Out of Africa The Incredible Human Journey

They say this is where it all began.

That we are all children of Africa.

But if so, why do we look so different?

And how on earth could a handful of African families become a whole world full of people?

I'm Alice Roberts, medical doctor and anthropologist.

I'm fascinated by what bones,

stones,

and even our bodies can reveal about the distant past.

I'm going in search of where the first people were born

and how they began their journey to populate the world.

'Leaving Africa was virtually impossible,

'but new evidence suggests just one tiny group might have done it.'

I just think it's absolutely remarkable.

Isn't that amazing? It's stunning.

'Can I find their trail out of Africa and across the world and discover

'how those journeys changed them to become who we are today?'

Come with me in the footsteps of our ancestors, on the most epic adventure ever undertaken.

Ask yourself, where do you come from?

How did the first humans become you?

It's a surprisingly tricky question.

And in search of an answer, I'm starting in East Africa.

I've dreamt about coming to this place since I was a teenager.

As unlikely as it sounds, palaeontologists now think

they have a pretty good idea of where we modern humans first appeared.

And I'm trying to get there.

But it is in one of the most remote parts of the continent.

I'm heading to Africa's Great Rift Valley,

and the Omo River in Ethiopia.

Very few foreigners ever come here.

The place I'm trying to reach lies on the far western side of the Omo.

There are no bridges for hundreds of miles,

so my best option is the slightly leaky passenger ferry...

past the crocodiles.

That's quite a welcoming committee.

Hello.

I'm looking for the route taken by a scientific expedition about 40 years ago.

They stumbled across perhaps the most important clue about the beginning of our species.

I've got map co-ordinates, but there are no obvious tracks to follow.

I think what I'm going to do is head to Kibish, the nearest village, and get some local help.

'Kibish is home to the Nyangatom tribe.'

Soya, salaam.

-How are you?

-I'm well. How are you?

I'm fine.

-I need to find a very particular place.

-Mm-hm.

'My only chance of help is if the chief agrees.'

THEY SPEAK IN DIALECT

Soya, can you tell him why I'm here?

Can you say that I'm here to find the place where people were digging?

This all sounds very promising.

-He said someone was digging.

-"Someone was digging..."

-And he found something like bone,

and, I don't know, he said that the bone had stayed there for a long time.

When can we go? Can you ask them?

THEY SPEAK IN DIALECT

-Let's go now.

-We can go now?

'I'm not sure that these guys know where they're going.

'But they seem to have come prepared for something.'

Why is he carrying a gun?

HE ASKS IN DIALECT

For protection.

For protection from whom?

-For protection from enemies.

-Right.

Like Surma, Turkana...and Mursi.

-So these are other tribes?

-Yeah, they're other tribes.

-Are they likely to attack us?

-Yeah, they just come to attack them.

-So there's always fighting going on?

-Yeah, they're always fighting.

-Right.

'It's noon and the temperature has soared into the 40s.

'Although I've wanted to come here for years,

'after four hours in this searing heat, I'm not sure I'm going to make it.'

-So what are they saying?

-They say it's there.

-Really?

-Yeah.

-That's where it was found? Just here? Just there?

Just there.

Well, this is it. This is the place, because this is where

the earliest human remains in the entire world were discovered.

It's been really difficult to find it.

It's taken us four hours to walk here and we've been on a circuitous route through the bush

and it seems really strange that

there's nothing to mark it,

because this is such an important place

in our story.

And it's as close as I can get

to where we all began.

Amazing.

'And this is what the archaeologists discovered.'

This is a cast of the skull that was found here

and which was dated to 195,000 years ago.

I think, considering it's so old, it's remarkably complete.

OK, the fragile face bones are missing,

but most of the brain case is here.

We can see the size of the brain

and we can see this very characteristic forehead.

'No other remains of our species even approaching this age

'have been found anywhere else on the planet.

'This is as near as we can get to the origin of our species.'

There's something very special about sitting here, looking out at the Omo.

I could be on the banks of any African river, apart from the fact we know that this landscape

has been home to humans, people like you and me,

for nearly 200,000 years.

So if this is where we first appeared, what did we come from?

The evidence suggests that the very first human-like creatures

evolved in Africa over 4 million years ago.

They were much more ape-like than us.

A series of human species

with gradually bigger brains came and went.

The most recent, and only surviving, is our own species -

Homo sapiens, modern humans.

Here is a skull of one of our nearest ancient human relatives, Homo heidelbergensis.

If we compare it with this modern skull, some things just leap out at you.

This heidelbergensis skull has an enormous brow ridge

and a swept-back, sloping forehead - much steeper in the modern skull.

In fact, the whole brain case here is much rounder.

Using the skull of the ancient human,

experts have reconstructed his face...

..to reveal our flatter-headed, beetle-browed predecessor.

Contrast with this reconstruction of a very old but modern human,

and I think you'll agree that she looks a lot more like me.

But if East Africa is where the first humans were born, there are some big questions to answer.

Are we all descended from black Africans?

If so, why do most of us look so different?

And how could a handful of people from such an isolated place

go on to colonise first Africa...

..and then the rest of the world?

So what do we know about these shadowy first families?

200,000 years ago, it's likely there were so few of them,

living such a precarious existence, that today they'd be classified as an endangered species.

Life was fragile and the African savannah was a dangerous place.

Well, I'm going to be spending the night out here in the bush,

presumably something our ancestors did all the time.

But years of living in civilisation have softened me.

I've got a big torch here, so if anything comes by I can get a better look at it in the dark.

And I've got this little camera so I can make a video diary throughout the night

and talk about what comes along.

I'm doing this for real.

I'm going to be out here all night and I really am quite scared.

ANIMAL CHATTERS

-WHISPERING:

-It's just amazing the amount of noises you suddenly hear.

About half an hour ago, there was the sound,

a really distinct sound, of something lapping water.

Maybe a hyena, maybe a leopard.

It sounded like a big cat. Literally like a cat lapping up milk.

Hopefully nothing can get through that.

I suddenly feel really vulnerable as an animal which is designed to be out in the daylight.

I mean, we can't see very well at night,

hearing's all right, just about enough to get you feeling scared.

-And sense of smell as well.

-SHE SNIFFS

Compared to all those other animals, might as well not have it.

-ROARING

-Did you hear that?

-I'm scared now.

-HOWLING

HOWLING RESUMES

Is that a...? Is that a lion?

Is that a leopard?

Is that...?

Is that a hyena?

HOWLING

Oh, I don't like that noise.

That's really spooky.

That's got to be one of the most frightening nights of my life.

I did get some sleep, but then I got woken up by these horrendous noises.

Sometimes it was hyenas

and then there was something that sounded like a stand-off

between a hyena and leopard or something. I don't know what it was.

Awful noises.

Really, really scary.

With the return of the crew, I pluck up my courage

and look for signs of the animals that I heard in the night.

Oh, just look at this.

This is a big male leopard paw print and there

are large hyena prints as well.

So these predators, these carnivores, were literally here,

about 25 metres away from where I was sleeping, underneath that tree.

They sounded really close during the night.

I can see now that they were.

At night time especially, our ancestors must have been very vulnerable.

So how did those first families survive,

let alone go on to spread across the world?

In the hope of finding out more, I'm heading south to Namibia.

I'm meeting one of the last groups of hunter-gatherers

on this continent - the bushmen of the Kalahari.

What's your name?

My name is Sedre.

-Se... Sedre?

-Sedre.

Their way of life is the closest I can find to that of our ancestors.

The bushmen are expert hunters.

But before I see how they do it, I want to persuade Kun and Au to take part in a little experiment.

Kun...

I need to check your body temperature using this. Is that all right?

I'm going to put it in your ear, like that.

Right, I'm just going to pop it in there.

-ELECTRONIC BEEP

-Lovely. 36.2.

-Oh, I see.

-That's how hot you are.

-That's my ears.

-Yes.

-OK.

Au, I need to do it to you as well. There we go. It's ready

to take your temperature.

-ELECTRONIC BEEP

-Right, 35.8.

You're even cooler. You're very cool.

THEY SPEAK IN DIALECT

It's turned into a competition.

'Humans usually hunt in the day, so I want to see how our bodies cope with this blazing heat.'

It's a pretty relentless pace.

'We're looking for the trail of an antelope.'

What have you found?

Right, this is really exciting. We've got an oryx track

and we're gonna follow it. I'm gonna have to be really quiet now.

'We've got to move fast to gain on the oryx.

'We've been walking and running for over an hour when we find more prints.

'But not the ones we were hoping for.'

THEY SPEAK IN DIALECT

I think we give up the chase at this point. The animal has been chased by a hyena.

We don't know if it lived to tell the tale either.

But no dinner for us.

'It's now just past midday and the temperature is in the high 30s.

'So what effect has all this running in the heat had on our body temperatures?'

37.4, so a bit hotter than you were before.

I'll try you as well.

ELECTRONIC BEEP

-Ooh, 36.7. Cooler than him.

-THE MEN LAUGH

Now what about me? Let's take mine.

ELECTRONIC BEEP

It's 36.9. We've beaten him!

'Incredibly, our temperatures have barely risen.'

The key to this is that we're all regulating our body temperatures, even in this heat.

And this is the secret - we keep cool by sweating,

something humans do more effectively than most mammals.

Not having fur, we can sweat from glands all over our bodies,

which allows us to keep moving in pursuit of prey for hours without overheating...

..even in the middle of the day, when most big predators are just trying to keep cool.

And there are other things about your body designed specifically for running.

And this is one of them.

Yes, it's a foot and it is brilliantly designed to provide spring.

The ligaments and tendons support the sprung arches of the foot,

so that every time our foot hits the ground,

the spring stores and then releases energy,

making running more efficient.

And there's a really important muscle in our bums.

Our gluteus maximus muscle is huge and we hardly use it at all when we're walking.

But it comes into its own when we run.

So all of these adaptations suggest that running,

especially over long distances, was really important to our early ancestors.

But there was something else that may have really given our ancient ancestors the edge.

SHE SPEAKS IN LANGUAGE WITH PALATAL CLICKS

'Language. The ability to communicate and plan.'

Red, yellow, green.

How do you say it?

THEY ANSWER WITH PALATAL CLICK

'We don't know when people started to speak,

'but there's evidence that languages like this, click languages, may be the oldest in the world.

SHE SPEAKS IN LANGUAGE WITH PALATAL CLICKS

'So it's possible the first families sounded a bit like this.'

It is an amazing language. Every sentence is peppered with these

clicks and tutting noises that are consonants.

They're just very unlike any consonants

that I'm used to pronouncing, so I'm struggling with it.

-So this is...

-SHE ATTEMPTS PALATAL CLICK

See, I think it's easier to say "yellow"!

'And it's a type of language that could have been crucial to our ancestors' survival.'

It may be that these click languages have been around for so long

because they're particularly useful during hunting.

Apparently, when the bushmen are stalking an animal, they drop

their voices to a whisper, so they're talking almost entirely in clicks, which make a lot of sense to me.

The clicks are high-pitched noises - they don't travel far through the bush,

so the hunters aren't going to scare off their quarry.

Equipped with language and hunting skills, we flourished.

And began to do something else - spread out.

We don't know for sure which routes they took,

but new evidence shows that very early on, modern humans

were living at the extreme southern edge of the continent.

I'm heading along the South African coast

to a place called Pinnacle Point.

Today, it's a playground for the rich.

But during the construction of this golf course,

archaeologists discovered something amazing deep beneath the fairway.

This could be the oldest known dwelling of our species anywhere in the world.

So, this is where you've been digging.

This is the oldest part of the cave.

What are the dates here then, as we go down through these layers?

These layers date from 130,000 to 167,000 years ago.

-It's just so incredibly ancient.

-It's amazing.

-Did you know how important what you were excavating really was?

-Not until we got those dates.

But, yeah. Amazing, stunning.

The evidence in this cave reveals that those ancient families were

behaving in ways quite unlike previous species of human.

That's not from this cave, is it? Cos I recognise this. This is a hand-axe.

Yes, that's more typical of what you would find from about 1.5 million years ago

-to about 300,000 years ago.

-So what sort of thing were you finding in the cave, then?

OK, tools like these.

Blades and points are much more typical of what we find here.

Made on quartzite, locally available on the beach down here.

In our oldest levels here, alongside these types of tools,

-we also have these very small bladelet tools.

-These are tiny.

'What could such minute blades have been used for?'

Obviously these weren't used just in your hand, like this, so how would they have been used?

It's more likely that those were set in some kind of a handle

to make a compound tool, maybe something more like this.

This is a series of small blades set into a handle for use as a knife.

Yes, I think that would work.

So you think that's how these stone tools were used then, as a knife?

That's one possibility. It's also possible they would have been used for hunting weapons.

'Kyle and his team have discovered you can make some lethal weapons with these bladelets.'

This one looks particularly vicious.

This is one interpretation of how

those small-back blades might have been mounted.

The advantage to this would be

that there's these barbs that would prevent

the tip from pulling out immediately and would inflict a greater injury.

So by 160,000 years ago, those early resourceful families

seemed to have colonised much of Africa.

But what about the rest of the world?

How did some of those ancient wanderers get out of Africa to become me and perhaps you?

It's one of the most baffling mysteries of our origins.

Africa south of the Sahara is cut off from the rest of the planet.

To the west, south

and east - ocean.

To the north, the vast deserts of the Sahara and Arabia.

So could there be another way that people first appeared all over the world?

Did they, as some have suggested, evolve separately on different continents?

It's a huge question.

A different branch of science is beginning to provide very surprising answers.

To find out more, I've come to Cape Town.

Cape Town today is a world city with representatives

of just about every group and creed you can possibly imagine.

And every single one of these people

unknowingly carries inside them a story of their ancient ancestors.

That's because buried in the genes of each of us is an indelible record of our past.

By studying DNA from people all over the world, geneticists are piecing together that ancient story.

Cape Town, a product of its colonial past, has citizens

who bring their own genetic stories from every corner of the planet.

And the minute differences in their DNA provide clues about

the ancient migrations that led our species to colonise the world.

Thanks again, folks, for coming.

This is the tree of humanity.

'Geneticist Raj Ramesar has used these differences to help

'build a global family tree by tracing genes down the female line.

'Our modern genes are the branches of the tree

'and geneticists have followed them back in time

'to find our ancient roots.

'The DNA of everyone alive today fits somewhere on this tree.

'Although it's not always obvious exactly where you fit.'

Stephen, where do you think your maternal heritage stems from?

Probably Southern Europe.

The Italian community - that's where my family comes from.

Well, actually, you are on a European branch but you're on a European branch up here.

That's much more Northern Europe. So I'm very sorry, you're not Italian, you're a Laplander!

LAUGHTER

But follow the branches back to the beginning and the tree reveals

that ultimately, we all have our roots in the same place.

There's no question from the genetic data that is generated

on the people here, as well as other studies

that have been done, that humanity arose in Africa.

That's where the depth of this thick trunk illustrates

where the majority of humanity can look for its roots.

So because we originated in Africa, there's been more time

for branches to develop here than there has been anywhere else?

Yeah, that's a crucial point.

Humanity has spent most of its life in Africa.

-I'm African!

-LAUGHTER

-Yes, my cousin!

-We all are.

Absolutely. It's only more recently that we see this aspect of the tree.

'But the really amazing thing is what the tree tells us about those who left Africa.

'You might expect lots of branches,

'lots of genetic lineages, leaving Africa at different times.

'But instead, the rest of the world connects back to Africa

'through one thin branch.

'What does that mean?'

There was a single branching out of Africa.

It amounts to, historically, a single band of individuals leaving the African continent.

So that was the original migration out of Africa that we can track with DNA.

From there, there were branchings out in many different directions,

into Europe, into the rest of Asia, Eurasia, to the north and then down

to Australia and Japan and ultimately to the Americas on the other side.

'Geneticists across the world have come to the same conclusions.

'Everyone outside Africa descends from not many, but just one tiny group of pioneers.'

I just think it's absolutely remarkable. Isn't that amazing?

It's stunning, yeah.

Oh, wow, man!

It may be that others tried too.

But their descendants have not survived.

So the genetics tells us our species

made just one successful attempt to leave and this wasn't a mass exodus.

It was a small group of people taking one route out of Africa.

And everybody in the world today who isn't African is descended from that handful of people.

It's just mind-boggling to think how different the

world would be today if it weren't for that small group of pioneers.

And it begs the next question -

which route did they take?

The genetics may be convincing, but the geography is a huge problem.

For these early families, deserts and oceans would have been massive obstacles.

But we know they did it somehow.

From this map, I think there are perhaps four possible routes out of Africa.

Across the Strait of Gibraltar here, so a bit of a sea-crossing.

From Tunisia, up through Sicily and Italy -

even more sea to cross there.

Down here, across the mouth of the Red Sea,

but you'd need a boat for that as well.

Or here, through the Sahara and Sinai deserts.

Well, all of those routes have their challenges,

but we know that it was just one of them that was taken.

So which one was it?

It's a real puzzle, but could it be

that the world was different back then?

Well, there is a way to find out.

We've asked a team of Britain's leading climate scientists to work out how

the global environment has changed,

going back over thousands of years.

And the answer is in here. With this climate computer,

I can look at the changing environment over time.

Starting at 140,000 years ago, we're moving towards the present.

Forests and grasslands are green and deserts, light brown.

Now this is interesting.

125,000 years ago, there's a change in the climate.

It's been very dry in this area and then suddenly it gets greener.

And the world's biggest, driest,

most-impassable desert briefly blossoms.

For just a few thousand years,

the Sahara, Sinai

and Arabian deserts were lush and green.

So it looks like 125,000 years ago it would have been possible for our ancestors to have walked

through the Sahara and leave Africa to the northeast.

I'm after some evidence that at least one band of pioneers

made it to the other side of the Sahara

and through that northern exit to the rest of the world.

I'm on my way to Israel and the site of an intriguing discovery.

But one which may present as many questions as answers.

Back in the 1930s, an international team of archaeologists

was excavating here at Skhul Cave.

But it's what was found outside the cave that was really interesting.

The archaeologists dug down through 1.5m of soil just here,

finding masses and masses of stone tools.

But as they got down close to the bedrock, they found something even more exciting -

human burials. Ten of them.

When the bones were dated, they were found to be

about 100,000 years old -

the oldest modern-human remains outside Africa.

The dates fit well with that greening of the Sahara.

So could these people be the pioneers I'm looking for,

whose descendants went on to populate the rest of the world?

Some of their remains are now kept in the Rockefeller Museum in Jerusalem.

This skeleton is incredibly well-preserved.

And the main reason for that is that the bodies at Skhul

weren't just left on the surface of the ground.

They were deliberately buried.

And not only that, they were buried with objects, with shell beads,

and one of them even had a boar's jaw enclosed in its arms.

Surely this is further evidence

for modern ways of thinking and behaving.

For spirituality,

and perhaps even a belief in the afterlife.

But not everything here is what it seems.

These people may well have been the first to leave Africa,

but it looks like they can't be our ancestors...

because the trail then dries up.

All evidence of modern humans disappears.

It looks like these families died out completely...

..around 90,000 years ago, when the Middle Eastern Sahara

returned to desert, and life here became impossible.

For our species, it seems that this was a dead end

and it shows just how fragile our existence was,

and what a massive impact climate change could have on a human population.

But it wasn't the end of the human journey.

So where was that elusive route out of Africa?

The Sahara desert once again closed the door on any migration north,

leaving just one of my four routes out of Africa - the Red Sea.

If they did try to cross it, the most likely point is at its mouth -

the Gate of Grief.

Could at least a few families have broken out of Africa here?

Below me is the Red Sea, and to the west, the small African state of Djibouti.

And over to the east, I can just about make out

the coast of Yemen on the tip of the Arabian Peninsula.

At this point, it is just 30km between Africa and Arabia.

30km of sea is still a big problem if you don't have a sea-going vessel.

But from about 90,000 years ago, something interesting began to happen.

The very same climate change that had turned the Sahara back to desert

had another impact.

It made sea levels drop.

And at the Gate of Grief,

the gap between Africa and Arabia became much smaller.

As sea levels fell, the distance across the Red Sea at this point dropped to just 11km.

So perhaps here at last was a chance to risk everything,

to cross the Gate of Grief and take a step into the unknown.

And geneticists working for this series have been able to estimate

how many people made that leap out of Africa,

whichever way they took.

They estimate the size of this group that made the crossing

from Africa to Arabia was just a few hundred people.

And geneticists have now tested the DNA of thousands and thousands of non-Africans

and not one single person has been found

who can't trace their ancestry back to this tiny group of wanderers.

It may have been just a single tribe.

And whatever you look like, if you're not African, you descend from them.

But getting beyond the Red Sea may have been the easy bit.

I'm leaving Africa to travel deep into Arabia.

And here I'm confronted by another great mystery.

How could those pioneers have survived here?

Back then, most of Arabia was brutal desert, pretty much as it is today.

Is it really possible that a handful of Stone-Age people

could have trekked through hundreds of miles of this and gone on to populate the whole world?

Well, here's one man who looks like he knows how to get around in the desert.

Archaeologist Jeff Rose has spent years scouring Arabia for evidence of our earliest ancestors.

And he's come to meet me in Oman.

-Jeff.

-Hello.

-Hello, how are you?

-So, Jeff, why are we in this desolate place?

-It's actually quite a special location.

You see all these black rocks that are lying across the surface?

Yeah, there's a particular concentration of them just round here.

Well, they're not really rocks. They're all ancient stone tools made by early humans.

If we just pick this piece up here,

it's got this flat surface and this surface with flake scars on it.

And they've done some re-touch on it.

They've hit it here and here to create this chisel-like edge.

So that can't have occurred naturally?

No. This couldn't have occurred naturally

because of the pattern of scars that we see here. It's called a burin.

They would have been used for working soft materials - hides, leather, bone, wood,

anything like that - for carving tools out of that.

-So it's a little bit like a chisel?

-Yeah.

It's amazing to pick up a stone tool just lying on the surface.

You get used to it working in Arabia cos they're everywhere. They cover the surface everywhere.

-If they've got flat surfaces on, are they likely to be...?

-Just about anything you see that's flat-lying.

-Even things like that?

-That's from the edge of a blade, so that's called "cortex".

-Yeah.

A lot of times they leave that cortex on because if you're using it, you're not gonna cut yourself.

So you can see how they would have held it. Something like that.

-That makes a neat little knife.

-Exactly.

-OK, so what is the date of this site?

-I'm putting you on the spot here!

-Well, it's hard to say.

It's a surface site, so it's impossible to date anything specifically.

But from that technology, from that core I showed you, we can say

it's anywhere between 70,000 and 12,000 years ago and maybe even earlier.

-As long ago as 70,000 years?

-There was a site that was recently found on the Red Sea coast in Yemen

that was dated to about 70,000 years ago and it's the same technology.

So there were people here 70,000 years ago.

I find that really difficult to believe because at that time

the landscape would have been just as dry and harsh as it is today.

I mean, OK, there's stone to make tools out of.

But where were they living?

The biggest problem for those pioneering families would have been the lack of water.

But a few short miles from these arid mountains, I'm in for a surprise.

Well, just look at this. I'm only two miles away from the desert here, but I could be in rural Somerset.

If it weren't for

the camels!

I'm definitely in Arabia.

This place, near the coast of Oman, sits right on the edge of the monsoon region of the Indian Ocean.

Every year, the monsoons turn this valley into a green oasis...

..somewhere you can imagine our ancestors flourishing.

But this is a green island in the middle of the desert.

The desert stretches on for hundreds of miles around here.

So how did our ancestors move through Arabia...

to reach the world beyond?

There's no way they could have done it without more widespread sources of fresh water.

But where are they?

I'm at sea just off the coast of Oman, a coastline that our ancestors may have passed along.

Except that 70,000 years ago, the coast wouldn't have been there

because the sea level was much lower -

it was up to 50km in that direction.

And Jeff Rose thinks that the key to our ancestors' journey along this coast lies at the bottom of the sea.

One of the strangest things about Arabia

is we have this dry surface, this completely arid landscape,

and yet beneath the surface there are heaps of fresh water

that's bubbling, running towards the coast, and coming up directly beneath us.

Down below, if you were to dive down with a canteen, you could fill it up with fresh water.

-So the springs down there are still working?

-Yes. There's heaps of fresh water coming towards the coast.

Only when the sea level was lower would it have been available.

It really shows why that coastline was so important for early humans moving out of Africa.

So around 70,000 years ago, the Arabian coastline was very different to today.

Freshwater springs bubbled up all the way along it.

If our ancestors attempted this route, they would have found a lifeline...

..stretching all the way from the Red Sea to the Persian Gulf...

..a place which back then was a great fertile plain.

So the Gulf as we know it today didn't exist.

It was a vast, green, lush plain.

Green and lush. You had estuaries and rivers and lakes.

It was probably the most important place in Southwest Asia for all early humans

because so much fresh water was available at that time.

-So they had everything they needed for survival.

-It sounds idyllic.

-It was.

Finding the route that our ancestors took out of Africa has been challenging.

But I really think that this could have been it.

And it's perhaps no wonder, with the obstacles they faced,

that there seems to have been just one successful attempt.

A massive leap in our ancestors' journey.

Africa was the original home of our species and it was our only home

for tens of thousands of years until a small handful of people made their way out of Africa.

And it was their descendants that went on to colonise the rest of the world.

I'm going to try to trace their footsteps as we continue on the Great Human Journey.

'Come with me as I travel right across the world...'

This is looking like a pretty big footprint.

'..in search of the traces left by our ancestors.'

-That's the original?

-Yes, all original.

-I didn't know any of it had survived.

'I want to know how so few people could have populated the rest of the planet.'

That makes us re-think all of our theories about early Americans.

'Facing the unimaginable...

'..rival species...

'and even near extinction...'

I don't think I've ever been so cold in my entire life.

'..to reach the most distant corners of the world.'

I'm worried we're gonna get swept in by these breakers.

'And how did those journeys change us into who we are today?'

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