Where does chicken collide?

In game theory, chicken is the two-player game in which each prefers to stand firm while the other yields, but mutual firmness is the worst outcome for both; the classic image is two drivers speeding at each other, where the one who swerves is the "chicken" and crashing is catastrophic. It has two pure equilibria in which the players take opposite roles, and it rewards credible commitment and brinkmanship. Rapoport and Chammah analysed it under this name. It is exactly the same payoff structure that biologists call hawk–dove and that others call the snowdrift game: one game wearing three names.[1]

Unit

The payoff ranking in which each prefers to stand firm only if the other yields

Recovery means

Not applicable

Measured by

Identified by its 2×2 payoff ordering (standing firm beats mutual yielding beats yielding beats mutual disaster) and its two asymmetric pure equilibria

In evolutionary biology the hawk–dove game models conflict over a resource: "hawks" escalate and risk injury while "doves" display and retreat, and a population settles at a mix where neither strategy can be invaded. Maynard Smith and Price introduced it to explain why animal contests are often ritualised rather than lethal, founding evolutionary game theory and the idea of an evolutionarily stable strategy. The payoff structure (mutual escalation is worst, and each type does best against the other) is identical to the game of chicken; the biologists simply named it after the contestants.[2]

Unit

The stable mix of escalating and displaying strategies in a population

Recovery means

Not applicable

Measured by

Found as the evolutionarily stable strategy or mixed equilibrium from the cost of injury and the value of the resource

In studies of cooperation the same game is told as the snowdrift: two drivers are blocked by a snowdrift, and clearing it benefits both, so each would rather the other dig but still prefers to dig alone over staying stuck. Unlike the prisoner's dilemma, cooperation here persists because the fallback of mutual defection is the worst outcome. Hauert and Doebeli used this framing to study how spatial structure affects cooperation. It is the same anti-coordination payoff structure as chicken and hawk–dove, under a third name.[3]

Unit

The equilibrium share who cooperate when defecting alone is tempting but mutual defection is worst

Recovery means

Not applicable

Measured by

Characterised by the cost-to-benefit ratio of cooperation, which sets the stable fraction of cooperators