Biological explanations of aggression Flashcards
Explain hormonal mechanisms in aggression
Studies of cultural differences find males are typically more aggressive than females. This could be an effect of environmental factors (e.g. SLT) but it is likely there are biological differences such as levels of testosterone. This hormone is produced by both males and females but males produce 10 times more than females. Highest levels of testosterone are produced in males aged 15-25, the group most likely to commit violent crimes.
Beeman - castrated male mice and found that aggression was reduced. He later injected the mice with testosterone which re-established their aggressiveness. Castration has since been used as a method for making domestic and farm animals more manageable.
Testosterone is also clearly related to aggression in humans. Dabbs - measured testosterone in saliva of 692 adult male prisoners and found higher levels in rapists and violent offenders than in burglars and thieves. Dabbs - also looked at 12 fraternities in 2 universities. Members of fraternities with highest levels of testosterone were described as boisterous and macho, those with lowest were attentive and helpful. The same effects were also found in women. Dabbs - tested female prisoners and found testosterone was highest in cases of unprovoked violence but lowest where violence was defensive (e.g. in domestic abuse cases).
Explain Neural mechanisms in Aggression - brain abnormality
Brain abnormality, as a result of injury or disease, can lead to aggression. normal aggressive behaviour is not dependent on separate and independently functioning brain structures, but an interaction of a system of structures, including the hypothalamus, amygdala and periaqueductal grey (PAG). These are organised hierarchically and moderated by the pre-frontal cortex. the role of the pre-frontal cortex is to control the expression of aggression. The amygdala has an important function in aggression. A taming effect was found in rhesus monkeys by removing part of the temporal lobes and therefore destroying the amygdala. This is known as Kulver-Bulcy syndrome. In humans, Narabyashi et al - found 43/51 patients whose amygdala was destroyed through psychosurgery showed reduced aggression afterwards. Mark & Ervin - conducted a case study of a female patient behaviour following electrical simulation of her amygdala. She exhibited facial grimacing, became very angry and flung herself at the wall. Ashford - showed temporal lobe epileptics often become aggressive, attacking furniture and people.
The pre-frontal cortex regulates the emotional responses driven by the amygdala. Damage to the pre frontal cortex results in impulsivity, immaturity and loss of control, and Anderson et al - found damage during infancy related to aggressive behaviour as adults.
Raine et al - investigated brain activity of 41 murderers using PET scans, and found reduced glucose metabolisms in prefrontal cortex suggesting this brain area is less active than in normal controls. Also, Volkow et al - found violent psychiatric patients has reduced cerebral blood flow to the prefrontal cortex.
Explain neural mechanisms in aggression - Neurotransmitters
Aggression in both animals and humans has been associated with
- low levels of serotonin
- high levels of dopamine
Normal levels of serotonin have a calming effect on neural firing in the brain. Low levels, particularly in the pre-frontal cortex remove this inhibitory effect. Individuals are then less able to control impulsive and aggressive responses.
Evidence for low levels of serotonin contribution to aggressive behaviour.
i) the major metabolite (waste product) of serotonin tends to be low in the cerebrospinal fluid of people who show impulsive and aggressive behaviour.
ii) the drug dexfenfluramine is known to reduce serotonin levels in the brain. Mann - gave the drugs to 35 healthy adults and used a questionnaire to assess hostility and aggression levels. They found that among males, but not females, the drug led to increased aggression levels.
iii) drugs to raise serotonin levels, such as trytophan have been given to juvenile delinquents and unpredictable institutionalised patients.
iv) research with vervet monkeys found reducing serotonin levels resulted in increased aggressive behaviour, whereas increasing serotonin decreased the aggressive occurrences.
Evaluate/AID neural and hormonal mechanisms in aggressive behaviour
-Much of this work is a biological approach. However, the role of the pre-frontal cortex to mediate aggressive responses suggests cognitive factors.
-Biological reductionism
-Some research uses animals
-Free-will versus determinism
-Ethics e.g. psychosurgery
Possible gender bias
Possible cultural bias
Practical application e.g. psychosurgery, drugs to treat aggression
What is proposed by the genetic theory?
Pure genetic theory proposes that genes are the cause of aggressive behaviour. Consequently, through genetic transmission, aggression can be passed from one generation to the net. Social psychological explanations are played down as influences of aggression. In reality genes do not directly cause aggression but influence elements of our biology that contribute to it. Some of these effects are structural i.e. the genes contribute elements necessary for aggression such as muscle and bone development. Other genetic effects can be considered functional, i.e. they influence neurochemical and hormonal systems. A combination of these structural and functional elements contributes to an animal’s aggressive behaviour.
Explain genetic factors in aggressive behaviour
Researchers have identified a number of ‘candidate genes’ that are thought to contribute to an increased risk of engaging in antisocial behaviour. Studies in this area typically examine whether one particular variant of a candidate gene occurs more often in people who display aggressive behaviour than a comparison group. A meta analysis of studies of the gene for the dopamine receptor D4 (DRD4) found a moderate association between DRD4 and a tendency to ADHD. Retz et al - found an association between a DRD3 variant (the gene for dopamine receptor DRD3) and both impulsivity and ADHD related symptoms in violent offenders.
Most recent research has focused on the gene responsible for regulating the enzyme MAOA (monoamine oxidase A). This enzyme breaks down the neurotransmitters serotonin, noradrenaline and dopamine, removing excess amounts and allowing neurons to communicate more effectively. The link between mood and these neurochemicals is well established and a build up may cause people to respond excessively and aggressively to stressful situations. there are a number of studies to support the role of this specific gene in aggressive behaviour.
Discuss research into genetic factors in aggressive behaviour
- Brunner - studied a family in the Netherlands in which the men had a history of extreme violence. It was discovered the violent men in the family had a genetic defect on their X chromosome, a defect that cripples an enzyme which regulates aggressive behaviour. Bruner analysed the X chromosomes and found a marker on the X chromosome. One particular gene for MAOA lay in the vicinity of this marker. They also tested men’s urine and found excess levels of all three neurotransmitters (dopamine, serotonin and noradrenaline) and extremely low levels of substances left over after MAOA has done its work. Excess neurotransmitters may in some way predispose the men to violence when under stress
Evaluation - role of environmental factors, limited influence of gene e.g. Not enough evidence to say MAOA is the gene that causes aggression . - - There are different forms of the MAOA gene - a low (L) activity version and a high (H) activity version. Research suggests that it is the MAOA-L gene which predisposes a person to violence. Mc Dermott (2009) demonstrated in controlled experimental conditions how those with the MAOA-L gene were more likely to force someone to eat hot chilli sauce, despite having to pay to punish, than someone with the MAOA-H gene.
Animal studies:
Selective breeding of aggressive characteristics in animals (e.g. fighting dogs and bulls) has been carried out for years. It involves choosing animals with high levels of aggression and breeding them with others with similarly high levels of aggression.
Lagerspetz- carried out an influential laboratory based selective breeding study. She isolated a group of mice after weaning in order to identify mice that were more prone to aggression. she then interbred the aggressive mice so that after 19 generations, rates of aggression were 10 times higher than in controls. The aggressive mice also had heavier testes and forebrains and altered levels of serotonin and noradrenaline supporting the notion that genes influence both the structural and functional aspects of an animals biology. Lagerspetz does not claim genes are the only cause of aggression as it was possible to condition these mice to behave less aggressively, something that is not surprising considering that wild animals can be tamed to an extent through conditioning.
Discuss twin and adoption studies into genetic factors in aggression
Coccaro et al - assessed the degree of genetic and environmental influences on aggression in male participants (182 MZ and 118 DZ twin pairs) and from data estimated that:
- genes accounted for more than 40% of the individual differences in aggression
-environmental influences accounted for around 50% of individual differences in physical aggression and about 70% of individual differences in verbal aggression.
Therefore, genetic factors are important in aggression, but not as important as environmental factors.
This study did specifically investigate aggression whereas most studies look generally at anti-social behaviour. However, it is gender biased as it only focuses on males and other research (Button et al) suggests that genetic effects may be different in females.
Findings from twin studies have been extremely variable, possibly because different measures of aggression have been used. However, whilst concordance varies, what remains constant across all studies is a greater association of aggressiveness with MZ twins in than DZ twins, whether reared together or apart. This is strongly indicating a genetic contribution even if there is disagreement about it’s magnitude.
AID genetic factors in aggression
There are problems for this type of approach to explaining aggression as it focuses on nature and ignores the influence of nurture. However, few would accept either as the sole cause of aggression and instead would adopt a more plausible interactionist approach. this is known as the diathesis-stress model and when applied to aggression would suggests that individuals may inherit a predisposition towards behaving in a more aggressive way but that environmental stressors and other factors are responsible for triggering the aggression.
The genetic theory of aggression is also an example of the application of physiological reductionism in psychology. It attempts to reduce complex behaviour to amino acid sequencing genes. The clear advantage of this is that it leads to the application of concise and concrete concepts which are then susceptible to scientific methods of research. However, reductionism may be appropriate for the physical sciences, but less appropriate when trying to explain behaviour that is more complex. This is because we may be more than the sum of parts and behaviours tend to stem from a variety of factors including social, psychological and physiological causes.
The genetic theory of aggression is also an example of behaviours being caused by factors outside an individual’s control (biological determinism). This has important implications for the question of responsibility for violent behaviour and the subsequent treatment and punishment for perpetrators. Can we really hold people responsible for their genetic make-up? Some legal experts now question the assumption that a violent offender can still exercise free will despite possessing a genetic predisposition to violent crime. However, genes should not be used as an excuse - genes do not equal destiny.
conclude genetic factors of aggression
Genes do play some role in aggression as indicated by twin, adoption and selective breeding studies. Many researchers have attempted to identify the genes responsible and it seems that DRD3, DRD4 and MAOA genes are likely to play some role in aggression. However, genes only play partial role and it is likely that experiences and socio-cultural factors are also important influences in aggressive behaviour.
