In the ongoing research agenda aimed at understanding cooperation in groups in humans, the role of punishment continues to be the subject of substantial empirical work and theoretical debate (e.g., Fehr & Fischbacher, 2003). In particular, careful scrutiny has been given to third party punishment: inflicting costs on others in transactions in which the punishing individual is not directly involved (Fehr & Fishbacher, 2004). This work is important because third party sanctioning has been suggested as a potentially powerful force in sustaining social norms in groups (Boyd & Richerson, 1992), including norms associated with cooperation (e.g, Fehr, Fischbacher, & Gächter, 2002)...<READ MORE>