Nova (1974–…): Season 37, Episode 5 - Becoming Human: Birth of Humanity - full transcript

Nova examines the ancestors of man by attempting to to reconstruct what they look like, what tools they used, and how they lived. Special focus is given to Homo erectus.

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NARRATOR:
Humans...

Without a doubt, the smartest
animal on earth,

yet we're unmistakably tied
to our ape origins.

Millions of years ago,

we were apes
living ape lives in Africa.

So how did we get from that...

to this?

What happened?

What set us on the path
to humanity?

The questions are huge.

But now, there are answers.



At the threshold of humanity,

one ancestor contains
tantalizing secrets.

It is known as Homo erectus.

RICHARD WRANGHAM:
Homo erectus had
a slightly smaller brain,

slightly bigger jaw,
but it's basically us.

NARRATOR:
Basically us--
almost two million years ago.

New finds are revealing
the truth about the ancestors

at the heart of our evolution.

Here were the trailblazers
who first left Africa--

the first fire makers,
the first hunters.

JOHN SHEA:
These creatures were capable

of analyzing possible uses
of tools

and coming up with
a technological solution

to the problem of how you kill
a big, dangerous animal



without getting killed yourself.

NARRATOR:
Homo erectus pioneered
what it means to be human,

colonizing whole continents

and creating the first
human societies.

SARAH HRDY:
Our ancestors began to care
about what others thought

and care about what that
individual thought about them.

NARRATOR:
Now, new discoveries are
bringing them alive

as never before.

At last, we come face to face
with the ancestors

at the birth of humanity,
right now on NOVA.

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NARRATOR:
The Great Rift Valley
of East Africa.

Two million years ago, these
spectacular plains and canyons

witnessed a mysterious event,

the birth of the first ancestor
we can really call human.

New discoveries are revealing a
creature surprisingly like us--

a world traveler, a toolmaker,
a hunter, tamer of fire,

creator of the first
human societies.

Amazingly, the qualities
that make us human

began not with our own species,
Homo sapiens.

The true birth of humanity began
much further back in time,

millions of years ago.

Imagine the entire span
of recorded human history,

about 5,000 years,

taking us back
to the Egyptian pyramids.

Double it-- 10,000 years,
to the time when plants

are domesticated
and agriculture begins.

Double it again-- 20,000 years.

Ice Age hunters are painting
stunning images on cave walls.

And keep doubling,
six more times.

Only then do we encounter
our ancestor Homo erectus

in Africa's Great Rift Valley.

For millions of years, this
massive geological fault line

running the length
of East Africa

was a stage on which our human
evolution was played out.

It all started with the first
apes to walk upright

on two legs about
six million years ago.

There were many different types,

all variations
on the same theme,

apelike creatures
with small brains.

The fossil known as Lucy
is the most famous example.

Here she is, just three foot,
eight inches tall,

with a brain the size
of a chimp's.

For millions of years, creatures
like her roamed the forests

and grasslands of Africa.

But then something changed.

About two million years ago,

new creatures appeared with
abilities never seen before

in the animal kingdom.

Meet Homo erectus,
a toolmaker and hunter.

One of the first members of our
genus, the genus Homo-- humans.

DANIEL LIEBERMAN:
The transition to Homo

was probably one of the most
important transformations

that occurred
in human evolution.

NARRATOR:
Arms got thinner, legs got
longer, brains got bigger.

It was a huge evolutionary step
from ape bodies

to bodies like ours.

But what about the things
that make us distinctly human--

creativity, intelligence,
caring for each other?

How can we know
when these got started?

With only skulls and bone
fragments to go on,

how could we ever know

what those first humans
were really like?

It would take a momentous find
to shed light on their lives.

Lake Turkana, northern Kenya,

surrounded by volcanoes and vast
expanses of baking desert.

In 1984, famed anthropologists
Richard and Meave Leakey

were working
at this remote inland sea.

MEAVE LEAKEY:
I was actually on
the east side of the lake.

Then Richard flew over
and said, "You've got to come.

There's something
really exciting."

NARRATOR:
As the first family
of paleoanthropology,

the Leakeys were used
to fossil finds.

But this was very special.

One of Leakey's team had found
a skull fragment

of one of those early humans.

He could tell from its size
and shape it was Homo erectus,

and there was more
than just a fragment.

So we starting looking
at the site

on a more extensive basis,
and of course once we did,

we found the rest of the skull.

NARRATOR:
A complete skull
was rare enough,

but it was just the beginning.

Soon, parts of
the Homo erectus skeleton

which had never been found
before started to emerge.

MEAVE LEAKEY:
We couldn't believe it, but we
started getting pieces of ribs.

These were parts
of Homo erectus

that nobody actually knew about,
nobody had ever seen before.

So every bone that
came out of the ground

was something brand new
to science

and we are looking
at these things

and it was really amazing.

NARRATOR:
And here they are, the actual
bones of a human ancestor

who lived over 1.5 million
years ago.

It's the earliest human skeleton
ever discovered.

The Leakeys called him
Turkana Boy.

His bones have revolutionized
our understanding

of the transition
from ape to human.

SUSAN ANT?N:
The really important thing
about Turkana Boy

is how complete he is.

We've got arms and legs and
bits of his spine and his ribs.

And usually when we find these
things we get very excited

about one little bit of bone,

but that little bit can't tell
us very much

about an individual,

so having a nearly
complete skeleton,

we can start to ask
big questions.

NARRATOR:
The first big question was,
what did he look like?

His skeleton tells us he was
five feet, three inches tall,

with a build closer to a man's
than an ape's.

But how close?

Paleoartist Viktor Deak
specializes

in painting and sculpting
our human ancestors

with precise anatomical
accuracy.

Viktor is going to add
Turkana Boy

to his family
of ancient faces.

DEAK:
At this stage of the game,

I know that Turkana Boy
is not an ape.

He is a very early true human,

and so here we have
a modern human skull.

The faces are very similar
to one another,

but Turkana Boy's skull
is a bit more primitive

and has a lower forehead and
a much smaller brain capacity.

NARRATOR:
Viktor will build Turkana Boy's
face muscle by muscle,

based on his studies of cadavers
and modern anatomy.

While his head may be primitive,

Turkana Boy's skeleton is
surprisingly human.

His hips are a little wider,
his arms a little longer,

but his overall body shape
is just like ours.

DEAK:
Turkana Boy and erectus--

that's something that
if you were to see

from a hundred feet away,
you'd think,

well, there's a large naked man
there, or woman or, you know.

But it's a human.

NARRATOR:
It will take Viktor a week
to flesh out Turkana Boy's face.

Meanwhile, a team of animators
is at work creating scenes

that will bring Turkana Boy
and his people to life.

To make sure they do it
accurately, they have enlisted

the help of Harvard
anthropologist Dan Lieberman.

They had a more
forward position

of the palms when they ran,
just slightly.

There you go.

NARRATOR:
The blue-suited actors are there
to create movement references

for the artists.

In the final animations,
they will be replaced

by Homo erectus bodies...

DIRECTOR:
And... action!

NARRATOR:
...their heads and faces based
closely on Viktor's model.

As Turkana Boy's forensically
reconstructed head

nears completion, a face emerges
that looks a lot like us.

Now for the first time in
a million and a half years,

here he is, our ancestor,

the Homo erectus
called Turkana Boy.

But what he looked like is only
the beginning of his story.

To reconstruct his life, we need
to find out how old he was.

And if we look
at his skeleton, we can see

that the growth
plates on his limbs

that would fuse when he's
fully adult are all unfused,

so even though he's very tall,
we know that he's still growing.

NARRATOR:
The fact that Turkana Boy
was not fully grown

has turned out to be
a boon to researchers.

MEAVE LEAKEY:
You can answer questions like,

did the boy grow up like
a modern human?

Or did he grow up
more like an ape?

NARRATOR:
Turkana Boy was already
five feet, three inches tall.

When scientists compared
his bones and teeth to ours,

he seemed to be
about 14 years old.

But when dental
specialist Chris Dean

began to study his teeth,
he was in for a shock.

It turns out that all teeth--
fossil or not--

preserve a remarkably precise
record of childhood.

DEAN:
This is a fossil tooth

and we can see the enamel cap

which covers the core of the
tooth, which is made of dentine.

Dentine is just another word
for ivory.

And within the enamel you can
see the rods, which are running

from the enamel-dentine
junction here

out to the surface
of the tooth.

NARRATOR:
Enamel has a regular
growth pattern,

like the rings of a tree.

Under an electron microscope,

it looks like rods
made of tiny beads.

DEAN:
Each of the little beads
along these prisms

represent one day's growth,

because the cells
which produce enamel

are actually under the influence
of a circadian, or daily, clock.

And those secretions
during the day

speed up and then slow down,

and there's a permanent record
of that in every tooth.

So you can see rods running all
the way through this tissue,

and every day along the rod
there is a wobble

where the tissue slows down

and then speeds up.

NARRATOR:
So if you count the beads
in these strings,

you can figure out
exactly how many days

that tooth has been growing.

When Chris looked
at the fossilized teeth

of Turkana Boy,
he got a huge surprise.

Turkana Boy
wasn't 14 years old.

He was eight.

DEAN:
What that implies is that
the growth of the Turkana Boy

resembled more closely
that of chimpanzees today.

NARRATOR:
To be five-foot three
at age eight,

Turkana Boy must have
grown up very fast,

at a rate closer to chimps
than us.

A chimpanzee's childhood
is short.

It is sexually mature
at about seven.

Human childhood is longer;
we reach puberty at about 12.

So as humans evolved from apes,
childhood was extended.

But what advantage
could be gained

by having helpless children
around to feed and care for

who take so long to grow up?

The mystery of prolonged
childhood is at the heart

of human evolution.

It may be related to brain size.

We humans have the biggest
brains in the animal kingdom

in relation to our body size.

They're so big that most of
our brain growth has to happen

outside the womb

or our heads would never
get through the birth canal.

A long, slow childhood
gives our brains time

to grow after birth

and time to learn everything
we need to function

in our complex human societies.

That's the advantage
of prolonged childhood

for us, at least.

But what about Turkana Boy?

His brain was
900 cubic centimeters,

smaller than ours but more than
twice as large as a chimp's.

So was he on the way to thinking
and talking like us?

Ralph Holloway believes he was.

He's been collecting the brain
endocasts of human ancestors

for over 30 years.

An endocast is a mold taken
from the inside of the skull

which reveals the shape
of the brain.

Ralph is particularly interested

in something called
the Broca's area.

HOLLOWAY:
Broca's area is involved

with memory functions,

executive functions, but it does
have a very important role

to play in the motor aspects
of speech.

NARRATOR:
In the brain of Turkana Boy,
Ralph believes he sees evidence

for something remarkable--

a change in the Broca's area
tied to communication.

HOLLOWAY:
Broca's caps regions

on the Turkana Boy

are fully modern in terms
of their appearance.

It is good, solid evidence
for having the ability

of symbolic communication--
in other words, language.

NARRATOR:
It's a controversial idea

and we'll never know for sure
if Turkana Boy could speak.

But there are other clues
to his intelligence--

the stone tools
he left behind.

Homo erectus made tools
like this hand ax here.

It's been chipped extensively
on both sides.

The point enables one to do
piercing tasks,

the heavy bit here can be used
for cracking bone

or chopping wood.

It's a very, very versatile tool
and a sharp one.

NARRATOR:
It may not look like much,
but the stone hand ax

marks the birth of technology.

Homo erectus has left us many
signs of his inventiveness.

Here in central Kenya,
Rick Potts has been studying

a treasure trove
of Homo erectus stone tools.

POTTS:
Stone tools represented
a momentous change,

because once you had tools
in your hands,

all the foods in the world
could open up to you.

That represented a tremendous
survival advantage.

NARRATOR:
Here is a cache
of over 500 stone hand axes

made by Homo erectus.

Just a mile away,
Rick visits the quarry

where for thousands
of years these ancestors came

to shape stone into tools,
leaving behind unused fragments.

In the crevices
at my feet,

there were thousands
of fragments of stone

from tool making.

And there are several scars
where Homo erectus

struck huge flakes.

We also see evidence that they
could recognize flaws.

They could see which ones would
break if they took them away,

so they simply
discarded them here.

What's amazing about that is
you could imagine

an early Homo erectus sitting
right here, making decisions.

NARRATOR:
The kind of decision-making
it takes

to create a stone tool has been
researched extensively

by John Shea.

SHEA:
I'm just going to tap it
a little bit.

I'm just checking it out to see
if there's any internal flaws

before I do it.

There may be one here.

It feels like there might be
something in there,

but I like a challenge
so I'll knap it anyway.

NARRATOR:
Even for an expert, making
a hand ax is not easy.

SHEA:
Yeah, there's the flaw,
but we can get around it.

NARRATOR:
A good toolmaker
has to understand

the properties of stone.

To make this thing nice
and thin, easier to carry,

easier to transport and more
of a sharp cutting edge,

I'm going to do something
kind of counterintuitive.

I'm going to dull the edge so
that the next time I strike it,

it won't fail until I have
a lot of pressure on it.

So if I hit it really hard, the
fracture will go much further

than it otherwise would.

So that Homo erectus did this

tells us they were capable
of thinking ahead

and planning the consequences
of their actions.

So let's have a look here.

What'll happen here?

NARRATOR:
Many of these stones
have hidden defects.

Failing to spot them
could spell disaster.

There's still
a flaw in there.

I can hear it.
I can tell.

Yeah, see this?

It's right there.

Now, I've worked around it,
but if I were an early human

and spotted this, I would stop
making the hand ax right now.

If I'm out running around in the
savannas, chasing a rhinoceros

and, you know,
or butchering a rhinoceros

as the lions are circling
and my hand ax breaks,

I'm in trouble.

So, you know, I go home tonight,
I'm still going to get fed,

even though I didn't make
a perfect hand ax.

As Homo erectus, I might end up
being the meal instead.

NARRATOR:
A skilled craftsman,

Homo erectus had evolved
a new type of intelligence.

But his bigger brain
came with hidden costs.

Modern brains consume
25% of our body's energy.

DONALD JOHANSON:
Our brain happens to be
the hungriest organ in the body.

And in order to support
a brain our size,

we need lots of calories.

NARRATOR:
With his big brain and body,

a Homo erectus like Turkana Boy
needed more nutrition

from his savanna environment.

SHEA:
Turkana Boy, had he grown
to adulthood,

would probably have stood
about six feet tall.

This is a big, strong creature

that would have had
a huge energy budget.

One can satisfy an energy budget
like that by eating plants,

but you have to eat a lot,
a lot of plants.

NARRATOR:
But there's one food that can
supply the nutrients

a growing brain and body need...

and Africa was filled with it.

LIEBERMAN:
The one high-quality resource
that's probably most important

for the evolution
of the genus Homo is meat

and meat byproducts such
as brain and marrow and fat.

They're high in protein,
they're high in calories,

and they're easy to digest.

But the one problem with getting
meat is that it's hard to get.

NARRATOR:
Most predators rely
on strength or speed

to kill their prey.

Our ancestors had neither.

Today we are on top of the food
chain, so it's hard to imagine

the predicament
of those early humans.

Here was a slow-moving creature
with no claws or fangs,

easy prey for the hungry
predators around him.

POTTS:
This is a fossil forehead
and brow ridge

of a Homo erectus,

and on the brow ridge
you can see the bite mark

of a carnivore.

Well, this reminds us that
these Homo erectus individuals

weren't at the top
of the food chain.

NARRATOR:
So how did Turkana Boy,

a weakling with a big brain
which needed calories,

get his meat?

SHEA:
Homo erectus faced a problem:

How do you kill a big,
dangerous animal

that has lots of meat
and fat in it

without that animal
also killing you?

I think the answer to that was a
very clever set of innovations,

and that is endurance running

and high activity
in the middle of the day.

NARRATOR:
The ancestors of Homo erectus,
small, hairy apes like Lucy,

were bipedal but probably
didn't do much running.

But Turkana Boy's kind were
built to run like us.

This is
an accelerometer.

NARRATOR:
Dan Lieberman believes they
could run long distances

because, like us, they had lost
their thick coat of body hair

and could keep cool by sweating.

This was the key
to their success.

But how do we know
if these crucial changes

go back all the way
to Turkana Boy's time,

over a million years ago?

Skin and hair are rarely
preserved in the fossil record,

so to find out, we have to look
to a creature

that's been intimately connected
with hair for a long time:

the louse.

MARK STONEKING:
All animals seem

to have some type of lice
to parasitize them.

Mammals have them,
birds have them,

even fish have types of lice.

But most other creatures have
only one type of lice

that parasitize them.

NARRATOR:
Humans have one kind of louse
on their heads

and another in the pubic area.

Geneticist Mark Stoneking
asked himself why.

STONEKING:
The answer that seems obvious

is that when we had body hair
all over our bodies,

we had one type of lice.

But then we became hairless

until we only had hair on our
heads and in our pubic region,

and so therefore
you would have

this hairless geographic barrier
to contact between the two.

NARRATOR:
Mark was surprised to find out

that the human pubic louse
is very different

from the human head louse.

Somehow in the past, it seems
to have come from gorillas.

STONEKING:
Because the pubic lice is
actually more closely related

to gorilla lice.

Now, how it is our ancestors got
pubic lice from gorillas

I wouldn't care to speculate.

But nonetheless,
one needs gorilla lice

in order to really work
this whole thing out.

NARRATOR:
The most likely scenario is that
when we lost our body hair,

the original human louse
migrated to our heads,

leaving the pubic area
temporarily unpopulated by lice.

When our ancestors had contact
with gorillas,

perhaps sleeping in their nests

or scavenging their bodies
for meat,

the gorilla louse colonized
their pubic region.

Eventually, it turned into
the human pubic louse of tod.

So if we could find out

when the human pubic louse and
the gorilla louse diverged,

we would have a rough idea
of when we lost our body hair.

Fortunately, there's a way
to figure that out:

the genetic dating technique
known as the molecular clock.

It's based on the fact that
the sequence of chemical bases

which make up DNA
mutate at a regular rate.

STONEKING:
It's just a very simple idea

that the rate of change
in DNA sequences

is more or less constant
over time.

And that means that you have
a way of determining

when two species last shared
a common ancestor.

NARRATOR:
By counting the number
of differences

in the genetic code
of two species,

scientists can determine how
long they've been evolving

away from each other.

When Mark used the molecular
clock to count the differences

between the DNA of gorilla lice
and human pubic lice,

he came up with a date
for their divergence.

STONEKING:
The estimated date
for the divergence

is roughly
three million years ago.

NARRATOR:
That means long
before Turkana Boy,

maybe even around Lucy's time,

our ancestors had slowly begun
to lose their body hair.

Turkana Boy was mostly hairless,
just like us...

...and that may be what gave him
an edge over other predators.

Most animals are at a
disadvantage in the midday sun

because they overheat.

They can only cool down
by panting.

And when they run fast,
they can't pant.

That means they can only run
in short sprints.

LIEBERMAN:
Quadrupeds can gallop
for about 10 to 15 minutes

and then they overheat,

but hominids can cool down
by sweating.

They use their entire body
like a dog's tongue.

NARRATOR:
Our hairless bodies allow air
to circulate freely on our skin

and cool us down
as sweat evaporates.

This makes us one of the best
long-distance runners

in the animal kingdom.

Dan Lieberman believes
this gave our ancestors

the ability to hunt
in a very unusual way.

It's called persistence hunting.

And he believes the modern
ethnographic record

can show us how it was done.

The Bushmen of the Kalahari
offer us an insight

into how Homo erectus might have
hunted two million years ago.

The Bushmen know that at midday
animals rest in the shade,

which is why it's the perfect
time to be hunting.

Once they locate their prey--
in this case a kudu--

the marathon begins.

Their strategy is simple:
run it to exhaustion.

Every time the animal tries to
rest, the hunters track it down

and get it moving again.

They never give it a chance
to cool down.

And the reason they can keep
going is that they can sweat.

So if the theory is right, the
Bushman hunt may help explain

how Turkana Boy got his meat.

Homo erectus had come up
with an innovative way

of feeding his hungry brain.

In this modern hunt, the Bushmen
ran in the fierce heat

for over four hours.

The kudu was finally immobilized
by heat stroke.

Turkana Boy wouldn't have
had steel-tipped spears

like the Bushmen, but he
wouldn't have needed them.

SHEA:
Homo erectus probably hunted
with close-quarters weapons--

with spears that were thrown at
animals from a short distance,

clubs, throw rocks,
weapons like that.

They weren't using long-distance
projectile weapons,

that we know of.

NARRATOR:
The Homo erectus hunt
was simple but effective.

It fed not just
their larger brains,

but the growing complexity
of that early human society.

There are other social animals,
but none quite like us.

Society is in every corner
of our lives--

our relationships,
communication,

rules, symbolism--

all the things
that bind us together.

What's behind it?

Why did we become so social?

Could it have something to do
with another innovation,

something unprecedented
in our evolution,

building fires and cooking?

Here we go to erectus, the first
species that looks like us,

and I think only cooking can
explain the magnitude

of this change.

NARRATOR:
The earliest evidence
that our ancestors

deliberately used fire
for cooking

dates to long
after Turkana Boy's time.

But Richard Wrangham is sure
Homo erectus was building fires

much earlier.

WRANGHAM:
Now for the first time we had
a species that was committed

to living on the ground,

because they lose
their climbing adaptations.

Well, how were they sleeping?

They had to be able to protect
themselves from wild animals.

NARRATOR:
On the African savanna, full
of predators who hunt by night,

Richard believes Turkana Boy
and his people

couldn't have survived
without fire.

And he thinks only cooking,

which makes food more soft
and digestible,

can explain why Homo erectus
evolved smaller teeth

and a much smaller gut.

WRANGHAM:
These things are compatible

with the reduced cost
of digestion

produced by cooking food.

Nothing else is.

NARRATOR:
As our ancestors reaped
the benefits of cooking,

something else happened too,
at least according to Wrangham--

we became more social.

WRANGHAM:
Humans have this wonderfully
calm temperament

compared to chimpanzees, say.

Where did it come from?

We were drawn to a common place,
the fireplace.

NARRATOR:
Wrangham believes we learned
to share and communicate

sitting around fires,
waiting for food to cook.

It's speculative,
but one thing is for sure:

In the Homo erectus world,

new social relationships
had to be evolving.

The bonds between mothers
and children must have been

very different from the apes.

SARAH HRDY:
For example, a mother orangutan
will not allow

any other individual
to take her infant,

will be in constant
skin-to-skin contact

with that baby for at least
the first six months of life.

Not a moment out of contact.

NARRATOR:
Secure in this unbreakable
mother-infant bond,

ape babies need less capacity
to read the intentions of others

than human babies, whose bond
with their mothers

is surprisingly less secure.

The shocking fact is that human
mothers abandon their infants

much more often
than ape mothers.

Infanticide by a mother
is more common among humans

than any other higher ape.

HRDY:
Maternal commitment

is a lot more contingent
in humans

than it seems to be
in other apes.

NARRATOR:
Unlike most primates,

human mothers share parenting
with others.

A child's survival can depend
on making itself appealing

to a number of caregivers.

Perhaps that's why human infants
have evolved

a uniquely acute sensitivity.

HRDY:
Human infants are born
connoisseurs of mothers,

reading her facial expression,
looking for signs of commitment.

NARRATOR:
We are born hard-wired
with an awareness

of the intentions and emotions
of others,

which is unique
in the animal world.

HRDY:
When did humans develop
this gift

for attributing mental states
and feelings to others

and for caring about what others
thought about them?

NARRATOR:
Could these social instincts
have developed

with Homo erectus,

along with cooperative hunting,
bigger brains,

longer childhoods
and the use of fire?

Perhaps Turkana Boy
and his people already had

social skills that would be
familiar to us.

Here were intelligent
social beings

with an increasing capacity
for cooperation.

It may be
this that made possible

another great achievement--
the exodus from Africa.

For millions of years,

our earliest ancestors stayed
on the African savannas.

But at some point,
they started to leave.

Ancient fossil skulls
and tools have been found

as far away
as China and Indonesia.

The question is, when did
they leave Africa, and why?

When Turkana Boy was found,

scientists thought
they had the answer.

Here was a strong,
large-brained ancestor

capable of an arduous migration.

He had the look
of a world conqueror.

ANT?N:
I the mid-1980s,

we were thinking that a hominid
like this one had left Africa

but had done it maybe
about a million years ago.

NARRATOR:
For decades, scientists believed

big, strapping humans
like Turkana Boy

left Africa a million years ago.

But new discoveries are showing
the migration may have started

a lot earlier than that.

Dmanisi, Georgia.

The mountains and plains
of the Caucasus,

thousands of miles
from the Great Rift Valley,

had never produced any fossils
of early human ancestors.

But then an astonishing
discovery was made.

(man speaking Georgian)

(translated):
It was a lower jaw,
with teeth downward...

this way in the ground.

So when I started to clean,
those front teeth came to light.

It became obvious to me that we
had found some kind of hominid.

But what kind?

NARRATOR:
The jaw seemed to be a primitive
form of Homo erectus,

but at first hardly anyone
believed it.

In '91, when we found this jaw,

this was... a lot of scientists
were quite skeptical about it,

because it was very hard
to imagine Georgia, Caucasus,

to be on the map
of the human evolution.

NARRATOR:
Since then, Dmanisi has been put
on the map of human evolution

in a big way.

The site has turned up
a treasure trove

of Homo erectus fossils.

They've transformed
our understanding

of who left Africa and when.

They showed that the first
humans to leave Africa

were much more primitive
than Turkana Boy.

JORDI AGUST?:
People thought that
the hominids that left Africa

were very tall

like Turkana Boy,
with big brains,

advanced technology,

and Dmanisi proved the opposite.

NARRATOR:
At 4 1/2 feet tall,

they were smaller
than Turkana Boy,

with more apelike shoulders
and a simple stone technology.

LORDKIPANIDZE:
They are much more primitive.

They have small brains

and the same time,
they were using

very primitive stone tools.

NARRATOR:
The next surprise came
when they dated the site.

The ancient Dmanisi landscape
has been built up layer by layer

over millions of years.

1.81 million years ago, massive
volcanic eruptions deposited

a layer of ash.

The fossils sat on top
of this ash,

so must have been
slightly younger--

around 1.8 million years old.

To the vast majority
of scientists who believe

that all our ancestors evolved
in Africa,

this was a stunning surprise.

How had a small, primitive
Homo erectus migrated

to the Caucasus
almost two million years ago,

long before Turkana Boy?

Scientists now accept that as
soon as Homo erectus appeared

on the savannas of Africa,
they started to leave.

Suddenly with the origin
of Homo erectus we get

this shift in body shape
and then boom,

they're out of Africa
right away.

NARRATOR:
The Georgia fossils proved

that Homo erectus left Africa
much earlier

than previously thought.

An even more provocative find

shows the migration may have
started even earlier.

5,000 miles from Africa...

the island of Flores, Indonesia.

In 2003, researchers made
a discovery so strange,

nobody knew what to make of it.

They found the bones
of a tiny human ancestor,

just over three feet tall--

even smaller
than the Dmanisi fossils.

They called this baffling new
ancestor Homo floresiensis

and, because of its tiny size,
nicknamed it "The Hobbit."

HOLLOWAY:
This has created a tremendous
amount of grief

because we're not really sure
what we're seeing here.

The size of the Hobbit brain
endocast is roughly 400 cc.

NARRATOR:
That's barely bigger
than the brain of Lucy,

the famous bipedal ape
from three million years ago.

RICHMOND:
It's not just a small brain
and a primitive-looking face,

but the foot's primitive,
the hand's primitive,

the leg is primitive.

SUSAN LARSON:
The lower limb is very much like
the Lucy skeleton.

That was a big surprise.

NARRATOR:
And in the cave

where this primitive creature
was found,

they also uncovered stone tools,
something Lucy never had.

SHEA:
People for a long time said,

"You need a big brain to make
stone tools."

Well, okay, if Homo floresiensis
is making stone tools,

this creature has a brain
the size of an orange;

clearly that equation's gone.

NARRATOR:
Everything about these
creatures is an enigma.

Where did they come from
and what were they?

RICHMOND:
Some researchers have argued

that floresiensis is just
a dwarfed population

of modern people that
suffered some kind of disease

that caused them to both dwarf

and have relatively
small brains.

NARRATOR:
But when scientists took
a closer look,

most saw no evidence
of disease.

The stone tools and the shape
of the face moved the focus

to our old friend, Homo erectus.

RICHMOND:
Some researchers think

that Homo floresiensis evolved
from Homo erectus.

NARRATOR:
But how did they get so small?

Something called island dwarfism
may be the answer.

Isolated on islands
with limited food,

large mammals sometimes shrink
over time.

On Flores, there were once pygmy
elephants the size of cows.

Could the same
evolutionary pressure

have acted on Homo erectus
to produce the Hobbit?

Or was this mysterious
creature descended

from an even more
primitive ancestor?

So perhaps we're sampling
a period

which is at the very beginning
of the Homo lineage.

NARRATOR:
So whatever the Hobbit was,
perhaps its ancestors were

the very first wave
of migration out of Africa,

some unknown creature:
part bipedal ape like Lucy

and part Homo erectus.

LIEBERMAN:
So if that's the case,

then what we see in Indonesia
makes sense.

It's a kind of a body

that existed before human bodies
became more modern.

NARRATOR:
What would push such primitive
creatures out of Africa?

A key driving force
behind the migration

was probably a climate shift

which spread grasslands
from Africa into Asia.

And with the grasses
went the game animals.

LIEBERMAN:
Animals are going to be moving
out of Africa,

and the hominids will just be
keeping pace with those animals.

After all,
that's their livelihood.

NARRATOR:
Of course, our ancestors
didn't know

they were leaving Africa.

They just followed the animals
they depended on,

through the Sinai, up into
the Middle East and beyond.

It's often been called
an exodus,

but it really wasn't like that.

SHEA:
When people think of an exodus

they think of the Bible
or they think of migration,

they think of Europeans coming
over here to the New World.

It probably wasn't like
any historical migration,

this dispersal of humans
out of Africa.

NARRATOR:
The process was probably
very, very slow,

much like the spread
of any other animal species

into new territories.

ANT?N:
You could imagine
a group of Homo erectus

moving their range

a kilometer a year
in one direction.

And doing that continually over
a long enough period of time,

you can get a distance from
Africa to Indonesia covered

in, say, 15,000 years.

NARRATOR:
By a million years ago, our
ancestors had populated Asia

from the Caucasus to Indonesia.

And they were in Europe too,

as a recent discovery
in Spain has shown.

Homo erectus had conquered
the Old World.

The fact that they made it
so far with limited technology

and relatively small brains

makes them seem
even more remarkable.

And their longevity
was astonishing.

A few pockets of Homo erectus

may have been still
clinging on in Asia

just 50,000 years ago.

That's a span
of two million years.

Our own species has only
been around for 200,000.

What was the secret
of Homo erectus's success?

The amazing finds at Dmanisi
have given us one last clue.

One of the skulls
belonged to an old man.

His jaw bone revealed
he had lost all his teeth

well before he died.

AGUST?:
That was a real surprise.

It means that this individual

survived two years
without teeth.

NARRATOR:
For an elder to have survived
that long without teeth

must mean that others in
the group were feeding him,

perhaps even chewing
his food for him.

HRDY:
I love this story.

This was a remarkable testimony
from the past

about the quality
of emotional life

that may have characterized
Homo erectus.

NARRATOR:
Here is a tantalizing clue
to what may be

this ancestor's
most important legacy:

the instinct
to look after each other.

And it helps us imagine Turkana
Boy's final day on earth.

In the animators' scenario,
he starts the day out on a hunt.

But he has trouble keeping up
with the hunting party.

Why?

The evidence from his skeleton
is that he was sick and in pain

at the time he died.

If we look at his lower jaw,

we can see right here,
under the teeth,

that we've got a bit of
an abscess and an infection.

That kind of an infection
could have entered

the rest of his body,
could have killed him.

NARRATOR:
An abscess that ate
away that much of his jawbone

would have been agonizing.

Turkana Boy is in so much pain,

he's unable to continue
the hunt.

Knowing he would be
looked after,

perhaps he returned to his
campsite to find comfort

among the females.

I think he was probably
a miserable fellow,

in a lot of pain
and very dependent

on support and handouts.

So it was a species
that already felt

that here's one of our weaklings
that, you know, we love

and must protect and care
for to have got him that far.

NARRATOR:
But however much they may have
wanted to help him,

there was nothing they could do
about the infection

that was probably spreading
through his body.

DEAK:
From what the evidence suggests,

I just always imagined him not
knowing what was wrong with him,

and there's a sadness to it,

but ultimately from that comes
this immortal being.

NARRATOR:
His skeleton was so complete,
it is likely he died in water,

which would have protected him.

MEAVE LEAKEY:
It's very unusual
to get a skeleton,

because normally these things
are eaten by carnivores,

and in this case, it seems

that the boy's body
was washed into a swamp,

and so the carnivores never saw
it and never destroyed it.

And it gradually decomposed
and as the rivers flooded,

brought in more sediment,
buried it,

and you could see footprints
of hippos

that had walked
all over the bones,

and some of the ribs and things
were standing vertically

instead of lying flat
on the ground.

You could sort of reconstruct
the situation

and how the boy... what had
happened after he died

and why he was complete.

It was just... it really was an
amazing experience to see it.

NARRATOR:
For almost two million years,

his bones were preserved
by the earth.

Their discovery opened a window
for us on an unknown world,

the world of the most successful
human ancestor of all time,

Homo erectus.

They've revealed to us
that mysterious moment

when almost everything human
was born:

our bodies, our minds,
our emotions.

Think of all we've become.

Trace the threads of our origins

back through the ancestors
who went before.

They all lead back
to Turkana Boy and his kind,

the first humans.

NOVA's got a brand-new
evolution Web site,

with lots to explore
about our ancestors.

We want to know
what you think.

Bookmark it today,
and give us your feedback.

For millions of years,
our ancestors shared the planet

with other human species.

Why were we the sole survivors?

Could the fate of the
Neanderthals hold the key?

MAN:
This is one of the main goals

of sequencing
the Neanderthal genome.

Groundbreaking evidence tells
a new story of human evolution,

our story.

Part three of Becoming Human,
"Last Human Standing,"

next time on NOVA.

Major funding for NOVA
is provided by the following:

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