Genetic factors Flashcards
Explain what twin studies have found about aggression. (coccaro)
Several twin studies have suggested that heritability accounts for about 50% of the variance in aggressive behaviour. For example, Coccaro studied male monozygotic and dizygotic twins. Because MZ twins share 100% of their genes but DZ share only 50%, we would expect to find greater similarities in aggressive behaviour between MZ twins if aggression is influenced by genetics. This is because both MZ and DZ twins are raised together in the same environment but MZ twins share a greater degree of genetic similarity than DZ’s. For aggressive behaviour, the researchers found concordance rates of 50% for MZ twins and 19% for DZ’s.
Explain what adoption studies have shown about aggression.
Similarities in aggressive behaviour between an adopted child and their biological parents suggest that genetic influences are operating. Similarities with the adopted parents suggest that environmental influences are operating.
What is the role of the MAOA gene in aggression?
Monoamine oxidase A (MAOA) is an enzyme. Its role is to mop up neurotransmitters in the brain after a nerve impulse has been transmitted from one neuron to another. It does this by breaking neurotransmitters such as serotonin into chemicals to be recycled or excreted. The production of this enzyme is determined by the MAOA gene. A dysfunctional MAOA gene leads to low MAOA activity in areas of the brain and has been associated with high levels of aggression.
Evidence for MAOA gene influence on aggression.
Brunner studied 28 male members of a large Dutch Family who were repeatedly involved in impulsively aggressive violent criminal behaviour such as rape, attempted murder and physical assault. The researchers found that these men had absolutely low levels of MAOA in their brains and the low-activity version of the MAOA gene.
Limitation of genetic factors in aggression (the interactionist approach)
Genes are crucial influences on aggressive behaviour but they do not function in isolation. low MAOA gene activity is only related to adult aggression when combined with early traumatic life events. For example,Frazzetto et al found an association between higher levels of antisocial aggression and the low-activity MAOA gene in adult males as expected but this was only in males who had experienced significant trauma during their first 15 years of life. Those who had not experienced this trauma did not have particularly high aggression levels of adults even if they possessed the low activity MAOA variant.
Limitation of genetic factors in aggression (measuring aggression).
Methods of measuring aggression differ significantly between studies e.g self reports, parent and teacher reports and direct observations. Research findings have shown that genetic factors had a greater influence on aggression in self-report studies rather than parent or teacher reports. If research findings vary depending upon how aggression is measured, then it becomes difficult to draw valid conclusions about the role of genetic factors.
