THE EVOLUTION OF FATAL FIGHTING

The evolution of fatal fighting was investigated using evolutionary game theory. General considerations about the lifetime consequences of fighting behaviour are first discussed. A sequential assessment game is then developed in which a fight can end because a contestant either gives up or is killed. The results show that the balance between the value of the contested resource and the value of the future is one important factor influencing the frequency of death or severe injury in fights. When the value of a contested resource is similar to or greater than the value of the future, strategies will evolve that result in contestants being severely injured or killed during fights. When the value of the future is close to zero contestants will never give up after starting to fight; such fights will always be fatal for at least one of the opponents. Factors that could decrease the cost of fighting, such as the assessment of fighting ability, kinship and role asymmetries, have little or no effect in these situations. Finally, empirical data on fatal fighting are reviewed and compared with theoretical predictions. Data show that dangerous fighting, often resulting in severe injuries or death, generally occurs in situations where a major part of a contestant's lifetime reproductive success is at stake. © 1990 The Association for the Study of Animal Behaviour.