As ethicists and metaphysicians we have been asked to discuss freedom, responsibility, and desert in connection with the possibility that a genetic marker will be discovered for “criminality” or aggressiveness. Some have thought that if there was a marker, then individuals with the marker could not be held responsible for whatever criminal or aggressive behavior they might engage in. Would we, they worry, be morally justified in punishing a murderer or a rapist if this person's genes predisposed him toward violent behavior?

Before answering this question, we should note a problem in its formulation. So far I have used as if they were interchangeable all of the following: “criminality,” “aggressiveness,” and “violent behavior.” Of course, they are not interchangeable terms, but the problem is that we don't know what a genetic marker, if found, would mark. Toward what would a person with the marker be predisposed? Anger? Or calculated, premeditated violence? Some sort of generic criminality (whatever that might be)? Or a sort of generic aggressiveness – a tendency to try to get one's way by force rather than by asking or negotiating? Or something more specific: a tendency to beat “loved” ones when they seem to be getting too independent? Or something specific and criminal but nonviolent: tax evasion or embezzlement or shoplifting?