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It's 1878.

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Sir Francis Galton[br]gives a remarkable talk.

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He's speaking to the anthropologic[br]institute of Great Britain and Ireland.

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Known for his pioneering work[br]in human intelligence,

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Galton is a brilliant polymath.

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He's an explorer,

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an anthropologist,

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a sociologist,

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a psychologist

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and a statistician.

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He's also a eugenist.

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In this talk,

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he presents a new technique[br]by which he can combine photographs

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and produce composite portraits.

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This technique could be used[br]to characterize different types of people.

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Galton thinks that if he combines[br]photographs of violent criminals,

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he will discover the face of criminality.

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But to his surprise,

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the composite portrait that he produces

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is beautiful.

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Galton's surprising finding[br]raises deep questions:

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What is beauty?

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Why do certain configurations of line[br]and color and form excite us so?

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For most of human history,

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these questions have been approached[br]using logic and speculation.

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But in the last few decades,

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scientists have addressed[br]the question of beauty

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using ideas from evolutionary psychology[br]and tools of neuroscience.

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We're beginning to glimpse[br]the why and the how of beauty,

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at least in terms of what it means[br]for the human face and form.

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And in the process,

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we're stumbling upon some surprises.

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When it comes to seeing[br]beauty in each other,

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while this decision is certainly[br]subjective for the individual,

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it's sculpted by factors that contribute[br]to the survival of the group.

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Many experiments have shown

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that a few basic parameters contribute[br]to what makes a face attractive.

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These include averaging, symmetry[br]and the effects of hormones.

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Let's take each one of these in turn.

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Galton's finding

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that composite or average faces[br]are typically more attractive

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than each individual face[br]that contributes to the average

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has been replicated many times.

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This laboratory finding fits[br]with many people's intuitions.

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Average faces represent[br]the central tendencies of a group.

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People with mixed features[br]represent different populations,

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and presumably harbor[br]greater genetic diversity

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and adaptability to the environment.

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Many people find mixed-race[br]individuals attractive,

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and inbred families less so.

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The second factor that contributes[br]to beauty is symmetry.

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People generally find symmetric faces[br]more attractive than asymmetric ones.

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Developmental abnormalities[br]are often associated with asymmetries,

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and in plants, animals and humans,

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asymmetries often arise[br]from parasitic infections.

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Symmetry, it turns out,

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is also an indicator of health.

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In the 1930s,

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a man named Maksymilian Faktorowicz

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recognized the importance[br]of symmetry for beauty

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when he designed the beauty micrometer.

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With this device,

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he could measure minor asymmetric flaws

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which he could then make up for[br]with products he sold from his company,

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named brilliantly[br]after himself, Max Factor,

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which, as you know,[br]is one of the world's most famous brands

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for "make up."

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The third factor that contributes[br]to facial attractiveness

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is the effect of hormones.

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And here, I need to apologize[br]for confining my comments

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to heterosexual norms.

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But estrogen and testosterone[br]play important roles

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in shaping features[br]that we find attractive.

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Estrogen produces features[br]that signal fertility.

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Men typically find women attractive

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who have elements[br]of both youth and maturity.

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A face that's too baby-like might[br]mean that the girl is not yet fertile,

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so men find women attractive

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who have large eyes,[br]full lips and narrow chins

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as indicators of youth,

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and high cheekbones[br]as an indicator of maturity.

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Testosterone produces features[br]that we regard as typically masculine.

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These include heavier brows,

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thinner cheeks

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and bigger, squared-off jaws.

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But here's a fascinating irony.

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In many species,

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if anything,

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testosterone suppresses the immune system.

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So the idea that testosterone-infused[br]features are a fitness indicator

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doesn't really make a whole lot of sense.

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Here, the logic is turned on its head.

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Instead of a fitness indicator,

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scientists invoke a handicap principle.

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The most commonly cited[br]example of a handicap

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is the peacock's tail.

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This beautiful but cumbersome tail[br]doesn't exactly help the peacock

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avoid predators

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and approach peahens.

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Why should such an extravagant[br]appendage evolve?

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Even Charles Darwin,

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in an 1860 letter to Asa Gray wrote

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that the sight of the peacock's tail[br]made him physically ill.

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He couldn't explain it[br]with his theory of natural selection,

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and out of this frustration,

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he developed the theory[br]of sexual selection.

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On this account,

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the display of the peacock's tail[br]is about sexual enticement,

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and this enticement means[br]it's more likely the peacock will mate

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and have offspring.

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Now, the modern twist[br]on this display argument

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is that the peacock is also[br]advertising its health to the peahen.

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Only especially fit organisms[br]can afford to divert resources

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to maintaining such[br]an extravagant appendage.

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Only especially fit men can afford[br]the price that testosterone levies

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on their immune system.

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And by analogy, think of the fact

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that only very rich men can afford[br]to pay more than $10,000 for a watch

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as a display of their financial fitness.

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Now, many people hear these kinds[br]of evolutionary claims

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and think they mean that we somehow[br]are unconsciously seeking mates

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who are healthy.

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And I think this idea[br]is probably not right.

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Teenagers and young adults are not exactly[br]known for making decisions

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that are predicated on health concerns.

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But they don't have to be,

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and let me explain why.

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Imagine a population

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in which people have three different[br]kinds of preferences:

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for green, for orange and for red.

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From their point of view,

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these preferences have[br]nothing to do with health;

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they just like what they like.

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But if it were also the case[br]that these preferences are associated

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with the different likelihood[br]of producing offspring --

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let's say in a ratio of 3:2:1 --

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then in the first generation,

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there would be 3 greens[br]to 2 oranges to 1 red,

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and in each subsequent generation,

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the proportion of greens increase,

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so that in 10 generations,

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98 percent of this population[br]has a green preference.

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Now, a scientist coming in[br]and sampling this population

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discovers that green[br]preferences are universal.

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So the point about this little[br]abstract example

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is that while preferences[br]for specific physical features

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can be arbitrary for the individual,

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if those features are heritable

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and they are associated[br]with a reproductive advantage,

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over time,

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they become universal for the group.

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So what happens in the brain[br]when we see beautiful people?

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Attractive faces activate[br]parts of our visual cortex

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in the back of the brain,

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an area called the fusiform gyrus,

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that is especially tuned[br]to processing faces,

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and an adjacent area called[br]the lateral occipital complex,

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that is especially attuned[br]to processing objects.

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In addition,

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attractive faces activate parts[br]of our reward and pleasure centers

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in the front and deep in the brain,

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and these include areas[br]that have complicated names,

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like the ventral striatum,

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the orbitofrontal cortex

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and the ventromedial prefrontal cortex.

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Our visual brain that is tuned[br]to processing faces

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interacts with our pleasure centers

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to underpin the experience of beauty.

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Amazingly, while we all[br]engage with beauty,

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without our knowledge,

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beauty also engages us.

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Our brains respond to attractive faces

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even when we're not thinking about beauty.

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We conducted an experiment[br]in which people saw a series of faces,

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and in one condition,

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they had to decide if a pair of faces[br]were the same or a different person.

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Even in this condition,

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attractive faces drove neural activity[br]robustly in their visual cortex,

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despite the fact that they were thinking[br]about a person's identity

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and not their beauty.

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Another group similarly found[br]automatic responses to beauty

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within our pleasure centers.

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Taken together, these studies suggest

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that our brain automatically[br]responds to beauty

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by linking vision and pleasure.

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These beauty detectors, it seems,

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ping every time we see beauty,

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regardless of whatever else[br]we might be thinking.

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We also have a "beauty is good"[br]stereotype embedded in the brain.

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Within the orbitofrontal cortex,

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there's overlapping neural activity

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in response to beauty and to goodness,

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and this happens even when people[br]aren't explicitly thinking

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about beauty or goodness.

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Our brains seem to reflexively[br]associate beauty and good.

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And this reflexive association[br]may be the biologic trigger

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for the many social effects of beauty.

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Attractive people receive[br]all kinds of advantages in life.

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They're regarded as more intelligent,

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more trustworthy,

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they're given higher pay[br]and lesser punishments,

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even when such judgments[br]are not warranted.

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These kinds of observations[br]reveal beauty's ugly side.

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In my lab, we recently found

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that people with minor facial[br]anomalies and disfigurements

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are regarded as less good, less kind,

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less intelligent, less competent[br]and less hardworking.

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Unfortunately, we also have[br]a "disfigured is bad" stereotype.

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This stereotype is probably[br]exploited and magnified

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by images in popular media,

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in which facial disfigurement[br]is often used as a shorthand

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to depict someone of villainous character.

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We need to understand[br]these kinds of implicit biases

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if we are to overcome them,

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and aim for a society[br]in which we treat people fairly,

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based on their behavior and not[br]on the happenstance of their looks.

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Let me leave you with one final thought.

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Beauty is a work in progress.

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The so-called universal[br]attributes of beauty

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were selected for during the almost[br]two million years of the Pleistocene.

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Life was nasty, brutish[br]and a very long time ago.

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The selection criteria[br]for reproductive success from that time

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doesn't really apply today.

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For example,

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death by parasite is not one[br]of the top ways that people die,

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at least not in the technologically[br]developed world.

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From antibiotics to surgery,

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birth control to in vitro fertilization,

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the filters for reproductive success[br]are being relaxed.

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And under these relaxed conditions,

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preference and trait combinations[br]are free to drift

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and become more variable.

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Even as we are profoundly[br]affecting our environment,

0:14:10.985,0:14:14.298
modern medicine[br]and technological innovation

0:14:14.322,0:14:16.075
is profoundly affecting

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the very essence of what it means[br]to look beautiful.

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The universal nature of beauty is changing

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even as we're changing the universe.

0:14:28.863,0:14:30.048
Thank you.

0:14:30.072,0:14:33.658
(Applause)