How genetic factors affect aggression - BIOLOGICAL EXPLANANTION

Twin studies AO1

• MZ twins share 100% genes

• So expect greater similarities in MZ twins if aggression is influenced by genetic factors

• Physical assault: MZ = 50% DZ = 19%

• Verbal aggression: MZ = 28% DZ = 7%

Twin studies AO3: STS

Rutter

• Meta analysis of twins aggressive behaviour

Findings

• DZ = 13-22% concordance rate of criminal behaviour

• MZ =26-51%

• Shows correlation between genetics and aggression but other factors also involved bc MZ not equal to 100%

Adoption research AO1

• Similarities between adopted child and biological parents show genetic factors influence aggression

• Similarities between adopted child and foster parents show environmental factors influence aggression

Adoption research AO3: STS

Rhee and Walksman

• Meta analysis of adoption studies on aggression and anti-social behaviour

Findings

• Genetic influences accounted for 41% of variance in aggression

MAOA gene AO1

• Low activity MAOA gene

• Dysfunctional MAOA enzyme

• So enzyme cannot mop up excess neurotransmitters

• So there’s abnormal activity causing aggressive behaviour

• MAOA on its own has no effect but males abused as children have a greatly enhanced chance of committing violent crime

MAOA gene AO3: STS 1

Brunner

• Studied 28 male members of Dutch family repeatedly involved in violent crime

Findings

• Research found they had abnormally low lvls of MAOA gene and the low activity version

MAOA gene AO3: STS 2

Frazzeto

• Found males w low activity MAOA gene without childhood trauma = not high lvls of aggression

• Those with low active MAOA gene + abuse = high lvls aggression