Genetic Explanations Flashcards
why do we use twin studies?
- Because MZ twins share 100% of their genes but DZ twins share only 50% ( they both share same environment)
- we would expect to find greater similarities in aggressive behaviour
between MZ twins if aggression is mostly influenced by genetic factors.
what did COCCARO ET AL. do in their twin study research?
Coccaro et al. (1997) studied men who were either monozygotic (MZ) or dizygotic (DZ) twins.
what were the results in COCCARO ET AL. twin study research?
Aggressive behaviour (defined as direct physical assault), found concordance rates of 50% for MZ twins and 19% for DZs.
- Figures for verbal aggression were 28% (MZs) and 7% (DZs).
why do we use adoption studies?
- Similarities in aggressive behaviour between an adopted child and their
biological parents suggest that genetic influences are operating. - Similarities between an adopted child and their adoptive parents suggest that environmental influences are operating.
what did Rhee and Waldman do in their adoption study
Rhee and Waldman (2002) carried out a meta-analysis of adoption studies of direct aggression and antisocial behaviour
what was the results in Rhee and Waldman adoption study?
They found that genetic influences accounted for 41% of the variance in aggression, more or less in line with findings from twin studies
what is the MAOA Gene? what does it do?
- Controls production of enzyme monoamine oxidase A
- Regulates (breaks down) the neurotransmitter serotonin
what is the MAOA-L gene?
The low-activity variant (MAOA-L) which results in low activity of the MAO-A enzyme
- MAOA-L variant that has been linked to high levels of aggressive behaviour.
what has the MAOA-L gene being nicknamed as?
- ‘warrior gene’
- Historically, the Maori people have had a reputation for being ferocious warriors, hence the nickname.
what has research shown about the MAOA-L gene in the Māori people?
Research showed that the MAOA-L variant was possessed by 56% of New Zealand Maori men (compared with 34% of Caucasians).
what did Brunner find about the MAOA-L gene?
Studied 28 men from a large Dutch family who were repeatedly involved in impulsively aggressive violent criminal behaviours such as rape, attempted murder and physical assault. These men had abnormally low levels of the enzyme MAO-A as well as the MAOA-L gene variant
what is meant by gene and environment interactions? how it this applied to the MAOA-L gene?
Genes are crucial but they do not function in isolation.
- MAOA-L gene activity is only related to adult aggression when combined with early traumatic life experiences
what is the association of the MAOA-L gene and trauma?
- association between higher levels of antisocial aggression and the MAOA-L gene variant in men
- this was only the case in those who had experienced significant trauma during the first 15 years of life
- those who had no traumatic event even if they possessed the MAOA-L variant, didn’t show aggression
What is the research supporting MAOA-L in aggression?
P: One strength is support for the role of the MAOA gene in aggression.
EE: Research shows that the low-activity variant of the MAOA (MAOA-L) gene is associated with greater aggression. Mertins et al. (2011) found that the converse is also true. Men with low-activity and high-activity variants of the MAOA gene took part in a money-distributing game. Men with the high-activity variant (MAOA-H) were more co-operative and made fewer aggressive moves than the low-activity participants.
L: This finding supports the relationship between MAOA-L gene activity and aggression
What is the counterpoint of research supporting MAOA-L in aggression?
P: counterpoint
EE: However, the study by Mertins et al. also showed than non- genetic factors are crucial. They found that even participants with the low-activity MAOA variant (MAOA-L) behaved co-operatively rather than aggressively when they were made aware that others in thestudy were behaving co-operatively (i.e. giving away money). Knowledge of a social norm partly determined how aggressive or co-operative MAOA-L participants were.
L: Therefore genes are influenced by environmental factors, and do not act alone, providing support for the interactionist theory.
What is a limitation of twin studies in genetic explanations?
P: A limitation of the genetic explanation is that twin studies may lack validity.
EE: In every pair of twins, both individuals share the same environment as each other (because each pair is raised together). However, DZ twins may not share their environment to the same extent that MZ twins share theirs. We assume they do and this is called the equal environments assumption. But the assumption may be wrong because one aspect of the environment is the way twins are treated by others. This may be wrong, because MZ twins’ aggressive behaviour is reinforced more equally than DZs.
L: This means that concordance rates are inflated and genetic influences on aggression may not be as great as twin studies suggest.
What is the limitation of the genetic explanations regarding MAOA-L and serotonin?
P: One limitation of the MAOA-serotonin-aggression link is that the precise mechanism is unclear.
EE: Previously, research linked aggression with low levels of serotonin (e.g. Virkkunen et al. 1994). But the MAOA-L gene causes low activity of the MAO-A enzyme which in turn should lead to higher serotonin (because MAOA gene should deactivate serotonin, so the low-activity enzyme will not decrease serotonin). In people with the 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.
L: This shows that the relationship between the MAOA gene, serotonin and aggression is not yet fully understood.
