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.

Running down Africa's south-west flank lies the Namib Desert.

2,000 kilometres long

and 200 kilometres wide,

this is not Africa's largest desert,

but it is its oldest.

Created by an 80-million-year feud

between the African coastline

and the full force of the Atlantic Ocean,

it's a startling place.

The rugged coast and its sea of dunes is the stuff of legend.

The wrecks of ships swamped by sand

show how treacherous this place is,

blinded by the regular sea fogs,

dashed on the rocks by the pounding ocean.

Even though it's been shaped by brutal forces,

the Namib is one of the greatest natural wonders on Earth -

but it's not for the faint-hearted.

And that's because the Namib seems to be missing

one of the fundamental building blocks of life -

water.

Some years, it doesn't rain at all.

So it would take some truly hardy creatures

to be able to survive in this barren, waterless place.

In fact, the only thing more extraordinary than the landscape

are the surprising creatures that call it home.

Sea lions sprawling in desert sands.

A chameleon, normally a tree dweller, but with no tree in sight.

And a blind mole

with no soil in which to dig.

In fact, the Namib is home

to over 180 species

found nowhere else on Earth.

To understand how this ecosystem works,

we're going to first have to understand

how life succeeds here at all.

We must take a closer look at these creatures,

explore their unique adaptations,

understand their interactions,

so that we can discover the secret

that allows life to tough it out

in the most inhospitable desert on Earth.

Let's start at the edge of the desert - the coast.

The freezing Antarctic waters are the key to the success

of one particular coastal species.

Where hot desert sands meet these icy waters,

the South African fur seal reigns,

in giant colonies

several thousand strong.

The cold currents flowing northward from Antarctica

bring with them deep, rich waters,

which, in contrast to the desert,

are teeming with life.

Seawater is far too salty to drink,

so fish provide the fur seals

with both food and water.

This saves them from the dryness of the desert.

But they are not immune to something else this desert has a lot of...

..heat.

They may be perfectly adapted for hunting in the breakers,

but they can't spend all their life at sea.

They have to come to shore to rest and to breed.

Out of the water, the seals are vulnerable.

The blubber that keeps them warm in the cold water

is now more of a hindrance than a help.

SEAL GROANS

But the seals have developed a behaviour to combat overheating.

Flipper sailing.

Their flippers are the only part of their bodies

not covered by blubber and fur

and so, by exposing them to the breeze, they can lose heat.

And, of course, if it gets too hot to bear,

like holiday makers,

the adults make a dash for the cold water to cool off.

But they have to come ashore to give birth

and their pups are too young to swim.

The effects of extreme heat can be lethal.

One in four fur seal pups

just won't make it.

But then, why with such a high death rate,

are the seals here in the first place?

The lethal heat and wind that helped create the dunes

act as an impassable barrier,

protecting them from the rest of Africa,

with all its deadly predators.

So the desert acts like a defensive wall,

and the loss of a few pups is a small price to pay

for the success of the whole colony.

But they're not completely isolated.

Black-backed jackals are one of the few animals

that have managed to reach the coast.

And now, they are heavily dependent on the seal colonies for survival.

A mutually beneficial relationship's developed

between these beach dwellers.

The dogs are not capable of taking healthy pups,

but, by scavenging on the dead and dying,

they clean up the colony, preventing the spread of disease.

It's a practical, if not a little morbid, arrangement.

But with the beach littered with pups,

the difference between the sick and the sleeping

is sometimes hard to spot.

PUP SQUEALS

Jackals are adapted to desert life,

having kidneys designed to handle water deprivation.

But, without the seal feast on the beach,

even they would struggle to survive out here.

The seals rely entirely on the ocean,

not just for food and water,

but as a means to escape the desert heat.

So understanding how they cope does not reveal

how the rest of life can survive here

with little to no water.

But the coast does hold the key

to how this desert was formed in the first place.

The sand grains that are continually deposited

on to the Namib's beaches by Atlantic waves

are blown into the interior by relentless winds...

creating a desert with some of the largest dunes in the world.

The grains of sand that shape these giants

may have journeyed here over 5,000 years ago.

These dunes are actually dynamic.

Like waves in very slow motion,

the winds are constantly shifting and changing them.

Bone-dry sand forms arcing crescents -

a back slope piled up against the prevailing wind

and a shorter, steeper slip face.

As more sand builds up on the back slope,

the angle of the slip face becomes critical.

It's only a matter of time before gravity takes hold

and the slip face crashes down.

In this way, each dune moves along slowly but surely.

The shifting sands are searingly hot.

Midday temperatures regularly exceed 60 degrees.

If a seafarer was lucky enough to escape the wrecking coast,

they wouldn't last long out here.

But there are animals and plants that survive here,

where humans have failed.

A few tough species have managed to find a foothold

in this constantly shifting environment.

They may be small, but they are the true giants of survival.

All properly built to handle the heat.

The shovel-snouted lizard's dance

may look bizarre,

but it has a purpose.

It looks like it's simply getting some respite

from the burning sand,

but there's more to it than that.

It's cleverly taking advantage

of the heat dynamics

of the dune surface.

The air temperature is a whole ten degrees cooler

just millimetres above the sand,

so a raised foot can cool down

just enough to bring relief.

This desert lizard is so highly adapted to this environment,

its behaviour so specific to the Namib,

that it's found nowhere else on Earth.

It's one of 23 species of reptile endemic to the Namib,

each with their own unique way

to combat the blistering heat.

We know chameleons as tree dwellers,

but, clearly, the Namaqua is not your average chameleon.

To survive here,

it too has developed an extraordinary heat-avoidance tactic.

Like all chameleons,

it can change its skin colour.

However, its colour changes

are not just about communication or camouflage.

Here, the Namaqua uses colour

to regulate its body temperature.

Following a cool desert night,

the cold-blooded chameleon

flattens its dull, grey body,

angling itself towards the rising sun,

absorbing the warmth of the early rays.

But, as the sun grows higher and hotter,

and with nowhere to hide,

the Namaqua undergoes a colour transformation.

By turning a brilliant white,

it now no longer absorbs the sun

but can reflect it.

An efficient thermostat.

This astounding animal has taken an ability to change colour

and adapted it to regulate its temperature.

A neat example of evolution at work.

But this is not the only way in which the Namaqua differs

from its forest-dwelling relatives.

Rather than the fused feet used by tree climbers to grip branches,

this lizard is able to splay its toes wide.

Not only does this prevent the indignity of sinking into the sand,

but it also affords this chameleon

something that its relatives lack -

speed.

And when the ground below you is searingly hot,

it doesn't do any good to hang around.

So, even in a world without shade or cover,

with supremely clever temperature controls,

or thermo-regulation as it's known,

life has learnt to survive.

But there is shade,

if you know where to look.

And so far, we've only scratched the surface of ingenuity here.

The desert ecosystem doesn't just exist on the surface.

There's more to discover by looking in the dune itself.

Sand is not nearly as densely packed as hard earth.

Between the grains, there's enough air to breathe.

And, as we can see on this thermal image,

the sand can be

up to 20 degrees cooler

just centimetres below the surface.

So it's the perfect bolt hole to keep cool.

Or to lay a trap.

The Namibian spoor spider is tough -

it can withstand higher temperatures

than any other spider in the world.

And its ability to tolerate the heat

is the key to how it gets food

in this lonely place.

It sets its trap near an isolated grass tuft,

then weaves sand grains together

to create a sunshade

that doubles as a trapdoor.

While the spider tunnels below,

it provides perfect camouflage.

Only a single strand of silk

reveals a more sinister agenda.

Dune ants, on patrol,

investigate the grass for food...

..and trigger the spider's warning systems.

Gotcha!

Now, the spider uses its tolerance to high temperatures

to its advantage.

Pinned to the burning sand,

the ant overheats rapidly.

Within seconds,

the ant's core temperature will have increased by two degrees,

enough to kill it.

Using the hot sand

to do its dirty work

is a brilliant technique.

And with food so scarce,

when it does come along,

the spider can't afford to miss.

While some sit and wait,

others have to hunt for food.

The sand shows evidence of another bizarre creature that lives here.

Like its arachnid neighbour,

it too makes use of the cooler, deeper sand.

But it takes advantage of the quirk of deserts around the world -

the days are hot, ferociously hot.

The nights are cold.

Temperatures drop by 40 degrees.

Now, it's cool enough for the golden mole,

in its thick fur coat,

to move around.

Having spent the day deep in the cool sand,

it emerges to hunt for termites at night.

Air trapped between the grains allows the mole to breathe,

but also makes the sand unstable.

And so, the golden mole leaves no tunnel.

He is a sand swimmer,

ploughing through the dunes

as his trail collapses behind him.

Despite its appearance,

this little mammal is not related to our European mole.

Instead, it's descended from an ancient group of African mammals

dating back over 40 million years.

So the mole has had plenty of time to adapt to life in the dunes.

He is entirely blind.

Sensible, really -

eyes would only be damaged by the sand.

With such little rain, plants are few and far between.

But termites are most reliably found around plant roots,

so the mole may have to travel

over five kilometres a night in search of food.

Without eyes, how does the mole find its insect prey

in this featureless desert?

Well, grasses blowing in the wind

send percussive vibrations

through the sand.

The golden mole

has an extraordinarily developed middle ear bone -

proportionally, 6,000 times bigger than our own.

It's not sight, but sound

that guides this remarkable little mammal.

It can detect the slightest movement of grass or insect.

By dipping his head into the sand,

the mole uses his super hearing

to navigate between grass clumps...

..and secure himself a meal.

It is perfectly evolved for hunting in the sand.

Well, most of the time.

And so, all of the Namibian desert's inhabitants

have developed unique ways in which to deal with this microworld.

But these adaptations

by the insects, reptiles and mammals

are because of this extreme environment.

Clever avoidance tactics, yes,

but not the reason why this system works.

It's not enough just to avoid the climate.

In order for an ecosystem to sustain,

its animals and plants must live long enough to grow, to reproduce.

And to do that, they MUST have water.

It's one of the most fundamental elements of life.

So where is it in this desert?

Well, the Namib is harbouring a life-giving secret.

The key to this puzzle has been created

by a meteorological quirk

as old as the desert itself.

Like our golden mole,

the secret to this desert success avoids the day's heat.

It comes by night.

Fog creeps through the dunes.

But a dense fog in one of the most arid environments on Earth -

how is this possible?

Well, the ocean knows.

The freezing cold currents

that support those seals and pound the Namib coast

have another role to play in life in the interior.

The cold, wet, heavy air

riding the winds above these currents meet the land

and are forced under the drier and lighter air from the desert.

Under normal atmospheric conditions,

cold air would sit high in the atmosphere,

above the warmer surface air.

Instead, these layers are reversed.

This quirk is known as an inversion layer.

Once trapped, the moisture within this cold layer forms a dense mist.

And it's this mist, this sea fog

that forms the life blood of the Namib Desert.

For fog is, in its essence, just suspended water,

an airborne reservoir.

You just need to know how to harvest it.

The few plants drip with it.

The desert crickets drink it from their stems.

A gecko collects water droplets

that have condensed on its warm eyeballs.

The sidewinding adder licks water droplets from its skin.

But perhaps the cleverest adaptation of all

can be attributed to a beetle

or, more accurately, to its back.

The settling fog triggers

the most unusual beetle behaviour.

They're not known as fog baskers without a reason.

They emerge from the sand in the early mornings

and, by standing on their heads,

present their backs to the rolling fog.

The beetle's back is riddled

with peaks that attract the fog,

encouraging droplets to form

which then roll down waxy troughs

into their open mouths.

This peculiar water harvesting tactic is highly productive.

By the time the fog has been broken by the sun,

a beetle might have consumed

40% of its body weight in water.

This fog is reliable enough

to allow the beetles to keep topping up with this vital fluid...

..becoming like walking water bottles

to other thirsty dune dwellers.

And forming the base of a complex fog web

in which water is passed through the ecosystem from prey to predator.

The beetle provides the chameleon

with enough water to live on

for several days.

The sidewinding adder,

a master of desert camouflage,

is also on the hunt for water.

Eyes positioned on top of its head

allow the adder to bury itself in the sand,

becoming almost completely invisible.

The adder may have to lie in wait for several hours

before the right target appears.

By twitching the tip of its tail,

the snake mimics a small insect in distress.

The perfect lure

for a nearby lizard.

The lizard,

full of water from the morning fog,

becomes a precious resource

to larger predators.

The adder is quick...

..but, on this occasion,

the lizard is faster.

So these fog harvesters act as both a food and water source

in this arid environment.

But, if these are the very bottom rung of the food chain,

what are they eating to survive?

In other ecosystems,

plants provide the most basic food source.

But, even with the fog,

the sand is too dry and unstable

to support any but the hardiest of plants

and they're not in sufficient numbers

to support this amount of life.

The Namib Desert has another trick up its sleeve.

The winds that bring the fog also bring another lifeline.

They blow in bits of dead plants,

the odd insect and droppings,

known collectively as detritus,

which is deposited on the dunes.

This collection of environmental scraps

may not seem like rich pickings,

but, for the species that form the lowest rung of the food chain,

it's manna from heaven.

Fog-basking beetles are detritovores,

feeding on dead and decomposing organic matter.

But this is fast food.

The beetles must work quickly

before their meal is once more blown away by the winds.

the energy from the detritus will be transferred to the predator,

making the success

of this entire ecosystem

dependent on the winds

that blow across this amazing land.

At first glance, Namibia's coastal desert might seem lifeless...

..but by looking closely

and examining the life here,

in this microworld,

where species succeed

because of their unique adaptations

that protect them against

the very climate in which they live.

We've discovered the true secret to life.

Not in the desert itself,

not in the structure of the dunes

or hidden in the coastal sands.

This ecosystem relies entirely on external forces.

Without cold ocean currents

and the winds that rush along this coast

bringing the key ingredients for life,

this desert would be truly barren.

Instead, animals forge an existence here

that cannot be found

anywhere else on the planet.

The secret to survival is in the very air of the Namib Desert...

..and the extraordinary creatures

that have evolved to harvest it.