Adaptive significance of winner and loser effects: rank-dependent optimal behaviour

Many animals including humans show winner and loser effects, whereby contest winners tend to win subsequent fights, while losers tend to lose again. Despite strong empirical evidence for these effects, their adaptive significance, especially that of loser effects, has not been critically examined. We posited that winner and loser effects enable rank-dependent optimal behaviour. Winners' assertive behaviour may deter opponents, and this can increase winners’ access to scarce resources and mates. Losers, in light of their competitive disadvantage, may either switch to alternative strategies in order to enhance their fitness prospects, or wait for competitive conditions to improve before competing again. We critically tested predictions derived from the rank-dependent optimal behaviour hypothesis in two experiments in which we randomly assigned human participants to win or lose in the video game Overwatch. In experiment 1, more losers than winners asked to switch to another video game for the second round. In experiment 2, more losers than winners requested to wait before playing the second round. Mood questionnaires indicated increased positive mood in winners and increased negative mood in losers. We suggest that change in mood is the proximate mechanism underlying rank-dependent optimal behaviour.