ABSTRACT
In recent behavioral economics, the idea of strong reciprocity has become central, both as an explanans and as an explanandum. On the one hand, it is used to account for altruistic behavior in experimental and non-experimental settings. On the other hand, it is explained as the outcome of natural selection possibly operating at the group level. In the development of these arguments, the work of Ernst Fehr and his network of collaborators has been especially important.
