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Identifying 'Criminal' Genes Will Never Prevent Violence But Might Help Explain It

A new study seems to have found two genes closely associated with violent crime, but environmental factors are still a big piece of the puzzle.

Photo via Flickr user ​Ian Britton

The subjects of a new Finnish study who helped establish the link between two genes and violent crime were an especially savage bunch. The group of 78 prisoners had committed more than 1,500 of the most brutal offenses in the criminal landscape—murder, manslaughter, attempted murder, and battery, according to the study, released in Nature at ​the end of last month. They also shared variations of two genes: Monoamine oxidase A (MAOA, also known as the "Warrior Gene") and CDH13. Basically, the combination of these two genes was bad for the study's subjects, and even worse for their victims.


"No substantial signal was observed for either MAOA or CDH13 among non-violent offenders, indicating that findings were specific for violent offending," the authors wrote. The 78 most violent prisoners were part of a larger group in the study, but represented the most concrete connection between the two genes and heinous crimes.

MAOA metabolizes dopamine, that wonderful hormone we feel surging through our bodies when lighting up a cigarette or taking a sip of liquor. The most violent offenders in the study—that group of 78—likely had larger bursts of dopamine when alcohol, cocaine, or other drugs were introduced into their systems. Those subjects also had a larger amount of "dopaminergic activity" than the average person, even without the addition of drugs, which can lead to aggressive behavior. Meanwhile, CDH13—to avoid some wonky scientific language—is a gene that affects switches in the brain most often associated with ADHD.

Both genes are "rather common," one of the study's authors, Jari Tiihonen, wrote me in an email, and can be found in 20 percent of the world's population. And, while the combination of MAOA and CDH13 represents a "risk of about 13-fold compared with the 'usual' genotype combination" for committing violent crimes, the majority of people with the gene combo won't be hacking up their families any time soon. Despite our national fascination with the daily drudgery of crime stories, incidents of violence are relatively low in developed countries. In the US, crime rates have been falling steadily for years, including a 5.4 percent drop in violent crimes in the first six months of 2013 compared to the same period of 2012, ac​cording to the FBI.


Speculation runs rampant as to why crime has dropped. Everything from harsh prison sentences to concealed carry are cited as reasons for the trend. But, like the rationale for committing crimes in the first place, the real answer is much more complex. And it's probably safe to say that it's far more complicated than the science behind Tiihonen's study.

"This is not a system where everybody that has a certain gene turns out to be violent," said Lawrence Kobilinsky, a professor in the forensic sciences department at the John Jay College of Criminal Justice in New York.

Anyone with a minimal knowledge of criminology knows that, starting with the increased urbanization that went into overdrive with the Industrial Revolution, the causes of crime are many and varied. Living conditions, access to basic services, income level, education and housing all play large roles. In addition to these factors and Tiihonen's two genes is the overwhelmingly influential role of environment—your brain has something to do with it, but your block​ matt​ers a hell of a lot, too.

"It seems to me that one's environment plays at least as important of a role, if not more so, than genetics," Kobilinsky said. "Even if one has genes that predisposes people to certain behavior, there's so many other factors that I don't know how much credence to put into that."

Like most things, the majority of gene science research has to do with money. There are obvious profits to be had if someone can identify genes that lead to cancer, heart disease, or other conditions that reduce life expectancy. But the field of behavioral gene research is more dependent on curiosity outside the bounds of capitalism. For decades, scientists have worked to identify genes associated with certain behaviors—autism and ADD, for instance—and even sexual orientation. But as with all things done by humans, the hardware inside our heads is only part of the equation. A person with the genes identified in the Finnish study may be more inclined to carrying out a brutal murder, but they're less likely to do so if they haven't undergone a litany of tragic experiences or been reared in a violent and poverty-stricken neighborhood.


In fact, Kobilinsky said, some people born with the Warrior Gene and others like it have done quite well for themselves.

"If you're on Wall Street, you want aggressive behavior because you want success," he told me. "But just because you have a certain gene doesn't mean you're going to have violent behavior."

The ruthlessness on display by those playing with absurd amounts of money is no different than street criminals deciding it's easier to off a competitor than to make a deal with him. Again, it all depends on perspective and environment. Making money is good. Making money through murder is bad, generally speaking.

"Twin studies," in which two people with identical genetics but dissimilar environments make different decisions, demonstrate this, according to Kobilinsky. In his analogy, the Wall Street banker with a dopamine deficiency—like the one found in Finnish study's subjects—would make decisions seen as more acceptable by society than his twin in the ghetto, where most would probably agree there are a different set of rules.

For those equipped with genes associated with violence, their identification might be more helpful at the tail-end of the criminal justice apparatus than the beginning. Unless we're going to start quarantining anyone with these genes at birth, and placing them in a padded room to ensure they don't kill anyone or ruin our economy with disastrous speculative lending practices, the study's results are just another piece of the puzzle.

"I think where this goes is, someone who commits a crime, they might raise this as a mitigating factor in their sentencing," Kobilinksy said. "That it wasn't a person's fault because they were genetically predisposed to violence."

If a defense attorney can cit​e "affluenza" as the reason why a rich kid from Texas got drunk and killed four people with his pickup truck, it stands to reason that actual science, in addition to environment, might explain why some crimes occur.

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