With their thick, wavy hair parted neatly on the side, cherubic faces and unfailingly polite manners, Derek King, 14, and his brother Alex, 13, come across like choirboys. But the Florida teenagers were sentenced last November to eight and seven years in prison, respectively, after admitting that they had bludgeoned their father to death with a baseball bat. The previous year brought two other trials of Florida kids who had committed murder: Lionel Tate, also 14, got a life sentence for beating a 6-year-old playmate to death, and Nathaniel Brazill, another 14-year-old, was sent to prison for 28 years for killing his middle-school teacher.
What could possibly turn kids this young into brutal killers? The recipe for violence is almost certainly a mix of bad genes and a bad environment, and the evidence is strong that the recipe is cooked up very early in life. Until about a decade ago, most experts assumed that it was a violent or impoverished upbringing that led to violent adults. "We're depraved," says one of the gang members in West Side Story, "on account of we're deprived." Indeed, studies had suggested a correlation between a harsh childhood and later criminality. The link was strongest for those who had been physically abused as kids. Still, not all abused children grow up to perpetrate violence in turn. Something else must be going on.
One possible answer began to emerge after a Dutch woman consulted her doctor about whether to have kids. Her family had a history of violence, including rape and attempted murder. Would her children be violent too, she asked? Her doctor consulted geneticist Hans Brunner, who discovered that the family carried a defective gene: it made too much of an enzyme, called monoamine oxidase A, resulting in excessive destruction of neurotransmitters that help keep us calm and happy.
The finding thrilled some scientists--here, finally, was an explanation for criminality--and appalled others, who feared that if genes dictate behavior, it could lead to genetic typecasting of entire races. But lots of violent men don't have the defective gene, while many noncriminals do. Here, too, the simple explanation was clearly not the whole story.
Last summer, though, scientists at the University of Wisconsin reported on a long-term study of 400 boys that had been going on for more than a quarter-century. The scientists had collected DNA from the boys and recorded their behavior at regular intervals. As with the earlier research, scientists found that neither genes alone nor childhood abuse alone could explain adult violence. But of the boys who had both mutation and early abuse, fully 85% had committed a violent act as an adult. The implication, says Terrie Moffitt, a professor of psychology at Wisconsin: "Genes influence people's susceptibility or resistance to environmental 'pathogens.'" Someone with a low genetic propensity will have to be pushed very hard to become violent; another individual with a different genetic makeup might have a hair trigger.