In June, a new study came out on how conflict has affected adolescents in southern Israel. As time went on, the researchers found, kids exposed to rocket attacks and terrorism weren’t much more anxious or depressed than their peers. But they were more violent: for each point a teen scored on a scale measuring exposure to such attacks, he or she was about twice as likely to commit violence later on .
Social scientists have identified a host of traits and behaviors that seem to spread via social networks: obesity, voting, happiness. What about violence? Common sense tells us that some kinds of bloodshed (war, gang activity) spread geographically. But is violence itself contagious, or are other underlying conditions—say, poverty—at work?
A study of insurgent attacks in Russia’s North Caucasus concluded that violence travels by the same routes as traffic and trade: it was transmitted more readily between villages that were connected by major roads than between those that weren’t . And yet, other research suggests that factors beyond proximity determine where conflict crops up. A 2010 study on ethnic violence in Germany investigated whether neighboring areas are likely to “catch” such violence from one another. After controlling for demographic variables, researchers found that violence was not contagious per se; it just seemed that way because adjacent areas were socially similar .
When violence spreads, it can have a long incubation period. For years, researchers have recognized a “cycle of violence,” in which victims eventually become perpetrators. A report by the National Institute of Justice shows that children who experience abuse or neglect are 30 percent more likely to be arrested for a violent crime by the time they reach their early 30s than peers who grow up in safer homes . (Sadly, victims aren’t only more likely to become perpetrators; they’re also at increased risk of being victimized multiple times: one recent study of African American teenage girls in Chicago found that those who had suffered sexual violence were more likely to report suffering other forms of violence .)
As for modes of transmission, violence seems to spread not just via human connections but also via media, even when the violence portrayed is fictional. One study found a correlation between a child’s television-viewing habits and aggressive behavior 15 years later. “Men who were high TV-violence viewers in childhood,” the authors wrote, “were convicted of crimes at over three times the rate of other men” . And in 2010, a major review of research involving more than 130,000 participants reported a causal relationship between exposure to violence in video games and aggressive behavior .
It’s been said that violence is a disease. At the very least, it seems to spread like one. Could we one day develop an effective vaccine?