PSYA3: Aggression

Overview

• According to social theorists such as Bandura, aggressive behaviour is learned either through direct experience or by vicarious experience, that is, by observing others and learning from their experiences.

Direct and vicarious experience

• Direct experience is derived from Skinner's principles of operant conditioning. Behaviour is more likely to occur if the action is reinforced.
• Vicarious experience occurs, for example, from when a child sees a role model behaving in a certain way and imitates the behaviour of the model. SLT claims that we learn to be aggressive primarily by observing the aggressive behaviour of those around us, particularly the behaviour of significant others in our life.

The likelihood of a person behaving a aggressively in a certain situation is determined by:

• Their previous experiences of aggressive behaviour - both their own and that of others
• The degree to which their behaviour was successful in the pasy
• The current likelihood of their behaviour being rewarded/punished
• Cognitive, social and environmental factors that are operating at the same time.
• Bandura claimed that for SLT to take place, individuals must be able to form a mental representation of the aggressive behaviour and any anticipated rewards or punishments that might be associated with it.

• Bandura and colleagues divided 66 nursery school children into three groups. All three groups watched a film where an adult model kicked and punched a Bobo doll, accompanying this with aggressive comments.
• Condition 1: Agressive model was neither rewarded nor punished; Condition 2: Aggressive model was rewarded by a seond adult; Condition 3: Aggressive model was punished by a second adult.
• After watching the film, each child watched at play with the doll and other toys, and any imitative aggressive acts were recorded by observers.
• The results were as follows:
• 1) In condition 1 and 2, there was a marked tendency for the child to show spontaneous, imitative aggressive acts; 2) Children in condition 2 behaved most aggressively; 3) Children in condition 3 behaved least aggressively.
• SLT predicts that the consequences of behaviour have a controlling effect on its performance.
• Therefore, although aggressive acts were not spontaneously demonstrated in the punished condition, the behaviour would have been accquired.

• Slt can account for the lack of consistency in peoples' aggressive behaviour. If someone is aggressive and domineering at home but meek and submissive at work, it means they have learned to behave differently in the two situations because aggression brings rewards in one context but not the other.
• A strength of SLT is that is it's ability to explain aggression across cultures - 'Wolfgang and Ferracuti proposes that some cultures emphasize the 'culture of violence' model and emphasize aggressive behaviour. Other cultures model non-aggressive behaviour, more likely to produce individuals with low levels of aggression (kung san tribe of the Kalahari desert).
• Biological explanations of aggression have stressed factors unrelated to social learning. High levels of the male hormone testosterone have been cited as a primary causal agent in aggressive behaviour, and PMS has even been cited in criminal trials as a reason for aggressive behaviour. Biological expressions then cast doubt on aggression being a purely learned behaviour.

• Hogg and Vaughan (2008) define deindividuation as 'a process whereby people lose their sense of socialised individual identity and engage in unsocialized, often antisocial behaviours'.
• In certain situations (in crowds), restraints on aggressive behaviour become relaxed, so people feel more comfortable in acting aggressively.
• Zimbardo distinguished between individuated and deindividuated behaviour - individuated is rational and conforms to acceptable social standards; deindividuated is based on primitive urges and does not conform to society's norms.
• Concept of deindividuation has been refined to distinguish between effects of reduced public self-awareness (being anonymous to others) and reduced private self-awareness.
• If individuals become submerged within a group, they may lose their self focus and become less privately self-aware.
• According to Prentice-Dunn and Rogers, reduction in private self-awareness is associated with increased anti-social behaviour rather than reduced public self-awareness.

• Zimbardo was interested in finding out whether the brutality reported among guards in American prisons was due to the sadistic personalities of the guards or had more to do with the prison environment.
• The 'prison', was reinacted in Stanford Uni, with students acting as prisoners and guards.
• The prison environment involved the prisoners dressing in 'smocks', and only addressed by their number, which appeared to be an important factor in creating the brutal behaviour of the 'guards'.
• Dehumanization of the prisoners by the guards, together with the relative anonymity of each group made it easier for the guards to treat the prisoners in a brutal manner so that the study had to be stopped just after 6 days.

The baiting crowd/Faceless crowd

• Mann (1981) used the concept of deindividuation to explain a particular form of collective behaviour: the 'baiting crowd'.
• Study of the 'baiting' or taunting lends support to the notion of the crowd as a mob.
• Mann analysed 21 incidents of suicides reported in American newspapers in the 60's and 70's.
• Found that 10/21 cases where a crowd gathered to watch, baiting had occurred.
• These incidents tended to happen at night when the crowd was large and some distance away from the person being taunted.
• Mann claimed that these features were likely to produce a state of deindividuation in the crowd.
• Mullen (1986) analysed newspaper cutting of sixty lynchings that took place in the USA between 1899-1946.
• As with the baiting crowd, the greater the people in the mob, the greater the deindividuation and the greater the savagery to victims.

• Much early evidence linked deindividuation and antisocial behaviour; other evidence shows that deindividuation may sometimes produce increases in prosocial behaviour rather than antisocial (Diener et al, 1980)
• Researchers have often dailed to distinguish between the effects of the anonymity of those being aggresssed against, as opposedto the anonymity of those doing the aggressing.
• Another issue is whether the likelihood of aggression is increased if our 'in-group' cannot recognize us or only if our 'out-group' cannot. Manstead and Hewstone (1995) argue that anonymity among the in-group does not really reflect the reality of most crowd situations, where many in-group members will recognize each other.
• According to deindividuation, when we are submerged in a group, this undermines the influence of social norms. Rather than individuals pursuing behaviour 'based on primitive urges'  they might be seen to conform to a 'local' group norm (Manstead and Hewstone).
• Norm need not necessarily be antisocial, and could thus account for some apparently contradictory findings that show an increase in prosocial behaviour when people are deindividuated. (Deiner et al)
• Zimbardo's study failed to tell us much about how real guards behave, but rather how people behave when they are asked to act like guards.
• A study of football hooliganism by Marsh et al found that what might appear to be an undisciplined mob on match days can actually consist of several different groups, each with their place in a status hierarchy.

• Watson tested the hypothesis that warrior who significantly changed their appearance when going to war would be more likely to torture, mutiliate and kill their victims than would warriors from societies that did not change their appearance.
• Found data from the 'Human Relations Area Files' relating to 23 societies, together with evidence of whether they changed their appearance significantly before going to war and how they treated their victims.
• 1/13 societies that killed, tortured and mutilated their victims, but but one changed their appearance prior to battle.
• 1/10 societies that were less brutal towards their victims, 7/10 did not change their appearance prior to battle, and thus were not deindividuated.

Instutional aggression

• Institutional aggression refers to violent behaviour that exists within and may be a defining feature of certain institutions and groups.
• Across England and Wales 2006, there were 11476 violent incidents between prisoners, a 541% rise on the 1791 violent incidents recorded a decade earlier.

The importation model

• Irwin and Cressey devised the importation model. This model claims that inmates who enter prison with particular characteristics are more likely to engage in interperson violence than other inamtes.
• According to this theory, interpersonal violence is not a product of the institution but rather of the characteristics of the individual.
• Adams 1981, study showed that younger inmates have a harder time adjusting to prison, and view violence as an appropriate response to conflicts.

• Support for the model: Harer and Steffensmeier analysed data from 58 US prisons and found that Black inmates displayed significantly higher levels of violent behaviour but lower rates of alcohol and drug misconduct compared to White inmates. They concluded that these differences reflected racial differences in these behaviours within US society generally.
• Keller and Wang found that prison violence is more likely to occur in facilities that hold the most troublesome inmates.
• Limitations:  McCorkle et al claim that this model fails to provide suggests for how best to manage violent offenders or how to reduce prison violence in general.
• The model also predicts that membership of a violent gang prior to confinement will result in increased levels of violence and misconduct in pirson, as gang members import their gang involvement into the prison setting.
• However, a study of over 800 male inmates by DeLisi et al found no evidence that gang membership prior to prison had any bearing on violence or misconduct within prison.

• The deprivation model claims that it is the characteristics of the prison itself rather than the prison population that accounts for prison violence.
• The model argues that it is primarily the experience of imprisonment that causes inmates extreme stress and frustration and which, in turn, leads to violence or aggression against other inmates and staff.
• Harer and Steffensmeier describe how inmate behaviour is a response to the 'problems of adjustment posed by the deprivations or pains of imprisonment'.
• These 'pains' according to Sykes, the loss of freedom and heterosexual relationships, isolation from the free community, boredom, discomfort and loneliness.
• As these 'pains' are experienced, they engage in interpersonal violence as a reaction to the hurt that they feel.

• Although some studies have provided support for the deprivation model of prison violence, one of the largest studies in this area (McCorkle et al) failed to support its major assumptions. The sample in this study included 371 state prisons in the US and found little evidence to support the connection between overcrowding and living conditions.
• McCorkle and colleagues also point out that levels of stress associated with imprisonment are generally constant, whereas serious outbreaks of violence, are not.
• They claim that serious violence is more a consequence of the management of prisons rather than the general deprivation that all prisoners endure.
• Model is also challenged by the finding that among juvenile offenders if 4 different instiutions, pre-institutional violence was the best predictor of inamte aggression (Poole and Regoli) This supports the importation model.

• Initiation rituals are special rituals and requirements for new members of a group.
• Having endured extreme initiation, the new recruit will feel part of a select group, all of whose members will have endured the same ritual.
• The major reason for hazing in the US is symbolically to take away the weakness of childhood and replace it with the confidence of adulthood (Raphael, 1988).

• McCorkle found that in prisons, the domination of the weak during initiation rituals was seen by inmates as essential to maintaining status.
• Most important explanation for the effectiveness of 'hazing' is provided by cognitive dissonance theory, Festinger.
• This states that when a person behaves in a way that does not fit in with an existing attitude or belief, they will experience an unpleasant state of dissonance because the action conflicts with the belief.  They will then change their behaviour in order to match the beliefs of the group.
• The 'value' of the initiation experience becomes an important part of group membership, and the degree of suffering endured during the initiation ritual becomes directly related to the value they place on it and on being a group member.

• Studies have shown that serotonin in normal levels exerts a calming, inhibitory effect on neuronal firing in the brain (Cases).
• Low levels in the pre-frontal cortex remove that inhibitory effect with the consequences that individuals are less able to control their impulsive and aggressive responses.
• Support for this claim comes from research that shows the metabolite of serotonin tends to be low in the cerebrospinal fluid of people who display impulsive or aggressive behaviour - Brown et al.
• Further research comes from studies where the levels of serotonin have been manipulated. Mann et al administered the drug dexfenfluramine to 35 healthy adults. The drug is known to deplete serotonin levels in the brain. The researchers used a questionnaire to assess hostility and aggression levels, and found that among males, hostility and aggression levels increased after treatment with the drug.

• Some evidence suggest that increases with dopamine activity are associated with increases aggressive behaviour - Lavine.
• Use of dopamine antagonists have been used as a successful  way of reducing aggressive behaviour in violent delinquents.
• Well established that dopamine is released in response to rewarding stimuli. Couppis et al have now found evidence that dopamine also plays an important reinforcing role in aggression. Their evidence suggests that some individuals intentionally seek out aggressive encounters because of the rewarding sensations, caused by the increase in dopamine, which these encounters provide.

• It is possible that aggression is not caused by low levels of serotonin, but by low serotonin metabolism which leads to increased numbers of receptors.
• Serotonin receptor density has an inverse relation to serotonin levels in the brain, such that an increase in the number of receptors is liely to occur under conditions of chronic serotonin depletion.
• Arora and Meltzer found a relationship between violent suicide and an elevate serotonin receptor density in the pre-frontal cortex.
• Badawy claims that the influence of serotonin on aggressive behaviour may be important in explaining the well-established relationship between alcohol and aggressive behaviour. Found that alcohol consumption causes major disturbances in the metabolism of brain serotonin.

• Ferrari et al provides support for both dopamine and serotonin in aggressive behaviour.
• They allowed a rat to fight every day for 10 days at precisely the same time. On the 11th day, the animal was not allowed to fight, but the researchers measured the levels of serotonin and dopmine in its brain.
• Found that an anticipation of an imminent fight, the rat's dopamine levels had increased and serotonin levels decreased, despite the fact that the animal did not actually fight.
• This shows that experience had changed the animals brain chemistry, gearing it up for a fight by altering levels of serotonin and dopamine in ways consistent with the onset of aggressive behaviour.

• Males produce testosterone in the testes. 
• Women also produce testosterone, but in smaller amounts by dehydroepiandroserone (DHEA) produced in the adrenal glands.
• Testosterone is one of the androgen hormones, so called because they produce male characteristics.
• The nature of the link between testosterone and aggressive behaviour makes it more likely that a behaviour will be expressed.
• Findings of research studies into testosterone and aggression include the following;
• Archer (1991) carried out a meta analysis of 5 studies and found a low pos correl between testosterone and aggression
• A larger meta analysis of 45 studies (Book et al) found a mean correlation of 0.14 between testosterone and aggression
• Olweus et al compared samples of institutionalized delinquent boys and non-delinquent male students. They found that although testosterone was slightly higher in the delinquent sample, the difference was not statistically significant.

• In one study, using a double-blind procedure, young men were given doses of either tesosterone or placebo. 
• They were then paired with a fictitious participant and told that each member of the par could, by pushing a button, reduce the amount of cash recieved by the other person.
• The participant was also told that the other individual was reducing the cash that the participant was recieving.
• Participants who recieved testosterone rather than the placebo pushed the button significantly more times (Kouri et al).

• A second study with the same design was carried out with men aged 20-50 years (Pope et al).
• This time, however, testosterone was administered over a 6wk period; in all other ways, the experimental design was the same.
• Results indicated that those who had recieved the testosterone pushed the button many more times than those who had recieved the placebo over the same time period. 

• Van Goozen et al claim that there is a link between aggression and the hormone cortisol.
• Cortisol is produced by the adrenal medulla and is an important part of the body's reaction to stress.
• The relationship however is an inverse correlation; lower levels of cortisol are associated with higher levels of aggression.
• Studies have reported low levels of cortisol in habitually violent offenders (Virkkunen 1985) and also aggressive schoolchildren (Tennes and Kreye 1985)
• Possibility of lower levels of cortisol linked to aggression by:
• Having low ANS arousal is aversive, or unpleasant; aggressive behaviour is then an attempt to create stressful situations which provoke ANS activation and cortisol release.
• Cortisol plays an important part in mediating role in aggression by inhibiting the likelihood of aggressive behaviour. A study by Popma et al revealed a significant interaction between cortisol and testosterone in relation to overt aggression; significant positive relationship with low levels of cortisol. 

• Bain et al found no significant differences in testosterone levels between men who had been charged with murder or violent assault, and men who had been charged with nonviolent crimes such as burglary.
• Kreuz and Rose also ound no difference in testosterone levels in a group of 21 young prisoners who had been classified, according to their prison records, as either 'fighting' or 'non-fighting' while in prison.
• However, the 10 prisoners with histories of more violent crimes in the adolescene did have significantly higher levels of testosterone than the 11 prisoners without such a history. 
• Zitzmann argues that the link between testosterone and aggression is most probably only relevant in strength athletes who may supplement their testosterone to excessively high levels. However, among many older males, testosterone supplements have been positive and found to enhance vigour and energy.

• In humans, aggressive behaviour is more highly correlated in identical twins than in fraternal twins. 
• McGuffin and Gottesman found a concordance rate of 87% for aggressive and antisocial behaviour for MZ twin pairs, compared with 72% for DZ pairs. This indicates that family environment shared across siblings, exerts an important influence on juvenile aggression.
• A meta-analysis by Mason and Frick of 12 twin studies involving 3795 twin pairs concluded that approx 50% of the difference between anti-social and non-antisocial behaviours could be attributed to genetic factors, with larger estimates of genetic influence found for more violent behaviours than for less violent behaviours.
• Coccaro et al in one of the few twin studies specifically to investigate aggressive behaviour, assessed the degree of genetic and environmental influences on aggression in male participants. Data from 182 MZ twin pairs and 118 DZ twin pairs were analysed. From the data they estimated that:
• 1) Genes accounted for more than 40% of the individual differences in aggression
• 2) Environmental influences accounted for around 50% of individual differences in physical aggression, and about 70% of individual differences in verbal aggression. 

• Finding large no's of MZ twins reared apart is difficult - in a classic twin study, researchers must compare MZ and DZ twins in order to assess which type of twin pair is more similar on a given trait. However, not only do MZ twins share genes, they also share an environment that frequently treats them more similarly that it treats DZ twins. 
• Button et al in a study of 258 twin pairs aged 11-18 found that both aggressive and non-aggressive anti-social behaviour are subject to significant genetic influences. The heritability of aggressive antisocial behaviour, however, was significantly higher in girls than boys. The results suggest a stronger genetic effect on aggression in females than in males. 

• Another way of studying genetic factors is by studying children who have been brought up by adults who are not their biological parents.
• If researchers find a greater similarity in levels of adopted children and their biological parents, than between adopted children and their adoptive parents, then this suggests an important genetic influence is at work.
• Hutchings and Mednick reviewed over 14000 adoptions in Denmark. They found a significant positive correlation between the number of convictions for criminal violence among the biological parents, and the number of convictions for criminal violence among their adopted sons.
• In a meta-analysis of 24 twin and adoption studies concerned with the genetic basis of aggression, Miles and Corey found a strong genetic influence, which accounted for as much as 50% of the variance in aggression. Although they found that both genes and family environment were influential in determining aggression in young people, at later ages the influence of rearing environment decreased and the influence of genes increased.

• Adoption studies have a number of methodological problems which can limit the conclusions that can be drawn from them.
• One problem is that in countries such as New Zealand and the US, children given up for adoption display a higher rate of antisocial behaviour at the time of their adoption compared with the general popn (Fergusson et al; Sharma et al).
• Tremblay maintains that the parents who give up their children for adoption also display higher levels of antisocial behaviour compared with the general popn and potential adoptive parents.
• Consequently, correlations between adoptees and their biological parents may be due to either the transmission of antisocial genes from bio parents or to environmental influences, or from feelings of abandonment.

Candidate genes: DRD4 and DRD3

• The dopamine receptor D4 has been the most heavily researched. A meta-analysis of studies of the gene for this recept (DRD4) found a modest association between DRD4 and a tendency to ADHD - Faraone et al.
• Another study (Retz et al) found an association between a DRD3 variant and both impulsivity and ADHD-related symptoms.

Candidate gene for MAOA

• Gene responsible for the enzyme monoamine oxidase A (MAOA) may also be associated with aggressive behaviour - it's job is to break down 3 neurotransmitters (noradrenaline, serotonin and dopamine) in the brain after they have carried impulses from one cell to the other.
• Bruner's research surrounding a particularly violent family in the Netherlands where the males suffered a genetic defect on their X chromosome, which cripples and enzyme that regulates aggressive behaviour. These low amounts of MAOA resulted in extremely high levels of serotonin, dopamine and noradrenaline. 
• MAOA was absent in the non-violent members. 

Candidate genes: DRD4 and DRD3

• The dopamine receptor D4 has been the most heavily researched. A meta-analysis of studies of the gene for this recept (DRD4) found a modest association between DRD4 and a tendency to ADHD - Faraone et al.
• Another study (Retz et al) found an association between a DRD3 variant and both impulsivity and ADHD-related symptoms.

Candidate gene for MAOA

• Gene responsible for the enzyme monoamine oxidase A (MAOA) may also be associated with aggressive behaviour - it's job is to break down 3 neurotransmitters (noradrenaline, serotonin and dopamine) in the brain after they have carried impulses from one cell to the other.
• Bruner's research surrounding a particularly violent family in the Netherlands where the males suffered a genetic defect on their X chromosome, which cripples and enzyme that regulates aggressive behaviour. These low amounts of MAOA resulted in extremely high levels of serotonin, dopamine and noradrenaline. 
• MAOA was absent in the non-violent members. 

• Morley and Hall argue that genes associated with aggression are not deterministic and only poorly predict the likelihood that an individual will display higher levels of aggressive behaviour than the general population.
• Additionally, the presence or absence of an enviromental risk factors cannot be identified by a genetic test, thus making the accurate prediction of specific behaviours even less likely.
• Morley and Hall suggest that information obtained from genetic studies may be used to help develop new treatments for personality disorders that have been identified as risk factors for criminal behaviour.
• Caspi et al found that male children who had been maltreated and possessed a variant of the gene that resulted in an increased expression in MAOA were less likely to express antisocial behaviour.
• Under normal circumstances, an increase in MAOA would be expected to result in a decrease in serotonin and therefore increased aggressive behaviour. 
• Caspi and colleagues believe that it is possible that early abuse alters serotonin in some way or that decreases in serotonin afect some types of anti-social behaviour but not others.

• Buss and Shackleford examined the mate retention tactics in married couples.
• Studied 214 individuals, and found that compared to women, men reported a significantly higher use of debasement (giving into her every wish) and intra-sexual threats (e.g threatening to beat up the other man).
• Women reported a greater use of verbal possession signals (indicating to other women that he was taken) and threats of punishing infidelity (leaving her man if he was ever unfaithful).
• Found that compared to men married to older women, men married to younger women reported devoting greater mate-retention tactics. 

• Cuckoldry occurs when a woman decieves her male partner into investing in offspring concieved with another male.
• Although the risks of cuckoldry are high for women, the risk is even higher for males - cuckolded men lose both invested resources and reproductive opportunity (Plateck and Shackelford).
• Men have evolved a number of strategies to prevent themselves from being cuckolded - mate retention strategies such as jealousy, as it is a way of dealing with paternal uncertainty.
• Sexual jealousy, therefore, serves to help prevent his female mating with other males outside the pair bond. 
• Sexual coercion (marital ****) is a tactic used to reduce the risk of cuckoldry.
• The 'cuckoldry risk hypothesis' (Camilleri) predicts that tactics such as partner **** occurs when the risk of cuckoldry is high, e.g. when they suspect infidelity.
• According to Lalumiere et al, men carry out partner **** in order to prevent paternity uncertainty.
• Thornhill argues that a woman who resists having sex with her partner may be signalling to him that she has been sexually unfaithful, thus increasing the male's sexual jealousy and fear of cuckoldry. 

• Shackleford and colleagues studied a sample of 461 men and 560 women from US universities or their surrounding communities in heterosexual, committed relationships.
• Study 1: Mean age of males 24.2 yrs; 23.2 yrs for females; length of rel 37.3m
• Study 2: Mean age of 560 females 21.5 yrs; partners was 23.7 yrs; length of rel 28.8m
• In study one, participants completed MRI (Mate Retention Inventory) concerning their use of 104 different mate retention strategies in the previous month, ranging from 0 (never) to 3 (often). Males were also asked how often they performed each of 26 violent acts against their partners, and how often their partners sustained injuries (20) as a result of their violence.
• In study two, females answered questions about their partner's use of mate-retention strategies with them, and the degree to which their partner had been violent towards them.

Results

• Men's use of broad types of mate retention pos correl with violence scores; two m-r strategies were 'intersexual-negative inducements' and 'direct guarding'. Men who consistently used emotional manipulation were more prone to use violence.
• Results of study 2 confirmed the validity of the findings from study 1; women also stated that male partners who used emotional manipulation were more likely to use violence against them.

• Sexual jealousy as a major cause of domestic violence is supported by studies of battered women, where victims frequently cite extreme sexual jealous on the part of male partners as the major cause of violence against them - Dobash and Dobash 
• The use of 'mate-guarding' is also evident in a study by Wilson et al, who found that among women who reported the use of this tactic by their male partners, 72% had required medical attention following an assault by their male partner. 

• Buss and Duntley propose that humans possess adaptations that have evolved specifically through the process of natural selection to produce now what we refer to as murder.
• The activation of these evolved adaptations is determined by factors such as: 1) the degree of genetic relatedness to the victim; 2) relative status of the killer and victim; 3) sex of killer and victim; 4) size and strength of the killers' and victims' families and social allies.
• They also claim that for our ancestors, murder was functional in solving adaptive problems such as 1) Preventing harm; 2) Reputation management; 3) Protecting resources.

• Daly and Wilson found that men are more likely to kill other men whom they percieve to be sexual rivals or those who challenge their position in the dominance hierarchy.
• Women on the other hand, are more likely to kill in self-defence.
• Murders tended to be age related, peaking for males around their early 20's, a time when males are in the peak years of their reproductive competition.
• Predisposing factors are:
• Sexual jealousy - Wilson summarised data from 8 studies of 'love triangles'. They found that 92% of these murders involved males killing males and only 8% of females killing females.
• Lack of resources - Wilson and Daly suggest that a lack of resources increases male-male competition and risk of murder. Murder statistics in Detriot, US, showed 43% of male perpetrators were unemployed, although the overall unemployment rate for adult males in Detroit at that time was just 11%.
• Threats to male status - Daly and Wilson argue that females are attracted to males who are dominant over other males, and, therefore, men are shaped by evolution to seek status. 

• The 'murder as adaptation' hypothesis is supported by comparitive studies of other species. Among mammals, there are many cases on conspecific killing. Male lions and cheetas have been observed killing the offspring of rival males - Ghiglieri.
• The evolved goal hypothesis argues that humans have evolved motivations for specific goals that were, among out ancestors, associated with greater reproductive success. According to this view, there need be no evolved mechanism to engage in a specific behaviour such as murder, only a mechanism to engage in a specific behaviour such as murder, only a mechanism to work out how best to achieve a specific goal. 
• Hardy claims that our early ancestors would consciously calculate the costs and benefits, as well as any future consequences, of different actions. These calculations might, on occassion, conclude that murder was the best solution to achieve a particular goal.

• An evolutionary approach to the understanding of aggression fails to explain why individuals might react in such different ways when faced with the same adaptive problem. Buss and Shackleford offer an example which highlights this shortcoming - different men, when confronted with their wife's infidelity, react in very different ways, such as violence or debasement, or simply avoid the issue by getting drunk. 
• Evolutionary perspective also fails to explain why some cultures seem to require male violence to attain social status, whereas in other peaceful cultures aggression leads to irreparable damage to the reputation of the aggressor - Buss and Shackleford

• Lynch mobs are when a group of people, without legal authority, kill a person for some presumed offence. The word 'mob' suggests that behaviour is without planning or direction, yet a display of such extreme violence may serve an important purpose for members of the mob that goes way beyond the killer of one individual.
• There were 2805 victims of lynch mobs between 1882-1930 in ten Southern states in the US.
• Reasons for lynch mob behaviour are:
• The power threat hypothesis: Blalock suggests that as a minority group membership grows, majority group members will intensify their efforts to maintain dominance. It represents a fear of political power in the hands of the minority. Ridley suggests that group displays of solidarity and discrimination against outsiders become more likely when groups feel at risk
• Dehumanization: Hyatt argues that through the 'hysterical desecration' of Black body lynchings, mob attempted to reduce the body to bits of bone and dead flesh, to form a form that was unrecognizable as a human being. Tolnay and Beck had suggested that years of racist propaganda had in the many minds of Whites, reduced Blacks to simplistic and often animalistic stereotypes. These debasing stereotypes further dehumanized the victim, reducing him to a hated object devoid of worth. 

• Clark studied murders by lynch mobs in Sao Paulo, Brazil and concluded that evidence contradicted the power-threat hypothesis. Afro- Brazillians, the victims of lynch mobs, were not seen to pose any particular threat, political, economic, to the dominant community.
• Rothenberg observes that although most cases are in response to serious crimes such as murder, others are for minor offences, such as stealing chicken or pickpocketing. Dehumanization of the victim makes it easier to kill by removing any moral constraints associated with killer other human beings. By reducing their victims to the status of animals, the elimination of rivals becomes easier, which is ultimately beneficial to group members.

• The Shia muslim practice of self-flagellation during Ashura commemorates the martyrdom at Karbala of Hussein, a grandson of Prophet Muhammed - extreme displays such as this appear to contradict the principles of natural selection. 
• Irons suggests that a universal dilemma faced by all groups is how to promote cooperation. He argues that in human history, the adaptive advantage of group living was the benefits that individuals gained through cooperating with each other. By engaging in painful rituals such as self-flagellation, an individual is signalling their commitment to a group and all that it stands for. A committed group member is likely to be a cooperative group member.
• A problem for all groups is how to deter a free-rider - the significant costs of many cultural and religious displays act as a deterrent for anyone who wants to join a group in order to take selfish advantage of the benefits available to group members.
• Zahavi refers to such 'costly signalling' rituals as handicaps. Handicaps are reliable indicators of things such as status and breeding potential because they are too costly to be displayed or performed by 'low quality' individuals.
• Sosis used the example of Isreali, Ultra-Orthodox Jews, known as Haredim.