All language subtitles for David.Attenboroughs.Galapagos.S01E03.Evolution.2160p.NOW.WEB-DL.DDP5.1.H.265-RAWR_track3_[eng]

Hidden away in the vastness of the
Pacific, and undiscovered by men

until only a few centuries ago, lies
a group of strange volcanic islands.

Each is a crucible where evolution
proceeds at extraordinary speed.

Galapagos.

Each island contains its own unique
community.

The discovery of these creatures
inspired an idea

that changed our
understanding of life on Earth...

Evolution.

And today, scientists on Galapagos
are continuing to make

discoveries that shed
light on that crucial process

and have revealed that human
beings can be just as powerful

a driving force for change as any
other factor.

Something here was the catalyst that
produced the most spectacular

explosion of biological
diversity in the world.

It's not just the number of species
that appeared,

but the rate at which they did so,
and the result is so extraordinary,

it inspired the most important of
all biological theories -

Charles Darwin's evolution by
natural selection.

And now, 200 years later,
we're beginning to understand

the deep-lying forces that produced
this biological wonderland.

One of those factors is isolation.

A part of Isabela Island,
the largest of the 16 in the

archipelago, is so difficult to
get to, it's hardly ever visited.

Wolf Volcano.

Its giant crater lies
exactly on the Equator,

and is encircled
internally by steep cliffs.

And on its flanks,

evidence was discovered
of a catastrophe that might,

paradoxically, eventually lead to
the creation of a new species.

This flow of recently solidified
lava

has created an impassable barrier
100 metres wide,

right through the vegetation.

The fresh lava is razor-sharp,
and almost impossible to cross.

On it lie bones.

Bleached white by the baking sun,
they're those of giant tortoises.

Some animals that got stuck
here are still clinging to life.

Tortoises are tough.

They can survive for months
without any food or water.

And that worsened their fate -

it will take them months to die.

Why so many tortoises tried to cross
the lava barrier, nobody knows.

What drove them to keep attempting
this impossible journey?

Perhaps they were desperately
trying to rejoin

other members of their group.

Their deaths, however,
are significant.

They illustrate a principle that
applies to the whole of nature.

It's not unique to the Galapagos,
but it's because of the Galapagos

that we first came to understand it.

This tragic scene,
filmed for the first time,

may provide a clue as to how a new
species may start to evolve.

The lava flow created an impassable
physical barrier

across the tortoises' territory,
dividing it into two.

So two tortoise populations that
were once one must now live apart.

If there is any significant
difference,

now or in the future,
between their two territories,

the tortoises may eventually become
two different species.

Animals and plants are evolving
throughout the natural world.

But it was the strange creatures
of Galapagos that first revealed

how that happens.

Nearly 200 years ago, the islands
were visited by a young naturalist.

On September 16th 1835,

HMS Beagle arrived in the Galapagos
Islands,

and the 26-year-old Charles Darwin
stepped ashore to explore.

At the time,

very little was known about the
natural history of the islands.

Darwin, initially, was
fascinated by its geology.

But it was the animals that gave him
his historic insight.

Darwin was only on these
islands for five weeks.

But in that short time,
there were things he saw

and conversations
he had which stuck in his mind.

For example, the British
vice-governor of Floreana Island

said that he could tell which island
a giant tortoise came from

simply by the shape of its shell.

He pondered on the vice-governor's
casual remark.

Why were populations of tortoises
on separate islands

all slightly
different from one another?

He set about making a collection of
animals and plants

from all the islands he visited.

Although it was the tortoises that
first alerted Darwin

to the differences between animals
on different islands,

it was his collection of these
undramatic little birds,

the finches, which provided him

with the most substantial
evidence for his great theory.

We now know that the ancestral
Galapagos finches

arrived in these
islands about 2 million years ago.

Since then, they have diversified
into a number of different species.

Today, there are 13 of them,

distributed throughout the
archipelago.

Each has its own special talents.

The woodpecker finch has discovered
how to use a tool

to winkle grubs out of their burrows
in the branches of trees.

The vampire finch has learned how to
extract blood from sitting birds.

Darwin, when he returned to England,
brought back with him

a wide variety of specimens
of all kinds,

and he spent years
studying his collections.

He had a range of finches
from several of the islands,

and he noticed one particular
way in which they differed.

They had beaks of different sizes.

Why?

An idea grew in his mind.

It would also apply to tortoises -
maybe to all animals and plants,

wherever they occurred.

Painstakingly, meticulously,
he started to accumulate

evidence from all over the world to
support his idea,

and he called the process that
produced new species

"evolution by natural selection."

And nowhere is its workings
more vividly evident

than here where it first occurred
to him in the Galapagos.

He realised why it was

that there were several species of
giant tortoises.

That original species probably had
a high-domed shell, like this one,

and that's very useful on
well-watered islands like this,

where you have to barge your way
through the vegetation.

But on other islands,
there are other problems.

In the southeast corner of the
archipelago lies Espanola Island.

Here, there is virtually no edible
vegetation at all.

Except, that is, for this prickly
pear cactus, opuntia.

But this species of opuntia
is very tall.

And it has a tough, woody trunk.

The only parts worth eating

are the fleshy leaves and flowers
at the top.

Any giant tortoise that could
reach them could get a meal.

Tortoises with low, round fronts
to their shells couldn't do that.

But those with
a peak at the front of their shell,

and long necks,
could just manage it.

So they were the ones that survived
and produced young.

Over many thousands of generations
and millions of years,

the shell shape of the Espanola
tortoise

became more and more
exaggerated.

Now, the peak at the front of the
shell is shaped like a saddle.

Such a change didn't happen
just on Espanola -

different islands
had their own versions.

Eventually, there were 15 different
species on the islands,

all descended from a single founder.

But why should the environments
of the islands be so different?

Well, a hint of that reason may
come from looking at films

I shot right here, back in 1978.

In these
programmes, we're going to survey

the immeasurable number of animals
that have been produced

by natural selection, and look
at them not as isolated oddities...

That image of me, shot 30 years ago,
indicates something extraordinary.

In that time, the rock on which
I was sitting has moved its position

by about a metre from where I was
then to where I am now.

In fact, the whole of this island

is drifting across the surface of
the globe

at a rate of about three
centimetres a year,

roughly the rate at which
my fingernails grow.

That may not sound much, but in
the 3 million odd years

since this island emerged above the
surface of the ocean,

it has drifted in a south-easterly
direction by about 60 miles.

Movements in the Earth's
crust are the key to understanding

the archipelago's extraordinary
evolutionary history.

A giant hotspot,
rising from the Earth's molten core,

began to build the Galapagos
4 million years ago.

But, as the island drifted
away from it,

other volcanoes replaced it,
one after the other.

Each was built from an accumulation
of ash and lava.

But then, as each moved away,
eruptions ceased.

So a group of islands appeared,
one after the other.

The islands were separated from
one another by water,

so their populations
can't, for the most part, mix.

But they're just close
enough for an occasional animal

to float across and
so seed a newly emerging island.

Because the islands
are of different ages,

they contain between them a great
variety of environments.

And each has moulded
its inhabitants in its own way.

That is why their animals are
so diverse.

Each is a separate
evolutionary community.

Darwin had noticed
some of the clearest differences.

But there are many others
that are less obvious.

An isolated population of animals
can change

not only in their anatomy,
but in their behaviour.

Little lizards like this are found
throughout the archipelago.

Each island has its own
distinct species.

And they differ not so much
in the way they look

as the way they behave.

This is a lava lizard.

There are lots of them
on the rocks around here.

And in the breeding season,
which is now,

the males are competing with one
another,

both for territory and for females.

And the way they do so is with
press-ups.

Watch.

Actually, this is a model that is
used by scientists

to investigate the way in which
these lizards communicate

with one another.

Let's see how he gets on.

And there's a response.

These press-ups vary, both
in the number and the intensity,

the speed at which they do it...

...and how high they bob their heads.

The interesting thing is that the
responses vary

from species to species.

In other words, each species
has its own language of gestures.

There are slight physical
differences

between the species of
lava lizard on different islands.

But now, because they have
developed different gestures,

they can't interbreed, even if
they meet.

They're separated by a language
barrier.

New technology
now enables scientists

to investigate
the workings of evolution

in ways that Darwin could hardly
have ever imagined.

X-rays are being used
to work out what's happening

to one of the least impressive
animals on the island -

a tiny land snail.

It's been known for a long time

that there are many different
snail species

all closely related.

But a recent study of their shells
using X-rays

has demonstrated
just how diverse they have become.

The length of the shell compared
to the diameter of the tube inside

is marginally different
in different populations.

It's certainly different enough
to define them as different species.

And there is an extraordinarily
large number of them

throughout the islands

with what seem to be
very complex interrelationships.

In fact,
there are more species of them

than any other kind of animal
on the islands.

Even one small island may
contain several different species.

But why?

It's all to do
with the different microclimates

that occur even within a single
small island.

Black lava rock has one species...

...and sandy beaches close by
a very different one.

A dark cave has one sort...

and a leafy forest growing
around its mouth, yet another kind.

And it seems to be connected
with humidity.

At the one extreme,
there are these with a wide mouth.

They come from relatively
well-watered islands.

And a wide mouth like that
has a body

which produces
a roughly globular shell.

But on dry islands,

the mouth has to be very small
to prevent evaporation

and that produces
a long, conical shape.

So, Galapagos' new species

range from the subtly different,
like snails,

to the obvious,
like the marine iguanas.

In other parts of the world,
evolution usually proceeds

in a slow, gradual way.

It can take millions of years
for new species to appear.

But in Galapagos it's been happening
in an evolutionary blink of an eye.

Galapagos, for its size,

has more unique species than
anywhere else on Earth.

And all have
appeared in the islands'

comparatively short history.

And that raises another
intriguing question.

Why did such a great number
appear so quickly?

The answer is to do
with the absence of some animals.

Predators.

The few that are here are all
very small.

This is one of the most lethal -
scolopendra, a centipede.

It roams the undergrowth
searching for prey,

which it kills by injecting venom

from the sharp claws
on its front legs.

But it's only 30cm long,

so its victims are mostly tiny.

Bigger animals, like mockingbirds,
can easily subdue one.

They even feed centipedes
to their chicks.

The greatest concentration of
predators in the whole archipelago

is found on the rocky island of
Fernandina.

But they too, of their kind,
are rather small

and comparatively ineffectual.

Snakes.

The Galapagos racer.

They search for prey
in the colonies of marine iguanas.

But all they can manage to do is to
pick off the young,

the weak and the dying.

And even that they find quite
difficult.

They hunt in the rocks
around the fringes of the colony.

They have to use a combination
of both venom and constriction

to make a kill.

And even then,
because they're small snakes,

it may take more than one to
overcome a victim.

And then there's a tug of war
between the winners to settle

who has the prize.

There are other predators that
prey on the iguanas from the air.

The Galapagos hawk.

But even this hunter is seldom
powerful enough to subdue

a big male.

It usually waits until it finds one
that is weak or encumbered.

A pregnant female, trying to find
a place to lay her eggs.

And there are not many hawks here.

Only 150 mated pairs,

because there's only a limited
number of nesting sites.

There are so few birds that they
make very little impact

on the iguana population.

So why are there no larger
predators on Galapagos?

Most of the Galapagos animals
came from the rainforests

of South America, 600 miles away.

There are plenty of big
predators in these forests.

Reptiles got to Galapagos
by floating across the ocean

on rafts of vegetation.

Only hardy animals like the iguanas
and tortoises

could make that 600 mile voyage.

The great predators of the jungles,
however, are mammals -

big, fast, and warm-blooded,
like jaguars.

If any of them had ever been carried
away on a raft of vegetation,

they would have perished out on the
open ocean within a few days.

So now, while there are many
kinds of herbivorous reptiles

in the Galapagos...

...there are no large predatory
mammals of any kind.

And this has had a profound effect
on the animals that did get here.

It's something noticed by every
visitor who comes to the islands.

All the animals here
are amazingly tame.

Even the little finches are happy to
bathe within inches of a stranger.

The lack of predators may have a
surprisingly widespread effect.

It's not just that animals are not
frightened of strangers,

the so-called "island tameness",

but that time that would be spent
hiding from attackers

can now be used to find food, find
mates and raise young,

and so produce more young, which
hastens the progress of evolution.

There is no more impressive
example of that

than Fernandina's iguana colony.

With no significant
predators around,

these herbivores produce
lots of young.

So many, that their problem is not
how to defend themselves,

but how to find enough food to
support their great numbers.

So they ventured into the sea
itself,

to graze seaweed on the sea floor.

And although swimming in the cold
sea cools them uncomfortably,

with no predators around,

they can soon put that
right by stretching out in the sun.

The lack of big predators has
had an effect

on all the animals of
the Galapagos.

They reproduce freely,
so populations increase rapidly.

And so, consequently,
does evolutionary change.

But island tameness has dangers.

If a major predator does appear,

then wildlife will be ill-equipped
to defend itself.

And one did.

In the year 1535,

the most successful predatory
animal of all arrived...

Man.

By the beginning of the 17th
century,

the islands had become
a haven for pirates.

By the 19th century,

whalers and merchantmen were calling
here regularly,

and all these ships
had a disastrous effect.

There is little or no fresh
water on these islands,

but they have a much rarer resource.

Giant tortoises can survive without
food or water for very long periods,

so ships could come here,
collect the tortoises,

stow them in the hold,
and then after weeks at sea,

bring one out, butcher it,
and have a meal of fresh meat.

Slow, lumbering, and with no
way of defending themselves,

the tortoises were easy victims.

The population was decimated.

Between the 16th and 20th centuries,

more than 100,000 were taken away
and slaughtered.

And the ships brought other dangers.

Rats.

They feasted on the tortoises' eggs.

On the island of Pinzon, rats
consume nearly every single egg,

leaving the tortoise population
on the brink of extinction.

But another island lost its
tortoise population altogether.

Pinta, located on the shipping route

around the northern fringe of the
archipelago,

was a favourite stopover for ships
and their hungry crews.

And the unique Pinta tortoise was
presumed extinct

by the early 20th century.

But in 1972, an amazing discovery
was made and filmed.

A living male Pinta tortoise was
discovered in the undergrowth.

He was taken off to a protected
enclosure on the main island,

to live out his days in comfort
and safety.

Here, he became
an international celebrity,

and he was given a name to
reflect his state -

Lonesome George.

He's about 80 years old,

and he's getting a bit
creaky in his joints...

As, indeed, am I.

He is arguably the rarest
animal in the world -

certainly, there can be none rarer,

for he is the last of his kind.

His female died a long,
long time ago.

When he dies, the Pinta species of
Galapagos tortoise will be extinct.

But he is a very important animal.

Probably more than any other single
creature,

he's focused the attention
of the world on the fragility

of our environment,
and he's stimulated science

to look into whole new areas
of research here in the Galapagos.

Just 14 days after we filmed
Lonesome, he died in his sleep.

But he's not forgotten.

Lonesome George's story, like
Darwin's fleeting but famous visit

200 years ago, has attracted many
visitors to the islands.

Today, the archipelago is the basis

of a multi-million dollar
tourist industry.

30,000 people live here,
in three small towns,

and fleets of small boats take
visitors on carefully-planned trips

to see the islands' main sights.

It took animals and plants
millions of years

to find and colonise the Galapagos.

Now, new species of animals and
plants from the world's continents

can get here in a matter of hours.

And, having got here,
they're often inadvertently spread

almost immediately
through the islands.

Seeds of foreign plants hitch a ride

on the air currents
generated by passing traffic.

And the Galapagos' network of roads

is now lined by foreign invaders.

Among them,
the common European blackberry -

a plant that can grow
a centimetre a day

and create impenetrable
thickets four metres thick.

They not only choke and kill
native plants,

they even block the paths of large
animals such as the tortoises.

Scientists are now trying to analyse
the impact of human beings

on the course of evolution in the
islands.

And, surprisingly perhaps,

the finches that Darwin made famous
are still providing new insights.

Biologist Andrew Hendry is looking
at how the finches' evolution

may have been affected by human
settlements.

When humans come into a new
location,

essentially what
they do is change the environment,

and that's changing selection that's
acting on the populations.

Hendry is studying one particular
species - the medium ground finch.

OK, yeah.

Remarkably, he's found that this
finch, in its natural setting,

is on the verge of dividing into two
separate species.

The two are defined by the size
of their beaks.

One is small, the other, large.

The difference between them has been
caused

by the types of food they eat.

So, if you feed on some small seed,
you tend to have a small beak,

and if you feed on large seed,
you tend to have a really big beak

and you tend to have a hard bite.

Remarkably, Hendry has found
that among medium ground finches

that live near human beings, the
distinct big and small beak forms

are getting fewer.

It's as if the two variants are here
merging back into one.

The presence of human beings has
stopped this finch from evolving.

We found that they feed a lot
on human food, ranging from rice

to fruit to grains to potato chips,
and feeding on those types

of different foods, it doesn't
really seem to matter what your beak

size is any more.

So there isn't that pressure to have

a small beak version
and a large beak version.

And there's no selection against
those intermediate birds any more.

There's plenty of foods
for them to eat.

So it seems like humans have caused
a speciation reversal -

they're fusing back together again
as a result of human influences.

So, human beings can be just as much
a part of nature as the forces

that first shaped these islands
and the organisms that live on them.

But human beings can not only
destroy... they can conserve.

In the 1970s, the tortoise
population reached an all-time low.

There were only a few thousand
of them left.

But now there's a major
breeding programme for them.

The tortoise population today
is increasing.

Once-threatened species have been
brought back from the brink.

And scientists are discovering
just how important and influential

this reintroduction programme
might be.

On Alcedo Volcano, home for the
largest population

of free-roaming giant tortoises,
a study has shown

that they're crucial to the health
of all the surrounding wildlife.

Today, there are some 15,000
tortoises on the Galapagos

and they're an essential
element in the islands' ecosystem.

One study in particular has shown
just how important they are.

Biologist Steve Blake uses satellite
tags to track their movements.

They reveal, to most people's
great surprise,

that the tortoises migrate over huge
distances,

from the depths of the crater,
right up to the rim.

It's just phenomenal.

Why would a 600lb reptile
migrate from sea level

to up to 1,000 metres on
some islands?

From the air, the routes the
tortoises take are clearly visible.

And they use the same highways,
year after year.

One of the fundamental drivers
of the migration seems to be food.

Tortoises tend to come to
the highlands

at the coolest time of year.

Up in the highlands, they can feed
on a year-round,

low-quality food source.

But then when the rains kick in,
the lowlands tend to green up,

and the tortoises go down there,
probably to fatten up.

But Blake's studies reveal much
more about the tortoises

than just where they go.

They demonstrate the extraordinary
effect that tortoises have

on their surrounding environment.

They create special conditions that
suit all kinds of other animals.

They shape and prune the landscape.

They disperse seeds,
trample down the undergrowth,

and trim the lowest
branches of the bushes.

And all that allows seeds to
germinate.

It disturbs insects, so that they
can be gathered by hungry predators.

Their dung is also crucial to the
survival of many other creatures.

Beetles lay their eggs in it,

and their larvae grow fat on the
nutriment that it still contains.

Tortoises are definitely
the megafauna of the islands.

They're like the elephants
of Galapagos.

They're out there in large numbers,
they've got big bodies,

they're creating myriad
microhabitats for other species.

They truly are the gardeners
of Galapagos.

That's probably the best way
to sum up their ecological role.

The implications are very
important -

they suggest that the
reintroduction of tortoises

to islands where their numbers have
been seriously reduced

could restore the richness of the
whole environment.

We have the chance to bring back
the full glory

of these fragile ecosystems.

Today, unlike many other tropical
islands elsewhere,

95% of Galapagos' biodiversity
still survives.

Just.

And, amazingly, new species are
still being discovered.

One was found just 35 miles
north of Alcedo,

on the giant, little-visited
volcano, Wolf.

To get to Wolf,
you really need a helicopter.

It's one of the most hostile and
least-explored parts

of the whole archipelago.

There had been rumours of
something strange

living up on these
remote, high slopes.

Something that lived in burrows,

and only emerged every now
and then to feed.

A scientific team went up to
investigate.

What they discovered
astonished everybody.

A completely new and unknown species
of reptile.

A pink iguana.

Until now, it was thought that the
Galapagos possessed

only three species of iguana.

The black marine iguana,
that lives on the seashore.

And two species of yellow iguana
that live inland,

feeding on cacti
and other vegetation.

This land iguana is certainly
the most closely related

to the newly discovered one.

Genetic studies of the 100 or
so individuals that make up this

tiny population have shown that it
diverged from its land iguana

cousins more than
5 million years ago.

So, amazingly, it has been here
just as long as the other two,

but has remained unknown to science
until now.

The discovery also means

that it is even older than
Wolf Volcano, where it now lives.

And of course, there is another
great mystery

that no-one has yet explained...

Nobody knows why it's pink.

Could it be that to be pink up here
brings something good?

We don't know.

Maybe this was once spread widely
over the island,

and this is just the relic
population that's left.

Again, we don't know.

Goodbye.

But there's one thing that is
quite certain,

and that is that there's a lot
we have yet to learn about the

enchanted islands, and about the
animals that have evolved here.

And of one thing, I have no doubt -
Charles Darwin would be delighted.

In just a few million years,

this empty expanse of ocean was
transformed.

A series of volcanoes broke
the surface and built the islands.

Against heavy odds,
a few species managed to reach them.

They adapted to what they found...

...and so evolved into a multitude
of new species.

Each new discovery we make gives
Darwin's theory a greater relevance.

But beyond the strange plants
and bizarre animals,

there is a greater significance.

What we've learned here has given us

a greater understanding
of our planet.

This small group of islands has
revealed in microcosm

the processes that have shaped
all life on Earth.

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