If people are generally good and care about others so much, then how could anyone possibly kill another human being, let alone participate in a suicide bombing or even genocide? Do aggressive events mean that people are naturally aggressive, violent, and hostile—or are they unusual events, shaped more by particularly extreme social situations that do not reflect the normal character of human beings? Social psychologists define aggression as behavior that is intended to harm another individual who does not wish to be harmed (Baron & Richardson, 1994). Because it involves the perception of intent, what looks like aggression from one point of view may not look that way from another, and the same harmful behavior may or may not be considered aggressive depending on its intent. Intentional harm is, however, perceived as worse than unintentional harm, even when the harms are identical (Ames & Fiske, 2013).
Social psychologists use the term violence to refer to aggression that has extreme physical harm, such as injury or death, as its goal. Thus violence is a subset of aggression. All violent acts are aggressive, but only acts that are intended to cause extreme physical damage, such as murder, assault, rape, and robbery, are violent. Slapping someone really hard across the face might be violent, but calling people names would only be aggressive.
The type or level of intent that underlies an aggressive behavior creates the distinction between two fundamental types of aggression, which are caused by very different psychological processes.
Emotional or impulsive aggression refers to aggression that occurs with only a small amount of forethought or intent and that is determined primarily by impulsive emotions. Emotional aggression is the result of the extreme negative emotions we’re experiencing at the time that we aggress and is not really intended to create any positive outcomes.
Instrumental or cognitive aggression, on other hand, is aggression that is intentional and planned. Instrumental aggression is more cognitive than affective and may be completely cold and calculating. Instrumental aggression is aimed at hurting someone to gain something—attention, monetary reward, or political power, for instance.
Social psychologists agree that aggression can be verbal as well as physical. Therefore, slinging insults at a friend is definitely aggressive, according to our definition, just as hitting someone is. Physical aggression is aggression that involves harming others physically—for instance hitting, kicking, stabbing, or shooting them. Nonphysical aggression is aggression that does not involve physical harm. Nonphysical aggression includes verbal aggression (yelling, screaming, swearing, and name calling) and relational or social aggression, which is defined as intentionally harming another person’s social relationships, for instance, by gossiping about another person, excluding others from our friendship, or giving others the “silent treatment” (Crick & Grotpeter, 1995). Nonverbal aggression also occurs in the form of sexual, racial, and homophobic jokes and epithets, which are designed to cause harm to individuals.
A belief in the innate aggressive tendencies of human beings—that the ability to be aggressive toward others, at least under some circumstances, is part of our fundamental human makeup—is consistent with the principles of evolutionary psychology. After all, the goal of maintaining and enhancing the self will in some cases require that we prevent others from harming us and those we care about. We may aggress against others because it allows us to gain access to valuable resources such as food and desirable mates or to protect ourselves from direct attack by others. And we may aggress when we feel that our social status is threatened. Therefore, if aggression helps with either our individual survival or in the survival of our genes, then the process of natural selection may well cause humans, as it would any other animal, to be aggressive. Human beings need to be able to aggress in certain situations, and nature has provided us with these skills (Buss & Duntley, 2006). Under the right situation, almost all of us will aggress.
However, just because we can aggress does not mean that we will. It is not necessarily evolutionarily adaptive to aggress in all situations. For one, aggressing can be costly if the other person aggresses back. Therefore, neither people nor animals are always aggressive. Rather, they use aggression only when they feel that they absolutely need to (Berkowitz, 1993a). In animals, the fight-or-flight response to threat leads them sometimes to attack and sometimes to flee the situation. Human beings have an even wider variety of potential responses to threat, only one of which is aggression. Again, the social situation is critical. We may react violently in situations in which we are uncomfortable or fearful or when another person has provoked us, but we may react more calmly in other settings. And there are cultural differences, such that violence is more common in some cultures than in others.
Read the following articles for more information on research that has been done on the evolutionary roots of aggression:
Nasty, Brutish and Short: Are Humans DNA-Wired to Kill? (Scientific American, 2017)
From Fruit Fly To Stink Eye: Searching For Anger's Animal Roots (NPR, 2019)
Aggression is controlled in large part by the area in the older part of the brain known as the amygdala. The amygdala is a brain region responsible for regulating our perceptions of, and reactions to, aggression and fear. The amygdala has connections with other body systems related to fear, including the sympathetic nervous system, facial responses, the processing of smells, and the release of neurotransmitters related to stress and aggression. In addition to helping us experience fear, the amygdala also helps us learn from situations that create fear. The amygdala is activated in response to positive outcomes but also to negative ones, and particularly to stimuli that we see as threatening and fear arousing. When we experience events that are dangerous, the amygdala stimulates the brain to remember the details of the situation so that we learn to avoid it in the future. The amygdala is activated when we look at facial expressions of other people experiencing fear or when we are exposed to members of racial outgroups (Morris, Frith, Perrett, & Rowland, 1996; Phelps et al., 2000).
Although the amygdala helps us perceive and respond to danger, and this may lead us to aggress, other parts of the brain serve to control and inhibit our aggressive tendencies. One mechanism that helps us control our negative emotions and aggression is a neural connection between the amygdala and regions of the prefrontal cortex (Gibson, 2002).The prefrontal cortex is in effect a control center for aggression: when it is more highly activated, we are more able to control our aggressive impulses. Research has found that the cerebral cortex is less active in murderers and death row inmates, suggesting that violent crime may be caused at least in part by a failure or reduced ability to regulate emotions (Davidson, Jackson, & Kalin, 2000; Davidson, Putnam, & Larson, 2000).
However, recent research suggests that aggression is not a result of lack of self-control. Read more here:
Aggression Is A Result of Self-Control, Not Lack Thereof (Neuroscience News, 2023)
Hormones are also important in creating aggression. Most important in this regard is the male sex hormone testosterone, which is associated with increased aggression in both animals and in humans. Research conducted on a variety of animals has found a strong correlation between levels of testosterone and aggression. This relationship seems to be weaker among humans than among animals, yet it is still significant (Dabbs, Hargrove, & Heusel, 1996). Although testosterone levels are much higher in men than in women, the relationship between testosterone and aggression is not limited to males. Studies have also shown a positive relationship between testosterone and aggression and related behaviors (such as competitiveness) in women (Cashdan, 2003). Although women have lower levels of testosterone overall, they are more influenced by smaller changes in these levels than are men.
Testosterone is not the only biological factor linked to human aggression. Recent research has found that serotonin is also important, as serotonin tends to inhibit aggression. Low levels of serotonin have been found to predict future aggression (Kruesi, Hibbs, Zahn, & Keysor, 1992; Virkkunen, de Jong, Bartko, & Linnoila, 1989). Violent criminals have lower levels of serotonin than do nonviolent criminals, and criminals convicted of impulsive violent crimes have lower serotonin levels than criminals convicted of premeditated crimes (Virkkunen, Nuutila, Goodwin, & Linnoila, 1987).
Read about other hormones that may have an effect on aggression:
Don’t Blame the Testes for All Aggression (Psychology Today, 2022)
If you were to try to recall the times that you have been aggressive, you would probably report that many of them occurred when you were angry, in a bad mood, tired, in pain, sick, or frustrated. And you would be right—we are much more likely to aggress when we are experiencing negative emotions. When we are feeling ill, when we get a poor grade on an exam, or when our car doesn’t start—in short, when we are angry and frustrated in general—we are likely to have many unpleasant thoughts and feelings, and these are likely to lead to violent behavior. Aggression is caused in large part by the negative emotions that we experience as a result of the aversive events that occur to us and by our negative thoughts that accompany them (Berkowitz & Heimer, 1989).
One kind of negative affect that increases arousal when we are experiencing it is frustration (Berkowitz, 1989; Dollard, Doob, Miller, Mowrer, & Sears, 1939). Frustration occurs when we feel that we are not obtaining the important goals that we have set for ourselves. We get frustrated when our computer crashes while we are writing an important paper, when we feel that our social relationships are not going well, or when our schoolwork is going poorly. How frustrated we feel is also determined in large part through social comparison. If we can make downward comparisons with important others, in which we see ourselves as doing as well or better than they are, then we are less likely to feel frustrated. But when we are forced to make upward comparisons with others, we may feel frustration. When we receive a poorer grade than our classmates received or when we are paid less than our coworkers, this can be frustrating to us.
Of course, negative emotions do not always lead to aggression toward the source of our frustration. If we receive a bad grade from our teacher or a ticket from a police officer, it is not likely that we will directly aggress against him or her. Rather, we may displace our aggression onto others, and particularly toward others who seem similar to the source of our frustration (Miller, Pedersen, Earleywine, & Pollock, 2003). Displaced aggression occurs when negative emotions caused by one person trigger aggression toward a different person. A recent meta-analysis has found clear evidence that people who are provoked but are unable to retaliate against the person who provoked them are more aggressive toward an innocent other person, and particularly toward people who are similar in appearance to the true source of the provocation, in comparison to those who were not previously provoked (Marcus-Newhall, Pedersen, Carlson, & Miller, 2000).
Just as negative feelings can increase aggression, positive affect can reduce it. In one study (Baron & Ball, 1974), participants were first provoked by an experimental confederate. Then the participants were, according to random assignment, shown either funny cartoons or neutral pictures. When the participants were given an opportunity to retaliate by giving shocks as part of an experiment on learning, those who had seen the positive cartoons gave fewer shocks than those who had seen the neutral pictures.
The idea that engaging in less harmful aggressive actions will reduce the tendency to aggress later in a more harmful way, known as catharsis, is an old one. It was mentioned as a way of decreasing violence by the Greek philosopher Aristotle and was an important part of the theories of Sigmund Freud. Many others believe in catharsis too. Russell, Arms, and Bibby (1995) reported that more than two-thirds of the people they surveyed believed in catharsis, agreeing with statements that suggested that participating in and observing aggressive sports and other aggressive activities is a good way to get rid of one’s aggressive urges. People who believe in the value of catharsis use it because they think that doing so is going to make them feel better (Bushman, Baumeister, & Phillips, 2001). The belief in catharsis leads people to engage in popular techniques such as venting and cathartic therapies or even to play violent video games (Whitaker, Melzer, Steffgen, & Bushman, 2013), even though numerous studies have shown that these approaches are not effective.
It is true that reducing negative affect and arousal can reduce the likelihood of aggression. For instance, if we are able to distract ourselves from our negative emotions or our frustration by doing something else, rather than ruminating on it, we can feel better and will be less likely to aggress. However, as far as social psychologists have been able to determine, attempting to remove negative emotions by engaging in or observing aggressive behaviors (that is, the idea of catharsis) simply does not work.
Read about some research on catharsis here:
You Can't Punch Your Way Out of Anger (Psychology Today, 2009)
As would be predicted by principles of social reinforcement, if we are rewarded for being aggressive, we’ll likely aggress again, but if we are punished for our violence, we may subsequently curb our aggression. The child who gets a toy by hitting another child and taking it is likely to continue being aggressive in the future, particularly if he or she is not punished for the action. Children who are more aggressive are also often seen as more competent, in part because they can use their aggression to get their way (Hawley, 2007). Björkqvist et al. (2001) found that girls who use nonphysical aggression reported being less lonely and were more likely to have higher status than did nonaggressive girls. In another study, aggressive boys were more likely to be accepted by their peers than were nonaggressive boys (Salmivalli, Kaukiainen, & Lagerspetz, 2000). Aggression seems to be paying off for these students.
Some aggression is learned through modeling the violence that we see all around us every day (Bandura & Walters, 1959). In his important research on aggression, Albert Bandura demonstrated that children learned new aggressive behaviors by observing aggressive models (Bandura, 1973). Bandura argued that we don’t just imitate the specific behaviors that we see, but that viewing aggression changes our schemas and our attitudes about aggression. Watching a parent hitting another person may not only increase a child’s likelihood of hitting but may also increase his or her beliefs that “hitting is OK” and that “one way to solve problems is by hitting.” Modeling teaches new ideas about aggression and can help explain why exposure to violence increases aggressive behavior in the long run (Huesmann & Kirwil, 2007).
Learn more about Bandura's groundbreaking work below:
Although rewards clearly increase aggression, perhaps punishment decreases it? Judicial systems are based in large part on punishing people for being aggressive, with fines, jail terms, and even the death penalty being used as punishments. There is, however, a problem with using punishment to reduce aggression, particularly when the punishment is itself aggressive. The problem is that the punishment may be modeled, which can increase the aggressive behaviors that we are trying to stop. In a meta-analysis, Gershoff (2002) found that although children who were spanked by their parents were more likely to immediately comply with the parents’ demands, they were also more aggressive, showed less ability to control aggression, and had poorer mental health in the long term. The problem seems to be that children who are punished for bad behavior may be more likely to change their behavior only for external reasons, rather than internalizing the norms of being good for its own sake.
Punishment is most effective when it is intense, prompt (before the person can derive much pleasure from the aggression), applied consistently and with certainty, perceived as justified, and replaced by a more desirable alternative behavior (Berkowitz, 1993). But even if punishment occurs under these ideal conditions, it may only suppress aggressive behavior temporarily (Baron & Richardson, 1994; Berkowitz, 1993).
One example of the use of violence to attempt to stop violence is capital punishment—the use of the death penalty. Although banned in many countries, capital punishment is used in countries such as the United States, Egypt, India, Saudi Arabia, Singapore, and Vietnam. Although many people believe that capital punishment deters crime, there is little evidence that it actually does (Archer, Gartner, & Beittel, 1983). For one, the time period between the crime and the punishment is typically many years long, which makes it less effective as a deterrent. Second, many of the crimes that are punished by the death penalty involve emotional aggression and are not premeditated. They occur during arguments or while the perpetrator is under the influence of alcohol or recreational drugs. In these cases, even if the perpetrator has knowledge of the death penalty, this knowledge is not likely to have much effect on reducing crime. And capital punishment also means that many innocent people are wrongly executed for crimes they did not commit.
Worldwide, the average child watches over three hours of television every day, and these programs contain both physical and nonphysical aggression at the rate of about three violent acts per minute (Archer & Coyne, 2005; Groebel, 1999; Shanahan, Hermans, & Hyman, 2003). Furthermore, the amount, intensity, and graphic nature of the violence that children view continues to escalate every year. According to a study of programming from 1993 to 2001 on six major Canadian television networks, depictions of physical violence increased by 378% over this period, to the tune of about 40 acts of violence per hour (Paquette, Gosselin, & DeGuise, 1997). These programs are punctuated with television advertisements, approximately 13% of which also contain violent content (Jones & Cunningham, 2008). At the same time, children are also exposed to violence in movies and video games, as well as in popular music and music videos that include violent lyrics and imagery.
Given your knowledge about the importance of the social situation, it might not surprise you to hear that these situational exposures to violence have an effect on aggressive behavior, and in fact they do. The evidence is impressive and clear: the more media violence people, including children, view, the more aggressive they are likely to be (Anderson et al., 2003; Cantor et al., 2001). The relation between viewing TV violence and aggressive behavior is about as strong as the relation between smoking and cancer or between studying and academic grades (Bushman & Huesmann, 2010). If you watch a lot of violence, you are likely to become aggressive!
The evidence is so clear because it has come through the accumulation of many studies conducted over many years, using a variety of research designs. These studies have included laboratory and field experiments, as well as both cross-sectional and longitudinal correlational studies, and have included people from many different cultures. In the correlational studies, many potential common-causing variables, such as intelligence, family background, socioeconomic status, and personality, have been controlled for. The potential for reverse causation has been eliminated through studies that have shown that viewing violence at a young age tends to predict aggressive behavior when the child is older, more than the other way around. Furthermore, laboratory studies in which people have been randomly assigned to view either violent or nonviolent material have shown the same results (Paik & Comstock, 1994; Zillman & Weaver, 1999). In one recent study, Coyne, Archer, and Eslea (2004) found that adolescents who viewed either physical or nonphysical aggression were subsequently more likely to behave in an aggressive manner than those who viewed no aggression.
But why might viewing violence increase aggression? Perhaps the strongest possibility is also the simplest—that viewing violence increases the cognitive accessibility of violence. When we see violence, violence is then activated in memory and becomes ready to guide our subsequent thinking and behavior in more aggressive ways.
Worldwide, about 1,000 people are killed every day as a result of gun violence. Of these, about 560 are the result of criminal homicides, 250 are direct war deaths, 140 are suicides, and 50 are accidents (International Action Network on Small Arms, 2006). Although school and workplace shootings have been of particular concern in recent years, even people who keep guns in their home for protection are likely to be killed by that gun—particularly at the hands of a family member—and are also likely to kill themselves with it (Cummings, Koepsell, Grossman, Savarino, & Thompson, 1997; Wintemute, Parham, Beaumont, Wright, & Drake, 1999).
Although it is true that it is people and not the guns themselves that do the killing, principles of social psychology make it clear why possessing guns is so dangerous. Guns provide cues about violence, which makes it more likely that people will respond to provocation with aggression. In any particular situation of conflict or confrontation, we have several choices. We might try to escape the situation, we might confront the person in a nonviolent way, or we might choose to use violence. The presence of guns reminds us that we may respond with violence. When guns are around, violence is highly cognitively accessible, and this accessibility increases the likelihood of responding to provocation with violence.
Research has shown that the presence of guns provides a highly salient cue, which reminds us that aggression is a possible response to threat. Anderson, Benjamin, and Bartholow (1998) found that just having participants think about guns primed thoughts about aggression. But the link does not end there. In addition to priming aggressive thoughts and feelings, viewing handguns also increases violent behavior, particularly when we are provoked (Carlson, Marcus-Newhall, & Miller, 1990).
Another way that viewing violence increases aggression is through modeling. Children (and even adults) may simply imitate the violence they observe. Indeed, there is substantial evidence that people do copy the aggression that they read about or see in the media. For instance, when Belgian teenager Alisson Cambier spurned the romantic advances of her 24-year-old neighbor Thierry Jaradin, he excused himself only to return to the room wearing a ghostface costume and carrying two knives, which he used to stab her 30 times. He later admitted that the murder was premeditated and inspired by the horror film Scream. Research also has found strong evidence for copycat suicides. The rate of suicide in the general population increases significantly in the months after famous people, for instance Marilyn Monroe or Kurt Cobain, commit suicide (Phillips & Carstensen, 1986). In short, viewing violence teaches us how and when we should be aggressive.
Another outcome of viewing large amounts of violent material is desensitization, the tendency to become used to, and thus less influenced by, a stimulus. When we first see violence, we are likely to be shocked, aroused, and even repulsed by it. However, as we see more and more violence over time, we become habituated to it, such that subsequent exposures produce fewer and fewer negative emotional responses. In the end, we may begin to see violence as a normal part of everyday life and become accepting of it.
Read about some of the research that has been done on this topic. Pay close attention to the research methods used and think about how those methods may have influenced the results:
Little By Little, Violent Video Games Make Us More Aggressive (Time Magazine, 2014)
What Research Says About Video Games And Violence In Children (NPR, 2018)
Study Finds No Evidence That More Violent, Difficult Video Games Spur Aggression (Association for Psychological Science, 2019)
Do video games cause violence? (Discover, 2023)
Given that travel often has frustrating moments, it may not be surprising that there are aggressive behaviors while traveling. Road rage is aggressive or angry behavior exhibited by motorists. These behaviors include rude and verbal insults, yelling, physical threats or dangerous driving methods targeted at other drivers, pedestrians or cyclists in an effort to intimidate or release frustration. Road rage can lead to altercations, damage to property, assaults, and collisions that result in serious physical injuries or even death. Strategies include (but are not limited to) cutting motorists off, inappropriate honking, using obscene gestures, flipping off another driver, swerving, tailgating, brake checking, and attempting to fight. Air rage is aggressive or violent behavior on the part of passengers and crew of aircraft, especially during flight. Air rage generally covers both behavior of a passenger or crew member that is likely caused by physiological or psychological stresses associated with air travel, and when a passenger or crew member becomes unruly, angry, or violent on an aircraft during a flight. Excessive consumption of alcohol is often a cause. Aggression during travel can also occur as delay rage after your flight (or other mode of travel) has been delayed.
Some recent research has suggested that the class divisions on airplanes is a leading cause of air rage. Read more below:
DeCelles, K. A. & Norton, M. I. (2016). Physical and situational inequality on airplanes predicts air rage. Psychological and Cognitive Sciences, 113(20), 5588-5591.