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 …