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There is a wild island in Indonesia.

Early in the morning, when the rays of the sun spread to the

foot of the mountain, a monster stirs from its sleep.

This is an island full of danger.

Predators are lurking in every shadow.

Finally, the monster begins to move.

This vicious and ill-tempered predator is the Komodo dragon.

The creature spies its target.

It rushes towards its prey at full speed.

The monster rarely fails in its hunting attempts.

It swallows both flesh and bone with its gaping jaws.

Wherever this monster goes, death

follows close on its heels.

Designated by UNESCO as a Natural Heritage,

Komodo National Park is a natural Komodo dragon reserve.

This giant lizard can grow up to 3 meters in length and

reach 70 kilograms in weight.

It is a fearsome predator and natural-born killing machine.

It can easily detect the movement of

prey with its sharp eyes.

Also, it uses its highly sensitive tongue in order to

track down and hunt its victims.

It can even sense prey as far as 4 kilometers away.

It is also armed with a tail powerful enough to fell a wild

boar with a single stroke.

And its saliva is a cocktail of toxic bacteria so that even

a single bite will cause its victim to die.

This animal was born to kill, and will

whenever it gets the chance.

Komodo dragons rush towards a freshly killed animal,

fighting for an extra morsel of flesh.

Such feasts also afford the dragons with an opportunity.

The Komodo dragons are solitary animals,

so they don't gather together very often.

So when you have a dead animal,

a carrion, and then you have different animals,

different komodo dragons that feed on those dead animals,

then you will have a mixture of males and females.

So that will be an opportunity for Komodo dragons actually to

meet at the same place.

The Komodo dragon is a solitary animal,

but from May to August which is mating season,

it begins to search for its other half.

But this mating instinct is often the

cause of fierce battles.

Only the strongest of this species can

earn the right to mate.

The males engage in fierce battles which often prove

to be fatal for the loser.

This is a sight that can only be seen during mating season.

When a male Komodo concedes defeat,

it may never get the chance to mate again.

And to the victor goes the spoils,

which in this case is a female.

Rubbing a female on the cheek is an act of courtship.

And if the female acquiesces, mating can commence in earnest.

Love seems to be a basic instinct to even to these

vicious and cruel creatures.

And it is this basic instinct that makes them

more aggressive than any prey could.

What is it about mating that makes the Komodo dragon risk

its life for the privilege?

We have millions of species.

We've had millions of species that have gone extinct

in the past and I think that without sex,

we will live in a much simpler, less interesting world.

Under the sea, a pair of Mandarinfish engage in an

elegant courtship dance.

The tiny ladybug holds marathon mating sessions that

last a mindboggling 9 hours.

Early in the autumn, a pair of Truljalia hibinonis

crickets enjoy making love.

This is a once-in-a-year occurrence for them.

Earthworms, which possess both male and female reproductive

organs, release sperm into each other's spermatheca.

In this way, mating is a wonderful and oftentimes

dangerous endeavor to undertake.

Countless creatures big and small mate all over the world

in order to produce offspring.

So, when did genders and sex first come into existence?

The answer to this riddle can be found in Chlamydomonas,

a kind of green algae.

This tiny, single-celled life form is invisible to the naked

eye, and it has no gender.

It copies its DNA in order to propagate.

3.5 billion years ago, Earth was home to such microorganisms.

For single-celled organisms, self-replication is the

fastest and most efficient way to propagate.

But as nutrients in the oceans began to dwindle due to a

change in the Earth's environment,

these organisms were pushed to the brink of extinction.

And they were forced to look for another

strategy for reproduction.

We moved Chlamydomonas to an environment

devoid of nutrients.

This caused pairs of Chlamydomonas to quiver

and collide with each other.

Soon thereafter, the two organisms fuse into one.

In order to survive in a nutrient-poor environment,

the two organisms decided to pool their resources.

A significant change occurs when the two single-celled

organisms come together.

The new organism retains the DNA of both

single-celled organisms.

When this organism undergoes mitosis,

a completely new species with a completely new

genetic sequence results.

And when this process is repeated, it results

in the creation of male and female, that is gender.

You can think of it as shuffling the deck in a game

of cards, that is, if you don't mix things up when you

prepare to play cards so that all the cards are re-assorted,

you'll end up getting the same cards over and

over again in the process.

And the reason why you want to mix things up is to

take advantage of increasing the diversity of

what you might get dealt.

This is a tropical rainforest in Peru, South America.

Somewhere in this forest lives an insect prized

for its rarity and beauty.

Each year, countless insect collectors venture into this

forest in order to find this precious species.

We find this rare insect amidst a patch of leaves

glistening in the sunlight.

It is an agrias butterfly, the jewel of the forest.

The butterfly spreads its wings,

revealing its beautiful vivid colors.

Each butterfly of the species is marked with a

different pattern on its wings.

The butterfly is testament to the diversity that arises

from sexual reproduction.

Such diversity is not merely an external phenomenon.

It also affects such important matters as the ability to

survive and adjust to various environments.

Sex is very good, enabling you and your offspring to quickly

find new combinations to changing circumstances,

whether it's the introduction of an antibiotic or a

different temperature, or some change in the environment.

Through sexual reproduction which brings together male and

female and allows for a combination of their

genes to be passed down to later generations,

creatures big and small were able to evolve a diverse array

of characteristics to help them adapt to Earth's

endlessly changing environment.

Also, males and females each took on specialized roles.

Males provided the sperm which fertilized the eggs of females.

But somehow, it seems that females became trapped in an

unfair arrangement where they must carry their offspring

and give birth all alone.

Nevertheless, this arrangement does have its

advantages for females.

This arrangement has given specialized roles

to the males and females.

Males must court females for a chance to reproduce,

while females are able to pick and choose their mates.

This is a tideland, home to countless species of fauna.

From May to August, during the low tide when the water

recedes, a unique courtship ritual takes place here.

It is the courtship ritual of the fiddler crab.

A male crab waves its large claws in the air in

a threatening manner.

This is actually a serenade of sorts.

It is courting females through this behavior.

The tidelands serve as a ballroom where fiddler crabs

perform their mating dance.

The males court the females ardently and persistently.

They even engage in fierce battles for the

affections of the females.

Such violent altercations are a chance for males to prove

their physical strength and prowess.

While the loser often meets with a tragic end,

the victor is able to court the female unimpeded.

It enters its home, waiting for the female to follow suit.

But the female does not seem at all interested.

The male has no choice but to resume his courtship.

Courting a female can be a trying and frustrating task,

but the male must not give up.

The male is the sex that must seduce while the female is the

sex that can pick and choose whichever partner she pleases.

This is a rule decreed by Mother Nature herself.

When mating season arrives, male fiddler crabs in the

tidelands began courting females.

Female fiddlers tend to be finicky and capricious.

They will break off a relationship even as they are

mating if something displeases them.

Finally, the male finds a willing partner

and begins to mate.

What is the true significance of the courtship

ritual of the fiddler crab?

Why must males struggle so hard to find a

female to mate with?

The female is the one who automatically makes a big

investment by having an egg and being pregnant.

The female has more to lose than the male who makes many

cheap sperm in a mating event.

So automatically those basic differences between the male

and the female where they exist ought to make the female

the more selective sex.

They have the most to lose so they are under more selective

pressure to make a good choice.

Fifteen days later, the female undergoes a physical change.

It is carrying eggs.

When a male fails to seduce a female,

this means that the male will fail to produce offspring.

While it is the common arrangement for males to court

and females to choose, there is a species that has adopted

an entirely different reproductive strategy.

The Okinawa-benihaze is a transparent

fish with an orange hue.

These tiny, 2-centimeter-long fish live in

homes as narrow as pipes.

The male stays in its home.

Then, when a female appears, it approaches it

and begins its courtship.

It circles the female in the hopes that it

will accept its overture.

The female seems hesitant at first.

Then, it follows the male inside its home.

This is a sign that it has accepted the male's courtship.

Now, after the female lays its eggs,

the male sprays its sperm to fertilize them.

This mating behavior seems typical

of other animal species.

But when the benihaze is faced with a dearth of partners,

it adopts an entirely different strategy for

producing offspring.

There are two female living with a male in this tank.

But when the scientist removes the male that inhabits the

pipe, only the two females remain.

We observed this situation to see what would happen.

16 minutes later, a female enters the pipe previously

occupied by the male.

After about 30 minutes, the female inside the pipe swims

outside in search of the other female.

It is behaving like a male.

4 days later, the female has transformed into a male.

The female benihaze had undergone a sexual

transformation and become a male.

This is the reproductive strategy of the species.

Sometimes, the opposite occurs.

We tried adding a new male to a tank occupied by

the lone benihaze male.

A moment later, a tussle occurs between the two males.

They are fighting to determine the stronger of the two fish.

The victor occupies the much coveted pipe.

The male benihaze which lost in the fight changes its sex

and becomes a female.

It employs this strategy in order to hand down its

genes to the next generation.

Male becomes female and female becomes male.

This shifting of genders is a strategy adopted to preserve

of the species in situations where sexual reproduction

seems all but impossible.

In 2006, an amazing phenomenon occurred in London Zoo which

overturned commonly held beliefs about mating.

At the center of this phenomenon was none

other than the Komodo dragon.

A female Komodo which had been isolated from males for years,

suddenly gave birth to a nest of eggs.

A DNA analysis of the Komodo's offspring revealed that the

mother Komodo had no contact with any male.

Basically this is a parthenogenetic event,

which is common in some species of reptiles.

It's particular because that was the first time that was

described on a large charismatic reptile like

the Komodo dragon.

It is commonly thought that sexual reproduction is much

more advantageous than asexual modes of reproduction.

Under normal circumstances, the Komodo dragon mates

through the union of male and female.

In other words, it was thought that a female that had no

contact with males could not lay eggs.

But in this instance, the female chose parthenogenesis

in order to reproduce.

In this way, animals often adopt outdated methods of

reproduction in order to preserve their species.

3.5 billions years ago, the first life appeared on Earth.

This simple single-celled life form gave rise to male and

female through its struggle to survive.

Afterwards, life on earth became increasingly diverse.

And each species adopted its own unique

strategy for propagation.

But it was an entirely different challenge to

successfully birth and raise the offspring which had

been created through mating.

This also required new and innovative strategies.

The traces of one such strategy can be found in the

fossil of a primitive fish which is housed in the Museum

of Natural History in London.

It is the fossil of a placoderm which lived

380 million years ago.

There is an important clue in the fossil.

It is the petrified images of fry which were found

inside the mother's body.

The Incisoscutum specimen in the British museum was very

exciting, very important because it showed that the

largest group of placoderm fishes,

the Arthrodira such as these ones here,

were actually giving birth to live young.

And therefore, they were reproducing

by having copulation.

380 million years ago, some of the seas of the world were

home to fish that gave birth to live young.

And the fossil of Incisoscutum is proof of this.

Why did this species choose to reproduce through

internal fertilization instead of external

fertilization like modern fish?

To switch from laying lots of eggs in the water,

where they can be easily eaten by prey,

to giving birth to just a few live young inside gave a

definite advantage to this group because they could

nurture their young to a point where they are able to be born

and then fend for themselves and be more able to survive.

This is Selingan Island in Malaysia.

But the beautiful oceans surrounding the island are as

perilous as they were 380 million years ago.

This is because they are full of vicious predators that prey

on the creatures of the sea.

Nevertheless, there is an animal which braves this

dangerous sea every August.

It is the sea turtle which swims thousands of kilometers

in order to reach this island.

The turtle returns to this island every year

in order to lay its eggs.

When night falls, the sea turtle climbs up to the beach.

It looks for an appropriate spot to lay its eggs and

begins to dig a hole.

While the eggs of the sea turtle are soft,

they are covered by an outer shell which keeps the eggs

from drying even when they are buried deep in the sand.

It is thanks to the shell that the eggs are

able to hatch successfully.

Once you got a shelled egg, you can lay it on land;

conditions in which amphibian eggs wouldn't

survive where it's much drier.

So you can begin to inhabit a greater area of land surface

than if you're tied to water the whole time.

Shells were adopted by creatures eons ago after they

left the sea for the land.

The shells protect eggs and keep them from drying up even

on land where they are not surrounded by water.

Thus, the eggs can be hatched successfully as long as they

are kept hidden from the prying eyes of predators.

Two months have passed since the mother

turtle returned to the sea.

The hatchlings, which have just come out of their shell,

crawl towards the water.

They must crawl as quickly as they can in order

to avoid hungry seagulls.

Even if they reach the water successfully,

most of the hatchlings will be devoured by fish and seagulls,

and only 5 percent will survive to see adulthood.

It will take years until these fragile turtle grow big enough

to fend off the attacks of predators.

It's the end of August, and the forests are becoming dense

with the foliage of summer.

It is egg-laying season here in Indonesia's

Komodo National Park.

This bird which is digging up dirt using its

red legs is the megapode .

Using the earth it digs up, it builds a nest that is

reminiscent of a grave.

But there is a creature lurking in the shadows and

watching the bird as it digs its nest.

It is a Komodo dragon.

These birds lay the eggs in the nest,

but also the Komodo dragons use these

nests to lay their own eggs.

During egg-laying season, you can see Komodo dragons digging

holes in the ground everywhere in Komodo National Park.

These Komodos are all carrying eggs.

This is a decoy nest.

Komodos hide their eggs inside the nest of the megapode

and dig multiple holes which serve as decoys

to trick hungry predators.

This increases the chance of the eggs' survival.

When they use these nests, they kind of excavate

different holes and they will choose only one

hole to lay their eggs.

The other holes are just fake.

It's the end of March, and the rainy season which has lasted

for half a year is coming to an end.

Thanks to the constant deluges,

the environment is pristine and the food abundant.

Around this time, one will find that there are baby

Komodos living high up in the trees.

Females, they lay their eggs from the end of August

to the beginning of October.

Then you have a period of incubation of the eggs that

will hatch at the end of the rain season,

where the environment is greener,

where there are more preys in terms of little lizards,

geckos, or little species that the hatchlings,

they are very small, about 40cm in length, can feed on.

The Komodo dragon is one of the largest predators on Earth.

Nevertheless, hatchlings are exposed to many dangers

because of their diminutive size.

They are easy prey for hungry predators and must take refuge

high up in the trees.

They live in the trees subsisting on insects until

they are large enough to survive on the ground.

When they have just been hatched, even these

fearsome predators are too weak to protect themselves.

Meanwhile, mammals adopted the strategy of giving birth to

live young and raising them.

The Australian kangaroo gives birth to live young and

raises them inside its pouch.

In the pouch, the baby kangaroo feels its mother's

warmth and listens to her heartbeat,

and this accelerates the growth of the baby.

The baby kangaroo stays inside its mother's pouch for

a year and feeds on her milk.

The baby kangaroo suckles its mother and receives her

protection inside her pouch until it grows big

enough to fend for itself.

Although the pouch provides the baby with protection,

it is an uncomfortable and dangerous

burden for the mother.

So, why did kangaroos adopt this strategy

for rearing their young?

Though I think the move towards live birth and a lot

of development really reflects ecological and evolutionary

conditions that select for fewer,

more competitive, fully equipped offspring.

Tsubaki the chimpanzee is about to give birth.

She thrashes around, unable to bear the pangs of labor.

Chimpanzees can go through up to 7 hours of labor.

In an act of desperation, the chimp

grabs onto her trainer's legs.

In chimps as in humans, labor seems to be a painful ordeal.

Natsumi the newborn chimp is so physically developed that

it is able to embrace its mother as soon as it's born.

6 years have passed since Natsumi the chimp was born

here in the Great Ape Research Institute.

This playful chimp running across the field with its

mouth full of food is Natsumi.

Her mother, Tsubaki, also seems to be in good health.

During the past 6 years, Tsubaki has additionally

given birth to Hatsuka.

Three-year-old Hatsuka is still young and needs her

mother to look after her.

Natsumi also grew up under the protection of her mother.

Like humans, chimps also live in clans and societies.

Usually, they spend their day picking each other's fur.

Chimps have a strictly hierarchical society.

This is Roy, the head of the chimp society here.

In the society of chimps, the alpha male always has the

first choice, whether it be in food or mates.

The alpha male's anger is stoked when a lower-ranked

male steals its food or mate.

Roy has been angered by Namba, the 2nd

ranked male in this society.

As a result, Namba has been brutally assaulted and injured

by the stronger alpha male.

Male chimpanzees often get into violent

confrontations over females.

In chimp society, males are able to mate with multiple females.

Also, the female may choose any male to mate with.

Because of this, female chimpanzees often goad the

males to fight over them.

Thanks to their mother's efforts to birth the strongest

possible young and protect them through childhood,

Natsumi and Hatsuka are healthy and strong.

And someday, they will find appropriate males to mate with

in order to give birth to a new generation of chimpanzees.

This is because it is the basic instinct of all living

things to birth offspring and preserve their species.

A planet where sex hadn't evolve would be very boring,

have very few life forms and within those life forms,

there would not be the elaborate beauty that we think

exists in the world.

In fact, you might not even be able to detect beauty if you

didn't have sex because beauty itself,

the ability of humans and other things to see things as

beautiful or not beautiful, is the result of sex.