This might be true… If the punishment for defection is always very severe after getting caught, then even with a very low probability of getting caught, but a low gain from defecting, evolution would favour co-operating on the last round (or single round) rather than defection. But this means that others’ commitments to vengeance have transformed the prisoner’s dilemma to a non-PD, which is my explanation 2 in the original article. (Or explanation 3 if vengeance is exacted by the whole tribe, including members who weren’t directly injured by the original defection.)
However, this just shifts the burden of explanation to accounting for why we (or whole tribes) are vengeful to such an extreme extent. After all, vengeance is enormously costly, and risks injury (the condemned can fight back) or counter-vengeance (whoever kills the original defector risks being killed in turn by the defector’s surviving family, and then the whole tribe splits apart in a cyle of killing). And notice that at that point, the original defection has already happened, so can’t be deterred any more, and the injury-risking, potentially-tribe-splitting vengeance has negative fitness. The tribe’s already in trouble—because of the betrayal—and the vengeance cycle could now destroy it. So why does it happen? What selection pressure maintains such severe punishment when it is fitness destroying?
This might be true… If the punishment for defection is always very severe after getting caught, then even with a very low probability of getting caught, but a low gain from defecting, evolution would favour co-operating on the last round (or single round) rather than defection. But this means that others’ commitments to vengeance have transformed the prisoner’s dilemma to a non-PD, which is my explanation 2 in the original article. (Or explanation 3 if vengeance is exacted by the whole tribe, including members who weren’t directly injured by the original defection.)
However, this just shifts the burden of explanation to accounting for why we (or whole tribes) are vengeful to such an extreme extent. After all, vengeance is enormously costly, and risks injury (the condemned can fight back) or counter-vengeance (whoever kills the original defector risks being killed in turn by the defector’s surviving family, and then the whole tribe splits apart in a cyle of killing). And notice that at that point, the original defection has already happened, so can’t be deterred any more, and the injury-risking, potentially-tribe-splitting vengeance has negative fitness. The tribe’s already in trouble—because of the betrayal—and the vengeance cycle could now destroy it. So why does it happen? What selection pressure maintains such severe punishment when it is fitness destroying?