Text: WTC-SWE
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 war;
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 kill, 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 penis
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 kill any cubs he finds.
The death of the cubs may seem brutal
but it was no senseless killing.
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.
Text: WTC-SWE