[narrator] Hey, you.
Do you usually fall for the cool, rebellious type?
Or are you more into the brooding artist?
Do you vibe with shy and nerdy
or charming and flirty?
Are you all about guys? Hmm.
Maybe you also like girls.
Does it matter?
Lanky, ripped, buzz cuts,
man buns, full beards, strong brows,
small breasts, big butts...
-[chattering] -[narrator] Is it more about their smile
-or how they make you laugh? -[laughs]
[narrator] Are you attracted to people you're embarrassed about,
-so you keep it a secret? -[gasps]
[narrator] We all have a type or a few types.
-I know I do. -[woman] Oh!
[narrator] So where do these types come from?
Why are we attracted to some people... and not others?
I think you're cute.
[theme music playing]
[Justin Timberlake] I mean, you know it if you have a chemistry with somebody.
If I'm vibin' that person, then that's...
You know, don't think about it too much.
[man] What you're sniffing
and searching for are the smells of somebody
who you think might be genetically compatible with you.
[narrator 2] Our brains are designed to latch onto people's attractive features
on our quest to find the right mate.
My body temperature changes. Um... [clicks tongue]
And I get-- I get that, like, warm, fuzzy feeling
usually, like, in the, you know, the guts.
And then it kind of, like, moves down the body.
[narrator] In the moment of attraction, your brain floods you with hormones
that make you feel...
[woman 1] Warm... and tingly,
and it's like my hair stands on end.
All of my senses feel like they're awake.
My heart flutters.
[man] My heart is beating extremely fast. I don't know what to say.
I'm shy. Sometimes I talk way too fast.
[narrator] Dopamine gives you the same pleasurable boost
-as eating sugar or taking drugs, -[person inhales]
with the same powerful cravings.
[woman 2] I feel myself, like, wanting to banter
or wanting to engage in, like, a debate
or, like, looking at their arms.
I'm, like, super into arms. [laughs]
[narrator] And then there's norepinephrine and adrenaline.
The fight-or-flight hormones.
I might get a little nervous feeling, a little anxious...
or I get really excited.
[narrator] Which can make it hard to sleep and eat.
In France, they call the moment of attraction "coup de foudre"
-or a "lightning bolt." -[thunder rumbles]
[narrator] In Arabic, it's "hawa," a wind.
In China, "yuanfen," a fated force.
And in Japan, they say "koi no yokan,"
the feeling when you meet someone that you're bound to fall in love.
How do I know if I'm attracted to someone? Um...
It's just kind of this, like, magnetic... [laughs]
Like, it's just kind of like...
I just feel drawn to that person.
When you're attracted to somebody, you shouldn't really be able to explain it
beyond just, like, I'm attracted to them, right?
It should just be visceral, and you should know it.
[narrator] But humans have tried to explain it.
I mean, how could we not?
And we have all kinds of theories.
An astrologer would say, if you're a Taurus,
try to match with a Capricorn.
-But a Sagittarius? No way. -[buzzer sounds]
[narrator] Indian astrologers have long used
an intricate, 36-point analysis to match the bride and groom.
You need at least 18 points for a successful marriage.
And then, in 2015, an article went viral
that claimed when two strangers asked each other these 36 questions,
it's led to love.
Questions like, "What is your most treasured memory?"
"What is your most terrible memory?"
And "Do you have a secret hunch about how you will die?"
According to the magazine Cosmo, you can make anyone fall in love with you
in 12 easy steps, including:
eye contact,
focusing on the ways you're similar,
hanging around them a lot,
and, uh, "love them"?
Okay, sure.
But scientists, for decades,
said it pretty much all came down to our genes,
and we're all attracted to the same type:
a fit and fertile mating partner.
Because we're animals, we just want to reproduce.
[man] More symmetric men smell better to women,
specifically to women who are at the fertile phase
of the menstrual cycle.
[narrator 2] Men are thought to have a preference for curved hips,
because this signals enough fat deposits on the hips
for health and fertility.
[narrator 3] Men choose women with large breasts
because they're seen as good child-rearing material.
So, there is a sense in which the body
of a woman has been designed through evolution
for the delectation of males.
[narrator] Maybe that's why male video game designers
make pretty much every female character look like this...
'cause they're more fertile. Mm-hmm.
There's definitely an evolutionary component to attraction,
but I think we have to be really careful
in distinguishing between "just so" stories:
Men like women with big breasts because it's good for the species.
There is no evidence of any link
between large breasts and a pretty face and fertility, all right?
If that were true, our planet would be populated
only with beautiful, large-breasted women,
and that is obviously not true.
One of the things we find quite consistently
is that the social culture in which you grow up
and which you live in has an impact on your body size ideal.
[narrator] Viren traveled to a region of South Africa
with incredibly high rates of HIV and conducted a study,
asking Zulu men living there
to rate a series of photos of women with different body sizes.
On average, the men found this body size
just as attractive as this one,
while all these body sizes were rated as less attractive.
Being extremely thin, in that particular context,
was associated with HIV.
[narrator] Viren also showed these images to Zulu men
who had recently moved to the UK.
Those men rated this body size as the ideal...
and rated these body sizes as less attractive.
The ideal body size changed very quickly
to match what was ideal in the UK, which was a relatively thin body.
[narrator] And if humans are just like any other animal,
something else doesn't make sense.
In a lot of animal species, the males are the ones
with the pressure to look pretty and impress the females.
Like in birds, where they get pretty sexy,
because they often have to compete for mates.
But mating in the human world looks different.
A 1989 study of 37 cultures around the world found that
men care more about their female partners being attractive and young...
as in "fertile," to have more babies to pass on their genes,
while women cared more about financial capacity,
ambition, and industriousness.
As in, they were or were going to be rich to provide for all those babies.
And especially if you watch a lot of reality TV, that feels true,
because these shows play up those different motives.
[woman 1] I know you're traveling a lot,
so thank you for letting me borrow the plane. I really appreciate it.
[Ronnie] Stereotypes for a guido,
the guy that always looks prettier than his girlfriend,
which is completely unacceptable.
I can't be with a girl that doesn't look prettier than me.
[woman 2] Bri, how old are you?
-So, I am 21. -Oh.
[narrator] A study of profile pictures on the dating app Tinder
also seemed to back this story.
Straight women were more likely than men
to take selfies angled from above,
so their eyes and foreheads looked big,
and everything else looked smaller.
So they look younger, aka, more fertile.
While men were more likely to use selfies angled from below,
so they look taller and more dominant.
In the animal world, that means "better able to acquire resources."
In the human world, that means "rich."
But a 2001 study that reviewed half a century of data
found that as more women entered the workplace and made their own money,
they started caring more about being with a good-looking guy.
And men started caring more about being with a woman
with good financial prospects.
[Viren Swami] The idea that we are simply animals
that only really care about reproducing,
-seems incredibly reductive. -[frog croaks]
It's not simply a biological drive
to have sex with that individual so you can produce offspring.
Now, I'm not saying that that doesn't happen
and that that's not shaping how we might behave
in some situations.
The point, more generally, is that to have a relationship,
to form a relationship with an individual,
or even just to have sex with an individual
requires so much more than just biology.
[narrator] Even identical twins...
same genes, same upbringing, same culture...
don't all have the same type.
In 2015, researchers had hundreds of identical twins rate faces
and plotted the results.
Each dot represents a twin pair.
The X-axis is one twin's rating,
and the Y-axis is the other twin's rating.
If the twins all agreed with each other,
you'd expect the correlations to look like this.
But it didn't.
The researchers found that a lot of what we're attracted to
comes down to unique environmental factors,
as in your individual life history.
I think I've always had a little bit
of the bad boy that I was attracted to.
[laughing] And that keeps coming back over and over again.
But I had--
You know, my father was a-- had a little of the "bad boy" in him.
I used to never like dating people who looked like me.
And then, I don't know, recently,
I've been mistaken for people that I've been attracted to.
[laughing] So, it's like, "This person actually looks just like me."
So, I guess it's about loving the self ultimately, you know?
All the guys that I like
end up looking like the stuffed animals I had when I was a kid.
[laughs] So I'm like, "Oh, maybe I'm just looking for security
and comfort that way."
Generally, what a lot of evolutionary psychology suggests
is that as long as you are having enough sex
with other sex partners to reproduce,
it really doesn't matter what else you're attracted to.
Really, evolution doesn't care what else you do with sexuality.
[narrator] Identical twins don't always have the same sexuality either.
In fact, a gay twin is more likely
to have a twin that's straight than gay.
Researchers found when it comes to sexual orientation,
environmental factors play a much more important role than genes.
For women, they're at least four times as important.
But environmental factors, in this case, doesn't mean culture or upbringing.
So, I think when we talk about environment,
we're often thinking, "Oh, your friends or your parents."
But when geneticists are talking about the environment,
we're talking about literally everything that's not a gene.
That's the placenta, right?
That's an environment, too.
[narrator] The womb is everyone's first environment,
and what happens there
may affect who you're attracted to when you grow up.
The amount and timing of hormones a fetus is exposed to
may play a role.
And for males, so could maternal antibodies
that target a certain brain protein made by the Y chromosome.
In some women, those can build up over time
with every male baby she has.
Which may explain why gay men, on average,
have more older brothers than straight men.
There are plenty of environmental influences
that are as fixed as any gene.
So, it's important to remember
that "genetic" doesn't mean "fixed,"
and "environmental" doesn't mean "unfixed."
The gene environment balance
for a trait doesn't really say anything
about the fixedness of that trait.
As a child I was like, "Oh, no, I just like boys.
I just like boys."
And my mother would always say to me,
"If you liked girls, too, it'd be okay." Like, she knew.
So, as I've grown up
and as I've started experiencing more sexuality
and getting out into the world more,
my sexuality has also changed.
If you're a man or if you're a woman, if you're trans, if you're not trans--
You know, those things, I think...
I've met all kinds of people, all kinds of ways,
and they've all been attractive, you know? [laughs]
[narrator] Gender is just another type.
[Lisa Diamond] Some individuals don't necessarily have
a gender-based orientation.
They are more focused on the individual.
Some individuals are just more gender-y than others.
[narrator] In early 19th century Iran,
people were drawn to characteristics that were not very gendered at all.
These young lovers look pretty similar.
And in recent years,
that beauty ideal has become popular in the West,
with some male and female models looking pretty similar,
as ideas of gender have become more fluid.
There is a lot of evidence that suggests that men are a bit more rigid
when it comes to the type of people that they're attracted to.
Women show a lot more flexibility.
[narrator] In one study, a small sample of gay and straight men and women
had their genital sexual response measured
while they were shown a variety of videos.
One was a man and a woman having sex.
Another was men having sex...
and women having sex...
and a man masturbating.
A woman masturbating.
A buff naked man taking a stroll.
A toned naked lady exercising.
And bonobos gettin' it on.
As you might expect,
straight men were more turned on by the videos with women in them.
And also, as you might expect,
gay men preferred the videos featuring men.
But the women,
they were turned on by pretty much everything.
Lesbians were even slightly more aroused by the bonobos than the strolling man.
One of the hallmarks of human sexuality
is that humans are able to use sexuality
for purposes other than reproduction.
It cements social alliances. It reduces stress.
And so, flexibility in the sexual system is a good thing.
It's a part of the ability of sex to serve multiple functions.
[narrator] And according to the latest research,
attraction mostly comes down to four main pillars...
and they're pretty simple.
The first one is physical appearance, obviously.
But then, the second pillar of attraction is... geography?
In the UK, for example, the majority of relationships
are formed between people who live relatively nearby,
probably between five and ten kilometers away at most.
[narrator] And we like people who have the qualities we value in ourselves.
Opposites almost never attract.
People who are too different or who have different values to us,
we often find that they-- they cause discomfort in us.
[narrator] The fact that you and your partner
have compatible star signs
matters less than the fact that you both care about star signs.
Well, you gotta be smart.
I always like someone who's smart. Down-to-earth, definitely.
Someone who's spiritual. That's really big for me.
Their kindness, their ability to be present.
Adventurous, playful, good communicator...
[narrator] And finally, we tend to find comfort
in people who reciprocate our expressions of intimacy.
For example, if I-- If I told you something
about my true self, who I really, really am,
are you going to reciprocate?
Are you going to tell me something about yourself in return?
[narrator] That could be why this experiment
of asking 36 questions to a stranger
actually worked for people.
Sharing your most treasured memories...
terrible memories...
and your secret hunches about how you're going to die
could get pretty intimate.
So, it turns out, Cosmo's advice is surprisingly scientific.
Focusing on the ways you're similar, mm-hmm.
Hanging around them a lot...
That's geography.
Loving them...
That's opening yourself up to reciprocity.
And eye contact... Well, that's just really sexy.
[theme music playing]