A red deer stag-
an icon of the animal world,
ozzing maleness in the highlands of Scotland.
Each stag bellows his intention
to possess a harem of hinds.
But the females are coy and show no loyalty to any particular male-
each has to prove his worth because females are not
in the market for wimps
Males fight for females
There's always a loser and the winner takes all.
By contrast, females are saddled
with all the parental care-
each calf takes nearly a year to raise.
Born reckless warriors, stags strive for superiority.
Females are so different: they're caring, relatively placid,
and get on well in groups.
Why do the sexes have such conflicting roles
in the mating game?
And why are there only two kinds of players?
Why bother with sex at all?
The sexes are forced to battle
because females have a score to settle,
and it all started about a billion years ago
when simple single -celled animals-
like these Paramecium -rocked the world.
All the individuals are virtually identical
in shape and from, but they differ genetically.
Only different''genetic types'' can come together and reproduce-
they fuse their membranes and exchange some
of their cell contents.
ln this form of simple sex,
they part after mating as new individuals.
There can be dozens of sexes in these animals,
Highlighted as different colours and there are no battles.
But that all changed long ago when one of them cheated.
A quirk of evolution made one of the ''sexes''smaller,
and this turned out to be one of the most significant events
in life on Earth.
The smaller types were more mobile and so monopolized the matings.
But the mates of the little cheats
could only produce viable offspring
if they grew fat to compensate for their partner's lack
of provision.
Now one sex was on a path to obesity,
the other to athletic swimming.
The presence of these over-sexed midgets drove all the other sexes
to extinction-
except for the huge fatty cells.
The small sex those that cheated became sperm and the large sex eggs.
Gender as we know it was bom.
And evolution packaged the genders into powerful males
and motherly females.
Today, females force males to compete for their precious eggs-
and this drives a wedge between their appearances,
and behaviour
But there are other ways of reproducing.
Cloning is another.
This is a single individual.
All corals expand and colonise
by exactly duplicating their anemone like polyps
this is a most effective way
to breed when the environment is stable and predictable,
like the warm seas of the tropics.
But even clones feud.
Neighbouring clones fight battles over space for decades,
and this is where sex can help.
These are hydroids and are similar to corals.
The colony grows by budding,
but in the overcrowded community of the reef,
it can quickly run out of space.
ln a clever trick,
the polyps alternate their celibate lives with sex.
Some generate miniature medusa which look like jelly fish
and are equipped with male or female sex organs.
They swim off and cast their sperm and eggs in the sea,
forming new hydroids that will settle
where there's more space.
ldeally,
all animals want to replicate themselves,
and cloning is the best way to do that.
However, sex provides the opportunity for change...
and one very formidable insect plays this double card
with aplomb.
This green aphid is populating the world with her self.
She's a virgin, and cloning herself,
she produces a genetically identical daughter
every twenty minutes.
The babies even have babies inside them-
so the mother aphid nurtures
her grand-daughters even before they're born.
Such prolific clones bent solely on breeding are easy pickings
for others.
This solitary wasp is laying her eggs
in the aphids body-
and they are a feast for voracious ladybirds.
Half the clones are born with wings to accelerate
their expanding empire
They disperse in the summer air to colonise neighbouring plants.
During the good times when plants are growing,
each aphid races to copy herself.
Males have no place, and don't exist
until later when Autumn draws near- now the females suddenly switch
to producing orange coloured babies.
Some will be males.
She engineers sex into her offspring
because the coming seasons are unpredictable-
the next summer might be very different
from the one in which she was born.
To copulate, the aphids fly off to fruit trees
and when they mature,
the females lose their wings and the males turn as rampant
as any red deer stag.
Because they have dispersed, it's very likely
that the mating partners come from different clones,
...having sex with your own clone
is the most useless sex imaginable.
By opting for sex,
the female aphid is cannily exploiting males
from other clones to inject a bit of variety
into her line when the future is uncertain.
Her eggs will over-winter,
and as the conditions next spring are unpredictable,
she has produced a brood of dormant embryos
which all differ from each other-
some are bound to survive.
Genetic variability is a weapon to battle
with environmental changes.
ln a perfect and stable world,
it's likely all females of all species would prefer to clone,
but getting rid of males is difficult once they're there.
Nevertheless this reptile has achieved it.
These are whip-tailed lizards, and every individual
in the population is female-
genetically the same female!
Every time they lay eggs,
a clutch of new female clones is born.
The lizards live in the deserts of Arizona and New Mexico.
They must be perfectly adapted to their surroundings,
and they don't want their good genes diluted
by the involvement of males.
The females have opted to hang onto their favourable genes
and have driven the males to extinction.
But the ghost of the male haunts their life nevertheless.
Near laying,
all the virgins need the stimulation
which a male would provide to make them ovulate.
With none around, the role is played by a female.
ln every sense she apes being a male.
Driven by a surge of the 'male'hormone testosterone,
she temporarily forsakes her true gender-
and goes through the motions of copulating.
Other females have also removed the male
from their lives
many live in the sea
like here in the Caribbean
Amongst the soft corals and sponges lives
the little known hamlet fish.
There are several different coloured varieties.
All are females but, amazingly,
they're able to make sperm as well as eggs.
These hamlets spend much of the day alone feeding,
and probably during this time, they fertilise their own eggs.
But within each female lies maleness-
and the potential to fertilise many more eggs
than she alone can produce.
So, at sundown, the hamlets go egg hunting,
pairing up with one of the same variety
and attempting to fertilise the other's eggs.
But who sheds the eggs?
Behaving like males, they don't trust each other.
The problem is- if one jettisons all her eggs,
the other would surely cheat,
simply fertilise them, and swim off.
So the couples trade a few eggs at a time in exchange
for their partners sperm.
When you can mate with yourself, why mate with another?
The answer is to satisfy the male imperative
to spread his genes far and wide.
And in another hermaphrodite,
this amazing behaviour takes an even more extraordinary turn.
Off the coast of Bermuda,
Portuguese man o'wars float in the ocean currents.
Amongst their stinging tentacles live these blue ocean slugs.
Much of their time is spent munching
the flesh of the Portuguese man o'war.
Like the hamlets they too can fertilise their own
strings of eggs.
But they also attempt to fertilise the eggs
of others by using their excess sperm.
Both have the same intention.
They want to give sperm but not receive it.
They manoeuvre to inject sperm into each other's hose like penis
and to spoil the other's efforts,
each tries to bite off his partner's sexual apparatus.
Competitive, demonic maleness
induces conflict even when imbedded deep within a female's body.
But much of life on earth lives in the midst of destructive forces
and sex is used as a weapon to combat them.
Disease is a major killer.
Microbes and parasites evolve rapidly
in the company of larger animals, like these Adelie penguins.
They are transmitted easily between crowded individuals
often breeding in squalid conditions-
in grime and fouled water.
Diseases weaken the body's immune system
and cause sickness.
Advertising resistance to disease is important
in mate selection.
Some creatures have incorporated it into their courtship
and the onus is on the male.
Here at 10,000 feet in the Sierra Nevada mountains
of California birds declare their bill of health.
These Sage grouse gather in open meeting places
to find their mates.
The males have been driven by the females to show
that they are disease free-
itself a reflection of strong genetic constitution
and a good immune system.
Healthy yellow skin pouches are the hall mark of fitness
and quality the females are looking for.
But this male has tuberculosis,
his skin tissues are inflamed and scarred by the condition.
He will never mate.
But those displaying strong immunity from such conditions will.
And this link between sex and disease
is even more apparent deep in the Amazon.
Here ravenous mosquitoes bite anything
with circulating warm blood,
and they inject a deadly parasite.
Among those that suffer from the mosquito's attention are
the white uakaris monkeys.
The mosquitoes carry malaria
one of the biggest killers in the tropics.
Malaria debilitates all,
except those with a genetic immunity acquired
from the creative process of sexual reproduction.
Both the male and female advertise to each other that they are free
from the grips of this mosquito
born parasite by their glowing red faces.
Mosquitoes bite the whole time,
injecting the parasites into the blood stream.
This male is infected may be his immune system
is deficient he's pale-faced, sickly and suffering.
Weakened by the effects of malaria
he's a far cry from a healthy male.
Sex has provided a means for some individuals
to evolve immunity to disease
in these uakaris only those with healthy red faces get
the matings.
This one stands no chance- he'll never mate,
and hand on his defective qualities.
The malarial mosquito is only found
in the so called white-water forest.
Across the river, in the black-water forest,
the malaria-carrying mosquitoes don't exist.
Here, the uakaris monkeys don't
have to advertise freedom from the killer disease.
And all their faces are black.
Sex has survival value because it speeds up the process of change-
and keeps our chemical defences ahead
of the fast breeding microbes-
but sexual behaviour itself is subject to the same process.
This is the remote island of North Rona off the coast of Scotland
it's a cold and windy place.
During the early winter months female grey seals gather
to come ashore.
They are heavily pregnant.
The bulls wait for them to land and jealously guard them.
After the female has produced her pup,
it isn't long before she comes into season-
liberating male aggression.
The victors of these fights are who the females want.
But often copulation is without the female's consent
and she is raped by a sore loser.
And yet things are changing,
even for these stalwarts of mammal breeding behaviour.
Some grey seals have recently been discovered,
who have opted out of the rough and tumble of the colony.
This male has never fought because he is paired to this cow,
whom he has been with for several years.
Each year she looks for him away from the main harems
where there's a lot of tension and disturbance.
For them, monogamy pays-
he's not a top bull
but at least he gets a mate- and she avoids being being raped
by defeated males- who are only left with that option.
These seals settle for peace and quiet,
and both do quite well-
perhaps their behaviour is inherited-
a variation spawned by the sexual process...
...that stupendously creative force which has provided,
and continues to provide our Earth with colour,
shape and form
Sex enables animals to discover every more ingenious
ways to live on our planet.
Amazing animals in worlds hidden from our inquisitive eyes.
lf we could find life elsewhere in the universe,
the natural forces shaping their bodies
would probably make them look very different.
And yet, for the same reasons that exist on earth,
extra-terrestrials would be reduced to males and females.
And the two genders will always be batting
to get the best deal out of sex.