genetic factors in aggression

• twin studies (coccaro et al):

  • direct physical abuse - MZ: 50% DZ: 19%
  • verbal aggression - MZ: 28% DZ: 7%
• adoption studies (hutchings +mednick):

  • 14000 males adopted in denmark
  • adoptee more likely to be criminal if bio + adoptive parents were criminals
  • bio parents especially fathers greater influence on criminality
• adoption studies findings:

  • bio criminal + adoptive criminal = 24.5%
  • bio criminal + adoptive non criminal = 20.5%
  • bio non criminal + adoptive criminal = 14.7%
  • bio non criminal + adoptive non criminal = 13.5%
• MAOA gene:

  • gene responsible for producing enzyme associated with aggressive behaviour
  • regulates metabolism of serotonin in brain
  • low levels = aggressive behaviour
• MAOA (brunner et al):

  • 28 male members of dutch family, repeated aggressive behaviour e.g rape + assault
  • low levels of MAOA (MAOA-L)
• caspi et al:

  • boys with MAOA-L likely to exhibit anti social behaviour if maltreated as child
  • boys with MAOA-H who were maltreated + boys with MAOA-L not maltreated didnt display anti social behaviour
  • MAOA-L more prevalent in countries with history of warfare
• EVALUATION: research support for genetics

  • miles + carey - metaanalysis 24 twin + adoption studies, aggressive + anti social behaviour product of genetics
  • age differences - genes + environment important in youth, decreased influence of environment when older
  • high reliability, consistent genetic influence
• EVALUATION: MAOA explains gender differences

  • niehoff - consequence of genetic vulnerability to MAOA linked to x chromosome
  • men inherit one x, women two - prevents expression of abnormal x chromosome
  • explains why men are more aggressive
• EVALUATION: biological reductionism

  • studies that contradict, concordance rates arent 100%
  • other factors involved, zimbardo - aggressive behaviour due to social psychological factors e.g deindividuation
  • explanation too simplistic, more holism