Roots of Revenge

From family feuds to ethnic, religious or national conflicts, the kind of long-simmering disputes that often seem senseless to outsiders appear to have a biological basis, according to a new study by Chinese researchers and a University of Maryland psychologist.

The experimental study, published online this week in the journal eLife, found that when members of a group observe one of their own being hurt by a member of another group, it activates a complex response that includes a release of oxytocin, the so-called “love hormone,” which is linked to empathy and plays a role in relationship building between individuals and within groups. 

Subsequent imaging of group members’ brains showed that they experienced common neurological activity that predicted a desire to seek revenge on members of the other group later.

“They didn’t just want revenge against the individual who hurt their in-group member, but against the other outgroup members who weren’t originally involved in the conflict,” said study co-author Michele Gelfand, a Distinguished University Professor in psychology. “That’s a new and important finding that could help explain how conflicts escalate—and become contagious from individuals to entire groups.”

The idea for the study came out of a meeting in China between Gelfand, widely known for research into how groups react to outside threats, and one of the senior authors Shihui Han, a neuroscientist at Peking University and world expert on the mechanisms of empathy. “I asked him, how would you like to take your research on empathy to the dark side, and look at revenge?” Gelfand said.

The experiment involved creating groups of test subjects in a laboratory. Members of one group were shown images of a compatriot feigning pained reactions to electric shocks from members of another group in the context of a game. Separately, a control group observed one of its members receiving shocks at the discretion of a computer, rather than a member of another group.

Those who witnessed shocks being administered by a member of another group experienced a release of oxytocin, measured in saliva and FMRI scans showed that levels of oxytocin predicted enhanced medial prefrontal cortex activity that correlated to a later urge to administer painful electric shocks to members of the other group. Members of the control group who witnessed computer-administered shocks did not experience the same responses, or seek to take revenge against the other group.

Gelfand, who developed what she termed the “tightness-looseness” theory to explain how groups with varying strengths of social norms and behavioral restrictions respond differently to outside threats and other stimuli, said she hopes to expand the study to include other cultures to learn what is universal and culture-specific regarding the neurobiology of revenge. 

“Is that same neurobiological pathway as strong in a place like the United States, where we have a looser more individualistic culture?” she said.

The finding could be used as a basis to study intractable conflict, from the Balkans to the Middle East and elsewhere, she said.

“Across history, we see this behavior where conflicts escalate across time to include people who were never involved in the conflict,” Gelfand said. “You may not even have been alive for a conflict, but simply hearing a story about how an out-group member harmed your in-group member could potentially activate that neurobiological pathway that predicts revenge-seeking behavior—something we want to investigate in the future.”