The brutality against Michael Brown, Eric Garner, the prisoners tortured by the CIA, the inmates on Riker’s Island in New York, the noncombatants executed by the Islamic State—I find myself asking the old, naive question, how can people be this brutal to one another?

For these are not the brutalities of one person attacking another to rob or rape or murder. Nor are they the horrors of the battlefield, the war for turf. They are the brutalities of members of dominant groups who already exert control over apparent violators or actual captives. This brutality is not a power struggle. Power has already been achieved, or so it seems. So why the brutality?

Many believe that it comes from the dark side of disturbed cops or fanatical ideologues or even humanity itself, the fury of our animal brain that killed to eat or defend itself. The implication of such a diagnosis is that if we were better managed or trained or screened or socialized, the demons might step back. But the dynamics behind coercive brutality seem to be not so simple and not so correctable.

A helpful book is Race and Police Brutality: Roots of an Urban Dilemma by Malcolm D. Holmes and Brad W. Smith (2008). Their thesis is that police brutality is rooted in our emotions about groups, our own and others, as well as in our aggressiveness.

Holmes and Smith point out that it is difficult to imagine two groups more opposite from each other than a group of police officers on patrol and the minority residents of the neighborhood they are patrolling. The police see themselves as safeguarding society from its worst elements, with the tacit approval of law-abiding citizens. The residents of the ghetto or barrio believe that most of those citizens are biased against them and that they, the residents, are trying to hold the line against oppression.  Both groups have grown up learning the stereotypes of the other, heard the tales of violence, and learned the signs of danger (the weapon, the uniform). “The police and minority groups members see one another as ongoing threats. They both believe that the other is a danger to them.”

“These subjective perceptions of danger reaffirm group identity and reinforce group cohesion” (502). Here is the essential situation that underlies each particular stand-off on the street: all humans are attached to, and quick to defend, the groups they belong to. Tightly knit, organized groups are a unique human achievement. They evolved over several million years when the more casual linkages among earlier primates were no longer adequate for finding food and protection. Our brains evolved to provide nuanced social emotions such as loyalty to hold groups together and prompt them to organize. The result is football teams and nations, businesses and religion. And universally, people have the same basic emotions about groups: they favor members of their own and denigrate and often dehumanize members of competing or opposing ones.

So a police patrol in a minority neighborhood is a situation deeply primed for violence. It is surprising that it does not explode more often than it does. Police are restrained not only by regulations about excessive force but also by the risk of losing control of a tense situation. So what is it that finally triggers a gun shot or a chokehold?

It is the sequence of aggression. Smith and Holmes describe two types of aggression, and brutality results when one follows the other. Emotional aggression is immediate, passionate. It is a lashing out that arises from a surge of fear, anger, or frustration. The other type of aggression is instrumental—aggression that achieves a purpose. An assassin may calmly kill for pay. A husband may beat his wife in order to establish dominance.

On the street, in the heat of the moment, a police officer who feels threatened, who thinks he or she sees a weapon, feels a surge of aggression towards a man who is arguing. A few seconds or minutes pass by and the impulse may dissipate. Or, on the other hand, it may strengthen; roughing up the guy may serve a purpose; it may, in the mind of the officer, reestablish authority at the scene, defend the status of the police, dispense “justice” that the courts failed to deliver, or send a message to the community (1644). Brutality results.

When we think of coercive brutality, we usually picture two individuals—Darren Wilson and Michael Brown, a prisoner and his CIA tormenter, the hooded ISIL figure and the kneeling victim. But it is really the ingroups and the outgroups that are at work more than autonomous individuals. We are passionate about the rightness of our own groups and callous about the ones that challenge ours. Ingroups are a triumph of the human mind, one of the jewels of evolution, but when the tension is high, when a figure looks threatening and there might be a weapon, when violence seems justifiable, brutality happens.