Genetic Factors in Aggression

Genetic Factors in Aggression

                                              Twins:Monozygotic twins share all same genes, dizygotic share 50%.Twin studies compare similarity of particular trait (E.G. aggression)If monozygotic twins = more alike = genes. Coccaro: studied aggressive behaviour in adult twin pairs. Nearly 50% of variance in direct aggressive behaviour = attributed to genetic factors.Evidence to support that genetics influence aggression has been found by Miles & Carey: Meta analysis, 24 twin & adoption studies.Most relied on parental/participant self-reports of aggressive tendencies. In self-reports, genetic factors explained large proportion of variance in aggression. Observations showed significantly less genetic contribution -greater environmental influence.Relies on self-reports - results may be open to demand characteristics.  Ppts may figure out purpose of exp. and manipulate child's environment.

                                          Adoption:Study children brought up by non-biological parents. If greater similarity in levels of aggression found between biological parents and adopted children, suggests genetic influence.If other way around, suggests environmental influences more important in development of aggressive behaviour. Adoption studies have demonstrated the importance of genes in aggression, for example ... Hutchings & Mednick:Study of 14,000+ adoptions in Denmark.Significant number of adopted boys with crim. convictions had biological fathers with same. Evidence for genetic effect.Study = individualistic.Used studies from Denmark alone - cannot be generalised as not collectivist.Issue because Denmark could be country who are more aggressive/accepting towards aggressive behaviour. Cannot be compared and generalised to others. 

                             Genetic Link:Monoamine Oxide A gene = responsible for producing MAOA - has been associated with aggressive behaviour. MAOA regulates metabolism of serotonin in brain.Low levels serotonin associated with impulsive & aggressive behaviour. Low levels MAOA = increase in impulsive behaviour.Evidence for the role of genes in aggression was found when Burner et al studied a Dutch family.Many of its male members behaved behaved in violent/aggressive manner - large proportion = involved in crimes of violence.Were found to have abnormally low levels of MAOA - defect in gene later identified. Real World ApplicationSuggested that public policy should be informed by result of 'biological' aggression studies.  If people  = predisposed to aggressive behaviour should be questions about treatment of behaviour. 

                                    Gene-Environment Caspi et al studied 500 children. Found variant gene associated with high levels of MAOA & variant gene associated with low levels.Those with low levels = more likely to exhibit antisocial behaviour - but only if maltreated as children. Children high levels, who were/weren't maltreated = didn't display aggressive b. Shows it is interaction between genes & environment that leads to aggression.Research that questions link between genes & behaviour conducted by Walters.Meta-analysis of studies investigating role of genetic factors in criminal behaviour. Found: Only low/moderate correlation between heredity & crime. Freewill/determinism debateSuggests level of MAOA in body determines how aggressive we are & how much impulsive behaviour we demonstrate. It fails to consider freewill - people may chose how they respond in situation.Two individuals may have low MAOA - one may chose lash out, one may remove themselves. 

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