Humans share aspects of aggression with non-human animals, and have specific aspects and complexity related to factors such as genetics, early development, social learning and flexibility, culture and morals. Konrad Lorenz stated in his 1963 classic,
On Aggression, that human behavior is shaped by four main, survival-seeking animal drives. Taken together, these drives—hunger, fear, reproduction, and aggression—achieve natural selection.
E. O. Wilson elaborated in
On Human Nature that aggression is, typically, a means of gaining control over resources. Aggression is, thus, aggravated during times when high population densities generate resource shortages. According to Richard Leakey and his colleagues, aggression in humans has also increased by becoming more interested in ownership and by defending his or her property. However,
UNESCO adopted the Seville
Statement of Violence in 1989 that refuted claims, by evolutionary scientists, that genetics by itself was the sole cause of aggression. Social and cultural aspects may significantly interfere with the distinct expression of aggressiveness. For example, a high population density, when associated with a decrease of available resources, might be a significant intervening variable for the occurrence of violent acts. However, Lawrence Keeley's 1996
War Before Civilization suggested that regular
warfare without modern technology was conducted by most groups throughout human history, including most
Native American tribes. Research on
hunter-gatherers has revealed a range of behavioral patterns. While aggression, conflict and violence can occur, direct confrontation is generally avoided, and disputes are often managed through various verbal and non-verbal social mechanisms. Different rates of aggression or violence—whether contemporary or historical—have been associated with social structures and environmental factors such as
resource distribution or
property acquisition,
land use,
subsistence strategies, and
population dynamics. American psychologist
Peter Gray hypothesizes that band hunter-gatherer societies are able maintain relatively
egalitarian and peaceful relationships through mechanisms such as fostering a pervasive
playful spirit, the use of humor to deter dominance, and non-coercive, indulgent child-rearing practices. Gray likens hunter-gatherer bands to social play groups, while stressing that such play is not frivolous or even easy at all times. According to Gray, "Social play—that is, play involving more than one player—is necessarily egalitarian. It always requires a suspension of aggression and dominance along with a heightened sensitivity to the needs and desires of the other players". Joan Durrant of the
University of Manitoba reports that multiple studies have found an association between
physical punishment and higher levels of aggression directed toward parents, siblings, peers, and spouses, even when controlling for other influencing factors. Similarly,
Elizabeth Gershoff of the
University of Texas at Austin has found that the more frequently children experience physical punishment, the more likely they are, as adults, to engage in violent behavior toward family members, including intimate partners. In countries where the physical punishment of children is more culturally accepted, its association with increased aggression tends to be weaker. However, research indicates that physical punishment predicts some increase in child aggression regardless of cultural context. Although these associations do not establish
causality, a number of
longitudinal studies suggest that experiencing physical punishment can have a direct causal impact on later aggressive behavior. Similar findings were reported in a 2010 study led by Catherine Taylor at
Tulane University, which identified a link between maternal spanking of three-year-old children and an increased risk of later aggressive behavior. Family violence researcher
Murray A. Straus contends that such evidence has often been overlooked, largely due to a prevailing belief that spanking is more effective than nonviolent forms of discipline. He warns, however, that this belief persists despite evidence of harmful side effects. Cultural and political interpretations of aggression are further complicated by the subjective use of the term "aggressive", which may reflect value judgments depending on the observer's cultural or ideological standpoint. Whether a coercive or violent act is viewed as aggression—or as legitimate or illegitimate aggression—often depends on the social positions of those involved relative to their culture's structure. Relevant factors may include: norms governing coordination and resource distribution; definitions of self-defense and provocation; attitudes toward outsiders and marginalized groups such as women, disabled individuals, or people of lower status; the presence of alternative conflict resolution mechanisms; levels of trade interdependence and participation in
collective security pacts; and broader material or social objectives.
Cross-cultural research has found differences in attitudes towards aggression in different cultures. In one questionnaire study of university students, in addition to men overall justifying some types of aggression more than women, United States respondents justified defensive physical aggression more readily than Japanese or Spanish respondents, whereas Japanese students preferred direct verbal aggression (but not indirect) more than their American and Spanish counterparts. Within American culture, men from the
southern United States were found in a study of university students to react more strongly and respond more aggressively than their northern counterparts when randomly insulted after being bumped into. This behavior was theorized to reflect a traditional
culture of honor prevalent in the Southern United States, associated with concepts such as "
saving face." Other cultural frameworks frequently considered in aggression research include contrasts between
individualistic and
collectivist orientations. These may influence how individuals respond to disputes—for example, through open competition or by accommodating others and
avoiding conflict. In a study including 62 countries, school principals reported higher levels of aggressive student behavior in cultures characterized as more individualistic and, correspondingly, less collectivist. Other cross-cultural comparisons related to aggression and conflict have examined differences between
democratic and
authoritarian political systems, as well as between
egalitarian and
stratified societies. Finally, the perceived legitimacy of aggressive acts are influenced by cultural and political attitudes regarding the social acceptability of certain actions or targets. These perceptions are often contested, particularly in cases involving religion or international disputes. One prominent example is the
Arab–Israeli conflict, where acts labeled as aggression by one group may be framed as defense or resistance by another.
Media Some researchers argue that behaviors such as aggression may be partially learned through observation and imitation of others, a concept rooted in social learning theory. This perspective includes the view that exposure to media violence may exert small effects on aggressive behavior. However, this remains a subject of ongoing debate, and other scholars have challenged the strength or consistency of such effects. For example, a prospective study of adolescents found no long-term relationship between violent video game use and subsequent youth violence or bullying. A meta-analysis concluded that the effect of violent video games on aggression is generally smaller than that found in studies on
television violence. The magnitude of this effect was positively associated with the intensity of violent content and
negatively associated with the amount of time spent playing. The study concluded that the available evidence was insufficient to establish a causal relationship between violent video games and increased aggression. Conversely, other research has reported associations between violent video game exposure and heightened aggressive thoughts, feelings, and behaviors both in laboratory settings and real-life contexts.
Children The frequency of physical aggression in humans peaks at around 2–3 years of age. It then declines gradually on average. These observations suggest that physical aggression is not only a learned behavior but that development provides opportunities for the learning and biological development of self-regulation. However, a small subset of children fail to acquire all the necessary self-regulatory abilities and tend to show atypical levels of physical aggression across development. They may be at risk for later violent behavior or, conversely, a lack of aggression that may be considered necessary within society. However, some findings suggest that early aggression does not necessarily lead to aggression later on, although the course through early childhood is an important predictor of outcomes in middle childhood. In addition, physical aggression that continues is likely occurring in the context of family adversity, including socioeconomic factors. Moreover, 'opposition' and 'status violations' in childhood appear to be more strongly linked to social problems in adulthood than simply aggressive antisocial behavior. Social learning through interactions in early childhood has been seen as a building block for levels of aggression which play a crucial role in the development of peer relationships in middle childhood. Overall, an interplay of biological, social and environmental factors can be considered. Some research indicates that changes in the weather can increase the likelihood of children exhibiting deviant behavior.
Typical expectations • Young children preparing to enter kindergarten need to develop the socially important skill of being
assertive. Examples of assertiveness include asking others for information, initiating conversation, or being able to respond to
peer pressure. • In contrast, some young children use aggressive behavior, such as hitting or biting, as a form of communication. • Aggressive behavior can impede learning as a skill deficit, while assertive behavior can facilitate learning. However, with young children, aggressive behavior is developmentally appropriate and can lead to opportunities of building conflict resolution and communication skills. • By school age, children should learn more socially appropriate forms of communicating such as expressing themselves through verbal or written language; if they have not, this behavior may signify a disability or developmental delay.
Aggression triggers •
Physical fear of others •
Family difficulties •
Learning,
neurological, or
conduct/behavior disorders •
Psychological trauma The
Bobo doll experiment was conducted by Albert Bandura in 1961. In this work, Bandura found that children exposed to an aggressive adult model acted more aggressively than those who were exposed to a nonaggressive adult model. This experiment suggests that anyone who comes in contact with and interacts with children can affect the way they react and handle situations. ;Summary points from recommendations by national associations: •
American Academy of Pediatrics (2011): "The best way to prevent aggressive behavior is to give your child a stable, secure home life with firm, loving discipline and full-time supervision during the toddler and preschool years. Everyone who cares for your child should be a good role model and agree on the rules he's expected to observe as well as the response to use if he disobeys." •
National Association of School Psychologists (2008): "Proactive aggression is typically reasoned, unemotional, and focused on acquiring some goal. For example, a bully wants peer approval and victim submission, and gang members want status and control. In contrast, reactive aggression is frequently highly emotional and is often the result of biased or deficient cognitive processing on the part of the student."
Gender Gender is a factor that plays a role in both human and animal aggression. Males are historically believed to be generally more physically aggressive than females from an early age, and men commit the vast majority of murders (Buss 2005). This is one of the most robust and reliable behavioral sex differences, and it has been found across many different age groups and cultures. However, some
empirical studies have found the discrepancy in male and female aggression to be more pronounced in childhood and the gender difference in adults to be modest when studied in an experimental context. When considering indirect forms of non-violent aggression, such as
relational aggression and
social rejection, some scientists argue that females can be quite aggressive, although female aggression is rarely expressed physically. An exception is
intimate partner violence that occurs among couples who are engaged, married, or in some other form of intimate relationship. Although females are less likely than males to initiate physical violence, they can express aggression by using a variety of non-physical means. Exactly which method women use to express aggression is something that varies from culture to culture. On
Bellona Island, a culture based on male dominance and physical
violence, women tend to get into conflicts with other women more frequently than with men. When in conflict with males, instead of using physical means, they make up songs mocking the man, which spread across the island and humiliate him. If a woman wanted to kill a man, she would either convince her male relatives to kill him or hire an assassin. Although these two methods involve physical violence, both are forms of indirect aggression, since the aggressor herself avoids getting directly involved or putting herself in immediate physical danger. See also the sections on
testosterone and
evolutionary explanations for gender differences above.
Situational factors There has been some links between those prone to violence and their alcohol use. Those who are prone to violence and use alcohol are more likely to carry out violent acts. Alcohol impairs judgment, making people much less cautious than they usually are (MacDonald et al. 1996). It also disrupts the way information is processed (Bushman 1993, 1997; Bushman & Cooper 1990). Recent research further demonstrates that in everyday situations, violations of social norms can be perceived as provocations that trigger aggression, experimental evidence shows that physical provocation affects the internal state (cognition, arousal, and affect) of the provoked person and shapes their responses. Pain and discomfort also increase aggression. Even the simple act of placing one's hands in hot water can cause an aggressive response. Hot temperatures have been implicated as a factor in a number of studies. One study completed in the midst of the civil rights movement found that riots were more likely on hotter days than cooler ones (Carlsmith & Anderson 1979). Students were found to be more aggressive and irritable after taking a test in a hot classroom (Anderson et al. 1996, Rule, et al. 1987). Drivers in cars without air conditioning were also found to be more likely to honk their horns (Kenrick & MacFarlane 1986), which is used as a measure of aggression and has shown links to other factors such as generic symbols of aggression or the visibility of other drivers. Frustration is another major cause of aggression. The
Frustration aggression theory states that aggression increases if a person feels that he or she is being blocked from achieving a goal (Aronson et al. 2005). One study found that the closeness to the goal makes a difference. The study examined people waiting in line and concluded that the 2nd person was more aggressive than the 12th one when someone cut in line (Harris 1974). Unexpected frustration may be another factor. In a separate study to demonstrate how unexpected frustration leads to increased aggression, Kulik & Brown (1979) selected a group of students as volunteers to make calls for charity donations. One group was told that the people they would call would be generous and the collection would be very successful. The other group was given no expectations. The group that expected success was more upset when no one was pledging than the group who did not expect success (everyone actually had horrible success). This research suggests that when an expectation does not materialize (successful collections), unexpected frustration arises which increases aggression. There is some evidence to suggest that the presence of violent objects such as a gun can trigger aggression. In a study done by
Leonard Berkowitz and Anthony Le Page (1967), college students were made angry and then left in the presence of a gun or badminton racket. They were then led to believe they were delivering electric shocks to another student, as in the
Milgram experiment. Those who had been in the presence of the gun administered more shocks. It is possible that a violence-related stimulus increases the likelihood of aggressive cognitions by activating the
semantic network. A new proposal links military experience to anger and aggression, developing aggressive reactions and investigating these effects on those possessing the traits of a serial killer. Castle and Hensley state, "The military provides the social context where servicemen learn aggression, violence, and murder."
Post-traumatic stress disorder (PTSD) is also a serious issue in the military, also believed to sometimes lead to aggression in soldiers who are suffering from what they witnessed in battle. They come back to the civilian world and may still be haunted by flashbacks and nightmares, causing severe stress. In addition, it has been claimed that in the rare minority who are claimed to be inclined toward serial killing, violent impulses may be reinforced and refined in war, possibly creating more effective murderers.
As a positive adaptation theory Some recent scholarship has questioned traditional psychological conceptualizations of aggression as universally negative. From this alternate view, although the recipient may or may not be harmed, the perceived intent is to increase the status of the aggressor, not necessarily to harm the recipient. Such scholars contend that traditional definitions of aggression have no validity because of how challenging it is to study directly. From this view, rather than concepts such as assertiveness, aggression, violence and criminal violence existing as distinct constructs, they exist instead along a continuum with moderate levels of aggression being most adaptive. ==See also==