Character motivation: belief or disbelief in a genetic predisposition to violence

Is there a genetic predisposition to violence? Some studies suggest there is. So, if a defendant–a diagnosed psychopath–has the gene, should he be given a lighter sentence on the theory that he is not as morally or personally responsible for his crime as others might be? Or a stiffer one, on the theory that he is more likely to re-offend, and only a longer sentence can protect the public?

Last month, NPR reported on a study published in the August 17, 2012 issue of Science magazine that asked judges to review facts–based on a real case–then compared their hypothetical sentences. (Here’s the abstract – full access is restricted.) The judges given a report detailing the neurobiological basis for the psychopathy gave shorter sentences–an average of 13 years compared to 14 years without the report.

As the NPR reporter said, “Our sympathy for the idea that biology might be responsible for criminal behavior is powerful.”

How will that sympathy affect your characters–or not? How will their different opinions influence their thoughts and dialogue, their actions and their relationships? What conflicts will result?