Aggression 2
Genetic factors
15-01-21
Twins studies
Have suggested about 50% of the variance for aggression is inherited
Coccaro et al (1997)
o Studied male MZ (identical) and DZ (non-identical) twins
o Found a 50% concordance rate in MZ twins
o Only has a 19% concordance rate in DZ twins
o When looking at verbal aggression it was 20% for MZ and 7% for DZ
Adoption studies
Rhee and Waldman (2002)
o Carried out a meta-analysis of adoption studies of direct aggressions
and antisocial behaviour
o Found that genetic influences accounted for 41% of the variance in
aggression
o This is in line with the findings from other studies
MAOA Gene
Monomine oxidase A is an enzyme
Mops up the neurotransmitters in the brain after a nerve impulse has been
transmitted
Breaks down the neurotransmitters into chemicals that can be recycled in the
body
A dysfunction may lead to abnormal activity of the MAOA enzyme
o This impacts serotonin levels in the brain
Also named the warrior gene
Brunner et al (1993)
o Studied 28 male members of a large Dutch family
o This family was involved in impulsively aggressive violent crimes like rape
o Found that the men had abnormally low levels of MAOA in their
brains
o Also low activity of the MAOA gene
Stuart et al (2014)
o Studied 97 men
o They had all been involved in inflicting intimate partner violence
o They were also all part of a batterer treatment programme
o Men with the low-activity MAOA gene were most violent
Gene-environment interactions (GxE)
Genes are crucial influences on aggressive behaviour
They don’t work independently however
MAOA gene activity is only related to adult aggression when combined with
early traumatic life events
Frazzetto et al (2007)
Genetic factors
15-01-21
Twins studies
Have suggested about 50% of the variance for aggression is inherited
Coccaro et al (1997)
o Studied male MZ (identical) and DZ (non-identical) twins
o Found a 50% concordance rate in MZ twins
o Only has a 19% concordance rate in DZ twins
o When looking at verbal aggression it was 20% for MZ and 7% for DZ
Adoption studies
Rhee and Waldman (2002)
o Carried out a meta-analysis of adoption studies of direct aggressions
and antisocial behaviour
o Found that genetic influences accounted for 41% of the variance in
aggression
o This is in line with the findings from other studies
MAOA Gene
Monomine oxidase A is an enzyme
Mops up the neurotransmitters in the brain after a nerve impulse has been
transmitted
Breaks down the neurotransmitters into chemicals that can be recycled in the
body
A dysfunction may lead to abnormal activity of the MAOA enzyme
o This impacts serotonin levels in the brain
Also named the warrior gene
Brunner et al (1993)
o Studied 28 male members of a large Dutch family
o This family was involved in impulsively aggressive violent crimes like rape
o Found that the men had abnormally low levels of MAOA in their
brains
o Also low activity of the MAOA gene
Stuart et al (2014)
o Studied 97 men
o They had all been involved in inflicting intimate partner violence
o They were also all part of a batterer treatment programme
o Men with the low-activity MAOA gene were most violent
Gene-environment interactions (GxE)
Genes are crucial influences on aggressive behaviour
They don’t work independently however
MAOA gene activity is only related to adult aggression when combined with
early traumatic life events
Frazzetto et al (2007)
