Importing social preferences across contexts and the pitfall of over-generalization across theories.

Claims regarding negative strong reciprocity do indeed rest on experiments lacking established external validity, often without even a small "menu of options." 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.