Skin.
We all have it.
And so does every vertebrate on the planet.
It keeps the outside out and the inside in.
Animals may look very different on the surface,
but we all share the same basic skin blueprint.
I'm Ben Garrod, Professor of Evolutionary Biology,
and I'm fascinated by this often-overlooked wonder of nature.
It's not just the case that it's hairless,
the skin's totally different.
Now, ground-breaking new science...
This is really quite remarkable.
It should be a game changer for so many people.
RATTLING That sound!
Oh, it makes the hairs on the back of your neck go up, doesn't it?
..is revealing skin's mysteries.
It really transforms our understanding of dinosaurs.
I'm going to explore the natural history of the body's largest organ,
to see how skin has allowed animals to conquer every habitat,
disappear into their surroundings and develop extra sensory abilities.
We're even discovering the complex ecosystem living on our skin.
Jim, that's awful.
It really is.
In this episode, I'll reveal how skin's amazing versatility
helps frigatebirds attract a mate...
..means frogs don't have to rely on their lungs to breathe...
..and lets microscopic animals live on our faces.
Animals that could change the story of our evolution.
I'll explore how skin's uniquely adaptable structure
allows vertebrates to overcome some of life's greatest challenges.
I'm going to reveal the secrets of skin.
There are more than 66,000 species of vertebrates
alive on the planet today.
They've conquered the water, land and air.
And have evolved into a dazzling array of shapes, sizes and colours.
And in my opinion, it's skin, the largest organ in any animal,
that holds the key to this diversity and success.
Over 500 million years of vertebrate evolution, skin's incredible
adaptability has enabled it to become tough...
..flexible...
..sensitive...
..and colourful.
It can grow feathers, scales, hair...
..and even teeth.
But that's just the tip of the iceberg.
The key to this incredible versatility is a remarkable
blueprint that forms the basis of vertebrate skin.
Fish, reptiles, amphibians, mammals and birds
all share the same basic skin structure.
On the surface, the epidermis,
made of a few thin layers of protective cells.
Beneath that, the dermis, rich in glands, nerves and blood vessels,
where hair, feathers and scales arise.
And then finally, the subcutaneous fat layer,
a bed of fatty tissue that helps insulate the body.
Adaptations in the form and function of these three basic layers
have led to the dazzling range of skin types
exhibited by vertebrates today.
And the story starts with the outermost layer - the epidermis.
The epidermis is the final, thin barrier
between an animal and its environment.
On my body, it varies
between one millimetre thick on the soles of my feet
to just 30 micrometres here on my eyelids.
On my little friend here, it can be even thinner,
between 50 and 12 micrometres.
It's estimated that the average human epidermis
contains up to 180 billion cells.
Its main function is to protect us from the outside world.
And it is constantly replacing itself.
I'm losing 20 million epidermal cells every single hour.
And in roughly a month's time, my entire epidermis
will effectively be brand-new.
This means mammal skin is a little bit like a flaky conveyor belt.
This endless cycle of epidermal renewal has two benefits.
Damaged skin falls away to be replaced by new, healthy cells.
And because our epidermis is constantly renewing,
it can grow with us.
But this isn't the case for all vertebrates,
particularly reptiles, because they have a problem.
Reptiles' outer layer of skin doesn't grow with them,
so they have to shed their entire epidermis in one go.
It's simply replaced by a bigger version growing underneath.
A snake's simpler body shape makes this process much easier.
Adult snakes do this up to four times a year,
although young, fast-growing individuals
can shed every two weeks.
This snake has just shed.
Her skin came off like one big sock
and every single bit of her
was replaced in one go, including the scales over her eyes.
Lizards and snakes shed like this because reptile skin
is toughened by large amounts of a fibre made in the epidermis.
Keratin - a complex of twisted proteins.
It's one of the toughest natural materials in existence.
Found in all vertebrates' skin, it's incredibly versatile.
But just how tough is it?
One place keratin is found in high concentrations
is the hard outer wall of a horse's hoof.
Wild stallions use their hooves as weapons
in violent battles over mares.
They're capable of delivering a kick with a force of up to a tonne,
with bone shattering results.
With this in mind, I need a safe way to see those tough hooves close up.
So I've come to Hill Livery Stables near Bristol,
to meet farrier Dan Downton.
Who have we got here? This is Jasper.
He's come in for a new set of shoes.
I'm really interested to see how it's done.
Shall we get on with it, then? Yeah, let's give a go.
So, first of all, we're going to take the shoe off. Yeah.
Dan, that looks quite brutal, but Jasper's not feeling that, is he?
No, he's got quite a lot of foot there,
and we're not touching any sensitive structures.
So it's fine.
And that's the nail we can see there, isn't it? Yeah.
So that's the hoof wall, this is the sole.
And this is the frog. OK.
A horse's hoof evolved from a single toenail, like one of ours.
And its dense wall of keratin grows out of the epidermis
in a similar way.
The keratin in an unshod hoof has to withstand incredible forces.
A galloping horse can generate 1000 kilograms through each foot.
Give that a rasp. He hasn't got a lot of foot on it.
Once the old shoe's off, Dan trims the hoof.
So this is like a big nail file?
So you've basically given Jasper a huge manicure right now?
That's it.
Just like our nails, a horse's hooves
don't contain nerves or blood vessels.
The keratin wall grows from the skin
at around six millimetres a month, an evolutionary response
to the constant wear and tear hooves experience.
Hooves are so important to the survival and wellbeing of a horse
that, for at least 2,000 years,
we've enhanced keratin's toughness with iron,
shoeing domesticated horses to maintain
the vital integrity of their hooves.
It's not just horses that rely on keratin's durability.
Many other animals have exploited its amazing attributes.
Pangolins, like this one here, are covered
in overlapping keratin scales.
They grow out of the epidermis and form this tough but flexible
suit of armour.
If the pangolin is attacked, it curls into a ball
to protect itself.
And even a lion's teeth and claws can't get through
those two millimetre thick scales.
Keratin isn't just produced for protection, vertebrates use it
in a huge range of skin-based structures.
It's a key component in all hair and quills...
..all feathers and scales...
...and claws and fingernails.
There are 30 different forms of keratin in mammals alone.
At its most chemically complex and tough,
it turns a rhino horn into a battering ram.
While the main function of the epidermis is protection,
the layer below, the dermis, combines intense biological activity
with some extraordinary physical attributes.
This is a male great frigatebird from the Galapagos Islands.
He's just won a hotly contested patch of ground to nest on.
Now he needs a mate.
Female frigatebirds are gliding overhead.
Somehow, he must attract their attention without abandoning
his hard won bit of turf.
His solution is this huge inflated balloon of skin on his throat.
Called a gular sac, it's almost as tall as he is and clearly visible
to the circling females. He adds to the dramatic effect by shaking
it from side to side and clacking his beak.
Eventually, his lonely hearts ad does the trick
and a female joins him at the nest site.
Job done.
His gular sac deflates and all but disappears.
The key to a male frigatebird's amazingly stretchy skin
is down to a fibrous protein that's found in the dermis
of all vertebrates.
It's called elastin. Named for its elastic properties
and looking and behaving like a mesh of tightly coiled microscopic
springs, elastin pulls stretched skin back into shape.
Human elastin production slows down as we get older.
And this means our skin not only gets less stretchy, but starts
to develop wrinkles.
The impressive elasticity of the dermis has led to some
extraordinary adaptations across the vertebrate world,
from kangaroo pouches to bat wings.
And none more so than frogs.
During the breeding season, male frogs' vocal sacs combine elastin
and very thin skin to amplify their mating calls.
The amphibian dermis is remarkable for another reason.
More than any other vertebrate,
they rely on their skin for the uptake of oxygen.
Amphibians, like this African bullfrog, use their thin permeable
skin effectively to breathe in water as well as on land.
Their skin has evolved to let oxygen pass through the cells
of the epidermis and dermis and into the bloodstream.
They can get as much as 20% of their oxygen through their skin.
One frog has taken this to the extreme.
The Titicaca frog, found in rivers and lakes high in the Andes,
is covered in folds of extra skin.
A dense network of capillaries in the dermis of these folds allows
the frog to absorb all the oxygen it needs from the water, meaning
it never has to surface to breathe.
But there are drawbacks to this type of respiration.
In order to survive, amphibians need to live in damp places,
where their skin remains moist.
If it dries out, it means that gases can't diffuse
across it and they suffocate.
Alongside its impressive physical attributes, the dermis is also
a hive of biological activity.
Specialised glands produce a huge array of natural compounds
which further enhance the skin's versatility.
And I've got a neat, low tech way to demonstrate this.
These are camphor boats,
and a tiny camphor crystal on the back of each one has them
shooting across the surface of the water like magic.
Of course, it's not magic.
Camphor is a pungent chemical harvested from camphor trees.
It dissolves in water, altering the surface tension and pushing
the little boats forward.
All it takes to stop them is a thin layer of grease on the water,
and I know just where to find some.
In common with most mammals, my skin is coated in a thin layer of oil.
This is a waxy substance called sebum that helps lubricate
and waterproof my skin.
It's produced by sebaceous glands in the dermis of all mammals.
These are often found next to hair follicles,
which is why our hair gets greasy. While we have an estimated
two million sebaceous glands all over our skin,
it's still a mystery why they're most abundant
on our scalp and faces.
Mammals aren't the only vertebrates producing natural oils
in the dermis.
Birds have sebaceous glands too.
But instead of lots of small glands all over the skin, they've evolved
one big one.
And if we're really careful, we can look at this conure's...
SQUAWKS ..because... Hello!
..just at the top of the tail, you can see a little patch that looks
like it's a bunch of soggy feathers.
That's the preen gland.
And it's this that produces oil which the bird then spreads
around its body using its beak and head.
Birds use this dermis-produced oil for lots of different reasons...
..keeping feathers supple for flying, sending odour-based chemical messages
to potential mates or rivals.
It also helps to keep feather colours vivid.
Many diving birds have large preen glands, which suggests it also plays
a vital role in waterproofing their feathers,
although biologists are unsure of exactly how.
Preen oil is an impressive but mysterious multi-purpose substance.
And the dermis still has more surprises in store.
In ancient mammal ancestors living more than 250 million years ago,
scientists believe the dermis evolved to secrete something
extraordinary - milk.
There are four different types of gland in the mammalian dermis,
and it's thought an adaptation of one, the sweat gland, led
to this vital step in mammal evolution.
We have a rough idea of how that might have worked from platypus
and echidnas, like this little guy here from Australia.
These are unusual mammals in that they lay eggs,
and they feed their offspring from milk that's secreted
to the surface of the skin by collections of pores.
This might have been an early step into the development of dedicated
nipples and mammary glands as we see in most
mammals alive today.
The versatility of the dermis allows it to make an array of unique
compounds that have shaped vertebrate evolution.
And there is one more - collagen, a protein with incredible tensile
strength which is found in every vertebrate dermis.
Only now are we understanding the far-reaching effect
it could have on our lives.
I'm going to see bio engineer Dr Claire Higgins.
She's testing a disc of human foot skin to see how it responds to a bit
of wear and tear.
So the machine compresses the piece of skin, and we measure the amount
of deformation in the tissue, so how much the tissue
is changing shape.
The disc of foot skin is repeatedly squashed up and down and side
to side, mimicking the forces produced by walking.
And what have the results shown so far?
So with compression foot skin deforms by about 15% whereas body skin
changes shape by about 25%.
And then, when we look at shear forces, foot skin deforms
by about 40% while leg skin actually deforms by as much as 150%.
Claire's tests reveal that, when it comes to dealing with wear and tear,
the skin on our feet significantly outperforms the skin on the rest
of our bodies.
To find out what makes foot skin so resilient, Claire's using laser microscopy.
So we're actually imaging collagen fibres,
and we're interested in collagen because it makes up about 90%
of the skin dermis and it's really the structural
protein that contributes to the integrity of the skin.
Fibres of collagen running through the dermis
are what give vertebrate skin its tensile strength.
So you can see, in this image here, this is collagen in foot skin. Mm-hm.
And this image on the right is collagen in leg skin.
The foot skin owes its impressive toughness to this dense
network of collagen.
The images show that the collagen fibres in foot skin are much
thicker than the ones in leg skin.
They're also about four times brighter, which is significant.
That brightness actually is an indication of tensile state.
The fibres in foot skin are pretensed, almost.
So basically these are ever ready little bundles of collagen
in anticipation for this heavy wear and tear that we're not seeing
elsewhere in the body?
Claire's ground-breaking research has revealed that our skin structure
varies with the job it has to do.
Her ultimate aim is to replicate the durability of foot skin in skin
on other parts of the body, changing lives in the process.
There are some circumstances, such as after amputation, that skin
on a stump is required to be load-bearing, but it's not
designed to be.
So we're hoping that we can try to reengineer skin, such as stump skin,
to make it stronger and make it capable of being load-bearing.
So you're talking about developing skin on people with disabilities or injuries here?
Yeah, re-engineering skin on the stump, essentially.
This is really quite remarkable, and it should be a game changer
for so many people.
We hope so. Yeah, absolutely.
Claire's discoveries are shedding new light, not just on the potential
of human skin, but the versatility of skin itself.
It's also a clear demonstration of just how much we still
have to learn.
Another remarkable discovery about human skin could change our
view of evolution.
It involves looking for an animal that lives on and in our skin.
They're so small that you can't feel them or see them with the naked eye,
but most of us do have them.
So I'm off to see whether I can find mine. They're skin mites.
And I've come to meet Dr Dave Patton, who's going to help me
track mine down.
Hi, Dave. Hello.
So we're going to look for mites on my face, are we? Yeah.
We're going to use an interesting technique involving
supergluing your head to a glass slide.
You say it like it's such a common thing!
OK. So we've literally got a glass slide and some superglue!
Yes. OK. Right.
So all we do is put some glue on the slide and then press it
onto your forehead for a minute.
Then it'll remove some of your forehead and, hopefully,
some skin mites. Not much of my forehead, though, right?
Um... A millimetre.
Mites live in greater concentrations on our faces than anywhere else,
particularly on our cheeks and foreheads.
You ready? I think so.
Right, OK.
OK. Can you hold that in place?
Yeah.
While the 60 seconds count down, I want to check something.
Have you done this to yourself? Yes. Yes.
Have you found any?
We have found one.
That's not a very high hit rate.
So, to be on the safe side, we'll need some backup samples.
I think, in that case, then, what I might do is to get slides
and samples from all the crew as well.
Why not? Come on, guys!
And so the crew bravely submits to the superglue treatment.
Just press that on. Thank you.
Thank you.
Argh! Sorry. It didn't hurt.
We have got a nice variety of peeled skin on there right now.
So now we've put those under a microscope and we see
whether we can find these little face mites stuck on the superglue?
Yeah. That's the plan.
Let's see if we can find some. Good luck, team.
Dave puts my sample in a scanning electron microscope
and, within minutes, I'm looking at the inside of my skin
magnified 200 times.
It's like a really horrible treasure trail cos
I don't want to find what's hiding!
So, to search, I'm just going to move one screen at a time. And we're looking
for a little head that's popping out next to the hair itself, aren't we?
Yeah, in the same pore, so parallel to the hair, looking
very similar to the hair.
But however hard we search, we just don't find any signs of life.
So what I think we should do is have a look at some of the other
film crew members to see what their skin's like.
So who have we got here, then, Dave? Andy, the sound man.
There's a pore there with hair coming
out of it. It's probably just a big bit of follicle there belonging to this hair.
Dave looks even closer, and bingo!
Look, look at that. There appear to be one, two, three Demodex.
Andy not only has mites -
he's got loads of them!
So you've got evidence of three little mites on one hair strand
from Andy's sample here?
It looks like it.
What we've found are Demodex mites - tiny, harmless arachnids that live
on my, your and Andy the soundman's skin.
Their long, thin bodies help them slide inside our hair follicles,
where they cling on with eight stumpy claws.
They spend their time hidden away, feeding on oils made in the dermis
and all those dead epidermal cells.
If that wasn't bad enough, these little animals are light
sensitive and only come out at night, when they mate...
..on our faces.
The only time we don't have Demodex mites
is when we're in the womb.
Once you're born, a few snuggles from your mum or dad,
and you've probably got mites.
While this is both fascinating and disturbing, it just goes to show
that our skin isn't just an organ - it's an entire ecosystem.
This discovery has opened up a whole new line of scientific inquiry.
By testing mite DNA from around the globe,
scientists revealed in 2015 that different human populations
have different mite populations, handed down through the generations.
This means we can map which continent a person's
ancestors came from
by studying the mites on their skin. We may even be able to trace ancient
human migration patterns by studying
mite DNA, shedding new light on our evolution.
And the extraordinary story doesn't end there.
Every mammal species tested so far has its own familial Demodex
mites - proof that skin still has its secrets.
When it comes to helping vertebrates thrive in an unpredictable world,
skin, which is both resourceful and adaptable, is the ultimate
multi-purpose tool. And it's still full of surprises.
Over the rest of this series,
I'll be unpacking the fascinating ways skin has evolved to make
vertebrate life on Earth possible
by helping animals defend themselves, disguise themselves,
and even communicate.
BARKS
In the next episode,
I discover why shark skin is covered in thousands
of tiny teeth...
I'm not about to give this one a stroke!
..how gecko skin allows them to defy the laws of gravity...
He's able to cling onto this piece of vertical smooth glass with ease.
..and I find out why loose skin is the ideal adaptation to life
underground as I explore the way skin has evolved
to help animals move.
Skin.
We all have it.
And so does every vertebrate on the planet.
It keeps the outside out...
..and the inside in.
Animals may look very different on the surface, but we all share
the same basic skin blueprint.
I'm Ben Garrod, professor of evolutionary biology,
and I'm fascinated by this often overlooked wonder of nature.
It's not just a case that he's hairless,
the skin's totally different.
Now, ground-breaking new science...
This is really quite remarkable.
It shouldn't be a game changer for so many people.
RATTLESNAKE TAIL RATTLES
That sound, it makes the hair on the back of your neck go up,
doesn't it?
..is revealing skin's mysteries.
It really transforms our understanding of dinosaurs.
I'm going to explore the natural history of the body's largest organ,
to see how skin has allowed animals to conquer every habitat,
disappear into their surroundings and develop extra sensory abilities.
We're even discovering the complex ecosystem living on our skin.
Oh, Jim, that's awful.
It really is.
In this episode, I'll find out why shark skin is covered
in thousands of tiny teeth.
Now, I love sharks, but I'm not about to give this one a stroke.
How birds have adapted their skin to rule the sky.
Ooh! Oh.
And down he goes.
And how a gecko's skin allows it to defy the laws of gravity.
He's able to cling onto this piece of vertical, smooth glass with ease.
As I explore how animals use their skin to move
through the world around them.
I'm going to reveal the secrets of skin.
Movement is critical for the survival of animals.
Fish swim.
Moles dig.
Sugar gliders leap and hummingbirds hover.
Muscles and bones might do a lot of the heavy lifting,
but it's adaptations to their skin which have allowed these animals
to move in the ways that they do.
As we'll discover, skin is essential for all types of movement.
Fish are shaped the way they are because they need to be
streamline enough to move through the water while using
the least amount of energy.
But one group of fish have taken streamlining to the next level,
with a super hydrodynamic surface to their skin.
Sharks, some of the most formidable hunters in the oceans.
The mako shark hunts some of the fastest fish in the sea,
such as tuna and swordfish.
So has evolved to be incredibly quick, reaching top speeds
of over 64kph.
And as with all sharks, their skin plays a crucial role
in helping them do this.
OK. We good?
I'm at Blue Planet Aquarium in Chester,
where I'm about to get very close to these predators.
In this tank in front of me, there are five different species of shark.
All of which are infinitely more suited to moving
through the water than I am.
Anyone who's been in a pool will know that moving through water
is a lot harder than moving through air.
When I move through the water like this,
my body is creating a huge amount of resistance.
And this really slows me down.
And it's because of this resistance that I can't move
through the water very fast.
But shark skin is perfectly adapted to reduce the resistance created
as they swim, and so they can slip through the water
with relative ease.
Now, I love sharks, but I'm not about to give this one a stroke.
But if I did, I would feel that from the head to the tail
is very smooth.
But from the tail to the head is actually very rough.
And that's because if you look at the skin of a shark
in microscopic detail,
you'll see their skin are effectively covered
in millions and millions of tiny teeth.
These dermal denticles grow out through the top layer
of skin, the epidermis.
They are made from a hard mineral called vitrodentine
on the outside, and softer dentine on the inside.
It's incredibly similar to the material human teeth are made from.
Denticles form a regular pattern all over the skin
of every shark in the oceans.
With each species having different shaped denticles unique to them.
These dermal denticles have evolved to allow the sharks to slip
seamlessly through the water.
It makes them more streamline and it reduces resistance.
And this allows sharks to swim not only fast and stealthily,
but by saving so much energy,
they can cover huge distances across oceans.
All of these things have helped turn sharks into very efficient hunters.
These incredible images are CT scans of baby sharks,
produced at the Natural History Museum in London.
The sharks in these images are only a few weeks old, but you can already
clearly see the regular arrangements that denticles form in the skin.
Dr Tom Fletcher, from Leicester University,
is an expert on shark hydrodynamics.
I've seen some amazing sharks recently and one thing
that really throws me is obviously they're covered in denticles,
but I don't fully get how those denticles help them move
through the water with such ease.
Scientists for years were perplexed by the roughness of these sharks
and how they were managing to reduce drag so effectively.
Not only are the denticles quite rough,
because there are lots of them, all jutting up next to each other,
like we have here,
but they're also very rough on the surface as well.
Obviously, these aren't actual denticles, you've had these
3D printed and they're much larger than real life, yeah?
Yes, they're about 1,000 times bigger than they should be.
If you look at shark denticles in real life,
they're like grains of sand, they're absolutely tiny.
And what we have here is, we have a section of shark skin.
These are different species.
This is a leopard shark, and we have a single one here.
This is probably the fastest shark that we've got in our oceans today.
It's the mako shark.
These show really nicely the microscopic structures
that are reducing drag.
The key are these riblets here, these peaks and troughs
that we have on the surface.
And the way they work is by reducing the friction of the swirling fluid
above the surface.
So if, for example, I'm the shark here and the fluid's moving
over the surface and it's completely smooth, that's a very large area
for friction to occur.
It's sort of like going onto an ice rink with big snowshoes on.
If you've got big, flat snowshoes that are nice and smooth,
actually, you've got lots of friction there.
Whereas an ice skater with that thin blade of metal interacting
with the ice, just like these riblets,
the friction is much reduced and you can go much faster.
In fact, shark denticles are so good at their job,
they're inspiring a whole host of new technologies.
People have been very interested in reducing drag by 10%,
that's really, really enormous and it can save a lot of energy.
In aircraft, for example, they've tinkered with this.
The underside of boats as well.
If you need to move a fluid across a solid surface,
then this could potentially really help.
Good old sharks.
If you look close enough, you'll find a hidden microscopic world
on the surface of the skin of many animals,
helping them move in ways which often appear impossible.
Like sharks, geckos use their skin to help them hunt prey.
However, when your food is an insect which could land virtually anywhere,
It's not just speed that you need, but also the ability to climb.
As geckos go, this tokay gecko is pretty heavy.
But still, he's able to cling onto this piece of vertical,
smooth glass with ease.
And as he spins around,
we're able to see just how he manages to do this.
You might think the surface of glass is totally smooth,
but like all materials, it's covered in microscopic imperfections.
And the skin on a gecko's toes is able to make use
of these imperfections and stick to the glass.
This is down to a physical property called Van der Waals force.
Named after the 18th-century Dutch physicist,
it's a weak electrical attraction that exists between all molecules
if they get close enough to each other.
If I were to place my hand on the glass,
there are so many ridges, lumps and bumps, things like fingerprints,
that there isn't enough surface area for me to be able to use
Van der Waals force to stick to the glass.
However, gecko toes have a remarkable micro structure.
Out of the epidermis protrude hundreds of thousands
of tiny filaments made of a protein called keratin,
the same stuff that makes our hair and nails.
These keratin filaments are so small,
that far more of the molecules on the gecko's toe
come into contact with the molecules on the glass.
This allows the gecko to use Van der Waals force,
and enables it to cling onto and move up vertical surfaces.
For any animal to move, their skin needs to be flexible.
And one subterranean rodent has taken this flexibility
to an extreme.
The most intriguing animal, with the strangest skin I know,
lives in Africa, underground, and is rarely seen.
Naked mole rats.
They're almost blind and virtually hairless.
And until relatively recently, these strange animals
were a total enigma to science.
Hi, Chris. Hi, Ben, how are you doing?
Look at these little guys. Yeah.
Dr Chris Faulkes has one of the largest captive colonies
of naked mole rats in the world.
It's not just a case that this little rodent is hairless,
the skin's totally different, it's really baggy.
Why are they so loose, how does it help them move, for example?
Well, we think that it helps them to pass each other
in very tight situations.
Sometimes you get a traffic jam, with several all trying
to get past each other and that loose skin helps there.
One theory is that almost like being in a sleeping bag,
the naked mole rats' loose skin helps them wriggle round
much more easily in tunnels,
where there's very little room for manoeuvre.
It also helps to have loose skin when you're living
with this many family members.
In the wild, they can live in social groups of up to 300 sometimes.
Yet, there's only one female that breeds, the queen, and the rest
act as either defenders or helpers.
So it's a bit like the mammal equivalent of a social insect.
Crawling through these small spaces means constantly bumping
or scratching yourself on sharp rocks in the earth.
But naked mole rats feel less pain than other rodents.
Evolutionary changes to the pain receptors in their skin
means that fewer pain signals are sent to their brain,
making them perfectly suited to their underground life.
Remarkably, they live incredibly long for a small rodent,
over 30 years - 34 years is the record at the moment.
So if you think of a similarly sized mouse, that lives for about
three years, so more than ten times longer than a mouse.
They resist all of the normal signs of ageing.
And that's not even the most remarkable thing
about their physiology.
They also resist getting cancer.
So probably less than 0.3% incidents of cancer,
compared to, in some mouse strains, up to 90% develop cancer.
Scientists believe this incredible ability to resist cancer
could be to do with a compound found in their skin.
There's a component in the skin called hyaluronan,
or hyaluronic acid, which all mammals have, we have it.
It's often present in skin creams and beauty products.
Now, naked mole rats have a unique kind of hyaluronan,
in terms of size and its molecular structure.
Hyaluronic acid is a component of the connective tissues
which form the structure of skin and other organs.
And naked mole rats have a unique form of hyaluronic acid
with a coiled molecular shape.
This makes the molecule act almost like a spring.
This gives the naked mole rats their stretchy skin,
and might be a key factor in their ability to resist cancer.
But research into this is still at an early stage.
Whether you think they're ugly or cute, what's not up for debate
is that these saggy-skinned members of the rodent family
are helping us understand and tackle
some of our most devastating diseases.
Life in challenging environments is often only possible
because of skin's incredible versatility.
One leading theory suggests that a subterranean existence drove
one particular group of animals to even more extreme adaptations.
Go back 150 million years and the ancestors of snakes
lived underground, but had four legs.
But these limbs would have just got in the way,
so over time, the snakes lost them and evolved
to propel themselves along on their bellies.
But now, with the majority of snakes living above ground,
there's one question that has puzzled scientists.
How are snakes able to get across flat surfaces without limbs?
The secret to how this snake is able to move
lies in the specially adapted scales on the underside of her belly there.
And while they may look very smooth, they're actually able to generate
a large amount of friction.
Each belly scale is made of keratin and populated
with microscopic protrusions.
The snake can grip the ground with its belly scales
by using these protrusions to catch on any imperfections on the surface.
It is then able to pull other parts of its body forward.
The arrangement of these tiny protrusions is key.
They're positioned so that when the belly scales slide forward
over the ground, they do so smoothly.
In one direction, the scale slips, in the other direction, it grips,
allowing snakes to move effortlessly through a range
of habitats, tackling virtually any surface they come across.
Throughout evolution, skin has used keratin in a variety
of ingenious ways.
It's the main component of nails, scales and hair.
But none of these are as complex as its real crowning achievement.
Feathers.
They grow in a similar way to our hair.
A shaft made of keratin grows out of follicles in the skin,
but that's where the similarity ends.
As the shaft emerges from the follicle,
branched keratin filaments open out, forming a flat surface,
known as the vein.
There are different types of feathers,
which come in all shapes and sizes.
And it's the flight feathers that birds grow from the skin
on their wings which enable them to take off and stay in the air.
I've come to the International Centre for Birds of Prey
in Gloucestershire, to see some really impressive flyers.
This is a Steller's sea eagle.
He's got a two-metre wingspan,
and he's one of the heaviest eagles on the planet.
And he can dive from a perch to catch his prey,
or he can soar using those massive wings to look for his next meal.
He's got huge flight feathers and each one is lightweight, stiff,
but importantly, really, really strong.
In flight, the shape of a bird's wing
means the air pressure under the wing is greater than that above.
And it's this difference in pressure which keeps them in the air.
But this is only possible because of the way
their flight feathers work.
And if you take one of these feathers and have a look,
you can actually see that on one side, there's just more feather.
And it's this asymmetry that allows him to be such an amazing flyer.
On flight feathers, one side of this keratin vein is larger.
As a bird flies, this larger part of the vein catches the air,
rotating the feathers slightly.
This twists the feathers so they interlock.
This then stops air passing through them,
and it's this that gives the wing lift and thrust.
This interlocking means that together,
all the feathers in the wing form a large surface area,
impermeable to the air.
Meaning the higher pressure underneath keeps the bird aloft.
Another type of feather, common to all birds,
is the contour feather.
Unlike flight feathers, the vein on contour feathers
is pretty symmetrical.
These feathers cover the torso,
giving the bird its aerodynamic shape.
Flight feathers and contour feathers share an amazing micro structure.
The veins' filaments have interlocking barbs which mesh
together to form an effective surface for the air to slip over.
This allows contour feathers to create a streamlined shape
around the bird's body.
And there's one group of birds of prey which take full advantage
of this aerodynamic feature.
When they hunt, some falcons can reach
an astonishing 320kph.
And I'm going to see one of them in action.
Jemima, this is a beautiful bird, and I've seen these in the wild.
This is a gyrfalcon, isn't it? That's right.
These are built for speed and built to kill, right? They are.
They've got these lovely long, pointed wings,
as have all the falcons.
And we have a special way to show you how this thing does fly.
So, we've gone modern and we have a robotic crow, the Rocrow.
So we're going to chuck up a robot and get it to fly,
and see if this beautiful beast can take it down?
That's what we're going to do. Brilliant, I want to see this.
Jemima uses this technique to train many of her falcons.
These birds typically hunt at a height of around 300 metres,
perfect for swooping down on their prey.
So he'll have to climb now, I guess, to get above the robot, won't he?
He has to climb and that's what he's got to learn.
He's quite young and not, as yet, very fit
and it's a windy day for him.
Falcons dive at their prey like bullets,
often stunning or even killing them in mid-air.
During this dive, their pointed wings and the interlocking
barbs on their feathers makes this family of birds
among the fastest animals on the planet.
The Robocrow doesn't stand a chance.
You can see those big, long flaps followed by
some really quick, thrusting beats there. Yeah.
He's just trying to get some speed.
And it doesn't stop either.
Whoa. Ooh, ooh. Oh!
He just hit... Oh, and Robocrow's down.
And down he goes. Good boy.
And this is what they use to hunt in the wild.
We saw different types of flight there,
and that last second hit, using the feathers,
using the wing shape to really bring all those things together
and take down its prey.
Well, I'm always happy when nature trashes a robot,
so that was great.
From the growth of small keratin protrusions, it's their skin
which has enabled birds to soar, hover, dive and glide their way
to dominating the skies.
But without feathers, how do you get into the air?
Living in the rainforests of Australia and Indonesia,
sugar gliders spend their time in the treetops,
gliding between branches.
These marsupials use wings made of flaps of skin
to harness the power of the air,
allowing them to glide up to 50 metres.
But how they manage to stay airborne for this distance
has remained a mystery.
Today, this will be tested for the first time
by Dr Jorn Cheney, a specialist in animal flight adaptations.
Hey, Jorn. Hey, Ben, nice to see you. Yeah, you too.
Who have you got here?
This is Chloe.
I've never seen a live sugar glider before.
Hello.
I'm absolutely fascinated by the structure of their skin.
Because they move through the air, but they don't fly
in a traditional sense, do they?
No, no, they're more gliders than flyers.
And traditionally, we think of flying as animals
that flap their wings and power themselves through the air.
Gliders mostly go down and then sideways.
It's super weird, because that's not how we fly.
We don't see birds fly that way, we don't build aircrafts that way.
And so I'm interested in why she's able to fly so well with such
an unusual shape.
For this experiment, we're at the Specialist Flight Research Centre
at the Royal Veterinary College in Hertfordshire.
I'll relieve her from you. Thank you.
Chloe has been hand-reared and her handler, Simon,
is going to help with the experiment.
So Chloe is going to start on that platform up there.
She's going to use that as a launch platform,
and Simon is going to hold that and coax her off
to jump over to you, just like that, where you'll be standing over there.
Jorn has set up four ultra high-speed cameras
to record Chloe's gliding.
Chloe takes her place on the launchpad and I do my best
to impersonate a tree.
Oh, oh, oh, she's thinking about it.
Perfect.
THEY CHUCKLE
Chloe gets into the swing of things immediately.
Come on, then.
Although her aim needs a little work.
This is one of the weirder experiments I've ever done,
I'm not going to lie.
I love that we're actually doing science
whilst trying to catch a sugar glider, this is brilliant.
It's the shape that Chloe's flexible skin wings take in the air
that will tell Jorn a lot about how she's using them.
Well done, little one.
And in order to see this, he's created a 3D model
of Chloe's wings with his cameras.
What have the results shown?
So, that beautiful thing is Chloe, just the top surface of her.
Yeah.
What you're able to pick up from this is the full 3D shape
that she's using when she glides.
And that's important because the aerodynamics
are entirely determined by the shape.
But also, she's not flat, she's curved.
Yeah, she's got a lot of curvature.
Jorn has worked out that Chloe's wings curved or billowed
by a surprising amount -
over three times more than the wings of a gliding bird.
All of that billowing helps guide the air downward and backward,
producing lift.
The more billowing you get, the more aerodynamic force you're producing.
So if the wing wasn't billowing like that,
she'd be a much worse flyer.
What's also clear is that Chloe is controlling this billowing.
The muscles in the middle of the skin flaps are relaxed,
while the muscles around the edge have been tensed.
So this flexible skin, we definitely don't see that with birds, do we?
We don't see it with birds, but we do see it with every other
gliding mammalian lineage.
All have, for whatever reason, converged upon the idea of
using skin as a wing and then embedding muscle into it.
And we're able to figure out that the muscle isn't the only thing
supporting the body weight, the skin is actually doing quite a bit.
There's still a lot more work to do to really understand
what is going on with gliding animals like Chloe.
But one day, Jorn is hoping experiments like this
could pave the way for new aircraft technology
using flexible material for wings.
Skin's adaptability is unparalleled.
Animals have used their skin to master movement on every surface,
patch of sky and body of water on Earth.
Next time, I'll show you how skin protects vertebrates
from the planet's most extreme conditions.
And I'll do that by testing my skin's response to intense cold...
My skin is literally trying to save me!
..discovering how a giraffe protects itself from the sun...
Hello, mate.
..and comparing cooling methods with my dog, Jack.
Yeah, I'm sweating.
Skin.
We all have it.
And so does every vertebrate on the planet.
It keeps the outside out...
..and the inside in.
Animals may look very different on the surface
but, amazingly, all share the basic skin blueprint.
I'm Ben Garrod, professor of evolutionary biology,
and skin is a subject that utterly fascinates me.
It's not just the case that he's hairless,
the skin's totally different.
We're discovering so much amazing new science...
This is really quite remarkable.
It should be a game-changer for so many people.
RATTLE SOUNDS
That sound, makes the hair on the back of your neck go up, doesn't it?
..about this often overlooked wonder of nature.
It really transforms our understanding of dinosaurs.
I'm going to explore the natural history of the body's largest organ,
to see how skin has allowed animals to conquer every habitat,
disappear into their surroundings,
and even develop extrasensory abilities.
And I will discover the complex ecosystem living on my own skin.
Oh, Jim, that's awful, it really is.
In this episode, I discover how the smell of my skin can help win
the war against malaria.
Hello, mate.
I'll reveal the secrets behind a giraffe's spots.
And find out how hippos produce their own sunscreen...
..to understand how skin has adapted in a multitude of ways to protect
animals against a hostile world.
I'm going to reveal the Secrets Of Skin.
At its most basic, skin is what separates our fragile,
vulnerable insides from the outside world.
Our planet is a dangerous and often unpredictable place.
So to work efficiently, we need to keep conditions
inside our bodies, like temperature, nice and constant.
Excess heat or cold can upset the stability
of our internal body temperature, which needs to be around
37 degrees Celsius regardless of the temperature outside.
Right now, I'm going to upset that stability in a big way.
Because I'm going to go into a freezer that's currently
minus 13 degrees Celsius.
SIGHS HEAVILY
Here we go.
Ooh!
Already, there's a blast of cold air that's just hit my face.
And it's taken about three seconds for my body to feel
really, really cold.
To get a better idea of what's happening to me, we're using
a thermal camera.
This reveals the heat given off by animal and human skin.
Lower temperatures appear as blue and purple, while warmer
temperatures appear red, yellow
and, hottest of all, white.
If my internal temperature drops just two degrees
to 35 degrees Celsius, hypothermia will set in
and my vital organs will begin to fail.
That's because my skin isn't well insulated enough
to keep the heat in.
So right now, the hair on my arms is all starting to stand on end.
That's because my skin is literally trying to save me.
In mammals, hair grows out of the dermis at an angle.
Each has a tiny muscle that contracts when the skin gets cold,
pulling the hair erect and causing goose bumps.
And it does this to try and trap a layer of warm air between our skin
and the hair itself.
It's not working right now, it's so cold.
That's because I'm just not hairy enough.
This automatic response is an echo from our evolutionary
past when our ancestors were much hairier.
Dense hair traps a layer of air next to the skin,
which acts as insulation and stops heat escaping.
Feathers work in the same way.
The more hair or feathers, the better they are at trapping air.
It's a brilliant system.
A polar bear can survive temperatures
down to minus 69 degrees Celsius.
While at minus 13, I'm really starting to struggle.
I'm getting really cold right now, and if I stay here,
I'm not going to survive very long.
And without hair like a polar bear,
the only thing that's going to keep me warm...
Thank you, Nigel.
..is some pretty serious Arctic gear.
Ah, that's better.
But even with the warmest of winter clothing,
I'm only going to stay so comfortable for so long.
So I think it's time to leave.
A polar bear's dense layer of inner hair helps insulate them.
But their hair is also special in being hollow,
allowing them to trap even more warmed air.
But they don't win the prize for the densest hair on the planet.
That goes to the sea otter.
These shellfish-eating ocean specialists have 400,000 follicles
per square centimetre.
That's 2,000 times the density of the hair on my head.
While sea otters have evolved external insulation
to slow down heat escaping in the chilly waters of the Pacific,
other marine mammals have ditched insulating hair altogether,
and gone for insulation under the dermis by developing
a thick protective layer of fat, which stops heat escaping,
known as blubber.
And the absolute blubber champions are cetaceans -
porpoises, dolphins and whales - which can vary the thickness
of their blubber depending on the time of year,
where they are and a host of other factors.
Imagine for a moment
that these doughnuts represent whale blubber.
Then the more doughnuts I use means the thicker the whale blubber is.
My first whale is the minke.
These filter-feeding whales live in warm, temperate waters
around the planet.
They have a maximum blubber thickness
of about seven centimetres.
That's the same as two doughnuts.
My next whale is a bit more cosmopolitan, it's the humpback.
They can spread their time between warm, equatorial waters
and colder waters towards the polar regions.
They have thicker blubber, which can reach about 12 centimetres thick.
Now the bowhead whale is an absolute champion at thriving
in sub-zero polar waters.
And with that, they need some pretty serious blubber.
Their blubber is the thickest on the planet,
and it allows them to survive in environments
that few other animals can survive in.
In fact, that's not enough.
Because bowhead whales have a layer of blubber that can be as much
as 50 centimetres thick.
That's about the same as 17 of these doughnuts.
So by using feathers and hair on land and blubber in the sea,
skin protects animals against the cold, allowing them
to colonise environments ranging from just above freezing
down to minus 69 degrees Celsius.
There's only one problem with being really well insulated
against the cold.
What do you do when you get too hot?
Come on, let's go, go.
Ha, ha, come on.
Come here.
Jack, Jack.
Even in cooler climates like Britain, heat generated
by muscles and metabolism can significantly
raise body temperature.
Come on, good boy.
The heat that Jack and I are generating right now,
will soon start to affect the smooth running of our bodies
if we can't get rid of it.
Come on.
Luckily for me, when I get too hot,
my skin produces this amazing coolant via the dermis,
which is pumped to the surface by specialised glands.
Yeah, I'm sweating.
As the sweat evaporates, my body cools and this keeps everything
inside at a safe temperature.
Some researchers believe that sweating as a cooling system
allowed our ancient ancestors on the African savannah to stay active
during the hottest part of the day.
It also enables humans to become the ultimate endurance runners.
I've got between two and four million sweat glands in my skin.
It's almost exactly the same number I was born with,
Even though my skin is now several times bigger
than it was when I was a toddler.
Nobody likes sweating.
In fact, we do all we can to avoid it sometimes.
But actually, sweating is amazing.
It's an incredible adaptation
and humans are unique in being the only species
to cool down in this way.
Hairy mammals like Jack
have far fewer sweat glands than humans,
and only produce between 10 and 20% as much sweat as a human
under conditions of high-heat exercise.
So Jack has to pant to cool himself down.
As water evaporates from his mouth and tongue,
it takes the heat with it.
The thermal camera shows the heat escaping from Jack's mouth.
Many birds and mammals, big and small,
have to cool down this way too.
And even when panting isn't enough,
some animals have developed another strategy.
In the intense heat of the Australian outback,
where temperatures can reach 50 degrees Celsius,
kangaroos lick their forearms.
As the saliva evaporates from their skin,
it cools the blood vessels under the skin,
making survival here possible.
If hair and feathers make it harder to lose heat,
then why do so many animals from hot countries still have them?
Well, they serve other vital functions, too,
including protecting these animals
from the damaging effects of UV rays.
UV rays from the sun
are one of the most dangerous things
the environment throws at the animal world.
And they are just the right wavelength
to damage the skin's fragile DNA, causing skin cancer.
Animals need to find a way to stop UV reaching their skin cells,
and a physical obstacle like hair or feathers is ideal.
But if you're as hairless as a hippo,
how do you protect yourself from the damaging effects of UV?
One tactic is to spend the day wallowing in mud and water,
although it's hard to completely submerge such a big body.
So there's always a bit of skin in the full glare of the sun.
But hippos never get sunburnt.
And the reason why was only discovered 20 years ago.
When exposed, the skin produces thick red droplets
from the dermis known as blood sweat.
And if I zoom in, I can really see that here.
Now, when scientists analysed this blood sweat,
they discovered it's not blood or actually sweat,
but instead is an oily mixture of
water repellent, antibiotic and a UV-blocking chemical
that turns red in sunlight.
Basically, hippo skin produces its own sunscreen.
Another iconic resident
of the African savannah is the giraffe.
It can survive in temperatures most other mammals can't cope with.
And it's only recently that scientists have discovered
those spots, as well as being a striking pattern,
perform a surprising function in keeping giraffes cool.
If you look at a giraffe through a thermal camera,
you can see the spots glow brighter than the background hair,
as they are giving off the most heat.
Each spot has a large blood vessel around the outside
and a network of smaller ones in the centre,
which carry excess body heat to the surface of the skin,
helping to cool the giraffe down.
They also have another adaptation that keeps them safe in the sun,
and to witness that, I need to join them for lunch.
Would you like a go? Yes, please. There you go.
You can see on Setanta here that his body is covered
with this lovely, thick, dense coat.
But there's one part of his body that's hairless
that spends a lot of time in the sun.
His tongue.
Now, giraffe tongues are really flexible
and can be up to 50 centimetres in length.
And in the wild, they use them
to strip the leaves of trees like acacias.
But in order to protect them from the harmful rays
of the sun
the outer layers are filled
with this very dark pigment called melanin.
And it's this that gives the tongue its purply black colour.
All kinds of vertebrates produce melanin,
a pigment made by specialist cells in the epidermis
to shield themselves from UV.
Scientists now know that even migrating blue whales produce
more melanin every summer, getting darker-skinned
as they migrate south to sunny waters to breed.
Melanin also gives human skin its colour.
The more melanin your skin has, the darker you are,
and the better protected from UV.
Melanin is produced by cells
called melanocytes in the epidermis.
Our direct ancestors, living in the blazing sun
of equatorial Africa some 2.5 million years ago,
needed all the melanin they could get.
And for human populations in sunny parts of the world,
that's still the case.
But there's a trade-off.
We need some UV to reach our dermis
in order for us to be able to make vitamin D,
which is essential for healthy bones.
UVB rays
from the sun turn a chemical in your skin into vitamin D3,
which is then carried to your liver and then to your kidneys
to transform it to active vitamin D.
The human skin colour variation
we see today is our skin's response
to this love-hate relationship with UV.
A trade-off between the skin as protector
and as a factory for making vitamin D.
Now, you can tell just by looking at me,
there's not a huge amount of melanin going on here.
I'm from Norfolk, born and bred.
I'm practically transparent.
What this means is that while my pale skin is great
at making vitamin D by letting in enough UVB,
it needs help protecting me from letting in so much that I burn.
To get a really accurate idea of how much
melanin I have in my skin,
we're using a UV camera.
This filters out the visible light from an image,
so all that is recorded are the ultraviolet rays.
Anything that absorbs UV, like melanin or the special coating
on my glasses, appears darker.
As you can see, I've got a few patches around here
where my poor skin has produced a little extra melanin,
but it's not much in terms of protection from UV.
So I need sunblock to replicate the protection
that darker-skinned people
get from their naturally-produced extra melanin.
OK, here goes.
I'm going to put a good amount
on one side of my face
and see what protection...
..that gives me.
Get the ears in.
And as you can see, one side of my face
is beautifully protected from the effects of these UV rays now.
Although I may have put the sunblock on
a little too enthusiastically.
Skin has devised impressive ways
of protecting animals against the worst
the physical environment has to offer.
But there are other threats out there from living organisms
that want to get in.
We are not alone.
We share our world with a whole host of viruses, bacteria and fungi.
But we don't think about them very often,
because they're too small to see.
Our skin does everything it can to keep them out.
Dr Jim Spencer is going to look for them for us.
I'm not entirely sure I'm looking forward to this.
A few days ago, I left my fingerprints on some agar jelly,
a substance used by scientists to help grow bacteria.
Now, I'm back to see the results.
So, Jim, I'm not going to lie, I'm a little bit nervous
about seeing what you're found on my culture.
What have we got? Well, let's have a look.
Oh, Jim, that's awful. It really is.
I can see roughly where my thumb was, and some vague places
where my fingers were.
There's loads, there's so much stuff on there, Jim.
The first thing is that everybody has a lot of bacteria on their skin.
So around ten million bacteria per square centimetre
of skin surface.
So it's not surprising that
we've grown a fair amount of organisms here.
There's a lot of diversity on here, as well.
Is there any way of telling what we might have here?
We can make some guesses based
on how the bacteria appear on the plate.
So, for example, this white one down here,
that could be a Staphylococcus epidermidis,
which is something that is pretty much ubiquitous.
Everybody will carry that on their skin.
Though harmless on the surface of our skin,
Staphylococcus epidermidis is thought to be
responsible for around 20% of post-operative infections,
when it enters the body through contaminated medical devices.
The yellow ones could be micrococci,
which again, are very common.
After that, it gets a little bit more difficult.
There've been studies that have identified over 150
different species of bacteria
in a single sample from a single human hand.
Jim, you're not looking too worried by my results here.
Should I be worried by this?
I don't think so.
We've got to remember that most of these bacteria
are either harmless, or actually positively beneficial.
For many of these tiny organisms,
an animal's body represents an ideal home.
It's warm, secure and has lots of raw materials.
They want in.
And while most microbes might be harmless,
there are others that are anything but.
For vertebrates, skin is the first line of protection against disease.
The epidermis presents a physical barrier to microbes,
but one group of animals
needs to give that outer layer a helping hand.
Amphibians, like this poison dart frog,
get oxygen through their skin,
so it's thin, moist and permeable.
All these factors make it incredibly vulnerable to infection
by bacteria and fungi, particularly as most amphibians
live in warm, wet places.
Frogs have launched a chemical war of retaliation against microbes.
Their skin secretes a cocktail
of antibacterial and anti-fungal peptides.
Chemicals so effective that the latest science now shows
potential for the development of new drugs to treat sepsis,
autoimmune diseases and even Type 2 diabetes.
Whatever cool moves vertebrate skin comes up with to prevent infection,
microbes always have a countermove.
It's a constant evolutionary arms race.
Skin versus the world.
If skin is too well defended for microbes to get
through it on their own,
then they need to find another way in.
And one such way is through skin penetration experts,
like blood-sucking insects.
Because vertebrate skin comes in so many thicknesses and types,
biting insects have evolved
to breach the defences of specific animals.
They've developed host specificity.
And apparently, the best way for me to demonstrate this
is to donate some blood.
Professor James Logan is an expert in insect-borne diseases.
What have we got here?
Well, we've got two different types of insect, biting insects.
I can see they're mosquitoes.
Yeah. These ones are aedes aegypti.
So these are the ones that transmit yellow fever, dengue, Zika as well.
And I've chosen these ones because they're highly adapted
to feeding on humans, and they're very hungry.
I've made sure they're hungry just for you.
Well, I'm happy to look but you want me to stick my hand in?
I want you to stick your arm right in.
That's the only way to experience this and see how they feed.
So can you stick your arm in there?
You're very brave. Very silly.
There we are.
James, they're straight on.
You can see, there's quite a few on there, there's probably about ten.
That's pretty fast, isn't it? Yeah.
Yeah, I'm quite surprised how quickly they've descended.
This is exactly how they've evolved.
So they've evolved to come in, steal your blood
without you even knowing it.
Their mouth parts are so fine that they're able to pierce the skin.
What they also do is inject saliva,
which has an anaesthetic so you don't feel it.
And also an anticoagulant, so your blood doesn't clot.
Well, James, I have had more fun, I'm not going to lie.
Really? Yeah.
But the weird thing is, I didn't, I'm going to feel it later, I know.
There'll be welts all popping up,
but I didn't feel it when they were biting.
You feel the tickle of the legs, but it's so gentle in that respect.
But they're not all like that, are they?
No, they are absolutely not all like that.
So we have these stable flies, bigger mouth parts.
Do you want to try that?
I'll be honest with you. I wouldn't do it.
Really?
I thought this is what you do! No, no, no.
But I think you've already signed up to this,
so there's no going back now.
They kind of look like house flies, don't they?
But the mouth parts are a little bit different.
So a housefly has sort of spongy mouth parts
that allow it to sort of suck up moisture.
These guys have much harder mouth parts, like little saws,
and that's so that they can get through some really tough skin.
So they will mostly feed on horses, cattle,
bigger animals.
If they can go through a horse,
they're going to rip through me, aren't they?
Yes. It probably will be a little bit more painful.
I'm actually quite nervous, James. Are you? Yeah, a little bit.
Oh. There we are.
Oh, and they're coming straight in!
So there's lots of stuff that activates flies to bite.
Heat coming from the skin, moisture coming from the skin,
carbon dioxide being released from the skin,
and other chemicals as well.
So there's one there.
Ow! Do you feel that? Yep.
Oh! I'll feel that one again.
Argh! This is the other thing, I can see what it's doing.
It's not just going in once, it's going in several times.
That's it, the same one. It doesn't hurt, then it does, then it doesn't.
Right now it's hurting again. Yeah.
You can imagine their mouth parts are gyrating like this,
like saws cutting through the skin,
and getting in and sucking up the blood.
Can you feel that? Oh, she's... Ow!
That's on the underside I can definitely feel that one.
I think that's probably enough time in there.
There is a serious point to this.
Studying what attracts insects to bite humans
is pioneering the research into finding a cure
for some of the world's most devastating diseases.
And the answer may well lie in the scent of our skin.
It all comes down to the way you smell.
So when you put your arm into those cages,
that was the thing that was really driving that behaviour,
that response to land on you, to feed.
It has to be the right cue.
These ones will preferentially be attracted to human odour,
whereas these guys would rather feed on cows.
And so, they find the smell of a cow much nicer than a human.
People who don't get bitten very much by biting insects
are producing different chemicals in their body odour.
So their skin is producing something
a little bit different, and it puts them off.
So it's actually natural repellents.
We've identified those repellents.
We now know as well it's controlled by our genes.
So we're now trying to identify the genes
that control the production of natural repellents
by the human body.
One day you might be able to take a pill when you go on holiday
that would up-regulate the production of natural repellents
by the body, and totally change the way that we repel mosquitoes
and protect ourselves against diseases like malaria.
Malaria causes half a million deaths a year around the world.
How amazing that the key to protecting humans against it
may lie in the smell of our skin.
When it comes to keeping animals safe
in an ever-changing and hostile world,
skin is an incredible, multi-purpose shield.
From thick fat to dense hair
and even slimy barriers,
skin has adapted to protect vertebrates
from whatever the world throws at them.
Next time, I'll uncover incredible new science
about puffins and their beaks,
witness a deadly snake
send me a warning signal without opening its mouth,
and learn to read the colour-coded messages mandrills
send to each other through their faces,
to reveal how skin has evolved to allow animals to communicate.
Skin.
We all have it.
And so does every vertebrate on the planet.
It keeps the outside out,
and the inside in.
Animals may look very different on the surface,
but we all share the same basic skin blueprint.
I'm Ben Garrod, Professor of Evolutionary Biology.
And I'm fascinated by this often overlooked wonder of nature.
It's not just the case that he's hairless...
..the skin's totally different.
Now, ground-breaking new science...
This is really quite remarkable.
It should be a game-changer for so many people.
RATTLING That sound! Oh, it
makes the hair at the back of your neck go up, doesn't it?
..is revealing skin's mysteries.
It really transforms our understanding of dinosaurs.
I'm going to explore the natural history of the body's largest organ,
to see how skin has allowed animals to conquer every habitat,
disappear into their surroundings
and develop extra-sensory abilities.
We're even discovering the complex ecosystem living on OUR skin.
Oh, Jim, that's awful.
It really is!
In this episode...
I'll uncover incredible new science about puffins and their beaks,
witness a deadly snake send me a warning signal
without even opening its mouth,
and learn to read the colour-coded messages mandrills send
to each other through their faces.
To marvel at how skin has evolved,
allowing animals to communicate...
..I'm going to reveal the secrets of skin.
Animals communicate through smell,
colour,
touch,
and sound.
And their skin has adapted to help them do just that.
I'm starting with a very familiar primate...
..ring-tailed lemurs, which use the smell of their skin
to figure out who's who and what's what.
With their distinct black-and-white markings and those unmissable
stripy tails, ring-tailed lemurs are hard to tell apart by sight alone.
So they've evolved a language of smell.
And it's the males I'm really interested in.
I love that classic lemur pose!
So, I've come to Twycross Zoo to get close to a group of captive males.
The one behind you is Zac.
So, he's got a very dark face.
And then we have got one, somewhere...
Here he is! So, Zeus, he's got his little cauliflower ear.
We've also got one with a shorter tail, so, this is Zazu up here.
While Kirsty - their keeper - can identify a few of them by sight,
lemurs use a totally different way of recognising one another.
They use scent.
Both sexes have scent glands in their genital regions,
but males have gone one step further and evolved scent glands
on their shoulders and forearms.
They'll use that to scent-mark all of their furniture in the enclosure.
They'll also do it a lot with their scent-marking.
They'll wipe it along their tails.
It's sort of, like, a territorial thing.
The scent glands are oil-producing sebaceous glands,
like we have in our skin.
But theirs have evolved,
and are unlike anything else in the animal kingdom,
producing an entire chemical language.
Scientists have identified over 200 chemical compounds that
make up the scent lemurs produce,
meaning that they can all create a personalised aroma to communicate.
The number of compounds in the scent drops by 10% if a lemur is injured,
something other males can use to their advantage,
by acting more aggressively to the weaker male.
Male ring-tailed lemurs also use their smell to fight.
They rub their tails in their scent glands, and then waft the smell
in the direction of their rivals.
These battles maintain social status while reducing physical aggression.
And their scent decides the winner.
Another group of primates has developed a different way of
communicating dominance through their skin -
colour, of their rump and face.
These are mandrills in Gabon, West Africa.
Charles Darwin wrote, "No other member in the whole class of mammals
"is coloured in so extraordinary a manner as the adult male mandrill."
Primatologist Jo Setchell has
been studying and photographing these mandrills for over 20 years.
Jo, I love these animals, one of the most recognisable members
of our primate family. Aren't they fabulous? They really are.
They have these remarkable red and blue noses.
And they're using this red and blue skin
to communicate with one another. What are they communicating?
Status, essentially.
So, if they can look at the red colour of another male,
decide instantly whether he's dominant -
and therefore, you should avoid him - or he's subordinate.
Then that avoids fights.
So, it pays off to signal rather than to fight it out, I guess?
Definitely, yes. Do we know what's going on beneath the skin?
Right beneath that red skin is blood,
and there's an awful lot of blood vessels, vascularisation.
And so the red of the blood is seen right through the skin.
Unlike humans, whose skin colour comes from melanin,
that intense red of a male mandrill's face owes itself
to oxygenated haemoglobin in blood vessels close to the skin's surface.
The blue colour is formed
by the structure of collagen within the dermis.
And it's aligned in a way that scatters the visible light,
which we see as blue.
So, here we have another adult male, and the first one was also
an adult male, and their red skin is extremely similar.
What that skin is saying is that they are of very similar dominance.
When there are two that are so similar...
..there must be issues with that? Yes.
So, these are the sorts of males that will fight with one another,
presumably because they can't tell easily from the red skin
who is dominant over whom.
Colour communication for male mandrills
can be a life-saving strategy.
Those canines are among the largest of any primate,
reaching up to 5cm in length.
They can inflict serious injury, and even death.
So fighting is a last resort.
These two males, of similar colour and status,
both want the right to mate with the females.
Only one will be victorious.
And a surge of testosterone, which causes the blood vessels
to dilate, will make his face even redder and more attractive.
And if you're the male who reaches the top of the pecking order...
..your face says it all.
He is impressive! He must be top dog?
He is. This is an alpha male, the most dominant in the group,
and has been for enough time for the red colour to move up into his eyes.
These animals live in groups of hundreds -
how many will reach this status?
As far as we know, there's just one who looks like this.
Once you hit this level,
what happens with the interactions between the other males -
the ones that ARE brightly coloured, but not like this?
Any male that is not this brightly coloured will stay away.
Primates may use colour, and even smell,
produced by the skin to communicate.
But when it comes to darker environments, with poor visibility,
one unique group of fish has evolved some really fascinating ways
to send out a message with the help of their skin.
This is a black ghost knifefish.
At first glance, it might not look very impressive -
it isn't brightly coloured, it doesn't have amazing spines,
or anything like that - in fact, it's just black
with a couple of white stripes and a rather impressive-looking frill.
But this little South American fish, thanks to its skin,
is almost able to defy the laws of nature.
Black ghost knifefish have evolved
a highly specialised way of communicating -
they use electricity.
There are more than 30,000 species of fish on the planet,
but only around 350 can produce their own electric field.
Strongly electric fish, like electric eels and some rays,
produce an electric discharge of up to 800 volts,
strong enough to stun their prey.
While weakly electric fish, like the black ghost knifefish,
produce less than one volt, and use this to navigate and communicate.
To show me just how they use their skin to do this,
PhD student Sarah Skeels has set up an experiment.
In the tank, there is a single fish, and a pair of electrodes
to pick up its electrical signal.
These are connected to a special amplifier which converts
electric signals into sound.
QUIET BUZZ
It doesn't sound much, but that's
the auditory representation of the field this little fish is making?
Exactly. So, they produce a continuous sine wave,
and that's what we're hearing, those tonal changes.
And it may be quite subtle, but it allows them to get more information
from what's in their environment.
Every time he moves away from his little branch, it changes slightly.
And every time he comes back, again the tone changes.
Black ghost knifefish have an electric organ running down
the length of their body, which is made up of modified muscle cells.
Each of these cells discharges a small amount of voltage,
producing the constant electric field around their body.
But it's the receptor cells in the skin that actually receive
this electric charge, allowing the fish to sense
their surroundings and communicate.
And is that why we're seeing this really weird anatomy?
They're typically called scaleless fish, but they actually have
very tiny scales. And this is an important thing,
because if they had lots of big scales, they'd just interfere
and the signal wouldn't be able to go very far.
It's the communication between two fish that I'm really interested in.
They have very poor vision, so it's their electric fields
which allow them to sense one another.
So, the moment you put the second fish in...
..you can hear there's something different with that tone. Yeah.
So, it's a combination of both of their signals that we can now hear.
And it's really interesting that every time they came closer
to one another, every time they're near one another,
you get this difference in the sound being generated here. Mm-hm.
As well as interpreting the electric signals as audible sound,
Sarah has an oscilloscope, which
displays a graph of the electric voltage being produced by the fish.
So, you can see on the top left, this trace is from one fish. Mm-hm.
And the bottom trace is from two fish.
So, you can see on the top one, when there's only one fish,
it's quite regular.
But if you see on the bottom,
there's a lot of distortion here and here,
where the signals from both fish
are combining and creating some kind of interference.
So, are they trying to outdo one another?
Are they trying to talk to one another? What's going on?
So, electric communication can be used for a number of roles.
So, here, we think we have a male and female,
and it could be used to elicit courtship displays.
But it can also be used to decide on territory,
who has - in this example - the pieces of wood.
It's not just two fish, effectively, trying to outshout one another.
There's something more going on here, isn't there?
They can produce something called the jamming response, where
they will change their frequency so both of them can signal
without interrupting the other.
This jamming response only occurs when fish of the same species,
with similar electric frequencies, get too close.
They change their signal so they can both still communicate
and navigate their surroundings.
So, it's their way of finding a method for both being able to
be near one another without losing this ability to sense their world
around them, while still communicating at the same time?
Exactly. It's very complex, isn't it?
Yeah, and the electroreceptors are absolutely key on the skin.
Without them, they wouldn't be able to do this kind of behaviour.
Using the skin to communicate via electric signals is very subtle.
But for much more obvious communication,
many animals have evolved to use colour.
From chameleons, who can change
the colour of their skin to show their mood...
..to sarcastic fringeheads, whose gaping, vibrant mouths
act as a warning signal to help defend their territory from rivals.
But nowhere is it more readily seen than in birds.
There are over 10,000 species of bird,
and their feathers represent a huge range in the colour spectrum.
Feathers are made from keratin,
a protein formed in tiny follicles in the epidermis.
Like in reptiles, mammals and fish, birds can be different colours
because of the pigments contained in their skin
and the way in which the keratin is structured.
The most widespread colour-producing pigment found in nature is melanin,
and it creates the darkest colours - blacks, browns and greys.
Melanin is produced by melanocytes,
specialised skin cells located in the epidermis.
And it can be seen in action in this golden plover feather.
These spots and stripes are perfect adaptations
for allowing the bird to almost disappear in its surroundings.
It's a great example of feathery camouflage.
And in terms of what it's saying to the world around it...
Well, it's pretty much, "There's nothing to see here."
Another type of pigment found across the animal kingdom are carotenoids.
Most of the reds, oranges and yellows seen in bird feathers
are coloured by these chemical compounds.
But, unlike melanin, they are not produced by the skin,
but obtained from the food the birds eat.
Carotenoid pigments are then
transported through the skin to their feathers.
Once in place, they absorb mostly blue light to produce
the orange, red and yellow colours that we see in these feathers.
You can see the carotenoids have clearly coloured
these little goldcrest feathers a fiery orange.
And this one is definitely
not trying to blend in with its surroundings.
It's from the cap of a male, and during the breeding season,
these little caps flash orange, yellows and golds.
And they're trying to say,
"Stay away, this is my territory."
As for the iridescent colours found in birds, they're not caused
by pigments in their skin, but by the structure of the feather itself.
Keratin within the feather is aligned in such a way
that it allows light
to twist, turn and separate into a rainbow of colours.
This feather is from a male peacock.
He's trying to say his genes are amazing.
He can waste energy in these big, bright, ostentatious feathers
because his genes are that good.
Basically, he's telling every other female in the area,
"You should mate with me."
From understanding how feathers are coloured in modern-day birds,
a whole new appreciation
of colouration in extinct species has been possible.
Advances in research over the last ten years or so have transformed
our knowledge of dinosaurs, allowing a deeper focus on
fossilised feathers, and a greater understanding of how colour is
produced - right across the animal kingdom - is making this possible.
Palaeontologist, Professor Mike Benton, is showing me
a fossilised feather under a scanning electron microscope.
He and his team made a breakthrough when it was discovered
that the shapes embedded in the fossils were melanosomes.
Melanosomes are made in melanocytes,
which are the melanin-forming cells found in the skin.
They're the site of synthesis, storage and transport
of melanin pigments, and provide tissues with colour.
In some of the fossils, we find these kind of sausage-shaped ones.
In others, we find spherical ones or ball-shaped ones.
And looking at evidence from modern birds and modern mammals,
we discover there's an exact correlation between the shapes
of the melanosomes and the colours that they have.
Every time we looked at a hair or a feather from a modern creature
where we know the colour, we found the sausage-shaped melanosomes.
You either get black if they're very tightly packed,
brown if they're more loosely packed, grey,
all the way through to blonde, where there's not very many at all.
And when we looked in modern feathers and hairs, say, from
a ginger-haired person, we found the other kind of melanin,
which is chemically different, and it gives only ginger colours.
And that corresponds to this kind of ball-shaped melanosomes.
Does that mean we're seeing browns and greys and whites,
and even gingers, in some of our dinosaurs?
Yes, and I think this has completely revolutionised
the way we see dinosaurs.
Dinosaurs were clearly more colourful than scientists
once thought, and it's not just blacks, browns and even gingers.
Fossilised remains indicate that dinosaurs had much the same
range that we see in birds today.
The fact that you get the same relationship
between colour and melanosome shape
in all the birds that people have looked at, and in all the mammals,
means that, probably, this is a general rule of nature.
And colour is only half the story.
From the fossil evidence,
Mike and his team have discovered patterns, as well.
They've been able to piece together
traces of different shaped melanosomes,
and create a more accurate image
of what a dinosaur would have looked like.
This is Sinosauropteryx.
We were sampling across the body, along the tail, and across the head,
and so on, and we were able to show very definitely that it has
these ginger and white stripes.
So, the first thing was we only found the ball-shaped melanosomes,
therefore, all ginger - we couldn't find any hint
of the sausage-shapes or black or brown colours.
And, in the areas showing white, we were finding no melanosomes.
What was Sinosauropteryx doing, what was his colouration for?
At first we saw the stripes, and we thought,
"Well, could it be camouflage?" I mean, that's a big function
of colour, of course, we think of tigers and zebras, and so on.
But the fact is the stripes don't occur across the whole body,
so it's not likely you would simply camouflage your tail.
So, the other function that seemed quite obvious would be display.
And, of course, a tail is a perfect display organ.
And, presumably, whoever had the brightest, longest, stripiest tail
probably would win the most mates.
Colour is one way to communicate using your skin.
But for more aggressive signals,
skin has evolved to produce its own sound.
HISSING
This is a desert horned viper.
I love this little snake, absolutely incredible!
But I'm not going to get any closer because it's venomous.
And, actually, more than that...
..this little snake is deadly.
And what I really love about this snake...
..is that noise.
STEADY HISSING
Right now, I'm being told, in no uncertain terms,
"Stay away."
"Get back, or else."
Desert horned vipers live in the Sahara, in North Africa.
They're sidewinders, and are
the most abundant and venomous snakes in this region.
Like all desert vipers, they've evolved to communicate through
their skin, telling anyone who can hear them that they are dangerous.
To do this, they have keeled scales,
which they use to produce a hissing sound of their own.
HISSING
He's arranging his body into a series of parallel S-shaped curves.
And once he's done that, he's rubbing these lateral scales,
the ones down the side of his body, against one another.
And that is how he's making this noise.
Keeled scales, unlike the smooth variety found in most other snakes,
have a ridge running down the centre line.
This gives the added advantage
of reducing the shine of the snake's skin,
helping with camouflage and keeping it out of harm's way.
It's a great natural deterrent.
In the wild, predators know to keep their distance, and this allows
the snake to keep its precious venom it can use to catch its prey.
Sound can be an effective way to convey a warning,
but some noises in the animal kingdom aren't created by skin.
Many animals have a voice box which, like in humans, is often used
to produce a wide array of sounds.
The furthest a human can project their voice is about 180m.
But one primate uses its specially adapted skin to throw its voice
more than ten times that distance.
GIBBONS CALL
And I've come to Twycross Zoo to take a closer look.
These beautiful animals are siamangs.
They're the largest of the gibbons,
and actually, one of the loudest animals on the planet.
They're not making a huge amount of noise right now
because they're having their breakfast, but when they call,
you can hear them from over 2km away.
And, if I was stand next to them,
they'd be louder than a rock concert.
SIAMANGS CALL
In their forest homes of Southeast Asia, visual gestures would be lost
in the dark canopy of the trees, so loud vocalisations play
an important role to fend off neighbouring siamangs.
And they can only do all this because of their skin.
They've got these incredible large inflatable throat sacs
that really helps throw their voice as far as possible.
It's the elastin and collagen within the skin that allows
the siamangs to inflate their throat sacs to the size of their heads.
But this skin doesn't get in the way when they're NOT calling.
Thanks to its physical properties,
the skin is able to spring back to normal when not in use.
The animal kingdom has evolved so many amazing ways to communicate
that we are only still just scratching the surface.
But brand-new science has changed our understanding
of how one little bird communicates using its skin.
The puffin.
Jamie Dunning is an ornithologist,
and he's been working with birds for over ten years.
Jamie, these are such amazing birds, they're instantly recognisable,
and they're one of our most-iconic seaside species.
And it's all down to this beautiful, vibrantly coloured beak.
But there's so much going on behind the scenes here, isn't there?
Yeah. So, the beak is almost certainly a big, kind of, ornament,
a flag to suggest fitness and sexual selection,
and help them choose mates.
Both males and the females have this beautiful bill.
As with all birds, the puffins' beaks are covered
in the complex protein keratin, which forms a hard outer layer.
Carotenoids have become concentrated in the keratin
covering to give these vibrant colours.
It must be quite difficult, in terms of the energy expenditure, then,
to invest in a bill like this year-round?
This is only half the story. So, you only need this in the summer,
it looks very different over winter.
Well, this is completely different, it's like a whole different
species of bird. Those bright colours are gone.
The majority of that big colourful bill just flakes off over winter.
There's no need for it.
So, we only see those brightly coloured bills in summer and spring,
their breeding months? We do, and that coincides with when we see
puffins, cos they only come to land during the breeding season.
The winter is spent out in the middle of the sea.
Jamie has made a ground-breaking discovery
about the skin on a puffin's beak.
To show me, he's brought a puffin along, which died naturally
and is now part of his study.
Jamie, this is amazing! It's so cool! I mean...
..it's glowing. So, this is fluorescence.
This is the seasonally developed bill.
So, this bit all drops off, including the fluorescent bit.
It's visible with this UV lamp and torch,
but a lot of birds can see UV colour, can't they?
Yeah, that's right. So, we have three types of colour receptor
in our eye, or cone cells - that's red, green and blue -
and we mix those to make all the colours that we can see.
Birds have a fourth, they have tetrachromatic vision.
And that fourth one allows them to see, to some degree, in UV light.
For birds, being able to see UV light has its benefits.
It enables a method of communication
which is invisible to potential predators,
but allows them to find a mate.
As this is the bit that falls off outside of the breeding season,
there's a very good chance that this is something to do with
sexual signalling and fitness and luring in the opposite sex.
It's amazing. These little birds that we kind of grow up knowing
so well actually have a load of secrets in their skin
that we didn't know before.
It's exciting. Until recently, we had no idea about this.
Skin has allowed animals to communicate.
From vibrant colours...
..to sound...
..to electrical sensing...
..the skin does it all.
Next time...
..I'll come face-to-face with a deadly frog...
..learn why rhinos need such heavily armoured skin...
..and find out how, in porcupine quills,
bigger is not always better...
..as I delve into the ingenious ways skin can be the ultimate defence.
Skin.
We all have it.
And so does every vertebrate on the planet.
It keeps the outside out...
..and the inside in.
Animals may look very different on the surface, but we all share
the same basic skin blueprint.
I'm Ben Garrett, professor of evolutionary biology,
and I'm fascinated by this often-overlooked wonder of nature.
It's not just a case that it's hairless,
the skin's totally different.
Now, ground-breaking new science...
This is really quite remarkable.
It shouldn't be a game-changer for so many people.
The sound...
Oh, it makes the hair on the back of your neck go up, doesn't it?
..is revealing skin's mysteries.
It really transforms our understanding of dinosaurs.
I'm going to explore the natural history of the body's largest organ
to see how skin has allowed animals to conquer every habitat,
disappear into their surroundings
and develop extra-sensory abilities.
We're even discovering the complex ecosystem living on our skin.
Jim, that's awful. It really is.
In this episode, I'll learn why rhinos
have the most heavily-armoured skin of any living mammal.
Why the smallest porcupine quills are often the most dangerous.
And discover why cuttlefish camouflage
is transforming the way scientists think about skin.
To delve into the ingenious ways skin defends animals
from physical attacks.
I'm going to reveal the secrets of skin.
This is a member of one of the most toxic groups of animals
on the planet.
She's a yellow-banded poison dart frog.
These tiny frogs secrete a very potent poison
through their skin.
Direct contact with some species
can cause nausea, paralysis...
..and even death.
There are almost 200 known species of poison dart frog
in the forests of Central and South America.
Each one combines toxic skin with vivid colours,
and the more toxic a species, the brighter colours it has evolved.
A single golden poison dart frog has enough poison in its skin
to kill ten people, making it the most toxic animal alive.
These bright colours are a stark warning for predators to back off.
But if a hungry bird does decide to ignore this warning
and takes a nibble, then it won't be making that mistake again.
Each frog species deploys a different range of toxins
but they all belong to a group of chemicals called alkaloids.
The frogs don't make these toxins from scratch.
They're derived from defensive chemicals in the ants,
beetles and millipedes they eat.
The toxins are stored in glands in the dermis
and released onto the surface via pores.
Poison dart frogs are active during the day
when predators can spot their warning colours and avoid them.
Most other frog species tend to come out at night.
These frogs got their name because their toxins were once used
by forest hunters to tip their darts.
Today, we're finding other uses for them.
Now scientists are studying the deadly chemicals these frogs deploy
in order to design new painkilling drugs and medicines.
One toxin, epibatidine, attacks nerves,
causing numbness and paralysis.
Researchers hope that by unpicking epibatidine's structure
and chemistry, they may be able to separate its beneficial
painkilling effects from its deadly toxicity.
Right, you.
Back in your tank.
Now, you might think this is a very silly thing to do.
But captive bred dart frogs...
..aren't toxic at all.
Frogs bred in captivity are fed harmless insects like fruit flies,
which means they never go on to develop the dangerous toxicity
of their wild relatives.
What we still don't fully understand is how wild frogs can eat
and store these toxic compounds without coming to harm.
A poison dart frog's skin is a weapon and a warning.
This is just the start of the extraordinary ways
animals use their skin to defend themselves.
One animal is infamous for the warning sound it makes
with a specialised part of its epidermis.
This is a rattlesnake's rattle.
It's made from the final few scales that cover the tip
of the snake's tail.
They form a series of hollow interlocking segments of keratin -
the same protein as my hair and nails.
The segments aren't fused to one another.
They're free to move.
So if I give this little structure a good shake...
The interlinked capsules rattle against one another.
Rattlesnakes shake their rattles to produce a loud buzz.
This alerts livestock and predators that there's a venomous snake nearby
that wants to avoid trouble.
Now, I can manage...
..a couple of rattles a second.
That's not really enough to grab anyone's attention.
To see how a rattlesnake uses the keratin on the tip of its tail
as a brilliant defence mechanism,
I need to find a way to shake it much faster.
I'm visiting an engineering lab to get help
from the reassuringly titled Lecturer in Non-destructive Testing,
Dr Rob Hughes.
Hey, Rob. What have we got here? How are we going to test this?
So, here we have a vibration stage. Now, this works in the same way
that a stereo speaker does,
so we can therefore essentially excite something up and down
at whatever frequency we want.
We do that using this function generator here,
through an amplifier, to then get sent to the speaker.
Using Rob's set-up, we'll be able to shake the rattle much faster
than I could do it myself.
This will allow us to find the right speed
to get the best sound out of these keratin capsules.
I thought we'd start out by moving it at five times per second.
That's 5Hz.
So, if we send the impulse signal in and start vibrating.
You can see that not much is really happening.
But what we can do is cycle through the frequencies,
increasing the pitch. OK.
Erm, so...
RATTLE GETS FASTER
So this is 10Hz, so ten times a second.
And then we're going to ramp up with more now.
So we'll go to 20.
Oh, we're already... Starting to sound like it.
Sounds like a rattlesnake, but it doesn't sound like
an angry rattlesnake just yet. That's a slightly disgruntled snake.
Depends how angry you want it to be. This is 30Hz.
RATTLE GETS FASTER
40Hz. Oh, it's getting there.
And 50Hz.
OK, it looks like a rattle from a rattlesnake now.
That weird, disjointed, chaotic rattle.
But that sound...
Oh, it makes the hair on the back of your neck go up, doesn't it? Yeah.
With the clamp vibrating at 50 times a second, replicating the action
of specialised tail-shaker muscles, the fragile capsules of skin
reach their full potential.
The warning is loud and clear.
It's done its job.
There is absolutely no doubt right now that if I heard that
in the wild, I'd be stepping away.
That's a rattlesnake to me.
While a rattler's noisy warning helps keep hunter and hunted apart,
some animals' skin defences are shaped by close contact.
Rhinos are some of the biggest animals on the planet,
reaching at least a tonne in weight.
They also have the most heavily-armoured skin
of any living mammal.
Thick armour, up to four centimetres in places,
combined with a huge body size and a top speed of 50km per hour,
makes them all but invulnerable to predators.
Of the three species living in Asia and two living in Africa,
the African white rhino is the largest and best-defended of all.
I've come to see this armoured skin close up
with the help of rhino keeper Mark Godwin.
Mark, he's blown me away. This guy is huge. Look at him.
What's this one's name? This is Monty.
He's about three and a half tonne. He's over six foot to the shoulder.
If you want to have a stroke, feel free.
OK, I can instantly feel there's no give here.
This skin is, it's covered in mud, but this is incredibly tough skin,
it really is.
Do we know how thick this skin can become on Monty?
It's supposed to be about to an inch and a half thick.
So you're talking four centimetres of skin there.
That is an impressive animal.
With an epidermis of only about one millimetre thick,
Monty's skin gets its strength and thickness
from densely-packed layers of collagen fibres in the dermis.
Now, in the wild, I can't imagine even the most determined bunch
of lions and hyenas are going to try and take Monty down.
His main threat, really, is other rhinos.
So most of the armament and that is for dealing with other bulls
when they come into contact over females.
Rhinos charge each other, using their horns as battering rams
in battles over territory and mating.
Researchers believe this aggressive behaviour has driven the evolution
of the rhino's thick armour.
It's far tougher than it needs to be to simply fend off predators.
Even if you just look at the way the legs are formed - the front legs
are very heavy, so it's all protection around the front.
They tend to like to face their problems,
so that's where the thicker, denser skin develops.
It's helping him get territory, helping him be a big dominant bull,
just by the thickness of the skin.
While adult rhinos are protected against all-comers
by their thick armour, it's a different story for calves.
Mark, these are lovely. Who have we got here?
This is Ruby and the little one is Stella.
She's about ten weeks old now, coming up.
And I guess being this small and having skin that's, well,
nowhere near as thick as Mum's, she's, in the wild, vulnerable.
Definitely. And that's why the mums are as possessive as they are.
Once they get to full size, really not much can touch them,
but, when they're this size and separated from Mum,
they're very much at risk.
Stella's skin is probably about a centimetre thick,
and while that's five times thicker than a ten-week-old human baby's,
it's nowhere near thick enough to protect her from predators,
so rhino mothers have to be vigilant.
What sort of predators would have a go at a baby rhino like Stella
in the wild? Lions, hyenas.
It would have to be the big ones or organised ones.
They'd have to deal with Mum as well. Yeah.
Obviously, while she's with Mum, she's very well protected,
but if anything happened, she got separated,
she would be at her most vulnerable.
It's an incredibly rare event and even more rarely witnessed,
but predators that hunt in groups, like hyenas or lions, are the only
animals that will even attempt to tackle a rhino mother and calf.
It takes around two years for a rhino calf to grow thick enough skin
and a big enough body to be able to defend itself
and finally leave its mother's protection.
Some babies are well defended from the day they're born.
In the forests of Madagascar's east coast,
a mother tenrec is leading her clutch of babies
out of the nest to forage for insects.
Their stripes help them hide in the dappled light of the forest floor.
They may look small and vulnerable, but the skin on their backs
is a forest of sharp black and yellow spines.
Their mother has them, too,
but they're hidden by her longer hair.
The babies were born without spines
but started to grow them in the first 24 hours after birth.
Tough and sharp, each spine is a modified hair
made of keratin and growing out of the skin.
And they're an excellent form of defence.
If a predator tries to bite a tenrec,
they get a mouthful of spines as a painful deterrent.
Spines and quills are such an effective weapon
that they've evolved several times in the skin
of different families of vertebrates in different parts of the world.
Hedgehogs are found across Europe, Africa and Asia.
In Australia, you get echidnas.
But, for me, the champions are porcupines.
There are two families of porcupine.
New World porcupines, found in North and South America,
and Old World porcupines, found in Europe, Asia and Africa.
In both families, the backs and sides of the porcupine
are covered with thousands of quills.
If a predator gets too close, they erect and spread the quills,
turning so their dangerous rear ends face the would-be attacker.
Even an expert hunter like a leopard,
capable of taking down a 900kg eland,
is no match for 30kg of well-defended porcupine.
Not only do porcupines have these long, strong quills
growing out of their skin, but they've evolved to be detachable.
And just like hair, they fall out from the skin
without harming the owner at all.
If a porcupine impales an attacker,
the lost quills will grow back in a matter of months,
while the predator learns a valuable lesson.
African porcupine quills are big and impressive
and they cause lots of damage to any would-be attacker.
I can demonstrate this with a piece of chicken.
Because when I stab the pointy end into the chicken,
it goes in nice and easily,
but also it comes out nice and easily, too.
When a predator like a lion is impaled by an African porcupine,
grooming by a pride member can often help remove the quills,
allowing the wounds to heal.
Here, I've got three quills from a North American porcupine.
Compared to the African quills, these look a bit underwhelming.
They're finer and much shorter.
But appearances can be deceptive.
And when I stab this quill into the chicken...
..it goes in nice and easily.
But when I try and pull it out...
..it's embedded.
It's stuck fast.
And, actually, to remove the quill...
..I've really got to pull it.
RIPPING SOUND
And you could hear the flesh tearing as I ripped this out.
It's not nice.
This is happening because North American porcupine quills
have backward-facing microscopic barbs,
as you can see here in this electron micrograph.
The barbs do two things.
They snag on muscle and skin, making the quills hard to pull out.
But research in 2012 revealed the barbs also halve
the penetration force needed to get the quills into the flesh.
Every year, many hundreds of North American dogs
learn about the dangers of barbed porcupine quills the hard way.
Using your skin to defend yourself can be extremely effective.
But concocting deadly skin toxins, carrying heavy armour
and dropping and replacing quills take time and effort.
Over millions of years, some vertebrates have evolved
a cheaper and more sophisticated way of staying safe.
Camouflage.
Hiding in plain sight, using their skin as a disguise.
Hair, feathers and skin can all help animals
blend into their environment.
How effective that camouflage is depends on who's looking.
Unless you're very, very lucky, you've probably only ever seen
a tiger in a zoo or wildlife park.
And against this sort of backdrop,
it's hard to imagine how such vivid stripes
could ever act as camouflage.
In their natural environment, the disguise is a bit more effective,
but there's still no mistaking a deadly predator.
But look at the world through a prey animal's eyes
and a tiger's camouflage finally makes sense.
Chital deer, the tiger's main prey,
have what is known as dichromatic vision.
They can't tell the difference between reds and greens.
So, to a deer, the predator blends into its background perfectly.
This makes it easier for the tiger to get within striking distance.
There's only one flaw in the tiger's strategy.
Chital herds are often found with groups of langurs.
The monkeys drop fruit as they feed.
But that's not the only reason the chital stay close.
Langur monkeys have full colour vision.
Chital have learned to recognise langur alarm calls
and run for their lives.
HOWLING
The tiger's cover is blown.
If those pesky monkeys are giving the game away,
why don't tigers go the whole hog and just have green hair?
That's because mammals, including humans,
use melanin to colour their epidermis and hair
and melanin can only make blacks, oranges and browns.
Only one group of mammals has mastered the art
of green jungle camouflage - the two and three-toed sloths.
These slow-moving mammals have green hair,
helping them blend in to their forest home.
But that colour isn't made by the sloth's skin.
It comes from tiny green algae that colonise their hair.
Each strand has cracks in it, which trap the moisture
the microscopic plants need to grow.
Moths living in the sloth's hair even help to fertilise the algae
with their nitrate-rich faeces.
Evolving camouflage skin to help you blend in to a particular habitat
is pretty impressive,
but some animals have taken a revolutionary next step.
I've come to Plymouth to find out more
from marine biologist Alix Harvey.
And while the animals she studies aren't vertebrates,
you can't talk about extraordinary skin defences
without including them.
Hi, Alix. Hi, Ben.
Look at these! I love these little animals.
They're amazing, aren't they? They're absolutely fantastic.
So these are the common cuttlefish,
sepia officinalis.
This is a species we find all around the UK.
They're one of the biggest species of cuttlefish we get.
And they're about five months old, these individuals.
I was going to say. I've seen much bigger than this.
These are tiny by comparison. That's right.
So they hatch out from eggs about one centimetre, about this big,
and, then, over their life cycle of about two years,
they get really, really big, up to about this size,
so these are all still, kind of, babies in my eyes.
Alix has cuttlefish in three different tanks.
So we've got sand here, we've got rocks and then we've got seaweed.
So these are all the natural environments
they would experience in the wild.
And, in each tank, the cuttlefish are beautifully camouflaged.
I'm just looking at this little one here
and it's blended in perfectly with the sandy surrounding.
You can really see just how well it's blended in.
It's managed to put some sand on its body
and it's really broken up the outline.
The cuttlefish in tank two, the rocky tank,
has very different skin colours and patterns.
And so you find here, in this rocky kind of habitat,
that they will get a very disruptive body pattern.
It's just slightly different.
And, then, at the end, we've got a much darker one.
So he's really adapted to the seaweed.
And you can imagine if he was sitting in amongst the weeds,
it would be very, very difficult to tell where he was,
particularly as he's actually lifting his tentacles
out of the water in order to disrupt his body
and really pretend to be a piece of seaweed.
Alix's cuttlefish are all the same species,
so how have they ended up looking completely different?
The answer is adaptive camouflage.
A cuttlefish's skin can rapidly change colour
to help it blend seamlessly into its surroundings in the blink of an eye.
One little animal will change from sandy to weedy to stoney,
but how do they do that?
So cuttlefish actually have three different colour-changing cells,
but the ones that allow them to do these different colour patterns
are called chromatophores.
These are basically cells that are packed full of pigment.
Found in the dermis, each chromatophore has muscles
attached to its outer wall.
When the muscles contract, the chromatophore is pulled open
and the pigment spreads out.
When the muscles relax, the chromatophore shrinks down,
compressing the pigment.
So when it's packed really, really tight, it's very difficult to see,
and this allows them to have a nice white colour,
and when it's splayed out, it becomes a nice dark splodge,
and when extrapolated over the whole body of the cuttlefish,
this is what allows them to achieve all kinds of body patterns.
All cephalopods, including octopus and squid, have this amazing skin.
And as well as changing colour, in some species,
it can change texture, too.
Muscles in the dermis push the skin into bumps called papillae,
which break up the outline of the body, helping them to hide.
Why are they hiding? I'm guessing from predators, right?
That's right. They are very soft-bodied animals.
They don't have external hard pieces.
They can't really protect themselves.
So the best thing for them in order to avoid being a meal
for something else is just not to be seen in the first place.
Adaptive camouflage is an amazing defensive strategy,
but there's a conundrum.
A cuttlefish's eyes are on the top of its body.
So how does it gather enough information about the surface
hidden beneath its body to match its colour and texture so well?
So we always used to think this was basically
that they're seeing their environment and then relaying
that information to their chromatophores by their brain.
We now think there may be something even more astounding going on,
which is that they have actually light-sensing-capabilities
within their skin.
Researchers have discovered traces of a protein called rhodopsin
in the cuttlefish dermis.
Exactly the same protein is found in the retina
of a cuttlefish's eyes.
It's a light-sensitive pigment that forms the basis
of cuttlefish vision.
Vertebrates use similar proteins in their eyes.
The research is in its early stages,
but the presence of rhodopsin in the skin
suggests cuttlefish skin may be able to see.
This is something that's very, very new
and we're hoping to conduct some experiments this year,
looking at whether, if they can't see
what the rest of their body's doing,
are they still able to adapt
and colour camouflage to their environment?
If Alix's research reveals that cuttlefish can sense light
and dark with their skin,
then we'll have to completely redefine cephalopod skin
as not just an amazing means of defence
but an extraordinary sensory organ, too.
These cryptic cuttlefish are further proof that skin still has secrets
we're only just beginning to understand.
When it comes to defending yourself from other animals,
skin provides an incredible selection of weapons and armour.
From deadly toxins and piercing quills,
right through to cryptic colouration.
For vertebrates and a few very special invertebrates,
skin will keep you safe.
In the next episode, I'll learn how microscopic bumps
on a crocodile's jaw help it track down prey...
..reveal how understanding the human sense of touch...
is inspiring the design of new robots...
..and how this venomous pit viper's skin
helps it aim its deadly strikes...
..to explore how skin enables vertebrates
to sense the world around them.
Skin.
We all have it.
And so does every vertebrate on the planet.
It keeps the outside out
and the inside in.
Animals may look very different on the surface,
but we all share the same basic skin blueprint.
I'm Ben Garrod, professor of evolutionary biology,
and I'm fascinated by this often overlooked wonder of nature.
It's not just a case that he's hairless.
The skin's totally different.
Now, ground-breaking new science...
This is really quite remarkable.
It should be a game-changer for so many people.
RATTLING That sound, ah!
It makes the hairs at the back of your neck go up, doesn't it?
..is revealing skin's mysteries.
It really transforms our understanding of dinosaurs.
I'm going to explore the natural history of the body's largest organ
to see how skin has allowed animals to conquer every habitat,
disappear into their surroundings
and develop extrasensory abilities.
We're even discovering the complex ecosystem living on our skin.
Oh, Jim, that's awful. It really is.
In this episode, I'll find out how skin
allows animals to have more than just five senses...
Oh! So powerful.
..like being able to detect electricity or even see heat.
That was incredibly quick, though. That was such a strike.
And I'll discover just how complex our sense of touch really is...
That must be so sensitive.
..as I explore how skin has evolved to give animals super senses.
I'm going to reveal the secrets of skin.
In all the varied habitats in which animals live,
their skin has come to play a key role
in helping them gather information about their different environments.
We often think about five main senses -
sight, hearing, taste, smell and touch,
but across the natural world,
skin helps animals sense in ways we find hard to imagine.
Animals detect touch in varying degrees of sensitivity...
..but sensitive doesn't always mean fragile.
Crocodiles, alligators, caiman and gharials
are collectively known as crocodilians.
There are 23 species living in tropical areas across the world.
As one of our planet's most formidable hunters,
they sit at the top of the food chain.
Their skin has an incredible sensitivity
which has given them the edge over other animals.
I've come to the UK's only crocodilian zoo,
just outside Oxford, to see some of them up close.
What species do we have in here?
So, these, this is our big group of Nile crocodiles.
We've got 35 individuals in this enclosure,
and they're all quite young. I mean, they get much bigger than this,
don't they? They do. They're one of the largest species of crocodilian
that we have on the planet, and adult males can reach lengths
of up to five metres, so quite a lot bigger than this.
That's me with you on my shoulders and then a bit more, isn't it? Yeah.
So what do Nile crocodiles eat in the wild?
Well, through their life, they eat different things,
so they start off when they're hatchlings
eating small invertebrates, small reptiles, amphibians,
fish, things like that,
and as the croc grows, their prey size increases, as well.
I'm suddenly feeling less confident stood near the edge,
cos they can jump, as well, can't they? They can jump.
The perfect apex predator on our planet.
It's time for these crocodiles' main meal -
chicken on a stick.
Oh!
So powerful.
Crocodilians didn't get to be the apex predators they are
simply by using brute force.
The real secret to their success is hidden in their skin.
In the murky water where they hunt,
crocodiles can't always rely on their eyes...
..so embedded in nearly every single scale across their bodies
are highly sensitive pressure receptors...
..and these are able to detect the smallest of ripples in the water...
..making it possible to judge the distance and position
of any animal without using their eyes.
The safest way to see these sensory organs up close
is on a baby alligator.
Sean, this one's much smaller than earlier.
I feel much happier being this close to this little guy -
but it's a different species as well, isn't it?
Yeah, this one's an American alligator.
But it's a good opportunity to really have a look at the skin
and see how it works and also how it helps him hunt.
You can see instantly, on the back, really strong, thick skin,
that really armoured area, but not the same around the mouth.
You can see it's a different type of skin,
and lots of spots or holes, really.
That's right. All those little black dots around the jaw
are sensory organs.
While alligators have these pressure receptors just on their snout,
crocodiles have them all over their bodies.
Each one is a millimetre-long dome on their skin
covered by a flexible scale.
Inside are hundreds of nerve fibres.
Any movement on the surface of the scale is picked up
by the nerve fibres underneath.
It's been estimated that each dome is ten times more sensitive
than a human fingertip.
They're effectively seeing, but without their eyes.
They're seeing where these vibrations are,
they're feeling these vibrations,
and that's in order to hunt prey, right? That's exactly right, yeah.
We want to see how these skin receptors work
by setting up a simple test involving our baby alligator.
The tubes are in place to make sure
the alligator can't see where the food is,
and to make sure it can't hear where the food is,
I've even added some white noise.
WHITE NOISE PLAYS
I drop some chicken into one of the pipes.
Filmed in slow motion,
as the chicken hits the water,
it creates small ripples.
These expand out into the pool,
and as they touch the alligator, it turns.
The moment I drop the chicken into that tube,
it turned and it looked, and it did come this way
a second or so after that chicken hit the water.
That could only have happened
if it felt the vibrations through its skin.
This has been shown in experiments under laboratory conditions.
Its skin is so sensitive,
this crocodile is able to react to the ripple
within a fraction of a second.
Crocodilians have the most powerful jaws of any living animal,
but by using the receptors in their skin,
these jaws also have the capacity to be surprisingly gentle.
And this sensitivity is something all crocodilians have
from the moment they hatch.
This female caiman's offspring are just emerging from their eggs.
THEY SQUEAK
Her young are fragile and need help getting to the water.
To perform this kind of task,
she needs a real lightness of touch -
something only her skin can provide.
Like crocodilians,
many animals use their snouts to perform essential tasks.
This makes the skin on the end of any snout
a particularly important sensory tool.
Here in North America lives the star-nosed mole.
At the end of its snout
is arguably the most sensitive patch of skin on the planet.
Its nostrils are surrounded by 22 fleshy appendages known as rays.
The skin on these is covered in 25,000 sensory touch receptors,
five times more than in the human hand.
The mole pats it to the ground 10 to 15 times a second,
searching for a meal in dark tunnels.
It's so sensitive,
the mole can tell what's edible in 227 milliseconds,
faster than any other mammal...
..but these snouts are sensitive in more than one way -
they can also smell underwater.
The mole does this by partially exhaling an air bubble
on the top of its snout.
This absorbs surrounding odours,
which it breathes back in to see if there's food nearby.
If not, it moves on.
Every vertebrate has a network of nerves
connected to their dermis and epidermis,
there to relay real time information
from all over the surface of the body.
CAT PURRS
This can be a source of pleasure
and act as a warning system against attacks.
From biting insects, for example.
HORSE NEIGHS
But reacting to what your skin is telling you can be tricky,
especially when all four of your limbs are on the ground.
Skin is pretty tough,
and is good at protecting us from the outside world,
but when it comes to biting insects... Hello!
For animals such as horses,
there are areas on their body they just can't reach
to dislodge pesky flies -
but horse skin has adapted to solve that problem.
Just below the skin and the subcutaneous fat layer
is a thin sheet of muscle called the cutaneous trunci muscle.
It's anchored to the dermis with connective tissue,
and so any movement in the muscle pulls the skin with it.
Imagine this feather is a fly,
intent on getting a meal out of the horse.
Fly lands...
..and we see that.
Now, this is a flinch in the muscle beneath the skin,
and it's that, that when the horse does it,
dislodges the fly or any other flying, biting insect
that would otherwise cause a nuisance.
This is an involuntary reaction.
Sensation on the skin travels through nerves
via the spinal cord to the muscle
without engaging the horse's brain at all.
Using touch is certainly one of the most effective ways
of getting a sense of an object or environment...
..but one group of animals has adapted their skin
to help gather information from a distance.
Virtually all of the 1,300 or so species of bat
around the world are nocturnal.
In order to navigate at night,
many of them emit high-frequency sound waves
from either their nose or mouth,
bouncing them off nearby objects to get a sense of what's around them -
a system called echolocation...
..but in the dense forests or caves where they often live,
this can cause a problem.
When flying around a forest,
you need to be able to focus on what's ahead,
especially if you want to avoid crashing into a tree.
If you were to make a wide echolocation beam,
like the wide beam of this torch,
then you'd be generating too much information,
which would be bouncing back from surrounding objects,
and for a bat, this risks being overwhelming and confusing.
Many bats have adapted to overcome this sensory problem,
but one group has found a way to enhance their echolocation
by using the skin on their faces,
like this pale spear-nosed bat.
It emits its echolocation beam from its nose,
and if you look, this bizarre structure on the front of the face
just here is called the nose-leaf.
The nose-leaf is made of skin and cartilage,
and by adjusting its shape,
the bats can manipulate the size of their echolocation beam.
This gives them the ability to focus their echolocation,
transforming a wide and diffuse beam
into a narrow and more focused one.
All bats from the nose-leaf and horseshoe bat families
have this ability.
By directing a more focused beam,
they are able to concentrate on the objects that really matter...
..important when it comes to avoiding trees
and crucial for homing in on food.
However, the information animals are able to gather using their skin
isn't always related to their next meal.
The sensitivity of an animal's skin
can directly influence how they interact with the world.
In fact, a small patch of skin found on some animals
has arguably had more of an impact on our planet than any other.
Some of the most sensitive skin is found on our fingertips,
giving them a heightened sense of touch.
The skin on each fingertip can detect ridges
four and a half thousand times smaller than a human hair.
This sensitivity gives our ten digits the power to grip,
feel, build, craft and even read,
abilities that are remarkable,
but which we often take for granted.
In order to fully explore just how our sense of touch really works,
we don't need a biologist,
we need an engineer.
Professor Nathan Lepora makes robots that mimic the human sense of touch,
research that sheds light on the complexity of our skin.
Hi, Nathan. Hi, Ben. How are you? Nice to meet you. Yeah, you, too.
What have we actually got here?
I can see cables and I can see the big black dome here.
What is this? This dome-like structure is, if you like,
a version of our fingertip.
And what happens if you touch the fingertip now? Go ahead.
Ah.
So what I'm seeing, I'm displacing those little lumps and bumps. Yeah.
Their movement gives information about the contact on the skin.
Engineers have been trying to replicate
our sense of touch for decades,
and these bumps on the inside of Nathan's artificial fingertips
mimic how actual fingertips work.
When you touch something,
movement on the surface of your skin is picked up by sensors
in your dermis and epidermis.
Called mechanoreceptors,
these send the signal via nerves to your brain.
There are about 200 mechanoreceptors per square centimetre
in the tips of your fingers,
and inside the robotic fingertip, a small camera does this job
by detecting the movement of the bumps.
It transmits that feeling, that sensitivity, that impact,
through to a central processing area -
not the brain, but the laptop.
Exactly. In this case, it uses vision and image,
whereas in our fingertips, we have nerves
which send that information to the brain.
I'm touching that so gently,
and you can see on your screen where it's moving.
That's incredible. It really is.
Most robots are pre-programmed to do the tasks they perform,
but Nathan's technology means that the robots of the future
will be able to react intelligently to the world around them.
This robot is going to use its own sense of touch
to feel over that quite delicate porcelain head
that I borrowed from my wife.
Now, that's an essential skill to have with our touch,
cos we use that to feel the shape of objects when we pick objects up
or to recognise objects.
The sensitivity of the mechanoreceptors in our skin
means our fingers can easily trace an object
while applying continuous pressure,
but this is actually a highly complicated task.
And this hasn't been pre-programmed at all, has it?
No, it's completely autonomous.
It's figuring it out for itself as it moves over the head.
Nathan knows that, in order to be useful,
these artificial fingertips need to be incredibly sensitive,
so he's adapted his fingertip design
to make a robot hand with a sense of touch.
I'll show you another experiment now
where we'll get the hand to pick up a very delicate object -
this origami crane... Right. ..without crushing it.
Here it goes.
As the robot's fingers come into contact with the crane,
it senses how much pressure to apply without bending the paper,
something we can do instinctively
using the mechanoreceptors in our skin.
Oh, look. Yep. See, it hasn't even squeezed the head in that much.
It's barely touching it.
I mean, that...that must be so sensitive.
That's so impressive.
It's basically the lightest possible grasp it can do
and still have enough security to hold the crane.
There must be so many applications for this in the future.
Well, there's a few pressing needs for this type of technology -
prosthetic hands.
So with this kind of technology,
you could, in principle, embed tactile sensors
within the prosthetic hand and restore a sense of touch
if you were able to connect it up to the human nervous system.
Endless possibilities. Yeah, exactly. There really are.
Finding food is high on everyone's list of priorities...
..but when your food doesn't want to be found,
having sharp senses can make all the difference -
and one hunter's skin has adapted to give it a massive advantage,
because it is able to sense electricity.
This amazing piece of biology is the snout of a sawfish.
We call it its rostrum.
You can see these projections all the way along.
They're made of the same stuff as things like human teeth,
but they're not quite teeth in the traditional sense.
However, what's amazing about the rostrum of a sawfish
is that not only is it a deadly weapon,
but it can also detect minute electrical impulses.
Sadly, sawfish are critically endangered,
and so are rarely seen in the wild.
The small fish and shrimp that they like to feast on
might try and stay hidden, but, like all fish,
they give off tiny electric charges,
creating incredibly weak electric fields...
..and these are a dead giveaway.
On the underside of this sawfish rostrum
are thousands of tiny little pores in the skin,
and if we were to peer inside one of these little pores,
then you'd see a tiny sensory organ called an ampulla of Lorenzini.
Named after the 17th-century Italian physician,
the ampullae of Lorenzini consist of a narrow tunnel in the dermis
filled with a conductive jelly.
At the end is a round structure called an ampullary bulb
containing electrosensitive cells...
..and these are able to pick up weak electrical signals,
something as faint as one billionth of a volt.
The sawfish is able to swim close to the seabed
where it uses its rostrum to forage for prey,
and when it detects something like a shrimp or small fish,
it'll use its rostrum to dislodge it before eating it.
But sawfish have a second sensory ability hidden in their skin -
one they share with every single fish on the planet.
In the southern Pacific Ocean, a tornado is forming.
It isn't made of swirling air, but millions of fish.
This is a bait ball,
a vast school of fish that moves as one when threatened by predators.
They are able to react in unison to any danger at lightning speed,
splitting and reforming behind oncoming strikes.
Gathering together like this helps to intimidate
and confuse potential attackers.
Their eyes help to judge the position of their neighbours,
but moving with this level of precision is made far easier
by a special sensory system in their skin
called the lateral line.
Made from a series of canals running the length of the body,
the lateral line is filled with a jelly-like substance
and links to the surrounding environment by a network of pores.
The water from outside moves through the pores,
stimulating tiny hair-like structures
in the walls of the canals called neuromasts.
All fish use the lateral line to sense pressure changes
in the water around them,
allowing them to perceive the smallest of movements
all the way around their bodies
and enabling them to maintain a constant distance
from the other fish on either side.
Scientists think this helps fish to migrate in huge schools
like these sardines.
As with all fish, they rely on their enhanced perception
they get from their skin.
In the forests of Southeast Asia, one animal is using its skin
to play a far more clandestine game of cat and mouse.
This is an Asian pit viper. It's an ambush predator.
It waits motionless on branches for small animals to approach.
To hunt in this way,
it relies on an incredible sensory ability hidden in its skin.
Jason Skinner is an expert snake handler.
What a beautiful snake.
He's gorgeous, Jason, isn't he? Yeah, great colours.
These snakes hunt at night,
and they do so using specialised pits in their skin
located between their eyes and their nostrils.
These pits are so sensitive, they are able to pick up
the tiny heat signature left by their prey in pitch dark.
Inside each pit is a membrane
which heats up when hit by infrared radiation,
like that emitted by a warm rodent.
This heat is converted into electric signals
which are sent to the snake's brain.
Pit vipers, pythons and boa constrictors
all have this ability.
And we're going to test just how sensitive
these heat-sensing pits really are.
OK, Jason. What have we got here?
So we've got two ping pong balls attached to these three-foot canes.
Right. So we're well outside the striking range. Good.
The ping pong balls are identical apart from one crucial difference -
one is filled with cold water,
the other with warm.
And I've got the warm one? Yes. Ooh, yeah. Yep.
If dangled in front of him at equal distances,
will our viper be able to tell which is which?
Quite nervous, Jason. I'm not going to lie.
Oh!
And he did!
Oh. THEY LAUGH
That was incredibly quick, though. That was such a strike.
And instantly, he went for the warmer one. Yeah.
There was a very definite response there.
The head turned away from yours. Yours was moving as much as mine.
It's as close. There's a very definite preference there.
Even at night, when the pit viper can't be seen by its prey,
it can still detect them...
..and when they come within striking range...
He definitely made his choice.
..one thing is clear -
if the ping pong ball was a mouse,
it wouldn't stand a chance.
Skin is clearly one of the most dynamic organs on the planet
and a crucial part of every animal's senses.
We often take skin for granted, yet through this series,
we've seen that it goes way beyond a simple barrier
between us and the outside world.
I've been intrigued to discover that my skin is its own habitat
and is easily as rich as any rainforest or coral reef.
But more than that, the way that skin is able to adapt...
..to protect...
..to sense...
..to swim...
..to fly...
..and even to communicate...
..reveals just what an extraordinary material skin really is.
It's a story of survival,
each adaptation allowing vertebrates
to dominate almost every part of the planet.
And what fascinates me most about skin
is that we still have so much more to find out.