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Biological and Evolutionary Explanations of Aggression

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Danielle Weston

on 4 May 2013

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Transcript of Biological and Evolutionary Explanations of Aggression

Neural and Hormonal Mechanisms Serotonin Evolutionary Explanations of Aggression Adapting to the environment
Natural selection
Sexual jealousy - act of jealousy as a result of threat of unfaithfulness to an intimate sexual relationship
Infedility - act of unfaithfulness to one's husband wife or lover
Aggressive towards the threat (person)
Fight off competitors
Help deals with the threat of losing sexual mate
Reduce the chances of cuckoldry - males only
Could result in homicide Genetic Factors Monozygotic - identical genetics/twins - same egg - 100%
Dizygotic - non-identical - different eggs - 50% Biological Explanations of Aggression Dopamine Testosterone Low levels of serotonin have been linked to impulsive behaviour, aggression and violent suicide (low levels found in children who torture animals and children with poor impulse control leading to disruptive behaviour) Scerbo & Raine
meta-analysis of 29 studies which looked at levels of neurotransmitters in anti-social children. P’s described as aggressive had low levels of serotonin (especially those who had attempted suicide) this was consistent over all studies. Bond - clinical drugs – anti-depressants have been found to lower levels of irritability and impulsive aggression 35 healthy P’s were given dexfenflatutamine – know to reduce serotonin levels. Questionnaire on hostility and aggression. Treatment with this drug was associated with high levels of hostility and aggression in males Explains the negative effects that alcohol had on aggression - serotonin depletion Mann - questionnaires are unreliable as they are self report techniques and could contain unreliable questions
Aggression could be caused by high serotonin receptor rather than low in the brain A reduction in aggressive behaviour was seen in violent delinquents taking anti-psychotic drugs (which reduce dopamine levels) High levels of dopamine result in aggressive behaviour Not yet well established claim Lavine
Increased levels of dopamine, via the use of amphetamines associated with displays of aggressive behaviour. Research into mice showed Mann et al Couppis and Kennedy Showed the reward pathways in the brain become engaged in response to an aggressive event Dopamine is involved as a positive reinforcement
Those who seek out aggressive encounters experience a sensation that is rewarding. Unreliable - low dope caused mice to have difficulty moving - not decreased aggression - decreased coordination - research on rats cannot apply to humans Androgen hormone produced in the male testes and the adrenal cortex. It plays a key role in development and differentiation in male traits and cell growth. It changes behaviour such as mood and memory. Evidence has shown that testosterone influences aggressive behaviour – during puberty androgen levels are higher which may lead to an increase in aggressive behaviour Wagner, Beuving and Hutchinson animal research, male mouse was castrated and overall levels of aggression reduced. If the mice were given testosterone the levels of aggression increased. Baucom et al women with higher levels of testosterone had higher occupation status due to assertiveness. Dabbs - High levels of testosterone – history of violent crimes (murder)Low levels of testosterone – history of non violent crimes (fraud) Behaviour can be manipulated by androgen Archer - Meta-analysis, 230 males over 5 studies, Showed a low but positive correlation between aggression and testosterone levels The Challenge Hypothesis – in Monogamous species testosterone rises in response to social challenge (male-male aggression) Surge of testosterone levels resulting in increased aggression (dispute over female) Correlation research - Difficult to establish a casual link between testosterone and aggressive behaviours as other factors are involved (dominance, impulsiveness and competitiveness) Testosterone is not the only factor that influences aggression, at times environmental factors have correlated strongly Individual differences Harrison - 56 men ages 20-50 given testosterone and asked to play a PC game to induce frustration. Aggression responses were significantly increased but not in the whole sample Although some studies show positive correlations others have found no relationship. The correlations are usually found using small samples of men in prison using self-report technique s + T T Concordance rate - compare (likelihood of one twin having something and the other having it too) High rates in MZ - genetic link Hereditory - genetics/inheriting (parents)
Predispose - more prone to be.. MAOA linked with aggression 500 male children Caspi MAOA MAOA Maltreated Maltreated Did not show anti-social beh Grow up with anti-social beh Interactions between genes and environment that determines beh such as agg MAOA controls levels of serotonin and influence of dopamine Genetic deflect Low levels of MAOA Abnormal serotonin and dopamine levels Aggression Pleasure (enjoy aggression) Mcguffin and Gottesman
Concordance rate of 87% for aggressive and anti-social beh for MZ twins - only 72% for DZ twins Identical twins had higher concordance rate - supporting genetics and nature
However, the high statistics for the DZ twins suggests that environment can have effect Hutchings and Mednick
14,000 adoptions in Denmark - a significant number of adopted boys with criminal convictions had biological parents with criminal convictions Evidence for genetic effect - the adoptive parents have no effect on boys Brunner
Dutch family - male family members behaved violently and aggressively (rape and arson)
Men were found to have low levels of MAOA
Defect in gene was later found - gene causes low levels Supports influence of nature - genetic factors within the male family members
As they are a family the research also supports nurture MAOA MAOA - gene that is known to regulate serotonin levels Drive to pass on genes Natural selection:
Adaptive beh continue
Aggression - adaptive Fight off competitors Find a mate: sexual selection: seek out potential partner with 'best' genes Natural selection:
Adaptive beh continue
Aggression - adaptive Mate retention strategies: direct guarding and negative inducements In extreme pass on genes by force: rape In extreme: Uxoricide to prevent rivals from passing on their genes with your partner Avoiding Cuckoldry
Uxoricide - possible if taken to far Retain the mate: to produce and raise offspring Jealousy Cuckoldry Direct guarding Negative inducements Uxoricide Overall outcome

Prevention strategies Mate retention strategies Up until 1974 in Texas when a man killed his wife's lover 'whilst in the act' would a remain unpunished Jealousy is found in all human culture - suggests it is an evolved behaviour - innate - not learnt through environment Sexual jealousy - found mostly in males - uncertainty
Females know the baby is biologically hers - males have to trust Woman Men Unfaithful husband - her and children survival at risk Woman who carried out a self-report Q and regarded their partners as being jealous were twice as likely to experience serious violence - 725 of those required medical attention
Men who expected their partner of infidelity over next year gave greater punishments for known or suspected infedility - supports claim that mate retention strategies are evoked only when adaptive problem is faced Unintended outcome of an adaptive function that was designed to deter partners from committing infidelity Pipat Lueprasitkul was freed from court in Thailand after battering his wife to death in a rage of jealousy - discovered that she had visited a former lover - he was subjected to 2 years in prisons after the court took his background, young children and the jealous situation into account Study found 50% of women in Thailand are subject to physical or sexual violence at some point in their lives Shakleford - suggests women who are younger at an age which is most reproductively valuable - greater risk of uxoricide - regardless of partner.
Uxoricide seems to contradict the evolutionary logic - women at younger age - more productive and therefore, valuable - killing her would be a significant loss Duntley and Buss
Infedility of a partner carries a double loss for a male - decreases his own reproductive fitness also increasing another mans fitness - by killing her he can prevent at least one loss - preventing another man from gaining reproductive fitness Prevents Loss Gain Evolution of Homicide Lack of resources:
Wilson and Daly found 73% of the male perpetrators were unmarried and 41% were unemployed - also found 68% male victims were unmarried and 43% were unemployed Sexual jealousy:
Men are predominantly the killers - victims sexual jealousy is potentially key antagonist for male-male homicide
Daly and Wilson - summary of 8 studies - found within 'love triangles' same-sex killings - 92% were male-male homicides only 8% female-female homicides Aggression in females:
If a female is aggressive - may provoke the opponent putting the female at risk - research has found mortality rates for children are much higher if the mother dies than the father - applied cross-culturally as mothers in Western culture are more likely to gain custody of the children in marriage break up - mother is concerned for her health to look after children
Mark and Nesse studies on fears and phobias - things women fear relate to things hunter-gatherers feared during time of evolutionary adaptation - agoraphobia - prevalent in young women and represent open space where vulnerable to attack Bettencourt and Miller
Meta-analysis on 127 lab studies - woman believed aggressors to be in greater danger - by displaying agg beh you may incite agg beh in an opponent Shakelford
Survey method to test evolutionary explanations
461 males and 560 females - uni or communities
All p's in committed relationships
Male p's answered Q on their mate retention strategies and were assessed on how often they performed each of the 26 diff violent acts against their partners
Female p's answered Q concerning their partners use of male retention strategies and the degree of the use of violence

Results shows 2 types of retention strategies (negative inducements and direct guarding) by men was positively correlated with their violence scores - use of emotional manipulation (kill themselves if they left him) specific tactics appeared to consistently predict men's violence against women
Same patterns emerged regardless of age or length of relationship
Female p's confirmed this trend - reports of direct guarding and negative inducements being positively correlated with their experience of female-directed violence Gender bias - studies focuses on male retention strategies and male violence against women - women also engage in retention strategies and violence - research suggests that women initiate and carry out physical assaults of their partners as often as men do Useful research - particular tactics of mate retention used by males can be early indicator of violence against female partner - alert friends and family to the danger signs - help can be found and offered before Individual and cultural differences - cannot explain why people act in such different ways when faced with some adaptive problem - Buss and Shakelford - current evolution perspective cannot account for why 3 men confronted with wife's infidelity will result in beating in one case - homicide in second - getting drunk in third case
Can't explain why some cultures seem to require male violence to attain status whereas in others violence results in reputation damage Compatibility with evolutionary theory - men kill their wives when they are most reproductively valuable - contradicts evolutionary logic as men should regard such women as 'prized property' An alternative explanation - evolved homicide module theory - partners infedility carries double loss for the male, particularly when the female is still of reproductive age - lose his partner but another man gains a partner increasing their reproductive chance - killing his wife prevents another man Sports events High levels of violence and prejudicial comments made between supporters of different clubs/countries Xenophobia - fear of strangers Agg towards out-group members = adaptive Increase chances of genes surviving if altruistic - self-less - towards in-group members and hostile towards potentially threatening out-group members Claims negative stereotyping = adaptive, better to overexagerate threat of outsides than underestimate Seen today in sports crowds - members show solidarity to in-group members and hostility to out-group members Polaliri and Balestri
Studied Italian football crowds - societal divides between Northern and Southern Italy were evident in football terraces
Chants and banners showed openly extremist and xenophobic messages - evident to support link between xenophobia and agg at sports events Divide = + Evans and Rowe
Analysed post match reports from 40 football matches in Europe
Found more aggression and violence associated with matches involving the national side than club side - supports the link between xenophobia and agg - national sides - less ethnically diverse therefore, stronger in-group and out-group associations Only football teams?
These types of people?
Maybe not all sports events? Can be argued that football violence is not disorganised set of violent acts - usually displayed by young males needing acceptance from peers Warfare By displaying agg in the form of a group there is greater chance of survival compared with acting alone as group offers more power and greater protection to individuals - thought that much can be gained by entering into a conflict which often occurs between local villages - increasing the size of the village they will increase manpower and level of skill - giving them confidence in victory and reduce the odd of being killed Chagnon - there is constant fighting between branches of Yanomamo tribes for access to women or to improve the status of one tribe over another Small villages easy target - adaptive response as increases manpower and their access to weaponry which increases likelihood of survival Pinker - found women's reproductive success is not determined by the number of available men - women are rarely involved in war - more risk
Consequence - no reason for them to be agg and raid other villages which contradicts the idea that group displays of agg are evolutionary advantage for women Supports the nature via nurture by implying that you have an innate drive to pass on your genes which is expressed dependent on your cultural influence - Implications of group displays of agg -
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