Behave

Violence

People are ambiguous about violence. Many fantasize about righteous violence against those who deserve punishment. Allusions to violence pepper the culture, like sports teams named for dangerous animals. Yet people denounce unethical violence. Violence has conceptual, emotional, cultural and physical components, so you must cross boundaries and disciplines to understand it. Start that quest with the human brain.

The Layers of the Brain

Think of the brain as having three layers. “Layer one” is an ancient section that humans share with reptiles. People share “layer two,” the limbic system, with mammals, and primates share the most development in “layer three,” the neocortex. These layers interact and exchange information.

Layer two, the limbic system, indirectly controls autonomic functions and emotion and releases hormones. It shares an interface with the frontal cortex, which handles analytical thinking and executive functions, such as planning and regulating impulses. Evolutionarily, the cortex emerged recently. The amygdala deals...