Genetic Factors In Aggression Flashcards
What twin studies on heritability were carried out linking to aggression?
- Emil Coccaro et al (1997) studied adult male monozygotic and dizygotic twins
- Because MZ twins share 100% of their genes but DZ twins share only 50% we wld expect to find greater similarities in aggressive behaviour between MZ twins if aggression is mostly influenced by genetic factors.
- This is because both MZ & DZ twins are raised together in the same environement but MZ twins have a greater degree of genetic similarity than DZ’s
- For aggressive behaviour defined as direct physical assault, the researchers found concordance rates on 50% for MZ twins & 19% for DZs
- The corresponding figures for verbal aggression were 28% (MZs) & 7% (DZs)
Give another twin study linking to aggression and genetic factors.
- Verude et al (2016)
- Conducted a meta-analysis
- Heritability of aggression ranged from 39% to 60% for children between ages 2 & 6
- and from 46% to 60% for children between ages 6 & 14
- While adults overall heritability was slightly lower & around 30%
- Less aggressive in adulthood- environmental factors
- Frontal lobe develops
- We can see differences in numbers because if the children had been told off for being aggressive while growing up then their heritability would be lower.
Give a lab study that investigated the role of aggression amongst twins.
- Dinic et al (2020) studied aggression in a laboratory with 478 adult twins (316 MZ twins, 162 DZ twins)
- Used competitive reaction time task (CRTT) where ppts were led to believe that they competed against each other in reaction time task & recieved “punishments”- blasts of loud noise- if they lost
- (These were not given although the “winning” twin thought they were)
- Ppts were competing against their twin, Aggression was measured by itensity & duration of the blast that the twin chose to deliver
- A control group of non twins completed the task- this was to identify impact of environment against genetic influence
What were Dininc et al (2020) findings?
- Found no significant difference between the control group & the experimental group
- Concluded that in this case aggression was not genetically linked
- However highly artifical & may have bee confounded by competing twin against twin
Evaulate the role of genetics in aggression for the twin studies.
- Methodology of twin studies lack reliability
- Operationalising aggression may vary from study to study & also methods of collecting data
- This may result in differences between studies, making it difficult to draw conclusions
- It is reductionist as it only looks at one variable & does not consider other explanations & we need to consider other explanations if we are to consider aggression
What adoption studies were conducted into genetic factors in aggression?
- Rhee & Waldman (2002) carried out a meta- analysis of adoption studies of direct aggression & antisocial behaviour, a prominent feature of which is aggressive behaviour
- They found that genetic influences accounted for 41% of the variance in aggression
-more or less in line with findings from twin studies
What research was conducted into the XYY chromosome and aggression?
- Jarvik et al (1973)
Meta analysis of studies into XYY males & aggression
- Found that although XYY males were only a small proportion of perpetrators of violent crimes, they were significantly larger proportion in the criminal population than general population
- Suggested an association of an extra Y chromosome with aggressive behaviour
- However later researcher found that XYY chromosomes also linked to high levels of learning difficulties- this could affect their behaviour & tendancy to be involved in crime, rather than aggressive levels
What is the MAOA gene?
- The gene responsible for the activity of the enzyme monoamine oxidase in the brain (serotonin) “(breaking down the serotonin)”
- MAOA is the enzyme that effectively sweeps up any serotonin left in the synaptic gap after neurotransmission is complete
- The low activity variant of the gene is closely associated w aggressive behaviour
What would happen if the MAOA enzyme wasn’t working?
- It would mean that there would be a build up of serotonin in the synapse
What are the two variants of the MAOA gene and what do they do?
- A low variant type- The low activity variant (MAOA-L) results in low activity of the MAOA enzyme (MAO-A deficiency)
- It is this MAOA-L variant that has been linked to high levels of aggressive behaviour (IMPULSIVE VIOLENCE HAS ALSO BEEN ASSOCIATED W THIS)
- A normal type
What does serotonin have to do with aggression?
- MAOA breaks down serotonin but also dopamine & noradrenaline
- The reason the low variant MAOA has been associated w aggressive behaviour is because there is not enough enzyme to break down neurotransmitters & the high levels in the brain lead to more aggression,
- High levels of serotonin from this effect are associated w higher levels of aggression
What animal research was conducted into the MAOA gene?
- Newman (2005)
- Looked at 45 unrelated male macaque monkeys raised w or without mothers
- Looked at MAOA activity
- Concluded that aggressiveness is influenced by MAOA activity, but might be changed by the environment the monkey is brought up in
What research was conducted into the low activity variant of the MAOA gene?
- Brunner et al (1993)
- They studied 28 members of a large Dutch family who were repeatedly involved in impulsively aggressive violent criminal behaviours such as rape, attempted murder & physical assault
- These men had abnormally low levels of the enzyme MAO-A as well as the MAOA-L gene variant
What does the MAOA-L gene activity only really relate to and what research is there to support this?
- It is only really related to adult aggression when combined with early traumatic life experiences
- Frazzetto et al found an association between higher levels of antisocial aggression & the MAOA-L gene variant in adult males
- But this was only the case in those who had experienced significant trauma (such as sexual or physical abuse) during the first 15yrs of life
- Those who had not experienced such childhood trauma did not have particularly high levels of aggression as adults
- Even if they possessed the MAOA-L variant
This is stong evidence of a gene-environment interaction (diathesis-stress)
