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  • Chris Anderson: So Robert spent the last few years

  • think about how weird human behavior is,

  • and how inadequate most of our language trying to explain it is.

  • And it's very exciting to hear him explain some of the thinking behind it

  • in public for the first time.

  • Over to you now, Robert Sapolsky.

  • (Applause)

  • Robert Sapolsky: Thank you.

  • The fantasy always runs something like this.

  • I've overpowered his elite guard,

  • burst into his secret bunker

  • with my machine gun ready.

  • He lunges for his Luger.

  • I knock it out of his hand.

  • He lunges for his cyanide pill.

  • I knock that out of his hand.

  • He snarls,

  • comes at me with otherworldly strength.

  • We grapple, we fight,

  • I manage to pin him down

  • and put on handcuffs.

  • "Adolf Hitler," I say,

  • "I arrest you for crimes against humanity."

  • Here's where the Medal of Honor version of the fantasy ends

  • and the imagery darkens.

  • What would I do if I had Hitler?

  • It's not hard to imagine once I allow myself.

  • Sever his spine at the neck.

  • Take out his eyes with a blunt instrument.

  • Puncture his eardrums. Cut out his tongue.

  • Leave him alive on a respirator,

  • tube-fed, not able to speak or move or see or hear, just to feel,

  • and then inject him with something cancerous

  • that's going to fester and pustulate

  • until every cell in his body is screaming in agony,

  • until every second feels like an eternity in hell.

  • That's what I would do to Hitler.

  • I've had this fantasy since I was a kid,

  • still do sometimes,

  • and when I do, my heart speeds up --

  • all these plans for the most evil, wicked soul in history.

  • But there's a problem,

  • which is I don't actually believe in souls or evil,

  • and I think wicked belongs in a musical.

  • But there's some people I would like to see killed,

  • but I'm against the death penalty.

  • But I like schlocky violent movies,

  • but I'm for strict gun control.

  • But then there was a time I was at a laser tag place,

  • and I had such a good time hiding in a corner shooting at people.

  • In other words, I'm your basic confused human when it comes to violence.

  • Now, as a species, we obviously have problems with violence.

  • We use shower heads to deliver poison gas,

  • letters with anthrax, airplanes as weapons,

  • mass rape as a military strategy.

  • We're a miserably violent species.

  • But there's a complication,

  • which is we don't hate violence,

  • we hate the wrong kind.

  • And when it's the right kind,

  • we cheer it on, we hand out medals,

  • we vote for, we mate with our champions of it.

  • When it's the right kind of violence,

  • we love it.

  • And there's another complication,

  • which is, in addition to us being this miserably violent species,

  • we're also this extraordinarily altruistic, compassionate one.

  • So how do you make sense of the biology of our best behaviors,

  • our worst ones and all of those ambiguously in between?

  • Now, for starters,

  • what's totally boring is understanding the motoric aspects of the behavior.

  • Your brain tells your spine, tells your muscles

  • to do something or other,

  • and hooray, you've behaved.

  • What's hard is understanding the meaning of the behavior,

  • because in some settings, pulling a trigger is an appalling act;

  • in others, it's heroically self-sacrificial.

  • In some settings, putting your hand one someone else's

  • is deeply compassionate.

  • In others, it's a deep betrayal.

  • The challenge is to understand

  • the biology of the context of our behaviors,

  • and that's real tough.

  • One thing that's clear, though, is you're not going to get anywhere

  • if you think there's going to be the brain region or the hormone

  • or the gene or the childhood experience

  • or the evolutionary mechanism that explains everything.

  • Instead, every bit of behavior has multiple levels of causality.

  • Let's look at an example.

  • You have a gun.

  • There's a crisis going on:

  • rioting, violence, people running around.

  • A stranger is running at you in an agitated state --

  • you can't quite tell if the expression is frightened, threatening, angry --

  • holding something that kind of looks like a handgun.

  • You're not sure.

  • The stranger comes running at you

  • and you pull the trigger.

  • And it turns out that thing in this person's hand

  • was a cell phone.

  • So we asked this biological question:

  • what was going on that caused this behavior?

  • What caused this behavior?

  • And this is a multitude of questions.

  • We start.

  • What was going on in your brain one second before you pulled that trigger?

  • And this brings us into the realm of a brain region called the amygdala.

  • The amygdala, which is central to violence, central to fear,

  • initiates volleys of cascades

  • that produce pulling of a trigger.

  • What was the level of activity in your amygdala one second before?

  • But to understand that, we have to step back a little bit.

  • What was going on in the environment seconds to minutes before

  • that impacted the amygdala?

  • Now, obviously, the sights, the sounds of the rioting,

  • that was pertinent.

  • But in addition,

  • you're more likely to mistake a cell phone for a handgun

  • if that stranger was male

  • and large and of a different race.

  • Furthermore, if you're in pain,

  • if you're hungry, if you're exhausted,

  • your frontal cortex is not going to work as well,

  • part of the brain whose job it is to get to the amygdala in time

  • saying, "Are you really sure that's a gun there?"

  • But we need to step further back.

  • Now we have to look at hours to days before,

  • and with this, we have entered the realm of hormones.

  • For example, testosterone,

  • where regardless of your sex,

  • if you have elevated testosterone levels in your blood,

  • you're more likely to think a face with a neutral expression

  • is instead looking threatening.

  • Elevated testosterone levels, elevated levels of stress hormones,

  • and your amygdala is going to be more active

  • and your frontal cortex will be more sluggish.

  • Pushing back further, weeks to months before,

  • where's the relevance there?

  • This is the realm of neural plasticity,

  • the fact that your brain can change in response to experience,

  • and if your previous months have been filled with stress and trauma,

  • your amygdala will have enlarged.

  • The neurons will have become more excitable,

  • your frontal cortex would have atrophied,

  • all relevant to what happens in that one second.

  • But we push back even more, back years,

  • back, for example, to your adolescence.

  • Now, the central fact of the adolescent brain

  • is all of it is going full blast

  • except the frontal cortex,

  • which is still half-baked.

  • It doesn't fully mature until you're around 25.

  • And thus, adolescence and early adulthood

  • are the years where environment and experience sculpt your frontal cortex

  • into the version you're going to have as an adult in that critical moment.

  • But pushing back even further,

  • even further back to childhood and fetal life

  • and all the different versions that that could come in.

  • Now, obviously, that's the time that your brain is being constructed,

  • and that's important,

  • but in addition, experience during those times

  • produce what are called epigenetic changes,

  • permanent, in some cases,

  • permanently activating certain genes, turning off others.

  • And as an example of this,

  • if as a fetus you were exposed to a lot of stress hormones through your mother,

  • epigenetics is going to produce your amygdala in adulthood

  • as a more excitable form,

  • and you're going to have elevated stress hormone levels.

  • But pushing even further back,

  • back to when you were just a fetus,

  • back to when all you were was a collection of genes.

  • Now, genes are really important to all of this,

  • but critically, genes don't determine anything,

  • because genes work differently in different environments.

  • Key example here:

  • there's a variant of a gene called MAO-A,

  • and if you have that variant,

  • you are far more likely to commit antisocial violence

  • if, and only if, you were abused as a child.

  • Genes and environment interact,

  • and what's happening in that one second before you pull that trigger

  • reflects your lifetime of those gene-environment interactions.

  • Now, remarkably enough, we've got to push even further back now,

  • back centuries.

  • What were your ancestors up to.

  • And if, for example, they were nomadic pastoralists,

  • they were pastoralists,

  • people living in deserts or grasslands

  • with their herds of camels, cows, goats,

  • odds are they would have invented what's called a culture of honor

  • filled with warrior classes,

  • retributive violence, clan vendettas,

  • and amazingly, centuries later,

  • that would still be influencing the values with which you were raised.

  • But we've got to push even further back,

  • back millions of years,

  • because if we're talking about genes,

  • implicitly we're now talking about the evolution of genes.

  • And what you see is, for example,

  • patterns across different primate species.

  • Some of them have evolved for extremely low levels of aggression,

  • others have evolved in the opposite direction,

  • and floating there in between by every measure are humans,

  • once again this confused, barely defined species

  • that has all these potentials to go one way or the other.

  • So what has this gotten us to?

  • Basically, what we're seeing here is,

  • if you want to understand a behavior,

  • whether it's an appalling one, a wondrous one,

  • or confusedly in between,

  • if you want to understand that,

  • you've got take into account what happened a second before

  • to a million years before,

  • everything in between.

  • So what can we conclude at this point?

  • Officially, it's complicated.

  • Wow, that's really helpful.

  • It's complicated,

  • and you'd better be real careful, real cautious

  • before you conclude you know what causes a behavior,

  • especially if it's a behavior you're judging harshly.

  • Now, to me, the single most important point about all of this

  • is one having to do with change.

  • Every bit of biology I have mentioned here can change in different circumstances.

  • For example, ecosystems change.

  • Thousands of years ago, the Sahara was a lush grassland.

  • Cultures change.

  • In the 17th century, the most terrifying people in Europe were the Swedes,

  • rampaging all over the place.

  • This is what the Swedish military does now.

  • They haven't had a war in 200 years.

  • Most importantly,

  • brains change.

  • Neurons grow new processes.

  • Circuits disconnect.

  • Everything in the brain changes,

  • and out of this come extraordinary examples of human change.

  • First one:

  • this is a man named John Newton,

  • a British theologian

  • who played a central role in the abolition of slavery from the British Empire

  • in the early 1800s.

  • And amazingly, this man spent decades as a younger man

  • as the captain of a slave ship,

  • and then as an investor in slavery,

  • growing rich from this.

  • And then something changed.

  • Something changed in him,

  • something that Newton himself celebrated in the thing that he's most famous for,

  • a hymn that he wrote:

  • "Amazing Grace."

  • This is a man named Zenji Abe on the morning of December 6, 1941,

  • about to lead a squadron of Japanese bombers to attack Pearl Harbor.

  • And this is the same man 50 years later to the day

  • hugging a man who survived the attack on the ground.

  • And as an old man,