Biological factors: Aggression

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  • Created on: 13-11-19 13:10

Neural and hormonal influences of aggression: assu

Assume that aggression is located within biological make-up of the individual rather than in the environment around them.

  • Low levels of serotonin
  • High levels of testosterone
  • Abnormalities in hippocampus functioning
  • Abnormalities in amygdala

Are associated with aggression

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Neural influences – fast response cannot conscious

The limbic system is an area of the brain that helps coordinate behaviour that satisfy motivational and emotional urges. Two key structures in the limbic system that are associated with aggression are amygdala and the hippocampus.

The amygdala: this quickly evaluates the emotional importance of sensory information and prompting an appropriate response if certain areas are stimulated electrically. An animal responds with aggression like snarling if these areas are surgically removed the animal would no longer respond to that stimuli  Kulver and Bucy 1937 discovered that the destruction of the amygdala in the monkey who was dominate in a social group caused it to lose its dominant place in the group – you can provoke it so you can measure through observation use FMRI or observe someone in a damaged brain. 

The hippocampus involved in formation in formation of long-term memory  and allows an animal had previously been attacked by another animal the next time they encounter that animal they encounter that animal they are likely to respond with aggression or fear whichever is more appropriate impaired hippocampal function prevents the nervous system from putting things into a relevant and meaningful context and so may cause the amygdala to respond inappropriately to sensory stimuli resulting in aggressive behaviour for example Boccardi et al found that habitually violent offenders exhibited abnormalities of hippocampal functioning.

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reserch support Amygdala: Pardini et al 2014: found that reduced amygdala volume can predict the development of severe and persistent aggression they carried out a longitudinal study of male participants from childhood to adulthood. Some 56 of the participants with varying histories of violence were subjected to a brain MRI at age 26 the results showed that participants with lower amygdala volume and aggressive behaviour remained even after other confounding variables were controlled this suggests that the amygdala plays an important role in evaluating the emotional importance of sensory information and that lower amygdala volume compromises this ability and makes a violent response more likely.

Research support: Hippocampus: Raine et al., (2004) support that role of hippocampus in aggressive behaviors with violent offenders. Suggested that asymmetry of the hippocampus may lead to inappropriate verbal and physical responses as the hippocampus and amygdala cannot work together effectively. This is correlational so this does not mean brain anomaly caused aggressive behavior (could be the other way around) the amygdala may be the trigger, but could be a factor


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role of serotonin

Serotonin this exerts a calming, inhibitory effect on neuronal firing in the brain serotonin typically inhibits the firing of the amygdala the part of the brain that controls fear and anger low levels of serotonin remove inhibitory effect with the consequence that individuals are less able to control impulsive and aggressive behaviour as a results the amygdala is stimulated by external events it becomes more active causing the person to act on their impulses and making aggression more likely. Although it was thought to reduce aggression by inhibiting responses to emotional stimuli that might otherwise lead to an aggressive response low levels of serotonin in the brain have been associated with an increased susceptibility to impulsive behaviour and aggression some drugs are thought to alter serotonin levels and increase aggressive behaviour

Evidence: Mann (1990) when levels of serotonin were artificially reduced by a drug (dexfenfluramine) participants responses to an aggression questionnaire were increased (not in females though!)  Findings on serotonin replicated in vervet monkeys with tryptophan (Raleigh et al, 1991)but, issues of:  extrapolation, Ethics

Findings on serotonin also confirmed via studies on anti-depressants

§  However, Leonard (2008) cautions that serotonin not just linked to aggression: also to impulsive behaviour, depression, over-eating, alcohol abuse; violent suicide. Are we sure, that serotonin cause’s aggression as It can cause other things. Cannot say it causes it but an factor or effect

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role of serotonin: evaluation

Research support serotonin: Duke et al 2013 provided support for serotonin deficiency as an explanation for aggressive behavior meta-analysis of 175 studied involving 6,500 P’s found inverse relationship relationship between serotonin levels and aggression anger and hostility they also found that the magnitude of the relationship varied with the methods used to assess serotonin functioning with year of publication and with self-reported aggression which was positively correlated to serotonin functioning this suggests that the relationship between serotonin and aggression is more complex than originally thought.

There may be cultural differences which suggests that aggression is not totally bias however suggest that environmental factors effect aggression to which could suggest that different cultures discourage/ encourage aggressive behavior. Tribes unite around aggressive behavior for survival. Or laddish behavior and gun culture

However low levels of MAOA when they have high levels of serotonin (can use to criticise serotonin-based explanation for aggression). As the individual still has a disposition to aggressive behaviours which argues the point that serotonin doesn’t have much of an influence over aggressive behaviours.

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Hormonal influences- slow response

Testosterone produces male characteristic’s, which reach peak level in young males the male sex hormone is though to influences aggression from young adulthood onwards due to its action on brain areas that involve controlling aggression. Sapolsky 1998 wrote how removing the source of testosterone in different species typically resulted in much lower levels of aggression subsequently reinstating normal testosterone levels with injections of synthetic testorone led to return of aggressive behavior.

The idea that testosterone is related to human aggression comes from various sources for example men are genually more aggressive then women. Archer 1990 in addition at an age when testosterone concentrations of testosterone than women in addition Dabbs said at any age when testosterone concentrations are at their highest there is an increase in male-on-male aggressive behavior. Dabbs 1987 measured salivary testosterone in violent and non-violent criminals. Carre and Olmstead 2015 claim that testosterone concentrations are not static but fluctuate rapidly in content of changes to the social environment changes in testosterone levels appear to influence aggressive behavior by increasing amygdala reactivity during the processing of social threat.

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Inconsistent evidence: Despite many studies showing a positive relationship between testosterone and oppression other studies find no such correlation for example positive correlations have been reported between levels of testosterone and self-reported levels and the likelihood of responding aggressively to provocation on the other hand no correlation was found between testosterone levels and actual violent behavior among male inmates in prison this suggests that the relationship between testosterone and aggression in humans remains unclear

Aggression or dominance Mazur 1985 suggests we should distinguish aggression from dominance individuals act aggressively when their intent is to inflict injury whereas they act dominantly is their wish is to achieve or maintain status over another individual they claim that aggression is just one form of dominant behavior in non-human animals the influence of testosterone on dominance behavior might be shown through aggressive behavior in humans however the influence of testosterone on dominance is likely to be expressed in more varied and subtle ways Elisenegger found that testosterone could make women act nicer rather than more aggressive this lends to support to the idea that rather than directly increasing aggression testosterone promotes status seeking behavior which is aggression type one.

Hard determinism as it assumes that this is only present within males alpha gender bias as it over emphasizes the differences between genders it is also hard to establish if testosterone causes aggression Cannot isolate what one hormone is responsible for.

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Genetic factors in aggression: twin studies

Looking for 100% concordance rates (for every one identical twin that displays the characteristics so does every second one. If 50% half the identical twins will show the characteristics) never 100% concordance rates as other factors involved

Monozygotic (MZ) (identical) twins share all of their genes while DZ twins (non-identical) share only 50%. researchers compare the degree of similarity for a particular trait between the sets of MZ twins and compare that with sets of DZ twins if the MZ twins are more alike in aggressive behaviour then this should be due to genes rather than environment. (Both sets of twins share the same environment and MZ twins share the same genes so if they are more alike in terms of aggressive behaviour this should be shared with genes)Coccarao et al 1997 found that nearly 50% of the variance in direct aggressive behaviour could be attributed to genetic factor

However many studies in this area have focused exclusively on individuals convicted of violent crime. Difficulty trying to draw meaningful conclusions from these studies. Convictions for violent crime are relatively few compared to the vast number of violent attacks that do not result in conviction therefore only represent a small minority. These studies also do not take into account that MZ may be treated more similarly in the environment than DZ twins causing them to develop similar behaviours.

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Genetic factors in aggression: adoption

Adoption studies-  adoption studies can help to untangle the relative contribution of environment and heredity in aggression.

14,000 adoptions in Denmark between 1927-1947 Hutching and Mednick 1975

-          Groups- base line criminal rate- 14%/  children of violent criminal biological parents adopted to non- criminal parents 20%/ Children of non-criminal biological parents adopted by criminal parents- 15%/ Both biological and adoptive parents – 25%

-          if a positive correlation is found between aggressive behaviour in adopted children and aggressive behaviour in their biological parents, a genetic effect is implied. As those with criminal parents show high % of those that go on to commit crime. And those with both criminal in biological and adoptive even higher. But other factors may affect why this rate is so high with emotional distress that may come from being adopted

 Genetic factors- Rhee and waldman (2002) combined the results of 51 twin and adoption studies and concluded that aggressive anti-social behaviour was largely a product of genetic contributions. However, in this study as with the miles and carey study above several variables including age and assessment method of aggression although genetic factors play a significant part in the development of aggressive behaviours the influence of other factors affects their expression.

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Genetic factors in aggression: adoption evaluation

However many of the reported studies of aggression have relied on either parental or self-reports of aggressive behaviour whereas other studies have made use of observational techniques. Meta-analysis found genetic factors explained a large proportion of the variance in aggressive behaviour studies that had used parental and self-reports use of observational methods showed less genetic contribution  and greater influence of genetic factors this makes it hard to assess the contributions of each factors.

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is responsible for regulation of metabolism of serotonin in the brain, which are associated with aggressive behaviours.

Genes and serotonin- it is argued that neurological levels are genetically determined the gene responsible for producing MAOA (Monoamine Oxidase) has been associated with aggressive behaviour A Dutch family with multiple brothers found that the males were very violent and they were all found to have low levels of MAOA and a defect on their X chromosome was also identified (Brunner et al 1993).  

Caspi et al 2002 found that children with low levels of MAOA + MAOA-L displayed more anti-social behaviour but only if they had been maltreated as children, children with high MAOA+ MAOA-L and who were maltreated and those with MAOA-L who were not mistreated were not likely to become aggressive ( if just mistreated psycho-dynamic approach)

The warrior gene MAOA-L is more frequent in populations with a history of warfare with about 2/3’s of people in these populations having this version of the gene by way of contrast only about 1/3 of people in western populations have this low activity this has led to it being referred to as the warrior gene McDermott et al 2009 found that MAOA-L participants displayed higher levels of aggression when provoked than did MAOA-H subjects

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May explain different rates of crime in male and female the MAOA gene is linked to the X chromosome women have two X where as men only have one women inheriting same gene unlikely to be affected this could explain why men exert behaviour that is more aggressive. However could lead to alpha gender bias

Tihonen et al (2015) found that MAOA-L in combination with another gene CDH13 was associated with extremely violent behaviour in Finnish prisoners there was no evidence of these genes amongst non-violent offenders however while these genes may lower the control of violent urges they do not predetermine violent behaviour 

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