NOVA

KEITH DAVID

It is an epic story... spanning all of human history.

MARTA LAHR

This man was shot at a distance twice with arrows.

LYNN HUNT

Torture was legal, it was administered in front of a judge.

DAVID

An age-old battle between our inner angels...

KAREN WYNN

We can see how the human mind is fundamentally built.

DAVID

...and our demons. (fire blazing) We're at war with ourselves. But one with a surprising twist.

JOSHUA BUCKHOLTZ

Contrary to what we might think from the news every day, rates of violence are actually declining over time.

STEVEN PINKER

The decline of violence might be the most significant development in human history.

DAVID

Has violence really declined? A lot of people just don't believe this.

CROWD

You will not replace us!

PHILIP DWYER

It is extraordinarily controversial. It's an interesting hypothesis to test.

DAVID

The stakes couldn't be higher.

MOHAMED SALIOU CAMARA

This is about our very existence.

DAVID

Now science is tackling violence. We're saying, like, "Here are things that we could do." From the streets of Baltimore...

MAN

We can see shootings go down.

DAVID

To war-torn regions of Iraq.

SALMA MOUSA

We're not just testing things in a lab environment, but we're really testing these in the field.

PINKER

We've done something right. Let's figure out what it is and keep doing it.

DAVID

Are we on the path to a more peaceful world? STEIN TONNESSON: It takes just one war to destroy the whole trend. "The Violence Paradox." Right now, on "NOVA." Major funding for "NOVA"

is provided by the following

(explosion, screaming,

REPORTER

The shooting started.

POLICE OFFICER (on radio)

Shots fired. More shots fired.

REPORTER

This was the horrific picture just moments after the white van... Multiple fatalities is what we're hearing from officials at this moment. Kim Jong Un has detonated what is widely believed to have been a hydrogen bomb. The world has devolved into a place where nobody can feel safe. (explosion, man shouting)

GERALDO PAGAN

Wars is everywhere. It's every corner of the world.

REPORTER

At least 40 people were killed...

JOSEPH SOLOMON

Every day, when you're on the news, there's more and more violence.

REPORTER 5

There has been tear gas, they have been pepper sprayed.

LINDA HARVEY

I'm afraid for my children in the world that they'll grow up in.

REPORTER

They let loose a hail of bullets. It keeps getting worse.

REPORTER 7

And this time, gunfire aimed at elementary school children.

REPORTER 8

This is the 22nd school shooting this year...

VICTOR RIVERA JR

There's gun violence, police brutality...

ERIC GARNER

I can't breathe. People coming and attacking our country. (explosion, shouting)

REPORTER

The first of the two explosions... That could happen to my city. That could happen to me. (people shouting)

MARQUIS VICTOR

The world is through and through a violent place. That's just a part of existence.

DAVID

Is this who we are... a species doomed to kill and be killed... a never-ending cycle of violence?

PINKER

The reality is that we may be living in one of the most peaceful eras in human existence.

DAVID

Peaceful? Could this possibly be true?

PINKER

Violence has been in decline. But that just doesn't count as news. You just never see a journalist saying, "I'm reporting live from a country that's at peace," or "a school that hasn't been shot up." (siren blaring)

DAVID

Psychologist Steven Pinker was reading an obscure text when he came across a chart that piqued his interest. It plotted a steep decline in rates of homicide in England.

PINKER

Once I stumbled upon this graph, I mentioned it in a blog post, and then I received correspondence from scholars in a variety of fields, telling me that I could've made an even stronger case.

DAVID

Intrigued, he looked further.

PINKER

I saw dataset after dataset, all of which showed declines in violence, in different parts of the world, with different kinds of violence, and I realized there was a story that needed to be told.

DAVID

A story that spans the entirety of human history, drawing on disciplines from archaeology to neuroscience, and has the potential to turn conventional wisdom on its head.

RICHARD WRANGHAM

To me, it's absolutely huge. If we think that life is better by going back into the past, we're making a very serious mistake. The greatest thing that's happened to humanity is that we've lowered our rates of violent death by 90%. This is the big story. (people clapping rhythmically)

DAVID

But could it be too good to be true?

RUBEN MENDOZA

The demographics of the past are not at all clear cut. And so as a result, we're making comparisons that we're drawing literally out of thin air.

CAROLYN ROBERTS

There's so many people who would hear Steven Pinker and think, "What world is he living in? This-this isn't my life at all." It depends on who you are and where you live.

REPORTER 10

North Korea's nuclear test...

BUCKHOLTZ

Steve's overarching claim flies in the face of common sense. That can't be true! The Cossacks are always coming, there's always danger.

CAMARA

We may or may not agree with his conclusions... (explosion) but it is important to understand the trends of violence so we can prevent, if possible, violence today.

DAVID

It's a controversial argument, but if physical violence really has declined, it presents us with a huge opportunity.

PINKER

To point out that things were worse in the past is not to say, "We should relax, our problems are all solved." Quite the contrary; it's by understanding how our predecessors were able to drive down rates of violence that we can be emboldened to try to drive them down even further.

DAVID

Has violence declined? And if so, can we uncover clues in our past to make us safer today? To find out, we have to go back, way back, to some of the earliest records of human prehistory... in one of the most desolate places on earth.

LAHR

Nataruk is a bleak part of the landscape. There's no vegetation, and it's got a dark gravel covering the surface.

DAVID

Marta Mirazn Lahr started excavating this site seven years ago.

LAHR

We arrived, and already you could see on the floor all these fragments of bones. The first thing we saw was in this area that we could see coming out of the ground the broken lower legs, the shin bones, of somebody. We started clearing and excavating, and the bones of another one appeared, so we would clean that one. And the bones of another one appeared. We found the remains of 27 people. They're not graves that have been dug or prepared. They are in positions that suggest that they just lied where they died. What we have here is actually an ancient crime scene.

DAVID

A crime that took place 10,000 years ago, when this desert looked very different.

LAHR

10,000 years ago, you had a very large lake that had formed a beach. (water splashing) You would have had palm trees and gazelles and hippopotamus. It would have been a really rich landscape. So what we had was a population of fisher-foragers, hunter-gatherers. And whenever there is something that one group has and another one doesn't, the potential for conflict exists.

DAVID

A conflict recounted in bones, now buried in a remote storeroom in northern Kenya.

LAHR

You read them like a book. And the skeletons are telling us a bit about their life but most about their death. (moving bones) When we found this skull, all we could see was the back of the head. But when we started excavating, we could see the whole skeleton lying face-down. And when you turn it around, you can see this bone has been crushed in. He received a blow with a blunt instrument and another one on the side of the head. (hitting)

DAVID

And he wasn't alone. Many of the skeletons bore signs of violence.

LAHR

There are injuries to the head that suggest there's a cut in the face of the skull. (hitting) Injuries to the spine that suggest projectiles, arrows. (men screaming, man groans) And this one was bound at the time of death. Inside the ribs we found the bones of a baby.

DAVID

Something terrible clearly happened here, but what?

LAHR

One of the most striking discoveries at Nataruk comes from what was probably the most difficult skeleton to excavate. However, we discovered the tip of an arrow still embedded in the head. We have direct evidence that people were attacked. But there's more. The arrow tip was made of obsidian, a material that is rare and of which we find no sources locally. And so it tells me that the attackers actually came from somewhere else. It wasn't just a chance encounter between two groups fishing that ended up in a fight. Because if you go out fishing, you are not carrying this range of weapons.

DAVID

The bones of Nataruk are the oldest known evidence of a planned raid-- a form of early warfare.

LAHR

And I think that as a behavior, as-as a characteristic of human societies, it probably goes back in time much, much deeper.

DAVID

The question is how deep?

CARLOS BUSTAMANTE

The archaeological record on every continent shows massive evidence of human-to-human destruction. (laughing): You know? There's just no other way of putting it, right? The paleolithic record is a horror show.

DAVID

From Otzi, the 5,000-year-old iceman found with an arrow in his back...

BUSTAMANTE

It looks like a hit job.

DAVID

To Kennewick Man, 8,500 years old-- a blow to the chest shattering six ribs; to Sima de los Huesos-- Spanish for "Pit of the Bones"-- where a 430,000-year-old Neanderthal was found with severe blunt-force trauma.

BUSTAMANTE

Head bashed in, indubitably. There's even evidence of cannibalism on almost every continent. You see violence time and time again in archaeological site after archaeological site.

DAVID

Of course, a handful of cases may not be a fair sample of the distant past. How violent were we?

PINKER

You can't answer that question by particular incidents, because there's violence in-in all societies. You really do have to count.

DAVID

And that's exactly what a group of Spanish scientists did... scouring the records of over 600 human populations between 50,000 years ago and today. Surveying the evidence-- a bashed-in skull here, an embedded arrow head there-- they found that the proportion of prehistoric people who suffered a violent death was up to three times greater than today.

PINKER

I was stunned at the high rates of violence. There's nothing close in any modern society.

DAVID

What has changed, and more importantly, why? To figure that out, you first need to understand some pretty basic things about us.

PINKER

People often ask, "Are humans violent by nature or peaceful by nature?" The reality is we're both.

DAVID

Pinker views our history as an epic struggle between our inner demons that push us toward violence... and our angels that pull us away.

PINKER

The brain is a complex place. It houses many circuits, some of which incline us toward violence and some of which inhibit us from violence.

DAVID ANDERSON

That tension between acting on an aggressive impulse and restraining ourself is fundamental in our brains, because we are clearly aggressive animals. (growling)

DAVID

From body-slamming seals... (buzzing)...to fighting fruit flies, violence, usually committed by males, is something we share with most animals on the planet. (eagle screeches) (growling)

ANDERSON

Aggression is one of the most common social behaviors across the animal kingdom. (growls) Almost every sexually reproducing species shows aggression. (wolf snarling) Including us.

DAVID

What in our brains drives aggression? That's what scientists at Cal Tech are trying to figure out. These mice have been genetically manipulated so that certain neurons in the brain can be activated by this blue laser.

ANDERSON

There are groups of neurons that if you activate these neurons in a mouse, you can trigger aggression.

DAVID

In the lab, Tomomi Karigo hooks up a mouse to the laser. Now, at the push of a button, she can remotely control the mouse's behavior. By stimulating a certain brain region, we can change the emotional state of the mouse. Just flipping the switch. (mice squeaking) This animal is now in an aggressive state, attacking the other mouse.

ANDERSON

There's some component of, like, a volume-control knob here, where as we stimulate them more intensely, we get more intense aggression. (squeaking)

DAVID

Look what happens when you turn the power down.

KARIGO

Now the light is off, and the animal retreats to the corner of the cage.

ANDERSON

Not only are we able to turn on aggression at will, we can also stop a fight dead in its tracks by inactivating these neurons.

DAVID

This experiment in mouse mind control has allowed them to pinpoint aggression in the brain.

ANDERSON

We've learned there are clusters of cells deep in the brain in a region called the hypothalamus that play a key role in organizing aggressive behavior.

DAVID

The same may be true with us. Turns out whether it is mice or humans, we share some of the same basic wiring.

ANDERSON

The parts of the brain that are in the mouse that control these behaviors are present in humans. They are some of the most evolutionarily ancient parts of the brain. (automatic knife clicks)

DAVID

So the wiring for aggression runs deep. But that's only half the story.

PINKER

We have circuits in our brain that incline us toward rage, toward revenge, toward sadism. On the other hand, there are other circuits in the brain that give us a sense of empathy, an ability to feel the pain of others. Even babies have a rudimentary sense of fairness. So I think we're ready for Ethan. Would you like to bring him into our testing room?

DAVID

Karen Wynn is a developmental psychologist at Yale who has created an ingenious experiment to find out whether babies are born with a sense of morality.

WYNN

We're going to just have you sit here... I was interested in the fundamental structures of the human mind. What do we bring with us when we come into the world, how do we understand the world? Up goes the curtain! (duck puppet squeaking)

DAVID

To figure that out, she puts on a two-act puppet show for babies.

WYNN

So this duck is looking inside this box, sees a nice toy inside of it, and is trying to open the box to get the toy, but is not being successful opening it. (box lid rattling) And this green shirted puppy very nicely helps the duck so it can get its toy. That's our nice puppet. (gurgling)

DAVID

In act two, this nice puppy takes center stage.

WYNN

And now, our nice puppy is playing with this ball, and he very nicely rolls it over to the blue-shirted puppet. And the blue shirted puppet rolls it nicely back to him. That was a nice interaction. (gurgling) Now this time he's going to invite the other kitty to play with him. "Will you roll it back to me?" "No." He steals the ball. What a jerk.

RESEARCHER

Hi!

DAVID

Next, the babies are given a choice. Which one do you like? Do they prefer the kitty who was nice to the nice puppy, or mean to the nice puppy?

WYNN

If you give them the choice, babies very robustly choose the nice one. Awesome job! Even a three-month-old can look at an interaction between two strangers and decide, "Oh, that's a good interaction, that's a nice human being." Or, "That was a bad interaction, that's a jerk, I don't like that jerk." (xylophone chiming)

RESEARCHER

Do you want to just show Dad where to sit?

DAVID

But that's just the half of it. Watch what happens when Wynn flips the script, and babies see a mean version of the same play.

RESEARCHER

Up goes the curtain. (duck puppet squeaking)

WYNN

This time this mean puppy comes along and slams the box lid shut. He's not nice at all. (buzzer buzzes)

DAVID

This time, the mean puppy is the star of act two. Just like his nice counterpart, he gets treated nicely by the blue kitty and then meanly by the orange kitty.

RESEARCHER

Do you see these?

DAVID

Will the babies still prefer the nice kitty? Do you see this one? Which one do you like? No. Now they consistently pick the mean one. Which one do you like? Turns out that even at this age, babies have the capacity to make simple moral judgments. Oh, good job.

WYNN

It's like, "You're not deserving "of having a friend play a nice game with you. "You treated someone else badly, you should be treated badly in your turn." So that tells us that well before their first birthday, babies are already developing notions of just desserts. That is morality.

DAVID

So both angels and demons are baked into our biology.

AZAR GAT

We have both of these behavioral strategies in our nature, instilled in us through the process of evolution, and we switch between them according to what we judge as more effective.

DAVID

If violence has declined since prehistoric times, what did our ancestors do that tipped the balance toward our better angels? One of the first violence reduction techniques was the state. Government can tamp down the cycles of violence.

CAMARA

The human species has come a long way for thousands of years to get where we are today. Because of government, we stay in line.

DAVID

Until about 5,000 years ago, humans lived in small, nomadic bands. But as agriculture took hold, populations grew, and the first governments emerged.

IAN MORRIS

As societies get bigger and bigger, more and more problems have to be solved, and the sort of almost inevitable result of this is people start to form governments.

DAVID

Governments that would need more complex systems of rules... and leaders to solve those problems. While those early kings and pharaohs waged plenty of wars, they had a strong incentive to reduce violence among their minions.

PINKER

It's not that the early kings and emperors had a benevolent interest in the welfare of their citizens. But just as a farmer has an incentive to prevent his cattle from killing each other, these early rulers wanted to prevent violence that deprived them of slaves and soldiers and taxpayers.

WRANGHAM

Much of the decline of violence is due to the existence of the state. Without government, the potential for chaos is huge.

DAVID

In fact, when researchers pooled together the work of anthropologists, ethnographers, and statisticians comparing those living in a state society to those who do not, the numbers are striking.

PINKER

Whenever there are data that actually count the bodies, you see that rates of violence in non-state societies are higher than in societies with the rule of law.

DAVID

Even so, for those living under the world's first governments, life was still pretty brutal. (man chanting)

PINKER

In general, rates of violence go down, but when people are pacified by a kingdom or an emperor, it's not that they're free of violence, because the violence of people killing each other is replaced by the violence of the state killing people.

MORRIS

Through pretty much the whole of history, one of the things you do if you're the ruler of a society is advertise just how violent you're going to be if somebody crosses you. (knife stabbing)

DAVID

From the Maya, who sacrificed to appease the gods... (crowd cheering)...to the Romans, who killed for spectacle. (swords stabbing) (man screaming, groaning)...to Han Dynasty China, where torture was legal. (man groaning) And if you think early religions were a paradigm of peace, think again.

PINKER

The Bible, the so-called good book, is one long cavalcade of violence, beginning with Cain slaying Abel; Noah's flood; you have Samson killing thousands with a jawbone of an ass. (shouts) And then the Israelites are commanded by God to commit total genocide. (people clamoring)

DAVID

It would appear that our ancestors were obsessed with violence.

REBEL OFFICER

Sir, enemy fighters coming in!

DAVID

And judging from our taste in entertainment today... Our battle will be legendary! (growls) So are we. (both groaning, yelping) (Spiderman groans) (Killmonger and T'Challa grunting) (shouts) Even the mild-mannered among us can have a taste for violence, especially when it comes to revenge, a pleasure we can witness in the brain.

DAVID CHESTER

We're going to have you do the competitive reaction time task, okay?

TEST SUBJECT

Yeah.

CHESTER

Here we go.

DAVID

Here at the University of Kentucky, David Chester scans the brain of a volunteer

as they play a simple game

who can press a button faster when a red square appears on the screen. (clicking) The winner gets to blast their opponent with an annoying sound at a volume of their choice. (shrill sound plays) Remember that one and two are pretty quiet, and three and four get pretty loud.

TEST SUBJECT

Okay.

DAVID

The subject thinks they are playing against a real opponent, but actually it's a computer. (shrill sound plays at low volume) And it's not going to play nice. (shrill sound plays loudly) She just saw that her opponent picked a four. So now she's been thoroughly provoked. The volunteer seeks revenge. (shrill sound plays loudly) She just picked a four. Seems as though she's a little upset. Now, Chester can peer inside the brain at the very moment of retaliation. The scanner reveals increased activity in the ventral striatum, part of the brain's so-called pleasure center.

PINKER

The circuits in the brain that light up are the same as the ones that light up when we crave chocolate or gamble or see an attractive person. So the old saying "Revenge is sweet" is literally true.

DAVID

On this level, it seems our impulses haven't changed much. But have we always acted on them? What do the numbers say? As humanity moves toward the Middle Ages, the investigation turns from archeology to written records.

FABIAN DRIXLER

Most human societies historically have not been in the business of creating vast amounts of writing. The societies of the West are rather unusual in the amount of documents that they created and then successfully preserved.

PINKER

The decline of violence is by no means a Western phenomenon, although until recently, a lot of the studies focused on the West, 'cause that's where the data were.

DAVID

And some of the strongest data was assembled by Manuel Eisner,

a historical criminologist with a singular obsession

murder.

EISNER

Over the years, I developed a little bit of a obsessive interest in trying to find all the publications in different languages that had been written on homicide. "Robert of Chinehem hit Emmis, daughter of Alice of Crotchall, on the head with a stick so that she died, and he fled at once..." "Evildoers came to Thomas of Inglefield's house and killed him." (readings overlapping in different languages) "...this morning to my wife?" And then he kills him.

DAVID

It all started when he read an article that claimed that since the Middle Ages, homicide rates in England declined 40-fold.

EISNER

I thought, "This can't be true." And so I started looking at more evidence, more data.

DAVID

Trouble was, the data didn't exist in any one place.

PINKER

Eisner had to go deep into archives, sometimes into the basements of old town halls and churches, brush off the mouse droppings, and tally the causes of death.

EISNER

I would be looking at court records, prison documents, account books, confessions, or pardon books.

DAVID

Each source added a data point. Over the course of a decade, Eisner was able to plot homicide rates for England, Italy, Scandinavia, the Netherlands and Belgium, Germany and Switzerland. In the process, an astonishing picture began to emerge.

EISNER

All these dots that I'd collected lined up over 800 years along one single line. That was kind of, like, just an amazing moment. For every 100 years, the homicide rate in Europe was cut in half.

PINKER

When Manuel Eisner showed that this decline had happened in pretty much every European country for which we had continuous data, I realized this is a real phenomenon. It is not just the history of one country, but it seems to be a general historical process.

DAVID

Eisner's work provided hard evidence

of a decline in violence

over eight centuries, homicide rates fell from one in a thousand to one in a million.

The big question is

why? When you realize that rates of violence can change, that something that our ancestors did in the past worked, it emboldens you to try to figure out what it is. (people chattering)

DAVID

One answer might be what some social theorists call "the civilizing process." (horse nickering)

EISNER

The civilizing process is the idea that as societies become more interdependent, we are penalized for behaving in a violent way against another person. (seagulls squawking)

DAVID

In Renaissance Europe, commerce was booming-- ships brought goods from around the world. Violence among the masses was becoming bad for business and bad for the king.

ANDREW REITER

If businesses want to trade, they want to make money, and people profit off that, they live better lives when the economy's going well. There's an incentive for states to prevent violence from happening.

DAVID

The theory is this new economic order went hand in hand with a new set of social norms.

EISNER

What changes is that as a man your importance in society is no longer ruled by how good you are in fighting, but it's governed by how self-controlled you are.

DAVID

According to some researchers, self-control was something that was sorely lacking when one considers daily life.

PINKER

The medievals were, in a word, gross. They would copulate in-in full view. (people laughing, glasses clinking) At the dinner table, they would gnaw on a bone and put it back in the serving dish, drink from the plate, smack their lips. If you were out in public, you might very well have to relieve yourself in public view, in a street, in a bunch of holes on a bench. (dog barking)

DAVID

And judging from these passages from popular etiquette books, things must have been pretty... different.

JUDITH MARTIN

"Don't foul the staircases. "Don't relieve yourself in front of ladies. "Don't touch your private parts "under your clothes with your bare hands. "If you come across something disgusting in the sheets, don't turn to your companion and say, 'I should like to know how much this stinks.'" Well, these are laughable rules to us now, because we accept the idea that you don't go around urinating in front of other people, because how you treat people matters. (swords clanging)

DAVID

But how in the world could something as mundane as manners contribute to a decline in violence?

PINKER

Manners are a sign of self-control, of not acting on every impulse. If someone insults you, if someone steps on your toe, you don't immediately pull out a knife and challenge them to a fight. You hold your horses; you count to ten.

DAVID

As it turns out, the connection between self-control and violence is long known to neuroscientists.

ADRIAN RAINE

We've known for a long, long time that violent offenders have poorer levels of self-control than people who are nonviolent.

DAVID

And that has to do with the prefrontal cortex-- the area of the brain thought to be involved in planning and controlling our impulses.

RAINE

We've brain-scanned 41 murderers. And we showed that the prefrontal cortex is functioning more poorly in these murderers.

DAVID

The red and yellow show a normal level of activity. The scans from the murderers show dramatically decreased activity. Is there anything that can be done to strengthen this part of the brain?

RESEARCHER

In today's session, you will be completing a series of survey questions...

DAVID

That's what Raine's team is trying to find out here at the University of Pennsylvania. During the stimulation itself, you will be completing two cognitive tasks on the computer.

WOMAN

Yeah.

RAINE

They get electrodes put on the prefrontal cortex. And they'll get 20 minutes of stimulation.

RESEARCHER

You may feel tingling, itching, kind of prickling sensation.

DAVID

That tingling is stimulating or upregulating a specific part of the brain. (buttons beeping)

RAINE

And then they are given scenarios of, "If you were provoked, would you pick up a bottle, would you hit somebody on the head?" We're looking to see whether upregulating the prefrontal cortex reduces a person's intention to commit a violent, criminal act. (machinery playing music) We showed that by upregulating the prefrontal cortex, we're able to reduce criminal intent by about 30% or 40%.

DAVID

Is it possible, then, that acquiring habits of self-control like manners could have had the same effect? By giving somebody training in exercising self-control, that activity may flex the prefrontal cortex and enhance that part of the brain. (dishes clinking)

ROY HAMILTON

It stands to reason that if you practice a set of behaviors, that engages areas of your brain, which leads to a sort of virtuous cycle, right? It improves the behavior, and then the behavior, if you continue to engage in it, allows you to further strengthen the circuit.

DAVID

The theory is self-control laid the groundwork for a cultural shift away from violence. And yet we all know "civilized" is a relative term. By some measures Europeans may have become less violent toward each other, but at the same time they were embarking

on one of the bloodiest chapters in human history

the colonial conquests.

TIFFINY TUNG

In Europe during these colonial regimes, there's less violence in the core of the empire, but if you think about the lives of the, of the indigenous peoples, life was treacherous, life was awful. (whip cracking, picks clanking)

DWYER

The colonial projects is one in which indigenous peoples are either physically and violently repressed or, in some instances, eliminated entirely. (carriage rumbling)

CAROLYN ROBERTS

During that same period of time that violence is going down, you have something like the transatlantic slave trade, the largest forced oceanic migration ever to occur in human history. These slave ships that are plying the Atlantic with human cargo, these are mini war zones, where you have mortality levels that are between ten and 25 percent on every voyage. And it lasts for nearly 400 years.

DAVID

Once they arrived, many slaves were literally worked to death. (machinery chugging) In fact, much of the expansion of the European and later the U.S. economy was built on the violent exploitation of the over 12 million people forced into the transatlantic slave trade. (ship creaking, shackles clattering) And slavery wasn't the only form of state-sanctioned violence.

PINKER

There are a number of practices that were routine through human history that we universally recognize today are barbaric.

DAVID

From infanticide as a routine form of birth control, to burning at the stake, witch hunts, and human sacrifice, across the globe, heinous practices were still rampant. And Europe was no exception. (fire crackling)

PINKER

You had gruesome punishments, sadistic forms of capital punishment like breaking on the wheel. (people clamoring) (man groans)

HUNT

Breaking on the wheel is incredibly unpleasant. You were strung up on a huge, wheel-like device with your various limbs attached to the wheel. And the executioner would break each one of your bones. And then you would be left to die of internal bleeding, and people would watch. (person breathing raggedly) (mechanical rotating)

DAVID

Back then, torture wasn't some random act performed by a sadistic psychopath... (man groans) but a routine part of the law.

HUNT

It's hard for us to imagine this, but torture was legal, it was administered in front of a judge, usually.

DAVID

But by the mid 1700s, this gruesome jurisprudence was quickly losing favor in western Europe. (whip cracking, man screaming, horse whinnying)

HUNT

How do you get from most people thinking it's perfectly fine to do unspeakable things to people to a situation in which people say, "This is disgusting. "It's barbaric, it's horrendous. We can't do this." And this change happens in a very short period of time.

DAVID

To Lynn Hunt, a historian at UCLA, the answer has to do with a notion often taken for granted today.

HUNT

Without question, the single most radical idea of the 18th century is the idea of equality. They live in an incredibly hierarchical society, in which everyone is supposed to be deferential to their betters, in which there are incredibly rigid social divisions. How do they think past that?

DAVID

The idea of equality-- while at first reserved for a small group of people-- had to come from somewhere. And Hunt thinks it started with the written word.

HUNT

Literacy and the expansion of print had a very, very, very big impact.

MORRIS

The first mass-literacy societies, where half or more of the people in the society can read, these come about in Europe in the 17th and 18th centuries, and it's driven almost entirely by people wanting to read the Bible. But as people develop this skill, they realized, "Well, of course I can use it for a lot more than just reading the Bible."

DAVID

It wasn't just that people could read, it was what they could read about.

HUNT

Newspapers got people to recognize that there was somebody else in another city who is having the same experiences as they are.

DAVID

It is difficult for us living in a hyperconnected world to appreciate how big an impact this could have.

HUNT

Print newspapers are incredibly important in creating this broader sense of community.

DAVID

And it wasn't just newspapers-- the newly literate masses developed a huge appetite for the novel.

HUNT

It allowed the reader to really get inside the mind of the characters. You don't see just what they're doing. You see what they're feeling and thinking as they're doing it.

ROBERTS

They're writing in a way to allow the reader to enter into the life-worlds of other people and get empathy that would drive them to political action.

DAVID

Action such as the abolitionist movement, which was bolstered by slave narratives and popularized by a single novel.

ROBERTS

A book like "Uncle Tom's Cabin" is bringing people into a world that amplifies the humanity of the enslaved and, by extension, that they are deserving of freedom.

DAVID

The theory is that reading novels made people more empathetic. But can fiction really do all that?

JAMIL ZAKI

There's psychological evidence from laboratory studies, that reading fiction can build our care even for different groups of people, groups who we might not care that much about otherwise. So, for example, one of the most famous is what's known as the "reading the mind in the eyes" test.

DAVID

"The mind in the eyes"-- a scientific experiment designed to test empathy. Participants are shown a series of photographs of just eyes and asked to guess the emotion. Readers of literary fiction score consistently higher.

ZAKI

You think of reading a novel as a very personal thing that's just, oh, you're just, you know, sitting on your couch indulging in something. But no, you're doing something a lot more profound. You're kind of going to the empathy gym.

DAVID

And things didn't stop with the novel. A parallel revolution in science would seed even more radical questions.

MORRIS

The scientific revolution drives people to ask these underlying questions like, well, "Why do things in the way that we do?"

ROBERTS

There was a new sense of rationality, where we want to understand knowledge based on what we see and what we can actually document.

DAVID

Observation, hypothesis, experiment. The modern scientific method didn't just explain the stars. It's like scientific reasoning spills over from the natural world-- the kind of thing that, you know, Galileo and Newton are interested in-- toward the social world.

PINKER

Rather than accepting things because that's the way they always have been or because that's what God decreed or because you can't criticize the king, people started to rethink social arrangements from the ground up.

HUNT

It made some people think about slavery. It made some people think about women. It made some people think about religious minorities. But mainly it made everybody think about equality.

DAVID

Equality-- even though it was narrowly defined to start with, 18th-century European thinkers stoked the embers on a revolutionary ideal. Once you unleash the light of freedom... You know, we say in Africa that, "When the sun rises, "if you don't want to see it, the only thing you can do "is to close your eyes. But the rest of the world will see." The cat is out of the bag. Still, some ideas resulting from the scientific revolution were far from perfect. And it's the same period in which pseudoscientific racism as we come to know it in the second half of the 19th century really begins. Perhaps reason and empathy helped fuel abolitionist movements. But at the same time, science was co-opted to justify racism.

ROBERTS

This is one of those scenarios where we have to hold two very difficult things together. Things are not always all good or all bad, but they are a complicated mixture of both.

DAVID

And that balance of good and bad, according to Pinker, was shifting in favor of our angels.

PINKER

The rise of science doesn't mean racism was eliminated. But it's not a coincidence that the first systematic arguments against slavery, against cruel punishment, against imperialism were made around that time. Ideas matter.

DAVID

But did those ideas change people's attitudes toward physical violence? Where's the evidence? Turns out, some clues were hidden in plain sight... in the records of the Old Bailey, the central criminal court of London.

TIM HITCHCOCK

The Old Bailey proceedings are, in my estimation, the most detailed account of everyday life ever produced in print.

DAVID

Tim Hitchcock spent 15 years digitizing 239 years of court proceedings. (gavel banging)

HITCHCOCK

They cover the period from 1674 to 1913, and they encompass 197,745 different trials. It is the largest body of recorded speech anywhere in the world.

DAVID

But this giant anthology presents a giant problem.

HITCHCOCK

At 197,000 trials, nobody's ever read all of them. It's huge, right? It's, it's unreadable.

DAVID

Enter Simon DeDeo, a data scientist at Carnegie Mellon University. He has a hunch that computers can see patterns in history that no human can.

DeDEO

I'm interested in how people see the world. And if I want to see it really big scale, over the course of a couple of centuries, then I have to do a very different kind of science.

DAVID

And to do that, he would need a really big data set. Hitchcock's 127 million words would do just the trick.

DeDEO

Somebody whispers in our ear, "Hey, there's this stuff sitting out there in Britain." That, for us, is a gold mine.

HITCHCOCK

We met at a pub for a couple of pints of beer. And where we ended up was with the realization that there were techniques that would allow us to pull out human behavior from this 127 million words of transcribed data.

DAVID

But how?

DeDEO

A computer can't read, it can't understand, you can't have a conversation with it. So what we have to do is transform all of those trials into something that a computer scientist can manipulate.

DAVID

Here's where Tim had an idea-- "How about we use 'Roget's Thesaurus?'"

HITCHCOCK

Roget, in the 19th century, sat down and went through the dictionary, and assigned every word to a particular meaning.

DeDEO

He groups them into collections of words that all kind of mean the same thing. Words like "cut" and "thrust," "lunge," "kick," "punch." All of those words mean, of course, different things. It's one thing to punch somebody, it's another thing to kick somebody. What Roget's classification allows us to do is say, "Look, forget the details. These are all examples of category 716, attack." And that enables the computer to summarize a trial.

HITCHCOCK

What quickly emerged from the analysis of the proceedings was that the words spoken in court reflect powerfully attitudes towards violence. (gavel banging) The way in which the state defined crime and chose to prosecute crime was changing decade by decade.

DAVID

For example, in the earliest accounts, the number of violent words often had nothing to do with the crime charged.

HITCHCOCK

"1770. "John Jones and Isaac Ely of Saint Sepulchre were indicted "for assaulting James Lowe upon the king's highway. (horse whinnying, men shouting) "One of them immediately stabbed him with a knife on the breast "and at the same time, they catched hold of his hat and wig, value 15 shillings." (horse whinnying) Despite the violence of this assault, the eventual indictment was for theft. But in later cases, that changes. Violent words strongly correlate with being on trial for a violent crime. 1909, William Musson was caught trying to steal goods and money from the Commercial Gas Company. But in the process he also tried to choke, suffocate, and strangle one of the guards. (man struggling) In this instance, the robbery itself didn't figure in the trial to any extent. And instead what they focused on was the violence of that assault.

DAVID

The records of the Old Bailey are hard evidence of a cultural shift away from interpersonal violence.

HITCHCOCK

People became much less tolerant of violence. The idea that a pub fight is normal, the idea that carrying a knife or sword was normal. (men struggling, blades clanking) By the early 20th century, people were expected to settle their disputes in ways that didn't involve breaking a nose or taking out a couple of teeth.

DAVID

A decline in homicide... (mechanical clanking) a retreat from heinous practices... (fire crackling) and a cultural shift in attitudes. (gavel banging) But these data are only for Europe. What about the rest of the world? AGUSTN

FUENTES

Can we actually draw some universal based on the European history? I would say yes and no. No, because Europe is a small backwater for all of humanity, but yes, because in the last 500 years, European philosophical, economic, and political systems have spread around the world and had massive impact.

PINKER

I focus on the West because that's where the data are best. But if this is a general historical process, it has to be shown worldwide, and in many cases it has been, such as data on rates of death in warfare. That comes from all over the world. (muskets firing intermittently) (cannon fires, horse whinnying)

DAVID

But surely the data from the 19th and 20th centuries would paint a grim picture of the world. (soldiers marching, blades clanking) From the Napoleonic Wars... (man shouting)...and the Taiping Rebellion... (men clamoring, rifles firing intermittently) to the massive colonial conquests... (cannons firing, airplanes droning)...and two world wars capped by the dropping of the atomic bomb... (bomb whistling, explosion, rumbling)...how in the world could we be getting less violent? (airplanes droning, bombs whistling)

PINKER

World War II undoubtedly was the most destructive event in human history. But more people were alive in the 1940s than were alive in earlier periods in history. So we also have to take into account just how many people there were.

DAVID

In absolute numbers, World War II may have killed the most people. But compare the death toll

to the number of people living at the time

2.3 billion. Looking at it this way, there were far deadlier events before World War II.

PINKER

When you plot how many people get killed as a proportion of the world's population, you can appreciate some of these trends.

DAVID

By this metric, World War II falls to number eight. The deadliest? The 13th century Mongol conquests launched by Genghis Khan, which reportedly killed roughly 40 million people-- almost ten percent of the world's population at the time. Of course, that's just an estimate. But there's one other number worth considering... zero. That's the number of wars waged directly between the major powers since the Korean War. The big national armies are not fighting each other. That's not some data construction, that's a fact. (explosion, rapid gunfire) Of course major powers have invaded smaller countries... and had a hand in numerous civil wars. But overall, deaths from every form of war have been on the wane.

GOLDSTEIN

War's like a cancer that used to be spreading and now it's in remission. It's getting smaller and smaller, the tumors are shrinking. There are not too many periods in world history where we've observed such a steep decline in violence. (shouting) (klaxon-like sound blaring)

DAVID

So how did we get from here... ...to here? Is it possible that something inside us has changed?

ROBERT CIERI

We know that violence has been decreasing in human history, and we have a lot of explanations of why that might be, whether they be social forces, or the way we think, the way we structure our society. But here we can offer a biological explanation as well.

DAVID

A biological explanation that pins some of humanity's push toward peace on evolution. But to understand it, you have to look at a groundbreaking experiment in 1950s Russia. (foxes barking)

CIERI

They took a population of wild foxes, and they just bred them solely for tameness. The ones that acted the friendliest, they bred those together. By breeding the most docile foxes in each generation to each other, over the generations, they ended up with something that looked remarkably like a domesticated dog. The foxes' behavior changed, and so did their physical appearance. The skulls became shorter, and also proportionately wider.

DAVID

The new shape of the skull appears to go along with decreased aggression. Over several generations, the foxes became domesticated. Is it possible that over a much longer timeframe something like this has happened to humans too? A kind of self-domestication? The self-domestication hypothesis is, I think, one of the most exciting hypotheses running out there today.

WRANGHAM

It would mean there was natural selection against aggressiveness. That over the last several hundred thousand years, our species has become less violent and, conceivably, that is still continuing today.

DAVID

To test this hypothesis, Robert Cieri gathered up human skulls from across 200,000 years. (clicks pen) Like the foxes, has the shape of our skulls changed? This particular specimen is about 90,000 years old. And I'm measuring the width... and the length of the face. And then I'm also going to measure the projection of the brow ridge. These skull measurements are tightly linked to levels of a hormone

known to facilitate violence

testosterone.

CIERI

In general, people with higher testosterone have different face shapes than people that have lower testosterone.

DAVID

To some, this harkens back to 19th century pseudoscience.

CIERI

Phrenology was a pseudoscientific practice where they would look at the shape of someone's skull and infer things about their personality. But this isn't phrenology. The trends we're showing line up with a lot of other forms of evidence.

DAVID

And it's more than the shape of the face.

CIERI

Testosterone's a very complicated hormone. But we do know that it seems to be correlated with levels of aggression and violence. It's not like, you know, you give somebody more testosterone, and they turn into the Incredible Hulk and start tearing things apart. But men who have been exposed to higher levels of testosterone during prenatal development or during pubertal development are more likely to engage in aggression throughout the lifespan.

DAVID

This link may partly explain why it is men who are responsible for most of the world's violence.

WRANGHAM

90-something percent of every kind of violence you can think of is due to males. If we got... somehow got rid of human males, then the entire situation would change.

DAVID

In fact, the situation may have already changed... and the evidence might be staring us in the face.

CIERI

We found that the shape of the skulls changed. The upper face became shorter, relative to its width. And the brow ridge projection went down over time. So, we're showing that testosterone levels have gone down over the last 200,000 years.

WRANGHAM

The anatomical evidence is very clear. Males became much less aggressive.

CIERI

Violence was an important social tool in human history. You can get things done by being violent. But we're moving into a world where that tool is less and less effective, and violence doesn't pay off as much.

DAVID

And the recent rise of nonviolent movements seems to bear this out. Consider Mahatma Gandhi, who showed the world the power of nonviolent resistance. The Salt March of 1930, where he drew in hundreds of thousands of Indians by marching 200-plus miles to the sea, had a profound effect on people's understanding of what nonviolent action could achieve. And Erica Chenoweth's research suggests Gandhi was by no means alone. The Salt March is now just one of over 300 cases of nonviolent resistance that occurred since 1900. (whistling, banging drums)

CHENOWETH

The Philippines People Power movement, the Polish Solidarity movement, the Serbian Anti-Milosevic movement, The Rose Revolution in Georgia, the Orange Revolution in Ukraine, the Tunisian Jasmine Revolution. (people chanting)

DAVID

But the most impressive thing is not the sheer number, it's their results.

CHENOWETH

Nonviolent action has been wildly more effective. In fact, the success rates of nonviolent mass movements are about twice as large as the success rates for violent campaigns.

DAVID

And this increase in nonviolent resistance has been paralleled with an expansion of human rights. The adoption of the Universal Declaration of Human Rights in 1948, though just words on paper, set a new goal for the world.

PINKER

The idea of universal human rights is a huge change in worldview. It meant that you couldn't enslave other people, it meant that you couldn't wage wars that devastated people by the millions.

DAVID

The rights revolution that sputtered forward in the 19th century was finally gaining momentum.

This is the thing about rights

the minute you declare their existence, you get people saying, "Well, if that, why not this?" You instantly have this kind of pressure for the recognition of more rights, which we still are living with today.

DAVID

And where there's reliable data, this expansion in rights often maps onto downturns in many quantifiable measures

of physical violence

genocide, homicide, rape, assault, child abuse, domestic violence, even spanking. They all point downward. But before we pat ourselves on the back, it's worth considering that these numbers only tally physical violence. Steven Pinker's focus on deadly violence is telling us part of the picture. It's an important question to ask, but it's not comprehensive, right, in the kinds of violence that affect people's daily lives.

BROWN

Lethality isn't the only way to measure violence. Mass incarceration is a form of violence. There's a kind of psychological violence, right, the destruction of other people's wills, that is happening on a mass scale that doesn't get counted in those statistics.

FUENTES

The definition of violence has to be expanded. What does it mean to live longer if you're suffering horribly, mentally, socially, cognitively? And so, how we think about ups and downs in violence has to take this broader perspective. (people shouting)

PINKER

We're at the point in which discussions of violence are evolving. And that is real progress from when discussions of violence were centered on world wars, genocides.

DAVID

Nonetheless, even if progress is being made, a trend is not necessarily a prediction. (loud explosion) With the enormous military capacities that states have today, it takes just one war to destroy the whole trend. (shouting in German) And just as German nationalism spawned Hitler, many see today's new wave of nationalism as a looming threat. In many countries, we've seen maybe a little bit of a backsliding towards more authoritarianism. TONNESSON: Voters who are motivated by nationalism, may elect leaders that could destroy it all. And blindly following those leaders, wherever they may lead us, is still a very real danger. At SWPS University in Poland, Tomasz Grzyb and Dariusz Dolinski, are revisiting a famous experiment first conducted in the 1960s by the American psychologist Stanley Milgram. In the aftermath of the Holocaust, Milgram wanted to understand how seemingly good people could follow terrible orders. (speaking Polish) Just as Milgram did, the experiment starts by setting up a fake study.

GRZYB

There are two participants and there is a guy who presents himself as a professor of psychology and he says that, "Well, you are a participant in an experiment which is devoted to find out how memory is working."

DAVID

Grzyb is masquerading as a participant-- the so-called "learner."

DAVID

The other participant is the "teacher."

DOLINSKI

(door closes)

DAVID

Grzyb pretends to memorize sets of letters. But his responses are scripted.

DAVID

The teacher is told that the student is hooked up to the machine, and they must administer a shock if he answers incorrectly.

DOLINSKI

(clears throat) (flicks switch, Grzyb coughing over speaker)

WOMAN

(coughs, grunts)

DAVID

Grzyb is only acting-- he is not really wired to the machine.

DAVID

Because the experiment is highly stressful for the real subject, the so-called teacher, it's controversial. So it will be stopped at 150 volts, the tenth switch on the panel which, if real, would be an extremely painful shock. Will anyone go so high?

DOLINSKI

(grunting,

panting) DOLINSKI

(Grzyb shouts)

DOLINSKI

(Grzyb shouts) (Grzyb shouts) (Dolinski talking, Grzyb shouting) (Grzyb

shouting) DOLINSKI

DOLINSKI

(Grzyb shouts, grunts)

DAVID

With an authority figure ordering them... (Grzyb shouts)...most people go all the way to the highest shock level. (Grzyb shouts) (man sighs)

GRZYB

We had about 220 participants and about 90% of them were able to go up to the tenth switch.

DAVID

Many people think they wouldn't follow orders to commit violence, (gunshot) but the work of Grzyb and Dolinski suggests this capacity is in most of us.

GRZYB

It's not a question of our personality. It's a question of situation. There's a high probability that each one of us would behave in the same way. Somehow by our internal construction, by our attitude to the world, we are ready to do bad things to other people. (men shouting)

REPORTER

Hate no longer hides behind hoods.

DAVID

Which lands us in the present. It's clear that the story of human violence is not simple. Peace is not a forgone conclusion.

REPORTER

...reminiscent of images from a dark American past.

IAN MORRIS

We can go backward again. (crowd chanting) Just as we move very quickly toward a peaceful world, we can move very quickly back toward a world where most of us think violence is the answer.

REPORTER

The president's extraordinary tweet raised the real possibility the U.S. and Russia could soon be shooting at each other. Peace is being treated as something that automatically comes to pass, and we really can't take it for granted. In the U.S., violent clashes broke out on Saturday in the city of Portland, Oregon.

PINKER

Our nasty impulses haven't gone away. To point out that things were worse in the past is not to say that things are perfect in the present.

REPORTER

We still don't know just how many gunmen are out there and when they will be found.

PINKER

Quite the contrary, it's precisely by understanding how our predecessors were able to drive down rates of violence that we can be emboldened to try to drive them down even further.

DAVID

And to do that requires stepping back and trying to understand why the world feels so violent in the first place.

ROBERT MUGGAH

We are in a super-saturated 24/7 information society. When it bleeds it leads. And there is a sense, probably accelerated by both conventional media but also social media, that things are spinning out of control.

REPORTER

Reynolds streamed what happened next live on Facebook. >> He was reaching for his wallet. And the officer just shot him in his arm.

BROWN

People are experiencing violence happening in other places all over the world right now in their own lives, in a way they just couldn't before. That is a sea change in our consciousness.

DAVID

All this information feeds a particular bias long known to neuroscientists and psychologists.

PINKER

We call it the availability heuristic. We judge risk and danger according to how quickly examples pop into mind.

REPORTER

The van raced along at close to 50 miles an hour...

PINKER

So if there's a terrorist attack in the news, we think that terrorism is skyrocketing upward. (shouting, siren blaring)

MUGGAH

But if you look at the actual risk of being a victim of a terrorist incident in, say, Western Europe or North America, it's less than being hit by lightning.

REPORTER

North Korea's nuclear test...

PINKER

A diet of news stories will fool us into thinking that violence is much more prevalent than it really is. (overlapping reporters speaking)

BUCKHOLTZ

I have that same reaction-- there has to be danger, and to let your guard down for a moment is to be a sap, is to make yourself vulnerable. And it's only my, you know, scientific training that allows me to say, "You know what, crazy brain, look at the data."

DAVID

But aggregate data can only tell you so much. For example, taking the U.S. as a whole, homicide rates have declined dramatically, to about five deaths per 100,000 people per year. But when you drill down, you find that some cities have rates up to ten times higher.

MUGGAH

We tend to think of this phenomena as affecting all people equally. But the reality when it comes to, say, homicide or terrorism, is that it's hyper concentrated in time, space among certain communities.

DAVID

Why are some places more violent than others? What can the past tell us about violence today? History suggests that some of the factors driving violence down are a strong government, education, and equality. But those conditions are not evenly distributed today.

MUGGAH

Income inequality has a very strong statistical relationship with overall levels of homicide.

DAVID

In fact, income inequality is one of the strongest predictors for violence. Here in Baltimore, the situation is particularly dire, fueled in part by a legacy of racism and an extreme lack of economic mobility.

DEDRA LAYNE

I don't think that people are getting up every morning and saying, "Who am I going to go shoot today?" I think people are getting up saying, "How am I going to eat today?" And if someone prevents them from doing what they think they have to do in order to feed themselves and their families, there's a ripe opportunity for violence.

REPORTER

Baltimore City has seen 250 murders so far this year... STANLEY "PORKY"

DENNIS

Once violence starts, it spreads.

REPORTER

You can see the gun in his left hand. The gunman is still on the loose here...

DENNIS

When you kill this person's brother, then they want to retaliate and they want to make somebody feel the pain that they felt, so they become shooters and killers. It's like a... it's like a demon. (chuckles) It spreads from souls to souls.

DAVID

Without the resources to fix the underlying problems, this neighborhood is turning to an innovative intervention to reduce violence.

SLUTKIN

With respect to violence, we're stuck in the past. Our thinking now is medieval. We're blaming people, not understanding what's going on actually, not applying approaches that have been shown to work.

DAVID

For epidemiologist Gary Slutkin, those approaches are based on data. After returning from over a decade fighting infectious diseases in Africa, he recognized a distinct pattern.

SLUTKIN

I'm looking at a graph of violence, it looks exactly like the graph of cholera. I'm looking at the map of the clustering of violence, it looks exactly like the mapping of AIDS. So I'm saying, "Oh my God, you know, this is exactly like every infectious disease."

DAVID

And just like a disease, under certain conditions, violent acts are contagious.

SLUTKIN

One case of violence causes more cases of violence, just as one case of flu causes more cases of flu.

DAVID

So could the same methods used to fight infectious diseases also stop shootings?

RASHAD SINGLETARY

The shootings that we have had, most of them, these two are inside here...

DAVID

That's an idea being tested at Baltimore's Safe Streets, one of a growing number of programs adopting Slutkin's approach. There's just a lot of shootings going on in the neighborhood, so we was really trying get to the bottom of that.

SLUTKIN

The starting point in any epidemic is to detect where the next event might occur and interrupt the exposure.

SINGLETARY

So what're we going to do today for canvassing? I mean it's been a lot of things going on in the neighborhood so I'm going to just take a tour.

DAVID

To do that, Slutkin created

a new type of public health worker

a "violence interrupter."

SLUTKIN

A violence interrupter is basically a health worker who can know what is going on and find where an event might be likely to happen, and then prevent its progression. So you're cutting off the epidemic spread itself.

DAVID

The first step in fighting any epidemic is to identify the initial outbreaks-- the so called "hot spots."

STEPHANIE IRWIN

The red dots are the firearm homicides and the yellow dots are the non-fatal shootings. So if we map out all of the violence in the area then we can sort of see, like, "Oh, there's was a cluster up here on the right where the staff should be focusing on. "Maybe down here on the left there's another little area that we tend to see more violence happening." And then we base our program decisions on that data.

DAVID

Once the hot spots are pinpointed, the violence interrupters are deployed. DAMIAN "BURT"

McNEIL

Lately, there's been a lot of activity in the community, so we're just coming through, try to make sure everything's at peace. (engine rumbling, children playing)

DAVID

This team works in Park Heights, one of the most dangerous neighborhoods in the city.

DENNIS

Most of the violence is, is spontaneous. So we just try to do our walks so we can be there to try to catch it.

McNEIL

What really makes the program is the guys that's out here doing the footwork, doing the groundwork, because it's our credibility that really keep the peace.

DENNIS

We just try to get in everybody's heads and everybody's mind and let them know the shootings and homicides are not normal. (siren blaring) It's not normal for somebody to lay right there with five and six bullet holes in him, and he's dying, and... and that ain't normal for kids to see. It ain't normal for a mother to lose her son to senseless violence like that. (blinker clicking)

DAVID

Steve Diggs, better known as "Peppy," knows these streets.

PEPPY

I'm born and bred Park Heights. I've been here my entire life. If you drop me in the ocean, in the middle of the night, I'll start swimming towards Park Heights. (laughs)

DAVID

And he knows all about the violence.

PEPPY

I fell in love with the streets, the whole lifestyle of it. The girls, the money, the respect that you get in your neighborhood. You know, all the way down to the part where I had to bust somebody in their head. Disrespecting me... could get a person beat nearly to death. Has gotten people beat nearly to death. I had to sit in jail for ten months because I beat a guy nearly to death. I was that person for 30 years. I had to let that person die and create this person right here. That's what qualifies all of us to do this. You walked the walk, you talked the talk, you're qualified to intervene. She told me that she was going to the police station and fill out a report on you. For what? I didn't do anything to her.

DAVID

Today, Peppy is following up on a violent altercation. I couldn't understand how it got that far in the first place. Look at my face. She beat me in my face, kicked me in my back. I felt a threat. She's yelling, belligerent.

PEPPY

We're going to do it one at a time, okay? Because you went to me like this. No! Uh-uh! Yes, you did, and then that's when I blacked out on you. You was pummeling me! All right. Because you were trying to grab stuff. I don't know what you're doing. I'm grabbing my phone! See how you're doing? Right now you're not listening to each other. You're not hearing nothing she said because you're so ready to talk back. Maybe it's something else, you understand what I'm saying? I don't have a problem. I want to leave because I feel out of place. Even though I knew they wasn't listening to each other, I think it was very helpful because they feel like they're vindicated. For them to be able to do that on their own, they wouldn't have been able to do it because it would have just went on and on and on until one of them threw a punch. (indistinct chatter) Women fight way differently from men. Guys, they run for their knife or their gun, which is so sad.

DAVID

Later, Peppy is dispatched to diffuse a potentially deadly dispute.

MAN

Unfortunately, we live by the gun around here, man.

DAVID

The man Peppy is talking to says that two nights ago he ordered a revenge killing. But his guys shot at the wrong person and now that person wants to take revenge. Let me see your hands, yo. You ain't seeing my (no audio). Let me see your hands, yo. You didn't come 'round here for no smoke. You didn't come 'round here for no smoke, right? Let me see your hands, yo. You didn't come 'round here for no smoke, right? Right? Listen, there's no smoke. (dog barking, phone ringing) Tell him what you just told me, yo. Let me see your hands, yo!

PEPPY

You keep your hands out your pockets. You're making me nervous, yo.

MAN 2

If it wasn't for this dude here, man, I'mma tell you something, man. (no audio) would go a lot different than this, right? And I know that. You know how I know this (no audio) ain't going to happen again? Because I'm right here. That's how you know it's not going to happen again, right?

MAN 1

Man, you'd do the same thing though! You're (no audio) right I would do the same (no audio) thing.

PEPPY

All right, okay, now we've got common ground. We've got common ground. You would have. Can we agree that you apologize, yo? Absolutely. I'm gonna accept that, man. But I'mma tell you this, man. You don't come back from that death (no audio). There ain't no coming back from that. I say you go and shake his hand. I say go shake his hand. I mean, like... Squash it, yo. Man, I'mma just leave this be, man. Back to you, right. That's a hell of a mistake to make. We are guys right directly in these neighborhoods. That can bring these two guys together in the midst of their anger, their hatred, and their want for revenge, and bring about a peaceful resolution. That's a big part of what Safe Streets do. (lighter clicks)

McNEIL

A lot of times guys want to put an end to the conflict. Especially when them guns get to goin'. The Safe Street guys give them a way to get out of there. "All right, Safe Street's squashed it "so now I'm not looking like a punk. Now I'm not looking like I'm scared of nothin'." (indistinct chatter) But it's not just about that. People out here really need resources. Not justifying nothing, but a lot of people be surprised what people be going through. All right, okay, so what's the next part? What you gotta do? What you gotta do to get yourself right? Stop all this other (no audio) from happening. I wanna leave drugs. Try to get a job. That's it. I swear straight up, I'm trying. Because, you know what? We gotta deal with one thing at a time, you know what I'm saying? We gotta deal with the big issue. It ain't funny, yo.

PEPPY

A lot of violence come from lack of. That's a lack of education, that's a lack of food, that's a lack of basic necessities like clothes, water.

LAYNE

When we interrupt the violence and we take a look at what the precipitating factors are that contributed to the violence, we see opportunity to connect folk to additional services of support. And those services could range anywhere from mental health, substance abuse, housing, transportation... Things that help people get on their feet so that they don't have to rely on the streets to feed themselves and their families.

DAVID

While Safe Streets connects people to a host of community services, they're not designed to take on the root causes of violence. (indistinct chatter)

Their success is measured in two key metrics

shootings and killings. While surrounding neighborhoods continued to see high levels of firearm homicide, from 2017 to 2018, the Park Heights post went 382 days without a single killing. And people are starting to take notice... Over 50 sites around the world have adopted the approach practiced by Cure Violence. And the data is clear. It's working. Because they come from the public health field, they set a very high bar for evidence.

SLUTKIN

Cure Violence has been evaluated for its work in Chicago, in Baltimore, in New York, in Honduras, in Mexico, in New Orleans, in South Africa, and repeatedly the findings are that shootings and killings go down by between 40% and 70%. And it's sustained. Behaviors that were formed years ago can be completely changed. That right there.

PEPPY

I am a case in point. Violence can be unlearned. Sometimes I hardly believe that... I found a job, employment that I love. That it's actually noticed that people like me stop so much more violence from happening.

PINKER

Focused programs on crime reduction have shown they can work. Even if you haven't cured blights like inequality and poverty and racism, you can prevent an awful lot of people from getting killed.

DAVID

Data can be a useful tool in tackling violence, but it is by no means enough. Knowledge is power only if you act on it. Consider mass shootings.

MUGGAH

Gun violence is still a big challenge in the United States. And yet, funding to do research on this public health challenge was taken away by the CDC because of let's call it disagreements in Congress.

DAVID

But the research that is available points towards solutions.

MUGGAH

It may seem impossible to talk about preventing and reducing gun violence in America today, but the fact is there are examples of where smart interventions have generated declines in gun violence.

DAVID

Take the example of Australia. Following a mass shooting in April 1996 that took 35 lives, reaction was swift. The prime minister, John Howard, tonight detailed sweeping plans to reform Australia's national gun laws.

MUGGAH

Instead of having an agonizing debate that went nowhere about what to do about it, what you had was action. To achieve a total prohibition on the ownership of all automatic and semiautomatic weapons. Within months the parliament in Australia had legislated that there ought to be a massive gun collection program and new constraints and controls and regulations around certain types of weapons.

DAVID

Assault weapons were banned and over 650,000 were turned into the government. (guns clattering) Gun-related homicides plummeted.

PINKER

When Australia passed a stringent gun-control measure, rampage killings, which had afflicted the country, fell pretty much to zero. (clicks button, machine whirring)

DAVID

In the 23 years after the ban, Australia had only two mass shootings with a total of ten dead. (machine whirring) The message is that gun regulations can reduce deaths. (shutter clicks) And that would appear to be true here in the U.S. In the aftermath of the Sandy Hook shootings, Connecticut passed some of the nation's most restrictive gun laws. Since then, the five-year average of gun-related homicides has dropped by a third. And it's not just Connecticut.

MUGGAH

States across the United States that have had tighter, more restrictive legislation, especially around carrying of firearms, tend to show lower rates of homicide, lower rates of intimate partner violence, lower rates of suicide.

DAVID

With the help of data, even the most intractable problems can become a little less daunting.

PINKER

There are some parts of the world that people tend to write off as just hotbeds of war and where there's nothing you can do about it.

DAVID

Take the recent genocides in Rwanda, Sudan, and Myanmar. Though in each case the root causes of violence are complex, one thing they share is long-standing ethnic and religious tensions. (loud explosion) Among the most challenging, the Middle East, where the wars in Syria and Iraq have displaced millions and brought chilling stories to the evening news.

REPORTER

The Syrian regime just attacked its own people with chemical weapons again. A war crime.

MOUSA

It is easy to be pessimistic about the Middle East. (explosion) The conflict is very raw. The distrust is very deeply ingrained. So if we can find even small effects in this setting, it suggests that elsewhere we might find bigger effects. (bell tolling)

DAVID

Can science do anything to reduce those underlying tensions? (man chanting) (music playing) (people singing in local language) Mass, in a church in the village of Qaraqosh in the Nineveh Plains of northern Iraq. (people praying aloud in local language) There are an estimated 400,000 Christians in Iraq. About 50,000 of them once lived in this predominantly Christian enclave. (man chanting, people repeating) The community, and the church, bear the scars of a bloody uprising. In 2014, ISIS militants swept through the Nineveh Plains. (baby fussing) Rami Hana is one of thousands that fled Qaraqosh as ISIS approached.

RAMI HANA (in Arabic)

(family praying)

DAVID

Rami's mother thought they would only be gone for a few days.

LOLA MALALHA EYLAS (in Arabic)

(rocket fires) (loud explosion, men shouting, gunfire)

DAVID

In fact, it was two years before the city was liberated. (child shouting) Rami's family returned to find their home looted and damaged beyond recognition. They were one of the lucky families. About a third of the homes had been set on fire. (footsteps, objects crunching) And occupying jihadists had tried to erase any evidence of Christianity from Qaraqosh... burning churches, destroying statues, toppling towers.

MOUSA

What ISIS did to the religious minorities in the Nineveh Plains region is classified now as a genocide or as ethnic cleansing by the State Department, by the U.N. These were communities targeted specifically because of their religious or ethnic background. (wind howling) There were kidnappings, killings, sex slaves. The armed forces just fled. So it really was a horrific experience. (cars driving by)

DAVID

Little by little, more residents have been returning to Qaraqosh. Among them, Mohammed Hussein. Today he prays at his mosque, thankful for the omnipresent security forces. (in

DAVID

Nonetheless, religious tensions still remain high.

MOUSA

In the wake of a conflict like this, the social trust just becomes obliterated. So you have neighbors that become suspicious of other neighbors, people are perceived as being collaborators on the basis of what community they belong to.

HANA

(children playing)

DAVID

ISIS may be gone, but two powerful ingredients for violence-- prejudice and sectarian hostility-- remain. (bell tolling)

MOUSA

Ethnic cleansing doesn't just happen overnight. The first step of that is like some level of prejudice toward another group. It turns into dehumanization of the other group. And that just escalates, where you come to a point where people actually feel justified inflicting harm on a group. (man chanting)

DAVID

Looking at what happened in Qaraqosh, it is difficult to imagine what could heal these wounds. (chanting continues, people chatting) One solution may lie in a rather unexpected place...

MOUSA

Soccer is something people do just for fun. We just add some tweaks in terms of how to mix up the team composition to test the idea of contact.

DAVID

Political scientist Salma Mousa traveled to Iraq to test an idea-- could something as simple as playing a game reduce prejudice and increase empathy? (playing drum) (man commentating) It's kick off in the Nineveh Plain Soccer League. (man commentating) (speaking Arabic) Rami, a Christian, captains his team.

HANA

(people shouting, man commentating)

DAVID

Trying to stop him scoring in the opposition's goal is Mohammed, a Muslim.

HUSSEIN

(man commentating) (man commentating)

DAVID

They come from different worlds and neither has any idea that they are taking part in an experiment, testing "contact theory."

ZAKI

The contact hypothesis is the idea that when we have a lack of empathy for others who are different from us, or feel prejudice against them, it's really because we don't know them very well. And if we were to merely come into contact with those outsiders, it would stop feeling as much like an us and them situation. (indistinct chatter)

DAVID

The theory suggests that contact would only work to increase empathy

under certain conditions

when the groups are on equal footing, sharing a common goal. (whistle blows) (speaking Arabic)

MOUSA

The idea behind contact theory is that contact can reduce prejudice. This idea has been around for a long time, but what is new is we now have the scientific methods and the rigor to try to test some of these things.

DAVID

Mousa created a new soccer league, and invited teams around Qaraqosh to join. Rabie Zakaria is the league's organizer. (men shouting, whistle blowing) He signed up 37 teams, with 444 players.

MOUSA

The teams in this area tend to be homogenous. So there are Christian teams, there are Muslim teams, there are Kurdish teams. (shouting, clapping) Once they signed up for the league, we said, "Well, social inclusion is part of our mandate, "and so we need to mix up some of the teams, so all the teams are going to get some added players."

DAVID

On Rami's team, he plays alongside three Muslim players. And Mohammed is one of three Muslims on his team. Mousa kept some of the teams all Christian as a control. (drum tapping) Would being on a mixed team do anything to change attitudes? When we asked other people to join them-- players-- it was kind of difficult at the beginning because some of the players felt not welcome in the team. But we asked them to train, and it got better. (man commentating) Gradually, the players started working together on the field. (man commentating, people cheering) But off the field, Mousa needed a way to test if her experiment was making a difference. To do that, first she had Rabie arrange a social event. (men chatting in Arabic) Would players from both communities turn up? (men chatting in Arabic)

MOUSA

The real moment where I thought there might be something to this was when I saw that the players who were on mixed teams were double as likely as those on the control teams to show up for this social event.

DAVID

But that was an event arranged by the study. What about on their own? To find out, Mousa had Rabie give the players vouchers to unfamiliar restaurants. Normally, people in this region don't go to restaurants owned by members of another faith. Periodically, Rabie collects the vouchers from the restaurants. So we have, almost more than 200. Each voucher is tagged with a specific I.D. number, and the restaurant owners help track if people came alone or with others. (bottles clink) (speaking excitedly in Arabic, laughter) The results showed a marked shift in behavior.

MOUSA

Being on a mixed team makes you more likely to go to a social event where people from the other group are present. It makes you more likely to go to different neighborhoods or different cities even that are... that are dominated by another group. (children playing)

DAVID

And though the changes were modest, her surveys showed a shift in belief that coexistence is possible.

MOUSA

Playing on a team with diverse teammates makes you more likely to say that it's important to treat each other as Iraqis first as opposed to other community identities.

DAVID

But tensions are high once again in Qaraqosh... (whistling, cheering) the final in the Nineveh League has ended in a draw and the tie must be decided on penalty kicks. (crowd cheering) Rami steps up to the spot... and scores. (crowd cheering)

MOUSA

I was watching on Facebook Live when we had our end of league celebration and we were handing out the trophies, and I saw Rami get his (laughing): like massive trophy, and he gave a little speech. Part of his speech was, "There are really like no boundaries when we play soccer, "and it doesn't matter where you're from or who you are, we're here to do the same thing."

HUSSEIN

MOUSA

I'd like to think that soccer can save the world. I know it's not that simple. (muted cheering) But if we find even some small effects on people's behaviors, considering that we're dealing in a very difficult environment, I think that's very promising. And I hope that we can use some of these insights to prevent violence on the basis of someone's identity.

DAVID

Though small steps like these may give people hope, it's important to keep such results in perspective.

TUNG

I don't think there's anything wrong in recognizing that there's progress. We just want to be sure that patting ourselves on the back for that doesn't obscure what else still needs to be done.

CAMARA

Human beings, we are so complex. But our understanding of ourselves, as a species, that understanding evolves.

DAVID

Even if we're a long way from a world free of violence, it's still possible to be inspired by how far our species has come. (people chanting)

PINKER

As you become aware of the historical decline of violence, the world starts to look different. You start to appreciate things that we can take for granted. (jet engine roaring)

DAVID

How major conflicts in the news have not escalated to world war. How new monuments are named for martyrs and civil rights leaders, not war heroes. (people chanting in local language) How the quest for human rights is crossing international borders. Our past has led us down this path.

The question is

will we stay on it? We're in a unique moment today in which we have a chance to sort of lock in some of this progress that humanity has made.

CHENOWETH

We should never take for granted that when we're enjoying a period of peace it's because it's inevitable. We have to continually work for peace.

PINKER

Until recently, we lived in a world in which slavery, and rape, and warfare were the norm, not the exception. What's changed over history is the better angels of our nature predominate over our inner demons. We can see shootings go down. We've done something right. Let's figure out what it is and make sure we keep doing it.

ROBERTS

Humans are a hot mess, and we have so much more to do. One of the benefits of Pinker's work is to remind ourselves of all that needs to be done. Major funding for "NOVA"

is provided by the following

To order this "NOVA" program on DVD, visit ShopPBS or call 1-800-PLAY-PBS. This program is also available on Amazon Prime Video.