First Peoples (2015): Season 1, Episode 3 - Australia - full transcript

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NARRATOR: TODAY,

THERE ARE 4 BILLION PEOPLE
LIVING IN ASIA--

ALL OF THEM MEMBERS
OF THE SAME SPECIES:

HOMO SAPIENS-- US.

BUT IT WASN'T ALWAYS THIS WAY.

WHEN WE LEFT AFRICA
AND ENTERED ASIA,

IT WAS ALREADY INHABITED BY
DIFFERENT SPECIES OF HUMAN.

THEY WERE VETERANS IN THIS LAND.

WE WERE THE ROOKIES.



AAH!

BUT WHAT HAPPENED NEXT?

IS IT POSSIBLE WE MATED
WITH THESE ANCIENT HUMANS

AND PICKED UP THEIR GENES?

WHEN WE ANALYZED
THE DNA FROM THIS,

THIS WAS A NEW FORM
OF EXTINCT HUMAN.

MAN: EVEN THOUGH THEY WENT
EXTINCT 30,000 YEARS AGO,

THEIR DNA LIVES ON
IN EACH OF US.

DIFFERENT MAN:
WE HAVE INSIDE OF US

THE GENES OF THESE
ANCIENT PEOPLE

INFLUENCING US
TODAY.

NARRATOR: BUT HOW HAVE
THEIR GENES HELPED US
COLONIZE THE PLANET?

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: SOUTHEAST ASIA,
63,000 YEARS AGO.

A BAND OF HUNTER-GATHERERS
ON THE LOOKOUT FOR FOOD.

THEY'RE NEWCOMERS HERE--
MIGRANTS FROM AFRICA--

AT THE EDGE OF
THE KNOWN WORLD.

[ANIMAL GRUNTING]

[PEOPLE SPEAKING
INDISTINCTLY]

PEOPLE IN THE TROPICS
TEND NOT TO LIVE IN CAVES.

THERE ARE TOO MANY
POISONOUS PREDATORS.

THEY USE THEM AS A SHELTER
TO ESCAPE THE RAIN.

[THUNDER]

BUT FOR ONE YOUNG WOMAN,

THIS CAVE WILL BE
HER FINAL RESTING PLACE.

HER REMAINS HAVE RECENTLY
BEEN DISCOVERED.

THEY MAY BE THE OLDEST
MODERN HUMAN REMAINS

FOUND ANYWHERE IN ASIA.

LAOS IS ONE OF THE MOST ISOLATED
COUNTRIES IN SOUTHEAST ASIA--

UNTIL RECENTLY, CUT OFF
FROM THE WESTERN WORLD.

BUT TWO WESTERN ARCHAEOLOGISTS
HAVE BEEN WORKING HERE

SINCE 2007.

LAURA SHACKELFORD FROM CHICAGO

AND FABRICE DEMETER
FROM FRANCE.

THEY CAME TO LAOS ON A HUNCH

THAT PREHISTORIC PEOPLE
MAY HAVE LIVED IN THESE HILLS.

THE NORTH OF LAOS
IS RIDDLED WITH CAVES.

DURING THE VIETNAM WAR,

THEY WERE USED AS SHELTER
AGAINST THE BOMBS,

BUT NO ONE HAS PROPERLY
EXPLORED THEM UNTIL NOW.

WITH THOUSANDS OF CAVES
TO CHOOSE FROM,

DEMETER AND SHACKELFORD
STARTED EXCAVATING HERE

AT THIS CLEFT
IN A MOUNTAINSIDE...

TAM PA LING.

ASSISTED BY A SMALL ARMY
OF LAO WORKERS,

THEY BEGAN DIGGING
THROUGH TONS OF CLAY.

WOMAN: DO YOU THINK
THAT THEY CAN FINISH
THIS LEVEL TODAY?

MAN: MAYBE NOT TODAY.
MORNING, I GUESS,
SHOULD BE OK.

I THOUGHT THERE
SHOULD BE SOMETHING--

THE WHITE, UM--
OH, THE WHITE...

THE WHITE LINE, YES.

YES. AND THAT'S IT.

YES. THAT IS
THE SAME ONE.

NARRATOR: EVEN WITH
A DIG THIS SIZE,

THEY WEREN'T CONFIDENT
OF FINDING ANYTHING.

WOMAN: THERE ARE VERY FEW
FOSSILS HERE IN ASIA,

IN LARGE PART BECAUSE THIS IS
A WET TROPICAL ENVIRONMENT.

UM, THINGS DON'T FOSSILIZE WELL
HERE FOR THAT REASON.

NARRATOR: BUT IN 2008,

THEY DISCOVERED SOME
FRAGMENTS OF CHARCOAL--

EVIDENCE, PERHAPS,
OF A PREHISTORIC CAMPFIRE.

SPURRED ON BY WHAT THEY FOUND,
THEY CARRIED ON DIGGING.

SHACKELFORD: WE OPENED UP
THE SAME PIT,

WE ENLARGED IT
JUST A LITTLE BIT,

AND IT WAS IN THAT FIRST--

THAT FIRST PIT THAT WE FOUND
OUR FIRST FOSSILS.

NARRATOR:
EMBEDDED IN THE SEDIMENT

WERE FRAGMENTS
OF A HUMAN SKULL.

[MAN SPEAKING FRENCH]

TRANSLATOR: HERE ARE THE HUMAN
REMAINS THAT WE DISCOVERED.

THE FRONT PART HERE CORRESPONDS
TO THE TOP OF THE SKULL.

AFTERWARDS, WE FOUND
A COMPLETE UPPER JAW.

WHEN I HAD TWO PIECES
IN MY HANDS,

I KNEW STRAIGHT AWAY
THAT IT WAS A MODERN HUMAN.

I WAS VERY EXCITED.

NARRATOR: A CT SCAN REVEALS

THE SIZE AND SHAPE OF THE SKULL

IS CLEARLY THAT

OF A YOUNG WOMAN,

BUT WHAT'S REMARKABLE

IS ITS AGE.

PREVIOUSLY, THE MOST ANCIENT
MODERN HUMAN

FOUND IN THIS PART OF THE WORLD
WAS 40,000 YEARS OLD,

BUT THIS SKULL WAS MUCH OLDER.

AT 63,000 YEARS OLD,

THIS IS THE OLDEST FOSSIL IN--
IN EAST OR SOUTHEAST ASIA,

AND IT REALLY PUTS
THE AGE OF MODERN HUMANS

IN THIS PART OF THE WORLD BACK
BY AT LEAST 20,000 YEARS.

[THUNDER]

[RAIN POURING]

NARRATOR: THE WOMAN
FROM TAM PA LING

IS NOW THE OLDEST
DEFINITIVELY MODERN HUMAN

FOUND ANYWHERE IN ASIA.

HER PEOPLE LEFT AFRICA

AND MIGRATED 4,000 MILES
EASTWARD FOLLOWING GAME--

LOOKING FOR NEW
SOURCES OF FOOD.

BUT THEIR PRESENCE IN
SOUTHEAST ASIA SO EARLY

RADICALLY ALTERS THE PREVAILING
THEORY OF HUMAN MIGRATION.

CONVENTIONAL WISDOM SAYS MODERN
HUMANS MIGRATED OUT OF AFRICA

AND INTO ASIA
ABOUT 60,000 YEARS AGO,

BUT THE WOMAN FROM TAM PA LING

WAS LIVING ON THE OTHER SIDE
OF THE CONTINENT--

IN THE HILLS OF LAOS--
63,000 YEARS AGO.

PEOPLE MUST HAVE LEFT AFRICA
EARLIER THAN PREVIOUSLY THOUGHT.

ARCHAEOLOGIST JEFF ROSE IS
TRYING TO PIECE TOGETHER

THE ROUTE TAKEN BY
THE FIRST PEOPLE OUT OF AFRICA.

HE'S LOOKING FOR EVIDENCE
WHERE THE JOURNEY BEGAN--

ON THE ARABIAN PENINSULA.

MAN: UP UNTIL JUST
A COUPLE YEARS AGO,

MOST ARCHAEOLOGISTS THOUGHT
THE GREAT HUMAN EXPANSION

OUT OF AFRICA OCCURRED
ALONG THIS COASTLINE.

PEOPLE CALLED IT
"COASTING OUT OF AFRICA,"

"COASTAL MIGRATION,"
"COASTAL EXPRESS."

THE IDEA WAS THAT
THEY HAD BECOME SEAFARERS.

THEY HAD SOMEHOW DEVELOPED
AQUATIC SUBSISTENCE.

THEY COULD FISH,

THEY COULD COLLECT SHELLFISH
ALONG THE COAST,

AND THAT THEN LED TO THIS
COLOSSAL EXPANSION INTO ASIA

AND THE REST OF THE WORLD.

NARRATOR: THAT'S THE THEORY.

BUT IS IT REALLY TRUE?

ROSE: IF AN AFRICAN CULTURE
CAME TO THIS PLACE,

THEY'RE GONNA LEAVE EVIDENCE
OF THAT CULTURE BEHIND

IN THEIR STONE TOOL TECHNOLOGY,

AND WE SHOULD BE
ABLE TO SEE THIS.

SO IT'S TESTABLE.

NARRATOR: IN 2010,

JEFF ROSE GOT FUNDING
TO EXCAVATE IN OMAN

AND FIND THAT EVIDENCE.

ANYTHING ON THE SHORE ITSELF

WOULD HAVE BEEN
WASHED AWAY LONG AGO,

BUT IN THE HILLS
BEHIND THE SHORE,

HE EXPECTED TO FIND SOME SIGN
OF PREHISTORIC HUMAN LIFE.

ROSE: NOW,
THIS MOUNTAIN RANGE HERE

RISES UP PRETTY STEEPLY
FROM THE COAST.

IT IS FULL OF CAVES.
IT'S LIKE SWISS CHEESE.

WE JUST THOUGHT,
"IT'S A FOREGONE CONCLUSION.

"IT'S JUST A MATTER OF TIME
NOT IF WE FIND ANYTHING,

BUT WHEN WE FIND ANYTHING."

WE DUG A TEST PIT
OVER THERE.

WE DUG ONE THERE.
WE DUG ONE THERE.

WE DUG ONE ON THE SLOPE
LEADING UP TO THE CAVE.

IN EACH CASE,
WE WENT DOWN REALLY DEEP--

AS FAR AS WE COULD GO--

AND IN ALL THAT TIME,
WE FOUND NOTHING.

WE NEVER FOUND
A SINGLE ARTIFACT.

I REMEMBER JUST SITTING THERE
AND SAYING,

"THAT'S IT. FORGET IT.
FORGET THE COAST.

"WE NEED TO GO
SOMEWHERE ELSE.

WE NEED A COMPLETELY
DIFFERENT STRATEGY."

NARRATOR:
THE PROJECT WAS FAILING,

SO JEFF ROSE HEADED INLAND.

OVER 100 MILES
FROM THE COAST,

IN THE MIDDLE OF THE DESERT,

HE CAME ACROSS
A DRIED-UP RIVERBED.

ROSE: THIS IS THE WADI GHADUN,

ONE OF THE BIGGEST
ANCIENT RIVER VALLEYS

IN ALL OF ARABIA, PERHAPS.

IT'S PROBABLY HALF A MILE
TO THE OTHER SIDE.

IT'S DRY NOW,
BUT 100,000 YEARS AGO,

THIS THING WAS FULL OF WATER.

ALL OF ARABIA WAS GREEN,
FOR THAT MATTER.

IT WAS COVERED IN
SAVANNAS AND LAKES,

AND YOU HAVE THIS VAST NETWORK
OF RIVER VALLEYS

THAT RUN THROUGH THIS PLATEAU.

NARRATOR: HE BEGAN TO
EXPLORE THE HILLTOPS

ABOVE THE ANCIENT RIVERBED,

AND HERE HE FOUND
A FIELD OF FLAKED ROCKS.

SO, LIKE, THIS IS THE STUFF
I'VE BEEN LOOKING FOR

ALL THOSE YEARS
ALONG THE COAST.

THIS IS CALLED CHERT,
OR FLINT,

AND IT'S THE RAW MATERIAL
THAT WAS ESSENTIAL

TO MAKE THE STONE TOOLS
THROUGHOUT PREHISTORY.

AND THE SITE LIKE THIS

IS LITERALLY COVERED IN
A CARPET OF THIS MATERIAL.

PREHISTORIC TOOL MAKERS
WOULD COME TO A SITE LIKE THIS.

THEY WOULD BANG AWAY,
MAKE THEIR STONE TOOLS,

LEAVE THE REFUSE BEHIND,

AND THEN GO OFF DOWN INTO
THE VALLEYS WHERE THE WATER WAS.

SO THIS IS
A PREHISTORIC WORKSHOP.

NARRATOR: IT WAS UNMISTAKABLE.

PEOPLE HAD PASSED THROUGH HERE

AND HUNG AROUND LONG ENOUGH
TO MAKE THOUSANDS OF TOOLS.

BUT WHO AND WHEN?

THE STONES TOLD HIM
ALL HE NEEDED TO KNOW.

ROSE: THAT IS GORGEOUS!

THAT IS A CLASSIC NUBIAN POINT.

THIS IS THE TOOL
THAT WAS MADE

BY THE FIRST PEOPLE
THAT LEFT AFRICA.

NARRATOR: NUBIAN POINTS
CAME FROM A PART OF AFRICA

NOW IN MODERN-DAY EGYPT.

THEY WERE MADE ABOUT
100,000 YEARS AGO.

IF THE SAME TOOLS
CAN BE FOUND IN OMAN,

IT SUGGESTS PEOPLE WERE
ON THE ARABIAN PENINSULA

AT THE SAME TIME--

100,000 YEARS AGO.

ROSE: WE'RE NOT
LOOKING AT SOMETHING

THAT LOOKS LIKE
IT MAY HAVE A SIMILARITY

TO AN AFRICAN TECHNOLOGY.

WE'RE LOOKING AT THE IDENTICAL
AFRICAN TECHNOLOGY.

NARRATOR: IF AFRICANS WERE
IN ARABIA 100,000 YEARS AGO,

THEN PEOPLE WERE
MIGRATING INTO ASIA

MUCH EARLIER THAN
ARCHAEOLOGISTS THOUGHT--

40,000 YEARS EARLIER.

BUT WHAT DROVE THEM ON
INTO THE UNKNOWN?

[THUNDER]

PERHAPS IT WAS THE CLIMATE.

TODAY, NORTHERN AFRICA
AND ARABIA ARE HOT AND DRY,

BUT 100,000 YEARS AGO,
THIS REGION WAS VERY DIFFERENT.

THE DESERTS BLOOMED.
THE LANDSCAPE WAS GREEN.

THE WORLD WAS IN A WET PHASE.

ROSE: THE CLIMATE HERE
IS CYCLICAL.

SO YOU HAVE THIS MONSOON SYSTEM

THAT'S CIRCULATING
THROUGH THE INDIAN OCEAN,

AND THEN EVERY ONCE IN A WHILE,
IT INTENSIFIES, IT STRENGTHENS,

AND IT PUSHES INTO
THE INTERIOR OF ARABIA.

RIVERS LIKE THIS THAT WERE
ONCE DRY WERE FLOWING AGAIN,

AND SO IT WAS ALMOST LIKE
THE HIGHWAYS WERE OPEN,

AND THEY JUST FILLED THEM UP.

NARRATOR: IT WASN'T THE BEACHES
THAT LURED PEOPLE INTO ARABIA,

BUT THE RIVERS
FILLED BY MONSOON WATERS.

ROSE: WHAT WE REALIZED

WAS THAT PEOPLE WEREN'T
INTERESTED IN THE COASTLINE.

THEY WEREN'T THESE FISHERMEN
WHO HAD ADAPTED A NEW TECHNOLOGY

AND WERE MOVING ALONG THIS--
THIS NEW ECOSYSTEM.

THEY WERE THE SAME PEOPLE
AS THEY WERE IN AFRICA,

AND THEY WERE OPPORTUNISTIC.

THESE RIVER VALLEYS
WOULD HAVE BEEN PARADISE,

BECAUSE NOT ONLY IS IT
THE EXACT LANDSCAPE

THAT THEY ALREADY KNEW,

IT WAS ALSO UNOCCUPIED,

SO THERE WAS NOBODY
TO COMPETE WITH.

SOME OF THE QUALITIES
THAT WE CAN SEE IN THESE PEOPLE

WHICH WE REALLY HAVEN'T SEEN
BEFORE IN PREHISTORY IS,

THEY'RE CURIOUS.

THERE WAS NO OVERPOPULATION,

SO THEY WEREN'T FORCED
OUT OF AFRICA,

BUT THEY WOULD WAKE UP EVERY DAY
ON ONE SIDE OF THE RED SEA,

AND THEY'D LOOK ACROSS,

AND AT SOME POINT,

SOMEBODY COULDN'T
STAND IT ANYMORE

AND HAD TO GO
SCRATCH THAT ITCH.

I THINK IT WAS THIS CURIOSITY
THAT WAS DRIVING THEM,

AND I THINK THAT'S--
THAT'S WHAT WE ARE.

THAT'S THE DEFINING ASPECT
OF OUR SPECIES,

IS WE WANT TO KNOW
WHAT'S ON THE OTHER SIDE.

[THUNDER]

NARRATOR: FOR THE FIRST PEOPLES,
THE WAY INTO ASIA WAS OPEN.

FROM ARABIA, THEY MIGRATED
EASTWARD INTO CENTRAL ASIA,

NORTHERN INDIA, AND BEYOND.

THEY WOULD HAVE FOLLOWED
A NETWORK OF RIVERS--

NATURAL CORRIDORS
THROUGH THE CONTINENT.

SOME OF THE LONGEST RIVERS
IN THE WORLD ARE IN ASIA--

A CONSTANT SOURCE OF
FRESH WATER AND FOOD.

STILL TODAY,

OVER 90% OF
THE WORLD'S POPULATION

LIVES WITHIN 10 MILES
OF A RIVER.

THE MEKONG RIVER FLOWS 2,000
MILES THROUGH SOUTHEAST ASIA.

IT'S KNOWN LOCALLY AS
THE MOTHER OF WATER.

IT COULD HAVE LED THE FIRST
PEOPLES TO THE HILLS OF LAOS

AND EVENTUALLY
ON TO TAM PA LING.

IF PEOPLE ENTERED ASIA
100,000 YEARS AGO,

THEY WOULD HAVE HAD MORE TIME
TO MIGRATE ACROSS THE CONTINENT.

THEY HAD TO MOVE ONLY TWO MILES
EVERY GENERATION

TO REACH HERE 63,000 YEARS AGO.

ARCHAEOLOGISTS KNOW SO LITTLE
ABOUT THESE PEOPLE

BECAUSE THEY FIND SO FEW
ARTIFACTS IN SOUTHEAST ASIA.

THE PROBLEM IS,

THERE'S BARELY ANY FLINT TO MAKE
TOOLS OR SPEAR POINTS.

BUT THERE IS SOMETHING ELSE--

BAMBOO.

IT'S DAWN IN BAN SA--
A VILLAGE IN NORTHERN LAOS.

THE WORK OF THE DAY BEGINS,
AND BAMBOO IS EVERYWHERE.

IT'S STRONG ENOUGH
TO BUILD HOUSES

BUT SUPPLE ENOUGH
TO BEND AT WILL

AND TENDER ENOUGH TO EAT.

BAMBOO IS A SUPERGRASS
THAT GROWS UP TO 3 FEET A DAY.

IT CAN WITHSTAND MORE WEIGHT
THAN CONCRETE,

AND WHEN DRY,
IT'S STRONGER THAN STEEL.

IN A LAND WITHOUT FLINT,

IT WOULD HAVE BEEN
A MULTIPURPOSE SOLUTION

FOR THE FIRST PEOPLES.

SHACKELFORD:
IF YOU'RE TRAVELING,

THEN STONE TOOLS AREN'T
NECESSARILY SOMETHING

THAT YOU WANT TO TRAVEL WITH.

ORGANIC MATERIALS
LIKE BAMBOO ARE EASY TO--

TO USE, TO DISCARD,
AND THEN TO--

TO MAKE AGAIN
WHEREVER YOU MOVE TO.

IT'S CERTAINLY SOMETHING

THAT PEOPLE 60,000 YEARS AGO
COULD EASILY HAVE USED.

NARRATOR: BUT BAMBOO IS
ALSO HIGHLY ABSORBENT.

ONCE IT GETS WET,
IT SOFTENS AND ROTS AWAY,

LEAVING NOTHING FOR
ARCHAEOLOGISTS TO FIND.

THAT MAKES THE TRAIL OF
THE FIRST ASIANS HARD TO FOLLOW.

SO MUCH OF THE EVIDENCE
HAS DISAPPEARED.

THE NEXT HINT OF THAT TRAIL

TURNS UP 300 MILES FURTHER EAST
IN SOUTHERN CHINA,

AMONG THE LIMESTONE OUTCROPS
OF GUANGXI PROVINCE.

CHANG ZHU JIN IS ONE OF CHINA'S
MOST EXPERIENCED GEOLOGISTS.

HE REALIZED
THIS WAS A LANDSCAPE

THAT WOULD HAVE ATTRACTED
PREHISTORIC HUMANS.

[MAN SPEAKING CHINESE]

TRANSLATOR: THAT OVER THERE
IS MULAN MOUNTAIN.

IT'S A TYPICAL
LIMESTONE FORMATION.

AND AS YOU CAN SEE,

IT HAS LOTS OF PEAKS
AND LOTS OF CAVES.

THEY'RE QUITE TREACHEROUS.

BUT THEY'RE NATURAL DWELLINGS,

AND FOR THE ANCIENT PEOPLE,
THEY PROVIDED A PERFECT HABITAT.

NARRATOR: IN 2007,

PROFESSOR JIN WORKED HIS WAY UP
MULAN MOUNTAIN TO THIS CAVE--

ZHIRENDONG.

LOCAL FARMERS HAD FOUND
ANIMAL FOSSILS AT THE ENTRANCE--

ANIMALS THAT MAY HAVE BEEN
BUTCHERED BY EARLY HUMANS--

SO PROFESSOR JIN DECIDED

TO EXPLORE THE INTERIOR
OF THE CAVE.

AFTER 18 MONTHS OF EXCAVATIONS,
HIS TEAM MADE A DISCOVERY.

A HUMAN JAWBONE-- A MANDIBLE.

[JIN SPEAKING CHINESE]

TRANSLATOR: THIS IS
WHERE WE FOUND THE BONE.

ABOVE IT, YOU CAN SEE
WHERE THE FIRST LAYER IS,

AND THEN DOWN HERE,
THERE'S ANOTHER LAYER.

AND IT WAS RIGHT THERE
IN THE MIDDLE OF THE TWO LAYERS

THAT WE FOUND
THE ZHIRENDONG JAWBONE.

NARRATOR: WHEN HE DATED
THE SURROUNDING LAYERS,

HE DISCOVERED THE MANDIBLE
WAS 102,000 YEARS OLD.

IT WAS OLDER THAN THE SKULL
AT TAM PA LING.

IT WAS OLDER EVEN
THAN THE TOOLS IN OMAN.

IF THE DATES ARE RIGHT,

PEOPLE MUST HAVE LEFT AFRICA
AND ENTERED ASIA

EVEN EARLIER THAN
THE EVIDENCE SUGGESTS--

REACHING CHINA AT LEAST
102,000 YEARS AGO.

BUT THERE IS
AN ALTERNATIVE EXPLANATION.

PERHAPS THE MANDIBLE
IS NOT FROM A MODERN HUMAN.

PERHAPS IT'S FROM
A DIFFERENT SPECIES.

EVERYONE ALIVE TODAY,
ALL 7 BILLION OF US,

ARE MEMBERS OF
THE SAME SPECIES...

HOMO SAPIENS.

WE ARE NOW THE ONLY HUMANS
ON THE PLANET,

BUT IT WASN'T ALWAYS THIS WAY.

THE HUMAN FAMILY TREE STARTS
MORE THAN TWO 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.

ANTHROPOLOGISTS CLASSIFY
ALL THOSE THAT CAME BEFORE US

AS ARCHAIC HUMANS.

THE MOST SUCCESSFUL OF THESE
SPECIES WAS HOMO ERECTUS.

DESPITE HAVING A BRAIN
ONLY 2/3 THE SIZE OF OURS,

HOMO ERECTUS
SPREAD OUT FROM AFRICA

11/2 MILLION YEARS
BEFORE MODERN HUMANS.

THEY, NOT US, WERE THE FIRST
INHABITANTS OF ASIA.

MAYBE THAT'S WHY THE MANDIBLE
FROM ZHIRENDONG IS SO ANCIENT.

IT MIGHT NOT BE HOMO SAPIENS.

IS IT HOMO ERECTUS?

WU LIU IS AN EXPERT

ON THE DIFFERENCES
BETWEEN THE TWO HUMAN SPECIES.

THE MANDIBLE IS
A DEFINING FEATURE--

IN PARTICULAR, THE SIZE
AND ANGLE OF THE CHIN.

IN HOMO SAPIENS, IT JUTS FORWARD
AHEAD OF THE TEETH,

BUT IN HOMO ERECTUS,
IT SLOPES BACKWARD.

NARRATOR: WHAT ABOUT
THE MANDIBLE FROM ZHIRENDONG?

IS IT ERECTUS OR SAPIENS?

BY ANALYZING IT
IN A CT SCANNER,

IT'S POSSIBLE TO MEASURE
THE ANGLE OF THE CHIN--

ALSO THE THICKNESS
OF THE BONES

AND THE SIZE OF
THE TEETH CAVITIES.

ON ALL THESE SCORES,

THE MANDIBLE SEEMS TO BE
BETWEEN SAPIENS AND ERECTUS--

A MIX OF BOTH SPECIES.

IT HAS LONG BEEN THOUGHT
HOMO ERECTUS WENT EXTINCT

BEFORE WE TURNED UP IN ASIA,

BUT WHAT IF THAT'S NOT TRUE?

WHAT IF THEY WERE
STILL AROUND,

AND THE TWO SPECIES
MET EACH OTHER?

[PEOPLE TALKING INDISTINCTLY]

NARRATOR: WOULD WE HAVE HAD
ENOUGH IN COMMON

TO INTERACT AND INTERBREED?

PERHAPS THAT'S WHY THE MANDIBLE
LOOKS LIKE A MIX OF TWO SPECIES.

IT'S THE RESULT
OF INTERBREEDING.

SO FAR, NO OTHER EVIDENCE
OF SUCH ENCOUNTERS

HAS BEEN FOUND
IN SOUTHERN CHINA,

BUT IT'S AN INTRIGUING IDEA
THAT MODERN HUMANS ARRIVED

AND MATED WITH OTHER
ARCHAIC TYPES OF HUMAN.

IF IT HAPPENED HERE, WHERE ELSE
MIGHT IT HAVE HAPPENED?

WHO ELSE WAS LIVING IN ASIA
WHEN MODERN HUMANS ARRIVED?

FOR THE FIRST ASIANS
THAT HEADED NORTH,

THIS WAS A NATURAL CORRIDOR

ACROSS THE WILDERNESS
OF SIBERIA.

AND HERE IN
THE ALTAI MOUNTAINS,

ARCHAEOLOGISTS HAVE FOUND A CAVE
LIKE NO OTHER-- DENISOVA.

MAN: YOU HAVE
THIS LARGE OPENING,

AND IT'S VISIBLE
FROM QUITE A DISTANCE

AS SOON AS YOU GET INTO
THAT PART OF THE VALLEY.

IT WAS INHABITED IN,
I THINK, THE 18th CENTURY

BY A HERMIT CALLED DENIS--
THE HOLY DENIS--

AND THE CAVE IS
NAMED AFTER HIM.

SO IT'S DENIS' CAVE--
DENISOVA CAVE.

NARRATOR:
DENISOVA WAS ONCE A HOME

TO THE ROCK STARS
OF PREHISTORY--

THE NEANDERTHALS.

OUR CLOSEST COUSINS,

THE NEANDERTHALS ARE
A SEPARATE SPECIES

THAT EVOLVED IN ICE-AGE EUROPE

BUT EXPANDED NORTHEAST
AS FAR AS SIBERIA.

SINCE THE 1970s,

ARCHAEOLOGISTS HAVE UNEARTHED
THOUSANDS OF ARTIFACTS

MADE BY NEANDERTHALS,

BUT THEY ALSO FIND ARTIFACTS
MADE BY MODERN HUMANS.

THERE ARE FEW CAVES IN THE WORLD
WHERE THERE'S EVIDENCE

THAT TWO TYPES OF HUMAN
LIVED IN THE SAME PLACE,

ALBEIT AT DIFFERENT TIMES.

BUT VERY FEW BONES
HAVE EVER BEEN EXCAVATED HERE,

SO IN 2008, ARCHAEOLOGISTS
INTENSIFIED THEIR SEARCH.

VIOLA:
I JOINED A RUSSIAN TEAM

THAT WAS EXCAVATING THE CAVE
SINCE A LONG TIME, UM,

AND MY ROLE WAS MOSTLY STUDYING
THE HUMAN REMAINS.

THE TEAM VERY CAREFULLY AND
GRADUALLY REMOVES THE SEDIMENTS

THAT ARE IN THE CAVE TO RECOVER
EVEN THE SMALLEST REMAINS.

A LOT OF WORK IS
ACTUALLY LOOKING AT

ALL THE LITTLE BONE PIECES
AND TRYING TO FIGURE OUT,

"IS THERE SOMETHING
HUMAN IN THERE?"

AND SOMETIMES YOU ACTUALLY
DO FIND HUMAN REMAINS.

NARRATOR:
WITHIN A LAYER OF SEDIMENT
THAT WAS 41,000 YEARS OLD,

RUSSIAN ARCHAEOLOGISTS UNCOVERED
A TINY FRAGMENT OF BONE

FROM A HUMAN FINGER.

VIOLA: WE HAVE AN ENLARGED 3D
PRINT, UM, OF THE FINGER BONE.

IT'S 5 TIMES AS LARGE
AS THE ORIGINAL.

IT'S PART OF THE--
PROBABLY OF THE LITTLE FINGER.

THIS FINGER WOULD
STILL BE GROWING.

IT'S A CHILD
THAT'S STILL DEVELOPING.

MAYBE A 5--
5- , 7-YEAR-OLD KID,

SOMETHING-- SOMETHING
AROUND THAT AGE.

THE ORIGINAL SIZE IS THIS HERE.

IT'S A TINY LITTLE PIECE,
AS YOU CAN SEE.

IT'S PROBABLY THE LEAST
SPECTACULAR FOSSIL

THAT EXISTS ANYWHERE--

A TINY FRAGMENT
OF A FINGER BONE OF A CHILD.

NARRATOR: WHO WAS THIS CHILD
IN THE SIBERIAN HILLS

41,000 YEARS AGO--

MODERN HUMAN OR NEANDERTHAL?

THERE'S ONLY
ONE WAY TO TELL...

DNA.

THE FINGER BONE WAS SENT TO
THE MAX PLANCK INSTITUTE--

TO SWEDISH GENETICIST
SVANTE PAABO,

A PIONEER IN THE FIELD
OF ANCIENT DNA.

WHEN HIS TEAM FOUND SOME DNA
STILL PRESERVED IN THE BONE,

THEY SET ABOUT ANALYZING IT.

AS DNA AGES,

IT BREAKS DOWN INTO BILLIONS
OF TINY FRAGMENTS

THAT ARE MIXED UP
AND CONTAMINATED

WITH THE DNA OF INSECTS,
BACTERIA, AND FUNGI.

THE CHALLENGE FOR A GENETICIST

IS TO IDENTIFY
THE HUMAN FRAGMENTS,

ISOLATE THEM,

AND REASSEMBLE THEM ALL
IN THE CORRECT ORDER.

A DECADE AGO, IT WOULD
HAVE BEEN IMPOSSIBLE,

BUT SUPERFAST
SEQUENCING MACHINES

HAVE MADE THE IMPOSSIBLE
MERELY IMPROBABLE.

MAN: THE WHOLE LAST 30 YEARS
IN MOLECULAR GENETICS

IS A HISTORY OF REVOLUTIONS
DRIVEN BY TECHNOLOGY.

THE BIG STEP WAS REALLY
THE ABILITY TO SEQUENCE

MILLIONS OF DNA MOLECULES
QUITE RAPIDLY AND INEXPENSIVELY,

AND THAT CHANGED
THE WHOLE BALL GAME.

NARRATOR: IN 2010, PAABO'S TEAM
CREATED AN INTERNATIONAL STORM.

THEY SEQUENCED THE GENOME
OF A NEANDERTHAL.

IT WAS THE FIRST TIME
ANYONE HAD MANAGED TO READ

THE GENETIC CODE
OF AN EXTINCT HUMAN.

THEY USED THE SAME TECHNIQUES
ON THE SIBERIAN FINGER BONE,

BUT ITS SEQUENCE
WAS NOT WHAT THEY IMAGINED.

WHEN WE ANALYZED
THE DNA FROM THIS,

WE EXPECTED IT TO BE EITHER
A NEANDERTHAL OR A MODERN HUMAN

THAT WOULD HAVE BEEN THERE.

WE WERE VERY SURPRISED TO FIND

THAT IT WAS ACTUALLY
SOMETHING ELSE.

THIS WAS A NEW FORM
OF EXTINCT HUMAN.

NARRATOR: FROM THE SINGLE
FINGER BONE OF A CHILD,

THEY HAD UNCOVERED A NEW BRANCH
OF THE HUMAN FAMILY TREE.

PAABO: WE HAD A BIG DEBATE

ABOUT WHAT WE WOULD CALL
THESE INDIVIDUALS,

AND WE CAME UP WITH
THE NAME "DENISOVANS"

AFTER DENISOVA CAVE,
WHERE THEY HAD BEEN FIRST FOUND.

THIS WAS THE FIRST TIME
THAT WE IDENTIFIED

A NEW FORM OF EXTINCT HUMAN
JUST FROM A GENOME SEQUENCE

AND HARDLY ANY INFORMATION AT
ALL FROM BONES OR STONE TOOLS--

JUST FROM A GENOME SEQUENCE.

NARRATOR: IT SOUNDS LIKE
SCIENCE FICTION.

FROM NOWHERE, A NEW POPULATION--
THE DENISOVANS--

ENTER THE HUMAN STORY.

AS MODERN HUMANS
PUSHED THROUGH ASIA,

THEY MUST HAVE MOVED INTO
DENISOVAN TERRITORY.

[SHOUTS
INDISTINCTLY]

NARRATOR:
WHAT HAPPENED NEXT?

[MEN SPEAKING INDISTINCTLY]

NARRATOR:
ACCORDING TO THE GENETICS,
THE TWO PEOPLES INTERBRED.

MAN: WHEN GENETICISTS LOOKED AT
THAT DENISOVAN GENOME

AND THEY LINED IT UP
NEXT TO MODERN HUMAN GENOMES,

THEY FOUND THAT
THERE WERE MODERN PEOPLE

WHO HAVE PIECES OF THIS
DENISOVAN GENOME INSIDE OF THEM.

THIS IS SO INCREDIBLE

THAT THIS ANCIENT POPULATION
IS STILL THERE INSIDE OF US.

NARRATOR: THIS IS NOT THE FIRST
EVIDENCE OF INTERBREEDING

BETWEEN MODERN
AND ARCHAIC HUMANS.

WHEN THE TEAM AT
THE MAX PLANCK INSTITUTE

SEQUENCED
THE NEANDERTHAL GENOME,

THEY FOUND THE SAME
SORT OF OVERLAP.

THEY CONCLUDED
THAT MODERN HUMANS

INTERBRED WITH NEANDERTHALS
55,000 YEARS AGO

AND CARRIED SOME OF THEIR GENES
WITH THEM INTO ASIA.

WE USED TO THINK OF
MODERN HUMANS ENTERING ASIA

AND ENTERING SOMEWHERE
THAT WAS RELATIVELY, YOU KNOW,

SPARSELY INHABITED, IF AT ALL.

WE NOW KNOW THAT THERE WERE
MULTIPLE POPULATIONS

OF THESE ARCHAIC HUMANS--

DENISOVANS, NEANDERTHALS,

MAYBE SOME LATE-SURVIVING
HOMO ERECTUS POPULATIONS--

AND THE MODERN HUMANS SHOW UP.

THEY'RE THE NEW KIDS
ON THE BLOCK

IN A PLACE WHERE THERE'S ALREADY
LOTS OF DIFFERENT PEOPLE

THAT ARE PRETTY
SUCCESSFUL THERE.

THERE MUST HAVE BEEN
INTERBREEDING,

AND THE PEOPLE WHO WERE THE
PRODUCTS OF THAT INTERBREEDING

WENT ON TO COLONIZE MUCH OF
THE EAST AND SOUTHEAST ASIA.

NARRATOR: THERE ARE 4 BILLION
PEOPLE IN ASIA TODAY.

ALL OF THEM HAVE GENES
INHERITED FROM ARCHAIC HUMANS.

BETWEEN 1% AND 3% OF THEIR DNA
COMES FROM NEANDERTHALS,

AND IN SOME PEOPLE,
UP TO 5% MORE FROM DENISOVANS.

ASIA-- THE GREAT MELTING POT
OF HUMAN DIVERSITY.

WHAT SORT OF GENES

MIGHT HAVE PASSED FROM ARCHAIC
TO MODERN HUMANS?

WHAT EFFECT DID
THEY HAVE ON US?

THE CLUES ARE TO BE FOUND
ON THE TIBETAN PLATEAU.

[METAL CLANKING]

IT'S EARLY MORNING
IN THE HIMALAYAS,

AND FARMERS ARE LETTING OUT
THEIR YAKS FOR THE DAY.

IT'S A FAMILIAR ROUTINE.

THEY LEAVE THE VILLAGE AND LOOK
FOR PASTURE UP THE MOUNTAINSIDE.

THIS IS 13,000 FEET
ABOVE SEA LEVEL.

THERE'S 40% LESS OXYGEN
THAN AT THE COAST,

BUT TIBETANS SEEM UNTROUBLED
WORKING AT THIS ALTITUDE.

THEIR BODIES HAVE ADAPTED TO
LIFE ON TOP OF THE WORLD.

RASMUS NIELSEN BELIEVES
THE KEY TO THEIR SURVIVAL

IS A LACK OF HEMOGLOBIN--

THE PROTEIN THAT CARRIES OXYGEN
IN RED BLOOD CELLS.

MAN: YOU MIGHT EXPECT THAT
IF YOU'RE AT HIGH ALTITUDE,

YOU NEED MORE HEMOGLOBIN,

BUT IN FACT, TIBETANS ACTUALLY
PRODUCE LESS HEMOGLOBIN.

THAT MIGHT SOUND BACKWARDS.

WHY WOULD THEY PRODUCE
LESS HEMOGLOBIN?

BUT THAT'S BECAUSE THAT
HAVING TOO MUCH HEMOGLOBIN

IN YOUR BLOOD CAN
ACTUALLY BE DETRIMENTAL,

BECAUSE IF YOU HAVE
TOO MANY RED BLOOD CELLS,

THEN YOUR BLOOD
BECOMES TOO THICK.

WE DON'T REALLY KNOW EXACTLY
HOW THE TIBETANS ARE FUNCTIONING

WITH LESS RED BLOOD CELLS
IN THEIR BLOOD.

WE THINK IT'S BECAUSE THEY'RE
BETTER AT PRODUCING ENERGY

IN THE MUSCLES
WITHOUT USING OXYGEN.

NARRATOR: ONE OF THE GENES
THAT CONTROLS

THE LEVEL OF HEMOGLOBIN
IS EPAS1.

EVERYONE HAS A COPY OF THIS GENE
LOCATED ON CHROMOSOME 2,

BUT TIBETANS HAVE
A SPECIAL VARIANT

THAT RESTRICTS
THEIR LEVEL OF HEMOGLOBIN

AND ALLOWS THEM TO WORK
IN THE HIGH PASTURES

WITHOUT ILL EFFECTS.

BUT WHERE DOES
THIS VARIANT COME FROM?

HOW DID IT ENTER
THE TIBETAN GENE POOL?

COULD IT BE THE RESULT
OF INTERBREEDING?

WHAT WE SAW WAS THAT THE DNA
SEQUENCE THAT THE TIBETANS HAVE

REALLY DIDN'T MATCH ANY OTHER
SEQUENCES IN ANY OTHER HUMANS.

BUT THEN WE LOOKED AT THIS OTHER
SPECIES-- THE DENISOVANS.

TO OUR SURPRISE,

WHAT WE FOUND WAS THAT THERE
WAS AN ALMOST COMPLETE MATCH

BETWEEN THE DNA IN THE TIBETANS
AND THE DENISOVAN SEQUENCE.

WE COULD SHOW THAT
THE TIBETAN SEQUENCE

HAD COME FROM THIS ARCHAIC
SPECIES-- THE DENISOVANS--

INTO THE TIBETANS.

WE DON'T KNOW VERY MUCH
ABOUT THE DENISOVANS,

BUT IT'S POSSIBLE THAT THEY WERE
ALSO HIGH-ALTITUDE ADAPTED.

BY INTERBREEDING WITH THEM,

MODERN HUMANS
PICKED UP THIS GENE

THAT THEN ALSO ALLOWED THEM
TO BE ADAPTED

TO THE HIGH-ALTITUDE
ENVIRONMENT.

NARRATOR: THE SAME GENE
IS STILL REGULATING

THE HEMOGLOBIN
OF TIBETANS TODAY.

IT'S AS IF THEY'VE HITCHED
A GENETIC RIDE

ON THE BACK OF THE DENISOVANS.

HAWKS: MIXTURE WITH
THESE ARCHAIC HUMANS

WAS A TREMENDOUS SHORTCUT
FOR NATURAL SELECTION.

THE THING IS THAT
IF YOU HAVE A TRAIT

THAT YOU'RE TRYING TO GET,
THAT'S USEFUL FOR YOU,

YOU'RE WAITING FOR
THE RIGHT MUTATIONS TO HAPPEN.

YOU COULD BE WAITING FOR
THOUSANDS OF GENERATIONS.

BUT ARCHAIC HUMANS HAVE HUNDREDS
OF THOUSANDS OF YEARS

OF ADAPTATION ALREADY.

EVERYTHING THAT'S USEFUL
FROM THIS POPULATION

HAS A HUGE POTENTIAL OF BEING
PICKED UP INTO MODERN HUMANS

WITH A LITTLE BIT
OF INTERBREEDING.

NARRATOR: EPAS1 IS THE FIRST
GENE SCIENTISTS KNOW OF

THAT'S CLEARLY PASSED FROM
ONE TYPE OF HUMAN INTO ANOTHER

THROUGH INTERBREEDING,

BUT IT'S LIKELY TO BE
JUST THE TIP OF THE ICEBERG.

MANY OTHER GENES HAVE PROBABLY
TAKEN THE SAME ROUTE

AND HAD A PROFOUND IMPACT
ON US-- MODERN HUMANS.

THE SKIN IS THE LARGEST ORGAN
IN THE HUMAN BODY.

IT WEIGHS UP TO 8 POUNDS.

IT'S PACKED WITH SWEAT GLANDS,

BLOOD VESSELS,
AND NERVE ENDINGS,

BUT IT'S ONLY 1/10
OF AN INCH THICK.

IT'S ALL THAT EXISTS BETWEEN US
AND THE OUTSIDE WORLD.

MAN: THESE GUYS ARE
PROVIDING A GOOD EXAMPLE

OF SHOWING WHY
THE HUMAN SKIN
IS SO IMPORTANT.

THEY'RE ABLE TO
WITHSTAND THE IMPACTS

BECAUSE OF
THE SPECIAL PROPERTIES
AND TOUGHNESS OF SKIN.

AND MUCH OF THAT
TOUGHNESS IS GOVERNED BY
A PROTEIN CALLED KERATIN,

WHICH IS A VERY TOUGH,
FIBROUS STRUCTURAL PROTEIN

THAT PROVIDES THE SKIN
WITH THINGS LIKE
ELASTICITY AND STRENGTH.

NARRATOR: ACCORDING TO
THE LATEST RESEARCH,

GENES THAT CONTROL
THE PRODUCTION OF KERATIN

WERE INHERITED FROM
ARCHAIC HUMANS--

NOT DENISOVANS THIS TIME,
BUT NEANDERTHALS.

THERE WAS SOMETHING BENEFICIAL
ABOUT NEANDERTHAL SKIN BIOLOGY

AND THE WAY
THEY PROCESSED KERATIN

THAT WAS PASSED ON
BY INTERBREEDING

AND HAS STAYED WITH US
EVER SINCE.

AKEY: IT COULD BE RELATED TO
SKIN PIGMENTATION.

IT COULD BE RELATED
TO WOUND HEALING.

BUT WE KNOW THAT INHERITING

THE NEANDERTHAL VERSION
OF THESE GENES

PROVIDED AN ADVANTAGE
TO OUR ANCESTORS.

WE'RE ONLY JUST
BEGINNING TO UNDERSTAND

ABOUT HOW HUMANS
AND NEANDERTHALS

AND OTHER ARCHAIC HUMANS
INTERACTED

AND WHAT THOSE
CONSEQUENCES WERE.

NARRATOR: GENETICS IS REWRITING
THE HUMAN STORY.

EVIDENCE OF ABOUT WHO MET WHOM,
WHERE, AND WHEN

SHOWS UP IN TODAY'S DNA
MORE CLEARLY THAN IN ANY FOSSIL,

AND THAT EVIDENCE SUGGESTS

OUR COUSINS WERE MORE IMPORTANT
TO US THAN WE EVER REALIZED.

AKEY: IN ANY INDIVIDUAL,

ABOUT 1.5% OF OUR GENOME
CAME FROM NEANDERTHAL ANCESTORS,

BUT MY 1.5% MIGHT BE DIFFERENT
THAN YOUR 1.5%.

IF YOU TAKE ALL OF
THE DIFFERENT 1.5%

AND YOU ADDED THEM
ALL TOGETHER,

YOU'D COME UP WITH ABOUT 20% OR
30% OF THE NEANDERTHAL GENOME,

WHICH IS QUITE REMARKABLE,

BECAUSE EVEN THOUGH NEANDERTHALS
WENT EXTINCT 30,000 YEARS AGO,

THEIR DNA LIVES ON
IN EACH OF US.

NARRATOR: JUST HOW INFLUENTIAL
WERE THE GENES

WE INHERITED FROM
OUR EVOLUTIONARY COUSINS?

THEY MAY MAKE THE DIFFERENCE
BETWEEN LIFE AND DEATH.

EVERY DAY, OUR BODIES ARE
UNDER ATTACK FROM MICROBES

SEEKING NEW HOSTS
TO INVADE AND INFECT.

BUT WHEN MICROBES ATTACK,
OUR BODY COUNTERATTACKS...

THANKS TO OUR IMMUNE SYSTEM,

WHICH ENLISTS AN ARMY
OF WHITE BLOOD CELLS

KNOWN AS NATURAL KILLERS.

JOHN TROWSDALE IS A PATHOLOGIST

AND AN EXPERT IN THE MECHANICS
OF HUMAN IMMUNITY.

MAN: THESE ARE KILLER CELLS.

NOW, KILLER CELLS WORK
BY KILLING ANY CELLS

INFECTED WITH A VIRUS
OR A MICROBE,

SO WE NEED THESE CELLS

IN ORDER TO TAKE OUT ANY
INFECTED CELLS IN OUR BODIES.

IN ORDER TO DO THAT, THOUGH,

THESE KILLER CELLS NEED
A SPECIAL NETWORK OF GENES,

AND THESE GENES
ARE CALLED HLA GENES.

THEY'RE KIND OF
AN EARLY WARNING SYSTEM.

NARRATOR: HLA GENES--
OR HUMAN LEUKOCYTE ANTIGENS--

HAVE LONG BEEN REGARDED AS KEY
IN THE BATTLE AGAINST DISEASE,

BUT SCIENTISTS HAVE
RECENTLY NOTICED

A GEOGRAPHICAL PATTERNING
TO THESE GENES.

MODERN-DAY ASIANS
HAVE CLUSTERS OF THEM

THAT DON'T EXIST
AMONG AFRICANS.

IT'S AS IF THEIR ANCESTORS
PICKED THEM UP

FROM A SOURCE
ALREADY LIVING IN ASIA.

MAN: SOME OF THOSE GENES
LOOK VERY DIFFERENT TO
MODERN HUMAN GENES.

IT LOOKS AS THOUGH
THEY'VE BEEN ACQUIRED
FROM A DIFFERENT SPECIES.

NARRATOR: IT SEEMS
INCREASINGLY LIKELY

THAT SOME TYPES OF HLA
WERE INHERITED

FROM NEANDERTHALS
OR DENISOVANS.

MAN: LET'S IMAGINE THESE DICE
REPRESENT DIFFERENT HLAs.

AND IN A POPULATION LIKE
THE AFRICAN POPULATION,

EACH NUMBER REPRESENTS
A DIFFERENT HLA

AND ACTUALLY PROVIDES
A DIFFERENT KIND OF
LEVEL OF IMMUNITY.

AND THE MORE VARIETY
IN THE POPULATION,

THE HARDER IT IS FOR A VIRUS TO
GET A HOLD ON THAT POPULATION.

BUT AS SMALL NUMBERS OF PEOPLE
MOVE OUT OF AFRICA,

THEY'VE GOT MUCH LESS VARIETY.

SO IN OTHER WORDS, THEY'RE MORE
VULNERABLE TO INFECTION.

SO HOW DOES THIS POPULATION
NOW ACQUIRE SOME MORE VARIETY?

WELL, IT CAN WAIT FOR A MUTATION
TO COME ALONG, BUT, OF COURSE,

MUTATION IN THE NORMAL COURSE
OF EVOLUTION IS VERY SLOW.

HOWEVER, IF THEY ACTUALLY MATE
WITH ANOTHER POPULATION--

LET'S SAY NEANDERTHALS
OR DENISOVANS--

THEY CAN GAIN MORE VARIETY.

SO THEY MIGHT GET A 5 HERE
OR A 6 HERE--

AN ADDITIONAL VARIETY
THAT WERE MISSING.

IN ADDITION TO THAT,

THEY CAN ACTUALLY ALSO ACQUIRE
SOME VERY NOVEL HLA GENES

THAT MAYBE WEREN'T
EVEN PRESENT IN THE--

IN THE AFRICAN POPULATION,

AND THEY PROVIDED RESISTANCE
TO PARTICULAR INFECTIONS

THAT WERE PREVALENT
IN THOSE ENVIRONMENTS.

SO IT'S A KIND OF EVOLUTIONARY
SHORTCUT, IN OTHER WORDS.

THESE GENES HAVE BEEN BORROWED
FROM OTHER POPULATIONS

AND INCORPORATED
INTO THE POPULATION

TO PROVIDE THAT VARIETY THAT--
THAT THEY WERE MISSING.

NARRATOR:
BILLIONS OF US TODAY

ARE BETTER AT
FIGHTING OFF DISEASE

BECAUSE OF ARCHAIC HUMANS.

WE ACQUIRED THEIR IMMUNITY.

GENES THAT WERE IN THEIR CELLS
ARE NOW INTEGRAL TO OUR BIOLOGY.

MAN: SOME PEOPLE SAY THAT
MAYBE 1% TO 3% OF OUR GENES

HAVE COME FROM NEANDERTHALS.

SO WHAT'S THE BIG DEAL?

I MEAN, 1% TO 3%
ISN'T VERY MUCH.

HOWEVER, IF YOU LOOK
AT HLA GENES,

IT APPEARS THAT THESE
HAVE ACTUALLY PROVIDED
A MAJOR ADVANTAGE,

AND IN SOME POPULATIONS,

IT'S ESTIMATED UP TO 90%
OF THE GENES HAVE COME FROM
NEANDERTHALS OR DENISOVANS.

SO IT MAY BE THAT
THE IMMUNITY THROUGH HLA

IS ONE OF THE MOST IMPORTANT
GIFTS WE'VE HAD

FROM THESE ANCIENT POPULATIONS.

NARRATOR: IT'S THE END OF
THE DAY ON THE TIBETAN PLATEAU.

FARMERS ARE BRINGING THEIR YAKS
HOME FOR MILKING.

[FARMER SHOUTS INDISTINCTLY]

NARRATOR:
THESE ARE HYBRID ANIMALS

THAT HAVE BEEN CROSSED
WITH DOMESTIC CATTLE

TO BECOME MORE RESILIENT
AND MORE PRODUCTIVE.

ALTHOUGH THE FARMERS
DON'T REALIZE IT,

THEY ARE ALSO HYBRIDS--

CROSSED WITH DENISOVANS,
NEANDERTHALS,

AND PERHAPS HOMO ERECTUS.

AS WITH THE YAKS,

HYBRIDIZATION SEEMS TO
HAVE MADE THEM STRONGER,

TOUGHER, AND HEALTHIER.

PEOPLE TODAY ARE STILL
LIVING WITH THE LEGACY

OF WHAT HAPPENED IN
THE ANCIENT FORESTS OF ASIA.

HAWKS: WHEN MODERN HUMANS
MOVED INTO ASIA,

THEY HAD SOME OF THE TOOLS
THEY NEEDED TO MAKE IT,

BUT NOT ALL OF THEM.

THEY MIXED WITH POPULATIONS

THAT HAD BEEN THERE FOR HUNDREDS
OF THOUSANDS OF YEARS,

AND THEY BEGAN TO PICK UP
SOME OF THE ADAPTATIONS

THAT ENABLED THEM TO SURVIVE
IN THAT NEW PLACE.

WE HAVE INSIDE OF US

THE GENES OF THESE ANCIENT
PEOPLE INFLUENCING US TODAY.

WE'RE ONLY BEGINNING TO LEARN
HOW MUCH WE OWE TO THEM--

THESE ENCOUNTERS THAT HAPPENED
TENS OF THOUSANDS OF YEARS AGO.

NARRATOR: THE IMPACT
OF INTERBREEDING GOES
WAY BEYOND ASIA.

THE SAME PEOPLE
WHO EXPANDED INTO SIBERIA

WOULD GO ON AND COLONIZE
NORTH AMERICA.

OTHERS FURTHER SOUTH

WOULD TAKE THE GREATEST
JOURNEY OF ALL

ACROSS THE SEA
INTO AUSTRALIA--

THE WORLD'S MOST
ISOLATED CONTINENT.

WHEREVER THEY WENT,

THEY TOOK WITH THEM
THE GENES OF ANCIENT SPECIES.

HYBRID HUMANS-- FIRST PEOPLES.