The quest for vengeance is a human universal and accumulating evidence shows avengers permeate the animal kingdom. There is a common neurological foundation and scientists suspect a pay-back mentality developed to promote social harmony by discouraging aberrant behaviours.
"Revenge takes place throughout the animal kingdom," reports Michael McCullough at the University of Miami. "Fish, birds and all kinds of primates retaliate."
Violations of trust are most often the cause for vengeful actions.
"A cheated person has bad feelings if the cheater does not get just punishment," observed Ernst Fehr at the University of Zurich, adding that people feel "satisfied" when others are punished for bad behaviour.
According to research by Dominique de Quervain and colleagues, "people derive satisfaction from punishing norm violators."
Revenge has an emotional geography. "(Avengers) are motivated to make sense of events when they seem unjust or disrupt perceived equity," concluded Robert Bies at Georgetown University and Thomas Tripp at Washington State University in a recent analysis. "They attempt to restore balance through their (retributive) actions."
Evidence shows that betrayal, emotional or physical pain, ingratitude and humiliation are among the most significant causes of a desire for retribution. In seeking to impose "just deserts" (coined in 1599), anger, frustration and resentment are mitigated through specific neurological mechanisms. The prospect of punishing offensive actions makes people feel better -- literally.
That is because there is a correlation between cerebral activity and the degree of magnitude of the anticipated retribution, Fehr's brain studies show.
"Activation in the dorsal striatum reflects the anticipated satisfaction from punishing others," de Quervain reported.
The desire for revenge has a gender bias. According to author Claire Gillman, research shows men are more vengeful than women, except in instances involving romance. Research shows that, in that case, there is a substantial validity to William Congreves' 1697 observation that "Hell hath no fury like a woman scorned."
Julie Exline at Case Western Reserve University thinks that women are more vengeful in romantic circumstances because they "often magnify offences."
"Gender differences between men and women consistently emerge (in vengeance situations)," she says. "Both genders are more forgiving when they see themselves as capable of committing a similar action to the offenders."
McCullough concludes that whereas taking vengeance was very popular historically, it has become a hidden desire more recently.
"We dare not use the word revenge to justify our behaviour... for fear of seeming petty, base, immoral, immature or just evil," he concludes.
But, he points out that an increased heart rate and blood pressure accompanies vengeful thoughts or action, confirming neurological foundations.
A strengthening "therapautic mindset" in the general public has increasingly considered "revenge as a disease with forgiveness its cure," he says.
Humans have self-image, and some scientists believe that in order to maintain and project a positive "self-schema," meting out punishment for transgressions is a contributing factor. A University of Waterloo study shows that self-affirmation is linked to taking retaliation measures. Fehr suggests that vengeful actions developed originally to enhance cohesion in societies, but that people learned to weigh "the potential cost of retaliatory measures" before initiating reprisals.
Robert Alison has a doctorate in zoology and is based in Victoria, B.C.