NARRATOR: AFRICA, OUR HOMELAND.

[WHISTLE BLOWING] THIS IS WHERE IT ALL BEGAN.

WE ARE ALL AFRICANS.

BUT WHEN OUR SPECIES EMERGED, THERE WERE OTHER, ANCIENT TYPES OF HUMANS STILL LIVING IN AFRICA.

[FOREST BIRDS CALLING] WHAT PART DID THEY PLAY IN OUR EVOLUTION?

DID WE INTERBREED WITH THEM AND PRODUCE HYBRID CHILDREN?

MAN: THIS SAMPLE MADE MANKIND MUCH OLDER THAN WHAT THE SCIENTISTS HAD BEEN THEORIZING FOR YEARS.

WOMAN: VARIATION IS KEY TO EVOLUTION.

IT'S WHAT EVOLUTION WORKS ON, AND IT'S EXACTLY WHY HYBRIDIZATION IS SUCH A POWERFUL EVOLUTIONARY FORCE.

SECOND MAN: IT'S A STORY OF MANY FIRST PEOPLES, NOT JUST ONE; IT'S A STORY ABOUT DIVERSITY.

NARRATOR: SCIENTISTS ARE RETHINKING THE ORIGINS OF OUR SPECIES.

WE ARE NOT THE PEOPLE WE THOUGHT WE WERE.

NARRATOR: THIS IS THE STORY OF OUR ANCESTORS, AS THEY SPREAD TO EVERY CONTINENT OF THE WORLD.

WHAT WAS THE SECRET TO THEIR SUCCESS?

THEIR STORY IS OUR STORY.

NARRATOR: EASTERN AFRICA-- 195,000 YEARS AGO.

HUNTERS ON THE SAVANNA.

THEY HAVE THE SAME BODY SHAPE AS US, THE SAME BRAIN.

ARCHAEOLOGISTS KNOW THIS MAN AS OMO 1.

[OVERLAPPING CHATTER] NARRATOR: HE IS DESTINED TO DIE WHILE STILL IN HIS 20s... [GASPING] BUT HIS DEATH WILL RESONATE THROUGH TIME.

IT'S THE FIRST WE KNOW OF BY A MEMBER OF OUR SPECIES.

HE IS ONE OF US.

[INDISTINCT CHATTER] NARRATOR: OMO 1 LIVED HERE, IN THE OMO VALLEY.

TODAY, IT'S BONE DRY, BUT 195,000 YEARS AGO, THIS WAS A LUSH WETLAND, A GREAT HOME FOR PREHISTORIC PEOPLE.

TWO U.S. SCIENTISTS KNOW THIS SITE WELL-- ANTHROPOLOGIST JOHN FLEAGLE AND ARCHAEOLOGIST JOHN SHEA.

THEY'RE BASED IN NEW YORK, BUT FOR THE LAST 15 YEARS, THEY'VE BEEN COMING HERE TO FIND OUT MORE ABOUT THE LIFE AND TIMES OF OMO 1.

[PANTING] THIS IS A VERY DIFFERENT WORLD FROM NEW YORK.

[EXHALES] YOU KNOW, IT'S, UH, LIKE A TRIP BACK IN TIME, A--A JOURNEY TO THE ORIGIN OF OUR SPECIES.

[DISTANT BIRD SCREECHING NARRATOR: OMO 1 WAS DISCOVERED IN 1967 BY AN INTERNATIONAL EXPEDITION TO SOUTHERN ETHIOPIA.

THEY CAME LOOKING FOR HUMAN FOSSILS ERODING OUT OF THE ANCIENT SEDIMENTS.

AND SURE ENOUGH, THEY FOUND THE REMAINS OF 3 PREHISTORIC HUMANS.

THE MOST COMPLETE SKELETON WAS THAT OF OMO 1.

BUT IN THE 1960s, NO ONE KNEW JUST HOW OLD HE WAS.

NARRATOR: FOR 3 DECADES, OMO 1 WAS A FOSSIL IN SEARCH OF A STORY.

[MEN PANT] NARRATOR: THAT CHANGED WHEN JOHN FLEAGLE AND JOHN SHEA CAME TO THE OMO VALLEY IN THE EARLY 2000s AND REOPENED THE SITE.

SHEA: THIS IS IT-- [SIGHS]--THE LOST WORLD.

FLEAGLE: PRETTY SPECTACULAR.

THE BIG QUESTION WAS HOW LONG AGO DID MODERN HUMANS ORIGINATE IN AFRICA?

UH, HERE WERE MODERN HUMAN SKELETONS, BUT WE DIDN'T KNOW HOW OLD THEY WERE, BUT THERE WERE HINTS THAT THEY WERE VERY, VERY OLD.

THERE WERE PEOPLE WHO WERE SAYING, YOU KNOW, THIS STUFF'S PROBABLY 20,000 OR 30,000 YEARS OLD.

THERE WAS AN OLD DATE THAT SAID IT WAS, PERHAPS, AS MUCH AS 100,000 YEARS OLD.

IT WAS SOMETHING THAT NEEDED TO BE RESOLVED.

NARRATOR: THE BONES WERE TOO OLD FOR CARBON-DATING.

THAT TECHNIQUE ONLY REACHES BACK 50,000 YEARS...

BUT BY ANALYZING LEVELS OF ARGON IN THE SEDIMENT, IT'S NOW POSSIBLE TO PRODUCE AN ACCURATE TIMELINE OF THE ENTIRE LANDSCAPE.

THE BONES OF OMO 1 WERE FROM A LAYER THAT WAS 195,000 YEARS OLD.

FLEAGLE: WHEN WE GOT THAT DATE OF 195, WE THOUGHT, "OH, MY!"

UM, WE NEVER--I DON'T THINK WE EVER THOUGHT IT WOULD QUITE BE THAT OLD.

NARRATOR: THE HUMAN FAMILY TREE STARTS 2 1/2 MILLION YEARS AGO.

BEFORE THAT TIME, WE WERE MORE APE THAN HUMAN.

EVER SINCE, THERE HAVE BEEN INNUMERABLE BRANCHES, TWIGS, AND SHOOTS, GIVING RISE TO DIFFERENT SPECIES WITH STRANGE NAMES.

ARCHAEOLOGISTS CLASSIFY THEM ALL AS ARCHAIC HUMANS.

WHAT MAKES OMO 1 SO SPECIAL IS THAT HE IS A MODERN HUMAN, A MEMBER OF OUR SPECIES-- OMO 1 STOOD AS TALL AS A MODERN-DAY AFRICAN AND WEIGHED 160 POUNDS.

HE HUNTED GIANT HOG AND ANTELOPE.

BUT ONE DAY, OMO 1 COULD HUNT NO MORE.

THERE'S NO EVIDENCE HIS BONES WERE EVER MOVED OR BURIED.

FOR 195,000 YEARS, THEY LAY WHERE HE DIED.

SHEA: THE ONE THING WE KNOW ABOUT THIS SITE, THE ONE IRREDUCIBLE FACT ABOUT OMO 1, IS THAT THIS IS THE PLACE WHERE OMO 1 DIED.

[RASPY BREATHING] SHEA: HE WOULD PROBABLY BE OFF TO THE SIDE SOMEPLACE, SURROUNDED BY MEMBERS OF HIS FAMILY: HIS WIFE, HIS CHILDREN, HIS--HIS BEST FRIEND, HIS BROTHER, HIS SISTER.

THEY'D BE CARING FOR HIM, TRYING TO MAKE HIM COMFORTABLE.

[RASPY BREATHING] SHEA: OR HE MIGHT HAVE BEEN LEFT BEHIND, AS OFTEN HAPPENS AMONGST HUNTER-GATHERERS... NOT CALLOUSLY, BUT THIS IS JUST WHAT HAPPENS, IS YOU CAN'T KEEP UP WITH THE GROUP AS IT'S MOVING, THEY GIVE YOU FOOD, THEY MAKE PEOPLE COMFORTABLE, AND THEY HAVE TO LEAVE THEM BEHIND.

THAT'S, YOU KNOW, PART OF LIFE.

[GASPS] [CRICKETS CHIRPING] NARRATOR: OVER THE YEARS, JOHN SHEA HAS BEEN COLLECTING EVIDENCE ABOUT THE WAY PEOPLE LIVED AT THE OMO VALLEY.

SHEA: YOU ALWAYS LOOK UNDERNEATH THE ACACIA BUSH.

THAT'S WHERE ALL THE GOOD STUFF STUFF HIDES.

[SIGHS] NARRATOR: HE'S IMPRESSED BY THEIR INGENUITY.

SHEA: IT'S A STONE TOOL.

YOU CAN TELL THIS BECAUSE THEY HAVE FEATURES ON THEM THAT SHOW WHERE THEY WERE STRUCK BY A HAMMER.

NATURE DOESN'T MAKE OBJECTS LIKE THIS BY ITSELF.

NICE.

I MEAN, THESE PEOPLE MADE EVERYTHING, FROM LITTLE TINY PIECES LIKE THIS TO GREAT, MASSIVE PIECES LIKE THIS AND EVERYTHING ELSE IN BETWEEN.

SHEA: SOMETIMES YOU'D FIND A LOT OF TOOLS; THAT MEANS THIS IS WHERE THEY MADE THEM.

BUT ISOLATED LITTLE TOOLS LIKE THIS, IT COULD BE THEY JUST DROPPED THEM, YOU KNOW, AND SAID, "ALL RIGHT, "I'M--I KNOW I'M GOING TO BE COMING BACK HERE.

"I'LL JUST LEAVE THESE TOOLS, SO HERE ALONG THE PATH, IF I EVER NEED A CUTTING EDGE, THERE'S ONE RIGHT THERE."

IT'S LIKE HAVING AN ATM MACHINE.

YOU DON'T HAVE TO CARRY BIG WADS OF CASH WITH YOU AROUND--AROUND CITIES BECAUSE YOU HAVE ATM MACHINES.

WITH THESE GUYS, THEY DON'T HAVE TO CARRY BIG, HEAVY ROCKS AROUND WITH THEM 'CAUSE THE LANDSCAPE'S FULL OF STONE TOOLS.

THINK OF THESE THINGS LIKE LITTLE--LITTLE DEBIT CARDS OF PRE-HISTORY.

[DISTANT ANIMALS GRUNTING] [BIRD CHIRPS] SHEA: THESE ARE PEOPLE LIKE US.

THEY HAD A SENSE OF HUMOR, THE HAD SADNESS, THEY HAD, YOU KNOW, JOY.

THERE'S NO REASON, YOU KNOW, TO ASSUME THAT THEY ARE DIFFERENT FROM US IN THEIR EMOTIONS, IN THEIR INTELLECT.

NOTHING IN THEIR BODY SAYS IT, NOTHING IN THE ARCHAEOLOGY SAYS IT.

THE ONLY THING THAT COMPELS US TO THINK THAT THESE PEOPLE WERE SIMPLER THAN US IS MYTHOLOGY, THIS IDEA THAT EARLIER IS PRIMITIVE, AND PRIMITIVE IS SIMPLE.

[CHOPPING SOUNDS] THESE GUYS SURVIVED BY THEIR WITS.

THEY--THEY THOUGHT, THEY PLANNED, AND EVIDENTLY THEY'RE PRETTY SUCCESSFUL BECAUSE THEIR DESCENDANTS, US, ARE STILL HERE.

NARRATOR: ANCIENT SKELETONS SUCH AS OMO 1 SUGGEST EASTERN AFRICA WAS THE CRADLE OF OUR SPECIES, OUR GARDEN OF EDEN.

THE PREVAILING THEORY IS THAT MODERN HUMANS BURST INTO LIFE IN THIS ONE REGION 200,000 YEARS AGO, AND FROM HERE, WE SPREAD OUT ACROSS AFRICA AND THEN ACROSS THE WORLD.

IT'S A THEORY BACKED UP BY DNA.

IN THE 1980s, GENETICISTS AT BERKELEY WORKED OUT HOW TO TRACE HUMAN ANCESTRY, USING MITOCHONDRIA.

THEY'RE THE ENERGY PACKS OF A CELL THAT SIT OUTSIDE THE NUCLEUS.

EACH OF THEM CONTAINS A TINY COIL OF DNA, PASSED ON FROM MOTHER TO DAUGHTER.

WOMAN: PEOPLE WEREN'T USED TO THINKING ABOUT DNA EVIDENCE HAVING ANYTHING TO DO WITH QUESTIONS ON HUMAN EVOLUTION OR ANTHROPOLOGY OR HUMAN ORIGINS.

SO THAT WAS A NEW CONCEPT, THAT THIS COULD ACTUALLY WEIGH IN ON THE DEBATE OF WHERE HUMANS CAME FROM AND--AND HOW LONG AGO, INSTEAD OF LOOKING AT JUST FOSSIL EVIDENCE.

[PEOPLE LAUGHING] NARRATOR: AS MITOCHONDRIAL DNA IS PASSED ON, IT PICKS UP MUTATIONS OVER TIME.

BY COUNTING THESE MUTATIONS, IT IS POSSIBLE TO WORK OUT WHEN EVERY WOMAN ON EARTH LAST SHARED A COMMON ANCESTOR.

[OVERLAPPING CHATTER] [CAMERA SHUTTER CLICKS] [LAUGHTER] NARRATOR: THE RESEARCH POINTED TO SOMEONE LIVING IN AFRICA ABOUT 200,000 YEARS AGO, THE SAME SORT OF TIME AS OMO 1.

[CAMERA SHUTTER CLICKING AT HIGH SPEED] NARRATOR: SHE BECAME KNOWN AS MITOCHONDRIAL EVE.

VIGILANT: SHE'S THE MOST RECENT COMMON ANCESTOR OF ALL OF US.

OF COURSE, SHE HAD A MOM, WHO WOULD THEN BE THE COMMON ANCESTOR OF ALL OF US AS WELL, BUT SHE WAS LIVING FURTHER BACK IN TIME; MITOCHONDRIAL EVE IS THE MOST RECENT COMMON ANCESTOR OF ALL OF US.

[OVERLAPPING CHATTER] NARRATOR: GENETICISTS HAVE TAKEN THE SAME APPROACH WITH THE "Y" CHROMOSOME, WHICH IS PASSED DOWN THE MALE LINE FROM FATHER TO SON.

[CAMERA SHUTTER CLICKING] NARRATOR: THE MOST RECENT COMMON ANCESTOR OF EVERY MAN ALIVE TODAY ALSO LIVED IN AFRICA.

[CAMERA SHUTTER CLICKING AT HIGH SPEED] NARRATOR: HE BECAME KNOWN AS "Y" CHROMOSOMAL ADAM.

GENETIC ADAM AND EVE.

THEY DIDN'T KNOW EACH OTHER, BUT THEY HAVE THE SAME STORY TO TELL.

VIGILANT: THE TAKE-HOME MESSAGE WAS THAT WE HAVE A VERY RECENT COMMON ORIGIN IN AFRICA, SO THAT THE DIFFERENCES THAT WE SEE AMONG US THAT ARE SO EVIDENT WITH HAIR AND SKIN COLOR ARE PERHAPS REALLY RECENT AND RATHER SUPERFICIAL.

[OVERLAPPING CHATTER] NARRATOR: IT'S BECOME A TRUISM THAT WE ARE A YOUNG SPECIES AND CAN ALL TRACE OUR ROOTS BACK TO A SINGLE SOURCE.

ACCORDING TO OUR GENES AND OUR BONES, THAT SOURCE WAS EASTERN AFRICA 200,000 YEARS AGO.

THAT'S THE THEORY, BUT IS IT ENTIRELY TRUE?

OUR CREATION STORY MAY NOT BE QUITE SO SIMPLE.

THE MAX PLANCK INSTITUTE IS ONE OF THE LEADING CENTERS IN THE WORLD FOR RESEARCH INTO HUMAN EVOLUTION.

THEY CAN ANALYZE FOSSILS HERE IN MINUTE DETAIL, USING A CT SCANNER TO CREATE 3D MODELS.

NARRATOR: THIS IS AN AFRICAN SKULL FROM A SITE KNOWN AS JEBEL IRHOUD.

IT'S 300,000 YEARS OLD-- 100,000 YEARS OLDER THAN OMO 1.

IT BELONGS TO AN ARCHAIC HUMAN, SOMEONE WHO WAS NOT YET FULLY MODERN.

MAN: IT'S A VERY ANCIENT-LOOKING SKULL WHEN YOU LOOK AT IT FROM THE SIDE, BUT, UH, IT HAS, ESPECIALLY CONSIDERING ITS OLD AGE, A VERY MODERN-LOOKING FACE.

AND BY THAT, I MEAN IT HAS A SMALL FACE THAT'S TUCKED UNDERNEATH THE BRAINCASE, YET THE BRAINCASE SHAPE IS VERY ELONGATED, WHICH IS WHAT WE FIND IN ARCHAIC HUMANS AND NOT IN MODERN HUMANS LIVING TODAY.

[COMPUTER MOUSE CLICKS] NARRATOR: WITH HIS MIX OF FEATURES, THE MAN FROM JEBEL IRHOUD APPEARS TO BE A FORERUNNER OF OUR SPECIES... A MODERN HUMAN IN WAITING.

GUNZ: THE START OF A SPECIES IS ALWAYS BLURRY AND MESSY.

THIS IS A PROCESS THAT, UM, TAKES THOUSANDS AND THOUSANDS OF YEARS, SOMETIMES MILLIONS OF YEARS.

AND, UH, AND WE CAN SEE HERE THAT MODERN HUMANS EVOLVED THEIR FACES FIRST AND THEIR BRAINCASES LATER.

NARRATOR: WHAT'S STRIKING ABOUT THIS MAN IS WHERE HE LIVED.

JEBEL IRHOUD IS NOT IN ETHIOPIA, BUT 3,000 MILES AWAY IN MOROCCO, ON THE OTHER SIDE OF AFRICA.

WHY WOULD A FORERUNNER OF OUR SPECIES HAVE LIVED SO FAR FROM OUR SUPPOSED BIRTHPLACE?

PERHAPS THERE WASN'T A SINGLE BIRTHPLACE, BUT DIFFERENT HOTSPOTS, ALL CONTRIBUTING SOMETHING TO OUR EVOLUTION.

[COMPUTER MOUSE CLICKING] GUNZ: THE SIGNIFICANCE OF THIS PARTICULAR FOSSIL FROM MOROCCO IS THAT IT SHOWS US THAT MODERN HUMAN ORIGINS WAS NOT RESTRICTED TO ONE PLACE IN EAST AFRICA, BUT IT HAPPENED ON A CONTINENTAL SCALE ALL OVER AFRICA.

NARRATOR: THE TRADEMARK FEATURES OF A MODERN HUMAN MAY HAVE EVOLVED SEPARATELY: A ROUNDER BRAINCASE IN ONE REGION; A HIGHER FOREHEAD IN ANOTHER; A SMALLER JAWBONE ELSEWHERE.

BUT HOW DID THESE FEATURES THEN MERGE TOGETHER INTO A SINGLE BLUEPRINT THAT BECAME MODERN HUMANS?

[BIRDS CHIRPING] IN THE EARLY DAYS OF OUR SPECIES, DIFFERENT GROUPS MUST HAVE BEEN CONNECTED IN SOME WAY.

PERHAPS THEY MET, MATED, AND SHARED GENES.

THAT'S WHAT ANTHROPOLOGIST JOHN HAWKS THINKS HAPPENED.

HE BELIEVES THAT SOCIAL NETWORKS EXISTED ACROSS THE CONTINENT.

IT ONLY NEEDED EACH GROUP TO EXPAND AS FAR AS THE NEXT FOR CONTACT TO BE MAINTAINED OVER HUGE DISTANCES.

[MEN SPEAKING ANCIENT LANGUAGE] HAWKS: ALL OVER AFRICA, ARCHAEOLOGISTS HAVE FOUND SHELLS LIKE THIS.

THIS IS A NASSARIUS SHELL, AND IT HAS A HOLE IN IT BECAUSE THIS SHELL WAS STRUNG ON A STRING AND WORN AS AN ORNAMENT.

THEY'VE BEEN FOUND IN NORTH AFRICA, IN SOUTH AFRICA, AND IN ISRAEL: THOUSANDS OF MILES APART, SAME KIND OF SHELL, THE SAME TECHNIQUE, THE SAME INTENT.

HAWKS: ANYBODY CAN PICK UP A SHELL AND BE INTERESTED IN IT, BUT THINKING OF HOW TO DRILL A HOLE AND WEAR IT AND CREATE A SIGNAL, THAT'S A REALLY DISTINCTIVE IDEA.

[MEN SPEAKING ANCIENT LANGUAGE] THAT KIND OF LONG-DISTANCE MOVEMENT OF IDEAS SUGGESTS THAT PEOPLE ARE MOVING INTO EACH OTHER'S TERRITORIES.

IT'S NOT ONLY IDEAS THAT ARE SPREADING, IT'S ALSO GENES.

THAT'S WHAT HUMANS DO WHEN THEY'RE IN CONTACT WITH EACH OTHER.

THEY START MATING, THEY'RE HAVING BABIES.

HAWKS: YOU START TO SEE POPULATIONS MERGING TOGETHER.

WHERE ONCE YOU'D HAD VERY DIFFERENT GROUPS OF PEOPLE-- REALLY DIFFERENT IN WHAT THEY LOOK LIKE, HOW THEY ACT-- YOU START TO SEE THE BUILDING OF A SINGLE COMMUNITY, A COMMUNITY THAT WE CALL MODERN HUMANS.

[ROLLING THUNDER] NARRATOR: THE MOVEMENT OF PREHISTORIC PEOPLE WAS AFFECTED BY THE CLIMATE, WHICH FLUCTUATED OVER THOUSANDS OF YEARS.

IN BAD TIMES, AFRICA WAS SO DRY, THE SAHARA WAS AN UNCROSSABLE BARRIER.

BUT IN GOOD TIMES, WHEN THE CLIMATE WAS WET, THE DESERT DISAPPEARED.

ANY ADAPTATION THAT EMERGED IN ONE PART OF AFRICA COULD SPREAD TO OTHER PARTS OF THE CONTINENT... JUST AS EASILY AS SHELL BEADS.

HAWKS: UNTIL RECENTLY, MANY ARCHAEOLOGISTS AND ANTHROPOLOGISTS WERE LOOKING FOR A SINGLE ORIGIN FOR MODERN HUMANS, LIKE A "GARDEN OF EDEN" SCENARIO THAT WOULD EXPLAIN WHY WE'RE ALL ALIKE.

BUT WE NOW KNOW THAT THINGS DIDN'T HAPPEN THAT WAY.

I THINK THAT OUR ORIGINS WERE VERY MUCH LIKE THIS... MORE LIKE A RIVER WHERE WATER IS FINDING ITS OWN PATH, SOMETIMES SEPARATING AND THEN COMING BACK TOGETHER, BUT ALWAYS FLOWING ON.

MODERN HUMAN ORIGINS IS LIKE THAT; IT'S A STORY OF MANY FIRST PEOPLES, NOT JUST ONE.

IT'S A STORY ABOUT DIVERSITY.

NARRATOR: ACCORDING TO THIS WAY OF THINKING, WE ARE A SPECIES BORN OF MANY PARENTS ACROSS AFRICA.

OUR ROOTS ARE MORE TANGLED THAN WE EVER REALIZED.

[FILM REEL CREAKING] NARRATOR: THE STORY HAS JUST GOTTEN MORE INTRIGUING, THANKS TO AMATEUR GENEALOGIST JACQUELINE JOHNSON.

SHE'S FASCINATED BY HER GREAT-GREAT-GRANDFATHER, ALBERT PERRY, WHO APPEARS ON THE 1870 CENSUS AS A FREED SLAVE IN SOUTH CAROLINA.

JOHNSON: HE'S 43, LISTED ON HERE, SO THAT MEANS HE WAS BORN ABOUT 1827.

AND THERE'S MY GREAT-GRANDFATHER, CLYDE, AT THE AGE OF 3, YOU KNOW, TODDLER.

THIS IS THE FIRST MAJOR CENSUS THAT SLAVES WERE INCLUDED ON, YOU KNOW, WITH THE LAST NAMES.

PRIOR TO THAT, IT WAS MOSTLY RECOGNIZED AS SOMEBODY'S PROPERTY.

NARRATOR: JOHNSON HAS BEEN ABLE TO TRACE HER ROOTS BACK 5 GENERATIONS, BUT SHE CAN'T FIND ANY RECORDS BEFORE 1870.

THIS IS OUR FAMILY TREE.

THIS IS MYSELF, MY MOTHER, MY GRANDMOTHER, AND THIS IS MY GREAT-GREAT-GRANDFATHER, ALBERT PERRY.

IT'S FRUSTRATING THAT YOU CAN'T GO BACK ANY FURTHER THAN HIM 'CAUSE, YOU KNOW, PEOPLE JUST DIDN'T POP UP AND START EXISTING IN 1870.

YOU KNOW, THEY WERE ALIVE BEFORE THEN, SO WHERE WERE THEY?

THEY WERE SOMEWHERE, YOU KNOW.

I WANT TO GIVE A VOICE TO THEIR STORY.

I WANT TO FIND OUT, WHO IS ALBERT PERRY?

HENRY LOUIS GATES, JR.: I'VE ENLISTED THE HELP OF 3 SCIENTISTS WHO USE GENETIC ANCESTRY TRACING IN THEIR RESEARCH... JOHNSON: IN 2006, I WAS WATCHING A PBS SPECIAL CALLED "AFRICAN AMERICAN LIVES," AND THEY WERE PRESENTING DNA.

GATES, VOICE-OVER: ...SEQUENCES, WE SUBMITTED SECOND DNA SAMPLES.

THESE SAMPLES CAN THEN BE COMPARED TO DNA SAMPLES TAKEN FROM AROUND THE WORLD.

JOHNSON: THEY WERE SHOWING PEOPLE, "OK, YOU WERE CONNECTED "TO THIS GROUP OF PEOPLE IN LIBERIA AND THIS GROUP OF PEOPLE IN NIGERIA," AND I WAS LIKE, "OH, THAT'S THE WAY I CAN DO IT.

"I CAN ACTUALLY TEST MY OWN DNA AND FIND OUT WHERE WE CONNECT IN AFRICA."

NARRATOR: TO TRACK ALBERT PERRY'S LINEAGE, SHE PERSUADED A MALE COUSIN TO PROVIDE A SAMPLE OF HIS "Y" CHROMOSOME.

IT WAS TESTED HERE, AT FAMILY TREE DNA.

BENNETT GREENSPAN RUNS THE COMPANY.

GREENSPAN: WHEN I CAME INTO WORK THE MORNING THAT THE SAMPLE HAD BEEN SCORED THE NIGHT BEFORE, THE TECHNICIANS WERE ACTUALLY VERY EXCITED BECAUSE THEY SAID, "WE'VE SEEN SOMETHING, AND WE'VE NEVER SEEN ANYTHING LIKE THIS BEFORE."

TYPICALLY, YOU MIGHT FIND ONE OR TWO OR THREE NOVEL MUTATIONS, BUT IN THIS SAMPLE, WE FOUND BETWEEN 40 AND 50 NOVEL MUTATIONS, WHICH MEANS IT DEFINES AN ENTIRELY NEW SUBSECTION OF THE TREE OF MANKIND.

NARRATOR: THE "Y" CHROMOSOME FROM JACQUELINE JOHNSON'S COUSIN WAS SO UNUSUAL, IT WAS GIVEN ITS OWN NAME-- A00.

GENETICISTS CHECKED THOUSANDS OF OTHER SAMPLES IN THEIR DATASETS, BUT FOUND NO ONE ELSE WITH THE SAME SIGNAL... UNTIL THEY LOOKED IN WESTERN AFRICA.

[DRUMS BEATING, DISTANT PEOPLE CHANTING] NARRATOR: THE TRAIL LEADS 7,000 MILES FROM HOUSTON TO MBETTA VILLAGE IN WESTERN CAMEROON.

[WHISTLE BLOWING] IN 2001, THERE WAS A PROGRAM TO SAMPLE DNA HERE.

WHEN THE SAMPLES WERE REVIEWED IN 2012, 11 OF THE MEN WERE A MATCH FOR A00.

NO ONE KNOWS WHO THEY ARE BECAUSE THE TESTS WERE ANONYMOUS, BUT THEY'RE THE ONLY OTHER PEOPLE IN THE WORLD KNOWN TO HAVE THE SAME "Y" CHROMOSOME AS JACQUELINE JOHNSON'S GREAT-GREAT-GRANDFATHER, ALBERT PERRY.

HE MUST HAVE LIVED IN MBETTA BEFORE BEING TRANSPORTED AS A SLAVE TO THE UNITED STATES, CARRYING WITH HIM THE A00 "Y" CHROMOSOME.

[WHISTLING AND CHANTING FADE] WHAT'S SO REMARKABLE ABOUT THIS CHROMOSOME IS ITS AGE.

BY COUNTING THE NUMBER OF MUTATIONS, IT'S BEEN DATED AT 338,000 YEARS OLD, WHICH MEANS IT ENTERED THE MODERN HUMAN GENE POOL BEFORE MODERN HUMANS WERE EVEN THOUGHT TO EXIST.

GREENSPAN: THIS SAMPLE WAS KIND OF HISTORY-SHATTERING.

IT WAS OLDER THAN ANYTHING THAT SCIENCE HAD EVER SEEN IN A MALE-INHERITED "Y" CHROMOSOME.

GREENSPAN: AND THAT'S WHAT MADE THIS DISCOVERY SO INTERESTING BECAUSE THIS MADE MANKIND ACTUALLY MUCH OLDER THAN WHAT THE SCIENTISTS HAD BEEN THEORIZING FOR YEARS.

NARRATOR: UNTIL RECENTLY, THE TIMELINE OF OUR SPECIES SEEMED CLEAR.

EVERY MAN ON EARTH COULD TRACE HIS ANCESTRY BACK TO GENETIC ADAM, EVERY WOMAN BACK TO GENETIC EVE.

THE EARLIEST FOSSIL EVIDENCE GOES BACK 195,000 YEARS TO OMO 1.

300,000 YEARS AGO LIVED A FORERUNNER OF OUR SPECIES, IN JEBEL IRHOUD.

BUT THIS "Y" CHROMOSOME WAS OLDER THAN ALL OF THEM, A PIECE OF MODERN HUMAN DNA THAT WAS 338,000 YEARS OLD, POTENTIALLY A NEW START DATE FOR OUR SPECIES.

JOHNSON: WHEN THE RESULTS CAME, I WAS EXCITED.

NOW HIS NAME IS IN A BOOK.

HA HA!

CAN YOU--YOU IMAGINE, FROM A SLAVE, UNKNOWN, KIND OF LIKE SOMEBODY'S PROPERTY, AND ALL OF A SUDDEN, IT'S KNOWN AROUND THE WORLD.

NARRATOR: TO UNDERSTAND MORE ABOUT THE A00 "Y" CHROMOSOME, GENETICISTS NEED MORE SAMPLES.

MATTHEW FOMINE FORKA IS THE LOCAL RESEARCHER WHO DID THE INITIAL SAMPLING IN MBETTA VILLAGE.

[OVERLAPPING CHATTER] FORKA: TODAY, WE ARE CONTINUING THE DNA COLLECTION THAT I STARTED IN 2001.

I AM GOING TO SWAB YOUR MOUTH WITH A STERILE COTTON.

NARRATOR: UNFORTUNATELY, THE CLIMATE OF CAMEROON IS TOO WET TO PRESERVE ANCIENT HUMAN FOSSILS.

SO DNA IS THE ONLY WAY TO FIND OUT IF OUR SPECIES REALLY DID EMERGE HERE.

BUT THERE IS ANOTHER POSSIBILITY, ANOTHER REASON FOR THE AGE OF THE A00 "Y" CHROMOSOME.

PERHAPS WE INHERITED IT FROM A DIFFERENT SPECIES OF HUMAN.

ALTHOUGH WE ARE NOW THE ONLY HUMANS ON THE PLANET, IT WAS NOT ALWAYS THIS WAY.

[OVERLAPPING CHATTER] [POUNDING ROCK] NARRATOR: FOR TENS OF THOUSANDS OF YEARS, THE FORESTS OF AFRICA WOULD HAVE BEEN SHARED...

BETWEEN MODERN HUMANS AND ARCHAIC HUMANS.

[DISTANT ANIMAL CALLING] IT'S BEEN ASSUMED THERE WAS LITTLE, IF ANY, CONTACT BETWEEN THEM.

BUT WHAT IF THAT ASSUMPTION IS WRONG?

WHAT IF DNA PASSED FROM ONE SPECIES OF HUMAN TO ANOTHER?

MAN: THERE MAY HAVE BEEN ARCHAIC FORMS OF HUMANS THAT LIVED IN WESTERN AFRICA THAT HAPPENED UPON MODERN POPULATIONS, AND THIS "Y" CHROMOSOME WAS INTRODUCED INTO THE MODERN POPULATION THROUGH INTERBREEDING.

NARRATOR: ALTHOUGH MODERN HUMANS WERE A DISTINCT SPECIES, THEY SEEM TO HAVE MATED WITH OTHER, OLDER SPECIES OF HUMAN AND PICKED UP PARTS OF THEIR DNA.

[MAN SHOUTS] HAMMER: THAT WOULD HELP TO EXPLAIN WHY WE FOUND A 338,000-YEAR-OLD "Y" CHROMOSOME IN A VERY SMALL POCKET OF HUMANITY IN WESTERN CAMEROON.

HAMMER: FOR THE LAST HUNDRED YEARS OR SO, IT'S BEEN VERY CONVENIENT TO THINK THAT HUMANS ORIGINATED IN A VERY SIMPLE WAY IN A GARDEN OF EDEN.

BUT NOW WE KNOW, FROM THE DNA ITSELF, THAT MATINGS BETWEEN DIFFERENT FORMS-- ARCHAIC FORMS, MODERN FORMS-- HAVE BEEN GOING ON WHO KNOWS HOW LONG THAT'S GOING BACK IN TIME, WHICH, IN FACT, MAKES US A LOT MORE LIKE THE REST OF NATURE.

NARRATOR: SOMETHING SIMILAR HAS SHOWN UP IN SOUTHERN CAMEROON.

[FOREST BIRDS CALLING] THESE RAINFORESTS ARE HOME TO THE PYGMIES.

[OVERLAPPING CHATTER] NARRATOR: THEY ARE SOME OF THE LAST TRADITIONAL HUNTER-GATHERERS ON EARTH, LIVING IN MUCH THE SAME WAY AS THEY HAVE FOR 100,000 YEARS, FINDING FOOD WHEREVER THEY CAN.

[ALL SHOUTING EXCITEDLY] [DOG BARKS] [SHOUTS] NARRATOR: GENETICALLY, THE PYGMIES ARE AS CLOSE AS ANYONE TO AFRICA'S FIRST MODERN HUMANS.

AND THEIR DNA IS VERY REVEALING.

RATHER THAN LOOKING ONLY AT THE "Y" CHROMOSOME, OR MITOCHONDRIA, GENETICISTS CAN NOW ANALYZE 6 BILLION FRAGMENTS ACROSS THE ENTIRE PYGMY GENOME... [FOREST BIRDS CALLING] AND THEY'RE FINDING REGIONS THAT ARE SO ANCIENT AND UNUSUAL, THEY LOOK MORE ARCHAIC THAN MODERN.

AGAIN, THEY SEEM TO BE THE RESULT OF INTERBREEDING.

BUT HOW CAN THIS BE?

ACCORDING TO THE HUMAN FAMILY TREE, ARCHAIC HUMANS ARE DIFFERENT SPECIES TO US MODERN HUMANS, AND DIFFERENT SPECIES ARE MEANT TO BE INCAPABLE OF INTERBREEDING.

BUT IN REALITY, IT ALL DEPENDS HOW CLOSELY RELATED THEY ARE, WHEN THEY LAST SHARED A COMMON ANCESTOR.

[ORCHESTRAL THEME MUSIC PLAYING] [MONKEYS SCREECHING] NARRATOR: MATING ACROSS THE SPECIES BARRIER WAS FIRST STUDIED MORE THAN 30 YEARS AGO.

[ROARS] IN ETHIOPIA'S AWASH VALLEY, THERE ARE TWO DIFFERENT SPECIES OF BABOONS LIVING SIDE-BY-SIDE-- [ROARS] HAMADRYAS AND OLIVE BABOONS-- AND BETWEEN THEM IS A HYBRID ZONE WHERE THEY MATE, INTERBREED, AND HYBRIDIZE.

DOCUMENTARY NARRATOR: THIS ADULT MALE HAS PINK BUTTOCKS, SIMILAR TO THE HAMADRYAS, WHILE THIS HYBRID MALE HAS THE GRAY BUTTOCKS OF AN OLIVE BABOON.

THIS VARIABILITY INDICATES THAT EXTENSIVE INTERBREEDING HAS OCCURRED.

[SCREECHING] NARRATOR: THE RESEARCH CONCLUDED THAT ANY TWO SPECIES OF PRIMATES CAN INTERBREED, AS LONG AS THEY SHARE A COMMON ANCESTOR WITHIN THE LAST TWO MILLION YEARS.

IT'S A RULE THAT APPLIES TO ALL PRIMATES...

INCLUDING HUMANS.

NARRATOR: DESPITE BEING DIFFERENT SPECIES, MODERN AND ARCHAIC HUMANS SHARED ANCESTORS WELL WITHIN THE LAST TWO MILLION YEARS, SO THERE WAS NOTHING TO STOP THEM FROM INTERBREEDING.

[SCREECHES] NARRATOR: BUT WHEN THE ORIGINAL RESEARCH WAS DONE, FEW PEOPLE SAW A CONNECTION BETWEEN HYBRID BABOONS AND HUMANS, AND ITS CONCLUSIONS WERE IGNORED.

TODAY, THE IDEA OF HYBRIDIZATION IS BEING RECONSIDERED.

REBECCA ACKERMANN IS TRYING TO WORK OUT WHAT A HUMAN HYBRID WOULD HAVE LOOKED LIKE BY STUDYING HYBRID MICE.

ACKERMANN: I KNOW USING MICE SOUNDS A LITTLE BIT STRANGE, BUT OBVIOUSLY YOU CAN'T HYBRIDIZE PEOPLE OR HYBRIDIZE, UM, PRIMATES IN ORDER TO ANSWER THESE TYPES OF QUESTIONS.

THESE HYBRID MICE ARE QUITE A BIT DIFFERENT FROM THE PARENT SPECIES, AND THEY DIFFER IN TERMS OF THEIR, UM, BODY SIZE, THEY'RE--THEY'RE BIGGER; UH, IN TERMS OF THEIR COAT COLOR; IN TERMS OF WHAT THEIR FACES LOOK LIKE.

AND EVEN MORE THAN THAT, THEY'RE INCREDIBLY VARIABLE, AND VARIATION IS THE-- IT'S THE KEY TO EVOLUTION.

IT'S WHAT EVOLUTION WORKS ON, AND THAT'S EXACTLY WHY HYBRIDIZATION IS SUCH A POWERFUL EVOLUTIONARY FORCE.

NARRATOR: THE AIM OF THE PROJECT IS TO STUDY EVERY ASPECT OF THE HYBRIDIZATION PROCESS, BY DISSECTING THE MUSCLES AND SOFT TISSUE OF THE BODY... AND EXAMINING THE SKELETONS IN A MINIATURE CT SCANNER.

[SCANNER EQUIPMENT HUMMING] ACKERMANN: THE MOST INTERESTING THING IS TO UNDERSTAND WHAT THE SKELETONS LOOK LIKE, AND THAT'S BECAUSE IT'S THE SKELETON THAT'S GOING TO ALLOW US TO LINK THIS BACK TO THE HUMAN FOSSIL RECORD BECAUSE, OF COURSE, FOSSILS ARE FOSSILIZED SKELETONS.

ONE OF THE THINGS THAT WE'RE SEEING IN MICE IS THAT THE HYBRIDS HAVE MUCH BIGGER FACES THAN THEIR PARENTS DO.

IN OTHER WORDS, HYBRIDIZATION IS, UM, UNLEASHING VARIATION, IF YOU WILL, AND--AND CAUSING FACES TO CHANGE.

IF YOU TRY AND LINK THAT BACK TO THE HUMAN FOSSIL RECORD, WE SEE THAT FACES ARE ONE OF THE THINGS THAT DO CHANGE OVER TIME.

AND SO THERE IS THAT POSSIBILITY THAT IT'S HYBRIDIZATION ITSELF THAT'S ACTUALLY DRIVING THAT CHANGE.

NARRATOR: AS THE POPULATION OF MODERN HUMANS GREW, SOME OF THEM MOVED OUT OF AFRICA, PERHAPS 100,000 YEARS AGO.

BUT THEY WERE NOT THE FIRST TO MAKE THIS MOVE.

ARCHAIC HUMANS HAD BEEN LEAVING AFRICA FOR AT LEAST 1 1/2 MILLION YEARS.

SOME HAD SPENT SO LONG IN EUROPE AND ASIA, THEY HAD EVOLVED INTO DIFFERENT SPECIES.

THE BEST-KNOWN OF THESE ARCHAIC HUMANS ARE THE NEANDERTHALS.

WHEN THEY WERE DISCOVERED IN THE 19th CENTURY, THE GULF BETWEEN THEM AND US WAS THOUGHT TO BE VAST.

THEY WERE APE-LIKE BRUTES, INFERIOR IN EVERY WAY.

BUT OVER TIME, THE NEANDERTHALS HAVE BEEN REHABILITATED.

THE EVIDENCE SUGGESTS THEY WERE MORE SIMILAR TO US THAN WE EVER GUESSED... OUR EVOLUTIONARY COUSINS.

IF SO, MIGHT WE HAVE INTERBRED WITH THEM AS WELL?

NARRATOR: IN 2010, GENETICISTS AT THE MAX PLANCK INSTITUTE MANAGED TO CRACK THE GENETIC CODE OF A NEANDERTHAL.

[ELECTRIC SAW BUZZING] THEY FOUND A SAMPLE OF SHIN BONE WHICH STILL CONTAINED READABLE DNA AFTER 38,000 YEARS IN A CAVE.

THEN THEY HAD TO SEQUENCE THE DNA, AND THAT WAS A COLOSSAL TASK.

AS DNA AGES, IT BREAKS DOWN INTO BILLIONS OF FRAGMENTS THAT ARE MIXED UP AND CONTAMINATED WITH THE DNA OF INSECTS AND BACTERIA.

THE CHALLENGE FOR A GENETICIST IS TO IDENTIFY THE NEANDERTHAL FRAGMENTS, ISOLATE THEM, AND REASSEMBLE THEM ALL...

IN THE CORRECT ORDER.

IT TOOK THE SEQUENCING MACHINES 2 1/2 YEARS TO PRODUCE THE FIRST GENOME OF AN EXTINCT HUMAN.

MAN: ONE OF THE FIRST QUESTIONS WE WERE INTERESTED IN WAS WHAT HAPPENED WHEN MODERN HUMANS CAME OUT OF AFRICA AND MET NEANDERTHALS.

DID ONE MIX WITH THEM OR NOT?

[CAMERA SHUTTER CLICKING] NARRATOR: THEY COMPARED THE NEANDERTHAL GENOME WITH THAT OF MODERN-DAY AFRICANS.

THEY FOUND NO EVIDENCE OF INTERBREEDING.

THAT WAS TO BE EXPECTED; NEANDERTHALS LIVED IN EUROPE, NOT AFRICA.

THEN THEY RAN THE SAME COMPARISON ON MODERN-DAY EUROPEANS AND GOT VERY DIFFERENT RESULTS.

[CAMERA SHUTTER CLICKING AT HIGH SPEED] PAABO: WE FOUND, TO MY BIG SURPRISE, THERE WAS SLIGHTLY MORE SIMILARITY BETWEEN THE GENOMES OF PEOPLE IN EUROPE TO THE NEANDERTHAL GENOME THAN BETWEEN PEOPLE IN AFRICA AND THE NEANDERTHAL GENOME.

AND EVEN MORE SURPRISING AT THAT TIME WAS THAT WE ACTUALLY FOUND THE SAME SORT OF EXCESS SIMILARITY WHEN WE LOOKED AT PEOPLE IN ASIA.

NARRATOR: WHEREVER THEY LOOKED, THEY KEPT SEEING THE SAME AMOUNT OF OVERLAP.

OUTSIDE AFRICA, IT SEEMS THAT EVERYONE IN THE WORLD HAS INHERITED BETWEEN 1% AND 3% OF THEIR DNA FROM NEANDERTHALS.

I WAS REALLY BIASED WHEN WE STARTED LOOKING AT THIS, THINKING THERE WOULD BE NO CONTRIBUTION.

BUT THE DATA SORT OF FORCED US TO SEE THAT WE WERE WRONG IN THAT CIRCUMSTANCE, AND IT WAS QUITE OBVIOUS THAT THE NEANDERTHALS LIVE ON IN MANY PEOPLE TODAY AROUND THE PLANET.

NARRATOR: THERE'S ONLY ONE EXPLANATION FOR THIS-- INTERBREEDING MUST HAVE HAPPENED SOMEWHERE OUTSIDE AFRICA, BUT ONLY JUST OUTSIDE, BEFORE WE HAD SPREAD AROUND THE WORLD, SOMEWHERE LIKE THE MIDDLE EAST.

ISRAEL IS A NATURAL CROSSROADS BETWEEN AFRICA, ARABIA, AND ASIA-- A MEETING PLACE, A MELTING POT OF DIVERSITY.

IT IS TODAY AND WAS THE SAME IN PREHISTORIC TIMES.

THE HILLS OF GALILEE ARE RICH IN ARCHAEOLOGICAL SITES.

THE LATEST IS KNOWN AS MANOT.

IT WAS DISCOVERED BY ACCIDENT IN 2008, WHEN A BULLDOZER WAS DIGGING A NEW SEWER LINE FOR THE LOCAL VILLAGE.

MAN: THE BULLDOZER WAS COMING THROUGH THIS WAY.

YOU CAN STILL SEE THE CUTS ON THE ROCKS.

THE BULLDOZER REACHED THIS POINT, EXACTLY WHERE I'M STANDING NOW.

NOW IMAGINE TO YOURSELF THE SCENE, THAT THE BULLDOZER IS CUTTING THROUGH THOSE HUGE ROCKS, AND BOOM, BOOM, BOOM!

AND SUDDENLY THERE WAS A HOLE THERE.

HERSHKOVITZ: OK, I'M GETTING DOWN.

MAN: BE ABLE TO GET DOWN NOW.

NARRATOR: ANTHROPOLOGIST ISRAEL HERSHKOVITZ WAS ONE OF THE FIRST PEOPLE INTO THE CAVE.

HERSHKOVITZ: VERY NICE.

NARRATOR: A FORMER COLONEL IN THE PARATROOPERS, HE RAPPELLED IN THROUGH THE HOLE CUT BY THE BULLDOZER.

HERSHKOVITZ: ONCE WE WENT IN, IT WAS TOTALLY DARK.

WE COULDN'T SEE FOR A METER IN FRONT OF US.

SO WHEN WE CAME DOWN, WE DIDN'T REALIZE THE-- THE--THE SIZE OF THE CAVE AND HOW BEAUTIFUL IT IS.

AND WHEN YOU LOOKED DOWN WITH A TORCH, IT WAS ONE OF THE MOST AMAZING PLACES I'VE BEEN TO MY WHOLE LIFE.

IT'S REALLY AN AMAZING CAVE.

NARRATOR: SINCE THEN, MANOT HAS BECOME A MAJOR EXCAVATION SITE.

[MAN SHOUTS] NARRATOR: ARCHAEOLOGISTS HAVE FOUND A MASS OF TOOLS, BONES, AND ORNAMENTS.

THIS COOL, WET CAVE WAS CLEARLY A PLACE FOR PREHISTORIC PEOPLE TO MAKE A HOME.

BUT THE STAR FIND WAS DISCOVERED AWAY FROM THE REST, IN A SIDE CHAMBER OF THE CAVE.

HERSHKOVITZ: IMAGINE TO YOURSELF GOING DOWN IN THE DARK WITH JUST A VERY SMALL TORCH.

IT LOOKS EMPTY, THE WHOLE ROOM LOOKS EMPTY, AND THEN SUDDENLY, YOU TURN YOUR HEAD TO THE RIGHT.

JUST ON THAT SHELF OVER THERE, THERE WAS A SKULL, JUST A SKULL, SITTING ON THE SHELF OVER THERE.

JUST COVERING WITH A THIN LAYER OF MUD.

THAT'S IT.

THERE ARE NO TOOLS, THERE ARE NO ANIMAL BONES, THERE ARE NOTHING; JUST A SKULL SITTING THERE ON THE SHELF FOR 55,000 YEARS, WAITING TO BE DISCOVERED.

NARRATOR: IT WAS A HUMAN BRAINCASE, BUT IT LOOKED UNUSUAL, LIKE A MIX BETWEEN A MODERN AND ARCHAIC HUMAN.

HERSHKOVITZ: THE SKULL IN ITS GENERAL SHAPE IS MODERN, BUT IT STILL HAS SOME ARCHAIC TRAIT.

ONE OF THEM IS THAT THE WHOLE AREA HERE, AT THE BACK OF THE SKULL, HAS A CUP-SHAPED APPEARANCE.

IT--IT IS PROTRUDING BACKWARDS LIKE--LIKE HAVING SOME KIND OF A BUMP OVER HERE, AT THE BACK OF YOUR HEAD.

NOW, IF WE TURN THE SKULL UPSIDE DOWN, WE CAN SEE THE--THE MARKS THAT WAS LEFT BY THE SINUSES OF THE BRAIN.

THE PATTERN THAT WE SEE HERE, IT'S NOT A MODERN PATTERN.

AND ONE OF THE WAY TO EXPLAIN THOSE MIXTURE OF CHARACTERISTICS IN ONE SINGLE SKULL IS TO ASSUME THAT THIS SPECIMEN REPRESENTS SOME KIND OF INTERBREEDING BETWEEN MODERN HUMANS AND NEANDERTHALS.

NARRATOR: 55,000 YEARS AGO, MODERN HUMANS WERE MIGRATING INTO THE MIDDLE EAST.

AT THE SAME TIME, A COLD SPELL IN EUROPE HAD PUSHED NEANDERTHALS FURTHER SOUTH.

THE TWO SPECIES WERE DESTINED TO MEET.

[SPEAKS ANCIENT LANGUAGE] NARRATOR: THIS WAS A KEY MOMENT IN THE HISTORY OF OUR SPECIES.

[NEANDERTHALS MURMUR IN ANCIENT LANGUAGE] NARRATOR: FACE-TO-FACE FOR THE FIRST TIME WITH OUR NEANDERTHAL COUSINS.

[MODERN HUMANS SHOUTING] NARRATOR: IT USED TO BE THOUGHT WE SIMPLY WIPED THEM OUT.

BUT HERE, IT SEEMS WE WERE CURIOUS ENOUGH ABOUT EACH OTHER TO BECOME NEIGHBORS.

[ALL MURMURING] HERSHKOVITZ: THERE ARE NO OTHER PLACES IN THE WORLD THAT MODERN HUMANS AND NEANDERTHALS WERE LIVING SIDE-BY-SIDE, IN CLOSE PROXIMITY TO EACH OTHER, FOR AT LEAST 10,000 YEARS.

NARRATOR: WHAT WAS ONCE SCIENTIFIC HERESY-- THAT WE MATED AND INTERBRED WITH NEANDERTHALS-- HAS BECOME SCIENTIFIC FACT.

[MURMURING] NARRATOR: DNA REVEALED IT.

NOW A SKULL FROM GALILEE CONFIRMS IT.

[SPEAKS ANCIENT LANGUAGE] HERSHKOVITZ: THIS IS THE ONLY SKULL AND THE ONLY EVIDENCE, THE ONLY ANTHROPOLOGICAL EVIDENCE, THE ONLY FOSSIL EVIDENCE THAT WE HAVE FOR INTERBREEDING BETWEEN NEANDERTHALS AND MODERN HUMANS.

THIS IS THE SMOKING GUN.

NARRATOR: THE HUMAN STORY IS GETTING A REWRITE.

WE USED TO THINK WE HAD A CLEAR, SIMPLE GENESIS.

NOW IT SEEMS OUR PAST IS FAR MESSIER.

BUT IT'S ALSO MORE INTRIGUING.

OURS IS A STORY OF CONTACT WITH OTHER SPECIES-- OUR ANCIENT COUSINS.

WE WERE NOT SEPARATE FROM THEM.

THEY ARE PART OF US.

HAWKS: WHEN WE LOOK AT THE ORIGIN OF MODERN HUMANS, WE SEE DIFFERENT PEOPLE.

AND WE PERCEIVE THEM AS BEING VERY DIFFERENT, AND SO WE GIVE THEM DIFFERENT NAMES: MODERN HUMANS, ARCHAIC HUMANS.

TO US, THOSE DIFFERENCES ARE REALLY IMPORTANT BECAUSE WE CAN SEE AND IDENTIFY THEM.

BUT LET'S LOOK AT IT FROM THEIR PERSPECTIVE.

WE DON'T KNOW WHETHER THEY THOUGHT THAT ANY OF THESE DIFFERENCES THAT THEY SAW AROUND THEM WERE IMPORTANT OR NOT.

WHAT WE KNOW IS THAT THEY WERE INTERBREEDING WITH EACH OTHER.

AND THE COOL THING IS THAT WE CAN LOOK WITHIN OUR OWN GENES AND SEE THE EVIDENCE OF THAT ANCIENT INTERBREEDING.

IT'S AS IF THESE ARCHAIC HUMANS STILL ARE LIVING ON INSIDE THE DNA OF US ALL.

NARRATOR: WE ARE ALL SHAPED BY OUR PAST, ENCOUNTERS THAT HAPPENED TENS OF THOUSANDS OF YEARS AGO.

AS A RESULT, OUR SPECIES IS A PATCHWORK OF DIFFERENT TYPES OF HUMANS.

WE ARE ALL HYBRIDS, 7 BILLION OF US ACROSS PLANET EARTH.

"FIRST PEOPLES" IS AVAILABLE ON DVD.

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