Brains Origins of Us

The shape of your face,

walking on two legs,

the way you see the world...

What makes you the person you are?

The story of each and every one of us can be traced back millions of years

to the plains of ancient Africa.

The answers to the question "What makes us human?"

lie buried in the ground in the fossils and other traces of our ancestors,

but also lie deep within our own bodies, in our bones, flesh and genes.

As an anatomist, I'm fascinated by the way our bodies

have been sculpted by our ancestors' struggle for survival.

But why did we leave behind the other apes in the forest...

..to become the only one of our kind left today?

How did living into old age,

and learning from each other, shape our large, clever brains?

The way our brains work today, the way we think, feel and behave,

is a direct consequence of our ancestors' struggle for survival.

But where other human species died out,

was it really our brains that gave us the edge?

I want to find out how our brains led us to be the successful, global species we are today,

and why we are the only humans left on the planet.

Our bodies are amazing machines,

honed over millions of years of evolution.

But our basic flesh and bones aren't that different from our closest ape relatives, chimpanzees.

Fundamentally, we are just another species of ape,

but we do feel ourselves to be different, to be special,

and that comes down to the very striking difference between us

and any other species on Earth. And that lies up here.

We are creatures of the mind.

We have an ability to think, imagine and create,

that has changed the world.

We have the ability to ponder the very nature of our own existence.

The emergence of the human mind is one of the great mysteries,

and it's a question which has been tackled by religion, philosophy and science.

And, as a scientist, I believe the answer is physical, the mind is a product of the brain.

And if we want to understand the way we think and act today,

we need to look at where we've come from.

This is the Rift Valley in east Africa.

It's here that the human story began.

This beautiful landscape is incredibly important to our story.

So many traces of our ancestors, going back millions of years,

have been found here.

So if we want to understand who we are,

there's not really a better place to start looking.

Fossilised fragments of bones unearthed here

show that we are the last of a large and ancient family of human-like creatures.

I'm going to use the shadow cast by these trees to recreate the human family tree.

It's more like a bush than a single branch of a tree,

but what I'm really interested in here is the size of the skulls.

To begin with, this is Sahelanthropus tchadensis, from Chad,

dating to about six-seven million years ago.

He's an upright walker, but has a tiny brain, about the same size as a chimpanzee's.

Around four million years ago, we see something a bit more human appearing, the Australopithecines.

This is Australopithecus africanus, a slightly bigger brain.

The next character is the first member of our own genus, Homo,

Homo habilis, the handyman, the tool maker, at around two and a half million years ago.

This is Homo erectus, brain size getting bigger,

appears around about two million years ago.

Jumping forwards in time, we get to Homo heidelbergensis,

appearing around 600,000 years ago.

The brain size is nearly as big as ours.

And finally, there's just one twig surviving to the present day,

and that is us.

In fact this is me - this is a replica of my skull.

So I'm going to represent Homo sapiens.

Looks like a fairly decent brain size in there.

The skulls of our ancestors clearly show an increase in brain size.

This important change defines our story.

Our evolutionary journey starts with the chimpanzee-like Sahelanthropus, in the forests of Africa.

The first apes to walk out of the forest on two legs were the Australopithecines.

And a million years later, Homo erectus, with a very tall, very modern-looking physique,

strode out onto the African savannah.

And all this time our ancestors' bodies and brains were getting bigger.

Today, our brains are almost four times the volume of our earliest ancestors,

shaping the way we think and behave.

So why did our ancestors' brains get bigger?

It's such a difficult question

and we're not going to be able to answer it just by looking at their skulls.

But what we can do is look at the wider context, the environment they lived in.

What was going on around here at the time our ancestors' brains were expanding?

The Rift Valley has been called the crucible of human evolution.

It's long been thought that it was the struggle to survive here,

in this harsh habitat, that drove our evolution.

But recently, scientists have been taking a closer look at the rocks here,

looking back in time to see what the environment was really like millions of years ago.

And here, on the side of this hill, is a bit of that environmental sequence.

And you can read it. This area here, that I'm standing on, this white, chalky layer,

is sediment from the bottom of an ancient lake. And inside it, there are microscopic algae diatoms,

that tell us that this was a very deep lake.

As we move up to this layer here, the lake is drying out,

it's becoming much more salty. There are diatoms in here that are salt-loving.

Then there's another change and we've got this yellow/brownish layer here, and that is an ancient soil,

and it's even got the root patterns within it of the grass which once grew on it.

And then this grey layer here is volcanic ash from a distant volcano,

the ash cloud billowed over and dumped right here.

As we walk further up, we start to get another white layer, so we're moving into a lake again.

And then the lake dries out, and we're left this time with a salt flat,

and you can see the surface of it just there.

And then after the salt flat, we're back to a lake again, with this white sediment.

And that spans just 5,000 years.

During our evolution, this area was changing every few hundred years.

This rapid rate of change would have made it difficult to adapt physically.

Instead, the apes here learned to change something else - their behaviour.

Only those individuals who were clever enough to find new ways

of getting food and water as the landscape changed

would have survived and passed on their genes.

At the time our ancestors' brains are expanding,

they were living in this highly fluctuating environment.

And one theory says the two are intrinsically linked,

that those big brains allowed our ancestors to develop highly flexible behaviour.

So rather than that old tale of ancient humans adapting to life on the savannah,

it seems that they were evolving to be adaptable,

to be able to survive and flourish in a range of different environments.

The way our ancestors might have behaved isn't preserved in the fossil record,

but clues can be found in the behaviour of our closest cousins.

Here at Edinburgh Zoo, researchers have been studying chimpanzees,

to get insights into the origins of human intelligence.

Hello. What do you think of me? I'm a bit like you.

Chimps and humans share a common ancestor, going back some seven million years ago.

So, if we compare ourselves with chimpanzees, then we can assume

that any behaviours we share may have been there in our ancestors,

whereas any differences have arisen on the way to becoming modern species.

Like us, the chimps live in a tight-knit social group.

But the social politics here are being thrown into turmoil

by the arrival of a new group from the Netherlands.

Betsy Herrelko is studying how they react.

So coming up in the middle is Claus, the dominant male from the Dutch group,

and we've got Kindia and Qafzeh, the dominant male from the Edinburgh group,

who are just starting to kind of throw ropes around

and it looks like there's a little bit of a face off.

The Dutch chimpanzees quickly assess who's who in the Edinburgh group,

working out whom they can challenge and whom they should suck up to.

Oh, and here we've got a little submission from Lianne,

so she's showing her bottom to him and she's doing a full bare-teethed grin.

In this changing power structure, making and keeping political allies is crucial.

Here we have Claus, with Sophie. Claus is the dominant male of the Dutch group

and Sophie is a lower-ranking female over there.

And she's lower ranking, but she's going up to him, she's not appeasing him, but she's trying to touch him,

just pay attention to him and make sure she's in his good graces, before she feeds right next to him.

So is it really important for the dominant chimp to have alliances, to have friends in the group?

It's very much like our political system, you have to play the field and see who can be your ally

and benefit you in some ways, and when you might need to drop them.

And if you're clever enough to work out whom you can bully,

and whom you need to run away from...

..you can work out other things,

like how to get that apple from the other side of the fence.

And it's mental flexibility like this that enabled our ancestors to adapt to their changing environment.

Looking at the behaviours that we share with chimpanzees,

it's clear that we've inherited cunning brains from our ancestors.

We are social animals, we have this acute sense of political awareness.

We understand what others are doing and where they fit in

in the social system, and we use that to our advantage.

But we differ from chimpanzees in a very important way.

Our ancestors developed a mental ability so useful that it's written into our faces today.

They say the eyes are the windows into the soul.

And our eyes are unique.

We are the only animals on the planet which show the whites of their eyes.

We can do something that no other animal on Earth can do -

we can tell what somebody's thinking just by looking at their eyes.

We can literally read their minds.

It's something most of us start to do naturally from the age of about four.

Children use people's eye gaze to tell what they're thinking.

So the first thing I'd like you to do is,

can you guess which sweets I like?

-No.

-I think this.

Chocolate mice.

You're so clever. How did you guess that?

Because, cos you... cos your eyes were looking at them.

Oh! And you're right.

Well, that seemed very simple,

but in fact our ability to read minds goes much further than that.

We can tell when people are happy, or sad, honest, or deceitful.

This mind-reading means that we don't always take things at face value.

'So here's another quick test.

'I've hidden a sweet under one of the three cups.

'Can they guess where it is, if I tell them one thing...'

I'll give you a clue - he might be under the blue cup.

'..But my eyes tell a different story.'

-Green.

-Green.

'The kids immediately realised I was fibbing

'and, by reading my mind, go straight for the sweets.'

These children are doing something incredibly complex,

they must be thinking, "I know you want me to think the sweet is under here,

"but I think you actually know it's there." So they're seeing through my deceit.

And this degree of mind-reading ability,

this understanding ourselves and others and what others are thinking, is unique to us,

and it underpins all of our ability to share knowledge and ideas with each other.

Our unique ability to read minds is thought to be linked

to one of the most important ideas to emerge in our evolutionary history - learning to make tools.

The ability to make stone tools is one of the defining features of humans, of our genus Homo.

And tools like this were made by the earliest humans, Homo habilis,

going back about 2.5 million years ago.

Homo habilis wasn't much like you or me.

He only had a brain half the size of ours.

Yet he's the first ancestor that we know had tools, and that's why he's called Homo, meaning human.

And these tools enabled him to overcome the challenges of his environment.

These tools allowed them to extend their own biological capabilities.

It was as though they were arming themselves with the tusks,

the sharp teeth and the claws that they didn't naturally possess.

And, crucially, those tools meant that they could get to a much wider range of food

than you'd normally expect an ape to be eating.

And, over time, those tools became more complex.

Within a million years, a new species had evolved, Homo erectus,

slender and tall, with a larger brain that his predecessors.

And that brain was being shaped by his tool-making technology.

Here at Olorgesailie, you can see where Homo erectus people made their tools.

Incredibly, they still lie scattered across the ground,

where they were dropped by ancient hands a million years ago.

Doctor Rick Potts has been studying how they were made.

It's a complex process, which starts with quarrying the rocks.

We're here at a place where the hand axe makers came, almost a million years ago,

and they quarried the volcanic rock

to test which rocks were the best ones to take away as hand axes.

So you're absolutely sure these rocks have been quarried

-by human hand, they're not just naturally broken?

-Yeah, let me show you.

What we found here were thousands and thousands of stone-flaking debris,

and so we're pretty sure that, where you're sitting, a Homo erectus sat,

one of these hand axe makers, a million years ago,

-making stone tools, testing the rock and seeing which hand axes to take away.

-That's amazing.

-This is a moment in time, that long ago.

-It is, yeah.

I sat in the spot, just like you did. It's extraordinary,

it's an intuitive connection to these ancestors, to the hands,

the things that they were capable of.

You can see right here,

where there is a large flake scar.

-Yep.

-And that was struck by using an enormous hammer stone right here.

They were very strong, these hand axe makers.

And we saw dozens of examples of rocks with imperfections that were left behind,

so you can really get a sense of the decisions that these hand axe makers were making right here.

Once the rocks had been selected, they then needed to be shaped,

and that's something you really need to be taught,

because it's far from straightforward.

The principle here is that you strike the edge,

and it sets up force that goes through the rock,

and out from the other side pops a sliver.

-Oh, wow.

-OK?

-Yeah, that's a decent flake.

So there's your flake here. So why don't you have a go?

OK, I'll try. All right then.

-There we go.

-Ooh, that's, oh, that's a nice one.

-There we go, that's a good one.

-Look at that.

-Yeah, that's pretty typical of what you would find at a hand axe site.

And you can see the platform, or the edge that you struck,

and this is the piece that came off and the scar where the flake came.

So the hand axe, when you're finished making it, will be a useful tool in its own right,

-but the flakes that come off it are also useful?

-That's right. The tool can be the sharp flake itself,

or it can be at the sharp edge of the hand axe.

-That's why they sometimes call it the Swiss army knife of the Stone Age.

-Brilliant!

Learning to make a Homo erectus hand axe is surprisingly complex,

and it's only really possible if you understand your teacher's aims and intentions.

You can imagine Homo erectus children sitting there watching their dads

-and possibly their mums making these hand axes and learning how to do it.

-Exactly, that's right.

Here is a real hand axe made by Homo erectus from 900,000 years ago.

Look what you've done, very similar to this, so I think you've done a great job.

That's brilliant. So that is my very own hand axe, I made that.

The tool-making culture of Homo erectus was a turning point in human history.

With tools to butcher meat and protect themselves,

our ancestors were able to spread into new territory and find food and shelter.

For over a million years, the hand axe was the cutting edge of stone tool technology.

A hand axe, together with the flakes that come off it, constitute an incredibly versatile tool kit.

And all these ancient hand axes that are found across the Rift Valley

wouldn't be there, were it not for humans' ability to copy from each other.

Stone Age culture gave us far more than just tools.

It crystallised in us an ability to learn from one another, and to share knowledge.

Stone hand axes, and the more complex culture that follows them,

tell us about the behaviour of our ancestors.

But they also do more than that, they tell us about their minds.

Because, in order to be able to make a complex stone tool,

it certainly helps to be able to understand what other people are thinking.

But you also have to have a mental image,

an abstract idea in your mind of what that tool is going to look like.

And it's been suggested that this mental ability to make stone tools

is related to something else - language.

And the plant life was out of this world.

Her job paid more and it made sense.

-Once the weather improves, I'll be on the allotment.

-What's it called? Brain's gone.

But I was never very sporty at school.

We are unique in our ability to speak.

But the moment when human language first evolved is shrouded in mystery.

Language is such an important human characteristic,

but there's no direct evidence of when it evolved.

We can't even look at the vocal tracts of our ancestors -

they're made of soft tissue, cartilage, muscles, ligaments, membranes.

They don't fossilise like bones do.

The only certainty is that language is central to one human species which emerged in Africa

around 200,000 years ago, and that is us, Homo sapiens.

Well, I'd always wanted to go to Machu Picchu.

We use language in every aspect of our lives,

from idle gossip to sharing our deepest thoughts.

Go to Australia, that's even worse.

Forming this range of sounds involves many parts of our anatomy.

This is a scan of my own head and neck, showing all the anatomy which I use to produce speech,

from the lips at the front, there,

to the teeth, which are there,

the palate, hard palate and then soft palate at the back there.

And this enormous mass of muscle here is my tongue,

which is very important in moulding the sounds coming out of my mouth.

There's the epiglottis, which protects the larynx, the voice box,

and, deep within the larynx, the vocal cords themselves.

Bulb went from my outside light, so he changed the bulb...

And on this amazing real-time MRI scan, you can see them all in action.

Air from my lungs is forced between my vocal cords, causing them to vibrate.

The sound passes upwards and is moulded by my tongue and my lips, emerging as speech.

Aaaaa, eeeee, oooooo.

Feel like a bit of a loony!

Our ability to vocalise our inner thoughts

gave our species the power to teach and learn

at a level of complexity no other animal on Earth can match.

Human language is so much more than just a series of sounds.

It draws on something else which seems to be uniquely human, and that is symbolic thought.

When we name something, we create an abstract representation of it,

and crucially, we can take that idea and share it with someone else.

With language, ideas are not just our own, they become common property.

Using language to share ideas, we could build on the knowledge

and culture of those who had gone before us.

Over time, our brains evolved to be much larger than those of all our ancestors.

But there is a price to pay for having a big brain.

MOANING

SHE PANTS

Giving birth is one of the most painful and dangerous experiences women have to endure.

I've come back to the hospital where I gave birth to my first baby 11 months ago.

And it's very strange being here - it stirs up a real mix of emotions.

I can remember back to certainly fear and pain, but also of course immense joy.

But it does seem rather odd, given that reproduction is essential to the survival of any species,

that, for humans, childbirth can be so difficult and painful.

Allionna is giving birth for the second time,

and although all is going smoothly,

even a straightforward delivery is challenging.

SHE WAILS

And that's all down to the large heads of our big-brained babies.

-The contraction is good, you rest now. OK?

-OK, I'll rest.

Mm, my baby took quite a while to appear.

Erm, she started coming and it took about three and a half days for her to actually emerge.

Erm, and I definitely needed help for that to happen.

It wasn't something I could've done on my own.

-Long pushes.

-I can't.

-Go on, yes you can. Go on, yes you can.

You need to get the baby out now. OK?

Humans are the only species that need help to give birth.

Our babies' heads are so big that it's astounding they can get out at all.

One more push, please. Go on.

OK, when you feel the pain, push against that pain, OK? Push hard.

So you can see the space through which the baby has to pass,

from the inside to the outside, and it is quite a narrow space.

If we look at the size of the baby's head,

you can see that it is going to be a pretty tight fit.

My baby got her head stuck in that position, which wasn't particularly helpful.

Let's put her back in a slightly more co-operative position,

and her head can now drop down inside the pelvis. But it's stuck again,

so she needs to tuck her chin in, rotate round like that, and then the back of her head can come out,

and then the shoulders can come out and the baby is born.

WOMAN SCREAMS

That's it, go on, keep on going, keep going. Keep going.

Come on, that's it, that's my girl, well done, that's it.

Yes, well done, that's it. Well done.

WOMAN SCREAMS

BABY CRIES

We're born with the biggest brain our mother's anatomy can cope with.

But to ensure that a baby like Reuben can be born,

he has to come out before his brain is really ready,

which means he's completely helpless.

Well, this is Reuben. He's such a perfect little baby.

But compared with most newborn mammals, his brain is relatively immature.

He doesn't have much control over his body and even less ability to make sense of the world around him.

It will be about eight years before his brain reaches its full size

and he'll be in his mid-teens before it's properly mature.

Growing our big brains takes time, and while it's happening, our children need looking after.

And that has shaped our lives in ways you might not expect.

To understand how a long childhood growing those big brains has affected our species,

I've come back to Africa.

I've come to meet the Hadza tribe in northern Tanzania.

These are modern people, but living in a similar way to our ancestors,

and their lifestyle gives us an insight into how we all evolved.

I want to talk to the women about something which affects all human societies,

it's a great concern to all of us, and that's childcare.

Getting enough food to feed everyone takes a long time.

Looking after young children whose brains are still developing is hard work.

Nibala has five children and she's got another on the way.

Nibala, how long did you breastfeed your babies for?

Yes, I've got a baby who is 11 months old.

Who is taking care of the baby?

My husband is taking care of my baby.

-Who is breastfeeding actually, Nibala, who is breastfeeding?

-Oh right, oh.

Erm, she, I've stopped breastfeeding now, so I breastfed her until seven months,

and then now she is having a bottle.

-Will it grow up?

-Yes, yes, yes!

LAUGHTER

I think she thinks this is very strange.

And I think, you know, I'm now looking at myself and thinking,

this must sound really odd, this must sound very unnatural and very, very strange. It is.

'It's normal for women here to have a baby every two to three years.

'Feeding the older children while breastfeeding is very difficult without help.

'For Nibala, the only way she can collect enough food is with help from her mother.

'As in many human cultures, it's the grandmothers that play a vital role in caring for their grandchildren.'

How important is their grandmother in providing for your children?

It's not even eight o'clock and it's already blazing.

'It's thought that the need to have extra help from older women

'has actually affected how long we evolved to live for.'

'Magdalena is in her seventies,

'and helps to look after five grandchildren.'

'And Magdalena isn't unusual. Even without modern medicine,

'many Hadza live well into their 70s.'

Having grandmothers around like this to help look after and provide for the children

is such a great advantage,

and one that may have driven the evolution of our unique life histories,

where women survive for decades after their reproductive years, after the menopause.

The fact that women live long past the end of their reproductive years originally baffled scientists.

But it's now thought that, by living into old age and looking after their grandchildren,

grandmothers could help their daughters produce lots of children in quick succession.

By living longer, our species is able to breed more quickly,

in far greater numbers than any other ape.

And this population growth has ensured the success of our species.

Grandmothers and grandfathers would not only pass on important information

to the younger generation, but by supporting their children and grandchildren,

they would help the human population to expand, and eventually spread across the globe.

With their tools, big brains and growing populations,

successive waves of human species left Africa.

First Homo erectus, the hand axe maker.

A million years later, they were followed by another human species, Homo heidelbergensis.

In Europe, they evolved into the Neanderthals.

And in Africa, they became us, Homo sapiens.

And it was from Africa that our species spread out to colonise the world.

With our large brains, we flourished in new environments.

But we weren't alone.

We know from fossils and archaeology that our pioneering ancestors

weren't heading into virgin territory.

Around the world, there were other species of humans

already living there when we arrived.

In Europe, Homo sapiens were entering the territory of the Neanderthals.

Neanderthals were a species of human very similar to us.

They were a physically formidable competitor, heavily built,

with short limbs adapted for the colder climate.

They may have been strong,

but they have developed a reputation for being dim-witted.

Because within a few thousand years of Homo sapiens arriving in Europe, the Neanderthals,

like every other human species before, went extinct.

It's always been thought the reason for our survival was our superior intelligence.

This is me, this is my skull, which is a perfect specimen, of course, of a modern human,

and this is a Neanderthal.

And I hope you'll agree that they look distinctly different,

especially when we look at the faces.

The Neanderthal has a massive brow ridge over the eyes,

and then a sloped-back, a swept-back forehead,

whereas I've got a very slight brow ridge, if it's there at all,

and then a very, very steep frontal bone, a steep forehead.

The faces are very different,

but there's an overwhelming similarity here,

and that is in the size of the brain cases. Neanderthals had about the same size brains as us.

So, if we're going on brain size alone,

there's nothing to suggest that I should be any cleverer than a Neanderthal.

So, if Neanderthals and Homo sapiens both had similarly large brains,

why is it that today there's just us left?

'At the Max Planck Institute in Leipzig, scientists are trying to understand

'the secret of our success at a genetic level.'

'They have achieved what was once thought impossible,

'by searching for clues within Neanderthal DNA.'

It's incredible to think that it's possible to extract tiny fragments of DNA

from the bones of somebody who lived tens of thousands of years ago,

and then to piece together those fragments to get the genetic code of an extinct human.

That genome holds clues to the workings of the Neanderthal body and brain.

Extracting DNA from ancient bones is a painstaking and complex process.

'Professor Svante Paabo is head of the team trying to compare our DNA with that of the Neanderthals.'

And what can Neanderthal DNA tell us about me?

First of all, what it confirms is that we are very close relatives to Neanderthals.

We share a common origin,

something like 2, 300,000 years ago.

Even since then, there have been interactions with Neanderthals,

there has been interbreeding between Neanderthals and early modern ancestors.

-So, in part, I'm a Neanderthal?

-Yes.

The Neanderthals are not quite extinct, if you like,

they live on in some of us a little bit today.

'As well as showing a degree of interbreeding between us and our cousins,

'Neanderthal DNA has revealed clues about their brains.

'The team here has discovered that Neanderthals share with us

'the exact same form of a gene called FOXP2, which is connected with language.

'So it's possible they had similar abilities to speak.'

The scientists in there are combing through the Neanderthal genome,

the vast majority of which is the same as ours.

But what's really remarkable, what they're really looking for are those differences,

so we're learning more about Neanderthals and about what makes us truly unique.

I think sort of the billion dollar question to me

over the next 20, 30 years in this field would be to find the genetic background

for things like why did technology and culture take off in fully modern humans as it has?

What made it possible for us to colonise the entire planet,

every speck of land, something that other early forms of humans never did?

'While the geneticists continue their search for answers,

'if we want to understand why we're here, and the Neanderthals aren't,

'we need to go back to where they lived.'

'I've come to the British colonial outpost of Gibraltar.

'We know that about 10,000 years after modern humans arrived in Europe,

'the Neanderthals had disappeared.

'So was this down to us outsmarting them?'

We know from the fossils that Neanderthals had brains as big as ours

and the genetics is now starting to give us glimpses of what that brain might have functioned like,

so we know that we share a gene with the Neanderthals which is involved in speech.

But the best chance we have of getting to know the Neanderthals

and finding out just how similar or different they were to us,

is by looking at the physical traces of their behaviour.

Archaeologist Clive Finlayson has been studying the traces of our extinct cousins.

So do you feel quite close to these people that you're investigating here?

Very much indeed. They're enigmatic, there are always more questions,

but you feel you begin to understand them

when you begin to uncover their way of life.

'Much of Clive's research has been centred on a site called Gorham's Cave.

'Today, it's only accessible by sea.'

Thanks, Darren.

'This cave has revealed much about the way Neanderthals lived and behaved,

'compared with the way modern humans were living at the same time.'

Yeah, it's amazing to stand here and imagine what it must have been like

when the sea was so much lower and so much further out.

There were times when the sea would've been all the way down as far as that ship in the distance,

and all this would have been the landscape, you know, of pine woods and wetlands,

a little paradise, a little Eden for the Neanderthals.

'It used to be thought that Neanderthals had a very limited diet, mostly eating big game.

'But the cave has revealed some surprising finds.'

-I can show you little bits of marine molluscs.

-Yep, little bits of shell.

The sea never came up here, so they would've been transported.

And you can see the little flakes of bits of flint, they were transported by people.

It's clear evidence that Neanderthals were eating marine molluscs,

-one of these things which is meant to be a speciality of modern humans.

-Yeah.

'Beyond the food waste left behind, the tools they used tell us a lot about their intelligence.'

This is a typical flake, made by a Neanderthal, multi-purpose, but still got a sharp edge as you can see.

-It's very sharp.

-So, nice for cutting. The modern humans tend to make these sort of blades,

which are more sort of long and narrower than the flakes.

Some people made this to be an important distinction

but it's probably just a different style of doing it.

So they're using a different tool kit, but they're achieving the same ends?

The evidence suggests that they're just as intelligent as we were,

but maybe did things a different way.

'It's clearly far too simplistic to dismiss Neanderthals as being too stupid to survive.

'Further back in the cave, Clive has uncovered more evidence of our extinct cousins.'

So welcome to the real Gorham's Cave.

-This is it.

-Oh, wow!

Gosh, you've got no idea of the extent of it as you come in.

-So were the Neanderthals living this deep in the cave?

-Absolutely. This was the big surprise.

It's not a normal thing for Neanderthals to live at the back of caves,

they didn't like it, but this seems to be a special cave in many ways.

As you come down this way - be careful because it's been wet -

it's rained a lot and it's slippery - but if you come along this way,

this is a huge cavern that goes back 35 metres. Now...

-Can I get, can I get in past there?

-You can get a little bit in, yes, by all means.

-Get an idea of how deep it is.

-So what they had was a large chamber,

and they're sleeping in there.

This feels like it would've been a safe place to spend the night.

It's a perfect choice. These guys knew what they were doing.

'It's back here that Clive made his most important discovery.'

-So are you OK there?

-Yep, yep.

-In there, we excavated a half a camp fire...

-Yep.

..made by Neanderthals.

And we got radiocarbon date to around 28,000 years ago.

And, to date, it's the last known site, the last place

where the Neanderthals lived on the planet, is right there.

This is a really special place, this cave -

the archaeology here is quite remarkable.

But it's also very emotive.

It's quite sad to sit here

and know that this was one of the last places that the Neanderthals lived in.

So, if they had brains as big as ours, and were just as clever as us,

why did Neanderthals die out, while we went on to flourish?

In the centuries before the Neanderthals' demise,

there was dramatic climate change across Europe.

The woodlands that Neanderthals were used to shrank,

giving way to open landscapes, where modern humans thrived.

Do you see the eventual demise of the Neanderthals then really being, you know,

a lot of chance but, but really being down to climate change?

I think their luck ran out. They were exploiting a kind of environment that needed some trees for cover.

They were ambush hunters, they got close to their prey.

But they weren't built to be out on the open plains.

It just happens that that landscape expanded at the moment

when those modern humans have come in, and they tracked these resources, so they spread with that environment.

And, as the modern human population increased,

the Neanderthal population declined, leaving small, isolated groups.

Something as simple as a bad winter or a prolonged drought could have easily wiped them out.

The more we learn about the Neanderthals, the more like us they seem to have been.

They were just another human population which, like so many others, has died out.

But, as the Neanderthals were disappearing from Europe,

something extraordinary was happening amongst the modern human populations who replaced them -

a huge cultural explosion.

Over the next 30,000 years,

we would leave our mark on the world,

creating wonderful art, and places of worship.

Inventing farming and engineering to create a new world,

building civilisations.

Mapping and exploring the planet,

we mechanised and urbanised and extended our reach up to the stars.

In the blink of an evolutionary eye, we have created a world for ourselves

which has changed beyond recognition.

There is this great mystery which lies at the heart of human evolution,

and it has to do with the way we use our brains.

Because, for tens of thousands of years, our modern human ancestors lived very simple lives

and made basic tools out of stone and wood.

And then look at where we are today, at what we can build, and our technology.

It just seems utterly mind-blowing that we're the same species which made those stone tools.

It's been suggested that all this cultural change must be linked to a biological change in our brains.

But the latest thinking suggests it's a product of something far more basic, a simple increase in numbers.

As populations increase, ideas are passed on to more and more people,

and there's a greater chance that any inventions, any innovations, will get picked up and will spread.

The ideas then take on a life of their own, competing with each other,

improving and proliferating, and that is cultural evolution.

What's it called? Brain's gone.

'Over millions of years, our brains evolved to enable us to pass on ideas,

'to learn from one another.' Oh wow.

'And to read each other's minds.

'Combine that with an ability to expand our numbers

'because we live longer, with grandmothers helping to raise our big-brained children,

'and what you have is a perfect storm of biological and cultural evolution,

'that has taken us from making simple stone tools

'to creating the vast edifices of the modern world.

'We have evolved to think and behave in ways that have turned out to be incredibly successful.'

We have an unrivalled ability to co-operate with each other,

to communicate, to understand what others are thinking and feeling,

and to generate culture and technology.

And as our population grew,

so too did the cumulative effects of people's contributions to society, generation on generation.

But all of those abilities that make us human, that bring us to where we are today,

really come down to just one thing, one bit of each of us,

our amazingly complex and clever brains.

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