Search Malamalama

May 2004, Vol. 29 No. 2
Read more from this issue

Related Stories

The Anatomy of War

Behavioral biology

Behaviors protect gecko clones February 2004

Brain hemisphericity November 2003

Human behavior

Program gives prison inmates a second chance November 2003

Avoiding road rage January 2002

For More Information

Pacific Biomedical Research Center

International Society for Research on Aggression

International Behavioral Neuroscience Society

Published May 2004

The Biology of Aggression

To the brain, it’s a matter of survival

Illustration of a reflection
by Jennifer Crites
illustrations by Jason Nobriga

Brutal dictatorships, domestic violence, road rage, schoolyard bullying, hostile takeovers, even office politics—aggression affects everyone one way or another, but what do we really know about this sometimes uncontrollable urge to threaten, demean, hurt or even kill?

First, there are two kinds of aggression, explains Caroline Blanchard, professor of cell and molecular biology in the University of Hawai'i at Manoa’s John A. Burns School of Medicine. They evolve from different systems in the brain and produce different behavior, but both are critical to survival. She and husband, Bob, a Manoa professor of psychology, study aggression and defense in mouse, rat and hamster models at the Pacific Biomedical Research Center. "These are the same brain anatomic systems that exist in you and me," says Bob. "By understanding them in primitive mammals, we can understand them better in humans."

Offense or defense

Offensive aggression is used to control other people and enhance your own status or get your own way. The cortex or complex higher brain plays a dominant role. "Many things that trigger aggression in people have learned or symbolic meanings related to challenges to someone’s status or control of resources," Caroline explains. In most of the western world, for example, if you flip somebody the bird you are likely to receive some type of aggression in response, though the gesture has no intrinsic meaning."

On the flip side, defensive aggression occurs when something immediately threatens your life. "Being hurt can trigger it, or being grabbed by someone scary," she says. "It’s most likely to happen when the threat comes from a living attacker. However, I once witnessed a car run over a dog’s hind legs. The dog twisted around and bit the tire. It’s at least partly reflexive."

The circuitry for defense is largely sub-cortical; the evolutionary, primitive lower parts of the brain do most of the heavy lifting in defensive aggression as in other biological responses to threat—risk assessment, hiding, flight, freezing. "Activity in primitive brain systems can also produce hyperactivity of the sympathetic nervous system, resulting in adrenaline-enhanced strength and endurance, a sort of Incredible Hulk effect," she observes.

Responding to aggression

People may understand and accept defensive aggression. Barring threat to a person’s safety, however, it’s harder to accept aggression as a legitimate, evolved and functional behavior. Yet, it can be, says Caroline, and its biological purpose is control of resources. "That often means access to females, probably the single most important resource that male mammals of all species, including humans, fight about.

Illustration of boy with gun
Guys between 15 and 30, especially unmarried ones, are responsible for a wildly disproportionate share of violent crimes, and what they often get out of this violence is money and status, enhancing their attractiveness to women."

Still, constant fighting is unproductive in both animal and human societies. So mammals have developed two aggression substrategies that reduce the need to fight—territories and social hierarchies. For example, a beach master elephant seal sets up his territory, and no other males go there unless deliberately looking for a fight. Other species, including chimpanzees, baboons, rats, dogs and, yes, people, establish social hierarchies. Granted, human hierarchies are more complex and incorporate factors other than aggression, but group-living species exhibit a strong impulse to fight for position in the dominance hierarchy, especially in males.

Subordination and depression

Why don’t such species fight more often? If you—and others—know where you stand in the group, it substantially reduces the need to fight. For any particular animal, there is a delicate balance between the impulse to challenge higher-ups and fear of being defeated.

Illustration of boy with gun
"This typically leads to a lot of sizing up of the opponent’s brawn and skills (each combatant displaying these as dramatically as possible) before a fight occurs," Caroline observes. "Rats do this and, in my limited experience observing fights in people, we do too."

Living in communal groups reduces fighting and provides a certain amount of safety from predators. Subordination affords protection, but it can also produce social stress. "Subordinate male rats make great models of depression. They show changes in the brain similar to those in human depression, and their behaviors echo some of the major symptoms of depression—reduced activity, altered sleep cycles and reduced interest in females and food," she says. "Stress is a potent part of the reason that people become depressed, too, but animals get over it faster, maybe because they don’t have the verbal skills to keep reminding themselves how lousy things are."

Chemical intervention

Both offensive aggression and specific defensive behaviors respond to drugs. With grants from the National Science Foundation and support from private companies, the Blanchards study the effects of various compounds on defensive behaviors that may be closely related to different types of anxiety, including generalized anxiety disorder and panic. Certain drugs can affect neurotransmitters, chemicals manufactured in nerve cells that carry messages throughout the brain, says Bob. "We’re working with drugs that influence those neurotransmitters to see how they change behaviors related to these disorders."

The couple also investigated some drugs that reduce offensive aggression. Less is known about that system because agencies are wary about funding such research, fearful that it could lead to a barrage of medical controls, Caroline says. "American culture has mixed views about aggression. Our country was founded on revolution. On some level, aggression is regarded as an appropriate response to intolerable or grossly unfair conditions. This is a big part of the American view of freedom and individuality," she explains. "It’s difficult to draw the line between legitimate and illegitimate aggression, and drug treatments or other medical controls might not be responsive to that line."

Despite such obstacles, Bob, who is 2004 president of the International Behavioral Neuroscience Society, and Caroline, 2004 president-elect of the International Society for Research on Aggression, remain committed to their research.

"Alcohol and drug related violence, spouse abuse, family murders, shootings such as Columbine and other acts of offensive aggression stem largely from the inability to control anger," notes Bob. "The first step in preventing such violence is to understand it. We could reduce an awful lot of sadness in this world if we could do that."


The Anatomy of War

If humans are biologically wired to behave aggressively, is war an inevitable result? Scholars don’t agree.

Some anthropologists argue that wars make states and then states make war, says University of Hawai'i at Manoa Professor of Anthropology Les Sponsel. "But when people started settling down on the land about 10,000 years ago, when more-or-less-permanent farming communities arose, that’s when we begin to see evidence of warfare, including fortified villages, weapons and skeletal remains with battle wounds."

Not all farming communities engaged in war, he emphasizes, just as there are peaceful societies today, including the well-documented Semai who live in the forests of Malaysia. "That’s not to say the Semai and other societies don’t exhibit some violence, but traditionally they have not engaged in warfare. Their culture includes a value system, attitudes and world view fostering peaceful behavior."

Then again, anthropologists inclined to peace hone in on peaceful societies while those inclined to war identify warlike societies, Sponsel admits. Neither extreme can be realistically extended to all humanity.

A long-standing, 18th-century belief holds that primitive man is in a state of grace and, left to himself, will be without problems," says Caroline Blanchard, professor of cell and molecular biology in the John A. Burns School of Medicine. The belief was bolstered by travelers like Captain Cook, who reported on peaceful South Seas inhabitants.

Yet there’s plenty of proof that early peoples were not necessarily peaceful—12,000- to 14,000-year-old human remains at oases in western Egypt with spear points and arrowheads in them; skull cuts consistent with pre-Columbus scalpings at probable Native American battlegrounds; the 5,000-year-old iceman found preserved in ice with a flint arrowhead embedded in his shoulder. Yanomamo and other Amazon tribes practiced homicide and warfare before becoming known to western civilization in the 1960s.

To the victors belong the spoils. The motivation for war has always been control of resources—power and influence as well as wealth, argues Blanchard. "Up through the Napoleonic wars, soldiers were supposed to pay themselves by the loot they stole, and nobody questioned that."

Today, although some looting still occurs, most countries pay their soldiers a salary, and the resources in question are deemed vital to national interests. "The world’s three biggest industries are arms, oil and illegal drugs," adds Sponsel. "Resource competition is often a decisive factor triggering war." Industries and the communities that house them benefit from the war economy, adds Susan Dixon, a Manoa lecturer whose classes include the geography of peace and war.

War is also a function of sanctioned aggression, Dixon says. "Human conflict is inevitable, but we have a choice to resolve conflict cooperatively or by force. Unfortunately, we don’t learn conflict resolution skills in school. We learn about war, not peace, in our history classes, and if we assume violence and war are inevitable, then we treat them as inevitable."

"Everything in our civilization encourages boys and men to use violence to resolve problems," says Manoa professor of Women’s Studies Meda Chesney-Lind—toy ads on television, the proliferation of increasingly larger toy guns and other weapons, bloody video games, movies that celebrate violence.

"We solve problems with guns. Our society is more celebratory of violence than ever before, yet we’re somehow stunned at Columbine. These boys were outcasts, picked on, and eventually they turned on their tormenters using the societally approved mechanism for fighting back—guns. We need to give boys the right, the legitimacy, to use emotions other than anger to express themselves."

Politicians may proclaim peace, yet presidential candidates Kerry and Bush duke it out over their war credentials. The message is a mixed one, Chesney-Lind says: "Even to be a peaceful man, you must establish your credentials as a warrior. War is a metaphor for American masculinity."

Biological impulses play a part, according to Blanchard. In a long-term study of baboons in Africa, Stanford biologist Robert Sapolsky found that, after a fight, the loser showed significant hormonal imbalance related to stress. "The loser can eliminate that stress immediately if he goes out and beats up somebody else," Blanchard notes.

For humans, too, there’s a certain biological urge to be in control. "Males in general have a tremendous need to show that they are better than and can physically dominate someone else to gain access to resources. In one sense, that’s what war is." Civilization merely enhances our ability to make war by providing more sophisticated weapons and the food and supplies needed to camp out in the field longer.

"The idea that violence is not an integral part of human nature does us a disservice," says Blanchard. "If you don’t recognize where violence comes from, your chances of understanding and controlling it are not very good."


table of contents