Hawk and dove

Hawk and dove is a hypothetical model for analyzing conflict through the costs and benefits of alternative behaviors. Its central result is that success is frequency-dependent: aggression can prosper when it is rare, yet become disadvantageous when it is widespread. The model illustrates how natural selection can maintain a stable mixture of strategies without requiring individuals to act for the good of a group.

The two strategies

The model distinguishes two types of contestant. Hawks fight with maximum intensity and withdraw only when seriously injured; doves use conventional threats but do not injure an opponent. A hawk meeting a dove wins, and the dove retreats without injury. Two hawks continue until one is seriously injured or killed. Two doves posture for a prolonged period until one backs down, so neither is hurt, though both lose time.

These labels describe stipulated strategies, not claims about the behavior of the birds whose names they borrow. The model also assumes that contestants cannot identify an opponent’s strategy in advance and have no memory of earlier contests with that individual. It therefore isolates how the composition of the population, rather than prior knowledge of a rival, affects the payoff to each strategy.

Costs, rewards, and frequency dependence

To make the comparison explicit, the model assigns 50 points to winning, zero to losing, a penalty of 100 points for serious injury, and a penalty of 10 for wasting time in a prolonged contest. The points stand for reproductive success: a higher average payoff corresponds to leaving more genes in the gene pool. Their exact numerical values are arbitrary, but they make the consequences of different encounters calculable.

In a population made entirely of doves, each individual wins half its contests, gaining 50 points but paying the 10-point delay penalty, and loses half, also paying that penalty. The average payoff is therefore 15 points per contest. A rare hawk meeting only doves wins every contest and receives 50 points, so hawk genes have an advantage and can spread.

That advantage changes as hawks become common. In an all-hawk population, each hawk wins half its contests for 50 points and loses half with a 100-point injury penalty, giving an average payoff of minus 25. A rare dove in that population loses every contest but avoids injury, earning zero. Doves therefore gain an advantage when hawks predominate. The strategy that succeeds against one population composition can lose against another.

The stable mixed population

The shift in advantage need not produce an endless swing from dove to hawk and back. Under the model’s particular point system, the stable composition is seven-twelfths hawks and five-twelfths doves, a hawk-to-dove ratio of 7:5. At that ratio, both strategies have the same average payoff, so selection favors neither over the other. If the proportion of hawks rises above the stable point, doves gain an additional advantage and the balance tends to move back; if it shifts the other way, the relative advantage reverses.

This equilibrium may resemble group selection because the population returns toward a stable ratio after disturbance. The resemblance is misleading: the account does not depend on some groups outcompeting others. It follows from the changing payoffs to individuals as the prevalence of each strategy changes. Indeed, the average payoff in the stable mixture is 6¼, lower than the 15 points available to each individual in an all-dove population. The model therefore distinguishes an individually maintained equilibrium from a collectively better outcome that would require everyone to remain a dove.

What the model explains

The example places aggression within a broader cost-benefit analysis of fighting: potential gains must be weighed against injury, time, and energy, and tactical choices during a contest have costs as well as benefits. The model’s payoff calculation makes that logic explicit while avoiding the assumption that an animal consciously works through it. The strategies are analytical descriptions of behavior and its evolutionary consequences, not deliberate plans attributed to the contestants.

As an illustration of gene-centered natural selection, Hawk and dove shows why neither unrestrained aggression nor non-injurious display must dominate in every circumstance. Their relative success depends on the behavior of the surrounding population, and selection can maintain both in a predictable proportion. The result is an equilibrium among competing individual strategies, not evidence that the population has been organized for a shared good.