Data from: Partner choice creates fairness in humans

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.