title: Partner choice creates fairness in humans.
abstract: Many studies demonstrate that partner choice has played an important role in the evolution of human cooperation, but little work has tested its impact on the evolution of human fairness. In experiments involving divisions of money, people become either over-generous or over-selfish when they are in competition to be chosen as cooperative partners. Hence, it is difficult to see how partner choice could result in the evolution of fair, equal divisions. Here, we show that this puzzle can be solved if we consider the outside options on which partner choice operates. We conduct a behavioural experiment, run agent-based simulations and analyse a game-theoretic model to understand how outside options affect partner choice and fairness. All support the conclusion that partner choice leads to fairness only when individuals have equal outside options. We discuss how this condition has been met in our evolutionary history, and the implications of these findings for our understanding of other aspects of fairness less specific than preferences for equal divisions of resources.
authors.affiliation: Institut de Biologie de l'Ecole normale supérieure (IBENS), INSERM 1024, CNRS 8197, Ecole normale supérieure-PSL Research University, Paris, France Institut Jean-Nicod (CNRS-EHESS-ENS), Département d'Etudes Cognitives, Ecole normale supérieure-PSL Research University, Paris, France sd@stephanedebove.net.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Debove
authors.affiliation: Institut des Sciences de l'Évolution, UMR 5554-CNRS-Université Montpellier 2, Montpellier, France.
authors.forename: Jean-Baptiste
authors.initials: JB
authors.lastname: André
authors.affiliation: Institut Jean-Nicod (CNRS-EHESS-ENS), Département d'Etudes Cognitives, Ecole normale supérieure-PSL Research University, Paris, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Baumard
mesh_terms: D002755:Choice Behavior; D003299:Cooperative Behavior; D005260:Female; D005716:Game Theory; D006801:Humans; D007398:Interpersonal Relations; D008297:Male; D008393:Marriage; D008960:Models, Psychological
keywords: biological market; egalitarianism; human evolution; human fairness; partner choice; ultimatum game