- [Narrator] Decide when
to pair up and with whom

is a riddle that evolutionary
psychologist Douglas Kenrick

has tried to solve for decades.

- If we all just went for good genes,

everyone would be unhappy
if the guys didn't end up

you know with Jennifer Lopez

or some other fashion model,

they would just stop then.

And the women would stop if
they couldn't get Brad Pitt

or some extremely handsome guy.

In real life, people have to
match up with one another.

(intense music)

- [Narrator] How does this
matching up process work?

To find out, Dr. Kenrick gathered 10 men

and 10 women from a fairly average range

of physical attractiveness
and prepared to perform

a few experiments in
human social dynamics.

First he stripped away as
many differences as possible

between the guinea pigs by dressing them

in identical and sexually neutral outfits.

- Okay now you're gonna play
a sort of a mating game.

You all have a number as you can see.

You can't see your own number,

but you can see the
other peoples' numbers.

Offer your hands to someone,

and if they accept it,
then you've paired up

and you walk back to the back.

If the person does not accept your offer,

then you'd move on and
offer it to someone else.

Again the task being to try
to get the highest number

that you can

and realizing that you have
a number on your own head

that they are responding to as well.

(mysterious music)

- [Narrator] The numbers, drawn at random,

are meant to represent desirability.

One being least and 10 being most.

In the real world,

where most of us don't know exactly

how attractive we are,

we tend to aim high, trying to snare a 10.

Then gradually we work
our way down to someone

who will accept us.

- Some of the people are trying

and not getting paired.

The two people who are
fives have paired up

with one another.

It wasn't like the 10s perfectly matched

and the ones perfectly matched,

but you did get a correlation.

The people with the high numbers

were able to hold back
a little bit longer,

and they got more offers.

The people with the low
numbers didn't get any offers.

And that's sort of what
happens in a real mating pool.

- [Narrator] The experiment opens a window

into the mind of an
adolescent who is not yet

fully aware of how
attractive he or she is.

- Let's imagine teenagers
in a high school.

You've got a guy and a girl

who are both 10s.

Well what's gonna happen to
them is they're gonna get

a lot of offers from the opposite sex,

and they're eventually
gonna have some sense

that they have lots of more opportunities.

If you're a five or a six,

as most people are,

they'll let you know.

You'll get feedback basically.

- [Narrator] This is something
we all have to learn,

and it can be a painful process.

(mysterious music)

To glimpse a sped-up version
of this learning curve,

Dr. Kenrick put a microphone on the woman

who was ranked number three
and asked her to narrate

her mate selection strategy.

- I guess everyone's
gonna start off going to

the number 10 guy.

Three, one, four, 10, oh 10 is taken now.

Nobody will make eye contact with me.

I'm not really used to that.

I like that one, yeah.

But his number's too low, I can do better.

Let's see, one, no, seven.

I could, oh he's being paired off.

I have a feeling I have a very low number

because no one's coming
over to me at all right now.

Come on, two, no,

I can do better than that.

We're running out of numbers.

One, eight,

I guess this is all that's left.

Okay I'm stuck with two.

(mysterious music)

- [Narrator] After using random numbers,

Dr. Kenrick wanted to see
how things would turn out

if he let true physical attractiveness

drive mate selection.

When the volunteers first arrive,

before the men and women met face-to-face,

Kenrick had them rate each
others' physical appearance

on a scale of one to 10.

He pooled the numbers for each person

and came up with an attractiveness rating.

Now it's time for the test subjects to try

and reel in the most physically
attractive person they can.

(drum music)

- We are going to change
the rules a little bit.

And we're gonna begin by asking the ladies

to take your head stockings off.

Okay now if the guys would all remove

their head coverings.

Let your own preferences now

you know have their way,

and again, keeping in mind the last game,

try to get the person who you regard

as the highest attractiveness
in your opinion.

(mysterious music)

- [Narrator] Just as Kenrick expected,

each person found a partner
within a point or so

of themselves.