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Violence is a contagious meme

Well this is absolutely fascinating.

Schneier on Security: Violence as a Contagious Disease

Intuitively we understand that people surrounded by violence are more likely to be violent themselves. This isn't just some nebulous phenomenon, argue Slutkin and his colleagues, but a dynamic that can be rigorously quantified and understood.

According to their theory, exposure to violence is conceptually similar to exposure to, say, cholera or tuberculosis. Acts of violence are the germs. Instead of wracking intestines or lungs, they lodge in the brain. When people, in particular children and young adults whose brains are extremely plastic, repeatedly experience or witness violence, their neurological function is altered.

Cognitive pathways involving anger are more easily activated. Victimized people also interpret reality through perceptual filters in which violence seems normal and threats are enhanced. People in this state of mind are more likely to behave violently. Instead of through a cough, the disease spreads through fights, rapes, killings, suicides, perhaps even media, the researchers argue.

[...]

Not everybody becomes infected, of course. As with an infectious disease, circumstance is key. Social circumstance, especially individual or community isolation �-- people who feel there’s no way out for them, or disconnected from social norms �-- is what ultimately allows violence to spread readily, just as water sources fouled by sewage exacerbate cholera outbreaks.

At a macroscopic population level, these interactions produce geographic patterns of violence that sometimes resemble maps of disease epidemics. There are clusters, hotspots, epicenters. Isolated acts of violence are followed by others, which are followed by still more, and so on.

There are telltale incidence patterns formed as an initial wave of cases recedes, then is followed by successive waves that result from infected individuals reaching new, susceptible populations. "The epidemiology of this is very clear when you look at the math," said Slutkin. "The density maps of shootings in Kansas City or New York or Detroit look like cholera case maps from Bangladesh."