Narrator: WHY WOULD A GOAT NEVER LEAVE A HORSE'S SIDE... FOR 16 YEARS?

WHAT WOULD POSSESS A BIG LION TO BOND WITH A LITTLE COYOTE?

Man: MOTHER NATURE IS TEACHING ME SOMETHING EVERY TIME I SEE A RELATIONSHIP LIKE THIS.

Narrator: SCENES LIKE THESE ARE OVERTURNING THE CONVENTIONAL WISDOM -- THAT ONLY HUMANS FORGE FRIENDSHIPS.

THERE'S A LOT OF PEOPLE THAT DON'T WANT TO ADMIT THAT ANIMALS HAVE EMOTIONS.

Narrator: IS IT COMPASSION OR COMPANIONSHIP THAT BONDS TWO ANIMALS OF DIFFERENT SPECIES TOGETHER?

Woman: WHEN THEY GREET EACH OTHER, I'VE NEVER SEEN ANYTHING LIKE IT.

IT'S NOT A DEER GREETING A DEER, IT'S NOT A DOG GREETING A DOG.

IT'S DEFINITELY SOMETHING THAT THEY HAVE BETWEEN THE TWO OF THEM.

Narrator: WHATEVER THE CASE, SOMETHING DEEP IS BEING EXPRESSED WHEN ANIMALS MAKE UNEXPECTED FRIENDS.

Narrator: AT BUSCH GARDENS IN FLORIDA, AN UNLIKELY COUPLE IS ABOUT TO ENTERTAIN THE VISITORS.

[ DOG BARKS ] IN ZOOS AND SANCTUARIES AROUND THE WORLD, RELATIONSHIPS BETWEEN DIFFERENT SPECIES ARE SHEDDING NEW LIGHT ON THE INNER LIVES OF ANIMALS AND THE POWERFUL BONDS THAT LINK US ALL.

MTANI, THE RETRIEVER, MAY WEIGH LESS AND NOT BE AS FAST AS THE CHEETAH, BUT SHE'S THE ONE WHO RULES THIS RELATIONSHIP.

AND KASI, THE NATURAL BORN HUNTER, IS JUST FINE WITH THAT.

IT'S AN INTERESTING RELATIONSHIP AND IT'S ONE THAT WE DEVELOP AND WE HELP THEM DEVELOP AND CULTIVATE.

BUT I DO BELIEVE THAT THEY HAVE GROWN TO DEPEND ON ONE ANOTHER.

DOGS AND CHEETAHS ARE SO CLOSE, OVERALL, IN THEIR DISPOSITION, THE WAY THAT THEY ARE SOCIALLY STRUCTURED, LENGTH OF LIFE -- THAT THEY CAN COEXIST IN A SPACE, EVEN THOUGH THEY'RE AT DIFFERENT PLACES ON THE LINE OF CARNIVORE.

Narrator: THESE SIMILARITIES LED THE KEEPERS AT BUSCH GARDENS TO EMBARK ON A PILOT PROJECT ONE YEAR AGO, PAIRING A YOUNG CHEETAH AND A PUPPY, TO SEE IF THEY COULD FORM A SUPPORTIVE RELATIONSHIP.

Smith: IN THE BEGINNING, WE MADE THE CHOICE TO PUT THEM TOGETHER.

THEY MADE THE CHOICE AS TO WHETHER OR NOT THAT WAS GOING TO WORK.

THEY WERE ACTUALLY BOTH ORPHANS, IF YOU WILL.

KASI, THE CHEETAH, WAS BORN AT THE JACKSONVILLE ZOO.

THE OTHER THREE CUBS ACTUALLY PASSED AWAY AND THE MOTHER CHEETAH WAS NOT ABLE TO RAISE HIM.

AND SO, AT THAT POINT, KASI NEEDED A HOME.

[ DOG BARKING ] MTANI HERE IS ACTUALLY A RESCUE DOG.

WE COLLECTED HER FROM ONE OF OUR LOCAL RESCUE CENTERS.

RELATIONSHIPS ARE ABOUT PERSONALITIES, AND THEM GELLING, YOU KNOW, AND IT DOESN'T MATTER SO MUCH WHAT THE SPECIES IS.

[ BARKING ] [ MTANI BARKING, KASI CHIRPING ] Narrator: CHEETAHS CHIRP AND DOGS BARK... AND THEY BOTH GROWL.

KASI AND MTANI'S COMFORT WITH EACH OTHER HAS BEEN SHAPED BY THEIR SHARED WAYS OF COMMUNICATING, WHICH GAVE THEM A RUNNING START AT UNDERSTANDING ONE ANOTHER.

[ BARKING ] Smith: THESE TWO HAVE FIGURED OUT HOW TO COMMUNICATE WITH ONE ANOTHER.

AND I THINK THAT'S THROUGH THE FACT THAT THEY'RE NOT SO DIFFERENT.

THERE'S A LOT OF SIGNALS THAT ARE GIVEN BY ANY ANIMAL.

AND YOU START TO LOOK AT THOSE THINGS, WHETHER IT BE THE EARS BACK OR THE TAIL IS TAUT, OR, YOU KNOW, THE BODY POSITIONING HIGH OR LOW.

BUT YOU ALSO NEED TO LOOK AT THE EYES, YOU KNOW -- ARE THE EYES KIND OF LAID BACK AND COMFORTABLE, OR ARE THEY REALLY INTENSE?

YOU CAN TELL A LOT FROM THE LIPS OF A DOG AND WHETHER THERE'S A LITTLE SNEER GOING ON, OR IF THEY'RE NICE AND RELAXED.

YOU SEE THOSE KINDS OF THINGS NOT ONLY IN THE DOG, BUT YOU CAN SEE THEM IN THE CHEETAH, AS WELL.

I THINK THEIR COMMUNICATION IS A FACTOR, BUT I ALSO THINK THAT THEY'RE LEARNING A NEW LANGUAGE.

THEY'RE NOT LEARNING THE CHEETAH LANGUAGE OR THE DOG LANGUAGE, THEY'RE LEARNING KASI-MTANI'S LANGUAGE.

AND THEY'VE HAD TO LEARN THAT THROUGH BUILDING RELATIONSHIPS AND TRUST.

THE THING THAT SURPRISES ME MOST IS HOW THEY SEEM TO NEED ONE ANOTHER.

KASI, THE CHEETAH, IN PARTICULAR, HE SEEMS TO NEED HER.

YOU KNOW, IF SHE'S NOT AROUND, HE'S LOOKING FOR HER.

I THINK THAT HE'D HAVE A MUCH MORE DIFFICULT TIME IF SHE WAS NOT A PART OF THIS ENVIRONMENT.

IT'S TIME TO CHASE.

IT'S MORE THAN JUST COMING OUT HERE AND RUNNING THE CHEETAHS AND DOGS FOR THE, YES, ENJOYMENT AND UNDERSTANDING -- IT'S REALLY AN EXERCISE PROGRAM.

EACH TIME THEY COME OUT, THEY GET A LITTLE BETTER AT EITHER RUNNING OR DODGING OR CHANGING DIRECTION.

THEY ARE BOTH REACHING 20 TO 30 MILES PER HOUR RIGHT NOW, WHICH IS PRETTY DARN GOOD WHEN YOU FIGURE AN ADULT CHEETAH IN THE WILD REACHES SPEEDS OF 60 TO 70 MILES PER HOUR.

IT'S KIND OF STRANGE, BUT AT THE END OF THE DAY, THE LABRADOR RETRIEVER ACTUALLY HAS A LOT MORE STAMINA.

SHE CAN GO FOR A LOT LONGER PERIOD OF TIME.

AND, SO, WE RUN HER A LOT MORE THAN WE DO HIM.

YOU KNOW, IT'S NOT SIMPLE -- IT DOESN'T MATTER WHETHER IT'S TWO HUMANS, TWO DOGS, A DOG AND A CHEETAH.

YOU KNOW, RELATIONSHIPS ARE REALLY TOUGH.

THERE'S PEOPLE THAT GO THROUGH LIFE THAT DON'T FIND THAT COMPANION.

THERE'S ANIMALS THAT GO THROUGH LIFE THAT LIVE COMPLETELY BY THEMSELVES.

THESE TWO HAVE A SHOT AT BEING COMPANIONS WITH ONE ANOTHER FOR THE REST OF THEIR LIVES, AND THEY SEEM TO BE MAKING THAT KIND OF A CHOICE.

Man: I THINK THE CHOICES ANIMALS MAKE IN CROSS-SPECIES RELATIONSHIPS ARE SIMILAR TO THE CHOICES THEY MAKE IN SAME-SPECIES RELATIONSHIPS.

LIKE, SOME DOGS DON'T LIKE EVERY OTHER DOG.

THEY MAY NOT ATTACK THE DOG, BUT THEY DON'T FORM THAT CLOSE RELATIONSHIP.

ANIMALS ARE VERY SELECTIVE ABOUT THE OTHER INDIVIDUALS WHO THEY LET INTO THEIR LIVES.

Woman: WELL, AS AN AUTISTIC PERSON, I AM AN EXTREME VISUAL THINKER.

EVERYTHING I THINK ABOUT IS IN A PICTURE.

AND THAT'S THE WAY ANIMALS ARE.

AN ANIMAL'S WORLD IS SENSORY BASED, IT'S NOT WORD BASED.

WHAT CROSS-SPECIES RELATIONSHIPS SHOW YOU IS THAT THERE'S BEHAVIORS AND EMOTIONS THAT JUST GO ACROSS SPECIES.

I MEAN, MAMMALS HAVE CERTAIN BEHAVIORS THAT GO ACROSS ALL THE SPECIES, BECAUSE THEY'RE MAMMALS.

YOU KNOW, I DON'T THINK SNAKES ARE GOING TO BE DOING THIS.

Narrator: WE NEED LOOK NO FURTHER THAN OUR RELATIONSHIPS WITH OUR PETS FOR EXAMPLES OF THE DEEP BONDS THAT CAN FORM BETWEEN DIFFERENT SPECIES.

BUT WE STILL HAVE A LOT TO LEARN ABOUT CROSS-SPECIES RELATIONSHIPS.

DO THE SAME ELEMENTS OF SOCIAL BONDING SPAN THE ANIMAL KINGDOM?

A QUESTION ALL THE MORE PERPLEXING WHEN ANIMALS BREAK BOUNDARIES WE'D THINK WOULD BE TOO STRONG TO OVERCOME.

Bekoff: THERE'S DEFINITELY A RISK INVOLVED IN RELATIONSHIPS THAT FORM BETWEEN ANIMALS, SAY, OF DIFFERENT SIZES, AND PREDATORS AND PREY, FOR EXAMPLE.

SO THERE IS A RISK, ESPECIALLY FOR THE PREY ANIMAL.

AND THAT'S WHAT I THINK IS SO INTRIGUING ABOUT THE CROSS-SPECIES RELATIONSHIPS.

THERE'S INCREDIBLE TRUST, AND IT HAS TO FORM IMMEDIATELY.

Man: I WAS IN SHOW BUSINESS, BOUGHT A COUPLE OF BABY TIGERS FOR ALL THE WRONG REASONS, AND DID A SHOW AT THE ALADDIN HOTEL CALLED 'PREDATOR'S PARADISE,' AND I JUST DIDN'T LIKE THE EXPLOITATION OF EXOTIC ANIMALS.

SO, I DECIDED TO START RESCUING ANIMALS.

ALL THE ANIMALS THAT WE HAVE HAVE EITHER BEEN RESCUED OR RETIRED FROM SHOW BUSINESS, OR THEY HAVE BEEN CONFISCATED BY GOVERNMENT AGENCIES, EITHER THE USDA OR THE DEPARTMENT OF WILDLIFE.

[ LION GROWLING ] Narrator: ANTHONY, THE LION, CAME TO KEEPERS OF THE WILD AS A SICKLY CUB WHO WAS DISCARDED AFTER BEING AUCTIONED OFF IN VIRGINIA.

RILEY, THE COYOTE, WAS RESCUED BY ARIZONA GAME AND FISH.

THEY CAME TOGETHER WHEN BOTH WERE JUST OVER A MONTH OLD -- TOO YOUNG, PERHAPS, TO UNDERSTAND THAT NATURE WOULD NEVER CAST THEM AS FRIENDS.

Kraft: SINCE THEY WERE BOTH THE SAME AGE, AND WE HAD THEM IN OUR HOUSE, WE FIGURED, 'WELL, YOU KNOW, LET'S RAISE THEM TOGETHER.'

AND SO THEY GREW UP TOGETHER FROM LITTLE BABIES ON.

WHEN THEY WERE VERY, VERY SMALL, IT WAS REAL EASY BECAUSE THEY WERE BOTH ABOUT THE SAME SIZE.

AND, OF COURSE, THE LITTLE COYOTE, SHE'S STAYED RELATIVELY SMALL, AND SHE JUST WATCHES HIM GROW UP TO BE A GIANT.

THE GENTLENESS BETWEEN THEM AND THE BOND AND THE CLOSENESS HAS NEVER CHANGED.

COYOTES ARE SOCIAL ANIMALS, AND SO ARE LIONS.

I THINK COMPANY IS VERY, VERY IMPORTANT TO SOCIAL ANIMALS.

Narrator: SOCIAL ANIMALS BUILD BONDS BY PLAYING TOGETHER, TESTING THEIR STRENGTHS AND LIMITS.

AND IN DOING SO, THEY LEARN ABOUT TRUST.

Kraft: I THINK IT'S A WONDERFUL EXERCISE FOR THEM TO ACT OUT THEIR HUNTING TECHNIQUES AND THEIR STALKING TECHNIQUES.

I ALSO SEE HER TEASING HIM -- SHE RUNS AWAY AND THEN SHE LETS HIM CATCH HER.

AND HE WILL JUMP HER -- HE WILL STALK HER AND JUMP HER, AND THEN SHE DOES A LITTLE YELP AND HE LETS HER GO RIGHT AWAY.

I HAVE NOT YET SEEN THEM INTENTIONALLY HURT EACH OTHER AT ALL.

I WOULD INTERVENE IF I FELT THAT THE COYOTE WAS IN DANGER -- I WOULD PULL HER IN A HEARTBEAT.

I DON'T WANT TO PUT HER IN ANY KIND OF JEOPARDY.

BUT I DON'T THINK THAT SHE THINKS THAT SHE'S A COYOTE.

I DON'T THINK SHE'S EVER SEEN OTHER COYOTES.

ANTHONY AND RILEY'S RELATIONSHIP MAKES THEM HEALTHIER.

IT'S KIND OF LIKE HUMANS, IF YOU'VE GOT A GOOD RELATIONSHIP, MORE THAN LIKELY YOU'LL BE HAPPIER, EVERYTHING IN YOUR BODY FUNCTIONS BETTER.

I THINK MENTALLY YOU'RE MORE STABLE, AND I THINK IT'S THE SAME THING WITH THE LION AND THE COYOTE.

I'VE BEEN AROUND BIG CATS FOR 20 SOME ODD YEARS NOW, AND I THOUGHT I'D SEEN IT ALL.

I MUST ADMIT THAT THIS IS EXTREMELY RARE.

BUT MOTHER NATURE IS TEACHING ME SOMETHING EVERY TIME, PARTICULARLY WHEN I SEE A RELATIONSHIP LIKE THIS.

Narrator: BUT ARE STRONG SOCIAL BONDS ENOUGH TO KEEP PREY ANIMALS SAFE IN THESE MISMATCHED RELATIONSHIPS?

Grandin: THERE'S A VERY STRONG INSTINCT IN THE PREDATOR ANIMALS, WITH A LION OR A TIGER, TO RUN AFTER SOMETHING THAT MOVES RAPIDLY.

NOW, THEY LEARN, YOU KNOW, WHAT ANIMALS ARE LUNCH AND WHAT ANIMALS ARE NOT.

YOU KNOW, TO SAY THAT AN ANIMAL IS JUST SORT OF A ROBOT THAT BLINDLY DOES INSTINCTUAL HARD-WIRED BEHAVIOR, THAT'S JUST RIDICULOUS.

WHEN IT COMES TO SOME OF THE EMOTIONAL THINGS AND COGNITION IN ANIMALS, I THINK SCIENTISTS ARE GOING TO PROVE THAT LITTLE OLD LADIES IN TENNIS SHOES WHO SAY THAT LITTLE FIFI REALLY CAN THINK, ARE RIGHT, BUT THAT DOESN'T MEAN THAT AN ANIMAL CAN THINK AT OUR LEVEL.

THERE'S STILL A LOT THAT'S NOT KNOWN.

BUT IT'S BEEN VERY CLEARLY SHOWN THAT IN ALL MAMMALS, YOU'VE GOT THE SAME EMOTIONAL DRIVERS DOWN IN THE BASE OF THE BRAIN THAT DRIVE BEHAVIOR -- FEAR, SEPARATION DISTRESS OR PANIC, SEEKING THE URGE TO EXPLORE NEW THINGS, RAGE, SEX BEHAVIOR, AND PLAY.

[ GOATS BLEATING ] ♪ HERE WE COME ♪ ♪ WALKING DOWN THE STREET ♪ ♪ WE GET THE FUNNIEST LOOKS FROM ♪ ♪ EVERYONE WE MEET ♪ ♪ HEY, HEY, WE'RE THE MONKEES ♪ ♪ AND PEOPLE SAY WE MONKEY AROUND ♪ ♪ BUT WE'RE TOO BUSY SINGING ♪ ♪ TO PUT ANYBODY DOWN ♪ ♪ WE'RE JUST TRYING TO BE FRIENDLY ♪ ♪ COME AND WATCH US SING AND PLAY... ♪ Narrator: BEFORE SCIENTISTS CAN BEGIN TO UNDERSTAND CROSS-SPECIES RELATIONSHIPS, THEY NEED TO LEARN MORE ABOUT THE COMPLEXITY OF THE BONDS ANIMALS FORM WITHIN THEIR OWN SPECIES.

Woman: I THINK SCIENTISTS ARE STARTING TO BUY INTO THIS IDEA THAT OTHER ANIMALS HAVE COMPLEX EMOTIONAL LIVES.

UNTIL VERY RECENTLY, AND WE'RE TALKING THIS YEAR, WE DIDN'T LIKE TO USE THE WORD 'FRIENDSHIP' WHEN WE WERE TALKING, YOU KNOW, ABOUT SERIOUS SCIENCE.

IN SORT OF PASSING, SPEAKING WITH OUR FRIENDS AND COLLEAGUES, WE WOULD TALK ABOUT FRIENDSHIP IN OTHER ANIMALS, BUT WE WOULD NEVER WRITE IT IN A SCIENTIFIC PAPER.

THE USE OF THE TERM FRIENDSHIP AND THE STUDY OF FRIENDSHIP, NOW IT'S REALLY KIND OF COME INTO ITS OWN AS A TOPIC.

IN FACT, BY STUDYING MONKEYS, I'M HOPING TO GET CLUES AS TO WHY FRIENDSHIP EVOLVED IN PEOPLE.

MONKEYS DO HAVE FRIENDS.

THEY INTERACT WITH INDIVIDUALS WHO THEY ARE NOT RELATED TO IN FRIENDLY WAYS.

EVEN THOUGH NO ONE IS GOING TO SAY THAT THE DEFINITION OF 'FRIENDSHIP' IN MONKEYS IS EXACTLY THE SAME AS HOW WE MIGHT DEFINE FRIENDSHIP IN HUMANS, IT'S KIND OF UNDENIABLE THAT THERE ARE INDIVIDUALS WHO AREN'T RELATED TO EACH OTHER WHO SPEND TIME TOGETHER IN A FRIENDLY FASHION.

SOMETIMES WE CALL IT SOCIAL BONDS, THAT THEY'RE BONDED.

BUT, I MEAN, WHAT IS THAT, OTHER THAN JUST SORT OF A MORE DESCRIPTIVE WORD FOR FRIENDSHIP?

BUT WHAT, EXACTLY, FRIENDSHIPS GET YOU, THAT IS VERY MUCH STILL OPEN, WE'RE STILL WORKING ON IT.

Narrator: CAYO SANTIAGO IS ONE OF THE FEW PRIMATE FIELD RESEARCH SITES IN THE WORLD DEVOTED TO THE LONG-TERM STUDY OF RHESUS MACAQUES.

PROFESSOR LAUREN BRENT HAS SPENT OVER SIX YEARS ON THE ISLAND STUDYING HOW NON-RELATED MONKEYS INTERACT AND FORM BONDS.

HER RESEARCH HAS LED TO SOME GROUND-BREAKING DISCOVERIES.

Brent: SO, WE CAN'T ASK A MONKEY, 'WHO IS YOUR BEST FRIEND?'

SO WE HAVE TO STUDY IT BY OBSERVING THEIR BEHAVIORS.

AND SO, WE DEFINE FRIENDSHIP IN MONKEYS AS WHO THEY SPEND A LOT OF TIME WITH, AND WHO THEY INTERACT WITH IN A FRIENDLY MANNER.

IN PARTICULAR, WE LOOK AT THINGS LIKE GROOMING, FEEDING NEXT TO EACH OTHER, WHO SPENDS TIME TOGETHER, WHO IS AGGRESSIVE TO WHO.

SO, WHATEVER THE MONKEYS ARE DOING, WE'RE FOLLOWING THEM AND RECORDING IT.

DO YOU KNOW THAT ONE?

SO, WE WOULD PICK AN INDIVIDUAL, AND WE DO TEN-MINUTE FOCAL FOLLOWS.

SO, FOR TEN MINUTES, RECORD EVERYTHING THAT THE FOCAL ANIMAL IS DOING, WHO THEY ARE INTERACTING WITH, AND SO, THE MONKEYS DICTATE WHAT HAPPENS.

SO, THAT'S 25-R.

I WAS TELLING JOEL THIS MORNING THAT 25-R USED TO BE A MEMBER OF THIS LITTLE BAND OF MALES THAT WERE ALL MIDDLE RANKING.

THEY WERE TOGETHER QUITE A LOT AND WOULD SUPPORT EACH OTHER IN FIGHTS.

BUT HIS BUDDIES HAVE DISPERSED TO ANOTHER GROUP.

SO, HE'S KIND OF LEFT ON HIS OWN, ALTHOUGH ONE OF THEM SEEMS TO HAVE MAYBE COME BACK, BUT I HAVEN'T SEEN THEM INTERACTING.

HE'S A GOOD GUY.

Narrator: THE MONKEYS HAVE TATTOOS TO IDENTIFY THEM, BUT IT'S STILL TRICKY.

THERE ARE OVER 1,000 ON THE ISLAND, SPREAD ACROSS AT LEAST EIGHT TROOPS WHOSE MEMBERSHIP CONSTANTLY CHANGES, MAKING LAUREN'S TEST TROOP A MOVING TARGET.

20-F REALLY... I DON'T KNOW IF YOU'LL NOTICE IT WHEN YOU COLLECT DATA, BUT IN PREVIOUS YEARS 20-F HAS BEEN REALLY ASOCIAL.

SO, SHE IS ALWAYS KIND OF THE PERIPHERY OF THE GROUP.

I DON'T KNOW IF I'VE EVER SEEN HER GROOMING ANYBODY.

[ MACAQUES CALLING ] IN TERMS OF MY RESEARCH, I'VE BEEN ABLE TO SHOW THAT FEMALES THAT HAVE TIGHTER SOCIAL BONDS HAD LOWER STRESS HORMONE LEVELS.

SO, WE MEASURE, IN THEIR FECES THEIR LEVEL OF CORTISOL, WHICH IS THIS HORMONE THAT YOU RELEASE WHEN YOU FEEL STRESSED.

AND FEMALES THAT HAVE TIGHTER KNIT SOCIAL CONNECTIONS HAD LOWER STRESS HORMONE LEVELS.

WE KNOW GROOMING FEELS GOOD, IT'S SORT OF LIKE A MASSAGE.

SO WHEN YOU'RE RECEIVING GROOMING, YOUR STRESS HORMONE LEVELS GO DOWN, YOU RELEASE SOMETHING THAT'S CALLED OXYTOCIN, WHICH IS THE, SORT OF, HORMONE OF LOVE, BECAUSE WHEN YOU'RE IN PHYSICAL CONTACT WITH ANOTHER INDIVIDUAL, YOU RELEASE OXYTOCIN -- IT HAS THIS CASCADING EFFECT ON YOUR PHYSIOLOGY.

SO, INTERACTING WITH ANOTHER INDIVIDUAL IN A POSITIVE WAY, IN BOTH PEOPLE AND MONKEYS, FEELS GOOD.

UM, SO, SCAN -- HE'S BEEN SOCIAL.

THE BENEFIT OF FRIENDSHIP IS MULTI-LEVELED.

FEMALES WHO HAVE STRONGER SOCIAL BONDS LIVE LONGER, HAVE MORE INFANTS, THEIR INFANTS ARE MORE LIKELY TO SURVIVE.

SO, MAYBE ALL OF THESE THINGS, THESE FAVORS THAT WE HAVE, THIS PHYSIOLOGICAL CORRELATION WITH FRIENDSHIP, THEN BUILDS TO THIS OUTPUT OF BETTER EVOLUTIONARY FITNESS.

WE KNOW NOW THAT HAVING SOCIAL BONDS WITH OTHER INDIVIDUALS HELPS YOU SURVIVE, HELPS YOU COPE WITH THE CHALLENGES THAT YOU FACE IN YOUR ENVIRONMENT.

Narrator: MAINTAINING TIGHT SOCIAL BONDS REQUIRES RECOGNIZING NOT ONLY YOUR FRIENDS, BUT ALSO THE FRIENDS OF YOUR FRIENDS, AND THE ENEMIES OF YOUR FRIENDS.

BUILDING FRIENDSHIPS IS A COMPLEX SOCIAL BEHAVIOR THAT SCIENTISTS SUCH AS LAUREN BRENT NOW BELIEVE EVOLUTION ENCODED INTO THE DNA OF HUMANS AND OTHER SPECIES.

Grandin: I'VE STUDIED A LOT OF THE NEUROSCIENCE OF EMOTIONS.

AND THERE'S BASIC EMOTIONS THAT ANIMALS DEFINITELY HAVE.

IT HAS BEEN IN THE NEUROSCIENCE LITERATURE FOR YEARS.

IT WAS IN THE NEUROSCIENCE LITERATURE WHEN I STUDIED PSYCHOLOGY BACK IN THE '60s.

PROBLEM IS, THERE'S THIS RESEARCH THAT'S ALL OVER IN NEUROSCIENCE, AND THERE'S A LOT OF PEOPLE, EVEN VETERINARIANS, THAT DON'T WANT TO ADMIT THAT ANIMALS HAVE EMOTIONS.

I JUST GOT AN E-MAIL FROM A VETERINARIAN THE OTHER DAY THAT SAYS, 'WELL, WE JUST CAN'T SAY THAT ANIMALS HAVE EMOTIONS.

IT'S JUST STRESS.'

I DON'T... I DON'T BUY THAT.

WE GOT A BANDIT IN THE TREE.

Woman: 16 YEARS AGO, I WAS TAKING IN DOGS AND CATS AND FARM ANIMALS, AND SOMEBODY BROUGHT ME A PAIR OF RACCOON KITS.

IN THE STATE OF OKLAHOMA, THE STATE OWNS THE WILDLIFE AND IN ORDER TO CARE FOR THEM, YOU HAVE TO HAVE A SPECIAL LICENSE FOR REHABILITATION.

AND I WENT LOOKING FOR A FACILITY THAT WOULD TAKE THEM AND TURN THEM LOOSE WHEN THEY WERE RAISED; THERE WASN'T ONE.

SO, WHAT I DECIDED TO DO WAS TO GET A LICENSE AND RUIN MY LIFE.

AT THE TIME, I DIDN'T KNOW I WAS RUINING MY LIFE.

I THOUGHT, A COUPLE OF RACCOON KITS, LOTS OF FUN, GET THEM WILD.

MY FIRST YEAR, I TOOK IN 860 ORPHANED AND INJURED WILD ANIMALS.

AND SO, I REALIZED THAT THERE WAS A HUGE NEED.

IN 16 YEARS, I'VE RELEASED WAY OVER 16,000 ANIMALS INTO THE WILD.

WE AVERAGE 1,000 A YEAR.

Narrator: THERE IS ONE ANIMAL AT WILD HEART RANCH WHO CAN NEVER BE RELEASED -- A 16 YEAR OLD LONE SITKA DEER NAMED AMY, WHO IS NOT NATIVE TO THE AREA.

Tucker: HER MOTHERING INSTINCTS ARE VERY DOMINANT.

SO, BECAUSE I HAVE MANY, MANY BABY DEER, IT WORKED OUT PERFECT, BECAUSE SHE'S WILLING TO ACCEPT THESE ORPHANS AS HER OWN AND TEACH THEM TO BEHAVE LIKE A DEER.

THE DOG IS A GOLDEN RETRIEVER PUPPY NAMED 'RANSOM.'

HE WAS BORN BLIND.

AT SIX WEEKS OLD, WE TOOK THE PUPPY IN, OTHERWISE THE PUPPY WOULD HAVE BEEN EUTHANIZED.

WHAT HAPPENED WAS, HERE'S THIS LITTLE BLIND PUPPY, AND WHEN I'M NOT AROUND, HE'S LOOKING FOR COMFORT, HE'S TRYING TO FIND SOMETHING TO NURTURE HIM.

AMY, BEING A NATURAL MOTHER, ADOPTED THIS BLIND PUPPY.

SO, WE SHARE CUSTODY.

AMY AND I HAVE JOINT CUSTODY OF THE DOG.

AND, WHETHER I'M HERE OR SHE'S HERE, IT ENRICHES HIS LIFE.

AND IT GIVES HIM A SENSE OF SECURITY.

SHE HAS A NATURAL COMPASSION.

SHE KNOWS IT'S NOT A DEER.

SHE'S HAD PLENTY OF DEER -- SHE KNOWS HE'S NOT A DEER.

THEY SLEEP TOGETHER AT NIGHT, AND THEN IN THE MORNING, HE WAKES UP, AND BEFORE HE STARTS HIS DAY, SHE SPIKES HIS COAT.

AND, I KNOW THAT HE'S GOTTEN HIS LITTLE HAIRDO FOR THE DAY FROM AMY, HIS DEER MOM.

RANSOM REGAINED HIS EYESIGHT SEVERAL WEEKS AGO.

IT WAS SUDDEN.

IT TURNED OUT HIS PROBLEM WAS NUTRITIONAL.

SO, NOW HE SEES AMY, HE KNOWS WHAT SHE IS, BUT TO HIM, THAT'S STILL MOM.

THAT'S THE RELATIONSHIP THAT'S BEEN FORGED AND NURTURED.

IT WORKS FOR RANSOM, AND AMY LOVES HIM.

Man: I THINK A LOT OF PEOPLE FIND THESE CROSS-SPECIES RELATIONSHIPS SURPRISING, BECAUSE THEY DON'T APPRECIATE THE RICHNESS OF THE EMOTIONAL LIVES OF NON-HUMAN ANIMALS.

THAT NON-HUMAN ANIMALS EXPERIENCE THE SAME EMOTIONS WE DO.

I LOVE STORIES ABOUT ANIMAL BEHAVIOR, AND I ALWAYS LIKE TO SAY THE PLURAL OF ANECDOTE IS DATA.

AND WHEN I HEAR 100 STORIES ABOUT AN IMPROBABLE RELATIONSHIP, AS A SCIENTIST, IT BEHOOVES ME OR SOMEONE TO GO STUDY THEM.

Narrator: ENDURING RELATIONSHIPS ACROSS SPECIES MAY BE RARE, BUT CARETAKERS OF ANIMALS HAVE OBSERVED SO MANY THAT SCIENTISTS NOW REGARD THEIR ACCOUNTS AS VALUABLE FIELD REPORTS, WARRANTING FURTHER STUDY.

THIS COULD HERALD A WHOLE NEW AREA OF SCIENCE.

Tucker: COME ON, BABIES.

COME HERE, CHARLIE HORSE. COME ON, HORSE.

THIS IS CHARLIE AND JACK.

CHARLIE IS A HORSE THAT I RESCUED.

HE'S EXTREMELY OLD -- HE IS 40 YEARS OLD.

HE'S LOST THE SIGHT IN BOTH OF HIS EYES.

WHEN HE LOST HIS EYESIGHT, WE DECIDED THAT WE NEEDED TO PUT HIM DOWN, BUT WE DIDN'T GIVE ENOUGH CREDIT TO RELATIONSHIPS AMONG OUR ANIMALS.

BECAUSE AS SOON AS CHARLIE LOST HIS EYESIGHT, JACK, MY OLD GOAT HERE, WHO'S 16, TOOK UP THE JOB OF BEING CHARLIE'S EYES.

ONE TIME WE HAD SOME TORNADO WEATHER, AND THERE WAS A MICROBLAST.

[ HORSE WHINNIES ] [ THUNDER CRASHING ] JACK CAME HOME SCREAMING.

AND IT WAS LIKE, 'TIMMY'S IN THE WELL!'

KIND OF THING -- HE'S RUNNING TO THE GATE, HE'S YELLING.

AND SO WE COME THROUGH THE GATE, AND JACK JUST TOOK OFF.

AND WHAT WE FOUND WAS THE MICROBLAST HAD TWISTED A GROVE OF TREES IN A CIRCLE, AND MY BLIND HORSE IS IN THE MIDDLE OF IT.

AND THERE WAS NO WAY FOR HIM TO GET OUT.

SO, JACK ACTUALLY CAME AND GOT US TO GO HELP HIS BUDDY BECAUSE HE COULDN'T LEAD CHARLIE OUT OF THAT.

AFTER THAT DAY, I'VE NO LONGER WORRIED ABOUT MY BLIND HORSE.

THE REASON I KNOW THAT JACK KNOWS THAT CHARLIE IS BLIND IS BECAUSE WHEN CHARLIE LOST HIS EYESIGHT IN THE ONE EYE, JACK WOULD LEAD HIM ON THE SIDE.

WHEN CHARLIE LOST THE EYESIGHT IN HIS REMAINING EYE, JACK STARTED LEADING IN THE FRONT.

THERE IS A PATCH OF GRASS THAT GROWS IN THE BACK OF THE PROPERTY, AND IT'S HARD TO GET TO.

AND FOR NO APPARENT REASON, JACK WILL TAKE CHARLIE BACK, LETS HIS FRIEND GRAZE.

WHEN CHARLIE'S DONE, JACK LEADS HIM BACK.

WHEN THEY ARE LEADING BACK, TYPICALLY THE GOAT WOULD BE FORAGING ALONG THE WAY HOME -- HE DOESN'T DO THAT; HE STAYS ON THE TRAIL.

HE LINES HIMSELF UP IN FRONT OF HIS BUDDY, KEEPS CHARLIE WITHIN 10 OR 15 FEET OF HIM, AND BRINGS HIM HOME SLOWLY.

CHARLIE CAN TELL THE DIFFERENCE BETWEEN JACK'S FOOTSTEPS AND THE OTHER HORSE OR PEOPLE.

CHARLIE KNOWS THOSE FOOTSTEPS LIKE HIS OWN HEARTBEAT.

ONCE CHARLIE KNOWS JACK HAS HIM ON THE TRAIL, YOU'LL NOTICE HE STOPS SWEEPING -- BECAUSE HE KNOWS JACK IS GOING TO LEAD HIM TO THIS AREA THAT CHARLIE IS MOST FAMILIAR WITH, AND THEN HE'S GOOD.

WE SAY THAT HUMANS ARE THE ONLY ONES WITH THE INSTINCT OF COMPASSION.

I SAY THAT'S WRONG.

I SAY THAT SOME PEOPLE ARE MORE COMPASSIONATE THAN OTHERS, SOME ANIMALS ARE MORE COMPASSIONATE THAN OTHER ANIMALS BUT WE'RE ALL CAPABLE.

WE ALL HAVE THE SAME INSTINCT TO BE COMPASSIONATE.

JACK GETS NOTHING OUT OF THIS RELATIONSHIP.

CHARLIE CAN NEITHER PROTECT HIM OR PROVIDE FOR HIM.

SO, WHAT JACK HAS DONE IS, HE IS PROTECTING HIS FRIEND, PERIOD, END OF STORY.

THERE IS NO CHARLIE WITHOUT JACK.

ALL OF THE THINGS THAT A NORMAL, SIGHTED HORSE WOULD HAVE, HE HAS, BASED ON A RELATIONSHIP WITH AN OLD GOAT.

Narrator: AFTER 16 YEARS WITH JACK, CHARLIE RECENTLY HAD HIS LAST MOMENT IN THE SUN AND DIED.

JACK WALKED OUT TO HIS FRIEND AND PUT HIS HEAD DOWN.

AND, UH, HE TURNED AROUND AND WENT HOME.

UM, AND THE WAY HE WENT HOME SURPRISED ME.

I KIND OF EXPECTED JACK TO HAVE AN EMOTIONAL REACTION, BUT HE REALLY DIDN'T.

HE TURNED AROUND, AND HE HEADED BACK HOME DOWN THE TRAIL.

AND WENT TO HIS FAVORITE PLACE TO BED DOWN AT NIGHT, AND HE WAS DONE.

AT FIRST, I THOUGHT, WELL, MAYBE HE DOESN'T UNDERSTAND CHARLIE HAS GONE.

BUT THEN I THOUGHT, WELL, HE'S NEVER LEFT HIS SIDE, AND SEEING CHARLIE LAYING DOWN LIKE THAT SHOULD ALARM JACK.

BUT, IT DIDN'T ALARM HIM.

HE JUST KIND OF WENT, 'OKAY, OLD FRIEND, YOU KNOW, WE'RE DONE.'

AND VERY QUICKLY, HE'S GONE DOWNHILL.

I DON'T WANT THIS LITTLE GOAT AND THIS LITTLE HORSE'S STORY TO PASS UNKNOWN.

THE STIGMA WITH ANIMALS THAT THEY'RE JUST MUSCLE AND BONE AND ALL THEY CARE ABOUT IS FOOD -- I MEAN, WHO WOULD THINK THAT A GOAT WOULD TAKE UP WITH A BLIND HORSE AND SPEND YEARS DOING NOTHING EXCEPT BABYSITTING THIS ANIMAL JUST BECAUSE HE NEEDED HELP?

THESE GUYS HAVE SO MUCH MORE TO THEM THAN WE GIVE THEM CREDIT FOR.

WE BURIED CHARLIE IN A SPOT IN THE WOODS UNDER THE TREES WHERE THEY USED TO HANG OUT.

AND YOU COULD GO THERE IN THE AFTERNOON, AND CHARLIE WOULD BE GRAZING, AND JACK WOULD BE LYING IN THE SUN, AND... THAT'S WHERE WE PUT CHARLIE, AND SOON JACK WILL JOIN HIS FRIEND RIGHT THERE.

Grandin: I THINK GRIEVING, YOU KNOW, WHEN YOU LOSE A FRIEND, IT'S A FORM OF SEPARATION DISTRESS.

THERE'S SOME BRAND NEW RESEARCH THAT SHOWS THAT PHYSIOLOGICALLY, THE PAIN CIRCUITS ACTUALLY GET INVOLVED IN EMOTIONAL PAIN.

THERE'S BEEN BRAIN SCAN STUDIES WHERE THEY'VE PUT PEOPLE IN SCANNERS AND SHOW THEM PICTURES OF DEPARTED LOVED ONES, AND THE PAIN CIRCUITS ARE TURNING ON.

Brent: WE ARE INTERESTED IN WHAT THEY PERCEIVE, AT LEAST WHEN IT COMES TO DEATH.

SO, WE'VE DESIGNED AN EXPERIMENT WHERE I SHOW MONKEYS PICTURES OF THE FACES OF OTHER MONKEYS.

MONKEY, LOOK LEFT.

LOOK RIGHT.

ON ONE SIDE OF THE APPARATUS, I'LL SHOW THEM THE PICTURE OF AN ANIMAL WHO'S IN THEIR GROUP, CURRENTLY ALIVE.

AND THE OTHER SIDE OF THE APPARATUS, I'LL SHOW THEM A PICTURE OF AN ANIMAL RECENTLY IN THEIR GROUP, BUT WHO HAS DIED.

AND I RECORD THEIR REACTION.

AND IF THEY SPEND MORE TIME LOOKING AT THE DEAD INDIVIDUAL, POTENTIALLY THIS IS AN INDICATOR THAT AT LEAST IT'S SOMETHING THAT THEY FIND INTERESTING.

WE WON'T BE ABLE TO SAY, 'OH, IT'S A SIGN OF GRIEF,' BUT AT LEAST IT'LL BE A FIRST STEP IN HAVING GOOD QUANTITATIVE EVIDENCE THAT THIS IS SOMETHING THAT THEY POTENTIALLY UNDERSTAND.

Narrator: PROFESSOR BRENT'S FIELD RESEARCH ON GRIEF AMONG MACAQUES CONTINUES; THE RESULTS OF HER EXPERIMENTS HAVE YET TO BE TABULATED.

Brent: CURRENTLY, WE DON'T ACTUALLY UNDERSTAND VERY MUCH IF ANYTHING ABOUT WHAT NON-HUMAN ANIMALS THINK ABOUT DEATH.

WE CAN'T SAY WITH ANY CERTAINTY THAT NON-HUMAN ANIMALS GRIEVE.

Bekoff: SOME PEOPLE LIKE TO THINK THAT WE ARE THE TEMPLATE AGAINST WHICH ALL OTHER ANIMALS SHOULD BE COMPARED.

BUT WE DON'T REALLY HAVE EXCLUSIVITY ON EMOTIONS.

WE HAVE JOY, OTHER ANIMALS HAVE JOY.

WE HAVE DEEP GRIEF, OTHER ANIMALS HAVE DEEP GRIEF.

OUR JOY MAY BE DIFFERENT FROM THE JOY OF A DOG, OR OUR GRIEF MAY BE DIFFERENT FROM THE GRIEF OF A DEEPLY GRIEVING GOAT WHO LOST THEIR HORSE FRIEND, OR AN ELEPHANT WHO LOST THEIR ELEPHANT FRIEND, BUT FROM THE FACT THAT IT'S DIFFERENT, IT DOESN'T MEAN IT'S LESS DEEP, IT'S JUST DIFFERENT.

Narrator: AT THE MONKEYLAND PRIMATE SANCTUARY IN SOUTH AFRICA, SURPLUS ZOO ANIMALS AND ABANDONED PETS ARE OFFERED A NEW BEGINNING.

KEEPERS HELP THEM GAIN THEIR NATURAL IDENTITIES IN A LARGE, PROTECTED HABITAT.

Schauerte: OUR MAIN CONCERN WITH PRIMATES IS THAT THEY ARE STILL BOUGHT AS A PET.

AND WE'VE SEEN IT WITH EXPERIENCE THAT MONKEYS DON'T MAKE GOOD PETS.

THE BACKGROUND TO MOST OF OUR INDIVIDUAL MONKEYS AREN'T REALLY WELL KNOWN TO US, BECAUSE THE PEOPLE WHO BRING THE MONKEYS TO US ARE NOT REALLY KEEN TO ACTUALLY EXPLAIN THE SCENARIO PRIOR TO THEM BEING DROPPED OFF HERE.

Narrator: ATLAS THE GIBBON WAS BORN IN A SOUTH AFRICAN ZOO.

HE WAS ONLY TWO WHEN HIS FATHER BECAME VERY AGGRESSIVE WITH HIM AND THE ZOO WAS FORCED TO TAKE ATLAS AWAY FROM HIS FAMILY.

AFTER 13 YEARS AT MONKEYLAND, HE IS STILL STRUGGLING TO FIT IN.

ATLAS SPENT HIS FIRST FEW MONTHS HERE IN A PRE-RELEASE CAGE WITH TWO OTHER GIBBONS.

THE KEEPERS HOPED HE WOULD BOND WITH MONKEYS THAT, ALTHOUGH DARKER IN COLOR, WERE OF HIS OWN KIND.

INSTEAD, ATLAS SPENT MORE TIME FOCUSING HIS ATTENTION ON THE MONKEYS OUTSIDE THE ENCLOSURE.

Schauerte: ALL THE MONKEYS THAT ACTUALLY LIVE IN MONKEYLAND ARE CURIOUS OF NEWCOMERS.

SO, ANY NEW INDIVIDUAL THAT IS ACTUALLY RELEASED INTO THE PRE-RELEASE CAGE WILL BE VISITED BY, TYPICALLY, NEARLY EVERY SINGLE MONKEY IN THE FOREST, JUST TO SEE WHO THEY ARE.

Narrator: ONE GROUP OF MONKEYS REALLY CAUGHT THE EYE OF YOUNG ATLAS.

Schauerte: NORMALLY WE DON'T SEE MUCH INTERACTION BETWEEN SPECIES, BUT CAPUCHIN MONKEYS, WE NOTICED THAT, ESPECIALLY THE JUVENILES, WERE ENGAGING ON THE FENCING OR ON THE ROOF OF THE CAGE, WERE ENGAGING IN PLAYFUL ACTIVITIES WITH ATLAS.

Narrator: WHEN IT CAME TIME TO BE RELEASED FROM THE CAGE, THE TWO OTHER GIBBONS BOUNDED OFF INTO THE FOREST, LEAVING ATLAS BEHIND.

THAT'S WHEN ATLAS MADE AN UNEXPECTED DECISION.

[ ATLAS CALLING ] HE JOINED THE CAPUCHINS, MAKING THEM HIS SURROGATE FAMILY.

IN THE WILD, MALE GIBBONS ARE SUBSERVIENT TO FEMALES, AND EVEN THEIR OWN OFFSPRING.

BUT FAMILY BONDS ARE TIGHT AND ENDURING.

THE BONDS ATLAS HAS FORMED WITH THE CAPUCHINS, HOWEVER, ARE GENERAL AND FLEETING.

HE ENGAGES THE PLAYFUL CURIOSITY OF THE JUVENILES UNTIL THEY GROW AND MOVE UP IN THE TROOP.

THEN HE CONNECTS WITH THE NEXT GENERATION.

Narrator: ATLAS WAITS WITH THE JUVENILES FOR HIS TURN TO EAT.

THE CAPUCHINS TOLERATE ATLAS; HE'S A MISFIT.

BUT EVEN AS A MARGINAL MEMBER OF THE TROOP, HE GAINS SOME FEELING OF COMPANIONSHIP.

THE CONFINES OF THE SANCTUARY BRING TOGETHER MONKEYS THAT WOULD RARELY COME INTO CONTACT IN THE WILD.

AND THEY ALL HAVE TO FIGURE OUT HOW TO GET ALONG.

LARGER AND MORE AGGRESSIVE, VERVETS ARE THE CAPUCHINS' MAIN RIVALS FOR FOOD.

THE YOUNG CAPUCHINS VALUE ATLAS AS A PROTECTIVE ALLY.

HE GUARDS THEM AS THEY FEED, DRIVING OFF THE COMPETITION.

Narrator: DESPITE HIS EFFORTS, ATLAS SEEMS DESTINED TO LEAD A SOLITARY LIFE.

MOST GIBBONS DO NOWADAYS, BECAUSE THEIR SPECIES IS ENDANGERED.

Schauerte: ANIMALS DON'T ALWAYS FIND THE RIGHT PARTNER AT THE RIGHT TIME, ESPECIALLY NOWADAYS WITH DEFORESTATION BEING A BIG ISSUE IN THE WILD.

SO, THEY MAY BE SPENDING MONTHS OR EVEN YEARS ALONE WITHOUT THE BECK CALL OF FEMALE THAT WOULD ACTUALLY PARTNER UP WITH THEM.

[ CALLING ] [ ATLAS'S CALLS ECHO AND FADE ] Bekoff: MANY ANIMALS HAVE A VERY STRONG SOCIAL DRIVE.

IT'S ALMOST AN INSTINCT TO BE WITH OTHER ANIMALS.

AND YOU'LL FIND VARIATION WITHIN SPECIES, BUT REALLY MOST INDIVIDUALS OF SOCIAL SPECIES HAVE THIS INNATE DRIVE TO HAVE FRIENDS AND TO BE PART OF A GROUP.

SOME OF THE CROSS-SPECIES RELATIONSHIPS ARE REALLY AMONG ODD COUPLES, IF YOU WILL.

Narrator: SOMETIMES, ANIMAL ATTRACTION IS A MYSTERY.

THIS 45-YEAR-OLD FEMALE ALDABRA TORTOISE WAS CHOSEN BY AN UNLIKELY SUITOR, A MALE BRANT GOOSE.

THE GOOSE FOLLOWS THE TORTOISE EVERYWHERE, AND WARY BE THE ONE WHO GETS TOO CLOSE TO HER.

[ HONKING ] BRANT GEESE MATE FOR LIFE, AND IN THE TORTOISE, OUR GOOSE HAS FOUND A ROCK STEADY PARTNER, BUT WHAT DOES THE TORTOISE GET OUT OF IT?

WELL, SHE GETS A PROTECTOR, A COMPANION, AND A COVETED SPACE AT THE ALL-YOU-CAN-EAT SALAD BAR.

[ HONKING ] THE TORTOISE IS ENTIRELY CAPABLE OF REBUFFING HIS ATTENTIONS, BUT SHE ACCEPTS THEM.

THEY'VE BEEN TOGETHER FOR OVER FOUR YEARS, AND THEIR KEEPERS HAVE NEVER SEEN ANYTHING LIKE IT.

Brent: WHEN IT COMES TO FORMING THESE COMPLICATED RELATIONSHIPS WITH OTHERS, I THINK WE HAVE TO ADMIT THAT WE'RE NOT THE ONLY ONES THAT DO THAT, AND THAT OTHER ANIMALS HAVE FRIENDS, TOO, AND POTENTIALLY EVOLVED THAT TRAIT FOR THE SAME REASON THAT WE DID.

THIS INCREDIBLY COMPLICATED, TIME CONSUMING, SOMETIMES PAINFUL, THING THAT WE DO -- GETTING A RELATIONSHIP WITH ANOTHER INDIVIDUAL -- IS NECESSARY FOR OUR SURVIVAL.

Bekoff: GOOD SCIENTISTS ARE REALLY TAPPING INTO STORIES AND THEN DOING MORE SYSTEMATIC RESEARCH.

IT'S GOING TO BE SLOW, BECAUSE SCIENTISTS WE'RE VERY SLOW TO ACCEPT THAT DOGS HAD EMOTIONS.

SO, THEY'RE GOING TO BE MORE RELUCTANT TO THINK ABOUT HIPPOS AND TORTOISES, OR, SAY, CHEETAHS AND DOGS.

BUT I THINK WITH THIS HEIGHTENED INTEREST IN UNLIKELY FRIENDSHIPS, YOU'RE GOING TO SEE A LOT MORE REPORTS OF IT FROM CREDIBLE FIELD BIOLOGISTS.

Narrator: THE RELATIONSHIPS WE'VE SEEN BETWEEN ANIMALS DRAWN TOGETHER ACROSS THE SPECIES DIVIDE SHOW ELEMENTS OF WHAT WE CALL FRIENDSHIP -- COMMUNICATION, TRUST, COMPASSION, EVEN ALTRUISM.

BUT THESE PARTNERSHIPS ARE BETWEEN DOMESTICATED ANIMALS, OR HAVE BEEN FOSTERED IN SOME WAY BY HUMANS.

WOULD AN ANIMAL IN THE WILD FEEL COMPELLED TO BUILD A FRIENDSHIP WITH ANOTHER FROM A DIFFERENT SPECIES?

Woman: IT WAS EITHER THE NEXT DAY OR THE DAY AFTER, I CAN'T QUITE REMEMBER, WE STARTED HEARING THE CALLING.

[ ANIMAL CRYING ] THE BABY SCREAMING, AND THEY SOUND LIKE A BABY.

THEY SOUND LIKE A CHILD.

AND WE COULD HEAR IT, WE DIDN'T KNOW WHAT IT WAS.

SO WE WENT OUT TO INVESTIGATE, AND WE COULDN'T SEE ANYTHING, BUT WE COULD HEAR IT.

AND THIS WENT ON FOR THREE DAYS.

IT WAS WANDERING AROUND, CRYING AND CRYING.

AND WE REALIZED THAT THE MOM HAD DESERTED IT.

EVENTUALLY IT GOT TO THE POINT WHERE WE THOUGHT, YOU KNOW, IT'S REALLY HOT OUT, SHE'S IN THE MIDDLE OF THE PADDOCK CRYING HER LITTLE EYES OUT.

SO WE WENT OUT AND BROUGHT HER IN THE HOUSE, AND THAT WAS THAT.

KATE INSTANTLY TOOK TO THE FAWN.

SHE ACTED AS IF THIS WAS WHAT SHE HAD ALWAYS BEEN WAITING FOR.

IT WAS AS IF A NEW MOM HAD STEPPED IN, AND THE FAWN INSTANTLY BRIGHTENED UP.

AND IT JUST WENT UP FROM THERE.

KATE WAS AMAZING.

SHE WAS SO PATIENT.

I WAS A LITTLE WORRIED BECAUSE THE FAWN WAS SO ROUGH SUCKLING ON HER, AND THERE'S NO MILK, SO SHE KEPT BOOTING HER, YOU KNOW, HOW THEY DO THAT WITH THEIR HEAD.

SHE NEVER RAISED A LIP.

SHE NEVER GROWLED, SHE NEVER DID ANYTHING.

GOOD DOG!

KATE JUST SEEMED TO KNOW THAT THIS LITTLE ANIMAL NEEDED LOOKING AFTER.

SHE USED TO TAKE HER AROUND THE EDGE OF THE LAWN QUITE A BIT, AND INTO THE FOREST A LITTLE BIT, BUT NOT TOO FAR.

SO I'M NOT SURE IF SHE WAS TEACHING HER BOUNDARIES OR NOT, BUT IT LOOKED LIKE IT.

SHE WOULD WALK AROUND SNIFFING AS IF SHE WAS GRAZING.

AND PIP WOULD BE RIGHT BESIDE HER GRAZING.

BUT I DON'T KNOW WHETHER KATE KNEW THAT SHE WAS TEACHING HER SOMETHING, BUT SHE DID.

YOU KNOW, I DON'T BELIEVE IN MAKING THEM INTO PETS.

WE WERE JUST TRYING TO SAVE HER LIFE.

I DIDN'T WANT TO BE PICKING HER UP AND CUDDLING HER, OR ANYTHING LIKE THAT -- SHE'S A DEER.

AND I WANTED HER TO LIVE A DEER'S LIFE.

AFTER ABOUT TWO WEEKS, SHE WANTED TO BE OUTSIDE AND SLEEPING IN THE WOODS, AND THAT'S THE WAY IT WENT.

AND IT WAS MORTIFYING, YOU KNOW, THINKING THAT SHE WAS SLEEPING OUT IN THE WOODS, ALL ON HER OWN -- BUT THAT'S WHAT DEER DO.

THEY HIDE THEIR BABIES FOR 12 HOURS AND GO OFF, AND DO WHATEVER.

AND THE BABY HAS A SUCKLE, AND THEN THE MOM'S GONE AGAIN.

SHE'D SLEEP IN THE WOODS FOR HOURS, AND THEN KATE WOULD GO AND FIND HER.

SHE'D COME IN AND HAVE HER MEAL, AND THEY'D PLAY FOR A FEW MINUTES, AND THEN SHE'D GO TO SLEEP AGAIN, JUST LIKE ALL BABIES -- YOU KNOW, PLAY, EAT, SLEEP.

Narrator: AS THE MONTHS PASSED, PIP GREW BY LEAPS AND BOUNDS.

AND SHE BEGAN TO STAY AWAY FOR DAYS AT A TIME.

KATE KEPT A CONSTANT VIGIL FOR HER FRIEND.

Springett: WHEN THEY GREET EACH OTHER, I'VE NEVER SEEN ANYTHING LIKE IT.

IT'S NOT A DEER GREETING A DEER, IT'S NOT A DOG GREETING A DOG.

IT'S DEFINITELY SOMETHING THAT THEY HAVE BETWEEN THE TWO OF THEM.

I THINK THE THING THAT SURPRISED ME MOST WAS WHEN THEY STARTED TO PLAY.

[ LAUGHING ] I'VE SEEN THEM BE VERY LOVING TO EACH OTHER, LIKE LAYING ON THE GRASS AND CURLING THEIR NECKS AROUND EACH OTHER, AND JUST RESTING ON EACH OTHER.

AND TO ME, IT LOOKS LIKE A LOVING FRIENDSHIP.

PIP HAS DONE A REALLY GOOD JOB OF FOLLOWING HER INSTINCTS AND NOT BECOMING TOO, UH, HUMANIZED.

OTHER DOGS SOMETIMES COME AROUND AND SHE DOESN'T REACT TO THEM AT ALL.

SHE DOESN'T COME NEAR THEM.

IT'S ONLY KATE THAT SHE IS ATTACHED TO.

Narrator: WHEN SHE'S NOT WITH KATE, PIP MERGES INTO THE HERD OF DEER THAT GRAZE ON ISOBEL'S PROPERTY.

Springett: IT'S AMAZING THAT SHE HAS A HUGE COMMUNITY THAT SHE'S WITH, OF DEER, AND SHE LEAVES THAT COMMUNITY AND COMES TO SEE KATE, I THINK IS REALLY COOL.

I THINK THAT'S AMAZING, AND I THINK THAT SPEAKS A LOT FOR ANIMALS -- NOT NECESSARILY INTELLIGENCE, BUT THAT WE DON'T GIVE THEM ENOUGH CREDIT FOR HOW MUCH THEY ABSORB IN THEIR LIVES, HOW MUCH INFORMATION THEY TAKE IN AND STORE AND THEY USE.

I THINK WE COULD BE GONE FOR YEARS AND COME BACK AND PIP WOULD STILL KNOW WHO KATE WAS.

WHEN WE'RE IN THE WOODS, SHE'LL OFTEN BE LOOKING FOR HER.

AND THEN WHEN SHE SEES HER, SHE'S HAPPY TO SEE HER, YOU KNOW -- THE WHOLE TAIL STARTS GOING, YOU KNOW.

THREE TIMES NOW, SHE HAS HAD HER FAWNS WITHIN A HUNDRED FEET OF THE HOUSE, AND I THINK THAT SHE FEELS THAT SHE'S GETTING SOME PROTECTION FROM KATE.

WHEN IT FIRST STARTED OUT, THERE WAS A LOT OF KATE LOOKING FOR PIPPEN.

SHE WOULD GO OFF INTO THE WOODS AND LOOK FOR WHERE SHE WAS SLEEPING, AND WAS SO THRILLED WHEN SHE WOULD FIND HER AND WOULD BRING HER BACK FOR HER FEEDING.

AND THAT WAS WHEN THERE REALLY WAS A LOT OF INVESTMENT BY KATE IN PIPPEN.

NOW, PIP COMES BACK TO FIND KATE.

SO, I THINK THAT SPEAKS A HUGE AMOUNT TO ANIMAL RELATIONSHIPS.

AND I THINK THAT'S THE BEAUTIFUL THING THEY CAN TEACH US, IS THAT IT DOESN'T MATTER WHAT YOU LOOK LIKE, IT DOESN'T MATTER WHAT SPECIES YOU ARE.

WE'RE ALL FROM THE SAME PLANET.

WE ALL NEED BASICALLY THE SAME THINGS.

WHY NOT A DOG AND A DEER?

WHY NOT?