Original subtitles

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.