in the coming century,

and perhaps in the next 10,000 years.

But I want to start with my work on romantic love,

because that's my most recent work.

What I and my colleagues did was put 32 people, who were madly in love,

into a functional MRI brain scanner.

17 who were madly in love and their love was accepted;

and 15 who were madly in love and they had just been dumped.

And so I want to tell you about that first,

and then go on into where I think love is going.

(Laughter)

"What 'tis to love?" Shakespeare said.

I think our ancestors --

I think human beings have been wondering about this question

since they sat around their campfires

or lay and watched the stars a million years ago.

I started out by trying to figure out what romantic love was

by looking at the last 45 years of the psychological research

and as it turns out,

there's a very specific group of things that happen when you fall in love.

The first thing that happens is,

a person begins to take on what I call, "special meaning."

As a truck driver once said to me,

"The world had a new center, and that center was Mary Anne."

George Bernard Shaw said it differently.

"Love consists of overestimating the differences

between one woman and another."

And indeed, that's what we do.

(Laughter)

And then you just focus on this person.

You can list what you don't like about them,

but then you sweep that aside and focus on what you do.

As Chaucer said, "Love is blind."

In trying to understand romantic love,

I decided I would read poetry from all over the world,

and I just want to give you one very short poem

from eighth-century China,

because it's an almost perfect example

of a man who is focused totally on a particular woman.

It's a little bit like when you are madly in love with somebody

and you walk into a parking lot --

their car is different from every other car in the parking lot.

Their wine glass at dinner

is different from every other wine glass at the dinner party.

And in this case, a man got hooked on a bamboo sleeping mat.

And it goes like this.

It's by a guy called Yuan Zhen.

"I cannot bear to put away the bamboo sleeping mat.

The night I brought you home, I watched you roll it out."

He became hooked on a sleeping mat,

probably because of elevated activity of dopamine in his brain,

just like with you and me.

But anyway, not only does this person take on special meaning,

you focus your attention on them.

You aggrandize them.

But you have intense energy.

As one Polynesian said, "I felt like jumping in the sky."

You're up all night. You're walking till dawn.

You feel intense elation when things are going well;

mood swings into horrible despair when things are going poorly.

Real dependence on this person.

As one businessman in New York said to me,

"Anything she liked, I liked."

Simple. Romantic love is very simple.

You become extremely sexually possessive.

You know, if you're just sleeping with somebody casually,

you don't really care if they're sleeping with somebody else.

But the moment you fall in love,

you become extremely sexually possessive of them.

I think there's a Darwinian purpose to this.

The whole point of this is to pull two people together

strongly enough to begin to rear babies as a team.

But the main characteristics of romantic love are craving:

an intense craving to be with a particular person,

not just sexually, but emotionally.

It would be nice to go to bed with them,

but you want them to call you on the telephone, to invite you out, etc.,

to tell you that they love you.

The other main characteristic is motivation.

The motor in the brain begins to crank, and you want this person.

And last but not least, it is an obsession.

Before I put these people in the MRI machine,

I would ask them all kinds of questions.

But my most important question was always the same.

It was: "What percentage of the day and night do you think about this person?"

And indeed, they would say,

"All day. All night.

I can never stop thinking about him or her."

And then, the very last question --

I would always have to work myself up to this question,

because I'm not a psychologist.

I don't work with people in any kind of traumatic situation.

My final question was always the same.

I would say, "Would you die for him or her?"

And, indeed, these people would say "Yes!"

as if I had asked them to pass the salt.

I was just staggered by it.

So we scanned their brains,

looking at a photograph of their sweetheart

and looking at a neutral photograph,

with a distraction task in between.

So we could look at the same brain when it was in that heightened state

and when it was in a resting state.

And we found activity in a lot of brain regions.

In fact, one of the most important was a brain region

that becomes active when you feel the rush of cocaine.

And indeed, that's exactly what happens.

I began to realize that romantic love is not an emotion.

In fact, I had always thought it was a series of emotions,

from very high to very low.

But actually, it's a drive.

It comes from the motor of the mind,

the wanting part of the mind, the craving part of the mind.

The kind of part of the mind

when you're reaching for that piece of chocolate,

when you want to win that promotion at work.

The motor of the brain.

It's a drive.

And in fact, I think it's more powerful than the sex drive.

You know, if you ask somebody to go to bed with you,

and they say, "No, thank you,"

you certainly don't kill yourself or slip into a clinical depression.

But certainly, around the world,

people who are rejected in love will kill for it.

People live for love.

They kill for love.

They die for love.

They have songs, poems, novels,

sculptures, paintings, myths, legends.

In over 175 societies,

people have left their evidence of this powerful brain system.

I have come to think

it's one of the most powerful brain systems on Earth

for both great joy and great sorrow.

And I've also come to think

that it's one of three basically different brain systems

that evolved from mating and reproduction.

One is the sex drive: the craving for sexual gratification.

W.H. Auden called it an "intolerable neural itch,"

and indeed, that's what it is.

It keeps bothering you a little bit, like being hungry.

The second of these three brain systems is romantic love:

that elation, obsession of early love.

And the third brain system is attachment:

that sense of calm and security you can feel for a long-term partner.

And I think that the sex drive evolved to get you out there,

looking for a whole range of partners.

You can feel it when you're just driving along in your car.

It can be focused on nobody.

I think romantic love evolved to enable you to focus your mating energy

on just one individual at a time,

thereby conserving mating time and energy.

And I think that attachment, the third brain system,

evolved to enable you to tolerate this human being

at least long enough to raise a child together as a team.

So with that preamble,

I want to go into discussing the two most profound social trends.

One of the last 10,000 years

and the other, certainly of the last 25 years,

that are going to have an impact on these three different brain systems:

lust, romantic love and deep attachment to a partner.

The first is women working, moving into the workforce.

I've looked at 130 societies

through the demographic yearbooks of the United Nations.

Everywhere in the world, 129 out of 130 of them,

women are not only moving into the job market --

sometimes very, very slowly, but they are moving into the job market --

and they are very slowly closing that gap between men and women

in terms of economic power, health and education.

It's very slow.

For every trend on this planet, there's a counter-trend.