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