Narrator: FOR EVERY MALE IN THE ANIMAL KINGDOM, THE MAIN GOAL IN LIFE IS THE SAME -- TO PASS ON HIS GENES TO THE NEXT GENERATION.

THAT'S HIS ONE SHOT AT IMMORTALITY.

BUT IT TAKES TWO TO TANGO.

NOW SCIENTISTS ARE LEARNING JUST WHAT MALES WILL DO TO WIN A MATE.

TO UNCOVER THE AMAZING TRUTH ABOUT SEXUAL SELECTION, THEY'RE USING UNORTHODOX TECHNIQUES... Man: THERE SHE GOES.

Narrator: AND NEW TECHNOLOGIES.

Woman: THIS WAS TOTALLY JAW-DROPPING.

Narrator: THEY'RE FINDING SPIDERS THAT DANCE AND SING...

THEY'RE LIKE THE PEACOCKS OF THE SPIDER WORLD.

Narrator: AND MONKEYS THAT PLAY THE DRUMS.

[ BANGING ] MALES WILL GO TO EXTREMES TO SHOW THEY HAVE WHAT IT TAKES.

Man: YOU CAN SEE JUST ABOUT ANYTHING.

THINGS THAT WOULD CURL YOUR HAIR.

Narrator: THEY'LL FACE DEATH IN BATTLE.

THEY'LL EVEN SACRIFICE THEIR LIVES.

ALL IN THE NAME OF LOVE.

Narrator: IN A RAIN FOREST IN SOUTHEASTERN AUSTRALIA, THE STILLNESS OF EARLY MORNING IS BROKEN BY A CHORUS OF BIRD SONG... AN ASSORTMENT OF CALLS RINGS THROUGH THE TREES -- THEY'RE SOME OF AUSTRALIA'S FINEST -- THE GLOSSY BLACK COCKATOO... [ BIRD CALLING ] THE PIED CURRAWONG... [ BIRD CALLING ] THE GRAY SHRIKE THRUSH... [ BIRD CALLING ] BELIEVE IT OR NOT, EVERY ONE OF THOSE CALLS IS BEING PRODUCED... BY THIS BIRD.

HE'S A MALE LYREBIRD.

A MALE SUPERB LYREBIRD, TO BE PRECISE.

A BORN MIMIC, HIS REPERTOIRE SEEMS BOUNDLESS.

[ CALLING ] HE ISN'T TRYING TO DECEIVE ANYONE.

HE'S JUST TRYING TO PERSUADE THIS FEMALE TO BE HIS MATE.

[ CALLING ] HE'S PERFECTED HIS VOCAL TALENTS TO A LEVEL BEST DESCRIBED AS... WELL, SUPERB.

A PERFORMANCE THIS GRAND DESERVES A SUITABLE STAGE.

DURING MATING SEASON, THE MALE LYREBIRD PREPARES A SERIES OF OPEN ARENAS FOR HIS DISPLAYS, STAMPING DOWN THE VEGETATION, DIGGING OUT ROOTS, AND SCRATCHING UP THE EARTH.

AT THE HEART OF THE ARENA, HE CONSTRUCTS A DISPLAY PLATFORM -- A MOUND MADE FROM STICKS, LEAVES, AND MOSS.

AND ON THIS LITTLE PLATFORM HE COMMENCES TO STRUT AND SING.

[ CALLING ] HIS COSTUME IS AS REMARKABLE AS HIS VOICE.

THE LYREBIRD'S CURVED PLUMAGE REALLY DOES RESEMBLE THE ANCIENT STRINGED INSTRUMENT CALLED A LYRE, WHICH IS WHERE HE GETS HIS NAME.

IT'S ANOTHER ASSET DESIGNED TO DAZZLE.

BUT TO ATTRACT A FEMALE'S ATTENTION -- TO GET HER TO NOTICE THOSE FEATHERS -- HE USES HIS VOICE.

LYREBIRDS DO HAVE THEIR OWN DISTINCTIVE CALLS, BUT UP TO 80% OF THEIR SONG LIST IS COPIED FROM OTHER SPECIES.

EVERY BIRD IN THE FOREST IS FAIR GAME.

HIS IMPRESSIONS ARE GOOD...

SO GOOD, THEY'RE A DEAD RINGER FOR THE GENUINE ARTICLE.

[ IMITATING KOOKABURRA ] THIS KOOKABURRA IS COMPLETELY TAKEN IN.

AND LYREBIRDS DON'T JUST MIMIC OTHER BIRDS.

THEY'LL COPY ANY SOUND WITHIN EARSHOT... NATURAL OR MANMADE.

[ CLICK ] A CAMERA CLICK... WITH THE WHIR OF A MOTOR DRIVE.

[ CLICK, WHIR ] [ REPEATS ] A SET OF HUMAN FOOTSTEPS.

[ IMITATES FOOTSTEPS ] THE SCREECH OF A CAR'S BRAKES.

[ SCREECHES ] BUT EVEN THE MOST SUPERB DISPLAY DOESN'T ALWAYS PAY OFF.

THIS FEMALE IS NOT PERSUADED.

HE'LL KEEP ON CALLING...

EVEN WHEN BREEDING SEASON IS OVER.

AFTER ALL...

PRACTICE MAKES PERFECT.

[ CONTINUES CALLING ] [ CALLING ] MALES OF MANY SPECIES USE SOUND FOR A VARIETY OF PURPOSES -- TO ESTABLISH TERRITORY... TO WARD OFF RIVALS... OR TO GET A FEMALE'S ATTENTION.

WHEN A MALE FROG WANTS TO ATTRACT A MATE, HE DOES IT WITH A SONG.

IT'S A GREAT WAY TO ADVERTISE, ESPECIALLY ON A DARK NIGHT.

Woman: A LOT OF ORGANISMS FIND THEMSELVES IN SITUATIONS WHERE THEY CAN'T NECESSARILY SEE ONE ANOTHER.

VISUAL OBSTRUCTIONS ABOUND.

YOU CAN BE IN WATER THAT'S MURKY, YOU CAN BE IN FORESTS WITH LEAVES, YOU DON'T WANT TO BE RELYING ON THIS.

YOU WANT TO BE RELYING ON "HEY."

Abraham: MAKING NOISE ALSO HELPS DEMONSTRATE A MALE'S FITNESS.

Man: THERE'S A LOT OF SUBSTANCE BEHIND ALL THIS.

THE MALE IS CARRYING GOOD GENES OR PERHAPS HE'S CARRYING REALLY GOOD BEHAVIORS FROM THE POINT OF VIEW OF CARING FOR THE PROGENY.

SO, IT'S NOT REALLY JUST A SHALLOW THING, THERE'S A LOT OF VALUE ADDED BEHIND ALL THOSE SIGNALS.

Abraham: INSECTS LACK THE PHYSIOLOGY FOR VOCAL SOUND, SO THEY HAVE TO USE OTHER BODY PARTS TO SEND A MESSAGE TO A POTENTIAL MATE.

NO INSECTS ARE MORE ELOQUENT, OR LOUDER, THAN CICADAS.

THE EMERGENCE OF THE 17-YEAR CICADA IS ONE OF THE MOST SPECTACULAR EVENTS IN NATURE... AND IT'S ALL ABOUT SEX.

THESE INSECTS SPEND 17 YEARS UNDERGROUND AS NYMPHS, BEFORE RISING EN MASSE AND SWARMING ACROSS THE FOREST FLOOR.

LATCHING ONTO THE NEAREST TREE, THEY BEGIN TO TRANSFORM THEMSELVES, SHEDDING THEIR EXTERNAL SKELETONS TO BREAK FREE AS WINGED ADULTS.

FOR THE MALES, IT'S TIME TO DO WHAT THEY CAME FOR -- MAKE A LOT OF NOISE.

[ CICADA SONG SWELLING ] THEY DO IT BY VIBRATING PAIRS OF RIBBED MEMBRANES NEAR THE BASE OF THE ABDOMEN.

AS A FEMALE DRAWS CLOSER, THE MALE CALLS FASTER.

A FLICK OF HER WINGS LETS HIM KNOW THAT HE'S PASSED THE AUDITION, AND BEEN ACCEPTED AS A MATE.

HEAD UPRIVER INTO THE DENSE RAIN FORESTS OF SURINAME, AND YOU ENTER A WORLD WHERE SOUND IS THE BEST WAY TO GET YOUR MESSAGE ACROSS.

AS RESEARCHER SUE BOINSKI HAS DISCOVERED, SOME MALES HERE GO TO EXTRAORDINARY LENGTHS TO MAKE THEIR PRESENCE KNOWN.

IN THE PERPETUAL TWILIGHT OF THE THICK UNDERGROWTH, BRIGHT COLORS MIGHT GO UNSEEN, AND EVEN LOUD CALLS SOMETIMES DON'T CARRY FAR ENOUGH.

BUT THE MALES OF ONE FOREST SPECIES HAVE COME UP WITH A NOVEL SOLUTION TO THE COMMUNICATION PROBLEM.

SUE BELIEVES THEY DISPLAY THEIR FITNESS BY USING TOOLS.

IT'S A REVOLUTIONARY THEORY.

AND NOW SHE'S COME BACK TO SURINAME TO CAPTURE THIS INCREDIBLE BEHAVIOR ON FILM.

MEET THE BROWN CAPUCHIN MONKEY.

THESE LITTLE PRIMATES ARE NAMED FOR THEIR DARK CROWNS OF FUR, WHICH LOOK LIKE THE COWLS OF CAPUCHIN MONKS.

THEY'RE NO MORE THAN TWO FEET LONG...

UNLESS YOU COUNT THEIR TAILS, WHICH CAN ADD ANOTHER TWO FEET.

YOUNG CAPUCHINS ENJOY AN EXTENDED CHILDHOOD.

THEY MAY NURSE FOR TWO YEARS, GRADUALLY GAINING STRENGTH AND SURVIVAL KNOW-HOW AND LEARNING ABOUT THE BOUNTY THAT THE JUNGLE HAS TO OFFER.

AS YOUNG MALES GROW UP, THEY DEVELOP A NUMBER OF OTHER, MORE SURPRISING SKILLS.

SUE HAS OBSERVED ADULT MALE CAPUCHINS DOING SOMETHING QUITE EXTRAORDINARY.

THESE MONKEYS PLAY THE DRUMS.

AND THEY DO IT TO WIN A MATE.

Boinski: MALES -- THEY NEED TO PROVE TO THE FEMALES AND TO THE OTHER MALES THEY'RE TOUGH STUFF.

BASHING SHOWS YOU'RE STRONG, HEALTHY... AND IT ALSO TAKES SKILL.

MALE CAPS NEED TO PRACTICE FOUR OR FIVE YEARS TO BECOME TOTALLY ADEPT, AND BY "ADEPT," I MEAN A GUY THAT CAN GO LIKE THIS 450 TIMES IN 90 MINUTES.

Abraham: THE TRUNKS AND BUTTRESSES OF THESE FOREST GIANTS HAVE JUST THE RIGHT RESONANCE TO CREATE A REALLY BIG SOUND.

AND THAT CAN SEND A MESSAGE LONG-DISTANCE -- MORE THAN A MILE.

A MALE'S NOISY DISPLAY LETS A FEMALE KNOW THAT HE'S STRONG, CLEVER, AND GOOD WITH HIS HANDS.

SO HE'S A GREAT CHOICE FOR A MATE.

Man: WHERE ARE YOU ON LEDGE?

WE'RE IN THE MIDDLE OF A SLIDE AND BAMBOO.

Abraham: TO CAPTURE THE BEHAVIOR THEY'RE INTERESTED IN, SUE AND HER STUDENTS FAN OUT ACROSS THE FOREST.

JUST LOCATING A TROOP CAN TAKE A LONG TIME.

IT'S HARDER THAN FINDING A NEEDLE IN A HAYSTACK... BECAUSE THESE NEEDLES ARE CONSTANTLY ON THE MOVE, ROAMING THE UNDERSTORY, AND CLIMBING THROUGH THE TANGLED BRANCHES.

Man: WHAT DO YOU GUYS HAVE?

[ BANGING ] Woman: HEAR SOME CHATTER FROM THE OTHER SIDE.

Abraham: FINALLY, THE MOMENT SUE'S BEEN WAITING FOR.

OH, YES!

Abraham: THIS CAPUCHIN IS USING A STICK TO TRANSMIT HIS MESSAGE LOUD AND CLEAR.

AND FOR SUE, THAT STICK IS THE SMOKING GUN.

Boinski: BASHING EQUALS SEXUAL SELECTION.

HONEST, CONDITION-DEPENDENT ADVERTISING OF MALE ABILITY, HEALTH, VIGOR, AND SKILL.

Abraham: MALE CAPUCHINS ARE CREATING AND USING TOOLS TO DETER RIVALS AND IMPRESS FEMALES.

THEY HARNESS THEIR BRAIN POWER TO WIN A MATE.

Boinski: BASED ON OUR RESEARCH, FEMALES ARE CHOOSING TO COPULATE WITH MALES THAT ARE GREAT BASHERS.

Abraham: IT'S SOPHISTICATED BEHAVIOR.

AND IT COULD HELP SCIENTISTS UNDERSTAND THE EVOLUTION OF PRIMATE INTELLIGENCE, TOOL USE... AND COURTSHIP.

BROWN CAPUCHIN MONKEYS AREN'T THE ONLY RAIN FOREST ANIMALS THAT USE TOOLS TO MAKE NOISE.

HALF A WORLD AWAY, IN NORTHERN AUSTRALIA, THE MALE PALM COCKATOO MUST BANG HIS OWN DRUM IF HE WANTS TO WIN A MATE.

AFTER CONSTRUCTING A NEST IN A HOLLOW LOG, HE DISPLAYS HIS ASSETS.

[ CALLING ] FIRST HE FLAUNTS HIS WIDE REPERTOIRE OF CALLS.

THEN IT'S TIME FOR A DRUM SOLO.

HE SELECTS AND SHAPES THE PERFECT STICK, DISCARDING THOSE THAT DON'T MEET HIS STANDARDS.

AND HE STARTS TAPPING.

[ TAPPING AND CALLING ] THE FEMALE MAY BE LISTENING FOR A RESONANT TONE, OR EVEN PICKING OUT A FAVORITE RHYTHM.

IF SHE LIKES WHAT SHE HEARS, AND HIS DRUMMING IS UP TO HER STANDARDS, SHE'LL STAY WITH HIM FOR LIFE.

THERE'S ANOTHER MUCH SMALLER CREATURE THAT CREATES HIS OWN PERCUSSIVE PERFORMANCE.

IN FACT, HE COMBINES SONG AND DANCE IN ONE OF THE MOST INTRICATE DISPLAYS IN NATURE... AND UNTIL RECENTLY, ONE OF THE LEAST UNDERSTOOD.

IN A LAB AT THE UNIVERSITY OF TORONTO, DAMIAN ELIAS HAS FIGURED OUT HOW MALE SPIDERS MAKE THEMSELVES IRRESISTIBLE TO FEMALES.

THE ARACHNIDS IN QUESTION ARE JUMPING SPIDERS.

THEY'RE MINUTE CREATURES, BUT DAMIAN FINDS THEM FASCINATING.

Elias: THEY'RE ABSOLUTELY BEAUTIFUL.

AND IT'S NOT SOMETHING THAT MOST PEOPLE KNOW ABOUT, BECAUSE MOST PEOPLE DON'T ACTUALLY LOOK AT THEM, CLOSE-UP.

THEY'RE LIKE THE PEACOCKS OF THE SPIDER WORLD.

Abraham: A JUMPING SPIDER IS MORE THAN JUST A PRETTY FACE.

THESE GUYS HAVE HIDDEN TALENTS, AND POWERS FAR BEYOND THOSE OF OTHER CREATURES.

JUMPING SPIDER EYESIGHT IS UNIQUE IN THE ANIMAL KINGDOM.

THEY HAVE VERY UNIQUE ADAPTATIONS THAT ALLOW THEM TO HAVE EXTREMELY ACUTE VISION.

THEY HAVE BETTER EYESIGHT THAN ANY INSECT OR SPIDER.

AND IT'S ON PAR WITH SOME VERTEBRATES.

Abraham: TO WIN A MATE, THE MALES MUST PERFORM AN ELABORATE DANCE, BUT DAMIAN IS CONVINCED THERE'S MORE TO IT THAN FANCY FOOTWORK.

Elias: FOR MANY YEARS, THESE GUYS HAVE BEEN CONSIDERED TO BE PREDOMINANTLY VISUAL.

BUT WHAT MY RESEARCH HAS SHOWN IS THAT THIS IS NOT THE CASE.

IN FACT, THIS WAS BASICALLY ONLY THE TIP OF THE ICEBERG.

THEY WERE NOT ONLY DOING THESE DANCES, BUT THEY WERE ALSO SINGING AS THEY WERE DANCING.

AND NOT ONLY THAT, THEY WERE COORDINATING BOTH THESE SINGING AND DANCING DISPLAYS, KIND OF LIKE A FLAMENCO DANCER DOES.

AND HIS DANCE HAD BETTER BE GOOD.

OTHERWISE, THE FEMALE MIGHT TURN HIM INTO A MEAL INSTEAD OF A MATE.

TO FIGURE OUT WHAT THIS COURTSHIP DISPLAY IS ALL ABOUT, DAMIAN NEEDS TO CONTROL THE SITUATION...

STARTING WITH THE FEMALE.

FIRST, YOU WANT TO KEEP HER FROM MOVING AROUND.

SO, WE ANESTHETIZE HER WITH CARBON DIOXIDE.

WHAT I DO NEXT IS, USING A LITTLE PIECE OF WAX, I GLUE HER TO THE HEAD OF A PIN.

IT'S BASICALLY MY OWN JUMPING SPIDER DECOY.

Abraham: ONCE THE FEMALE IS MOUNTED ON A PIN, DAMIAN SETS UP A NYLON PLATFORM MADE FROM PANTYHOSE AND A NEEDLEPOINT FRAME.

Elias: IT'S ACTUALLY A VERY GOOD SUBSTRATE FOR VIBRATIONS.

THEN WE CAN POSITION THE FEMALE SO IT LOOKS LIKE SHE'S ABLE TO TURN, SO WE CAN BASICALLY GET THE FEMALES TO ATTRACT A MALE'S SORT OF GAZE.

I REALLY, LIKE, LOVE THESE THINGS MORE THAN PROBABLY A LOT OF PEOPLE IN THE WORLD.

BUT I HAVE TO DO VERY BAD THINGS TO THEM ALL THE TIME.

Abraham: A HIGH-SPEED VIDEO CAMERA RUNNING AT 500 FRAMES PER SECOND WILL CAPTURE THE MALE'S DANCE STEPS, WHICH ARE TOO FAST FOR THE HUMAN EYE TO SEE.

A LASER DOPPLER VIBROMETER WILL RECORD THE SEISMIC SIGNALS THAT THE MALE PRODUCES WHILE HE'S DANCING.

Elias: NOW IT'S TIME TO BRING IN THE MALES, AND WE'LL SEE IF THEY DISPLAY FOR US TODAY.

AND SEE THEM SING AND DANCE.

THE TRICK IS TO GET THE MALE TO PAY ATTENTION TO THE FEMALE AND NOT ESCAPE.

WHOA...

HE'S PARTIALLY PAYING ATTENTION.

OOPS.

IT'S ON MY FINGER.

LET'S TRY THIS AGAIN.

Abraham: THIS SPIDER SEEMS TO HAVE COLD FEET... ALL EIGHT FEET.

Elias: HE'S ZEROING-IN ON THE FEMALE AND NOW HOPEFULLY HE'LL TAKE THE BAIT.

VERY FEW PEOPLE HAVE EVER SEEN THIS.

MOVE THE FEMALE AROUND.

OH, THERE YOU GO.

HE'S STARTING TO COURT NOW.

[ THUMPING ] THERE WE GO!

NOW WE JUST LET NATURE TAKE ITS COURSE, AND SEE AND HEAR WHAT THE ANIMAL'S DOING.

[ RAPID VIBRATING ] IT BUILDS TO A CRESCENDO.

JUST FASTER AND FASTER THE BEAT BECOMES.

AND THEN, HE'LL JUST RAPIDLY FLICK THE LEGS.

[ THREE RAPID THUMPS ] AND THEN HE SORT OF MOVES INTO THIS NEXT PHASE WHERE HE STARTS TO SORT OF BEAT HIS ABDOMEN AND THEN HE STARTS TO MOVE HIS LEGS REALLY RAPIDLY.

IT'S KIND OF LIKE THAT HE'S TRYING TO HYPNOTIZE HER, I'VE ALWAYS THOUGHT.

[ RHYTHMIC VIBRATING ] AND THE MALE IS JUST TRYING ITS HARDEST TO SAY, "I AM THE BEST MALE YOU'RE GOING TO FIND, AND JUST LOOK AT ALL THESE THINGS I CAN DO."

[ TAPPING, VIBRATING ] AND THERE, HE'S GOING TO TRY TO MOUNT NOW.

Abraham: HE DIDN'T HAVE A CHANCE TO MATE, BUT THIS COURTSHIP WAS SUCCESSFUL IN ONE SENSE.

WE CAN LOOK AT THE HIGH-SPEED VIDEOS TO SEE WHAT ACTUALLY IS HAPPENING.

NOW, HERE'S OUR MALE SPIDER.

YOU'LL NOTICE THAT THERE'S A LOT MORE DETAIL.

YOU COULD SEE, ONE, TWO, THREE.

Abraham: THE LASER VIBROMETER REVEALS WHAT'S REALLY GOING ON.

THE FEMALE SPIDER ISN'T JUST WATCHING THE MALE, SHE'S LISTENING, IN THE ONLY WAY A CREATURE WITH NO EARS CAN LISTEN -- BY PICKING UP VIBRATIONS.

AND THE VIBRATIONS SHE'S INTERESTED IN ARE NOT TRIGGERED BY THOSE WILDLY WAVING LEGS.

Elias: IF YOU PAY ATTENTION TO THE ABDOMEN, YOU'LL SEE THAT'S IT'S GRINDING AWAY, MOVING VERY, VERY RAPIDLY.

AND IF YOU LINE THESE UP, WHAT YOU SEE IS THAT THE SOUND IS BEING PRODUCED SEPARATELY FROM THE VISUAL SIGNALS, AND THEY'RE JUST COORDINATING BOTH OF THEM TOGETHER.

[ THUMPING ] Abraham: BESIDES DANCING, HE'S SINGING A SONG, FROM THE HEART... OR AT LEAST, FROM HIS ABDOMEN.

Elias: MY RESEARCH IS SUGGESTING THAT FEMALES ARE LOOKING FOR MORE COMPLEX THINGS.

THEY WANT MORE AND MORE.

AND SO MALES HAVE EVOLVED THESE VERY, VERY INTRICATE DISPLAYS.

THEY STARTED USING THESE SOUNDS TO SORT OF, FIRST EMPHASIZING THE DANCE MOVEMENTS, AND THEN PRETTY SOON THEY BECAME THESE VERY COORDINATED DISPLAYS, WHERE IT'S REALLY A SONG AND DANCE.

AND THE COORDINATION OF BOTH OF THEM IS WHAT'S IMPORTANT.

Abraham: FOR THE MALE JUMPING SPIDER, IT'S A RISKY BUSINESS.

HE HAS TO GET IT JUST RIGHT.

IF HIS PERFORMANCE IS FLAWED, HE'S LIABLE TO END UP AS DINNER.

AND HE'S CERTAINLY NOT THE ONLY MALE IN DANGER OF BEING EATEN BY HIS MATE.

FEMALE BLACK WIDOW SPIDERS ARE NOTORIOUS FOR DEVOURING MALES AFTER SEX...

IT'S WHY THEY'RE CALLED "BLACK WIDOWS."

AND A FEMALE PREYING MANTIS DOESN'T EVEN WAIT UNTIL THE SEX IS OVER TO START MUNCHING ON HER MATE.

BUT FOR THE MALE MANTIS, IT MAY BE WORTH THE SACRIFICE.

Patricelli: IN TERMS OF EVOLUTION, YOU'RE BETTER OFF BEING THE PREYING MANTIS WHO GETS EATEN WHILE YOU'RE PASSING ON YOUR GENES.

HE GETS TO MATE BEFORE HE DIES, BUT IT IS A BIG PRICE TO PAY FOR IT.

Abraham: ONE REASON FEMALES EAT THEIR MATES... IS BECAUSE THEY CAN.

FEMALES LIKE THIS REDBACK SPIDER ARE OFTEN MUCH LARGER THAN MALES, SINCE THEY HAVE SUCH DIFFERENT EQUIPMENT.

Man: FEMALES HAVE VERY EXPENSIVE REPRODUCTIVE ORGANS.

THEIR EGGS ARE MUCH MORE EXPENSIVE.

WHEREAS MALES CAN BE A DIME A DOZEN.

AND SO MALES CAN BE TINY.

THEY'RE JUST A LITTLE SPERM PACKET.

Abraham: FOR THOSE LITTLE MALES, COURTSHIP CAN BE DEADLY.

BUT IT'S THE ONLY ROAD TO REPRODUCTIVE SUCCESS.

LIKE THE PREYING MANTIS OR THE BLACK WIDOW, THE MALE FIREFLY CAN ALSO FACE DEATH WHEN HE'S TRYING TO WOO A FEMALE.

THAT FAMILIAR FLASH IS A SEXUAL SIGNAL.

MALES FLASH IN A PRECISE CODED PATTERN TO ALERT FEMALES, AND THE FEMALES FLASH BACK...

IF THEY'RE INTERESTED.

EACH OF THE 2,000 VARIETIES OF FIREFLIES HAS ITS OWN UNIQUE CODE.

THE DURATION OF EACH FLASH SEEMS TO BE TIED TO A MALE'S FITNESS -- A CLUE THAT WOULD BE OBVIOUS AND IMPORTANT TO A FEMALE.

BUT IN THE WORLD OF SEXUAL SELECTION, THINGS ARE NOT ALWAYS WHAT THEY SEEM.

AMAZINGLY, FEMALE FIREFLIES OF THE PHOTURIS GENUS HAVE CRACKED THE CODE OF ANOTHER GROUP, THE PHOTINUS.

BY MIMICKING THEIR MATING SIGNAL, A PHOTURIS FEMALE ATTRACTS PHOTINUS MALES.

HER MOTIVE ISN'T SEXUAL.

IT'S...CULINARY.

BUT IT'S NOT JUST NUTRITION SHE'S AFTER.

BY DEVOURING THE PHOTINUS, SHE ABSORBS A CHEMICAL IN HIS BODY THAT SHE CAN USE LATER ON TO WARD OFF PREDATORS.

THE POOR MALE FIREFLY WAS EXPECTING A ROMANTIC LIAISON.

INSTEAD, HE'S BEEN LURED TO HIS DEATH BY A TRUE FEMME FATALE.

FOR MOST MALES, A PROSPECTIVE MATE IS NOT A MORTAL THREAT, BUT THEY DO HAVE TO CONTEND WITH THE COMPETITION.

HERE IN THE CALIFORNIA DESERT, SEXUAL RELATIONS CAN GET PRETTY COMPLICATED...

IN FACT, THEY'RE A LITTLE WEIRD.

AMONG MALE SIDE-BLOTCHED LIZARDS, THERE'S A COLOR WAR GOING ON.

THE TEAMS NOT ONLY LOOK DIFFERENT, THEY PLAY BY RADICALLY DIFFERENT RULES.

THE STAKES COULDN'T BE HIGHER.

ALL THREE ARE AFTER THE SAME THING -- SEX.

AND THEY USE COMPETING STRATEGIES TO GET IT.

WE CALL THEM "SIDE-BLOTCHED," BUT THEY WEAR THEIR TEAM COLORS ON THEIR THROATS.

ORANGE... YELLOW... AND BLUE.

EACH HAS ITS OWN FORMULA FOR VICTORY.

THE ORANGE TEAM -- THEY'RE AGGRESSIVE AND PUSHY... TOUGH LITTLE SCRAPPERS.

THE YELLOWS MAKE UP IN STEALTH WHAT THEY LACK IN STRENGTH.

IN FACT, THEY'RE A BUNCH OF SNEAKS.

THE BOYS IN BLUE USE THE BUDDY SYSTEM.

THEY WORK TOGETHER TO GUARD A MATE.

ALL THREE TEAMS BELONG TO THE SAME SPECIES, AND THEY'RE VYING FOR THE SAME FEMALES.

SO WHY DO THEY GO ABOUT IT IN SUCH DIFFERENT WAYS?

BARRY SINERVO HAS STUDIED THESE LIZARDS FOR TWO DECADES, LONG ENOUGH TO GET A GOOD HANDLE ON THEIR COMPLEX PLAYBOOKS.

HE'S BEEN TRYING TO FIGURE OUT WHETHER ANY OF THESE LIZARD TEAMS -- ORANGE, YELLOW, OR BLUE -- HAS THE WINNING EDGE IN MATING.

Sinervo: THE QUESTIONS WE'RE ASKING ARE ABOUT THE ROLE OF SEXUAL SELECTION AND HOW IT CHANGES ORGANISMS OVER EVOLUTIONARY TIME.

AND SEXUAL SELECTION HAS SHAPED THESE LIZARDS INTO ONE OF THE MORE INTERESTING MATING SYSTEMS IN THE ANIMAL KINGDOM, BECAUSE YOU'VE GOT THREE COMPLETELY DIFFERENT STRATEGIES FOR MAKING IT.

Abraham: TO UNDERSTAND THEIR MATING STRATEGIES, BARRY HAS TO STUDY THE LIZARDS UP CLOSE... AND THAT MEANS CATCHING THEM.

OVER THE YEARS, HE'S REELED THEM IN BY THE THOUSANDS.

AND LIKE ANY GOOD FISHERMAN, HE LOVES TO TALK ABOUT HIS TECHNIQUE.

Sinervo: I'M HERE TO CATCH OUT ALL THE LIZARDS ON THESE ROCKS.

I'VE GOT A COUPLE OF FISHING RODS HERE.

WE ACTUALLY CALL THEM NOOSES.

I'M GOING TO TIE A COUPLE OF SILK NOOSES.

IT'S TIME TO CATCH LIZARDS.

OH -- RIGHT THERE!

NO LIZARD HAS EVER BEEN INJURED DURING THE NOOSING PROCEDURE.

ALL RIGHT.

YOU KNOW, THE CRAZY THING IS THAT SOMEBODY PAYS ME TO CATCH LIZARDS.

IT'S LIKE EVERY 10-YEAR-OLD'S DREAM JOB.

THERE SHE GOES.

RIGHT OVER HERE.

Abraham: THE LIZARDS' MATING GAME INVOLVES MORE THAN COLORS AND STRATEGIES.

LIKE ATHLETES IN ANY SPORT, THEY ALSO DEPEND ON A COMPLICATED SET OF SIGNALS.

BARRY HAS SPENT YEARS LEARNING TO DECIPHER THEM.

Sinervo: THE LIZARDS ARE DOING ALL THESE HEAD BOBS, AND THEY'RE COMMUNICATING ALL KINDS OF DIFFERENT THINGS.

SO, WHEN THEY DO THE HEAD BOBS, PUSHUPS, THEY'RE DOING PUSHUPS, THEY DO ALL THESE REALLY COOL SIGNALS.

THEY DO THIS LITTLE HAND WAVE... HAND WAVE...

THEY'RE FLICKING THEIR TAIL -- WE'RE LITERALLY TRYING TO FIGURE OUT THE LANGUAGE OF LIZARD LAND.

Abraham: IT'S A COMPLICATED ARRANGEMENT, BUT IT GETS EVEN MORE COMPLICATED THAN THAT.

OUT HERE IN THE DESERT, THERE'S ANOTHER PLAYER.

IT'S NOT A MEMBER OF ONE OF THE THREE TEAMS.

IT'S NOT EVEN A LIZARD.

BUT IT HAS A LOT TO SAY ABOUT WHO GETS TO REPRODUCE.

[ RATTLING ] THIS IS WHAT SCIENTISTS CALL AN "AGENT OF SEXUAL SELECTION."

BY PREYING ON LIZARDS, SNAKES LIKE THE WESTERN DIAMONDBACK PLAY A CRITICAL ROLE IN THINNING OUT THEIR RANKS, FINE-TUNING THE COMPETITION AMONG ORANGE, YELLOW, AND BLUE.

BUT EVEN WITH THAT PREDATORY PRESSURE, BARRY HAS FOUND THAT ALL THREE COLORS HAVE A WAY OF GETTING WHAT THEY WANT.

THIS YELLOW IS SNEAKING AROUND, LOOKING FOR HIS CHANCE TO SCORE.

TO HELP HIM GET RID OF THAT PESKY ORANGE MALE, HE MIMICS THE HEAD BOBBING THAT FEMALES USE TO REJECT THEIR MATES.

THE ORANGE MALE THINKS HE'S BEEN GIVEN THE COLD SHOULDER... AND NOW THE YELLOW INTRUDER CAN HORN IN ON HIS FEMALE.

MEANWHILE, THIS BLUE IS HELPING HIS BUDDY KEEP AN EYE ON THEIR FEMALE.

BLUES USE A SIGNATURE MOVEMENT TO IDENTIFY THEMSELVES TO THEIR TEAMMATES.

TOGETHER THEY CAN GUARD AGAINST YELLOWS OR HOLD OFF AN ORANGE.

ONE BLUE WILL EVEN SACRIFICE HIS LIFE FOR HIS BUDDY.

THEY SHARE SO MANY GENES, IT DOESN'T MATTER WHICH ONE MATES WITH THE FEMALE.

BUT ON THIS PLAYING FIELD, THERE ARE NO GUARANTEES.

AND THERE'S NO DEFENSE AGAINST A RATTLER.

WITH HIS TEAMMATE PERMANENTLY SIDELINED, THIS LONE BLUE IS NO MATCH FOR AN ORANGE INVADER.

HIS DEEP PUSHUPS ADVERTISE HIS STRENGTH AND FITNESS TO THE FEMALE.

AND HE CAN CLAIM HIS PRIZE...

THE ONLY PRIZE THAT COUNTS -- A MATE.

BUT IN THIS GAME, NO SINGLE STRATEGY DOMINATES THE FIELD, AND NO TEAM GAINS A PERMANENT ADVANTAGE.

BARRY'S RESEARCH HAS REVEALED THAT EACH OF THE MALES' COLOR-CODED GAME PLANS WORKS -- ORANGE, BLUE, OR YELLOW.

THEY ALL WIN ENOUGH MATES TO ENSURE THEIR CONTINUED EXISTENCE.

THAT'S HOW THESE STRATEGIES EVOLVED IN THE FIRST PLACE.

AT THE END OF THE BREEDING SEASON, FEMALES LAY THEIR EGGS, TO FIELD A NEW GENERATION OF PLAYERS.

THE YOUNG ROOKIES WILL GROW UP TO RECOGNIZE THEIR TEAMMATES AND PLAY THE GAME THEY WERE PROGRAMMED FOR.

SIDE-BLOTCHED LIZARDS ARE LOCKED IN AN ENDLESS CYCLE OF REPRODUCTIVE RIVALRY.

THEIR COLOR WARS WILL GO ON INDEFINITELY.

LIZARDS CERTAINLY AREN'T THE ONLY ANIMALS THAT FIGHT FOR THE RIGHT TO MATE.

IT'S THE CLASSIC SCENARIO OF SEXUAL SELECTION -- TWO POWERFUL MALES GOING HEAD-TO-HEAD TO CLAIM A FEMALE.

FOR MANY ANIMALS, PHYSICAL COMBAT IS THE ONLY ROUTE TO REPRODUCTION.

Patricelli: ELEPHANT SEALS, FOR EXAMPLE, FIGHTING FOR HAREMS ON THE BEACH...

IT'S EXTREMELY BLOODY.

BECAUSE IT'S WHAT'S ON THE LINE.

EVERYTHING'S ON THE LINE.

SOMETIMES THEIR ONLY CHANCE TO EVER REPRODUCE IS HOW WELL THEY DO IN A BATTLE.

YOU GET SPECIES WHERE IT ALL COMES DOWN TO ONE EVENT.

AND THAT CAN BE A FIGHT TO THE DEATH.

Abraham: EVEN SOME VERY SMALL CREATURES BATTLE FOR THE PRIVILEGE OF MATING.

STALK-EYED FLIES, NO BIGGER THAN A DIME, HAVE EYES MOUNTED ON ELONGATED STEMS.

FEMALES ARE ATTRACTED TO THOSE STEMS... AND THE LONGER, THE BETTER.

MALES CONGREGATE IN COURTSHIP ARENAS, AND COMPETE FOR TERRITORY.

WHEN THERE ARE FEMALES AROUND, THESE GUYS GET READY TO RUMBLE.

AND JUST LIKE THE BIG BOYS, THEY DUKE IT OUT FOR BREEDING RIGHTS.

THE MALES WITH LONGER EYE-STALKS TEND TO WIN THE FIGHTS... OFTEN SIMPLY BY INTIMIDATING THEIR OPPONENTS.

THE WINNER GETS THE ULTIMATE REWARD...

THE CHANCE TO MATE.

SEXUAL COMBAT CAN TAKE A DIFFERENT TWIST FOR SHARKS.

A MALE WHITE-TIP SHARK UNLEASHES HIS AGGRESSION ON HIS MATE.

HE BITES HER DURING COURTSHIP TO ASSERT HIS INTENTIONS.

AND WHILE THEY COPULATE, HE USES HIS POWERFUL JAWS TO REMAIN FIRMLY ATTACHED.

FORTUNATELY FOR THE FEMALE, HER SKIN IS SEVERAL TIMES THICKER THAN HIS... A BUILT-IN DEFENSE, FOR SAFER SEX.

FOR SOME LAND ANIMALS, TOO, THE PURSUIT OF A FEMALE CAN BE A BRUTAL AFFAIR.

IN NARCISSE, MANITOBA, SPRING ARRIVES LATE.

IT CAN BE MID-MAY BEFORE THE GROUND WARMS UP ENOUGH TO TRIGGER ONE OF NATURE'S MOST AMAZING COURTSHIP RITUALS.

IT STARTS HERE, IN THE UNDERGROUND DENS OF RED-SIDED GARTER SNAKES.

THEY LIVE FARTHER NORTH THAN ANY REPTILE ON THE CONTINENT.

AND THEY SPEND EIGHT MONTHS OF THE YEAR DOWN HERE, SHELTERED FROM THE FROST.

WHEN THEIR SHORT BREEDING SEASON BEGINS, THE MALES LEAVE THE DENS AND CLIMB TO THE SURFACE.

THEY FORM A LIVING CARPET OF WRIGGLING REPTILES... WITH JUST ONE THING ON THEIR MINDS.

HERPETOLOGIST KATE JACKSON HAS BEEN EXPECTING THEM.

Jackson: LOOK AT THAT.

THE MALES ACTUALLY EMERGE BEFORE THE FEMALES DO, AND THEY WAIT AROUND IN A BIG GROUP.

Abraham: WHEN A FEMALE SHOWS UP, THEY KNOW IT RIGHT AWAY.

AND THEY PILE ON TO SEIZE THE OPPORTUNITY.

HERE'S THE FEMALE.

YOU SEE HOW BIG SHE IS.

JUST LOOK AT ALL THOSE MALES.

AS I LIFT HER UP, THEY'RE ALL GOING AFTER HER.

Abraham: THAT FEMALE IS STILL COLD AND STIFF AFTER HER LONG HIBERNATION, SO SHE CAN'T ESCAPE THE MALES.

THEY FORM A MATING BALL... A WRITHING MASS OF SNAKES, WITH THE SOLITARY FEMALE BURIED NEAR ITS HEART.

Jackson: THEY'RE PUSHING AND SHOVING AND RUBBING THEMSELVES AGAINST HER SCALES, AND WRAPPING THEIR TAILS AROUND HER TAIL... BECAUSE THEY'RE ALL HOPING THAT THEY'LL BE THE ONE SNAKE OUT OF ALL THESE WHO GETS TO MATE WITH HER.

IF A MALE FINDS HIMSELF IN THE RIGHT PLACE AT THE RIGHT TIME, HE'S WELL-EQUIPPED TO TAKE ADVANTAGE.

Jackson: MALES HAVE TWO PENISES, HEMIPENES, BOTH FORKED.

AND THEY ARE KEPT FOLDED INSIDE THE TAIL.

AND THEY EVERT THEM WHEN THEY'RE GOING TO USE THEM FOR MATING.

Abraham: THE SNAKES CONTINUE TO ROLL AROUND UNTIL A SINGLE MALE GETS LUCKY.

HERE WE HAVE AN ACTUAL COPULATION TAKING PLACE.

IF I CAN UNTANGLE IT WITHOUT UNTANGLING THEM.

YEAH, THIS THING THAT HE'S GOT, THE PURPLE THING THERE, IS HIS HEMIPENE.

AND IT'S INSIDE THE CLOACA OF THE FEMALE, MATING WITH HER.

Abraham: IT MAY APPEAR THAT A MATING BALL LEVELS THE PLAYING FIELD, GIVING ALL THE MALES A GOOD SHOT AT A FEMALE.

IN FACT, THE ONE THAT CAN WRIGGLE THE BEST, SCORES.

Jackson: IN TERMS OF SEXUAL SELECTION, CLEARLY THIS IS NOT FEMALE CHOICE.

I MEAN, LOOK AT THIS, THE FEMALE HAS NO CHOICE IN THE MATTER.

IT'S ALL IN THE HANDS OF THE MALES.

ANOTHER MECHANISM OF SEXUAL SELECTION IS OFTEN MALE COMBAT, AND THIS ISN'T REALLY MALE COMBAT.

THEY'RE NOT FIGHTING EACH OTHER, THEY'RE JUST PUSHING EACH OTHER OUT OF THE WAY TO GET TO THAT FEMALE.

Abraham: ONCE A MALE MANAGES TO GET TO THE FEMALE, THE PARTY'S OVER.

HE'LL LEAVE BEHIND A GELATINOUS PLUG TO PREVENT OTHER MALES FROM MATING WITH HER.

NOW SHE'S FREE TO MOVE ON.

BUT HER FIRST MATING MAY NOT BE HER ONLY ONE.

THAT PLUG WILL JUST LAST A DAY OR TWO... AND THEN SHE'LL HAVE A SECOND CHANCE AT LOVE.

BOB MASON IS AN EXPERT ON THE COMPLEX SEX LIFE OF RED-SIDED GARTER SNAKES.

Mason: OH, THIS IS GREAT -- THIS IS A FEMALE THAT HAS MATED ABOUT 36 HOURS AGO, AND NOW HER PLUG HAS DISSOLVED, AND YOU CAN SEE SHE'S BECOME ATTRACTIVE AGAIN TO THESE MALES.

BUT THERE'S SEVERAL DIFFERENCES -- ONE, SHE'S MUCH WARMER, AND SHE'S MUCH MORE AGILE AND ABLE TO MOVE AROUND.

AND, TWO, UNLIKE THE FIRST MATING AT THE ENTRANCE TO THE DEN, THIS FEMALE HAS A MUCH SMALLER MATING BALL COMPOSED OF MUCH LARGER MALES.

Abraham: SHE'S LOOKING FOR THE BIG GUYS, THE ONES WHO ARE FASTER, AND FITTER.

Mason: WE'LL SEE IF SHE'S GOING TO MOVE OFF AND TEST THOSE MALES.

THERE SHE GOES.

Abraham: SHE'LL LEAD SEVERAL MALES ON A MERRY CHASE.

AND THIS TIME, THE OUTCOME WON'T DEPEND ON A CHANCE ENCOUNTER.

Mason: EVENTUALLY, ALL THESE MALES WILL PEEL OFF UNTIL JUST ONE IS LEFT, AND THAT'S THE MALE SHE'LL CHOOSE FOR THAT SECOND MATING.

Abraham: WHILE THEY COPULATE, SHE MAY CONTINUE TO TEST HIS METTLE, ACTUALLY DRAGGING HIM AROUND BY HIS HEMIPENE.

IF HE HAS THE STRENGTH AND STAMINA, HE'LL HANG ON LONG ENOUGH TO FINISH THE JOB.

THIS SECOND MATING GIVES THE FEMALE OPTIONS.

NOW SHE HAS HER CHOICE OF SPERM.

IN SOME CASES, THE FEMALE ACTUALLY EXERTS CHOICE OF WHICH SPERM IN HER OWN REPRODUCTIVE TRACT SHE'S GOING TO USE TO FERTILIZE HER EGGS.

SO, THAT'S WHAT WE CALL "CRYPTIC" FEMALE CHOICE, BECAUSE IT'S NOT OBVIOUS FROM THE OUTSIDE.

Abraham: CRYPTIC CHOICE IS A VALUABLE STRATEGY FOR FEMALES THAT CAN'T ALWAYS RESIST THE ADVANCES OF AGGRESSIVE MALES.

Patricelli: SHE CAN CHOOSE WHICH SPERM TO UTILIZE.

IF SHE MATES WITH MULTIPLE MALES, SHE MAY HAVE SOME CONTROL OVER WHICH MALE SPERM SHE USES TO FERTILIZE HER EGGS.

AND IF SHE WAS FORCE-COPULATED, OR DIDN'T WANT TO MATE WITH THAT MALE, SHE CAN EJECT THE SPERM.

Sinervo: THAT FINAL DECISION IN SEXUAL SELECTION, IT REALLY LIES IN THE HANDS OF FEMALES, BECAUSE FEMALES DO HAVE THAT FINAL SORT OF STEP IN THE PROCESS.

THEY GET TO FERTILIZE THE EGGS.

Abraham: NOT ALL MALES GIVE UP CONTROL SO EASILY.

AMONG DUCKS, FEMALE CRYPTIC CHOICE HAS TRIGGERED A GAME OF EVOLUTIONARY ONE-UPMANSHIP.

Man: EXCELLENT.

Abraham: AT A WILDLIFE SANCTUARY IN CONNECTICUT, SCIENTISTS ARE ONLY NOW UNLOCKING THE SECRETS OF THIS BIZARRE BATTLE OF THE SEXES.

YALE BIOLOGIST PATRICIA BRENNAN HAS MADE A SURPRISING DISCOVERY ABOUT THE DUCKS' BASIC SEXUAL EQUIPMENT.

THIS MAY BE A LITTLE EMBARRASSING FOR THE DUCK, BUT HE'S GOT NOTHING TO BE ASHAMED OF.

Brennan: SO I'M GOING TO EVERT THE PHALLUS OF A MALLARD DUCK.

SO, RIGHT NOW WE'RE IN THE BREEDING SEASON, SO HE SHOULD BE IN PEAK DEVELOPMENT.

AND IT JUST KEEPS GOING.

I MEAN, YOU CAN SEE IT JUST KEEPS UNFOLDING.

Abraham: A MALE DUCK'S PHALLUS IS PRETTY PECULIAR.

SPERM TRAVELS ALONG A GROOVE ON THE OUTSIDE.

AND THAT GROOVE GIVES THE WHOLE APPARATUS A CORKSCREW SHAPE.

I'M JUST GOING TO TAKE SOME PICTURES OF THE PHALLUS, USING A RULER SO THAT I CAN COMPARE IT WITH WHAT IT'S BEEN IN THE PREVIOUS WEEKS.

Abraham: THE PHALLUS ACTUALLY GROWS LONGER DURING THE BREEDING SEASON.

IN SOME DUCKS IT CAN GROW TO HALF THEIR BODY LENGTH, OR MORE.

Brennan: THREE MONTHS AGO, YOU WOULDN'T HAVE SEEN THIS STRUCTURE THE WAY WE'RE SEEING IT NOW.

THERE WAS ALMOST NOTHING THERE.

Abraham: FOR PATRICIA, THAT ORNATE ORGAN PROMPTED A QUESTION -- IF THE MALE'S GOT SUCH A FANCY CAR, WHERE DOES HE PARK IT?

INCREDIBLY, BIOLOGISTS HAD NEVER REALLY INSPECTED THE GARAGE...

THE FEMALE DUCK'S REPRODUCTIVE ORGANS.

IN HER LAB, PATRICIA TOOK A CLOSE LOOK AT SPECIMENS FROM A NUMBER OF DUCK SPECIES, AND SHE WAS AMAZED BY WHAT SHE SAW.

Brennan: THIS IS A VERY ELABORATE OVIDUCT, UNLIKE THAT OF ANY OTHER BIRD THAT WE KNOW OF.

Abraham: MALE DUCKS HAVE SUCH COMPLICATED GENITALS BECAUSE FEMALES DO TOO.

Brennan: THE FEMALE SPIRALS IN ONE DIRECTION, AND THE MALE SPIRALS IN THE OPPOSITE DIRECTION.

SO THEY ACTUALLY DO NOT MATCH.

AND THAT IS AN INDICATION TO US THAT THE FEMALE IS SOMEHOW PREVENTING MALES FROM EASILY ACHIEVING FERTILIZATION.

Abraham: AS WITH THE FEMALE GARTER SNAKE, THIS IS ANOTHER EXAMPLE OF CRYPTIC CHOICE, A DEFENSE AGAINST FORCED COPULATION.

THE OPPOSING SPIRAL MAKES IT MORE DIFFICULT FOR A MALE TO HAVE HIS WAY WITH HER, UNLESS SHE COOPERATES.

Brennan: EVEN IF THE MALE ACHIEVES COPULATION, THAT DOESN'T MEAN THAT HE HAS TO FERTILIZE THE EGGS.

WE THINK THAT THE FEMALE HAS THESE ANATOMICAL BARRIERS IN HER OVIDUCT SO THIS PHALLUS, BASICALLY, WILL HAVE TO TRAVEL ALL THIS DISTANCE, AND BYPASS ALL THESE BARRIERS, IN ORDER TO BE SUCCESSFUL AT DEPOSITING THE SPERM.

Abraham: PATRICIA BELIEVES THAT DUCKS ARE IN THE MIDST OF AN EVOLUTIONARY ARMS RACE.

THE MALES' ELABORATE PHALLUS EVOLVED IN RESPONSE TO THE FEMALES' DEFENSES.

Brennan: ONE POSSIBILITY IS THAT THE MALES ARE JUST GROWING LONG PHALLUSES TO OUT-COMPETE ONE ANOTHER, AND BE ABLE TO DEPOSIT SPERM INSIDE OF THE FEMALE MORE EFFECTIVELY.

ANOTHER POSSIBILITY, THOUGH, IS THAT FEMALES ARE FORCING THE MALES INTO GROWING LONGER PHALLUSES BY PLACING BARRIERS IN THEIR OVIDUCTS THAT DON'T PERMIT THE MALES TO COPULATE AS EASILY.

THEREFORE THEY HAVE TO ELONGATE THE PHALLUS TO BE ABLE TO DEPOSIT THEIR SPERM.

SO, BIGGER MAY NOT NECESSARILY BE BETTER.

WE'RE NOT ENTIRELY SURE RIGHT NOW.

WE'RE TRYING TO FIGURE THAT OUT.

Abraham: THE FEMALES SEEM TO HAVE THE UPPER HAND.

IN SOME DUCK SPECIES, UP TO A THIRD OF THE COPULATIONS ARE FORCED...

BUT THEY PRODUCE ONLY 3% OF THE YOUNG.

SO WHILE THOSE PUSHY MALE DUCKS MAY THINK THEY CONTROL THE MATING GAME, EVOLUTION HAS GIVEN FEMALES THE EDGE.

SCIENTISTS ARE CONTINUALLY AMAZED BY THE CREATIVE POWER OF SEXUAL SELECTION... AND BY ITS ABILITY TO TRANSFORM MALE PHYSIOLOGY.

[ HIGH-PITCHED HUM ] THAT STRANGE NOISE IS A SERENADE... A LOVE CALL.

IT'S PRODUCED BY A MANIKIN, A LITTLE RAIN FOREST BIRD THE SIZE OF A SPARROW.

IF A MALE MANIKIN HOPES TO BREED, HE HAS TO MAKE A VERY UN-BIRDLIKE SOUND.

♪♪♪ AND HE DOES IT IN A WAY UNLIKE ANY OTHER BIRD.

♪♪♪ KIM BOSTWICK IS AN ORNITHOLOGIST AT CORNELL UNIVERSITY.

SHE FILMED MALE MANIKINS USING HIGH-SPEED VIDEO, TO SEE JUST HOW THEY MAKE THAT SOUND.

♪♪♪ AND SHE DISCOVERED SOMETHING ASTOUNDING.

[ CLICKING ] Bostwick: JUST A LITTLE BIRD, DOESN'T LOOK LIKE HE'S DOING MUCH.

LEANS FORWARD, AND HE FLICKS HIS WINGS, AND OUT COMES THIS SOUND.

IF IT WAS JUST HIS VOICE, IT WOULD BE NOT VERY INTERESTING.

BUT THE FACT THAT THE MOUTH IS CLOSED, AND THIS TONE IS COMING OUT, THAT'S WHAT'S REALLY EXCITING.

Abraham: AS THE BIRD DISPLAYS, ONLY HIS WINGS ARE MOVING.

SOMEHOW THE MANIKIN IS USING HIS WINGS AS A MUSICAL INSTRUMENT, BEATING THEM TOGETHER 100 TIMES A SECOND TO CREATE THAT HIGH-PITCHED HUM.

THAT SEEMS PRETTY FAR-FETCHED.

HUMMINGBIRDS BEAT THEIR WINGS ABOUT 50 TO 75 CYCLES A SECOND.

THIS BIRD IS GOING AT ABOUT 100 CYCLES A SECOND, SO IT'S FASTER THAN HUMMINGBIRDS, IT'S FASTER THAN RATTLESNAKES.

THESE ARE EXTREMELY FAST MOTIONS.

Abraham: KIM WANTED TO KNOW EXACTLY HOW MANIKINS MANAGE THIS TRICK, SO SHE EXAMINED THE WINGS MORE CLOSELY.

I WAS LOOKING AT THESE FEATHERS, KNOWING THAT THEY HAD SOMETHING TO DO WITH THE SECRET OF HOW THIS BIRD WAS MAKING ITS SOUND, BUT NOT SURE EXACTLY WHAT.

Abraham: THEN SHE NOTICED THAT ONE WING FEATHER HAS RIDGES, WHILE A NEIGHBORING FEATHER HAS A CURVED TIP.

Bostwick: WE KNOW THAT THAT BIRD IS MOVING ITS WING BACK AND FORTH.

AND WHAT'S GOING TO HAPPEN IS THEY'RE GOING TO COME AND KNOCK TOGETHER OVER AND OVER AGAIN.

BUT THESE TWO FEATHERS ARE GOING TO INTERACT IN A VERY SPECIAL WAY.

Abraham: AS THE MALE MANIKIN KNOCKS HIS WINGS TOGETHER, THE FEATHERS ACT LIKE A SPOON AND WASHBOARD.

THEY GENERATE VIBRATIONS AT JUST THE RIGHT FREQUENCY TO ATTRACT A FEMALE.

♪♪♪ IT WAS AN ASTONISHING DISCOVERY.

BUT KIM DECIDED TO TAKE HER ANALYSIS ONE STEP FURTHER, TO FIND OUT HOW THE WINGS COULD SUPPORT SUCH HIGH-SPEED MOVEMENT.

SHE ORDERED UP A CT-SCAN.

NO ONE HAD EVER EXAMINED A MANIKIN'S SKELETON BEFORE.

AND KIM COULD SEE RIGHT AWAY THAT THIS BIRD'S WING BONES WERE SUPER-SIZED.

Bostwick: IF YOU'RE USED TO LOOKING AT SKELETONS, YOU'LL IMMEDIATELY BE BLOWN AWAY.

I WOULD HAVE EXPECTED THE ULNA, WHICH IS THIS BONE ON ME AND THIS BONE ON THIS SPECIMEN, TO LOOK THE SAME SIZE AND SHAPE AS THE BIRD'S FEMUR.

YOU CAN SEE THAT THIS IS A MASSIVE BONE, COMPARED TO WHAT IT SHOULD BE.

IT'S FOUR TIMES WIDER IN DIAMETER.

AND YOU CAN SEE IT'S A VERY ODD-SHAPED BONE.

IF YOU'VE EATEN A CHICKEN WING, YOU SHOULD KNOW WHAT THIS BONE SHOULD LOOK LIKE.

IT SHOULD BE SMOOTH, COLUMNAR.

BUT IT HAS THESE AMAZING GROOVES AND BUMPS ON IT.

Abraham: THOSE GROOVES AND BUMPS PROVIDE SUPPORT FOR THE WINGS, ALLOWING THEM TO MOVE AT HIGH SPEED.

TO MAKE IT EVEN STRONGER, THE WING BONE IS ALSO VERY DENSE.

Bostwick: THIS WAS TOTALLY JAW-DROPPING.

EVERY ORNITHOLOGIST KNOWS THAT BIRDS HAVE HOLLOW BONES.

IT'S JUST PART OF WHAT DEFINES A BIRD AS A BIRD.

THEY'RE HOLLOW BECAUSE THEY NEED TO FLY, AND THEY NEED TO LIGHTEN-UP THEIR SKELETON.

NOT ONLY IS IT NOT HOLLOW, IT IS SOLID AND IT'S MORE DENSE ON THE INSIDE THAN ON THE OUTSIDE.

Abraham: THE WINGS OF THE MALE MANIKIN EVOLVED SO THAT HE CAN CREATE THE PERFECT PITCH, PRECISELY THE SOUND A FEMALE IS LOOKING FOR IN A PROSPECTIVE MATE.

♪♪♪ Bostwick: WE USUALLY THINK THAT, IN SEXUAL SELECTION, IT'S GOING TO MODIFY THE SUPERFICIAL PARTS OF YOU.

BEAUTY IS ONLY SKIN DEEP.

THAT'S WHERE THAT SAYING COMES FROM.

INSTEAD, IT PERMEATES THIS BIRD'S BIOLOGY, IN ORDER TO ATTRACT A FEMALE WITH THE SOUND, SO THAT HE CAN MATE AND PASS ON HIS GENES TO FUTURE GENERATIONS.

AND THAT'S WHAT SEXUAL SELECTION CAN DO TO YOU.

♪♪♪ Abraham: SEXUAL SELECTION PROVIDES MALES OF EVERY SPECIES WITH CUSTOMIZED SOLUTIONS TO THE PROBLEM OF SECURING A MATE.

ONE OF NATURE'S MOST FLAMBOYANT COURTSHIP RITUALS TAKES PLACE IN THE DENSE JUNGLES OF AUSTRALIA'S CAPE YORK PENINSULA.

IT'S PERFORMED BY THE MAGNIFICENT RIFLEBIRD.

HE DOESN'T LOOK ALL THAT MAGNIFICENT.

EXCEPT FOR HIS SHINY BLUE THROAT, HE'S PRETTY NONDESCRIPT.

DRESSED IN BASIC BLACK.

BUT IN ORDER TO IMPRESS A FEMALE, THE RIFLEBIRD GIVES IT HIS ALL.

ONCE HE GETS WARMED UP, HE'LL SEND OUT AN INVITATION.

[ CALLING ] UNFORTUNATELY, IT LOOKS LIKE THIS FEMALE IS NOT IN THE MOOD.

THERE'S NOTHING HE CAN DO BUT KEEP ON CALLING AND HOPE THAT ANOTHER FEMALE APPRECIATES HIS EFFORTS.

[ CALLING ] AND SOON ENOUGH, HE GETS HIS CHANCE.

NOW THAT HE HAS HER ATTENTION, HE LAUNCHES HIS DISPLAY...

IN ALL ITS GLORY.

SHE IS JUDGING EVERY MOVE, GAUGING HIS SKILL AND HIS FITNESS.

IF SHE LIKES WHAT SHE SEES, SHE'LL LET HERSELF BE SWEPT INTO A FOND EMBRACE.

THAT'S THE MOMENT HE'S BEEN WORKING FOR -- THEIR BRIEF MATING, DISCREETLY HIDDEN FROM VIEW.

HIS DANCE IS INSTINCTIVE, AND IT'S UNIQUE TO HIS SPECIES.

JUST ONE OF COUNTLESS STRATEGIES THAT MALES USE TO WIN MATES AND PASS ON THEIR GENES.

FOR SCIENTISTS WHO STUDY THE NATURE OF SEX, THE SUBJECT SEEMS TO BE INEXHAUSTIBLE.

Sinervo: THERE IS NO ONE GOOD STRATEGY.

THAT'S WHAT'S REALLY COOL ABOUT NATURE.

SEXUAL SELECTION NEVER STOPS.

IT'S ALWAYS EVOLVING AND CHANGING THINGS AND NEW SPECIES ARE CREATED BY THE PROCESS.

Abraham: THERE'S JUST NO END TO WHAT FEMALES WANT... AND MALES WILL DO.

Bostwick: FEMALES WANT EVERYTHING.

WE KNOW WHAT FEMALES WANT, THEY WANT THEIR CAKE AND THEY WANT TO EAT IT, TOO.

Hunter: MALES WILL TRY AND CHEAT.

THEY'LL TRY ANYTHING THEY CAN TO COPULATE WITH THE FEMALE.

WE KNOW THAT.

Bostwick: EVERYBODY KNOWS NATURAL SELECTION.

NATURE, TOOTH AND CLAW.

WITH SEXUAL SELECTION, THE SKY'S THE LIMIT.

NATURAL SELECTION IS ENGINEERING.

SEXUAL SELECTION IS ART.