The Murder Gene

Last September in Italy, a man convicted of what would, in this country, be called second-degree murder or manslaughter had his 9-year sentence reduced on appeal on the grounds that he exhibited

abnormalities in brain-imaging scans and in five genes that have been linked to violent behaviour — including the gene encoding the neurotransmitter-metabolizing enzyme monoamine oxidase A (MAOA). … Giving his verdict, [the judge] said he had found the MAOA evidence particularly compelling.

The ruling marks the first time a defense based on behavioral genetics — the argument that a defendant’s genes caused him to commit the crime — has affected the outcome of a criminal case in any European court. To my knowledge, no defendant has ever succeeded with this argument in America, either, though many have tried.

I have written before about the implications of behavioral genetics for criminal law, which is built on the assumption that we are generally responsible for our own actions. Surely this is an issue the criminal courts will have to face: some people may indeed be genetically hard-wired for violence. But this decision comes as a surprise to me because the science does not seem to justify it, not yet. We simply don’t know that a single gene like MAOA causes specific behaviors, even in very specific gene-environment interactions. It is a bad decision but a telling one: as the science of behavioral genetics advances, at some point the courts will find it impossible ignore. (To learn more, a great scholarly article by law professor Owen D. Jones is here.)

For now, though, the idea of a “murder gene” is the stuff of novels, not science. My own next novel takes up this very issue. It involves a man named Andy Barber, who descends from a long line of violent men and whose teenage son Jacob is accused of murdering a classmate. Jacob, it turns out, also carries the MAOA gene variant — sometimes called the “warrior gene.” Preparing for his son’s murder trial, Andy says,

The legal question we discussed most … was the relevance of Jacob’s violent bloodline. We referred to this issue as the “murder gene” to express our contempt for the idea, for its backwardness, for the way it warped the real science of DNA and the genetic component of behavior, and overlaid it with the junk science of sleazy lawyers, the cynical science-lite language whose actual purpose was to manipulate juries, to fool them with the sheen of scientific certainty. The murder gene was a lie. It was also a deeply subversive idea. It undercut the whole premise of the criminal law. In court, the thing we punish is the criminal intention — the mens rea, the guilty mind. There is an ancient rule: actus non facit reum nisi mens sit rea — “the act does not create guilt unless the mind is also guilty.” This is why we do not convict children, drunks, and schizophrenics: they are incapable of deciding to commit their crimes, not with a true understanding of the significance of their actions. Free will is as important to the law as it is to religion or any other code of morality. We do not punish the leopard for its wildness. But that is the argument Logiudice [the prosecutor] would make if he had the chance: born bad. He would whisper it in the jury’s ear, like a gossip passing a secret. We were determined to stop him, to give Jacob a fair chance.

The murder gene may indeed be junk science, for now at least, but it is a haunting idea. We are quite comfortable with the idea that certain benign traits may inherited — musical talent, athleticism. Why not a talent for violence?

Image: Bryan Christie, “Pharmaceutical Brain”


“There’s certainly a brain basis to crime … the brains of violent criminals are physically and functionally different from the rest of us.”
— Adrian Raine

A burgeoning science suggests that crime is caused in part by biological factors, that is, by traits inherited through DNA or by the brain malfunctioning in very specific ways. Adrian Raine, a “neurocriminologist” and chair of the criminology department at the University of Pennsylvania, says,

“Seventy-five percent of us have had homicidal thoughts. What stops most of us from acting out these feelings is the prefrontal cortex…. When the prefrontal cortex is not functioning too well, maybe an individual, when angry, is more likely to pick up a knife and stab someone or pick up a gun.”

Some criminals, it seems, are biologically different from us.

“People who are psychopaths or who have antisocial personality disorder are literally cold-blooded. They have lower heart rates.  When they’re stressed, they don’t sweat as much as the rest of us. They don’t have this anticipatory fear that the rest of us have.”

Obviously I am not qualified to judge the science. But if it is true, as seems increasingly likely, that “freedom of will is not as free as you think,” as Professor Raine puts it, that fact would undercut the entire philosophy of our criminal law, which is that we punish the guilty mind, the mens rea — the conscious, purposeful decision to commit a crime. Where the defendant’s free will or judgment is compromised, because he is drunk or insane or a child, for example, generally the law attaches a lesser degree of culpability, sometimes no culpability at all (the proper finding for an insane defendant is “not guilty by reason of insanity,” not “guilty but insane”).

My third novel, to be published in February 2012, turns on just these sorts of questions. The story involves a father whose teenage son is accused of a murder, a crime that may have been triggered by the boy’s genetic inheritance — a “murder gene.” How should we think of such a criminal? It is not simply a question about crime or criminal law. It is the fundamental subject of crime novels, it is the reason we read them, to ask: What does crime tell us about ourselves and our nature? Modern neuroscience and genetics are beginning to provide answers Dostoyevsky could never have imagined.

Here is Professor Raine on the legal and ethical implications of neurocriminology: