35:53,980 --> 00:35:56,020
If you look at shark denticles
in real life,

551
00:35:56,020 --> 00:35:58,660
they're like grains of sand,
they're absolutely tiny.

552
00:35:58,660 --> 00:36:01,580
And what we have here is,
we have a section of shark skin.

553
00:36:01,580 --> 00:36:02,980
These are different species.

554
00:36:02,980 --> 00:36:06,100
This is a leopard shark,
and we have a single one here.

555
00:36:06,100 --> 00:36:09,100
This is probably the fastest shark
that we've got in our oceans today.

556
00:36:09,100 --> 00:36:10,780
It's the mako shark.

557
00:36:10,780 --> 00:36:13,700
These show really nicely
the microscopic structures

558
00:36:13,700 --> 00:36:15,420
that are reducing drag.

559
00:36:15,420 --> 00:36:18,180
The key are these riblets here,
these peaks and troughs

560
00:36:18,180 --> 00:36:19,620
that we have on the surface.

561
00:36:19,620 --> 00:36:23,300
And the way they work is by reducing
the friction of the swirling fluid

562
00:36:23,300 --> 00:36:25,180
above the surface.

563
00:36:25,180 --> 00:36:28,500
So if, for example, I'm the shark
here and the fluid's moving

564
00:36:28,500 --> 00:36:31,740
over the surface and it's completely
smooth, that's a very large area

565
00:36:31,740 --> 00:36:34,180
for friction to occur.

566
00:36:34,180 --> 00:36:37,340
It's sort of like going onto an
ice rink with big snowshoes on.

567
00:36:37,340 --> 00:36:40,060
If you've got big, flat snowshoes
that are nice and smooth,

568
00:36:40,060 --> 00:36:42,100
actually, you've got lots
of friction there.

569
00:36:42,100 --> 00:36:45,220
Whereas an ice skater with that thin
blade of metal interacting

570
00:36:45,220 --> 00:36:47,660
with the ice,
just like these riblets,

571
00:36:47,660 --> 00:36:51,940
the friction is much reduced
and you can go much faster.

572
00:36:51,940 --> 00:36:55,220
In fact, shark denticles
are so good at their job,

573
00:36:55,220 --> 00:36:58,500
they're inspiring a whole
host of new technologies.

574
00:36:58,500 --> 00:37:01,420
People have been very interested
in reducing drag by 10%,

575
00:37:01,420 --> 00:37:04,460
that's really, really enormous
and it can save a lot of energy.

576
00:37:04,460 --> 00:37:07,660
In aircraft, for example,
they've tinkered with this.

577
00:37:07,660 --> 00:37:09,420
The underside of boats as well.

578
00:37:09,420 --> 00:37:12,340
If you need to move a fluid
across a solid surface,

579
00:37:12,340 --> 00:37:14,340
then this could potentially
really help.

580
00:37:14,340 --> 00:37:16,340
Good old sharks.

581
00:37:18,020 --> 00:37:21,660
If you look close enough, you'll
find a hidden microscopic world

582
00:37:21,660 --> 00:37:24,900
on the surface of the skin
of many animals,

583
00:37:24,900 --> 00:37:28,660
helping them move in ways
which often appear impossible.

584
00:37:30,220 --> 00:37:34,420
Like sharks, geckos use their skin
to help them hunt prey.

585
00:37:36,220 --> 00:37:41,180
However, when your food is an insect
which could land virtually anywhere,

586
00:37:41,180 --> 00:37:46,100
It's not just speed that you need,
but also the ability to climb.

587
00:37:49,980 --> 00:37:53,980
As geckos go, this tokay gecko
is pretty heavy.

588
00:37:56,340 --> 00:38:00,460
But still, he's able to cling
onto this piece of vertical,

589
00:38:00,460 --> 00:38:02,260
smooth glass with ease.

590
00:38:03,500 --> 00:38:05,900
And as he spins around,

591
00:38:05,900 --> 00:38:11,820
we're able to see just how
he manages to do this.

592
00:38:11,820 --> 00:38:16,820
You might think the surface
of glass is totally smooth,

593
00:38:16,820 --> 00:38:21,340
but like all materials, it's covered
in microscopic imperfections.

594
00:38:21,340 --> 00:38:25,100
And the skin on a gecko's toes
is able to make use

595
00:38:25,100 --> 00:38:28,780
of these imperfections
and stick to the glass.

596
00:38:29,780 --> 00:38:34,100
This is down to a physical property
called Van der Waals force.

597
00:38:34,100 --> 00:38:37,300
Named after the 18th-century
Dutch physicist,

598
00:38:37,300 --> 00:38:41,460
it's a weak electrical attraction
that exists between all molecules

599
00:38:41,460 --> 00:38:44,900
if they get close enough
to each other.

600
00:38:44,900 --> 00:38:48,700
If I were to place my hand
on the glass,

601
00:38:48,700 --> 00:38:53,820
there are so many ridges, lumps
and bumps, things like fingerprints,

602
00:38:53,820 --> 00:38:57,660
that there isn't enough surface
area for me to be able to use

603
00:38:57,660 --> 00:39:01,020
Van der Waals force
to stick to the glass.

604
00:39:05,580 --> 00:39:09,780
However, gecko toes have
a remarkable micro structure.

605
00:39:09,780 --> 00:39:13,060
Out of the epidermis protrude
hundreds of thousands

606
00:39:13,060 --> 00:39:17,060
of tiny filaments made of a protein
called keratin,

607
00:39:17,060 --> 00:39:20,460
the same stuff that makes
our hair and nails.

608
00:39:22,940 --> 00:39:25,780
These keratin filaments
are so small,

609
00:39:25,780 --> 00:39:29,100
that far more of the molecules
on the gecko's toe

610
00:39:29,100 --> 00:39:32,820
come into contact with the molecules
on the glass.

611
00:39:34,620 --> 00:39:37,860
This allows the gecko to use
Van der Waals force,

612
00:39:37,860 --> 00:39:44,220
and enables it to cling onto
and move up vertical surfaces.

613
00:39:51,580 --> 00:39:55,620
For any animal to move, their skin
needs to be flexible.

614
00:39:56,820 --> 00:40:00,220
And one subterranean rodent
has taken this flexibility

615
00:40:00,220 --> 00:40:02,060
to an extreme.

616
00:40:05,220 --> 00:40:09,220
The most intriguing animal,
with the strangest skin I know,

617
00:40:09,220 --> 00:40:13,580
lives in Africa, underground,
and is rarely seen.

618
00:40:14,820 --> 00:40:17,060
Naked mole rats.

619
00:40:17,060 --> 00:40:20,020
They're almost blind
and virtually hairless.

620
00:40:20,020 --> 00:40:23,300
And until relatively recently,
these strange animals

621
00:40:23,300 --> 00:40:25,620
were a total enigma to science.

622
00:40:28,820 --> 00:40:31,380
Hi, Chris.
Hi, Ben, how are you doing?

623
00:40:31,380 --> 00:40:33,500
Look at these little guys. Yeah.

624
00:40:35,260 --> 00:40:38,740
Dr Chris Faulkes has one of
the largest captive colonies

625
00:40:38,740 --> 00:40:41,060
of naked mole rats in the world.

626
00:40:42,900 --> 00:40:46,380
It's not just a case that this
little rodent is hairless,

627
00:40:46,380 --> 00:40:49,740
the skin's totally different,
it's really baggy.

628
00:40:49,740 --> 00:40:52,740
Why are they so loose, how does it
help them move, for example?

629
00:40:52,740 --> 00:40:55,260
Well, we think that it helps
them to pass each other

630
00:40:55,260 --> 00:40:57,780
in very tight situations.

631
00:40:57,780 --> 00:41:00,260
Sometimes you get a traffic jam,
with several all trying

632
00:41:00,260 --> 00:41:04,660
to get past each other and that
loose skin helps there.

633
00:41:04,660 --> 00:41:08,300
One theory is that almost
like being in a sleeping bag,

634
00:41:08,300 --> 00:41:11,700
the naked mole rats' loose skin
helps them wriggle round

635
00:41:11,700 --> 00:41:13,780
much more easily in tunnels,

636
00:41:13,780 --> 00:41:17,020
where there's very little room
for manoeuvre.

637
00:41:18,260 --> 00:41:20,940
It also helps to have loose skin
when you're living

638
00:41:20,940 --> 00:41:23,580
with this many family members.

639
00:41:23,580 --> 00:41:28,420
In the wild, they can live in social
groups of up to 300 sometimes.

640
00:41:28,420 --> 00:41:32,540
Yet, there's only one female that
breeds, the queen, and the rest

641
00:41:32,540 --> 00:41:35,020
act as either defenders or helpers.

642
00:41:35,020 --> 00:41:40,060
So it's a bit like the mammal
equivalent of a social insect.

643
00:41:40,060 --> 00:41:43,420
Crawling through these small spaces
means constantly bumping

644
00:41:43,420 --> 00:41:47,380
or scratching yourself on
sharp rocks in the earth.

645
00:41:48,500 --> 00:41:52,700
But naked mole rats feel less pain
than other rodents.

646
00:41:52,700 --> 00:41:56,020
Evolutionary changes to the pain
receptors in their skin

647
00:41:56,020 --> 00:42:00,100
means that fewer pain signals
are sent to their brain,

648
00:42:00,100 --> 00:42:03,740
making them perfectly suited
to their underground life.

649
00:42:05,740 --> 00:42:09,180
Remarkably, they live incredibly
long for a small rodent,

650
00:42:09,180 --> 00:42:13,140
over 30 years - 34 years is
the record at the moment.

651
00:42:13,140 --> 00:42:16,380
So if you think of a similarly sized
mouse, that lives for about

652
00:42:16,380 --> 00:42:19,580
three years, so more than ten times
longer than a mouse.

653
00:42:19,580 --> 00:42:23,820
They resist all of the normal
signs of ageing.

654
00:42:23,820 --> 00:42:26,460
And that's not even the most
remarkable thing

655
00:42:26,460 --> 00:42:28,180
about their physiology.

656
00:42:28,180 --> 00:42:30,900
They also resist getting cancer.

657
00:42:30,900 --> 00:42:35,140
So probably less than 0.3%
incidents of cancer,

658
00:42:35,140 --> 00:42:40,380
compared to, in some mouse strains,
up to 90% develop cancer.

659
00:42:42,820 --> 00:42:46,380
Scientists believe this incredible
ability to resist cancer

660
00:42:46,380 --> 00:42:50,860
could be to do with a compound
found in their skin.

661
00:42:50,860 --> 00:42:55,060
There's a component in the skin
called hyaluronan,

662
00:42:55,060 --> 00:42:58,020
or hyaluronic acid, which all
mammals have, we have it.

663
00:42:58,020 --> 00:43:01,940
It's often present in
skin creams and beauty products.

664
00:43:01,940 --> 00:43:06,140
Now, naked mole rats have
a unique kind of hyaluronan,

665
00:43:06,140 --> 00:43:09,700
in terms of size and its
molecular structure.

666
00:43:09,700 --> 00:43:13,860
Hyaluronic acid is a component
of the connective tissues

667
00:43:13,860 --> 00:43:17,900
which form the structure
of skin and other organs.

668
00:43:17,900 --> 00:43:22,180
And naked mole rats have a unique
form of hyaluronic acid

669
00:43:22,180 --> 00:43:24,660
with a coiled molecular shape.

670
00:43:24,660 --> 00:43:27,460
This makes the molecule
act almost like a spring.

671
00:43:28,780 --> 00:43:31,740
This gives the naked mole rats
their stretchy skin,

672
00:43:31,740 --> 00:43:35,940
and might be a key factor in their
ability to resist cancer.

673
00:43:35,940 --> 00:43:39,580
But research into this
is still at an early stage.

674
00:43:41,420 --> 00:43:45,300
Whether you think they're ugly
or cute, what's not up for debate

675
00:43:45,300 --> 00:43:49,500
is that these saggy-skinned members
of the rodent family

676
00:43:49,500 --> 00:43:52,860
are helping us understand and tackle

677
00:43:52,860 --> 00:43:55,700
some of our most
devastating diseases.

678
00:43:57,980 --> 00:44:01,740
Life in challenging environments
is often only possible

679
00:44:01,740 --> 00:44:04,700
because of skin's
incredible versatility.

680
00:44:10,900 --> 00:44:15,140
One leading theory suggests that
a subterranean existence drove

681
00:44:15,140 --> 00:44:19,820
one particular group of animals
to even more extreme adaptations.

682
00:44:23,260 --> 00:44:28,420
Go back 150 million years
and the ancestors of snakes

683
00:44:28,420 --> 00:44:31,500
lived underground,
but had four legs.

684
00:44:34,140 --> 00:44:36,900
But these limbs would have just
got in the way,

685
00:44:36,900 --> 00:44:39,940
so over time, the snakes
lost them and evolved

686
00:44:39,940 --> 00:44:43,540
to propel themselves along
on their bellies.

687
00:44:48,260 --> 00:44:51,620
But now, with the majority of snakes
living above ground,

688
00:44:51,620 --> 00:44:55,180
there's one question that has
puzzled scientists.

689
00:44:55,180 --> 00:44:59,900
How are snakes able to get across
flat surfaces without limbs?

690
00:45:02,340 --> 00:45:05,660
The secret to how this snake
is able to move

691
00:45:05,660 --> 00:45:10,740
lies in the specially adapted scales
on the underside of her belly there.

692
00:45:13,900 --> 00:45:17,660
And while they may look very smooth,
they're actually able to generate

693
00:45:17,660 --> 00:45:20,180
a large amount of friction.

694
00:45:24,740 --> 00:45:27,860
Each belly scale is made
of keratin and populated

695
00:45:27,860 --> 00:45:30,420
with microscopic protrusions.

696
00:45:30,420 --> 00:45:33,780
The snake can grip the ground
with its belly scales

697
00:45:33,780 --> 00:45:39,660
by using these protrusions to catch
on any imperfections on the surface.

698
00:45:39,660 --> 00:45:43,700
It is then able to pull other
parts of its body forward.

699
00:45:45,300 --> 00:45:48,460
The arrangement of these
tiny protrusions is key.

700
00:45:48,460 --> 00:45:51,780
They're positioned so that when
the belly scales slide forward

701
00:45:51,780 --> 00:45:54,860
over the ground,
they do so smoothly.

702
00:45:54,860 --> 00:46:00,700
In one direction, the scale slips,
in the other direction, it grips,

703
00:46:00,700 --> 00:46:03,940
allowing snakes to move
effortlessly through a range

704
00:46:03,940 --> 00:46:08,340
of habitats, tackling virtually
any surface they come across.

705
00:46:14,980 --> 00:46:18,460
Throughout evolution,
skin has used keratin in a variety

706
00:46:18,460 --> 00:46:20,380
of ingenious ways.

707
00:46:23,700 --> 00:46:27,780
It's the main component
of nails, scales and hair.

708
00:46:29,820 --> 00:46:34,060
But none of these are as complex
as its real crowning achievement.

709
00:46:36,900 --> 00:46:38,260
Feathers.

710
00:46:40,820 --> 00:46:43,660
They grow in a similar way
to our hair.

711
00:46:45,740 --> 00:46:49,900
A shaft made of keratin grows
out of follicles in the skin,

712
00:46:49,900 --> 00:46:53,300
but that's where
the similarity ends.

713
00:46:53,300 --> 00:46:55,820
As the shaft emerges
from the follicle,

714
00:46:55,820 --> 00:46:59,860
branched keratin filaments open out,
forming a flat surface,

715
00:46:59,860 --> 00:47:01,300
known as the vein.

716
00:47:03,540 --> 00:47:06,260
There are different types
of feathers,

717
00:47:06,260 --> 00:47:07,980
which come in all shapes and sizes.

718
00:47:10,260 --> 00:47:12,940
And it's the flight feathers
that birds grow from the skin

719
00:47:12,940 --> 00:47:17,700
on their wings which enable them
to take off and stay in the air.

720
00:47:18,940 --> 00:47:21,620
I've come to the International
Centre for Birds of Prey

721
00:47:21,620 --> 00:47:25,460
in Gloucestershire, to see some
really impressive flyers.

722
00:47:26,660 --> 00:47:28,940
This is a Steller's sea eagle.

723
00:47:28,940 --> 00:47:30,980
He's got a two-metre wingspan,

724
00:47:30,980 --> 00:47:34,380
and he's one of the heaviest eagles
on the planet.

725
00:47:34,380 --> 00:47:36,860
And he can dive from a perch
to catch his prey,

726
00:47:36,860 --> 00:47:41,180
or he can soar using those massive
wings to look for his next meal.

727
00:47:41,180 --> 00:47:45,780
He's got huge flight feathers
and each one is lightweight, stiff,

728
00:47:45,780 --> 00:47:48,340
but importantly,
really, really strong.

729
00:47:50,140 --> 00:47:53,060
In flight, the shape of
a bird's wing

730
00:47:53,060 --> 00:47:57,460
means the air pressure under
the wing is greater than that above.

731
00:47:58,420 --> 00:48:02,380
And it's this difference in pressure
which keeps them in the air.

732
00:48:02,380 --> 00:48:05,140
But this is only possible
because of the way

733
00:48:05,140 --> 00:48:06,900
their flight feathers work.

734
00:48:06,900 --> 00:48:10,900
And if you take one of these
feathers and have a look,

735
00:48:10,900 --> 00:48:14,900
you can actually see that on one
side, there's just more feather.

736
00:48:14,900 --> 00:48:19,820
And it's this asymmetry that allows
him to be such an amazing flyer.

737
00:48:22,700 --> 00:48:27,980
On flight feathers, one side of
this keratin vein is larger.

738
00:48:27,980 --> 00:48:32,860
As a bird flies, this larger part
of the vein catches the air,

739
00:48:32,860 --> 00:48:36,060
rotating the feathers slightly.

740
00:48:36,060 --> 00:48:39,180
This twists the feathers
so they interlock.

741
00:48:39,180 --> 00:48:41,540
This then stops air
passing through them,

742
00:48:41,540 --> 00:48:45,500
and it's this that gives the wing
lift and thrust.

743
00:48:45,500 --> 00:48:49,260
This interlocking means
that together,

744
00:48:49,260 --> 00:48:52,980
all the feathers in the wing
form a large surface area,

745
00:48:52,980 --> 00:48:55,420
impermeable to the air.

746
00:48:55,420 --> 00:48:59,220
Meaning the higher pressure
underneath keeps the bird aloft.

747
00:49:00,300 --> 00:49:02,860
Another type of feather,
common to all birds,

748
00:49:02,860 --> 00:49:04,940
is the contour feather.

749
00:49:04,940 --> 00:49:08,660
Unlike flight feathers,
the vein on contour feathers

750
00:49:08,660 --> 00:49:10,500
is pretty symmetrical.

751
00:49:10,500 --> 00:49:12,300
These feathers cover the torso,

752
00:49:12,300 --> 00:49:14,940
giving the bird
its aerodynamic shape.

753
00:49:17,540 --> 00:49:22,780
Flight feathers and contour feathers
share an amazing micro structure.

754
00:49:22,780 --> 00:49:26,900
The veins' filaments have
interlocking barbs which mesh

755
00:49:26,900 --> 00:49:30,700
together to form an effective
surface for the air to slip over.

756
00:49:33,300 --> 00:49:36,660
This allows contour feathers
to create a streamlined shape

757
00:49:36,660 --> 00:49:38,820
around the bird's body.

758
00:49:41,900 --> 00:49:45,340
And there's one group of birds
of prey which take full advantage

759
00:49:45,340 --> 00:49:47,740
of this aerodynamic feature.

760
00:49:47,740 --> 00:49:52,140
When they hunt,
some falcons can reach

761
00:49:52,140 --> 00:49:54,940
an astonishing 320kph.

762
00:49:54,940 --> 00:49:58,220
And I'm going to see
one of them in action.

763
00:49:58,220 --> 00:50:01,940
Jemima, this is a beautiful bird,
and I've seen these in the wild.

764
00:50:01,940 --> 00:50:04,500
This is a gyrfalcon,
isn't it? That's right.

765
00:50:04,500 --> 00:50:07,020
These are built for speed and
built to kill, right? They are.

766
00:50:07,020 --> 00:50:09,460
They've got these lovely long,
pointed wings,

767
00:50:09,460 --> 00:50:10,740
as have all the falcons.

768
00:50:10,740 --> 00:50:14,460
And we have a special way to
show you how this thing does fly.

769
00:50:14,460 --> 00:50:19,580
So, we've gone modern and we have
a robotic crow, the Rocrow.

770
00:50:19,580 --> 00:50:22,460
So we're going to chuck up a robot
and get it to fly,

771
00:50:22,460 --> 00:50:24,700
and see if this beautiful beast
can take it down?

772
00:50:24,700 --> 00:50:27,820
That's what we're going to do.
Brilliant, I want to see this.

773
00:50:36,420 --> 00:50:40,460
Jemima uses this technique
to train many of her falcons.

774
00:50:41,980 --> 00:50:46,380
These birds typically hunt at
a height of around 300 metres,

775
00:50:46,380 --> 00:50:49,140
perfect for swooping down
on their prey.

776
00:50:49,140 --> 00:50:52,220
So he'll have to climb now, I guess,
to get above the robot, won't he?

777
00:50:52,220 --> 00:50:55,460
He has to climb and that's what
he's got to learn.

778
00:50:55,460 --> 00:50:57,660
He's quite young
and not, as yet, very fit

779
00:50:57,660 --> 00:50:59,780
and it's a windy day for him.

780
00:51:01,700 --> 00:51:04,180
Falcons dive at their prey
like bullets,

781
00:51:04,180 --> 00:51:07,300
often stunning or even
killing them in mid-air.

782
00:51:08,380 --> 00:51:11,580
During this dive, their pointed
wings and the interlocking

783
00:51:11,580 --> 00:51:14,580
barbs on their feathers
makes this family of birds

784
00:51:14,580 --> 00:51:17,180
among the fastest animals
on the planet.

785
00:51:19,380 --> 00:51:22,140
The Robocrow doesn't stand
a chance.

786
00:51:23,700 --> 00:51:25,980
You can see those big, long flaps
followed by

787
00:51:25,980 --> 00:51:29,620
some really quick,
thrusting beats there. Yeah.

788
00:51:29,620 --> 00:51:31,580
He's just trying to get some speed.

789
00:51:31,580 --> 00:51:33,300
And it doesn't stop either.

790
00:51:34,820 --> 00:51:37,100
Whoa. Ooh, ooh. Oh!

791
00:51:38,580 --> 00:51:41,900
He just hit...
Oh, and Robocrow's down.

792
00:51:41,900 --> 00:51:43,700
And down he goes. Good boy.

793
00:51:47,220 --> 00:51:49,500
And this is what they use
to hunt in the wild.

794
00:51:49,500 --> 00:51:51,420
We saw different types
of flight there,

795
00:51:51,420 --> 00:51:54,020
and that last second hit,
using the feathers,

796
00:51:54,020 --> 00:51:57,580
using the wing shape to really
bring all those things together

797
00:51:57,580 --> 00:51:59,060
and take down its prey.

798
00:51:59,060 --> 00:52:02,260
Well, I'm always happy
when nature trashes a robot,

799
00:52:02,260 --> 00:52:04,180
so that was great.

800
00:52:05,860 --> 00:52:10,220
From the growth of small keratin
protrusions, it's their skin

801
00:52:10,220 --> 00:52:15,060
which has enabled birds to soar,
hover, dive and glide their way

802
00:52:15,060 --> 00:52:17,260
to dominating the skies.

803
00:52:19,580 --> 00:52:23,780
But without feathers,
how do you get into the air?

804
00:52:27,300 --> 00:52:30,460
Living in the rainforests
of Australia and Indonesia,

805
00:52:30,460 --> 00:52:33,580
sugar gliders spend their time
in the treetops,

806
00:52:33,580 --> 00:52:35,420
gliding between branches.

807
00:52:37,740 --> 00:52:41,060
These marsupials use wings
made of flaps of skin

808
00:52:41,060 --> 00:52:43,980
to harness the power of the air,

809
00:52:43,980 --> 00:52:46,940
allowing them to glide
up to 50 metres.

810
00:52:48,620 --> 00:52:51,580
But how they manage to stay
airborne for this distance

811
00:52:51,580 --> 00:52:54,220
has remained a mystery.

812
00:52:54,220 --> 00:52:56,820
Today, this will be tested
for the first time

813
00:52:56,820 --> 00:53:02,260
by Dr Jorn Cheney, a specialist
in animal flight adaptations.

814
00:53:02,260 --> 00:53:05,260
Hey, Jorn. Hey, Ben, nice
to see you. Yeah, you too.

815
00:53:05,260 --> 00:53:06,500
Who have you got here?

816
00:53:06,500 --> 00:53:08,420
This is Chloe.

817
00:53:08,420 --> 00:53:12,060
I've never seen a live
sugar glider before.

818
00:53:12,060 --> 00:53:13,540
Hello.

819
00:53:13,540 --> 00:53:17,540
I'm absolutely fascinated by
the structure of their skin.

820
00:53:17,540 --> 00:53:19,860
Because they move through the air,
but they don't fly

821
00:53:19,860 --> 00:53:21,540
in a traditional sense, do they?

822
00:53:21,540 --> 00:53:24,340
No, no, they're more gliders
than flyers.

823
00:53:24,340 --> 00:53:26,700
And traditionally, we think
of flying as animals

824
00:53:26,700 --> 00:53:29,380
that flap their wings and
power themselves through the air.

825
00:53:29,380 --> 00:53:31,420
Gliders mostly go down
and then sideways.

826
00:53:31,420 --> 00:53:34,060
It's super weird,
because that's not how we fly.

827
00:53:34,060 --> 00:53:37,420
We don't see birds fly that way,
we don't build aircrafts that way.

828
00:53:37,420 --> 00:53:40,420
And so I'm interested in why she's
able to fly so well with such

829
00:53:40,420 --> 00:53:41,700
an unusual shape.

830
00:53:41,700 --> 00:53:45,900
For this experiment, we're at the
Specialist Flight Research Centre

831
00:53:45,900 --> 00:53:49,500
at the Royal Veterinary College
in Hertfordshire.

832
00:53:49,500 --> 00:53:51,820
I'll relieve her from you.
Thank you.

833
00:53:51,820 --> 00:53:54,540
Chloe has been hand-reared
and her handler, Simon,

834
00:53:54,540 --> 00:53:56,700
is going to help with
the experiment.

835
00:53:56,700 --> 00:53:59,420
So Chloe is going to start
on that platform up there.

836
00:53:59,420 --> 00:54:02,020
She's going to use that
as a launch platform,

837
00:54:02,020 --> 00:54:04,380
and Simon is going to hold that
and coax her off

838
00:54:04,380 --> 00:54:09,020
to jump over to you, just like that,
where you'll be standing over there.

839
00:54:09,020 --> 00:54:12,460
Jorn has set up four
ultra high-speed cameras

840
00:54:12,460 --> 00:54:14,340
to record Chloe's gliding.

841
00:54:14,340 --> 00:54:19,100
Chloe takes her place on
the launchpad and I do my best

842
00:54:19,100 --> 00:54:20,500
to impersonate a tree.

843
00:54:23,740 --> 00:54:26,020
Oh, oh, oh, she's thinking about it.

844
00:54:29,540 --> 00:54:30,980
Perfect.

845
00:54:30,980 --> 00:54:32,580
THEY CHUCKLE

846
00:54:32,580 --> 00:54:35,260
Chloe gets into the swing
of things immediately.

847
00:54:37,020 --> 00:54:38,500
Come on, then.

848
00:54:38,500 --> 00:54:41,460
Although her aim needs
a little work.

849
00:54:44,900 --> 00:54:47,820
This is one of the weirder
experiments I've ever done,

850
00:54:47,820 --> 00:54:49,380
I'm not going to lie.

851
00:54:52,540 --> 00:54:54,700
I love that we're actually
doing science

852
00:54:54,700 --> 00:54:57,820
whilst trying to catch
a sugar glider, this is brilliant.

853
00:54:57,820 --> 00:55:01,540
It's the shape that Chloe's flexible
skin wings take in the air

854
00:55:01,540 --> 00:55:04,980
that will tell Jorn a lot
about how she's using them.

855
00:55:04,980 --> 00:55:07,060
Well done, little one.

856
00:55:07,060 --> 00:55:10,820
And in order to see this,
he's created a 3D model

857
00:55:10,820 --> 00:55:13,380
of Chloe's wings with his cameras.

858
00:55:13,380 --> 00:55:15,180
What have the results shown?

859
00:55:15,180 --> 00:55:19,180
So, that beautiful thing is Chloe,
just the top surface of her.

860
00:55:19,180 --> 00:55:20,300
Yeah.

861
00:55:20,300 --> 00:55:23,300
What you're able to pick up
from this is the full 3D shape

862
00:55:23,300 --> 00:55:25,260
that she's using when she glides.

863
00:55:25,260 --> 00:55:27,460
And that's important
because the aerodynamics

864
00:55:27,460 --> 00:55:29,340
are entirely determined
by the shape.

865
00:55:29,340 --> 00:55:32,020
But also, she's not flat,
she's curved.

866
00:55:32,020 --> 00:55:34,060
Yeah, she's got a lot of curvature.

867
00:55:34,060 --> 00:55:37,540
Jorn has worked out that Chloe's
wings curved or billowed

868
00:55:37,540 --> 00:55:39,660
by a surprising amount -

869
00:55:39,660 --> 00:55:43,940
over three times more than
the wings of a gliding bird.

870
00:55:43,940 --> 00:55:47,420
All of that billowing helps guide
the air downward and backward,

871
00:55:47,420 --> 00:55:49,260
producing lift.

872
00:55:49,260 --> 00:55:52,420
The more billowing you get, the more
aerodynamic force you're producing.

873
00:55:52,420 --> 00:55:54,620
So if the wing wasn't billowing
like that,

874
00:55:54,620 --> 00:55:56,100
she'd be a much worse flyer.

875
00:55:56,100 --> 00:56:00,820
What's also clear is that Chloe
is controlling this billowing.

876
00:56:00,820 --> 00:56:04,140
The muscles in the middle
of the skin flaps are relaxed,

877
00:56:04,140 --> 00:56:08,180
while the muscles around the edge
have been tensed.

878
00:56:08,180 --> 00:56:11,020
So this flexible skin, we definitely
don't see that with birds, do we?

879
00:56:11,020 --> 00:56:13,860
We don't see it with birds,
but we do see it with every other

880
00:56:13,860 --> 00:56:15,420
gliding mammalian lineage.

881
00:56:15,420 --> 00:56:18,460
All have, for whatever reason,
converged upon the idea of

882
00:56:18,460 --> 00:56:21,700
using skin as a wing and then
embedding muscle into it.

883
00:56:21,700 --> 00:56:24,780
And we're able to figure out
that the muscle isn't the only thing

884
00:56:24,780 --> 00:56:27,980
supporting the body weight, the skin
is actually doing quite a bit.

885
00:56:27,980 --> 00:56:31,020
There's still a lot more work
to do to really understand

886
00:56:31,020 --> 00:56:34,020
what is going on with
gliding animals like Chloe.

887
00:56:34,020 --> 00:56:37,260
But one day, Jorn is hoping
experiments like this

888
00:56:37,260 --> 00:56:39,980
could pave the way for
new aircraft technology

889
00:56:39,980 --> 00:56:43,300
using flexible material for wings.

890
00:56:44,980 --> 00:56:47,500
Skin's adaptability is unparalleled.

891
00:56:47,500 --> 00:56:52,860
Animals have used their skin
to master movement on every surface,

892
00:56:52,860 --> 00:56:55,860
patch of sky and body of water
on Earth.

893
00:56:58,340 --> 00:57:01,940
Next time, I'll show you how
skin protects vertebrates

894
00:57:01,940 --> 00:57:05,220
from the planet's most
extreme conditions.

895
00:57:05,220 --> 00:57:09,900
And I'll do that by testing my
skin's response to intense cold...

896
00:57:09,900 --> 00:57:13,940
My skin is literally trying
to save me!

897
00:57:13,940 --> 00:57:16,580
..discovering how a giraffe protects
itself from the sun...

898
00:57:16,580 --> 00:57:17,940
Hello, mate.

899
00:57:17,940 --> 00:57:22,340
..and comparing cooling methods
with my dog, Jack.

900
00:57:22,340 --> 00:57:24,540
Yeah, I'm sweating.

901
00:57:56,380 --> 00:57:57,820
Skin.

902
00:57:57,820 --> 00:57:59,300
We all have it.

903
00:57:59,300 --> 00:58:03,260
And so does every vertebrate
on the planet.

904
00:58:03,260 --> 00:58:05,060
It keeps the outside out...

905
00:58:06,140 --> 00:58:07,860
..and the inside in.

906
00:58:09,180 --> 00:58:11,860
Animals may look very different
on the surface

907
00:58:11,860 --> 00:58:15,460
but, amazingly, all share
the basic skin blueprint.

908
00:58:17,500 --> 00:58:21,220
I'm Ben Garrod, professor
of evolutionary biology,

909
00:58:21,220 --> 00:58:25,220
and skin is a subject
that utterly fascinates me.

910
00:58:25,220 --> 00:58:27,780
It's not just the case
that he's hairless,

911
00:58:27,780 --> 00:58:29,500
the skin's totally different.

912
00:58:29,500 --> 00:58:32,620
We're discovering so much
amazing new science...

913
00:58:32,620 --> 00:58:34,100
This is really quite remarkable.

914
00:58:34,100 --> 00:58:36,740
It should be a game-changer
for so many people.

915
00:58:36,740 --> 00:58:37,780
RATTLE SOUNDS

916
00:58:37,780 --> 00:58:40,900
That sound, makes the hair on the
back of your neck go up, doesn't it?

917
00:58:40,900 --> 00:58:44,180
..about this often overlooked
wonder of nature.

918
00:58:44,180 --> 00:58:48,340
It really transforms our
understanding of dinosaurs.

919
00:58:48,340 --> 00:58:52,860
I'm going to explore the natural
history of the body's largest organ,

920
00:58:52,860 --> 00:58:57,660
to see how skin has allowed animals
to conquer every habitat,

921
00:58:57,660 --> 00:58:59,980
disappear into their surroundings,

922
00:58:59,980 --> 00:59:03,380
and even develop
extrasensory abilities.

923
00:59:05,500 --> 00:59:10,140
And I will discover the complex
ecosystem living on my own skin.

924
00:59:10,140 --> 00:59:13,260
Oh, Jim, that's awful, it really is.

925
00:59:13,260 --> 00:59:18,300
In this episode, I discover how
the smell of my skin can help win

926
00:59:18,300 --> 00:59:19,700
the war against malaria.

927
00:59:19,700 --> 00:59:20,980
Hello, mate.

928
00:59:20,980 --> 00:59:24,100
I'll reveal the secrets
behind a giraffe's spots.

929
00:59:25,140 --> 00:59:28,900
And find out how hippos
produce their own sunscreen...

930
00:59:30,900 --> 00:59:35,780
..to understand how skin has adapted
in a multitude of ways to protect

931
00:59:35,780 --> 00:59:39,020
animals against a hostile world.

932
00:59:39,020 --> 00:59:41,940
I'm going to reveal
the Secrets Of Skin.

933
00:59:48,620 --> 00:59:52,220
At its most basic, skin is
what separates our fragile,

934
00:59:52,220 --> 00:59:55,260
vulnerable insides
from the outside world.

935
00:59:56,780 --> 01:00:01,380
Our planet is a dangerous
and often unpredictable place.

936
01:00:01,380 --> 01:00:04,180
So to work efficiently,
we need to keep conditions

937
01:00:04,180 --> 01:00:08,180
inside our bodies, like temperature,
nice and constant.

938
01:00:08,180 --> 01:00:11,100
Excess heat or cold can upset
the stability

939
01:00:11,100 --> 01:00:13,740
of our internal body temperature,
which needs to be around

940
01:00:13,740 --> 01:00:18,660
37 degrees Celsius regardless
of the temperature outside.

941
01:00:18,660 --> 01:00:22,700
Right now, I'm going to upset
that stability in a big way.

942
01:00:24,180 --> 01:00:27,540
Because I'm going to go
into a freezer that's currently

943
01:00:27,540 --> 01:00:30,180
minus 13 degrees Celsius.

944
01:00:31,620 --> 01:00:32,900
SIGHS HEAVILY

945
01:00:32,900 --> 01:00:35,860
Here we go.

946
01:00:35,860 --> 01:00:36,900
Ooh!

947
01:00:40,340 --> 01:00:45,300
Already, there's a blast of cold air
that's just hit my face.

948
01:00:46,460 --> 01:00:49,060
And it's taken about three seconds
for my body to feel

949
01:00:49,060 --> 01:00:50,540
really, really cold.

950
01:00:52,780 --> 01:00:55,780
To get a better idea of what's
happening to me, we're using

951
01:00:55,780 --> 01:00:57,340
a thermal camera.

952
01:00:57,340 --> 01:01:01,260
This reveals the heat given off
by animal and human skin.

953
01:01:03,740 --> 01:01:07,300
Lower temperatures appear as blue
and purple, while warmer

954
01:01:07,300 --> 01:01:09,580
temperatures appear red, yellow

955
01:01:09,580 --> 01:01:12,340
and, hottest of all, white.

956
01:01:12,340 --> 01:01:15,740
If my internal temperature
drops just two degrees

957
01:01:15,740 --> 01:01:19,820
to 35 degrees Celsius,
hypothermia will set in

958
01:01:19,820 --> 01:01:22,940
and my vital organs
will begin to fail.

959
01:01:22,940 --> 01:01:25,500
That's because my skin
isn't well insulated enough

960
01:01:25,500 --> 01:01:27,540
to keep the heat in.

961
01:01:27,540 --> 01:01:32,820
So right now, the hair on my arms
is all starting to stand on end.

962
01:01:34,580 --> 01:01:39,180
That's because my skin is
literally trying to save me.

963
01:01:39,180 --> 01:01:43,420
In mammals, hair grows out of
the dermis at an angle.

964
01:01:43,420 --> 01:01:47,580
Each has a tiny muscle that
contracts when the skin gets cold,

965
01:01:47,580 --> 01:01:51,380
pulling the hair erect and causing
goose bumps.

966
01:01:51,380 --> 01:01:57,380
And it does this to try and trap
a layer of warm air between our skin

967
01:01:57,380 --> 01:01:59,820
and the hair itself.

968
01:02:01,660 --> 01:02:04,980
It's not working right now,
it's so cold.

969
01:02:06,460 --> 01:02:09,460
That's because I'm just not
hairy enough.

970
01:02:09,460 --> 01:02:12,820
This automatic response
is an echo from our evolutionary

971
01:02:12,820 --> 01:02:16,060
past when our ancestors
were much hairier.

972
01:02:17,380 --> 01:02:20,420
Dense hair traps a layer
of air next to the skin,

973
01:02:20,420 --> 01:02:24,340
which acts as insulation
and stops heat escaping.

974
01:02:24,340 --> 01:02:27,220
Feathers work in the same way.

975
01:02:27,220 --> 01:02:30,820
The more hair or feathers,
the better they are at trapping air.

976
01:02:32,300 --> 01:02:34,460
It's a brilliant system.

977
01:02:34,460 --> 01:02:36,500
A polar bear can
survive temperatures

978
01:02:36,500 --> 01:02:39,740
down to minus 69 degrees Celsius.

979
01:02:39,740 --> 01:02:44,500
While at minus 13, I'm really
starting to struggle.

980
01:02:45,780 --> 01:02:48,780
I'm getting really cold right now,
and if I stay here,

981
01:02:48,780 --> 01:02:52,100
I'm not going to survive very long.

982
01:02:52,100 --> 01:02:54,700
And without hair like a polar bear,

983
01:02:54,700 --> 01:02:58,140
the only thing that's going
to keep me warm...

984
01:02:58,140 --> 01:03:00,540
Thank you, Nigel.

985
01:03:00,540 --> 01:03:06,180
..is some pretty serious
Arctic gear.

986
01:03:06,180 --> 01:03:08,580
Ah, that's better.

987
01:03:10,700 --> 01:03:16,020
But even with the warmest
of winter clothing,

988
01:03:16,020 --> 01:03:21,300
I'm only going to stay
so comfortable for so long.

989
01:03:21,300 --> 01:03:23,420
So I think it's time to leave.

990
01:03:23,420 --> 01:03:28,660
A polar bear's dense layer of
inner hair helps insulate them.

991
01:03:28,660 --> 01:03:31,700
But their hair is also special
in being hollow,

992
01:03:31,700 --> 01:03:34,940
allowing them to trap
even more warmed air.

993
01:03:36,980 --> 01:03:40,540
But they don't win the prize
for the densest hair on the planet.

994
01:03:40,540 --> 01:03:43,340
That goes to the sea otter.

995
01:03:43,340 --> 01:03:48,620
These shellfish-eating ocean
specialists have 400,000 follicles

996
01:03:48,620 --> 01:03:51,300
per square centimetre.

997
01:03:51,300 --> 01:03:56,380
That's 2,000 times the density
of the hair on my head.

998
01:03:58,380 --> 01:04:01,820
While sea otters have evolved
external insulation

999
01:04:01,820 --> 01:04:05,340
to slow down heat escaping in
the chilly waters of the Pacific,

1000
01:04:05,340 --> 01:04:09,260
other marine mammals have ditched
insulating hair altogether,

1001
01:04:09,260 --> 01:04:13,180
and gone for insulation under
the dermis by developing

1002
01:04:13,180 --> 01:04:17,700
a thick protective layer of fat,
which stops heat escaping,

1003
01:04:17,700 --> 01:04:20,140
known as blubber.

1004
01:04:20,140 --> 01:04:24,460
And the absolute blubber champions
are cetaceans -

1005
01:04:24,460 --> 01:04:28,180
porpoises, dolphins and whales -
which can vary the thickness

1006
01:04:28,180 --> 01:04:31,340
of their blubber depending on
the time of year,

1007
01:04:31,340 --> 01:04:34,260
where they are and a host
of other factors.

1008
01:04:35,940 --> 01:04:37,380
Imagine for a moment

1009
01:04:37,380 --> 01:04:40,700
that these doughnuts
represent whale blubber.

1010
01:04:40,700 --> 01:04:44,660
Then the more doughnuts I use means
the thicker the whale blubber is.

1011
01:04:44,660 --> 01:04:48,620
My first whale is the minke.

1012
01:04:48,620 --> 01:04:52,180
These filter-feeding whales
live in warm, temperate waters

1013
01:04:52,180 --> 01:04:54,060
around the planet.

1014
01:04:54,060 --> 01:04:56,580
They have a maximum
blubber thickness

1015
01:04:56,580 --> 01:04:58,540
of about seven centimetres.

1016
01:04:58,540 --> 01:05:01,500
That's the same as two doughnuts.

1017
01:05:03,620 --> 01:05:07,740
My next whale is a bit more
cosmopolitan, it's the humpback.

1018
01:05:07,740 --> 01:05:11,100
They can spread their time
between warm, equatorial waters

1019
01:05:11,100 --> 01:05:14,620
and colder waters towards
the polar regions.

1020
01:05:14,620 --> 01:05:19,860
They have thicker blubber, which can
reach about 12 centimetres thick.

1021
01:05:19,860 --> 01:05:24,380
Now the bowhead whale is
an absolute champion at thriving

1022
01:05:24,380 --> 01:05:28,140
in sub-zero polar waters.

1023
01:05:28,140 --> 01:05:32,180
And with that, they need some pretty
serious blubber.

1024
01:05:32,180 --> 01:05:35,420
Their blubber is the thickest
on the planet,

1025
01:05:35,420 --> 01:05:38,860
and it allows them to survive
in environments

1026
01:05:38,860 --> 01:05:41,780
that few other animals
can survive in.

1027
01:05:43,540 --> 01:05:46,420
In fact, that's not enough.

1028
01:05:46,420 --> 01:05:51,260
Because bowhead whales have a layer
of blubber that can be as much

1029
01:05:51,260 --> 01:05:53,460
as 50 centimetres thick.

1030
01:05:53,460 --> 01:05:57,420
That's about the same as
17 of these doughnuts.

1031
01:06:01,620 --> 01:06:06,460
So by using feathers and hair on
land and blubber in the sea,

1032
01:06:06,460 --> 01:06:09,700
skin protects animals against
the cold, allowing them

1033
01:06:09,700 --> 01:06:13,860
to colonise environments ranging
from just above freezing

1034
01:06:13,860 --> 01:06:16,260
down to minus 69 degrees Celsius.

1035
01:06:19,260 --> 01:06:21,900
There's only one problem with
being really well insulated

1036
01:06:21,900 --> 01:06:23,500
against the cold.

1037
01:06:23,500 --> 01:06:26,140
What do you do when you get too hot?

1038
01:06:26,140 --> 01:06:28,140
Come on, let's go, go.

1039
01:06:30,420 --> 01:06:32,420
Ha, ha, come on.

1040
01:06:34,660 --> 01:06:36,100
Come here.

1041
01:06:36,100 --> 01:06:37,500
Jack, Jack.

1042
01:06:37,500 --> 01:06:40,580
Even in cooler climates
like Britain, heat generated

1043
01:06:40,580 --> 01:06:43,260
by muscles and metabolism
can significantly

1044
01:06:43,260 --> 01:06:44,940
raise body temperature.

1045
01:06:45,940 --> 01:06:47,220
Come on, good boy.

1046
01:06:50,780 --> 01:06:54,580
The heat that Jack and I are
generating right now,

1047
01:06:54,580 --> 01:06:57,980
will soon start to affect
the smooth running of our bodies

1048
01:06:57,980 --> 01:06:59,220
if we can't get rid of it.

1049
01:06:59,220 --> 01:07:00,420
Come on.

1050
01:07:06,340 --> 01:07:09,540
Luckily for me, when I get too hot,

1051
01:07:09,540 --> 01:07:14,500
my skin produces this amazing
coolant via the dermis,

1052
01:07:14,500 --> 01:07:21,420
which is pumped to the surface
by specialised glands.

1053
01:07:23,860 --> 01:07:25,860
Yeah, I'm sweating.

1054
01:07:27,500 --> 01:07:31,340
As the sweat evaporates, my body
cools and this keeps everything

1055
01:07:31,340 --> 01:07:33,820
inside at a safe temperature.

1056
01:07:36,100 --> 01:07:39,820
Some researchers believe that
sweating as a cooling system

1057
01:07:39,820 --> 01:07:44,340
allowed our ancient ancestors on
the African savannah to stay active

1058
01:07:44,340 --> 01:07:46,860
during the hottest part of the day.

1059
01:07:48,620 --> 01:07:53,220
It also enables humans to become
the ultimate endurance runners.

1060
01:07:54,220 --> 01:07:58,740
I've got between two and four
million sweat glands in my skin.

1061
01:07:58,740 --> 01:08:02,860
It's almost exactly the same number
I was born with,

1062
01:08:02,860 --> 01:08:05,940
Even though my skin is now
several times bigger

1063
01:08:05,940 --> 01:08:08,660
than it was when I was a toddler.

1064
01:08:08,660 --> 01:08:10,380
Nobody likes sweating.

1065
01:08:10,380 --> 01:08:14,220
In fact, we do all we can to avoid
it sometimes.

1066
01:08:14,220 --> 01:08:17,220
But actually, sweating is amazing.

1067
01:08:17,220 --> 01:08:19,180
It's an incredible adaptation

1068
01:08:19,180 --> 01:08:21,980
and humans are unique
in being the only species

1069
01:08:21,980 --> 01:08:24,620
to cool down in this way.

1070
01:08:24,620 --> 01:08:26,100
Hairy mammals like Jack

1071
01:08:26,100 --> 01:08:28,660
have far fewer sweat glands
than humans,

1072
01:08:28,660 --> 01:08:33,340
and only produce between
10 and 20% as much sweat as a human

1073
01:08:33,340 --> 01:08:36,100
under conditions of high-heat
exercise.

1074
01:08:36,100 --> 01:08:39,340
So Jack has to pant to cool himself
down.

1075
01:08:39,340 --> 01:08:41,940
As water evaporates
from his mouth and tongue,

1076
01:08:41,940 --> 01:08:44,060
it takes the heat with it.

1077
01:08:44,060 --> 01:08:48,380
The thermal camera shows the heat
escaping from Jack's mouth.

1078
01:08:49,980 --> 01:08:52,780
Many birds and mammals,
big and small,

1079
01:08:52,780 --> 01:08:54,940
have to cool down this way too.

1080
01:08:56,860 --> 01:08:59,380
And even when panting isn't enough,

1081
01:08:59,380 --> 01:09:02,620
some animals have developed
another strategy.

1082
01:09:04,500 --> 01:09:07,300
In the intense heat
of the Australian outback,

1083
01:09:07,300 --> 01:09:10,620
where temperatures can reach
50 degrees Celsius,

1084
01:09:10,620 --> 01:09:13,700
kangaroos lick their forearms.

1085
01:09:13,700 --> 01:09:16,660
As the saliva evaporates
from their skin,

1086
01:09:16,660 --> 01:09:19,180
it cools the blood vessels
under the skin,

1087
01:09:19,180 --> 01:09:21,340
making survival here possible.

1088
01:09:23,340 --> 01:09:27,060
If hair and feathers make it harder
to lose heat,

1089
01:09:27,060 --> 01:09:32,260
then why do so many animals from
hot countries still have them?

1090
01:09:32,260 --> 01:09:34,860
Well, they serve
other vital functions, too,

1091
01:09:34,860 --> 01:09:37,260
including protecting these animals

1092
01:09:37,260 --> 01:09:39,980
from the damaging effects
of UV rays.

1093
01:09:42,020 --> 01:09:43,940
UV rays from the sun

1094
01:09:43,940 --> 01:09:45,580
are one of the most dangerous
things

1095
01:09:45,580 --> 01:09:48,340
the environment throws
at the animal world.

1096
01:09:48,340 --> 01:09:50,340
And they are just the right
wavelength

1097
01:09:50,340 --> 01:09:53,780
to damage the skin's fragile DNA,
causing skin cancer.

1098
01:09:56,180 --> 01:10:00,300
Animals need to find a way to stop
UV reaching their skin cells,

1099
01:10:00,300 --> 01:10:04,260
and a physical obstacle
like hair or feathers is ideal.

1100
01:10:05,820 --> 01:10:08,460
But if you're as hairless
as a hippo,

1101
01:10:08,460 --> 01:10:13,100
how do you protect yourself from
the damaging effects of UV?

1102
01:10:13,100 --> 01:10:17,820
One tactic is to spend the day
wallowing in mud and water,

1103
01:10:17,820 --> 01:10:22,100
although it's hard to completely
submerge such a big body.

1104
01:10:22,100 --> 01:10:26,500
So there's always a bit of skin
in the full glare of the sun.

1105
01:10:26,500 --> 01:10:28,860
But hippos never get sunburnt.

1106
01:10:28,860 --> 01:10:32,780
And the reason why was only
discovered 20 years ago.

1107
01:10:32,780 --> 01:10:36,260
When exposed, the skin produces
thick red droplets

1108
01:10:36,260 --> 01:10:38,980
from the dermis known
as blood sweat.

1109
01:10:38,980 --> 01:10:42,900
And if I zoom in, I can really see
that here.

1110
01:10:42,900 --> 01:10:45,420
Now, when scientists analysed this
blood sweat,

1111
01:10:45,420 --> 01:10:49,300
they discovered it's not
blood or actually sweat,

1112
01:10:49,300 --> 01:10:51,740
but instead is an oily mixture of

1113
01:10:51,740 --> 01:10:57,060
water repellent, antibiotic
and a UV-blocking chemical

1114
01:10:57,060 --> 01:10:59,500
that turns red in sunlight.

1115
01:10:59,500 --> 01:11:03,060
Basically, hippo skin
produces its own sunscreen.

1116
01:11:07,420 --> 01:11:09,020
Another iconic resident

1117
01:11:09,020 --> 01:11:11,700
of the African savannah
is the giraffe.

1118
01:11:12,700 --> 01:11:16,180
It can survive in temperatures most
other mammals can't cope with.

1119
01:11:18,740 --> 01:11:21,900
And it's only recently
that scientists have discovered

1120
01:11:21,900 --> 01:11:25,460
those spots, as well as being
a striking pattern,

1121
01:11:25,460 --> 01:11:29,540
perform a surprising function
in keeping giraffes cool.

1122
01:11:30,660 --> 01:11:33,380
If you look at a giraffe
through a thermal camera,

1123
01:11:33,380 --> 01:11:37,060
you can see the spots glow brighter
than the background hair,

1124
01:11:37,060 --> 01:11:39,980
as they are giving off
the most heat.

1125
01:11:41,900 --> 01:11:45,980
Each spot has a large blood vessel
around the outside

1126
01:11:45,980 --> 01:11:48,740
and a network
of smaller ones in the centre,

1127
01:11:48,740 --> 01:11:52,780
which carry excess body heat
to the surface of the skin,

1128
01:11:52,780 --> 01:11:54,620
helping to cool the giraffe down.

1129
01:11:56,860 --> 01:12:01,380
They also have another adaptation
that keeps them safe in the sun,

1130
01:12:01,380 --> 01:12:05,060
and to witness that,
I need to join them for lunch.

1131
01:12:07,420 --> 01:12:09,300
Would you like a go?
Yes, please. There you go.

1132
01:12:10,500 --> 01:12:14,460
You can see on Setanta
here that his body is covered

1133
01:12:14,460 --> 01:12:17,540
with this lovely, thick, dense coat.

1134
01:12:17,540 --> 01:12:19,860
But there's one part of his body
that's hairless

1135
01:12:19,860 --> 01:12:22,180
that spends a lot
of time in the sun.

1136
01:12:23,420 --> 01:12:24,940
His tongue.

1137
01:12:24,940 --> 01:12:28,220
Now, giraffe tongues are really
flexible

1138
01:12:28,220 --> 01:12:32,180
and can be up to
50 centimetres in length.

1139
01:12:32,180 --> 01:12:33,900
And in the wild, they use them

1140
01:12:33,900 --> 01:12:37,580
to strip the leaves of trees
like acacias.

1141
01:12:37,580 --> 01:12:40,180
But in order to protect
them from the harmful rays

1142
01:12:40,180 --> 01:12:42,500
of the sun

1143
01:12:42,500 --> 01:12:45,300
the outer layers are filled

1144
01:12:45,300 --> 01:12:48,620
with this very dark
pigment called melanin.

1145
01:12:48,620 --> 01:12:51,700
And it's this that gives
the tongue its purply black colour.

1146
01:12:56,420 --> 01:12:58,900
All kinds of vertebrates produce
melanin,

1147
01:12:58,900 --> 01:13:02,420
a pigment made by specialist cells
in the epidermis

1148
01:13:02,420 --> 01:13:04,660
to shield themselves from UV.

1149
01:13:07,260 --> 01:13:10,940
Scientists now know that even
migrating blue whales produce

1150
01:13:10,940 --> 01:13:14,500
more melanin every summer,
getting darker-skinned

1151
01:13:14,500 --> 01:13:17,700
as they migrate south
to sunny waters to breed.

1152
01:13:19,540 --> 01:13:22,260
Melanin also gives human skin
its colour.

1153
01:13:22,260 --> 01:13:25,460
The more melanin your skin has,
the darker you are,

1154
01:13:25,460 --> 01:13:27,740
and the better protected from UV.

1155
01:13:29,700 --> 01:13:31,660
Melanin is produced by cells

1156
01:13:31,660 --> 01:13:34,740
called melanocytes
in the epidermis.

1157
01:13:34,740 --> 01:13:37,940
Our direct ancestors,
living in the blazing sun

1158
01:13:37,940 --> 01:13:41,220
of equatorial Africa some
2.5 million years ago,

1159
01:13:41,220 --> 01:13:44,140
needed all the melanin
they could get.

1160
01:13:44,140 --> 01:13:47,940
And for human populations
in sunny parts of the world,

1161
01:13:47,940 --> 01:13:50,260
that's still the case.

1162
01:13:50,260 --> 01:13:51,780
But there's a trade-off.

1163
01:13:51,780 --> 01:13:54,140
We need some UV
to reach our dermis

1164
01:13:54,140 --> 01:13:57,620
in order for us to be able
to make vitamin D,

1165
01:13:57,620 --> 01:14:00,180
which is essential
for healthy bones.

1166
01:14:00,180 --> 01:14:01,500
UVB rays

1167
01:14:01,500 --> 01:14:06,540
from the sun turn a chemical
in your skin into vitamin D3,

1168
01:14:06,540 --> 01:14:10,500
which is then carried to your
liver and then to your kidneys

1169
01:14:10,500 --> 01:14:13,140
to transform it to active vitamin D.

1170
01:14:14,220 --> 01:14:16,260
The human skin colour variation

1171
01:14:16,260 --> 01:14:18,140
we see today is our skin's response

1172
01:14:18,140 --> 01:14:20,460
to this love-hate relationship
with UV.

1173
01:14:20,460 --> 01:14:23,780
A trade-off between
the skin as protector

1174
01:14:23,780 --> 01:14:26,620
and as a factory
for making vitamin D.

1175
01:14:28,140 --> 01:14:30,300
Now, you can tell just
by looking at me,

1176
01:14:30,300 --> 01:14:33,900
there's not a huge amount
of melanin going on here.

1177
01:14:33,900 --> 01:14:35,580
I'm from Norfolk, born and bred.

1178
01:14:35,580 --> 01:14:37,980
I'm practically transparent.

1179
01:14:37,980 --> 01:14:41,060
What this means is that while
my pale skin is great

1180
01:14:41,060 --> 01:14:44,420
at making vitamin D
by letting in enough UVB,

1181
01:14:44,420 --> 01:14:49,420
it needs help protecting me from
letting in so much that I burn.

1182
01:14:52,700 --> 01:14:55,340
To get a really accurate idea
of how much

1183
01:14:55,340 --> 01:14:57,300
melanin I have in my skin,

1184
01:14:57,300 --> 01:14:59,100
we're using a UV camera.

1185
01:15:00,140 --> 01:15:03,300
This filters out the visible
light from an image,

1186
01:15:03,300 --> 01:15:06,180
so all that is recorded
are the ultraviolet rays.

1187
01:15:07,980 --> 01:15:11,820
Anything that absorbs UV,
like melanin or the special coating

1188
01:15:11,820 --> 01:15:13,900
on my glasses, appears darker.

1189
01:15:15,660 --> 01:15:19,100
As you can see, I've got
a few patches around here

1190
01:15:19,100 --> 01:15:22,580
where my poor skin has produced
a little extra melanin,

1191
01:15:22,580 --> 01:15:26,060
but it's not much in terms
of protection from UV.

1192
01:15:27,780 --> 01:15:30,380
So I need sunblock to
replicate the protection

1193
01:15:30,380 --> 01:15:32,220
that darker-skinned people

1194
01:15:32,220 --> 01:15:35,540
get from their naturally-produced
extra melanin.

1195
01:15:36,780 --> 01:15:38,460
OK, here goes.

1196
01:15:39,700 --> 01:15:43,500
I'm going to put a good amount

1197
01:15:43,500 --> 01:15:46,140
on one side of my face

1198
01:15:46,140 --> 01:15:48,420
and see what protection...

1199
01:15:50,740 --> 01:15:52,140
..that gives me.

1200
01:15:55,780 --> 01:15:56,820
Get the ears in.

1201
01:16:04,340 --> 01:16:06,500
And as you can see,
one side of my face

1202
01:16:06,500 --> 01:16:10,220
is beautifully protected from
the effects of these UV rays now.

1203
01:16:10,220 --> 01:16:13,620
Although I may have
put the sunblock on

1204
01:16:13,620 --> 01:16:17,460
a little too enthusiastically.

1205
01:16:17,460 --> 01:16:19,740
Skin has devised impressive ways

1206
01:16:19,740 --> 01:16:21,620
of protecting animals
against the worst

1207
01:16:21,620 --> 01:16:23,940
the physical environment
has to offer.

1208
01:16:24,980 --> 01:16:29,020
But there are other threats out
there from living organisms

1209
01:16:29,020 --> 01:16:30,460
that want to get in.

1210
01:16:31,780 --> 01:16:34,420
We are not alone.

1211
01:16:34,420 --> 01:16:39,900
We share our world with a whole host
of viruses, bacteria and fungi.

1212
01:16:41,260 --> 01:16:43,300
But we don't think about them
very often,

1213
01:16:43,300 --> 01:16:45,420
because they're too small to see.

1214
01:16:47,740 --> 01:16:51,500
Our skin does everything it can
to keep them out.

1215
01:16:51,500 --> 01:16:55,580
Dr Jim Spencer is going
to look for them for us.

1216
01:16:55,580 --> 01:16:59,700
I'm not entirely sure
I'm looking forward to this.

1217
01:17:00,940 --> 01:17:05,180
A few days ago, I left my
fingerprints on some agar jelly,

1218
01:17:05,180 --> 01:17:09,740
a substance used by scientists
to help grow bacteria.

1219
01:17:09,740 --> 01:17:13,020
Now, I'm back to see the results.

1220
01:17:13,020 --> 01:17:15,100
So, Jim, I'm not going to lie,
I'm a little bit nervous

1221
01:17:15,100 --> 01:17:17,180
about seeing what you're
found on my culture.

1222
01:17:17,180 --> 01:17:20,580
What have we got?
Well, let's have a look.

1223
01:17:20,580 --> 01:17:23,860
Oh, Jim, that's awful.
It really is.

1224
01:17:23,860 --> 01:17:27,100
I can see roughly where my thumb
was, and some vague places

1225
01:17:27,100 --> 01:17:28,820
where my fingers were.

1226
01:17:28,820 --> 01:17:32,140
There's loads, there's so
much stuff on there, Jim.

1227
01:17:32,140 --> 01:17:35,420
The first thing is that everybody
has a lot of bacteria on their skin.

1228
01:17:35,420 --> 01:17:39,900
So around ten million bacteria
per square centimetre

1229
01:17:39,900 --> 01:17:41,260
of skin surface.

1230
01:17:41,260 --> 01:17:42,700
So it's not surprising that

1231
01:17:42,700 --> 01:17:45,060
we've grown a fair amount
of organisms here.

1232
01:17:45,060 --> 01:17:46,780
There's a lot of diversity
on here, as well.

1233
01:17:46,780 --> 01:17:49,260
Is there any way of telling
what we might have here?

1234
01:17:49,260 --> 01:17:50,780
We can make some guesses based

1235
01:17:50,780 --> 01:17:52,780
on how the bacteria appear
on the plate.

1236
01:17:52,780 --> 01:17:55,420
So, for example,
this white one down here,

1237
01:17:55,420 --> 01:17:57,580
that could be a Staphylococcus
epidermidis,

1238
01:17:57,580 --> 01:17:59,860
which is something
that is pretty much ubiquitous.

1239
01:17:59,860 --> 01:18:02,260
Everybody will carry that
on their skin.

1240
01:18:02,260 --> 01:18:04,940
Though harmless
on the surface of our skin,

1241
01:18:04,940 --> 01:18:07,660
Staphylococcus epidermidis
is thought to be

1242
01:18:07,660 --> 01:18:12,060
responsible for around 20%
of post-operative infections,

1243
01:18:12,060 --> 01:18:16,940
when it enters the body through
contaminated medical devices.

1244
01:18:16,940 --> 01:18:18,780
The yellow ones could be micrococci,

1245
01:18:18,780 --> 01:18:20,540
which again, are very common.

1246
01:18:20,540 --> 01:18:23,300
After that, it gets a little bit
more difficult.

1247
01:18:23,300 --> 01:18:26,420
There've been studies
that have identified over 150

1248
01:18:26,420 --> 01:18:27,820
different species of bacteria

1249
01:18:27,820 --> 01:18:30,260
in a single sample
from a single human hand.

1250
01:18:30,260 --> 01:18:33,060
Jim, you're not looking too worried
by my results here.

1251
01:18:33,060 --> 01:18:34,860
Should I be worried by this?

1252
01:18:34,860 --> 01:18:36,300
I don't think so.

1253
01:18:36,300 --> 01:18:39,460
We've got to remember that most
of these bacteria

1254
01:18:39,460 --> 01:18:43,260
are either harmless,
or actually positively beneficial.

1255
01:18:44,420 --> 01:18:46,500
For many of these tiny organisms,

1256
01:18:46,500 --> 01:18:49,460
an animal's body represents
an ideal home.

1257
01:18:49,460 --> 01:18:53,060
It's warm, secure and has lots of
raw materials.

1258
01:18:53,060 --> 01:18:54,100
They want in.

1259
01:18:55,140 --> 01:18:58,300
And while most microbes
might be harmless,

1260
01:18:58,300 --> 01:19:01,180
there are others
that are anything but.

1261
01:19:02,300 --> 01:19:07,620
For vertebrates, skin is the first
line of protection against disease.

1262
01:19:07,620 --> 01:19:11,100
The epidermis presents a physical
barrier to microbes,

1263
01:19:11,100 --> 01:19:12,820
but one group of animals

1264
01:19:12,820 --> 01:19:16,100
needs to give that outer layer
a helping hand.

1265
01:19:18,420 --> 01:19:21,300
Amphibians, like this poison dart
frog,

1266
01:19:21,300 --> 01:19:23,700
get oxygen through their skin,

1267
01:19:23,700 --> 01:19:26,900
so it's thin, moist and permeable.

1268
01:19:26,900 --> 01:19:30,060
All these factors make it incredibly
vulnerable to infection

1269
01:19:30,060 --> 01:19:33,900
by bacteria and fungi,
particularly as most amphibians

1270
01:19:33,900 --> 01:19:35,740
live in warm, wet places.

1271
01:19:38,260 --> 01:19:42,860
Frogs have launched a chemical war
of retaliation against microbes.

1272
01:19:43,820 --> 01:19:45,700
Their skin secretes a cocktail

1273
01:19:45,700 --> 01:19:49,260
of antibacterial and
anti-fungal peptides.

1274
01:19:49,260 --> 01:19:52,860
Chemicals so effective
that the latest science now shows

1275
01:19:52,860 --> 01:19:56,900
potential for the development
of new drugs to treat sepsis,

1276
01:19:56,900 --> 01:20:00,220
autoimmune diseases and
even Type 2 diabetes.

1277
01:20:03,780 --> 01:20:08,500
Whatever cool moves vertebrate skin
comes up with to prevent infection,

1278
01:20:08,500 --> 01:20:10,940
microbes always have a countermove.

1279
01:20:10,940 --> 01:20:13,340
It's a constant evolutionary
arms race.

1280
01:20:13,340 --> 01:20:15,540
Skin versus the world.

1281
01:20:15,540 --> 01:20:18,700
If skin is too well defended
for microbes to get

1282
01:20:18,700 --> 01:20:20,060
through it on their own,

1283
01:20:20,060 --> 01:20:22,980
then they need to find
another way in.

1284
01:20:22,980 --> 01:20:28,140
And one such way is through
skin penetration experts,

1285
01:20:28,140 --> 01:20:30,220
like blood-sucking insects.

1286
01:20:31,300 --> 01:20:35,020
Because vertebrate skin comes
in so many thicknesses and types,

1287
01:20:35,020 --> 01:20:36,500
biting insects have evolved

1288
01:20:36,500 --> 01:20:39,540
to breach the defences of
specific animals.

1289
01:20:39,540 --> 01:20:41,780
They've developed
host specificity.

1290
01:20:43,260 --> 01:20:45,820
And apparently, the best
way for me to demonstrate this

1291
01:20:45,820 --> 01:20:47,940
is to donate some blood.

1292
01:20:51,940 --> 01:20:55,780
Professor James Logan is an expert
in insect-borne diseases.

1293
01:20:57,980 --> 01:20:59,940
What have we got here?

1294
01:20:59,940 --> 01:21:04,660
Well, we've got two different types
of insect, biting insects.

1295
01:21:04,660 --> 01:21:06,060
I can see they're mosquitoes.

1296
01:21:06,060 --> 01:21:08,740
Yeah. These ones are aedes aegypti.

1297
01:21:08,740 --> 01:21:13,060
So these are the ones that transmit
yellow fever, dengue, Zika as well.

1298
01:21:13,060 --> 01:21:15,620
And I've chosen these ones
because they're highly adapted

1299
01:21:15,620 --> 01:21:17,620
to feeding on humans,
and they're very hungry.

1300
01:21:17,620 --> 01:21:19,540
I've made sure they're hungry
just for you.

1301
01:21:19,540 --> 01:21:22,100
Well, I'm happy to look
but you want me to stick my hand in?

1302
01:21:22,100 --> 01:21:23,500
I want you to stick your arm
right in.

1303
01:21:23,500 --> 01:21:25,820
That's the only way to experience
this and see how they feed.

1304
01:21:25,820 --> 01:21:28,180
So can you stick your arm in there?

1305
01:21:28,180 --> 01:21:30,500
You're very brave. Very silly.

1306
01:21:30,500 --> 01:21:32,460
There we are.

1307
01:21:32,460 --> 01:21:34,260
James, they're straight on.

1308
01:21:34,260 --> 01:21:37,540
You can see, there's quite a few on
there, there's probably about ten.

1309
01:21:37,540 --> 01:21:39,100
That's pretty fast, isn't it? Yeah.

1310
01:21:39,100 --> 01:21:42,100
Yeah, I'm quite surprised how
quickly they've descended.

1311
01:21:42,100 --> 01:21:43,820
This is exactly how they've evolved.

1312
01:21:43,820 --> 01:21:46,340
So they've evolved to
come in, steal your blood

1313
01:21:46,340 --> 01:21:47,740
without you even knowing it.

1314
01:21:47,740 --> 01:21:51,340
Their mouth parts are so fine that
they're able to pierce the skin.

1315
01:21:51,340 --> 01:21:53,060
What they also do is inject saliva,

1316
01:21:53,060 --> 01:21:55,380
which has an anaesthetic
so you don't feel it.

1317
01:21:55,380 --> 01:21:59,340
And also an anticoagulant,
so your blood doesn't clot.

1318
01:21:59,340 --> 01:22:02,660
Well, James, I have had more fun,
I'm not going to lie.

1319
01:22:02,660 --> 01:22:04,060
Really? Yeah.

1320
01:22:04,060 --> 01:22:07,260
But the weird thing is, I didn't,
I'm going to feel it later, I know.

1321
01:22:07,260 --> 01:22:08,620
There'll be welts all popping up,

1322
01:22:08,620 --> 01:22:10,340
but I didn't feel it
when they were biting.

1323
01:22:10,340 --> 01:22:13,420
You feel the tickle of the legs,
but it's so gentle in that respect.

1324
01:22:13,420 --> 01:22:14,940
But they're not all like that,
are they?

1325
01:22:14,940 --> 01:22:16,540
No, they are absolutely
not all like that.

1326
01:22:16,540 --> 01:22:19,420
So we have these stable flies,
bigger mouth parts.

1327
01:22:19,420 --> 01:22:21,260
Do you want to try that?

1328
01:22:21,260 --> 01:22:23,100
I'll be honest with you.
I wouldn't do it.

1329
01:22:23,100 --> 01:22:24,540
Really?

1330
01:22:24,540 --> 01:22:27,140
I thought this is what you do!
No, no, no.

1331
01:22:27,140 --> 01:22:28,980
But I think you've
already signed up to this,

1332
01:22:28,980 --> 01:22:31,100
so there's no going back now.

1333
01:22:31,100 --> 01:22:33,020
They kind of look like house flies,
don't they?

1334
01:22:33,020 --> 01:22:34,820
But the mouth parts are
a little bit different.

1335
01:22:34,820 --> 01:22:36,780
So a housefly has sort
of spongy mouth parts

1336
01:22:36,780 --> 01:22:38,860
that allow it to sort
of suck up moisture.

1337
01:22:38,860 --> 01:22:42,260
These guys have much harder mouth
parts, like little saws,

1338
01:22:42,260 --> 01:22:44,860
and that's so that they can get
through some really tough skin.

1339
01:22:44,860 --> 01:22:48,340
So they will mostly feed
on horses, cattle,

1340
01:22:48,340 --> 01:22:49,660
bigger animals.

1341
01:22:49,660 --> 01:22:50,900
If they can go through a horse,

1342
01:22:50,900 --> 01:22:52,820
they're going to rip through me,
aren't they?

1343
01:22:52,820 --> 01:22:56,860
Yes. It probably will be
a little bit more painful.

1344
01:22:56,860 --> 01:23:00,060
I'm actually quite nervous, James.
Are you? Yeah, a little bit.

1345
01:23:00,060 --> 01:23:01,540
Oh. There we are.

1346
01:23:01,540 --> 01:23:04,380
Oh, and they're coming
straight in!

1347
01:23:04,380 --> 01:23:07,580
So there's lots of stuff that
activates flies to bite.

1348
01:23:07,580 --> 01:23:09,980
Heat coming from the skin,
moisture coming from the skin,

1349
01:23:09,980 --> 01:23:11,940
carbon dioxide being
released from the skin,

1350
01:23:11,940 --> 01:23:13,140
and other chemicals as well.

1351
01:23:13,140 --> 01:23:14,420
So there's one there.

1352
01:23:14,420 --> 01:23:16,060
Ow! Do you feel that? Yep.

1353
01:23:16,060 --> 01:23:18,580
Oh! I'll feel that one again.

1354
01:23:18,580 --> 01:23:20,900
Argh! This is the other thing,
I can see what it's doing.

1355
01:23:20,900 --> 01:23:23,100
It's not just going in once,
it's going in several times.

1356
01:23:23,100 --> 01:23:26,020
That's it, the same one. It doesn't
hurt, then it does, then it doesn't.

1357
01:23:26,020 --> 01:23:27,540
Right now it's hurting again. Yeah.

1358
01:23:27,540 --> 01:23:30,500
You can imagine their mouth parts
are gyrating like this,

1359
01:23:30,500 --> 01:23:32,340
like saws cutting through the skin,

1360
01:23:32,340 --> 01:23:35,300
and getting in and
sucking up the blood.

1361
01:23:35,300 --> 01:23:36,740
Can you feel that? Oh, she's... Ow!

1362
01:23:36,740 --> 01:23:40,740
That's on the underside
I can definitely feel that one.

1363
01:23:40,740 --> 01:23:43,180
I think that's probably
enough time in there.

1364
01:23:45,300 --> 01:23:47,740
There is a serious point to this.

1365
01:23:47,740 --> 01:23:50,380
Studying what attracts insects
to bite humans

1366
01:23:50,380 --> 01:23:53,420
is pioneering the research
into finding a cure

1367
01:23:53,420 --> 01:23:56,940
for some of the world's
most devastating diseases.

1368
01:23:56,940 --> 01:24:01,020
And the answer may well lie
in the scent of our skin.

1369
01:24:02,180 --> 01:24:03,900
It all comes down to
the way you smell.

1370
01:24:03,900 --> 01:24:05,860
So when you put your arm
into those cages,

1371
01:24:05,860 --> 01:24:08,420
that was the thing that was really
driving that behaviour,

1372
01:24:08,420 --> 01:24:11,300
that response to land
on you, to feed.

1373
01:24:11,300 --> 01:24:13,180
It has to be the right cue.

1374
01:24:13,180 --> 01:24:16,220
These ones will preferentially
be attracted to human odour,

1375
01:24:16,220 --> 01:24:18,540
whereas these guys would rather
feed on cows.

1376
01:24:18,540 --> 01:24:22,220
And so, they find the smell of
a cow much nicer than a human.

1377
01:24:22,220 --> 01:24:25,500
People who don't get bitten
very much by biting insects

1378
01:24:25,500 --> 01:24:28,060
are producing different
chemicals in their body odour.

1379
01:24:28,060 --> 01:24:29,740
So their skin is producing something

1380
01:24:29,740 --> 01:24:31,740
a little bit different,
and it puts them off.

1381
01:24:31,740 --> 01:24:33,860
So it's actually natural repellents.

1382
01:24:33,860 --> 01:24:35,740
We've identified those repellents.

1383
01:24:35,740 --> 01:24:38,220
We now know as well
it's controlled by our genes.

1384
01:24:38,220 --> 01:24:40,260
So we're now trying to
identify the genes

1385
01:24:40,260 --> 01:24:42,620
that control the production
of natural repellents

1386
01:24:42,620 --> 01:24:44,100
by the human body.

1387
01:24:44,100 --> 01:24:46,820
One day you might be able to take
a pill when you go on holiday

1388
01:24:46,820 --> 01:24:49,580
that would up-regulate
the production of natural repellents

1389
01:24:49,580 --> 01:24:53,860
by the body, and totally change
the way that we repel mosquitoes

1390
01:24:53,860 --> 01:24:57,700
and protect ourselves
against diseases like malaria.

1391
01:24:57,700 --> 01:25:02,220
Malaria causes half a million deaths
a year around the world.

1392
01:25:02,220 --> 01:25:06,140
How amazing that the key
to protecting humans against it

1393
01:25:06,140 --> 01:25:09,140
may lie in the smell of our skin.

1394
01:25:11,380 --> 01:25:13,460
When it comes to
keeping animals safe

1395
01:25:13,460 --> 01:25:16,060
in an ever-changing
and hostile world,

1396
01:25:16,060 --> 01:25:20,260
skin is an incredible,
multi-purpose shield.

1397
01:25:20,260 --> 01:25:22,780
From thick fat to dense hair

1398
01:25:22,780 --> 01:25:25,540
and even slimy barriers,

1399
01:25:25,540 --> 01:25:28,300
skin has adapted to
protect vertebrates

1400
01:25:28,300 --> 01:25:31,100
from whatever the world
throws at them.

1401
01:25:38,100 --> 01:25:41,620
Next time, I'll uncover
incredible new science

1402
01:25:41,620 --> 01:25:44,580
about puffins and their beaks,

1403
01:25:44,580 --> 01:25:46,500
witness a deadly snake

1404
01:25:46,500 --> 01:25:50,540
send me a warning signal
without opening its mouth,

1405
01:25:50,540 --> 01:25:53,900
and learn to read the colour-coded
messages mandrills

1406
01:25:53,900 --> 01:25:56,940
send to each other
through their faces,

1407
01:25:56,940 --> 01:26:01,580
to reveal how skin has evolved
to allow animals to communicate.

1408
01:26:35,420 --> 01:26:37,020
Skin.

1409
01:26:37,020 --> 01:26:38,780
We all have it.

1410
01:26:38,780 --> 01:26:42,940
And so does every vertebrate
on the planet.

1411
01:26:42,940 --> 01:26:45,460
It keeps the outside out,

1412
01:26:45,460 --> 01:26:47,300
and the inside in.

1413
01:26:48,780 --> 01:26:51,580
Animals may look very different
on the surface,

1414
01:26:51,580 --> 01:26:54,980
but we all share the same
basic skin blueprint.

1415
01:26:56,780 --> 01:27:01,100
I'm Ben Garrod, Professor
of Evolutionary Biology.

1416
01:27:01,100 --> 01:27:05,020
And I'm fascinated by this often
overlooked wonder of nature.

1417
01:27:05,020 --> 01:27:07,620
It's not just the case
that he's hairless...

1418
01:27:07,620 --> 01:27:09,300
..the skin's totally different.

1419
01:27:09,300 --> 01:27:11,940
Now, ground-breaking new science...

1420
01:27:11,940 --> 01:27:13,500
This is really quite remarkable.

1421
01:27:13,500 --> 01:27:16,140
It should be a game-changer
for so many people.

1422
01:27:16,140 --> 01:27:18,100
RATTLING
That sound! Oh, it

1423
01:27:18,100 --> 01:27:20,860
makes the hair at the back
of your neck go up, doesn't it?

1424
01:27:20,860 --> 01:27:23,660
..is revealing skin's mysteries.

1425
01:27:23,660 --> 01:27:27,980
It really transforms
our understanding of dinosaurs.

1426
01:27:27,980 --> 01:27:32,380
I'm going to explore the natural
history of the body's largest organ,

1427
01:27:32,380 --> 01:27:37,420
to see how skin has allowed animals
to conquer every habitat,

1428
01:27:37,420 --> 01:27:39,940
disappear into their surroundings

1429
01:27:39,940 --> 01:27:42,740
and develop extra-sensory abilities.

1430
01:27:44,420 --> 01:27:49,340
We're even discovering the complex
ecosystem living on OUR skin.

1431
01:27:49,340 --> 01:27:51,100
Oh, Jim, that's awful.

1432
01:27:51,100 --> 01:27:52,740
It really is!

1433
01:27:52,740 --> 01:27:54,340
In this episode...

1434
01:27:54,340 --> 01:27:59,820
I'll uncover incredible new science
about puffins and their beaks,

1435
01:27:59,820 --> 01:28:03,260
witness a deadly snake send me
a warning signal

1436
01:28:03,260 --> 01:28:05,660
without even opening its mouth,

1437
01:28:05,660 --> 01:28:09,980
and learn to read the colour-coded
messages mandrills send

1438
01:28:09,980 --> 01:28:12,300
to each other through their faces.

1439
01:28:12,300 --> 01:28:14,940
To marvel at how skin has evolved,

1440
01:28:14,940 --> 01:28:17,300
allowing animals to communicate...

1441
01:28:17,300 --> 01:28:20,860
..I'm going to reveal
the secrets of skin.

1442
01:28:28,340 --> 01:28:30,980
Animals communicate through smell,

1443
01:28:30,980 --> 01:28:32,420
colour,

1444
01:28:32,420 --> 01:28:33,820
touch,

1445
01:28:33,820 --> 01:28:35,460
and sound.

1446
01:28:36,860 --> 01:28:40,140
And their skin has adapted
to help them do just that.

1447
01:28:41,700 --> 01:28:44,940
I'm starting
with a very familiar primate...

1448
01:28:44,940 --> 01:28:48,260
..ring-tailed lemurs,
which use the smell of their skin

1449
01:28:48,260 --> 01:28:50,980
to figure out who's who
and what's what.

1450
01:28:54,060 --> 01:28:57,220
With their distinct black-and-white
markings and those unmissable

1451
01:28:57,220 --> 01:29:03,100
stripy tails, ring-tailed lemurs are
hard to tell apart by sight alone.

1452
01:29:03,100 --> 01:29:05,940
So they've evolved
a language of smell.

1453
01:29:05,940 --> 01:29:09,220
And it's the males
I'm really interested in.

1454
01:29:12,140 --> 01:29:15,780
I love that classic lemur pose!

1455
01:29:15,780 --> 01:29:20,300
So, I've come to Twycross Zoo to get
close to a group of captive males.

1456
01:29:22,300 --> 01:29:24,820
The one behind you is Zac.

1457
01:29:24,820 --> 01:29:26,860
So, he's got a very dark face.

1458
01:29:28,100 --> 01:29:31,900
And then we have got one,
somewhere...

1459
01:29:31,900 --> 01:29:36,100
Here he is! So, Zeus, he's got
his little cauliflower ear.

1460
01:29:36,100 --> 01:29:40,700
We've also got one with a shorter
tail, so, this is Zazu up here.

1461
01:29:40,700 --> 01:29:45,180
While Kirsty - their keeper - can
identify a few of them by sight,

1462
01:29:45,180 --> 01:29:48,940
lemurs use a totally different way
of recognising one another.

1463
01:29:50,380 --> 01:29:52,340
They use scent.

1464
01:29:52,340 --> 01:29:55,940
Both sexes have scent glands
in their genital regions,

1465
01:29:55,940 --> 01:30:00,340
but males have gone one step
further and evolved scent glands

1466
01:30:00,340 --> 01:30:02,780
on their shoulders and forearms.

1467
01:30:02,780 --> 01:30:07,140
They'll use that to scent-mark all
of their furniture in the enclosure.

1468
01:30:07,140 --> 01:30:10,300
They'll also do it a lot
with their scent-marking.

1469
01:30:10,300 --> 01:30:12,780
They'll wipe it along their tails.

1470
01:30:12,780 --> 01:30:15,460
It's sort of, like,
a territorial thing.

1471
01:30:15,460 --> 01:30:18,820
The scent glands are oil-producing
sebaceous glands,

1472
01:30:18,820 --> 01:30:21,020
like we have in our skin.

1473
01:30:21,020 --> 01:30:22,980
But theirs have evolved,

1474
01:30:22,980 --> 01:30:26,060
and are unlike anything else
in the animal kingdom,

1475
01:30:26,060 --> 01:30:28,940
producing an entire
chemical language.

1476
01:30:31,340 --> 01:30:35,220
Scientists have identified
over 200 chemical compounds that

1477
01:30:35,220 --> 01:30:37,660
make up the scent lemurs produce,

1478
01:30:37,660 --> 01:30:41,540
meaning that they can all create
a personalised aroma to communicate.

1479
01:30:46,100 --> 01:30:51,780
The number of compounds in the scent
drops by 10% if a lemur is injured,

1480
01:30:51,780 --> 01:30:54,820
something other males can use
to their advantage,

1481
01:30:54,820 --> 01:30:57,620
by acting more aggressively
to the weaker male.

1482
01:31:01,340 --> 01:31:05,300
Male ring-tailed lemurs also use
their smell to fight.

1483
01:31:05,300 --> 01:31:09,020
They rub their tails in their scent
glands, and then waft the smell

1484
01:31:09,020 --> 01:31:12,220
in the direction of their rivals.

1485
01:31:12,220 --> 01:31:17,140
These battles maintain social status
while reducing physical aggression.

1486
01:31:17,140 --> 01:31:19,460
And their scent decides the winner.

1487
01:31:31,580 --> 01:31:35,060
Another group of primates has
developed a different way of

1488
01:31:35,060 --> 01:31:37,500
communicating dominance
through their skin -

1489
01:31:37,500 --> 01:31:40,900
colour, of their rump and face.

1490
01:31:41,980 --> 01:31:45,740
These are mandrills
in Gabon, West Africa.

1491
01:31:45,740 --> 01:31:50,020
Charles Darwin wrote, "No other
member in the whole class of mammals

1492
01:31:50,020 --> 01:31:54,780
"is coloured in so extraordinary a
manner as the adult male mandrill."

1493
01:31:56,900 --> 01:31:58,700
Primatologist Jo Setchell has

1494
01:31:58,700 --> 01:32:02,620
been studying and photographing
these mandrills for over 20 years.

1495
01:32:06,380 --> 01:32:09,420
Jo, I love these animals, one
of the most recognisable members

1496
01:32:09,420 --> 01:32:12,660
of our primate family. Aren't they
fabulous? They really are.

1497
01:32:12,660 --> 01:32:15,980
They have these remarkable
red and blue noses.

1498
01:32:15,980 --> 01:32:17,780
And they're using this red
and blue skin

1499
01:32:17,780 --> 01:32:21,100
to communicate with one another.
What are they communicating?

1500
01:32:21,100 --> 01:32:22,900
Status, essentially.

1501
01:32:22,900 --> 01:32:26,220
So, if they can look at the red
colour of another male,

1502
01:32:26,220 --> 01:32:28,900
decide instantly whether he's
dominant -

1503
01:32:28,900 --> 01:32:32,140
and therefore, you should avoid
him - or he's subordinate.

1504
01:32:32,140 --> 01:32:33,580
Then that avoids fights.

1505
01:32:33,580 --> 01:32:36,700
So, it pays off to signal rather
than to fight it out, I guess?

1506
01:32:36,700 --> 01:32:40,580
Definitely, yes. Do we know what's
going on beneath the skin?

1507
01:32:40,580 --> 01:32:42,740
Right beneath that red skin is
blood,

1508
01:32:42,740 --> 01:32:46,300
and there's an awful lot of blood
vessels, vascularisation.

1509
01:32:46,300 --> 01:32:51,060
And so the red of the blood is
seen right through the skin.

1510
01:32:51,060 --> 01:32:54,140
Unlike humans, whose skin colour
comes from melanin,

1511
01:32:54,140 --> 01:32:57,940
that intense red of a male
mandrill's face owes itself

1512
01:32:57,940 --> 01:33:02,700
to oxygenated haemoglobin in blood
vessels close to the skin's surface.

1513
01:33:05,700 --> 01:33:07,220
The blue colour is formed

1514
01:33:07,220 --> 01:33:10,100
by the structure of collagen
within the dermis.

1515
01:33:10,100 --> 01:33:13,260
And it's aligned in a way
that scatters the visible light,

1516
01:33:13,260 --> 01:33:15,100
which we see as blue.

1517
01:33:16,140 --> 01:33:19,380
So, here we have another adult male,
and the first one was also

1518
01:33:19,380 --> 01:33:22,940
an adult male, and their red
skin is extremely similar.

1519
01:33:22,940 --> 01:33:26,420
What that skin is saying is that
they are of very similar dominance.

1520
01:33:26,420 --> 01:33:28,900
When there are two
that are so similar...

1521
01:33:28,900 --> 01:33:31,380
..there must be issues with that?
Yes.

1522
01:33:31,380 --> 01:33:34,060
So, these are the sorts of males
that will fight with one another,

1523
01:33:34,060 --> 01:33:37,260
presumably because they can't
tell easily from the red skin

1524
01:33:37,260 --> 01:33:38,740
who is dominant over whom.

1525
01:33:42,300 --> 01:33:44,620
Colour communication for male
mandrills

1526
01:33:44,620 --> 01:33:46,380
can be a life-saving strategy.

1527
01:33:47,580 --> 01:33:50,860
Those canines are among
the largest of any primate,

1528
01:33:50,860 --> 01:33:54,020
reaching up to 5cm in length.

1529
01:33:54,020 --> 01:33:57,180
They can inflict serious injury,
and even death.

1530
01:33:57,180 --> 01:33:59,660
So fighting is a last resort.

1531
01:34:01,380 --> 01:34:04,860
These two males, of similar
colour and status,

1532
01:34:04,860 --> 01:34:07,740
both want the right to mate
with the females.

1533
01:34:09,580 --> 01:34:11,660
Only one will be victorious.

1534
01:34:11,660 --> 01:34:14,780
And a surge of testosterone,
which causes the blood vessels

1535
01:34:14,780 --> 01:34:19,180
to dilate, will make his face even
redder and more attractive.

1536
01:34:21,060 --> 01:34:24,380
And if you're the male who reaches
the top of the pecking order...

1537
01:34:24,380 --> 01:34:25,780
..your face says it all.

1538
01:34:28,780 --> 01:34:31,580
He is impressive!
He must be top dog?

1539
01:34:31,580 --> 01:34:35,620
He is. This is an alpha male,
the most dominant in the group,

1540
01:34:35,620 --> 01:34:41,340
and has been for enough time for the
red colour to move up into his eyes.

1541
01:34:41,340 --> 01:34:43,940
These animals live in groups
of hundreds -

1542
01:34:43,940 --> 01:34:46,020
how many will reach this status?

1543
01:34:46,020 --> 01:34:49,260
As far as we know, there's
just one who looks like this.

1544
01:34:49,260 --> 01:34:50,420
Once you hit this level,

1545
01:34:50,420 --> 01:34:53,380
what happens with the interactions
between the other males -

1546
01:34:53,380 --> 01:34:55,980
the ones that ARE brightly
coloured, but not like this?

1547
01:34:55,980 --> 01:34:59,100
Any male that is not this
brightly coloured will stay away.

1548
01:35:01,340 --> 01:35:04,060
Primates may use colour,
and even smell,

1549
01:35:04,060 --> 01:35:06,540
produced by the skin to communicate.

1550
01:35:06,540 --> 01:35:10,140
But when it comes to darker
environments, with poor visibility,

1551
01:35:10,140 --> 01:35:15,220
one unique group of fish has evolved
some really fascinating ways

1552
01:35:15,220 --> 01:35:18,500
to send out a message
with the help of their skin.

1553
01:35:18,500 --> 01:35:22,300
This is a black ghost knifefish.

1554
01:35:22,300 --> 01:35:25,500
At first glance, it might
not look very impressive -

1555
01:35:25,500 --> 01:35:28,860
it isn't brightly coloured,
it doesn't have amazing spines,

1556
01:35:28,860 --> 01:35:31,900
or anything like that -
in fact, it's just black

1557
01:35:31,900 --> 01:35:36,620
with a couple of white stripes and
a rather impressive-looking frill.

1558
01:35:36,620 --> 01:35:40,620
But this little South American
fish, thanks to its skin,

1559
01:35:40,620 --> 01:35:44,460
is almost able to defy
the laws of nature.

1560
01:35:44,460 --> 01:35:46,860
Black ghost knifefish have evolved

1561
01:35:46,860 --> 01:35:49,980
a highly specialised way
of communicating -

1562
01:35:49,980 --> 01:35:52,140
they use electricity.

1563
01:35:55,340 --> 01:35:59,380
There are more than 30,000
species of fish on the planet,

1564
01:35:59,380 --> 01:36:04,540
but only around 350 can produce
their own electric field.

1565
01:36:04,540 --> 01:36:08,260
Strongly electric fish,
like electric eels and some rays,

1566
01:36:08,260 --> 01:36:12,060
produce an electric discharge
of up to 800 volts,

1567
01:36:12,060 --> 01:36:14,700
strong enough to stun their prey.

1568
01:36:14,700 --> 01:36:17,860
While weakly electric fish,
like the black ghost knifefish,

1569
01:36:17,860 --> 01:36:23,060
produce less than one volt, and use
this to navigate and communicate.

1570
01:36:24,420 --> 01:36:27,620
To show me just how they use
their skin to do this,

1571
01:36:27,620 --> 01:36:31,220
PhD student Sarah Skeels
has set up an experiment.

1572
01:36:34,900 --> 01:36:38,460
In the tank, there is a single fish,
and a pair of electrodes

1573
01:36:38,460 --> 01:36:40,780
to pick up its electrical signal.

1574
01:36:40,780 --> 01:36:44,060
These are connected to a special
amplifier which converts

1575
01:36:44,060 --> 01:36:45,780
electric signals into sound.

1576
01:36:47,700 --> 01:36:49,780
QUIET BUZZ

1577
01:36:49,780 --> 01:36:51,260
It doesn't sound much, but that's

1578
01:36:51,260 --> 01:36:54,380
the auditory representation of the
field this little fish is making?

1579
01:36:54,380 --> 01:36:57,220
Exactly. So, they produce
a continuous sine wave,

1580
01:36:57,220 --> 01:37:00,180
and that's what we're hearing,
those tonal changes.

1581
01:37:00,180 --> 01:37:04,100
And it may be quite subtle, but it
allows them to get more information

1582
01:37:04,100 --> 01:37:06,140
from what's in their environment.

1583
01:37:06,140 --> 01:37:09,700
Every time he moves away from his
little branch, it changes slightly.

1584
01:37:09,700 --> 01:37:12,460
And every time he comes back,
again the tone changes.

1585
01:37:15,980 --> 01:37:18,980
Black ghost knifefish have
an electric organ running down

1586
01:37:18,980 --> 01:37:23,660
the length of their body, which
is made up of modified muscle cells.

1587
01:37:23,660 --> 01:37:26,860
Each of these cells discharges
a small amount of voltage,

1588
01:37:26,860 --> 01:37:29,860
producing the constant electric
field around their body.

1589
01:37:32,100 --> 01:37:35,340
But it's the receptor cells
in the skin that actually receive

1590
01:37:35,340 --> 01:37:38,380
this electric charge,
allowing the fish to sense

1591
01:37:38,380 --> 01:37:40,780
their surroundings and communicate.

1592
01:37:41,980 --> 01:37:45,300
And is that why we're seeing
this really weird anatomy?

1593
01:37:45,300 --> 01:37:48,060
They're typically called scaleless
fish, but they actually have

1594
01:37:48,060 --> 01:37:50,740
very tiny scales.
And this is an important thing,

1595
01:37:50,740 --> 01:37:53,140
because if they had lots of big
scales, they'd just interfere

1596
01:37:53,140 --> 01:37:56,100
and the signal wouldn't be able
to go very far.

1597
01:37:56,100 --> 01:38:00,460
It's the communication between two
fish that I'm really interested in.

1598
01:38:00,460 --> 01:38:03,780
They have very poor vision,
so it's their electric fields

1599
01:38:03,780 --> 01:38:05,780
which allow them
to sense one another.

1600
01:38:10,380 --> 01:38:13,300
So, the moment you put
the second fish in...

1601
01:38:13,300 --> 01:38:15,940
..you can hear there's something
different with that tone. Yeah.

1602
01:38:15,940 --> 01:38:20,780
So, it's a combination of both of
their signals that we can now hear.

1603
01:38:20,780 --> 01:38:23,460
And it's really interesting
that every time they came closer

1604
01:38:23,460 --> 01:38:25,700
to one another,
every time they're near one another,

1605
01:38:25,700 --> 01:38:29,380
you get this difference in the sound
being generated here. Mm-hm.

1606
01:38:29,380 --> 01:38:32,980
As well as interpreting the electric
signals as audible sound,

1607
01:38:32,980 --> 01:38:35,260
Sarah has an oscilloscope, which

1608
01:38:35,260 --> 01:38:39,860
displays a graph of the electric
voltage being produced by the fish.

1609
01:38:39,860 --> 01:38:43,860
So, you can see on the top left,
this trace is from one fish. Mm-hm.

1610
01:38:43,860 --> 01:38:46,500
And the bottom trace is
from two fish.

1611
01:38:46,500 --> 01:38:49,380
So, you can see on the top one,
when there's only one fish,

1612
01:38:49,380 --> 01:38:50,940
it's quite regular.

1613
01:38:50,940 --> 01:38:52,940
But if you see on the bottom,

1614
01:38:52,940 --> 01:38:56,060
there's a lot of distortion
here and here,

1615
01:38:56,060 --> 01:38:57,780
where the signals from both fish

1616
01:38:57,780 --> 01:39:00,700
are combining and creating
some kind of interference.

1617
01:39:00,700 --> 01:39:02,980
So, are they trying to outdo
one another?

1618
01:39:02,980 --> 01:39:05,300
Are they trying to talk
to one another? What's going on?

1619
01:39:05,300 --> 01:39:08,780
So, electric communication can be
used for a number of roles.

1620
01:39:08,780 --> 01:39:10,980
So, here, we think we have a male
and female,

1621
01:39:10,980 --> 01:39:13,540
and it could be used to elicit
courtship displays.

1622
01:39:13,540 --> 01:39:16,900
But it can also be used
to decide on territory,

1623
01:39:16,900 --> 01:39:20,380
who has - in this example -
the pieces of wood.

1624
01:39:20,380 --> 01:39:23,580
It's not just two fish, effectively,
trying to outshout one another.

1625
01:39:23,580 --> 01:39:25,820
There's something more
going on here, isn't there?

1626
01:39:25,820 --> 01:39:28,180
They can produce something called
the jamming response, where

1627
01:39:28,180 --> 01:39:31,820
they will change their frequency
so both of them can signal

1628
01:39:31,820 --> 01:39:33,940
without interrupting the other.

1629
01:39:33,940 --> 01:39:37,500
This jamming response only occurs
when fish of the same species,

1630
01:39:37,500 --> 01:39:40,780
with similar electric frequencies,
get too close.

1631
01:39:40,780 --> 01:39:44,660
They change their signal
so they can both still communicate

1632
01:39:44,660 --> 01:39:46,980
and navigate their surroundings.

1633
01:39:46,980 --> 01:39:50,340
So, it's their way of finding
a method for both being able to

1634
01:39:50,340 --> 01:39:53,180
be near one another without losing
this ability to sense their world

1635
01:39:53,180 --> 01:39:55,700
around them, while still
communicating at the same time?

1636
01:39:55,700 --> 01:39:57,660
Exactly. It's very complex,
isn't it?

1637
01:39:57,660 --> 01:40:00,180
Yeah, and the electroreceptors
are absolutely key on the skin.

1638
01:40:00,180 --> 01:40:03,460
Without them, they wouldn't be able
to do this kind of behaviour.

1639
01:40:05,460 --> 01:40:10,060
Using the skin to communicate via
electric signals is very subtle.

1640
01:40:10,060 --> 01:40:12,500
But for much more obvious
communication,

1641
01:40:12,500 --> 01:40:14,900
many animals have evolved to use
colour.

1642
01:40:17,700 --> 01:40:19,740
From chameleons, who can change

1643
01:40:19,740 --> 01:40:22,620
the colour of their
skin to show their mood...

1644
01:40:22,620 --> 01:40:26,660
..to sarcastic fringeheads,
whose gaping, vibrant mouths

1645
01:40:26,660 --> 01:40:30,700
act as a warning signal to help
defend their territory from rivals.

1646
01:40:33,180 --> 01:40:37,100
But nowhere is it more readily seen
than in birds.

1647
01:40:38,900 --> 01:40:41,980
There are over
10,000 species of bird,

1648
01:40:41,980 --> 01:40:45,820
and their feathers represent
a huge range in the colour spectrum.

1649
01:40:50,580 --> 01:40:52,620
Feathers are made from keratin,

1650
01:40:52,620 --> 01:40:56,100
a protein formed in tiny follicles
in the epidermis.

1651
01:40:57,500 --> 01:41:02,260
Like in reptiles, mammals and fish,
birds can be different colours

1652
01:41:02,260 --> 01:41:05,380
because of the pigments contained
in their skin

1653
01:41:05,380 --> 01:41:08,460
and the way in which
the keratin is structured.

1654
01:41:08,460 --> 01:41:12,580
The most widespread colour-producing
pigment found in nature is melanin,

1655
01:41:12,580 --> 01:41:17,340
and it creates the darkest colours -
blacks, browns and greys.

1656
01:41:19,620 --> 01:41:22,220
Melanin is produced by melanocytes,

1657
01:41:22,220 --> 01:41:25,740
specialised skin cells
located in the epidermis.

1658
01:41:25,740 --> 01:41:29,340
And it can be seen in action
in this golden plover feather.

1659
01:41:31,860 --> 01:41:35,260
These spots and stripes
are perfect adaptations

1660
01:41:35,260 --> 01:41:39,700
for allowing the bird to almost
disappear in its surroundings.

1661
01:41:39,700 --> 01:41:42,700
It's a great example
of feathery camouflage.

1662
01:41:42,700 --> 01:41:46,340
And in terms of what it's
saying to the world around it...

1663
01:41:46,340 --> 01:41:49,460
Well, it's pretty much,
"There's nothing to see here."

1664
01:41:51,140 --> 01:41:56,020
Another type of pigment found across
the animal kingdom are carotenoids.

1665
01:41:56,020 --> 01:41:59,580
Most of the reds, oranges and
yellows seen in bird feathers

1666
01:41:59,580 --> 01:42:02,380
are coloured by these
chemical compounds.

1667
01:42:02,380 --> 01:42:05,740
But, unlike melanin,
they are not produced by the skin,

1668
01:42:05,740 --> 01:42:08,420
but obtained from the food
the birds eat.

1669
01:42:11,860 --> 01:42:13,660
Carotenoid pigments are then

1670
01:42:13,660 --> 01:42:16,620
transported through the skin
to their feathers.

1671
01:42:16,620 --> 01:42:20,380
Once in place, they absorb
mostly blue light to produce

1672
01:42:20,380 --> 01:42:24,140
the orange, red and yellow colours
that we see in these feathers.

1673
01:42:26,420 --> 01:42:29,140
You can see the carotenoids
have clearly coloured

1674
01:42:29,140 --> 01:42:31,940
these little goldcrest feathers
a fiery orange.

1675
01:42:33,780 --> 01:42:35,300
And this one is definitely

1676
01:42:35,300 --> 01:42:37,940
not trying to blend in with
its surroundings.

1677
01:42:37,940 --> 01:42:41,620
It's from the cap of a male,
and during the breeding season,

1678
01:42:41,620 --> 01:42:45,820
these little caps flash
orange, yellows and golds.

1679
01:42:45,820 --> 01:42:47,620
And they're trying to say,

1680
01:42:47,620 --> 01:42:49,780
"Stay away, this is my territory."

1681
01:42:51,580 --> 01:42:55,060
As for the iridescent colours
found in birds, they're not caused

1682
01:42:55,060 --> 01:42:59,060
by pigments in their skin, but by
the structure of the feather itself.

1683
01:43:00,980 --> 01:43:04,100
Keratin within the feather
is aligned in such a way

1684
01:43:04,100 --> 01:43:05,820
that it allows light

1685
01:43:05,820 --> 01:43:10,420
to twist, turn and separate
into a rainbow of colours.

1686
01:43:10,420 --> 01:43:12,580
This feather is from a male peacock.

1687
01:43:12,580 --> 01:43:15,700
He's trying to say his
genes are amazing.

1688
01:43:15,700 --> 01:43:19,700
He can waste energy in these big,
bright, ostentatious feathers

1689
01:43:19,700 --> 01:43:21,860
because his genes are that good.

1690
01:43:21,860 --> 01:43:25,020
Basically, he's telling
every other female in the area,

1691
01:43:25,020 --> 01:43:26,620
"You should mate with me."

1692
01:43:29,060 --> 01:43:32,740
From understanding how feathers
are coloured in modern-day birds,

1693
01:43:32,740 --> 01:43:34,500
a whole new appreciation

1694
01:43:34,500 --> 01:43:38,300
of colouration in extinct species
has been possible.

1695
01:43:38,300 --> 01:43:42,300
Advances in research over the last
ten years or so have transformed

1696
01:43:42,300 --> 01:43:46,060
our knowledge of dinosaurs,
allowing a deeper focus on

1697
01:43:46,060 --> 01:43:50,540
fossilised feathers, and a greater
understanding of how colour is

1698
01:43:50,540 --> 01:43:55,020
produced - right across the animal
kingdom - is making this possible.

1699
01:43:55,020 --> 01:43:58,340
Palaeontologist, Professor
Mike Benton, is showing me

1700
01:43:58,340 --> 01:44:02,140
a fossilised feather under a
scanning electron microscope.

1701
01:44:02,140 --> 01:44:05,460
He and his team made a breakthrough
when it was discovered

1702
01:44:05,460 --> 01:44:09,620
that the shapes embedded
in the fossils were melanosomes.

1703
01:44:09,620 --> 01:44:12,100
Melanosomes are made in melanocytes,

1704
01:44:12,100 --> 01:44:16,500
which are the melanin-forming
cells found in the skin.

1705
01:44:16,500 --> 01:44:19,660
They're the site of synthesis,
storage and transport

1706
01:44:19,660 --> 01:44:23,940
of melanin pigments,
and provide tissues with colour.

1707
01:44:23,940 --> 01:44:28,100
In some of the fossils, we find
these kind of sausage-shaped ones.

1708
01:44:28,100 --> 01:44:31,980
In others, we find spherical ones
or ball-shaped ones.

1709
01:44:31,980 --> 01:44:36,660
And looking at evidence from
modern birds and modern mammals,

1710
01:44:36,660 --> 01:44:39,500
we discover there's an exact
correlation between the shapes

1711
01:44:39,500 --> 01:44:42,580
of the melanosomes
and the colours that they have.

1712
01:44:42,580 --> 01:44:45,900
Every time we looked at a hair
or a feather from a modern creature

1713
01:44:45,900 --> 01:44:49,660
where we know the colour, we found
the sausage-shaped melanosomes.

1714
01:44:49,660 --> 01:44:52,740
You either get black
if they're very tightly packed,

1715
01:44:52,740 --> 01:44:55,420
brown if they're more
loosely packed, grey,

1716
01:44:55,420 --> 01:44:58,380
all the way through to blonde,
where there's not very many at all.

1717
01:44:58,380 --> 01:45:01,700
And when we looked in modern
feathers and hairs, say, from

1718
01:45:01,700 --> 01:45:05,700
a ginger-haired person, we found
the other kind of melanin,

1719
01:45:05,700 --> 01:45:09,020
which is chemically different,
and it gives only ginger colours.

1720
01:45:09,020 --> 01:45:12,660
And that corresponds to this kind
of ball-shaped melanosomes.

1721
01:45:12,660 --> 01:45:15,620
Does that mean we're seeing
browns and greys and whites,

1722
01:45:15,620 --> 01:45:18,340
and even gingers,
in some of our dinosaurs?

1723
01:45:18,340 --> 01:45:21,980
Yes, and I think this has
completely revolutionised

1724
01:45:21,980 --> 01:45:23,780
the way we see dinosaurs.

1725
01:45:23,780 --> 01:45:26,460
Dinosaurs were clearly more
colourful than scientists

1726
01:45:26,460 --> 01:45:30,700
once thought, and it's not just
blacks, browns and even gingers.

1727
01:45:30,700 --> 01:45:34,100
Fossilised remains indicate
that dinosaurs had much the same

1728
01:45:34,100 --> 01:45:36,860
range that we see in birds today.

1729
01:45:36,860 --> 01:45:40,140
The fact that you get the
same relationship

1730
01:45:40,140 --> 01:45:42,980
between
colour and melanosome shape

1731
01:45:42,980 --> 01:45:46,420
in all the birds that people have
looked at, and in all the mammals,

1732
01:45:46,420 --> 01:45:49,500
means that, probably, this is
a general rule of nature.

1733
01:45:51,220 --> 01:45:53,900
And colour is only half the story.

1734
01:45:53,900 --> 01:45:55,500
From the fossil evidence,

1735
01:45:55,500 --> 01:45:58,700
Mike and his team have
discovered patterns, as well.

1736
01:45:58,700 --> 01:46:00,420
They've been able to piece together

1737
01:46:00,420 --> 01:46:03,100
traces of different shaped
melanosomes,

1738
01:46:03,100 --> 01:46:04,740
and create a more accurate image

1739
01:46:04,740 --> 01:46:06,940
of what a dinosaur
would have looked like.

1740
01:46:09,220 --> 01:46:11,340
This is Sinosauropteryx.

1741
01:46:11,340 --> 01:46:15,140
We were sampling across the body,
along the tail, and across the head,

1742
01:46:15,140 --> 01:46:18,420
and so on, and we were able to
show very definitely that it has

1743
01:46:18,420 --> 01:46:20,700
these ginger and white stripes.

1744
01:46:20,700 --> 01:46:25,260
So, the first thing was we only
found the ball-shaped melanosomes,

1745
01:46:25,260 --> 01:46:28,140
therefore, all ginger - we couldn't
find any hint

1746
01:46:28,140 --> 01:46:31,020
of the sausage-shapes or black
or brown colours.

1747
01:46:31,020 --> 01:46:34,660
And, in the areas showing white,
we were finding no melanosomes.

1748
01:46:34,660 --> 01:46:37,860
What was Sinosauropteryx doing,
what was his colouration for?

1749
01:46:37,860 --> 01:46:39,980
At first we saw the stripes,
and we thought,

1750
01:46:39,980 --> 01:46:42,380
"Well, could it be camouflage?"
I mean, that's a big function

1751
01:46:42,380 --> 01:46:46,300
of colour, of course, we think
of tigers and zebras, and so on.

1752
01:46:46,300 --> 01:46:49,780
But the fact is the stripes don't
occur across the whole body,

1753
01:46:49,780 --> 01:46:54,060
so it's not likely you would
simply camouflage your tail.

1754
01:46:54,060 --> 01:46:57,740
So, the other function that seemed
quite obvious would be display.

1755
01:46:57,740 --> 01:47:01,020
And, of course, a tail
is a perfect display organ.

1756
01:47:01,020 --> 01:47:05,580
And, presumably, whoever had the
brightest, longest, stripiest tail

1757
01:47:05,580 --> 01:47:07,900
probably would win the most mates.

1758
01:47:07,900 --> 01:47:11,260
Colour is one way to communicate
using your skin.

1759
01:47:11,260 --> 01:47:13,420
But for more aggressive signals,

1760
01:47:13,420 --> 01:47:16,180
skin has evolved
to produce its own sound.

1761
01:47:18,580 --> 01:47:20,660
HISSING

1762
01:47:20,660 --> 01:47:23,100
This is a desert horned viper.

1763
01:47:24,700 --> 01:47:28,780
I love this little snake,
absolutely incredible!

1764
01:47:28,780 --> 01:47:31,300
But I'm not going to get any closer
because it's venomous.

1765
01:47:31,300 --> 01:47:32,980
And, actually, more than that...

1766
01:47:32,980 --> 01:47:35,180
..this little snake is deadly.

1767
01:47:36,300 --> 01:47:40,140
And what I really love
about this snake...

1768
01:47:40,140 --> 01:47:41,620
..is that noise.

1769
01:47:41,620 --> 01:47:44,060
STEADY HISSING

1770
01:47:45,780 --> 01:47:49,460
Right now, I'm being told,
in no uncertain terms,

1771
01:47:49,460 --> 01:47:50,940
"Stay away."

1772
01:47:50,940 --> 01:47:52,980
"Get back, or else."

1773
01:47:58,500 --> 01:48:02,580
Desert horned vipers live
in the Sahara, in North Africa.

1774
01:48:03,980 --> 01:48:05,660
They're sidewinders, and are

1775
01:48:05,660 --> 01:48:08,700
the most abundant and venomous
snakes in this region.

1776
01:48:10,980 --> 01:48:14,620
Like all desert vipers, they've
evolved to communicate through

1777
01:48:14,620 --> 01:48:18,340
their skin, telling anyone who can
hear them that they are dangerous.

1778
01:48:20,340 --> 01:48:22,340
To do this, they have keeled scales,

1779
01:48:22,340 --> 01:48:25,340
which they use to produce
a hissing sound of their own.

1780
01:48:27,580 --> 01:48:30,380
HISSING

1781
01:48:30,380 --> 01:48:35,580
He's arranging his body into a
series of parallel S-shaped curves.

1782
01:48:35,580 --> 01:48:38,300
And once he's done that, he's
rubbing these lateral scales,

1783
01:48:38,300 --> 01:48:41,020
the ones down the side of his body,
against one another.

1784
01:48:41,020 --> 01:48:43,900
And that is
how he's making this noise.

1785
01:48:47,180 --> 01:48:51,460
Keeled scales, unlike the smooth
variety found in most other snakes,

1786
01:48:51,460 --> 01:48:54,260
have a ridge running
down the centre line.

1787
01:48:54,260 --> 01:48:55,940
This gives the added advantage

1788
01:48:55,940 --> 01:48:58,220
of reducing the shine of the snake's
skin,

1789
01:48:58,220 --> 01:49:02,380
helping with camouflage and
keeping it out of harm's way.

1790
01:49:02,380 --> 01:49:04,500
It's a great natural deterrent.

1791
01:49:04,500 --> 01:49:08,820
In the wild, predators know to keep
their distance, and this allows

1792
01:49:08,820 --> 01:49:13,540
the snake to keep its precious venom
it can use to catch its prey.

1793
01:49:18,460 --> 01:49:21,460
Sound can be an effective way
to convey a warning,

1794
01:49:21,460 --> 01:49:25,340
but some noises in the animal
kingdom aren't created by skin.

1795
01:49:27,140 --> 01:49:31,860
Many animals have a voice box
which, like in humans, is often used

1796
01:49:31,860 --> 01:49:34,460
to produce a wide array of sounds.

1797
01:49:34,460 --> 01:49:39,580
The furthest a human can project
their voice is about 180m.

1798
01:49:39,580 --> 01:49:44,220
But one primate uses its specially
adapted skin to throw its voice

1799
01:49:44,220 --> 01:49:46,700
more than ten times that distance.

1800
01:49:46,700 --> 01:49:50,620
GIBBONS CALL

1801
01:49:53,140 --> 01:49:56,260
And I've come to Twycross Zoo
to take a closer look.

1802
01:49:59,940 --> 01:50:02,460
These beautiful animals
are siamangs.

1803
01:50:02,460 --> 01:50:04,780
They're the largest of the gibbons,

1804
01:50:04,780 --> 01:50:08,340
and actually, one of the loudest
animals on the planet.

1805
01:50:08,340 --> 01:50:10,780
They're not making a huge amount
of noise right now

1806
01:50:10,780 --> 01:50:13,300
because they're having their
breakfast, but when they call,

1807
01:50:13,300 --> 01:50:16,220
you can hear them
from over 2km away.

1808
01:50:16,220 --> 01:50:17,900
And, if I was stand next to them,

1809
01:50:17,900 --> 01:50:19,940
they'd be louder than a rock
concert.

1810
01:50:22,140 --> 01:50:24,380
SIAMANGS CALL

1811
01:50:24,380 --> 01:50:28,860
In their forest homes of Southeast
Asia, visual gestures would be lost

1812
01:50:28,860 --> 01:50:32,620
in the dark canopy of the trees,
so loud vocalisations play

1813
01:50:32,620 --> 01:50:36,220
an important role to fend off
neighbouring siamangs.

1814
01:50:39,020 --> 01:50:42,580
And they can only do all this
because of their skin.

1815
01:50:42,580 --> 01:50:46,100
They've got these incredible
large inflatable throat sacs

1816
01:50:46,100 --> 01:50:50,580
that really helps throw
their voice as far as possible.

1817
01:50:50,580 --> 01:50:54,020
It's the elastin and collagen
within the skin that allows

1818
01:50:54,020 --> 01:50:58,140
the siamangs to inflate their throat
sacs to the size of their heads.

1819
01:50:58,140 --> 01:51:01,740
But this skin doesn't get in the way
when they're NOT calling.

1820
01:51:01,740 --> 01:51:03,900
Thanks to its physical properties,

1821
01:51:03,900 --> 01:51:07,180
the skin is able to spring back
to normal when not in use.

1822
01:51:12,980 --> 01:51:17,020
The animal kingdom has evolved
so many amazing ways to communicate

1823
01:51:17,020 --> 01:51:21,340
that we are only still just
scratching the surface.

1824
01:51:21,340 --> 01:51:24,700
But brand-new science has
changed our understanding

1825
01:51:24,700 --> 01:51:28,940
of how one little bird communicates
using its skin.

1826
01:51:28,940 --> 01:51:30,180
The puffin.

1827
01:51:31,620 --> 01:51:33,620
Jamie Dunning is an ornithologist,

1828
01:51:33,620 --> 01:51:36,220
and he's been working with birds
for over ten years.

1829
01:51:37,780 --> 01:51:41,260
Jamie, these are such amazing birds,
they're instantly recognisable,

1830
01:51:41,260 --> 01:51:44,700
and they're one of our most-iconic
seaside species.

1831
01:51:44,700 --> 01:51:48,220
And it's all down to this beautiful,
vibrantly coloured beak.

1832
01:51:48,220 --> 01:51:50,580
But there's so much going on behind
the scenes here, isn't there?

1833
01:51:50,580 --> 01:51:54,540
Yeah. So, the beak is almost
certainly a big, kind of, ornament,

1834
01:51:54,540 --> 01:51:57,260
a flag to suggest fitness
and sexual selection,

1835
01:51:57,260 --> 01:51:59,500
and help them choose mates.

1836
01:51:59,500 --> 01:52:03,780
Both males and the females
have this beautiful bill.

1837
01:52:03,780 --> 01:52:06,820
As with all birds,
the puffins' beaks are covered

1838
01:52:06,820 --> 01:52:11,700
in the complex protein keratin,
which forms a hard outer layer.

1839
01:52:11,700 --> 01:52:15,020
Carotenoids have become
concentrated in the keratin

1840
01:52:15,020 --> 01:52:17,700
covering to give these
vibrant colours.

1841
01:52:19,420 --> 01:52:22,500
It must be quite difficult, in terms
of the energy expenditure, then,

1842
01:52:22,500 --> 01:52:24,540
to invest in a bill like this
year-round?

1843
01:52:24,540 --> 01:52:27,900
This is only half the story. So,
you only need this in the summer,

1844
01:52:27,900 --> 01:52:29,900
it looks very different over winter.

1845
01:52:29,900 --> 01:52:33,220
Well, this is completely different,
it's like a whole different

1846
01:52:33,220 --> 01:52:35,620
species of bird. Those bright
colours are gone.

1847
01:52:35,620 --> 01:52:39,540
The majority of that big colourful
bill just flakes off over winter.

1848
01:52:39,540 --> 01:52:41,260
There's no need for it.

1849
01:52:41,260 --> 01:52:44,620
So, we only see those brightly
coloured bills in summer and spring,

1850
01:52:44,620 --> 01:52:47,420
their breeding months? We do,
and that coincides with when we see

1851
01:52:47,420 --> 01:52:49,820
puffins, cos they only come to land
during the breeding season.

1852
01:52:49,820 --> 01:52:52,580
The winter is spent
out in the middle of the sea.

1853
01:52:52,580 --> 01:52:55,100
Jamie has made a ground-breaking
discovery

1854
01:52:55,100 --> 01:52:57,060
about the skin on a puffin's beak.

1855
01:53:00,060 --> 01:53:03,820
To show me, he's brought a puffin
along, which died naturally

1856
01:53:03,820 --> 01:53:05,540
and is now part of his study.

1857
01:53:08,620 --> 01:53:12,820
Jamie, this is amazing!
It's so cool! I mean...

1858
01:53:12,820 --> 01:53:15,580
..it's glowing.
So, this is fluorescence.

1859
01:53:15,580 --> 01:53:17,780
This is the seasonally developed
bill.

1860
01:53:17,780 --> 01:53:20,500
So, this bit all drops off,
including the fluorescent bit.

1861
01:53:20,500 --> 01:53:22,980
It's visible with this UV lamp
and torch,

1862
01:53:22,980 --> 01:53:25,860
but a lot of birds can see
UV colour, can't they?

1863
01:53:25,860 --> 01:53:28,620
Yeah, that's right. So, we have
three types of colour receptor

1864
01:53:28,620 --> 01:53:31,540
in our eye, or cone cells -
that's red, green and blue -

1865
01:53:31,540 --> 01:53:34,220
and we mix those to make
all the colours that we can see.

1866
01:53:34,220 --> 01:53:37,740
Birds have a fourth,
they have tetrachromatic vision.

1867
01:53:37,740 --> 01:53:41,540
And that fourth one allows them
to see, to some degree, in UV light.

1868
01:53:41,540 --> 01:53:45,780
For birds, being able to see
UV light has its benefits.

1869
01:53:45,780 --> 01:53:47,860
It enables a method of communication

1870
01:53:47,860 --> 01:53:50,340
which is invisible
to potential predators,

1871
01:53:50,340 --> 01:53:52,420
but allows them to find a mate.

1872
01:53:55,060 --> 01:53:58,020
As this is the bit that falls off
outside of the breeding season,

1873
01:53:58,020 --> 01:54:00,900
there's a very good chance
that this is something to do with

1874
01:54:00,900 --> 01:54:06,020
sexual signalling and fitness
and luring in the opposite sex.

1875
01:54:06,020 --> 01:54:10,260
It's amazing. These little birds
that we kind of grow up knowing

1876
01:54:10,260 --> 01:54:13,260
so well actually have a load
of secrets in their skin

1877
01:54:13,260 --> 01:54:14,940
that we didn't know before.

1878
01:54:14,940 --> 01:54:18,340
It's exciting. Until recently,
we had no idea about this.

1879
01:54:26,340 --> 01:54:29,340
Skin has allowed animals
to communicate.

1880
01:54:30,620 --> 01:54:32,460
From vibrant colours...

1881
01:54:32,460 --> 01:54:34,140
..to sound...

1882
01:54:34,140 --> 01:54:36,620
..to electrical sensing...

1883
01:54:36,620 --> 01:54:38,300
..the skin does it all.

1884
01:54:40,060 --> 01:54:41,660
Next time...

1885
01:54:41,660 --> 01:54:45,260
..I'll come face-to-face
with a deadly frog...

1886
01:54:45,260 --> 01:54:49,220
..learn why rhinos need
such heavily armoured skin...

1887
01:54:49,220 --> 01:54:52,580
..and find out how,
in porcupine quills,

1888
01:54:52,580 --> 01:54:56,220
bigger is not always better...

1889
01:54:56,220 --> 01:55:01,220
..as I delve into the ingenious ways
skin can be the ultimate defence.

1890
01:55:35,580 --> 01:55:36,980
Skin.

1891
01:55:36,980 --> 01:55:38,820
We all have it.

1892
01:55:38,820 --> 01:55:41,940
And so does every vertebrate
on the planet.

1893
01:55:42,940 --> 01:55:45,340
It keeps the outside out...

1894
01:55:45,340 --> 01:55:47,340
..and the inside in.

1895
01:55:48,820 --> 01:55:52,540
Animals may look very different
on the surface, but we all share

1896
01:55:52,540 --> 01:55:55,060
the same basic skin blueprint.

1897
01:55:56,820 --> 01:56:00,820
I'm Ben Garrett, professor
of evolutionary biology,

1898
01:56:00,820 --> 01:56:04,820
and I'm fascinated by this
often-overlooked wonder of nature.

1899
01:56:04,820 --> 01:56:07,260
It's not just a case
that it's hairless,

1900
01:56:07,260 --> 01:56:09,340
the skin's totally different.

1901
01:56:09,340 --> 01:56:11,820
Now, ground-breaking new science...

1902
01:56:11,820 --> 01:56:13,780
This is really quite remarkable.

1903
01:56:13,780 --> 01:56:16,340
It shouldn't be a game-changer
for so many people.

1904
01:56:16,340 --> 01:56:17,700
The sound...

1905
01:56:17,700 --> 01:56:21,060
Oh, it makes the hair on the back
of your neck go up, doesn't it?

1906
01:56:21,060 --> 01:56:23,580
..is revealing skin's mysteries.

1907
01:56:23,580 --> 01:56:26,860
It really transforms our
understanding of dinosaurs.

1908
01:56:27,860 --> 01:56:31,980
I'm going to explore the natural
history of the body's largest organ

1909
01:56:31,980 --> 01:56:37,460
to see how skin has allowed animals
to conquer every habitat,

1910
01:56:37,460 --> 01:56:39,820
disappear into their surroundings

1911
01:56:39,820 --> 01:56:43,100
and develop extra-sensory abilities.

1912
01:56:44,580 --> 01:56:49,580
We're even discovering the complex
ecosystem living on our skin.

1913
01:56:49,580 --> 01:56:51,860
Jim, that's awful. It really is.

1914
01:56:52,860 --> 01:56:55,580
In this episode,
I'll learn why rhinos

1915
01:56:55,580 --> 01:56:59,340
have the most heavily-armoured skin
of any living mammal.

1916
01:57:01,980 --> 01:57:05,340
Why the smallest porcupine quills
are often the most dangerous.

1917
01:57:07,820 --> 01:57:10,340
And discover why
cuttlefish camouflage

1918
01:57:10,340 --> 01:57:13,660
is transforming the way
scientists think about skin.

1919
01:57:15,580 --> 01:57:19,820
To delve into the ingenious ways
skin defends animals

1920
01:57:19,820 --> 01:57:21,580
from physical attacks.

1921
01:57:23,580 --> 01:57:26,980
I'm going to reveal
the secrets of skin.

1922
01:57:33,580 --> 01:57:38,060
This is a member of one of the most
toxic groups of animals

1923
01:57:38,060 --> 01:57:39,820
on the planet.

1924
01:57:41,820 --> 01:57:44,820
She's a yellow-banded
poison dart frog.

1925
01:57:46,340 --> 01:57:50,900
These tiny frogs secrete
a very potent poison

1926
01:57:50,900 --> 01:57:52,580
through their skin.

1927
01:57:54,340 --> 01:57:57,820
Direct contact with some species

1928
01:57:57,820 --> 01:58:01,140
can cause nausea, paralysis...

1929
01:58:02,140 --> 01:58:03,820
..and even death.

1930
01:58:06,340 --> 01:58:10,340
There are almost 200 known species
of poison dart frog

1931
01:58:10,340 --> 01:58:13,340
in the forests of Central
and South America.

1932
01:58:14,340 --> 01:58:17,820
Each one combines toxic skin
with vivid colours,

1933
01:58:17,820 --> 01:58:21,580
and the more toxic a species,
the brighter colours it has evolved.

1934
01:58:22,820 --> 01:58:27,340
A single golden poison dart frog
has enough poison in its skin

1935
01:58:27,340 --> 01:58:31,660
to kill ten people, making it
the most toxic animal alive.

1936
01:58:33,060 --> 01:58:38,380
These bright colours are a stark
warning for predators to back off.

1937
01:58:38,380 --> 01:58:42,340
But if a hungry bird does decide
to ignore this warning

1938
01:58:42,340 --> 01:58:46,820
and takes a nibble, then it won't
be making that mistake again.

1939
01:58:47,820 --> 01:58:51,060
Each frog species deploys
a different range of toxins

1940
01:58:51,060 --> 01:58:55,060
but they all belong to a group
of chemicals called alkaloids.

1941
01:58:56,060 --> 01:58:58,820
The frogs don't make these toxins
from scratch.

1942
01:58:58,820 --> 01:59:01,820
They're derived from defensive
chemicals in the ants,

1943
01:59:01,820 --> 01:59:03,900
beetles and millipedes they eat.

1944
01:59:04,900 --> 01:59:07,820
The toxins are stored in glands
in the dermis

1945
01:59:07,820 --> 01:59:10,500
and released onto the surface
via pores.

1946
01:59:11,500 --> 01:59:13,980
Poison dart frogs are active
during the day

1947
01:59:13,980 --> 01:59:17,340
when predators can spot their
warning colours and avoid them.

1948
01:59:17,340 --> 01:59:20,820
Most other frog species
tend to come out at night.

1949
01:59:22,060 --> 01:59:25,820
These frogs got their name
because their toxins were once used

1950
01:59:25,820 --> 01:59:28,100
by forest hunters
to tip their darts.

1951
01:59:29,820 --> 01:59:32,820
Today, we're finding
other uses for them.

1952
01:59:34,820 --> 01:59:39,700
Now scientists are studying the
deadly chemicals these frogs deploy

1953
01:59:39,700 --> 01:59:44,060
in order to design new
painkilling drugs and medicines.

1954
01:59:45,060 --> 01:59:48,340
One toxin, epibatidine,
attacks nerves,

1955
01:59:48,340 --> 01:59:50,820
causing numbness and paralysis.

1956
01:59:50,820 --> 01:59:54,340
Researchers hope that by unpicking
epibatidine's structure

1957
01:59:54,340 --> 01:59:57,580
and chemistry, they may be able
to separate its beneficial

1958
01:59:57,580 --> 02:00:00,420
painkilling effects
from its deadly toxicity.

1959
02:00:01,420 --> 02:00:02,820
Right, you.

1960
02:00:02,820 --> 02:00:05,060
Back in your tank.

1961
02:00:09,580 --> 02:00:13,580
Now, you might think this is
a very silly thing to do.

1962
02:00:14,580 --> 02:00:17,820
But captive bred dart frogs...

1963
02:00:18,820 --> 02:00:20,580
..aren't toxic at all.

1964
02:00:23,340 --> 02:00:27,580
Frogs bred in captivity are fed
harmless insects like fruit flies,

1965
02:00:27,580 --> 02:00:31,060
which means they never go on
to develop the dangerous toxicity

1966
02:00:31,060 --> 02:00:32,820
of their wild relatives.

1967
02:00:35,060 --> 02:00:39,060
What we still don't fully understand
is how wild frogs can eat

1968
02:00:39,060 --> 02:00:42,580
and store these toxic compounds
without coming to harm.

1969
02:00:44,580 --> 02:00:48,340
A poison dart frog's skin
is a weapon and a warning.

1970
02:00:50,340 --> 02:00:53,060
This is just the start
of the extraordinary ways

1971
02:00:53,060 --> 02:00:55,820
animals use their skin
to defend themselves.

1972
02:00:56,820 --> 02:01:00,060
One animal is infamous
for the warning sound it makes

1973
02:01:00,060 --> 02:01:02,580
with a specialised part
of its epidermis.

1974
02:01:06,060 --> 02:01:08,820
This is a rattlesnake's rattle.

1975
02:01:11,060 --> 02:01:14,340
It's made from the final few
scales that cover the tip

1976
02:01:14,340 --> 02:01:16,060
of the snake's tail.

1977
02:01:16,060 --> 02:01:21,340
They form a series of hollow
interlocking segments of keratin -

1978
02:01:21,340 --> 02:01:24,340
the same protein as my hair
and nails.

1979
02:01:25,340 --> 02:01:27,820
The segments aren't fused
to one another.

1980
02:01:27,820 --> 02:01:29,420
They're free to move.

1981
02:01:29,420 --> 02:01:32,220
So if I give this little structure
a good shake...

1982
02:01:32,220 --> 02:01:35,340
The interlinked capsules
rattle against one another.

1983
02:01:36,580 --> 02:01:40,060
Rattlesnakes shake their rattles
to produce a loud buzz.

1984
02:01:40,060 --> 02:01:44,060
This alerts livestock and predators
that there's a venomous snake nearby

1985
02:01:44,060 --> 02:01:46,060
that wants to avoid trouble.

1986
02:01:48,820 --> 02:01:50,580
Now, I can manage...

1987
02:01:51,820 --> 02:01:53,820
..a couple of rattles a second.

1988
02:01:53,820 --> 02:01:57,340
That's not really enough
to grab anyone's attention.

1989
02:01:58,820 --> 02:02:02,820
To see how a rattlesnake uses
the keratin on the tip of its tail

1990
02:02:02,820 --> 02:02:04,980
as a brilliant defence mechanism,

1991
02:02:04,980 --> 02:02:07,820
I need to find a way
to shake it much faster.

1992
02:02:13,220 --> 02:02:15,820
I'm visiting an engineering lab
to get help

1993
02:02:15,820 --> 02:02:19,580
from the reassuringly titled
Lecturer in Non-destructive Testing,

1994
02:02:19,580 --> 02:02:21,340
Dr Rob Hughes.

1995
02:02:21,340 --> 02:02:24,340
Hey, Rob. What have we got here?
How are we going to test this?

1996
02:02:24,340 --> 02:02:28,060
So, here we have a vibration stage.
Now, this works in the same way

1997
02:02:28,060 --> 02:02:29,820
that a stereo speaker does,

1998
02:02:29,820 --> 02:02:32,820
so we can therefore essentially
excite something up and down

1999
02:02:32,820 --> 02:02:34,580
at whatever frequency we want.

2000
02:02:34,580 --> 02:02:37,180
We do that using this
function generator here,

2001
02:02:37,180 --> 02:02:40,740
through an amplifier,
to then get sent to the speaker.

2002
02:02:40,740 --> 02:02:44,820
Using Rob's set-up, we'll be able
to shake the rattle much faster

2003
02:02:44,820 --> 02:02:46,900
than I could do it myself.

2004
02:02:46,900 --> 02:02:49,580
This will allow us to find
the right speed

2005
02:02:49,580 --> 02:02:52,660
to get the best sound
out of these keratin capsules.

2006
02:02:52,660 --> 02:02:56,340
I thought we'd start out by moving
it at five times per second.

2007
02:02:56,340 --> 02:02:57,980
That's 5Hz.

2008
02:02:57,980 --> 02:03:02,060
So, if we send the impulse signal in
and start vibrating.

2009
02:03:05,060 --> 02:03:07,700
You can see that not much
is really happening.

2010
02:03:07,700 --> 02:03:10,580
But what we can do is cycle
through the frequencies,

2011
02:03:10,580 --> 02:03:12,340
increasing the pitch. OK.

2012
02:03:12,340 --> 02:03:13,700
Erm, so...

2013
02:03:13,700 --> 02:03:16,060
RATTLE GETS FASTER

2014
02:03:16,060 --> 02:03:19,340
So this is 10Hz,
so ten times a second.

2015
02:03:20,580 --> 02:03:23,060
And then we're going to ramp up
with more now.

2016
02:03:23,060 --> 02:03:24,900
So we'll go to 20.

2017
02:03:24,900 --> 02:03:27,820
Oh, we're already...
Starting to sound like it.

2018
02:03:27,820 --> 02:03:30,340
Sounds like a rattlesnake,
but it doesn't sound like

2019
02:03:30,340 --> 02:03:33,580
an angry rattlesnake just yet.
That's a slightly disgruntled snake.

2020
02:03:33,580 --> 02:03:36,220
Depends how angry you want it to be.
This is 30Hz.

2021
02:03:36,220 --> 02:03:38,660
RATTLE GETS FASTER

2022
02:03:38,660 --> 02:03:40,820
40Hz. Oh, it's getting there.

2023
02:03:41,820 --> 02:03:43,340
And 50Hz.

2024
02:03:45,820 --> 02:03:49,060
OK, it looks like a rattle
from a rattlesnake now.

2025
02:03:49,060 --> 02:03:51,580
That weird, disjointed,
chaotic rattle.

2026
02:03:51,580 --> 02:03:53,100
But that sound...

2027
02:03:53,100 --> 02:03:57,060
Oh, it makes the hair on the back of
your neck go up, doesn't it? Yeah.

2028
02:03:57,060 --> 02:04:01,340
With the clamp vibrating at 50 times
a second, replicating the action

2029
02:04:01,340 --> 02:04:05,580
of specialised tail-shaker muscles,
the fragile capsules of skin

2030
02:04:05,580 --> 02:04:07,580
reach their full potential.

2031
02:04:07,580 --> 02:04:10,220
The warning is loud and clear.

2032
02:04:10,220 --> 02:04:11,900
It's done its job.

2033
02:04:11,900 --> 02:04:15,060
There is absolutely no doubt
right now that if I heard that

2034
02:04:15,060 --> 02:04:17,060
in the wild, I'd be stepping away.

2035
02:04:17,060 --> 02:04:19,060
That's a rattlesnake to me.

2036
02:04:23,060 --> 02:04:27,580
While a rattler's noisy warning
helps keep hunter and hunted apart,

2037
02:04:27,580 --> 02:04:31,820
some animals' skin defences
are shaped by close contact.

2038
02:04:34,580 --> 02:04:37,580
Rhinos are some of the biggest
animals on the planet,

2039
02:04:37,580 --> 02:04:39,700
reaching at least a tonne in weight.

2040
02:04:41,340 --> 02:04:43,980
They also have the most
heavily-armoured skin

2041
02:04:43,980 --> 02:04:45,660
of any living mammal.

2042
02:04:49,060 --> 02:04:52,340
Thick armour,
up to four centimetres in places,

2043
02:04:52,340 --> 02:04:56,980
combined with a huge body size
and a top speed of 50km per hour,

2044
02:04:56,980 --> 02:04:59,820
makes them all but invulnerable
to predators.

2045
02:05:02,340 --> 02:05:06,340
Of the three species living in Asia
and two living in Africa,

2046
02:05:06,340 --> 02:05:10,340
the African white rhino is the
largest and best-defended of all.

2047
02:05:12,820 --> 02:05:15,580
I've come to see this
armoured skin close up

2048
02:05:15,580 --> 02:05:18,340
with the help of rhino keeper
Mark Godwin.

2049
02:05:23,340 --> 02:05:26,820
Mark, he's blown me away.
This guy is huge. Look at him.

2050
02:05:26,820 --> 02:05:29,220
What's this one's name?
This is Monty.

2051
02:05:29,220 --> 02:05:33,180
He's about three and a half tonne.
He's over six foot to the shoulder.

2052
02:05:33,180 --> 02:05:35,820
If you want to have a stroke,
feel free.

2053
02:05:35,820 --> 02:05:38,580
OK, I can instantly feel
there's no give here.

2054
02:05:38,580 --> 02:05:43,340
This skin is, it's covered in mud,
but this is incredibly tough skin,

2055
02:05:43,340 --> 02:05:44,860
it really is.

2056
02:05:45,860 --> 02:05:48,900
Do we know how thick this skin
can become on Monty?

2057
02:05:48,900 --> 02:05:51,620
It's supposed to be about
to an inch and a half thick.

2058
02:05:51,620 --> 02:05:54,220
So you're talking
four centimetres of skin there.

2059
02:05:54,220 --> 02:05:56,060
That is an impressive animal.

2060
02:05:56,060 --> 02:05:59,060
With an epidermis of only
about one millimetre thick,

2061
02:05:59,060 --> 02:06:01,660
Monty's skin gets its strength
and thickness

2062
02:06:01,660 --> 02:06:05,340
from densely-packed layers of
collagen fibres in the dermis.

2063
02:06:05,340 --> 02:06:08,500
Now, in the wild, I can't imagine
even the most determined bunch

2064
02:06:08,500 --> 02:06:11,340
of lions and hyenas are going to
try and take Monty down.

2065
02:06:11,340 --> 02:06:13,580
His main threat, really,
is other rhinos.

2066
02:06:13,580 --> 02:06:16,660
So most of the armament and that
is for dealing with other bulls

2067
02:06:16,660 --> 02:06:18,980
when they come into contact
over females.

2068
02:06:18,980 --> 02:06:22,580
Rhinos charge each other,
using their horns as battering rams

2069
02:06:22,580 --> 02:06:25,340
in battles over territory
and mating.

2070
02:06:26,340 --> 02:06:29,820
Researchers believe this aggressive
behaviour has driven the evolution

2071
02:06:29,820 --> 02:06:31,660
of the rhino's thick armour.

2072
02:06:31,660 --> 02:06:35,340
It's far tougher than it needs
to be to simply fend off predators.

2073
02:06:37,340 --> 02:06:40,580
Even if you just look at the way the
legs are formed - the front legs

2074
02:06:40,580 --> 02:06:43,340
are very heavy, so it's all
protection around the front.

2075
02:06:43,340 --> 02:06:45,500
They tend to like to face
their problems,

2076
02:06:45,500 --> 02:06:48,060
so that's where the thicker,
denser skin develops.

2077
02:06:48,060 --> 02:06:51,340
It's helping him get territory,
helping him be a big dominant bull,

2078
02:06:51,340 --> 02:06:53,340
just by the thickness of the skin.

2079
02:06:53,340 --> 02:06:56,060
While adult rhinos are protected
against all-comers

2080
02:06:56,060 --> 02:06:59,340
by their thick armour,
it's a different story for calves.

2081
02:07:00,340 --> 02:07:02,820
Mark, these are lovely.
Who have we got here?

2082
02:07:02,820 --> 02:07:05,340
This is Ruby
and the little one is Stella.

2083
02:07:05,340 --> 02:07:07,620
She's about ten weeks old now,
coming up.

2084
02:07:07,620 --> 02:07:11,060
And I guess being this small
and having skin that's, well,

2085
02:07:11,060 --> 02:07:14,580
nowhere near as thick as Mum's,
she's, in the wild, vulnerable.

2086
02:07:14,580 --> 02:07:17,740
Definitely. And that's why the mums
are as possessive as they are.

2087
02:07:17,740 --> 02:07:20,500
Once they get to full size,
really not much can touch them,

2088
02:07:20,500 --> 02:07:23,060
but, when they're this size
and separated from Mum,

2089
02:07:23,060 --> 02:07:24,820
they're very much at risk.

2090
02:07:24,820 --> 02:07:28,860
Stella's skin is probably
about a centimetre thick,

2091
02:07:28,860 --> 02:07:33,340
and while that's five times thicker
than a ten-week-old human baby's,

2092
02:07:33,340 --> 02:07:37,820
it's nowhere near thick enough
to protect her from predators,

2093
02:07:37,820 --> 02:07:40,220
so rhino mothers
have to be vigilant.

2094
02:07:40,220 --> 02:07:43,580
What sort of predators would have
a go at a baby rhino like Stella

2095
02:07:43,580 --> 02:07:45,220
in the wild? Lions, hyenas.

2096
02:07:45,220 --> 02:07:47,660
It would have to be the big ones
or organised ones.

2097
02:07:47,660 --> 02:07:49,820
They'd have to deal with Mum
as well. Yeah.

2098
02:07:49,820 --> 02:07:52,740
Obviously, while she's with Mum,
she's very well protected,

2099
02:07:52,740 --> 02:07:55,060
but if anything happened,
she got separated,

2100
02:07:55,060 --> 02:07:57,060
she would be at her most vulnerable.

2101
02:07:57,060 --> 02:08:00,580
It's an incredibly rare event
and even more rarely witnessed,

2102
02:08:00,580 --> 02:08:04,820
but predators that hunt in groups,
like hyenas or lions, are the only

2103
02:08:04,820 --> 02:08:08,580
animals that will even attempt
to tackle a rhino mother and calf.

2104
02:08:12,820 --> 02:08:16,580
It takes around two years for a
rhino calf to grow thick enough skin

2105
02:08:16,580 --> 02:08:19,580
and a big enough body
to be able to defend itself

2106
02:08:19,580 --> 02:08:22,580
and finally leave
its mother's protection.

2107
02:08:28,820 --> 02:08:32,340
Some babies are well defended
from the day they're born.

2108
02:08:37,580 --> 02:08:40,060
In the forests
of Madagascar's east coast,

2109
02:08:40,060 --> 02:08:42,820
a mother tenrec is leading
her clutch of babies

2110
02:08:42,820 --> 02:08:45,820
out of the nest to forage
for insects.

2111
02:08:45,820 --> 02:08:50,300
Their stripes help them hide in the
dappled light of the forest floor.

2112
02:08:50,300 --> 02:08:54,140
They may look small and vulnerable,
but the skin on their backs

2113
02:08:54,140 --> 02:08:57,340
is a forest of sharp
black and yellow spines.

2114
02:08:58,820 --> 02:09:00,820
Their mother has them, too,

2115
02:09:00,820 --> 02:09:03,340
but they're hidden
by her longer hair.

2116
02:09:14,340 --> 02:09:16,580
The babies were born without spines

2117
02:09:16,580 --> 02:09:20,340
but started to grow them
in the first 24 hours after birth.

2118
02:09:20,340 --> 02:09:23,820
Tough and sharp,
each spine is a modified hair

2119
02:09:23,820 --> 02:09:27,340
made of keratin
and growing out of the skin.

2120
02:09:28,340 --> 02:09:30,700
And they're an excellent
form of defence.

2121
02:09:30,700 --> 02:09:33,060
If a predator tries to bite
a tenrec,

2122
02:09:33,060 --> 02:09:36,780
they get a mouthful of spines
as a painful deterrent.

2123
02:09:42,580 --> 02:09:45,580
Spines and quills are such
an effective weapon

2124
02:09:45,580 --> 02:09:48,220
that they've evolved several times
in the skin

2125
02:09:48,220 --> 02:09:51,820
of different families of vertebrates
in different parts of the world.

2126
02:09:52,820 --> 02:09:56,340
Hedgehogs are found across
Europe, Africa and Asia.

2127
02:09:56,340 --> 02:09:58,980
In Australia, you get echidnas.

2128
02:10:02,580 --> 02:10:06,340
But, for me, the champions
are porcupines.

2129
02:10:08,060 --> 02:10:10,340
There are two families of porcupine.

2130
02:10:11,340 --> 02:10:15,580
New World porcupines,
found in North and South America,

2131
02:10:15,580 --> 02:10:20,500
and Old World porcupines,
found in Europe, Asia and Africa.

2132
02:10:20,500 --> 02:10:24,060
In both families, the backs
and sides of the porcupine

2133
02:10:24,060 --> 02:10:26,700
are covered with thousands
of quills.

2134
02:10:27,700 --> 02:10:31,820
If a predator gets too close,
they erect and spread the quills,

2135
02:10:31,820 --> 02:10:35,500
turning so their dangerous rear ends
face the would-be attacker.

2136
02:10:36,820 --> 02:10:39,340
Even an expert hunter
like a leopard,

2137
02:10:39,340 --> 02:10:42,580
capable of taking down
a 900kg eland,

2138
02:10:42,580 --> 02:10:46,820
is no match for 30kg
of well-defended porcupine.

2139
02:10:49,580 --> 02:10:53,060
Not only do porcupines have
these long, strong quills

2140
02:10:53,060 --> 02:10:57,580
growing out of their skin, but
they've evolved to be detachable.

2141
02:10:57,580 --> 02:11:01,820
And just like hair,
they fall out from the skin

2142
02:11:01,820 --> 02:11:04,700
without harming the owner at all.

2143
02:11:05,700 --> 02:11:08,340
If a porcupine impales an attacker,

2144
02:11:08,340 --> 02:11:11,820
the lost quills will grow back
in a matter of months,

2145
02:11:11,820 --> 02:11:14,820
while the predator learns
a valuable lesson.

2146
02:11:18,340 --> 02:11:21,580
African porcupine quills
are big and impressive

2147
02:11:21,580 --> 02:11:25,820
and they cause lots of damage
to any would-be attacker.

2148
02:11:25,820 --> 02:11:29,140
I can demonstrate this
with a piece of chicken.

2149
02:11:30,140 --> 02:11:34,340
Because when I stab the pointy end
into the chicken,

2150
02:11:34,340 --> 02:11:36,580
it goes in nice and easily,

2151
02:11:36,580 --> 02:11:40,340
but also it comes out
nice and easily, too.

2152
02:11:41,340 --> 02:11:45,060
When a predator like a lion
is impaled by an African porcupine,

2153
02:11:45,060 --> 02:11:48,340
grooming by a pride member
can often help remove the quills,

2154
02:11:48,340 --> 02:11:50,340
allowing the wounds to heal.

2155
02:11:52,580 --> 02:11:57,580
Here, I've got three quills
from a North American porcupine.

2156
02:11:57,580 --> 02:12:01,580
Compared to the African quills,
these look a bit underwhelming.

2157
02:12:01,580 --> 02:12:04,060
They're finer and much shorter.

2158
02:12:04,060 --> 02:12:06,300
But appearances can be deceptive.

2159
02:12:06,300 --> 02:12:09,340
And when I stab this quill
into the chicken...

2160
02:12:10,340 --> 02:12:12,580
..it goes in nice and easily.

2161
02:12:12,580 --> 02:12:14,820
But when I try and pull it out...

2162
02:12:15,820 --> 02:12:17,340
..it's embedded.

2163
02:12:17,340 --> 02:12:18,860
It's stuck fast.

2164
02:12:18,860 --> 02:12:21,060
And, actually,
to remove the quill...

2165
02:12:22,580 --> 02:12:24,660
..I've really got to pull it.

2166
02:12:24,660 --> 02:12:26,340
RIPPING SOUND

2167
02:12:26,340 --> 02:12:29,460
And you could hear the flesh tearing
as I ripped this out.

2168
02:12:29,460 --> 02:12:31,060
It's not nice.

2169
02:12:32,580 --> 02:12:35,820
This is happening because
North American porcupine quills

2170
02:12:35,820 --> 02:12:38,820
have backward-facing
microscopic barbs,

2171
02:12:38,820 --> 02:12:42,340
as you can see here
in this electron micrograph.

2172
02:12:42,340 --> 02:12:44,340
The barbs do two things.

2173
02:12:44,340 --> 02:12:48,820
They snag on muscle and skin,
making the quills hard to pull out.

2174
02:12:48,820 --> 02:12:53,620
But research in 2012
revealed the barbs also halve

2175
02:12:53,620 --> 02:12:57,580
the penetration force needed to
get the quills into the flesh.

2176
02:12:59,060 --> 02:13:02,340
Every year, many hundreds
of North American dogs

2177
02:13:02,340 --> 02:13:06,580
learn about the dangers of barbed
porcupine quills the hard way.

2178
02:13:11,580 --> 02:13:15,820
Using your skin to defend yourself
can be extremely effective.

2179
02:13:15,820 --> 02:13:19,580
But concocting deadly skin toxins,
carrying heavy armour

2180
02:13:19,580 --> 02:13:23,260
and dropping and replacing quills
take time and effort.

2181
02:13:25,860 --> 02:13:29,340
Over millions of years,
some vertebrates have evolved

2182
02:13:29,340 --> 02:13:33,220
a cheaper and more sophisticated
way of staying safe.

2183
02:13:33,220 --> 02:13:34,820
Camouflage.

2184
02:13:36,500 --> 02:13:40,340
Hiding in plain sight,
using their skin as a disguise.

2185
02:13:44,060 --> 02:13:47,580
Hair, feathers and skin
can all help animals

2186
02:13:47,580 --> 02:13:49,660
blend into their environment.

2187
02:13:52,420 --> 02:13:56,580
How effective that camouflage is
depends on who's looking.

2188
02:14:00,820 --> 02:14:04,740
Unless you're very, very lucky,
you've probably only ever seen

2189
02:14:04,740 --> 02:14:07,580
a tiger in a zoo or wildlife park.

2190
02:14:07,580 --> 02:14:10,340
And against this sort of backdrop,

2191
02:14:10,340 --> 02:14:13,900
it's hard to imagine
how such vivid stripes

2192
02:14:13,900 --> 02:14:16,580
could ever act as camouflage.

2193
02:14:17,580 --> 02:14:21,340
In their natural environment, the
disguise is a bit more effective,

2194
02:14:21,340 --> 02:14:24,340
but there's still no mistaking
a deadly predator.

2195
02:14:25,340 --> 02:14:28,580
But look at the world
through a prey animal's eyes

2196
02:14:28,580 --> 02:14:31,700
and a tiger's camouflage
finally makes sense.

2197
02:14:32,700 --> 02:14:35,340
Chital deer, the tiger's main prey,

2198
02:14:35,340 --> 02:14:38,340
have what is known
as dichromatic vision.

2199
02:14:38,340 --> 02:14:41,420
They can't tell the difference
between reds and greens.

2200
02:14:42,420 --> 02:14:46,900
So, to a deer, the predator blends
into its background perfectly.

2201
02:14:49,580 --> 02:14:53,340
This makes it easier for the tiger
to get within striking distance.

2202
02:15:07,580 --> 02:15:10,820
There's only one flaw
in the tiger's strategy.

2203
02:15:16,340 --> 02:15:20,060
Chital herds are often found
with groups of langurs.

2204
02:15:22,740 --> 02:15:25,340
The monkeys drop fruit as they feed.

2205
02:15:26,500 --> 02:15:29,820
But that's not the only reason
the chital stay close.

2206
02:15:30,820 --> 02:15:34,060
Langur monkeys have full
colour vision.

2207
02:15:36,500 --> 02:15:39,820
Chital have learned to recognise
langur alarm calls

2208
02:15:39,820 --> 02:15:41,660
and run for their lives.

2209
02:15:41,660 --> 02:15:43,700
HOWLING

2210
02:15:54,580 --> 02:15:57,100
The tiger's cover is blown.

2211
02:16:02,580 --> 02:16:05,580
If those pesky monkeys
are giving the game away,

2212
02:16:05,580 --> 02:16:09,820
why don't tigers go the whole hog
and just have green hair?

2213
02:16:11,820 --> 02:16:14,580
That's because mammals,
including humans,

2214
02:16:14,580 --> 02:16:17,580
use melanin to colour
their epidermis and hair

2215
02:16:17,580 --> 02:16:21,340
and melanin can only make
blacks, oranges and browns.

2216
02:16:22,820 --> 02:16:25,340
Only one group of mammals
has mastered the art

2217
02:16:25,340 --> 02:16:29,820
of green jungle camouflage -
the two and three-toed sloths.

2218
02:16:30,820 --> 02:16:33,820
These slow-moving mammals
have green hair,

2219
02:16:33,820 --> 02:16:36,340
helping them blend in
to their forest home.

2220
02:16:37,340 --> 02:16:40,580
But that colour isn't made
by the sloth's skin.

2221
02:16:40,580 --> 02:16:44,820
It comes from tiny green algae
that colonise their hair.

2222
02:16:48,580 --> 02:16:51,820
Each strand has cracks in it,
which trap the moisture

2223
02:16:51,820 --> 02:16:54,340
the microscopic plants need to grow.

2224
02:16:57,340 --> 02:17:02,060
Moths living in the sloth's hair
even help to fertilise the algae

2225
02:17:02,060 --> 02:17:04,340
with their nitrate-rich faeces.

2226
02:17:08,580 --> 02:17:12,820
Evolving camouflage skin to help
you blend in to a particular habitat

2227
02:17:12,820 --> 02:17:14,500
is pretty impressive,

2228
02:17:14,500 --> 02:17:17,980
but some animals have taken
a revolutionary next step.

2229
02:17:19,820 --> 02:17:22,580
I've come to Plymouth
to find out more

2230
02:17:22,580 --> 02:17:25,060
from marine biologist Alix Harvey.

2231
02:17:25,060 --> 02:17:28,340
And while the animals she studies
aren't vertebrates,

2232
02:17:28,340 --> 02:17:31,060
you can't talk about extraordinary
skin defences

2233
02:17:31,060 --> 02:17:32,700
without including them.

2234
02:17:33,700 --> 02:17:35,100
Hi, Alix. Hi, Ben.

2235
02:17:35,100 --> 02:17:37,340
Look at these!
I love these little animals.

2236
02:17:37,340 --> 02:17:40,580
They're amazing, aren't they?
They're absolutely fantastic.

2237
02:17:40,580 --> 02:17:42,660
So these are the common cuttlefish,

2238
02:17:42,660 --> 02:17:44,340
sepia officinalis.

2239
02:17:44,340 --> 02:17:46,820
This is a species we find
all around the UK.

2240
02:17:46,820 --> 02:17:49,820
They're one of the biggest species
of cuttlefish we get.

2241
02:17:49,820 --> 02:17:52,580
And they're about five months old,
these individuals.

2242
02:17:52,580 --> 02:17:55,140
I was going to say.
I've seen much bigger than this.

2243
02:17:55,140 --> 02:17:57,340
These are tiny by comparison.
That's right.

2244
02:17:57,340 --> 02:18:00,420
So they hatch out from eggs about
one centimetre, about this big,

2245
02:18:00,420 --> 02:18:02,900
and, then, over their life cycle
of about two years,

2246
02:18:02,900 --> 02:18:05,580
they get really, really big,
up to about this size,

2247
02:18:05,580 --> 02:18:08,740
so these are all still, kind of,
babies in my eyes.

2248
02:18:08,740 --> 02:18:12,300
Alix has cuttlefish
in three different tanks.

2249
02:18:12,300 --> 02:18:16,060
So we've got sand here, we've got
rocks and then we've got seaweed.

2250
02:18:16,060 --> 02:18:18,340
So these are all the natural
environments

2251
02:18:18,340 --> 02:18:20,340
they would experience in the wild.

2252
02:18:20,340 --> 02:18:24,060
And, in each tank, the cuttlefish
are beautifully camouflaged.

2253
02:18:25,060 --> 02:18:27,340
I'm just looking at
this little one here

2254
02:18:27,340 --> 02:18:30,940
and it's blended in perfectly
with the sandy surrounding.

2255
02:18:30,940 --> 02:18:33,620
You can really see just how well
it's blended in.

2256
02:18:33,620 --> 02:18:36,300
It's managed to put some sand
on its body

2257
02:18:36,300 --> 02:18:38,660
and it's really broken up
the outline.

2258
02:18:38,660 --> 02:18:41,580
The cuttlefish in tank two,
the rocky tank,

2259
02:18:41,580 --> 02:18:44,580
has very different skin colours
and patterns.

2260
02:18:45,580 --> 02:18:49,340
And so you find here,
in this rocky kind of habitat,

2261
02:18:49,340 --> 02:18:51,980
that they will get a very
disruptive body pattern.

2262
02:18:51,980 --> 02:18:53,660
It's just slightly different.

2263
02:18:53,660 --> 02:18:57,980
And, then, at the end,
we've got a much darker one.

2264
02:18:57,980 --> 02:19:00,340
So he's really adapted
to the seaweed.

2265
02:19:00,340 --> 02:19:03,140
And you can imagine if he was
sitting in amongst the weeds,

2266
02:19:03,140 --> 02:19:05,820
it would be very, very difficult
to tell where he was,

2267
02:19:05,820 --> 02:19:08,500
particularly as he's actually
lifting his tentacles

2268
02:19:08,500 --> 02:19:10,820
out of the water
in order to disrupt his body

2269
02:19:10,820 --> 02:19:13,060
and really pretend to be
a piece of seaweed.

2270
02:19:13,060 --> 02:19:15,820
Alix's cuttlefish
are all the same species,

2271
02:19:15,820 --> 02:19:19,340
so how have they ended up
looking completely different?

2272
02:19:21,060 --> 02:19:24,180
The answer is adaptive camouflage.

2273
02:19:24,180 --> 02:19:27,820
A cuttlefish's skin
can rapidly change colour

2274
02:19:27,820 --> 02:19:31,900
to help it blend seamlessly into its
surroundings in the blink of an eye.

2275
02:19:32,900 --> 02:19:37,060
One little animal will change
from sandy to weedy to stoney,

2276
02:19:37,060 --> 02:19:39,020
but how do they do that?

2277
02:19:39,020 --> 02:19:42,820
So cuttlefish actually have three
different colour-changing cells,

2278
02:19:42,820 --> 02:19:45,980
but the ones that allow them to do
these different colour patterns

2279
02:19:45,980 --> 02:19:47,660
are called chromatophores.

2280
02:19:47,660 --> 02:19:50,580
These are basically cells
that are packed full of pigment.

2281
02:19:50,580 --> 02:19:53,580
Found in the dermis,
each chromatophore has muscles

2282
02:19:53,580 --> 02:19:55,580
attached to its outer wall.

2283
02:19:55,580 --> 02:19:59,340
When the muscles contract,
the chromatophore is pulled open

2284
02:19:59,340 --> 02:20:01,140
and the pigment spreads out.

2285
02:20:01,140 --> 02:20:04,340
When the muscles relax,
the chromatophore shrinks down,

2286
02:20:04,340 --> 02:20:06,340
compressing the pigment.

2287
02:20:08,540 --> 02:20:11,820
So when it's packed really, really
tight, it's very difficult to see,

2288
02:20:11,820 --> 02:20:14,340
and this allows them to have
a nice white colour,

2289
02:20:14,340 --> 02:20:17,340
and when it's splayed out,
it becomes a nice dark splodge,

2290
02:20:17,340 --> 02:20:20,340
and when extrapolated over
the whole body of the cuttlefish,

2291
02:20:20,340 --> 02:20:23,820
this is what allows them to achieve
all kinds of body patterns.

2292
02:20:23,820 --> 02:20:28,580
All cephalopods, including octopus
and squid, have this amazing skin.

2293
02:20:28,580 --> 02:20:32,060
And as well as changing colour,
in some species,

2294
02:20:32,060 --> 02:20:34,340
it can change texture, too.

2295
02:20:36,340 --> 02:20:40,340
Muscles in the dermis push the skin
into bumps called papillae,

2296
02:20:40,340 --> 02:20:44,260
which break up the outline of
the body, helping them to hide.

2297
02:20:45,260 --> 02:20:47,940
Why are they hiding? I'm guessing
from predators, right?

2298
02:20:47,940 --> 02:20:50,340
That's right.
They are very soft-bodied animals.

2299
02:20:50,340 --> 02:20:52,340
They don't have external
hard pieces.

2300
02:20:52,340 --> 02:20:54,340
They can't really protect
themselves.

2301
02:20:54,340 --> 02:20:57,060
So the best thing for them
in order to avoid being a meal

2302
02:20:57,060 --> 02:20:59,820
for something else is just not
to be seen in the first place.

2303
02:20:59,820 --> 02:21:03,340
Adaptive camouflage is an amazing
defensive strategy,

2304
02:21:03,340 --> 02:21:05,340
but there's a conundrum.

2305
02:21:05,340 --> 02:21:08,820
A cuttlefish's eyes
are on the top of its body.

2306
02:21:09,820 --> 02:21:13,340
So how does it gather enough
information about the surface

2307
02:21:13,340 --> 02:21:17,340
hidden beneath its body to match
its colour and texture so well?

2308
02:21:18,420 --> 02:21:20,820
So we always used to think
this was basically

2309
02:21:20,820 --> 02:21:23,580
that they're seeing their
environment and then relaying

2310
02:21:23,580 --> 02:21:26,340
that information to their
chromatophores by their brain.

2311
02:21:26,340 --> 02:21:29,500
We now think there may be something
even more astounding going on,

2312
02:21:29,500 --> 02:21:32,500
which is that they have actually
light-sensing-capabilities

2313
02:21:32,500 --> 02:21:34,060
within their skin.

2314
02:21:34,060 --> 02:21:37,340
Researchers have discovered traces
of a protein called rhodopsin

2315
02:21:37,340 --> 02:21:39,340
in the cuttlefish dermis.

2316
02:21:39,340 --> 02:21:42,060
Exactly the same protein
is found in the retina

2317
02:21:42,060 --> 02:21:44,060
of a cuttlefish's eyes.

2318
02:21:44,060 --> 02:21:46,820
It's a light-sensitive pigment
that forms the basis

2319
02:21:46,820 --> 02:21:48,580
of cuttlefish vision.

2320
02:21:48,580 --> 02:21:51,340
Vertebrates use similar proteins
in their eyes.

2321
02:21:52,340 --> 02:21:54,580
The research is in its early stages,

2322
02:21:54,580 --> 02:21:57,060
but the presence of rhodopsin
in the skin

2323
02:21:57,060 --> 02:22:01,060
suggests cuttlefish skin
may be able to see.

2324
02:22:02,060 --> 02:22:04,220
This is something
that's very, very new

2325
02:22:04,220 --> 02:22:06,900
and we're hoping to conduct
some experiments this year,

2326
02:22:06,900 --> 02:22:08,740
looking at whether,
if they can't see

2327
02:22:08,740 --> 02:22:10,580
what the rest of their body's doing,

2328
02:22:10,580 --> 02:22:12,340
are they still able to adapt

2329
02:22:12,340 --> 02:22:14,820
and colour camouflage
to their environment?

2330
02:22:14,820 --> 02:22:18,180
If Alix's research reveals
that cuttlefish can sense light

2331
02:22:18,180 --> 02:22:19,980
and dark with their skin,

2332
02:22:19,980 --> 02:22:23,260
then we'll have to completely
redefine cephalopod skin

2333
02:22:23,260 --> 02:22:26,340
as not just an amazing means
of defence

2334
02:22:26,340 --> 02:22:29,820
but an extraordinary
sensory organ, too.

2335
02:22:30,820 --> 02:22:35,340
These cryptic cuttlefish are further
proof that skin still has secrets

2336
02:22:35,340 --> 02:22:38,180
we're only just beginning
to understand.

2337
02:22:40,820 --> 02:22:43,820
When it comes to defending yourself
from other animals,

2338
02:22:43,820 --> 02:22:48,260
skin provides an incredible
selection of weapons and armour.

2339
02:22:48,260 --> 02:22:51,300
From deadly toxins
and piercing quills,

2340
02:22:51,300 --> 02:22:53,900
right through to
cryptic colouration.

2341
02:22:54,900 --> 02:22:59,060
For vertebrates and a few
very special invertebrates,

2342
02:22:59,060 --> 02:23:01,420
skin will keep you safe.

2343
02:23:03,260 --> 02:23:06,580
In the next episode,
I'll learn how microscopic bumps

2344
02:23:06,580 --> 02:23:10,060
on a crocodile's jaw
help it track down prey...

2345
02:23:11,340 --> 02:23:14,820
..reveal how understanding
the human sense of touch...

2346
02:23:14,820 --> 02:23:17,420
is inspiring the design
of new robots...

2347
02:23:18,420 --> 02:23:21,340
..and how this venomous
pit viper's skin

2348
02:23:21,340 --> 02:23:23,580
helps it aim its deadly strikes...

2349
02:23:25,060 --> 02:23:27,660
..to explore how skin
enables vertebrates

2350
02:23:27,660 --> 02:23:29,980
to sense the world around them.

2351
02:24:04,660 --> 02:24:06,060
Skin.

2352
02:24:06,060 --> 02:24:07,980
We all have it.

2353
02:24:07,980 --> 02:24:12,220
And so does every vertebrate
on the planet.

2354
02:24:12,220 --> 02:24:14,980
It keeps the outside out

2355
02:24:14,980 --> 02:24:16,620
and the inside in.

2356
02:24:18,260 --> 02:24:20,780
Animals may look very different
on the surface,

2357
02:24:20,780 --> 02:24:24,300
but we all share the same
basic skin blueprint.

2358
02:24:26,140 --> 02:24:30,380
I'm Ben Garrod, professor
of evolutionary biology,

2359
02:24:30,380 --> 02:24:34,340
and I'm fascinated by this often
overlooked wonder of nature.

2360
02:24:34,340 --> 02:24:36,500
It's not just a case
that he's hairless.

2361
02:24:36,500 --> 02:24:38,660
The skin's totally different.

2362
02:24:38,660 --> 02:24:41,380
Now, ground-breaking new science...

2363
02:24:41,380 --> 02:24:42,820
This is really quite remarkable.

2364
02:24:42,820 --> 02:24:45,060
It should be a game-changer
for so many people.

2365
02:24:45,060 --> 02:24:46,860
RATTLING
That sound, ah!

2366
02:24:46,860 --> 02:24:50,220
It makes the hairs at the back
of your neck go up, doesn't it?

2367
02:24:50,220 --> 02:24:52,940
..is revealing skin's mysteries.

2368
02:24:52,940 --> 02:24:57,420
It really transforms our
understanding of dinosaurs.

2369
02:24:57,420 --> 02:25:01,820
I'm going to explore the natural
history of the body's largest organ

2370
02:25:01,820 --> 02:25:06,820
to see how skin has allowed animals
to conquer every habitat,

2371
02:25:06,820 --> 02:25:09,460
disappear into their surroundings

2372
02:25:09,460 --> 02:25:12,300
and develop extrasensory abilities.

2373
02:25:14,060 --> 02:25:19,100
We're even discovering the complex
ecosystem living on our skin.

2374
02:25:19,100 --> 02:25:21,300
Oh, Jim, that's awful. It really is.

2375
02:25:23,140 --> 02:25:26,380
In this episode,
I'll find out how skin

2376
02:25:26,380 --> 02:25:29,620
allows animals to have more
than just five senses...

2377
02:25:30,740 --> 02:25:33,300
Oh! So powerful.

2378
02:25:33,300 --> 02:25:38,100
..like being able to detect
electricity or even see heat.

2379
02:25:38,100 --> 02:25:41,140
That was incredibly quick, though.
That was such a strike.

2380
02:25:41,140 --> 02:25:45,940
And I'll discover just how complex
our sense of touch really is...

2381
02:25:45,940 --> 02:25:48,220
That must be so sensitive.

2382
02:25:48,220 --> 02:25:53,140
..as I explore how skin has evolved
to give animals super senses.

2383
02:25:54,340 --> 02:25:57,740
I'm going to reveal
the secrets of skin.

2384
02:26:01,540 --> 02:26:04,420
In all the varied habitats
in which animals live,

2385
02:26:04,420 --> 02:26:07,060
their skin has come
to play a key role

2386
02:26:07,060 --> 02:26:11,100
in helping them gather information
about their different environments.

2387
02:26:11,100 --> 02:26:14,460
We often think about
five main senses -

2388
02:26:14,460 --> 02:26:18,460
sight, hearing, taste,
smell and touch,

2389
02:26:18,460 --> 02:26:20,460
but across the natural world,

2390
02:26:20,460 --> 02:26:23,860
skin helps animals sense in ways
we find hard to imagine.

2391
02:26:29,580 --> 02:26:33,580
Animals detect touch in varying
degrees of sensitivity...

2392
02:26:36,380 --> 02:26:39,900
..but sensitive doesn't
always mean fragile.

2393
02:26:43,380 --> 02:26:46,660
Crocodiles, alligators,
caiman and gharials

2394
02:26:46,660 --> 02:26:48,940
are collectively known
as crocodilians.

2395
02:26:50,700 --> 02:26:54,540
There are 23 species living in
tropical areas across the world.

2396
02:26:58,380 --> 02:27:01,420
As one of our planet's
most formidable hunters,

2397
02:27:01,420 --> 02:27:03,420
they sit at the top
of the food chain.

2398
02:27:06,820 --> 02:27:09,780
Their skin has an
incredible sensitivity

2399
02:27:09,780 --> 02:27:12,260
which has given them
the edge over other animals.

2400
02:27:14,020 --> 02:27:17,020
I've come to the UK's
only crocodilian zoo,

2401
02:27:17,020 --> 02:27:20,780
just outside Oxford,
to see some of them up close.

2402
02:27:21,940 --> 02:27:23,420
What species do we have in here?

2403
02:27:23,420 --> 02:27:26,380
So, these, this is our big group
of Nile crocodiles.

2404
02:27:26,380 --> 02:27:29,460
We've got 35 individuals
in this enclosure,

2405
02:27:29,460 --> 02:27:32,220
and they're all quite young. I mean,
they get much bigger than this,

2406
02:27:32,220 --> 02:27:35,100
don't they? They do. They're one of
the largest species of crocodilian

2407
02:27:35,100 --> 02:27:37,860
that we have on the planet,
and adult males can reach lengths

2408
02:27:37,860 --> 02:27:40,100
of up to five metres, so
quite a lot bigger than this.

2409
02:27:40,100 --> 02:27:43,220
That's me with you on my shoulders
and then a bit more, isn't it? Yeah.

2410
02:27:43,220 --> 02:27:45,940
So what do Nile crocodiles
eat in the wild?

2411
02:27:45,940 --> 02:27:48,260
Well, through their life,
they eat different things,

2412
02:27:48,260 --> 02:27:50,540
so they start off
when they're hatchlings

2413
02:27:50,540 --> 02:27:54,420
eating small invertebrates,
small reptiles, amphibians,

2414
02:27:54,420 --> 02:27:55,860
fish, things like that,

2415
02:27:55,860 --> 02:27:59,980
and as the croc grows, their prey
size increases, as well.

2416
02:28:02,820 --> 02:28:05,220
I'm suddenly feeling less
confident stood near the edge,

2417
02:28:05,220 --> 02:28:07,420
cos they can jump, as well,
can't they? They can jump.

2418
02:28:07,420 --> 02:28:09,780
The perfect apex predator
on our planet.

2419
02:28:11,540 --> 02:28:14,700
It's time for these
crocodiles' main meal -

2420
02:28:14,700 --> 02:28:15,860
chicken on a stick.

2421
02:28:15,860 --> 02:28:17,380
Oh!

2422
02:28:19,820 --> 02:28:20,860
So powerful.

2423
02:28:22,500 --> 02:28:26,020
Crocodilians didn't get to be
the apex predators they are

2424
02:28:26,020 --> 02:28:28,620
simply by using brute force.

2425
02:28:28,620 --> 02:28:32,820
The real secret to their success
is hidden in their skin.

2426
02:28:36,420 --> 02:28:38,820
In the murky water where they hunt,

2427
02:28:38,820 --> 02:28:41,300
crocodiles can't always
rely on their eyes...

2428
02:28:43,500 --> 02:28:47,660
..so embedded in nearly every
single scale across their bodies

2429
02:28:47,660 --> 02:28:50,180
are highly sensitive
pressure receptors...

2430
02:28:53,100 --> 02:28:56,700
..and these are able to detect the
smallest of ripples in the water...

2431
02:28:59,380 --> 02:29:02,260
..making it possible to judge
the distance and position

2432
02:29:02,260 --> 02:29:04,740
of any animal without
using their eyes.

2433
02:29:09,180 --> 02:29:12,540
The safest way to see these
sensory organs up close

2434
02:29:12,540 --> 02:29:14,820
is on a baby alligator.

2435
02:29:14,820 --> 02:29:17,300
Sean, this one's much
smaller than earlier.

2436
02:29:17,300 --> 02:29:19,660
I feel much happier being
this close to this little guy -

2437
02:29:19,660 --> 02:29:21,660
but it's a different species
as well, isn't it?

2438
02:29:21,660 --> 02:29:23,540
Yeah, this one's
an American alligator.

2439
02:29:23,540 --> 02:29:26,060
But it's a good opportunity to
really have a look at the skin

2440
02:29:26,060 --> 02:29:28,860
and see how it works and
also how it helps him hunt.

2441
02:29:28,860 --> 02:29:32,900
You can see instantly, on the back,
really strong, thick skin,

2442
02:29:32,900 --> 02:29:35,780
that really armoured area, but
not the same around the mouth.

2443
02:29:35,780 --> 02:29:38,620
You can see it's a different
type of skin,

2444
02:29:38,620 --> 02:29:40,780
and lots of spots or holes, really.

2445
02:29:40,780 --> 02:29:43,500
That's right. All those little
black dots around the jaw

2446
02:29:43,500 --> 02:29:45,780
are sensory organs.

2447
02:29:45,780 --> 02:29:49,820
While alligators have these pressure
receptors just on their snout,

2448
02:29:49,820 --> 02:29:52,460
crocodiles have them
all over their bodies.

2449
02:29:55,020 --> 02:29:58,220
Each one is a millimetre-long
dome on their skin

2450
02:29:58,220 --> 02:30:00,020
covered by a flexible scale.

2451
02:30:01,060 --> 02:30:04,460
Inside are hundreds of nerve fibres.

2452
02:30:04,460 --> 02:30:07,540
Any movement on the surface
of the scale is picked up

2453
02:30:07,540 --> 02:30:10,300
by the nerve fibres underneath.

2454
02:30:10,300 --> 02:30:14,340
It's been estimated that each dome
is ten times more sensitive

2455
02:30:14,340 --> 02:30:15,980
than a human fingertip.

2456
02:30:15,980 --> 02:30:19,100
They're effectively seeing,
but without their eyes.

2457
02:30:19,100 --> 02:30:20,940
They're seeing where
these vibrations are,

2458
02:30:20,940 --> 02:30:22,500
they're feeling
these vibrations,

2459
02:30:22,500 --> 02:30:26,100
and that's in order to hunt prey,
right? That's exactly right, yeah.

2460
02:30:26,100 --> 02:30:28,620
We want to see how
these skin receptors work

2461
02:30:28,620 --> 02:30:32,140
by setting up a simple test
involving our baby alligator.

2462
02:30:34,260 --> 02:30:36,140
The tubes are in place to make sure

2463
02:30:36,140 --> 02:30:38,220
the alligator can't see
where the food is,

2464
02:30:38,220 --> 02:30:41,460
and to make sure it can't
hear where the food is,

2465
02:30:41,460 --> 02:30:43,380
I've even added some white noise.

2466
02:30:43,380 --> 02:30:45,620
WHITE NOISE PLAYS

2467
02:30:47,940 --> 02:30:50,780
I drop some chicken
into one of the pipes.

2468
02:30:52,300 --> 02:30:54,100
Filmed in slow motion,

2469
02:30:54,100 --> 02:30:56,100
as the chicken hits the water,

2470
02:30:56,100 --> 02:30:59,020
it creates small ripples.

2471
02:30:59,020 --> 02:31:02,500
These expand out into the pool,

2472
02:31:02,500 --> 02:31:06,180
and as they touch
the alligator, it turns.

2473
02:31:06,180 --> 02:31:09,460
The moment I drop
the chicken into that tube,

2474
02:31:09,460 --> 02:31:12,900
it turned and it looked,
and it did come this way

2475
02:31:12,900 --> 02:31:16,340
a second or so after
that chicken hit the water.

2476
02:31:16,340 --> 02:31:17,900
That could only have happened

2477
02:31:17,900 --> 02:31:20,100
if it felt the vibrations
through its skin.

2478
02:31:24,500 --> 02:31:28,980
This has been shown in experiments
under laboratory conditions.

2479
02:31:28,980 --> 02:31:31,060
Its skin is so sensitive,

2480
02:31:31,060 --> 02:31:33,540
this crocodile is able
to react to the ripple

2481
02:31:33,540 --> 02:31:35,380
within a fraction of a second.

2482
02:31:45,300 --> 02:31:50,220
Crocodilians have the most powerful
jaws of any living animal,

2483
02:31:50,220 --> 02:31:53,580
but by using the receptors
in their skin,

2484
02:31:53,580 --> 02:31:57,860
these jaws also have the capacity
to be surprisingly gentle.

2485
02:32:00,580 --> 02:32:04,460
And this sensitivity is something
all crocodilians have

2486
02:32:04,460 --> 02:32:05,780
from the moment they hatch.

2487
02:32:07,220 --> 02:32:12,140
This female caiman's offspring
are just emerging from their eggs.

2488
02:32:12,140 --> 02:32:14,980
THEY SQUEAK

2489
02:32:14,980 --> 02:32:18,900
Her young are fragile and need
help getting to the water.

2490
02:32:32,540 --> 02:32:34,380
To perform this kind of task,

2491
02:32:34,380 --> 02:32:36,820
she needs a real
lightness of touch -

2492
02:32:36,820 --> 02:32:39,540
something only her skin can provide.

2493
02:32:45,300 --> 02:32:46,700
Like crocodilians,

2494
02:32:46,700 --> 02:32:50,180
many animals use their snouts
to perform essential tasks.

2495
02:32:51,940 --> 02:32:54,660
This makes the skin on
the end of any snout

2496
02:32:54,660 --> 02:32:56,860
a particularly important
sensory tool.

2497
02:32:58,380 --> 02:33:02,140
Here in North America
lives the star-nosed mole.

2498
02:33:06,620 --> 02:33:08,380
At the end of its snout

2499
02:33:08,380 --> 02:33:11,860
is arguably the most sensitive
patch of skin on the planet.

2500
02:33:13,660 --> 02:33:19,140
Its nostrils are surrounded by
22 fleshy appendages known as rays.

2501
02:33:19,140 --> 02:33:24,620
The skin on these is covered in
25,000 sensory touch receptors,

2502
02:33:24,620 --> 02:33:27,140
five times more than
in the human hand.

2503
02:33:31,020 --> 02:33:34,780
The mole pats it to the ground
10 to 15 times a second,

2504
02:33:34,780 --> 02:33:38,340
searching for a meal
in dark tunnels.

2505
02:33:38,340 --> 02:33:39,820
It's so sensitive,

2506
02:33:39,820 --> 02:33:45,060
the mole can tell what's
edible in 227 milliseconds,

2507
02:33:45,060 --> 02:33:46,860
faster than any other mammal...

2508
02:33:49,060 --> 02:33:52,420
..but these snouts are sensitive
in more than one way -

2509
02:33:52,420 --> 02:33:54,900
they can also smell underwater.

2510
02:33:57,500 --> 02:34:00,500
The mole does this by partially
exhaling an air bubble

2511
02:34:00,500 --> 02:34:02,260
on the top of its snout.

2512
02:34:02,260 --> 02:34:04,420
This absorbs surrounding odours,

2513
02:34:04,420 --> 02:34:08,060
which it breathes back in
to see if there's food nearby.

2514
02:34:08,060 --> 02:34:10,020
If not, it moves on.

2515
02:34:16,020 --> 02:34:18,460
Every vertebrate has
a network of nerves

2516
02:34:18,460 --> 02:34:21,140
connected to their dermis
and epidermis,

2517
02:34:21,140 --> 02:34:23,700
there to relay real time information

2518
02:34:23,700 --> 02:34:25,500
from all over the surface
of the body.

2519
02:34:25,500 --> 02:34:27,020
CAT PURRS

2520
02:34:27,020 --> 02:34:30,500
This can be a source of pleasure

2521
02:34:30,500 --> 02:34:33,500
and act as a warning system
against attacks.

2522
02:34:33,500 --> 02:34:35,900
From biting insects, for example.

2523
02:34:35,900 --> 02:34:37,940
HORSE NEIGHS

2524
02:34:37,940 --> 02:34:41,900
But reacting to what your skin
is telling you can be tricky,

2525
02:34:41,900 --> 02:34:46,460
especially when all four of
your limbs are on the ground.

2526
02:34:46,460 --> 02:34:48,380
Skin is pretty tough,

2527
02:34:48,380 --> 02:34:51,500
and is good at protecting us
from the outside world,

2528
02:34:51,500 --> 02:34:55,380
but when it comes to biting
insects... Hello!

2529
02:34:55,380 --> 02:34:57,140
For animals such as horses,

2530
02:34:57,140 --> 02:35:00,780
there are areas on their body
they just can't reach

2531
02:35:00,780 --> 02:35:03,620
to dislodge pesky flies -

2532
02:35:03,620 --> 02:35:07,660
but horse skin has adapted
to solve that problem.

2533
02:35:07,660 --> 02:35:10,860
Just below the skin and
the subcutaneous fat layer

2534
02:35:10,860 --> 02:35:15,220
is a thin sheet of muscle called
the cutaneous trunci muscle.

2535
02:35:15,220 --> 02:35:18,460
It's anchored to the dermis
with connective tissue,

2536
02:35:18,460 --> 02:35:22,140
and so any movement in the muscle
pulls the skin with it.

2537
02:35:25,180 --> 02:35:27,460
Imagine this feather is a fly,

2538
02:35:27,460 --> 02:35:30,820
intent on getting a meal
out of the horse.

2539
02:35:30,820 --> 02:35:31,860
Fly lands...

2540
02:35:33,060 --> 02:35:34,100
..and we see that.

2541
02:35:34,100 --> 02:35:37,420
Now, this is a flinch in
the muscle beneath the skin,

2542
02:35:37,420 --> 02:35:39,980
and it's that, that when
the horse does it,

2543
02:35:39,980 --> 02:35:43,500
dislodges the fly or any
other flying, biting insect

2544
02:35:43,500 --> 02:35:46,340
that would otherwise
cause a nuisance.

2545
02:35:46,340 --> 02:35:48,740
This is an involuntary reaction.

2546
02:35:48,740 --> 02:35:51,460
Sensation on the skin
travels through nerves

2547
02:35:51,460 --> 02:35:54,060
via the spinal cord to the muscle

2548
02:35:54,060 --> 02:35:56,700
without engaging
the horse's brain at all.

2549
02:36:00,900 --> 02:36:04,420
Using touch is certainly one
of the most effective ways

2550
02:36:04,420 --> 02:36:07,420
of getting a sense of an object
or environment...

2551
02:36:09,140 --> 02:36:12,140
..but one group of animals
has adapted their skin

2552
02:36:12,140 --> 02:36:14,500
to help gather information
from a distance.

2553
02:36:17,900 --> 02:36:21,220
Virtually all of the 1,300
or so species of bat

2554
02:36:21,220 --> 02:36:23,140
around the world are nocturnal.

2555
02:36:24,540 --> 02:36:26,700
In order to navigate at night,

2556
02:36:26,700 --> 02:36:29,980
many of them emit
high-frequency sound waves

2557
02:36:29,980 --> 02:36:32,020
from either their nose or mouth,

2558
02:36:32,020 --> 02:36:36,180
bouncing them off nearby objects to
get a sense of what's around them -

2559
02:36:36,180 --> 02:36:38,060
a system called echolocation...

2560
02:36:40,580 --> 02:36:43,740
..but in the dense forests
or caves where they often live,

2561
02:36:43,740 --> 02:36:45,140
this can cause a problem.

2562
02:36:49,820 --> 02:36:51,500
When flying around a forest,

2563
02:36:51,500 --> 02:36:54,380
you need to be able
to focus on what's ahead,

2564
02:36:54,380 --> 02:36:58,740
especially if you want to avoid
crashing into a tree.

2565
02:36:58,740 --> 02:37:02,300
If you were to make a wide
echolocation beam,

2566
02:37:02,300 --> 02:37:04,700
like the wide beam of this torch,

2567
02:37:04,700 --> 02:37:07,380
then you'd be generating
too much information,

2568
02:37:07,380 --> 02:37:10,500
which would be bouncing back
from surrounding objects,

2569
02:37:10,500 --> 02:37:15,020
and for a bat, this risks being
overwhelming and confusing.

2570
02:37:17,620 --> 02:37:21,700
Many bats have adapted to overcome
this sensory problem,

2571
02:37:21,700 --> 02:37:25,340
but one group has found a way
to enhance their echolocation

2572
02:37:25,340 --> 02:37:28,180
by using the skin on their faces,

2573
02:37:28,180 --> 02:37:30,020
like this pale spear-nosed bat.

2574
02:37:31,300 --> 02:37:35,100
It emits its echolocation
beam from its nose,

2575
02:37:35,100 --> 02:37:39,180
and if you look, this bizarre
structure on the front of the face

2576
02:37:39,180 --> 02:37:42,940
just here is called the nose-leaf.

2577
02:37:44,100 --> 02:37:47,260
The nose-leaf is made
of skin and cartilage,

2578
02:37:47,260 --> 02:37:48,780
and by adjusting its shape,

2579
02:37:48,780 --> 02:37:53,540
the bats can manipulate the size
of their echolocation beam.

2580
02:37:53,540 --> 02:37:56,700
This gives them the ability
to focus their echolocation,

2581
02:37:56,700 --> 02:37:59,660
transforming a wide
and diffuse beam

2582
02:37:59,660 --> 02:38:03,300
into a narrow and more focused one.

2583
02:38:04,620 --> 02:38:07,940
All bats from the nose-leaf
and horseshoe bat families

2584
02:38:07,940 --> 02:38:10,220
have this ability.

2585
02:38:10,220 --> 02:38:12,140
By directing a more focused beam,

2586
02:38:12,140 --> 02:38:15,740
they are able to concentrate on
the objects that really matter...

2587
02:38:17,420 --> 02:38:20,820
..important when it comes
to avoiding trees

2588
02:38:20,820 --> 02:38:23,780
and crucial for homing in on food.

2589
02:38:34,340 --> 02:38:38,700
However, the information animals
are able to gather using their skin

2590
02:38:38,700 --> 02:38:41,420
isn't always related
to their next meal.

2591
02:38:42,780 --> 02:38:45,140
The sensitivity of an animal's skin

2592
02:38:45,140 --> 02:38:48,780
can directly influence
how they interact with the world.

2593
02:38:52,540 --> 02:38:56,620
In fact, a small patch of skin
found on some animals

2594
02:38:56,620 --> 02:39:01,060
has arguably had more of an impact
on our planet than any other.

2595
02:39:04,060 --> 02:39:08,460
Some of the most sensitive skin
is found on our fingertips,

2596
02:39:08,460 --> 02:39:11,100
giving them a heightened
sense of touch.

2597
02:39:12,860 --> 02:39:15,980
The skin on each fingertip
can detect ridges

2598
02:39:15,980 --> 02:39:20,420
four and a half thousand times
smaller than a human hair.

2599
02:39:20,420 --> 02:39:24,700
This sensitivity gives our ten
digits the power to grip,

2600
02:39:24,700 --> 02:39:28,940
feel, build, craft and even read,

2601
02:39:28,940 --> 02:39:31,220
abilities that are remarkable,

2602
02:39:31,220 --> 02:39:33,620
but which we often take for granted.

2603
02:39:35,980 --> 02:39:40,580
In order to fully explore just how
our sense of touch really works,

2604
02:39:40,580 --> 02:39:42,580
we don't need a biologist,

2605
02:39:42,580 --> 02:39:43,740
we need an engineer.

2606
02:39:46,300 --> 02:39:51,020
Professor Nathan Lepora makes robots
that mimic the human sense of touch,

2607
02:39:51,020 --> 02:39:54,140
research that sheds light on
the complexity of our skin.

2608
02:39:54,140 --> 02:39:57,380
Hi, Nathan. Hi, Ben. How are you?
Nice to meet you. Yeah, you, too.

2609
02:39:57,380 --> 02:39:58,700
What have we actually got here?

2610
02:39:58,700 --> 02:40:02,020
I can see cables and I can see
the big black dome here.

2611
02:40:02,020 --> 02:40:05,900
What is this? This dome-like
structure is, if you like,

2612
02:40:05,900 --> 02:40:07,940
a version of our fingertip.

2613
02:40:07,940 --> 02:40:10,860
And what happens if you touch
the fingertip now? Go ahead.

2614
02:40:13,020 --> 02:40:14,180
Ah.

2615
02:40:14,180 --> 02:40:17,180
So what I'm seeing, I'm displacing
those little lumps and bumps. Yeah.

2616
02:40:17,180 --> 02:40:21,260
Their movement gives information
about the contact on the skin.

2617
02:40:21,260 --> 02:40:23,740
Engineers have been trying
to replicate

2618
02:40:23,740 --> 02:40:25,660
our sense of touch for decades,

2619
02:40:25,660 --> 02:40:29,820
and these bumps on the inside of
Nathan's artificial fingertips

2620
02:40:29,820 --> 02:40:32,220
mimic how actual fingertips work.

2621
02:40:34,900 --> 02:40:36,420
When you touch something,

2622
02:40:36,420 --> 02:40:40,100
movement on the surface of
your skin is picked up by sensors

2623
02:40:40,100 --> 02:40:42,180
in your dermis and epidermis.

2624
02:40:42,180 --> 02:40:44,100
Called mechanoreceptors,

2625
02:40:44,100 --> 02:40:46,980
these send the signal
via nerves to your brain.

2626
02:40:48,660 --> 02:40:52,820
There are about 200 mechanoreceptors
per square centimetre

2627
02:40:52,820 --> 02:40:55,220
in the tips of your fingers,

2628
02:40:55,220 --> 02:40:59,860
and inside the robotic fingertip,
a small camera does this job

2629
02:40:59,860 --> 02:41:02,180
by detecting the movement
of the bumps.

2630
02:41:02,180 --> 02:41:06,260
It transmits that feeling,
that sensitivity, that impact,

2631
02:41:06,260 --> 02:41:08,180
through to a central
processing area -

2632
02:41:08,180 --> 02:41:09,660
not the brain, but the laptop.

2633
02:41:09,660 --> 02:41:13,900
Exactly. In this case,
it uses vision and image,

2634
02:41:13,900 --> 02:41:15,780
whereas in our fingertips,
we have nerves

2635
02:41:15,780 --> 02:41:17,940
which send that information
to the brain.

2636
02:41:17,940 --> 02:41:20,020
I'm touching that so gently,

2637
02:41:20,020 --> 02:41:23,780
and you can see on your screen
where it's moving.

2638
02:41:23,780 --> 02:41:25,500
That's incredible. It really is.

2639
02:41:27,340 --> 02:41:32,220
Most robots are pre-programmed
to do the tasks they perform,

2640
02:41:32,220 --> 02:41:35,740
but Nathan's technology means
that the robots of the future

2641
02:41:35,740 --> 02:41:40,100
will be able to react intelligently
to the world around them.

2642
02:41:40,100 --> 02:41:42,980
This robot is going to use
its own sense of touch

2643
02:41:42,980 --> 02:41:46,220
to feel over that quite
delicate porcelain head

2644
02:41:46,220 --> 02:41:47,580
that I borrowed from my wife.

2645
02:41:47,580 --> 02:41:49,940
Now, that's an essential skill
to have with our touch,

2646
02:41:49,940 --> 02:41:52,860
cos we use that to feel the shape
of objects when we pick objects up

2647
02:41:52,860 --> 02:41:55,020
or to recognise objects.

2648
02:41:55,020 --> 02:41:58,260
The sensitivity of the
mechanoreceptors in our skin

2649
02:41:58,260 --> 02:42:01,420
means our fingers can
easily trace an object

2650
02:42:01,420 --> 02:42:04,340
while applying continuous pressure,

2651
02:42:04,340 --> 02:42:08,180
but this is actually
a highly complicated task.

2652
02:42:08,180 --> 02:42:10,620
And this hasn't been pre-programmed
at all, has it?

2653
02:42:10,620 --> 02:42:12,060
No, it's completely autonomous.

2654
02:42:12,060 --> 02:42:16,740
It's figuring it out for itself
as it moves over the head.

2655
02:42:16,740 --> 02:42:19,660
Nathan knows that,
in order to be useful,

2656
02:42:19,660 --> 02:42:23,980
these artificial fingertips need
to be incredibly sensitive,

2657
02:42:23,980 --> 02:42:26,940
so he's adapted
his fingertip design

2658
02:42:26,940 --> 02:42:29,780
to make a robot hand
with a sense of touch.

2659
02:42:29,780 --> 02:42:31,780
I'll show you another experiment now

2660
02:42:31,780 --> 02:42:35,540
where we'll get the hand to pick
up a very delicate object -

2661
02:42:35,540 --> 02:42:38,780
this origami crane... Right.
..without crushing it.

2662
02:42:42,660 --> 02:42:43,700
Here it goes.

2663
02:42:44,940 --> 02:42:48,660
As the robot's fingers come
into contact with the crane,

2664
02:42:48,660 --> 02:42:53,940
it senses how much pressure to apply
without bending the paper,

2665
02:42:53,940 --> 02:42:56,420
something we can do instinctively

2666
02:42:56,420 --> 02:42:58,620
using the mechanoreceptors
in our skin.

2667
02:43:00,140 --> 02:43:04,540
Oh, look. Yep. See, it hasn't even
squeezed the head in that much.

2668
02:43:04,540 --> 02:43:06,060
It's barely touching it.

2669
02:43:06,060 --> 02:43:09,420
I mean, that...that
must be so sensitive.

2670
02:43:09,420 --> 02:43:11,420
That's so impressive.

2671
02:43:11,420 --> 02:43:15,300
It's basically the lightest
possible grasp it can do

2672
02:43:15,300 --> 02:43:19,340
and still have enough security
to hold the crane.

2673
02:43:19,340 --> 02:43:22,060
There must be so many applications
for this in the future.

2674
02:43:22,060 --> 02:43:26,900
Well, there's a few pressing needs
for this type of technology -

2675
02:43:26,900 --> 02:43:28,140
prosthetic hands.

2676
02:43:28,140 --> 02:43:30,860
So with this kind of technology,

2677
02:43:30,860 --> 02:43:33,780
you could, in principle,
embed tactile sensors

2678
02:43:33,780 --> 02:43:36,940
within the prosthetic hand
and restore a sense of touch

2679
02:43:36,940 --> 02:43:40,740
if you were able to connect it up
to the human nervous system.

2680
02:43:40,740 --> 02:43:43,700
Endless possibilities.
Yeah, exactly. There really are.

2681
02:43:45,820 --> 02:43:49,300
Finding food is high on everyone's
list of priorities...

2682
02:43:50,900 --> 02:43:53,740
..but when your food
doesn't want to be found,

2683
02:43:53,740 --> 02:43:57,900
having sharp senses can
make all the difference -

2684
02:43:57,900 --> 02:44:03,140
and one hunter's skin has adapted
to give it a massive advantage,

2685
02:44:03,140 --> 02:44:05,580
because it is able
to sense electricity.

2686
02:44:07,820 --> 02:44:12,860
This amazing piece of biology
is the snout of a sawfish.

2687
02:44:12,860 --> 02:44:14,860
We call it its rostrum.

2688
02:44:14,860 --> 02:44:17,860
You can see these projections
all the way along.

2689
02:44:17,860 --> 02:44:21,060
They're made of the same stuff
as things like human teeth,

2690
02:44:21,060 --> 02:44:24,660
but they're not quite teeth
in the traditional sense.

2691
02:44:24,660 --> 02:44:28,100
However, what's amazing
about the rostrum of a sawfish

2692
02:44:28,100 --> 02:44:30,980
is that not only is it
a deadly weapon,

2693
02:44:30,980 --> 02:44:35,100
but it can also detect minute
electrical impulses.

2694
02:44:37,300 --> 02:44:40,140
Sadly, sawfish are
critically endangered,

2695
02:44:40,140 --> 02:44:42,060
and so are rarely seen in the wild.

2696
02:44:43,300 --> 02:44:46,340
The small fish and shrimp
that they like to feast on

2697
02:44:46,340 --> 02:44:49,180
might try and stay hidden,
but, like all fish,

2698
02:44:49,180 --> 02:44:51,780
they give off tiny electric charges,

2699
02:44:51,780 --> 02:44:54,820
creating incredibly
weak electric fields...

2700
02:44:56,300 --> 02:44:58,940
..and these are a dead giveaway.

2701
02:45:01,780 --> 02:45:05,460
On the underside of
this sawfish rostrum

2702
02:45:05,460 --> 02:45:10,300
are thousands of tiny
little pores in the skin,

2703
02:45:10,300 --> 02:45:14,580
and if we were to peer inside
one of these little pores,

2704
02:45:14,580 --> 02:45:19,940
then you'd see a tiny sensory organ
called an ampulla of Lorenzini.

2705
02:45:21,140 --> 02:45:24,300
Named after the 17th-century
Italian physician,

2706
02:45:24,300 --> 02:45:28,460
the ampullae of Lorenzini consist
of a narrow tunnel in the dermis

2707
02:45:28,460 --> 02:45:30,900
filled with a conductive jelly.

2708
02:45:30,900 --> 02:45:34,700
At the end is a round structure
called an ampullary bulb

2709
02:45:34,700 --> 02:45:37,340
containing electrosensitive cells...

2710
02:45:39,140 --> 02:45:42,660
..and these are able to pick up
weak electrical signals,

2711
02:45:42,660 --> 02:45:46,300
something as faint as
one billionth of a volt.

2712
02:45:46,300 --> 02:45:50,020
The sawfish is able to swim
close to the seabed

2713
02:45:50,020 --> 02:45:54,060
where it uses its rostrum
to forage for prey,

2714
02:45:54,060 --> 02:45:58,700
and when it detects something
like a shrimp or small fish,

2715
02:45:58,700 --> 02:46:03,340
it'll use its rostrum to dislodge
it before eating it.

2716
02:46:06,300 --> 02:46:10,580
But sawfish have a second sensory
ability hidden in their skin -

2717
02:46:10,580 --> 02:46:13,580
one they share with every
single fish on the planet.

2718
02:46:16,900 --> 02:46:20,460
In the southern Pacific Ocean,
a tornado is forming.

2719
02:46:24,220 --> 02:46:28,100
It isn't made of swirling air,
but millions of fish.

2720
02:46:32,540 --> 02:46:34,100
This is a bait ball,

2721
02:46:34,100 --> 02:46:38,180
a vast school of fish that moves
as one when threatened by predators.

2722
02:46:42,900 --> 02:46:47,180
They are able to react in unison
to any danger at lightning speed,

2723
02:46:47,180 --> 02:46:50,020
splitting and reforming
behind oncoming strikes.

2724
02:46:55,540 --> 02:46:57,980
Gathering together like
this helps to intimidate

2725
02:46:57,980 --> 02:46:59,780
and confuse potential attackers.

2726
02:47:03,700 --> 02:47:08,020
Their eyes help to judge
the position of their neighbours,

2727
02:47:08,020 --> 02:47:11,940
but moving with this level
of precision is made far easier

2728
02:47:11,940 --> 02:47:14,500
by a special sensory system
in their skin

2729
02:47:14,500 --> 02:47:16,260
called the lateral line.

2730
02:47:16,260 --> 02:47:19,980
Made from a series of canals
running the length of the body,

2731
02:47:19,980 --> 02:47:23,260
the lateral line is filled
with a jelly-like substance

2732
02:47:23,260 --> 02:47:27,540
and links to the surrounding
environment by a network of pores.

2733
02:47:27,540 --> 02:47:30,780
The water from outside
moves through the pores,

2734
02:47:30,780 --> 02:47:33,620
stimulating tiny
hair-like structures

2735
02:47:33,620 --> 02:47:36,660
in the walls of the canals
called neuromasts.

2736
02:47:36,660 --> 02:47:39,980
All fish use the lateral line
to sense pressure changes

2737
02:47:39,980 --> 02:47:41,540
in the water around them,

2738
02:47:41,540 --> 02:47:44,500
allowing them to perceive
the smallest of movements

2739
02:47:44,500 --> 02:47:46,900
all the way around their bodies

2740
02:47:46,900 --> 02:47:49,940
and enabling them to maintain
a constant distance

2741
02:47:49,940 --> 02:47:52,620
from the other fish on either side.

2742
02:47:52,620 --> 02:47:56,980
Scientists think this helps fish
to migrate in huge schools

2743
02:47:56,980 --> 02:47:58,380
like these sardines.

2744
02:47:59,580 --> 02:48:03,380
As with all fish, they rely
on their enhanced perception

2745
02:48:03,380 --> 02:48:05,220
they get from their skin.

2746
02:48:10,500 --> 02:48:14,900
In the forests of Southeast Asia,
one animal is using its skin

2747
02:48:14,900 --> 02:48:19,940
to play a far more clandestine
game of cat and mouse.

2748
02:48:19,940 --> 02:48:23,660
This is an Asian pit viper.
It's an ambush predator.

2749
02:48:23,660 --> 02:48:27,580
It waits motionless on branches
for small animals to approach.

2750
02:48:29,500 --> 02:48:30,900
To hunt in this way,

2751
02:48:30,900 --> 02:48:35,420
it relies on an incredible sensory
ability hidden in its skin.

2752
02:48:38,220 --> 02:48:41,500
Jason Skinner is
an expert snake handler.

2753
02:48:41,500 --> 02:48:44,620
What a beautiful snake.

2754
02:48:44,620 --> 02:48:47,420
He's gorgeous, Jason, isn't he?
Yeah, great colours.

2755
02:48:48,500 --> 02:48:50,580
These snakes hunt at night,

2756
02:48:50,580 --> 02:48:54,420
and they do so using specialised
pits in their skin

2757
02:48:54,420 --> 02:48:56,940
located between their eyes
and their nostrils.

2758
02:48:56,940 --> 02:49:00,540
These pits are so sensitive,
they are able to pick up

2759
02:49:00,540 --> 02:49:05,620
the tiny heat signature left
by their prey in pitch dark.

2760
02:49:06,660 --> 02:49:09,340
Inside each pit is a membrane

2761
02:49:09,340 --> 02:49:12,300
which heats up when hit
by infrared radiation,

2762
02:49:12,300 --> 02:49:15,100
like that emitted by a warm rodent.

2763
02:49:17,300 --> 02:49:20,340
This heat is converted
into electric signals

2764
02:49:20,340 --> 02:49:22,300
which are sent to the snake's brain.

2765
02:49:24,460 --> 02:49:27,420
Pit vipers, pythons
and boa constrictors

2766
02:49:27,420 --> 02:49:29,060
all have this ability.

2767
02:49:31,220 --> 02:49:33,860
And we're going to test
just how sensitive

2768
02:49:33,860 --> 02:49:36,420
these heat-sensing pits really are.

2769
02:49:37,540 --> 02:49:39,660
OK, Jason. What have we got here?

2770
02:49:39,660 --> 02:49:43,300
So we've got two ping pong balls
attached to these three-foot canes.

2771
02:49:43,300 --> 02:49:46,700
Right. So we're well outside
the striking range. Good.

2772
02:49:46,700 --> 02:49:50,980
The ping pong balls are identical
apart from one crucial difference -

2773
02:49:50,980 --> 02:49:53,100
one is filled with cold water,

2774
02:49:53,100 --> 02:49:54,660
the other with warm.

2775
02:49:54,660 --> 02:49:57,220
And I've got the warm one?
Yes. Ooh, yeah. Yep.

2776
02:49:59,220 --> 02:50:02,020
If dangled in front of him
at equal distances,

2777
02:50:02,020 --> 02:50:04,820
will our viper be able
to tell which is which?

2778
02:50:05,940 --> 02:50:08,340
Quite nervous, Jason.
I'm not going to lie.

2779
02:50:16,620 --> 02:50:17,660
Oh!

2780
02:50:18,900 --> 02:50:20,100
And he did!

2781
02:50:21,980 --> 02:50:24,620
Oh.
THEY LAUGH

2782
02:50:24,620 --> 02:50:27,620
That was incredibly quick, though.
That was such a strike.

2783
02:50:27,620 --> 02:50:30,500
And instantly, he went
for the warmer one. Yeah.

2784
02:50:30,500 --> 02:50:32,500
There was a very definite
response there.

2785
02:50:32,500 --> 02:50:36,020
The head turned away from yours.
Yours was moving as much as mine.

2786
02:50:36,020 --> 02:50:40,340
It's as close. There's a very
definite preference there.

2787
02:50:43,380 --> 02:50:47,340
Even at night, when the pit viper
can't be seen by its prey,

2788
02:50:47,340 --> 02:50:49,260
it can still detect them...

2789
02:50:50,620 --> 02:50:53,060
..and when they come
within striking range...

2790
02:50:56,740 --> 02:50:59,420
He definitely made his choice.

2791
02:50:59,420 --> 02:51:00,980
..one thing is clear -

2792
02:51:00,980 --> 02:51:04,180
if the ping pong ball was a mouse,

2793
02:51:04,180 --> 02:51:06,020
it wouldn't stand a chance.

2794
02:51:08,540 --> 02:51:12,780
Skin is clearly one of the most
dynamic organs on the planet

2795
02:51:12,780 --> 02:51:16,140
and a crucial part of
every animal's senses.

2796
02:51:17,980 --> 02:51:22,140
We often take skin for granted,
yet through this series,

2797
02:51:22,140 --> 02:51:25,020
we've seen that it goes way
beyond a simple barrier

2798
02:51:25,020 --> 02:51:27,140
between us and the outside world.

2799
02:51:29,620 --> 02:51:33,900
I've been intrigued to discover
that my skin is its own habitat

2800
02:51:33,900 --> 02:51:38,780
and is easily as rich as any
rainforest or coral reef.

2801
02:51:38,780 --> 02:51:42,940
But more than that, the way
that skin is able to adapt...

2802
02:51:42,940 --> 02:51:45,740
..to protect...

2803
02:51:45,740 --> 02:51:48,660
..to sense...

2804
02:51:48,660 --> 02:51:51,020
..to swim...

2805
02:51:51,020 --> 02:51:53,060
..to fly...

2806
02:51:53,060 --> 02:51:55,140
..and even to communicate...

2807
02:51:56,340 --> 02:52:00,900
..reveals just what an extraordinary
material skin really is.

2808
02:52:00,900 --> 02:52:02,980
It's a story of survival,

2809
02:52:02,980 --> 02:52:05,380
each adaptation allowing vertebrates

2810
02:52:05,380 --> 02:52:08,420
to dominate almost
every part of the planet.

2811
02:52:10,020 --> 02:52:12,700
And what fascinates me
most about skin

2812
02:52:12,700 --> 02:52:16,380
is that we still have
so much more to find out.