All language subtitles for 3 Secrets.Of Skin

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.

[ RATTLING ]THAT SOUND!

OH, IT 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.

--Captions by VITAC--
www.vitac.com

CAPTIONS PAID FOR BY
DISCOVERY COMMUNICATIONS

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 ]
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.

OH! 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 CENTIMETER.

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

AND 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 CENTIMETERS.

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 CENTIMETERS THICK.

NOW THE BOWHEAD WHALE IS
AN ABSOLUTE CHAMPION

AT THRIVING
IN SUBZERO 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 CENTIMETERS 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 COLONIZE 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!

[ LAUGHS ] COME ON.

COME HERE.

JACK, JACK. JACK!

EVEN IN COOLER CLIMATES
LIKE BRITAIN,

HEAT GENERATED BY MUSCLES
AND METABOLISM

CAN SIGNIFICANTLY
RAISE BODY TEMPERATURE.

COME ON. GOOD BOY.

[ PANTING ]

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
VIA SPECIALIZED 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 SAVANNA

TO STAY ACTIVE DURING
THE HOTTEST PART OF THE DAY.

IT ALSO ENABLED 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 U.V. RAYS.

U.V. 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 U.V.
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 U.V.?

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 ANALYZED
THIS BLOOD SWEAT,

THEY DISCOVERED IT'S NOT BLOOD,
OR ACTUALLY SWEAT,

BUT INSTEAD IS AN OILY MIXTURE
OF WATER REPELLENT, ANTIBIOTIC,

AND A U.V.-BLOCKING CHEMICAL
THAT TURNS RED IN SUNLIGHT.

BASICALLY, HIPPO SKIN PRODUCES
ITS OWN SUNSCREEN.

ANOTHER ICONIC RESIDENT OF THE
AFRICAN SAVANNA 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 CENTER,

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 CENTIMETERS IN LENGTH.

AND IN THE WILD, THEY USE THEM

TO STRIP THE LEAVES
OFF 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 COLOR.

ALL KINDS OF VERTEBRATES
PRODUCE MELANIN,

A PIGMENT MADE
BY SPECIALIST CELLS

IN THE EPIDERMIS
TO SHIELD THEMSELVES FROM U.V.

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 COLOR.

THE MORE MELANIN YOUR SKIN HAS,
THE DARKER YOU ARE,

AND THE BETTER PROTECTED
FROM U.V.

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 U.V.
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 COLOR VARIATION
WE SEE TODAY

IS OUR SKIN'S RESPONSE

TO THIS LOVE-HATE RELATIONSHIP
WITH U.V. --

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 U.V. CAMERA.

THIS FILTERS OUT THE VISIBLE
LIGHT FROM AN IMAGE,

SO ALL THAT IS RECORDED
ARE THE ULTRAVIOLET RAYS.

ANYTHING THAT ABSORBS U.V.,

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 U.V.

SO I NEED SUNBLOCK TO REPLICATE
THE PROTECTION

THAT DARKER-SKINNED PEOPLE
GET FROM

THEIR NATURALLY PRODUCED
EXTRA MELANIN.

OKAY, 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 U.V. 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'VE FOUND ON MY CULTURE.

WHAT HAVE WE GOT?

WELL, LET'S HAVE A LOOK.

OH, JIM, THAT'S AWFUL.
[ LAUGHS ] IT REALLY IS.

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
10 MILLION BACTERIA

PER SQUARE CENTIMETER
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 POSTOPERATIVE 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 ANTIFUNGAL 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 DEFENSES
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?

[ BOTH LAUGH ]

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 10.

IT'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 ANESTHETIC
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'S LITTLE 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.

THEY LOOK 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 GET
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.

OHH.
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.OH, YEAH.

AH!

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.

IF 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.

[ LAUGHS ]

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 BEHAVIOR,

THAT RESPONSE TO LAND ON YOU,
TO FEED.

IT HAS TO BE
THE RIGHT CUE.

THESE ONES WILL PREFERENTIALLY
BE ATTRACTED TO HUMAN ODOR,

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 ODOR.

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 UPREGULATE

THE PRODUCTION OF NATURAL
REPELLENTS BY THE BODY,

AND TOTALLY CHANGE THE WAY
THAT WE REPEL MOSQUITOES

AND PROTECT OURSELVES
AGAINST DISEASES LIKE MALARIA.

[ INSECTS BUZZING ]

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
MULTIPURPOSE SHIELD.

FROM THICK FAT TO DENSE HAIR
AND EVEN SLIMY BARRIERS,

SKIN HAS ADAPTED
TO PROTECT VERTEBRATES

FROM WHATEVER THE WORLD
THROWS AT THEM.