A typical problem faced by many social groups is the tragedy of the commons, a scenario in which individuals of a group have unlimited access to a limited resource. Altruists benefit the group through sharing the resource while selfish individuals undermine altruism through over-consuming the resource at the expense of the group. Here lies the paradox of the evolution of altruism in the face of self-interest.

Game theory provides a useful framework for pitting strategies against one another in evolutionary models. Typical models purpose mechanisms, such as kinship or reciprocity that enable altruism to evolve. However, it is often overlooked that selfish strategies themselves suffer a decline in fitness as selfishness becomes more prevalent in the population. I propose that selfish strategies themselves, through eliminating other selfish strategies, cause selfishness to be a self-limiting strategy, enabling altruists to coexist in a stable equilibrium.

Recently, punishment has emerged as a method of curtailing selfishness, but punishment can be costly, making it susceptible to the same pitfalls as altruism. Through an analytical model I identify a strategy called "selfish punisher" that involves behaving selfishly while at the same time punishing other selfish individuals. Selfish punishers cause selfishness to be a self-limiting strategy, promoting altruism within groups. Furthermore, a second simulation model reveals that altruism and punishment traits become negatively correlated when both traits are independently and uniformly distributed in the initial population. This polymorphism can be regarded as a division of labor, in which the benefits obtained by exploiting altruism can be re-applied to eliminate selfishness.

Empirically, I am exploring self-limiting strategies in the water strider Aquarius remigis. Hyper-aggressive males over-exploit mating resources by aggressively pursuing females, driving harassed females to marginal habitats, diminishing the mating opportunities of the group. Within groups, hyper-aggressives maintain a relative fitness advantage over non-aggressive males; however, due to the negative consequences on overall group fitness, groups with fewer hyper-aggressives out-produce groups with greater frequencies of hyper-aggressives, favoring more prudent males. The multi-level effect of hyper-aggressives indicates that the mix of social strategies within the group as well as the population structure determine the outcome of selection.