KEVIN DUTTON: Although psychopaths don't feel emotions like us. They are masters at pushing those emotional hot buttons that elicit emotions in others, in us. Sympathy being one of the major, major motivators.

JAMES FALLON: They're not going to kill you or rape you or maybe even take your money but they're going to manipulate the situation, make you look bad or use you in some way. Something bad is going to happen and if you sense that, people have a sense that something is wrong with somebody, you walk away. You don't fight these guys because they're an intraspecies predator. A human that is a predator on other humans.

KEVIN DUTTON: They're not really attuned to your feelings. They don't really care about your feelings. Really, ultimately, the world surrounds them. Psychopaths are also very charming. They're very manipulative, especially when they're in a crowd. Especially when they're in company. But behind the scenes when they're alone with you they can be very, very controlling, sometimes, but not always, aggressive. But psychologically controlling as well, okay.

JAMES FALLON: It's hard to look at the actual behavior of a psychopath and say 'that thing is psychopathic or not.' Because psychopaths will come to the rescue of people. "Can I help you up, ma'am?" They can see the outward behaviors and they just can mimic it to get along. But fundamentally they don't feel it.

KEVIN DUTTON: We all know about the psychopath's enhanced killer instinct, their finely tuned vulnerability antennae. But it may surprise you to know that there are some situations in which psychopaths are actually more adept at saving lives than they are at taking them. So, let me give you an example of what I mean by that. Imagine you've got a train and it's hurtling down a track. In its path, five people are trapped on the line and cannot escape. Fortunately you can flick a switch which diverts the train down a fork in that track, away from those five people but at a price. There is another person trapped down that fork and the train will kill them instead. Though the thought of flicking the switch isn't exactly a nice one, the utilitarian choice, as it were, killing just the one person instead of the five represents the least worst option.

But now let me give you a variation. You've got a train speeding out of control down a track and it's going to plow into five people on the line. But this time you are standing behind a very large stranger on a footbridge above that track. The only way to save the people is to heave the stranger over. While the score in lives is precisely the same as in the first scenario—five to one—one's choice of action appears far trickier. Now, why should that be? Well, the reason, it turns out, all boils down to temperature, okay. Case one represents what we might call an impersonal dilemma. It involves those areas of the brain primarily responsible for what we call cold empathy. For reasoning and rational thought. Case two on the other hand represents what we might call a personal dilemma. It involves the emotion center of the brain known as the amygdala, the circuitry of hot empathy, what we might call the feeling of feeling what another person is feeling. Now, psychopaths, just like most normal members of the population, have no trouble at all with case one. They flick the switch and the train diverts accordingly killing just the one person instead of the five. But, this is where the plot thickens. Quite unlike normal members of the population, psychopaths also experience little difficulty with case two. Psychopaths, without a moment's hesitation, are perfectly willing to chuck the fat guy over the rails if that's what the doctor orders. Now, moreover, this difference in behavior has a distinct neural signature.

MICHAEL STONE: There are a number of areas in the brain that are very important in social decision making and moral attitudes. And there's a more primitive part of the brain that deals with emotion called the limbic system. In the limbic system there is a small organ called the amygdala that registers emotion but particularly has an ability to recognize when somebody else out there has a fearful face or is in a state of fright or upset. The interesting thing about the kind of coldhearted murderers is that their amygdalas don't function properly the way ours does and they may recognize, dimly, that so and so out there is afraid, but they don't have the concern that you or I would, let's say, if we saw a crying kid in a department store who probably got separated from its mother. They would recognize it but they would take advantage of the child, pretend to take it to the information booth to get it reconnected with its mom and then kidnap the kid or something like that.

Another important area is the front part of the brain called the orbitofrontal cortex. That area is involved in moral decision making, figuring out what's right versus what's wrong, that we learn as we grow up and are instructed by our parents and our teachers. So if that area of the brain is not operating at full tilt it may be possible then to carry out an act which would be repugnant and very much against the law. But think of the orbitofrontal cortex as A kind of a braking system which, if it's operating, will put the brakes on a thought or a desire that may have preceded it that 'I'd like to kill that son of a bitch' or 'I want to take that kid and kidnap him.' Then when thinking of the consequences, 'Oh my god, I'd be eating cheese sandwiches in jail for the rest of my life. I won't go there.' But if that cortex is not operating the person would just go ahead and do it.

KEVIN DUTTON: The pattern of brain activation in both normal people and psychopaths is identical on the presentation of the impersonal moral dilemma, but radically different when things start to get a bit more personal. Imagine that I went to hook you up to a brain scanner, a functional magnetic resonance imaging machine, and were to present you with those two dilemmas. What would I observe as you went about trying to solve them? Well, at the precise moment that the nature of the dilemma switches from impersonal to personal I would see the emotion center of your brain, your amygdala and related brain circuits, the medial orbitofrontal cortex, for example, light up like a pinball machine. I would witness the moment, in other words, when emotion puts its money in the slot. But in psychopaths I would see precisely nothing and the passage from impersonal to personal would slip by unnoticed because that emotion neighborhood of their brains, that emotional zip code, has a neural curfew. And that's why they're perfectly happy to chuck that fat guy over the side.

JAMES FALLON: Orbital cortex and the amygdala. Orbital cortex is involved in inhibiting your behavior. Now the amygdala on the other hand really causes behavior and normally they're in balance, they inhibit each other. Now, in a psychopath they're both turned off so they don't inhibit each other and they don't regulate it so the normal balance of animal drives and your social interactions, your morality, are not right. That's never right. There's a time for aggression. There's a time for killing, even. There's a time for sex. And part of it is how the rest of the brain is able to tell your orbital cortex the social context is correct now. Psychopaths don't have that. They're doing things completely out of context, out of social context, and that's the problem.

KEVIN DUTTON: If we remove the definition of psychopath away from the kind of more clinical setting to an everyday life scenario, psychopaths tend to have quite a few positive characteristics going for them. They tend to be assertive. They don't procrastinate. They focus on the positives of situations. They don't take things personally. They don't beat themselves up when things go wrong.

JAMES FALLON: Another thing is you're not very susceptible to pain. Pain doesn't bother you. And also, when you're caught doing something, you have no tells. You could be caught red handed having an affair with somebody and you could say 'No, that's not me.' It's like, are you going to believe me or your lying eyes? And so it's the ability to lie without any tells.

KEVIN DUTTON: Those kinds of characteristics can actually really help us get along in life so let's give you a very simple example if you like. The Nike slogan, Just Do It—there's a psychopathic slogan for you if ever there was one. Psychopaths do not procrastinate. Psychopaths, if they want something, they go for it and they go for it now. Top sportsmen are very high in certain psychopathic characteristics. Now, let me just go through them. You've got ruthlessness, you've got fearlessness, you've got mental toughness, you've got coolness under pressure, you've got the ability to focus remorselessly on a goal. I mean, these things are straight out of the sports psychology textbooks in many ways so anyone from top golfers to top cyclists to top boxers to top athletes, they are going to be high on these psychopathic characteristics.

JAMES FALLON: Usually the question is what percent do you think is due to genetics and what percent is due to environment? And it turns out not to be the great question to ask, because it looks like the answer is if you are born with the biological markers for psychopathy, for example, that is the genetics and the altered brain pattern early on, if you are a susceptible kid then environment means everything. It means a lot, maybe 80 percent.

KEVIN DUTTON: Where we start getting into the realms of criminal psychopaths is when we look at natural aggression levels and perhaps natural levels of intelligence. If you've got those characteristics right there that I've told you about and you happen to be naturally violent and you also happen to be naturally stupid—not a very politically correct word there—but you happen to be low in intelligence, then your prospects, to be perfectly honest with you, are not going to be that great, okay. You're going to wind up smacking a bottle over someone's head in a bar and you are going to wind up in prison pretty quickly, okay. However, if you've got those traits I've just mentioned to you and you are not naturally violent and you are also intelligent then it's a different story altogether. Then, as the famous Reuter's headline once mentioned, you are more likely going to make a killing in the market than anywhere else.