The natural world is full of extraordinary animals
with amazing life histories.
Yet certain stories are more intriguing than others.
The mysteries of a butterfly's life cycle,
or the strange biology of the emperor penguin.
Some of these creatures were surrounded by fantastic myths
and misunderstandings.
Others have only recently revealed their secrets.
These are the creatures that stand out from the crowd,
the curiosities that I find particularly fascinating.
Some animals take fighting and sparring to an extreme.
Kangaroos have kicks that can disembowel an opponent...
..while Siamese fighting fish will battle to the bitter end.
What makes these animals such ferocious fighters?
These are grey kangaroos.
It's hard to imagine that anyone could think
that such gentle, enchanting creatures
could once have been considered as superb fighters.
And yet, 120 years ago,
one of them was put into a boxing ring
and matched against a human opponent.
In 1891, the Melbourne Punch published a cartoon
about Jack the fighting kangaroo,
who was pitted against a man named Professor Lendermann.
The show attracted huge crowds,
and soon Jack was not the only kangaroo
to be seen in a boxing ring.
All across the world,
gloves were being strapped on kangaroos' front legs,
and the questionable sport became a full-blown trend,
which lasted well into the 20th century.
Kangaroo boxing was big money,
and some animals became celebrities in their own right.
When Jack died, not surprisingly,
he was quietly replaced with another Jack.
Today, kangaroos are among the most familiar animals...
..and yet, when they were first discovered,
they confused the scientific community.
Early explorers described them as creatures with heads like deer,
that stood upright like men, but hopped like frogs.
The first image of a kangaroo seen by 18th-century Britons
was this beautiful painting by George Stubbs.
It was commissioned after Captain Cook's ship, the Endeavour,
arrived back from his first voyage in 1771,
bringing with it numerous specimens of animals
totally unknown to Europeans.
And one of the strangest was the kangaroo.
Cook's crew encountered a kangaroo
when they became the first Europeans
to sail up the east coast of Australia,
and their ship was beached for repairs.
The men explored their surroundings
and saw what the ship's naturalist described
as "an animal as large as a greyhound,
"of a mouse colour and very swift.
"To compare it to any other animal," he went on, "would be impossible,
"as it has not the least resemblance to any one that we've seen.
"Its forelegs are extremely short, and of no use to it in walking.
"Its hind legs again as disproportionately long."
Before they left, they learned that the local aboriginal people
called the mysterious animal a kangaroo.
George Stubbs struggled to work out
what the living creature must have looked like.
He only had one or two simple pencil sketches like this one,
which was drawn by one of the ship's artists.
But he also had a dried kangaroo skin,
and it's likely that he softened it
and then inflated it with air
to work out the extraordinary proportions
of this really amazing creature.
Eventually, he produced a likeness
that captured the public's imagination.
Although Stubbs' painting enchanted the Western world,
there is still some debate today as to what kind of kangaroo
Captain Cook's crew actually encountered.
Early naturalists, thinking that it must be a gigantic rat,
first gave it the name Jerboa giganteus, or "giant leaping rat".
Today, we know that there are in fact over 50 different species
of hopping creatures in Australia,
and, strictly speaking,
only the largest are called kangaroos.
Those that are medium-sized are known as wallabies...
..while the smaller species go by fascinating names
like quokka, bettong and potoroo,
to name just a few.
All these animals are known as macropods,
and nearly all of them hop.
It's this particular way of moving that may also be the reason
for the kangaroo's unique style of kick boxing.
This is the skeleton of a red kangaroo,
and it's typical of all macropods.
Kangaroos have the same basic leg bones as we do,
but they are modified for hopping.
The thigh bone, here, is relatively short...
..while the two bones of the lower leg are relatively long.
The tendons, which connect with the muscles along the lower leg,
act as springs, and the longer they are, the more energy they can store,
and this allows the kangaroo to jump higher and faster.
The ankle, on the other hand, can only move in one plane -
backwards and forwards.
And this gives it more stability
when it impacts with the ground.
And then there are these overly long feet -
which are the reasons for the group's name, macropod,
which means, literally, "big foot".
The kangaroo skeleton is adapted for a life of hopping.
But powering each hop
are exceptionally strong elastic tendons and muscles.
They compress with each bound...
..and then, when the energy is released,
it propels the kangaroo into the air.
And the large tail acts as a counterbalance
to stabilise the motion.
The impact from each landing can be so hard
that most other animals would suffer damaged knees and broken feet.
But kangaroos have evolved thick pads of cartilage
which act as shock absorbers
and help to minimise wear and tear.
Kangaroos are not the only animals to hop,
but they are by far the largest.
So, it's not hard to imagine the astonishment and disbelief
of the early European explorers
at the sight of the giant hopping creature.
It was not until the first live animals began to arrive in Europe
at the end of the 18th century
that we began to understand their curious body shape.
Kangaroos adapted well to captivity,
and soon became popular in early British zoos.
People flocked to see the unusual creature.
Soon, kangaroos were breeding so freely across the country
that in 1806 an eminent naturalist said,
"The kangaroo may now be considered as a great degree naturalised
"in England, promising to render this most elegant animal
"a permanent acquisition to our country."
It was not long after that this book was published,
which has an intriguing picture that sheds light
on how the sport of kangaroo boxing may have come about.
The author, Thomas Smith,
visited a menagerie in the Exeter Exchange in London,
and he describes how the animal
wrestled with and kicked at its keeper for 10-15 minutes
until it was reunited with its female.
And his description was accompanied by this drawing.
It's the first image of a boxing kangaroo,
and shed some light on how the sport of kangaroo boxing
may well have originated.
Today, we know that, in the wild, this boxing happens
when two males compete for dominance and mating rights.
Most contests are brief and settled by posturing.
Males will rise up on their back legs
and display their size and large muscular forelimbs
to impress their opponents...
..but when two rivals are evenly matched,
things can get really violent.
With their huge feet,
they deliver kicks that can break bones and rip open a stomach.
It's these ferocious battles
that gave kangaroos the reputation for being champion boxers.
The kangaroo's strange technique of fighting
is a consequence of its odd body shape.
Those powerful hind legs with which it strikes
evolved in order to enable it to hop,
and that muscular tail on which it props itself upright
serves, normally, as a counterbalance
when it's hopping.
But why did this odd shape occur in the kangaroo family
and in no other large animals in the world?
The reason, it seems, is because of a shift
from a life in the trees to life on the ground.
The kangaroo's early ancestors were tree-living, possum-like creatures
that came down to the forest floor.
As the continent of Australia drifted north,
some five or ten million years ago,
a period of global cooling and drying
saw rainforests give way to vast grassy plains.
This provided an abundant supply of food for ground-dwelling grazers.
And what better way to cruise the plains than by leaps and bounds?
Hopping, in fact, is a very energy efficient way of getting around.
Kangaroos can reach speeds of 40mph,
yet they use half as much energy
as a similar sized animal running on four legs.
When kangaroos speed up,
they don't increase the frequency of their hops,
but, instead, lengthen their stride.
The longer the stride,
the more energy they pack into their muscles and tendons.
In a vast, dry country like Australia,
being able to travel long distances while using minimal energy
may be crucial to survival.
There is another, more recent, theory
as to why it is that kangaroos hop.
Like most mammals in Australia,
kangaroos carry their babies in a pouch.
But when the baby is first born,
it's no bigger than a jelly bean,
and it has to haul its way across its mother's abdomen
to get into her pouch.
To do that, it could be more important to have short, muscular,
powerful arms to help pull themselves through the bristly fur
than to have long front legs
suitable for standing up and for running.
The tiny baby is born blind and naked.
It now has to haul itself through the thick fur on its mother's belly
and up into her pouch.
If it can't make the journey, it won't survive.
The hind limbs, however, develop like those of other mammals,
and they're much longer,
so it could be that the kangaroo's hop evolved
because of the difference in the growth of their fore and hind limbs.
For the first 12 months of its life,
the young joey spends most of its time in its mother's pouch.
But when outside, it practises hopping and jumping,
as well as the art of boxing.
And its patient mother puts up with being used as a punching bag.
It'll be another few years before this young joey
is ready to fight for real stakes.
With the kangaroo,
we discovered a creature so fascinating
that we took it into the boxing ring and made a show of it.
Thankfully, this cruel sport is no longer deemed acceptable today.
Now, kangaroos have lost much of their mystique.
But their familiar exterior conceals an extremely efficient body design
that continues to impress us.
Our next animal also has a reputation for fighting -
so much so that it's called the fighting fish.
What makes this small creature so aggressive?
These are Siamese fighting fish -
or, to give them their scientific name, Betta splendens -
and they come in a great variety of ravishing colours.
So it's not difficult to understand
why they are very popular aquarium fish.
I used to keep them myself.
They swim with all the grace of a virtuoso ballet dancer -
but don't be deceived.
Watch what happens when I lift this...
..and they see one another.
Because the males are so aggressive,
it's illegal to put them together in the same tank.
Even so, each is determined to defend its territory.
They distend their fins and push out their gill covers
so that they appear larger and more imposing.
If these two males were kept together in the same tank,
they would soon turn on each other
and one of them would almost certainly be killed.
In the wild, fights between males only last a few minutes
before one fish backs off -
but in a confined space, they can carry on for hours
and cause severe damage to each other.
It's this fierceness that first attracted the attention
of local people in Southeast Asia,
where Siamese fighting fish occur in the wild,
and this led to them being bred as fighting fish,
on which people would bet.
Villagers collected the fish from shallow pools and rice paddies
and pitted them against each other to determine a village champion.
It was a favourite pastime for centuries.
And it wasn't long before people started breeding the fish
for their fighting abilities.
Seeing the popularity of the fights in the 19th century,
the King of Thailand, or Siam, as it was once known,
started collecting the fish himself.
In 1840, the king gave some of his prized fish to a friend,
who passed them to a physician working in Calcutta at the time,
Dr Theodore Cantor.
Cantor was the first to draw and describe the wild fish,
and, by the turn of the century,
the first ones were being imported into Europe and North America.
One of the species that we know today
as the Siamese fighting fish arrived in Britain in 1897.
And this is the actual specimen.
It looks very different
from the flamboyant aquarium fish we know today.
The name betta was given to the fish
after a tribe in northern Siam who were ferocious warriors.
For centuries,
Siamese fighting fish were bred to increase their aggressiveness.
But soon, different colours and fin shapes
started to be valued, as well.
It's likely that there were variations between populations
and that breeders selected the more vibrant colours.
Selective breeding also created a variety of tail fins,
some draping down like a veil...
..others spiky, or half-moon shaped.
Although today Siamese fighting fish are more widely sought after
for their showy appearance,
they're still one of the most aggressive of all fish.
Given a chance,
they will lock mouths and tear at each other's fins
with their sharp teeth.
It's a way of fighting that at first sight seems much the same
as that used by many other fish.
Cichlids in Lake Tanganyika fight in a very similar way.
The males face their rivals head on and lock mouths.
Each tries to push the other to the bottom.
Cichlids may fight in much the same way as the Siamese fighters,
but they seldom wound and never kill one another.
Most animals fight for territories or for mates,
and some will risk serious injury in doing so -
but few will fight to the death, as these Siamese fish do.
Why should this little fish be so aggressive?
Well, it seems that it may have something to do
with the extreme conditions in which they live.
In the wild, they live in rice paddies
in shallow pools and ditches.
But suitable breeding territories in such places are in short supply.
Keeping rivals at bay is particularly difficult,
and only the most ferocious
will be able to hold a territory and attract a mate.
And the fish have another problem.
The warm, stagnant water is low in oxygen,
and their small gills can't keep up with the vigour of a fight.
But they've evolved a way of dealing with that.
Most fish breathe
by extracting oxygen from the water with their gills.
But one group has an additional structure
which sits directly above the gills.
It's called the labyrinth organ,
and it enables the fish to extract oxygen directly from the air,
much as our lungs do.
It's a remarkable adaptation that allows Siamese fighting fish
to live in waters that contain so little oxygen
that no other fish could survive there.
When males fight,
they come to the surface regularly for gulps of air...
..but the rivals face a tactical problem.
If one comes to the surface alone,
it makes him vulnerable to attack from its opponent below...
..and from predators above.
So, Siamese fighting fish
have come to a seemingly gentlemanly arrangement.
They both surface at the same time.
This way, neither risks being attacked by the other
when its back is turned.
At the end of the day, all the fighting is about one thing only,
how to attract a female and produce young.
The female is much more drab, doesn't have the same huge fins,
and she will do very little apart from producing the eggs.
It's the male who builds a nest
and cares for the young until they hatch.
So, these males have good reason to be fierce -
they invest a lot in breeding,
and fighting off rivals is just the first step.
They build a nest from bubbles.
The male takes a gulp of air...
..and blows a bubble enclosed in mucus.
He does this again and again,
until he's created a whole raft of bubbles
floating just underneath the surface.
Within a few hours, the nest is complete.
In the wild, the bubble nest is crucial
for the survival of the eggs.
It ensures that they remain floating near the surface
of this stagnant water, and so get sufficient oxygen.
Siamese fighting fish are unlikely to survive for more than a year,
and they will produce maybe three or four broods in that time,
but even so, each brood is very precious.
Mating takes place directly beneath the nest,
and the male has to lead the female to the right position.
He now tempers his aggression
and courts her in a surprisingly tender way.
Finally, she releases the eggs.
He catches each one in his mouth
and deposits it within the nest.
During nesting, males are at their most aggressive.
They can't leave the eggs unguarded
because the bubble nest is fragile and constantly needs repair.
And other fish, including their own females,
will also eat the eggs, given the chance.
So, as soon as the female has released her eggs,
he will turn on her and chase her off.
But the usually aggressive male takes great care of his brood.
He continually adds bubbles to the nest,
replacing those that have burst.
If the temperature of the water rises,
he fans the eggs with his fins to keep them aerated.
After 36 hours, the small fry are ready to hatch.
Within a few months,
the young fish will be fighting fit and ready to mate.
And there may be another reason
why Siamese fighting fish are so aggressive.
Recent research on coral reef fish
have shown that some species, as the temperature rises,
undergo a personality change.
Researchers working on Australia's Great Barrier Reef
have found that some reef fish
are either consistently timid or consistently bold.
But global warming seems to have had an effect on their temperament.
A rise in water temperature of just 1 or 2 degrees
has made them 30 times more active and aggressive.
So, could the Siamese fighters also be affected
by the temperature of the water?
We know that Siamese fighting fish display more the warmer the water,
and that they can survive in temperatures
of up to 30 degrees centigrade.
So, perhaps it's the warmth of the stagnant water
that makes them so aggressive.
So, it seems that Siamese fighting fish
will fight to the death to produce offspring...
..while the kangaroo's lethal kick and punch
is the result of a body made for hopping.
Both have certainly earned their reputations as ferocious fighters.