The Incredible Human Journey (2009) s01e05 Episode Script

The Americas

ALICE ROBERTS: 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 the traces left by our African ancestors and their journeys to populate the world.
This time, the Americas, seemingly impossible to reach.
Ow! In one direction, a vast wall of ice.
In the other, thousands of miles of empty ocean.
It just doesn't seem to stack up.
That makes us rethink all of our theories about early Americans.
So how did people reach the Americas? Come with me in the footsteps of our ancestors on the most epic adventure ever undertaken.
With a modern population of almost a billion, it's easy to forget that until quite recently not a single person lived in the Americas.
For our ancient ancestors, there were two very good reasons for this.
To the south, the vast, uncrossable Pacific Ocean, and to the north, ice.
At the peak of the last Ice Age much of North America was swathed in a massive blanket of ice up to 3 kilometres deep.
I've come to the Ipsuit Glacier in Canada, a remnant of those ancient ice sheets, to try to understand the challenge facing our ancestors.
JIM: Just do everything very gently.
ROBERTS: My guide is Jim Orava.
He's climbed some of the world's most formidable peaks.
This is making me somewhat nervous.
Jim is going up a vertical wall of ice with a couple of ice axes and crampons.
Okay, we're just about to bring you up now, Alice.
Jim's just put an ice screw in up there and he's belaying me with this rope.
So if I do fall, I shouldn't fall too far.
Okay, climbing.
(GROANS) Ice can be treacherous and deceptive.
I can hear the ice creaking.
It's hard to tell what's solid.
JIM: You're doing very well.
My heart is in my mouth.
JIM: It's steep.
-You got me there, Jim? -I've got you, yeah.
This really is nerve-wracking.
I am standing on the very edge of this precipice-like crevasse.
And I've got to walk up this knife edge.
I cannot rely on the snow this side.
I don't wanna be at the bottom of that crevasse.
JIM: Don't stand on the snow, 'cause that could be a trapdoor.
-Well done.
Tricky bit.
Oh, thank you.
Even with crampons, ice picks and Jim's help, it's been a challenge.
So imagine Stone Age families on a 5,000-kilometre trek across ice with no guide, no safety gear, and only as much food as they can carry.
Surely every bit as impossible as crossing the oceans.
And that's what's so puzzling about the peopling of the Americas.
Because this was a land that was, to all intents and purposes, unreachable.
And yet we know that people got here.
So just how did our ancestors do it? My investigation starts in Calgary.
(DRUMS BEATING) (SINGING) Every summer, descendants of the first Americans gather together.
I've come to the annual powwow of the Tsuu T'ina Nation.
For them, it's a chance to celebrate their roots.
What a beautiful dress.
And for me, it's a chance to search for some hint of their past.
(SINGING) ROBERTS: Are those leaders from lots of different tribes? No, from this tribe.
-From the Tsuu T'ina? -The leaders of this land.
-Yeah, from the Tsuu T'ina.
Recent scientific discoveries suggest that around 70,000 years ago a tiny group of us left Africa and went on to populate the rest of the world.
But how we reached the Americas, whether from the north or across the oceans, is a mystery.
Does Tsuu T'ina folklore say anything about how their ancestors got here? Chief, I'm very interested in how the Tsuu T'ina came to be in this place.
Well, what was told to us by our ancestors, the old people, was that thousands of years ago we were travelling, migrating across the ice over a disagreement in a huge camp.
So they were going across ice? They were going across the ice at Slave Lake.
And there was a young child that was on her grandmother's back.
And there was a horn sticking out of the ice.
So the child was asking for that horn, so they had to stop the migration.
So they started to chip away at that ice to get that horn out and then it cracked and split in two.
So the clans that were already on the south side continued to migrate south, and the ones in the north stayed up in the north.
That's what we've been told through history.
That's fascinating.
It's really intriguing that this story of the first Tsuu T'ina hints at a journey across the ice.
But it's how these people look that might be a more important clue.
I visited a tribe in Siberia and I think that there are some similarities between your people and those people in Siberia.
And it might just be quite interesting to look at these pictures of Evenki faces.
So there's an old lady And a mum and a child.
Do you think these faces look similar? The eyes are similar to the real far-northern Dene up in the Yukon and that.
-very similar.
-These almond-shaped eyes.
And high, wide cheekbones.
very wide cheekbones, yeah.
CHIEF: Prominent noses.
And it's not just facial similarities.
This teepee is almost identical to the tchum of the Siberian Evenki.
Could this be more evidence that the first American families came from Siberia? Or is it just coincidence? If the ancestors of the Tsuu T'ina did come from the north, they could have made it as far as Alaska.
Because instead of the Bering Straits, 20,000 years ago there was a vast swath of land, Beringia.
But a huge eXpanse of ice still blocks the way to the rest of the Americas.
It's time to look at those ice sheets in more detail.
Well, climate scientists can now do something rather wonderful.
They can let us peer back in time and give us an ancient weather report.
I'm looking here at a map of North America as it was 22,000 years ago.
So actually before the peak of the last Ice Age.
And you can see this massive sheet of ice right across the top here.
Well, I'm gonna run this through time and we'll see what happens to that ice sheet.
It's moving at the edges.
And in fact it's splitting in two.
It parts into two separate ice sheets and a corridor appears.
So there was a way down at about 1 3,500 years ago.
Was this corridor the gateway to the Americas? Hello.
Are you Bert? BERT: I'm Bert.
If a few adventurous hunters did come through the corridor in the ice, we can be sure of one thing - it wouldn't have been easy.
Even today, it feels as though the Ice Age still has a grip on these mountains.
Trucker Bert Van de Wetering knows how treacherous this northern landscape can suddenly become.
ROBERTS: So it's the middle of summer and you've still got snow.
That's correct.
The area that we're gonna get into here in a little bit has all these chutes coming down, so there are slides, and the highway is closed a lot of the time because of these avalanches.
I presume it gets quite icy and slippery in the depths of winter.
BERT: It can get very crazy here.
You can get freezing rain, you can get real cold temperatures.
Sometimes we see a lot of snow.
How cold does it get? We get minus 20.
I think it's been colder in the past, but we're still getting minus 20.
That's cold enough.
Oh, yeah.
But that's nothing compared with the ice-free corridor 1 3,500 years ago.
Any families coming through that corridor would surely have faced a hellish journey, huddled against the howling wind in a land of torrential rivers and floating ice.
So did anyone try? And if so, did they make it? The answers to all these questions lie in that direction.
Because right across North America archaeologists have been finding thousands of objects like this.
They're called Clovis points.
And they date from just a few hundred years after the corridor in the ice appeared.
So this could have been the way in.
But what kind of a world would these pioneers find on the other side of the ice? The tools themselves are important clues.
And to find out how, I'm meeting archaeologist Andy Hemmings.
So these are these really classic stone Clovis spear points.
It's important to understand about Clovis, though, that they aren't just stone points, they also made some very lethal and effective bone and ivory points as well.
These are state-of-the-art, lethal killing machines from 1 3,000 years ago.
And what sort of animals do you think they would have hunted with them? The most common that we've found them directly associated with are mammoths, bison and mastodon, in that order.
But at clovis sites across the New World, we've found more than 1 25 species of plants and animals.
So they're general hunters, but you really think they were hunting mammoth? Oh, absolutely.
The best example probably is a site in southeast Arizona, where eight Clovis points were found with one mammoth body.
Five of them were found behind the back of the head and in front of the shoulder blades, any one of which probably would have been about a lethal wound.
Andy shows me how he thinks they did it.
Andy, that doesn't look much like a mammoth to me.
There's no animal in the Pleistocene that had a hide that tough.
And if we can poke a hole in that If you can poke a hole in that, we could've eaten anything.
Just like the Clovis people did.
So I've got my spear thrower.
ANDY: Let's see what you can do.
A glancing blow, you've slowed him.
-Got his feet.
-Try again.
Scratched it.
Do you wanna show me how it's done, Andy? I'll give it a try.
ROBERTS: Oh, my God! Well, that's made a hell of a dent in this metal door.
I hit it pretty cleanly, and you can see I just destroyed the end of my spear.
It would have stuck in the hide of a mammoth or a mastodon.
The mammoth and mastodon, two of the mighty animals roaming this vast landscape.
But little match for people with a weapon as deadly as the Clovis point.
Some think that these pioneers of the new frontier plunged into an orgy of slaughter, wiping out Ice Age animals like the mammoth.
The evidence is questionable.
But that image of the mighty hunter has stuck.
(BARKING) So it looks as if small groups of men, women and children made that first push into America about 1 3,500 years ago.
Using their sophisticated tools, they made the most of their new home and spread right across the continent from coast to coast.
Until recently, this was the version of American prehistory that most experts agreed on.
But a new discovery here in Texas is threatening to rewrite the entire story.
Archaeologist Mike Collins is a very patient man.
For 1 5 years, he's been digging away in this small field near Austin.
And he's found something that no one eXpected.
So, Mike, what sort of dates have you got coming out of here? We have the entire prehistory of central Texas represented at this site.
The kinds of artefacts we find and the few absolute dates that we have tell us that people were here from 500 years ago, back 1 3,500 years ago.
Even more importantly, we have stuff below that.
Below Clovis, so older than Clovis? Older than Clovis.
-Right here at this site.
But for years archaeologists have thought that Clovis was the first culture in the Americas.
Yeah, most archaeologists have thought that, but there's a few of us that have known better.
And over on the other side of the site, you can see the Clovis level and you can see artefacts below it.
-You want to see that? -I'd love to see it.
Let's go see it.
Mike, this is an incredibly deep test pit.
Yes, it's a deep test pit and we're really interested in this part of it, right here.
Because right through here we get Clovis artefacts, but as we dug down we continued to get artefacts below that for about 20 or 25 centimetres more.
A nice flake here, for example, with a platform and good flake scars on it.
We have one date from down here of 1 4,400 years.
1 4,400? Yeah.
So that's pre-Clovis.
By a thousand years.
I mean, that's amazing, because that makes us rethink all of our theories about early Americans.
Yes, we have to rethink our paradigm.
We have to come up with a new accounting of the peopling of the Americas.
Mike, how sure are you about the date of these artefacts? It's just one date, so you need to corroborate it with further evidence.
And that's what we're working on.
Now, we can only draw tentative conclusions from the evidence emerging here, but our grand theory about how humans first got into North America is starting to look decidedly dodgy.
Because if there really were people living here at Gault as early as Mike says there were, then there must have been another route into the Americas, because the ice-free corridor wasn't open yet.
But what I need is more proof.
And if the claims coming out of South America are to believed, then they may have even earlier and more compelling evidence than I've seen here in Texas.
It's time to leave North America for the South.
Ahead of me is a three-day journey, but one I hope will be worth it.
Because what I'm off to see could change everything.
My destination is Santarem in Brazil.
And it's got a rather eXcellent prehistoric transport link - the Amazon.
I'm about to embark on a seven-hour river journey to reach a very special place, the home of some of the earliest South Americans.
And unless I want to be standing the whole way, I'd better get a move-on.
I think this is going to be quite comfortable.
Looking around at my fellow passengers, I have a sense of deja vu.
I'm sure I can see those same East Asian features that I saw in the north.
Could it be that these are still echoes of an ancient Siberian ancestry? Impromptu fireworks finally announce our arrival at the tiny port of Monte Alegre.
Well, we're just coming into port, so my journey's almost over for today.
But I've still got quite a long way to go tomorrow.
-Oi! Hello.
Oi! The neXt morning, I'm picked up by Nelsi Sadeck, a man with a wealth of knowledge about the special site he's going to show me.
It's a long drive, and I've been warned it could get a bit rough.
(LAUGHING) As well as being incredibly bumpy, you've got to watch out for your head.
(LAUGHING) Ow! We're just going to clear some foliage out of the way before we can go any further.
I can see why it isn't a major tourist attraction.
MAN: Okay! Ooh, it's hot now.
(BATS SQUEAKING) We really have to proceed with caution here, because there are bats, I can hear them.
So a risk of rabies, and there are poisonous wasps as well that have made their nests all over this cave.
So we don't want to disturb them.
Oh, look, look.
NELSI: Many bats.
(NELSI SPEAKING PORTUGUESE) vampire bats? -Honestly? -Yes.
Even more cautious, then.
When these caves were eXcavated, it became clear that they had been home to ancient people.
Archaeologists found animal bones, shells and some eXquisite stone tools.
Well, this is a replica of some of the points that have been found in these caves.
And it's very beautiful.
Perhaps an arrowhead or a harpoon point.
very finely worked, and you can see the stem here, where it's designed to be attached to a shaft.
And it's also very different from those characteristic points that we saw in North America.
And, in fact, all of the stone tools are different down here.
They tell us that people are surviving in a very different environment.
There's a whole other way of life going on here.
A rainforest culture with new foods and threats, a world away from the open plains of the north.
It's a wonderful eXample of our ability to adjust to new environments.
So this is the main part of the cave.
Locals call this the Cave of the Painted Rock.
No one knows the meaning of these strange symbols, painted in red ochre.
But during the eXcavations, the cave started to yield other treasures.
So, Nelsi, it was in this cave that you were excavating in the early 1 990s? (SPEAKING PORTUGUESE) MAN: Yes, from the ground down, we eXcavated 2.
2 metres.
And in each layer, many things were found.
Many bones from birds, from fishes.
Not to mention plant remains.
ROBERTS: And those plant remains helped give archaeologists their most important piece of information, a date.
(SPEAKING PORTUGUESE) MAN: The evidence in the deepest layers dates to around 1 3,000 years ago.
These are the oldest dates we have for humans living here.
1 3,000 years.
That's an incredibly early date for South America.
(AGREES IN PORTUGUESE) MAN: Yes, these dates are very ancient.
And you must have been incredibly excited when you found out that date.
Yes, yes, yes.
Now, this date of around 1 3,000 years ago is actually problematic.
It challenges the traditional story of how the Americas were colonised.
Because it means that people were here in Pedra Pintada at the same time as those hunters in North America.
The date is so early that I find it really difficult to believe that their ancestors came through that ice-free corridor.
Because if they did, that means they would have had just a few hundred years to work their way all the way down through North America, Central America and down here to the Amazon basin, adapting to all the diverse environments as they went.
I don't believe it.
It now looks even more unlikely that the ice-free corridor was the first route into the Americas.
The dates from the Cave of the Painted Rock just don't fit.
But there's another even more incredible discovery from South America that should settle this argument for good.
The archaeological trail leads 5,000 kilometres south to a part of Chile, called Los Lagos, the lake district, famous for its stunning, volcanic landscape.
It's the middle of the Chilean winter, and after the heat and humidity of Brazil, the conditions feel very different here.
I'm headed to a place called Monte verde, a tiny hamlet of no real significance at all, were it not for the fact it's the site of perhaps the most important archaeological discovery in the whole of the Americas.
The finds from Monte Verde are nothing short of miraculous.
It's quite strange, there's no evidence at all of it ever having been an archaeological site.
There are sheep grazing.
There's nothing obvious at all.
But a few years back, local villagers came across something strange sticking out of the river bank.
Bones from a mastodon, a prehistoric relative of the modern elephant.
It was a bank just like this that the animal bones were originally found in that alerted people to the fact that this was an archaeological site.
As eXperts dug down, they discovered much more than just ancient animal bones.
Layer by layer, the remains of an entire human settlement emerged.
Home to a community of perhaps 20 or 30 people, with shelters, work areas and rubbish tips.
A unique relic of our prehistoric past.
The main structure on this site was a very long hut, 20 metres long.
I'm gonna have a go at measuring it out, but I think I might come into some difficulties, because of where the stream is today.
Because this log is actually around about 7 metres long.
(CHUCKLES) Ten metres is gonna take me up to there.
I don't want to go any further, 'cause I don't want to end up in that very cold stream.
But you can imagine how far this hut extended.
And amazingly, we know how this hut was built, because the remains of the wooden stakes and the animal hides that covered it were preserved in the waterlogged ground.
And inside this long hut the archaeologists found hearths, and in them the remains of nuts and berries and seeds that people had been eating.
The hearths were lined with clay.
And in part of this clay that presumably was wet at some point, there was somebody's footprint.
About 30 metres away was this strange outline of what was, perhaps, another much smaller hut.
Outside it there were butchered mastodon bones, but inside it there were some very intriguing finds indeed.
Some plant remains, a few of them seaweeds that are still used by the Mapuche Indians today as medicines.
Incredibly, the team even discovered the remains of potato skins.
It's the first evidence anywhere in the world of humans using, eating potatoes.
It's amazing to have this degree of preservation on an archaeological site.
This really is a treasure trove.
Monte Verde gives us an incredibly rare and wonderful window into our ancestors' daily lives.
But for all that, what's most astonishing about Monte Verde is its age.
The 50,000-odd artefacts from the site are now stored here at the University of Southern Chile.
The archaeological finds from Monte verde really are extraordinary.
This piece of wood here has obviously been worked by human hand.
It's been drilled or gouged into here.
Perhaps used to make fire.
This piece of wood has been sharpened into a point.
It was found stuck in the ground, as though it was a tent peg.
And this is really wonderful.
This is a piece of mastodon hide.
Just look at that.
Using radiocarbon dating on charred wood from the site, scientists could pinpoint its age.
And what those dates tell us is that there were people down here in southern Chile 1 4,500 years ago.
That's even earlier than the evidence I looked at in Brazil.
So early as to completely rule out the idea that the first Americans came through the ice-free corridor once and for all.
People must have got to the Americas long before the corridor appeared.
But how did people get here, when the way down through North America was blocked by solid ice? Well, maybe I've just been missing the obvious and there was another way we could have reached this continent.
Up until now, I've assumed that people got into the Americas from the north, from Beringia.
But what if they didn't? What if they came straight from Asia from across the ocean? Then the ice sheets wouldn't have even been an issue.
Is it really such a crazy idea? If the forefathers of those early South Americans couldn't have arrived through the ice-free corridor, then maybe they did come across the Pacific.
And if they did, that might eXplain one of the great mysteries of our human journey.
I'm back in Brazil, this time in Rio de Janeiro, where I'm going to see some very ancient human remains that I'm hoping will shed some light on this idea of our migration across the Pacific.
So precious are these remains that they've been kept for 30 years under lock and key at Brazil's National Museum.
This beautiful skull has been nicknamed Luzia.
It belonged to a woman who was in her early 20s when she died.
And it dates to around 1 3,000 years ago.
But it's not just the date that I'm interested in.
It's what she looks like.
Anthropologist Walter Neves believes that he's uncovered a secret about Luzia.
Well, this is Luzia's skull.
And the bad news are that she doesn't look like she should look like.
So what would you expect her to look like? Well, as you know, Native Americans came from East Asia.
And I will show you a typical skull from East Asia.
And as you can see, they have very different faces.
One of the greatest differences, in terms of facial morphology, happens in the cheekbones.
You see that Asians, they have very wide cheekbones.
-Okay? Kind of laterally projecting.
-Yes, it gives this very wide face.
-That's right.
-Doesn't it, across the cheekbones? -That's right.
Yeah, yeah.
If you go to Luzia, you find kind of narrow cheekbones.
Okay, if Luzia and her population don't look like East Asians and they don't look like modern Native Americans, who do they look like? We discovered that, amazingly, she looks much more like Australasians, than with East Asians or Native Americans, if you want.
ROBERTS: Australasian? It sounds bizarre.
But Walter found that Luzia had more similarities with Australasian skulls than any others.
And when Luzia's features are reconstructed, it's even more obvious that she looks nothing like modern Siberians or Native Americans.
It suggests a superhuman feat of seafaring.
So if these early Americans look more like Australians or Melanesians, does that mean that they arrived here across the Pacific? No, no, no, because if you take into account the technology available like 1 2-1 3,000 years ago, that would be impossible.
But then how do you explain the fact that modern living Native Americans don't look like Luzia, they do look like East Asians? It's very easy to explain.
Because if you go back to Asia, around 1 4,000 years ago, the people that lives today in Asia, with their typical morphology, they were not there.
Right, so you're saying that Luzia's people came into the Americas before the appearance of East Asian features.
Definitely, definitely.
But they used the same route as the Mongoloids did some couple of thousand years later.
So this is absolutely not evidence for any sort of trans-Pacific crossing.
Definitely not a crossing.
ROBERTS: Walter is adamant that Stone Age people could not have made it across the Pacific.
He believes Luzia's ancestors did come from Asia, but before those classic East Asian features became common.
However, Walter hasn't solved the mystery of how Luzia's ancestors found a way past all that ice.
Well, it looks like I've reached a dead end again.
There doesn't seem to be any evidence for a migration across the Pacific.
So that means the only way into South America was from the north, across the ice sheets, but that just doesn't make sense.
Unless, rather than coming across the ice, the first Americans found a way to get around it.
Perhaps the sea might hold the answer after all.
If they didn't cross the open ocean, could they possibly have followed the coast? It still seems unlikely.
It's time to retrace my steps, and head back up north to the west coast of Canada.
There should be evidence along these shores.
But there's a problem.
How do you search for something that's hidden beneath a hundred metres of water? Well, at the peak of the last Ice Age the water level would have been so much lower than it is today that many of these fjords would have been steep-sided valleys.
Today, those same valleys, where our ancestors may have lived, are full of water.
So as much as this could be the perfect place to look for signs of a coastal route The frustrating thing is that so much of the evidence is probably down there.
this is the point at which direct evidence of humans in North America runs out.
But can we discover whether such a coastal journey was at least possible? I'm in Vancouver to meet forensic botanist Rolf Mathewes.
His skills are often called upon in high-profile murder cases.
(SIRENS WAILING) FEMALE REPORTER: On Sunday, the partially-clothed body of the little girl was discovered floating in ROBERTS: When the body of a young girl was recently discovered in a lake, Rolf's identification of plant remains in her hair helped convict the killer.
But when he's not solving murders, Rolf has a passion for trying to solve riddles of the past.
And the evidence he relies on is so minuscule as to be invisible to the naked eye.
This is one pollen grain of a sedge.
And they're fairly nondescript-looking things, but I can put it on the screen over here.
It's only about thirty-thousandths of a millimetre in size.
So this is a sedge pollen grain from a marine core? Well, it's not a marine core.
It's a core taken under 30 metres of water in the Hecate Strait.
When the sea level was much lower, this area was dry land with marshes and rivers and lakes on it.
-But now it's submerged.
-Now it's submerged.
So have you got dates on this pollen, then? Have you been able to radiocarbon date them? We can't radiocarbon date individual pollen grains, but this core where this sample has come from, this sample is about 1 7,000 years old.
So 1 7,000 years ago, then, in the Queen Charlotte Islands here off the west coast of Canada, the ice sheets are pulling back and we've got vegetation.
Not as a single straight-line wall.
It came back in very irregular lobes, and pulled back at various rates, depending on how thick the ice was, and so forth.
Now, what I'm really interested in is the possibility of a coastal route into North America for the first colonisers.
-So is this, the pollen on those islands, an isolated incidence or do we actually find vegetation along the coast? By the time you get to about 1 6,000 years ago, there are a number of ice-free areas from the Gulf of Alaska all the way to down to southern British Columbia, which were also de-glaciating rapidly.
So do you think humans could have been coming down this de-glaciated route? Well, I think absolutely.
The possibilities are very strong.
In fact, the only other route I can think of that they could have come is really down the coastal corridor, using these early de-glaciated areas as stopping places, as they worked their way south.
ROBERTS: At last it feels like I'm getting somewhere.
Before I met Rolf, I imagined the ice rising straight up out of the sea, and stretching from coast to coast, forming an impenetrable barrier.
But what the pollen in his cores proves is that it would have been at least possible for humans to have got around the edge of the ice along the coast, long before the ice-free corridor opened further inland.
But it wouldn't have been easy.
Families inching along the coast would often have found the way blocked where the ice still reached right down to the sea.
So if our ancestors did come this way, then at least part of their journey must have been made by boat.
But is there anything to support this idea of ancient seafaring? 1,500 kilometres away, on the coast of California, something remarkably rare has turned up.
An ancient treasure, which for thousands of years has managed to escape the clutches of the sea.
I'm on my way to a string of rocky islands just off the southern Californian coast.
They're called the Channel Islands.
And the one I'm interested in is Santa Rosa.
Now, there's no daily ferry, and visitor numbers are strictly controlled.
So instead, it's a short hop by air taxi.
We're just coming in to land on Santa Rosa.
And I'm really lucky to actually be getting there, because speaking to Mike the pilot, on many days it's actually too foggy to land here.
Today our problem isn't the fog, but the wind.
PILOT: Watch your knees, bit bumpy there.
-Beautifully done.
-Thank you.
That's one taXi driver who deserves a big tip.
Morning reveals Santa Rosa's lonely beauty.
(BIRDS CHIRPING) Thanks to their isolation, these islands are home to some 1 50 plant and animal species found nowhere else on the planet.
And thousands of years ago, the wildlife was even more eXotic, with weird and wonderful creatures, like the giant mouse and pygmy mammoth.
The evidence of Santa Rosa's unique past is everywhere.
Look at that.
If I'm not mistaken, that is a mammoth bone.
That's a limb bone and then there are vertebrae, bones from the backbone, all the way through here.
So these bones have been sealed in these sediments for tens of thousands of years, and are now just appearing again.
In 1959, a local archaeologist came across what looked like more ancient animal bones.
But what he'd found was something even more exciting.
And these are the replicas.
Sticking out of the hillside here, he found the fragmented remains of two human femurs, or thigh bones.
Radiocarbon dating revealed that the bones belonged to a person who lived here almost 13,000 years ago.
And the discovery of these bones is really surprising.
Because back then, this island would still have been 1 0 kilometres away from the mainland.
And that means the only way to have got here would have been by boat.
So it doesn't seem so far-fetched to imagine that the very first people to reach America might also have had small boats, allowing them to travel from one headland to the neXt, in the hope that around the corner the ice would have melted enough to allow them to feel dry land again.
But perhaps that's rather a lot to read into a couple of old leg bones.
It's frustrating that the archaeological evidence for such a coastal route is so scarce.
But there is something else that I'm hoping will help to settle this controversy about how the Americas were colonised once and for all.
John Johnson is an eXpert on the prehistory of the American west coast.
But there are other genetic lineages among the Chumash that show them to be a very ancient group ROBERTS: And for 15 years he's been collecting DNA from living Native Americans.
John and his colleagues have pieced together what seems to be nothing less than an ancient genetic route map.
A few years ago, a friend of mine called me up and told me that they had just identified DNA from an ancient jawbone found in southern Alaska, in a cave in southern Alaska.
What's so fascinating is this is a rare type of DNA.
It's only found among 2% of American Indians.
ROBERTS: When John compared the DNA from the ancient jawbone with modern samples from across the two continents, he noticed a pattern.
Okay, we have here in southern Alaska the original DNA from the jaw.
Then we have the Chumash Indians that live in this part of California.
We've also found this type in northwest Mexico.
We've found it among the Caiap6 Indians in coastal Ecuador.
We've also found it among the Mapuche Indians in southern Chile.
Among the Yagan people of southern Patagonia.
And here in prehistoric burials in Tierra del Fuego.
All the way down the Pacific coast.
Primarily Pacific coastal in distribution.
So for you, does this really clinch it? Does this mean that there was a coastal dispersal? I think this is the best evidence to date.
Indirect evidence of an ancient coastal migration, that this particular group gradually moved down the Pacific coast, taking advantage of coastal resources.
And left behind descendants today who still live in all of these areas.
ROBERTS: It feels as if the great mystery of this, our last human journey, is resolved.
Looking at all these strands of evidence, then, it seems the most likely route taken by the first Americans was not down through the ice sheets, as many archaeologists used to think, but all the way down along the Pacific coast of the Americas.
We can imagine those first pioneers paddling along the edge of the ice some 17,000 years ago.
And their descendants moving down along the coast, reaching the southernmost tip of the Americas, within just a couple of thousand years.
With a foothold in this New World, the first Americans flourished here, until eventually, some 15,000 years later, they were to come face to face with some distant members of their family tree.
In 1492, a small group of European eXplorers arrived on the shores of the Americas, where they were met by bewildered locals.
Even though both groups were branches of that original exodus from Africa some 70,000 years ago, the Europeans didn't see the inhabitants of America as long-lost cousins, but rather as wild, savage, even unhuman.
And the Native Americans saw those strange visitors as deities possessed of supernatural powers.
They just didn't recognise each other.
Over the neXt 400 years or so, this physical and cultural divide would help fuel the slaughter of the native people.
Even conservative estimates run into hundreds of thousands dead.
A tragedy which seems so much more senseless in light of what we now know about our human story.
Our origins in Africa, the journeys our ancestors made and the close genetic bond we all share.
The differences between us all are really just superficial.
We're all members of a young species that goes back less than 200,000 years, and we're all surprisingly closely related.
This is the story that has emerged from the study of stones, bones and our genes.
That wherever we've ended up all over the world, we are Africans under the skin.
And uncovering that story, retracing the steps of our ancestors, has given me a profound sense of our common humanity, our shared past and our shared future.