This chapter explores the meaning and moral significance of claims that particular genetic features predispose a person to violent or antisocial behavior. It argues that credible evidence of genetic influence is unlikely to have straightforward implications for moral responsibility. While such evidence may encourage observers to hold the agent less responsible for his aggressive or impulsive actions, it may also tempt them to see the agent as essentially impulsive or aggressive. It is, if anything, likely to deepen the ambivalence we already feel toward individuals who appear disposed to crime and violence.

There is a perennial tension in the criminal law between the desire to punish dangerous, recalcitrant offenders more severely, because they are more difficult to deter and less susceptible to reform, and the uneasy recognition that the conditions that make them more dangerous may also make them less responsible. This tension is often seen in terms of a conflict between utilitarian and retributivist approaches to punishment, with the former appearing to favor stronger deterrents or longer incapacitation in the face of greater recalcitrance, and the latter appearing to favor weaker punishment in the face of diminished responsibility. The tension is more complex, however, because there is also a conflict among retributivist intuitions.

On the one hand, evidence that a person has a violent or antisocial predisposition may seem powerfully mitigating. It may invite the suspension of blame and its replacement with a more custodial or therapeutic attitude.