Antisocial personality disorder: An evolutionary game theory analysis.

Purpose: To develop a multi-person evolutionary game, with population replicator dynamics based on the payoffs of the Chicken (Hawk-Dove) game, to model Antisocial Personality Disorder (APD), and to offer an explanation for the relatively stable prevalence of APD in widely diverse societies despite increasing resources devoted to reducing antisocial behaviour. Methods: Beginning with a basic two-person game, a multi-person evolutionary model is developed. According to the model, changes in the frequency of APD in the population depend on frequency-dependent Darwinian selection or a form of social evolution that mimics it. Results: The population evolves to a stable equilibrium with a fixed proportion of individuals habitually behaving antisocially, and with suitable payoffs the proportion of antisocial individuals corresponds to the known prevalence of APD. An unexpected result of the analysis is the finding that the prevalence is necessarily low when the relative gain from behaving antisocially towards a cooperator is very much smaller than the relative loss to the cooperator. Conclusions: The model provides an evolutionary game-theoretic explanation for the low but stable prevalence of APD. If the evolutionary mechanism is social rather than biological, then removing increasing numbers of antisocial individuals from society will result in others taking their places, and the population will return to the equilibrium point.