The Anatomy of Violence

Cho Seung-Hui turned his gun on himself before a neuroscientist could get him into a brain-imager and scan his cortex for aberrant activity. No geneticist had analyzed his DNA for genes associated with impulsivity, aggression or violence. And although a physician at a psychiatric hospital concluded in late 2005, after Cho had stalked two female students, that his "affect is flat and mood is depressed," no psychologist had the opportunity to ask him why he wrote such disturbing, demon-haunted plays and essays that his professor referred him for counseling last fall. No sociologist had probed how American society had shaped this 23-year-old South Korean immigrant during his 15 years in the United States.

While the temptation is to dismiss Cho as crazy and leave it at that, no one will ever know for sure why Cho murdered two fellow students in a dormitory at Virginia Tech and then gunned down 30 more people in a classroom building across campus just over two hours later. But the unasked, and perhaps unanswerable, questions show the new sophistication of research on the etiology of violence.

Not long ago, scientists invoked genes or brain circuitry, hyper-activity or brutal parental discipline or America's "gun culture" to explain horrors ranging from Charles Whitman's rampage at the University of Texas, Austin, clock tower in 1966, to George Hennard's 23 murders at a Killeen, Texas, diner in 1991, to the Columbine High School shootings in 1999. But although some people with a particular gene variant do grow up to be sociopaths, others with the same variant do not. And while some with overactivity in particular regions of the brain commit violent crimes, others do not. And if every kid who became inured to violence through Grand Theft Auto or who witnessed chronic conflict between his parents during early childhood—risk factors for violence—went on a murder spree, well, then crimes like Cho's wouldn't have network-news anchors rushing to the sites of the massacres to do their broadcasts.

Scientists who study criminal violence—that committed outside of wars and civil conflicts—now believe that its roots are equally planted in the biology of an individual, the psychology that reflects the interaction of innate traits and experiences, and the larger culture. No single cause is sufficient, none is deterministic. "It's like a kid piling up a tower of blocks," says Loyola University, Chicago, psychologist James Garbarino, who has studied school shooters. "Eventually, it falls over. You could point to the final block and say, that one's the cause. But it's an accumulation of risk factors."

A genetically identical clone of Cho growing up with different experiences in a different environment would likely not have set an American record for mass murder: although the biology would have been sufficiently twisted, the psychology—the product of experiences interacting with that biology—would not have been. Similarly, a Cho who grew up in, say, Japan would almost certainly not have acted on his hatred and fury: biology and psychology set the stage for homicidal violence, but the larger culture would likely have prevented its execution. (Japan is not immune from heinous murders, of course: one day after the Virginia Tech shootings, the mayor of Nagasaki was fatally gunned down on a sidewalk, apparently by a mobster.) What is becoming clear is that criminal violence reflects and requires the dark hand of individual biology, life experiences and the larger cultural surround—and the will to take lives in cold blood.

When behavioral genetics was in its heyday a decade or two ago, one of its grails was a gene predisposing people to violence—and an extended family of Dutch sociopaths seemed to be just what scientists were looking for. Fourteen men in the family had committed impulsive, aggressive crimes including arson and attempted rape. In 1993, scientists reported that all 14 had the identical form of a gene on the X chromosome. The gene makes an enzyme called MAOA, which breaks down such brain chemicals as serotonin and noradrenaline. The normal version of the gene produces lots of MAOA; the aberrant form produces low amounts. Studies in animals had linked low enzyme levels to aggression, perhaps because when MAOA is in short supply the brain remains jacked up on neurochemicals in a way that induces aggression.