Aggression Flashcards
Name neural mechanisms involved with aggression
- the limbic system (amygdala and hippocampus)
- serotonin
Describe the role of the limbic system
- area of the brain that helps to coordinate behaviours that satisfy motivational and emotional urges, such as aggression and fear
- Papez and Maclean linked the limbic system to emotional behaviours including aggression
- 2 key structures associated with aggression are the amygdala and hippocampus
Describe the role of the amygdala in aggression
- responsible for quickly evaluating the emotional importance of sensory information and generating an appropriate response
- If certain areas of the amygdala are stimulated electrically then an animal responds with aggression such as snarling and adopting an aggressive posture
- If the same area is surgically removed, the animal no longer responds to stimuli that would have led to rage
- Similarly, in humans, removal of the amygdala results in a reduction in violent behaviour
Research surrounding the role of the amygdala in aggression
- Narabayashi et al (1972) reported that 43 out of 51 patients who received operations to destroy their amygdala showed more normal social behaviour afterwards, including reduced aggression
- Gospic et al (2011)- some PPs subjected to mild provocation- when PPs reacted aggressively fMRI scans showed fast and heightened response by the amygdala
- a benzodiazepine drug (reduces arousal of the autonomic nervous system) taken before the provocation led to 2 effects- decreased activity of the amygdala and halved the number of rejections (reduced aggression)
Describe the role of the hippocampus in aggression
- involved in the formation of long-term memories
- This means that an animal can compare the conditions of a current threat with similar past experiences, so that they show an appropriate response (e.g., fear or aggression).
- Impaired hippocampal function may prevent 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
Research evidence for the role of the hippocampus in aggression
Boccardi et al (2010)- found that habitually violent offenders exhibited abnormalities of hippocampal functioning
Limbic system diagram
Limbic system and aggression- strengths
Evidence for role of amygdala:
- Pardini et al (2014)
- longitudinal study of male PPs from childhood to adulthood
- some of 56 PPs received MRI scan at age of 26
- discovered that that lower amygdala volume were associated with higher levels of aggression and violence
- relationship remained even after the researchers controlled for confounding variables s
- suggests that the amygdala plays an important role in evaluating the importance of sensory information and that lower amygdala volumes compromises this ability and makes a violent response more likely
Evidence for role of hippocampus:
- Raine et al (2004)
- Provided support for the role of the hippocampus in aggressive behaviour
- Two groups of violent criminals
- One group acted impulsively, the other ‘cold calculating criminals’
- Criminals who acted impulsively had differing sizes of their hippocampus
- The asymmetry of their hippocampus impacts the ability of the amygdala and the hippocampus to work together
- Emotion information not processed properly, leading to inappropriate verbal and physical responses
Evidence to link limbic system to aggression:
- Sumer et al (2007)
- reported on case study of a 14yo girl, who following an MRI scan was diagnosed with a tumour in the limbic system
- investigated because she had been experiencing epileptic seizures and was behaving in very aggressive manner
- when the tumour was treated with drugs, the girls level of aggression returned to normal
- provides support for the idea that high levels of aggression could be linked to the limbic system
Limbic system and aggression- weaknesses
Other brain structures involved:
- limbic structures (e.g. the amygdala) function together with the orbitofrontal cortex (OFC) which is not part of the limbic system
- the OFC is convolved in impulse regulation and inhibition of aggressive behaviour
- Coccaro et al (2007)- OFC activity is reduced in those with psychiatric disorders that feature aggression
- this reduced activity disrupts the OFCs impulse control function, which in turn causes aggressive behaviour
- shows that the neural explanation of aggression is more complex than theories focusing on the amygdala suggest
Direct or indirect effects:
- some argue that neural factors are directly linked to agression- e.g. Gospic et als study of amygdala creativity and benzodiazepines supports
- however, the role of neural factors may be indirect as may be other factors that influence it
Exact role of amygdala unclear:
- whilst some studies suggest that lower amygdala volume/amygdala activity is associated with higher levels of aggression, others have found the opposite
- e.g. Muller et al (203)- showed 6 male psychopaths and 6 normal male controls a series of positive and negative pictures whilst having their brain activity monitored using and fMRI and found that psychopaths had increased activity in amygdala
Correlational research:
- most research looking at neural influences on aggression is correlational
- good ethical reasons because opportunities to experimentally manipulate brain structures are limited but when two variables are correlated, it is impossible to establish which one is the cause of the other, or if there is a third variable involved
Describe the role of serotonin in aggression
- neurotransmitter involved in communication of impulses between neurones
- studies have shown that serotonin in normal levels exerts a calming, widespread inhibitory effect on neuronal firing in the brain
- therefore, it is claimed that low levels of serotonin, particularly in the prefrontal cortex, remove this inhibitory effect resulting in individuals being less able to control their impulsive and aggressive responses (deficiency leads to loss of self-control and increase in impulsive behaviour incl. aggression- Denson e al 2012)
Research evidence for role of serotonin in aggression
Mann et al (1990):
- gave 35 healthy individuals dexfenfluramine which is known to deplete serotonin
- using a questionnaire to assess hostility and aggressive levels, found that dexfenfluramine treatment in males (but not females) was associated with an increase in hostility and aggression scores
Virkkuenen et al (1994):
- the major metabolite 5-HIAA (waste product) of serotonin tends to be low in the cerebrospinal fluid of violent impulsive and violent non-impulsive offenders
- significantly lower in impulsive offenders
Role of serotonin- strengths
Research evidence:
- Crockett et al (2009)
- used game playing and moral dilemmas to observe behaviours
- One group had their serotonin levels reduced by manipulation of their diets
- others had their levels increased by being administered an SSRI
- this was temporary change
- found PPs given restrictive diet displayed higher levels of retaliation against their opponents, and the PPs who had higher levels of serotonin responded to emotional moral dilemmas with increased compassion
- These results together suggest that low serotonin levels can induce aggressive responses
BUT could be argued that this study has low validity because game playing is not a direct physical aggressive response- It could be, for example, that there is no effect of serotonin when measuring actual aggression
Animal studies:
- Raleigh et al (1991)
- found that vervet monkeys fed on experimental diets high in tryptophan (which increases serotonin levels in the brain) exhibited decreased levels of aggression
- Individuals fed on diets that were low in tryptophan exhibited increased aggression behaviour, suggesting that the difference in aggression could be attributed to their serotonin levels
Criminal studies:
- Davidson et al (2000)
- suggested that serotonin may provide an inhibitory function i.e. high serotonin levels may lower aggressive behaviour
- When comparing violent criminals to non-violent ones, the levels of serotonin found in violent criminals were markedly lower
Practical applications:
- has been shown that increasing serotonin levels in both juvenile delinquents (Morand) and in institutionalised patients (Greenwald) reduces their aggressive tendencies.
- Therefore, this means that aggression and violence can be controlled for the benefit of society
Drug research:
- Drugs (e.g. paroxetine) that increase serotonin have been found t also reduce levels of aggressive behaviour
- Berman et al (2009) gave PPs either placebo or dose of paroxetine
- PPs then took part in a lab-based game that involved giving and receiving electrical shocks in response to provocation (e.g. insults)
- the paroxetine group consistently gave fewer and less intensive shocks than the placebo group
- this study is evidence of a causal link between serotonin function and aggression
Role of serotonin- weaknesses
Direct vs indirect effects:
- role of neural factors may be indirect
- e.g. Denson et al found link between serotonin and aggression
- however, this is an indirect link because other factors (e.g. social, psychological) may influence it
Correlational research:
- most research looking at neural influences on aggression is correlational
- good ethical reasons because opportunities to experimentally manipulate neurotransmitters are limited but when two variables are correlated, it is impossible to establish which one is the cause of the other, or if there is a third variable involved
Determinism:
- this view of human behaviour is very deterministic
- The link of aggressive behaviour to the reduction of serotonin in these criminals does not allow for the idea of free will
- This has an important implication in that perhaps violent criminals are not to blame for their actions as their serotonin levels are beyond their control
Name hormones associated with aggression
- testosterone
- cortisol
- progesterone
Describe the role of testosterone in aggression
- reliable observation that males more aggressive than females- attention on male sex hormone testosterone
- androgen responsible for the development of masculine features
- therefore found in much higher concentrations in males compared with females
- influences aggression in young adulthood onwards - has a role in regulating social behaviour via its influence on certain areas of the brain associated in aggression
- testosterone levels peak in young adult males [21-35]
- at this age there is an increase in male on male aggressive behaviour- (Daly and Wilson, 1998)
- changes in testosterone levels appear to influence aggressive behaviour by increasing a mcdelivery activity during the processing of social threats- e.g. angry facial expressions
Describe studies surrounding the role of testosterone in aggression
- castration studies of animals shows that removing the testes- the source of testosterone- reduces aggression in males of many species
- Giammanco et al (2005)- giving injections of testosterone to the same animals restores some aggressive behaviour
- Dolan et al (2001)- study of prison population of violent offenders- found positive correlation between testosterone levels and aggressive behaviours in a sample of 60 male offenders in UK maximum security hospitals- mostly had personality disorders, such as psychopathy, and histories of impulsively violent behaviour
Describe the role of cortisol in agression
- Van Goozen et al (2007)- claim link between aggression and the hormone cortisol
- purchased by the adrenal mitchele, important parts of bodies reaction to stress
- inversive correlation between cortisol and aggression- lower levels of cortisol are associated with higher levels of aggression
- also suggested that when cortisol is high, testosterones influence on aggression is blocked
Describe research studies into the role of cortisol in aggression
- studies have reported low levels of cortisol in habitually violent offenders
- Carre and Mehta (2011)- dual-hypothesis- suggests high levels of testosterone lead to aggressive behaviour but only when levels of cortisol are low- when cortisol high, testosterone influence on aggression blocked
Describe the role of progesterone in aggression
- some evidence that progesterone- female ovarian hormone- plays an important role in aggression in women
- levels of progesterone vary during the ovulation cycle and are lowest during and just after menstruation
- Ziomkiewicz et al (2012)- found a negative correlation between progesterone levels and self-reported aggression- suggests that low levels of progesterone are linked to increased aggression in women
Strengths of the hormonal mechanisms of aggression
Animal studies:
- Wagner et al (1970)- showed that if a male mouses castrated then overall levels of aggression tend to decrease
- if the castrated mouse receives testosterone injections, the aggression levels increase
- Giammanco et al (2005)- review of studies confirms role of testosterone- e.g. in male Rheus Monkeys, there is an increase in both testosterone levels and aggressive behaviour during the mating season
- in rats, castration of males reduces testosterone and also mouse killing behaviour, injecting female rats with testosterone increases mouse killing
- these findings show the role of testosterone in a range of animal species
COUNTERPOINT-
- research using non human animals must always be generalised to humans with care due to differences in Physiology
- Carre and Mehta’s findings concerning cortisol applied only to human aggression
- cognitive factors play a greater role in human aggression, especially in ‘cold blooded’ proactive aggression
- BUT- Potegal et al (1994)- states that humans aren’t known humans are more similar than dissimilar and so we should be able to generalise with confidence
Evidence from criminals:
- Dabbs et al. (1987)- measured salivary testosterone in violent and nonviolent criminals
- Those with the highest testosterone levels had a history of primarily violent crimes, whereas those with the lowest levels had committed only non-violent crimes
- Studies of non-prison populations have found similar trends
Research for cortisol:
- McBurnett et al (2000)- 4-year longitudinal study on 38 boys who had been referred to a clinic for problem behaviours
- found that the boys with lower cortisol levels (measured using saliva tests) exhibited three times the number of
aggressive symptoms compared with boys with higher levels
- They were also labelled as the most
aggressive and the ‘meanest’ by their peers
- supportes the link between low levels of cortisol and increased aggression
Dual-hormone hypothesis:
- Carre and Methas dual-hypothesis- see previous cards- suggests that combined activity of testosterone and cortisol may be a better predictor of aggression than either hormone alone
Weaknesses of the hormonal mechanisms of aggression
Inconsistent evidence:
- Despite many studies showing a positive relationship between
testosterone and aggression, others studies found no such relationship
- E.g. positive correlations have been reported between levels of testosterone and self-reported levels of aggression among prison inmates (Albert et al., 1994) and between testosterone levels and the likelihood of responding aggressively to provocation (Olweus et al, 1988)
- On the other hand, no correlation was found between testosterone and actual violent behaviour among male inmates in prison
- This suggests that the relationship between testosterone in humans is unclear
Name ways in which genetic factors in aggression are investigated
- Twin studies
- Adoption Studies
Outline the nature of twin studies for aggression
- researchers compare the degree of similarity for a particular trait (such as aggression) between sets of monozygotic (MZ) twins and dizygotic (DZ) twins
- If the MZ twins are more alike in terms of their aggressive behaviour, then this should be due to their genes rather than their environment (both types of twins share the same environment but MZ twins are more genetically alike)
Describe findings of twin studies into aggression
Several studies suggested that heritability account for about 50% of
the variance in aggressive behaviour:
Coccaro et al (1997)-
- studied adult male MZ and DZ
twins
- aggressive behaviour (direct physical assult- concordance rates of 50% for MZ twins and 19% for DZ twins
- corresponding figure for verbal aggression- 28% (MZs) and 7% (DZs).
Describe the nature of adoption studies in investigating aggression
- can help to untangle the relative contributions of environment and heredity in aggression
- positive correlation is between aggressive behaviour in adopted
children and aggressive behaviour in their biological parents implies genetic influence on aggression - If a positive correlation is found between the adoptee’s aggressive behaviour and the rearing family, then an environmental effect is implied
Describe examples/findings of adoption studies into aggression
Hutchings and Mendick (1975):
- study of over 14,000 adoptions in Denmark
- found that a significant number of adopted boys with criminal convictions had biological parents (particularly fathers) with convictions for criminal violence, providing evidence for a genetic influence
Rhee and Wladam (2002):
- meta-analysis of adoption studies of direct aggression and anti-social behaviour (aggression is a prominent feature of this)
- Found genetic influences accounted for 41% of variance in aggression
Strengths of twin/adoption studies into aggression
Research evidence:
- Miles and Carey
(1999)- meta-analysis of 24 twin and adoption studies that demonstrated the genetic basis of aggression
- results suggested a strong genetic influence that could account for as much
- Rhee and Waldman (2002)- meta-analysis- see previous notes
HOWEVER-
- in both of these studies, several variables, including age of participant and assessment method for aggression, moderated the genetic influence on aggression
- suggests that although genetic factors play a significant part in the development of aggressive behaviours, the influence of other factors affects their expression.
Weaknesses of twin/adoption studies into aggression
Problems of assessing aggression in genetic studies:
- 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
- Miles and Carey meta-analysis- the mode of assessment was found to be a significant moderator of aggressive behaviour in the 24 studies that made up analysis
- found that genetic factors explained a large proportion of the variance in aggressive behaviour in studies that had used parental or self-reports
- However, those that used observational ratings showed significantly less genetic contribution and a greater influence of environmental factors
- These inconsistencies in findings make it difficult to assess the relative contributions of genetic and environmental factors in aggression
Issues with twin studies:
- twin studies may lack validity
- MZ twins may have more similar environment than DZ twins- assume they have the same but this is equal environments assumption
- assumption may be wrong because MZ twins treated very similarly (especially by parents)- more so than DZ twins
- means concordance rates ar inflated and genetic influences on aggression may not be as great as twin studies suggest
Problems with isolating genetic influences:
- difficult to establish how influential genes are in aggressive behaviour
- One reason for this is the difficulty researchers have in separating genetic and environmental factors
- individual may possess a gene associated with aggression but that behaviour is only expressed if the environmental conditions are favourable
- Therefore, even though an individual may inherit aggressive tendencies, these will only be expressed if the environmental conditions warrant it (e.g., provocation)
Nature vs Nurture:
- evidence that environmental factors are appointment
- e.g. early childhood trauma plays role- should take consideration of this when describing aggression
Name an example of a specific gene that has been linked to aggression
MAO-A gene
Describes the workings of the MAOA gene
- controls production of enzyme Monoamine oxidase A (MAO-A)
- MAO-A regulates the neurotransmitter serotonin- breaks it down into its constituent chemicals to be recycled or excreted
- Low activity variant of the MOA (MAO-L) gene results in low activity of the MAO-A enzyme (MAO) deficiency
- MAO-L variant (aka ‘warrior gene’ has been linked to high levels of aggressive behaviour
Describe research into the effects of the MAO-A gene on aggression
Brunner et al (1993):
- studied 28 male members of a large Dutch family who were repeatedly involved in impulsive aggressive violent behaviours such as rape, attempted murder and physical assault
- found these men had abnormally low levels of MAOA enzyme in brain, and MAOA-L gene variant
Lea and Chambers (2007):
- MAO-L variant possessed by 56% of New Zealand Maori Men (compared with 34% of caucasians)- historically have reputation for being ferocious warriors- hence name of gene
Describe gene-environment interactions in aggression
- suggested that MAOA-L gene activity is only related to adult aggression when combined with early traumatic life experiences
- Frazetto et al (2007)- found association between higher levels of antisocial aggerssion in men and the MAO-L gene varient in men, but this was only the case in men who has experienced significant trauma (e.g. sexual/physical assault) in the first 15 years of life
- those with no such childhood trauma did not have particularly high levels of aggression as adults, even if they possessed the MAO-L varient
- this is strong evidence of a gene-environment interaction- DIATHESIS-STRESS
Strengths of role of MAO-A gene in aggression
Research evidence:
- Caspi et al (2002)- 500 male children- discovered that those with the low variant of MAOA were significantly more likely to grow up to exhibit anti-social behaviour than those with the high variant
- McDermott et al (2009)- showed, using a controlled experiment measuring actual behavioural aggression, that participants with the MAOA-L gene displayed higher levels of aggression in response to provocation than those with the MAOA-H variant
- Mertins et al (2011)- money-distributing gene- men with high-activity varient (MAOA-H) were more cooperative and made fewer aggressive moves than the low-activity PPs
COUNTER-
- Mertins et al study found that even PPs with MAOA-L variant behaved co-operatively rather than aggressively when they were made aware that others in the study were behaving cooperatively
- knowledge of a social norm partly determined how aggressive or cooperative MAOA-L PPs were
- therefore genres are influenced by environmental factors that are at leased as important in aggression
Animal studies:
- Cases et al (1995)
- disabled the MAOA gene in the X chromosome of mice and found that without the MAOA enzyme, levels of dopamine and serotonin increased and males became highly aggressive but females were unaffected
- also discovered that restoring the function of the gene returned male mice to a normal state
- This research on mice suggests that MAOA is implicated in the expression of aggression in males
Positive implications:
- Findings from genetic research on antisocial and violent behaviour may have some valuable uses in offender treatment and rehabilitation
- Hall (2003) suggests 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
HOWEVER- less certain what the consequences of such genetic tests might be for criminal cases, where the finding may be cited as evidence of a defendant’s diminished responsibility
Weaknesses of role of MAO-A gene in aggression
Genes and Environment:
- both Caspi and McDermott have found evidence for a gene/environment interaction
- Caspi found that those that had the MAOA-L variant were more likely to grow up to exhibit anti-social behaviour only if they had been maltreated as children
- In McDermott’s study aggressive responses were moderated by environmental factors
- They showed that participants with the low-activity MAOA gene behaved aggressively in their laboratory based money allocation game, but only when they were provoked- Otherwise they demonstrated no more or less aggressive behaviour than other participants
- Therefore, both of these studies suggest that the impact of having the MAOA-L gene is only significant when the environment interacts with the gene variation
- means that there may be many individuals with the gene variation that do not show heightened levels of aggression as their environment has been positive
- It may only be those who are abused or in provoking situations that demonstrate aggression- means that the MAOA is not a complete explanation
Determinism:
- If we find that there are genes implicated in aggressive behaviour, such as the MAOA, then people may be deemed as being biologically determined to commit aggressive acts exercising little or no free will
- implications of this- e.g., for sentencing, for monitoring these
individuals
Complex link:
- precise mechanism of MAOA-seratonin-sgression link is unclear
- Aggression linked to low-levels of seratonin
- however, MAOA-L gene causes low activity of the MAOA enzyme which in turn should read to higher serotonin as the low-activity enzyme doesn’t deactivate serotonin, leaving more serotonin for synaptic transmission
- in people with MAOA-L variant, it may be more accurate to say that their serotonin levels are disrupted, rather than being higher/lower than normal
- shows the relationship between MAOA gene serotonin, and regression is not yet fully understood
Outline the ethological explanation of aggression
- Suggests that the main function of aggression is adaptive
- seeks to understand the innate behaviour of animals (including humans) by studying their natural environment
Describe 2 ways in which aggression can be adaptive (ethological explanation)
Dispersion:
- Aggression is beneficial to survival because a ‘defeated’ animal is rarely killed, but rather is forced to establish territory elsewhere
- this means that members of a species spread out over a wider area and have to discover resources in a different place, which reduces competition pressure and the possibility of starvation
Dominance hierarchies:
- Aggression is adaptive because it can establish dominance hierarchies
- Male chimps use aggression to climb in their troop’s social hierarchy
- Their dominance gives them special status such as mating rights over females
- also happens in humans- Pettit et al (1988)- studied groups of young children and observed how aggression played an important role in the development of dominance hierarchies- this would be adaptive (and thus naturally selected) because dominance over others brings benefits such as access to resources (e.g. food and mates).
Name elements of the ethological explanation of aggression
- ritualistic aggression
- innate releasing mechanisms
- foxed action patterns
Describe ritualistic aggression
- A ritual is a series of behaviours carried out in a set order
- Lorenz (1966) observed that fights between animals of the same species produced little actual physical damage- most aggressive encounters consisted of a prolonged period of ritualistic signalling (e.g. displaying claws and teeth, facial expressions of threat)
- threat displays are important as they help individuals to assess their relative strength before deciding to escalate a conflict- means they make costly and dangerous physical aggression less likely e.g. male gorillas use a variety of techniques such as vocalisations (hooting) and gestures (chest pounding) to intimidate an opponent without the need for physical contact
- in humans, anthropologists have found evidence of ritualised aggression in tribal warfare- Gardner and Heider (1968) described how the Dani of New Guinea engaged in highly ritualised patterns of intergroup hostility
Describe appeasement displays
- Lorenz also pointed out that intra-species aggressive confrontations end with ritual appeasement displays- these indicate acceptance of defeat and inhibit further aggressive behaviour in the victor, preventing any damage to the loser r.g. at the end of an aggressive confrontation a wolf will expose its neck to the victor, a submissive appeasement gesture making itself vulnerable to a single bite to its jugular vein
- This is adaptive because if every aggressive encounter ended with the death of one of the combatants, that could threaten the existence of the species
Describe Innate releasing mechanisms (IRM)s
- inbuilt physiological process or structure, e.g. a network of neurons (a circuit) in the brain
- An environmental stimulus (such as a certain facial expression) triggers the IRM, which then ‘releases’ a specific sequence of behaviours (FAP)
- ethological explanations states that all members of the same species have a repertoire of stereotyped behaviour which occurs in specific conditions that do not require learning (innate)
Describe fixed action patterns (FAPs)
Stephen Lea- 6 main features:
- Stereotyped- relatively unchanging sequences of behaviours
- Universal- because the same behaviour is found in every individual of a species
- Unaffected by learning- the same for every individual regardless of experience
- ‘Ballistic’- once the behaviour is triggered it follows an inevitable course and cannot be altered before it is completed
- Single-purpose- the behaviour only occurs in a specific situation and not in any other
- A response to an identifiable specific sign stimulus (or, if it involves communication between
members of the same species, it is known as a releaser)
name research into the ethological explanation
Tinnenberg (1961)
Describe Tinnenbergs research procedure
- presented sticklebacks with a series of wooden models of different shapes
- Male sticklebacks are highly territorial during the spring mating season, when they also develop a red undershot on their underbelly
- if another male enters their territory, aa sequence of highly stereotyped aggressive behaviours is initiated (FAP)
- the sign stimulus (particular feature of a stimulus) that triggers the innate releasing mechanism in the sight of the red spot
Describe Tinnenbergs research findings
- regardless of the shape, if the model had a red spot the male stickleback would aggressively display and even attack it
- however, if there was no red spot, ether was not aggression, even if the model looked realistically like a stickleback
- also found that these aggressive FAPs were unchanging from one encounter to another
- once triggered, the FAP always ran its course to completion without any further stimulus
Strengths of the ethological explanation of aggression
Research evidence:
- support from research related to genetics and evolution
- Brunner et al (1993)- shoed the MAOA-L gene is closely associated with aggressive behaviour in humans
- twin and adoption studies showed ether is a significant genetic component to aggression in humans
- Wilson and Daly- adaptive function of aggression- genetically based
- these lines if research point to innate basis of aggressive behaviour
- suggests the ethological approach is correct in claiming aggression is genetically determined, heritable, and adaptive
BUT-
- aggressive behaviour differs from one culture to another, sometimes even within the same country
- Nisbett (1993) found that one type of homicide (the result of reactive
aggression) was more common amongst white men in the southern United States than in the northern states
- Reactive aggression is a response to threats fromsomeone else
- Nisbett concluded that the difference was caused by a’culture of honour’ in the southern US- this is less prevalent in the north, which is why ‘reactive aggression ‘homicide rates are lower there
- Therefore this kind of aggressive behaviour comes from a learned social norm, rather than being instinctive- culture can override innate predispositions, which is hard for ethological theory to explain
Benefits of ritualised aggression:
- Ritualised aggression can prevent conflicts escalating into dangerous physical aggression
- Chagnon (1992)- among the Yanomamo people of South America, chest pounding and club fighting contests can settle a conflict short of extreme violence
- shows that, even in moderately to highly violent cultures such as the Yanomamo, rituals have the effect of reducing actual aggression and preventing injury or death of the combatants
- So in this way, ritualistic innate aggression is seen as an adaptive response
Weaknesses of the ethological explanation
Aggression against same species is not only ritualistic:
- Goodall (2010) observed a ‘four-year war during which male chimps from one community killed al the members of another group in a systematic way
- On some occasions, a victim would be held down by rival chimps while others hit it in an attack lasting many minutes
- The violence continued even though the victims offered appeasement signals- signals did not inhibit the aggressive behaviour of the attackers as predicted by the ethological explanation
- challenges the ethological view that same-species aggression has evolved into a self-limiting and relatively harmless ritual
FAPs not fixed:
- Lorenz’s original view of FAPs is outdated
- He saw FAPs as innate and unchanging, but Hunt (1973) has pointed out that FAPs are actually greatly influenced by environmental factors and learning experiences e.g. an aggressive FAP is typically made up of several behaviours in a series
- The duration of each behaviour varies from one individual to another, and even in the same individual from one encounter to another
- Lehrman (1953) criticised Lorenz’s instinctual explanation of aggressive behaviour believing that he had underestimated the importance of the environment- believed that environmental factors, learned mostly from learning and experience, interact with innate factors in complex ways
- Because they are modifiable by experience, many ethologists now prefer the term ‘modal behaviour pattern’ to reflect this
- Therefore patterns of aggressive behaviour are much more flexible than Lorenz thought, especially in humans
May not be inevitable:
- ethologists argue aggression is an innate instinct
- implication of this view is that humans will inevatibelu be aggressive an flight each other (e.g. in wars), however, other approaches e.g. the cognitive approach suggest that aggression is not inevitable as it is more under rational control than instinctive- it is also less innate and more affected by learning experiences than ethologists accept
Unjustified application to humans:
- A number of human FAP have been identified such as smiling and an ‘eyebrow-flash’ as a sign of greeting
- However, because the environment in which humans exist changes so rapidly, it is suggested that FAPs such as aggression are no longer adaptive in modern times
- The flexibility of humans to be able to respond to ever- changing environments has proved more effective than the production of stereotypical, fixed patterns of behaviour
- This suggests that, although non-human species may respond aggressively to specific sign-stimuli, human behaviour is far more varied and less predictable
Outline evolutionary explanations for aggression
- focus on the adaptive nature of behaviour, i.e., modern behaviours are believed to have evolved because they solved challenges faced by our distant ancestors and so become widespread in our gene pool
- Aggression is a strategy that would have been effective for solving a number of adaptive problems
- Those adaptive problems include: gaining resources, intimidating or eliminating male rivals for females, and deterring mates from sexual infidelity
- Solving these problems enhanced the survival and reproductive success of the individual, and as a result these behaviours would have been passed down
name elements of the evolutionary explanation of aggression
- sexual competition
- sexual jealousy
- aggression in warfare
- evolutionary explanation of bullying
Outline sexual competition in aggression
- Ancestral males seeking access to females would have had to compete with other males (i.e., sexual competition)
- One way of eliminating competition would have been through aggression- potentially physical competition
- Those individuals who used aggression successfully against competitors would have been more successful in acquiring mates and so would have been more successful in passing on their genes to offspring
- This would have then led to the development of a genetically transmitted tendency for males to be more aggressive towards other males
Describe research evidence for sexual competition in aggression
- Puts (2010)- argues various male traits seem to imply that competition with other males did take place among ancestral males e.g. men have 75% more muscle mass than women, are far more aggressive than women, and are far more likely to die violently (Buss, 2005)
- Anthropological evidence shows that, universally, males have thicker jawbones which Puts believes may have come from men hitting each other and those with the thicker jaws survived and passed on their genes to subsequent generations (resulting in an increase in thicker jaws)
