The idea that hatred is an evolved adaptation has not been thoroughly elaborated (though see Waller Reference Waller2004; Petersen et al. Reference Petersen, Sell, Tooby, Cosmides and Høgh-Olesen2010; Sell Reference Sell2011). I give a brief outline here of how a selection pressure distinct from those considered in the target article could design a system – hatred – that enacts revenge in response to different triggers, moderated by different variables and designed for different purposes.

Consider the following selection pressure: The existence and well-being of another individual has some impact on your lifetime fitness; sometimes that impact is negative. Such an individual could have a low Welfare Tradeoff Ratio (WTR) towards you (e.g., a bully); could be someone who values you highly but nevertheless imposes large costs (e.g., a flirtatious student whose inappropriate behavior threatens your marriage); or even be someone who doesn't know you exist (e.g., the person who holds the job you want). This selection pressure would design a mechanism that identifies these individuals and then deploys – when cost-effective – behavioral strategies that reduce the target's ability to impose costs by limiting interactions with the target, reducing their power, or killing them. Let us call the mechanism “hatred,” recognizing that in layman's terms “anger” and “hatred” are often conflated.

According to the recalibrational theory, and consistent with the arguments made by McCullough et al. in the target article, the function of anger-based revenge is to raise the target's WTR (Sell et al. Reference Sell, Tooby and Cosmides2009; Sell Reference Sell2011). The function of hatred, in contrast, is to reduce costs that emanate from another individual by isolating, weakening, or killing them. These are different designs and should generate distinct predictions about their antecedent conditions and behavioral strategies.

The triggers of hatred are theoretically distinct from those of anger. As discussed in the target article, anger is triggered by indicators that another does not value one's welfare highly. Hatred is triggered by indicators that another's existence and well-being will cause harm. Both anger and hatred can be triggered by the intentional imposition of large costs for trivially small benefits. But hatred can also be triggered by rivals for mates or status, even when these rivals hold the hateful person in high regard (i.e., have high WTRs towards the hateful individual). Targets can also be hated for the imposition of frequent small “justified” costs that do not indicate a low WTR but nonetheless bear on the hateful individual's future welfare. Such an explanation could explain the perversely high prevalence of physical aggression against elders who require living assistance (Lachs & Pillemer Reference Lachs and Pillemer2004; Pillemer & Finkelhor Reference Pillemer and Finkelhor1988) and disabled children who require additional investment (Westcott & Jones Reference Westcott and Jones1999).

Also unlike anger, hatred can motivate seemingly vengeful behavior when the target has done nothing other than be harmed by the hateful person. Harming someone will cause them to lower their WTR, retaliate, or spread word of the misdeed to others. This makes the original victim into a person whose existence predicts future costs for the offender. As paradoxical as it seems, subjects who were made to insult or harm others did indeed dislike them for it (Schopler & Compere Reference Schopler and Compere1971), but they cannot be said to have been “angry” at their victims.

The behavioral consequences of hatred and anger partly overlap, specifically with the enactment of revenge. Both anger and hatred can fulfill their functions by imposing costs on the target individual. However, if the selection pressures responsible for each emotion are distinct, then we would predict certain differences in their behavioral strategies. One difference is that hatred should be largely indifferent to apologies or signals of recalibration. In fact, apologies – to the extent that they indicate the hated person is suffering – could be experienced pleasantly and incentivize more cost infliction. This is because the “off switch” to anger and hatred are different. Anger has served its function when the target recalibrates, but hatred has fulfilled its function only when the target has been significantly de-powered, killed, or ostracized. Indeed, anger-based aggression is frequently negotiative in design with clearly demarcated starting and ending points, turn taking, escalation starting with low-cost assessments of formidability, and an understanding of “fairness” that tracks the accuracy of assessments; for example, hitting someone while they are asleep does not demonstrate your formidability and bargaining power (see Sell Reference Sell2011). Revenge stemming from hatred is predicted to have none of these features.

As indicated in the target article, bargaining power (such as physical strength in men) is a predictor of anger-based aggression (Sell et al. Reference Sell, Tooby and Cosmides2009), because those with better bargaining power will have more success deploying that tactic. For anger to fulfill its function, one must confront the target and convince them that one's interests are worthy of being weighted more highly. Hatred, on the other hand, can fulfill its function without the target ever knowing the mental state of the hateful person, and by taking advantage of temporary fluctuations in bargaining power. For this reason, when faced with an individual who holds a low WTR, a person with high bargaining power can recalibrate the target (and evidence shows they do), whereas a person with low bargaining power will instead hate the target and look for subtle opportunities to impose costs or temporary shifts in bargaining power that can be used to weaken or kill the target (e.g., backstabbing, gossip, sabotage). Consistent with this, there is evidence that physical strength in men positively correlates with anger and aggression, but does not predict their tendency to ruminate or seethe over affronts (Sell et al. Reference Sell, Tooby and Cosmides2009).

The relationship between anger and hatred is complex. Anger can trigger hatred if a person resists recalibration and becomes the perpetual cost inflictor that is strategically better addressed by hatred. Conversely, a hated individual who raises his WTR may become less hated because of the benefits he will bestow. Finally, both emotions can run in parallel, attempting to recalibrate the target's WTR while limiting their ability to impose costs. Regardless of these complications, anger and hatred appear designed by separate selection pressures with different triggering conditions, moderating variables, and behavioral strategies. Revenge reflects the operation of both adaptations and will have to be understood that way.