3.1 Aggression

neural and hormonal explanations- outline 1

The limbic system coordinates behaviour that satisfies emotion and motivational urges such as fear and aggression

Associated with aggression is the amygdala and hippocampus

Amygdala = evaluates sensory information and prompts a response

If certain areas are stimulated animals response with aggression. Removing the amygdala eliminates the aggressive responsive

Hippocampus = involved in forming long term memories 

If an animal encounters one it had been attacked by it will respond aggressively

Impaired functioning -> stops the nervous system putting stimulus in context. Can cause inappropriate aggressive responses

Boccardi (10)- habitually violent offenders show impaired hippocampus functioning

neural and hormonal explanations- evaluation 1: research support

Amygdala → Pardini (14) – carried out a longitudinal study of 56 male participants with varying histories of violence

MRI scans showed those with lower amygdala volumes exhibited higher levels of aggression

Suggests that the amygdala plays a key role in evaluating sensory information, a lower volume makes aggression more likely

neural and hormonal explanations- evaluation 2: research support

In the role of the hippocampus in aggression through MRI scans of hippocampi symmetry

Raine (04) found that the hippocampus in the right and left hemispheres were different in size in unsuccessful criminals but not in successful violent criminals

Hippocampi symmetry possible arises early in brain development

These asymmetries might impair the ability of the amygdala and hippocampus to work together leading to difficulties processing emotional stimuli leading to inappropriate responses

neural and hormonal explanations- outline 2

Serotonin is an inhibitory neurotransmitter which is involved in inhibiting responses to emotional stimuli which may provoke an aggressive response

Low levels of serotonin are associated with an increased susceptibility to impulsive behaviour -> aggression and suicide

Low brain serotonin makes communication between the limbic system and the frontal lobes weaker. So it is more difficult for the pre-frontal cortex to control emotional responses to anger that are generated within the amygdala.

Research evidence= Mann gave 35 healthy participants dexfenfluramine which depletes serotonin. A questionnaire was then used to assess hostility and aggression levels, the findings showed that the dexfenfluramine increased aggression and hostility but this was only in males

neural and hormonal explanations- evaluation 3: research support

For the link between low levels of serotonin and increased aggression

Raleigh- study of vervet monkeys. Some of them were fed on experimental diets containing high levels of tryptophan which increases serotonin levels

These monkeys then exhibited low levels of aggression. Those fed on diets which were low in tryptophan exhibited increased aggression which suggests that differences in aggression could be attributed to their serotonin levels

However, the generalisability of this study is questionable due to the fact that it focuses on animals, not humans, the results may not be generalizable

neural and hormonal explanations- outline 3

Testosterone is a male sex hormone that is thought to influence aggression from puberty onwards

During puberty is when peak production of testosterone takes place leading to a peak in aggression

Research support for this= Dabbs measured salivary testosterone in 692 violent and non-violent criminals, the findings showed that those who had a history of violence had a history of violence had higher levels of testosterone

This study shows that a high level of testosterone correlates with high levels of aggression

neural and hormonal explanations- evaluation 4: research support

The link between testosterone and aggression comes from a meta-analysis of 45 studies

Book- established there was a mean correlation of 0.14 between testosterone and aggression

Shows a low correlation which remains statistically significant as many studies were used

However, as the correlation is low, it is best viewed that testosterone is a contributory factor of aggression

neural and hormonal explanations- evaluation 5: inconclusive evidence

Research into testosterone as a cause of aggression

Albert- suggested that some studies showed that there was in fact no link at all

There are also many methodological issues with some studies into the link between testosterone and aggression such as the severity of crime, small samples and self-reports of aggression

Drawing causal conclusions is therefore extremely difficult

genetic explanations- outline 1

Psychologists use twin studies to investigate the possible genetic basis for aggression

MZ share all the same genes whereas DZ –twins share up to 50%. If MZ twins have higher concordance rates in terms of aggression, then it could be inferred that there is a genetic basis for aggression

Most studies have focused on criminality but some on aggression

Cocarro- 50% of the variance in direct aggression could be attributed to genetics.

This suggests that genes may contribute to aggression rather than directly cause it

genetic explanations- outline 2

Adoption studies can help to untangle the complex relationship between genetic and the environment

The focus is on adopted children and looking for a positive correlation between the child and the biological parents – this would imply a genetic effect

Hutchings and Mednick- looked at 14,000 adoptions in Denmark. They found a considerable number of boys with criminal convictions had biological parents with criminal convictions

This again suggests that genes do play a role in aggressive behaviour

genetic explanations- outline 3

While work is ongoing in identifying a single gene responsible for aggression or gene combinations, initial research in this area was conducted by Brunner

Brunner- studied a Dutch family that were particularly aggressive, many of which were engaged in aggressive and violent crimes. The findings showed that they all had abnormally low levels of MAOA, and later research identified a defect in the gene responsible for MAOA

Since then Monoamine Oxidase A (MAOA) has been associated with aggression

While historically low serotonin has been associated with aggression ‘serotonin deficiency hypothesis’ MAOA regulates / metabolises serotonin and low levels of serotonin activity leading to a build-up of serotonin is also associated with aggression

genetic explanations- evaluation 1: strength

research into genetic causes of aggression may help to explain gender differences in terms of aggression. The MAOA gene is linked to the X chromosome

When men inherit the defective X chromosome they are more likely to be affected by it, whereas women inheriting the same gen are largely unaffected

This could explain gender differences. However aggression shown by women is often under-studied and under reported so gender differences are perhaps not well understood

genetic explanations- evaluation 2: limitation

a difficulty researching in this area is determining the role of genetic and environmental factors

This is compounded by a number of issues. More than one gene usually contributes to a given behaviour, and there are many environmental factors to consider

Even identical twins receive special treatment that may lead to or explain their behaviour

These influences interact with each other – genetic factors may influence which environmental factors have an influence

genetic explanations- evaluation 3: research support

the relationship between genetics and aggression may be best explained through a combination of nature and nurture

Caspi (02) demonstrated that those with low levels of MAOA are only likely to develop aggressive tendencies if maltreated. Individuals with low levels of MAOA who were well treated were not more aggressive

Individuals may therefore be predisposed to aggression but their environment will determine if this is triggered

genetic explanations- evaluation 4: research support

 more recent research has identified possible Gene combinations responsible for aggression

Tiihonen (2015) studied Finnish prisoners revealing that MAOA – L in combination with the gene CDH13 was associated with extremely violent behaviour. There was no substantial evidence of these genes in non-violent offenders

Any behaviour is unlikely to be attributable to a single gene so as our understanding progresses the interaction of particular genes and the environment is likely to further our understanding

ethological explanations- outline 1

Ethological explanations stress the adaptive value of animal behaviours. Ethologists study the behaviour patterns of animals in their natural environments

Members of the same species have Fixed Action Patterns – a repertoire of stereotyped behaviours, which occur in specific conditions (i.e. in response to triggers) and which do not require learning

Fixed action patterns are triggered by Innate Releasing Mechanisms which are a neural network when stimulated by the presence of the sign stimulus communicates with motor control circuits to activate the fixed action pattern associated with that sign stimulus

An example is a male stickleback fish; their red underbelly is a sign stimulus that triggers an IRM which activates the FAP

ethological explanations- outline 2

In Lorenz’s Hydraulic Model he suggests that an Action Specific energy (ASE) builds up and then when the appropriate sign stimulus is observed the IRM is triggered, and the energy is released in the form of the FAP

The FAP may also be produced when too much ASE build up even without the sign

ethological explanations- outline 3

Some aggression is observed in ritualistic fashion

Ritualistic Aggression is in the form of threat displays which are designed to make opponents back down without fighting, meaning more dangerous aggression is less likely

An example of ritualistic aggression is gorillas pounding their chests to intimidate a rival and make their opponents back down

ethological explanations- outline 4

it is thought that predator species have instinctive inhibitors that prevent animals using weapons on their own species

Species such as wolves have behavioural inhibitions that allow them to express dominance and submission to establish pack order while not killing. This is especially important in terms of survival as the pack size will be a key variant in survival

Non hunting species without natural weapons have not developed inhibitors. It is thought that humans have no natural weapons so have not developed the inhibitions

ethological explanations- evaluation 1: benefits of ritualised aggression

evident in human cultures in the same way they are amongst animals

Ritualised aggression is evident in tribal communities where it prevents aggression from escalating into dangerous physical aggression

Among the Yanomamo people chest pounding and club fighting can settle conflicts and among the Inuit community’s song duels are often used to minimise harm (Hobel 67)

Such rituals serve an adaptive advantage in minimise harm by preventing serious injury or death thus preserving the all-important numbers within a tribe or community essential for their protection and survival

ethological explanations- evaluation 2: criticisms

Firstly, the instinctive view, in that FAP’s are innate is challenged by the research

Lehman suggests that learning and experience interact with innate factors in complex ways. Research has shown that there are subtle differences between conspecifics in the production of aggressive behaviour

This shows that aggressive behaviour patterns are not fixed as Lorenz had claimed but there is an innate potential that is then developed within the environment

This would support Bandura’s SLT theory of aggression in which there may be biological underpinnings of aggression, but the environment is the key variable in determining the learnt response of aggression

ethological explanations- evaluation 3: debate to whether humans have fixed action patterns in terms of aggression

Humans do have some FAP’s such as smiling as a sign of greeting

But the human environment has changed so rapidly that aggressive FAP’s are no longer adaptive in modern times

This suggests that while some animals may respond to sign stimulus humans as a more advanced species may not respond to such signs

ethological explanations- evaluation 4: limitation

Of the Hydraulic Model

It is suggested that a FAP’s cannot be reproduced until a build-up of ASE occurs

However, Van Holst (54) showed that performing an aggressive behaviour can increase rather than decrease the likelihood of further aggression

This suggests that Lorenz was incorrect regarding FAP’s leading to a reduction in action specific energy and the likelihood of further aggression

ethological explanations- limitation

killing conspecifics is not rare

In some species this is common, the male lion will kill the cubs of other males and male chimpanzees will routinely kill members of other groups

This suggests that killing conspecifics is not as rare as Lorenz believed and as such the idea of instinctive inhibitions lacks validity

the evolutionary model- outline 1

Evolutionary explanation of aggression would suggest that the human brain is the product of natural selection. Therefore, aggression as a strategy would have to have been effective at solving adaptive problems

Solving such problems would have enhanced survival and reproductive success and as a result would have been spread among the gene pool

A first explanation would be that aggression is the result of sexual competition. Ancestral males would have had to compete with other males for access to females. Individuals who used aggression would have been more successful in acquiring mates and passing on their genes to offspring. This would have led to the development of a genetically transmitted tendency for males to be aggressive towards other males

Putts (10) argues that that increased muscle mass implies that competition with other males did take place among ancestral males

the evolutionary model- outline 2

A second explanation is that aggression is the result of sexual jealousy because of parental uncertainty

As a result of this men are always at risk of cuckoldry which is the consequence of a partner’s infidelity. The adaptive functions of sexual jealousy are to minimize the risk of cuckoldry

Buss (88) suggests that sexual jealousy may result in violence or mate retention strategies to prevent a partner from straying or aggressive behaviour towards a perceived love rival, this is all to protect an individual’s reproduction capability meaning their family tree will be carried on

the evolutionary model- outline 3

Warfare as an act of aggression can also be explained from an evolutionary perspective in that any behaviour that is associated with warfare must have evolved due to the adaptive benefits to the individual and their offspring.

for example male warriors tended to have more sexual partners and more children suggesting a direct link with the aggressive behaviour and the reproduction benefits

Furthermore, displays of aggression and bravery in battle will also increase a warrior’s status. Meaning these individuals are more likely to share the benefits associated with that status

the evolutionary model- evaluation 1- research support

For the evolutionary explanations of aggression through research that claim that aggression confer status.

Campbell has found in gangs that the highest status in the gang is given to those who are the more aggressive ones, furthermore researchers have shown that in tribes the higher status is given to the members who had committed murder

Additionally, there is evidence to suggest that the main cause of male-on-male violence is when one male is perceived to be questioning another man’s status (Buss)

As a result, this shows that aggressive behaviour has dual benefits it increases status, but it is also used to defends one’s status as well

the evolutionary model- evaluation 2- limitation

All these ideas suggest that higher levels of aggression in males is therefore a genetic adaptation however, Prinz suggests that the gender differences can be better explained through socialization

He suggests that males may be more prone to receiving physical violent punishments from parents, which could lead to an increase in male violence

Furthermore, females are usually verbally told that what they did were wrong as a punishment, as females realize they are not a physically powerful as men they need a different strategy of displaying aggression, this is usually done verbally

Females tend to adopt more social forms of aggression rather than physical forms of aggression

This challenges the view that males alone have evolved aggression as a way of dealing with rivals, as females have simply developed a different form of aggression

the evolutionary model- evaluation 3- limitation

limitation of evolutionary explanations is that aggression may be more maladaptive rather than adaptive

There is an issue with associating aggressive behaviour with successfully dealing with social challenges, this is because sometimes aggressive/ violent behaviour is sometimes maladaptive

for example an aggressive male may be rejected as a mate or social ostracism

However, Buss claims that the adaptive benefits of aggressive behaviour must have outweighed the costs and the benefits of the other strategies to be evolved and past on through generations and not fall away like the other strategies will have

the evolutionary model- evaluation 4- limitation

This is because it is suggested that female behaviour is not accurately reflected in war due to the lack of female warriors

There is a distinctive lack of female warriors as there is much greater cost to women of taking part in warfare, this being the reproductive cost

Furthermore, there is less benefit to the women as they do not increase in fitness or status as much as males do from war

The main source of information regarding displays of aggression is from war as a result this information is limited to men due to the lack of female warriors meaning it may not be applicable to women at all

the evolutionary model- evaluation 5- limitation

there are issues with the evolutionary explanation of aggression being created post hoc

The evolutionary explanation suggests that war is passed on through the genes however this is unlikely, war is more likely to have derived from when there was a switch from the nomadic existence to settlements causing war to be a rational response in terms of battling for resources and mates

Therefore, warfare may actually be caused by environmental change rather than genetics leading to an issue for this explanation