Aggression, PSYA3

Antisocial agression - aggresion that goes against the social norms. The intention to cause physical or psychological harm to another person. e.g. swearing, pushing

Prosocial aggression - aggression used to help others e.g. helping someone to fight off a mugger

Sanctioned aggression - aggression that is approved of e.g. soliders, sport, police

Overt aggression - aggression that we can see/hear

Covert aggression - aggression that is hidden e.g. thoughts & feelings

We learn aggressive behaviour through observation & imitation - 

People learn the specifics of aggressive behaviour and also its consequences by seeing others being rewarded or punished for their aggressive behaviour (vicarious reinforcement/learning)

By observing the consequences of aggression, they learn when it is and isn't appropriate.

There are four types of stages in SLT:

• Attention - how much attention is paid to the aggressive role model
• Retention - remembering (storing) the information observed
• Reproduction - copying (imitating) the behaviour
• Motivation - wanting to imitate the behaviour. This will depend upon the likelihood of reward.

We are more likely to imitate people who:

• Have authority
• Are similar to us (Duck) e.g. friends, siblings
• Have power
• Are more dominant e.g. celebrities, parents, teachers

The likelihood of a person behaving aggressively is determined by:

• Previous experience of aggression (was it successful?)
• The likelihood of reward or punishment. If the expectation of reward is greater than punishment, behaviour will be imitated.
• Self-efficacy - children must develiop confidence in their ability to successfully carry out the learned aggressive behaviours. Children who have been unsuccessful in their use of aggression in previous situations may develop less self-efficacy concerning their ability to use aggression & turn to other means of resolving conflict.

Bandura claimed that for SLT to take place, mental representations are required. The child must also represent possible rewards or punishments for their aggressive behaviour in terms of expectancies of future outcomes. 

Heusmann - children use aggressive TV models as scripts for their own behaviour. These scripts are stored & strengthed through repitition. 

Bandura divided 66 nursery school children into three groups. All three groups watched a film where an adult model kicked and punched a Bobo Doll.

• Condition 1: Children saw the adult model being rewarded by a second adult.
• Condition 2: Children saw a second adult telling off the adult model for the aggressive behaviour.
• Condition 3: The adult model was neither rewarded nor punished.

The children were then allowed to play in the room with the Bobo doll whilst experimenters watched through a one-way mirror. Results showed that children in Condition 1 behaved most aggressively, and those in Condition 2 behaved least aggressively. 

However, an important distinction must be made between learning & performance. All the children learnt how to behave aggressively, but those in Condition 2 did not perform as many acts until later, when they were offered rewards to do so. When this happened, they quickly showed that they had learned (acquired) as many aggressive techniques as the children in Condition 1.

- The study was only conducted on nursery school children and therefore the findings cannot be generalised to teenagers or adults.

- Exposing children to aggressive behaviour with the knowledge that they may reproduce it in their own behaviour raises ethical issues concerning protecting participants from psychological harm.

- The Bobo doll studies lack validity because children in these studies may well have been aware of what was expected of them and responded accordingly (i.e. they responded to demand characteristics). Noble supports this claim with a report that at least one child reported that "that's the doll we have to hit".

- Also the studies have focused on aggression towards a doll rather than a real person; howeber, Bandura carried out a study using an adult beating up a live clown. Children who observed this behaviour later did imitate the aggressive behaviour.

Strengths

• Explains cultural differences (IDA) - aggression is rare among the !Kung San people because parents do not reward physical aggression in children (lack of direct reinforcement), nor do they model aggression, therefore there is no motivation for children to act aggressively.
• Explains adult aggressive behaviour too - Philips found that SLT is not only restricted to the learn of aggressive behaviour in children. He found that daily homicide rates in the US almost always increased in the week following a major boxing match, suggesting viewers were imitating behaviour they had watched.
• Real-world application (IDA) - 2 year old Jamie Bulger was murdered by 2 boys ages 10 & 11. Prior to the murder they has watched 'Child's Play 3' horror film.
• Context-dependent aggression can be explained by SLT - people behaved differently in different situations because they have observed that aggression is rewarded in some situations and not in others, i.e. they learn behaviours that are appropriate to different contexts. This is a strengh of this theory in that it can predict whether aggressive behaviour is likely in any specific situation dependent on previous experience. 

Limitations

• Deterministic (IDA) - SLT is said to be deterministic as it suggests that children will imitate observed behaviours without logical thought (they don't choose to imitate so have no free will).
• Ethical issues in testing SLT (IDA) - Exposing children to aggressive behaviour knowing that they may imitate it raises ethical issues concerning protecting participants from psychological harm. As a result, experimental studies such as the Bobo doll studies would no longer be allowed. This means it is difficult to test experimental hypotheses about the social learning of aggressive behaviour in children.
• Runciman - rejects the claims of SLT and suggests that aggression is due to relative deprivation (feeling deprived of something you believe you should have)
• Imposed etic - SLT can be criticised for imposed etic because Bandura based his theory on Western societies and assumes that the process of learning is the same for all cultures which may not be the case.
• Biological approach (IDA) - the biological approach rejects that claims of SLT. High levels of testosterone are said to be one of the main causes of aggression. Premenstrual syndrome has been cited in criminal trials as a reason for aggressive behaviour. 

Zimbardo - when part of a relatively anonymous group, people lose their personal identity & their inhibitions about violence.

Based on LeBon's Crowd Theory - in a crowd, anonymity, suggestibility & contagion mean that a 'collective mind' is taken on. Individuals lose self control and often act in ways that go against person & social norms.

The nature of deindividuation is a psychological state characterised by lowered self-evaluation and decreased concerns about evaluation by others. This leads to an increase in behaviours that would normally be inhibited by personal or social nroms. The psychological state of deindividuation is aroused when individuals are in:

• Crowds or large groups
• Situations that increase anonymity
• A state of altered cosciousness (e.g. through drugs & alcohol)

They do not take responsibility for these acts - being anonymous makes them feel less accountable (there is a diffusion of responsibility).

People move from an individuated state to a deindividuated state when inhibitions concerning aggressive behaviour are removed. In large groups, the individual loses awareness of their individuality & feels faceless & anonymous. As a result, inner restraints are reduced and inhibited behaviours (such as aggression) are increased.

Prentice-Dunn et al believe that aggression in a group occurs due to reduced self-awareness, rather than simply anonymity.

Self-focused individuals act according to their own attitudes and moral standards and are therefore less likely to be aggressive.

However, those who have lost self-awareness submurge themselves in the group,a and therefore are less able to regulate their behaviour and therefore are more likely to be aggressive. 

Strengths

• Research support - Zimbardo divided undergraduates into two groups: One group was in a deindividuated condition (in lab coats & hoods) and the other group was in an individuated state (wearing normal clothing & wearing a name tag). Those in the deindividuated state shocked the 'learner' for twice as long as did those in an individuated state. 
• Real-world application - Mann used the concept of deindividuation to explain the behaviour of 'baiting crowds'. Suicide jumpers were encouragedto jump when crowds were under conditions of deindividuation (e.g. large crowd, night time, some distance for the potential jumper etc.) 

Limitations

• Lacks consistency - The loss of indentity in a crowd does not always lead to anti-social behaviour for example a mexican wave is not anti-social.
• Aggression as a result of deindividuation may be more of a male characteristic than a female one. Cannavale et al found that males & female groups responded differently under deinidividuated conditions. An increase in aggression was obtained only in the all-male groups.

- There are cultural differences - Research by Watson found that tribes that significantly changed their appearance through war paint or body decoration (i.e. became deinidividuated) when going to war were far more aggressive (e.g. torturing & mutilating their victims) than those who did not. 

- Methodological issues - It is difficult to test the theory of deindividuation on aggressive behaviour in controlled laboratoty conditions due to ethical issues such as deception, protection from harm (e.g. making someone aggressive), informed consent etc.

- Lack of research support - Evidence for deinidividuation theory is mixed. Postmes & Spears conducted a meta-analysis and concluded that there was insufficient support for the claim that aggressive behaviour is more common in large groups & anonymous settings.

- Deindividuation does not necessarily lead to aggression - Johnson & Downing conducted a similar study to Milgram and found that people dressed in nurses uniforms were less likely to give electric shocks. This suggests that a uniform gibes a person an identity & nurses are seen as pro-social people and therefore aggression wasn't appropriate. 

Institutions are structures and mechanisms of social order and cooperation governing the behaviour of a set of individuals. People's behaviours are governed by a set of rules.

Examples of insititutions:

• Prisons
• Schools
• Hospitals 
• Military bases

Institutional aggression is therefore concerned with aggression that is influenced by the institutional setting.

Factors which might cause aggression within an insitition are: the type of institution, rebelling against rules, frustration & for attention.

The Deprivation Model suggests that feelings of deprivation lead to aggression.

Situational factors - prisoner aggression or patient aggression (in mental institutions) is a consequence of stressful & oppresive conditions, including overcrowding, physical conditions of heat & noise, and a lack of any meaningful activity. Crowding, for example, is assumed to increase fear & frustration levels, which then leads to aggression. (Paterline & Peterson). Steffensmeiser similar suggests that overcrowding, loss of rights & strict regimes of institutions cause aggression.

Sykes described the specific deprivations within a prision which might be linked to an increase in violence:

• Lack of liberty (freedom)
• Lack of autonomy (independence)
• Lack of goods & services
• Lack of heterosexual relationships
• Lack of security

Zimbardo's prison study clearly shows how the situation can increase aggression (shown by the prison guards).

Hellman was the most aggressive of all the guards. However, he came from a middle-class, academic family, was a musician, loved socialising and considered himself as a scientist.

The situation of Zimbardo's study had therefore changed his normal way of thinking, causing him to carry out aggressive acts on the prisoners in this study. 

Research support 

• McCorkle et al found that overcrowding, lack of privacy and a lack of meaningful activity all signigicantly increased violence in prisons, supporting the view that aggression was a direct consequence of situation factors that deprived prisoners of normal living standards.
• Davies and Burgess found that the length of service by prison staff affected assaults, where more experienced officers were less likely to suffer an assault.
• Hodgkinson et al found that trainee nurses are more likely to suffer violent assaults than experienced nurses.
• Gaes & Macuire found that overcrowding can lead to prison violence.

Strengths

• Real world application - Wilson showed that changes to such deprived environments (e.g. reducing levels of noise, heat & crowding) resulted in a dramatic decrease in violent assaults on prison staff & inmates. 
• The model can be applied to a number of insitutional settings e.g. it could explain why some children in schools are more aggressive than others in the playground.

• One might argue that prisoners are in prison because they have broken the law, and therefore the deprivations they experience are a necessary form of punishment. 

Limitations

• Poole & Regoli found that the best indicator of violence among juvenile offenders was pre-institutional violence regardless of any situational factors in the institution.
• The deprivation model does not work in all types of insitutions. Nijman et al found that, in psychiatric institutions, increasing personal space failed to decrease violent behaviour among patients. 
• Reductionist - it reduces aggressive behaviour down to feelings of deprivation.
• Deterministic - it suggests that all people will be aggressive if they feel deprived, however, not every person will choose to be aggressive within an institutional setting, suggesting that we do have free will. 
• Research in this area tends to be from US prison settings. The findings from such research therefore cannot be generalised to other institutional settings around the world.
• Doesn't take into account individual differences - lacks internal vailidity
• Gender bias - males - can't generalise to women 

Large scale natural study using data from more than 371 US state prisons. Some of the variables examined were crowding, security level, officer-to-inmate ratio, program involvement, the size of the institution & unemployment rate of the community where the prison was located.

• White-black guard ratio & security level were positively related to assault rates
• Poor prison management led to individual acts of violence
• Interfering with priveledges triggered outbursts of violence by individuals
• Prison were a large proportion of prisoners were involved in education & industry programs reported lower rates of violence against inmates & staff
• Overcrowding was not related to inmate-on-inmate assault rates

Factors within insititutions do make people more aggressive but not all deprivation will lead to aggressive behaviour. 

Strengths

• Natural experiment - no demand characteristics
• Large sample size - findings will be conclusive
• Looked at lots of factors which can cause aggression

Limitations

• Gender bias - all male, therefore cannot generalise to women
• Study only conduceted in the US - ethnocentric
• Ignores peoples biology & individual differences

This study supports the deprivation model because security levels were positively related to assault rates & poor prison management led to acts of violence & interfering with priveledges triggered outbursts of violence. However, this study rejects the deprivation model because it found that overcrowding was not related to inmate-on-inmate assault rates.

Serotonin

Low levels of serotonin are associated with aggressive behaviour.

Serotonin usually reduces aggression by inhibiting responses to stimuli that might otherwise lead to aggressive behaviour.

Low levels of serotonin have been associated with an increased susceptibility to impulsive & aggressive behaviour.

Mann et al found that drugs which deplete serotonin (e.g. dexfenfluramine) have been shown to increase aggression levels in participants.

Strengths

• Scerbo & Raine conducted a meta-analysis and found lower levels of serotonin in individuals described as being aggressive. This supports the claim that serotonin depletion leads to aggressive behaviour. 
• If drugs that lower serotonin activity lead to raised aggression levels, then drugs that raise serotonin levels should lead to lower levels of aggression. This is what was found in clinical studies of antidepressant drugs, further supporting the link between serotonin & aggression.

Limitations

• The explanation is reductionist - it reduces aggression down to biological factors and takes no other factors into account, for example social factors or past events. 
• It only supports the nature side of the nature-nurture debate as it doesn't consider environmental factors.
• Most of the research on serotonin has been conducted in Western countries, therefore it is culturally biased. 

Dopamine

Increases in dopamine levels have been shown to produce increases in aggressive behaviour. 

Demonstrated in studies that used amphetamines (to increase doamine activity in the brain) and found an associated increase in levels of aggressive behaviour - Lavine

Studies that have reduced dopamine levels through the use of antipsychotic drugs have reported a reduction in aggressive behaviour - Buitelaar

Limitations

• Evidence for the causal role played by dopamine in aggression is inconclusive, but a study by Couppis & Kennedy suggests that it may be a consequence rather than a cause. Some individuals may seek out aggressive encounters because dopamine is released as a positive reinforcer int he brain when they engage in aggressive behaviours. 
• A meta-analysis by Scerbo & Raine examine neurotransmitter levels in antisocial children & adults. They found lower levels of serotonin in individuals described as aggressive, but found no significant rise or fall in dopamine levels for this group compared to 'normal' individuals. 
• It is hard to do studies as it would involved giving someone a drug to increase their dopamine levels to potentially make them aggressive which is ethically worng because it is not protecting them from harm. 
• Biological explanations as a whole ignore any outside factors that may cause aggression e.g. upbringing or environmental factors.

Testosterone

Testosterone is thought to increase aggression in adults due to its action on brain areas involved in controlling aggression.

Dabbs found that criminals with the highest levels of testosterone tendered to have a history of mainly violent crimes, whereas those with the lowest levels has committed mainly non-violent crimes.

Lindman et al found that young males who behaved aggressively when udner the influence of alcohol has higher testosterone levels than those who did not act aggressively.

The challenge hypothesis proposes that testosterone would only rise above the baseline level in reponse to social challenges e.g. to status, with a resultant rise in aggressive behaviour. 

Limitations

• Although many studies show a link between testosterone & aggressive behaviour, many others do not. Most of the studies that do find a positive correlation between testosterone levels & aggression have used small sample sizes of men within prisons relying on self-reports of aggressive behaviour. Also correlations only show a link and doesn't show a casual relationship - we cannot be sure that testosterone actually causes aggression.
• Most studies of the links between testosterone & aggression have involved male participants, yet research suggests that the link between testosterone & aggression may be even stronger for females (Archer et al). Studies suggest that successful career women have higher testosterone levels. 
• Mazur claims that aggression is just one form of dominance behaviour. In humans, the influence of testosterone on dominance is likely to be expressed in more varied & subtle ways rather than only through aggressive behaviour.
• The theory is very reductionist. It claims that the cause of aggression is testosterone, which in itself may not be true since testosterone has been found to not always lead to aggression; it is often associatied with positive characteristics such as sporting abilities & spacial awareness.

Cortisol

Cortisol is said to have a mediating effect on testosterone. High levels of cortisol inhibit testosterone levels and so inhibit aggression. And low levels of cortisol is associated with increased levels of testosterone and therefore increased aggression. 

Virkkunen conducted a study into cortisol levels and aggression and reported low levels of cortisol in habitual violent offenders. 

Tennes and Kreye also conducted a study into cortisol & aggression and found that there were low levels of cortisol in violent school children. 

This suggests that, although testosterone may be the main biochemical influence on aggressive behaviour, low cortisol levels incresae the likelihood of aggressive behaviour.

Twin Studies

MZ twins share all of their genes, while DZ twins share a maximum of 50%. If MZ twins are more alike than DZ twins in terms of their aggressive behaviour (they have a higher concordance rate), then this suggests a strong genetic influence. 

Studies of adult twins suggest that at least 50% of the variance in aggression can be explained in terms of genetic factors. 

Supporting research:

Most twin studies have focused on criminal behaviour generally, but one of the few studies to specifically study aggressive behaviour using adult twin pairs found that nearly 50% of the variance in direct aggressive behaviour could be attributed to genetic factors (Coccaro et al) 

Rutter et al conducted a meta-analysis of twin studies & criminality and found a higher concordance rate in MZ twins. A strength of this study is that due to it being a meta-analysis it is more reliable because it is a conclusion from a collection of studies.

Adoption Studies

If a positive correlation is found between an adopted child's aggressive behaviour and that of a biological partent, this implies a genetic effect.

If the correlation is stronger between the adopted child and their adoptive family, then this suggests that environmental influences are stronger. 

Research support:

A study of over 14,000 adoptions in Denmark found that a significant number of adopted boys with criminal convictions had biological parents (particularly fathers) with criminal convictions (Hutchings & Mednick) providing evidence for a genetic effect. 

The link was found to be even stronger when biological & adoptive parents had criminal convictions - this suggests the environment also plays a part too. 

The role of MAOA

One of the genese responsible for producing MAOA is associated with aggression. MAOA regulates the metabolism of serotonin in the brain, and low levels of serotonin are associated with aggression.

Research support:

Brunner et al conducted a study on a violent Dutch family and found that many of the men had abnormally low levels of MAOA and also had a defective gene for the production of MAOA. 

• Miles & Carey's research supports the role of genetic influences on aggressive behaviour because 50% of variance can be down to genetics. 
• However, the research can also contradict the role of genetic influences because there are other contrbuting facotrs as CR would be 100% if aggressive behaviour was solely down to genetics. 
• Even though studies of twins do show MZ twins to have higher CR's for aggression than DZ twins, the CR is never 100%. This suggests that there must be environmental influences also which could possibly make up the remaining 50%
• Although many studies show support for aggression being inherited, many studies study 'criminality' rather than 'aggression' itself. This may be a problem because not all crimes are aggressive, for example, an aggressive crime would be associated with murder, however other crimes such as fraud & tax evasion would not be classed as aggressive but are still classed as a crime. 
• Mednick et al found the biggest effect in their study was for non-violent crime. Brennan compared the criminal history of adopted males & their biological & adoptive parents. They found that genetic influences were significant in cases of property cime but not violent crime. From this research we can conclude that genes may be a key factor for non-violent crime but not aggressive crimes.

• MZ twins look identical to each other as well as sharing the same biological make-up. And this could have a negative effect on the outcome of research because they are often treated the same (treated as if they were the same person) and they share the same environment. Therefore twin studies aren't a good genetic vs. environment study.
• Button et al found that the genetic heritability of aggressive anti-social behaviour was much higher for girls than for boys (this was not the case for non-aggresive anti-social behaviour such as truancy & lying). This suggests that research into aggressive twins may be gender bias. 
• This explanation reduces aggression down to a single gene, which can be easily diagnosed & treated, but it does ignore the role of hormones, brain structure & the environment. Aggression is caused and therefore determine by our genes, which can be scientifically tested for suggesting psychology is a science. Determinism ignores the role of free will and therefore this means there is reduced responsibility for aggression.
• Genetics fail to explain cultural differences in aggression, for example in the !Kung San community, aggressive behaviour is not displayed at all which portrays the fact that there must be environmental factors involved because they have grown up without learning aggression and therefore do not display it. 

Gene-Environment Interaction

It is unsure whether genes really cause aggression on their own. A better view is the gene-environment interaction. It is the combination of the environment and genetics that causes people to be aggressive. 

Research Support:

Caspi made a link between MAOA to aggression by conducting a study on 500 male children. Researchers found a variant of the gene associated with high levels of MAOA & a variant associated with low levels. Those with low levels of MAOA were significantly more likely to grow up to exhibit anti-social behaviour but only if they had been maltreated as children. Children with high levels of MAOA who were maltreated and those with low levels who were not maltreated did not display anti-social behaviour. This shows that it is the interaction between genes and environment that determines behaviour such as aggression.

Moffat et al examined the history of abuse & criminal convictions, violence & any symptoms of anti-social personality disorder in males from New Zealand. He found a link between low levels of MAOA and the risk of being convicted of a violent crime. However, this was only when participants suffered from abuse as children.

Evolutionary psychologists believe that aggression is an adaptive response.

How can aggression increase survival?

• Gain territory or status
• Defend against attacks
• Fighting over mates - passing on genes
• Maintaining or gaining status and power
• Detering rivals from future aggression
• Detering mater from infidelity

Evolutionary psychologists suggest that aggression is due to sexual competition. Natural selection effectively weeds out characteristics that confer no advantage for survival & reproduction and selects those that do. These are know as adaptive traits.

Jealousy is an emotional response to anticipated loss of affection and/or status. 

Cascardi & Vivvan - participants explained that the most common cause of aggression in their relationships was jealousy.

Canary, Spitzberg & Semic also found that jealousy caused aggression and anger in relationship conflict.

Why do men & women express jealousy differently?

• High status, dominant, aggressive women are not preferred as mates so there is no adaptive value in over aggression
• 40% of domestic violence victims are men. This suggests that men are more violent & women are less likely to use aggression but it still occurs
• Men need to compete with other men for access to females
• Women take fewer risks with violence & use more indirect forms of aggression e.g. bitching, name calling
• If a male is unfaithful, the female partner risks losing their time, resources, energy & protection & commitment to their children.
• For women, the costs of aggressive behaviour exceed the benefits
• Women only use direct aggression when competing for resources that will aid their survival
• Men cannot risk wasting time & resources on offspring who are not their own so they show more jealous violent aggression both towards the male competitors & their female mates if infidelity is suspected, especially if the female is young & reproductively valuable
• Women can always guarentee that their offsrping are their own & compete with other women for the quality of fathers rather than for the availability

MEN

Daly & Wilson - examined murders in Detroit in 1972. The motive behaind most of the conflicts was status. Victims & offenders were unemployed & unmarried young men (LOW STATUS & WITHOUT A MATE)

This study shows that aggression is an evolved trait because low status men are more at risk of not reproducing and therefore indulge in violence to gain higher status. 

• The study is ethnocentric - only conducted in Detroit
• Only studied murders - not accounting for all types of aggression

WOMEN

Young: Asked students to describe their likely reactions to a jealousy inducing scenario. Men said they'd respond angrily, become drunk and threaten their rival. Women said they'd cry, pretend not to care & try to increase their own attractiveness to ragain male attention.

This study shows that aggression is an evolved trait because men said they'd threaten their rival, trying to deter them from their mate. Women said they'd try to increase their attractiveness so the man doesn't leave her - she needs him to protect her.

• Self report study - social desirability bias
• Sample was students - biased
• Scenario was made up - artificial (lacks external validity) and it's not true to real life

Cuckoldry refers to the reproductive cost that may be inflicted on a man as a result of his partner's infedelity.

The consequence of cuckoldry is that a man may unwittingly invest his resources in offspring that are not his own.

The adaptive functions of sexual jealousy, therefore, would have been to deter a mate from sexual infidelity, therefore minimising the risk of cuckoldry.

Males have a number of strategies that have evolved specifically for the purpose of keeping a mate. Men try to stop their partners infedelity by offering benefits or inflicting costs. But not all men have the resources to provide benefits so are more likely to use costs (violence, or the threat of violence) to keep a mate (Shakelford).

Buss suggests that men use two strategies in order to keep a mate:

• Direct Guarding e.g. looking at texts
• Negative inducements

They prevent the female from straying & also deter rivals from gaining access to her. Another way to prevent cuckoldry is by s*xual coercive tactics such as partner r*pe, to increase the change of the male bing the father of the child. Thornhill & Thornhill suggest that women who resist having s*x might be doing so because they have been sexually unfaithful.

Studies of battered women show that in the majority of cases, women cite jealousy as the key cause of violence towards them (Dobash & Dobash). 

Male s*xual jealousy is claimed as the most common motivation for killings in domestic disputes in the US & in the UK. 

A summary of eight studies (Wilson & Daly) of same-s*x killings involving 'love triangles' found that 92% were male-male murders and only 8% were female-female murders.

Infidelity is unfaithfulness of partners. There are two types of infidelity:

• Sexual infidelity - any behaviour involving sexual contact e.g. kissing, touching, sexual intercourse
• Emotional infidelity - formation of an affectional attachment to another person

The detection or suspicion of infidelity is a key predictor of partner violence (Daly et al)

A consequence of men's perceptions of infidelity in their partner is s*xual coercion or partner r*pe (Goetz et al). 

S*xual assault of a female by her mate is directly linked to the perceived risk of her infidelity. Female victims of partner r*pe are likely to have engaged in extra-marital r*pe. 

A man risks lowering his reproductive success if his partner becomes pregnant with another man's child. 

The function of violence directed towards an unfaithful female may, therefore, be to terminate the pregnancy to eliminate the potential offspring of a male rival. 

Men can guard against their partner's infidelity by either conferring benefits or inflicting costs (such as violence).

As not all men possess resources that might be used to provide benefits, some men are especially prone to the use of violence instead.

Daly & Wilson argue that the death of the partner as a result of physical violence is an unintended consequence of an adaptation designer for control rather than death. 

Strengths

• Harvey et al support the idea that jealousy is a motivator for violence, however they do suggest that the causes of jealousy are exteremely complex. 
• Research support - Shackelford et al found a clear relationship between s*xual jealousy, the use of mate retention strategies & violence towards women. Buss & Shakelford found that men who suspected that their wives might be unfaithful over the next year used greater punishment for a known or suspected infidelity than did men who didn't expect future infidelities. 
• Shackelford and Goetz found that men who had s*xually coerced their partners (forced them to have s*x) were more likely to report that their partners were being unfaithful. Also women who had been coerced by their partners ertr motr likely to have actually cheated on their partner.
• Mate-retention strategies can be a predictor of violence against women. Awareness of the use of mate retention strategies by the male partner can be used to alert friends & family to the danger signs that violence may follow. At this point, help can be offered before inter-mate violence even happens. 

Limitations

• Most studies are gender biased as they focus on men's violence against women, but it does happen the other way too. Research suggests that women carry out as many physical assults on partners as often as men do - Archer's study found equal rates of assaults by women & men, and Felson found that women were twice as likely to murder out of jealousy as men. 
• The evolutionary explanation doesn't explain why people react in different ways when face with infidelity. A wife's infidelity could lead to a beating in once case, a murder in another, and getting drunk in another.
• The evolutionary explanation also doesn't explain why some cultures require violence to maintain status, whereas violence is completely frowned upon in others (!Kung San people)
• Some critics feels that the evolutionary explanation justifies violence by men against women as something natural & inevitable.
• Many studies use self-report techniques to gather data, which can be problematic in terms of social desirability bias, epecially when dealing with sensitive topics such as domestic violence.

Groups displays are when people come together as a group and act aggressively. 

Group displays serve the function of determining dominance or status hierachies in relation to ownership of territory and intimidating of other groups.

Two groups displays of aggression are sport and warfare.

Psychologists suggest that ritualised aggression is used at sports events. However, they are not always intended to be violent, but can easily lead to violent acts taking place. Working as a group in sports events gains status, dominance, territory & mates. Group displays discourage rivals - group cohesion is vital for survival.

Xenophobia (a fear of outsiders) is a trait that has evolved through natural selection. By anticipating outsiders as a threat & overexagerating the threat leads to survival. In sport, the outsiers are the opposing team. Xenophobia is evident in chants & banners at sports events. Podaliri & Balestri observed the behaviour of Italian football crowds, finding evidence of xenophobia, suggesting that it does occur. 

Winning a football game means you will gain higher status both for the fans and for the players. This therefore will mean they can attract a woman and reproduce and pass on their genes. In sports events it is usually the lower status males who want to increase their status and therefore they are going to be the more aggressive ones. 

Cialdini conducted a field experiment in large lecture halls across 7 prestigious football schools across America, where they observed student clothing on a Monday following a big football game. The researchers found that students tending to wear more clothing associating themselves with their own school (e.g. a jumper or scarf) when the football team won compared to when they lost. They also interviewed students at random about the performance of their school's football game. They found that people tended to use the pronoun "we" more to describe thei team when they wom and "they" more when the team had lost. 

The students behaviour can be explained by the evolutionary approach because when the team wins, the students want to be associated with their school because it'll increase their status, however, when they lose they don't want to be associated with their school at it'll lower their status. 

• One strength of the sports events evolutionary explanation for group displays is real world applications. They have experimented in trying to reduce xenophobia at sports events by using, for example, slogans. It has been found that reducing xenophobia also reduces aggression at sport events. 
• Schwarz & Barkey believed sporting teams win more games at home than away due to social support of supporters suggesting that crowd support is a significant factor contributing to a home advantage. 
• The theory, however, is gender biased. Most aggression at sporting events is carried out by men and therefore we cannot generalise this theory to women. However, women play and watch sports too.

• There is a universiality of war dances meaning that they are carried out all over the world & were are therefore able to apply them to different places. War dances (such as the Haka) are used to initimidate the opposing team and also to motivate their own team to make sure they're confident that they can win.
• Some people suggest that warrior displays, such as the Haka are for entertainment & not for evolotionary purposes such as to gain status, attract women & pass on their genes. 
• There are also opposing arguments - evolutionary or social? One social psychological explanation of aggression may explain it better such as deinidividuation. People lose their identity in a crowd and there is a diffusion of responsibilty. This means that people feel they can be aggressive at sports events, such as chanting, fighting, swearing, being racist and throwing things because it won't just be them that's doing it. 

Why go to war? The costs of going to war are loss of life & serious injury. However, the benefits of going to war are support, survival & protection. 

Soldiers go to war to gain territory, status & resources. Soldiers' going to war as a group gives them a better change of winning & surviving as they can support & protect each other.

Soldiers are seen as being brave which is an attractive trait to women because it means she has someone to protect her. This would therefore allow the man to pass on his genes. Natural selection means that bravery has been kept as a trait, which is useful in war. But it is also essential for sexual selection because bravery is an attractive trait & it therefore can be passed onto their children. 

If soldiers are more aggressive, they will gain higher status among the group & therefore they will have greater protection by the group & their chance of survival is a lot higher. If the soldiers win war, they will achieve a higher status & will be able to attract a woman and will be able to pass on his genes. 

• One strength of the warfare explanation of group displays of aggression is that it's universal because we can apply it to lots of different countries & can therefore generalise it to most people. We can apply this explanation to the war that is happening in Afghanistan & Iraq at the moment & we can see that it does happen in real life situations.
• However, a weakness of the warfare explanation is that it is gender bias. The theory is based on men passing on their genes. However, women go to war as well but not necessarily to pass on their genes. Aggression is seen as unattractive in women and the theory therefore cannot explain this. 
• The theory doesn't account for the loss that can occur in war such as death. If a soldier dies whilst fighting in way, he can no longer protect his woman and therefore he can no longer pass on his genes. Therefore this is contradicting the theory. 
• There is little evidence for bravery being a genetic trait - traits won't be passed on. It may be a learn trait instead and therefore the SLT may be a better explanation instead. 

• There are opposing arguments against the evolutionary explainations for group displays of aggression such as the social psychological explanation (nurture). One social psychological explanation of group displays of aggression is deindividuation. It is suggest that when in a crowd individuals lost self-control and often act in ways that go against person & social norms. During war when soldiers have uniform on they may feel deindividuated and therefore feel able to carry out aggressive acts such as shooting. 
• There are methodological problems with this theory because the data is retrospective. This means that we are sort of guessing what happened with our ancestors. We can't go back in time and interview people. We also can't interview soldiers whilst they're fighting as it's dangerous, so you'd have to interview them afterwards and they may forget what happened. This would therefore mean the data lacks reliability.