Original subtitles

Our Planet is the greatest living puzzle in the universe.

A collection of worlds within worlds.

Each one a self-contained ecosystem

bursting with life.

But how do they work?

The intricate web of relationships

and the influence of natural forces

makes each microworld complex and unique.

So, to discover their secrets,

we need to explore them one by one.

Untangle their interlocking pieces

and ultimately reveal the vital piece,

the key to life itself

hidden deep within each of nature's microworlds.

Galapagos is arguably

the most pristine archipelago on Earth.

It's a unique living world of truly enchanting islands.

Nowhere else on our planet

are the connections and dependencies within ecosystems so clear.

Charles Darwin was the first to see this

when he visited the islands over 170 years ago,

but, as we will discover,

he only saw part of the picture.

What the makes the Galapagos so unique

is that many of the creatures that live here

are found nowhere else on Earth.

Even more extraordinary is that there is life here at all

on these barren, isolated islands.

And what life!

It's a bizarre collection of creatures...

..from swimming lizards

to tropical penguins

and cormorants that can't fly.

How has a place so harsh and isolated

become a showcase for evolution

and home to such a motley crew of creatures?

And what is the pivotal piece

that links all these animals to each other

and to the islands they inhabit?

To discover that,

we must look at how these islands were created in the first place.

Galapagos lies on the Equator,

600 miles off the coast of Ecuador.

In this isolation lies part of the reason

for the archipelago's unique wildlife.

These islands are not a broken off piece of a continent.

And they haven't been created from coral reefs

like some other tropical archipelagos.

This microworld has been born from forces deep within the Earth.

Galapagos is one of the most volcanic places on the planet.

And it regularly proves it with spectacular geological shows.

The archipelago is plumbed into Earth's molten core.

The islands have been created by a unique quirk of geology,

known to scientists as the Galapagos hotspot.

It's a thin part of the Earth's crust

that periodically pushes up molten rock towards the surface.

And the eruptions create islands.

For 20 million years,

the hotspot has continued to give birth to new land.

As new islands form,

they are carried away

from the hotspot

on shifting tectonic plates

towards South America

creating the string of islands

we see today.

This raw geology makes for a very tough place to live.

And affects the bizarre creatures and relationships in Galapagos.

But how did life get all the way out here in the first place?

To colonise such remote islands,

life would face many daunting challenges.

To get here, any living thing would first have to cross 600 miles

of open ocean from the nearest mainland.

Plants are the first pioneers of any new landscape.

Their seeds float here

or are blown in,

or they may be carried in the feathers or droppings of sea birds.

Just getting here is a formidable challenge.

Getting a foothold in the lava landscape is something else.

But life finds a way.

The whole terrestrial system is dependant on a few plants

to kick start the colonisation.

Mangroves are true ocean voyagers.

Their seeds are tough enough

to withstand the desiccating effect of months in salt water.

Lava cactus pioneer the colonisation of the land.

While Opuntia cactus open up the land still further.

With so few species,

the delicate dependencies between those species

makes for some incredible relationships.

Many of the native flowering plants in Galapagos are yellow.

And that's because the only species of bee

that's managed to make it here and pollinates the flowers

is attracted to yellow.

So there's little point in being anything else.

The integrity of the food chain relies on the few insects

pollinating the plants,

because the next layer of creatures depend on them.

Reptiles are a true hallmark of Galapagos,

not necessarily because they deal better with the conditions here,

but because they managed to get here in the first place.

Reptiles are adept at surviving in salt water,

so they stand a good chance of getting through a vast ocean crossing.

Once here, they had to adapt to what's on offer

and, in doing so, became the next integral layer of the ecosystem.

Land iguanas rely on Opuntia cactus as their staple food.

On the more barren islands,

the shells of saddle back giant tortoises

have evolved quirky shapes to allow them to stretch their necks upwards

to higher, tasty cactus morsels.

But the cactus also relies on the tortoise.

They spread their seeds in their droppings as they roam the islands.

At the top of the food chain, the surprising relationships continue.

The top predator here isn't what you might expect.

This is the Galapagos hawk.

The challenge for a female hawk is to find enough food

to raise her young in such a barren place.

With next to no small mammals to hunt

she turns her attention to what dominates the land here.

Marine iguanas nest for only a few weeks each year.

Which doesn't leave her much time.

But she simply must succeed.

One life ends...

..and another begins.

But there's another reason so many creatures here,

like the Galapagos hawk, are endemic,

found nowhere else on Earth.

In Galapagos, we see unique species everywhere we look.

Not just on land, but also at sea.

Galapagos sea lions might look like any other sea lion.

But the science proves otherwise.

Their ancestors arrived here from California 2.5 million years ago,

but they've continued to evolve here in isolation

and are now so different

they're considered a new species.

Though they come ashore to breed,

water is their natural environment

and they depend on the richness of the seas.

The flightless cormorant is a real Galapagos oddity

and has evolved to suit a purely aquatic existence.

With no real land predators to escape from,

flight was of limited use.

Under water their wings were actually a hindrance,

and, over time, they dwindled to mere stubs.

The entire species are now bound

to a tiny stretch of the Galapagos coast.

Even some creatures that can easily leave the islands

are also considered endemic.

Like the waved albatross.

After months fishing further out at sea,

the first touchdown isn't always graceful.

95% of the world's population

return to just one Galapagos island each year to breed.

These birds mate for life.

The first challenge is to find their partners.

When they do, they rekindle their relationship with a delightful duet.

THEY SQUAWK

Over the last few hundred years,

the Galapagos has been seen as a living laboratory,

helping us to understand

how creatures specialise

and evolve to suit their environment.

There is one example, above all others,

that reveals just that - Darwin's finches.

Few terrestrial birds managed to make it to these isolated islands.

The finches that did make it

now fill all the various niches available.

The finches share a common ancestor,

but have evolved into many different forms

to exploit their new habitats.

Different finches each rely on different plants

and creatures to make a living.

They have evolved to take the place of woodpeckers.

They've become tool users.

Others have developed larger beaks for cracking seeds.

They've even turned into vampires.

These finches learnt that sea bird blood makes a nutritious meal,

full of protein and minerals.

These avian vampires don't kill their host,

though the blood meal must surely weaken the larger bird.

Galapagos finches are such a clear example of how creatures can evolve

that Darwin eventually saw in these little birds

the foundations for his big theories

on evolution by natural selection.

These would shock the world

and revolutionise biology.

But there is a further key to working out how all this life

is interconnected and intrinsically linked to the islands.

Something even Darwin didn't realise.

To discover what that is,

we must look to where island life concentrates -

the coast.

The community of coastal creatures is heavily interlinked

and the dependency between them is clear to see.

Sally Lightfoot crabs clean dead skin off the basking marine iguanas.

Lava lizards also use the iguanas as lookout posts.

These endemic animals are true opportunists.

Any advantage here is worth taking.

Sea lions become hunting grounds.

It's a relationship that works for everyone.

Well, except the fly.

On the coast, we see creatures that depend on the land to breed.

And on the seas to feed.

Their lives are linked to the sea.

There is something special about the seas here

that all coastal creatures rely on.

And a clue to what that is can be found beneath the beds of lava.

There is one seabird here that you'd never expect to find on the equator.

The world's only tropical penguins.

These lava tubes once flowed with molten magma.

Now the penguins rely on them

to hide their vulnerable chicks from the baking sun.

But the real secret to how Galapagos penguins can survive here

is down to something in the seas.

Although the archipelago lies in the path

of a number of warm water systems,

Galapagos is also washed

by a tongue of cold, Antarctic water

called the Humboldt Current.

The penguin's ancestors

were brought to Galapagos by that cool Humboldt Current,

and it continues to sustain the surviving population to this day.

This cooler water holds more life-giving oxygen

than warmer tropical waters that are typically found at this latitude.

The cool water combines with the equatorial sun

to feed the marine ecosystem.

It makes for one of the most productive tropical marine environments in the world.

All sea creatures depend on these life-giving currents.

It's the reason the fish life so is rich,

both in abundance and diversity.

The volcanic character of the islands also plays its part.

The flanks of the volcanoes draw cold water up

from the deep ocean to the surface.

It makes the seas around the youngest, most barren islands

the most productive in the archipelago.

And it is here that we find the largest communities

of a truly bizarre creature

that has evolved a lifestyle linked to the productivity of the seas.

Galapagos Marine iguanas are the only sea-going lizard

found in the whole world.

The barren lava shore offers little to feed on,

so it's not surprising that their terrestrial ancestors

took to the rich waters to find food.

What is astonishing is that they've evolved to eat only marine algae.

But in doing this, the iguanas face a dilemma.

They need the algae but it lies in cold water,

a real problem for a cold-blooded creature.

If they get too chilled, they become sluggish and eventually can't swim.

So they need to offset periods of diving

with time spent in strong equatorial sun.

We can see how it works by looking at the iguanas in thermal imagery.

As they bask, the lethal chill is driven away,

giving them more energy to take the plunge again.

By raising their temperature to 37 degrees centigrade,

they buy themselves time.

They can return to the cold water to find the algae.

Smaller, younger individuals forage in the shallows.

The larger individuals must dive deeper and for longer

to tap the richer pastures that will sustain their greater size.

Larger males can hold their breath for up to 30 minutes.

But the clock is ticking.

It is crucial to find food, feed and get out.

They return to the safety of shore

but their temperature is now dangerously low.

But basking will re-warm them

and aid in the digesting of that algae meal.

Every day they walk this temperature tightrope.

It's a remarkable lifestyle that's evolved over millennia.

Their reliance on a single resource can be very productive,

but also very precarious.

The dependency of creatures on the cool water currents

comes sharply into focus

when that life-giving current is switched off.

And when it is, the results can appear catastrophic.

Every three to six years,

the seas around Galapagos undergo a dramatic change.

Pacific trade winds slacken

and warm water shoots East across the ocean.

The blanket of warm water engulfs Galapagos.

It chokes off the cool life-giving currents that feed the archipelago.

And the marine food chain collapses.

This is El Nino,

one of the most destructive weather systems on Earth.

Its position on the equator

means that Galapagos is right in the line of fire

and gets more and stronger El Nino events than anywhere else.

For creatures linked to the land, isolated on these islands,

there is nowhere to go when El Nino hits.

The El Nino of 1982

was the most extreme in 400 years.

Populations of animals were decimated.

El Nino creates a seesaw of productivity

for a number of years every time it hits.

But it's not all bad.

The warm water creates wetter weather,

so, while the marine creatures suffer,

the land system goes into overdrive.

There is an explosion of life

and an increase in colonisation between the islands.

The seesaw then swings back.

When cooler seas return,

the marine system rebounds

but the land system now suffers

until normal conditions return.

El Nino appears to be one of nature's great destructive events.

But El Nino also reveals with great clarity

the natural processes at work in Galapagos.

The stress El Nino creates acts as a gruelling test

in the race of survival of the fittest.

The individuals that do survive thrive.

They and their offspring flourish after the crisis.

With less competition, this becomes a land of opportunity.

El Nino shows how crucial the upwelling cool water is

to feeding Galapagos.

And it also shows how profoundly the islands' isolation

affects the resident creatures here.

But there is a twist in this tale of isolation,

a final key that unlocks a greater understanding of the Galapagos.

That key lies in how the archipelago came to be in the first place.

For there is more to the unique geological story

and how that affects the creatures here than many realise.

The islands are born from the Galapagos hotspot

and are carried towards the continent of South America,

but they never get there.

As the islands get carried towards the mainland,

the tectonic plate on which they sit slides beneath the continent,

taking the islands with it.

Each island is born,

lives

and then disappears on a conveyor belt of geology.

The Galapagos conveyor belt has created a geological treadmill,

a continually changing home

for the creatures that reside here.

The archipelago may have existed

for over 20 million years,

but the oldest island we see today

is only three million years old.

Incredibly, marine iguanas as a species

are older than the islands on which they live.

Their ancestors arrived to islands

that have since disappeared beneath the waves.

Their species has moved along the geological treadmill,

island hopping as it evolves.

And this is the great revelation of Galapagos,

the reason for the creatures and relationships

that define this place.

The volcanic conveyor belt has, for millennia,

created a truly isolated archipelago.

The isolation has forced the life that managed to get here

to have to continually adapt and evolve.

The upwelling currents are the lifeblood of the system.

They feed and sustain life.

It's this combination of the islands' unique geology

and the upwelling currents that makes Galapagos so special.

Darwin saw in the Galapagos

a "little world within itself"

and, 170 years on,

this still holds true.

The islands that inspired his groundbreaking theories

continue to give us new insights

into how Galapagos and all the microworlds of our planet work.