Can Your Genes Make You Kill?

 Science’s search for the roots of violence.

- Lois Parshley

The killer read his Bible. He drank. Heavily.

It was a fall night in 2006, when Bradley Waldroup walked out of his rural trailer in southeastern Tennessee, carrying his .22 caliber hunting rifle. His estranged wife and her friend, Leslie Bradshaw, had just pulled up to drop off the Waldroups’ four children. Waldroup began arguing with his wife and Bradshaw, who was unloading the car. Drawing his gun, Waldroup shot Bradshaw eight times, killing her. He used a knife to cut her head open. He then chased his wife with the knife and a machete, managing to slice off one of her pinkies before dragging her into the trailer. There, he told their frightened children, “Come tell your mama goodbye,” because it was the last time they’d ever see her. Miraculously, his wife managed to slip his grasp and escape.

Three years later, in a county court, Waldroup admitted the whole thing. He said he had “snapped.” “I’m not proud of none of it,” he told the judge. Convicted of felony murder, he faced the death penalty.

To save his life, his legal team took an unusual approach, never before admitted in a capital-murder case. They sent a sample of Waldroup’s blood to the molecular genetics lab at Vanderbilt University in Nashville. Lab techs there were told to look at a specific gene. Sure enough, they found Waldroup had a genetic variant on his X chromosome, one that coded the enzyme monoamine oxidase-A (MAOA).

MAOA’s job is to break down crucial neurotransmitters, such as dopamine and serotonin. If left unchecked, these potent chemicals can build up in the brain and cause a loss of impulse control and an increase in violence and rage. In part, Waldroup’s lawyers were claiming, his genes made him do it.