Aggression

Reactive aggression

  • in response to perceived threat, impulsive accompanied with physiological arousal.

Neural and hormonal mechanisms in aggression

Proactive aggression

  • response in anticipation of a rewards, planned method of getting what you want.

Serotonin works on the frontal area (orbital frontal cortex) of the brain to inhibit the firing of the amygdala which controls fear and aggression. Serotonin has a calming effect therefore low levels of serotonin means that people can’t control their impulsive and aggressive behaviour. reduce firing of neurons and self control. Serotonin also regulates the prefrontal cortex therefore lower levels of serotonin affect our responses to external stimuli this causes the person to become aggressive easily and prevents them from responding in a “normal” way such as they can’t anticipate risk so consequently the impulsively engage in aggressive behaviour.

Research questioning serotonin in aggression, Ferrari et al allowed adult male rats to fight with another rat at a specific time for 10 days. On the 11th day, the rat wasn’t allowed to fight. However, they found that the rats' dopamine levels had risen by 65% and their serotonin levels were reduced by 35%. Even though the rat was not fighting, the experience had changed its brain chemistry. This research raises the question of whether low levels of serotonin causes aggression or whether they are an effect of aggression. The rats were assessed after fighting so it is difficult to establish cause and effect. If lower levels of serotonin are the effect of aggression, rather than the cause, then this substantially lowers the validity of the explanation as to the cause of aggression. Nevertheless, Ferraris research clearly demonstrates the complexity of the role of serotonin in aggression.


Mann et al administered a drug which depletes serotonin in the brain to 35 healthy adults. They used a questionnaire to assess hostility and aggression levels, which rose following the administration of the drug amongst males, but not amongst females. This research supports the role of serotonin in aggression as when participants' serotininlebels were lowered they became more aggressive. However Manns research demonstrates the issue of beta bias which is common in neural explanations of aggression. This shows that males and females may not be subject to the same physiological factors when explaining aggression. Therefore, we should be cautious when generalising this research. Social desirability bias also be present during the questionnaire as participants may lie.

Testosterone is a male androgen involved in the development of male characteristics and affects brain structure. Testosterone levels peak in adolescence. Males are generally more aggressive than females, they have higher testosterone levels. It inhibits serotonin production and transmission, high testosterone means low serotonin therefore low inhibitors and more aggressive behaviour.

Research that shows a link between testosterone and aggression is animal research conducted by Wagner. He found low levels of aggression in male mice after castration, and that their aggression returned to pre-castration levels after testosterone injections. This supports the theory of testosterone because when testosterone was removed there were reduced levels of aggression as serotonin levels increased (low level aggression) when testosterone was added it caused aggression and increased the levels. This could be due to the inhibition of serotonin and linked to high aggression.

One problem with hormonal explanations of aggression is that it is gender bias. The explanation is androcentric as it only explains male aggression and male testosterone levels. It also demonstrates alpha bias as testosterone is linked to males and this explanation over exaggerates male aggression and tends not to explain females. It also does not display a direct link to humans, a human is far more complicated than a rat due to having many other factors explaining the aggression levels which is not explained during this. The explanation is too simplified and ignores complex human biology. Nevertheless, Nelson found a correlation between the level of androgens circulating in the body and aggressive behaviour in male and female prisoners. Therefore showing that high levels of testosterone in both sexes is linked with aggression, increasing the validity of the hormonal mechanisms. Testosterone was only collected after si it is difficult to establish cause and effect as there is no baseline. We don’t know if aggression produces testosterone or results in aggression. Prisoners are not typical of the population so it is difficult to generalise to the whole population.

The limbic system is a part of the brain consisting of a number of connected areas, situated deep inside the brain. It connects the cingulate gyrus, which is responsible for focussing attention on emotionally significant events. It also has connections to the prefrontal cortex (PFK) which is involved in forward planning and anticipation of reward. The PFK regulates social behaviours and aggressive responses, so if damaged reduces the inhibition of the amygdala which is associated with higher levels of aggression. It has key roles in how an organism responds to environmental threats and challenges and thus is believed to be a key factor in whether we respond aggressively or not to an external stimulus.

Research that supports the limbic system is Kluver & Bucky (1939). They examined Rhesus monkeys after the removal of the main parts of the limbic system, including the amygdala, hippocampus and surrounding cortical areas. They found the monkeys had an absence of emotional reactions normally associated with stimuli or situations that elicit fear and anger. They lost social understanding of hierarchies and would fight more dominant larger monkeys. When the monkeys had the main parts of the limbic system removed they had a loss of control (emotional change) causing them to have no fear and react aggressively to more dominant monkeys.

However animal research can’t be extrapolated to compare to humans, we are physiologically different. Monkeys act based on singing and social survival of the fittest, humans act based on complicated emotions and social norms, monkeys brains differ from humans.

General problems with research into neural and hormonal influences in general are that research may demonstrate a correlation between 2 variables (e.g. serotonin and aggression) but it risks over simplifying the mechanisms involved. This is because other factors which may influence or cause aggression are overlooked. This means that the neural and hormonal regulation of it are more complex than our current understanding suggests. Therefore the research tends to follow a reductionist approach.

Ethnological explanations

The amygdala is important in the perceptions of emotions and control of aggressive responses through modulating other brain areas, how human/animal respond to threat and challenges.

Zagrodzka et al examined cats and found that damage to their amygdala contributed to predatory behaviours and attacks. This clearly supports the role of amygdala in aggression shows as it shows when it is damaged there is reduced control of aggressive responses. Yet a problem with animal research is the difficulty of extrapolating the research to humans.

However there is supporting evidence from Wong et al, human participants had compared MRI scans of 19 violent male criminals with 20 ‘normal’ controls. They found the criminals had significantly reduced size amygdala , smaller size was increased aggressive behaviours. A problem with this may be there is no baseline size, restricted male sample, beta bias, already violent and lacks populational validity.

Nevertheless Wong prodvides evidence that the amygdala plays a role in human aggression as well. Although there is uncertainty although there is uncertainty to the exact role due to differences between many studies, but evidently important.

Ethological explanations seek to understand the innate behaviours of animals by studying them in their natural environment. Their focus is to try to account for behaviour in terms of its adaptive value to specific species. Ethologists state aggression can help survival as it protects: resources, hierarchy/dominance, mates.

Lorenz states aggression is often ritualistic, in social animals, they tend to inflict relatively little harm to others. Ritualistic (or symbolic) aggression is more adaptive than direct aggression, as it means the animal is not harmed. As if they are harmed, it could affect their survival - reproduction or even death. Therefore, signs of aggression (ritualistic) would deter the opponent without physical harm = more adaptive behaviour. Examples: bearing teeth, drawing claws, arching back, standing tall.

Ritualistic aggression is used to assert power and maintain status. Done through a series of escalating signalling which are very rarely physical. The escalation ends when one displays an appeasement gesture, which shows acceptance of defeat and inhibits aggression in victor. Eg wolves expose their jugular vein.
The ethological explanation proposes that aggression is a result of an evolved automatic biological response in the brain.

Genetic explanations of aggression

MOAO gene*
Associated with increased aggressiveness, produces and controls Monoamine Oxidase A, an enzyme that is involved in the breakdown of the nuerotransmitters serotonin, dopamine and noradrenaline is synapses. If the gene is defective, the production of the enzyme is low thus resulting in a buildup of neurotransmitters. If serotonin does not get broken down properly it means that the brain ends up being bathed in such high levels of serotonin that it becomes desensitised. As a result the inhibitory effect that is usually associated with excess serotonin is lost meaning more impulsive and aggressive behaviour.

Twin studies

Twin studies

Coccaro et al used a questionnaire designed to measure hostility in order to assess aggressive tendencies in 182 MZ and 118 DZ twins. For aggressive behaviour defined as direct physical assault, they found concordance rates of 50% for MZ and 19% for DZ. For verbal aggression, MZ = 28%, DZ = 7%.

What does this show? supports genetic factors in aggression as M2 twins who share 100% of the same genes have higher concordance rate than d2 twins showing that behaviour/ aggressive characteristics are inherited.

AO3: questionnaire: may lie- social desirability bias concordance rates not 100% so not purely genetic. higher concordance rates in M2 could be an unusually closer relationship- so more influential on each other's behaviour. (SLT)- learnt behaviour. They also share the same upbringing so it is difficult to violate the role of genetics and environment. Following genetics ignores the role the environment plays.

Case study

Brunner studied a large Dutch family whose male members had a history of violence and aggression. They found that many of the males had a faulty MAOA gene, which resulted in higher than normal levels of serotonin. Thus suggesting that abnormal MAOA activity is associated with aggression. However, female members of the family were not affected by mutation.

The MAOA gene is carried on the x chromosome, as Fs have two Xs, if they did possess the dysfunctional MAOA gene their functional MAOA gene from corresponding x chromosome would be dominant. Therefore, this questions the validity of the MAOA gene explanation in aggression as may only explain male aggression. – beta bias

Frazzetto et al found an association between higher levels of aggression and low MAOA activity in males, but only in those who had experienced significant trauma (abuse) in the first 15 years. Those who didn’t experience trauma but had low MAOA activity did not have higher levels of aggression in adulthood.
This highlights that research into genetic explanations of aggression are inconclusive. The research clearly shows there is a link between genes and aggression but it is not a definite link. Frazzetto’s study suggests that genetics interact with environmental factors to influence aggression levels. Therefore, the diathesis stress model may be a more comprehensive explanation of aggression, as this suggests it is the combination of biology (faulty MAOA gene) and environment (abuse) that influences behaviour. This combination of nature and nurture produces the complex behaviour of aggression. Highlights the relative contribution of heredity and environment.

Evolutionary explanations in aggression

Examines how behaviours that were adaptive to our human ancestors are passed down through genetic transmission from one generation to the next.
- Buss and Duntley suggested several adaptive functions of aggression: 1. Retaining a mate, 2. Gaining status, 3. Acquiring resources.
- These behaviours ensured survival and increased their reproductive opportunities, males use aggression to eliminate competition for females.
- More likely to survive if aggression is displayed as protecting mates and would sexually attract potential females.
- It allowed ancestors to establish hierarchical dominance within a group, this can lead to greater resources in general.

  • Sexual jealousy is a major motivator for aggression, they can never be sure if they are the father as fertilisation of the egg is hidden from them, could result in cuckholdery which is a waste of resources, investment of males resources ensures the survival of his rival genes, ‘father’ has fewer resources for own offspring. To prevent cuckholdery jealousy leads to aggression in the form of domestic violence which will discourage females form cheating on their mate.
  • Males have evolved to use male retention strategies Wilson and Daly identified these strategies which involve aggression and even physical violence:
  1. Direct guarding -male violence over partners behaviour e.g. checking phone, coming home early, tracking
  2. Negative inducements - issuing threats of dire consequences for infidelity e.g. ill keep the kids if you cheat.

Shackleford studied Intimate partner violence I.V in heterosexual couples. Males and Females in 207 married couples completed questionnaires. Males answered the Mate Retention Inventory (assessed MR behaviours) and females answered the Spouse Infuence Report (assessed partner's violence). Shackleford found a strong positive correlation between males reports of retention Strategies Shackleford found a strong, post hackeford believed retention behaviour reliably.

  • This research supports the evolutionary explination that grgressive males use mate retention strategies but it is not conclusive tat the strategies are an avolved haviour. The bhaviour may have been learned rather than innate. Domestic violence has become less cosmically acceptable than 100 years ago, this demonstrates the effect of culture and learning. Individuals demonstrating strategies may have learned them from role models and slt could be a valid explination, difficult to separate the effect of nature and nurture.

A strength of evolutionary explanations is that there is research support for the link between aggression and status. Daly and Wilson found that many tribal societies bestow increased status and honour to men who have committed murder. This phenomenon is also evident in Western societies such as the US, where the most violent gang members often have the highest status among their peers (Campbell). This supports evolutionary explanations of aggressions as it suggests that not only is aggression an important way of gaining status among males, but it is also a consequence of threats to that status.

Gender differences in aggression may be better explained by socialisation. Researchers argue that differences in the aggressive behaviour of males and females may also be the product of different socialisation experiences. For example, Smetana found that parents are more likely to physically punish boys for bad conduct, whereas when girls misbehave, parents tend to explain to them why their actions were wrong. This, suggests researchers, could increase male physical violence. Girls may learn to adopt other more social forms of aggression (harming another's self-esteem) rather than physical. Therefore, this casts doubts on the claim that males alone have evolved aggression as a way of dealing with rivals, as females have simply developed a different form of aggressive behaviour.

Evolutionary explanations have been criticised for being difficult to test empirically, and therefore being unscientific. Explanations are based on understanding behaviour that came thousands of years ago, an understanding that is based on assumption rather than sound evidence. Additionally, evolutionary explanations are correlational, so only ever indicates a relationship between aggression and sexual jealousy, but it does not establish a cause; we cannot say for definite that sexual jealousy is the cause of male aggression. Furthermore, aggression is a complex behaviour that has many triggers and factors, and individuals vary considerably not only in their levels of aperession but also how they respond to it. Therefore, evolutionary explanations appear far too simplistic for such a complex behaviour.

Social learning theory applied to aggression

Aggression can be learned by the indirect mechanism of observational learning. Imitation, aggressive acts from a role model will be internalised and more likely reproduced, if rewarded a child sees an effective way of getting what they want. Also through vicarious reinforcement. Bandura proses 5 cognitive factors that mediate:

  1. Attention- watch
  2. Retention- placed in LTM
  3. Reproduction- physically capable to replicate
  4. Motivation-positive reinforcement for modelled behaviour
  5. Self-efficacy- must believe behaviour will attain a goal.
    Bandura believes imitation of family members is most prominent source of modelling, parents are role models (more likely for same gender)

Positive evaluation As shown in Bandura study within the three different conditions the child acted based off the reinforcement. During condition one the role model was positively reinforced the child retained and imitated, condition two with a negative reinforcement the child didn’t reproduce, during condition three no reinforcement. Condition one was the most aggressive behaviour was displayed, condition two with least. Boys were shown to have more aggressive behaviour than girls this supports the social learning theory of aggression as vicarious reinforcement showed aggression is learned through observation and imitation of a role model imitating behaviour.

Negative evaluation there is no baseline measure we don’t know home environments, lack of realism, not applicablee to real life as doll therefore no consequence or reaction. Reductionist and boys also have effect of testosterone.

Christianson (2006) studied the Kung San people and found aggressive behaviour was very rare in this society. Kung San parents do not use physical punishment and no value is placed on aggressive behaviour, so vicarious reinforcement is a rare experience. This supports the SLT as it suggests as there are no cultural norms for aggression, children do not display aggressive behaviour. Thus supporting that children learn aggressive behaviour through aggressive role models. However highlights SLT being complex and questions whether the SLT in relation to aggression may be appplied to western cultures, demonstrates an issue of culture bias.

Nevertheless, SLT can explain inconsistencies in individual's aggressive behaviour. Eg a young child may behave aggressively when out with friends, but not in school. SLT can explain this in terms of the consequences of acting aggressively in the two situations. When out with friends, aggressive acts may be more likely to receive positive consequences (eg status), whereas positive outcomes are less likely in school. Therefore, the expectation of consequences in each situation determines the likelihood of aggression being used. Consequently, ST allows us to predict whether or not aggression is likely in a particular situation.

Frustration-Aggression Hypothesis

Prosposed by Dollard et al, who stated that frustration always leads to aggression and aggression is always the result of frustration, based on psychodynamic approach of catharsis (process of releasing and thereby providing a relief from strong or repressed emotions)
- Views aggression as a psychological drive same as biological drives, when our goal is blocked by external factors it leads to frustration, it creates an aggressive drive therefore behaviours e.g. violent fantasy.
- Aggression is not always directed towards the source of frustration, cause is abstract e.g.economical situation of economy, cause is powerful and risk punishment, cause is unavailable. Therefore aggression is displayed onto an alternative that is available such as a inanimate object (phone) or younger sibling. The strength of aggression is determined by leve of frustration which depends on how much you want to reach the goal, how close you were and how big the setback, also the difference if the aggression is justified or unjustified.

Harris investigated people's reaction to when a confederate pushed in front of them in a queue. People displayed more aggression when they were close to the front than when they were near the back. People nearer the front would’ve been closer to their goal the wait already would’ve caused frustration, the people interfering by pushing in would’ve further increased the anger this is unjustified.

The FAH has real world applications as it can explain sports violence. Priks studied violent behaviour among Swedish football fans, he used teams/ changed position in the league as a measure of frustration and the number of objects thrown during a match as a measure of aggression. Priks found when a team performed worse than expected, its supporters threw more things onto the pitch, and were more likely to fight opposition supporters. A one position drop in the league led to a 5% increase in anti-social behaviour.

Aggression is also triggered by negative feelings (jealousy or pain), not just frustration, Reifman studied baseball games in the US and found that, as temperatures increased, so did the likelihood pitchers would display aggressive behaviour towards the batter. Furthemore, the outcome of frustration is not always aggression, e.g. failing a test may be frustrating but may lead to despair or determination. Therefore, the FAH may be inadequate as it may only explain how aggression arises in some situations but not all. Consequently a better explanation may be Berkowitz' revised frustration aggression hypothesis.

Berkowtiz gave participants the opportunity to shock a confederate, half the participants had been angered beforehand (given electric shocks), and the other half had not. There were 3 different conditions: one with an aggressive cue (a gun), a non aggressive cue (badminton racket), and no cue at all. Berkowtiz found those who were angered before and had an aggressive cue gave higher levels of shocks than those who had been angered but in presence of either other cue.