2 - Genetic Factors In Aggression Flashcards
What are genetic factors?
Causal factors related to genes (made up of DNA strands) producing instructions for an organism’s physical + psychological features
What are the 2 ways of studying genetic factors in aggression?
- Twin studies
- Adoption studies
What do twin studies do?
Compare traits of MZ + DZ twins to assess the role of genetic heritability in aggression
What are MZ twins?
Identical twins that share 100% of genes
What are DZ twins?
Non-identical twins that share 50% of genes
What have twin studies suggested about the cause of aggression?
Genes account for approx 50% of variance in aggression
If MZ twins are more alike in terms of aggression levels than DZ twins what does this suggest?
Aggression is dictated by genetics (nature) not the environment (nurture)
What is the research support for twin studies identifying a genetic influence on aggression?
Coccaro et al
- Studied MZ + DZ twins raised in same environ
- Physical assault concordance rate: 50% in MZ + 19% in DZ
- Suggests genetics play a role in aggression
What do adoption studies do to look at genetic factors in aggression?
Look at similarity in aggression between adopted child + biological parents/adoptive parents
- Similarities between child + biological -> genetic influence
- Similarities between child + adoptive -> environmental influence
What have adoption studies suggested about the cause of aggression?
Genes account for approx 40% of variance in aggression
What is the research support for adoption studies identifying a genetic influence on aggression?
Mednick + Hutchings
- Studied 14,000 adoptions in Denmark
- Looked at boys with criminal convictions
- Significant number had biological parents with criminal convictions
- Suggests genetics play a role in aggression
What is the main genetic factor we look at in influencing aggression?
MAOA Gene
Is MAOA a gene or enzyme?
Gene
Is MAO-A a gene or enzyme?
Enzyme
What does MAOA gene do?
Controls production of MAO-A enzyme (which regulates serotonin production - which influences aggression levels)
What does MAO-A enzyme do?
Regulates the neurotransmitter serotonin - which plays a role in impulsive aggressive behaviour
How is the MAOA gene thought to cause aggression?
MAOA-L (low activity variant of MAOA gene) results in low activity MAO-A enzyme + low serotonin levels, linked to high aggression levels
What are the 2 variants of the MAOA gene + which is linked to aggression?
MAOA-H (high activity - NOT linked to aggression)
MAOA-L (low activity - linked to aggression)
What is another word for the MAOA-L gene variant? Why?
‘Warrior gene’
Research by Lea + Chambers
- Studied MAOA-L in NZ
- Found the gene variant in 56% male Māoris + only 34% Caucasians
- Nicknamed ‘warrior gene’ because of Maoris’ aggressive warrior history
What is the research to support the role of MAOA in aggression?
Brunner
- Studied large Dutch family (28 males with history or rape, violence, impulsive aggression, learning disabilities)
- These men had the MAOA-L variant
- Concluded that this gene is likely to cause aggression + learning disabilities in males
What proportion of western males have the MAOA-L variant?
1/3
What is the GXE Interactions theory?
Theory that genetics only cause aggression when combined with environmental factors
What model does the GXE theory fit?
Diathesis-Stress Model
What is the Diathesis-Stress Model for aggression?
Diathesis + Stress = Aggression
- Diathesis = MAOA-L gene variant
- Stress = Traumatic early life experiences (e.g. abuse)
What research supports the GXE Interactions approach to aggression?
Frazzetto et al
- Found association between high antisocial aggression + MAOA-L variant in adult males
- This association was only found in those who experienced trauma in first 15yrs of life
- Suggests a genetic vulnerability isn’t enough to cause aggression
Give 4 evaluation points for genetic factors in aggression
POS:
Multiple research for central genetic factor (MAOA-L gene)
- Brunner + Lea and Chambers support
- Mertins et al falsified theory (found MAOA-H ppts were less aggressive + more cooperative in a money distributing game)
NEG: Issues with twin studies - May lack internal validity - Equal environments assumption - If MZ twins are treated more similarly, higher concordance of aggression may be due to this not genetics
Low understanding of how MAOA-L increases aggression
Recognition of environmental role
- Genetics as an individual cause isn’t strong
- Research by Frazzetto et al influences environmental importance too
