How your brain decides what is beautiful

It's 1878.

Sir Francis Galton
gives a remarkable talk.

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

Known for his pioneering work
in human intelligence,

Galton is a brilliant polymath.

He's an explorer,

an anthropologist,

a sociologist,

a psychologist,

and a statistician.

He's also a eugenist.

In this talk,

he presents a new technique

by which he can combine photographs
and produce composite portraits.

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

Galton thinks that if he combines
photographs of violent criminals,

he will discover the face of criminality.

But to his surprise,

the composite portrait that he produces

is beautiful.

Galton's surprising finding
raises deep questions.

What is beauty?

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

For most of human history,

these questions have been approached
using logic and speculation,

but in the last few decades,

scientists have addressed
the question of beauty

using ideas from evolutionary psychology
and tools of neuroscience.

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

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

And in the process,

we're stumbling upon some surprises.

When it comes to seeing
beauty in each other,

while this decision is certainly
subjective for the individual,

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

Many experiments have shown

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

These include averaging, symmetry
and the effects of hormones.

And let's take each one of these in turn.

Galton's finding

that composite or average faces
are typically more attractive

than each individual face
that contributes to the average

has been replicated many times.

This laboratory finding fits
with many people's intuitions.

Average faces represent the central
tendencies of a group.

People with mixed features
represent different populations,

and presumably harbor
greater genetic diversity

and adaptability to the environment.

Many people find mixed-race
individuals attractive,

and inbred families less so.

The second factor that contributes
to beauty is symmetry.

People generally find symmetric faces
more attractive than asymmetric ones.

Developmental abnormalities
are often associated with asymmetries,

and in plants, animals and humans,

asymmetries often arise
from parasitic infections.

Symmetry, it turns out,

is also an indicator of health.

In the 1930s,

a man named Maksymilian Faktorowicz

recognized the importance
of symmetry for beauty

when he designed the beauty micrometer.

With this device,

he could measure minor asymmetric flaws

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

named brilliantly after himself:

Max Factor,

which as you know is one of the world's
most famous brands for makeup.

The third factor that contributes
to facial attractiveness

is the effect of hormones.

And here, I need to apologize
for confining my comments

to heterosexual norms.

But estrogen and testosterone
play important roles

in shaping features
that we find attractive.

Estrogen produces features
that signal fertility.

Men typically find women attractive

who have elements of both
youth and maturity.

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

so men find women attractive

who have large eyes,
full lips and narrow chins

as indicators of youth,

and high cheekbones as an
indicator of maturity.

Testosterone produces features
that we regard as typically masculine.

These include heavier brows,

thinner cheeks

and bigger, squared-off jaws.

But here's a fascinating irony.

In many species,

if anything,

testosterone suppresses the immune system.

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

doesn't really make a whole lot of sense.

Here, the logic is turned on its head.

Instead of a fitness indicator,

scientists invoke a handicap principle.

The most commonly cited
example of a handicap

is the peacock's tail.

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

avoid predators and approach peahens.

Why should such an extravagant
appendage evolve?

Even Charles Darwin,

in an 1860 letter to Asa Gray wrote

that the sight of the peacock's tail
made him physcially illl.

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

and out of this frustration,

he developed the theory
of sexual selection.

On this account,

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

and this enticement means
that it's more likely

that the peacock will mate
and have offspring.

Now, the modern twist
on this display argument

is that the peacock is also
advertising its health to the peahen.

Only especially fit organisms
can afford to divert resources

to maintaining such
an extravagant appendage.

Only especially fit men can afford
the price that testosterone levies

on their immune system.

And by anaology,

think of the fact that only very
rich men can afford

to pay more than $10,000 for a watch
as a display of their financial fitness.

Now, many people hear these kinds
of evoulutionary claims

and think they mean that we somehow
are unconciously seeking mates

who are healthy,

and I think this idea
is probably not right.

Teenagers and young adults are not
exactly known for making decisions

that are predicated on health concerns.

But they don't have to be,

and let me explain why.

Imagine a population in which people
have three different types of preferences:

for green, for orange, and for red.

From their point of view,

these preferences have
nothing to do with health,

they just like what they like.

But if it were also the case

that these preferences are associated
with the different likelihood

of producing offspring,

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

then in the first generation,

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

and in each subsequent generation,

the proportion of greens increase

so that [intention rations] 98 percent
of this population has a green preference.

Now, scientists coming in
and sampling this population

disover that green
preferences are universal,

so the point about this
little abstract example

is that while preferences
for specific physical features

can be arbitrary for the individual,

if those features are hertiable

and they are associated
with a reproductive advangtage,

over time,

they become universal for the group.

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

Attractive faces activate parts of our
visual cortex in the back of the brain;

an area called the fusiform gyrus

that is especially attuned
to processing faces,

and an adjacent area called
the lateral occipital complex

that is especially attuned
to processing objects.

In addition,

attractive faces activate parts
of our reward and pleasure centers

in the front and deep in the brain,

and these include areas
that have complicated names,

like the ventral striatum,

the [orbitofrontal] cortex

and the ventromedial prefrontal cortex.

Our official brain that is attuned
to processing faces

interacts with our pleasure centers

to underpin the experience of beauty.

Amazingly, while we all
engage with beauty,

without our knowledge,

beauty also engages us.

Our brains respond to attractive faces
even when we're not thinking about beauty.

We conducted an experiement in which
people saw a series of faces,

and in one condition,

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

Even in this condition,

attractive faces drove neural activity
robustly in their visual cortex

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

and not their beauty.

Another group similarly found
automatic responses to beauty

within our pleasure centers.

So taken together,

these studies suggest

that our brain automatically
responds to beauty

by linking vision and pleasure.

These beauty detectors,

it seems,

ping ever time we see beauty
regardless of whatever else

we might be thinking.

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

Within the [orbitofrontal] cortex,

there's overlapping neural activity

in response to beauty and to goodness,

and this happens even when people
aren't expllicitly thinking

about beauty or goodness.

Our brains seem to reflexively
associate beauty and good.

And this reflexive association
may be the biologic trigger

for the many social effects of beauty.

Attractive people receive
all kinds of advantages in life.

They're regarded as more intelligent,

more trustworthy,

they're given higher pay
and lesser punishments,

even when such judgments
are not warranted.

These kinds of observations
reveal beauty's ugly side.

In my lab,

we recently found that people with minor
facial anomalies and disfigurements

are regarded as less good, less kind,

less intelligent, less competent
and less hardworking.

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

This stereotype is probably
exploited and magnified

by images in popular media

in which facial disfigurement
is often used as a shorthand

to depict someone of villainous character.

We need to understand
these kinds of implicit biases

if we are to overcome them,

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

based on their behavior and not
on the happenstance of their looks.

Let me leave you with one final thought.

Beauty is a work in progress.

The so-called universal
attributes of beauty

were selected for --

during the almost two million
years of the Pleistocene.

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

The selection criteria for reproductive
success from that time

doesn't really apply today.

For example,

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

at least not in the
technologically-developed world.

From antibiotics to surgery,

birth control to in vitro fertilization,

the filters for reproductive
success are being relaxed,

and under these relaxed conditions,

preference and trait
combinations are free to drift

and become more variable.

Even as we are profoundly
effecting our environment,

modern medicine and technological
innovation is profoundly effecting

the very essence of what
it means to look beautiful.

The universal nature of beauty is changing

even as we're changing the universe.

Thank you.

(Applause)