Forgiveness is institutionally mediated, not an isolable modular output

McCullough et al. recognize that revenge and forgiveness jointly constitute a functional strategic complex. However, they model the halves of the complex as outputs of modules selected for regulating dyadic relationships. This is backwards. Forgiveness is a culturally evolved institution that can be exapted for use in dyadic contexts; it would be cheap talk among dyads were it not for the shadow of society.