| Hawk | Dove | |
|---|---|---|
| Hawk | (V-C)/2 = -25 | V = 50 |
| Dove | 0 | V/2 = 25 |
This simulation models a population where individuals can adopt one of two strategies when competing for resources:
Hawk strategy: Always fight aggressively for the resource. When two Hawks meet, they fight until one gets the resource (V) and the other suffers an injury (cost C). On average, each gets (V-C)/2.
Dove strategy: Always display but never fight. When two Doves meet, they share the resource, each getting V/2. When a Dove meets a Hawk, the Dove retreats and gets nothing (0), while the Hawk gets the full resource (V).
After each generation, individuals reproduce based on their success (fitness). Strategies that gain more resources produce more offspring with the same strategy, changing the population composition over time.
An Evolutionary Stable Strategy (ESS) is a strategy which, if adopted by a population, cannot be invaded by any alternative strategy. It represents a stable equilibrium in evolutionary dynamics.
In the Hawk-Dove game, the ESS depends on the ratio between the value of the resource (V) and the cost of injury (C):
When V > C (resource worth more than injury cost): The ESS is 100% Hawks. Being aggressive always pays off.
When V < C (injury cost exceeds resource value): The ESS is a mixed population with V/C proportion of Hawks and (1-V/C) proportion of Doves.
For example, if V = 50 and C = 100, the ESS is 50% Hawks and 50% Doves. This mixed strategy is stable because at this ratio, neither pure Hawks nor pure Doves can invade the population.
The Hawk-Dove game illustrates several key concepts from Dawkins' "The Selfish Gene":
Game theory in evolution: Natural selection can be modeled as a game where individuals compete for reproductive success. The Hawk-Dove game is discussed in Chapter 5 of the book, showing how seemingly altruistic behaviors (Dove strategy) can persist alongside aggressive behaviors (Hawk strategy).
Genes as strategies: In this model, the "Hawk gene" and "Dove gene" compete for representation in the gene pool. Whichever strategy leads to greater reproductive success will increase in frequency.
Evolutionary stability: Dawkins emphasizes that not all possible strategies are evolutionarily stable. The ESS concept helps explain why certain behaviors persist in nature while others do not, even when they might seem advantageous in the short term.