All language subtitles for BBC.Horizon.2009.Whats.the.Problem.with.Nudity.WS.PDTV.XviD.MP3.MVGroup.org.Eng

There's one thing you do every
day in the privacy of your home

that you'd never dream of doing
in front of strangers.

Get undressed.

So what's stopping you?

These eight volunteers
are about to find out.

They face an unforgiving
48-hour ordeal as Horizon

exposes their minds and bodies
to the problem of nudity.

It was more extreme than I imagined.

It didn't even occur to me
that they were naked.

My heart rate shot up
to a ridiculous degree.

It's quite relaxing
actually being, you know,

walking round the house naked.

When that penny dropped
and I knew what was happening,

that was just
the most awful experience.

Why humans have a complex
relationship with nudity

challenges scientists
from Finland to Florida,

from Africa to California.

They're finding answers
in unexpected places -

in the chest hair
of Finnish students,

and in the extraordinary
family history of lice,

in the sweat
of an unusual African monkey

and in our instinct
to stare at the human body.

With each discovery
comes new insight

on what it means
to be human and naked.

So would you strip
in front of strangers?

What about on national television?

What IS the problem with nudity?

Just really really horrible,
really horrible.

At this anonymous house
in the heart of London,

Horizon has brought together
eight complete strangers

to take part in a unique study.

From a ballet instructor
to a data analyst,

a policeman to a history student,

they've travelled to London
from all over the UK.

Ahead lies a series of tasks

designed to confront
the volunteers' inhibitions

and challenge the way
they think about the human body.

They'll be guided
by a team of psychologists

led by Dr George Fieldman,

a specialist in the evolution of
social and sexual relationships.

I think it's going to be
a very interesting study.

This is the first time these people
have ever been naked in public.

It'll be interesting to see

how they challenge their own taboos
and society's taboos in this context.

I have no preconceptions.

Quite a few fears.

You know the nudity bit,
and having an erection

or something like that, that's,
that's probably one of my fears.

I suppose there's a fear
that people will laugh,

that there'll be that element
of ridicule or shock.

However they're expecting
to feel about nudity,

there's only one way to know
for sure -

and there will be
no gentle introduction.

In the first task,
half of our subjects

are going to end up completely naked

and they'll stay naked
for the rest of the day.

In a basement room,

a mirror hangs on a dividing wall -
but it's no ordinary mirror.

Behind it is a lone chair.

Whoever sits here
can see straight through the mirror

and secretly watch
what happens in the adjacent room.

First,
we're pairing Foyez with Phil.

In a few moments,
one of them will be naked.

They don't yet know who.

As they take their positions
either side of the mirror,

we check for signs of stress.

Neither of them
has ever stripped in public,

let alone surrounded by TV cameras.

With no idea what's in store,
they wait for instructions.

INTERCOM: OK - please turn over
and read your cards.

"Please stand
in front of the mirror.

"When instructed,
remove all your clothes,

"placing them
in the basket provided.

"Please speak
only in response to questions."

Unknown to Phil,
Foyez sits back to watch.

INTERCOM: Please begin.

INTERCOM: Can you please
rate your discomfort

on a scale from one up to ten?

Two.

Four.

INTERCOM: Do you notice anything
unusual about the mirror?

I know Foyez is behind there,

but I have no problem standing here
otherwise I wouldn't be here.

Under normal circumstances
this would be quite uncomfortable.

I certainly wouldn't sit in a bar

naked next to a,
next to a guy I didn't know.

Our subjects follow in pairs,
each rating their own discomfort.

Kath from Dorset
faces Alex from Manchester.

OK, ten.

Er...seven.

INTERCOM: Kath, do you notice
anything unusual about the mirror?

I'm really hoping
that's not a two-way mirror!

That experience was totally surreal.

I can't imagine anything
that's ever happened before

or is going to happen after
that will ever be like that again.

Lucy from Birmingham
is up against Rosie.

INTERCOM: Rate your discomfort
on a scale from one up to ten.

About five.

Three?

That was strange, that was strange.

I tried to just block them out and
imagine I was in my bedroom at home,

somewhere comfortable.

Finally it's our oldest volunteer,
Helen, watching Ian from Edinburgh.

Wandering up and down the stairs

with somebody you've just met
the night before naked

walking behind you,
and you sort of think "Wow!

"This is really different."

Most of our subjects owned up

to this being
a pretty unpleasant experience,

but their physical responses
were even more revealing.

The physiological data indicate that

everyone was more stressed
naked than clothed.

The women might have been slightly
more anxious in anticipation of

taking off their clothes than the
men. The men seemed more anxious,

to judge by the data,
when they were actually naked.

The interesting thing is that these
people volunteered for this study.

They knew that it involved nudity
and taking off their clothes

but in spite of that they were very
anxious under these circumstances.

I felt like I wanted the floor
to open up.

There was part of me
that didn't want to be there.

I could feel my heart racing.

Why did simply
taking off their clothes

cause our volunteers such distress?

The links between nudity and sex
may provide one answer.

There was just for a moment
where I thought,

"This is very voyeuristic."

Obviously I'd have preferred
a woman to be watching me.

But is sex the whole story?

I think the sexual thing is more
when you've got bits of clothing on,

that's more sexual than just
seeing somebody in the altogether.

For a deeper understanding
of nudity, we must leave London

and ask a more fundamental question
about the human body.

In a world where all other primates
are covered with fur,

why don't we have any?

Many of the biggest questions
about the evolution

of the naked body can be answered
here in East Africa.

To anthropologists, this landscape
is known as the cradle of mankind.

It's widely believed that here,
modern naked humans

evolved around
a quarter of a million years ago,

the last in a long line
of primate ancestors.

Anthropologist Nina Jablonski

has spent twenty years researching
the evolution of human skin.

Her research
has brought her to Kenya

in an attempt to understand
one of our skin's biggest mysteries.

Ever since people really got to grips
with the idea of human evolution,

they've been trying to understand
why we don't have any hair.

Fur is one of the great products
of mammalian evolution.

Waterproof, insulating
and protective,

it's an essential asset
to any mammal.

So the question is,

why did we lose what had taken
millions of years to gain?

From the moment
Charles Darwin proposed

that humans
were descended from apes,

scientists
have puzzled over this question.

And the first of many theories
came from Darwin himself,

150 years ago - that it was all
down to sexual attraction.

Charles Darwin was one of the first
to opine on these matters

and he felt quite strongly
that humans became hairless

as a result of sexual selection,

actual preference
for a hairless condition.

Well, really Darwin was positing that
certain individuals, notably females,

would choose certain males
because of their hairless condition,

and they would preferentially mate
with them and so those individuals

who had less hair would be
more reproductively successful,

so that's how he tied it in with
his own theory of natural selection.

Simple though it sounds, Darwin's
theory is still controversial.

But at Finland's Turku University,

Dr Markus Rantala
aims to change that.

HEAVILY ACCENTED:
Charles Darwin...

VOICEOVER: Charles Darwin was
fascinated with sexual selection

and he always thought
that all differences between races

and also different animals
were mostly connected

with sexual selection, but there's
no experimental evidence for that.

Dr Rantala is launching
an international research project

to find out
if Darwin's theory stands up.

Do women really find hairy men
less attractive?

These prime male specimens

are making a great sacrifice
to help Dr Rantala's research.

He's creating an unusual
set of photographs.

First, of the men
in their natural state.

But then the men have each agreed
to have their bodies shaved

so that Dr Rantala can produce a
second set of hairless photographs.

Dr Rantala plans to use these images
to find out if people

really do have an underlying
aversion to body hair.

And in London, our subjects are to
provide some of the very first data.

OK, so we're going to be showing you
some images of male torsos

and we'd just like you
to rate the attractiveness

of the torsos
on the sheet in front of you.

Of course, physique
is going to affect their judgement.

But that's not important here.

Dr Rantala wants to see
how each natural photo

fares against
its shaved counterpart.

So how did our subjects vote?

They rated pictures one,

47 and 53 the most attractive.

All similar physiques,
but not entirely hairless.

However, 60% of the torsos

were rated more attractive
in the shaved photograph,

a marked preference
for smoother skin.

In your ratings of attractiveness,

could you state something
about the influence of body hair

in that assessment? Definitely
for me it plays a big part.

I don't find body hair attractive.
Don't? No.

Less body hair's not so bad
but more body hair it's... No.

There was a twist
to this test though.

Amongst the photos were four torsos
they might recognise.

Alex,

Phil,

Foyez,

and Ian,

were all in the slide show
with their chest hair intact.

And they didn't fare too well.

All placed in the bottom
half of the ranking -

Alex at number 32,

Phil at 41,

Ian at 47,

and our hairiest subject,
Foyez the policeman, ranked at 56,

the least attractive of all.

The fact I was rated last
doesn't really bother me that much,

you know, because I'm quite confident
as I am and...

when I look at myself in the mirror
I think I'm pretty good,

so yeah, if other people's opinion is
that, then yeah, more power to them.

I felt, I felt very sorry
for Foyez because...

I, because my views
are very strong on body hair,

and I, I felt a bit guilty
after I'd said what I said

because he had identified himself
as having quite a lot of body hair.

I am currently trying to improve
the way I look,

but as for keeping the hair there,

the chest hair,
no, that's mine to keep.

I like it. I ain't gone round
boasting about it...

Anyway, to lose that,
I'd feel somewhat emasculated.

This first test

seems to confirm that humans do
find hairless bodies more attractive

and that supports Darwin's theory,

that over many generations where the
least hairy men got all the girls,

the genes for hairiness
all but died out.

But Darwin's theory isn't enough.

By the rules of evolution, it simply
doesn't make sense on its own.

Well really, for much of our history
as primates

and in the early history
of our own lineage,

having hair
was probably extremely important

and the lack of hair would have
been considered a sign of illness

or, or certainly undesirability.

Our ancestors would have been
attracted to healthy mates

by their thick glossy fur.

They wouldn't look twice
at one with balding fur.

That's how evolution
weeds out weakness and disease.

So before naked skin
could become attractive to humans,

it must have become beneficial
to lack hair.

Only then could a balding ape

be considered a good prospect
as a mate.

One then has to think about,

well what is the good reason
rooted in natural selection

that can lead us to understand
the evolution of hairlessness?

What was it that gave humans
greater reproductive success

as a result of being hairless?

Professor Jablonski believes the
answer lies millions of years ago,

with our earliest
and furriest ancestors.

While homo sapiens,
the hairless modern human,

evolved
a quarter of a million years ago,

the human family tree
stretches much further back,

to around six million years ago,

when a distant ancestor
split from the chimpanzee line.

It was almost certainly
covered in fur.

What could have happened since then
to prompt the loss of our fur

while so many other animals
kept theirs?

All of these animals
that we see around us

have a lot of hair
for a very good reason.

It may seem stupid that a fur coat

is actually a good thing to have
in this hot, open, sunny environment,

but in fact it is a good thing.

Still naked, Ian from Edinburgh

is about to find out why
fur is so useful in the heat.

He's joined by Alex in a challenge

that's not going to be comfortable.

They're standing in the intense heat
of industrial radiators

while a thermal camera reveals
how their bodies are affected.

On the right, Ian's skin is hot,
turning from yellow to red,

while those white patches on Alex's
clothes show they're even hotter.

But Alex's loose clothes
are actually protecting

his body from the heat.
Underneath, his skin stays cool.

This is exactly how fur

protects most animals
from the heat of the sun.

But one theory suggests
our ancestors found a better way,

that by combining
three remarkable attributes,

their fur became redundant.

First, they stood upright.

Next, they were very active,

ranging great distances
on the open savannah.

And third, just as Alex and Ian
are now, they began to do something

no other animal can match...

to sweat profusely.

It's this unique solution to keeping
cool that drove the loss of our fur,

according to
Professor Peter Wheeler.

Humans rely on whole body cooling,
and their combination of a naked skin

and highly developed sweat glands
enables them to lose heat at a rate

not approached by any other mammal.

Humans are the sweatiest creatures
in history.

Our skin contains
the most sweat glands,

and at nearly a litre an hour,

produces the greatest volume
of sweat of any animal.

The surface of our entire body
is an active cooling system.

This means that the human
can lose heat

at a rate in excess of one kilowatt.

Now that's the amount of heat
put out by a one bar electric fire.

Alex and Ian are both dripping,

but Alex's shirt soaks up the sweat,

just like fur would,
and he feels little benefit.

If you possess body hair,
you still can lose heat by sweating,

but it's less effective because
the airflow over the skin surface

is greatly reduced, reducing the rate
at which water is going to evaporate.

Peter Wheeler believes
sweating into a fur coat

was no use to our ancestors.

By losing their body hair, what
they're able to do is evaporate water

both more efficiently and effectively
from the skin surface.

While the sweat
soaks into Alex's shirt,

it can evaporate freely
from Ian's naked skin,

and with it, goes all the excess
heat generated by his active body.

The more he sweats,
the more he cools.

The theory that sweating
drove our loss of fur is persuasive,

but it's impossible to prove.

That's why Professor Jablonski
is in Kenya.

She believes that
out on the African savannah,

there's living evidence

that supports the controversial
sweat theory.

She's on the trail
of a very unusual primate

which appears to be following
our own evolutionary footsteps,

the Patas monkey.

Patas are really of interest to me
because they live in open

environments very much like those
in which we imagine early members

of our own genus, the genus homo,
to have lived,

and they really provide
something of a model for how

we think humans may have moved during
early parts of their evolution.

Patas and humans share
many fascinating characteristics,

because they have
similar body proportions

in that Patas have relatively
long limbs compared to other monkeys.

They're very good
at walking long distances.

They range very, very widely,

they have a larger home range
than any other primate.

But Patas monkeys share
another of the attributes

that made our ancestors'
fur redundant.

As well as being very active,

they've followed our solution
to keeping cool.

Most primates don't sweat very much,
but Patas monkeys sweat copiously,

and that's what gets anthropologists
really excited about studying them.

It's this ability to sweat
that suggests to Professor Jablonski

that right before our eyes,

the Patas monkey is echoing
our own early evolution.

It was survival of the best sweaters

that really was part
of our evolutionary process.

We're talking about
early members of the human lineage

that had a little bit less hair, that
had more productive sweat glands,

and those individuals would have had
an incremental reproductive advantage

over others, and that made
the difference in human evolution,

driving the loss of body hair
and an increase in the number

'and activity of sweat glands.'

Oh, I've got a great view!

But if Patas monkeys are following
our evolutionary steps,

why do they still have fur?

Even though they do have hair,

their hair is very different
from that of other monkeys.

It's not as dense, it's quite
coarse, and so when they sweat,

they can also lose heat through
evaporation just like humans can.

They may have thinner fur,

but Professor Jablonski believes
Patas will never go naked,

because they lack one crucial
feature that made all the difference

to our ancestors - walking upright.

On all fours,
Patas are exposed to too much sun.

Despite their ability to sweat,

they can't afford to lose
their protective fur.

If humans had been quadrupedal,

walking on all four legs, we probably
wouldn't have lost our fur,

but humans became bipedal,

and when they did come out
in this open sunny environment,

there was every reason for them
to lose their fur,

and they lost it on their front
and on their backs,

but they did retain a little bit of
it in a very strategic position,

right on the tops of their heads.

This final evidence
convinces Professor Jablonski

that uniquely equipped
against the heat of the sun,

our naked ancestors
had a huge advantage

over their hairy relatives.

And that made them
the first primate

able to exploit the harsh
environment of the open savannah.

But to the scientists
behind the sweating theory,

going naked had an even bigger
pay-off for mankind,

and particularly for our brains.

The human brain produces
something like 20 watts of heat.

That doesn't sound very much but
if you put a 20-watt light bulb

in a small box the size of the skull,
it's soon going to overheat.

One or two degrees and it starts
to impair brain functioning.

Three or four degrees,
and it's usually fatal.

This risk of overheating

drastically limits the size of
most animals' brains, but not ours.

It's probably no coincidence today
that the mammal

that's got the largest brain relative
to its body size, that is humans,

also possess the most
powerful cooling system

of any mammal to protect it.

It was this superior cooling system

that would change
the course of evolution.

Without losing hair,
without our sweatiness,

we wouldn't have been able
to evolve the big brains

that characterise us today,

and that really make us
the modern human species that we are.

Essentially, being hairless was the
key to so much of human evolution.

The next question is, when did we
reach this pinnacle of evolution?

Were modern humans
the first naked ape,

or our older cousins,
the Neanderthals?

It could have been an earlier
ancestor from the genus homo

that lived between
one and two million years ago.

Was it Australopithecus, living
two million years before that?

Or even Ardipithecus,

the species that branched
from the chimpanzee line

six million years ago?

It's a question
that's never been answered,

because, although fossils tell us
so much about our ancestors' bodies,

the length of their limbs,
the size of their brains,

one thing that is never preserved
is their skin.

But there is a surprising
new source of evidence.

It's not from humans or from apes,
but from a quite different creature

that's been our constant companion
throughout evolution.

Florida University geneticist
Dr David Reed has found that

the chequered family history
of human lice is very revealing.

When you think of human hair,
that's the habitat of these lice,

and it offers us the opportunity
to study these lice

and how they've evolved
with their hosts.

If you look at the genetics
of these lice,

written in their genetic code
is our own evolutionary history.

Watershed events like losing
the complete body hair on a host

would have a huge impact on
where parasites can go on the body,

and whether parasites persist or not.

Dr Reed has been doing some
unusual genetic detective work.

So we collect these parasites
from humans,

and then we bring them back
to the lab.

Then we extract the DNA
from these lice,

and we magnify that DNA
through DNA sequencing.

We can use those DNA sequences
to build

evolutionary trees that describe
the relationships of these lice.

The family tree that Dr Reed
has built for lice

provides a mirror
for the tree of human evolution.

And we see that if you date when
chimpanzee and human lice diverged,

it matches up perfectly

with when humans and chimps
last shared a common ancestor.

What most interests Dr Reed
is the extraordinary relationship

between humans and lice.

Generally each primate species
only has a single louse species.

Humans are somewhat unique
in that we have three types of lice.

The louse that most people
would be familiar with

that occurs on humans
is of course the head louse.

We think that this is
the ancestral type of louse

that we've had all along
throughout our evolutionary history.

With us for six million years,
the head louse originally lived

all over the bodies of our
earliest hominid ancestors.

But if that hominid
loses all of its body hair,

and retains perhaps only head hair
that's suitable habitat,

now you have one refuge
on the entire body.

So how does Dr Reed explain
our next species of louse,

the pubic or crab louse?

The crab louse is somewhat different
from the human head louse

in terms of its size and shape,

and it's well adapted
to holding onto hairs

that are much larger in diameter
and much farther apart in spacing.

Its closest living relative
is actually found on gorillas.

To Dr Reed, understanding how this
new species colonised our bodies

is critical to understanding
the evolution of human hair.

How would we have acquired
a gorilla louse?

What must have happened in terms of
changes in our body to allow that?

What's interesting to me is that

that move could not have happened

until the habitat
was there and available.

First, we must have
lost our body hair,

and second,
we must have acquired pubic hair.

Even with the earlier species
confined to our heads,

the new lice couldn't move in
till we'd evolved a patch

of suitably coarse
gorilla-like hair...

though exactly
how they made the move

is open to question.

For lice to move among individuals,

there usually has to be
direct physical contact.

If we're talking about a louse
moving from gorillas

to the pubic region of humans, of
course, the imagination can run wild.

Whatever the route,

the new arrivals separated from
their gorilla ancestors

to create a new species,
the human pubic louse.

Dr Reed realised that this branching
of the louse family tree

provides the best evidence yet for
when humans lost their body hair.

The genetic data that we studied
from these lice tell us that the move

from gorillas to humans occurred
roughly three million years ago.

Therefore we might assume that the
body hair changes in humans happened

roughly three million years ago.

It's an astonishing conclusion,

placing the original loss
of body hair

long before the evolution
of modern humans.

Certainly this very old timeframe
of three million years

for the loss of body hair
flies against the general convention

that only modern humans much more
recently lost their body hair.

To think about archaic hominids
having no body hair

for millions of years is quite
interesting, and quite controversial.

By Dr Reed's calculation,

nudity goes right back
to Australopithecus.

From that early ancestor,

every branch of the human family
tree inherited naked skin,

right up to Neanderthals,

and modern humans.

The answer to one final mystery
of human evolution

lies in the genetic
evidence of lice,

one that's essential
to our concept of nudity.

The clothing louse is a direct
descendant of the head louse

and, like the crab louse,

it could only evolve
once its habitat existed.

What's remarkable about this one is,
of all the lice,

it's the only one that lays its eggs

or lives in anything other than
fur or feathers.

It lives entirely in the clothing.

By dating this branch
in louse evolution,

Dr Reed could reveal something
that fossils never could.

When humans first got dressed.

We can look at the molecular data
for human head lice

and clothing lice, and deduce when
those populations began diverging,

and when we do that, we see that they
diverged about 650,000 years ago.

Dr Reed has re-written
the history books on human nudity.

By his calculation, ancestral
humans lived completely naked

for at least two million years.

Only then did they begin
to cover up their nudity,

just over half a million years ago.

From the moment
we covered up our bodies,

clothes began to shape
our culture and our identity.

If you're clothed, then you don't
have to posture yourself as much,

because the clothes you wear
will do a lot of the...

the messages that needs
to be said about you.

When you've got clothes on you can
create an image for yourself.

Nudity to me is like
a blank piece of canvas,

and when you put clothes on,
you're kind of painting yourself.

But clothes also created a whole set
of uniquely human problems.

For a start they concealed
all the bits of the body

that were most important

for the essential business
of sexual attraction.

At the University of California
in Los Angeles,

Dr Kerri Johnson is investigating
the secrets of human attraction.

She wants to find out how we
still manage to attract each other

despite wearing clothes.

My research examines how people

make very fundamental social
judgments about one another.

When you see them across the room,
you know virtually instantly

whether it's a man or a woman,

how masculine or feminine
the target is,

and consequently whether
he or she is sexually attractive.

We use eye tracking methods
that covertly measure the direction

of gaze of our participants,

allowing us to pinpoint precisely
where our participants are looking.

In her experiments,
Dr Johnson asks people

how attractive they find a series
of computer-animated silhouettes.

They are neither nude
nor are they clothed,

and this is really an important
factor in our experiment.

If the target is naked,
they're likely to look at

the areas that are
the most informative -

the genitals, the breasts,
presence or absence of those things.

So that's the judgment
that you'll be making.

Is the image depicting
a man or a woman?

The aim is to find out how we
tune into each other's sexuality

when none of the obvious
signals is visible.

Man.

My research has found that
the body's shape and body's motion

are very important for
judgments of attractiveness.

A woman's body
is much more hourglass in shape,

and a man's body
is much more tubular in shape.

It reliably differs
between men and women,

and this is referred to
as the waist-to-hip ratio.

A typical female walk
would include a lateral hip sway.

This is the hips moving
back and forth,

and actually a bit up and down
as women walk.

If you think about
the way a man moves his body,

we refer to that as
shoulder swagger.

So when people are deciding whether
a target is a man or a woman,

they look intently
at a region of the body

that varies between men
and women, the waist and hips.

The result is clear. With clothes
covering up our naked bodies,

humans have perfected a new, more
subtle code of sexual attraction.

Woman.

So we're talking about
how the body is shaped,

the physical proportions
of the body,

and how the body moves,

and both of those
are available to observers

regardless of whether
they're wearing clothing or not.

We're going to find out
how well our subjects

can tune into these
subtle sexual signals.

Foyez and Helen are being
fitted with eye-tracking glasses.

We're going to watch
where their eyes wander

as they scan the bodies
of their fellow subjects,

clothed and naked.

First up is 25-year-old Rosie.

Helen's eyes are all over the place,

picking up details
of Rosie's clothing,

but she's definitely lingering
on her waist and hips,

exactly as predicted.

But Foyez seems to have
locked his gaze on Rosie's head

and he's keeping his eyes
unnaturally still.

How will they deal with
a naked body?

Step forward Phil,
our 39-year-old data analyst.

Helen's not fazed.

She's scanning
his entire body again,

picking up the shape
of Phil's waist and hips,

but not focusing on the obvious
sexual features.

And Foyez...

..it seems nothing
is going to shift his gaze...

and he's sticking to that strategy.

Something is stopping Foyez
from following his instinct to look.

Helen seems at ease whether
her targets are naked or not.

She's quite naturally drawn
to the most sexually revealing parts

of the body - the waist and hips.

My intuition is that the eye
movements demonstrated by Helen

were probably completely
natural and spontaneous.

I suspect that Foyez
may have been maybe embarrassed,

or for whatever reason,
wishing to control his movements,

so that he looked very much
at the person's face

rather than anywhere else.

Maybe, of course,
it would be interesting to know

if he'd be looking in that way

if he hadn't known that his eyes
were being monitored.

I didn't want to be labelled
as a voyeur or a pervert.

I mean I was well aware
that this footage

would be sort of reviewed
afterwards.

I just treated it more like
a video game.

A lot of self-control was involved
even while all of this was going on,

so I was quite impressed
with myself.

I think Foyez was very much
controlling his natural response.

I just can't believe a male
confronted with a nude female

is going to look, you know,
at their, at their heads.

It was nice of him to show
that degree of control.

Probably made me feel a bit better

because I actually found it
more uncomfortable

watching myself on the screen.

Despite Foyez's self-control,

it's clear the signals of sexual
identity carried in human shape

and movement are much more subtle
than the ones most primates use.

Without the barrier of clothing,
primates use striking visual signals

advertising exactly
when they're ready for sex.

Females show that they're fertile
by displaying a swollen red behind,

leaving no doubt in the minds
of any amorous males.

Under our clothes, signals like
these would be useless to humans,

so it's no surprise that
women don't have such a display.

But does that mean that humans
have to rely on guesswork

to pick the right moment to mate?

In another Los Angeles laboratory,

that's exactly what Dr Martie
Haselton is trying to find out.

I think that for men
detecting cues of fertility,

whether they be cycling fertility,

fertility over the course
of the month,

or fertility associated
with changes in age,

I think that those play a very
dramatic role in mate preferences

and therefore in sexual selection.

Dr Haselton collects photographs
of women

at various stages
of their menstrual cycle,

including ones taken
just before ovulation

when they are most fertile.

Then she asks men to choose
which is most attractive.

We found that judges chose
the high fertility photograph

as the one in which
she was dressed up more.

About 60 per cent of the time
that was well beyond chance.

That led us to wonder, "Well...

"are there detectable cues
of ovulation

"that male partners
are able to pick up on?"

This was quite a revelation.

For decades scientists had believed
that people simply couldn't detect

human fertility levels.

We know now that other things
are happening far off the radar

of conscious perception.

There are cues of cycling fertility,
cues of ovulation

that are detectable
even by complete strangers.

It seems that humans have developed
some kind of sixth sense,

giving us incredible sensitivity
to these secret signals.

There was a recent study done
that looked at the amount of tips

that lap dancers earned
on varying days of the cycle

and on high fertility days,
men tipped them more generously.

No-one has yet worked out exactly
what these fertility signals are,

but Dr Haselton has identified
one likely candidate.

Women's body odours change.

They become more attractive on high
as compared with low fertility days

of the cycle.

And this discovery
promises to solve another mystery

about the naked human body.

What pubic hair is for.

One explanation is that body hair is
a conduit for scent, communication.

In the moist warmth
of our pubic hair,

bacteria feed on hormones
in our sweat

and produce distinctive aromas.

So for example underarm and pubic
hair could be a way of transmitting

body odours out into the environment
to enhance attraction amongst lovers.

Humans don't need
flashy fertility displays.

Beneath our clothes, pubic hair
has become our secret weapon

of sexual attraction.

After a day and a half naked,

four of our subjects finally
get the news they're waiting for.

I'd like each of you to...
get dressed again, please.

But as these four are reunited
with their clothes,

the tables are about to be turned
on the remaining subjects

who are left guessing
what lies ahead.

Maybe there'll be wrestling. Oh, no!
Can't bear to think about that, no.

Or maybe we'll do body artwork,
you know they'll cover us in paint

and we'll just run into a canvas
or something.

It's a scientific experiment
in hairlessness.

Not painting us.

In fact we're going to ask them
to do something more intimate

than any of them feared.

Undressing is a very common
thing we all do every day,

but undressing in front of someone,

only usually done under very special
circumstances

when a couple feel very safe
with each other.

Here we've got something
very different,

people are undressing
or rather being undressed,

by someone they've only recently met
in a room full of people.

Those of you standing on the floor,

we'd now like you to undress the
person on the podium in front of you.

The subjects are paired,

so that they're not all undressed
by someone of the opposite sex...

and they're clearly
not finding this easy.

I felt quite relieved
to be back in my clothes again.

I think that the whole thought of
people taking their clothes off,

there's a sexual connotation to it.

There's that kind of, you only do it
when certain things are gonna happen

and there's an uncomfortableness
about that, I guess.

Unsurprisingly they found this one
pretty stressful.

The tables were being turned. The
people who had been naked previously

are now undressing the others.

It's also a reminder that...nudity
is associated with sexuality

and being undressed is very much
close to a sexual encounter.

Our subjects have reached
a crucial point

in their exploration of nudity.

However hard they try, they can't
escape the intense emotions

provoked by the simple act
of undressing.

But does this sensitivity
to nudity serve any purpose?

Scientists have long searched
for an answer

and evolutionary psychologist,
Professor Dan Fessler,

thinks he's found one.

Two emotions play an important role
in sexual modesty.

At the less extreme end
of the spectrum,

minor inappropriate exposure of
the body results in embarrassment.

At the more extreme end
of the spectrum,

grossly inappropriate exposure
of the body

and exposure of one's sexuality
results in shame.

Professor Fessler believes that,
first of all,

the expression of shame
is a simple self-defence mechanism.

All around the world
individuals feel great shame

when they know that others know

that they have failed to be
adequately modest.

Essentially they're signalling to
those around them,

"I understand what the social norm
is and I understand that you know

"that I have failed in this regard,
so please don't hurt me."

But it's the fact that all humans
are sensitive to sexual modesty,

even in largely naked cultures,
that convinces Professor Fessler

there's a real biological reason
for it.

He believes it's a direct result
of our large brains.

Our very large brains
in themselves create a problem.

We have a tight fit between
the size of an infant skull

and the size
of a mother's birth canal.

One solution to this is to
take the bun out of the oven

before it's fully baked,

so our infants are born premature
compared to those of many primates.

With their brains
only partly developed at birth,

human babies are helpless
for many years

and this has a major consequence
for human sexual relationships.

What this means is that
essentially human children require

a great deal of care.

Because of this,
the human mating strategy,

if we look at humans around
the world, is one in which often -

not always - but often,

men mate monogamously. At any one
time they have a single partner,

and they raise offspring together.

Pairing for life ensures our babies
get all the care

they need to survive
and pass on our genes.

But it's a high-risk strategy.

Humans are considerably more
social than the average primate.

We live in large populations

and we co-operate with
large numbers of individuals.

This poses a challenge
because those groups, of course,

provide a source of temptation.

Potentially both sexes
can benefit...

by cheating on their partners.

The human body is a supreme
sexual advertisement.

Flaunting it
can send out a dangerous message.

Nudity is a threat
to the basic social contract

because it is an invitation
to defection.

They have exposed their person,
their body and their sexual selves

in a way that presents
an opportunity

for sexual behaviour outside
of the principal union.

Professor Fessler believes the shame
of nudity serves a real purpose.

It encourages us to stay
faithful to our partners

and share the responsibility
of bringing up our children.

It was an interesting experience.

I'd say, up until now the only people
I've really undressed,

probably are ex-partners and my wife
when they've been a little inebriated

and I had to sort of put them to bed.

I thought I would feel like I would
be...the vengeful thing, "Ha-ha!

"I'm in control now,"
but as I said when it came to it,

I...I just wanted to make sure
she was OK.

I felt almost quite empowered
going through that exercise,

sort of being in control
of the whole situation.

And I can, I can sympathise
with the fact that the other guys

might have been feeling quite
uncomfortable

and possibly quite vulnerable
with us going through that motion.

After two days
looking at each other naked,

we're pushing the subjects
way beyond the normal limits

of social acceptance.

In the final test, they will touch.

They're painting the body
into comfort zones.

Green is fine to touch.

Yellow is not
and red is a no-go zone.

But despite the potential
for embarrassment,

our subjects seem to be enjoying
themselves.

If they'd done the body painting
exercise right at the beginning,

it might not have been
all the fun and games

that it seemed to turn out to be
at the end.

It might have been a pretty stressful
and aversive exercise.

I think as the weekend's gone on and
they've gone through these exercises,

they've somewhat
habituated to the stress.

They're more relaxed
and they know each other,

so it's become a more comfortable
and congenial setting overall.

Lucy, a 42-year-old mother,
clearly still has some reservations.

But Brummie Phil, 27-year-old Alex
and especially Kath from Dorset

have become surprisingly
matter-of-fact about nudity.

Their attitudes and inhibitions
have changed,

and this is the crucial thing
about our relationship with nudity.

We're not born with sexual modesty,

so we're free to shift the
boundaries of what's acceptable...

and what is not.

So long as everyone agrees,
we can create new rules

and avoid the risk of offence
just like at a nudist camp.

Within this house, our subjects
have created their own set of rules.

After two days of social nudity,
it's mostly OK.

It's mostly green.

I feel really quite happy, you know,

and...I feel somewhat
more confident now,

also, that I didn't make a woman

feel sort of uncomfortable round me,
you know.

I think if I'd been asked to do
the task any other day,

there'd have been a lot more,
sort of like, red,

red and sort of yellow painting.

I was quite impressed
at his complete cool...

approach to it and the fact
that he was just, you know,

quite nonchalant about the fact that
he didn't mind touching me anywhere,

so that was quite a surprise to me.

I think once you've been painted by

or you've been painting
someone else's body,

that's a pretty big bonding
experience.

At the end of their naked weekend,

our volunteers are finally
comfortable to be nude together.

For scientists, the extreme emotions
that nudity can cause

will always be a paradox.

The irony of human nudity
and hairlessness

is that really it's the apex
of human evolution.

Only humans have moral emotions
such as shame

that enforce cultural standards.

One can think of nudity
and sexual modesty as exemplifying

our uniquely human
emotional morality.

The state of nudity
is the state of being human.

Essentially having a naked skin
and understanding the evolution

of that naked skin is understanding
everything about being human.

For our volunteers,
there's a last chance to reflect

on their naked experience.

Hmm...I'm relieved
that it's all over, firstly.

I was more relieved when he said,
"Put your clothes back on."

The whole sort of terror
of the first experiment

and as that developed and I realised
I was taking my clothes off

in front of what I thought
was just a normal mirror

and the awful realisation that
it was actually a two-way mirror

and there was someone
sat the other side of it,

that was just really terrifying.

This is the first time
we've done something normal

and we're all naked!

To be honest the whole painting
thing, I wouldn't have imagined

something that extreme and the fact
that somebody else had to undress me.

So, yeah, in a way I sort of
exceeded my expectations

because it was more...

bizarre than I imagined it would be,
definitely.

It's just how...how comfortable we
became around each other gradually,

you know, in that, I mean when
we were all nude and everything,

it didn't even occur to me
that they were naked at all.

One thing I think I'll take away
from this weekend

is how actually easy it was to bond
with complete strangers

in what should really be
an artificial environment

and one that should,
by all society's standards,

we should've been uncomfortable with.

Our volunteers ended the weekend
naked together,

but how many will accept
the final challenge -

to leave the privacy of the house?

Six out of eight
step out into the street.

For Lucy and Helen,
even after a weekend of nudity,

this is a step too far.

Subtitles by Red Bee Media Ltd

E-mail subtitling@bbc.co.uk

Comic Relief
takes these 10 celebrities