How can you tell if someone is a serial killer? While the actions of infamous serial murderers (like Jeffrey Dahmer and Ted Bundy) may seem unrelated — they all actually have this *one* neurological component in common. Neurologist Jim Fallon — who’s actually related to Lizzie Borden — studied the brain scans and genetic analysis of 70 different serial killers and discovered they all had damage to their orbital cortex and, more specifically, the MAO-A gene (or the major violence gene). Often, this gene is passed on by the mother in utero, and exposes a person to too much serotonin early on — causing a sort of tolerance that prevents people from feeling calm or relaxed later in life. But it is more complicated than that. “If you have that gene, and you see a lot of violence in a certain situation,” Fallon says. “This is the recipe for disaster, absolute disaster.”