Genetic factors Flashcards
(17 cards)
What have twin studies suggested?
Heritability accounts for about 50% of the variance in aggressive behaviour
Who did a twin study on aggression?
Coccaro et al
What did Coccaro et al study?
Men who were monozygotic or dizygotic twins
MZ - share 100% of their genes
DZ - share 50% of their genes
If influenced mostly by genetic factors then MZ would have greater similarities of aggression
Both raised together in same environment
MZ have greater degree of genetic similarity than DZ
Aggressive behaviour defined as direct physical assault - researchers found concordance rate of 50% for MZ twins
DZ - 19%
Corresponding figures for verbal aggression were
MZ - 28%
DZ - 7%
What do adoption studies suggest?
Similarities in aggressive behaviour between adopted child and biological parents suggest genetic influences are operating
Similarities between adopted child and adoptive parents suggest environmental influences operating
Who researched adoption studies?
Rhee and Waldman
What did Rhee and Waldman find about adoption studies?
Meta analysis
Adoption studies
Direct aggression and antisocial behaviour - Prominent feature of which is aggressive behaviour
Found genetic influences accounted for 41% of the variance in aggression
More or less in line with findings from twin studies
What does the MAOA gene do?
Control production of an enzyme called monoamine oxidase A
MAOA - the gene
MAO-A - the enzyme
What does the MAO-A do?
Regulates neurotransmitter seretonin
What does it mean if genes come in different variants?
Low activity variant - MAOA-L
Results in low activity of the MAO-A enzyme (MAO-A deficiency)
MAOA-L variant has been linked to high levels of aggressive behaviour
Who talked about warrior gene?
Lea and Chambers
What did Lea and Chambers research?
MAOA-L variant was possessed by 56% of New Zealand Maori men (compared with 34% of caucasians)
Maori people have had reputation for being ferocious warriors
What did Brunner et al study?
28 men
Large Dutch family
Repeatedly involved in impulsively aggressive violent criminal behaviours
Eg. rape, attempted murder, physical assault
Men had abnormally low levels of enzyme MAO-A as well as the MAOA-L gene variant (Brunner syndrome)
What did Frazzetto et al find about gene-environment interactions?
Association between higher levels of antisocial aggression and the MAOA-L gene variant in men
Only case in those who has experienced significant trauma during the first 15 years of life
Those who had not experienced such childhood trauma did not have particularly high levels of aggression as adults, even if they possessed the MAOA-L variant
Strong evidence of a gene-environment interactions (diathesis stress)
What is a strength of the MAOA gene in aggression?
Research support
Shows low activity variant of the MAOA gene is associated with greater aggression.
Mertins et al
Converse is true
Men with low activity and high activity variant of the MAOA gene took part in money distributing game
Men with high were more cooperative and made fewer aggressive moves than those with low activity participants
Supporting relationship between MAOA gene activity and aggression
What was a counterpoint to the Mertin et al research support?
Non genetic factors are also crucial
Participants with the low activity MAOA variant behaved cooperately rather than aggressively when they were made aware that others in study were behaving cooperatively
Knowledge of a social norm partly determined how aggressive or cooperative participants were
Genes are influenced by environmental factors that are at least as important in aggression
What is a limitation of the MAOA-seretonin-aggression link?
Complex link
Precise mechanism is unclear
MAOA-L gene causes low activity of the MAO-A enzyme which in turn should lead to higher serotonin
Low activity enzyme does not deactivate serotonin, leaving more serotonin for synaptic transmission
May be more accurate to say that their serotonin levels are disrupted rather than they are lower or higher than normal
Showing the relationship between the MAOA gene, serotonin and aggression is not yet fully understood
What is a limitation of the genetic explanation?
Twin studies may lack validity
Both individuals share same environment as each other
DZ may not share their environment in the same way that MZ twins do
Equal environment assumption
Assumption may be wrong - one aspect of the environment is the way that twins are treated by others.
MZ - treated similarly, especially by parents
DZ - treated less similar ways
Meaning concordance rates are inflated and genetic influences on aggression may not be as great as twin studies suggest
