“Are we a nation in which violence is out of control and will plague us and will interfere with our freedom?” asks Felton Earls, professor of social medicine at Harvard Medical School and professor of human behavior and development at Harvard School of Public Health. “Violence reduces confidence that all the other things that we stand for are working to make this a successful country – it tests the very foundation of a society.”

A self-described child of the 1960s, Earls has spent much of the past 15 years trying to understand violence in society. In a Nov. 17, 2005 lecture, he posed the question: “Is violence a medical problem?” but he didn’t answer it. “Researchers ask questions,” he said. “Only after time, research, and experience should you be in the position to answer the question. I can say that violence is a health problem, but I’m cautious about answering the question of whether it’s a medical problem.”

Violence is commonly understood to be a public health problem, which means that it’s a problem that can be studied among populations and the structures, institutions, and regulations that affect those populations. Medical problems are focused on individuals. Clearly, the effects of violence are often medical problems, but violence itself?

A study, whose authors include Earls and School of Public Health research fellow Jeffrey Bingenheimer, which appeared in the May 27, 2005, issue of Science, suggests that violence acts as a social infectious disease. The study looked at adolescents who witnessed or have been victims of life-threatening gun violence. “We were interested in what happens when young people witness close-up violent episodes in their families or in their neighborhoods,” said Earls. “And what’s the likelihood that witnessing such an event will mobilize them in such a way as to have them become perpetrators of violence.” What they found was that even after controlling for a huge number of variables – including aggression, drug use, gender, and ethnicity – that those who witnessed firearm violence were three times more likely to perpetrate firearm violence within two years than their peers who didn’t witness the violence. Thus, violence can be viewed as a disease that “infects” its witnesses.

The ramifications for violence prevention are profound: “If we can stop a violent incident, not only have we stopped a victim from being injured,” said Earls, “but we have diminished the probability that a whole network of witnessing peers will perpetrate violence. You can actually break down the cycle in which exposure leads to violent incidence.”