I'm Scott Lilienfeld, department of psychology at Emory University. And the title of my talk is, Are Some People Born Violent? We begin our talk with this man, who many people regard as the epitome of evil, certainly the epitome of violence. His name is Ted Bundy, Ted Bundy. Was responsible for the brutal murder of at least thirty women and was eventually executed by the US government in 1989. Bundy would often accomplish his horrific crimes by feigning illness, feigning disability. For example, he might pretend as though he had a broke arm, lure. And innocent victim into his car. And they were never seen from again. What is striking about Bundy is not merely the horrific nature of his crimes. But also, and I think this is quite chilling, also the extent to which he showed utterly no remorse. At least until perhaps a day or two before he died. For his crimes. In an unusual moment of insight, he said, I'm the most cold-hearted son of a bitch you'll ever meet. And the Bundy case I think raises some interesting questions and some troubling questions I think that really cut to the hear of my talk. Number one, are individuals such as Bundy born or made? In fact, this question applies not just to people like Bundy or terrifically violent and, and violent in really atrocious ways. But also applies to more garden variety forms of violence, both physical and verbal violence. So are these individuals born or made or is it a bit of both? A bit of mixture of nature and nurture as we often say. Number two, how do we begin to find out? And what kinds of approaches do scientist use to try to distinguish nature from nurture? And number three, if we were to somehow magically rewind the tape. And start off Bundy from his birth or if we were to somehow magically clone him, which I would most definitely not recommend. Would the outcome have been different? Would we have ended up with the same Ted Bundy, the same person who engaged in this horrific violence? As we'll see scientists don't have definitive answers to these questions, but they've made some substantial inroads. Let's start with a few basic findings about violence and I think any attempt to understand the causes of violence. Have to come to grips with these basic findings, which hold across virtually every culture. First, about 5 to 7% of people or so, account for 50% or more of cases of crime, including violence. And this again is a very cross cultural general finding. That does not indicate the violence is genetic in any way, but it does suggest that there are some specific risk factors. Perhaps both genetic and environmental, and a mix of both. That put certain individual, a small number of individuals, at particular risk for violence. We also know that most forms of crimes actually involve theft and other kinds of property offences. Only a minority involve violence. So violence is relatively rare. But, of course, when it does occur, it can cause tremendous social and physical harm. And finally, we know that men tend to engage in higher rates of violence than do woman. Again, this holds in, in just about every culture that has been studied. Interestingly it also holds in just about every species that has been studies, so it's quite generalizable across the animal kingdom. There is interestingly exception here that proves the rule, the one exception that I'm aware of is the spotted hyena. In which females are more aggressive than males. Although even here, we have an aggression, we have an exception that proves the rule. Because the female spotted hyena is imbued with high levels of masculine hormones. So again, we have some evidence of a biological basis. At least some suggestion of a biological basis. For violence and aggression across many, if not all species. So scientist have used a variety of different approaches, to help them understand the correlates, and causes of crime and violence. I'll talk about each of these in turn. First we have behavior genetic studies, particularly twin and adoption studies. That are designed to disentangle the effects of nature from nurture. And again I'll come back to these in some more detail. We then have molecular genetic studies, which are in some cases a bit of a variant of behavioral genetics studies. Except these studies tend to look at particular generic variants that might predispose people toward violence. And then finally number three, brian imaging studies. Studies that actually study the brain both structurally that is the morphology of the brain and the size. And shape of the brain and also functionally those that can actually depict the brain online in action. I should point out brain imaging studies do not by themselves. Look at genetic bases of crime directly, but they may tell genetic investigators where to look. And give them a better sense of, of what kinds of brain areas might be affected by the genes. That also perhaps predispose people to certain kinds of violence. Genetic studies, as I mentioned earlier, allow investigators, when they're done properly. To separate the effects of genes from environment. What Sir Francis Galton, who was actually a cousin of Charles Darwin in the 19th century, called nature and nurture. There is, I think, a common misunderstanding that one still sometimes hears in the literature, which is that one really can't study. This issue because nature, nurture are somehow inseparable. The famous Canadian Neuroscientist, Donald Hebb, said that behavior is always 100% nature, 100% nurture. But in fact, that's only true within one individual. It is true that one can't separate out the effects of nature, nurture within one person. But one can study the differential contributions of nature and nurture to what we call individual differences. That is, the sources of violence risk across individuals. That's what we're talking about here, we're not talking about within one person, we're talking about the extent to which genes. Versus environment, contribute to risk across people. Similarly, in many sports, take soccer .We know that offense and defense often meld together seamlessly. One can't distinguish between office and defense very clearly, in one team. But we know, across soccer teams. Across many sports teams. We can still meaningfully ask the question. Due teams that have a better offense, for example, tend to do better than teams that have a better defense. That's the kind of approach that we're looking at here. We are looking at individual differences here. This often looks at twins and there's a reason for that. Biogeneticists loves twins in part because twins are a perfect natural experiment so on the left of your slide, you see a pair of. Monozygotic twins, those that are the product of the fertilization of one egg. One zygote, which is a fertilized egg. And on the right, you see a pair of dizygotic twins, who result from the fertilization of two different eggs. Two different zygotes. And in twin studies, typically we compare these two types of twins, mz twins, monozygotic twins, often loosely called identical twins. With dizygotic, or loosely called, fraternal twins. And as I mentioned earlier, this is in many ways a perfect natural experiment because MZ twins share essentially 100% of their genes. They are essentially genetic clones of each other. In contrast DZ twins on average share 50% of their genes. And they are no more like that ordinary siblings except for the fact that they share a common womb. And what we see in twin studies is that typically what investigators would do is compare the similarity. Compare correlation of the trait in this case violence risk for example in MZ twins versus DZ twins. Depending on a couple of assumptions I won't get into here because in generally, these assumptions are fairly technical and hold up pretty well. If you see a higher correlation of the trait in MZ than DZ twins. You can generally and fairly confidently assume that there is at least some genetic basis to the trait. We also have adoption studies. These are a bit harder to do in most cases and our less commonly done. Which typically examine the criminal histories of individuals who were separated soon after birth from biological parents. In this case, biological parents with histories of crime and perhaps violence. Very often we have a comparison group in which we can. Contrast individuals who are adopted away from biological parents without histories of crime. If, and again, based on a couple of exceptions here I won't get into, if we see that the children who've been adopted away from parents with. With histories of crime, biological, parents' histories of crime, tend, themselves to have higher rates of crime than other, children. That often leads us to think that there is, some kind of genetic basis. There is one, important methodological challenge to adoption studies we call selective placement. We know, from a lot of data. That adoption agencies often prefer to place adopted children in homes that are somewhat similar to biologic homes. Which can create a bit of a confound. So we have to control for selective placement in these kinds of studies. And investigators have typically. Been able to do that. So by-and-large, in very broad brush terms, what do we find when we look at twin and adoption studies? First, it's safe to say that the risk for crime, and perhaps to some extent violence. Appears to be moderately heritable in both men and women. The estimates are roughly about 40 to 60 percent. What that means is that the difference is among people across individuals. And their risk for crime and perhaps violence is on the order of 40 to 60 percent. Of course what that tells you, is at the risk for crime and violence as also substantially environmental. In fact what's ironic is behaved genetic studies, twin studies in particular. Actually provide the most persuasive evidence available for environmental affects on crime although they do not tell us. What these environmental effects are. They probably include things like peer influence, the effects of poverty, parenting, other kinds of social factors. As well as cultural factors, but we don't yet know what they are. We also know number two, that in adults, the genetic risk seems to be higher for property crimes. Theft and vandalism, than for violent crimes. Violent crimes often seem to have a genetic basis that is weaker than those for property crimes. We don't know why that is. But we do know tha violent crimes seems to be more influenced by environmental facts. Again, perhaps some of the ones I mentioned earlier. It's also though important to understand what these findings do now mean. They do not mean that the risk for crime or violence is somehow directly genetic. It's very very like that there are no specific genes for violence. It's instead very likely that the risk for violence operates indirectly, nonspecifically, through various personality traits. Such as weak impulse control, hostility and aggressiveness, perhaps callousness and lack of empathy. That in turn in combination and perhaps in interaction, I'll get to that in a minute. With environmental factors increases the risk, for violence. Finally, adoption studies often find evidence for what, psychologists call Gene-Environment interaction. In Gene-Environment interaction, the effects of, genes on behavior. Or affected by, influenced by the environment and visa versa, the affects of the environment are influenced by genes. And a particular we often see is a potentiating interaction. And that the risk for crime is particularly high when individuals who are at elevated genetic risks are also exposed to adverse environmental risks. What does that mean in this case? If individuals are born. To parents, who have a biological history of crime, and then adopted by parents who were also criminal, the risk suddenly goes way up. Again, this gets to the issue of gene environment interplay, which I'll say a bit more about before I close. Molecular genetic studies I won't say quite as much about because. Frankly, the, the literature here is much more mixed. There have been a couple of promising leads for a few molecular genetic variance. The most comely studied probably has been something called monoamine oxidase A or MAO-A. Which is a particular enzyme that is related to the metabolism or breakdown of certain neurotransmitters. Which are basically chemical messengers in the brain. Such as serotonin. If you've heard of serotonin, that's probably because it is involved in a number of medications. For example, Prozac and Zoloft are involved in serotonin metabolism. In particular, individuals with a low MAO variant. Tend to be in some studies at somewhat high risk for crime and violence. But even here, the findings are inconsistent. More recent evidence has called the strength of that association into question. Also, some early studies indicated that individuals with that low MAO variant. Who were also physically abused or maltreated in childhood, had particularly high violence risks. There is some evidence for that. But other studies have not replicated that, so again, it's a bit of a mixed bag. The one consistent finding here is that no identified genetic variant. None that we found, accounts for more than a tiny percentage, no more than one to two percent. And even I would regard that percentage as charitable, of the differences in risk for aggression. What does that mean? Maybe it means we're looking in the wrong place. Maybe there are some genes that we have not been looking at that account for much more risk. That's possible. More likely in my view, and I think in the view of most scholars. What we increasingly are coming around to think is that, in fact, the risk for violence, if it is genetic, is extremely multi determined, multi-faceted. And we're talking about large numbers, hundreds, perhaps thousands of genes. That exert very, very small effects on personality and behavior, that in turn may increase the risk for violence. Finally, brain imaging studies. There is some consistent literature here, the most consistent finding probably, is that individuals who are prone. To aggression and a social behavior perhaps viones show smaller frontal lobe volume. In structural brain imaging studies as well as less frontal lobe activity in functional studies. The frontal lobes play a major role in inhibition. In particularly the Ventromedial frontal cortex plays a key role in decision making that involves. Strong emotions, other forms of impulse control. We also know that there are well documented deficits in amygdala activation. Amygdala is a very small area, it's actually shaped like an almond. In fact amygdala is the Greek word for almond. It's a small area very deep in the brain. That seems to be heavily involved in the processing of emotion, especially in fear. So let me say just a bit about each of these. Here's one example of the link between frontal lobe activity and frontal lobe integrity. And impulse control. Famous story, classic case in the history of psychology/neurology, Phineas Gage. In 1848, he was a Vermont rail worker, was trying to tamp down various explosive charges and a metal rod. Iron road, about three and a half feet long was hurled through his skull. Basically, he survived, but he sustained tremendous damage to his frontal cortex. Now, Gage did not exactly become violent so far as we know, but he became, according to most accounts, a rather different person. He became. Even though he did actually continue to live, and, and serve some kind of functioning role in low level jobs. He became very prone to fits of anger, he became impulsive. He became prone to profanity to the point that many people who knew him said they no longer recognized him. And again, what we know from a number of other studies is that people who have sustained severe prefrontal damage. Often are prone to poor impulse control, in some cases also prone to aggressive or violent behavior. That red spot there is depicting the amygdala. As I mentioned earlier what we often see is that there is under activation of the amygdala in people who are prone to aggression, prone to fear. I study as part of my work people with psychopathic personality who are often. Superficially charming, guiltless, often devoid of fear and that's actually a very consistent finding in individual's with psychopathic personalities. Who in turn are often prone to a somewhat high risk of violence. People's psychopathic personality often show less activation to certain stimuli. I'm actually going to show you a stimulus right now. By the way if you're afraid of snakes close your eyes. If you're not afraid of snakes, you might want to lean forward just a bit for this demonstration. Now if, if you saw this image and you leaned forward a bit, you might have found yourself recoiling just a bit. In fact I, find myself recoiling just a bit. And what it typically found in literature is that people with. Diminished amygdala activity show less behavioral and less physiological activity. As well as less brain imaging activity in response to these kinds of frightening stimuli. And again, what this suggests is that fear may play a very important role in the inhibition of violence. And also emotions like guilt, which many psychologists believe, developmentally evolve from fear. Also play a very important role in the inhibition of antisocial behavior, in the inhibition of aggression, in the inhibition, in some cases, of violence. So, where does this leave us? What's the bottom line? Number one, are some people born violent, and it's rare in psychology that we give definitive answers to questions, but I'm going to give one here. My answer is no, people are not directly born violent. There are no specific genes, it's very unlikely that there's specific genes for violence. However, certain people may be born with non specific genetic vulnerabilities to violence. What I mean, there are genetic vulnerabilities that are not unique to violence but in fact cut across a number of psychological attributes. Particularly personality traits like poor impulse control. Aggressiveness, again, perhaps low empathy and, and so on. So, going back full circle to the question I posed at the beginning, if we were to somehow rewind the tape and start with Ted Bundy. Day one, expose him to a slightly different set of environmental conditions, would he have ended up the way he was? The answer is. Very unlikely that he would, which actually give us a bit of room for optimism. Because it suggests that perhaps we could learn to prevent violence, prevent aggression in people who are genetically predisposed to it. And this brings us to a closely related issue which is that environmental factors we know play critical roles in the causes of violence. In fact, behavior genetics studies I would argue provide the most powerful evidence. That environmental factors play key roles in aggression and violence although they don't tell us what those environmental factors are. We also know increasingly that genetic and environmental factors have a very complex interplay. Although we have yet to understand the exact nature of that interplay. >> Again, I think once we understand how genes and environment transact, interact with each other. We will have a much better understanding of both the causes of violence. And also we'll have a better understanding perhaps, one day, of how best to treat and prevent it. Thanks very much.