His treatment embraces all forms of cooperation, from cases of by-product mutualism in which the recipient gains from an activity that the donor would have engaged in anyway, to "true" altruism where to assist another individual participants suffer fitness costs, such as a loss of mating opportunities or an increased risk of predation.
Dugtakin shows how these three routes (by-product mutualism, kin selection, and reciprocal altruism) to cooperation, as well as a fourth one, trait-group selection, can be examined using a single game: the "cooperators dilemma." The cooperators dilemma features a payoff matrix similar to that used to define the prisoners dilemma.
If this inequality holds, cooperative predator inspection is best explained by reciprocity; if not, then by-product mutualism can account for the behavior.