We question whether the postulated revenge and forgiveness systems constitute true adaptations. Revenge and forgiveness are the products of multiple motivational systems and capacities, many of which did not exclusively evolve to support deterrence. Anger is more aptly construed as an adaptation that organizes independent mechanisms to deter transgressors than as the mediator of a distinct revenge adaptation.

Market models are indeed indispensable to understanding the evolution of cooperation and its emotional substrates. Unfortunately, Baumard et al. eschew market thinking in stressing the supposed invariance of moral/cooperative behavior across circumstances. To the contrary, humans display contingent morality/cooperation, and these shifts are best accounted for by market models of partner choice for mutually beneficial collaboration.

In addition to questions of the representativeness of Western, educated samples vis-à-vis the rest of humanity, the prevailing practice of studying individuals who are culturally similar to the investigator entails the problem that key features of the phenomena under investigation may often go unrecognized. This will occur when investigators implicitly rely on folk models that they share with their participants.

Claims regarding negative strong reciprocity do indeed rest on experiments lacking established external validity, often without even a small Guala's review should prompt strong reciprocity proponents to extend the real-world validity of their work, exploring the preferences participants bring to experiments. That said, Guala's approach fails to differentiate among group selection approaches and glosses over cross-cultural variability.