All language subtitles for Sex A Horizon Guide

Sex.

A simple word for the most intimate,
sensitive and complex of subjects.

Sex is at the core of our deepest
relationships.

It's part of what makes us human -
it drives our passions,

our frustrations and our moments
of greatest ecstasy.

One way or another it defines us.

But unravelling the secrets of sex

has been a contentious
and risky business for science...

..and an equally big challenge
for television.

For more than 45 years,
Horizon and the BBC

have reported on how science has
improved our understanding of sex,

strived to solve our problems
with it,

and even tried to help us
do it better.

In this programme we'll also
look at how science helped us

understand gender and fertility.

But can science really save the day
when sex goes wrong?

Biologically, of course,
sex is about reproduction,

but that falls rather short of
what it means to us as a species.

Arousal, desire, sexuality,
fertility

are all incredibly personal
to each of us.

And because of that,

science got involved in our
sex lives rather late in the day.

Until recently, we knew very little

about the most basic aspects
of human sexuality.

So how did scientists
uncover our sexual secrets

and what did they learn?

To truly understand a subject
so complex, delicate

and sometimes plain embarrassing,

someone needed to ask difficult
and intimate questions

about what we got up to
behind closed doors.

Perhaps the first person
to approach sex

in a systematic and scientific way
was Dr Alfred Kinsey.

Kinsey's lifelong passion
was collecting insects.

But in the 1930s
he switched his attention

to collecting the sexual habits
of humans.

When asked by the bright young
students of Indiana University

to teach a course that covered
human sexual behaviour,

Kinsey discovered that very little
research had been carried out

on the sexual habits of people.

We knew far more about copulation in
other animals than we did in humans.

I discovered that there is
practically nothing known

about human sexual behaviour

in comparison with what we knew about
the sexual behaviour of other animals

and in comparison in what we knew
about the activities

of other parts of the human body.

In order to get meaningful data
about the sex lives of humans,

he asked his own students
about their intimate experiences.

And, for the sake of science,
he pulled no punches.

He asked me questions about the...

..dimensions of my sex organs
which I couldn't answer.

"Well, take this envelope
and this piece of paper,

"go home and measure yourself
and send it to me."

Kinsey's curiosity became obsession.

In less than ten years
he personally collected

sexual information
on more than 7,000 people.

Kinsey's results were published
in two books

that both became best sellers.

Sexual Behaviour in the Human Male
appeared in 1948,

followed by Sexual Behaviour
in the Human Female in 1953.

For the first time,
science was attempting to obtain

objective data on what ordinary
people did behind closed doors.

Don't forget, this was in early days,
when there were a lot of suspicions

about such things, and in addition
it was the McCarthy era,

so Kinsey had to be absolutely
circumspect in everything.

This related to things like dirty
jokes, we were never permitted

to do such things,
tell such things, on the staff.

Kinsey's work revealed that
affairs in marriage

were extremely common
for both men and women.

But that was the least of it.

His findings showed that even before
the sexual revolution of the 1960s,

nearly 50% of women
had premarital sex.

Amongst 10,000 interviewees,

92% of men and 65% of women
said that they masturbated.

Just under half of the women
interviewed

reported an erotic experience
with another woman.

And 8% of men and 3% of women

admitted to some kind of
sexual activity with animals.

It was clear that the laws governing
sexual activity in America -

particularly in the more
conservative states -

were far more restrictive
than the reality

of many Americans' sex lives.

He told me,
with an absolutely straight face,

perhaps just the trace of a smile,

that what he knew about the laws
of Indiana,

and what he had learned about
the males of Indiana,

indicated to him that 85% of us
should be in jail.

Kinsey's findings were added to
through the decades

until we had a vivid picture

of the spectacular variety
of human sexual behaviour.

But scientists didn't just deal with
behaviour during sex.

They were interested
in the rules of attraction.

Males are almost always prepared
for sexual behaviour,

but females usually run away
from males,

and that, after all,
creates male interest.

But when females are receptive
they ensure that, whatever happens,

they're caught.

At certain times in her cycle,

the female will allow herself
to be caught even more readily.

The male may appear as a mere toy

in the hands of
a manipulative female,

but it's probable that each
is influenced by hormones.

More than 30 years on,

the role of female hormones in
influencing sexual desirability

is still being investigated.

A group of scientists
recently decided

to conduct a most unusual experiment
in a most unusual place.

They recruited 18 lap dancers

and asked them to keep detailed
records over two months

of how much they earned every night
in tips.

They also asked the dancers
to record data

about their menstrual cycles.

Looking at how earnings
varied over their monthly cycle,

they discovered something
remarkable.

During six days around the middle of
their monthly cycle,

when the dancers would have been
at their most fertile,

they were earning an average
of around $70 an hour.

In the rest of the month
they earned just $45 an hour.

If money talks, this suggests

that male clients found the dancers
far more attractive

when they were
at their most fertile.

The men may have been responding to
chemical or physical signals

that the women were
unconsciously producing.

Understanding what turns us on
is one thing,

but scientists wanted to find out
about the physiology of sex.

In the 1950s, two researchers
opened the bedroom door

in an attempt to quantify exactly
what happened to the human body

before, during and after sex.

The films they made
as part of their research

still make for uncomfortable
viewing.

In a physiology laboratory,
you have to have means...

create means and measures of
evaluating response.

We needed to know heart rate,

body temperatures,
skin changes...so on.

And we're the first to say
that our work was primitive.

In 1958, William Masters and
Virginia Johnson made this film

of volunteers in their laboratory
having sex

and becoming sexually aroused
through masturbation.

The areolae begin to swell,

the entire breast shows
increase in size.

Unsurprisingly,
their work was controversial,

but they made an effort to be
as objective as possible

in the way they collected
and reported their findings.

We did everything to take out the
titillation in those early times.

We kept a very low profile,
and yet a very strong one

within the research and medical,
scientific community,

but they still find it
very discomforting

to think about the means, which is
someone in a laboratory,

someone under lights,
someone wired up.

Even though there's a lot of that
going on

at every other kind of research
under the sun...

when it's sex, it's different.

From the 1950s onwards, scientists
continued to investigate sex,

building on the work of
Masters and Johnson

and delving even deeper
into the physiology of sex.

And now, with orgasm,

the involuntary contraction
of the outer vaginal ring.

Laboratory studies led to
revelations

about what happened to
the female body during sex.

The lubrication of the vagina
came from its walls

and not from the cervix
as previously thought,

the important role of the clitoris
in female orgasm was confirmed,

the vagina could contract and expand

to accommodate a variety of sizes
of penis,

and sexual satisfaction didn't seem
to depend on penis size.

By understanding
the physiology of normal sex,

Masters and Johnson hoped to help
those with sexual problems.

Science was starting to get to grips
with sex -

to understand how our bodies carried
out this important function.

But although their findings
were detailed,

those sexual pioneers
lacked the technology

to get the whole picture
of how we made love.

In particular,

they couldn't see what was going on
inside the human body during sex.

Reproductive physiologist
Dr Roy Levin

has struggled with the technical
limitations of studying sex

for decades.

we didn't really
have the apparatus

to allow us to do the measurements,
and there was a long period of time

when you could only guess
what was happening

from the external appearances
of men and women in coitus,

so you couldn't really tell
what was happening inside

because you just can't see.

Our understanding of sex
hasn't moved on much

since Leonardo da Vinci
first started dissecting corpses

and studying them over 500 years ago.

The Queen holds this drawing
by Leonardo

in her very own private collection.

The machine Dr Levin's come to see
is this fMRI scanner.

It's basically a camera
which uses magnetic fields

to penetrate human flesh.

Today, in the interests of science,

Michael DeGroot
and his girlfriend Liz Leahy

are going to attempt to have sex
in its cramped confines.

Well, this is the machine.

As you can see inside
it's got, like, two doughnuts,

those are the very large magnets,

and in between is the space that
you'll lie down in and have coitus.

So, it's been specially adapted,

that means just a single board
has been put down

and you'll lay in between
the two magnets,

and hopefully that will capture
the images of what's going on

during sexual intercourse. OK.

Dr Levin is well aware of the
problems that need to be overcome

if this experiment
is to be successful.

It's not the easiest thing
in the world to maintain an erection

and have intercourse
in terms of this particular set-up.

They're brave people
that go into these machines.

I'm interested to see how
we're going to manoeuvre ourselves

in there, because it looks like
a pretty constricted space.

I know they want us
in one certain position,

so I hope that we're able
to situate ourselves

so that they get the images
that they want.

That's my main concern.

The scanner takes a picture
every three seconds

and produces images of the body
from top to bottom.

This is the first time
that such images have been seen

on British television.

You can sort of see the penis here,

that's outside the body
from about here,

and this is the root of the penis
inside the body,

and this is inside the female's
body, that's her pubic symphysis,

the bone, and here would be
the pubic hair just around here.

That's, of course, her bottom

and this is the vagina
that the penis is in,

and at the top here is the glans.

And the thing that is obvious
in this cross-section

is the unusual shape of the penis
during intercourse.

Well, it's like a boomerang,

that's what we've found out
by these machines, actually.

That in fact the penis
does look like a boomerang.

It isn't straight, like they
drew it in the early times.

In fact it is bent,
as you can see quite clearly.

It's actually incredible,

because as far as
when you're having an erection,

you think it's as hard and solid
as...rock or wood or something,

but when you look at those pictures
it's unbelievable,

you have the 90-degree angle,

and you can't even imagine
that it would bend that way.

It's really fascinating
to see what the body does.

Nobody knows why the penis
has to go through

such extraordinary contortions.

One theory is that
it's a relic from our past,

when sex was more commonly done
on all fours, and not face to face.

Understanding the mechanics
of sex and desire

gave scientists the knowledge they
needed to move to the next stage,

of trying to fix
our many sexual problems.

Male impotence seemed to be one of
the most obvious issues to tackle.

But the first idea of how to fix
erectile dysfunction

wouldn't come
from a scientific laboratory.

Instead, the breakthrough came
from a man named Geddings Osbon.

He ran a tyre retreading company,

but he became one of history's
most unexpected medical innovators

when he came up with a very
practical mechanical solution

for his own impotence.

The only thing he knew about
was maybe taking a small pump.

At this time he got
a regular bicycle pump.

This tube is tubing that was used
on the windshield wipers of cars.

This metal valve is the kind of
metal valve you find on truck tyres.

He reversed the cylinder in here,

to make it to where...

when he pulled up,
it created negative pressure.

So he found that if he could take
this tube here and connect it,

that he could pull the air
out of the cylinder,

so then he would place this against
his body and he would pull up

and it would pull blood
into the penis,

and then in the cylinder
he would get an erection.

Geddings Osbon's invention
achieved mechanically

what the body normally does itself -

drawing blood
into the spongy erectile tissue

which runs the length of the penis.

When an erection happens naturally,

the rising pressure inside the penis
closes down the veins

to stop blood leaving
and maintain the erection.

Osbon used an elastic band.

His system was reluctantly adopted
by the medical community

in the 1980s.

For years, the vacuum erection pump
was the only mainstream solution

to a very common problem.

But it's easy to understand
that Osbon's invention

didn't suit every man
suffering from impotence.

What was needed
was something more convenient,

that didn't ruin the moment.

The solution came in the form
of a chemical compound

developed in the late '90s.

Scientists at Pfizer were
looking for a new drug for angina,

something that would relax
the blood vessels around the heart.

After screening
hundreds of thousands of compounds,

they ended up with UK-92,480.

But its trials in humans
were a letdown.

It was about to be consigned
back to the stores

when the triallists came back
reporting an unusual side effect -

lots of erections.

Add the drug, and the relaxations
get larger.

But it's... The trace's upside down.

By making a crude mock-up
of the human sexual apparatus,

senior scientist Chris Wayman
found an ingenious way

to test this anecdotal evidence.

These are actually
penile blood vessels

that we have in a tissue bath.

Think of this as the brain, this is
the brain and the spinal cord.

When you become aroused,
your brain switches on.

We can mimic this

by switching on the equivalent of the
central nervous system in the brain.

It sends electricity down to the
tissue baths and across the tissues.

And when we pass an electric current

across these small pieces
of penile tissue, they relax,

and ultimately that's what happens
during penile erection.

Relaxed penile blood vessels
mean more blood flow to the penis,

and so an erection.

What Chris did was take penile
blood vessels from impotent men,

vessels that didn't respond
when he flipped the brain-switch,

and then added UK-92,480
to the tissue bath.

What was most amazing
about this study

was that we saw a restoration of
erectile response.

It's very rare
in any tissue preparation

to convert dysfunctional
to normal function.

So now we were onto something that
can only be described as special.

UK-92,480 was renamed Viagra.

And within weeks of going on sale,

tens of thousands of prescriptions
were being written every day.

You would never have been able
to predict

that this was going to
have beneficial effects

on millions and millions of men
throughout the world.

A little bit of science having
an effect of self-esteem, anxiety,

depression levels and ultimately
creating enhanced relationships.

Today, Viagra is one of
the most widely prescribed drugs

in the world, with about six tablets
being dispensed every second.

By fumbling in the dark,

science had fixed a problem
that had plagued men for centuries.

But there are bigger
and deadlier problems

when it comes to sex,

and some of them would prove
much more resistant

to scientific solutions.

Sex brings bodies into intimate
physical contact with each other.

But it also allows sexually
transmitted diseases to travel

from one person to another.

But by the 1970s many of these
diseases were under control -

in the developed world at least.

Then, in the early 1980s, along came
a terrifying new sexual infection.

Horizon broadcast
one of the first documentaries

about this terrible new disease.

The first troubling signs
were noticed

in the homosexual communities
of America,

in particular in
New York's Greenwich Village.

Gay men were contracting
bizarre infections

that seldom infected healthy people.

Toxoplasmosis,
Pneumocystis carinii pneumonia,

Cryptosporidiosis,
and types of tuberculosis

that normally only infected birds
were killing men in their prime.

Then the disease was noticed
in intravenous drug users,

many of who were in prison by the
time they started having symptoms.

Prisoner Castranova's speech
is affected.

He may have Toxoplasmosis

as well as the pneumonia.

This is one of his better days.

What's rough now is,

I don't know
if I'll ever see my kids again.

Scientists were horrified
when they looked at blood

taken from these patients.

The numbers of a particular
white blood cell,

known as a T helper cell,
were at rock bottom.

Without this vital cornerstone
of the immune system,

infections which would normally be
easily fended off

could become lethal.

Finally, behind all these
odd infections,

scientists discovered
a puppet master.

Something that was weakening
the immune system,

allowing other, usually mild,
infections to wreak havoc.

They tracked down the cause

of what had become known as acquired
immunodeficiency syndrome - AIDS.

It was a virus - HIV.

Like a walking time bomb.

You know?

That's what they said.

"You're like a walking time bomb."

He died soon after.

And Mrs Castranova also died.

She was incubating AIDS
while her husband was in prison.

Since HIV was first identified,

over 60 million people have become
infected worldwide.

Of those who contracted the virus,
AIDS has killed 30 million people.

It's one of the worst pandemics
the world has ever known.

In the intervening years,
science has scrambled to find drugs

that could cure the disease,
with only limited success.

COCKEREL CROWS

But then something surprising
was noticed

in a valley in Central Africa.

Something which would suggest
an effective way

of combating the disease.

On one side of the valley people
are dying of AIDS in their hundreds,

while their neighbours, with the same
apparent behaviour and risk,

are far less affected by the disease.

MAN SPEAKS IN OWN LANGUAGE

In this school, if the epidemic
continues to spread,

60% of these children
will die from AIDS.

But the extraordinary thing is

that if they were children
just a mile away

on the other side of this valley,

their chances of dying
would be three times less.

Scientists realised
the only difference

between the AIDS-free side
of the valley and the other

was that the boys
on the healthy side

had been circumcised,
according to local custom.

Removing the foreskin seemed
to have an almost miraculous effect

in preventing the men
from getting infected.

Intrigued by the idea,

anthropologist Priscilla Reining
compiled data

on hundreds of circumcised
and uncircumcised tribes.

When this data was matched up
with a map of HIV prevalence,

the correlation was startling.

This was the map which we published,

and the black are depicting
ethnic groups

which do not practice circumcision
as a norm, and the grey

are groups
which do practice circumcision.

So this is a corridor which runs
from the southern Sudan

down into South Africa.

Here is an overlay of HIV.

And you can see that
there's a high degree of conformity

between the red, which is
relatively high HIV rates.

There is red
down the same band, and...

..interestingly,
over here as well.

The statistical...

statistical relationship was .90,
which is very good.

And so, you know, wow,
it really is there.

But why should circumcision

so drastically cut the risk
of HIV infection?

The answer lay in particular cells
of the immune system

present in the foreskin.

Cells which HIV was targeting.

The green cells
are Langerhans cells.

They're in the front line of
the body's battle against infection.

They capture infectious agents
like viruses

and show them to other cells
of the immune system,

which can actively fight
the infection.

But HIV uses the Langerhans cells
as a gateway to the body.

It's a Trojan horse, basically.

The Langerhans cell is in fact
allowing the virus to enter the body,

and carry to the very system,
namely the lymph glands,

where those viruses
can start proliferating.

Circumcision reduces the risk of
being infected by HIV by over 60%,

and is now recommended
by the World Health Organisation

as an important part
of disease prevention.

It's hoped that HIV/ AIDS
will be vanquished one day,

but for the moment the disease
is being held at bay

by a mixture of anti-retroviral
drugs and sex education.

As well as tackling diseases
that spread amongst us

through sexual contact,

scientists have also tried to help
with problems of gender identity.

Biologically speaking,
it should be straightforward.

After all, the chromosomes we get
from our parents determine our sex.

Two X chromosomes for a girl,
an X and a Y chromosome for a boy.

Beyond that simple equation, though,
scientists are still studying

how exactly our genes
turn us into either men or women.

Of course, there's much more
to being female or male

than just which body parts
you do or don't have.

What makes us feel
and act like men or women?

There has been a long debate
over how much our gender identity

is controlled by nature or nurture.

And for the latter half
of the 20th century,

the argument focused
on the tragic story of one boy.

On 27th April 1966, Janet Reimer
took her baby twin boys

Bruce and Brian to her local
hospital in Winnipeg, Canada,

for a routine circumcision.

But instead of using a knife,

doctors chose to use an electric
cauterisation technique.

Bruce went first,
but the equipment malfunctioned,

and Bruce's penis
was burned beyond repair.

Janet was devastated.

Daily, I was crying.

Every time I changed his diaper
I'd cry.

I was in shock...

..for a while.

I guess about a year I was in shock.

Janet had no idea what to do
after the botched operation.

Until, one night,
she saw a glimmer of hope

when she was watching a talk show.

One of the guests was a radical
psychologist called Dr John Money.

Dr John Money, a psychologist
at John Hopkins,

is one of the leading advocates
of sex-change operations.

Dr Money is in the bear pit
tonight with Alvin Davis.

Dr Money, it's still a pretty
drastic procedure, isn't it?

Well, it's a drastic procedure
by your standards and mine,

but for the people
who are living in desperation,

perhaps the best way
to understand it

is that it seems no more drastic
to them than circumcision.

Hoping that something
could be done for her son,

Janet wrote to Dr Money.

He called back as soon as
he got her letter.

Dr Money needed Bruce's
unique case to prove a theory

he had been working on.

His theory was that gender
wasn't just down to genes -

that it was much more malleable.

He believed that you could take a
child who was genetically one sex

and raise it successfully
as the other -

provided you started in infancy.

His theory was known
as Gender Neutrality.

Faced with an almost impossible
decision,

on Dr Money's advice, Janet had
her two-year-old son castrated.

From then on he was dressed
and raised as a girl, called Brenda.

When Dr Money announced his work
with the Reimers to the world,

he was hailed as a genius.

His theory on the malleability
of gender became hugely influential

amongst doctors and psychologists
around the world.

But there was a problem.

Unbeknownst to
the scientific community,

the experiment had gone wrong.

I didn't like dressing like a girl,

I didn't like behaving like a girl,

I didn't like acting like a girl.

Brenda Reimer was now living
as a man called David.

After the operation, Brenda had been
taught to dress and act like a girl.

But she felt like a boy.

Well, I wore dresses on occasion.

And I never played
with girl's stuff,

I usually got stuck with dolls
or something like that,

for my birthday or Christmas.

They sat in a corner
collecting dust.

I played with my brother's things.

During the early years, I thought
we had made the right choice -

that it would work out. Dr Money
kept saying it would work out.

And I thought, well, he should know.

But when Brenda was 14, her parents,
realising the confusion and misery

caused by her changed identity,
told her and her brother the truth.

You don't wake up one morning
and say, "Oh, I'm a boy today."

You know? You know!

It's in you! You know, it's in
your genetics, it's in your brain.

Nobody has to tell you who you are.

Dr Money's experiment to
raise a boy as a girl had failed,

and the story of the Reimer brothers
ended with tragedy.

Unable to deal with
what had happened to David,

his brother Brian became depressed
and died from a drug overdose.

Traumatised by his brother's death,

and with a catalogue of personal
disasters in his adult life,

in 2004, David shot himself.

It didn't work because that's life.

Because you're human,
and you're not stupid,

and eventually...
you'll end up being who you are.

The tragic story of David Reimer
seems to show that

the roots of our gender identity
lie in genetics and not in nurture.

And indeed evidence that Dr Money's
theory might have been flawed

was already emerging
in the late 1960s,

just as he was announcing
his supposedly successful theory.

That evidence came from the brain
of a rat in Los Angeles.

A team from the University
of California

were comparing male
and female rat brains

in minute detail.

They were hoping to find
a physical difference

that would explain differences
in male and female behaviour.

Slice by slice,
millimetre by millimetre,

they mapped the tiny organs.

And one day, they found something.

Comparing tissue
from the hypothalamus,

right in the centre of the brain,

they noticed a structural
difference between the sexes.

A discrete part of the hypothalamus
was twice as big

in the male rat's brain,
on the left,

as in the female's, on the right.

Here's that part, isolated
from the brain of a male rat.

They called it the sexually
dimorphic nucleus, or SDN.

And here it is in
the female rat's brain.

Here was a clear
anatomical difference

between the brains of
male and female rats.

These differences are created by
sex hormones before the rat is born.

While a male rat is in the womb,

testosterone is already
shaping its brain.

The SDN is also larger
in the human male brain,

compared with the female.

And the SDN is involved
in sexual behaviour.

The discovery of the SDN was
important because it showed

that there were real differences
in the brains of men and women.

And other real-life cases
showed that gender identity

was already permanently
programmed at birth.

Dr Money's experiment
was ultimately flawed, because of

the way that hormones affected
the fledgling brain of the baby.

But while gender identity is
fixed at birth for most people,

for others,
it's much less cut-and-dried.

If called upon,
science sometimes has a solution.

Max Toft, a software engineer, is
physically and genetically a woman.

But she wants to be a man.

I remembered having this
distinct moment where I thought

that God had made a mistake and
that I should have been a boy -

which was interesting, because
I grew up in an atheist household!

To make her body more male,

Max is going to undergo
a course of testosterone.

Dr Ruben Gur,
one of the leading scientists

on how hormones affect the brain,

is going to put Max though a series
of physical and psychological tests

before and after her treatment.

Go.

UPBEAT MUSIC PLAYS

Stop.

Max shows a fairly
typical female, erm,

profile, cognitively.

Erm, and, er, I'd be curious to see
whether there is a change in that.

After six months of
testosterone therapy,

the most obvious changes
are to Max's body -

his voice is deeper,
and he's got more body hair.

But it's the psychological
and practical tests Max underwent

before and after hormone treatment
which have been the most startling.

What we are seeing, really, is, er,

is a female brain turning into
a male brain. It was quite, er,

quite amazing to see it
on a single individual.

This is a scan of Max's brain
when he was a woman.

The red areas show
the parts of the brain he used

when trying to read emotions.

And this is a scan of Max's brain
doing the same task but as a man.

The more red in the scan picture,
the harder the brain is working.

And as you can see, it seems
that he found it much easier

to read emotions when he
was a woman than he does now.

In his case, the second time, he had

more difficulties with the task,
he had to put in more effort

in order to perform that
particular...that particular task.

So, he's... His brain
responds more like a male brain

to the task of trying
to distinguish the emotions.

But how did Max do
in the practical tests?

All the changes are in the direction
that we expected,

in terms of becoming more masculine.

Interesting. Er, so,
remember the finger-tapping?

Uh-huh. You managed to squeeze in
another three taps

per minute. Whoo-hoo!

His spatial awareness
has also dramatically improved.

Last time, you did 75 correct.

This time, you did 118 correct.

Right. That's pretty much
the end of the good news... Right.

..because, er, with becoming a male,

erm, you also lost a little bit.

Max's visual memory
has deteriorated,

and he's not as good with words.

I was actually surprised.
I didn't...

I was thinking maybe one or two...

tests would change, and, er...

Erm, this is after all
a fairly brief period of time.

You would expect changes
on those tests

to take place over a longer period.

Max is still sceptical

about the extent to which
testosterone has changed his brain.

But he acknowledges
it has affected how he feels.

My body is changing, and it has
been surprising to go through that.

It's been kind of exciting, and
there were changes that I wasn't...

that I didn't expect to go through.
There was a period of time

where I had a really hard time
crying,

and it felt biological to me.

There was something biochemical
preventing me from doing it.

Like, it really felt
like a big block,

and that was kind of
a scary moment for me.

For most people, the biggest
impact that science has had on

our sex lives has been in giving us
greater control over reproduction.

Thanks to medical advances
over recent decades,

today, more healthy babies
are born than ever before.

And the invention of
the contraceptive pill

gave women the power
to decide when they have them.

As pills go, THE Pill
is a particularly tiny one,

and yet its effect
on the sex lives of women

has been monumental.

But behind this little piece
of sexual liberation

is the story of
an intrepid scientist

who went to the ends of the earth,
and then disappeared.

In order to make
a contraceptive pill for women,

scientists needed a source
of the sex hormone progesterone.

But in the early part
of the last century,

producing these hormones
in a laboratory

was difficult,
and phenomenally expensive.

But Professor Russell Marker,
of Pennsylvania State University,

had an idea.

He knew that some animal hormones

were very similar
to chemicals in plants,

and he identified
a raw botanic ingredient

that theoretically could be used
to produce progesterone.

Using the roots of a yucca plant

he found in the
south-western United States,

he proved his chemical principle.

However, this plant didn't naturally
produce enough of the raw material

to ever be economically viable.

Then, in November 1941, Marker
found what he was looking for.

In an old botany textbook,
he saw a rare type of wild yam

with an enormous root system that
was said to weigh almost 100 kilos.

But there was a problem -

the yam only grew in an isolated
region of the Mexican jungle.

The intrepid Marker
travelled there alone

and smuggled two huge roots
of this rare plant

back to the United States.

Once home, he successfully
synthesised 2kg of progesterone -

far more than anyone
had ever seen before.

Marker wanted to go into business,

but he was shunned by
the major pharmaceutical companies,

so he founded his own,
called Syntex,

and began to produce
more progesterone.

But in 1949, with
business about to boom,

Marker mysteriously vanished.

His work would lay the foundations

for the production of the modern
contraceptive pill in the 1960s.

But Marker himself was
still nowhere to be found.

It was rumoured that he'd died
in a mental institution in Mexico.

But in 1977, Horizon tracked down
the elusive professor.

He was living just a few miles away
from Penn State University,

where he first made
his remarkable discovery.

In this interview from the time,
it's not difficult to see

why Marker had become
so disillusioned with big business.

At the end of the year,

when I thought the profits
should be distributed...

I knew that there
were very nice profits,

including the profit
that was obtained

from the first 2kg of progesterone
that I had made.

And I had made
25 or 30kg during the year

of progesterone - it was
selling for over $25 a gram

at that time.

I went to the senior partner
in the firm

and asked him about the profits,
and he said there were no profits.

And he eventually told me that, er,

he had taken the profits as salary,

and there was nothing
I could do about it.

So I walked out of Syntex.

The Pill gave women the power
to prevent unwanted pregnancies.

But for couples who want children,

becoming pregnant
can sometimes be difficult.

Many problems can interfere
with conception,

causing anguish for parents.

It was once thought that being able
to control this natural process

would be impossible.

Then, in 1978, a baby was born
using a radical new technique

that has revolutionised
the treatment of infertility.

Researchers removed eggs
from the mother

and combined them with sperm
from the father in a Petri dish.

The embryologists could then check

to see if the embryo's development
was proceeding normally

before re-implanting
only the most healthy embryos

back into the mother,
for nature to take its course.

The technical name for the procedure
is in vitro fertilisation,

or IVF.

The media coined the phrase
"test-tube babies".

At the time, it was
highly controversial.

Since those early days, hundreds
of thousands of healthy babies

have started their lives
in this way,

and the stigma has gone.

It's one of science's
greatest success stories.

But the moral dilemmas thrown up
by test-tube babies didn't vanish.

People began to worry that

the technique gave scientists
the opportunity

to do far more than simply helping
infertile couples have babies.

IVF meant that it one day
might be possible

to tamper with the DNA
of an embryo in the lab

and create a bespoke baby.

30 years ago, Horizon made a drama

where families were no longer
prepared to leave the appearance

and character of their children
to chance.

You've got two girls - are you
certain you don't want a boy?

Yes, quite sure - we really do
want another girl. Yes, definitely.

Right. Well, you've had a chance
to view the data at home?

Yes. We've narrowed it down
to zygote 3 and 6 -

we're not really sure
which one to choose.

What sort of characteristics
were you thinking of?

We definitely don't want to tamper

with the physical side of things
in any way. No, except that

we would like her to have
my father's red hair.

Ah. Ah, well, that's easy.

We can make her homozygous
on the three hair colour genes.

What about her character
and emotions? Ah, well, yes,

there are a few things we'd like
to have modified if possible.

We'd like to reduce shyness,

and susceptibility to depression...

..without necessarily damaging...
any artistic potential.

Also, we'd like her to be musical,
and if possible,

also we want her to be ambitious.

A world where we could pre-order
genetic traits for our children

might seem fanciful,
but in some ways,

it's already here.

IVF has given embryologists
the opportunity to screen embryos

for genetic problems.

These techniques have helped women
like Philippa Handyside,

for whom having children
was impossible.

Just kept miscarrying all the time.

And it just actually got quite normal
- that was actually how awful it was.

It was very hard,
and it sounds really harsh,

but you just kind of get...
It just becomes part of life.

I used to get pregnant, lose it,
pregnant, lose it, and that was it.

Philippa Handyside wasn't trying
to create the perfect child -

she just wanted to have a baby.

But she wasn't having any luck.

So she underwent testing to see why
she was having so many miscarriages.

The cause of her miscarriages
was genetic -

the result of a chromosome disorder.

It meant most of her embryos didn't
have the right combination of genes

they needed to grow healthily.

There was nothing Philippa's
local hospital could do for her -

it seemed she might never
have children.

But then, Philippa
heard about a new technique.

It's a technique some people think
could lead to designer babies.

The technique is called
preimplantation genetic diagnosis,

or PGD.

Using PGD, scientists can
screen embryos outside the womb,

long before they develop
into babies.

Then, they can select just those
embryos that carry healthy genes

to ensure the baby is free
from genetic abnormalities.

PGD is one of those ideas
that's so clever

that it seems impossible to do.
I mean, how could you possibly

take a very early embryo and
take out a cell and diagnose it?

Well, in the end,
it transpired that the embryo

is such a tough little beast

that it actually allows you to do
fairly outrageous things to it,

without noticing.

To do PGD, the doctors first

had to extract eggs
from Philippa's ovaries.

These eggs were then fertilised
by her husband's sperm in a lab.

The fertilised eggs were allowed
to develop into a cluster of cells.

You phone every day and you're
told how they're getting on.

It's like having children
in nursery - you're told every day

how they're progressing through.

Then, 48 hours after fertilisation,

acid was used to etch a hole
in the membrane of each embryo,

and a single cell sucked out.

And on day three
after their collection,

we've taken a single cell
from each embryo,

and we've sent those cells to
our genetics team across the road,

so they can make
the molecular diagnosis.

The theory is that if the analysis

shows the genes are normal
in the single cell,

then the embryo is came from
will also be genetically normal.

That's OK - two blue...

Two green,

two red, so that's fine.

Eventually, they found cells
from two of Philippa's embryos

that had healthy genes.

They called us through and said,

"Yep, we've got a couple."
The geneticist said,

"There's one that...
it's not divided so well,

"but the other one, brilliant,
absolutely brilliant.

"So, we're going to implant,
if you're happy, two back in."

So, it was a case of,
get ready, and get kind of...

into the room, and ready to
have the implantation...done.

PGD allows mothers like Philippa

to have children they would
otherwise have been denied.

But there are those who still worry

that this is the thin end
of the wedge,

and that in the future, people
would be able to select embryos

on the basis of much more
controversial genetic traits.

The forefront of research
into sex and fertility

continues to present us
with much trickier ethical problems

then we've ever had to grapple with
in the past.

But at the same time,
the science of sex

has helped us learn about ourselves,

to combat sexual problems
and to restore fertility.

Sex is still the most intimate
and personal aspect of our lives.

But since science
got into bed with us,

we've had a much better chance
of decoding this tricky subject,

and of understanding ourselves.

We know so much more about sex now
than we did just a few decades ago,

and I think our lives
are better for it.