Bad to the bone; the genes and brains of psychopaths

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The manipulative con-man. The guy who lies to your face, even when he doesn’t have to. The child who tortures animals. The cold-blooded killer. Psychopaths are characterised by an absence of empathy and poor impulse control, with a total lack of conscience. About 1% of the total population can be defined as psychopaths, according to a detailed psychological profile checklist. They tend to be egocentric, callous, manipulative, deceptive, superficial, irresponsible and parasitic, even predatory. The majority of psychopaths are not violent and many do very well in jobs where their personality traits are advantageous and their social tendencies tolerated. However, some have a predisposition to calculated, “instrumental” violence; violence that is cold-blooded, planned and goal-directed. Psychopaths are vastly over-represented among criminals; it is estimated they make up about 20% of the inmates of most prisons. They commit over half of all violent crimes and are 3-4 times more likely to re-offend. They are almost entirely refractory to rehabilitation. These are not nice people.

So how did they get that way? Is it an innate biological condition, a result of social experience, or an interaction between these factors? Longitudinal studies have shown that the personality traits associated with psychopathy are highly stable over time. Early warning signs including “callous-unemotional traits” and antisocial behaviour can be identified in childhood and are highly predictive of future psychopathy. Large-scale twin studies have shown that these traits are highly heritable – identical twins, who share 100% of their genes, are much more similar to each other in this trait than fraternal twins, who share only 50% of their genes. In one study, over 80% of the variation in the callous-unemotional trait across the population was due to genetic differences. In contrast, the effect of a shared family environment was almost nil. Psychopathy seems to be a lifelong trait, or combination of traits, which are heavily influenced by genes and hardly at all by social upbringing.

The two defining characteristics of psychopaths, blunted emotional response to negative stimuli, coupled with poor impulse control, can both be measured in psychological and neuroimaging experiments. Several studies have found decreased responsiveness of the amygdala to fearful or other negative stimuli in psychopaths. They do not seem to process heavily loaded emotional words, like “rape”, for example, any differently from how they process neutral words, like “table”. This lack of response to negative stimuli can be measured in other ways, such as the failure to induce a galvanic skin response (heightened skin conduction due to sweating) when faced with an impending electrical shock. Psychopaths have also been found to underactivate limbic (emotional) regions of the brain during aversive learning, correlating with an insensitivity to negative reinforcement. The psychopath really just doesn’t care. In this, psychopaths differ from many people who are prone to sudden, impulsive violence, in that those people tend to have a hypersensitive negative emotional response to what would otherwise be relatively innocuous stimuli.

What these two groups have in common is poor impulse control. This faculty relies on the part of the brain called the prefrontal cortex, most particularly the orbitofrontal cortex. It is known that lesions to this part of the brain impair planning, prediction of consequences, and inhibition of socially unacceptable behaviour – the cognitive mechanisms of “free won’t”, rather than free will. This brain region is also normally activated by aversive learning, and this activation is also reduced in psychopaths. In addition, both the prefrontal cortex and the amygdala show substantial average reductions in size in psychopaths, suggesting a structural difference in their brains.

These findings have now been united by a recent study that directly analysed connectivity between these two regions. Using diffusion tensor imaging (see post of August 31st 2009), Craig and colleagues found that a measure of the integrity of the axonal tract connecting these two regions, called the uncinate fasciculus, was significantly reduced in psychopaths. Importantly, connectivity of these regions to other parts of the brain was normal. These data thus suggest a specific disruption of the network connecting orbitofrontal cortex and amygdala in psychopaths, the degree of which correlated strongly with the subjects’ scores on the psychopathy checklist.

All of these findings are pointing to a picture of psychopathy as an innate, genetically driven difference in connectivity between parts of the brain that normally drive empathy, conscience and impulse control. Not a fault necessarily, and not something that could be classified as a disease or that is always a disadvantage. At a certain frequency in the population, the traits of psychopathy may be highly advantageous to the individual.

This conclusion has serious ethical and legal implications. Could a psychopath mount a legal defense by saying “my brain made me do it”? Or my “genes made me do it”? Is this any different from saying my rotten childhood made me do it? Psychopaths know right from wrong – they just don’t care. That is what society calls “bad”, not “mad”. But if they are constitutionally incapable of caring, can they really be blamed for it? On the other hand, if violent psychopaths are a continuing danger to society and completely refractory to rehabilitation, what is to be done with them? Perhaps, as has been proposed in the UK, people with the extreme psychopathic personality profile (or maybe in the near future even a specific genetic profile?) should be monitored or segregated even before they commit a crime.

While it is crucial that these debates are informed by good science, these issues have no clear-cut answers. They will be resolved on a pragmatic basis, weighing the behaviour that society is willing to tolerate versus the rights of the individual, whatever their brains look like, to define their own moral standards.

Craig, M., Catani, M., Deeley, Q., Latham, R., Daly, E., Kanaan, R., Picchioni, M., McGuire, P., Fahy, T., & Murphy, D. (2009). Altered connections on the road to psychopathy Molecular Psychiatry, 14 (10), 946-953 DOI: 10.1038/mp.2009.40


  1. Oops! Sorry I posted this twice by mistake!

  2. I like Steven Pinker’s response to this quandry in the Blank Slate. If the psychopath argues that his genes made him commit a violent crime, then the judge could just as easily argue that his genes are making him (or her) throw the criminal in jail. Appealing to genetic causes is not a very strong argument in this case, because one could respond that the rest of the public has a genetically-based instinct to punish criminals, and you’re back to square one. Whose genes win out? It comes back to a question of rights.

    And the fact that most psychopaths can’t be rehabilitated is not necessarily a big moral issue, if we are trying to balance the rights of the public versus the rights of the individual. In this case, the right of the public to not be harmed wins out over individual freedom, something that is not problematic to most people. It’s only under the false presumption that jail is purely for punishment and/or rehabilitation that this appears to be a major dilemma. Prisons also exist to isolate criminals from their potential victims.

  3. I also liked Steven Pinker’s take on this. His view of the law is based more on motivation than blame.

    Even if a psychopath’s genes are to blame, what matters is that society punishes this sort of behavior, thereby motivating it to occur less. This is especially important in the case of psychopaths, who can only be incentivized by punishment and reward and not by empathy.

  4. “The manipulative con-man. The guy who lies to your face, even when he doesn’t have to. The child who tortures animals. The cold-blooded killer.”

    I used to see a distinction between “sociopaths” (#1) and “psychopaths” (#3). It seemed helpful, so why has it disappeared?

  5. There’s a strong correspondence between preemptive incarceration for psychopaths, and quarantine for those with an infectious illness. In both cases, people are taken prisoner without an actus reus (criminal act), mens rea (guilty mind), habeus corpus, nor even a court hearing; for the legitimate goal of protecting society from that person’s hypothetical danger.

    Is the criminal justice system even an appropriate venue to deal with this? Or do we need independent Centers for Psychopath Control (CPC) with broad powers to locate, investigate, isolate, and detain suspected psychopaths?

  6. I wonder if there are degrees of psychopathy? It seems to me that there are a lot of people who display varying degrees of these kinds of behaviors (at least that is my experience from 30 years in law enforcement)and probably constitute significantly more than 1% of the population.

    This study confirms what I and many others in law enforcement had intuitively thought for many years, i.e, a genetic link to violent crime.

    As far as incarceration is concerned, I prefer to think that we are not simply locking up people who are victims of genetic determinism, but rather we are locking up their genes.

  7. I buy the compatibilist viewpoint that determinism and free will are compatible, so I see no problem with punishing a psychopath for a crime. Even if we found an absolute “murder gene” where 100% of people with the gene murdered someone, I would still punish him. Our genes don’t make us act against our will; they give us our will in the first place.

    If you give me the choice between eating a cookie and getting my hand chopped off, I’m going to pick the cookie. That’s determinism. I really did have the option of the hand, but I chose the cookie. That’s free will. No contradiction.

    In the long run, I see this kind of research as a good thing. A common argument of people who want lenient sentencing is, “You would have done the same thing in his shoes.” Now I can say, “BS”.

    I’ve heard estimates that 3-4% of people are sociopaths. As far as I know, a sociopath is just a psychopath who is either too smart or too lazy to commit the sort of crime that would label him a psychopath.

  8. Relevant recent inaugural paper by Anthony Cashmore in PNAS argues as follows: free will is an illusion with no support from experiment or basic physics (cf. Wegner’s very nice book The Illusion of Conscious Will); the criminal justice system is designed to decide guilt based on the assumption of free will (illegal action plus mens rea) and hold blameless those who are judged to lack free will (via insanity plea); science continues to accumulate reasons which further undermine the notion of free will in human actions (influence of genes), making the situation worse and worse the more we learn; this is all quite dysfunctional. The alternative he proposes is a system of justice in which “the illogical concept that individuals are in control of their behavior in a manner that is something other than a reflection of their genetic makeup and their environmental history” is removed. Society decides on the laws; if you are found to have broken them, regardless of your state of mind or the reasons why, you are convicted and punished/treated.

    Cashmore, A, “The Lucretian Swerve: The biological basis of human behavior and the criminal justice system,” PNAS 2010 (open access)

  9. Thanks, Al Gebraic. Just as baffling as belief in a god, is belief in free will. Both are magical beliefs.

  10. NP. The Green & Cohen paper linked by TGGP riffs on very similar themes.

  11. Here is a concise paper speculating on the evolutionary basis of psychopathy:

  12. If a psychopath claims “my genes made me do it” then the judge can say “well in that case you’ll be sterilized too.” If psychopaths constitute a mere 1% of the population then it’s possible bread psychopathy out of the population all together (and screen immigrants for the condition.)

  13. > free will [has] no support from experiment or basic physics

    Neither do qualia have any. Unless of course simply having qualia is an experiment eo ipso, which it is. Qualia have experimental support but are not accounted for by physical theory.

  14. Well it didn’t take long to get to a suspension of human rights and eugenics did it?

    Anybody thought about the positive aspects of psycopathy for the population. A little bit of psycho/sociopathy may well be a useful attribute for survival, on both an individual and population level (see

    As an (unprovable) example contrast the Ancient Greeks contribution to progress and their prediliction for spending the summer kicking the s**t out of each. You tinker with the germ line at some risk.

  15. “Anybody thought about the positive aspects of psycopathy for the population. A little bit of psycho/sociopathy may well be a useful attribute for survival, on both an individual and population level.”

    This is in my opinion the problem when people speculate about real-life problems and real-life consequences from a laboratory or classroom. I spent a week hanging out with homeless people addicted to drugs as an experiment. I can tell you right now these people are some of the most conniving and manipulative people you could ever come across, and I had to cut ties with them as a result (though not completely, because I like learning from them and gaining a different life perspective). But this experience was very instructive for understanding the way psychopaths lure victims and try to use them for their own ends. I also gained expert-level insights on stealing from local businesses (knowledge I don’t care to apply). They really are worthless people, and it’s sad they will never feel the full pleasure of loving and being loved. They suffer anosognosia of morals, a “sickness” on par with the worst case of stupefied schizophrenia. They have nothing in common with the ancient Greeks.

  16. To clarify, some homeless addicts are of decent character (other than their lack of self-control with regard to drugs), but it was obvious to me that psychopaths tend to orbit around their circles. I am referring specifically to these types.

  17. It strikes me that you’re talking about three things: A1.) “lack of impulse control” and B1.) “blunted emotional response to negative stimuli” and B2.)”hypersensitive emotional reaction”. Not mentioned are B3.) normal reaction to emotional stimuli and A2.) normal impulse control.

    If you fill out the paradigm:

    1. A1 B1 = psychopath
    2. A2 B1 = criminal mastermind, cold-blooded but careful. Or, strategic planner. Or world conqueror.
    3. A1 B2 = hot-blooded killer (murder 2nd degree)
    4. A2 B2 = hysterical, moody
    5. A1 B3 = impulsive but harmless: Kramer in Seinfeld
    6. A2 B3 = normal

    The typology seems to be crime-based, so A2 B1 gets left out, since these are less likely to enter the criminal justice system.

    It’s possible that A and B are correlated, but as far as I know that hasn’t been shown. If they aren’t, my typology is better. The given typology is distorted by the specific practical context it comes from, which is specifically intended to describe criminals.

    The pure, objective, dispassionate, univeralistic, morally neutral scientist, the Stoic philosopher, the Olympian observer, etc., all of which have valorized in our society, have the emotional flatness in common with the psychopath and the world conqueror / criminal mastermind. What differentiates them? Less ambitious and activist than the world-conqueror, better impulse control than the psychopath and, on top of that, some kind of general good will which is not emotional in origin. But in fact, pure philosophers can be heartless and effectively cruel at times, so maybe it’s just that they are less activist.

  18. “I used to see a distinction between “sociopaths” (#1) and “psychopaths” (#3). It seemed helpful, so why has it disappeared?”

    People thought they understood what the terms meant, so the APA had them abolished.

    Keep in mind that poor impulse control isn’t necessarily a feature of sociopathy – it’s just the one that tends to make people visible as obvious sociopaths. Actors and politicians often score very highly on manipulative behavior, but they’re often also the ones that can behave according to societal expectations – when it benefits them.

  19. John Emerson’s classification with the Ax and Bx made me think of something that I’ve spent considerable time thinking about. There’s a difference between being unresponsive to/not caring much about other people’s feelings in a “neutral” way, and actively disregarding other people’s feelings. The latter is what people usually refer to when they speak of “not caring about others’ feelings”, but in the extreme it amounts to caring about them a lot, just not in a positive way.

    A lot of nerdy or just really intellectual people seem to have their greatest passions for things other than the world of humans, which tends to create a certain lack of caring toward that human world. I know I sometimes wonder how clueless I am about what it means to really love someone.
    I think the difference is, I realize that dealing with people is better left to those who really care about working with people, in a positive way, and so I seek to avoid being put in situations where I have to show emotional connection–rather than treating people like I would treat a computer and going “tough luck”, which seems to be what psychopaths do.

  20. I have a genetic disposition to chubbiness, but I choose whether to have that brownie or not. Is my weight my fault?

  21. Psychopathy is neither a necessary nor sufficient condition for someone to be extremely dangerous, a multiple murderer or even a criminal.

    For example Jeffrey Dahmer scored 22 on the PCL-R, well below the 30 needed to technically be a psychopath, but he had so many other disorders going on that he was an individual way more dangerous than the average psychopath.

    The proposed UK system of DSPD (dangerous and severe personality disorder) is mentioned. It is actually much more nuanced than merely dividing psychopaths from non-psychopaths.
    for details.

  22. How can someone be a psychopath if they never get into trouble; you might as well say there are lots of schizophrenics who always behave perfectly normally.

    Here is a card carrying psychopath James “Fur” Sammons

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