How your brain decides what is beautiful

It's 1878.

Sir Francis Galton
gives a remarkable talk.

He's speaking to the Anthropologic
Instisitute of Great Britain and Ireland.

Known for his pioneering work
in human intelligence,

Dalton is a brilliant polymath.

He's an explorer,

and antrhopologist,

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.

Dalton 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 hisotiry,

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
rare genetic diversity

and adaptibility 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 symmetic faces
more attractive than asymmetic ones.

Developmental abnormalities
are often associated with asymmetries,

and in plants, animal and humans,

asymmetries often arise
from parasitic infections.

Symmetry it turns out,

is also an indicator of health.

In the 1930s,

a man named MAximallian Fector Rowis

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 woman 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.

Now, 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 a 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 a 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 espeically fit men can afford
the price that testorone 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 htink 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.

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

for green, for orange and for red.

From their point of view,

their 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 ration of three
to two to one,

then in the first generation,

there would be three greens
to two organges to one 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

disovers that green preferences
are universal