The United States is often cited as the most generous nation on Earth. Unfortunately, it is also one of the most violent, having one of the highest murder rates of any industrialized country. Why this tragic paradox?

In an absorbing article excerpted below, backed by sound research, Anthropologist Eric Michael Johnson points to the lack of social capital on a local and national scale. Here, social capital is defined as interpersonal trust that promotes cooperation between citizens and groups for mutual benefit.

So, combine a culture that allows convenient access to very effective weapons with broad inequality, social isolation and distrust, and you get a very sobering picture — a country where around 70 people are killed each day by others wielding guns (25,423 firearm homicides in 2006-2007, based on Centers for Disease Control statistics).

[div class=attrib]From Scientific American:[end-div]

The United States is the deadliest wealthy country in the world. Can science help us explain, or even solve, our national crisis?

His tortured and sadistic grin beamed like a full moon on that dark night. “Madness, as you know, is like gravity,” he cackled. “All it takes is a little push.” But once the house lights rose, the terror was lifted for most of us. Few imagined that the fictive evil on screen back in 2008 would later inspire a depraved act of mass murder by a young man sitting with us in the audience, a student of neuroscience whose mind was teetering on the edge. What was it that pushed him over?

In the wake of the tragedy that struck Aurora, Colorado last Friday there remain more questions than answers. Just like last time–in January, 2011 when Congresswoman Gabrielle Giffords and 18 others were shot in Tucson, Arizona or before that in April, 2007 when a deranged gunman attacked students and staff at Virginia Tech–this senseless mass shooting has given rise to a national conversation as we struggle to find meaning in the madness.

While everyone agrees the blame should ultimately be placed on the perpetrator of this violence, the fact remains that the United States has one of the highest murder rates in the industrialized world. Of the 34 countries in the Organisation for Economic Co-operation and Development (OECD), the U.S. ranks fifth in homicides just behind Brazil (highest), Mexico, Russia, and Estonia. Our nation also holds the dubious honor of being responsible for half of the worst mass shootings in the last 30 years. How can we explain why the United States has nearly three times more murders per capita than neighboring Canada and ten times more than Japan? What makes the land of the free such a dangerous place to live?

Diagnosing a Murder

There have been hundreds of thoughtful explorations of this problem in the last week, though three in particular have encapsulated the major issues. Could it be, as science writer David Dobbs argues at Wired, that “an American culture that fetishizes violence,” such as the Batman franchise itself, has contributed to our fall? “Culture shapes the expression of mental dysfunction,” Dobbs writes, “just as it does other traits.”

Perhaps the push arrived with the collision of other factors, as veteran journalist Bill Moyers maintains, when the dark side of human nature encountered political allies who nurture our destructive impulses? “Violence is our alter ego, wired into our Stone Age brains,” he says. “The NRA is the best friend a killer’s instinct ever had.”

But then again maybe there is an economic explanation, as my Scientific American colleague John Horgan believes, citing a hypothesis by McMaster University evolutionary psychologists Martin Daly and his late wife Margo Wilson. “Daly and Wilson found a strong correlation between high Gini scores [a measure of inequality] and high homicide rates in Canadian provinces and U.S. counties,” Horgan writes, “blaming homicides not on poverty per se but on the collision of poverty and affluence, the ancient tug-of-war between haves and have-nots.”

In all three cases, as it was with other culprits such as the lack of religion in public schools or the popularity of violent video games (both of which are found in other wealthy countries and can be dismissed), commentators are looking at our society as a whole rather than specific details of the murderer’s background. The hope is that, if we can isolate the factor which pushes some people to murder their fellow citizens, perhaps we can alter our social environment and reduce the likelihood that these terrible acts will be repeated in the future. The only problem is, which one could it be?

…

The Exceptionalism of American Violence

As it turns out, the “social capital” Sapolsky found that made the Forest Troop baboons so peaceful is an important missing factor that can explain our high homicide rate in the United States. In 1999 Ichiro Kawachi at the Harvard School of Public Health led a study investigating the factors in American homicide for the journal Social Science and Medicine (pdf here). His diagnosis was dire.

“If the level of crime is an indicator of the health of society,” Kawachi wrote, “then the US provides an illustrative case study as one of the most unhealthy of modern industrialized nations.” The paper outlined what the most significant causal factors were for this exaggerated level of violence by developing what was called “an ecological theory of crime.” Whereas many other analyses of homicide take a criminal justice approach to the problem–such as the number of cops on the beat, harshness of prison sentences, or adoption of the death penalty–Kawachi used a public health perspective that emphasized social relations.

In all 50 states and the District of Columbia data were collected using the General Social Survey that measured social capital (defined as interpersonal trust that promotes cooperation between citizens for mutual benefit), along with measures of poverty and relative income inequality, homicide rates, incidence of other crimes–rape, robbery, aggravated assault, burglary, larceny, and motor vehicle theft–unemployment, percentage of high school graduates, and average alcohol consumption. By using a statistical method known as principal component analysis Kawachi was then able to identify which ecologic variables were most associated with particular types of crime.

The results were unambiguous: when income inequality was higher, so was the rate of homicide. Income inequality alone explained 74% of the variance in murder rates and half of the aggravated assaults. However, social capital had an even stronger association and, by itself, accounted for 82% of homicides and 61% of assaults. Other factors such as unemployment, poverty, or number of high school graduates were only weakly associated and alcohol consumption had no connection to violent crime at all. A World Bank sponsored study subsequently confirmed these results on income inequality concluding that, worldwide, homicide and the unequal distribution of resources are inextricably tied. (see Figure 2). However, the World Bank study didn’t measure social capital. According to Kawachi it is this factor that should be considered primary; when the ties that bind a community together are severed inequality is allowed to run free, and with deadly consequences.

But what about guns? Multiple studies have shown a direct correlation between the number of guns and the number of homicides. The United States is the most heavily armed country in the world with 90 guns for every 100 citizens. Doesn’t this over-saturation of American firepower explain our exaggerated homicide rate? Maybe not. In a follow-up study in 2001 Kawachi looked specifically at firearm prevalence and social capital among U.S. states. The results showed that when social capital and community involvement declined, gun ownership increased (see Figure 3).

[div class=attrib]Read the entire article after the jump.[end-div]

[div class=attrib]Image: Smith & Wesson M&P Victory model revolver. Courtesy of Oleg Volk / Wikpedia.[end-div]