Episode 5 David Attenborough's Natural Curiosities

Why do some animals advertise themselves

with bold patterns or dazzling colours?

I've been lucky enough, one way or another,

to meet some of our planet's most enchanting animals,

but some I find particularly intriguing.

We've known about some of these creatures for centuries.

Others, we have discovered more recently.

In this series, I share their stories

and reveal why they really are natural curiosities.

The natural world is full of colours and patterns.

For most of us, many animals are simply beautiful,

sometimes so beautiful they become highly collectable.

But what role do colours and patterns play

in the lives of the animals that display them?

The zebra

has stripes unlike any other mammal.

When they first became widely known outside Africa,

during the 18th century, they were much-prized pets

in menageries of the nobility and royalty.

But while they fascinated the public, they baffled scientists.

What on earth could be the function of these extraordinary stripes?

Well, the answers that have been suggested over the centuries

have been truly astounding.

To begin with, all that was known about zebras

was that they lived in herds on the vast plains of Africa.

But as zebras became more familiar to European society

we began to learn more.

One particular zebra became something of a celebrity

in Georgian England,

so much so that it was painted

by the famous racehorse painter, George Stubbs.

This is a copy of his picture.

It was a belated wedding present to Queen Charlotte

from her husband, King George III,

and it actually lived in the grounds of Buckingham House,

as Buckingham Palace was then known.

Queen Charlotte was a passionate collector of exotic animals

and the zebra soon became the most famous animal in her collection,

attracting crowds of visitors.

Georgian London was not unfamiliar with bizarre and exotic creatures.

Many curiosities were being sent back

from the expanding British Empire.

But the strange striped horse was particularly intriguing.

Early zebra collectors, in trying to tame them,

stumbled upon one possible reason for their stripes.

Queen Charlotte wasn't the only famous European

to be fanatical about zebras.

So was this gentleman, Lord Clive of India,

the British Army officer who established British interest there

in the 18th century.

He actually owned two, a male and a female,

and so keen was he to try and get a zebra that would be tameable,

he tried to mate his female zebra with a male donkey.

To make the male donkey more attractive to the female,

believe it or not, he painted it with stripes -

and the experiment was a success.

In due course, the female zebra produced a foal.

As this old newsreel shows,

the offspring of such unions are partially striped.

They're also sometimes fertile.

Lord Clive's success in producing one

might suggest that the stripes are indeed important

in making one partner attractive to the other.

Charles Darwin built on that idea.

He noticed that each individual zebra

had its own unique stripe pattern.

He suggested that the stripes were a way for individuals

to recognise each other during courtship.

Occasionally, however, a zebra appeared with a coat pattern so odd

that it challenged that explanation.

In 1968, a picture of a very strange zebra appeared in the press.

It's fair to say that this animal is dotted, rather than striped,

and that could give us an insight

into the function of its coat patterns.

If it's to do with social cohesion

then you would expect that such a strange creature

would be shunned by the rest of the herd,

but that was not so.

It was treated just like any other member.

So maybe its coat patterns

are not primarily to do with social cohesion.

Other theories suggest the stripes play an important role

in defence against predators.

But how?

It's been claimed that the moving striped bodies of a herd of zebras

confuse a lion, making it difficult for it to judge distance,

and so time its pounce.

Others have argued that the stripes break up the zebras' outlines,

so they're hard to spot, especially amongst vegetation.

However, research comparing the zebra and the tiger

concluded that, while a tiger's stripes makes it

blend with its background, at least to our eyes,

the regular spacing of the zebra's stripes

actually make it more conspicuous.

The bold stripes of Queen Charlotte's zebra

drew huge crowds to Buckingham Palace,

but the animal itself was proving to be quite a handful.

The Queen's lone pet was a somewhat temperamental animal and its

keepers had to warn spectators that it was likely to kick and bite.

And that's hardly surprising, bearing in mind the strange food

it was given, which was a mixture of raw meat and tobacco -

hardly the sort of thing to give to a grazing animal.

It also became a way of lampooning the royal family.

The animal itself was known as the Queen's Ass, and its stripes

were used to indicate the king and queen's son, Prince George.

The Victorians continued the Georgian obsession

with taming zebras, but they had a practical reason for doing so.

A reason that may provide another explanation for the stripes - flies.

Flies carry fatal diseases that affect both humans and cattle,

and one of the most dangerous in Africa is the tsetse fly.

It spreads a disease called sleeping sickness that kills people,

cattle and horses.

Early Victorian settlers noticed that, while their domestic

horses fell ill from sleeping sickness, zebras were not affected.

So they set about taming them.

Over the years, many people have attempted to tame zebras, but the

efforts of one Victorian eccentric were particularly spectacular.

These zebras were once part of a menagerie of a Victorian aristocrat,

who became obsessed with taming them.

Walter Rothschild was a member of the great Rothschild

banking family, but he wasn't much good as a banker.

His main passion was for wildlife.

And he had a particular fondness

of zebras and spent a great deal of time and effort training them.

Rothschild succeeded where others failed.

This extraordinary photograph shows him on a journey

to Buckingham Palace, with his carriage being drawn by tame zebras.

It was a time-consuming process.

He trained each zebra individually, using a small carriage.

And they didn't take easily to being bridled,

but eventually all three of his zebras, and a pony,

pulled his carriage all the way through London to Buckingham Palace.

It must have been a strange spectacle to anybody passing by,

but perhaps they didn't notice the zebras.

Walter's brother Charles remarked that the stripes of the zebra

made them almost disappear as they travelled through the city streets.

Despite Rothschild's efforts, zebras never really became

an alternative to the horse in England or in Africa.

The observation by those early settlers, that zebras seemed

immune to the bites of tsetse flies, was not entirely correct.

Zebras can be bitten by flies

and can suffer the same sickness as the domestic horse.

But nonetheless, evidence suggests they attract fewer flies.

Some scientists have theorised that the zebra's stripes may in some way

make it more difficult for biting flies to land on a zebra's body.

To test this theory, a number of Hungarian scientists

took four horse-shaped models.

One they painted black, another they painted brown, the third was white

and the fourth was painted with the stripes of a zebra.

Then they put these four models in a field

and covered them with sticky glue.

Then, after a certain length of time, they went

and counted the number of flies that had landed on the different bodies

And believe it or not, there were fewest flies on the zebra's body.

How could this be?

Well, an insect's eyes are compound, they have a lot of elements in them,

and they navigate using horizontally polarised light. And it may be that

the stripes of the zebra in some way disrupt that polarised light and

make it much more difficult for the flies to land on the zebra's body.

These recent findings

do not prove definitively why zebras got their stripes.

There could be several other benefits.

But they do suggest that the stripes are more about avoiding

being bitten, rather than avoiding being eaten.

Whatever the biological reason for its stripes,

zebras have fascinated us for centuries.

Queen Charlotte was so besotted by hers

that eventually she bought another.

The first had proved to be so ill-tempered

that she sold it to a friend of King George III.

From there, it went to a travelling menagerie and when it died,

its body was stuffed and put on display

in the Blue Boar Inn in York,

something of a come-down from the grounds of Buckingham House.

The zebra has taken a basic striped pattern and stuck with it.

Our second patterned animal has done quite the opposite

and has produced thousands, if not millions, of variations on a theme.

Victorian naturalists seemed to have been obsessed with butterflies.

Their assembled specimens fill the cabinets of many a museum.

London's Natural History Museum has over three million of them, alone.

And it's easy to see why those naturalists were so obsessed.

Butterflies are so astonishingly varied and stunningly beautiful.

When it comes to pattern,

nature seems to have excelled herself with the butterfly wing.

Why nature has refashioned the wing into so many

different patterns has long fascinated science.

The vast majority of the specimens here come from the Victorian era,

a period when a passion for amateur collecting reached its peak.

Many of those early collectors

recognised the relationship between the colour and pattern

of a butterfly's wing, and its identity as a species.

Each species has its own signature pattern and hue.

Magnifying a wing shows how these patterns are created.

The surface is covered with millions of tiny scales.

They're made of chitin

and contain different pigments, that tend to fade.

But there is another kind of wing colouration that gives

some butterflies a particular spectacular brilliance.

And this remains long after the butterfly is dead.

These Morpho butterflies were collected over 100 years ago

and they are as bright today as the day on which they were collected.

That is because their wings contain tiny microscopic structures

called gyroids.

When the light hits one of them, it is bent and refracted,

so that the colour it produces varies,

according to the angle on which you look at it.

The gyroid, in fact, is not a pigment, which would fade,

it's a crystal structure.

Darwin pondered on the reason for such bright colours.

They could, after all, make the butterfly

highly visible to predators. So why be so colourful?

Victorian naturalists were aware that male and female butterflies

of the same species could be very different in colour.

The male Large Blue is, indeed, blue,

but the female, on the other hand, is a drab brown.

For Darwin, such species were a perfect example of a process

he called "sexual selection".

A colour or pattern arises among males that is attractive

to the opposite sex,

so the most brightly-coloured male is more likely to get a mate.

Remarkably, it's sometimes possible to see the male colouration

and female colouration in a single, individual butterfly,

like this one.

That side is female and that's male.

Such individuals are called gynandromorphs

and they're extremely rare.

They're also infertile, but, nonetheless,

they can reveal a great deal about sex and colouration in butterflies.

Studying the genetics of gynadromorphs

has enabled scientists to understand the role male and female genes

play in the development of wing colour and shape.

But why should it be the females who are drab

and the males more colourful?

That's because, in such species, males are territorial

and bright colours, visible from a distance, keep other males away.

The females, on the other hand, are egg layers,

and it's often better for them to be less conspicuous.

But not all butterflies show such clear differences between the sexes.

I once visited the winter home of the Monarch butterfly in Mexico.

Here, tens of millions of butterflies, having left

North America, to escape the winter, cluster together on trees.

Males and females are hardly any different.

Both are bright orange, with black stripes.

It's a magnificent spectacle,

and one might think that, with all these butterflies in one place,

they would be a feast for predators. But remarkably, few animals

are able to eat Monarch butterflies, because they are poisonous.

Today, our understanding of wing pattern and colour,

as a means of defence, is largely due to the work

of one of those impressive Victorian butterfly collectors.

In 1848, a young British naturalist, called Henry Bates,

began a collecting expedition to the Amazon

that would continue for 11 years.

Bates was of humble origin and largely self-educated,

so he was rather different from other scholars of the time.

He travelled to the Amazon with fellow naturalist,

Alfred Russell Wallace, who wrote that the aim of their journey

wasn't just to collect, but to "gather facts towards solving

"the problem of the origin of species."

He stayed on the Amazon for more than a decade

and amassed thousands of specimens, as well as discovering more than

100 new species of butterfly.

His work wasn't just an insight

into the diversity of life in the tropics.

It was his theory on butterfly colouration that would

bring him to the attention of the great Charles Darwin.

He recorded differences in butterfly behaviour.

Some species flew in a purposeful way.

Others were slow, and fluttery, fliers,

Yet they were left largely alone, despite their conspicuous markings.

Bates was aware that some of the butterflies in his collection

were distasteful to predators.

He knew from his time in the Amazon that some species, like these

on the left, avoid predation because they contain poisons.

But here was a butterfly that was almost identical, but not quite.

In fact, it belongs to a totally different group.

As he worked through his huge collection, he began to see a trend.

Each poisonous, or distasteful, species of butterfly

had a matching copycat and he drew them side by side in his book.

He called these copycats mimics.

Bates had stumbled upon a different reason for butterfly patterns,

one where colours are a warning sign of danger to would-be predators.

Those mimics with a similar wing pattern to the distasteful species

were more likely to be avoided by predators.

Those that looked less convincing were more likely to be killed.

So, over time, evolution causes these copycats to be

almost identical in pattern and colour to the model they mimic.

Darwin was delighted with Bates' observations.

The butterfly wing pattern

fitted nicely into his new theory of evolution.

Bates also discovered that the wing pattern of a butterfly

could vary over distance.

This is the butterfly called Heliconius,

and this is what it looks like in the south of the Amazon basin.

But this is what it looks like in the north.

But, even more remarkably, he also discovered that the mimic

varies in the same sort of way.

That is what the mimic looks like in the south

and this is what it looks like in the north.

While Bates explained the importance of wing pattern in anti-predation,

there was one question he was never able to answer...

..how did the mimic avoid mating with the model?

After all, they're almost identical, to our eyes, at any rate.

We now know that many butterflies can see a much broader band

of the light spectrum, even the ultraviolet end.

This Heliconius butterfly on the left is closely matched

by its mimic, on the right.

To our eyes, they look very similar, but view them in ultraviolet,

and we can see that, now, the mimic is more drab and darker.

So butterflies themselves

can see the difference more easily than we can.

The evolution of wing pattern in butterflies

is clearly more complex than those early Victorian collectors

could have imagined.

Indeed, many different factors may play a role in shaping

the colour and pattern of each species' wing.

But we have Henry Bates to thank for revealing the connection

between colour and defence.

When Henry Bates returned from the Amazon,

he described his 11 years in the tropics as the best of his life.

He would spend the remainder of his career

working as Assistant Secretary to the Royal Geographical Society,

a job that really didn't stretch his amazing scientific mind.

Many collectors have contributed butterfly specimens

to this impressive collection in the Natural History Museum,

but thanks to Bates, we are able to see beyond

the dazzling variety of wing colours and find the evolutionary connection

between the many different patterns on the butterfly wing.

So, the striped coat of the zebra

and the colourful markings of a butterfly's wing

may play similar roles,

helping protect the animals they decorate.

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