theory, while sociological theories of social ties and intergroup comparisons suggest that bilateral cooperation can be … implemented by letting subjects make a positive contribution to a public good if they choose to defect from cooperation, i ….e. cooperation is collusive since the gains are at the expense of the public. We find that this negative externality increases …

the need for a new theory of how cooperation emerges. … daher die Notwendigkeit einer neuen Theorie über die Entstehung von Kooperation nahe. …