Aggression


 * ''For other usage, see Aggression (war crime)

In psychology and other social and behavioral sciences, aggression refers to behavior that is intended to cause harm or pain. Aggression can be either physical or verbal. Behavior that accidentally causes harm or pain is not aggression. Property damage and other destructive behavior may also fall under the definition of aggression. Aggression is not the same thing as assertiveness.

Types of aggression
Aggression is a complex phenomenon that is composed of a number of more specific types of behavior.

Moyer Classification
Moyer (1968) presented an early and influential classification of seven different forms of aggression, from a biological and evolutionary point of view.


 * 1) Predatory aggression: attack on prey by a predator.
 * 2) Inter-male aggression: competition between males of the same species over access to resources such as females, dominance, status, etc.
 * 3) Fear-induced aggression: aggression associated with attempts to flee from a threat.
 * 4) Irritable aggression: aggression induced by frustration and directed against an available target.
 * 5) Territorial aggression: defence of a fixed area against intruders, typically conspecifics.
 * 6) Maternal aggression: a female's aggression to protect her offspring from a threat. Paternal aggression also exists.
 * 7) Instrumental aggression: aggression directed towards obtaining some goal, considered to be a learned response to a situation.

Current
Currently, there is a consensus in the scientific community for at least two broad categories of aggression, variously known as hostile, affective, or retaliatory aggression, versus instrumental, predatory, or goal-oriented aggression. Empirical research indicates that this is a critical difference, both psychologically and physiologically. Some research indicates that people with tendencies toward affective aggression have lower IQs than those with tendencies toward predatory aggression.

Biology of aggression
Aggression is directed to and often originates from outside stimuli, but has a very distinct internal character. Using various techniques and experiments, scientists have been able to explore the relationships between various parts of the body and aggression.

Aggression in the brain
Many researchers focus on the brain to explain aggression. Scientisists have discovered at least two areas that directly regulate or affect aggression. The amygdala has been shown to be an area that causes aggression. Stimulation of the amygdala results in augmented aggressive behavior, while lesions of this area greatly reduce one's competitive drive and aggression (Bauman et al 2006). Another area, the hypothalamus, is believed to serve a regulatory role in aggression. The hypothalamus has been shown to cause aggressive behavior when electrically stimulated but more importantly has receptors that help determine aggression levels based on their interactions with the neurotransmitters serotonin and vasopressin. In a non-mammalian example, a gene called fruitless that is found in fruit flies can be mutated to cause males flies to fight more like females, and vice versa.

Neurotransmitters and hormones
Various neurotransmitters and hormones have been shown to correlate with aggressive behavior. The most often mentioned of these is the hormone testosterone. Testosterone has been shown to correlate with aggressive behavior in mice and in some humans, but in contrast to some long-standing theories, various experiments have not shown a relationship between testosterone levels and aggression in humans. The possible correlation between testosterone and aggression could explain the "roids rage" that results from anabolic steroid use.

Another chemical messenger with implications for aggression is the neurotransmitter serotonin. In various experiments, serotonin was shown to have a negative correlation with aggression (Delville et al. 1997). This correlation with aggression helps to explain the aggression-reducing effects of selective serotonin reuptake inhibitors such as fluoxetine (Delville et al. 1997), aka prozac.

While serotonin and testosterone have been the two most researched chemical messengers with regards to aggression, other neurotransmitters and hormones have been shown to relate to aggressive behavior. The neurotransmitter vasopressin causes an increase in aggressive behavior when present in large amounts in the anterior hypothalamus (Delville et al. 1997). The effects of norepinephrine, cortisol, and other neurotransmitters are still being studied.

Genetics and aggression
Another biological question concerning aggression is that of its heritability. While the exact amount of influence that genetics have is still questioned, studies on animals have shown that a tendency towards aggression is at least partly inherited.

Evolution of aggression
Like most behaviors, aggression can be examined in terms of its ability to help an animal reproduce and survive. Animals may use aggression to gain and secure territories, as well as other resources including food, water, and mating opportunities. Researchers have theorized that aggression and the capacity for murder are products of our evolutionary past.

Aggression against outsiders
The most apparent type of aggression is that seen in the interaction between a predator and its prey.

An animal defending itself against a predator becomes aggressive in order to survive and to ensure the survival of its progeny. Because aggression against a much larger enemy or group of enemies would lead to the death of an animal, animals have developed a good sense of when they are outnumbered or outgunned. This ability to gauge the strength of other animals gives animals a “fight or flight” response to predators; depending on how strong they gauge the predator to be, animals will either become aggressive or flee.

The need to ensure the continuation of one’s genes leads to a phenomenon known as altruism. An example of an altruistic act is the alarm call that is given when a predator is approaching. While this call will inform the community of a predator’s presence, it will also inform the predator of the whereabouts of the animal that gave the alarm call. While this would appear to give the alarm caller an evolutionary disadvantage, it would facilitate the continuation of this animal’s genes because it's relatives and progeny would be more able to avoid predators.

According to many researchers, predation is not aggression. Cats do not hiss or arch their backs when in pursuit of a rat, and the active areas in their hypothalamuses are more similar to those that reflect hunger than those that reflect aggression.

Aggression within a species
Aggression against conspecifics serves a number of purposes having to do with breeding. One of the most common of these purposes is the establishment of a dominance hierarchy. When certain types of animals are first placed in a common environment, the first thing they do is fight to assert their role in the dominance hierarchy. In general, the more dominant animals will be more aggressive than their subordinates. . The majority of conspecific aggression ceases about 24 hours after the introduction of the species tested.

In establishing itself in a dominance hierarchy, an animal also sets its attractiveness. In a variety of species, a high social ranking means more and healthier mates. Thus, while aggression carries the risk of wounding the animal it benefits the animal by giving its progeny healthier genes if it is successful in the hierarchy (Dewsbury 1982).

Once a female has given birth to an offspring, this female develops maternal aggression. This maternal aggression is directed mainly at conspecifics and is believed to be intended to prevent the mother’s offspring from harassment by other individuals (Maestripieri 1992). Maternal aggression is especially strong and often leads to the mother driving away even male conspecific intruders (Figler et al. 1995).

Aggression in humans
Although humans are similar to non-human animals in some aspects of aggression, they differ from most of these animals in the complexity of their aggression because of factors such as culture, morals, and social situations. A wide variety of studies have been done on these situations. Alcohol, drugs, pain and discomfort, frustration, and violence in media are just a few of the factors that influence aggression in humans.

Aggression and culture
Culture is a distinctly human factor that plays a role in aggression. Anthropological research has found that some cultures are relatively low on aggression, such as the Kung Bushmen, who were described as the "harmless people" by Elizabeth Marshall Thomas (1958). Other researchers, however, have countered this point of view, calculating that the homicide rate among Bushmen is actually higher than that of most modern industrial societies (Keeley, 1996). Lawrence Keeley argues that the "peaceful savage" is a myth that is unsupported by the bulk of anthropological and archeological evidence. Hunter gatherer societies do not have possessions to fight over, but they may still come to conflict over status and mating opportunities.

Empirical cross-cultural research has found differences in the level of aggression between cultures. In one study, American men resorted to physical aggression more readily than Japanese or Spanish men, whereas Japanese men preferred direct verbal conflict more than their American and Spanish counterparts (Andreu et al. 1998). Within American culture, southerners were shown to become more aroused and to respond more aggressively than northerners when affronted (Bowdle et al. 1996). There is also a higher homicide rate among young white southern men than among white northern men in the United States (Nisbett 1993).

Aggression in media
Behaviors like aggression can be learned by watching and imitating the behavior of others. A considerable amount of evidence suggests that watching violence on television increases the likelihood of violent behavior in children (Aronson, Wilson, & Akert, 2005), though for a dissenting viewpoint, see Freedman (2002). Individuals may differ in how they respond to violence. The greatest impact is on those who are already prone to violent behavior. Adults may be influenced by violence in media as well. A long-term study of over 700 families found "a significant association" between the amount of time spent watching violent television as a teenager and the likelihood of committing acts of aggression later in life. The results remained the same in spite of factors such as family income, parental education and neighborhood violence (Aronson, Wilson, & Akert, 2005).

Although exposure to violence in media is associated with the risk for violent behavior, none of these studies provide evidence for a definitive causal mechanism. Instead, violence in media may be one of many factors, or it may play a maintenance role since violent media tend to be selected by people who are prone to violence.

Situational factors
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). A drunk person is much more likely to view an accidental event as a purposeful one, and therefore act more aggressively. Pain and discomfort also increase aggression. Even the simple act of placing ones hands in cold 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).

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, a group of students were collecting donations over the phone. Some of them were 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 with high expectations was much more upset and became more aggressive when no one was pledging (Kulik & Brown 1979).

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.

Aggression and gender
Gender is a factor that plays a role in both human and animal aggression. Males are generally more aggressive than females (Coi & Dodge 1997, Maccoby & Jacklin 1974), 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. There is evidence that males are quicker to aggression (Frey et al 2003) and more likely than females to express their aggression physically (Bjorkqvist et al. 1994). However, some researchers have suggested that females are not necessarily less aggressive, but that they tend to show their aggression in less overt, less physical ways (Bjorkqvist et al. 1994, Hines and Saudino 2003). For example, females may display more verbal and relational aggression, such as social rejection.

Aggression in children
The frequency of physical aggression in humans peaks at around 2-3 years of age. It then declines gradually on average (Tremblay 2000). These observations suggest that physical aggression is mostly not a learned behavior and that development provides opportunities for the learning of self-regulation. However, a small subset of children fails to acquire the necessary self-regulatory abilities and tends to show atypical levels of physical aggression across development (Bongers et al. 2004; National Institute of Child Health and Human Development Early Child Care Research Network 2004). These may be at risk for later violent behavior.


 * What is typically expected of children?
 * 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.
 * 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


 * What triggers aggressive behavior in children?
 * Physical fear of others
 * Family difficulties
 * Learning, neurological, or conduct/behavior disorders
 * Emotional trauma
 * Exposure to violence on television, film or other media sources.


 * Summaries of best practice recommendations

(1) American Academy of Pediatrics : 'Set firm, consistent limits to help children self monitor emotions and behavior; make sure all care takers agree to the same limits. Provide examples of effective and socially acceptable ways of managing anger; be careful not to reinforce aggression with aggressive forms of punishment. Also, model acceptable behavior as a caretaker by managing your own temper. Remember that occasional outbursts are normal. If aggressive behavior continues for more than a few weeks, consult a pediatrician or mental health professional.'

(2) National Association of School Psychologists: 'Overly aggressive behavior can signify a social skills deficit; direct instruction, modeling, and coaching can help children acquire the skill of assertion, which as a replacement behavior may help prevent aggressive behavior.' (NASP Best Practices in School Psychology 2002):

War and sports
Two basic models of the relationship between war and sports have been identified: the drive discharge model and the culture pattern model. According to the drive discharge model, tendency towards aggression is innate, a buildup of aggressive tension causes warfare, and warlike sports make war less likely by providing an alternative outlet for aggressive tension. The culture pattern model holds that the intensity and configuration of aggressive behavior is acquired from the surrounding culture, aggression levels are consistent across multiple areas of a culture, and behaviors and attitudes concerning war tend to match those concerning warlike sports. The drive discharge model suggests that levels of aggression do not vary across societies, although the type of aggressive behavior can vary, with an inverse relationship between the propensity to war and to warlike sports. The culture pattern model predicts that levels of aggression vary across societies, with a direct relationship between the propensity to war and to warlike sports.