David Attenborough's Natural Curiosities

The natural world is full of extraordinarily shaped creatures...

but how have the stretched bodies of some given them an edge?

I have had the fortune to meet

some of the planet's most enchanting creatures -

but some stand out more than others

because of their intriguing biology.

Our knowledge of some of these creatures extends back centuries.

Others, we've discovered more recently.

In this series, I share their stories

and reveal why they are considered natural curiosities.

In this programme, I investigate two creatures

that have taken the ordinary and make it extraordinary.

The chameleon, that has an extra long tongue to catch prey...

and the giraffe, with a neck so long it can reach the top of trees.

How and why have these animals stretched nature to the limit?

The chameleon is a truly bizarre creature,

both in its behaviour and its appearance

unlike anything else on Earth.

So, not surprisingly, it has given rise

to all kinds of legends and myths.

This is the History of the Four-Footed Beasts

by Edward Topsell,

written in the 17th century, and he calls the chameleon

"a fraudulent, ravening and gluttonous beast,"

"impure and unclean by the law of God."

Some believed it was constructed by the devil

from parts of other animals -

the tail of a monkey, the skin of a crocodile, the tongue of a toad,

the horns of a rhinoceros, and the eyes of - who knows what?

It was a creature sent to the world to spy for a demon master.

When I first came face to face with a chameleon, more than 50 years ago,

I was struck not only by its beauty, but intrigued by its strange body.

Particularly by its tongue.

The outlandish appearance of the chameleon made it much sought after

by curiosity hunters -

but scientists and naturalists, too,

were greatly puzzled by its extraordinary behaviour and anatomy.

It looked and behaved like no other reptile.

Even today, we are still discovering new things about its unique eyes,

its astonishing tongue,

and its ability to change its appearance.

Chameleons are

notoriously hard to find.

Partly because they move so slowly,

but also because they match their surroundings,

in terms of colour, so very well.

This one in front of me is a dwarf chameleon

from Natal in South Africa.

If it is threatened by a snake,

it doesn't bother to change its colour very much

because a snake's colour vision is not very good,

but if it is threatened by a bird,

it does camouflage itself very well indeed.

Some species of chameleon -

and there are 85 different species in the family -

can even fine-tune their camouflage.

If they detect a snake approaching from below,

they become lighter in colour and so less noticeable against the sky.

On the other hand, if the threat comes from above,

they become darker to match the background beneath them.

A chameleon's colour is affected not only by its surroundings,

but by the temperature and the light and its emotional state.

Behind this screen, there is a rival male.

Let's see what happens if I remove the screen

and let them see one another.

This highly coloured male is dominant,

and he immediately adds bright, aggressive colours to his display.

The other male remains dark

and too frightened to change colour and fight back.

It's clear who's the boss.

Chameleons are emotional creatures.

Darker colouration signals anger.

This female on the right is not in the mood to accept the approaches

of this brightly coloured and hopeful male.

Exactly how chameleons achieve such dramatic colour changes

greatly puzzled early naturalists.

An Englishman named Barrow,

who travelled in Africa in the 19th century,

thought that changing colour was caused by something to do with air.

He wrote, "Previous to the chameleon assuming a change in colour",

"it makes a long inspiration,"

"the body swelling up to twice its usual size,"

"and as this inflation subsides,"

"the change of colour gradually takes place."

Well, that's an accurate observation of what happens

when a chameleon gets angry, and then its anger subsides -

but actually the change of colour has nothing to do with air.

A French biologist, Milne-Edwards, soon after that got it about right.

He wrote,

"There exist two layers of membranous pigment

"placed one above the other,"

"but disposed in such a way to appear simultaneously"

"under the cuticle"

"and sometimes in such a manner that one may hide the other."

Which is indeed so.

Today, we know that the chameleon's skin has three layers

of expandable pigmented cells called chromatophores.

They contain red, yellow, blue and white pigments,

with a deeper layer of darker melanin,

which controls the reflection of light.

The chameleons use colour change not only to camouflage themselves,

but also to communicate with one another.

Anyone who looks closely at a chameleon

is bound to be fascinated by its eyes.

They protrude on either side of its heads,

as though they were mounted on turrets.

And in fact, their eyelids are fused together,

except for one tiny spot right in the middle.

But the most extraordinary thing about them

is that they move independently.

So that means the chameleon at one and the same time

can be viewing above it and below it,

so any insect that lands nearby

is going to be spotted almost immediately.

It seems that its brain

receives separate messages

from each eye

and views them and receives them

alternately, very fast,

but independent to one another.

They are not integrated.

But the advantage of that

is that it does give this all-round three-dimensional view

which is unrivalled.

This extraordinary vision is an essential element

in the way the chameleon uses its most astonishing feature,

its hugely elongated tongue.

How this tongue worked and its construction

greatly intrigued early naturalists -

and understandably.

This remarkable preserved specimen shows us in detail

the impressive elongated tongue of a chameleon.

The physical structure

of the chameleon's tongue was easy enough to explain,

although it proved to be a somewhat complicated organ -

a hollow tube

with a tapered cartilaginous rod at its base.

The pad at the end

was thought to be rough and sticky

so that it could snag its prey.

But the mystery of how a contraption like this

could be lengthened and projected out of the mouth

took a little longer to fully explain.

Perhaps the way a frigate bird inflates the balloon under its beak,

or how a calling frog blows up its throat sac could give clues.

Both do it with air.

Or maybe the tentacles that carry a snail's eyes -

it projects them by using its blood as a hydraulic fluid.

But none of them fitted the bill.

It is a much more complex process.

The tongue is a muscular tube that, when relaxed,

sits on a rod of cartilage.

When the chameleon is ready to strike,

muscles at the back of the tongue push it into launch position.

When the prey is lined up and the distance detected,

super fast muscles contract

and propel the tongue forward at lightning speed.

As the tongue shoots off the end of the cartilage,

an extra wave of energy drives it forward to its target.

Then, like a stretched elastic band,

its elasticity pulls it back into the chameleon's mouth.

Recently, high speed images revealed a new detail.

The tip of the tongue, once thought to be sticky,

is covered in microscopic protrusions

that generate suction and secure its prey.

Chameleons really are the most extraordinary creatures,

and they hold surprises for us even today.

Only this year,

a scientist working in Madagascar discovered a tiny little chameleon,

only 29 millimetres long.

It's the smallest known vertebrate in the world.

It's astounding to realise