Original subtitles

NARRATOR: In the ongoing drama of evolution, species come and go.

They live, they compete, they die out.

MAN: Extinction is the termination

of a species.

We can think of a species having a birth date,

it lives for a while, it goes extinct and it dies out.

95% to 99% of all species that have ever been on the planet

have gone extinct.

NARRATOR: On average

a species dies out after four million years of existence.

It could take less time, it could take much more.

But it's all part of the normal process of extinction,

always there, always happening.

MAN: Conditions change, a new predator arises.

Perhaps the climate changes.

Perhaps a mountain range suddenly appears geologically.

Through those processes

this particular species is no longer able to live;

it dies out.

NARRATOR: The extinction of species that can't adapt or compete

creates opportunities for new species, new forms of life

in an endless cycle.

So evolution and extinction are in balance.

But what happens when a planetwide catastrophe

kills off many species in a great mass extinction?

(thunder crashing)

MAN 2: The game of evolution has changed its rules a little bit

when one of these massive extinction events takes place.

Suddenly you've leveled the playing field.

NARRATOR: It was a level playing field

that made our very existence possible

after a mass extinction 65 million years ago.

Now it's we who may be causing a new one.

But this time, we may not be as lucky

as we face evolution's severest test.

NARRATOR: Five times in the past 500 million years

a mass extinction wiped out

most of the species alive at the time.

The Earth itself tells the stunning story

with its geological and fossil record

stretching back through time.

Today, sheep roam the highlands of South Africa's Karoo desert

but 250 million years ago

the Karoo played host to creatures we can barely imagine.

It was their world, and then they were gone.

Geologist Peter Ward is here to study the secrets

of history's greatest mass extinction

which swept those creatures away.

It's a challenge that anyone would find daunting.

WARD: In late 1999, I spent three weeks camping in a tent

next to an old, abandoned farmhouse.

And behind this farmhouse, I wandered the grounds

and found this beautiful old graveyard.

One of the tombstones had a husband and his wife.

There were two sons off to the right.

The dates on the tombstones ranged from 1892, I believe

to about 1897.

The mother was the first to go, and the youngest son,

who was only 42-years-old at the time,

was the last to go in 1897.

All die out in this five-year time span.

There's a tragedy that has happened here

yet we have so little record of it.

MAN: Looking at the epitaph:

"Nem dom fry mos stoffer adder."

Translated into English, that is:

"Take my ashes and set them free on Earth."

WARD: So, a hundred years

these people are just wiped off the face of the Earth.

And we have no idea what killed them? MAN: Yes.

And if that's the case

how am I going to figure out what killed animals

that lived in those hills

the fossils of which we have from 250 million years ago?

NARRATOR: 250 million years ago

marks the end of the geological time period called the Permian.

It's the rocks of the Permian

that give Peter Ward his first clues.

WARD: These types of layered rocks often have fossils.

In fact, here in the Karoo

we find within these green, layered rocks lots of fossils.

There are two types: we find skeletons

and we find the remains of activity of animals.

Some animals burrow, they make little tunnels in the strata.

As a matter of fact

there's probably one sitting right back here.

This is either a bone or a burrow.

Here's the piece of a burrowing organism of some sort.

Some animal was living and digging through the strata.

It gives us a sense

that not only were there larger vertebrate creatures here

but a wide diversity of smaller animals.

Sometimes they died or were killed

or predators took them down.

Their skeletons fall in this sediment

and we find it as fossils.

NARRATOR: At the South African Museum in Cape Town

the fossils of dozens of species have been recovered

from this lost Permian world.

MAN: I was walking on a farm track

and there in the middle of the farm track

was this little piece of bone sticking out of the shale

and not a very exciting piece.

But I took my pick and started to work around it

and revealed the back of the skull here.

And then down towards the snout and when finding the tusk here,

this beautiful faceted tusk,

I knew that I had a complete skull.

Then I began the long task of uncovering the back of the skull

uncovering vertebrae after vertebrae

working down this way, with the ribs beginning to develop here.

After 2� hours to three hours

I knew that it was a complete, articulated lystrosaurus.

NARRATOR: Lystrosaurs were the Permian's most common plant eaters.

Gorgons, ferocious predators up to ten feet long

ruled the plains.

Then suddenly, the Permian ended.

The rock record reveals a cataclysmic change

at the threshold of the next geological period, the Triassic.

WARD: We geologists can climb through time.

I'm going to climb about 50 feet up, through here.

I'll go through 2,000 to 5,000 years of time when I do it.

This is the very last layer of the Permian.

As soon as I climb above this, I'm now in the Triassic.

We're sitting in the very bottom beds of the Triassic.

In these beds, we have no fossils whatsoever.

All the Permian creatures that we saw right down there

have disappeared entirely.

A few of them, we know, survived

because one or two species will be found a little higher up.

But in these beds, we found nothing.

Not only are there no fossils

there aren't any of the burrows or the tunnels

or the traces of animal activity.

We see instead, layers of rock

that could only have formed in the absence of animal life.

So catastrophic was that mass extinction

that even the small creatures have died out,

it's not just the mighty, it's the meek.

This place is dead.

NARRATOR: What could destroy so much?

What could turn day into a seemingly endless night?

It may have been a comet, as some new evidence suggests

or a combination of factors.

(tremendous explosion)

Sea levels dropped.

There was a dramatic rise in global temperature.

Volcanoes erupted

depositing a million cubic kilometers of lava.

The atmosphere changed

as the level of carbon dioxide increased.

Ecosystems around the world were ravaged.

(thunder)

Mass extinction followed,

the most dramatic turn possible in the course of evolution.

The Permian extinction was a time

when, if you were playing Russian roulette

and you had a gun with ten chambers in it

you put nine bullets in it, spin it, put it to your head;

you've got one chance out of ten of surviving.

NARRATOR: In a mass extinction

when species die, they don't die alone.

The collapse of one species helps bring down others.

WARD: You could almost analogize that to a house of cards.

Each species props up another, in a sense.

Because the creature that you eat

is that card that is sitting under you

that gives you your energy.

Now, let's pretend

that we start kicking out card after card after card.

And that's what a mass extinction does, isn't it?

It starts knocking out a species here

knocks out a species there

but pretty soon, lots of species are gone.

And it's not just the disappearance of species now

the whole house of cards falls down.

You start really snowballing in this effect;

and that's really what a mass extinction is.

NARRATOR: The rocks tell the extraordinary story of what happened next.

Above the barren layer, new signs of life.

WARD: We know that very few animals that were present

prior to the extinction here survived it.

(blowing)

(blowing)

Wow...

I just found a carnivorous mammal-like reptile

in strata that we have just above the mass extinction.

This is a creature that has survived it.

NARRATOR: The mammal-like reptiles

looked like crosses between dogs and lizards.

But they weren't the only survivors.

WARD: Two lineages that get through

have tremendous consequences later in time.

Both are pretty small in size.

They start evolving because the world was empty

and empty worlds really begot

tremendous amount of evolutionary diversifications.

NARRATOR: Evidence of what was to come

is in one of the best fossil collections

of post-extinction survivors, gathered by a single family

over three generations.

WARD: Of all the skulls in this museum, this is my favorite.

This creature leads to the dinosaurs.

At the same time that it exists in the earliest Triassic Period

right after the mass extinction

we find a second small carnivore, very different.

This little skull is the species that leads to us.

Two of these predators, the small mammal

the larger reptilian creature that becomes the dinosaurs,

really duke it out in head-to-head competition.

In the Triassic Period, there's a clear winner: the dinosaurs.

NARRATOR: It took around 20 million years

for the first dinosaurs to evolve

on their way to the giant creatures we think of today.

MAN: Dinosaurs get big.

They're baroquely diverse with all kinds of weird adaptations,

with armor, with predatory animals,

with birdlike animals,

the dominant animal features of the landscape.

Mammals just scurry around in the shadows.

They're small, shrew-like, or rat-like, in many ways.

They look like some of the least dramatic things we have today.

NARRATOR: Michael Novacek has been fascinated by dinosaurs

ever since he learned of a series of expeditions

to the Gobi desert.

NOVACEK: My personal history with the Gobi started a long time ago,

I was seven years old.

There was this very dramatic explorer, Roy Chapman Andrews

who wanted to go to Central Asia to look for early humans

and ended up finding a lot of dinosaurs.

He wrote books about it and kids loved those books

and I was one of those kids.

NARRATOR: In the 1930s

Roy Chapman Andrews made several trips to the Gobi.

Traveling in style, he brought along six motor cars

a team of scientists and a hundred camels.

He didn't find evidence of early humans

but he did find something far more ancient.

Buried in the sandstone

were 80-million-year-old dinosaur bones and eggs...

and fossils of tiny mammals.

NOVACEK: Mammals were part of the dramatic finds

that the Andrews expedition uncovered.

They weren't the biggest things,

a lot of these mammals are little, nugget-sized creatures,

but they were very, very important to science

because at that time

we knew virtually nothing about mammals that old,

mammals so old that they lived alongside of the dinosaurs

nearly 100 million years ago.

NARRATOR: The Gobi Desert is one of the most isolated places

in the world.

When China reopened it to foreign scientists

more than a decade ago, they flooded in.

Most, including members of Novacek's team

were looking for dinosaur fossils.

The desert had what they wanted...

more of those extremely rare dinosaur eggs.

But this time, Novacek was after something even rarer.

NOVACEK: We were actually heading a little west

but en route, our gas tanker got stuck

and so we had to dig it out.

And as the truck was being excavated

a few of us took a couple of jeeps up to a little hill.

And there I saw a mammal skull just lying on the ground.

And about every 15 minutes

it seemed someone said, "I got a mammal."

And then I'd say, "I've got one, too."

We had about 50 mammal skulls by lunchtime.

We had already matched the amount

that's been recovered from the Gobi entirely

over a period of seven decades.

This is about as big as they get.

This is the skull, and you can see the front teeth here.

It's really no larger than a squirrel

or what we would call a small mammal today.

It contrasts dramatically with some of the smaller skulls.

This encompasses practically the entire size range of mammals

during the time of the dinosaurs.

NARRATOR: Like many of their descendants today

the mammals survived by being nearly invisible.

They were nocturnal.

They scavenged.

They reproduced quickly.

NOVACEK: Mammals are beginning to get better-developed brains.

The eyes are becoming larger.

And even in the skeleton behind the skull, we see a number

of very interesting transitional features.

In the pelvic region, there's evidence of splint-like bones

that suggest support for the abdominal cavity.

And this probably supported a pouch

very much like living marsupials like opossums and kangaroos,

a transition between a more primitive, egg-laying behavior

and a more advanced behavior, a more advanced reproduction

that we see in today's placental mammals, like us.

NARRATOR: But mammals remained second-class citizens

in a world where dinosaurs ruled

until the inconceivable happened again, 65 million years ago.

It's thought that an asteroid larger than Mt. Everest

reached the Earth traveling 25,000 miles per hour.

The mammals were used to avoiding dinosaurs

but an asteroid was something else entirely.

(explosion)

Known as the KT Event

the impact changed the face of life on Earth.

The small mammals survived

but in a landscape of death and destruction.

The house of cards

built since the last mass extinction collapsed

but this time, it was the dinosaurs

that fell the furthest.

With few places to hide, less food

and little ability to protect their eggs or young

the dinosaurs died out, while the mammals went on living.

NOVACEK: Mammals that survived this event

stay small, maybe for a couple million years.

They start to get slightly larger and diversify.

We have a sort of a lag effect with the KT event,

a recovery of, perhaps, the ecosystem,

and then the mammals really take off.

NARRATOR: Mass extinction had provided an unexpected opportunity.

NOVACEK: You can think of mammals after the KT event as colonizers;

they first landed and made a toehold on a new land

where there are lots of tremendous advantages to them

and they're not competing

with these large, big, plant- eating or meat-eating dinosaurs.

NARRATOR: They spread out to all parts of the world.

They competed and diversified...

until most of the largest animals on Earth were mammals.

About 35 million years ago, mammal evolution produced

the first true monkeys and apes from earlier, smaller primates.

Then, generation after generation

the process of adaptation and change,

of evolution, continued.

Around five to six million years ago, in Africa

the first humanlike primates emerged.

Some of their descendants would play an unprecedented role

in evolution's future.

They left their bones on the valley floor

in caves and on lake beds.

They began to walk upright.

They left their footprints in volcanic ash that hardened.

One lineage branched, some species went extinct

while others evolved into the ancestors of modern humans.

Today, the world is bursting at the seams with people.

(whistle blowing)

This is Bangkok, Thailand,

population ten million and growing.

(whistle blowing)

There are now six billion of us on the planet.

Even the dinosaurs would run for their lives.

We have caused the rate of extinction to soar.

It's now over 100 times greater than normal.

Many scientists worry that we are the new asteroid

bringing about the sixth great mass extinction on Earth.

(birds singing)

This is Kaengkrachan National Park, population zero

in an area twice the size of Bangkok.

From all appearances

a hidden world, unspoiled, timeless.

Just 300 miles from Bangkok

it's protected by natural barriers.

The Tenasserim mountain range runs through it

creating a steep, rugged terrain.

The forest is dense.

The Petchaburi River can be difficult to navigate.

But no one knows if the animals living here

have found a sanctuary or have disappeared from the forest.

MAN: We're in grave danger of the "empty-forest" syndrome,

having a beautiful, seemingly intact forest, on the surface

but inside that forest the natural components

which maintain the flow of energy through the system

it's disrupted.

Now, people say

"So what does it matter if one component's gone?

"What if you don't have the Sumatran rhino?

What if the civet species are all gone, or other things?"

But each thing has evolved

to play an incredibly important role within this complex puzzle.

NARRATOR: Alan Rabinowitz wants to know if Kaengkrachan has escaped

the escalating rates of extinction found elsewhere.

So he and his colleague, Tony Lynam, collect data

on the actual number of animals living in the park,

especially the carnivores.

RABINOWITZ: Large carnivores, such as tigers,

are often the first animals to be wiped out from a system.

You go into an area and find

relatively abundant sign of large carnivores

you know what you're dealing with, by necessity

is a very healthy

at least seemingly stable natural habitat.

NARRATOR: A typical habitat works this way:

sunshine, nutrients and water make plants grow.

The plants are eaten by herbivores

which in turn are eaten by carnivores.

About a hundred pounds of plants generally sustain

about ten pounds of herbivore

which sustain about one pound of carnivore.

Healthy carnivores mean a healthy forest.

When Alan Rabinowitz was here last

the news about the forest was good.

RABINOWITZ: More than ten years ago

I landed here in Kaengkrachan National Park.

We got down in here, and I was very pleased to see

that the place was beautifully intact

in terms of the vegetation

but more importantly

I was able to find tiger sign virtually everywhere I looked.

I would hike through small rivers

and there'd be families of otters

starting to swim around me.

Elephants came to my camp at night.

Gibbons sang every single morning.

Hornbills flew overhead all the time.

All the signs

of a healthy, intact, relatively unhunted forest were there

which made it probably one of the few places in Thailand

and, in fact, when I surveyed throughout the entire country

at the end of the survey it became even more clear

that Kaengkrachan was easily the most pristine,

the most untouched piece of forest left

in this entire country.

NARRATOR: But is it the same today?

On a search for life, every stop offers more clues.

Hmm, fresh elephant, nice size.

There's cat, small cat.

NARRATOR: The group uses well-traveled elephant paths

to navigate the forest.

It's an elephant trail.

Here's a trail that elephants

are walking on constantly.

And every time they walk past this vine

they just push it back this way

and then push it back this way

and all the bark has started to come off.

NARRATOR: Three other teams are in the park

each retrieving special cameras with motion sensors

which were carefully placed a month before.

Called "camera traps"

they take a photo when triggered by an animal walking by.

LYNAM: Out of batteries, I guess.

The camera's taken a whole roll of film and it's rewound.

So there's 36 shots taken.

RABINOWITZ: What the camera traps will help us do

is start wrapping some numbers around these things

helping us quantify.

It's one thing to say, "Boy, sign of tiger is everywhere."

It's another to say, "Just on this one survey

we have taken pictures of a minimum of X numbers of tigers."

NARRATOR: The cameras serve as an unseen observer.

In one day, a camera trap can catch more tigers on film

than Rabinowitz's team could see in months.

LYNAM: I'd say, tonight, camp here.

Tomorrow morning, go down the stream and check out this area

and check out what we've got in terms of Siamese crocs.

And that's where you think

we might have Siamese crocodile?

Yeah.

That would be neat.

That would be something else.

NARRATOR: The Siamese crocodile is a species that, 30 years ago

lived throughout the tropical forests of Asia

but they have been relentlessly hunted for their skins.

Not a single one has been seen in over a decade.

Is this it, Tony?

LYNAM: Yeah...

These are some fresh ones, right?

Oh, yeah, those are fresh.

RABINOWITZ: Siamese crocodile,

a species thought to be either virtually extinct

or extinct in this country and incredibly endangered

throughout all of its existing range.

If we prove the existence

of a population of Siamese crocodile in Kaengkrachan

that in itself, apart from everything else, will make this

one of the most important areas in the entire country.

Over on the other side of the bank there

we saw tracks of Asiatic Black bear

which is the largest bear species in Thailand

and also tracks of a large tiger.

So we call this place Carnivore Corner

because it's got all of the three carnivores.

NARRATOR: With another roll of film and sightings of carnivore tracks

the team presses on to pick up the rest of the cameras.

But suddenly, there's a hitch.

Camera's gone.

You're kidding.

The camera's gone.

Where the hell is it?

Somebody...

Somebody stole it.

Damn it, somebody stole it.

Yeah, you can see it's been cut.

It's been cut right here.

Somebody's come and cut the bamboo and taken the trap.

It could mean we have a thieving problem

or it could mean that this area's being more hunted

than we think it's being hunted.

It's gone.

It's gone.

The camera trap is gone.

And that one?

It's gone.

I can't believe this.

This is stupid.

Why is this happening?

Why would they want to take the cameras?

RABINOWITZ: Ramifications of losing these cameras...

there's a lot of ramifications.

In terms of data, it's a major loss.

It takes an incredible amount of planning

and time and effort to even get to do an area like this.

This area was chosen for its remoteness.

The fact that it's quite obvious

that these cameras are being both stolen and vandalized

is very bad.

I've never seen this in my 20-plus years in the field.

It looks like somebody has come along

in front of the camera

taken a picture of themselves.

They didn't want that to happen.

So they tried to take the camera

tried to slash the lock

but the lock has got a steel cable on it.

And they couldn't take it off.

So instead of taking it off

they tried to destroy the picture, destroyed the film.

So they got a knife

and they've just slammed the knife

into the top of the camera.

It doesn't surprise me

that people are anywhere anymore in this world.

I'd be more surprised if we found a spot

where there really weren't any people penetrating there.

It's a male.

It's a male.

It's a young male.

It looks like two years old.

RABINOWITZ: A lot of people ask me why I do the work I do.

There's a lot of reasons.

But basically, I'm just tired of watching animals die.

NARRATOR: A fisherman from a village next to the park may have information

on just how much hunting is going on.

(man speaking Thai)

(speaking Thai)

LYNAM: So now there are fewer tigers than before

because there are more people here

and the tigers are found further into the forest.

RABINOWITZ: Ask him about snares.

(Lynam speaking Thai)

(speaking Thai)

RABINOWITZ: He says that they don't use snares

that they don't hunt, that there's no hunting.

It's probably the truth

somewhere a little in between.

NARRATOR: Rabinowitz's team has retrieved only three cameras out of ten.

The expedition could be a failure

unless the other teams have better luck.

The journey ends at the village of Bongluek

a settlement of 70 families near the park border.

If there's anything more to learn

the local headman will know it.

Ask him if he's ever seen this animal.

Does he know what this animal is?

(speaking Thai)

Ah, okay.

So there used to be rhinos here

but hunters have wiped them out.

(headman speaking Thai)

(Lynam and headman speaking Thai)

RABINOWITZ: There's no doubt that the major cause of extinction

on a global level is human-related.

Everything from clear-cutting forests

to removing intact habitats

to just desecrating them, changing them.

NARRATOR: Habitat destruction is now the number one cause of extinction

people spreading out, or just trying to survive in a world

where most of the habitable land is already occupied.

There's nothing to do now

but wait to hear from the other teams, and hope for the best.

Thailand isn't alone.

Hawaii is another once-isolated place.

For centuries, it's had to battle

the number-two cause of extinction:

biological invaders,

foreign species that can overwhelm native life.

Born of lava from undersea volcanoes

the Hawaiian Islands were barren at first

and every species was an invader.

The ocean swept in life.

Spiders, lifted into the air by their own webs

were carried here.

Birds arrived on the back of storms

carrying animal hitchhikers and the seeds of plants.

Thousands of visitors made it by sea or by air

and evolved into species

that were found nowhere else on Earth.

With little competition and few predators

they had found a paradise.

But now the paradise is under siege.

Paleoecologist David Burney, here with his son

is exploring the Hawaiian island of Kauai

to better understand what happened

after the Polynesians arrived around 600 A.D.

BURNEY: I'm trying to find sites that will really give

a general picture of what the whole landscape was like

where you have a record of plants and animals

and human activity

and everything that you could possibly reconstruct

about the whole landscape,

what I call my "poor man's time machine."

(engine rumbling)

NARRATOR: The time machine is a sinkhole

where mud and water have preserved

10,000 years of Hawaiian evolution.

With two small generators and hoses

Burney drains it every day.

BURNEY: I like to think of it

as sort of like trying to open a window into the past

downward into the past

in order to get all of these different kinds of fossils

that would give you details

of nearly everything that was there.

We often recover

a very large amount of very well-preserved material

including, in this case, for instance

bones of a number of birds and snails

possibly even a few plants that were unknown to science.

NARRATOR: It's a tedious, messy job

but the mud preserves the evidence perfectly.

In a given day, Burney carries a thousand pounds of sediment

out of the sinkhole.

Volunteers then wash, screen and pick through it

for fossils and artifacts.

BURNEY: As soon as the Polynesians get here

we see evidence in the sediments for big changes.

NARRATOR: That's because the Polynesians didn't come alone.

They brought with them biological invaders:

plants, dogs, pigs, rats

new predators that fed on and displaced

Hawaii's native species.

Ah, there's one of our culprits.

Jawbone of the Pacific rat, probably about 1,000 years old.

Once we start finding these

a lot of the native species start rapidly disappearing.

NARRATOR: The sediment tells the tale.

BURNEY: Over the ensuing 1,000 years or so

the human population grows.

You know, at first, we're talking about

a relatively small number of people

who came in outrigger canoes.

There couldn't have been that many.

But over time, the population on this island

in prehistoric times built up

to probably something like the population of the island today.

There were a lot of people here.

People have a big job transforming the landscape

cutting down trees

burning off the grasslands and the brush lands.

And as a result of these impacts

then smaller creatures began to go extinct.

At the time that Captain Cook arrived

the wave of biological invasions really crests.

Suddenly there are all these goat bones and goat teeth

in that layer.

Suddenly there's a lot fewer birds and trees around.

The Polynesians brought only

a small number of species with them.

Europeans have brought hundreds and hundreds of species.

We're now to the point

where there are about 1,000 native species of plants

in the Hawaiian islands

and over 1,000 naturalized invasive species

things that have been introduced by people.

The evolution has now entered a new mode.

Something new altogether is happening, and it has to do

with what humans do to the evolutionary process.

NARRATOR: The invasion of Hawaii is a microcosm

of what's happening throughout the world today.

At any moment, 100,000 people are suspended in planes

over the Atlantic Ocean

traveling from one continent to another.

Cargo is sent to the furthest corners of the earth

in a matter of days, or even hours.

And with it comes other, smaller passengers

who are not going to get back on the plane and go home.

(ship's horn blasts)

In ships, ballast water is taken up in one port

and discharged in another.

With it comes invasive species like the zebra mussel

which arrived in the United States in 1988.

Quick to reproduce

these two-inch-long mollusks encrust spawning grounds

clog water pipes and consume plankton

which native fish and mussels need to survive.

In the past decade, the U.S. government has spent

four billion dollars trying to control them.

Many animals and plants that find their way in

can easily adapt to new environments and flourish.

Some of them don't cause problems

but there are others we'd rather were not so good at sneaking in.

In our new, interconnected world

the invasive species we carry with us

are dramatically increasing

the rate of extinction of native life.

MAN: Some of these animals were brought in

by private individuals, as pets.

Some were brought in either for resale as far as food products.

And some of these actually stowed away

on some of our aircrafts and ships

that arrived here in Hawaii.

NARRATOR: The brown tree snake is one of them.

Originally from New Guinea, it can grow up to 11 feet long.

During World War II

the snakes began to climb the landing gear of planes

and curl up in the wheel housings

or hitchhike rides on cargo ships.

When they arrived in Guam

the snakes would slither off and head for the jungle.

Then they would climb trees in search of food.

The eggs of the native birds were easy targets

and nine of Guam's 11 forest bird species

were driven to extinction.

That's it, over here.

NARRATOR: Hawaii's Department of Agriculture now has to use

trained beagles to sniff out the snakes.

Where is it?

NARRATOR: This time it's a test for training.

But the next time, it will be for real.

That a girl, good girl!

MAN: The last brown tree snake that showed up here

was found in the wheel well

of a Continental Micronesia 747 aircraft

that arrived the day before from Guam.

It does show that the snakes are getting up there.

The main worry for the Hawaiian Department of Agriculture

is that the Brown Tree snake becomes established in Hawaii.

Hawaii leads the nation

in the amount of endangered species

and many of those species are birds.

If Hawaii loses our native birds

we also lose a lot of our native plants

and the whole ecosystem in Hawaii will be affected forever

and the paradise we know might not be in years to come.

BURNEY: My suspicion is that

of all of the things that we've done to the planet so far

whether it's climate change

things we've done to the atmosphere

things we've done to the water, pollution problems,

all of those are bad things.

But I think, as it stands right now, at least

that the thing we've done, which will be most visible

in the fossil record in a million years

is going be these biological invasions.

NARRATOR: Scientists have a term for biological invaders.

They call them weed species.

Like weeds, they survive and adapt almost anywhere

and push out the native competition.

They are the ultimate survivors.

NOVACEK: There's quite a bit of speculation and theorizing

about why invaders seem to be so successful

in moving into a new area.

The animals that tend to invade are more mobile

maybe more adaptive to more general changes in habitats

more flexible with environmental change.

That confers some kind of competitive advantage.

NARRATOR: Of all the weed species on Earth

we are the most mobile, the most adaptable

and the most flexible by far.

The good news is we'll probably be around for a long time.

The bad news is the world around us may be very different.

As the rate of extinction accelerates

every species that disappears

leaves one less to prop up others.

So the question is, in our own modern world

with our own house of cards,

how close are we to that whole edifice coming down?

Have we reached that threshold?

NARRATOR: This is the Great Plains state of North Dakota, farm country.

It's where one of the battles against human-caused extinction

is being fought

only this time by pitting two biological invaders

against each other.

The enemy here is a weed called leafy spurge,

so well-adapted and tenacious

it threatens to kill off native grasses.

It's already spread across a million acres.

A century ago

pioneers accidentally brought it with them in bags of seed.

Now the settlers' descendants are faced with the consequences.

MAN: The leafy spurge limits the number of cattle

that I can put in a pasture.

I mean, they'll eat the grass that's in there

but if it's infested with leafy spurge they just won't touch it.

There's a milky substance to it and it's pretty bitter.

They don't like it.

NARRATOR: Cy Kittleson's great-grandfather homesteaded the land.

Today, Cy and his father own 4,000 acres.

The weed covers over a third of their ranch.

They've tried spraying it with a weed-killer

but leafy spurge is not easily beaten.

I look at it as cancer to the land

and it makes the land just totally useless.

The chemicals, it costs between $90 and $100 a gallon

and it takes about a gallon to cover one acre of land

and so that's $100 an acre

and that's not counting your time.

And that's about all the land is worth.

How many acres would that cover?

NARRATOR: Chuck Wiser, the local bank's agricultural loan officer

understands the financial toll of a biological invasion.

He has battled leafy spurge in one way or another

for 25 years.

WISER: Leafy spurge is

a very deep-rooted perennial

that is competitive for nutrients and moisture

with our native grass.

And so it has an advantage

both in food storage in its root system

and ability to regenerate growth.

NARRATOR: If a chemical won't stop it

how can farmers fight an invader that's taking over

the ecological niche of native grasses?

The solution may be another invader

discovered when scientists learned

what kept leafy spurge in check in its native Russia.

It's the flea beetle,

a case of fighting evolutionary fire with fire.

WISER: Flea beetles feed on the roots and in the crown of the plant

and bore holes allowing molds to get in.

They deplete the food reserve in the root

and so they're just kind of beating it up

so it's weaker and weaker

and eventually does not produce any top growth.

NARRATOR: Flea beetles were first brought to Ward County in 1984.

Each summer, teams harvest beetles

and move them to infested areas.

The beetles reproduce so rapidly

that a release of a hundred in one year

yields a harvest of two million the next.

That just leaves the challenge

of actually getting them to the right place.

WISER: We found that on the large infestations of spurge

in really rough country that's hard to get into

we can put out more beetles faster

using a light airplane, than any other method.

Our flight today consisted of 150 canisters we dropped

with approximately 5,000 beetles in a canister.

We put out somewhere around 750,000 beetles.

Weeds grab life from us.

If we don't do something, we'll be taken over by them.

KITTLESON: It started out small.

And now, every spring now, I go out and harvest these bugs

and spread them around

and I can really see some good results with it now.

It's going to take a while, it's going to take a long time

but I can see the results.

NARRATOR: The story of Cy's farm is a story of hope.

It means that we can do more

than just watch native species go extinct.

We can fight back.

But that requires information we may not have.

In Thailand, the research expedition is still waiting

for the data it needs.

Will the scientists discover that it's already too late

for Kaengkrachen?

Has it become an empty forest?

The other teams have collected all their cameras

without trouble, 33 rolls of film in all.

(laughs)

Oh, look at this.

That's a beauty, but I got a better one for you.

Look at this.

Wow.

Now, that's a nice picture.

Tiger and leopard.

Another leopard.

Another tiger!

(laughs)

Holy cow!

Look at that.

I'm assuming this is a sambar deer.

That's a nice tiger.

Boy, that's a nice shot.

Oh, this is really interesting.

Poachers or local people or something or other.

This is the Petchaburi River.

This is the second route.

This is the one where I walked up ten years ago?

That one?

That is some area.

Look at this tapir.

Tapir, yeah.

Phew.

Look at that.

We've got great...

Look at this.

Siamese crocodile.

Oh, there it is.

Look at that!

Crocodile.

This is the first recent photo

of a Siamese crocodile in Thailand.

RABINOWITZ: While we were sleeping, while we were walking,

while we were swimming in the river

all these animals were wandering around us.

The tigers were walking around us, the leopards.

The Siamese crocodile might have been in the water

at another part of the stream

at the same time we were jumping in and cooling off.

It was definitely near us when we were standing on its beach.

I know the tigers heard us.

Probably several saw us.

I know that the elephants froze there in the forest

when we went by as if, "Wow, what a neat forest."

There are still places left

where the natural evolutionary processes are going on.

Most of my career involves documenting species

on the verge of extinction.

But every now and then, you get a place like this

and you say, "It's not lost yet.

It's not gone yet."

Really, it's that close.

RABINOWITZ: Knowledge is definitely our greatest tool

against extinction. There is no doubt about it.

Many species are on a very quick, downward slide

possibly to extinction, faster than they would be normally

because of human-related activities.

But we're not at an endpoint here by any means.

We're still in the middle

of a completely complex, changing scenario.

Evolution is going on around us.

NARRATOR: If we can slow the rate of human-caused extinction

and avoid a mass extinction by our own hands

then the natural cycle of death and life

extinction and evolution

can play itself out at its own speed

as we try to learn more about it.

In 1859, Charles Darwin wrote

"We need not marvel at extinction.

"If we must marvel, let it be at our own presumption

"in imagining for a moment that we understand

"the many complex contingencies

on which the existence of each species depends."

"The appearance of new forms and the disappearance of old forms

are bound together."

Continue the journey

into where we're from and where we're going

at the Evolution web site.

Visit www.pbs.org.

The seven-part Evolution boxed set

and the companion book

are available from WGBH Boston Video.

To place an order, please call: