The figure shows the proportion of Hawks in a population of individuals who, at each time step, are randomly matched in pairs to play a symmetric Hawk–Dove game (also called snowdrift or chicken). The payoffs in this game are: a Hawk meeting a Dove gets the highest payoff (3), but if he meets another Hawk they both get the lowest payoff (0). A Dove meeting a Hawk gets 2, and when two Doves meet they both get 1. At the end of each time step, after all individuals have played the game, one randomly selected player revises her strategy—Hawk or Dove—according to the following rule: "I look at another (randomly selected) individual; if and only if she got a payoff higher than mine, I adopt her strategy".