So I'm starting us out today with a historical mystery.

In 1957, there were two young women,

both in their 20s,

both living in the same city,

both members of the same political group.

That year, both decided to commit violent attacks.

One girl took a gun and approached a soldier at a checkpoint.

The other girl took a bomb and went to a crowded café.

But here's the thing:

one of the those girls followed through with the attack,

but the other turned back.

So what made the difference?

I'm a behavioral historian, and I study aggression,

moral cognition

and decision-making in social movements.

That's a mouthful. (Laughs)

So, the translation of that is:

I study the moment an individual decides to pull the trigger,

the day-to-day decisions that led up to that moment

and the stories that they tell themselves about why that behavior is justified.

Now, this topic --

it's not just scholarly for me.

It's actually a bit personal.

I grew up in Kootenai County, Idaho,

and this is very important.

This is not the part of Idaho with potatoes.

We have no potatoes.

And if you ask me about potatoes,

I will find you.

(Laughter)

This part of Idaho is known for mountain lakes,

horseback riding,

skiing.

Unfortunately, starting in the 1980s,

it also became known as the worldwide headquarters

for the Aryan Nations.

Every year, members of the local neo-Nazi compound

would turn out and march through our town,

and every year,

members of our town would turn out and protest them.

Now, in 2001, I graduated from high school,

and I went to college in New York City.

I arrived in August 2001.

As many of you probably are aware,

three weeks later,

the Twin Towers went down.

Now, I was shocked.

I was incredibly angry.

I wanted to do something,

but the only thing that I could think of doing at that time

was to study Arabic.

I will admit,

I was that girl in class that wanted to know why "they" hate "us."

I started studying Arabic for very wrong reasons.

But something unexpected happened.

I got a scholarship to go study in Israel.

So the Idaho girl went to the Middle East.

And while I was there, I met Palestinian Muslims,

Palestinian Christians,

Israeli settlers,

Israeli peace activists.

And what I learned is that every act has an ecology.

It has a context.

Now, since then, I have gone around the world,

I have studied violent movements,

I have worked with NGOs and ex-combatants in Iraq,

Syria,

Vietnam,

the Balkans,

Cuba.

I earned my PhD in History,

and now what I do is I go to different archives

and I dig through documents,

looking for police confessions,

court cases,

diaries and manifestos of individuals involved in violent attacks.

Now, you gather all these documents --

what do they tell you?

Our brains love causal mysteries,

it turns out.

So any time we see an attack on the news,

we tend to ask one question:

Why?

Why did that happen?

Well, I can tell you I've read thousands of manifestos,

and what you find out is that they are actually imitative.

They imitate the political movement that they're drawing from.

So they actually don't tell us a lot about decision-making

in that particular case.

So we have to teach ourselves to ask a totally different question.

Instead of "Why?" we have to ask "How?"

How did individuals produce these attacks,

and how did their decision-making ecology contribute to violent behavior?

There's a couple things I've learned from asking this kind of question.

The most important thing is that

political violence is not culturally endemic.

We create it.

And whether we realize it or not,

our day-to-day habits contribute to the creation of violence

in our environment.

So here's a couple of habits that I've learned contribute to violence.

One of the first things that attackers did

when preparing themselves for a violent event

was they enclosed themselves in an information bubble.

We've heard of fake news, yeah?

Well, this shocked me:

every group that I studied had some kind of a fake news slogan.

French communists called it the "putrid press."

French ultranationalists called it the "sellout press"

and the "treasonous press."

Islamists in Egypt called it the "depraved news."

And Egyptian communists called it ...

"fake news."

So why do groups spend all this time trying to make these information bubbles?

The answer is actually really simple.

We make decisions based on the information we trust, yeah?

So if we trust bad information,

we're going to make bad decisions.

Another interesting habit that individuals used

when they wanted to produce a violent attack

was that they looked at their victim not as an individual

but just as a member of an opposing team.

Now this gets really weird.

There's some fun brain science behind why that kind of thinking is effective.

Say I divide all of you guys into two teams:

blue team,

red team.

And then I ask you to compete in a game against each other.

Well, the funny thing is, within milliseconds,

you will actually start experiencing pleasure -- pleasure --

when something bad happens to members of the other team.

The funny thing about that is if I ask one of you blue team members

to go and join the red team,

your brain recalibrates,

and within milliseconds,

you will now start experiencing pleasure

when bad things happen to members of your old team.

This is a really good example of why us-them thinking is so dangerous

in our political environment.

Another habit that attackers used to kind of rev themselves up for an attack

was they focused on differences.

In other words, they looked at their victims, and they thought,

"I share nothing in common with that person.

They are totally different than me."

Again, this might sound like a really simple concept,

but there's some fascinating science behind why this works.

Say I show you guys videos of different-colored hands

and sharp pins being driven into these different-colored hands,

OK?

If you're white,

the chances are you will experience the most sympathetic activation,

or the most pain,

when you see a pin going into the white hand.

If you are Latin American, Arab, Black,

you will probably experience the most sympathetic activation

watching a pin going into the hand that looks most like yours.

The good news is, that's not biologically fixed.

That is learned behavior.

Which means the more we spend time with other ethnic communities

and the more we see them as similar to us and part of our team,

the more we feel their pain.

The last habit that I'm going to talk about

is when attackers prepared themselves to go out and do one of these events,

they focused on certain emotional cues.

For months, they geared themselves up by focusing on anger cues, for instance.

I bring this up because it's really popular right now.

If you read blogs or the news,

you see talk of two concepts from laboratory science:

amygdala hijacking and emotional hijacking.

Now, amygdala hijacking:

it's the concept that I show you a cue -- say, a gun --

and your brain reacts with an automatic threat response

to that cue.

Emotional hijacking -- it's a very similar concept.