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Genetic Factors in Aggression - Coggle Diagram
Genetic Factors in Aggression
Twin Studies
twin studies have suggested that heritability accounts for about 50% of the variance in aggressive behaviour
Coccaro et al (1997)
studied adult male MZ twins and DZ twins
found concordance rates of 50% for MZ twins and only 19% for DZ twins for physical assault
( for verbal aggression is was 20% for MZ and 7% for DZ twins)
Adoption studies
similarities in aggressive behaviour between adopted child and their:
biological parent = genetic influence
adoptive parent = environmental influence
Rhee and Waldman (2002)
carried out a meta-analysis of adoption studies of direct aggression and antisocial behaviour
genetic influences accounted for 41% of the variance in aggression (similar to findings from twin studies)
the MAOA gene
(aka the Warrior Gene!)
controls production of the 'Monoamine oxidase A' enzyme (MAO-A)
MAO-A regulates serotonin
MAOA-L = low activity variant of the gene - linked to aggressive beahviour
low version just means less activity in the gene = less regulation of serotonin = aggression
Lea & Chambers (2007)
found 56% of male Maoris in New Zealand had the MAOA-L variant, compared to 34% of Caucasians
Brunner et al (1993)
studied 28 male members of a large Dutch family who were repeatedly involved in impulsively aggressive violent criminal behaviours such as rape
found that these men had abnormally low levels of MAO-A in their brains & the MAOA-L gene variant
Gene-environment (GxE) interactions
genes are crucial influences on aggressive behaviour but they do not function in
isolation
MAOA-L gene activity is only related to adult aggression when combines with early
traumatic life events
Frazzetto et al (2007)
found an association between high levels of antisocial aggression and MAOA-L gene but in adult males
but this was
only the case
in those who has experienced significant
trauma
(such as sexual/physical abuse) during the first 15 years of life
those without trauma were not aggressive as adults even if they possessed the MAOA-L variant
Evaluation
research support
P: support for MAOA gene in aggression
E: research show that low activity variant of the MAOA gene (MAOA-L) is associated with greater aggression. Mertins et al (2011) also found the converse true. men with low-activity and high-activity variants of the MAOA gene took part in money distributing game. men with high-activity gene (MAOA-H) were more co-operative & made fewer aggressive moves than MAOA-L ppts.
E: strength - findings support relationship between MAOA gene activity & aggression
Counterpoint
P: Study by Mertin et al. also showed non-genetic factors are crucial
E: found even ppts with MAOA-L behaved co-operatively rather than aggressively when made aware that other ppts were behaving co-operatively (i.e. giving away money). knowledge of social norm party determined how aggressive/co-operative MAOA-L ppts were.
E: limitation - means genes are influenced by env factors (knowing about others' behaviours) that are at least as important in aggression.
Complex Link
P: precise mechanism of MAOA-serotonin-aggression link is unclear
E: research linked aggression with low levels of serotonin . but MAOA-L gene causes low activity of MAO-A enzyme which in turn should lead to higher serotonin - because low-activity enzyme does not 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 they are lower or higher than normal
E: limitation - shows that the relationship between the MAOA gene, serotonin and aggression aren't yet fully understood.