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ELLA AL-SHAMAHI:
Neanderthals roamed
for around 400,000 years.

Why did they go extinct

and Homo sapiens survive?

If you were going to place a bet

on who would be left standing,

you'd probably bet
it wouldn't be us.

The traces
Neanderthals left behind

are transforming
our understanding of them.

The Neanderthals were
masters of their environment.

They had evolved here for
hundreds of thousands of years.

And then they met us.

Neanderthal and Homo sapiens
interbreeding,

people were just not ready
to accept that.

AL-SHAMAHI:
What really happened

to our powerful human cousins?

"Human: Neanderthal Encounters,"

right now, on "NOVA."

Major funding for "NOVA"
is provided by the following.

AL-SHAMAHI:
Sometime around 20,000
to 30,000 years ago,

a child was born

into a new world.

The first child born
onto a planet

in which we, Homo sapiens,
were alone.

This was the first time
in history

that only one species of human
walked this Earth.

All the others were now gone.

And in a tale written
by the sole survivors,

it's actually quite easy
to forget

that we weren't destined
to be the only ones.

And yet here we are.

How this happened

is one of the most poignant
chapters in the human story.

And it's one
that's etched into the DNA

of every single one of us
alive today.

For hundreds of thousands
of years,

Homo sapiens evolved in Africa.

60,000 years ago,

some dispersed
into the Middle East

and, over generations,

continued onwards
as far as Australia.

But our species
didn't stop there.

Other groups began to make
their way north, into Europe.

For thousands of years,

Europe had been out of reach
to Homo sapiens,

repelled by its icy climate.

But now a shift in conditions

opened up a route
into this new realm.

And some members of our species

left the familiar behind...

...and stepped into the unknown.

We don't really know
why they came.

Was it a romantic notion,
like pure curiosity,

or was it something
much more practical?

Say, the need for food.

Or perhaps
it was the same forces

that drive migrants today,

that need for shelter
and safety.

We don't know the exact routes
they took.

But by following rivers
and coasts

or wandering along
mountain ranges like this...

...they slowly made their way
into new lands.

And not long after
these migrants reached Europe,

they would've encountered
something unexpected.

When they got here,
they would have discovered

that another species
had beat them to it.

Two other human species
were widespread at the time.

To the east, from Siberia
to Southeast Asia,

lived the mysterious Denisovans,

known only to us from
DNA preserved in a few fossils.

Across lands to the west,

all the way from Russia to
the Atlantic coast of Europe,

were the Neanderthals.

Homo sapiens
were latecomers to Europe.

It had been home
to the Neanderthals

for almost 400,000 years
before we showed up.

Now, these Homo sapiens
venturing into Europe

would have met
another sort of human.

People who looked a lot like us,
but with obvious differences.

We can only imagine
what these early migrants

would have made
of this other species...

...when our two cultures,

perhaps just two families,

encountered each other
for the first time.

Neanderthals were close
relatives of Homo sapiens,

but we had evolved
along separate branches

of the human family tree.

There's often this belief

that we evolved
from Neanderthals,

so we came from Neanderthals.

Actually, that's incorrect.

We shared a common ancestor
with them,

and then, due to chance
and the environment,

we went on these two really
different evolutionary journeys.

So, we evolved--
Homo sapiens-- for Africa.

We ended up taller and leaner.

Now, the Neanderthals

evolved for much cooler,
more wooded environments.

So, they were shorter.

On average, the males
were about five-foot-five.

They had shorter limbs

and they seem to have had
bigger torsos.

And they used
a lot of brute force

because they were
close-range hunters.

The Neanderthals were
masters of their environment.

They had evolved here for
hundreds of thousands of years.

If you were going to place a bet
on who would be left standing,

you'd probably bet
on the obvious choice,

and it wouldn't be us.

Neanderthals were clearly
highly skilled survivors.

Yet, in the 19th century,

when the first Neanderthal
fossils were unearthed...

...scientists quickly jumped
to conclusions...

...that have persisted
ever since.

As a result,

Neanderthals haven't had
the best PR.

If somebody calls you
a Neanderthal,

it's probably not a compliment,

and that stereotype
of Neanderthals

has been with us
since the very beginning.

And it kind of suited us

to see ourselves
as the pinnacle of evolution

and them as these
knuckle-dragging ape men.

But partly, that stereotype

is actually just
a mistake of science.

Paleoanthropology at the time
was quite a new science,

and when they came
to reconstruct

this one Neanderthal,
called La Chapelle-aux-Saints,

they portrayed it
as kind of really hunched over

and knuckle-dragging,
which was just wrong--

this kind of brutish,
hairy Neanderthal,

looking like
it's about to attack.

It's incredibly aggressive.

I personally love Neanderthals,

and the more
we learn about them,

the more we study them,

the more we discover about them,

the more we realize that this

is actually
incredibly incorrect.

This now-outdated image
of the simple, brutish caveman

is finally being replaced...

...with a picture

of a once-vibrant,
thriving culture.

We keep finding things
at Neanderthal sites

that really challenge us.

Things like beaded shells
with pigmentation on them,

almost like they're being used
as necklaces.

Eagle talons,
probably for a similar purpose.

And then there's
my actual favorite,

which is evidence of feathers.

But not just any feathers.

No, the Neanderthals seemed
to be really interested

in black and colored feathers
from things like red kites.

And you've got to wonder,

why were they so interested
in those particular colors?

And it's presumably 'cause
they're high-value,

they're beautiful.

You kind of have
an impression of them

as having these
incredible headdresses,

or maybe cloaks made of these
brilliant, bright feathers.

When you put this all together,

you paint a picture
of a Neanderthal

not as this aggressive creature,

standing behind a rock
with a massive club,

but actually as

these beings very interested
in adorning themselves.

Interested in looking beautiful,
with necklaces

and gorgeous colored
headdresses.

Suddenly,
you're looking at beings

who aren't just interested
in food and shelter.

They're interested in the way
they are seen by the world.

This, all this,

makes them tangibly human.

For thousands of years,

Homo sapiens and Neanderthals
lived in close proximity.

But how close were we?

For decades, most assumed

interbreeding
between our two species

didn't happen.

But in the early 2000s,

this was called into question...

...by new finds in Romania,

bone fragments dating back

to around 40,000 years ago,

which were painstakingly
reassembled

to reveal humans with
a mysterious mix of features.

It even smells...

...like a fossil.

This, I assume, is Oase 1.

This one is Oase 1.

And that's Oase 2.

Skull-- that's Oase 2.

This is quite special,

'cause I've read about them,

I've studied them.

They're hugely
significant fossils,

but I've never...

I've never seen the originals.

I've never been this close
to them, it's...

It looks and it is a modern
Homo sapiens...

Yeah.

But it has some features
which,

which are more like Neanderthal.
Yeah.

Like this one, it's quite clear

it's a mandible
of a modern human

with this, this chin.

Because it's,
there's a chin.
There's a chin, yeah.

And Neanderthals
don't have a chin,

Neanderthals' chin
kind of recedes.

But then you, you see the,

- the size of the molars.
- Yeah.

Which are really huge.

More a Neanderthal feature.

Modern sapiens... Yeah.

...but with Neanderthal
teeth.

Yeah, Oase 2 has
the same hybrid features.

Mm-hmm.

Like, if you look at
the face.

You look at that and you,

you do think that's

Homo sapiens.

And then it has these features
on it,

which are

more Neanderthal,

like this occipital bone here
at the back,

that bulge at the back
of the skull here.

Yeah, that's kind of strange.

It's not a Neanderthal,
but it's,

it has Neanderthal features,

which prompt us to think about
some sort of interbreeding.

Neanderthal and Homo sapiens
interbreeding,

it was pretty controversial.

People were just
not ready to accept that.

AL-SHAMAHI:
Around a decade after the bones
were discovered

came a revolutionary
breakthrough.

Advances in genetic analysis
allowed scientists

to extract DNA
from ancient fossils.

Proving these two species

could and did produce offspring.

How did it feel
to be proven right,

to be vindicated,

especially over something
so controversial?

I feeled, felt relieved.

Yeah.

Like, "Okay."

"Now you know."

Yeah, we were happy
to be right.

Yeah.

You know, there's people
who spend their whole lives,

their whole lives,
trying to find a fossil

as significant as this,

and...

Wow, that's just amazing.

AL-SHAMAHI:
Since the discovery of Oase 1,

evidence has continued to grow,

proving hybrids like this
were not just possible,

but may have been
relatively common.

We'll never know the full story

of Oase 1 and the other hybrids.

And to be honest,
we'll never know

the full circumstances
under which they were conceived.

For all we know,

it could have been
non-consensual,

or it could have been the result
of a romantic notion, like love.

Or it might have been the result
of a practical decision,

like as part
of a trade agreement.

But whatever it was,

what must it have been like
to have been a hybrid child?

Did these children
feel like they belonged

or were they teased
and ostracized?

We'll never know,
but what we do know,

because I held Oase 1
in my hands,

is that they existed.

And so, somebody loved them,

and somebody was raising them
to adulthood.

And so, we tangibly know

that the Neanderthals
and the Homo sapiens,

they didn't just meet,
they joined.

We now know
that for a time, at least,

Homo sapiens and Neanderthals

managed to live
alongside one another.

But survival in this region

meant braving
challenging conditions

that would push both species
to their limits.

Because it's likely
Homo sapiens arrived here

during a brief thaw
in the weather.

And by doing so,
they had walked into a trap.

Within just a few centuries,

Europe's winters became colder,

drier, and more hostile.

Unrecognizable to us today.

Rainfall in some areas
fell to half its modern level

and much of the continent
became tundra,

a vast, inhospitable plain.

Homo sapiens
had to try to adjust

to this colder world.

There's no way for them
to have known it,

but before the
first Homo sapiens arrived,

most of Europe would've been
in the depths of winter.

Ice sheets like this one
would have spread from here

all the way down to Britain.

It's currently
minus-eight degrees.

I am wearing so many layers,
it's actually ridiculous.

And yet, I am still
completely miserable.

It is so cold,
I can't feel parts of my face.

These families, they were here,

and they were trying
to keep young children alive.

These conditions would have
been life-threatening.

While Homo sapiens
had originally adapted

to the warmer weather
in Africa...

...Neanderthals had evolved
to survive in colder climates

over almost 400,000 years.

It's thought they stored
more brown fat

than Homo sapiens.

This burns more calories
and generates more heat,

conserving energy in the cold.

And their larger nasal passages

provided increased surface area,

warming and moistening
the icy air

before it reached the lungs.

Without the Neanderthals'
adaptations or knowledge,

these early
European Homo sapiens

would have been doing
everything they could

just to cling on.

And yet, the bitter cold

was just the beginning.

This glacier is a remnant
of one of the great ice sheets

that have grown and shrunk
from the poles for millennia.

Deep within are clues
about the world

these Homo sapiens
would have found themselves in.

We're working
in mountain glaciers

like Folgefonna
because we can use

the evidence of how the glaciers
have changed

in the past to understand

how they behaved in response
to climate change.

Many of the places
we live in now,

where I live in Bergen,

would have been underneath
a kilometer of ice.

AL-SHAMAHI:
Yeah, I mean, there were times
when Britain was part of that.

So, this is where
we're drilling the ice core.
AL-SHAMAHI: Yeah.

So, it's manual drilling, then?

Yes, exactly, and there's blades
at the bottom

that are cutting through the ice

that would...
How tough is that?

That's, it's quite, it can be
quite hard work.
Yes.

And then we lift it out

and we bring it over here.

You can see...
AL-SHAMAHI:
Look at that.

If we hold it up to the light,
we can see the air bubbles.

So basically,

this is effectively
a time capsule.

Yes.

And this is young ice
from Folgefonna glacier.

But if this was deep,
old ice core,

those air bubbles
would tell us about

what the atmosphere
was like in the past.

We can look at what we see...

Mm-hmm.
...from the ice cores
in Greenland.

This shows us how the climate
changed through that period

- in the North Atlantic region.
- Yeah.

There was a relatively cold
but stable climate... Mm-hmm.

...from 70,000 to 60,000 years
ago.

And then, between 60,000
and 30,000 years ago,

the climate
in this region jumped

by eight to ten degrees
warmer...

Mm-hmm.
...over maybe
one or two decades.

That's quite a lot, yeah.
It's huge, it's huge.

And that cycle is repeated
all through that period.

And then it cooled again,
and then jumped,

and this carried on,

and we see then a cold

but slightly more stable
climate before we

then warm into
the present day.

I mean, how do you exist

if the climate changes
like that,

in such an extreme fashion?
Well, it's very
challenging.

It's, it's maybe
not even possible, because

everything you know about
how to live, how to...

Yeah....raise children

becomes, in ten, 20 years,
totally changes.
Obsolete.

Yeah, yeah, yeah.
Totally changes.

AL-SHAMAHI:
Over just a few hundred years,

entire ecosystems transformed.

Forests became barren plains...

...lakes dried up,

and rivers froze over.

The real enemy wasn't just cold,

it was change.

As landscapes shifted,

herds of animals disappeared...

...and sources of food
grew scarce.

Imagine what it would be like
for our ancestors

to live in this world

where the land
of their grandparents

was not the land
of their grandchildren.

And when that happens,

intergenerational knowledge,

knowledge that's passed on
from one generation to the next,

that's so important for
survival in these environments,

suddenly,

that knowledge isn't actually
very useful,

because the plants, the animals,

the landscape,
it's all different.

To survive, Homo sapiens
had to be adaptable...

...roaming farther in search
of dwindling resources

that might not be there.

Homo sapiens and Neanderthals
would have been forced

to look for better conditions
wherever they could...

...and seek refuge
in the few habitable places

they could find.

55,000 years ago,

the south of France was still
in the thick of the ice age.

Yet compared to the deep freeze
of the north,

it was one of the
more bearable places

in an otherwise hostile
landscape.

And here, at Grotte Mandrin,

archaeologists have spent
over three decades

unearthing its secrets...

...layer by layer...

...revealing a place that was
home to Neanderthals

for more than 80,000 years.

Shoes off.
Yes.

There we go.

And we are barefoot

because if there was a flint
or a bone

below your feet,
you will immediately feel it.

It's a pretty slow work--
as you can see,

we only excavated something

like 50 to 60 centimeters

for 33 years.

So here we have
a very nice section

where we can understand
what happened.

So you have yellow, black...

Yeah.
...orange.

So it's like a barcode.

And so right there,

about there, we are at 42,000.

By here, we are at 50,000.
Uh-huh.

And there, this step here

of yellow sands, we are at
54,000.

So what you're seeing here
is phases of occupation

over 80,000 years.

Yeah.
And because you've got
incredible resolution,

you can really hone in on that.

There we have all

the records of all the
societies, how they were living.

You can precisely reconstruct

how these people were living
in the landscape.

AL-SHAMAHI:
For millennia, this cave
was home to Neanderthals.

But one layer stood out,

containing finely crafted tools.

Small and precise.

Techniques that suggested
they were made

not by Neanderthals,
but by Homo sapiens.

A suspicion confirmed

when the earth revealed
another treasure.

So, this is a molar...

Mm-hmm.
...from a child,

from a sapiens,
dated at 54,000.

AL-SHAMAHI:
That, then, is
conclusive evidence

that that layer,
with those strange,

unusual stone tools...
Yeah.

...is definitely a Homo sapien
layer.
Yes.

These elements that allow us
to rewrite

a large part
of the history of Europe.

AL-SHAMAHI:
These discoveries tell us
a story of one group

of Homo sapiens.

Among the first
to come to Europe.

They had ventured
into Neanderthal territory...

...seeking refuge in this cave
in the depths of the ice age.

When we imagine the past,
we often

don't imagine children.

We imagine,
well, a man, a caveman.

Yeah.
-
- Right?

But actually,
these were

"cavechildren."

But imagine to have
been born,

the first of your people
to, to turn up there.

And we don't know-- they might
have been born somewhere else.

Yeah, but the kids, we don't...
But it's fascinating.

Fantastic, yes.
Wow.

Suddenly, it became
something very concrete.

AL-SHAMAHI:
Using advanced
dating techniques,

the team were able to uncover
even more precise details

about the people who lived here.

When you see
this dark line here,

all what is dark here

is due to the burning wood,
burning bones.

It's when people come in thecave,

they make fire,

and the roof became black.

AL-SHAMAHI:
- So, people were building fires.
- Yeah.

The fire created soot.

- That would end up on the roof.
- Exactly.

And then bits of the roof
would collapse and end up

in your archaeological layers.
Yes.

AL-SHAMAHI:
It's literally telling you

when they're using this place.
Exactly.

AL-SHAMAHI:
By counting the microscopic
layers of soot

deposited on the cave ceiling,

the team could tell how often
these people came here.

The soot allow us to know

that they came once a year

during 40 years.

40 years, it's a lifetime!

But what happened
to them?

We know that after 40 years,

suddenly, the population
are no longer here.

Did they die?

Did they move
on another territory?

We just don't know.

AL-SHAMAHI:
This exceptional site
tells the story

of a pioneering group
of Homo sapiens

who lived here in a break

between tens of thousands of
years of Neanderthal occupation.

But then,
all traces of them vanished.

It's one small
but very important chapter

in our bigger story.

We don't know what happened
to that particular group

of Homo sapiens
from Grotte Mandrin,

but it's likely that their story

reflects what was unfolding
across the continent.

This wave of Homo sapiens

was lured into Europe
during a warmer spell.

They were pioneers, for sure,

but they were trying to survive
in a brand-new environment

as best as they could, as best
as they knew how, really.

Finding temporary places
to shelter

before, in the blink of an eye,
moving on,

or worse, dying out completely.

Because that band of Homo
sapiens from Grotte Mandrin

would be the last of our species
found on this continent

for thousands of years.

Perhaps unprepared for the harsh
environment they faced,

this early wave of Homo sapiens
in Europe did not survive.

Once again,
and for thousands of years,

it became exclusively
Neanderthal territory.

Neanderthals had survived,

while Homo sapiens died out
in Europe.

Yet today,
we're the only ones left.

How did our stories
end so differently?

Part of the answer
lies deep within the forests

of Northern Spain.

Where evidence hints

that even without competition
from Homo sapiens,

the Neanderthals were failing
to cope

with the changing conditions.

A struggle uncovered in a cave
known

as the Tunnel of Bones.

Oh, wow.

So, this is
the famous El Sidrón Cave.

It is, yes, yes.

AL-SHAMAHI:
It's got more character

than I was expecting, actually.
Yeah.

Here is where we found
2,500 Neanderthal bones.

We found 13
Neanderthal individuals

of different ages and sexes.

AL-SHAMAHI:
Such a, a diverse group
in terms of individuals,

all found in one spot.

Genetic studies told us
that they are related.

So it's a family group.

We know, for example,

that one female--
we are not completely sure--

genetic information said

was, uh, uh, red hair.

And you know
when you say that one

of those people
had red hair,

it, it suddenly brings
what were

just fossils, really, to life.

AL-SHAMAHI:
It's a cave that's filled
with ghosts.

We think these, these people
were killed by other group.

AL-SHAMAHI:
This was not a natural death.

Cracked skulls and precise cuts
on the bones...

...suggest that this was
a brutal massacre.

13 people killed
by another Neanderthal group.

But closer analysis
of their remains...

...revealed
an even darker truth.

So what do the bones
actually tell us?

The first thing
the bones tell us

is that this Neanderthal group
cannibalized another group.

They were really eating
these 13 individuals?
Yeah, yeah, yeah, yeah.

So how do we know
that this was cannibalism,

as opposed to just
straight-up murder,

or, for that matter,
an animal coming?

Well, because we have seen,
on the bones,

what we call "cut marks."

And also, we have found

a lot of bones broken

just to get the marrow.

Yeah-- oh!

So, there are the,
both things.

We have cut marks,
and then...

...they broke the bones
to get the marrow.

Yeah, if you're getting
bone marrow,

that, that is...
That's, that's...

...an indication
of cannibalism, sure.
Yes, yes, sure.

AL-SHAMAHI:
This murder-cannibalism

of 13 members of a family group

isn't the only dark thing
that's happening here.

No, we have other informations

in El Sidrón bones.

For example, here.

Uh, bone defects.

We have found that one adult

and one adolescent

retains the baby teeth,
in, in this case, the canine.

That's unusual--
that's a congenital anomaly.

And then the atlas vertebra,
there is a,

a hole down there
that also is not normal.

And congenital anomalies
and defects

that tells us maybe
that there are inbreeding

between related persons.

AL-SHAMAHI:
So basically, you've got
an inbred population.

Inbreeding and the consequences
of that inbreeding,

but different generations,

and this number of anomalies
is, is high.

It's painting a picture,
isn't it?

Of those,
those final thousands...

Yes.
...thousands of years
before they...

Yes.
...eventually became extinct.

I think this is a silentproblem.

Silent pathology, you know?

Yeah, it's a silent killer,
you're right.

It's, goes, goes, goesdown.
Yeah.

But it's continuously, next
generation, next generation.

Illnesses, you know, all thosethings.

At the end, Neanderthals areextinct.

AL-SHAMAHI:
The El Sidrón bones hint at more

than the suffering
of one family.

Because this pattern

of starvation, cannibalism,
and violence

was happening across Europe.

This was a species in free fall.

This is a haunting place.

It's not exactly Neanderthals
in their heyday, is it?

If anything, it's kind of
like the end of days for them.

They've been driven into
this evolutionary cul-de-sac,

reduced to eating each other
and having children

with their relatives,
and that inbreeding

would have made them
more susceptible to disease.

If, on the evolutionary
timescale,

12:00 midnight represents

extinction for the Neanderthals,

this site is past 11:30.

This once-resilient species

was now reduced
to just a few isolated groups...

...turning on one other.

But any chance
Neanderthals may have had

of weathering this storm...

...was shattered by the return
of another species.

Homo sapiens.

Several thousand years
after Homo sapiens

had disappeared from Europe,

our species would return.

Waves of new settlers,

finding their way into Europe
for the first time.

But even though the climate
was as volatile as ever...

...they were not deterred.

Innovations like weaving

and the ability
to make warmer clothing

likely increased
infant survival,

even in the harshest months.

Each advance, however small,

added up, giving Homo sapiens

the one thing Neanderthals
lacked:

strength in numbers.

The Neanderthals had existed

for around 400,000 years.

Developing a rich culture.

And withstanding
brutal conditions.

But the relentless climate,

dwindling resources...

...and another species
growing in strength

all may have pushed

this once-resilient species
to the brink.

But what delivered
the final blow?

How does an entire species
of human disappear

from the face of the Earth?

Part of the answer may lie
in the smallest of things:

the genes we exchanged

in the form
of our hybrid children.

I'm going to try and do a demo
to explain genetics.

So, let's see how this goes.

Let's say that these are
the Neanderthals

and these are the Homo sapiens,

and they interbreed.

We don't know where
the hybrid children ended up.

Did they end up
with the Neanderthals

or did they end up
with the Homo sapiens?

So, let's just say
they went back 50-50.

And we see
a little Homo sapiens DNA

in the Neanderthal group.

And a little Neanderthal DNA
in the Homo sapiens group.

The Neanderthals lived in small,
isolated populations,

but the Homo sapiens were
probably a little bit better

at keeping their kids alive.

And also, importantly,
they were constantly

replenishing
from source populations

in the Middle East, Africa,
and elsewhere.

Numbers made all the difference.

As more Homo sapiens migrated
into Europe,

Neanderthals
were already declining.

So, when the two interbred,

the impact on Neanderthals
was far greater.

If you're a huge population,

that interbreeding doesn't have
the same impact as it does

on the much smaller
Neanderthal population.

It's already a little bit
interbred.

Perhaps they were simply
absorbed

into the larger Homo sapiens
population

that just kept on replenishing.

Over time, Neanderthal DNA
became increasingly diluted

by the much larger Homo sapiens
population.

So it doesn't actually
need to be

this big act of aggression.

It might just be the fact
that we were there,

that we were interbreeding
with them,

and that we had
large population sizes.

Perhaps that was enough

to push the Neanderthals
to extinction.

It was a perfect storm
for Neanderthals.

By around 40,000 years ago,

their gene pool was diminishing.

Until only a handful

of distinct Neanderthal
populations remained.

Hanging on in just
a few isolated enclaves.

We don't know where the last
Neanderthal outpost was.

It was likely a very
remote part of Europe or Asia.

But around 40,000 years ago,

that place probably acted

as a refuge to the very,
very last of their kind.

Archaeologists have
pieced together what may be

among the final moments
of Neanderthal extinction...

...uncovering remains
of what could be

the last surviving
Neanderthal groups.

Some of that evidence
has been discovered

in coastal caves
in Southern Spain.

We don't know what truly
happened in those final moments

or who was left at the end.

But there was an ending.

Because after that,
Neanderthals,

who had existed for
around 400,000 years...

...vanish from the
archaeological record

completely.

Our remarkable abilities

to connect, innovate,
and explore

have led to our success.

But time and time again,

that seems to come at the
expense of those around us.

Homo sapiens' arrival
in Europe triggered

a slow, unwitting war
of attrition

against our human cousins

until they simply faded away.

But this wasn't the only ending.

After the last Neanderthals,
the Denisovans,

the species
who once spanned much of Asia,

may have survived for another
10,000 to 20,000 years

until they, too, were likely
overwhelmed by Homo sapiens.

This story starts with
three species,

but it ends with one,

and it's part of a wider pattern

that always goes the same way.

The survival of our species

leading to the demise
of everyone else.

Today, these events
have faded from memory.

But it's not quite
the end of the story.

Because we carry a piece
of this history within us.

One of the most striking
revelations

over the last few years

is that everybody from
outside of Sub-Saharan Africa

has about two percent
Neanderthal DNA.

And that DNA is associated

with negative things
like Crohn's disease.

But it's also associated
with all kinds of positives,

like being better adapted
to the cold.

And now we know
that Denisovan DNA

has been found
in Homo sapiens populations.

It could be as high as five
percent in the Philippines.

And it's associated with things

like being able to survive
better at high altitude.

And if you think about it,

it actually makes perfect sense,

because when we were leaving
Africa,

the Neanderthals
and the Denisovans

had already spent hundreds
of thousands of years

adapting and evolving
to their local environments

and pathogens.

And so, what we were doing
by interbreeding with them

was effectively a quick fix.

We were adopting adaptations

that would ultimately aid
our survival.

No matter where you're from,

it's likely you have traces

of Neanderthal or Denisovan DNA
within you.

An echo of the human story

connecting us to this long line
of distant ghosts.

Two percent might not sound
like a lot,

but my two percent is different
from your two percent.

And collectively,
all of that Neanderthal DNA

that exists within humans
living today

would make up at least half
of the Neanderthal genome.

And so, in a very real sense,

Neanderthals and Denisovans

have been assimilated
into our bodies.

And it's just the loveliest
thought, isn't it?

That they live on
and exist within us.

Our planet was once home
to many human species.

Bit by bit,
they've all disappeared,

leaving only one
to carry on their legacy.