Genetic Factors in Aggression Flashcards
Genes alone don’t cause aggression
What do they do?
They affect the production of hormones and neurotransmitters which in turn affect aggression.
What do genetic explanations of aggression assume
Aggressive behaviour is the result of inherited traits/characteristics that have adapted across generations because of their evolutionary usefulness (i.e. aggression is a trait necessary for survival)
AO1
Sapolsky (1997) genes’ influence on hormones
Genes are the ‘hand behind the scenes’ directing testosterones actions.
- Genes control how much testosterone, oestrogen and other hormones/neurotransmitters are produced and how they work in the body.
What are the 3 types of studies used in genetic studies
- twin studies
- animal studies
- adoption studies
AO1/AO3
Animal Studies: Turner (2007)
Studied aggression in pigs (pigs are intelligent so when they get bored tey can become aggressive)
PROCEDURE:
He selectivley bred animals and found that he could breed less aggressive pigs by breeding from less aggressive pigs and so on
AO3 POINTS:
REAL WORLD/ECONOMIC IMPLICATIONS: This has implications as it suggests that pig farmers could breed non-aggressive pigs - leading to aggression falling by 5% annually.
- This can contribute to farmers recieving less expensive vets bils and higher stocks of pork which has economic implications
What is the correlation coefficient
Measures correlation (i.e. a statisical measure of the strength between a relationship between 2 variales)
- e.g. 60% condordence rate = 0.6 corellation
Why do genetic studies usually involve twins
This because twins share DNA especially MZ twins who share 100% of DNA.
- This allows researchers to determine the extent which genetic factors contribute to certain behaviours.
What are monozygotic (MZ) twins
MZ twins develop from a single fertalized egg that splits into 2.
- This means they share 100% of DNA
What are Dizygotic Twins (DZ)
DZ twins develop from 2 separate fertalized eggs from 2 different sperms
- They share on average 50% of genes just like regular siblings.
What do researchers do with MZ and DZ twin study results
They compare how similar the behaviour is of MZ twins to that of DZ twins
AO1/AO3
Dinic et al (2020) - MZ and DZ twin studies
+ AO3 limitation
Studied aggression in the lab with 478 adulttwins (316 MZ twins, 172 DZ twins)
USing Comptitive reaction time where PPT’s were led to believe they competed against reaction time.
- The twin who lost was subjected to a large blast of noise given by the other twin
- aggression was measured through the intensity and duration of the blast the twin chose to deliver
A control group of non-twins completed the task - this was to identify the impact of the environment against genetic influence.
FINDINGS
- no significant difference between the control gorup and the twin experimental group
- concluded that in tis case aggression was not genetically linked
Low mundane realism + extraneous variables (argument before test)
AO1/AO3: Strength
Twin Studies: Coccaro et al (1997) MZ/DZ twins and aggression
Studied adult Male MZ and DZ twins.
Direct physical aggression: concordence rates of 50% fror MZ twins and 19% for DZ
Verbal Aggression: 28% for MZ twins, 7% for DZ twins
This demonstrates that higher concordence rates are likely due to genetic factors because both MZ and DZ twins are raised in the same environment.
Higher concordence rates in MZ twins than DZ supports the genetic explanation as there is a greater degree of genetic similarity between them.
AO3: Limitation
Twin Studies: Methodology lacks reliability
How do we Operationalise aggression? (kicking, spitting etc)
- This method of data collection may vary across studies
This may result in differences between studies meaning there is low replicability as well as comparability which makes it difficult to draw conclusions as well as test the populatory validity of the studies if we were to repeat it.
What do adoption studies suggest
similarities in aggressive behaviours between and adopted child and adopted parents suggest a similar trait is due to the environement rather than inheritance.
AO1/AO3: Strength
Adoption studies: Rhee and Waldman (2002) meta analysis
Rhee and Waldman’s meta analysis of adoption studies found genetic influences accounted for 41% of the variance in aggression.
What does the MAOA genes control
+ what does it do
The MAOA gene codes for the production of the enzyme MAOA.
This enzyme is involved in the breaking down of neurotransmitters in the synapse, especially serotonin.
The break down of serotonin is a part of neurotransmission and the MAOA enzyme effectivley sweeps up any serotonin left in the synaptic gap after neurotransmission is complete.
What is the role of serotonin in modulating aggression
+ findings from neural research: role f serotoin
Serotonin had been linked to mood, speciffically in the balancing of mood. (i.e. low or disrupted levels of serotonin may be a factor in mood affectve disorders such a depression and also aggressive behaviour)
+serotonin typically inhibits the firing of the amygdala meaning it controls aggressive impulses - because a hyperactive amygdala has shown to be linked to aggression.
What happens if the MAOA enzyme (caused by a mutaton in the MAOA gene) isnt working
It would cause a build up of serotonin in the synapse which normally has a calming effect on the brain and mean that synaptic transmission of serotonin is partially inhibited.
What are the 2 types of MAOA genes
+ which one leas to aggression
1: normal variant
2: low variant (MAOA-L) <- This one has a predisposition to aggression due to the build up of serotonin in the synapse.
AO1/AO3: Strength
Maori research on the MAOA gene (warrior gene)
MAOA-L variant was possessed by 56% of New Zealand Maori Males.
- This supports research on the function of the MAOA gene as these men were notably aggressive
AO1/AO3 Strength
Brunner et al: Dutch Family + MAOA-L variant
Studies 28 male family members who were convicted repeatdedly for violent crimes. - found that the aggressive males in one family all shared the same dysfunctional genes which led to low levels of MAOA enzyme, leading to unregulated levels of serotonin in the synapse - this is linked to aggression.
How did Brunner et al’s dutch study on the MAOA gene possibly explain differences in male/female aggression
The trait was handed from mother to son - this suggested the root of the disorder was a defect on the X chromasome
Men are more vunderable to such a defect because they only have one X chromasome. WOmen have 2 so if the second one is normal, they don’t feel the effects of a defect on the first, but the can be carriers.
The violent men in the study all had the marker, and so did some of the women - meaning presumably they were carriers of the gene.
AO3: Strength (of the geneic explanation of aggression)
Biological Evidence
provides empirical evidence (such as saliva, DNA analysis etc)
- This means we can compare structures between individuals and identify repeating patterns which could lead us to draw accurately represented conclusions about which genes influence aggressive behaviour
AO3: Strength (of the genetic explanation of aggression)
Twin/Adoption studies use large sample sizes
studies tend to use large sample sizes (e.g. Dinic et al - 478 adult twins)
- Therefore external validity is high because the studies have high population validity due to the large sample size, making it more reliable and accuratley reprasentative.
AO3: Weakness (of the geneic explanation of aggression)
Inconsistent concordence rates
+ what this suggests
If genetic factors alone were responsible for aggression, then concordence rates for MZ twins would b 100%.
- This is because they share 100% of DNA, so if one twin was aggressive, according to the genetic thoery of aggression, both twins would have the same gene expressed an therefore shown through the same aggressive behaviour.
For example; a study by Coccaro showed
- Direct physical assault; CR of 50% for MZ and 19% for DZ
- Verbal aggression: 28% MZ and 7% DZ
This reduces the validity of the genetic explanation when used in isolation, and research evidence provides that there must be an extraneous influence upon behaviour.
AO3: Weakness (of the geneic explanation of aggression)
Frazzetto et al (2007) diathesis stress model
Found an association between antisocial aggression + MAOA-L gene in adult males BUT only in those who experienced significant trauma (e.g. physical abuse during the first 15 years of life)
Those with no trauma weren’t significantly aggressive as adults even if they possessed the MAOA-L gene
THis provides strong evidence that genes and evironment interact to create aggressive behaviour - known as the diathesis stres model.
AO3: Strength (of the geneic explanation of aggression)
Mertins et al (2011) support for the role of the MAOA gene
Mertins found that on the contrary, people with a high variant MAOA gene were more cooperative and less aggressive in a money distribution game than those with the normal variant and low variant MAOA gene.
- These findings support the relationship between the MAOA gene activity and aggression
- This improves the validity of the thoery through external research.
