Baumard et al. provide an intriguing model where morality emerges from the dynamics of partner choice in mutualistic interactions. I discuss evidence from human and nonhuman primates that supports the overall approach, but highlights a gap in explaining the human specificity of moral cognition. I suggest that an essential characteristic of human fairness is to override concerns about merit in favor of promoting the welfare in others who are needy.

Baumard et al. propose a functional explanation for the evolution of a sense of fairness in humans: Fairness preferences are advantageous in an environment where individuals are in strong competition to be chosen for social interactions. Such conditions also exist in nonhuman animals. Therefore, it remains unclear why fairness (equated with morality) appears to be properly present only in humans.

Applying a non-developmental evolutionary metatheory to understanding the evolution of psychological capacities leads to the creation of models that mischaracterize developmental processes, misattribute genes as the source of developmental information, and ignore the myriad developmental and contextual factors involved in human decision-making. Using an evolutionary systems perspective, we argue that revenge and forgiveness cannot be understood apart from the development of foundational human psychological capacities and the contexts under which they develop.

This commentary focuses on how third parties impact the course of acts of revenge based on their world views, such as belief in a just world. Assuming this belief to be true, the following questions could be asked: (a) What are the consequences of a third party's worldview in terms of secondary victimization? (b) Are bystanders actually aware of these consequences? (c) If so, then why do they let it happens?

We address how trait self-control and trait concern for others relate to the concepts of monitored and intrinsic Welfare Tradeoff Ratios (WTRs), respectively, and how recent work on personality, revenge, and forgiveness are informed by the adaptationist perspective proposed in the target article. We also discuss how the proposed adaptationist perspective provides clues to some previously puzzling findings on revenge.

We question whether the postulated revenge and forgiveness systems constitute true adaptations. Revenge and forgiveness are the products of multiple motivational systems and capacities, many of which did not exclusively evolve to support deterrence. Anger is more aptly construed as an adaptation that organizes independent mechanisms to deter transgressors than as the mediator of a distinct revenge adaptation.

Research indicates that individuals have incoherent intuitions about particular features of the criminal justice system. This could be seen as an argument against the existence of adapted computational systems for counter-exploitation. Here, I outline how the model developed by McCullough et al. readily predicts the production of conflicting intuitions in the context of modern criminal justice issues.

McCullough et al. propose an evolved cognitive revenge system which imposes retaliatory costs on aggressors. They distinguish between this and other forms of punishment (e.g., those administered by judges) which are not underpinned by a specifically designed evolutionary mechanism. Here we outline mechanisms and circumstances through which the revenge system might nonetheless infiltrate decision-making within the criminal justice system.

The psychology underlying revenge in an intergroup context is built around a small handful of recurrent interaction types. Analyzing the cost/benefit calculations of each agent's role within these interaction types provides a more precise way to characterize intergroup conflict and revenge. This in turn allows for more precise models of the psychology of intergroup conflict to be proposed and tested.

Insofar as South Africa underwent a rapid transformation from apartheid to democracy, it may provide a unique laboratory for investigating aspects of revenge and forgiveness. Here we suggest that observations and data from South Africa are partially consistent with the hypotheses generated by MCullough and colleagues. At the same time, the rich range of revenge and forgiveness phenomena in real-life settings is likely to require explanatory concepts other than specialized modules and their computational outputs.

We propose that revenge responses are often influenced more by affective reactions than by deliberate decision making as McCullough et al. suggest. We review social psychological evidence suggesting that justice judgments and reactions may be determined more by emotions than by cognitions.

McCullough et al. suggest that revenge and forgiveness rest upon risk computation. Risk computation is implemented by emotions that evolved for additional functions, giving rise to phenomena such as betrayal aversion and taboo-tradeoffs, and specific patterns of forgiveness we have documented. A complete account of revenge and reconciliation should incorporate broader constructs from social psychology, including emotions and values hierarchies.

McCullough et al. argue that humans possess evolved computational systems for implementing retaliatory behavior that both deters aggression and promotes subsequent reconciliation. However, they do not apply this analysis to the sphere of intergroup relations. We believe their model can be usefully extended to this domain and discuss why this would be possible, pertinent, and productive.

McCullough et al. propose adaptations that motivate forgiveness when the potential benefits of continuing the relationship outweigh the costs incurred by the transgression. The costs incurred are definite, whereas future benefits of forgiveness are only probabilistic. This situation exposes the forgiver to cheating in the form of repeat transgression. Adaptations motivating genuine forgiveness are therefore unlikely to evolve.

There are interesting parallelisms between McCullough et al.'s article and studies of revenge presented by French legal anthropologist Raymond Verdier, particularly as regards the discussion of the increasing likelihood of revenge with increasing social distance. Additionally, the observation that many peoples speak of revenge in the language of debt and repayment, links it with exchanges of benefits as well as costs.

Humans have the cognitive abilities to implement the revenge and forgiveness systems hypothesized by McCullough et al., but the evidence suggests that simpler processes may underlie most revenge cases in humans and other animals. The mediating role of emotions can be at the basis of the flexibility needed in the hypothesized systems and the associated assessment of social relationships.

McCullough et al.'s functionalist model of revenge is highly compatible with the person-centered approach to moral judgment, which emphasizes the adaptive manner in which social perceivers derive character information from moral acts. Evidence includes act–person dissociations in which an act is seen as less immoral than a comparison act, yet as a clearer indicator of poor moral character.