19x08 - Triumph of Life: The Mating Game

[bunniefuu]

Life is full of beauty
and drama...

and its driving force is sex.

Every animal on earth
is descended

from a four-billion-year dynasty
of successful breeders.

We now know that the urge
to breed is driven by genes

which compel animals to fight
and even die for sex.

The evolution of sex has been

the greatest breakthrough
in the history of life.

It's a battleground where only
the sexiest will triumph.

Many of nature's bloodiest
battles are fought

for the sake of sex.

It's easy to take such passion
for granted

but why should males and females
suffer so much for sex?

The real payoff lies
not in the act itself

but in continuing
their family line.

Sex is life's gateway
to the future

a way for genes to pass from
one generation to the next.

and genes drive both males
and females to behave

in extraordinary ways
in the quest for immortality.

For animals,
that vital quest can be

life's ultimate challenge.

The struggle to breed makes
heavy demands.

One sex often pays
a higher price than the other.

Many females are burdened
with bringing up babies

while for most males, the only
chore seems to be sex itself.

Except for sex, it often seems

that females could raise
families on their own.

Even when it comes to hunting

it's often the females
that do all the work

and take the greatest risks.

Even when caught, prey can
still injure the hunters.

Despite all this effort

the lionesses don't have long
to enjoy their spoils.

The bigger, stronger male
soon claims the lion's share.

Many females seem to get
a bad deal out of life

for the sake of sex.

But they are simply being driven
by their genes.

The females instinctively make
sacrifices in order to breed.

Throughout the animal world

equality rarely has
a place in sex.

But just occasionally,
it's the male, not the female

that makes
the ultimate sacrifice.

A male redback spider has found
a female's lair.

But will he be recognized
as a potential suitor

or will this female see him
as her next meal?

His footsteps vibrate the web,
sending all the right signals.

she gets the message
and stays still

Tentatively, he maneuvers
into place.

One false move
and he could be dead.

His palps, resembling
tiny boxing gloves

are packed with sperm.

He drums them against her

as the prelude to an
extraordinary sexual act.

He's in,
and the sperm transfer begins.

But at this climactic moment
he makes a bizarre move

He flips his body over
into her jaws.

He forfeits his own life--
all for the sake of sex.

But there's method
in his madness.

While she's busy eating,
he's still pumping.

And more sperm means
more of his babies.

For his genes,
it makes perfect sense.

He has to die sometime,
and by trading in his life early

he's ensuring a bigger stake
in the next generation.

Such suicidal strategies
have evolved surprisingly often

in the mating game.

In this river

sockeye salmon are reaching
the end of their lives.

The past few weeks have taken
their toll.

They've swum 1,500 miles
upstream from the ocean

in search of sex,
driven by instinct to push on and on.

It's the journey of a lifetime.

They've made it to the gravel
bed where they first hatched.

Exhausted by their struggle,
they have one last mission:

They must compete for mates.

Males jostle one another

for a chance to fertilize
a female's eggs.

The stakes are high:

Those that breed are winners
in the evolutionary w*r;

those that don't are destined
to evolutionary oblivion.

Every salmon will die

but some will live on,
through their offspring.

Within each egg lie
the blueprints of life--

genes, inherited
from both parents.

Instructed by those genes

a shapeless egg turns
into a baby salmon--

a salmon with a genetic pedigree
to breed successfully.

The secrets of success
are passed

down countless generations

within genes
that approach immortality.

The individuals that carry them
live only a few years.

But there are far easier ways
to pass on genes

without the sacrifices of sex.

Remarkably, these sea anemones
can reproduce without a partner.

They don't need sex.

The anemones simply split
themselves down the middle

to create two identical animals -
clones.

It seems drastic, but it's
a very effective way to breed:

no need to search for a mate, no
risk of being exploited by one.

And it's quick-- in just
a few hours one anemone divides

into babies that can reproduce
in exactly the same way.

The young anemone is
a perfect clone of its parent

sharing identical genes.

And cloning as a means
of rapid reproduction

is a method used by
more complex animals, too.

In the wake of
a tropical cyclone

a raft of vegetation
drifts in the ocean.

On board is a small passenger:
a female gecko.

The raft runs aground
on a remote island.

It's a safe haven, but there
are no other geckos here.

So there's no chance
of her finding a mate.

But this gecko is
no average castaway.

For her, isolation isn't a
problem, it's an opportunity.

She's fully equipped
to reproduce alone.

And once in the shady
interior of the island

she will waste no time
in starting her own colony.

She lays eggs, but she does not
need a male to fertilize them.

Inside each,
an embryo will develop

identical to its mother--
a perfect clone.

A few weeks later,
the baby geckos hatch.

They're all female

and can also lay eggs
without needing to mate.

Soon, the island will
be crawling with geckos

all descended from
the single mother.

In this species
there are no males.

Breeding without sex might
work well on a paradise island

but it's a perilous strategy
elsewhere in the world

where predators and
disease are rampant.

In the Australian outback

cloned geckos have
a much tougher time.

They must keep an eye
open for danger.

This goanna is just one
of the predators to avoid.

And there are other threats that
are much harder to hide from.

Tiny parasitic mites around
the gecko's eye suck her blood.

Unseen diseases can also k*ll,
and if one gecko falls ill

the whole population of
identical clones is at risk.

Like their island relatives,
these geckos multiply rapidly.

Each gives birth alone
to female clones.

But here, cloning is
a double-edged sword.

If a parasite finds
a weakness in one gecko

it can infect all the others.

The population can crash
even faster than it grew.

But living alongside the clones
are other female geckos

which do pair with males
and multiply through sex.

half as quick--
males don't have babies..

But sex has
a distinct advantage--

it mixes genes and
creates unique offspring

each with its own unique
defense against infection.

Parasites have a tough time

spreading through
this population.

These geckos, by shuffling
their genes during sex

stay one step ahead.

This key advantage helps explain
why sex is so widespread.

But the advantages
of sex may reach deeper

than merely shuffling
the pack of genes.

Sex revitalizes
the genes themselves.

The two sets of genes
that come together during sex

each have their
own imperfections

because genes get damaged
from time to time.

Sex repairs these faulty genes

by replacing them with good
copies from the other partner.

So with each passing generation

sex rejuvenates genes, handing
them the key to immortality.

Throughout its
two-billion-year history

sex has been swapping genes.

The new combinations that result

are the raw material
that feeds evolution.

Through sex,
evolution has created

our planet's amazing
diversity of life.

To breed, sexual animals
must swap genes.

And in the mating game, the
challenge is to find the best.

This is how albatross do it.

After spending months apart
alone at sea

the birds are compelled
by their sexual urge

to spend hour after hour
in an elegant dance.

This is no frivolous flirtation.

They're picking partners

to share their investment
in the future.

Inside the female, this
investment has already begun.

She's carrying
a single large egg...

an expensive life-support system
for the next generation.

But a male produces
millions of sperm...

tiny inexpensive
packages of genes--

a difference in size
almost as old as sex itself.

Two billion years ago,
when it first evolved

sex was a simple matter.

Cells just bumped
into each other...

and then swapped genes.

But for an average cell
living in a big ocean

this wasn't always easy.

Smaller more agile cells were
better at finding partners.

And larger, fatter cells.
well stocked with energy

were more easily found.

Combining their talents

these odd couples paired off
faster than the rest.

Soon, the seas were filled
with cells specialized for sex.

Large eggs and tiny sperm
were here to stay.

Today, the difference in size
between eggs and sperm

has reached amazing extremes.

From the outside,
this female kiwi

looks almost identical
to her male partner.

But look inside her...

and there's a truly
enormous egg--

so large that she'll only
produce a few in her lifetime.

The male, in contrast,
produces millions of sperm

every time he mates--

enough to fertilize every
female kiwi on the planet.

Quantity versus quality...

male versus female.

Each sex has its own
rules in this game...

even those curious creatures
that play on both sides.

On Australia's
Great Barrier Reef

some animals are both male
and female: hermaphrodites.

These flatworms produce
both eggs and sperm.

But they don't
fertilize themselves.

They need new genes
to mix with their own

so they must cruise
the reef in search of sex.

When they meet,
an expected move might be

for one to play male
and the other female.

But flatworms have
their own game plan.

Each tries to be male

stabbing at the other
with a harpoon-like p*nis

that can pierce any part
of the other worm's skin.

In this strange duel, the
rules of engagement are simple:

stab and avoid being stabbed.

These flatworms even
have a double harpoon

perhaps twice as effective

and all the better
to inject their sperm

into as many other
worms as possible.

Their sperm are small and cheap
and they've plenty to spare.

But they keep their large,
valuable eggs in reserve.

In every contest
there has to be a loser

but there's triumph
in this defeat.

The loser's eggs will
be fertilized by sperm

with winning genes, an asset
to the next generation.

For male animals

spreading their genes is
cheap and relatively easy.

The hardest task for some
is finding females.

Especially when they live

in the vast tangled
swamps of Venezuela.

Here, all eyes are
on the lookout

for a dangerous
predatory female.

She's an anaconda,
the swamp's largest hunter.

She would have no problem
eating a caiman...

or a capybara.

She's 18 feet long

and weighs more than 200 pounds.

The larger she is,
the more young she can have.

Her fertile body acts like
a beacon to male anacondas.

She need make
no effort to find them.

The male, only one-fifth her
weight, is puny by comparison.

But, like the sperm he carries,
he's sleek and mobile

and his all-important task
is finding her.

He's tracked her down.

But he's not the first.

Eight male anacondas are already
wrapped around the female.

They may remain entwined
for a month or more.

Each male has a pair of spurs
for tickling the female

stimulating her to mate.

The males wrestle
to be the winner

in this serpentine battle
for sex.

The struggle becomes clearer
when the action is speeded up.

The big female seems passive

but she's hugely attractive,
and need do little else.

While the males compete
among themselves

she saves her energy
to nurture her eggs.

But not all females are
as languid as the anaconda.

Sharp-eyed and
on the lookout for males

female marine iguanas are
waiting for their chance.

They pick males
based on their territories

so the larger males must compete
for the best spots.

Until clear winners have emerged

eating, not mating, is
the females' priority.

Now is the best time,
when the tide's out

so they race for the shore.

For males seeking sex,
food is off the agenda;

they must stay and fight.

These often bloody battles
sort out the men from the boys--

important if the females are
to know who's who.

The females, meanwhile, gorge
on fresh seaweed.

Food is vital to nourish
the eggs growing inside them

no matter how hard it is
to reach.

The battles on the rocks
continue

through the heat of the day.

The winner will take
center stage

ready for the females' return.

As the females travel
up the beach, they are watched

by smaller males without
the strength to win fights.

Their tactic is
to jump on passing females.

But she wants a male that has
fought to prove his strength.

She continues on
towards the rocks.

A winning male welcomes females
onto his patch.

He sniffs them to see
if they're ready to mate

and to accept his genes.

But still the males must wait
until the females accept them.

Female iguanas pick their
partners from a crowd of males.

But how do other female animals
choose the best

when they only meet
one male at a time?

A surprising answer has been
found in the woods of Ohio.

In spring, wolf spiders
start looking for mates.

The female stays hidden,
wary of predators

but she leaves a trail of silk
that a male might find.

When he stumbles on it
he detects the presence of a potential mate.

She senses his tapping signal...

then sees his waving legs.

But why does she choose
this male above all others?

Something about him
really attracts her.

He has long bristles
on his front legs

tufts that seem to serve
no practical purpose.

He shows them off
by giving her a wave.

But could it really be
hairy legs

that catch
a female spider's eye?

To find out, spiders' viewing
habits have been analyzed.

This is video dating,
spider style.

A mini TV screen plays life-size
images of courting males.

But there's something missing.

This male has no hair tufts
on his legs.

The female is unimpressed.

But show her a male
with normal leg tufts

and she's interested.

And if he has huge leg tufts...

then she's really excited.

If females find hairy legs sexy,
so will their daughters

and they'll have sons
with hairy legs, too.

For these spiders,
hairy legs are here to stay.

Battles between males using good
looks to attract choosy mates

have led to extremes
of flamboyance

especially among birds.

These birds put a surprising
value on their gaudy appearance

even at the risk of catching
a predator's eye.

But there may well be sense

in a female's choice
of flashy plumage.

Complex patterns can be
easily damaged.

So peacocks
with perfect plumage

are probably in better condition
than most.

Peahens are known
to lay more eggs

for peacocks with splendidly
symmetrical tails.

There can also be
a hidden message

behind a male's showy colors.

Sometimes bright colors hint
at a good diet.

Male house finches
are colored red

by chemicals in the fruit
and seeds they eat.

This female wants a male
that's good at finding food.

Red feathers suggest just that

while pale feathers could be due
to poor foraging.

Bright males are advertising
their feeding skills.

They're the ones
that she'll prefer as a partner.

In the weeks to come, the bright
males that are good providers

will make good fathers.

But that's not the whole story.

By choosing a bright male

the female is also choosing
a healthy partner.

Bright males have very few fleas
and lice among their feathers.

Duller males often have more

which might infest
the nest and chicks.

The bright males are
the best choice.

They're well fed
and parasite-free--

literally flushed with health.

Across the bird world

females carefully choose
the best males they can find.

But for some females,
the search doesn't end

even when they've found a mate.

Blue-footed boobies live
in densely packed colonies.

Eachthese birds appears
to remain faithful

to one partner for life

but "love thy neighbor" is
closer to the truth.

The female has a partner she can
depend on to feed her chicks.

But when he's away
she's not averse to a new romance.

Now the female is home alone.

Male neighbors are eager
to step in.

While her mate's away,
she's free to play the field.

For her, infidelity makes sense.

She already has
a committed partner

but he may not have
the best genes.

Another male, like this one,
might have more to offer.

She obviously likes
the look of him.

And he responds.

A brief courtship heads
towards an inevitable end.

Like all males

he's just trying to spread
his genes far and wide.

And the real bonus
of this affair is

that he won't have to bring up
the chicks.

Meanwhile her regular partner
goes on fishing

in blissful ignorance.

But on his return,
he soon reclaims his partner.

It's to his advantage to do so.

In a world full of infidelity

his repeated mating will keep
his sperm

in the race to fertilize
her eggs.

Such competition often breeds
dirty tricks

and to further his own cause

a male can use all manner
of cunning ploys.

Cherry blossom time in Japan...

the mating season
for many animals.

But these squirrels breed
all year.

Their liaisons are extremely
brief encounters

in which males use
devious tactics to succeed.

Males are far from faithful.

They'll mate with any females

they can attract
using special calls.

Alerted by the noise,
other males join the chase.

But the commotion also draws
unwelcome attention.

Seeing the kite,
a male squirrel calls in alarm.

Other squirrels hearing this
sit very still

especially those
out in the open.

They wait for the danger
to pass.

Safe once more, the squirrels relax

and their mating game
can begin again.

There's another warning call...

and sure enough, the squirrels
all freeze in their tracks.

All except one-- the squirrel
that raised the alarm.

His call was a hoax.

While the other males freeze,
he can go on mating.

His trick has bought him time...

until the others believe
the danger has passed.

In the mountain meadows
of Poland

lives a male creature that does
more than cheat a few rivals.

He can excludeallhis rivals.

He's an Apollo butterfly.

Males appear before the females

ready to mate quickly
when the time comes.

Down below, a female is about
to emerge from this pupa.

She'll be mated only once

by a fast-acting male
that can beat the competition.

As soon as she emerges

something about her,
probably her scent

alerts males to her presence

and the race to find
this virgin prize is on.

Even before her maiden flight,
she's discovered by this male.

But how can he make sure

that he's the only mate
she will ever have?

She receives his sperm;
the mating is successful.

And now he fits her
with the insect equivalent

of a chastity belt

to be certain that his will be
the only winning genes.

He leaves, victorious.

No other male can mate with her

because he has sealed off
all access

with an impenetrable spiked plug
that has now set hard.

The female had little choice
in this mating game

But sometimes, females
have surprising influence

despite the physical power
of males.

This harem
of female elephant seals

has been won by a single male.

And it would seem that females
have no choice in the matter.

But the females'
discriminating tastes

will soon be revealed
by a sly visitor to the harem.

Sneaking in from the sea

a young Casanova is looking
for an opportunity.

He's intent on seduction.

But the females raise objection
to his advances.

The beachmaster awakes.

He soon chases off
the upstart bachelor.

Clearly, biggest is best...

but the sneak was really
put back where he belongs

by the females' protests.

These females won't settle
for second best.

The harem master is dominant

but not without a little help
from those he seems to exploit.

These females are
willing concubines.

Female lions, too, are willing
subjects of powerful males.

Females do the hunting

but males are
strong defenders...

from other lions.

When the males in a pride die

the females and cubs are left
extremely vulnerable.

There are always rogue males
on the prowl

ready to take control.

It is a harsh rule
of this mating game

that an invading male
will k*ll any cubs he finds.

The death of the cubs
may seem brutal

but it was no senseless k*lling.

The new male makes sure that
he won't be wasting his time

protecting cubs
that aren't his own.

The female will soon
bear his young

so he'll stick around
to protect them

from other marauding males.

In doing so, he also protects
the female's new investment.

This savage story shows
that, despite their conflicts

males and females must co-operate.

They need each other to bring
there genes together

in a vital combination--

a renewal of life.

All around us live
the descendants

of a four-billion-year battle
for survival.

At the heart of that battle
lies sex.

Despite its cost and complexity

its effort and investment,
its deception and guile

sex is here to stay.

New life is born every minute

equipped with the right genes
from both parents

to survive in
an ever-changing world.

The triumph of the mating game
is a future for life.