There once was a man and his concubine from the Israeli tribe of Ephraim who were travelling in the land of Benjamin, another Israeli tribe. As the couple dined in the city of Gibeah, a mob assembled outside and pounded on the door. The mob captured the concubine, then raped and beat her to death. The man collected her corpse the next day and travelled home. The other tribes of Israel were outraged at the crime, assembled an army and razed several Benjamite cities, killing every man, woman, child and animal they could.

Around 500 students recently read a version of this story, which is based on a passage from the Old Testament, as part of a psychological study. For half of the participants the tale contained an additional passage: when the man returned home, his tribe prayed to God and asked what they should do. God commanded the tribe to “take arms against their brothers and chasten them before the Lord”.

After reading the story, the students participated in another exercise intended to measure aggression. About half of the study participants came from Brigham Young University, a religious university in Provo, Utah, and almost all were members of the Church of Jesus Christ of Latter-Day Saints. The other half came from the Free University in Amsterdam. Only 50% of the Dutch group believed in God and 27% in the Bible. But for both groups — whether the students were based in the Netherlands or the United States, and believed in God or not — the trend was the same: those who were told that God had sanctioned the violence against the Israelite were more likely to act aggressively in the subsequent exercise.

The study is indicative of a growing interest among psychologists and sociologists in the origins of religious violence. That subject was taboo until recently for many psychologists, and past research tended to focus on the role of religion in psychological healing. But heightening concern about religious terrorism has pushed negative uses of religion to the forefront. “People often use God as a justification for committing violent acts,” says Brad Bushman, a social psychologist at the University of Michigan in Ann Arbor and lead author of the study. “And that just bothers me, I guess.”

If violence is presented as the authoritative voice of God, it can increase the possibility of more violence.

The results of Bushman's study, to be published in the March issue of Psychological Science, do not indicate that religious people are more aggressive than non-religious people (B. J. Bushman et al. Psychol. Sci. 18, 204–207; 2007). Furthermore, the story us ed was an isolated example of scriptural violence taken out of context, and thus does not reflect the experience of reading the Bible as a whole. But it does suggest that selective exposure to violent passages in a scriptural canon can promote aggression.

That response probably reflects a long-standing finding in psychology that people respond more aggressively to a depiction of violence that they feel is justified, says Robert Ridge, a social psychologist at Brigham Young University and a co-author ofthe study.

Sociologist Mark Juergensmeyer of the University of California, Santa Barbara, says his research has also pointed to the motivational power of scriptural violence, but that the context of the message is key. “If violence is presented as the authoritative voice of God, it can increase the possibility of more violence,” says Juergensmeyer. “But everything depends on how it is presented.” The same passage placed in a non-threatening, historical context might not promote aggression, he argues.

Nevertheless, when scriptural violence is used to promote hostility, it is extremely effective, Juergensmeyer adds. Invoking religious justification allows a political leader to believe in promises of immortality and spiritual rewards that can be powerful motivators. “Religion is not the problem,” he says. “But it can make a secular problem worse.”

God's sanction can be a motivator for aggression. Credit: CORBIS

People often choose to ignore the violent side to religion, says John Hall, a sociologist at the University of California, Davis, and they tend to dismiss those who commit religiously inspired violence as members of the fringe. “There are built-in cultural lenses that we use to dissociate religion from violence,” he says. “When we see religious movements that are prophetically inspired and engaged in violence, there's a cultural tendency to say 'oh, they're not really religious'.”

That view represents a misleading, selective interpretation of most religious canons, agrees theologian Hector Avalos of Iowa State University in Ames. “People who choose the violent interpretation are no less arbitrary than those who choose the peaceful one,” he says. Avalos has proposed a radical solution to theologically inspired violence — cut the violent passages out of the scripture.

It's a wildly controversial idea that ought not to be, he says, because spiritual leaders effectively do that on a regular basis. “A lot of churches have a series of passages that they read during the year,” says Avalos. “And usually they don't choose the passages involving genocide.”