Original subtitles

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.