Curious Cures 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 particularly fascinating.

Some animals have intriguing ways of protecting their skin.

The hippopotamus lives in Africa under the hot tropical sun,

yet doesn't get sunburnt.

And capuchin monkeys live in insect-infested jungles

but hardly ever get bitten.

How do these animals beat the elements

and protect themselves from sun, parasites and disease?

Hippos are large land mammals that can weigh up to three tonnes

and they need to keep their huge bodies cool

and protected from the sun.

To avoid the heat, they spend much of the day swimming,

as they are doing now in the waters behind me.

But, when they're on land,

strangely, they don't appear to get sunburnt.

The secret of their sun tolerance lies within their skin.

It can sometimes appear shiny and greasy.

It has unique properties that shocked the early explorers

and now excites modern scientists.

Hippos live in Africa south of the Sahara,

where temperatures can reach 40 degrees Centigrade.

But they spend much of the day submerged in rivers,

lakes and swamps, and so avoid the worst of the sun's rays.

They possess formidable teeth

but they are, in fact, herbivores

and eat mostly grass, great quantities of it.

And they graze mostly at night.

Even so, continually moving in and out of water

together with being roasted by the rays of the sun

could be very damaging to their skin.

But, curiously, hippos remain healthy.

Throughout history,

the hippopotamus has been the subject of many strange tales.

The Greeks claimed they sweated blood,

and the Romans said they deliberately pierced their skin

on sharp rushes to release blood.

It seemed bizarre that an animal would make itself bleed on purpose.

In the 19th century, one special hippopotamus

allowed people to get a closer look at these strange skin secretions.

In 1849, the British Consul for Egypt, Charles Augustus Murray,

formally requested that the Pasha of Egypt help capture a hippo

for the Zoological Society Of London.

Hunters searched the reeds on a remote island called Obaysch,

2,000 kilometres up the Nile from Cairo.

They discovered a male hippo that was only a few days old.

When they tried to grab it, a strange thing happened.

Murray describes how a slimy exudation lavishly poured forth

from the innumerable pores in the skin,

rendering it so slippery that the animal was impossible to hold.

The hunters dropped the baby hippo back

into the waters of the Nile

but they managed to retrieve it again using the hook of a spear.

The prize hippo was named Obaysch after the island of its capture,

and here he is.

Before his capture, young Obaysch lived with his mother.

She had moved away from the herd to give birth alone,

and she protected him from lions and crocodiles.

Whether Obaysch became accidentally separated from his mother,

we will never know, but we do know that secretions from his skin

made him so slippery that he very nearly escaped capture.

At this time, very little was known about hippos

and many people believed that they were some kind of horse

that had taken to living in rivers.

In the early 20th century,

naturalists decided that they were closely related to pigs.

DNA evidence, however, now shows that, in fact,

their ancestors were cetaceans,

the group that contains whales and dolphins.

So, hippos still retain many adaptations for a life in water.

Hippos are very heavy animals

but, for most of their time, their bodies are supported by water.

They are not really very good swimmers.

In the water, they move by bounding across the bottom.

They are well adapted to a semi-aquatic life

because their ears, their eyes and their nostrils

are all towards the top of their head

which enables them to lie almost totally submerged

and yet still keep notice of what's going on on land.

But their skin is almost entirely hairless

so, on land, it has to be kept moist.

In order to prevent young Obaysch from sunburn and drying out,

the Egyptian pasha had a boat built with a bathing pool

to transport Obaysch in comfort all the way down the River Nile.

Accompanied by several cows to supply him with milk,

he arrived safely in Cairo four months later.

On receiving Obaysch,

the British Consul wrote excitedly to the Zoological Society Of London,

confirming that the hippo was alive, and as tame and playful as a puppy.

But his travels were not yet over.

In the spring of 1850, Obaysch was taken to Alexandria

to board a P&O steamship called the Ripon.

A special hippo house with a water tank was built on the deck

and, in May, Obaysch arrived safely in Southampton.

With the help of block and tackle,

he was loaded onto a train bound for London.

And, at ten o'clock at night,

the tired hippo and his keeper reached London Zoo.

His home was a newly constructed enclosure

complete with a heated swimming pool.

After many hours of travelling,

the hippo gratefully plunged into the water.

Obaysch, the hippo sensation, had arrived.

A journey of over 5,000 miles by sailboat,

steamboat and a train brought a hippo to England,

the first one since Roman times.

Now Europeans had a chance to get close to this unusual creature

and, perhaps, learn more about its strange skin secretions.

Later, more hippos arrived at other zoos

and the blood-red sweat was seen again.

In the cooler climate of Europe, hippos don't sweat very much.

But zookeepers have reported that sometimes, in the morning,

they see red trickles forming on the flanks of these animals.

It comes from particularly large pores

which form streaks on the animal's side

which does look a little like blood.

We've known for some time that this is a moisturiser

but why it's red has only just been discovered.

A little more?

Come on!

There we go.

Recently, Japanese scientists were intrigued to see photos

of a wild baby hippo with light pink skin

that still didn't burn under the harsh African sun.

They wondered if the red secretion played a role

in protecting its pale skin.

So they collected hippo secretion from captive hippos

to look at its composition.

They discovered two pigments,

a red one that they named hipposudoric acid,

and an orange one that they called norhipposudoric acid.

The red pigment was found to absorb harmful wavelengths of light,

and both pigments were antibacterial.

Here was the answer to why hippos never got sunburnt

and why the wounds of battling males rarely became infected.

The mysterious slime was neither blood nor sweat

but a specialised secretion that turns red in sunlight

and protects the hippo's skin.

So, what became of Obaysch, the first-ever hippo in captivity

that gave us a close-up view of these curious creatures?

For several years, he was a sensation at London Zoo.

He even inspired the hippo polka, a popular dance of its time.

The visitors grew weary of him.

Some were disappointed not to see a giant river horse.

And others expected a ferocious beast, not a gentle giant.

Obaysch died in 1878 at the age of 28,

and he and others that followed taught us some intriguing things

about hippos, including the reason for the blood-red droplets

found on their skin.

So, hippos can produce their very own natural sun cream

that is waterproof, moisturising and antibacterial.

Next, we meet another animal that has its own natural cure.

Capuchin monkeys have a surprising way of protecting their skin

from stings and bites.

When early explorers reached the Americas in the 15th century,

they encountered small monkeys with patches of

dark brown fur on their heads that resembled hoods.

So they named them after a group

of Franciscan friars called Capuchin monks.

Capuchin monkeys quickly charmed their way into our hearts.

With dextrous hands and inquisitive personalities,

they seemed very humanlike.

They were also adept at learning tricks

and soon became popular performers on our streets.

In the past, we used to teach monkeys how to do things,

how to perform tricks.

But things are different today.

Today, monkeys are teaching us things.

Watch what happens when I give them a few spring onions

and some chilli peppers.

They're clearly not eating what I offered them,

they're rubbing themselves with the peppers and the onions.

You might think that's because they're captive monkeys

and they are just doing that to entertain themselves.

But not so.

I've seen capuchins do just that in the wild.

These white-faced capuchins in Costa Rica

reacted in much the same way when they came across

a particular rainforest plant, the piper plant.

These leaves have a distinctive liquorice scent

and they're hard to come by.

So, when they do find them,

the monkeys pass the leaves around the troop

so everyone can have a share.

Both in the wild and in captivity,

capuchin monkeys become similarly excited

at the sight of lemons or limes

and again the same frenzied activity and fur rubbing follows.

What is it about these plants that gets the monkeys so excited?

We know they all give off a pungent smell,

so could this be what the capuchins are after?

Smell plays an important part in the lives of many primates

but none more so than in the lives of these lovely ring-tailed lemurs.

They use it both to establish their position within the troop,

and also the boundaries, the frontiers of their territory.

If you look at the inside of their forearms,

there is a black patch without fur

and there the skin is loaded with glands that produce

a very strong smell.

And when these boys go into battle... Whoops!

When they go into battle,

they draw their furry tail through their forearms,

loading it with scent from those glands,

and then they would wave it over their backs

in the direction of their enemies in a kind of stink fight.

You understand that, don't you?

LEMURS SQUEAK

Oh!

The pungent scent is also used by males during the mating season.

This male has rubbed his own distinctive smell onto his tail

and he now wafts it towards a female to signal his intentions.

But she is not entirely convinced.

Unlike lemurs, capuchins don't have scent glands,

so some thought that they could be using the smell of certain plants

for communication.

But it turns out that they have a different perfume for that job -

urine, which they apply lavishly to their fur.

So why then do they also anoint themselves with other smells?

The answer may be found in our own history.

The early Romans noticed some 2,000 years ago

that the fruits and leaves of the lemon plant

have an exceptionally strong scent

that can be used to ward off insects.

A further clue as to why capuchins might cover themselves

in such pungent smells comes from this plant, the piper plant.

Throughout the Amazon, Indian tribes apply it as an antiseptic on wounds.

And in Costa Rica it's used as an insect repellent.

Could it be that capuchin monkeys protect themselves

against the onslaught of mosquitoes in much the same way as humans do

by rubbing themselves with mosquito repellent?

In 1993, scientists at Oxford University

decided to put the question to the test.

They collected some feather lice

and put them into Petri dishes overnight.

Into one dish, they also placed a slice of lime.

The next day, the lice without the lime were mostly alive.

Whilst in the other dish, two-thirds had died

and the remainder were paralysed.

Clearly, the lime contains a lethal insecticide.

Today, we know that citrus fruit peel

does indeed contain insecticides

which disrupt the nervous system of many small insects,

causing them to become uncoordinated and paralysed.

The leaves of the piper plant are antiseptic and contain substances

that protect against fungal and bacterial infection.

And chilli pepper extract is commonly used in households

and gardens to deter small mammals and insect pests.

So it seems that the clever monkeys know

exactly how to make the best use of nature's remedies.

Recent research has also revealed that capuchins anoint themselves

far more during the wet season when mosquitoes are more abundant

and the risk of infection is higher.

Troops use different plants,

possibly simply because they have to use what's locally available.

But there's one substance with insect repellent qualities

that appeals to primates, including capuchins,

that comes not from a plant but from an animal.

An animal like this.

A giant millipede.

When attacked or in danger,

tropical millipedes often produce a powerful defensive secretion.

And black lemurs have worked out how to use this to their advantage.

When they find a millipede, they give it a gentle bite to the head

to make it release its secretion, and then rub this through their fur.

The toxic fluid has a strong smell and is highly irritating,

but it protects the lemurs against mosquitoes.

This pungent secretion has apparently another strange effect.

It seems to act as a narcotic,

sending the lemur into a kind of trance.

Like other drugs, it has powerful side effects.

We still don't understand how capuchins and lemurs

select the plants that they use for medicinal purposes.

These capuchins behind me were born and raised in captivity

so they've never encountered the plants

that their parents and ancestors would have used.

So how did the monkeys know which plants to choose?

Can they detect particular substances in them?

Or is it something they learn from others?

We don't yet know the answers

but it could be that babies learn by watching the adults

and that it's passed down the family line.

It's clearly a great social event with everyone joining in.

And, afterwards, the entire group appears to be more tightly bonded.

When Europeans first saw monkeys in the wild,

they thought that they were imitating what people did

in some of their behaviours.

But quite the reverse,

it now turns out that many of the local people did things

that the monkeys had taught them, using plants as medicines.

So it seems clever monkeys have taught us a trick or two.

So, it's clear that we're not alone in using medicines

against injuries and infections.

Both capuchin monkeys and hippos discovered some medical remedies

long before we did.