The Brain and Aggression

Aggression is defined as “attack, assault, or active struggle.” In other words, it’s a situation where an organism fights against a source of trouble—most often, for example, a source of pain—and tries to eliminate it, aiming to solve the problem radically. This is a highly energy-consuming and potentially dangerous situation. As I mentioned in my lecture on fear, aggression is usually a secondary choice: first comes passive-defensive behavior, and if that doesn’t work, then active defense kicks in. Even a seemingly weak animal, when cornered, may start to defend itself seriously. A rat or a rabbit trapped in a confined space can put up a fierce fight.

So, if you’re interacting with someone and trying to make them do something by appealing to unpleasant emotions, be careful: you might push too far and, instead of compliance, trigger an aggressive outburst when the brain switches to a different program. At that point, things can spiral out of control, because if a fight breaks out, it’s for real. Still, I repeat, aggression is costly and traumatic, so before a truly aggressive reaction occurs, the organism often gives warning signs: “One more step, and there will be a fight—be careful.”

When we observe the behavior of fish, reptiles, birds, or mammals, we often see so-called threatening postures or facial expressions. Before attacking, an animal usually tries to look bigger: “Look how big and scary I am—run away before it’s too late, or I’ll bite you.” A fish flares its fins, a toad stands tall and puffs up, birds ruffle their feathers, and a cat arches its back—its fur standing on end. Often, “weapons” like claws or teeth are displayed. Human aggressive facial expressions are also linked to bared teeth—a very characteristic look. Aggressive expressions are among the basic facial expressions, like smiling or grimacing in pain or crying. Our visual systems recognize these signals innately. Basic facial expressions powerfully affect the brain, instantly triggering corresponding emotions and reactions. You start to fear the aggressive individual and adjust your behavior to anticipate possible aggression or a fight.

The Role of Aggression in Behavior

Originally, aggression appears as one of two types of responses to real or potential danger. But it turns out that aggression has a much broader significance. Animal behavior is structured so that aggression can be added to almost any unsuccessful activity. When you interact with another organism—especially a family member, pack member, or someone close—and something goes wrong (like disputes over territory, not enough food, or disrupted mating behavior), aggression can be added to the current program and become a major factor directing behavior. This is serious business.

As a result, aggressive reactions can accompany a wide range of events and arise whenever a person experiences failure. In these cases, aggression injects extra energy into behavior, and despite obstacles, you try to break through—sometimes with quite destructive actions. This doesn’t always lead to positive results, but that’s how we’re wired. Our brains are designed to switch to active defensive behavior when needed.

Brain Structures Responsible for Aggression

Looking at the nervous system, the hypothalamus is responsible for aggression, producing endocrine and autonomic responses. The amygdala is also involved. Another key player is the cingulate gyrus, located on the inner surface of the cerebral hemispheres, which compares actual and expected outcomes of behavior. The cingulate gyrus, together with the frontal cortex, predicts our behavior and its consequences. The more developed and efficient this system is, the less aggressive a person tends to be. In other words, a person evaluates the consequences of aggressive reactions and realizes that, in a few steps, it will likely lead to negative outcomes, so aggression is blocked. But if the amygdala dominates over the “cingulate gyrus–frontal cortex” connection, there’s more aggression, and we talk about a choleric temperament. Such people exist, and sometimes they’re needed, because there are situations where you have to ignore danger and negative consequences to break through to a better future, even if the risks can’t be fully calculated.

I like a quote from Napoleon in this context. When asked, “Emperor, do you have a battle plan?” he replied, “We’ll get involved, and then we’ll see.” That’s a somewhat aggressive approach to situations. Sometimes it’s justified, but it should be treated with great caution.

One of the great thinkers of the 20th century, zoologist Konrad Lorenz, urged people to be very careful with aggression, calling it a time bomb planted in our brains. Aggressive reactions can lead to interpersonal conflicts and even conflicts between nations. Lorenz said that aggression is the main danger to humanity’s existence. So, everything is good in moderation. Reasonable aggression can add energy to our actions and achievements, but too much aggression is usually destructive, and sometimes very much so.

Examples of Aggression in Behavior

Since aggression can attach itself to various behavioral patterns, let’s look at a few examples:

• Maternal Aggression: On one hand, the mother-child bond is sacred. On the other, if you try to harm her baby, you’ll get a fierce reaction. Everyone knows a mother will do anything to protect her child. A hen defending her chicks will attack a huge dog, and the dog understands the hen will fight to the end and runs away. Maternal aggression is a clear, vivid example.
• Sexual Aggression: Aggression often arises when an organism’s needs don’t match real-world events. For example, if there’s one female and several males, they have to compete to see who’s stronger. Evolution of sexual behavior leads to such situations. Initially, animals mate upon meeting, and the female cares for the offspring. But over time, it became advantageous for the male to stick around after mating—to guard territory or bring food. Since the female will be with the male for weeks or months, it’s better to choose the best one. So, when several males gather, they first compete. This competition signals to the female which male is the strongest and best, influencing her choice of mate.

Aggression during courtship, or so-called tournament behavior among males, is very characteristic. There’s butting, biting, and other active-defensive behaviors aimed at reproduction, but using reactions originally meant for dealing with danger.

Over the course of evolution, sexual behavior in animals usually shifts from direct fighting to rituals. It’s not practical to injure each other, so male tournaments often become displays: two males show off, and the bigger one wins. Sometimes, as with giraffes, it’s more like arm wrestling—they entwine necks to test their strength and back off in time. Sexual aggression is usually highly ritualized to avoid injuring weaker males, who are often just younger and will be useful later. The strongest male, with the best genes, gets to father the offspring. Females really do keep track of this. In species where sexual behavior includes such rituals, males are often much larger than females. A classic example is sea lions, where males can be five to ten times bigger than females.

Even the fact that men are generally larger than women is a result of sexual selection—female Homo sapiens have preferred larger, possibly more aggressive, males for thousands or millions of years. Our species has evolved in this direction.

• Food-Related Aggression: Food is a limited resource, and animals sometimes have to fight for it. Over evolutionary time, this often becomes ritualized as territorial behavior. Available territory is divided into plots—one tiger per plot, or a wolf family, or a hyena pack. Territorial behavior is based on food scarcity, and territory is divided through aggressive interactions. Early in evolution, aggression is real and violent, but as it becomes ritualized, it gets less physical and less harmful. This is good for the species, as it avoids unnecessary injuries.

In this sense, great apes and especially Homo sapiens are relatively young biological species. Our mechanisms for ritualizing aggression are not well developed. If we look at chimpanzees, our closest relatives, they are very aggressive. They guard and defend their territory, and males constantly patrol the borders. If a male from another group is found, there will be a fight, and sometimes he’s even killed. This is very serious. Unfortunately, this is deeply rooted in the human brain as well. That’s why human history is a history of wars and conflicts.

To quote Konrad Lorenz again: aggression is a bomb planted in our brains, and we must treat it with great caution. Sometimes it’s appropriate, but it requires serious control, or else your behavior will become ineffective and harmful not only to yourself but to everyone around you.