The Psychology of Revenge: Biology, Evolution and Culture

The Murder of Agamemnon - A Revenge Killing?

“Revenge is a dish best served cold…” 

(Ancient Klingon Proverb)

When I was younger I longed for revenge. I remember school-companions doing unspeakably cruel things to me — stealing my lunch, laughing at my misfortune and so forth (hey, it all seemed cruel at the time). I would carefully plot my revenge. The revenge almost always consisted of performing some similarly unspeakably cruel act towards them. Occasionally, my thoughts turned to violence. Sometimes I even lashed out in response.

I’m less inclined towards revenge these days. Indeed, I am almost comically non-confrontational in all aspects of my life. But I still feel the pangs. When wronged, I’ll briefly get a bit hot under the collar and my thoughts will turn to violence once more. I’ll also empathise with the characters in the innumerable revenge narratives that permeate popular culture, willing them on and feeling a faint twinge of pleasure when they succeed. I don’t think I ever act on the impulses anymore, but I have come close. And I’m sure everyone has had similar feelings.

But why is this? Why do we so frequently seek revenge? And how can we stop ourselves from acting on the impulse? I want to look at some potential answers to those questions today. In particular, I want to cover three related topics. First, I want to consider the psychology and neurobiology of revenge, focusing on why revenge can oftentimes feel pleasurable. Second, I want to consider the supposed ‘rationality’ of revenge, i.e. why the instinct for revenge is sometimes a good thing, and why the instinct may have evolved. And third, I want to examine the various methods that can be used to minimise the amount of vengeance being sought in society at any given time.

In doing all this, I’ll be drawing heavily from the discussion in Steven Pinker’s book The Better Angels of our Nature, and from the various studies cited therein.


1. The Mechanics of Revenge
One thing that is noticeable about revenge is how common it is. Literary classics of the distant and recent past often extoll its virtues in poetic terms; and it is a frequent motive for state and non-state violence (consider the use of reprisals in international conflicts). In addition to this, Pinker, following work by McCullough and Daly and Wilson, suggests that blood feuds — cases in which one tribe/gang kill the members of rival tribe/gang in retaliation for a similar attack on themselves — are endorsed by around 95% of the world’s cultures.

The commonality of revenge suggests that there is something deep within the architecture of the typical human brain that facilitates it. This seems to be borne out by a variety of studies. For one thing, it is easy enough to provoke people into seeking revenge in simple psychological experiments. Once more citing the work of McCullough, Pinker mentions studies done on college students (as pretty much all psychological experiments are…) in which the students are first given an insulting evaluation written by a fellow student, and then given the opportunity to punish the evaluator in a variety of ways (electric shocks, blasts with an air horn). It is very easy to induce students to engage in such revenge attacks.

So which brain systems undergird this thirst for revenge? Pinker mentions two. The first is the so-called Rage Circuit. This is a pathway linking the midbrain to the hypothalamus and amygdala. The rage circuit works by receiving pain signals from other parts of the nervous system and then responding, rapidly, with aggressive behavioural patterns. If activated, it provokes an animal to lash out at the nearest available victim. Jaak Panksepp performed experiments on the rage circuits of cats. The experiments involved activating the rage circuit with an electrical current. This provoked an instantaneous reaction from the cat. It would leap towards Panskepp with its claws and fangs bared, while hissing and spitting. It is likely that the thirst for revenge starts with the rage circuit: when we are hurt, we have an instant urge to lash out.

But it doesn’t end there. It is known that the stimulation of the rage circuit is unpleasant and animals will often work to switch it off. But the desire for revenge can linger. The reason for this seems to be that other brain systems support the quest for revenge. In particular, there is the so-called ‘Seeking’ system, named by Panskepp. This is a network within the brain that facilitates reward and pleasure seeking behaviour and incorporates the mesolimbic and mesocortical dopamine systems. You have probably come across some description of them before. The original experimental work on them involved rats placed in Skinner boxes. Every time the rats pressed a lever in the box they would stimulate their dopamine systems. It was found that rats would do so until they dropped dead from exhaustion. For a long time, this was thought to provide the neurobiological basis for addiction, although nowadays scientists realise that addiction is a more complex phenomenon.

Anyway, the important point here is that revenge seems to activate the seeking system. People appear to crave revenge, hoping that it will prove satisfying and rewarding. Studies done by Dominique de Quervain and his colleagues scanned the brains of men who had been wronged in a simple trust game (they entrusted another with some money and that other kept it for himself). The men were given the opportunity to punish the wrongdoer at some cost to themselves. It was found that part of the striatum (a key component in brain’s seeking system) lit up as they pondered the opportunity, and that the more it lit up, the more likely the men were to punish the others. This seems to indicate that reward seeking is part of the motivation for revenge.


2. The Rationality of Revenge
The commonality of revenge, and the fact that people seem to crave it, poses another question: why have we evolved (or been enculturated) to pursue revenge? After all, there is something of a paradox underlying our lust for revenge. It is a costly endeavour, and no matter how much pain we inflict on the wrongdoer, we can never really correct for the historical wrongdoing that provokes our revenge. And yet revenge persists.

Pinker favours a ‘deterrence’ explanation for revenge. We seek revenge, and derive pleasure from it, because it is an effective means of deterring would-be wrongdoers. Now, on a previous occasion, I discussed a whole range of psychological evidence suggesting that people’s punishment-related behaviours did not, in fact, follow the logic of deterrence. Au contraire, those studies suggested that people were natural-born retributivists: they sought revenge because they felt it was important for people to get their ‘just deserts’, and not because it would deter other wrongdoers. But the contradiction between these experimental findings and Pinker’s preferred explanation is more apparent than real. The studies discussed in that earlier post focused on the proximate psychological causes of revenge, i.e. on what best explained individual judgments and patterns of behaviour. Pinker’s explanation focuses on the ultimate societal causes of revenge, i.e. on what best explains the persistence of revenge in spite of its costly nature. His claim is that deterrence is the best ultimate explanation for this persistence. That is perfectly consistent with the claim that most individuals follow a retributivist (non-deterrentist) logic.

What evidence can be adduced in favour deterrence explanation? Pinker discusses two main pieces. Both come from studies of iterated prisoner’s dilemmas (IPDs) (note: I am not going to explain what the PD or IPD is here because I have discussed it on previous occasions - the important point is that PDs are thought to provide a good model for many social dilemmas). The first piece of evidence is largely theoretical, and focuses on computer-based simulations of IPDs. These computer-based simulations seem to confirm the long-term effectiveness of vengeance in achieving deterrence. The second is largely experimental, and focuses on how real people behave in lab-based IPDs. These also seem to confirm the willingness to seek and effectiveness of revenge. (You may dispute my calling the computer-based simulations ‘theoretical’ as opposed to ‘experimental’ evidence. I guess they are a type of experiment, but they are experimental tests of highly formalised strategies, not tests of the behaviour of real people.)

The computer-based simulations of IPDs are fascinating, and have generated a rich literature over the years. As you probably know, the standard PD involves two players, each faced with two choices: cooperate or defect. Collectively, the best strategy is to cooperate; but, individually, the best strategy is to defect (it dominates all other choices). But this is only true if the PD is a once off. If the players repeatedly interact in PD-style games, over multiple rounds and with different opponents, then other strategies can prevail. This is the key insight from the computer-based simulations. One of the earliest, and most enduring, findings from those simulations was that a simple programme called TIT FOR TAT could beat out most competitors in an IPD tournament. The TIT FOR TAT programme embodied the logic of deterrence-based revenge. It involved cooperation on the first round of the tournament, and then a change in subsequent rounds, depending on what the opponent did in the previous round. Thus, for example, if the opponent defected in the first round, TIT FOR TAT would defect in the second round; if the opponent cooperated in the second round, TIT FOR TAT would switch back to cooperation in the third round; and so on. The idea is that this models deterrence-based revenge because it rewards and punishes opponents with a view to changing outcomes in future rounds.

The success of TIT FOR TAT in IPDs is attributed to the fact that it is nice, clear, retaliatory and forgiving. But TIT FOR TAT is not an unbridled success. One difficulty is that it can easily degenerate into an endless cycle of defection (sometimes called a ‘death spiral’), particularly if one TIT FOR TAT is playing against another TIT FOR TAT and they happen to first interact on a round when they are both playing ‘defect’. Alternative strategies can be more effective in the right environments. For instance, GENEROUS TIT FOR TAT, which randomly restarts cooperating on some rounds, or TIT FOR TWO TATS, which avoids immediate retaliation by waiting to see whether its opponent defects in two successive rounds, or CONTRITE TIT FOR TAT, which tries to correct for its own mistakes, can be more effective.

I could go on about the details and variations, but that would be unnecessary. The important point is that strategies that all these strategies incorporate some degree of revenge (and, importantly, forgiveness), and can help to sustain long-term cooperation. This supports the deterrence-explanation. I should probably note at this point that after Pinker published his book there was an interesting paper published by Press and Dyson on IPDs. The paper proved that extortionate strategies (called ‘Zero Determinant’ strategies), i.e. ones that weren’t simply vengeful and forgiving, were optimal in some IPDs. There has been much hype about this result, and you can read explanations of it here, but it doesn’t completely undermine the long-term effectiveness of TIT FOR TAT and its variations.

So much for the theoretical bit of evidence, what about the work done on actual human beings? Since the late 1990s, a whole series of studies have been published showing that costly punishment can help to sustain cooperation in repeated PD-style interactions (researchers refer to the phenomenon as 'altruistic punishment'). The most famous study in this vein comes from Fehr and Gachter. The study involved a Public Goods game wherein people were given the opportunity to contribute to a common investment fund (which would benefit them all), or to free ride on the good will of others who invested. If experimental subjects were allowed to punish free riders, free-riding was eliminated over repeated plays of the game. Furthermore, other experiments have found that people are more likely to punish when they think others are watching. This demonstrates a willingness to seek a reputation for revenge in a social setting. This again seems to confirm the deterrence explanation because a reputation for revenge is important for deterrence.

The upshot is that deterrence — and the pursuit of mutually beneficial cooperation — look like reasonable explanations for the long-term persistence of revenge.


3. The Modulation of Revenge
Granting that revenge is common, and occasionally rational, there remains a challenge: how can we ensure that there is not too much of it? It is clear that too much revenge can be destructive. This is obvious to anyone who has lived through seemingly endless cycles of blood-feuding (the real-world equivalent of the TIT FOR TAT ‘death spirals’). It might be trite and simplistic to put it this way, but such cycles seem to be part of the reason for the persistence of sectarian violence in Northern Ireland. Or, at least, it seemed that way to me as child growing up in the Republic of Ireland.

Is it possible to prevent such destructive cycles of revenge? Would it be possible to create a world in which there was no need to seek revenge, i.e. in which revenge lost its rationality? In his analysis, Pinker identifies five factors which seem to modulate and reduce the need for revenge. I won’t discuss them in too much detail here. Instead, I will simply give short descriptions and links to relevant supporting evidence:

A. The Presence of Leviathan: The Leviathan is, of course, Hobbes’s famous term for the state. The Leviathan effectively functions as a means for outsourcing violence (in particular revenge). We all have Leviathans in our lives. When I was a school-child, I did not necessarily need to lash out at the cruel behaviour of my companions, I could sometimes outsource my revenge to a teacher who could punish the bullies on my behalf. This outsourcing of revenge can have two major benefits. First, the Leviathan can function as a more effective deterrent if it can create the belief that it is ‘all-seeing’ and ‘all-knowing’ (or close enough) and capable of retaliating even if the wrongdoer crushes their victim. Second, the Leviathan may be less prone to the distorting biases that fuel cycles of revenge. It is well-known that victims often overestimate the degree of harm they have suffered, and consequently can punish wrongdoers in excess. Shergill et al performed an experiment in which people placed their finger under a bar that applied a precise amount of force. They were then asked to press down on the finger of another experimental subject with the same amount of force. It was found that they used approximately eighteen times more force than they originally received, highlighting the gap between perceived harm and reality. Pinker refers to this as part of the ‘moralization gap’ and highlights further evidence in support of it. Leviathan, as a third party, may avoid the excesses of this gap.

B. Civic-Mindedness and Perceptions of Governmental Legitimacy: The mere presence of Leviathan is not enough in itself to eliminate destructive cycles of revenge. It is clear that the people who are subjected to the authority of Leviathan must have some degree of civic-mindedness, i.e. must be committed to the institutional basis for Leviathan and perceive them to be legitimate. Herrmann, Thoni and Gachter performed a cross-cultural study of Public Goods games which highlighted this. They found, somewhat surprisingly, that in some cultures players actually punished people who contributed generously to the public investment fund. This is odd since generous contributors of this sort actually benefitted the group as a whole. When they dug into the data a little deeper, Herrmann, Thoni and Gachter found that a major predictor of this willingness to spitefully punish generous contributors was the degree of civic mindedness in the respective cultures. In other words, cultures in which the commitment to the rule of law was weak (e.g. countries where people didn’t pay taxes, cheated on social welfare payments etc.) were more likely to engage in spiteful punishment.

C. Expanding the Circle of Empathy: This is an obvious one. It is well-known that we are more likely to forgive people who fall within our natural circle of empathy (kin, friends etc) for their transgressions. This modulates our desire for revenge. Thus, creating an expanded circle of empathy can help prevent destructive cycles of revenge. The question, of course, is how to do this. Various cultural practices and rituals can help to create ‘fictive kinships’ which are often effective means of expanding the circle of empathy. Religions have been good at this, and often explicitly invoke kinship metaphors (e.g. ‘brothers and sisters in Christ’). But there is a dark side to this too as you can often create an excessive in-group/out-group mentality, which can in turn fuel revenge and associated forms of violence.

D. Shared Goals: A simple way to overcome excessive in-group/out-group mentalities is to generate common interests, i.e. to make the success of one group dependent on the success of another. There was a famous experiment to this effect performed on a group of boys at the Robbers Cave summer camp back in the 1950s. The boys were arbitrarily divided into two separate groups at the start of camp. This generated intense loyalty within the groups, and intense rivalry between them, with acts of provocation and retaliation following soon after. But the experimenters found that they could reduce this rivalry by bringing the groups together and forcing them to work together for mutual benefit, e.g. in having to restore the camp’s water supply. The value of such mutual interdependencies is often highlighted as a major reason why countries that trade with one another are less likely to go to war.

E. Creating a Perception of Harmless: A final way to reduce destructive cycles of revenge is to cultivate a reputation for non-violence. That is: to signal to the other side that you are not going to continue with a destructive conflict. Apologies and reconciliation events are central to this, but apologies are often deemed ‘cheap talk’. They are easy to make and easy to break. There is some suggestion that physiological responses like blushing are a way in which evolutionary forces facilitated costly signaling of apologies. There is also evidence from the study of international and civil conflicts that apologies and reconciliation events are more likely to work when they are costly, involve some symbolic (but incomplete) justice, and involve participants with some shared history. The work of Long and Brecke is the key source here.

I have illustrated these five modulators in the diagram below.

4. Conclusion
To briefly sum up, revenge seems to be common, occasionally rational and capable of being reduced. Its commonality is illustrated by its near-universal endorsement, and the ease with which it can be endorsed. It seems to be undergirded by two major brain systems: the Rage circuit, which facilitates rapid violent responses to perceived harm; and the Seeking circuit, which facilitates reward-seeking behaviours. The rationality of revenge is illustrated by its utility as a deterrence mechanism in iterated versions of the prisoner’s dilemma. And the ability to reduce the amount of destructive revenge is illustrated by the five factors listed above.