title: Humans choose representatives who enforce cooperation in social dilemmas through extortion.
abstract: Social dilemmas force players to balance between personal and collective gain. In many dilemmas, such as elected governments negotiating climate-change mitigation measures, the decisions are made not by individual players but by their representatives. However, the behaviour of representatives in social dilemmas has not been investigated experimentally. Here inspired by the negotiations for greenhouse-gas emissions reductions, we experimentally study a collective-risk social dilemma that involves representatives deciding on behalf of their fellow group members. Representatives can be re-elected or voted out after each consecutive collective-risk game. Selfish players are preferentially elected and are hence found most frequently in the 'representatives' treatment. Across all treatments, we identify the selfish players as extortioners. As predicted by our mathematical model, their steadfast strategies enforce cooperation from fair players who finally compensate almost completely the deficit caused by the extortionate co-players. Everybody gains, but the extortionate representatives and their groups gain the most.
authors.affiliation: Department of Evolutionary Ecology, Max-Planck-Institute for Evolutionary Biology, August-Thienemann-Strasse 2, 24306 Plön, Germany.
authors.forename: Manfred
authors.initials: M
authors.lastname: Milinski
authors.affiliation: Department of Organismic and Evolutionary Biology, Department of Mathematics, Program for Evolutionary Dynamics, Harvard University, One Brattle Square, Cambridge, Massachusetts 02138, USA.|Institute of Science and Technology Austria, Am Campus 1, Klosterneuburg 3400, Austria.
authors.forename: Christian
authors.identifier: http://orcid.org/0000-0001-5116-955X
authors.initials: C
authors.lastname: Hilbe
authors.affiliation: Department of Evolutionary Ecology, Max-Planck-Institute for Evolutionary Biology, August-Thienemann-Strasse 2, 24306 Plön, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Semmann
authors.affiliation: Department of Evolutionary Ecology, Max-Planck-Institute for Evolutionary Biology, August-Thienemann-Strasse 2, 24306 Plön, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Sommerfeld
authors.affiliation: Max Planck Institute for Meteorology, Department "The Ocean in the Earth System", 20146 Hamburg, Germany.
authors.forename: Jochem
authors.initials: J
authors.lastname: Marotzke
mesh_terms: D057231:Climate Change; D003299:Cooperative Behavior; D005260:Female; D005716:Game Theory; D006801:Humans; D007398:Interpersonal Relations; D008297:Male; D008962:Models, Theoretical; D055815:Young Adult