Verified by 
Key points
- The biology of anger and aggression is the root cause of most violent behavior.
- Data show that a murderer is twice as likely to be the victim's friend or acquaintance than a stranger.
- Most of the time, the neural circuits of aggression are life-saving, but sometimes they misfire and violence explodes inappropriately.
Violence at political rallies, terrorism, and horrifying workplace shootings bewilder us, but they shouldn’t. Traditional approaches to understanding violence seem played out. What we need is an understanding of violence at the level of brain circuitry. Violence, like all human behavior, is controlled by the brain. From everyday road rage to domestic violence to a suicide bombing, the biology of anger and aggression is the root cause of most violent behavior.
Viewing violence narrowly from the perspective of psychological dysfunction shirks the larger truth that the biological roots of rage exist in all of us. The leading risk of death throughout the prime of life is not disease. It is violence. If you survive into old age, you will most likely die from disease, but according to CDC statistics for deaths in the United States for the year 2014, life ends at the hand of another human so frequently that from early childhood through middle age, homicide is the third to fifth most common cause of death in all age brackets between 1-44 years.
A psychopath or a foreign terrorist is not the likely villain. The data show that the murderer is twice as likely to be your friend or acquaintance as it is to be a stranger. Deadly violence against oneself (suicide) is second only to accidental injury as the most frequent way we die between the ages of 10 and 34.
The most important factor in violence is not pathology, psychology, or politics—it is biology. Nine out of 10 people in prison for violent crime are men. Males die from homicide at three times the rate of women. When the victim is a spouse or intimate partner women are murdered at 3.3 times the rate of men. Males commit suicide at four times the rate of females. Violence and maleness is a biological fact that runs through the vast diversity of cultures and through our ancestral tree to other primates.
We have neural circuits of rage and violence because we need them. As a species we needed deadly violence to obtain food, to protect ourselves, our family, our group, and unfortunately we still need them today. Order in society is maintained through violence, meted out methodically by police and nations according to laws that benefit society at large, but this organized violence is founded on the same neurocircuitry of aggression wired into the human brain of every individual.
We are on the brink of a new understanding of the neuroscience of violence. Like detectives slipping a fiber optic camera under a door, neuroscientists insert a fiber optic microcamera into the brain of an experimental animal and watch the neural circuits of rage respond during violent behavior. Neurons genetically modified to flash bursts of light when they fire reveal where these circuits of rage are in the brain, and neuroscientists can stimulate or squelch the firing of a neuron they target by laser beam. With the flip of a switch, neuroscientists can launch an animal into a violent attack or arrest a violent battle underway by activating or quelling the firing of specific neurons in the brain’s rage circuits. Technological advances in monitoring brainwaves and brain imaging are bringing new insight into this same circuitry at work in the human brain. These circuits of aggression are part of the brain’s threat detection mechanism embedded deep in the unconscious region of the brain where sex, thirst, and feeding are also controlled. Struggling to comprehend a suicide bomber’s “thinking” or police searching for “motives” in cases where violence is driven by perceptions of threat, alienation or emotion is a search in vain. Such violence is not driven by reason. It is driven by rage.
Our current perspective views violence as pathology and seeks to find common elements that unite all violent behavior. “The different forms of violence—child abuse and neglect, youth violence, intimate partner violence, sexual violence, elder abuse and suicidal behavior—are interconnected and often share the same root causes,” the CDC concludes in its strategic vision statement. But lumping together all forms of violence in an attempt to find a common denominator has created the incomprehensible muddle we find ourselves in today, as we struggle to comprehend a school shooting, or worshipers slaughtered inside a church by racial hatred. The sickening violence of Sandy Hook, which was the product of a broken mind, cannot be lumped together with the violence of the terrorists in San Bernardino, or violence committed in a robbery, or the everyday violence of barroom brawls, domestic violence, or deadly road rage. Each of these violent acts can be understood as specific behaviors that are controlled, as are all behaviors, by specific circuits in the brain activated by specific triggers.
Most of the time, the neural circuits of aggression are life-saving, as when a mother instantly reacts aggressively to protect her child in danger, but sometimes they misfire and violence explodes inappropriately, as in a road rage shooting. The pressures of modern life constantly press on these triggers of rage. International communication and high-speed transportation increase opportunities for conflict between different groups of people. Weapons of violence amplify the lethal effects of one enraged mind well beyond the power of any individual to combat with bare hands. Add to this the toxic effects of psychoactive drugs for treating mental illnesses and drugs of abuse, compounded by the increasing stress, crowding, and sensory bombardment of the modern world, and we see the human brain struggling to cope with an environment it was never designed to confront.
We cannot hope to control violence if we are bewildered by it. The CDC statistics strongly suggest that in addition to understanding the biological basis of disease, there is a much greater unmet need for neuroscience research to understand the biological underpinnings of violent behavior. We cannot change the biology of our brain, but if we choose to, we can comprehend it at the same level of detail that we comprehend the biology of a human heartbeat.
