Spontaneous evolution of social exchange—An experimental study

Each of several exchange partners owns a specific commodity which she can share with others. Unlike in other social dilemma scenarios like prisoners’ dilemma, public goods games, etc., voluntary cooperation relies on bilateral exchanges whose profitabilities are interdependent. How will mutual sharing evolve? Will it include all group members or will smaller groups be more efficient? Our experimental data shed partly new light on older topics: cooperation is now relation specific, allowing for discrimination; group size effects are explored dynamically rather than in one-shot interaction; and, finally, we have weakened demand effects for voluntary cooperation by realistic efficiency gains.