Episode 2 David Attenborough's Natural Curiosities

'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

listening 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.