Nova (1974–…): Season 37, Episode 6 - Becoming Human: Last Human Standing - full transcript

Nova examines the early ancestors of mankind and examines why Homo sapiens won out over Neanderthals in the evolutionary race.

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More than six million years ago, we took the first step

to separate from the apes.

Since then there have been

at least 20 types of human ancestor in our family tree.

Some of them were on their way to being us.

Others were evolutionary dead ends.

DONALD JOHANSON: As recently as 50,000 years ago,

there were probably four different kinds of humans

living at the same time.

Yet today, we are a species alone.

Why did we survive and all the others disappear?

New discoveries are shining light

on the final stages of our evolution.

We're finding out where our species, Homo sapiens,

came from.

CURTIS MAREAN: The genetic record shows us

that all modern humans are descended

from a small population

of approximately 600 breeding individuals.

And we are discovering how they spread through the world,

pushing out other ancient humans like the Neanderthal.

JEAN-JACQUES HUBLIN: Neanderthals were

very successful humans.

They have lived in Europe for maybe 300,000, 400,000 years,

but eventually they were replaced by modern humans.

But why were they replaced by modern humans?

The mystery of the Neanderthal disappearance

is finally being solved

as the secrets of their genetic code are unlocked.

We're discovering exactly what made them different from us

and how we're unique.

So join us as we explore the origins of our own species.

Find out why we're the last human standing--

right now on NOVA.

Imagine a world with only a tiny number of us in it,

perhaps just a few thousand.

A recently evolved species,

we are completely at the mercy of the natural forces around us.

140,000 years ago,

Homo sapiens teetered on the brink of extinction.

New discoveries are revealing how,

from these humble beginnings,

we took over the planet,

eventually replacing other ancient humans

who were already living there--

Homo erectus and the Neanderthals.

Humans have a very intensive way of using the environment.

Humans move into the Middle East.

The Homo erectus starts going extinct.

When humans move into Europe, the Neanderthals go extinct.

For almost 400,000 years,

the Neanderthals lived in Ice Age Europe.

Superb hunters, they had brains bigger than ours

and a record of survival twice as long.

They were the most advanced humans on earth

until we arrived.

And then they vanished.


Finally we're unearthing the answers.

The remains of a 100,000-year-old child

are revealing what we had that they didn't.


Essential to figure out what are the differences

between the Neanderthals and us,

to figure out what is special about us.

Was it some new physical ability?

Or was it a new way of thinking?

These questions go to the heart of what makes us human.

To answer them we must travel back in time

to the beginning of our human story.

Imagine the entire span of recorded human history,

taking us back to the Egyptian pyramids 5,000 years ago.

Double it-- 10,000 years ago, when plants were domesticated

and agriculture begins.

Double it again, to the time when Ice Age hunters

paint stunning images on cave walls.

And keep doubling, six more times,

and we are finally entering the world

of Homo erectus, the remarkable ancestor who pioneered

what it means to be human.

Homo erectus appeared on the African plains

almost two million years ago.

They were the first ancestors who had bodies like ours.

They were hunter-gatherers and toolmakers,

beings who lived in social groups and cared for each other.

The most famous Homo erectus is the fossil called Turkana Boy.

VIKTOR DEAK: Well, Turkana Boy and his ancestors,

they represent a threshold.

They represent that point in our evolution

when we were... we weren't quite fully a human,

but we were no longer an ape.

Paleoartist Viktor Deak specializes in creating

scientifically based sculptures of ancient humans

from their fossil remains.

As he reconstructs Turkana Boy's head,

apelike features emerge--

heavy brow ridges, a protruding lower face,

a skull still smaller than our own.

But despite these differences,

Turkana Boy is definitely starting to look

like a human being.

And behind those eyes, his mind was becoming human too.

I suspect that complex feelings

and behaviors had their beginnings

with Turkana Boy's kind

and that what it is to truly be a human

had its bubblings at that point.

NARRATOR: It was probably Homo erectus,

almost two million years ago,

who first started to leave Africa.

Ever since, Africa has been the engine of our evolution,

pumping out wave after wave of ancient humans

who populated Europe and Asia.

Settling in far-off places,

they developed in their own special ways.

An early wave gave rise in Indonesia

to the extraordinary Hobbit,

perhaps a type of dwarf Homo erectus.

Another wave took Homo erectus all the way to China,

where fossil remains have been dated

to over 700,000 years ago.

Soon after, another wave left Africa,

this time heading for Europe.

This was the species that would one day give rise

to the Neanderthals.

Ever since the first skull was discovered

in Heidelberg, Germany,

they have been called Homo heidelbergensis.

But almost nothing was known about them

until one extraordinary find was made.

Atapuerca in northern Spain.

These rolling hills have turned out to be

an archaeological goldmine.

When a railway was built over a hundred years ago,

it cut right through the hills.

Archaeologists later discovered this had exposed

over a million years of ancient human habitation,

including the oldest human remains in Europe.

Nearby, on the crest of one of the hills,

they also found the entrance to some caves.

To explore them took years, but it has been worth it.

They have discovered a labyrinth of chambers and corridors

reaching far inside the hills.

At the end of the labyrinth is

one of the most inaccessible archaeological sites

in the world,

a treasure trove of human fossils they call

"The Pit of Bones."

JUAN LUIS ARSUAGA: This is the entrance to the whole system.

The pit itself is very far from here.

It is a long way,

and in some places you have to crawl.

It's a difficult place to work.

Today, it takes half an hour of walking, crawling

and scrambling in the dark to reach the 50-foot vertical shaft

that drops into the pit.

But it took almost ten years for the site to give up its secrets.

We started to find small pieces of human bones.

Difficult to recognize in the beginning,

because they were very fragmentary.

But so many tiny fragments made them think

they were on to something big.

Even without talking to each other,

we started to think

that maybe there were, down there, skeletons.

As bone after bone came out of the pit,

they realized they had not one, but many complete skeletons.

We have around 30 complete skeletons

half a million years old,

and this is absolutely unique.

These are the skeletons

of the ancestors called Homo heidelbergensis--

one of the earliest to populate Europe.

But why were so many complete skeletons collected

in one place?

Juan Luis Arsuaga believes they were put there intentionally

by their kin.

Half a million years ago, the Pit of Bones,

now deep underground, had an opening to the surface.

Perhaps Homo heidelbergensis dropped the bodies into the pit

in a sort of primitive burial.

And there is evidence it may have been ceremonial.

Along with the bones, Juan Luis found a single artifact--

a hand ax made of pink quartz,

a mineral which must have been brought from a long way away.

The team called it Excalibur

after King Arthur's famous sword.

They believe it was an offering, the first symbol ever found.

If this is right,

here were beings with complex minds

capable of symbolism and belief.

Half a million years ago, in these European populations,

there was planning, there was consciousness,

there was a human mind,

and there was also symbolic behavior.

We used to think these qualities belonged

only to us, Homo sapiens--

that the earliest evidence for them was in the painted caves

of southern France, just 30,000 years ago.

But the extraordinary finds at Atapuerca

may have pushed the beginnings of that mental evolution back

almost half a million years.

Homo heidelbergensis would continue to evolve,

eventually becoming the species who would populate Europe,

the Neanderthals.

Of all ancient humans,

the Neanderthals were the closest to us.

Their brains were slightly larger than ours.

Their short, heavy-set bodies helped them survive

repeated ice ages.

They were hunters, living off the big game that roamed

the edges of the great ice sheets

covering Europe and Central Asia.

When Neanderthal fossils were first discovered,

Darwin had yet to publish his theory of evolution.

The idea that modern humans had descended

from more primitive forms would generate furious controversy.

MICHEL TOUSSAINT : This is the skull of Engis 2.

It is the first Neanderthal fossil

ever found on earth.

It was discovered at the end of 1829.

But back then, people were not happy with the idea

that this could be a human being like us.

Many claimed that the Neanderthals were just

diseased, misshapen humans.

Then, as evolutionary ideas took hold, people wondered

if they were the missing link between us and the apes.

If we go back to the beginning of the 20th century,

Neanderthals were seen as sort of apelike creatures.

But since then hundreds of fossil finds have revealed

their physical similarities to us.

After the '70s, there was a so-called rehabilitation

of the Neanderthals,

so we tend to see them in a more human way.

But did they think and act like us?

Today, the remains of a young boy who died 100,000 years ago

are helping researchers penetrate the mysteries

of the Neanderthal mind.

The Meuse Valley in Belgium.

It was caves and rock shelters here that gave up

the very first Neanderthal fossils 150 years ago.

Today they are revealing deeper secrets

of the Neanderthal world.

For over 20 years, Michel Toussaint and Dominique Bonjean

have been excavating a cave called Scladina.

One millimeter at a time,

they've been sifting through the debris

that once filled the cave.

Their painstaking work paid off.

I've had the chance to be present

when one of my students discovered

the Neanderthal child.

And when we have come there and see that... this piece,

we were so surprised!

We couldn't believe it.

What they uncovered was the jawbone of a young boy

100,000 years old.

Nearby they found more fragments and teeth,

until they had almost a complete mouth.

Since then, they have been trying to reconstruct

the life of the boy from Scladina.

They know the woodlands and caves of the Meuse Valley

were his home.

He probably lived here with his extended family.

Already he would have been learning from his father

the skills to become a hunter.

But what else can we infer about his way of life?

His bones are full of clues.

And new techniques are allowing scientists to decipher them.

Michel is taking a piece of the jaw

to one of the few places in the world

where the tests he needs can be done.

The Max Planck Institute in Leipzig, Germany,

is one of the world's foremost centers

for human evolutionary studies.

Here, the jawbone of the child from Scladina

is put through a high-powered CT scan.

This allows researchers to peer into the internal structure

of the teeth and bone.

So this is the mandible

that was scanned yesterday, the Scladina mandible.

And we have built up what we call a surface model,

which is basically a virtual representation of the mandible

in a computer.

We can separate all the teeth from the bone in this specimen.

The features that we can explore show us how Neanderthals

are similar to us in many aspects,

but also how they are different.

The teeth of children are among the most prized

of all archaeological finds,

because only they can tell us

how fast those children were growing up.

If we look at the pattern of eruption of the teeth,

the Scladina child, by modern standards, should be

about 11 or 12 years old.

The second molar is almost completely erupted.

But when we look at the internal structures

of the enamel and dentine,

it has been shown that it's in fact much younger.

We know that this child died aroundight years old.

Although the boy from Scladina would have looked like us,

he probably grew up much more quickly.

That means he had much less time

for brain development and learning.

But is it safe to assume

the Neanderthals were less intelligent than we are?

The crucial evidence comes from skulls.

Endocasts, impressions taken

from the inside of Neanderthal skulls,

have revealed brains with many similarities to ours.

RALPH HOLLOWAY: When we look

at the Neanderthal endocast, we find a frontal lobe

that we can't really differentiate

from modern Homo sapiens.

The Broca's caps that have to do with the motor control,

motor aspects of speech

are thoroughly human in terms of their form.

So if the front of the Neanderthal brain

is similar to ours, what about the rest of it?

Today, scientists like Katerina Harvati

are trying to measure fossil skulls with new precision.

She uses a special instrument to digitize the skulls

and create perfect three-dimensional images.

We've known for a long time

that Neanderthals looked different from modern humans

ever since they were first discovered and described,

but the question then becomes

what does this difference actually mean?

This is a digitized 3-D image of our own skull

with its characteristic high dome.

By contrast, the Neanderthal skull is low and elongated,

possibly indicating a different brain shape.

The parts of the Neanderthal brain

called the parietal and temporal lobes

may have been slightly smaller.

That small difference could have had a large impact

on their mental ability.

There are regions

of the parietal lobes and the temporal lobes

that are very important in cognition,

particularly in terms of language, in memory,

in remembering spatial locations.

The reduced size of those regions of Neanderthal brains

might be a sign of limited thinking powers.

But the boy from Scladina's jawbone has more to tell us

about other limitations.

Back at the Max Planck Institute,

Mike Richards is delving even deeper

into the micro structure of the bone to find out about his diet.

The food we eat leaves a chemical signature

in our bodies.

These signatures are incorporated

into the protein of our bones.

So what we do is get the bone

and we take that protein out and measure those signatures.

We can work backwards and say this is the food

that this human ate over their lifetime.

He's discovering that Neanderthals

were almost exclusively meat eaters,

although there were many fruits, berries and edible roots

in their environment.

We don't see any evidence

that plant protein was at all important in their diet.

And it doesn't look like they had marine food at all.

They were hunting large herbivores

like bison or reindeer and things like that.

They were carnivores

with a diet closer to that of a predator like a wolf

than a human.

And they showed few signs of change,

no matter where they lived.

So far we've measured the type specimen from Germany,

the Neanderthals from Scladina,

Neanderthals from France and Croatia

over about 100,000 years.

And in every case, in all these different environments,

the Neanderthals do the same thing.

So the bones of the boy from Scladina and his people

are revealing important clues to Neanderthal behavior.

They did one thing, hunting large game,

and they just kept on doing it

for hundreds of thousands of years.

Their technology tells a similar story.

Neanderthal technology is quick and dirty.

It's simple.

There's very few tools that Neanderthals made

that one can't copy in a few seconds or even minutes.

Although they hunted large animals, they didn't have

throwing spears or arrows.

None of the stone tools that the Neanderthals made

are the size and shape

sufficient to be a projectile point.

They're all too big.

Which suggests they're either knives

or tips of thrusting spears.

That meant Neanderthal hunters

had to get close to their prey to kill them,

which made hunting a risky business.

Most Neanderthal male skeletons have multiple fractures.

Neanderthal lives were tough and they were short.

Their skeletons tell us

that very few lived beyond the age of 30.

But as a species, the Neanderthals were long-lived.

They lasted for almost 400,000 years.

That's twice as long as we have.

But one day, their time on earth would come to an end.

By 25,000 years ago, they vanish from the fossil record.

So what happened?

To find out, we have to return to Africa.

The Great Rift Valley,

the stage on which so much of human evolution has played out.

It was here, millions of years ago, that nature began

its grand experiment with creatures like Lucy

who walked upright.

It was here, just over a million years ago,

that Turkana Boy and his kind,

with their bigger brains and bodies,

formed the first hunter-gatherer societies.

And it was here, about 200,000 years ago,

that the skulls of a new species start to be found--

the last human to evolve, Homo sapiens.

They are still not completely us.

Their brow ridges are a little heavier,

their faces a little bigger,

and their technology is still simple.

You have stone tools made by Neanderthals

and stone tools made by Homo sapiens,

and they're identical.

You can't tell which one made the stone tools,

because they were making the same kinds of tools.

So what changed?

What made us into the versatile beings we are today?

All the evidence points to climate upheaval.

We enter one of the longest, coldest

glacial stages on record.

Around 200,000 years ago, vast ice sheets descend.

In Africa, megadroughts turn much of the continent

into a desert.

SPENCER WELLS: And so basically you've got

this double whammy of climatic challenges

slamming the African population, and the people dwindle.

Geneticist Spencer Wells believes

that ancient population crashes have left a footprint

in our genes.

It's called the bottleneck effect.

Humans, although on the surface

we seem to be so different from each other,

actually have remarkably little genetic diversity.

We're 99.9% identical.

Look at other apes like chimps or gorillas or orangutans,

they have between four and ten times as much diversity

at the DNA level.

The lack of diversity in human DNA is a clue to a crisis

that may have wiped out whole populations.

The reason that we have

so little diversity at the genetic level

is because we lost it at some point.

Imagine that this bottle of jellybeans

is the initial population;

you've got so much diversity in here.

What happens during a bottleneck,

when you go through the bottleneck,

only a few of the lineages survive.

So that's the drop in population size right there.

Everyone alive today is a descendant of these individuals,

and you can see that we're missing many of the colors

that you see in the initial population.

That's how a bottleneck works.

And everybody alive today is a descendant

of that small number of individuals who made it

through the bottleneck.

Ancient climate data shows that around 140,000 years ago,

most of tropical Africa became uninhabitable.

Our ancestors were forced to seek refuge

on coasts and highlands.

It looks like four to six potential locations in Africa

that would still be supportive of hunter-gatherer populations.

Despite the refuges,

there is evidence our ancestors were pushed

to the brink of extinction.

The genetic record shows us that all modern humans are descended

from a small population

of approximately 600 breeding individuals.

There's disagreement about the numbers and timing,

but it does seem that all people on earth

are descended from a very small original population in Africa.

Curtis Marean believes

they lived on the South African coastline

and that it was life by the sea that forced them to change.

At Pinnacle Point, South Africa, he has found caves

used by early Homo sapiens ancestors

during the megadrought period.

They're full of clues

that hint at new ways of thinking and behaving.

Here he has found some of the earliest evidence

that humans were living off the sea.

This darkish material here is ash from a fireplace.

And the vast majority of this material is burnt shell.

So clearly there is quite a bit of cooking of shellfish

that was taking place at this exact spot.

76,000 years ago, somebody had a nice shellfish dinner there.

Here was a population that was broadening its diet

away from meat...

requiring ingenuity unknown among earlier ancestors.

You go out to collect shellfish at the wrong time, you're dead.

You have to be able to time your access to the coastline

so that you're here when the tides are right

to collect those shellfish.

The best time to collect shellfish

is at extreme low tides.

And to predict those,

it helps to understand the cycles of the moon.

Those are the times

that you want to be collecting shellfish.

All the shellfish are exposed, so this water which you see here

is out there at that point, where that rock is.

So the smart coastal hunter-gatherer

knows how to use the moon to signal to them

when to come to the coastline to collect the shellfish.

The people of Pinnacle Point

were not just harvesting shellfish.

They were also hunting on the plains behind the coast

and gathering berries and roots.

Their way of life reflected a new versatility.

The systematic use

of coastal resources does suggest a cognitive complexity.

Our ancestors occupied these caves for over 140,000 years,

leaving behind an amazing record of their transformation.

This site documents

a change in the way that people made stone tools.

At the bottom of the sequence, they made stone tools

with this rough quartzite material.

And then right at about 71,000 years ago,

which occurs just about there in the sequence,

they make a shift to making stone tools on this silcrete

in the form of long, thin blades.

Before flaking it, the people here were heating this material

in the fire and through heating it, improved its flakability.

And that was at about 71,000 years ago,

about 40,000 years older

than that has been found anywhere else in the world.

The technology of our ancestors was expanding

from the single all-purpose hand ax

to a variety of lighter specialized tools.

Then they started to make these kinds of things.

They made tools with special little points

for perforating tasks.

They made others with special chisel ends for carving tasks.

Specialized tools allowed our ancestors

to get more out of their environment,

but this wasn't the only change.

At this point,

we begin to see people treating stone tools as symbols.

They're making them more complex than they need to be

to accomplish a particular cutting task.

So, at this point,

stone tools are no longer just tools for cutting things,

they're instruments of carrying social information

about their owners.

A new type of symbolic consciousness was emerging.

The first evidence of decorative art

made from a naturally occurring mineral called red ochre

has been found at Blombos,

another cave along the South African coast.

CHRISTOPHER HENSHILWOOD: While we were excavating

more or less in this area you can see over here,

we found a chunk of ochre, and when we brushed up

the surface of the ochre, we realized

that there was actually a design on the one side,

and once we looked at it in more detail,

held it up to the light,

we could see a cross-hatch pattern

that had lines zigzagged across the surface

of this flat ground surface

and also had lines across the top, through the middle

and along the bottom.

You can imagine it was enormous excitement,

because we did not expect to find

something that might represent a symbolic image

in these 75,000-year-old levels.

So this really was an enormous, enormous surprise for us.

At Blombos they've also found shells

with holes drilled in them,

believed to have been used for necklaces.

So our ancestors were now wearing ornaments

and probably painting their bodies as well.

HENSHILWOOD: For me, what is really important

is here for the first time, really ever,

we have evidence that people can store information

outside of the human brain.

It is the birth of a new type of human culture,

more complex but easier to pass on

from generation to generation.

60,000 years ago, our ancestors emerged

with new technology and new culture.

Thousands of years of drought had forced them to change.

They were ready to explore the world.

As the climate improved, they started to stream out of Africa.

They might have been surprised to discover continents

already populated by other humans--

remnants of earlier, more primitive migrations.

As they moved into Asia,

they might have come across Homo erectus or the tiny Hobbit.

There's no evidence for such a meeting,

but there is one encounter we can be more certain about.

As a separate wave slowly moved through the Middle East

into Europe,

they must have met the Neanderthals.

What were those meetings like?

For many years, scientists speculated

that early Homo sapiens populations

absorbed the Neanderthals through interbreeding.

If they did, there would be traces of Neanderthal DNA

in our genes today.

But there was no way to detect Neanderthal DNA

until researchers at the Max Planck Institute

set out on a daring scientific odyssey--

the quest to sequence the Neanderthal genome.

The human genome contains

approximately three billion chemical bases--

the A's, T's, C's and G's that make up our genes.

Mapping that was hard enough.

The idea of mapping the genome of a long-extinct species

seemed pure fantasy.

The first problem was to get DNA

from Neanderthal bones over 30,000 years old.

In most cases, DNA degrades steadily over time,

leaving only minute fragments.

My group is involved since over 20 years now

in developing techniques to retrieve ancient DNA

from fossils and old bones.

And of course always a dream was to do the Neanderthal,

our closest relative.

But finally, taking great care

not to contaminate it with their own,

they isolated the first piece of Neanderthal DNA.

Svante's dream is now a reality.

He and his team have made a draft

of the entire Neanderthal genome.

Now scientists all over the world can compare

key parts of it to the human genome.

And one such comparison is already giving us

deeper insight into the Neanderthal brain--

the gene called FOXP2.

It's the only gene we know of today

that's involved in speech and language development in humans.

We know that because if one copy is lost in a human

due to a mutation, we have a severe speech problem.

When first discovered,

FOXP2 created a lot of excitement.

Although many animals have the FOXP2 gene,

the human version is unique.

Some thought it was the gene for language.

We now know that complex traits like language

are controlled by many genes.

Yet researchers agree, the human version of FOXP2

is closely tied to some of the basic motor skills

necessary for speech.

And a big question was, of course,

Is that shared with Neanderthals or not?

And when we now look at it in the Neanderthal,

indeed it looks to be identical with us.

It's tantalizing evidence

that despite their mental limitations,

the boy from Scladina and his people

may have been able to speak.

If we share the capacity for language with the Neanderthals,

could we both have inherited it from the same source,

a common ancestor who gave rise to both species?

Who was it?

With a technique called the molecular clock,

scientists can now find out.

That's because DNA mutates or changes

at a surprisingly regular rate.

By counting the differences

in the genetic code of Neanderthals and ourselves,

simply comparing the A's, T's, C's and G's in our DNA,

scientists can calculate

how long the two species have been diverging.

We can then estimate when there was

a common ancestor population

where some individuals went on to become modern humans,

some went on to become Neanderthals.

It's in the order of, say, 300,000, 400,000 years ago.

The timing points straight to the intriguing ancestors

who left Africa half a million years ago

and buried their dead in the hills of northern Spain,

leaving a distinctive pink hand ax at the spot.

This is Homo heidelbergensis...

who we now know is our ancestor too.

In Europe they evolved into the Neanderthals.

In Africa, groups that had not yet migrated

evolved into Homo sapiens.

So DNA is revealing

we share a common ancestor with the Neanderthals.

But do we carry some vestige of Neanderthal DNA in our genes?

Proof that we absorbed them by interbreeding?

Some people claim that there are some hybrids

of Neanderthals and modern humans.

In the genetical record we don't see clear evidence of that.

The big story is that there were Neanderthals that were replaced

by other people, and after a rather short time,

we don't see any trace of the Neanderthals in Europe,

and certainly today we don't see really traces

of Neanderthal genes.

With no evidence of interbreeding,

it now seems more likely that as our population grew,

we simply pushed the Neanderthals

out of their environments.

Humans have a very intensive way

of using the environment.

We seem to have the ability to pump out lots of babies,

and our babies seem to have a high probability of surviving.

So population growth is a really important part

of the human adaptation.

NARRATOR: The arrival of Homo sapiens was not the only thing

the Neanderthals had to contend with.

Europe was gripped by wild climate swings.

The Neanderthals were already struggling to survive.

Probably the density

of Neanderthals in the landscape was very low.

And there was a good reason for that.

Neanderthal technology was limited

and their energy needs were huge.

They had this big body, this big brain,

living in a rather cold environment,

so we have estimates of their energy consumption every day.

It's about 5,000 kilocalories.

It's about what someone racing the Tour de France

is spending every day.

But with slimmer, taller bodies,

modern humans had lower energy demands

and an ever-improving toolkit.

They now developed yet another breakthrough technology,

projectile weapons-- throwing spears.

These are two very different kinds of spears.

These are the big, heavy wooden spears

that Neanderthals and their ancestors used.

These are the lighter, bone-tipped spears

that Homo sapiens used.

These weapons have different

kind of performance characteristics.

The heavy spears are effective,

but they're effective at a very short range,

and they're heavy.

You can only carry so many of them in one hand.

The bone-tipped spears are lighter, they're more durable,

they have a longer effective range.

In essence, the bone-tipped spears that our ancestors used

allowed them thunt a wider range of animals more safely

and therefore to have a broader ecological niche.

These big, heavy spears with their, you know, their weight,

their relatively short range, it's like hunting with a pistol,

whereas using these things

is like hunting with a semiautomatic rifle.

One has more than one shot, one has greater range.

It's a more effective weapon.

Throwing spears allowed our ancestors

to go after a wider range of game

with less risk to themselves.

The modern humans have this trend

of intensifying their exploitation of the environment

to sort of squeezing out everything possible

from the environment.

That trend, already established in Africa,

would become more pronounced as our ancestors spread

around the world.

Archaeologists have been able to track their movements

by the extinctions of large animals.

In Europe and Asia, the arrival of Homo sapiens coincides

with the disappearance of the hairy mammoth,

the cave lion and other large mammals.

In Australia, most animals weighing over 100 pounds vanish

within a few thousand years of our arrival.

The effects of Homo sapiens on large animal communities

become more profound as you move further and further from Africa.

So, very few major extinctions in Africa,

a few extinctions associated

with Homo sapiens moving into Eurasia,

and then when they hit Australia and the New World,

it's a wipeout.

The Neanderthals were just one

of many species that disappeared when we arrived.

Gradually, they were pushed into marginal areas of Europe.

Their last refuge seems to have been

the Rock of Gibraltar 28,000 years ago.

Then they vanished,

leaving no legacy but their fossilized bones.

For the first time,

there was only one type of human on the planet.

But this species, it covered the whole planet.

It went to places where other hominids lived,

led them to extinction actually.

They went to Australia, they went to Americas,

they went to the moon, and they will go to Mars.

And this is very peculiar,

because the way this species intensified

its exploitation of the environment is really unique.

In the beginning,

climate upheavals made us what we are.

They taught us a new inventiveness,

which has led to a cascade of technological advances.

But exactly what made us different is still an enigma.

Soon we'll discover the genetic changes unique to our species.

But genes are only part of what makes us special.

The other part is that mysterious creation

unique to humans-- culture.

JOHANSON: Homo sapiens is

the most adaptable species in the human career,

meaning that no matter what happens in the world,

we have a way of adapting to it.

Today that way is called culture.

If glaciers came to Arizona where I live,

we wouldn't be growing thick fur and thick skin;

we would be building more fireplaces and heating systems.

Culture is the storehouse

of our complex ways of thinking and perceiving.

And we pass it on to our children

as surely as we pass on our genes.

The ways in which cultural evolution

and genetic evolution interact

will be at the forefront of the research of tomorrow,

because one thing is for sure-- evolution is not stopping.

The rate of evolution

at the genomic level has increased

over the last 10,000 years, and it probably will continue

over the next few thousand years.

Where it will take us, nobody knows,

but we're still a young species.

There is a long future ahead.