subjects in a brain scanner and invited them to play a bargaining game where they could punish someone who acted unfairly to them — personal revenge — or punish someone who acted unfairly to someone else — impersonal punishment. For each subject, Strobel also collected information on a gene called COMT Met. This gene has three different forms, linked to differences in activity level in the frontal lobe of the brain, which are linked to differences in the levels of dopamine, which are linked to differences in the experience of reward. Given the different forms of COMT Met, at least part of what we experience as the feeling of reward or gratification was determined by our parents, and our parent’s parents, and their parent’s parents, all the way back to our ape-like cousins who evolved this gene. When Strobel looked at the brain scans of his subjects, he found that the same circuitry was engaged for personal revenge and impersonal punishment, with significant activity in the striatum — a reward area — as well as in the insula — an area involved in the feeling of disgust. When we detect an injustice, we feel disgusted, a feeling that may motivate our desire for retribution. The striatum finishes off the process, rewarding us for our punitive response, and wiping out the negative feeling of disgust. Importantly, individuals with the high expressing form of COMT Met, and thus, higher levels of dopamine, showed stronger activation in the striatum, and were more likely to punish those who act unfairly. Strobel suggests that those with the high expressing form punished more because they anticipated a higher level of reward. If this explanation is right, it has profound consequences for how we think about individual participation in the policing of norms and the honey hits associated with aggression. Some people will have a natural bias to shy away from punishment, not because they fail to see the importance of ratting out cheaters, but because they don’t anticipate feeling