All language subtitles for Natural Curiosities S01E02 - Skin and Armour CC HDTV x264 AC3 1080p

'The natural world is
full of extraordinary animals

'with amazing life histories.

'Yet certain stories are more
intriguing than most.'

The mysteries of a butterfly's
life cycle,

or the strange biology
of the emperor penguin.

Some of these creatures
were surrounded by myth

and misunderstandings
for a very long time.

And some have only recently
revealed their secrets.

These are the animals that
stand out from the crowd -

the curiosities I find
most fascinating of all.

'The elephant and the mole rat -'

they're both extremely wrinkled,

starting their young lives
looking ancient,

and remaining that way into old age.

Yet they outlive most other
animals their size.

What are their secrets?

Nature has twisted
the task of the narwhal

and the shells of snails
and their relatives.

But what is the purpose of the twist?

'Spirals are common
in the natural world.

'We seldom pay attention to them.

'But in fact, they have
remarkable characteristics'

which many animals exploit.

And some creatures,
having developed a spiral,

have reworked it in many intriguing
and beautiful ways.

In this programme, I'll try
to discover why the spiral

is so important to two very different
kinds of animals.

Elephants are truly
strange creatures,

both in looks and behaviour.

Aristotle described them as,

"The beast that passeth
all others in wit and mind."

But the more we learn about
its curious body and behaviour,

the more remarkable it appears to be.

The evolution of such a
strange-looking creature
is no accident.

Its fascinating body is the key
to allowing elephants

to live a long life.

For elephants, even young ones,
it's an advantage to be wrinkly,

and not at all a sign of old age.

Elephants evolved from mammoths
over 55 million years ago.

Today, they're the heaviest
land mammals alive,

and one of the longest lived,

with a life expectancy
of about 70 years.

Big creatures usually live
a long time largely

because they have slow metabolisms.

However, elephants have particular
characteristics

that help them reach old age.

One of the most important,
a family structure

in which the oldest matriarchs
pass on vital experience.

And their bodies have developed
some special features

to deal with the problems
of being so big.

Their trunk is one of them.

This, surely,

is the most extraordinary nose
possessed by any living creature.

It can be moved with ease
and dexterity,

to gently caress,

tear down trees,
suck up litres of water.

The trunk is, in fact, a union
between the nose

and the upper lip,
and it's highly sensitive,

with over 100,000
muscle units in it.

The end of the trunk can move
rather like a hand.

This mobile tip allows the elephant
to feel and pick up

delicate objects
such as a single blade of grass.

The stretched nose
is a masterpiece of evolution,

and key to how the elephant
can survive

with such a large and curious body.

ELEPHANT SNORTS

If they hadn't developed a trunk,

elephants couldn't have become
so big.

It enables them,
in spite of their huge, stocky body,

to reach down to the ground
to collect food and water.

Fuelling a big body
is a full-time job,

and an elephant has to consume
its own weight in food every 20 days.

One might think this great weight
would be a stress on joints

and teeth, and wear elephants
out before old age.

'But not so.'

Eating vegetation is of course
very tough on the teeth,

and there are some animals,
that when their teeth are worn down,

simply starve and die.

But elephants can live
to 70 years old,

and the secret lies
in their extraordinary molar teeth.

They have two pairs -
two at the top, two at the bottom -

and here's one of them.

This is the grinding surface,

which is capable of shredding
twigs and bark, and even wood,

and of course, it wears.

But as it wears down,

so another tooth is developing
within the jaw, which finally emerges

and pushes this forward until it
actually breaks off and is shed.

Acquiring new teeth in that way

enables elephants to remain
well-fed and healthy into old age.

In elephant society,
the older females are invaluable,

and pass on the wisdom they've
gained during their long lives

to younger members of the family.

ELEPHANT GROWLS

Mature females spend
long periods of time

Iistening out for vital sounds
of danger and warn the group.

Such sensitivity to sound
was the subject

of one of the very first
animal behaviour experiments.

Someone in France
in the early 18th century noted

that elephants in menageries
appeared to react

to faint, distant sounds
outside their enclosures.

So they tested two elephants -
Hans and Parki -

and engaged a palace orchestra
to play love music to them.

One elephant was very impressed
by the French horn player.

It was reported that,
"The animal knelt down before him,

"caressed him with his trunk
and expressed to him in all sorts

"of pretty ways the pleasure which
it had felt in listening to him."

We now know that the French horn
can produce a low-frequency sound

that's very like the rumble
that elephants produce

using a similar resonating chamber
in their heads.

LOW RUMBLING

They can also hear very deep sounds
beyond our own hearing.

The oldest, experienced females
are experts at interpreting them.

Such frequencies create
vibrations in the ground

that travel a very long way,

which the elephants can detect
through their feet.

Their feet, in fact, are not
as solid as they might look,

but have special
internal cushioning

to soften the impact of the animal's
weighty footsteps.

For such a large creature,
that can be 40 times our weight,

this foot seems unfeasibly small.

Its surface area is little more
than twice our own feet,

but this foot has
a surprising structure.

The elephant walks on five toes,

and the back part of its foot
consists of a highly spongy heel.

The raised heel can compress
and expand to absorb shock,

and shield the other heavy bones
in the body from pressure.

It's as if the elephant were wearing
a high-heeled training shoe.

When an elephant runs,
it bounces on this spongy heel

and its leg bones act
like pogo sticks

to push the animal upwards.

This system protects the bones
and inner tissues.

And wild elephants rarely get
arthritis.

Despite their large size,
they live active, physical lives

without too much damage
to their bodies.

Males, as they mature,
usually go off to live by themselves.

But the females stay
with the family group

and play a very important part
in guiding the younger ones.

Young elephants tend to look old
even at the start of their lives

because of their wrinkly skin.

But, for elephants,
wrinkles are not signs of ageing.

On the contrary,
they're extremely important

for an elephant's very survival.

The elephant's thick, creased skin

has been the subject of much debate
over the years.

And early anatomists had
some novel ideas about it.

Many believed that the elephant
could actually move its skin

to crush flies between the wrinkles.

I may say,
that was never witnessed in action.

But the skin WAS thought to be
enormously thick and insensitive.

But in fact
it varies across the elephant's body

and can be as thick as
two or three centimetres

around the top of its trunk
and along the back

and as thin as paper
around the eyes.

Although the skin looks tough and
wrinkly, it's remarkably sensitive.

An elephant can feel small flies
on its body,

even if it can't crush them
between its wrinkles.

But these wrinkles really do
have an important function.

The patterned crevices hold water,

which travels along them
all over the body.

Wrinkly skins can contain five to ten
times more water than smooth ones.

So moisture collected
during the wallowing

stops the skin from dehydrating
and overheating

for a long time afterwards.

Significantly, African elephants,
that lived in hotter, drier places,

have more deeply wrinkled skins
than Asian elephants.

So, wrinkles for the elephant
are ways of protecting the skin,

not the unwanted consequence
of old age.

The elephant was once considered
an oddity of nature.

For centuries, we've been fascinated
by their large ears,

their extraordinary trunks,

the stocky feet, the wrinkly skins.

But over the years, we've come
to understand their significance.

The elephant's unique biology
is key to its long-term survival

and its ability to seemingly avoid
the rigours of old age.

Elephants, understandably,
live a long time

because of the slow metabolism
of their huge bodies.

But small, naked mole rats
live much longer

than any other mammal
of a comparable size.

Why?

Could it be that the body
of this bizarre little creature

holds the secret of eternal youth?

When a German naturalist,
Wilhelm Ruppell,

discovered a lone, hairless,
wrinkled, naked mole rat

in 1842 in Ethiopia,

he was convinced
that he had stumbled across

a decrepit, old individual,

and he gave it the name
Heterocephalus glaber,

which loosely translated means

a smooth-skinned animal
with an oddly shaped head.

He noted that the form of the body,
because of its hairlessness,

gives an unpleasant impression.

It does.

For the next 40 years,

these bizarre-looking creatures were
largely ignored by scientists.

Then, in 1885, a British zoologist
in London's Natural History Museum,

called Oldfield Thomas
decided to examine in detail

the museum specimens that had been
sitting in store for decades.

Here we can see some of his drawings.

Thomas declared that the weird
animal described by Ruppell

was in fact normal.

We now know that all mole rats
look like this, whatever their age.

However, what those early naturalists
couldn't have known

was that they had
chanced upon a mammal

that would fascinate and intrigue
scientists for the next 150 years.

A creature that might even
shed light

on the secrets of ageing
and longevity.

Its body hardly seemed to alter,
no matter how long it lived.

Old mole rats stayed physically
young throughout their lives.

And not only that,
the strangest discovery of all

was that they sometimes lived
for almost 30 years.

The lifespan of animals
varies enormously.

Amongst mammals, a tiny little shrew
like this lives just two or so years.

While a giant whale
can reach the age of 100.

Lifestyle is an important factor
in defining lifespan.

A shrew has a fast and furious life,

producing many young
of which few survive.

Whales, on the other hand, breed
slowly and don't have many predators.

Generally, big animals live longer.

So it's very odd indeed

that mole rats live
up to nine times longer

than any other similar-sized rodent.

Why?

In the 1960s, more than 100 years
after their discovery,

scientists started keeping
the animals in laboratories

to try and answer that question.

The results were confusing.

The mole rats lived in colonies

and only a few females
ever reproduced.

Around that time,

an evolutionary biologist called
Richard Alexander was studying

the way colonial insects, such as
termites, organised their colonies.

They have a single breeding female

who produces huge numbers
of non-breeding workers.

A system called eusociality.

He speculated that if there were
such things as a eusocial mammal,

it too, like termites, would live
underground in hard soil.

He was right.

The naked mole rat perfectly fits
Alexander's description

of what a eusocial animal
should be like.

There it is.

It lives underground
in large social groups

and digs for tubers

in exceptionally hard soil.

Physically,
it's evolved for a life below ground.

It has a long, thin body with short
legs that suit life in a tunnel.

Its enlarged, strong teeth
are used for digging,

its skull is strong,
the head quite large.

Lips close behind its teeth to stop
any soil going into its mouth.

Also, it's almost entirely bald,
except for a few sensory hairs.

Could it be that these
extraordinary characteristics

have something to do
with their ability

to live very, very long lives?

They are certainly key to the mole
rat's unusual life underground.

The queen is at the heart
of the colony.

She mates with just
two or three males

and produces babies in huge litters,

sometimes of more than 20.

The workers feed the queen, care
for the young and guard the tunnels.

Their role is essential -

the colony would not survive if all
its members didn't work together.

The tubers that they eat are hard
to find on the dry African plains,

and the workers have to dig miles
of tunnels in their search for them.

The fact that they don't breed
might seem hard,

but their mother, the queen, does.

And her DNA is virtually
identical to theirs.

And by working together,

the colony can live in places where
an individual mole rat could not.

But this still doesn't explain
why these creatures live so long.

More recently, another adaptation
to life underground threw up a clue.

Fossil records show that mole rats
started living underground

about 24 million years ago.

Not surprisingly,
they are now highly adapted

to a life in dark
and humid tunnels.

Conditions in a sealed,
two-metre-deep tunnel system

don't fluctuate greatly.
And maybe because of this,

mole rats have lost the ability to
regulate their own body temperature.

So, to prevent getting chilled,

they huddle together in groups.

They also, like reptiles, absorb heat

by basking in the warmer,

shallow surface tunnels.

Being hairless might be an advantage

for an animal that's
essentially cold-blooded

and needs to get some of its heat
from its surroundings,

and that may explain why naked
mole rats are virtually bald.

But why are not other warm-blooded
mammals that live underground
also bald?

Badgers, for example,
have hairy coats.

Well, badgers come above ground
to feed

and then they need their hairy coats
to keep warm.

Naked mole rats, on the other hand,
never see the light of day.

Nonetheless, one might think

that being soft-skinned and bald
is a huge disadvantage.

For mole rats live
in stuffy, insanitary conditions.

Mole rat colonies can contain
several hundred individuals,

and conditions underground are dark
and dank and often quite toxic.

Oxygen levels can be very low
and carbon dioxide high,

yet, mysteriously,
mole rats show no discomfort

and suffer very little from disease.

This tolerance to such hostile
conditions may also be related

to their strange, wrinkled skin
and the cells below it.

Apparently they lack a key
neurotransmitter called substance P,

that is normally responsible
for sending pain signals

to the central nervous system.

This may explain their ability
to survive the toxic conditions

underground without stress
and damage to their bodies.

It could also be one of the secrets
of their youthful appearance,

if you can call it that,
and even their longevity.

Most animals react strongly to pain,
and this can damage their bodies.

In mole rats,
this effect is eliminated

by cutting out the pain response.

Incredibly, no mole rat has ever
been found with cancer.

But even if a normal animal
survives disease, it still ages.

This is largely due
to other chemicals in the body

called oxidising agents.

They build up with time
and break down the body tissues.

This leads to the tell-tale signs
of old age.

Incredibly, mole rats appear
to have no physical reaction

to high levels of oxidising agents.

They grow very old,
yet they don't physically age.

In wild mole rats,
the queen is the most long-lived.

And one of them, here,

is 24 years old.

Yet she still has
the body of a two-year-old.

No-one is sure how mole rats avoid
the symptoms of old age,

but a unique physiology, evolved
in response to the underground life,

has created an animal
that is almost supernatural.

Here's a creature
that's seemingly impervious to pain

and with an iron constitution.

It's virtually cold-blooded,
with a slow metabolism,

and has evolved an unusual mix
of strategies

to deal with its
challenging lifestyle.

In the future,
these remarkable animals may help us

solve some of our own problems,
such as pain control,

degenerative disease

and how we might avoid old age
and wrinkly skins.

Here is a natural curiosity

that is well worth pursuing.

Both elephants and mole rats remain
much the same as they grow old.

And surprisingly,
the small naked mole rat lives,

relatively speaking,
even longer than the elephant.

The narwhal lives in the cold waters
of the Arctic sea.

It's rarely seen and little is known
about its life, even today.

But 400 years ago, it was a source
of myths and tall tales

that fooled everyone, including
the royal households of Europe.

These tapestries, hanging
in Stirling Castle, are modern,

but they are accurate copies
of medieval originals.

And they show several images
of that most wonderful creature -

the unicorn.

In the Middle Ages, the unicorn was
thought to be a real animal.

And what's more,
one with magical powers.

So, the King of Scotland incorporated
one in his coat of arms,

and that in due course was inherited
by the British coat of arms

and is shown sitting opposite
the English lion.

During the Middle Ages,
it was believed

that a unicorn horn could detect
poison and neutralise it.

So it's not surprising that
most of the kings of Europe wanted

one of these wonderful
and powerful objects.

Such treasures, however,
weren't easy to come by.

But in the 16th century, an English
seaman accidentally discovered one.

In 1576, Martin Frobisher
sailed across the North Atlantic

in search of a sea route to connect
the Atlantic with the Pacific.

And when he reached the chilly coast
of northern Canada,

he found, lying on the seashore,
a unicorn's horn.

He brought it back to Britain
and soon found a buyer -

Elizabeth I.

This is very like the object

that Sir Martin Frobisher presented
to Queen Elizabeth.

It's said that she paid
£10,000 for it.

In today's money, that's about
half a million or more.

Weight for weight, unicorn horn
was worth more than gold.

But the object was not what
Queen Elizabeth supposed it to be.

It was not the horn
of a mythical animal,

it was the tusk of a kind of whale
that swam in the Arctic seas -

the narwhal.

The first examples were brought south
by the Vikings.

They almost certainly knew
exactly what its origin was,

but, for 400 years,
they maintained the story

that it came from
the mythical unicorn.

But farther south in Europe,
no-one knew about narwhals,

and scholarly natural history books

confidently described unicorns
in detail, as if they were real.

Since unicorn horns
were hard to come by,

unscrupulous dealers met the demand
by grinding up rhinoceros horn.

In fact, the horn of a rhino
and a narwhal

could hardly be more different.

You can see from this narwhal skull,

the hole where the horn
would normally sit.

It grows outwards through the lip.

But whereas rhino horn is
actually made of keratin -

the same stuff
as our fingernails are made of -

the narwhal's great horn is
actually made largely of dentine.

It's not a horn at all,
it's an enormous canine tooth -

a tusk.

Some female narwhals possess tusks,

but by and large
male narwhals grow the long tusks

which can reach
three metres in length.

It's been described
as a cross between

a corkscrew and a jousting lance.

But its true purpose has baffled
scientists for centuries.

Very few creatures have tusks.

The most well-known, of course,
are elephants.

Their tusks are in fact
enlarged incisor teeth.

Both male and female elephants
develop them

and they're used in many ways,
but primarily for getting food -

digging into the ground, ripping up
grass or pushing over trees.

The obvious difference between
elephant and narwhal tusks

is that the narwhal possesses just
one, whereas the elephant has two.

But that may not always
have been the case.

This is a rare curiosity indeed.

It's the skull of a narwhal
with two tusks.

It's possible that such a rarity
offers a window on the past.

Perhaps the ancient ancestors of
the narwhals were once twin-tusked,

but over time, they lost one.

But what was it for?

One early suggestion was that
the narwhal used it to spear fish.

Though how it would manage
to transfer its catch

from the end of its tusk to its mouth
was never explained.

Someone else suggested
that the animal used its horn

to stab holes through the Arctic ice.

That's not unreasonable,

since narwhals spend
a lot of time under ice,

and being mammals, they have to
get to air in order to breathe.

But it seems strange
that only males have a tusk.

After all, females need
to breathe too.

Charles Darwin had
another explanation.

He likened the tusk to the antlers
carried by male deer -

stags.

Antlers help stags to establish
hierarchies during the mating season.

This stag with the biggest antlers
asserts his dominance

by showing them off
and occasionally fighting with them.

Darwin proposed that
the long tusk of the narwhal

functioned in just the same way -

as a declaration of dominance
and, if necessary, as a weapon.

That would explain why male narwhals
possess the long tusks.

And why, when males meet,

they sometimes cross tusks in what
might be a ritualised form of combat.

Darwin's theory has
long been accepted.

But recently, scientists have been
exploring other possibilities.

Our teeth are covered with
a thick enamel layer

that protects the softer material
beneath.

If that erodes or is damaged,

then it exposes the nerves
within the tooth

which can make them extremely
sensitive to temperature.

Narwhal tusks don't possess
that external enamel covering.

And high-magnification photography
has revealed something

very unusual about the exterior
surface of this huge elongated tooth.

The surface of the tusk is cratered
with millions of tiny pits

called tubules. Each tubule contains
a fluid, and at its base, a nerve.

The fluid reacts to
the narwhal's environment,

so the tusk must be highly sensitive.

Tests on narwhals have shown
that they can detect tiny changes

in the temperature
and salinity of water,

key factors that govern
the formation of ice.

Their migration is tied to
the seasonal shrinking

and expanding of the ice cap.

So perhaps the tusk plays a role
in detecting ice or open water.

But its sensory powers
could be even greater.

Perhaps the tusk is able to detect
movement in the water.

Or even changes in the fertility
of female narwhals.

These are theories yet to be tested.

If this is a sensory tool,

then it would put a very different
interpretation on the male jousting.

Perhaps males enjoy
rubbing their tusks together.

There could be a third explanation,
a more practical one.

Tusks from old narwhals
often become coated with algae,

which might block the pores
that lead to the nerves.

So, perhaps males rub their tusks
together to help clean them.

Could this be not fighting,
but cooperative grooming?

Why mainly male narwhals carry
a sensory tool is still unexplained.

Rather than being a weapon,

perhaps the highly sensitive tusk
helps males to find female partners.

More than likely,
the tusk serves many functions.

But why should it be twisted?

The twist increases the surface area,

so it's possible
more nerve endings are exposed.

And this would
increase its sensitivity.

But there's another theory
that suggests that the twist

actually helps to keep
the tusk straight.

That may sound counterintuitive,

but tusks of other large animals
tend to curve down or up.

A spiral growth may actually help
the tusk to keep pointing forwards,

and so reduce drag in the water.

There's another way in which
a twist could help in swimming.

As the animal moves forward,
the water around the tusk

spirals away from it
in a way that might reduce drag.

But at least today we know
the true identity of the animals

that produce these wonderful
and spectacular ivory spears.

The myth that they came from the
unicorn was finally exploded in 1638

by a Danish scientist, Ole Worm,

who gave a public lecture
proving conclusively

that they came from the narwhal.

So then, of course,
their value plummeted.

Today, we no longer believe
they have magical properties,

but there's still quite a lot
about them we don't fully understand.

Our second subject belongs
to a group of animals

that have taken the spiral

and adapted it
into a multitude of variations -

snails.

When the first snails crawled
out of the sea and up onto dry land,

they carried with them the shells

that were to be crucial
to their survival out of water.

They themselves
were distant relatives

of other shelled creatures
that had dominated the seas

for millions of years.

They were the ammonites.

This is one of them, and this is
about 160 million years old.

Although they experimented in some
degree with the shape of the shell,

nearly all of them are like this -

flat,

spiral

and symmetrical.

In due course, the ammonites
themselves became extinct.

But since then, other creatures
have developed the shell

into a whole variety
of different shapes and sizes.

This variety shows how successful
the spiral can be

as the basis for a shell's design.

And how it can be elaborated
and decorated.

Snail shells,
like the shells of birds' eggs,

are made of calcium carbonate.

They appear at the very beginning
of a young snail's life,

and they are never shed, but simply
become enlarged as the animal grows.

But whatever their shape and size,
they are almost always spiralled.

Spirals have been used by animals
for a very long time.

We can trace them back
to a group of sea creatures

that first appeared
around 500 million years ago.

And some are still around today.

This is one - the nautilus.

Today, it's only found in the deep
waters of the Indo-Pacific ocean.

But millions of years ago,
animals like it were widespread.

Its earliest ancestors, however,
had a very different shape.

There's evidence that
the nautiloids started out

more or less straight, like this one,

just a little curl at the beginning,

and then running straight like that,

with the separate chambers
running along there.

But as millions of years passed,

they began to coil until
they became species like this one.

And then, millions of years later,

another group adopted
the symmetrical coil.

These were called ammonites.

But why did these animals
coil their shells?

Well, if their shells remained
straight as they increased in size,

they would inevitably become
somewhat cumbersome.

Coiling them made them
more compact and perhaps more mobile.

Whatever the reason, the change
in shell shape was a great success.

Thousands of new species appeared,
all with coiled shells.

These fossilised shells
tell us little

about the soft-bodied creatures
that lived in them,

but the living nautilus can give us
some clues about that.

At the start of its life, the shell
consists of just a few chambers.

But by the time it's mature,

there may be as many as 30.

Richard Owen, the founding director
of London's Natural History Museum,

wrote the first full description
of the nautilus.

This is Owen's own personal copy,

and it's full of exquisite sketches.

His drawings show just how the animal
is placed inside a shell.

Almost all the soft tissues -
its body and tentacles -

are held in the outermost chamber.

And a long tube, called a siphuncle,

runs through the chambers,

through which the animal can pump in
water or remove it,

and so regulates its buoyancy.

So, the nautilus's spiral shell

not only protects its soft body
from enemies,

but enables it to cruise around.

And it's so strong that the nautilus
can descend as deep as 700 metres,

where pressure would kill
a human being.

At the peak of their success,

there were thousands of different
kinds of nautiloids.

But their cousins, the ammonites,
were even more varied and diverse.

Their buoyant shells allowed
some of these creatures

to grow to a huge size.

Some were as big as a human being.

But it would be impossible for such
a creature to move out of water

with a shell like this. It would
be far too heavy and too cumbersome.

Nonetheless, something was about
to happen to the molluscs

that would allow them to leave
the water and move up onto land.

The ammonite dynasties
were developing

different shapes to their shells,

uncoiling them in all sorts of ways.

Some of these new forms
fed on the sea floor

and therefore had
less need to be mobile.

But other shelled relatives of the
ammonites were going even further,

changing both their shell shape
and twisting their soft bodies.

And these are their descendants -

snails.

The problem with a symmetrical shell

is that each whorl has to grow

on the outside of the other one,

so that the shell very quickly
becomes very big.

But by becoming asymmetrical,

and offsetting each whorl
to the side,

the shell can remain
much more compact

and rounded and easier to manipulate.

The shift in the snail's symmetry
seems to have been triggered

by the action of a single gene.

But this change can bring
complications.

Because of their asymmetric shape,

snails have to position themselves
carefully during mating.

In most snails,
this is not a problem,

as the body plan of snails
is usually the same.

But not all.

Just like humans, who are either
right-handed or left-handed,

snail shells can twist

to the left...

or the right.

The vast majority of snail shells
are right spiralling.

But in one particular area of Japan,
the left-handed form

of this particular species
has a clear advantage.

That is all because of this creature,
a snail-eating snake.

It's so specialised for eating snails

that its jaws have evolved to become
asymmetrical, just like its prey.

The right side of its lower jaw
has more teeth than the left.

Recently, scientists in Japan filmed
the hunting behaviour of this snake.

When it attacks a snail
with a right spiral shell,

its row of extra teeth dig
into the snail's flesh,

and by moving its jaws
back and forth,

it separates the snail's body
from its shell.

But attacking a snail
with a left-spiralled shell

is not so straightforward.

The position of the shell means
that the snake can't use

its specialised jaws so effectively.

And it gives up.

Shells help land-living snails
to conserve moisture

and also protect them
from their enemies.

The snails' soft bodies are,
of course, welcome meals

to any predator
that can crack their shells.

Some snails have
strengthened their shells.

Some have protected them with spines.

Others have become very thick indeed,

and almost uncrackable.

Some scientists believe that this
could be the golden age of the snail.

They've never been more diverse,
in terms of species

or indeed the variety
of their shells.

But while the snails
are more varied,

that is not the case
with the nautilus.

The oceans were once dominated
by creatures like this,

and today, just a handful
of different types exist.

While snails have taken the spiral
and modified it endlessly,

the modern nautilus has stuck
with a symmetrical spiral

that's hardly changed
for hundreds of millions of years.

So it's fair to say

that the nautilus shell is
a window on the distant past,

to a time when the simple,
but symmetrical, spiral

dominated the seas.

So, both whales and snails have
benefited from the twist,

a design that first appeared
500 million years ago

and is still widespread today.