The Joker's Wild: On the Ecology of Gun Violence in America | The Primate Diaries, Scientific American Blog Network

“The social life of a male baboon can be pretty stressful,” writes Stanford University neuroscientist Robert Sapolsky in his book Why Zebras Don’t Get Ulcers, “you get beaten up as a victim of displaced aggression; you carefully search for some tuber to eat and clean it off, only to have it stolen by someone of higher rank; and so on.” Over time the build up of stress hormones, known as glucocorticoids, can cause serious physiological damage and the development of stress-related illnesses. But the most common result whenever a male loses a fight, or is harassed by a higher-ranking male, is to displace that aggression elsewhere (typically on someone smaller). “Stress-induced displacement of aggression,” Sapolsky writes, “works wonders at minimizing the stressfulness of a stressor. It’s a real primate specialty as well.”

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.

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

“My tendency would be to reverse the causality,” said Frans de Waal, C. H. Candler Professor of Primate Behavior at Emory University in Atlanta, Georgia, via e-mail. “In order to have a highly skewed distribution of resources or reproductive privileges you will need a lot of aggression to maintain it. So, it’s not the inequality that causes aggression, but the other way around.” As primates we don’t simply respond to our environment; we actively build it through our interactions with others and the shared culture we create in a process known as niche construction, to use the technical jargon. And, as any baboon can tell you, what we construct isn’t always good for the least among us. Fortunately, as Forest Troop has demonstrated, there is no law of nature forcing things to stay that way.