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

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

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Get undressed.

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So what's stopping you?

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These eight volunteers
are about to find out.

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They face an unforgiving
48-hour ordeal as Horizon

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exposes their minds and bodies
to the problem of nudity.

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It was more extreme than I imagined.

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

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My heart rate shot up
to a ridiculous degree.

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It's quite relaxing
actually being, you know,

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walking round the house naked.

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When that penny dropped
and I knew what was happening,

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that was just
the most awful experience.

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Why humans have a complex
relationship with nudity

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challenges scientists
from Finland to Florida,

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from Africa to California.

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They're finding answers
in unexpected places -

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in the chest hair
of Finnish students,

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and in the extraordinary
family history of lice,

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in the sweat
of an unusual African monkey

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and in our instinct
to stare at the human body.

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With each discovery
comes new insight

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on what it means
to be human and naked.

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So would you strip
in front of strangers?

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What about on national television?

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What IS the problem with nudity?

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Just really really horrible,
really horrible.

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At this anonymous house
in the heart of London,

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Horizon has brought together
eight complete strangers

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to take part in a unique study.

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From a ballet instructor
to a data analyst,

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a policeman to a history student,

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

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Ahead lies a series of tasks

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designed to confront
the volunteers' inhibitions

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and challenge the way
they think about the human body.

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They'll be guided
by a team of psychologists

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led by Dr George Fieldman,

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a specialist in the evolution of
social and sexual relationships.

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

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

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It'll be interesting to see

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

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I have no preconceptions.

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Quite a few fears.

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You know the nudity bit,
and having an erection

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

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

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

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However they're expecting
to feel about nudity,

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there's only one way to know
for sure -

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and there will be
no gentle introduction.

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In the first task,
half of our subjects

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are going to end up completely naked

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

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In a basement room,

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

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Behind it is a lone chair.

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Whoever sits here
can see straight through the mirror

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and secretly watch
what happens in the adjacent room.

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First,
we're pairing Foyez with Phil.

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

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They don't yet know who.

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As they take their positions
either side of the mirror,

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we check for signs of stress.

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Neither of them
has ever stripped in public,

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let alone surrounded by TV cameras.

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

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

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"Please stand
in front of the mirror.

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"When instructed,
remove all your clothes,

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"placing them
in the basket provided.

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"Please speak
only in response to questions."

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Unknown to Phil,
Foyez sits back to watch.

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INTERCOM: Please begin.

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INTERCOM: Can you please
rate your discomfort

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on a scale from one up to ten?

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Two.

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Four.

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INTERCOM: Do you notice anything
unusual about the mirror?

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I know Foyez is behind there,

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

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Under normal circumstances
this would be quite uncomfortable.

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I certainly wouldn't sit in a bar

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

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

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Kath from Dorset
faces Alex from Manchester.

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OK, ten.

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Er...seven.

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

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

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That experience was totally surreal.

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

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

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Lucy from Birmingham
is up against Rosie.

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

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About five.

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Three?

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That was strange, that was strange.

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

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somewhere comfortable.

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

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Wandering up and down the stairs

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with somebody you've just met
the night before naked

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

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"This is really different."

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Most of our subjects owned up

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to this being
a pretty unpleasant experience,

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but their physical responses
were even more revealing.

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The physiological data indicate that

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everyone was more stressed
naked than clothed.

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The women might have been slightly
more anxious in anticipation of

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

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

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

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They knew that it involved nudity
and taking off their clothes

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

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I felt like I wanted the floor
to open up.

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

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I could feel my heart racing.

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Why did simply
taking off their clothes

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cause our volunteers such distress?

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The links between nudity and sex
may provide one answer.

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There was just for a moment
where I thought,

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"This is very voyeuristic."

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

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But is sex the whole story?

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

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

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For a deeper understanding
of nudity, we must leave London

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and ask a more fundamental question
about the human body.

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

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why don't we have any?

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Many of the biggest questions
about the evolution

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

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

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It's widely believed that here,
modern naked humans

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evolved around
a quarter of a million years ago,

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the last in a long line
of primate ancestors.

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Anthropologist Nina Jablonski

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has spent twenty years researching
the evolution of human skin.

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Her research
has brought her to Kenya

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

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

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

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Fur is one of the great products
of mammalian evolution.

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Waterproof, insulating
and protective,

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it's an essential asset
to any mammal.

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So the question is,

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

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From the moment
Charles Darwin proposed

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that humans
were descended from apes,

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scientists
have puzzled over this question.

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And the first of many theories
came from Darwin himself,

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

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

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and he felt quite strongly
that humans became hairless

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as a result of sexual selection,

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actual preference
for a hairless condition.

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

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would choose certain males
because of their hairless condition,

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and they would preferentially mate
with them and so those individuals

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who had less hair would be
more reproductively successful,

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

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

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But at Finland's Turku University,

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Dr Markus Rantala
aims to change that.

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HEAVILY ACCENTED:
Charles Darwin...

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VOICEOVER: Charles Darwin was
fascinated with sexual selection

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and he always thought
that all differences between races

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and also different animals
were mostly connected

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

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Dr Rantala is launching
an international research project

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to find out
if Darwin's theory stands up.

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Do women really find hairy men
less attractive?

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These prime male specimens

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

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He's creating an unusual
set of photographs.

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First, of the men
in their natural state.

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

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

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

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really do have an underlying
aversion to body hair.

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

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

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and we'd just like you
to rate the attractiveness

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of the torsos
on the sheet in front of you.

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Of course, physique
is going to affect their judgement.

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But that's not important here.

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Dr Rantala wants to see
how each natural photo

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fares against
its shaved counterpart.

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So how did our subjects vote?

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They rated pictures one,

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47 and 53 the most attractive.

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All similar physiques,
but not entirely hairless.

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However, 60% of the torsos

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were rated more attractive
in the shaved photograph,

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a marked preference
for smoother skin.

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00:14:38,920 --> 00:14:41,640
In your ratings of attractiveness,

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00:14:41,640 --> 00:14:45,320
could you state something
about the influence of body hair

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00:14:45,320 --> 00:14:48,920
in that assessment? Definitely
for me it plays a big part.

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00:14:48,920 --> 00:14:52,480
I don't find body hair attractive.
Don't? No.

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

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There was a twist
to this test though.

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Amongst the photos were four torsos
they might recognise.

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00:15:04,120 --> 00:15:06,760
Alex,

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Phil,

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00:15:10,360 --> 00:15:14,640
Foyez,

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and Ian,

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

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And they didn't fare too well.

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All placed in the bottom
half of the ranking -

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Alex at number 32,

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00:15:29,040 --> 00:15:31,520
Phil at 41,

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00:15:33,240 --> 00:15:37,000
Ian at 47,

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00:15:37,000 --> 00:15:42,160
and our hairiest subject,
Foyez the policeman, ranked at 56,

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the least attractive of all.

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

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

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

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

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

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

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

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

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00:16:13,880 --> 00:16:17,320
I am currently trying to improve
the way I look,

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but as for keeping the hair there,

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

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

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00:16:25,680 --> 00:16:29,360
Anyway, to lose that,
I'd feel somewhat emasculated.

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00:16:29,360 --> 00:16:32,200
This first test

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seems to confirm that humans do
find hairless bodies more attractive

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and that supports Darwin's theory,

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

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the genes for hairiness
all but died out.

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But Darwin's theory isn't enough.

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00:17:00,280 --> 00:17:04,720
By the rules of evolution, it simply
doesn't make sense on its own.

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00:17:06,640 --> 00:17:09,600
Well really, for much of our history
as primates

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and in the early history
of our own lineage,

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00:17:12,400 --> 00:17:15,480
having hair
was probably extremely important

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00:17:15,480 --> 00:17:19,720
and the lack of hair would have
been considered a sign of illness

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00:17:19,720 --> 00:17:21,720
or, or certainly undesirability.

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00:17:23,800 --> 00:17:26,800
Our ancestors would have been
attracted to healthy mates

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00:17:26,800 --> 00:17:29,000
by their thick glossy fur.

246
00:17:29,000 --> 00:17:31,720
They wouldn't look twice
at one with balding fur.

247
00:17:31,720 --> 00:17:35,560
That's how evolution
weeds out weakness and disease.

248
00:17:35,560 --> 00:17:39,320
So before naked skin
could become attractive to humans,

249
00:17:39,320 --> 00:17:42,400
it must have become beneficial
to lack hair.

250
00:17:42,400 --> 00:17:44,600
Only then could a balding ape

251
00:17:44,600 --> 00:17:47,320
be considered a good prospect
as a mate.

252
00:17:47,320 --> 00:17:48,800
One then has to think about,

253
00:17:48,800 --> 00:17:52,680
well what is the good reason
rooted in natural selection

254
00:17:52,680 --> 00:17:56,040
that can lead us to understand
the evolution of hairlessness?

255
00:17:56,040 --> 00:18:01,000
What was it that gave humans
greater reproductive success

256
00:18:01,000 --> 00:18:03,240
as a result of being hairless?

257
00:18:07,640 --> 00:18:11,160
Professor Jablonski believes the
answer lies millions of years ago,

258
00:18:11,160 --> 00:18:14,040
with our earliest
and furriest ancestors.

259
00:18:16,480 --> 00:18:19,480
While homo sapiens,
the hairless modern human,

260
00:18:19,480 --> 00:18:21,920
evolved
a quarter of a million years ago,

261
00:18:21,920 --> 00:18:25,720
the human family tree
stretches much further back,

262
00:18:25,720 --> 00:18:28,640
to around six million years ago,

263
00:18:28,640 --> 00:18:32,400
when a distant ancestor
split from the chimpanzee line.

264
00:18:32,400 --> 00:18:35,760
It was almost certainly
covered in fur.

265
00:18:35,760 --> 00:18:40,880
What could have happened since then
to prompt the loss of our fur

266
00:18:40,880 --> 00:18:44,080
while so many other animals
kept theirs?

267
00:18:46,680 --> 00:18:49,240
All of these animals
that we see around us

268
00:18:49,240 --> 00:18:52,040
have a lot of hair
for a very good reason.

269
00:18:52,040 --> 00:18:54,760
It may seem stupid that a fur coat

270
00:18:54,760 --> 00:18:58,520
is actually a good thing to have
in this hot, open, sunny environment,

271
00:18:58,520 --> 00:19:00,720
but in fact it is a good thing.

272
00:19:09,760 --> 00:19:12,840
Still naked, Ian from Edinburgh

273
00:19:12,840 --> 00:19:16,960
is about to find out why
fur is so useful in the heat.

274
00:19:16,960 --> 00:19:19,960
He's joined by Alex in a challenge

275
00:19:19,960 --> 00:19:22,200
that's not going to be comfortable.

276
00:19:23,800 --> 00:19:27,720
They're standing in the intense heat
of industrial radiators

277
00:19:27,720 --> 00:19:31,120
while a thermal camera reveals
how their bodies are affected.

278
00:19:35,800 --> 00:19:41,360
On the right, Ian's skin is hot,
turning from yellow to red,

279
00:19:41,360 --> 00:19:46,640
while those white patches on Alex's
clothes show they're even hotter.

280
00:19:46,640 --> 00:19:49,440
But Alex's loose clothes
are actually protecting

281
00:19:49,440 --> 00:19:54,920
his body from the heat.
Underneath, his skin stays cool.

282
00:19:54,920 --> 00:19:57,560
This is exactly how fur

283
00:19:57,560 --> 00:20:01,480
protects most animals
from the heat of the sun.

284
00:20:03,680 --> 00:20:07,680
But one theory suggests
our ancestors found a better way,

285
00:20:08,720 --> 00:20:12,000
that by combining
three remarkable attributes,

286
00:20:12,000 --> 00:20:14,200
their fur became redundant.

287
00:20:19,800 --> 00:20:21,920
First, they stood upright.

288
00:20:24,320 --> 00:20:26,560
Next, they were very active,

289
00:20:26,560 --> 00:20:30,320
ranging great distances
on the open savannah.

290
00:20:30,320 --> 00:20:35,880
And third, just as Alex and Ian
are now, they began to do something

291
00:20:35,880 --> 00:20:38,720
no other animal can match...

292
00:20:38,720 --> 00:20:40,760
to sweat profusely.

293
00:20:44,520 --> 00:20:48,400
It's this unique solution to keeping
cool that drove the loss of our fur,

294
00:20:48,400 --> 00:20:51,680
according to
Professor Peter Wheeler.

295
00:20:53,040 --> 00:20:56,760
Humans rely on whole body cooling,
and their combination of a naked skin

296
00:20:56,760 --> 00:20:59,920
and highly developed sweat glands
enables them to lose heat at a rate

297
00:20:59,920 --> 00:21:02,000
not approached by any other mammal.

298
00:21:02,000 --> 00:21:05,880
Humans are the sweatiest creatures
in history.

299
00:21:05,880 --> 00:21:09,040
Our skin contains
the most sweat glands,

300
00:21:09,040 --> 00:21:11,120
and at nearly a litre an hour,

301
00:21:11,120 --> 00:21:14,040
produces the greatest volume
of sweat of any animal.

302
00:21:15,680 --> 00:21:19,320
The surface of our entire body
is an active cooling system.

303
00:21:20,400 --> 00:21:23,840
This means that the human
can lose heat

304
00:21:23,840 --> 00:21:25,640
at a rate in excess of one kilowatt.

305
00:21:25,640 --> 00:21:29,880
Now that's the amount of heat
put out by a one bar electric fire.

306
00:21:29,880 --> 00:21:32,640
Alex and Ian are both dripping,

307
00:21:32,640 --> 00:21:35,800
but Alex's shirt soaks up the sweat,

308
00:21:35,800 --> 00:21:39,720
just like fur would,
and he feels little benefit.

309
00:21:39,720 --> 00:21:43,640
If you possess body hair,
you still can lose heat by sweating,

310
00:21:43,640 --> 00:21:47,080
but it's less effective because
the airflow over the skin surface

311
00:21:47,080 --> 00:21:51,360
is greatly reduced, reducing the rate
at which water is going to evaporate.

312
00:21:51,360 --> 00:21:54,160
Peter Wheeler believes
sweating into a fur coat

313
00:21:54,160 --> 00:21:56,800
was no use to our ancestors.

314
00:21:56,800 --> 00:22:00,720
By losing their body hair, what
they're able to do is evaporate water

315
00:22:00,720 --> 00:22:04,240
both more efficiently and effectively
from the skin surface.

316
00:22:04,240 --> 00:22:07,760
While the sweat
soaks into Alex's shirt,

317
00:22:07,760 --> 00:22:11,600
it can evaporate freely
from Ian's naked skin,

318
00:22:11,600 --> 00:22:17,080
and with it, goes all the excess
heat generated by his active body.

319
00:22:17,080 --> 00:22:20,400
The more he sweats,
the more he cools.

320
00:22:25,520 --> 00:22:30,000
The theory that sweating
drove our loss of fur is persuasive,

321
00:22:31,560 --> 00:22:33,320
but it's impossible to prove.

322
00:22:40,600 --> 00:22:44,120
That's why Professor Jablonski
is in Kenya.

323
00:22:44,120 --> 00:22:46,840
She believes that
out on the African savannah,

324
00:22:46,840 --> 00:22:48,320
there's living evidence

325
00:22:48,320 --> 00:22:50,720
that supports the controversial
sweat theory.

326
00:22:52,320 --> 00:22:55,680
She's on the trail
of a very unusual primate

327
00:22:55,680 --> 00:22:59,400
which appears to be following
our own evolutionary footsteps,

328
00:22:59,400 --> 00:23:02,040
the Patas monkey.

329
00:23:02,040 --> 00:23:07,360
Patas are really of interest to me
because they live in open

330
00:23:07,360 --> 00:23:13,440
environments very much like those
in which we imagine early members

331
00:23:13,440 --> 00:23:16,880
of our own genus, the genus homo,
to have lived,

332
00:23:16,880 --> 00:23:19,880
and they really provide
something of a model for how

333
00:23:19,880 --> 00:23:24,520
we think humans may have moved during
early parts of their evolution.

334
00:23:26,080 --> 00:23:29,760
Patas and humans share
many fascinating characteristics,

335
00:23:29,760 --> 00:23:33,880
because they have
similar body proportions

336
00:23:33,880 --> 00:23:38,280
in that Patas have relatively
long limbs compared to other monkeys.

337
00:23:38,280 --> 00:23:41,320
They're very good
at walking long distances.

338
00:23:41,320 --> 00:23:42,960
They range very, very widely,

339
00:23:42,960 --> 00:23:46,000
they have a larger home range
than any other primate.

340
00:23:49,560 --> 00:23:52,760
But Patas monkeys share
another of the attributes

341
00:23:52,760 --> 00:23:55,160
that made our ancestors'
fur redundant.

342
00:23:57,000 --> 00:23:58,840
As well as being very active,

343
00:23:58,840 --> 00:24:01,760
they've followed our solution
to keeping cool.

344
00:24:02,880 --> 00:24:07,720
Most primates don't sweat very much,
but Patas monkeys sweat copiously,

345
00:24:07,720 --> 00:24:11,960
and that's what gets anthropologists
really excited about studying them.

346
00:24:11,960 --> 00:24:17,040
It's this ability to sweat
that suggests to Professor Jablonski

347
00:24:17,040 --> 00:24:19,120
that right before our eyes,

348
00:24:19,120 --> 00:24:22,440
the Patas monkey is echoing
our own early evolution.

349
00:24:24,240 --> 00:24:27,920
It was survival of the best sweaters

350
00:24:27,920 --> 00:24:31,240
that really was part
of our evolutionary process.

351
00:24:31,240 --> 00:24:34,520
We're talking about
early members of the human lineage

352
00:24:34,520 --> 00:24:39,200
that had a little bit less hair, that
had more productive sweat glands,

353
00:24:39,200 --> 00:24:43,040
and those individuals would have had
an incremental reproductive advantage

354
00:24:43,040 --> 00:24:47,040
over others, and that made
the difference in human evolution,

355
00:24:47,040 --> 00:24:52,480
driving the loss of body hair
and an increase in the number

356
00:24:52,480 --> 00:24:54,680
'and activity of sweat glands.'

357
00:24:56,240 --> 00:24:58,480
Oh, I've got a great view!

358
00:24:58,480 --> 00:25:02,800
But if Patas monkeys are following
our evolutionary steps,

359
00:25:02,800 --> 00:25:05,480
why do they still have fur?

360
00:25:05,480 --> 00:25:08,680
Even though they do have hair,

361
00:25:08,680 --> 00:25:11,920
their hair is very different
from that of other monkeys.

362
00:25:11,920 --> 00:25:15,080
It's not as dense, it's quite
coarse, and so when they sweat,

363
00:25:15,080 --> 00:25:20,240
they can also lose heat through
evaporation just like humans can.

364
00:25:20,240 --> 00:25:22,240
They may have thinner fur,

365
00:25:22,240 --> 00:25:26,160
but Professor Jablonski believes
Patas will never go naked,

366
00:25:26,160 --> 00:25:30,400
because they lack one crucial
feature that made all the difference

367
00:25:30,400 --> 00:25:32,840
to our ancestors - walking upright.

368
00:25:32,840 --> 00:25:37,040
On all fours,
Patas are exposed to too much sun.

369
00:25:37,040 --> 00:25:39,480
Despite their ability to sweat,

370
00:25:39,480 --> 00:25:43,080
they can't afford to lose
their protective fur.

371
00:25:43,080 --> 00:25:46,400
If humans had been quadrupedal,

372
00:25:46,400 --> 00:25:51,000
walking on all four legs, we probably
wouldn't have lost our fur,

373
00:25:51,000 --> 00:25:52,920
but humans became bipedal,

374
00:25:52,920 --> 00:25:56,920
and when they did come out
in this open sunny environment,

375
00:25:56,920 --> 00:26:00,680
there was every reason for them
to lose their fur,

376
00:26:00,680 --> 00:26:03,680
and they lost it on their front
and on their backs,

377
00:26:03,680 --> 00:26:07,800
but they did retain a little bit of
it in a very strategic position,

378
00:26:07,800 --> 00:26:09,400
right on the tops of their heads.

379
00:26:11,000 --> 00:26:14,760
This final evidence
convinces Professor Jablonski

380
00:26:14,760 --> 00:26:17,960
that uniquely equipped
against the heat of the sun,

381
00:26:17,960 --> 00:26:20,680
our naked ancestors
had a huge advantage

382
00:26:20,680 --> 00:26:22,760
over their hairy relatives.

383
00:26:22,760 --> 00:26:25,480
And that made them
the first primate

384
00:26:25,480 --> 00:26:29,240
able to exploit the harsh
environment of the open savannah.

385
00:26:34,360 --> 00:26:37,080
But to the scientists
behind the sweating theory,

386
00:26:37,080 --> 00:26:41,680
going naked had an even bigger
pay-off for mankind,

387
00:26:41,680 --> 00:26:44,680
and particularly for our brains.

388
00:26:48,160 --> 00:26:52,400
The human brain produces
something like 20 watts of heat.

389
00:26:52,400 --> 00:26:56,040
That doesn't sound very much but
if you put a 20-watt light bulb

390
00:26:56,040 --> 00:27:00,120
in a small box the size of the skull,
it's soon going to overheat.

391
00:27:00,120 --> 00:27:03,280
One or two degrees and it starts
to impair brain functioning.

392
00:27:03,280 --> 00:27:05,800
Three or four degrees,
and it's usually fatal.

393
00:27:05,800 --> 00:27:08,440
This risk of overheating

394
00:27:08,440 --> 00:27:13,720
drastically limits the size of
most animals' brains, but not ours.

395
00:27:13,720 --> 00:27:16,560
It's probably no coincidence today
that the mammal

396
00:27:16,560 --> 00:27:20,120
that's got the largest brain relative
to its body size, that is humans,

397
00:27:20,120 --> 00:27:22,600
also possess the most
powerful cooling system

398
00:27:22,600 --> 00:27:24,000
of any mammal to protect it.

399
00:27:28,400 --> 00:27:30,640
It was this superior cooling system

400
00:27:30,640 --> 00:27:33,200
that would change
the course of evolution.

401
00:27:34,280 --> 00:27:37,480
Without losing hair,
without our sweatiness,

402
00:27:37,480 --> 00:27:40,480
we wouldn't have been able
to evolve the big brains

403
00:27:40,480 --> 00:27:42,000
that characterise us today,

404
00:27:42,000 --> 00:27:45,240
and that really make us
the modern human species that we are.

405
00:27:53,760 --> 00:28:00,160
Essentially, being hairless was the
key to so much of human evolution.

406
00:28:01,960 --> 00:28:06,960
The next question is, when did we
reach this pinnacle of evolution?

407
00:28:06,960 --> 00:28:10,800
Were modern humans
the first naked ape,

408
00:28:10,800 --> 00:28:13,560
or our older cousins,
the Neanderthals?

409
00:28:16,600 --> 00:28:20,200
It could have been an earlier
ancestor from the genus homo

410
00:28:20,200 --> 00:28:23,320
that lived between
one and two million years ago.

411
00:28:24,320 --> 00:28:29,320
Was it Australopithecus, living
two million years before that?

412
00:28:29,320 --> 00:28:31,040
Or even Ardipithecus,

413
00:28:31,040 --> 00:28:33,760
the species that branched
from the chimpanzee line

414
00:28:33,760 --> 00:28:35,800
six million years ago?

415
00:28:40,120 --> 00:28:43,600
It's a question
that's never been answered,

416
00:28:43,600 --> 00:28:48,200
because, although fossils tell us
so much about our ancestors' bodies,

417
00:28:48,200 --> 00:28:51,240
the length of their limbs,
the size of their brains,

418
00:28:51,240 --> 00:28:55,280
one thing that is never preserved
is their skin.

419
00:28:55,280 --> 00:28:59,320
But there is a surprising
new source of evidence.

420
00:29:04,160 --> 00:29:09,480
It's not from humans or from apes,
but from a quite different creature

421
00:29:09,480 --> 00:29:13,920
that's been our constant companion
throughout evolution.

422
00:29:24,640 --> 00:29:29,040
Florida University geneticist
Dr David Reed has found that

423
00:29:29,040 --> 00:29:33,400
the chequered family history
of human lice is very revealing.

424
00:29:36,200 --> 00:29:39,480
When you think of human hair,
that's the habitat of these lice,

425
00:29:39,480 --> 00:29:42,200
and it offers us the opportunity
to study these lice

426
00:29:42,200 --> 00:29:44,440
and how they've evolved
with their hosts.

427
00:29:44,440 --> 00:29:46,600
If you look at the genetics
of these lice,

428
00:29:46,600 --> 00:29:49,840
written in their genetic code
is our own evolutionary history.

429
00:29:53,080 --> 00:29:56,720
Watershed events like losing
the complete body hair on a host

430
00:29:56,720 --> 00:30:00,400
would have a huge impact on
where parasites can go on the body,

431
00:30:00,400 --> 00:30:02,760
and whether parasites persist or not.

432
00:30:04,960 --> 00:30:08,040
Dr Reed has been doing some
unusual genetic detective work.

433
00:30:08,040 --> 00:30:11,040
So we collect these parasites
from humans,

434
00:30:11,040 --> 00:30:13,160
and then we bring them back
to the lab.

435
00:30:13,160 --> 00:30:15,240
Then we extract the DNA
from these lice,

436
00:30:15,240 --> 00:30:18,600
and we magnify that DNA
through DNA sequencing.

437
00:30:19,640 --> 00:30:21,800
We can use those DNA sequences
to build

438
00:30:21,800 --> 00:30:25,520
evolutionary trees that describe
the relationships of these lice.

439
00:30:27,080 --> 00:30:29,880
The family tree that Dr Reed
has built for lice

440
00:30:29,880 --> 00:30:33,120
provides a mirror
for the tree of human evolution.

441
00:30:35,040 --> 00:30:39,120
And we see that if you date when
chimpanzee and human lice diverged,

442
00:30:39,120 --> 00:30:40,400
it matches up perfectly

443
00:30:40,400 --> 00:30:44,080
with when humans and chimps
last shared a common ancestor.

444
00:30:44,080 --> 00:30:47,400
What most interests Dr Reed
is the extraordinary relationship

445
00:30:47,400 --> 00:30:51,040
between humans and lice.

446
00:30:51,040 --> 00:30:55,160
Generally each primate species
only has a single louse species.

447
00:30:55,160 --> 00:30:58,880
Humans are somewhat unique
in that we have three types of lice.

448
00:30:58,880 --> 00:31:01,480
The louse that most people
would be familiar with

449
00:31:01,480 --> 00:31:04,080
that occurs on humans
is of course the head louse.

450
00:31:04,080 --> 00:31:06,560
We think that this is
the ancestral type of louse

451
00:31:06,560 --> 00:31:09,840
that we've had all along
throughout our evolutionary history.

452
00:31:09,840 --> 00:31:13,080
With us for six million years,
the head louse originally lived

453
00:31:13,080 --> 00:31:17,160
all over the bodies of our
earliest hominid ancestors.

454
00:31:17,160 --> 00:31:20,000
But if that hominid
loses all of its body hair,

455
00:31:20,000 --> 00:31:23,960
and retains perhaps only head hair
that's suitable habitat,

456
00:31:23,960 --> 00:31:26,160
now you have one refuge
on the entire body.

457
00:31:27,200 --> 00:31:31,080
So how does Dr Reed explain
our next species of louse,

458
00:31:31,080 --> 00:31:34,080
the pubic or crab louse?

459
00:31:34,080 --> 00:31:37,320
The crab louse is somewhat different
from the human head louse

460
00:31:37,320 --> 00:31:38,880
in terms of its size and shape,

461
00:31:38,880 --> 00:31:41,280
and it's well adapted
to holding onto hairs

462
00:31:41,280 --> 00:31:45,360
that are much larger in diameter
and much farther apart in spacing.

463
00:31:45,360 --> 00:31:48,480
Its closest living relative
is actually found on gorillas.

464
00:31:49,560 --> 00:31:54,560
To Dr Reed, understanding how this
new species colonised our bodies

465
00:31:54,560 --> 00:31:59,240
is critical to understanding
the evolution of human hair.

466
00:31:59,240 --> 00:32:01,880
How would we have acquired
a gorilla louse?

467
00:32:01,880 --> 00:32:05,400
What must have happened in terms of
changes in our body to allow that?

468
00:32:05,400 --> 00:32:07,160
What's interesting to me is that

469
00:32:07,160 --> 00:32:09,560
that move could not have happened

470
00:32:09,560 --> 00:32:12,120
until the habitat
was there and available.

471
00:32:12,120 --> 00:32:14,880
First, we must have
lost our body hair,

472
00:32:14,880 --> 00:32:18,360
and second,
we must have acquired pubic hair.

473
00:32:18,360 --> 00:32:22,280
Even with the earlier species
confined to our heads,

474
00:32:22,280 --> 00:32:25,120
the new lice couldn't move in
till we'd evolved a patch

475
00:32:25,120 --> 00:32:27,880
of suitably coarse
gorilla-like hair...

476
00:32:27,880 --> 00:32:31,280
though exactly
how they made the move

477
00:32:31,280 --> 00:32:33,240
is open to question.

478
00:32:33,240 --> 00:32:35,160
For lice to move among individuals,

479
00:32:35,160 --> 00:32:37,760
there usually has to be
direct physical contact.

480
00:32:37,760 --> 00:32:40,800
If we're talking about a louse
moving from gorillas

481
00:32:40,800 --> 00:32:45,440
to the pubic region of humans, of
course, the imagination can run wild.

482
00:32:45,440 --> 00:32:46,760
Whatever the route,

483
00:32:46,760 --> 00:32:49,880
the new arrivals separated from
their gorilla ancestors

484
00:32:49,880 --> 00:32:54,680
to create a new species,
the human pubic louse.

485
00:32:57,520 --> 00:33:00,800
Dr Reed realised that this branching
of the louse family tree

486
00:33:00,800 --> 00:33:06,320
provides the best evidence yet for
when humans lost their body hair.

487
00:33:06,320 --> 00:33:10,600
The genetic data that we studied
from these lice tell us that the move

488
00:33:10,600 --> 00:33:14,360
from gorillas to humans occurred
roughly three million years ago.

489
00:33:14,360 --> 00:33:18,080
Therefore we might assume that the
body hair changes in humans happened

490
00:33:18,080 --> 00:33:20,640
roughly three million years ago.

491
00:33:20,640 --> 00:33:23,240
It's an astonishing conclusion,

492
00:33:23,240 --> 00:33:25,520
placing the original loss
of body hair

493
00:33:25,520 --> 00:33:28,480
long before the evolution
of modern humans.

494
00:33:28,480 --> 00:33:31,520
Certainly this very old timeframe
of three million years

495
00:33:31,520 --> 00:33:34,680
for the loss of body hair
flies against the general convention

496
00:33:34,680 --> 00:33:39,240
that only modern humans much more
recently lost their body hair.

497
00:33:39,240 --> 00:33:42,640
To think about archaic hominids
having no body hair

498
00:33:42,640 --> 00:33:45,920
for millions of years is quite
interesting, and quite controversial.

499
00:33:45,920 --> 00:33:48,040
By Dr Reed's calculation,

500
00:33:49,160 --> 00:33:52,040
nudity goes right back
to Australopithecus.

501
00:33:54,080 --> 00:33:55,520
From that early ancestor,

502
00:33:55,520 --> 00:33:59,280
every branch of the human family
tree inherited naked skin,

503
00:33:59,280 --> 00:34:02,400
right up to Neanderthals,

504
00:34:02,400 --> 00:34:03,720
and modern humans.

505
00:34:06,600 --> 00:34:09,840
The answer to one final mystery
of human evolution

506
00:34:09,840 --> 00:34:13,000
lies in the genetic
evidence of lice,

507
00:34:13,000 --> 00:34:16,560
one that's essential
to our concept of nudity.

508
00:34:19,880 --> 00:34:23,200
The clothing louse is a direct
descendant of the head louse

509
00:34:23,200 --> 00:34:25,720
and, like the crab louse,

510
00:34:25,720 --> 00:34:29,760
it could only evolve
once its habitat existed.

511
00:34:29,760 --> 00:34:33,160
What's remarkable about this one is,
of all the lice,

512
00:34:33,160 --> 00:34:35,000
it's the only one that lays its eggs

513
00:34:35,000 --> 00:34:37,640
or lives in anything other than
fur or feathers.

514
00:34:37,640 --> 00:34:39,480
It lives entirely in the clothing.

515
00:34:41,960 --> 00:34:45,920
By dating this branch
in louse evolution,

516
00:34:45,920 --> 00:34:49,400
Dr Reed could reveal something
that fossils never could.

517
00:34:49,400 --> 00:34:52,800
When humans first got dressed.

518
00:34:55,000 --> 00:34:57,960
We can look at the molecular data
for human head lice

519
00:34:57,960 --> 00:35:02,360
and clothing lice, and deduce when
those populations began diverging,

520
00:35:02,360 --> 00:35:06,920
and when we do that, we see that they
diverged about 650,000 years ago.

521
00:35:08,520 --> 00:35:13,080
Dr Reed has re-written
the history books on human nudity.

522
00:35:13,080 --> 00:35:16,800
By his calculation, ancestral
humans lived completely naked

523
00:35:16,800 --> 00:35:20,120
for at least two million years.

524
00:35:20,120 --> 00:35:23,080
Only then did they begin
to cover up their nudity,

525
00:35:23,080 --> 00:35:25,400
just over half a million years ago.

526
00:35:31,040 --> 00:35:33,760
From the moment
we covered up our bodies,

527
00:35:33,760 --> 00:35:38,600
clothes began to shape
our culture and our identity.

528
00:35:38,600 --> 00:35:43,000
If you're clothed, then you don't
have to posture yourself as much,

529
00:35:43,000 --> 00:35:46,680
because the clothes you wear
will do a lot of the...

530
00:35:46,680 --> 00:35:49,040
the messages that needs
to be said about you.

531
00:35:49,040 --> 00:35:53,200
When you've got clothes on you can
create an image for yourself.

532
00:35:53,200 --> 00:35:55,600
Nudity to me is like
a blank piece of canvas,

533
00:35:55,600 --> 00:35:58,720
and when you put clothes on,
you're kind of painting yourself.

534
00:35:58,720 --> 00:36:05,200
But clothes also created a whole set
of uniquely human problems.

535
00:36:05,200 --> 00:36:07,800
For a start they concealed
all the bits of the body

536
00:36:07,800 --> 00:36:10,120
that were most important

537
00:36:10,120 --> 00:36:13,560
for the essential business
of sexual attraction.

538
00:36:16,520 --> 00:36:19,480
At the University of California
in Los Angeles,

539
00:36:19,480 --> 00:36:23,120
Dr Kerri Johnson is investigating
the secrets of human attraction.

540
00:36:24,720 --> 00:36:27,880
She wants to find out how we
still manage to attract each other

541
00:36:27,880 --> 00:36:30,040
despite wearing clothes.

542
00:36:31,080 --> 00:36:33,280
My research examines how people

543
00:36:33,280 --> 00:36:36,520
make very fundamental social
judgments about one another.

544
00:36:36,520 --> 00:36:40,800
When you see them across the room,
you know virtually instantly

545
00:36:40,800 --> 00:36:42,360
whether it's a man or a woman,

546
00:36:42,360 --> 00:36:44,520
how masculine or feminine
the target is,

547
00:36:44,520 --> 00:36:47,640
and consequently whether
he or she is sexually attractive.

548
00:36:47,640 --> 00:36:52,720
We use eye tracking methods
that covertly measure the direction

549
00:36:52,720 --> 00:36:54,920
of gaze of our participants,

550
00:36:54,920 --> 00:36:58,680
allowing us to pinpoint precisely
where our participants are looking.

551
00:37:00,080 --> 00:37:02,880
In her experiments,
Dr Johnson asks people

552
00:37:02,880 --> 00:37:07,080
how attractive they find a series
of computer-animated silhouettes.

553
00:37:07,080 --> 00:37:09,600
They are neither nude
nor are they clothed,

554
00:37:09,600 --> 00:37:14,680
and this is really an important
factor in our experiment.

555
00:37:14,680 --> 00:37:17,200
If the target is naked,
they're likely to look at

556
00:37:17,200 --> 00:37:19,480
the areas that are
the most informative -

557
00:37:19,480 --> 00:37:23,000
the genitals, the breasts,
presence or absence of those things.

558
00:37:23,000 --> 00:37:25,440
So that's the judgment
that you'll be making.

559
00:37:25,440 --> 00:37:27,840
Is the image depicting
a man or a woman?

560
00:37:30,160 --> 00:37:34,320
The aim is to find out how we
tune into each other's sexuality

561
00:37:34,320 --> 00:37:37,400
when none of the obvious
signals is visible.

562
00:37:38,440 --> 00:37:39,760
Man.

563
00:37:41,440 --> 00:37:44,800
My research has found that
the body's shape and body's motion

564
00:37:44,800 --> 00:37:47,640
are very important for
judgments of attractiveness.

565
00:37:47,640 --> 00:37:50,680
A woman's body
is much more hourglass in shape,

566
00:37:50,680 --> 00:37:53,080
and a man's body
is much more tubular in shape.

567
00:37:53,080 --> 00:37:56,160
It reliably differs
between men and women,

568
00:37:56,160 --> 00:37:58,760
and this is referred to
as the waist-to-hip ratio.

569
00:37:59,800 --> 00:38:03,480
A typical female walk
would include a lateral hip sway.

570
00:38:03,480 --> 00:38:05,840
This is the hips moving
back and forth,

571
00:38:05,840 --> 00:38:08,520
and actually a bit up and down
as women walk.

572
00:38:08,520 --> 00:38:11,680
If you think about
the way a man moves his body,

573
00:38:11,680 --> 00:38:13,720
we refer to that as
shoulder swagger.

574
00:38:13,720 --> 00:38:17,200
So when people are deciding whether
a target is a man or a woman,

575
00:38:17,200 --> 00:38:19,360
they look intently
at a region of the body

576
00:38:19,360 --> 00:38:23,160
that varies between men
and women, the waist and hips.

577
00:38:23,160 --> 00:38:27,560
The result is clear. With clothes
covering up our naked bodies,

578
00:38:27,560 --> 00:38:31,360
humans have perfected a new, more
subtle code of sexual attraction.

579
00:38:31,360 --> 00:38:32,440
Woman.

580
00:38:32,440 --> 00:38:35,920
So we're talking about
how the body is shaped,

581
00:38:35,920 --> 00:38:38,360
the physical proportions
of the body,

582
00:38:38,360 --> 00:38:39,760
and how the body moves,

583
00:38:39,760 --> 00:38:42,480
and both of those
are available to observers

584
00:38:42,480 --> 00:38:45,360
regardless of whether
they're wearing clothing or not.

585
00:38:53,400 --> 00:38:56,120
We're going to find out
how well our subjects

586
00:38:56,120 --> 00:38:59,480
can tune into these
subtle sexual signals.

587
00:39:00,640 --> 00:39:04,240
Foyez and Helen are being
fitted with eye-tracking glasses.

588
00:39:04,240 --> 00:39:08,080
We're going to watch
where their eyes wander

589
00:39:08,080 --> 00:39:10,640
as they scan the bodies
of their fellow subjects,

590
00:39:12,880 --> 00:39:14,440
clothed and naked.

591
00:39:21,760 --> 00:39:24,320
First up is 25-year-old Rosie.

592
00:39:25,720 --> 00:39:28,440
Helen's eyes are all over the place,

593
00:39:28,440 --> 00:39:30,960
picking up details
of Rosie's clothing,

594
00:39:30,960 --> 00:39:34,440
but she's definitely lingering
on her waist and hips,

595
00:39:34,440 --> 00:39:35,960
exactly as predicted.

596
00:39:38,120 --> 00:39:44,000
But Foyez seems to have
locked his gaze on Rosie's head

597
00:39:44,000 --> 00:39:46,760
and he's keeping his eyes
unnaturally still.

598
00:39:50,640 --> 00:39:53,200
How will they deal with
a naked body?

599
00:39:53,200 --> 00:39:57,040
Step forward Phil,
our 39-year-old data analyst.

600
00:39:59,800 --> 00:40:00,880
Helen's not fazed.

601
00:40:00,880 --> 00:40:03,760
She's scanning
his entire body again,

602
00:40:03,760 --> 00:40:06,360
picking up the shape
of Phil's waist and hips,

603
00:40:06,360 --> 00:40:09,800
but not focusing on the obvious
sexual features.

604
00:40:11,440 --> 00:40:12,560
And Foyez...

605
00:40:13,640 --> 00:40:17,280
..it seems nothing
is going to shift his gaze...

606
00:40:17,280 --> 00:40:19,000
and he's sticking to that strategy.

607
00:40:20,120 --> 00:40:24,200
Something is stopping Foyez
from following his instinct to look.

608
00:40:24,200 --> 00:40:29,640
Helen seems at ease whether
her targets are naked or not.

609
00:40:29,640 --> 00:40:32,880
She's quite naturally drawn
to the most sexually revealing parts

610
00:40:32,880 --> 00:40:35,680
of the body - the waist and hips.

611
00:40:38,840 --> 00:40:41,960
My intuition is that the eye
movements demonstrated by Helen

612
00:40:41,960 --> 00:40:44,800
were probably completely
natural and spontaneous.

613
00:40:44,800 --> 00:40:48,880
I suspect that Foyez
may have been maybe embarrassed,

614
00:40:48,880 --> 00:40:51,920
or for whatever reason,
wishing to control his movements,

615
00:40:51,920 --> 00:40:54,840
so that he looked very much
at the person's face

616
00:40:54,840 --> 00:40:56,880
rather than anywhere else.

617
00:40:56,880 --> 00:40:59,400
Maybe, of course,
it would be interesting to know

618
00:40:59,400 --> 00:41:01,120
if he'd be looking in that way

619
00:41:01,120 --> 00:41:03,800
if he hadn't known that his eyes
were being monitored.

620
00:41:04,960 --> 00:41:09,080
I didn't want to be labelled
as a voyeur or a pervert.

621
00:41:09,080 --> 00:41:12,480
I mean I was well aware
that this footage

622
00:41:12,480 --> 00:41:15,640
would be sort of reviewed
afterwards.

623
00:41:15,640 --> 00:41:17,960
I just treated it more like
a video game.

624
00:41:17,960 --> 00:41:21,600
A lot of self-control was involved
even while all of this was going on,

625
00:41:21,600 --> 00:41:23,800
so I was quite impressed
with myself.

626
00:41:23,800 --> 00:41:28,160
I think Foyez was very much
controlling his natural response.

627
00:41:28,160 --> 00:41:32,520
I just can't believe a male
confronted with a nude female

628
00:41:32,520 --> 00:41:36,520
is going to look, you know,
at their, at their heads.

629
00:41:36,520 --> 00:41:39,000
It was nice of him to show
that degree of control.

630
00:41:39,000 --> 00:41:40,840
Probably made me feel a bit better

631
00:41:40,840 --> 00:41:43,400
because I actually found it
more uncomfortable

632
00:41:43,400 --> 00:41:45,000
watching myself on the screen.

633
00:41:47,200 --> 00:41:49,440
Despite Foyez's self-control,

634
00:41:49,440 --> 00:41:53,040
it's clear the signals of sexual
identity carried in human shape

635
00:41:53,040 --> 00:41:57,400
and movement are much more subtle
than the ones most primates use.

636
00:41:59,920 --> 00:42:04,360
Without the barrier of clothing,
primates use striking visual signals

637
00:42:04,360 --> 00:42:09,240
advertising exactly
when they're ready for sex.

638
00:42:09,240 --> 00:42:13,680
Females show that they're fertile
by displaying a swollen red behind,

639
00:42:13,680 --> 00:42:16,520
leaving no doubt in the minds
of any amorous males.

640
00:42:18,520 --> 00:42:23,080
Under our clothes, signals like
these would be useless to humans,

641
00:42:23,080 --> 00:42:27,480
so it's no surprise that
women don't have such a display.

642
00:42:27,480 --> 00:42:30,320
But does that mean that humans
have to rely on guesswork

643
00:42:30,320 --> 00:42:32,760
to pick the right moment to mate?

644
00:42:38,400 --> 00:42:41,080
In another Los Angeles laboratory,

645
00:42:41,080 --> 00:42:45,320
that's exactly what Dr Martie
Haselton is trying to find out.

646
00:42:45,320 --> 00:42:48,280
I think that for men
detecting cues of fertility,

647
00:42:48,280 --> 00:42:50,280
whether they be cycling fertility,

648
00:42:50,280 --> 00:42:52,320
fertility over the course
of the month,

649
00:42:52,320 --> 00:42:55,120
or fertility associated
with changes in age,

650
00:42:55,120 --> 00:42:58,360
I think that those play a very
dramatic role in mate preferences

651
00:42:58,360 --> 00:43:00,160
and therefore in sexual selection.

652
00:43:01,840 --> 00:43:05,560
Dr Haselton collects photographs
of women

653
00:43:05,560 --> 00:43:08,760
at various stages
of their menstrual cycle,

654
00:43:08,760 --> 00:43:10,800
including ones taken
just before ovulation

655
00:43:10,800 --> 00:43:12,680
when they are most fertile.

656
00:43:12,680 --> 00:43:17,160
Then she asks men to choose
which is most attractive.

657
00:43:17,160 --> 00:43:21,080
We found that judges chose
the high fertility photograph

658
00:43:21,080 --> 00:43:24,360
as the one in which
she was dressed up more.

659
00:43:24,360 --> 00:43:27,840
About 60 per cent of the time
that was well beyond chance.

660
00:43:27,840 --> 00:43:29,960
That led us to wonder, "Well...

661
00:43:29,960 --> 00:43:32,200
"are there detectable cues
of ovulation

662
00:43:32,200 --> 00:43:34,240
"that male partners
are able to pick up on?"

663
00:43:36,200 --> 00:43:38,040
This was quite a revelation.

664
00:43:38,040 --> 00:43:43,400
For decades scientists had believed
that people simply couldn't detect

665
00:43:43,400 --> 00:43:45,160
human fertility levels.

666
00:43:45,160 --> 00:43:48,720
We know now that other things
are happening far off the radar

667
00:43:48,720 --> 00:43:50,560
of conscious perception.

668
00:43:51,640 --> 00:43:55,360
There are cues of cycling fertility,
cues of ovulation

669
00:43:55,360 --> 00:43:58,480
that are detectable
even by complete strangers.

670
00:44:02,880 --> 00:44:06,120
It seems that humans have developed
some kind of sixth sense,

671
00:44:06,120 --> 00:44:09,840
giving us incredible sensitivity
to these secret signals.

672
00:44:13,600 --> 00:44:16,560
There was a recent study done
that looked at the amount of tips

673
00:44:16,560 --> 00:44:20,280
that lap dancers earned
on varying days of the cycle

674
00:44:20,280 --> 00:44:24,720
and on high fertility days,
men tipped them more generously.

675
00:44:26,040 --> 00:44:29,960
No-one has yet worked out exactly
what these fertility signals are,

676
00:44:29,960 --> 00:44:33,480
but Dr Haselton has identified
one likely candidate.

677
00:44:35,600 --> 00:44:37,720
Women's body odours change.

678
00:44:37,720 --> 00:44:41,320
They become more attractive on high
as compared with low fertility days

679
00:44:41,320 --> 00:44:42,440
of the cycle.

680
00:44:44,880 --> 00:44:47,720
And this discovery
promises to solve another mystery

681
00:44:47,720 --> 00:44:50,480
about the naked human body.

682
00:44:50,480 --> 00:44:54,720
What pubic hair is for.

683
00:44:54,720 --> 00:45:00,160
One explanation is that body hair is
a conduit for scent, communication.

684
00:45:00,160 --> 00:45:02,960
In the moist warmth
of our pubic hair,

685
00:45:02,960 --> 00:45:06,120
bacteria feed on hormones
in our sweat

686
00:45:06,120 --> 00:45:09,040
and produce distinctive aromas.

687
00:45:09,040 --> 00:45:14,920
So for example underarm and pubic
hair could be a way of transmitting

688
00:45:14,920 --> 00:45:19,400
body odours out into the environment
to enhance attraction amongst lovers.

689
00:45:21,760 --> 00:45:24,920
Humans don't need
flashy fertility displays.

690
00:45:24,920 --> 00:45:29,920
Beneath our clothes, pubic hair
has become our secret weapon

691
00:45:29,920 --> 00:45:31,600
of sexual attraction.

692
00:45:34,400 --> 00:45:36,160
After a day and a half naked,

693
00:45:36,160 --> 00:45:39,360
four of our subjects finally
get the news they're waiting for.

694
00:45:39,360 --> 00:45:44,000
I'd like each of you to...
get dressed again, please.

695
00:45:46,560 --> 00:45:49,840
But as these four are reunited
with their clothes,

696
00:45:49,840 --> 00:45:53,360
the tables are about to be turned
on the remaining subjects

697
00:45:53,360 --> 00:45:55,960
who are left guessing
what lies ahead.

698
00:45:55,960 --> 00:46:00,520
Maybe there'll be wrestling. Oh, no!
Can't bear to think about that, no.

699
00:46:03,920 --> 00:46:07,720
Or maybe we'll do body artwork,
you know they'll cover us in paint

700
00:46:07,720 --> 00:46:10,400
and we'll just run into a canvas
or something.

701
00:46:10,400 --> 00:46:13,800
It's a scientific experiment
in hairlessness.

702
00:46:13,800 --> 00:46:16,160
Not painting us.

703
00:46:17,240 --> 00:46:21,080
In fact we're going to ask them
to do something more intimate

704
00:46:21,080 --> 00:46:22,960
than any of them feared.

705
00:46:22,960 --> 00:46:25,480
Undressing is a very common
thing we all do every day,

706
00:46:25,480 --> 00:46:27,360
but undressing in front of someone,

707
00:46:27,360 --> 00:46:30,080
only usually done under very special
circumstances

708
00:46:30,080 --> 00:46:32,360
when a couple feel very safe
with each other.

709
00:46:32,360 --> 00:46:34,160
Here we've got something
very different,

710
00:46:34,160 --> 00:46:36,360
people are undressing
or rather being undressed,

711
00:46:36,360 --> 00:46:39,640
by someone they've only recently met
in a room full of people.

712
00:46:40,680 --> 00:46:42,880
Those of you standing on the floor,

713
00:46:42,880 --> 00:46:46,520
we'd now like you to undress the
person on the podium in front of you.

714
00:46:49,640 --> 00:46:51,840
The subjects are paired,

715
00:46:51,840 --> 00:46:56,560
so that they're not all undressed
by someone of the opposite sex...

716
00:46:56,560 --> 00:47:00,120
and they're clearly
not finding this easy.

717
00:47:00,120 --> 00:47:03,560
I felt quite relieved
to be back in my clothes again.

718
00:47:03,560 --> 00:47:07,000
I think that the whole thought of
people taking their clothes off,

719
00:47:07,000 --> 00:47:08,760
there's a sexual connotation to it.

720
00:47:08,760 --> 00:47:11,960
There's that kind of, you only do it
when certain things are gonna happen

721
00:47:11,960 --> 00:47:18,200
and there's an uncomfortableness
about that, I guess.

722
00:47:18,200 --> 00:47:21,560
Unsurprisingly they found this one
pretty stressful.

723
00:47:21,560 --> 00:47:25,200
The tables were being turned. The
people who had been naked previously

724
00:47:25,200 --> 00:47:27,040
are now undressing the others.

725
00:47:27,040 --> 00:47:32,880
It's also a reminder that...nudity
is associated with sexuality

726
00:47:32,880 --> 00:47:39,320
and being undressed is very much
close to a sexual encounter.

727
00:47:41,280 --> 00:47:43,680
Our subjects have reached
a crucial point

728
00:47:43,680 --> 00:47:46,160
in their exploration of nudity.

729
00:47:46,160 --> 00:47:50,400
However hard they try, they can't
escape the intense emotions

730
00:47:50,400 --> 00:47:54,440
provoked by the simple act
of undressing.

731
00:47:58,880 --> 00:48:02,240
But does this sensitivity
to nudity serve any purpose?

732
00:48:05,360 --> 00:48:08,920
Scientists have long searched
for an answer

733
00:48:08,920 --> 00:48:11,800
and evolutionary psychologist,
Professor Dan Fessler,

734
00:48:11,800 --> 00:48:13,320
thinks he's found one.

735
00:48:16,560 --> 00:48:19,920
Two emotions play an important role
in sexual modesty.

736
00:48:19,920 --> 00:48:22,040
At the less extreme end
of the spectrum,

737
00:48:22,040 --> 00:48:27,160
minor inappropriate exposure of
the body results in embarrassment.

738
00:48:27,160 --> 00:48:29,200
At the more extreme end
of the spectrum,

739
00:48:29,200 --> 00:48:31,400
grossly inappropriate exposure
of the body

740
00:48:31,400 --> 00:48:34,080
and exposure of one's sexuality
results in shame.

741
00:48:35,480 --> 00:48:38,840
Professor Fessler believes that,
first of all,

742
00:48:38,840 --> 00:48:42,960
the expression of shame
is a simple self-defence mechanism.

743
00:48:44,000 --> 00:48:47,760
All around the world
individuals feel great shame

744
00:48:47,760 --> 00:48:50,000
when they know that others know

745
00:48:50,000 --> 00:48:52,480
that they have failed to be
adequately modest.

746
00:48:52,480 --> 00:48:55,280
Essentially they're signalling to
those around them,

747
00:48:55,280 --> 00:49:00,000
"I understand what the social norm
is and I understand that you know

748
00:49:00,000 --> 00:49:03,120
"that I have failed in this regard,
so please don't hurt me."

749
00:49:06,840 --> 00:49:11,080
But it's the fact that all humans
are sensitive to sexual modesty,

750
00:49:11,080 --> 00:49:14,920
even in largely naked cultures,
that convinces Professor Fessler

751
00:49:14,920 --> 00:49:18,120
there's a real biological reason
for it.

752
00:49:18,120 --> 00:49:23,320
He believes it's a direct result
of our large brains.

753
00:49:25,160 --> 00:49:28,440
Our very large brains
in themselves create a problem.

754
00:49:31,240 --> 00:49:34,680
We have a tight fit between
the size of an infant skull

755
00:49:34,680 --> 00:49:36,640
and the size
of a mother's birth canal.

756
00:49:37,720 --> 00:49:40,560
One solution to this is to
take the bun out of the oven

757
00:49:40,560 --> 00:49:42,080
before it's fully baked,

758
00:49:42,080 --> 00:49:46,400
so our infants are born premature
compared to those of many primates.

759
00:49:46,400 --> 00:49:49,880
With their brains
only partly developed at birth,

760
00:49:49,880 --> 00:49:52,880
human babies are helpless
for many years

761
00:49:52,880 --> 00:49:56,720
and this has a major consequence
for human sexual relationships.

762
00:49:56,720 --> 00:50:00,880
What this means is that
essentially human children require

763
00:50:00,880 --> 00:50:02,240
a great deal of care.

764
00:50:02,240 --> 00:50:04,880
Because of this,
the human mating strategy,

765
00:50:04,880 --> 00:50:08,800
if we look at humans around
the world, is one in which often -

766
00:50:08,800 --> 00:50:10,720
not always - but often,

767
00:50:10,720 --> 00:50:15,720
men mate monogamously. At any one
time they have a single partner,

768
00:50:15,720 --> 00:50:17,800
and they raise offspring together.

769
00:50:20,280 --> 00:50:23,400
Pairing for life ensures our babies
get all the care

770
00:50:23,400 --> 00:50:27,000
they need to survive
and pass on our genes.

771
00:50:27,000 --> 00:50:30,240
But it's a high-risk strategy.

772
00:50:32,480 --> 00:50:36,400
Humans are considerably more
social than the average primate.

773
00:50:36,400 --> 00:50:38,640
We live in large populations

774
00:50:38,640 --> 00:50:41,520
and we co-operate with
large numbers of individuals.

775
00:50:42,840 --> 00:50:46,080
This poses a challenge
because those groups, of course,

776
00:50:46,080 --> 00:50:47,760
provide a source of temptation.

777
00:50:49,960 --> 00:50:54,760
Potentially both sexes
can benefit...

778
00:50:54,760 --> 00:50:57,400
by cheating on their partners.

779
00:50:57,400 --> 00:51:02,720
The human body is a supreme
sexual advertisement.

780
00:51:02,720 --> 00:51:06,280
Flaunting it
can send out a dangerous message.

781
00:51:06,280 --> 00:51:09,720
Nudity is a threat
to the basic social contract

782
00:51:09,720 --> 00:51:14,400
because it is an invitation
to defection.

783
00:51:14,400 --> 00:51:18,600
They have exposed their person,
their body and their sexual selves

784
00:51:18,600 --> 00:51:21,160
in a way that presents
an opportunity

785
00:51:21,160 --> 00:51:25,600
for sexual behaviour outside
of the principal union.

786
00:51:30,400 --> 00:51:35,080
Professor Fessler believes the shame
of nudity serves a real purpose.

787
00:51:35,080 --> 00:51:37,720
It encourages us to stay
faithful to our partners

788
00:51:37,720 --> 00:51:41,480
and share the responsibility
of bringing up our children.

789
00:51:46,280 --> 00:51:48,640
It was an interesting experience.

790
00:51:48,640 --> 00:51:51,880
I'd say, up until now the only people
I've really undressed,

791
00:51:51,880 --> 00:51:55,720
probably are ex-partners and my wife
when they've been a little inebriated

792
00:51:55,720 --> 00:51:58,080
and I had to sort of put them to bed.

793
00:51:58,080 --> 00:52:02,480
I thought I would feel like I would
be...the vengeful thing, "Ha-ha!

794
00:52:02,480 --> 00:52:05,720
"I'm in control now,"
but as I said when it came to it,

795
00:52:05,720 --> 00:52:09,840
I...I just wanted to make sure
she was OK.

796
00:52:09,840 --> 00:52:13,280
I felt almost quite empowered
going through that exercise,

797
00:52:13,280 --> 00:52:15,640
sort of being in control
of the whole situation.

798
00:52:15,640 --> 00:52:19,040
And I can, I can sympathise
with the fact that the other guys

799
00:52:19,040 --> 00:52:21,160
might have been feeling quite
uncomfortable

800
00:52:21,160 --> 00:52:24,280
and possibly quite vulnerable
with us going through that motion.

801
00:52:34,000 --> 00:52:36,840
After two days
looking at each other naked,

802
00:52:36,840 --> 00:52:39,560
we're pushing the subjects
way beyond the normal limits

803
00:52:39,560 --> 00:52:40,720
of social acceptance.

804
00:52:42,560 --> 00:52:46,440
In the final test, they will touch.

805
00:52:50,120 --> 00:52:52,760
They're painting the body
into comfort zones.

806
00:52:52,760 --> 00:52:54,080
Green is fine to touch.

807
00:52:54,080 --> 00:52:58,520
Yellow is not
and red is a no-go zone.

808
00:53:02,120 --> 00:53:05,040
But despite the potential
for embarrassment,

809
00:53:05,040 --> 00:53:07,480
our subjects seem to be enjoying
themselves.

810
00:53:10,520 --> 00:53:13,920
If they'd done the body painting
exercise right at the beginning,

811
00:53:13,920 --> 00:53:16,920
it might not have been
all the fun and games

812
00:53:16,920 --> 00:53:19,240
that it seemed to turn out to be
at the end.

813
00:53:19,240 --> 00:53:22,680
It might have been a pretty stressful
and aversive exercise.

814
00:53:22,680 --> 00:53:26,680
I think as the weekend's gone on and
they've gone through these exercises,

815
00:53:26,680 --> 00:53:29,320
they've somewhat
habituated to the stress.

816
00:53:29,320 --> 00:53:31,680
They're more relaxed
and they know each other,

817
00:53:31,680 --> 00:53:35,320
so it's become a more comfortable
and congenial setting overall.

818
00:53:37,600 --> 00:53:42,640
Lucy, a 42-year-old mother,
clearly still has some reservations.

819
00:53:43,720 --> 00:53:49,600
But Brummie Phil, 27-year-old Alex
and especially Kath from Dorset

820
00:53:49,600 --> 00:53:52,400
have become surprisingly
matter-of-fact about nudity.

821
00:53:54,280 --> 00:53:58,240
Their attitudes and inhibitions
have changed,

822
00:53:58,240 --> 00:54:02,320
and this is the crucial thing
about our relationship with nudity.

823
00:54:04,400 --> 00:54:06,480
We're not born with sexual modesty,

824
00:54:06,480 --> 00:54:09,800
so we're free to shift the
boundaries of what's acceptable...

825
00:54:09,800 --> 00:54:11,760
and what is not.

826
00:54:11,760 --> 00:54:14,760
So long as everyone agrees,
we can create new rules

827
00:54:14,760 --> 00:54:18,440
and avoid the risk of offence
just like at a nudist camp.

828
00:54:27,920 --> 00:54:33,280
Within this house, our subjects
have created their own set of rules.

829
00:54:33,280 --> 00:54:39,240
After two days of social nudity,
it's mostly OK.

830
00:54:40,920 --> 00:54:43,040
It's mostly green.

831
00:54:45,920 --> 00:54:48,320
I feel really quite happy, you know,

832
00:54:48,320 --> 00:54:51,280
and...I feel somewhat
more confident now,

833
00:54:51,280 --> 00:54:55,080
also, that I didn't make a woman

834
00:54:55,080 --> 00:54:57,480
feel sort of uncomfortable round me,
you know.

835
00:54:57,480 --> 00:55:00,920
I think if I'd been asked to do
the task any other day,

836
00:55:00,920 --> 00:55:04,160
there'd have been a lot more,
sort of like, red,

837
00:55:04,160 --> 00:55:07,560
red and sort of yellow painting.

838
00:55:07,560 --> 00:55:10,800
I was quite impressed
at his complete cool...

839
00:55:10,800 --> 00:55:13,760
approach to it and the fact
that he was just, you know,

840
00:55:13,760 --> 00:55:17,560
quite nonchalant about the fact that
he didn't mind touching me anywhere,

841
00:55:17,560 --> 00:55:19,120
so that was quite a surprise to me.

842
00:55:19,120 --> 00:55:22,040
I think once you've been painted by

843
00:55:22,040 --> 00:55:24,440
or you've been painting
someone else's body,

844
00:55:24,440 --> 00:55:27,640
that's a pretty big bonding
experience.

845
00:55:30,960 --> 00:55:33,920
At the end of their naked weekend,

846
00:55:33,920 --> 00:55:37,240
our volunteers are finally
comfortable to be nude together.

847
00:55:45,520 --> 00:55:49,560
For scientists, the extreme emotions
that nudity can cause

848
00:55:49,560 --> 00:55:51,760
will always be a paradox.

849
00:55:51,760 --> 00:55:54,880
The irony of human nudity
and hairlessness

850
00:55:54,880 --> 00:55:58,120
is that really it's the apex
of human evolution.

851
00:56:00,280 --> 00:56:05,040
Only humans have moral emotions
such as shame

852
00:56:05,040 --> 00:56:06,840
that enforce cultural standards.

853
00:56:06,840 --> 00:56:10,480
One can think of nudity
and sexual modesty as exemplifying

854
00:56:10,480 --> 00:56:13,760
our uniquely human
emotional morality.

855
00:56:15,200 --> 00:56:18,800
The state of nudity
is the state of being human.

856
00:56:18,800 --> 00:56:23,800
Essentially having a naked skin
and understanding the evolution

857
00:56:23,800 --> 00:56:27,800
of that naked skin is understanding
everything about being human.

858
00:56:27,800 --> 00:56:32,720
For our volunteers,
there's a last chance to reflect

859
00:56:32,720 --> 00:56:34,480
on their naked experience.

860
00:56:36,800 --> 00:56:41,560
Hmm...I'm relieved
that it's all over, firstly.

861
00:56:41,560 --> 00:56:46,280
I was more relieved when he said,
"Put your clothes back on."

862
00:56:49,440 --> 00:56:52,960
The whole sort of terror
of the first experiment

863
00:56:52,960 --> 00:56:55,800
and as that developed and I realised
I was taking my clothes off

864
00:56:55,800 --> 00:56:58,080
in front of what I thought
was just a normal mirror

865
00:56:58,080 --> 00:57:01,440
and the awful realisation that
it was actually a two-way mirror

866
00:57:01,440 --> 00:57:03,800
and there was someone
sat the other side of it,

867
00:57:03,800 --> 00:57:05,760
that was just really terrifying.

868
00:57:05,760 --> 00:57:08,520
This is the first time
we've done something normal

869
00:57:08,520 --> 00:57:09,720
and we're all naked!

870
00:57:09,720 --> 00:57:13,160
To be honest the whole painting
thing, I wouldn't have imagined

871
00:57:13,160 --> 00:57:16,840
something that extreme and the fact
that somebody else had to undress me.

872
00:57:16,840 --> 00:57:20,640
So, yeah, in a way I sort of
exceeded my expectations

873
00:57:20,640 --> 00:57:23,120
because it was more...

874
00:57:23,120 --> 00:57:26,120
bizarre than I imagined it would be,
definitely.

875
00:57:28,240 --> 00:57:33,480
It's just how...how comfortable we
became around each other gradually,

876
00:57:33,480 --> 00:57:39,000
you know, in that, I mean when
we were all nude and everything,

877
00:57:39,000 --> 00:57:42,080
it didn't even occur to me
that they were naked at all.

878
00:57:43,680 --> 00:57:46,240
One thing I think I'll take away
from this weekend

879
00:57:46,240 --> 00:57:51,400
is how actually easy it was to bond
with complete strangers

880
00:57:51,400 --> 00:57:53,880
in what should really be
an artificial environment

881
00:57:53,880 --> 00:57:57,760
and one that should,
by all society's standards,

882
00:57:57,760 --> 00:58:00,240
we should've been uncomfortable with.

883
00:58:04,240 --> 00:58:07,680
Our volunteers ended the weekend
naked together,

884
00:58:07,680 --> 00:58:10,680
but how many will accept
the final challenge -

885
00:58:10,680 --> 00:58:13,040
to leave the privacy of the house?

886
00:58:16,560 --> 00:58:19,080
Six out of eight
step out into the street.

887
00:58:21,440 --> 00:58:25,640
For Lucy and Helen,
even after a weekend of nudity,

888
00:58:25,640 --> 00:58:28,440
this is a step too far.

889
00:58:37,040 --> 00:58:39,720
Subtitles by Red Bee Media Ltd

890
00:58:39,720 --> 00:58:42,400
E-mail subtitling@bbc.co.uk

891
00:59:03,560 --> 00:59:04,520
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