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For millions of years our ape ancestors lived in the trees.
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But then they came down to the ground, and in an evolutionary leap
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that was to advance them over all other species,
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stood up on their hind legs.
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It was a critical stage on the way to becoming modern man.
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But there was an unavoidable consequence to our becoming upright.
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Suddenly the sexual organs were now frontally exposed
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in the male
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and the female. This was to have a profound effect on our
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sexuality then and now. Today, all our lives are affected by
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that one simple anatomical fact.
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I'm a biologist, and this is a program about human courtship.
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But if you think I'm going to be concentrating on
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human sexual behaviour, you'll be wrong.
With the human animal, love
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is much more important than sex.
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But what is love anyway?
Is it purely a human emotion?
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In the animal kingdom,
as you move from group to group
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you find huge variations in the way
sexual behaviour is organized.
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Some animals have gaudy sexual signals.
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Some do not. Some mate for life.
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Most do not. In some species the
males mate with as many
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females as they can cover. In other species
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it's the females that control the time and place of mating.
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Some animals indulge in
elaborate courtship displays.
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Our nearest relatives
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however have little or no courtship.
Some fathers play a
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role in bringing up their young.
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But most offspring are brought up with no paternal help.
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Since the 1950s when I first began
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my studies of chimpanzees at London Zoo,
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I've been fascinated by this species,
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our closest relative. Chimps are in fact, so close that
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we share 98% of our genetic makeup with them. In the wild,
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their courtship is perfunctory to say the least.
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And females may be mated by one male after another. The act of copulation
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lasts only a few seconds,
and the females appear remarkably
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unmoved by the event.
Chimpanzees don't form lasting partnerships
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and the males play little part in raising the young.
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How is it that we humans are so different in this respect?
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I'm on the record as describing human beings
as the sexiest primates alive.
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Now when I said that, people felt I was being provocative,
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but that wasn't the case.
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I was making an accurate scientific statement.
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There are some very specific ways in which human sexuality
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differs from that of our animal relatives.
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And the biggest differences are found in the human female.
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For instance,
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she doesn't advertise when she's fertile.
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Indeed, she may not even know herself when she is. So she sexually
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active all the time and we'll make love even when there's
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no possibility of conception.
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Whereas female primates only come on heat for brief periods,
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the human female has no sexual season. Throughout most of
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her monthly cycle,
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she stays attractive to men and is prepared to mate.
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Indeed, human females are capable of reproduction and remain sexually
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appealing throughout the whole year.
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Not only that, females are sexually responsive through most
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of their pregnancy and can become sexually active again quite
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soon after giving birth.
Indeed human females can stay sexually
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active for a large part of their adult lives. Frequently for
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more than half a century.
Human males experience a sexual
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climax similar to that of other primates, but unusually,
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the human female also experiences an intense orgasm.
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The phases of human courtship and the sexual act itself are
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all much longer, more elaborate
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and more intense than in any other primate.
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This extended sexuality isn't some sort of cultural decadence.
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It's a basic biological characteristic of our species.
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Why have we abandoned the 8-second mating act of the typical baboon.
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Finding the answer to this question was the task.
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I set myself back in the early 1970s when I began work on
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my book
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Intimate Behaviour.
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I called it Intimate Behaviour because I wasn't just looking
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at human sexuality,
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I was looking at the whole subject of loving relationships.
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Now, we all talk a lot about love,
but very few of us
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stop to analyse it scientifically.
I suppose we feel if we do that,
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we'll somehow destroy the magic.
But that's not the case.
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In fact, the more we understand love,
the more fascinating
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the subject becomes. But how does it all begin?
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How does boy meet girl?
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When children stop being toddlers and go to school,
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something strange happens. All over the world
a major split now occurs
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between the sexes.
Boys gather together in gangs. And girls
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keep to themselves in all female groups. And the groups are
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not really separate,
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they're often actively hostile to one another.
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This is an important step in sexual development.
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In this pre sexual phase, young males
and females must become strangers
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to one another so that, when puberty arrives, they can forge
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an entirely new kind of relationship.
One in which undue familiarity
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does not dull the excitement of discovery.
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The all-male and all-female groups start to lose their mutual
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hostility and replace it with mutual curiosity.
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The new attachments are powerful,
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but so too is the sense of belonging to one's old gang.
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But sooner or later, the childhood gangs will lose this unequal
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struggle for loyalty.
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A new activity now arrives on the scene. Parading.
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All over the world, young adults can be observed gathering together
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in large informal groups.
On sea fronts, parks, High streets
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or clubs.
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The main preoccupation is simply making visual contact with
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as many members of the opposite sex as possible.
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Parading leads to a more direct
display of interest. This bolder eye
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to eye contact is the first step
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on the lengthy sequence of human courtship.
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During this phase, primeval sexual influences are at work below
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the surface. Careful research in certain nightclubs
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has revealed that the closer girls are to their moment of ovulation,
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the skimpier their costumes will be. Their display
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of naked flesh is unconsciously dictated by their physiology.
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For some young males, this visual phase of mate selection
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becomes an exciting game to be relished and refined.
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Here, it's skillfully played out on scooters in the streets of Rome.
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In this purely visual stage of courting a mate,
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decisions can be made in an instant, within the glance of an eye.
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The brain has evaluated hundreds of pieces of visual information
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and has made a judgment.
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She's attractive or she's not.
He likes her or he does not.
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Some of her signals
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he will understand consciously.
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Others, he'll be reacting to without even realising it.
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So what are these sexual signals?
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What does the human animal see as sexy?
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Throughout the animal kingdom, males are attracted to females who
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transmit signals of health and fertility. Positive signals
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of potential childbearing and child-rearing.
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The same is true for human males.
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Even if breeding success is farthest from their minds when
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they look at a passing female,
it still influences their feelings
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towards her.
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It's the same for human females.
When they look at males,
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their ancient impulses encourage them
to seek out signs of masculine power
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and strength, indications of protective prowess.
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Although health and vigour are important displays for both sexes,
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many human sexual signals are specific to one gender or the other.
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Some of these gender signals are obvious enough, such as the
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broader shoulders of the male or the narrower waist of the female.
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The smooth skin and
soft roundedness of the female body,
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and of course the high-pitched voice,
are juvenile qualities
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making males feel protective.
The thick neck, facial hair, deep voice
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and muscular torso of the male offer a strong visual
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contrast saying I'm a protector.
Many male costumes exaggerate
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these gender signals.
Male shoulders are widened by padded jackets,
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or even further enlarged by adding epaulets,
or huge shoulder pads.
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And sometimes by extraordinary ritualistic costumes
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like these deliberately imposing uniforms of these Tibetan Monks.
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Emancipated females who wish to be more assertive
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in modern society mimic the broad torso look when they power dress.
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For the fashion industry, manipulating all these visual signals,
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improving our nature, becomes a matter of professional expertise.
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What I'd like to do Phillip, I'd like to dilate
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her pupils, to open them up more and to make her irises green
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to change them from brown to green and clean
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the whites of her eyes
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so her eyes are going to stand out much more. We could put a mask
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over the whole eye, lighting the eye out a little bit and
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then put the green in. Yes, that's the green looks great.
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By making the irises paler,
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they contrast more with the black of the pupil.
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So when the pupil itself is artificially enlarged, the impact
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is even greater. Enlarged pupils are a normal reaction to sexual arousal.
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So they are unconsciously appealing.
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The whiteness of the whites of the eyes is associated with
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youthful health and vigour.
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So this is also exaggerated.
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Now she has super eyes, but what about the rest of the face?
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Let's, let's clean up first the little crease marks just here
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on the edge of her lips.
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Again, a flawless complexion indicates health and the inherent
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sexuality of youthfulness.
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That's why any small crease lines are so carefully removed.
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I kind of like this colour here.
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That would be good, more red.
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Just bring out the muscular.
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The lips are made slightly more red,
imitating the change
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in colour that occurs during sexual arousal.
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So if we now just do a colour correction
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to bring all of the skin,
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I'd like all her skin just to be a little richer
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and the skin colour is warmed up a little
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to create the impression of a healthy sexual glow.
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That's perfect.
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That's perfect.
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We've got it.
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So what I want to do here is to stretch her legs along quite
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considerably maybe as much as 20% really we need to go through
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the legs stretching the thigh bone and the shinbone more.
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Less stretch on the feet and the knees so that we keep
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it as realistic as possible while making it as languid and
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as long as possible.
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Exaggerated leg length is an important
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sexual signal, especially in females.
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This is because the legs grow longer in relation to the rest
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of the body as puberty approaches.
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So super long legs means super adultness,
and therefore super sexuality.
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Tiny bit more.
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Yeah, let's see a before and after. Yeah, that's great.
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That's great.
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That's long. Doesn't look too unrealistic and good proportions.
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When people meet there are many ways in which
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they can transmit sexual signals.
With a smile, of course.
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And for long-haired individuals, the unconscious grooming
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of the hair, which says in effect,
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look I'm making myself more attractive, more appealing for you.
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Then there's that human speciality made possible by
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our naked skin, the blush. This blushing of the visible skin
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as a social signal is superficially similar to the flushing that
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occurs in the final stages of lovemaking. The blush starts
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at one spot in the centre of each cheek and then spreads
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to cover the whole of the face, the neck and even the upper torso.
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To the male onlooker,
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this skin change is strangely attractive because it
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of its implied innocence. It has a virginal quality that appeals
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to him.
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The use of a so-called blusher in modern makeup, supposedly
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to highlight the cheekbones, mimics the start of a blush and
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inevitably acquires some of its appeal.
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The rounded hemispherical breasts of the human female transmit
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a powerful sexual signal unique to our species. Monkeys and apes
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are completely flat chested when they're not giving
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milk to their young. But the human female retains her swollen breasts
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throughout her adult life.
Breasts may have a maternal function,
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but their shape is purely sexual in significance.
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This breast shape appears to have evolved
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as a mimic of the rounded buttocks.
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Most female primates' sexual signals occur
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in the rump region, but in our species with its vertical body posture,
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it was necessary to have a frontal display as well.
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If you think that's far-fetched,
just look at these two cleavages
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to see how similar the shapes are.
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Great.
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Milder sexual signals are also transmitted by the rounded
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female shoulders, and the smooth rounded knees, again providing
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visual echoes of the primeval buttock display.
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Another form of self mimicry. The large female lips in both
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shape and colour mimic the external genitals. When the labia
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redden during sexual arousal, the lips also become swollen
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and redder, a change artificially heightened by the application
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of lipstick. A cultural exaggeration that's been employed
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by women since the days of ancient Egypt.
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When it comes to the basics of
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sexual attraction,
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we may be animals, but we can be very sophisticated animals.
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We have a conscious perception of what is beautiful
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and what is sexy, as well as a biological one.
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And one culture's ideal of beauty can differ greatly from another's.
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In the West for example, a slender figure is considered especially
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attractive for females.
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And a moderately muscular frame is preferred for males.
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In contrast, among the Maasai of East Africa, an incredibly
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slim figure which, to us, looks almost effeminate, is the epitome
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of masculine beauty. This contrasts strikingly with the much
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heavier body that spells beauty in many of the islands of
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the South Pacific, where it applies to both males and females.
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Wherever you look as you go around the globe, there are local
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beauty standards that are sometimes strange to foreign eyes.
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They're often too subtle to be appreciated by outsiders,
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but of enormous importance within the societies concerned.
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For instance among the Toga of Southern India, female hairiness
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is especially appealing to men.
Even to the extent of heavy
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female eyebrows.
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But although beauty standards do vary around the world,
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there are a few universals that apply to the whole human species.
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The outline of the adult male body for instance.
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To be sexually appealing, the male needs to have a triangle
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formed by wide shoulders above a narrow waist.
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To females, another important male signal, is a compact muscular behind.
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Perhaps because of its sexual thrusting power.
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Male muscularity in general is appealing.
But the dividing line between the
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well-muscled and the muscle-bound is a fine one.
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Because an over cultivated physique implies vanity.
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By contrast, a flabby body lacks the key signals.
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Another quality that has universal sex appeal, is youthfulness.
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Sex drive and fecundity are at their highest levels among
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the youngest adults. The male sex drive peaks at the age of 18,
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and the females fecundity, at 22.
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When a survey of sexual appeal was made in 190 different
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societies around the world.
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It was discovered that the most important feature common
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to all cultures was a healthy body and a clear unblemished skin.
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Beyond the eyeing up stage,
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we come to the next phase of the human courtship sequence.
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The pickup.
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How do people break the ice?
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Well a useful device is the cultivation of the lucky accident.
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Some irrelevant completely non-sexual factor, like exercising
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the dog is introduced into the equation.
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The individuals involved are not actively seeking a partner,
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that would be too obvious.
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Instead, they're engaged in a common pursuit which just happens to
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bring them together.
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More formal meetings between young people offer an opportunity
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to parade, eye up, display and pick up, all at the same time.
300
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These young Maasai males show off their prowess by leaping up and down
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in their vertical dance.
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They're watched discerningly by the young girls of the village,
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who, even at this tender age are already deeply involved in
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the exciting business of mate selection.
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The hair flick signals the interest of a male in a particular female.
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All around the world new connections are being made.
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New links are being forged, as friendly words take over from
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shy glances.
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We've arrived at the chatter.
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This is the information exchange phase in which people find
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out as much as possible about one another's backgrounds,
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their likes and dislikes. This reciprocal
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detective work may take some time,
but it's a vitally important
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process when embarking on a long-term breeding partnership.
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00:23:24,400 --> 00:23:27,700
In this particular region of modern China, the young men and
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women have a traditional way for overcoming the greatest
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problem of the chat up, shyness.
Instead of simply mingling
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and chatting.
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They keep apart and sing their conversation
from one group to another.
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They might sing about their personal skills
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or bravery which can cause a lot of amusement.
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The reply might be about property.
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The number of tractors in their village for instance.
324
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In the bars of Los Angeles, the chat up technique, like the
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clothing, is much more casual. But it works well enough.
327
00:24:57,900 --> 00:24:58,900
328
00:25:06,100 --> 00:25:09,500
Here, contact has been made, and personal involvement
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has begun. Now talking becomes the key activity.
330
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Any inconsequential chatter keeps the conversation
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going, while the opportunity is taken to slip in important questions.
332
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What's the other's marital status?
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00:25:32,400 --> 00:25:36,500
What is his or her job?
In other words, apart from looks,
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what extra benefits could each bring with them to a relationship.
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Having received sufficient encouragement,
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he can now move in closer, and is rewarded with the first bodily contact.
337
00:26:02,600 --> 00:26:04,700
The problem now is to get rid of one of his new
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companions, so that he can end up in a twosome.
339
00:26:07,200 --> 00:26:10,600
But this time, he fails, and they both say goodbye.
340
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Perhaps next time?
It's not easy finding the ideal partner
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00:26:19,100 --> 00:26:22,600
and there'll be many false starts before the blend is right, but
342
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once it is, we see a whole new phase developing, characterised
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surprisingly, by what appears to be a return to infancy.
344
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Couples cuddle and caress one another,
345
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call each other silly names,
talk in high-pitched voices and
346
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even rock together in one another's arms.
347
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This is the stage
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we usually refer to as falling in love.
349
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Dave loves Sue. Joe loves Kim.
Love. What is love?
350
00:27:02,200 --> 00:27:05,800
Perhaps it's just a polite word for sex.
A romantic way of describing
351
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sexual attraction. Well it isn't.
It's much more than that.
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Love is a basic biological mechanism and it has a very specific function.
353
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The first time we encounter love is as tiny babies.
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This is the age of total security, protection and trust.
355
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But even at this early stage, another urge is beginning to
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express itself. The urge to strike out on one's own.
357
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And the process of growing up is the process of this new
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urge gradually asserting itself, as the need for maternal
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protection grows weaker.
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When the infant becomes a teenager, the urge for independence
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gains the upper hand, and the bond between parent and child starts
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to collapse. Eventually, in what turns out to be a more traumatic event
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than either parent or teenager had expected, comes the
364
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moment of first true separation.
Here, the first day at College
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00:28:18,500 --> 00:28:21,300
churns up the emotions as one long-term
366
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love bond slips
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into the past tense, and the prospects of a brand new one are
368
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about to appear on the horizon.
369
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It's an intriguing fact, that for a new couple, the first evening
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00:28:35,200 --> 00:28:40,200
out together usually involves food and drink. We tend to take this for granted,
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but there may be a special, deeper reason.
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It's almost as if, as with many bird species,
humans indulge in courtship feeding.
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A hidden camera catches this couple at
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the very start of just such a dinner date.
As the meal progresses,
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their growing intimacy happens as we watch.
376
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They start smiling and leaning forward, not taking their eyes off one another.
377
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Now the first touch, leading to a gentle hand kiss.
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And now, like two parents with small infants they each
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spoon feed the other.
380
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Finally, again like courting birds, a gift is offered.
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The encounter comes to an end.
In this familiar event,
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we are in reality seeing not only pseudo parental feeding,
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but also the reenactment of a primeval exchange deeply embedded
384
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in our species after a million years as hunter-gatherers.
385
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Food sharing, which in primeval times was the very basis of
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human society.
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00:31:19,400 --> 00:31:22,400
As the sexual attachment of the couple increases, we see
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them displaying a variety of what a called tie signs.
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00:31:26,400 --> 00:31:29,600
These are forms of body contact that tell other people that
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an exclusive pair is forming.
391
00:31:32,200 --> 00:31:35,200
So while they reinforce the closeness of the couple,
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they also serve to exclude us from that relationship.
393
00:31:40,500 --> 00:31:42,500
There's the arm around the shoulder.
394
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This is not yet particularly intimate, but there are other
395
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tie signs that will show a gradually increasing mutual trust
396
00:31:49,500 --> 00:31:54,000
between the couple. The arm around the waist.
397
00:32:00,200 --> 00:32:05,300
The double embrace, and next in increasing intimacy, rather unexpectedly,
398
00:32:05,500 --> 00:32:09,000
the contacts move up towards the head region. Because of the
399
00:32:09,000 --> 00:32:09,900
sense organs there,
400
00:32:09,900 --> 00:32:13,300
this is a highly protected area, available only to our most
401
00:32:13,300 --> 00:32:14,700
trusted companions.
402
00:32:22,100 --> 00:32:25,300
With the knee touch, the contacts begin to approach the most
403
00:32:25,300 --> 00:32:26,800
intimate region of the body.
404
00:32:33,500 --> 00:32:35,400
There are two particular aspects of human anatomy
405
00:32:35,400 --> 00:32:38,900
that make us sexually very different from most other animals.
406
00:32:39,600 --> 00:32:40,700
First,
407
00:32:40,800 --> 00:32:44,700
we have near-naked skins, and we've used that nakedness to
408
00:32:44,700 --> 00:32:47,800
gain an additional source of intimate stimulation.
409
00:32:47,800 --> 00:32:50,000
Something denied to our hairier cousins.
410
00:32:52,900 --> 00:32:55,600
There's another sexual difference between us
and our animal relatives.
411
00:32:55,600 --> 00:32:59,900
All male monkeys and apes, and indeed
412
00:32:59,900 --> 00:33:03,000
most male mammals have what is called an "os" penis.
413
00:33:03,000 --> 00:33:04,400
This is a penis bone,
414
00:33:04,400 --> 00:33:08,700
and this is one from inside the penis of a walrus.
415
00:33:09,400 --> 00:33:14,400
And this tiny one here is from the penis of a hedgehog.
416
00:33:15,600 --> 00:33:18,700
The function of this bone is to produce an instant erection
417
00:33:18,700 --> 00:33:21,100
the moment that a male approaches a female sexually.
418
00:33:21,100 --> 00:33:23,300
The loss of this bone
419
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in the human male means that his female has to arouse
420
00:33:25,900 --> 00:33:28,600
him strongly before he can penetrate her.
421
00:33:28,700 --> 00:33:32,900
This means that human pre copulatory behaviour becomes much
422
00:33:32,900 --> 00:33:35,000
longer and much more sensuous.
423
00:33:40,600 --> 00:33:45,300
So sex in humans has evolved to be more than merely procreative.
424
00:33:46,300 --> 00:33:49,900
By becoming increasingly pleasurable, less automatic,
425
00:33:49,900 --> 00:33:52,100
it's more subtle and more complex.
426
00:33:55,600 --> 00:33:59,800
And in its final stages, courtship becomes even more prolonged
427
00:33:59,800 --> 00:34:01,300
and intensely erotic.
428
00:34:08,690 --> 00:34:13,100
This is not some modern sophistication.
Evolution has programmed us
429
00:34:13,100 --> 00:34:17,400
for this extended body intimacy. For this skin to skin contact.
430
00:34:17,400 --> 00:34:21,500
Using it as a means of strengthening the attachment
431
00:34:21,500 --> 00:34:25,500
of the male and the female for one another.
432
00:34:25,690 --> 00:34:28,800
An attachment that will become biologically very important for them
433
00:34:28,800 --> 00:34:32,800
in the new role they're about to play.
434
00:34:38,900 --> 00:34:41,500
In animal behaviour terms, they've pair-bonded.
435
00:34:41,500 --> 00:34:45,000
That's what love is. The formation of a lasting pair bond.
436
00:34:45,400 --> 00:34:49,690
But what's its function? For true understanding of human sexuality,
437
00:34:50,100 --> 00:34:53,100
we have to look at our children.
At the progeny that result
438
00:34:53,100 --> 00:34:54,400
from the sexual act.
439
00:34:56,400 --> 00:34:59,300
As with other monkeys and apes, our offspring, as we all know,
440
00:34:59,600 --> 00:35:03,700
are nurtured inside the female body, but unlike other monkeys
441
00:35:03,700 --> 00:35:07,800
and apes, human babies are totally helpless at birth.
442
00:35:07,800 --> 00:35:11,800
The human baby now goes through 10, perhaps 15 or more years of being
443
00:35:11,800 --> 00:35:13,300
dependent on its parents.
444
00:35:14,000 --> 00:35:17,700
It's a task beyond the resources of a single parent.
445
00:35:17,700 --> 00:35:21,200
Perhaps not in today's welfare state, but certainly in any primeval society.
446
00:35:21,200 --> 00:35:26,000
So they have to be two and there has to be a biological
447
00:35:26,200 --> 00:35:28,800
function to keep the couple together in the interests of the child,
448
00:35:28,800 --> 00:35:34,300
and that mechanism is the pair bond. Nearly all societies
449
00:35:34,300 --> 00:35:37,500
encourage some sort of official reinforcement of the pair bond.
450
00:35:37,500 --> 00:35:47,100
Typically a wedding ceremony. Whether the wedding is highly
451
00:35:47,100 --> 00:35:54,100
traditional, or more flamboyantly modern. Whether it's a protracted
452
00:35:54,100 --> 00:35:55,900
event full of ancient rites.
453
00:35:57,700 --> 00:36:00,000
Or merely, a drive-in quickie.
454
00:36:00,300 --> 00:36:02,800
It always carries the same public message.
455
00:36:02,800 --> 00:36:06,500
Namely we're an exclusive couple now. Hands off.
456
00:36:18,400 --> 00:36:21,800
Even in an arranged marriage, where love has played no part so far.
457
00:36:21,800 --> 00:36:26,700
This muslim man, who's never seen his bride before
458
00:36:26,700 --> 00:36:30,100
his wedding day is saying to the world when he touches her hand,
459
00:36:30,400 --> 00:36:32,900
from now on, we two are unavailable
460
00:36:32,900 --> 00:36:34,800
for pair bonding with anyone else.
461
00:36:42,700 --> 00:36:46,100
And so at last the final stage of the pair bonding process.
462
00:36:46,300 --> 00:36:49,800
The sexual act itself. For those who have enjoyed the natural
463
00:36:49,800 --> 00:36:51,300
process of falling in love,
464
00:36:51,400 --> 00:36:55,100
it's the end of the long courtship sequence. And the mating act too,
465
00:36:55,100 --> 00:36:58,800
is long and intense. Because in our species it's not
466
00:36:58,800 --> 00:37:02,800
concerned merely with procreation, but with mutual sexual rewards.
467
00:37:03,500 --> 00:37:07,100
The first tender caresses are made more exquisite
468
00:37:07,200 --> 00:37:11,500
by the suddenly super sensitive skin.
The first of many physiological
469
00:37:11,500 --> 00:37:16,400
changes that now take place. Lips becoming swollen and sensitive.
470
00:37:17,900 --> 00:37:22,500
Eyes glistening as a film forms across their surface.
471
00:37:22,500 --> 00:37:25,200
Pupils dilating to become huge dark pools.
472
00:37:29,400 --> 00:37:32,300
Respiration increases dramatically as the body starts to
473
00:37:32,300 --> 00:37:36,000
need quantities of oxygen for the vigourous physical actions involved.
474
00:37:37,000 --> 00:37:41,200
The nostrils flare as the respiration rate increases
475
00:37:41,200 --> 00:37:47,100
to nearly four times the normal speed. More and more air is
476
00:37:47,100 --> 00:37:49,800
drawn into the body where the lungs begin to pump harder
477
00:37:49,800 --> 00:37:51,200
and harder.
478
00:37:55,500 --> 00:38:00,900
The heart beats faster as the body embarks on a wholesale redistribution of
479
00:38:00,900 --> 00:38:01,900
the blood supply.
480
00:38:05,100 --> 00:38:09,000
Inside the arteries, natural body chemicals have been released
481
00:38:09,000 --> 00:38:14,100
that produce feelings of euphoria and elation.
Blood is pumped from the internal organs
482
00:38:14,100 --> 00:38:16,200
through the arteries to the veins
483
00:38:16,200 --> 00:38:18,900
and capillaries near the surface of the skin.
484
00:38:29,600 --> 00:38:33,300
Sweat glands open, supplying copious perspiration as a cooling agent,
485
00:38:33,300 --> 00:38:37,600
and also as a source of personal scent which unconsciously
486
00:38:37,600 --> 00:38:41,100
stimulates the partner. The whole body becomes much hotter
487
00:38:41,100 --> 00:38:44,500
to the touch and waves of heat can be seen escaping from
488
00:38:44,500 --> 00:38:46,400
the skin and the open mouth.
489
00:38:54,200 --> 00:38:57,800
A heat-sensitive camera reveals the developing pattern of
490
00:38:57,800 --> 00:39:00,800
body heat. The red areas being the hotter ones.
491
00:39:01,500 --> 00:39:05,500
They spread around the face. The soft erectile tissue on the
492
00:39:05,500 --> 00:39:07,800
side of the nose, an erogenous zone.
493
00:39:09,700 --> 00:39:13,600
The lips swollen with blood becoming increasingly hot to
494
00:39:13,600 --> 00:39:14,400
the touch.
495
00:39:16,300 --> 00:39:21,000
The earlobes, another erogenous zone, and eventually,
496
00:39:21,000 --> 00:39:21,700
the whole of the head.
497
00:39:28,500 --> 00:39:29,800
Lower down on the body,
498
00:39:29,900 --> 00:39:32,900
it's possible to see the genital region of the female becoming
499
00:39:32,900 --> 00:39:37,400
intensely heated as sexual arousal progresses and the labia
500
00:39:37,400 --> 00:39:38,600
engorge with blood.
501
00:39:46,800 --> 00:39:49,600
The female breast enlarges dramatically during sexual intercourse,
502
00:39:49,600 --> 00:39:55,200
increasing its size by up to 25%. Blood is pumped
503
00:39:55,200 --> 00:39:58,400
into erectile tissues faster than it can be pumped away.
504
00:40:02,900 --> 00:40:06,400
The nipples swell and become extra sensitive, increasing in
505
00:40:06,400 --> 00:40:08,800
height by as much as one centimetre.
506
00:40:13,200 --> 00:40:16,900
The penis also become swollen and stiffly erect.
507
00:40:16,900 --> 00:40:18,700
Doubling its normal length in the process.
508
00:40:19,800 --> 00:40:22,400
The erect penis is a marvel of fluid mechanics.
509
00:40:22,400 --> 00:40:26,500
The erection is caused by a rush of blood in, up to 60 times
510
00:40:26,500 --> 00:40:29,700
the normal level, and a simultaneous reduction in blood flow out
511
00:40:29,700 --> 00:40:31,800
that helps to maintain it.
512
00:40:35,300 --> 00:40:38,700
At high intensities of arousal, a sex flush appears on the
513
00:40:38,700 --> 00:40:43,100
female body and the shared experience of lovemaking is ultimately
514
00:40:43,100 --> 00:40:48,000
to be reinforced by the orgasm. As the man's muscles spasm,
515
00:40:48,200 --> 00:40:49,800
on his face is portrayed not pleasure,
516
00:40:49,800 --> 00:40:53,700
but surprisingly pain, caused by the extreme physical intensity
517
00:40:53,700 --> 00:40:58,400
of the moment. The male orgasm fulfills its biological function
518
00:40:58,600 --> 00:41:02,300
to deliver a pool of ejaculate inside the vagina, as close
519
00:41:02,300 --> 00:41:03,700
as possible to the cervical aperture.
520
00:41:03,900 --> 00:41:04,200
521
00:41:12,000 --> 00:41:15,000
With a mating act as intense as that, one might imagine that
522
00:41:15,000 --> 00:41:17,700
the human pair bond would be safe for life.
523
00:41:17,700 --> 00:41:20,100
But as we all know, this is not the case.
524
00:41:29,800 --> 00:41:30,900
So what goes wrong?
525
00:41:40,100 --> 00:41:43,200
One of the problems of modern life, is that it puts undue demands
526
00:41:43,200 --> 00:41:46,400
on a breeding system that evolved to operate in small
527
00:41:46,400 --> 00:41:49,600
tribal communities where males are only away from their females
528
00:41:49,600 --> 00:41:53,900
for short periods of time.
Today, separations may be much longer.
529
00:42:03,300 --> 00:42:06,700
The pair bond evolved to protect the husband and wife and
530
00:42:06,700 --> 00:42:10,300
the offspring at just such times of conflicting emotion and vulnerability.
531
00:42:12,300 --> 00:42:15,100
But the pair bond is not a perfect system.
532
00:42:19,300 --> 00:42:23,100
Appealing members of the opposite sex may attract a roving eye,
533
00:42:23,100 --> 00:42:27,500
causing repeated conflict of loyalty, even if only in
534
00:42:27,500 --> 00:42:29,200
thought rather than deed.
535
00:42:30,300 --> 00:42:31,900
In complex societies,
536
00:42:32,200 --> 00:42:35,500
there's a temptation to experiment with new sexual experiences
537
00:42:35,700 --> 00:42:39,200
and to stray from the narrow confines of a single pair bond.
538
00:42:42,500 --> 00:42:46,100
Adultery and adulterers have been common throughout history.
539
00:42:46,800 --> 00:42:49,100
The advantage to the male is clear enough.
540
00:42:49,400 --> 00:42:52,900
He may be a caring husband and a good father, but he also
541
00:42:52,900 --> 00:42:57,100
gains from scattering his genetic material over a wider range.
542
00:42:57,600 --> 00:43:00,500
Through his additional offspring his genes will go marching on.
543
00:43:00,500 --> 00:43:05,100
The risk he runs, is that if he's found out, he may damage
544
00:43:05,100 --> 00:43:07,900
his pair bond and disrupt the rearing of his children.
545
00:43:13,600 --> 00:43:15,900
When it's discovered, an adulterer is nearly always attacked
546
00:43:15,900 --> 00:43:19,600
by society and feelings of guilt can become intense.
547
00:43:20,300 --> 00:43:23,300
You are also accused I use the word accused because no one likes it.
548
00:43:23,300 --> 00:43:24,300
of being a womanizer.
549
00:43:24,300 --> 00:43:25,900
What do they mean by a womanizer?
550
00:43:27,600 --> 00:43:29,700
They mean that I wasn't faithful, to my wife.
551
00:43:29,900 --> 00:43:30,500
Was that true?
552
00:43:30,600 --> 00:43:31,000
Yes.
553
00:43:32,300 --> 00:43:33,500
Did you stop that?
554
00:43:35,100 --> 00:43:39,200
Yes, I don't think it's something I want to talk a great
555
00:43:39,200 --> 00:43:39,900
deal about.
556
00:43:41,400 --> 00:43:45,200
Of course females may stray from the pair bond as well as males.
557
00:43:48,200 --> 00:43:50,100
Among the Wodaabe Nomads in Niger,
558
00:43:50,300 --> 00:43:55,000
this married man is meeting this married woman. In this tribe.
559
00:43:55,000 --> 00:43:58,400
it's accepted as a woman's right that if she's not satisfied
560
00:43:58,400 --> 00:43:59,400
with her own husband,
561
00:43:59,500 --> 00:44:04,100
she can go off with someone else's.
In most societies, this pattern of behaviour
562
00:44:04,100 --> 00:44:06,800
is strongly attacked. But its existence
563
00:44:06,800 --> 00:44:10,100
suggests that their must be some genetic advantage for
564
00:44:10,100 --> 00:44:13,000
an adulterous female, as well as for an adulterous male.
565
00:44:13,200 --> 00:44:14,300
What could that be?
566
00:44:14,700 --> 00:44:15,900
She can't scatter her genes
567
00:44:16,200 --> 00:44:17,800
like an unfaithful male.
568
00:44:18,100 --> 00:44:19,900
So what can she gain from it?
569
00:44:26,800 --> 00:44:30,500
To understand this we must return to the moment of the orgasm.
570
00:44:35,200 --> 00:44:39,500
When the male ejaculates, a sperm pool is deposited near to
571
00:44:39,500 --> 00:44:43,700
the cervix, the entrance to the womb.
The female usually takes
572
00:44:43,700 --> 00:44:45,800
a little longer to reach her orgasm.
573
00:44:46,200 --> 00:44:49,000
But when she does, it's just as intense.
574
00:44:51,200 --> 00:44:54,900
Her muscular contractions
spread through the genital region
575
00:44:55,300 --> 00:45:00,400
to the cervix itself.
And seen here on film for the first time
576
00:45:00,400 --> 00:45:04,500
these contractions help to dip the mouth of the uterus
577
00:45:04,500 --> 00:45:07,100
repeatedly into the sperm pool.
578
00:45:07,700 --> 00:45:11,800
And in this way, increase the chances of fertilisation.
579
00:45:13,400 --> 00:45:17,200
It's now thought that by varying the timing of her orgasms,
580
00:45:17,400 --> 00:45:20,700
the human female can increase or decrease her chances of
581
00:45:20,700 --> 00:45:24,000
fertilisation by the sperm of any particular male.
582
00:45:25,500 --> 00:45:28,900
If unfaithful, she could for instance favour the sperm of a
583
00:45:28,900 --> 00:45:32,600
young healthy lover, while continuing to gain protection from
584
00:45:32,600 --> 00:45:35,400
a powerful older husband.
585
00:45:35,600 --> 00:45:38,800
Intriguingly her husband's sperm have their own secret answer to this.
586
00:45:38,900 --> 00:45:44,100
It's what we might call sperm wars.
It's usually imagined that
587
00:45:44,100 --> 00:45:47,400
all the millions of sperm deposited by the male are struggling
588
00:45:47,400 --> 00:45:50,700
to fertilise the egg, but new research has proved that this
589
00:45:50,700 --> 00:45:54,900
is not the case. Only a small proportion of them are actual
590
00:45:54,900 --> 00:45:59,300
egg seekers. The rest have another task.
They ignore the egg,
591
00:45:59,300 --> 00:46:02,900
because it's their job to fight a rearguard action, to destroy
592
00:46:02,900 --> 00:46:05,500
any foreign sperm that may arrive on the scene.
593
00:46:07,100 --> 00:46:09,900
There are two kinds of these protective sperm.
594
00:46:10,200 --> 00:46:13,800
The first are active ones that search for and kill alien sperm,
595
00:46:13,800 --> 00:46:19,900
but they have no interest in finding the egg.
596
00:46:19,900 --> 00:46:23,500
New research suggests that a man can unconsciously control the numbers
597
00:46:23,500 --> 00:46:24,300
of these killer sperm
598
00:46:24,400 --> 00:46:27,700
in his ejaculate and that would depend on whether or
599
00:46:27,700 --> 00:46:28,600
not he believed
600
00:46:28,600 --> 00:46:32,200
he was the first or second male to mate with a particular woman.
601
00:46:32,200 --> 00:46:34,900
Here's one in action.
602
00:46:40,300 --> 00:46:44,000
This is chemical warfare, again filmed for the first time,
603
00:46:44,600 --> 00:46:47,900
and when the two sperm separate one is left dead.
604
00:46:57,600 --> 00:47:00,100
Other protective sperm are more passive.
605
00:47:00,100 --> 00:47:04,500
These are the blockers. They swim little, but curl their tails are
606
00:47:04,500 --> 00:47:08,500
interlock them. Massing together to form a barrier against invaders.
607
00:47:09,500 --> 00:47:13,000
They will let later sperm from the same male pass but block
608
00:47:13,000 --> 00:47:15,300
the way of sperm from other males.
609
00:47:15,700 --> 00:47:19,500
It's a kind of internal chastity belt which presumably will
610
00:47:19,500 --> 00:47:22,900
not have evolved without some promiscuity to counter
611
00:47:22,900 --> 00:47:24,200
in the first place.
612
00:47:27,300 --> 00:47:31,900
Drenched in a film of sweat, the lovers rest. Now mutually
613
00:47:31,900 --> 00:47:35,800
rewarded through their shared orgasms. Inside the woman's body,
614
00:47:35,800 --> 00:47:37,700
the sperm are active.
615
00:47:38,100 --> 00:47:40,900
Some will be starting their marathon journey in search of an egg.
616
00:47:40,900 --> 00:47:44,600
Others will be standing guard, needed or not.
617
00:47:45,700 --> 00:47:48,500
Promiscuity is a high-risk strategy for the human-animal.
618
00:47:49,000 --> 00:47:52,600
On balance, we're better off less stressed with our pair bonds.
619
00:47:52,600 --> 00:47:57,900
Even today, 99% of humans live in a pair bond.
620
00:47:59,100 --> 00:48:02,400
It's the fundamental condition of the human species.
55575
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