Shortcomings of the PrisonerÝs Dilemma:
Does not take into account group formation.
Individuals are not capable of choosing partners, as in real life, in this model.
Factors involved in changing interaction partners, such as migration, mutation, etc. are not taken into consideration.
Such shortcomings were found as recently as the late 1990Ýs.
ZeggelinkÝs Social Evolution Model (SEM), published in June 2000, offers a more inclusive simulation to study, but results, such as findings for existence of an ideal population density, are inconclusive.