Applying Game Theory to the Study of Aggression

Photo by M. Farish illustrating pigs "sizing each other up"

Photo by M. Farish illustrating pigs "sizing each other up"

Today, Google Scholar gives nearly 400,000 hits for “game theory + aggression” and many other texts hint toward the theory by using the words “fighting ability” and “assessment” in between lines. Here we provide a brief explanation on game theory and how it can be applied to research on aggression.

Game theory is a branch of applied mathematics, initially developed by economists to model human strategic decision making, and popularised with well-known examples such as the Prisoner’s Dilemma, and Russell Crowe’s portrayal of the Nobel laureate John Nash in the film A Beautiful Mind. However, biologists were quick to spot the utility of game theory for evolutionary biology. Amongst them was John Maynard Smith who was the first to apply game theory to the study of animal contests, producing the now classic ‘Hawk/Dove’ game (Maynard Smith & Price 1973, Nature). This demonstrated the idea of an evolutionarily stable strategy (ESS) such that frequency dependent selection will result in a population of “aggressive” hawks and “non-aggressive” doves with the proportions of each depending on the costs and benefits of fighting.
The hawk/dove model set the scene for the development of more realistic game theory models of animal contests that incorporated opponent asymmetries in fighting ability, termed resource holding potential (RHP), a concept that aims to capture the potential of the individual to win a fight, and is based on differences such as body weight or weapon size. In addition, the models incorporated various information gathering strategies regarding own and opponent fighting ability and the value of the contested resources (see Arnott & Elwood 2009, Animal Behavior for review). 

The utility of this approach is that the models yield testable predictions regarding contest outcomes and fighting durations for winners and losers which have been seized upon by empiricists. One aspect of current debate is the extent of information gathering that actually occurs during a contest. For example, some models assume opponents assess relative fighting ability, also entering popular culture with terms used in wildlife documentaries of competing animals like “they are sizing each other up.” This is termed mutual assessment and we humans excel at this. However, some models are based on an alternative assumption, termed self assessment, in which animals only have information about their own fighting ability, being unable to assess the opponent. Indeed, contrary to our human abilities and assumptions, in recent years there has been accumulating evidence for self assessment in animal contests, leading to calls for researchers to carefully test for mutual assessment, rather than assume that it occurs. 

While game theory has been influential for furthering our understanding of animal contest behaviour in an evolutionary biology setting, more recently it has also been applied to human warfare (Briffa 2014, PLOS ONE). Moreover, we are currently translating game theoretical principles to study aggression as an applied animal welfare issue of captive animals, examining aggression in pigs upon regrouping (a routine procedure in commercial farming which results in intense aggression). Reflecting on the ISRA World Meeting in Sydney, there are many possibilities to apply game theory to topics that have been addressed at the congress. For example, the decisions that gamers may make during online gaming could be analysed in a game theoretical approach by using aggressiveness during gaming as a measure of RHP against the duration and outcome of the game. For any game theory ideas or information, please contact us or have a read at the below listed references.     

Dr. Gareth Arnott is a Lecturer in Animal Behaviour and Welfare at Queen's University Belfast. He may be contacted at
Dr. Irene Camerlink is a postdoctoral researcher in Animal Behaviour and Welfare at Scotland’s Rural College (SRUC). She may be contacted at

Arnott, G., & Elwood, R.W. (2009). Assessment of fighting ability in animal contests. Animal Behaviour, 77(5), 991-1004.

Briffa, M. (2014). What determines the duration of war? Insights from assessment strategies in animal contests. PLOS ONE, 9(9), e108491.

Camerlink, I., Turner, S.P., Farish, M., & Arnott, G. (2015). Aggressiveness as a component of fighting ability in pigs using a game-theoretical framework. Animal Behaviour, 108, 183-191.

Camerlink, I., Arnott, G., Farish, M., & Turner, S.P. (2016). Complex contests and the influence of aggressiveness in pigs. Animal Behaviour, in press.
Smith, J.M., & Price, G.R. (1973). The Logic of Animal Conflict. Nature, 246, 15.