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First off, I would like to just introduce
attractiveness a little bit to you.

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Especially thinking about

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why should we even bother
thinking about attractiveness?

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Well, first, psychological research
has shown that people largely agree

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on who is attractive
or who is perhaps, less so.

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So I'm pretty sure
most of you in this room would agree

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that Angelina Jolie is perhaps
somewhat more attractive than Ugly Betty.

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And this perception of attractiveness
even hold universally.

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So even if you went
to a very different culture,

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people would probably still agree
that Angelina Jolie is more attractive.

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In addition to this, work in psychology
over the last two decades or so

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has shown that attractiveness
has advantages

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over and above perhaps getting bought
a drink in a bar on a night out.

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And specifically,
these advantages include things

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like being seen as more honest,
more socially competent,

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more successful, more trustworthy,
friendlier, and even smarter.

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And that last bit is quite important
because even in your career,

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your attractiveness levels matter.

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And this holds by the way
for men just as much as for women.

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If you are more attractive,
you are more likely to have a good career.

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Being attractive literally pays.

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And we call this the Halo Effect,

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which means that simply
because you look a certain way,

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people make all sorts of attributions
about what you're like.

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And while that might seem
a little bit gloomy for some,

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there's actually a flip side to this coin

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which is: can you make yourself
more attractive?

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I'm not talking about
going and getting plastic surgery,

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or going to a salon and paying
for very expensive beauty treatments.

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I'm talking ... - oh, not about that! -
I'm talking about changing your health.

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With that in mind, I'd like to turn
to the animal kingdom for a moment.

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You can see these beautiful birds on here,

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and they have something in common
which is that they are all colorful;

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and these colours aren't just there
for us to think of them as beautiful

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But they're actually signals
that they use to attract mates.

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The more colorful these birds are,

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the more likely they are
to find another bird

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who's willing to mate with them.

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And this is important
and relevant for humans,

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because the colors in these birds
are not actually something

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they produce from their own biology.

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This is something they can only produce
following their diet.

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They eat something
that makes them colorful.

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And this something are carotenoids.

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Carotenoids are little pigments;
they are a group of pigments.

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There's about 500 or 600 different ones.

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But they have something in common,

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which is that they are all red,
yellowish, orangey in color,

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and they are contained
in almost all fruit and vegetables.

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Importantly, they are actually contained

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not only in carrots
that are obviously orange

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but even in fruit and vegetables
that are perhaps less clearly colorful,

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including green vegetables;

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and fruit, for that matter.

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And these pigments in the birds

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signal that these birds are able

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to go out and look for a healthy diet

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by foraging through perhaps
the forest or the fields,

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which they couldn't do
if they were in poor health condition.

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So in those birds, being very colorful
suggests to a mate that they are healthy.

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Of course, us humans,

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don't have to go in to the forest
to get fruit and vegetables,

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we can walk in to the supermarket
and buy any food that we desire.

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Our problem is more, perhaps,
that we'd choose foods we shouldn't eat.

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I'm sure you're all aware
that we are supposed to eat

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about a third of our diet
from fruit and vegetables.

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This is also often referred to
as the five a day:

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you're supposed to at least eat five
portions of fruit and vegetables per day.

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So if eating fruit and vegetables

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- which have all sorts of health benefits

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including getting vitamins, getting fiber,

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and getting a whole range
of relevant products into you body -

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if that is important for birds,
then what about humans?

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Do we perhaps also somehow
signal in our appearance

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the fact that we have eaten
lots of fruit and vegetables?

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So, to recap how this works:

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the carotenoids that we've consumed
with fruit and vegetables

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work and function in our immune system.

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So if some nasties, some bugs
enter your system,

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one thing that the immune system
can do is use carotenoids

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that are stored in our system
as antioxidants

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that will then fight these nasties
and cause them to disappear.

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If there are carotenoids
left over, as it were,

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after this immune function has happened,

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these carotenoids can then
be layered into our skin.

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This happens through a process whereby
carotenoids are entered into the sweat

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which is then of course sweated out
through the sweat glands

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and are literally layered onto our skin.

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And this layering process causes our skin 
to turn somewhat goldenish yellow.

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This is just a representation;
it's not accurate.

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You're not going to turn
exactly that color,

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if you eat more fruit and veg,
but it illustrates the point.

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There's a different scenario
that we could imagine

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whereby again, we have
plenty of carotenoids,

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but this time, there isn't just
four of these nasties but many more;

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which should hopefully appear
on screen in a moment.

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There we go.

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And in this situation, the majority
of our carotenoids stored

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might be used up to fight these nasties.

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And then, there's very little leftover
to go into our skin,

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which then causes our skin

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to turn a lighter color again.

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This is because the carotenoids

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that were originally layered
into our skin get rubbed off,

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and our skin of course
rejuvenates all the time.

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So if you don't replenish constantly,

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then our skin color will change back

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to a less attractive version of itself.

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That led us to the interesting question

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of whether this different skin color
is perhaps found attractive in humans.

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Remember, in birds,
the high-carotenoid coloration

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was something they use to attract mates,

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which is similar
to attractiveness in humans.

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And given this is a cue of somehow health,
so you have a lot of disease burden,

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you might not be able to create
this lovely skin color,

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this might actually be a cue
of your appearance.

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So, for this, we conducted an experiment.

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We first measured empirically

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the axis of color change in skin
associated with carotenoids.

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To do this, we had a group of students

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that eat a lot of fruit and vegetables
in their regular diet,

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and we measured their skin color;

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we also had a group of students

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that didn't eat
very many fruit and vegetables

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- It was more easy to recruit
in that group unsurprisingly -

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and we match these groups
on their sex, on their age,

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and on other lifestyle characteristics

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so that we could be relatively certain

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that the only consistent difference
between these groups

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was their fruit and vegetable consumption.

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After we measured
each individual's skin color,

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we averaged this skin colors,
and could then calculate

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the difference between the color
of the high carotenoid intake group

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and the low carotenoid intake group.

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We could derive this kind of color axis.

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This allows us to take a photograph
of anybody, for example this girl,

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or anybody in this room,

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and we are then able 
to transform this image

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to become either higher
or lower in carotenoid color.

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We then asked people, in an experiment

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which color they think is more attractive.

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So let's try this here:
you see the two versions of her face.

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Who thinks the girl on the left
is more attractive?

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One … not many, good.

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Who thinks the girl on the right
is more attractive?

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That's a vast majority,

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and this is consistent
with what we found in our experiments

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where of course we wouldn't present
people with only this one girl

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but with a large range of faces
that we have manipulated in this way.

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We find that in fact,
nine out of ten people approximately

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chose the higher carotenoid version
of faces as more attractive.

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So this is a really good indication

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that there is something about this color
that makes people more attractive.

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We also looked at other cultures

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and found that in Asian
and African cultures the same holds:

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people who had
a more carotenoid-linked skin color

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were seen as more attractive.

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And even some people were still
arguing back at us and saying,

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"Oh, this is just about sun-tanning."

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We all like a suntan, so you all know
you like to go out in the sun,

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you like to go to the beach,

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and it leads to of course a somewhat sort
of brownish yellowish color on your skin.

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This color is caused
by a pigment called melanin,

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which is activated by UV rays

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and it's meant to protect your skin
to some degree from a sunburn.

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A lot of research in the past has shown

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that a suntan is thought of as attractive
at least in our societies.

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People argued with us, that perhaps,

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what is going on is
that carotenoid coloration

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looks somewhat similar to a suntan;
it's also a little bit yellow,

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so perhaps people like a tan.

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And because they like a tan,

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they also like this color
which looks somewhat similar.

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So we investigated this question.

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We investigated it by asking people

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which face they prefer

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out of a high carotenoid face
and a high suntanned face.

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So we manipulated the tan in the same way
I showed you before for the carotenoids.

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And now, let's do this again: who thinks
the face on the left is more attractive?

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OK, and who thinks the face
on the right is more attractive?

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Fewer. Interesting.

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Right, I'm sure you all now want to know

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which of these is the tan
and which of these is the carotenoids.

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Well, this one if the carotenoid face;
and the majority of you prefer this face.

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We find the same pattern
of results in our research

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with eight out of ten people on average

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preferring the carotenoid face
over a suntan.

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That really means
that there's something specific

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about this color that people like,

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even when we compare it to another color

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which is normally liked
by people in this culture.

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This also might actually mean

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that the reason or part
of the reason we like a tan

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is because it mimics to some degree
this healthy color of carotenoids.

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We've seen that eating
fruit and vegetables

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makes your skin change color,

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and that this new color
is seen as attractive.

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But remember, at the start, I told you
attractiveness isn't the end of the story,

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but other traits such as being perceived
as more trustworthy or smarter

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are also associated with attractive faces.

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So we were interested to assess
whether these traits

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might also be associated
with a carotenoid skin color.

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We've conducted two studies to date:

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we once looked
at trustworthiness judgments,

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and we also looked
at leadership judgments,

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so how good a leader
people thought a person was.

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And in both cases, we found that having
a high carotenoid coloration in your skin

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influenced these judgments
quite dramatically.

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People really thought the people
with the healthy carotenoid coloration

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were more trustworthy
and would be much better leaders.

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So that should give you
some food for thought hopefully.

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But to finish off,

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there is one important question
to answer, isn't there?

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How much do you actually need
to eat of the stuff?

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Do you need to eat
25 carrots every day to get this effect

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which might be rather unmanageable?

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Well, colleagues
at the University of St. Andrews

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have conducted a study into this

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and found that actually eating
only two more portions a day,

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this might be for example eating an apple
and drinking a glass of orange juice,

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or eating a portion
of vegetables twice a day,

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is enough to change
your skin color within six weeks

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to be perceived as more attractive.

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the difficulty is though,
as you might recall,

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that if you don't keep it up,
your skin color will go back down.

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So really what this means 
is you have to eat

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more fruit and veg
for the rest of your life.

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Thank you very much.

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(Applause)