Discuss genetic explanations of aggression (4+8 marks)
One gene which has been linked to aggression is the gene coding for the production of monoamine oxidise A (MAOA). Brunner et al 1993 studied the men in a family with a tradition of violent men, they discovered that the gene responsible for producing the enzyme MAOA may be associated with aggressive behaviour. The normal gene that makes an enzyme which metabolises hormones and neurotransmitters (including adrenaline and noradrenaline). With a mutated gene there is less enzymes and so the levels of brain chemicals build up leading to excess adrenaline which therefore leads to more aggression.
There has also been a modest association between DRD4 and a tendency to attention deficit hyperactivity disorder (ADHD) which was found by Faraone et al 2001. As well as this, association between a DRD3 variant and both impulsivity and ADHD-related symptoms in violent offenders (Retz et al 2003).
The role of genetic factors in aggression can be tested in twin studies. Genes are identical in sets of monozygotic twins but are different between sets of dizygotic twins, meaning that if monozygotic twins are more alike in terms of aggression than dizygotic twins are, this similarity can be attributed to genetics. These twin studies have generally found that almost 50% of variance in aggressive behaviour can be attributed to genetic factors (Coccaro et al 1997).
Adoption studies can help determine the relative contributions of environment and heredity in aggression. Positive correlation between adopted children and their biological parents implies a genetic effect, while positive correlation between the child and their adoptive parents implies an environmental effect. A study of over 14,000 adoptions in Denmark found that a significant number of adopted boys with criminal convictions had biological fathers with criminal convictions, demonstrating a genetic effect.
Having genes itself cannot determine behaviour, it depends on other factors such as environmental risk factors.
There has also been a modest association between DRD4 and a tendency to attention deficit hyperactivity disorder (ADHD) which was found by Faraone et al 2001. As well as this, association between a DRD3 variant and both impulsivity and ADHD-related symptoms in violent offenders (Retz et al 2003).
The role of genetic factors in aggression can be tested in twin studies. Genes are identical in sets of monozygotic twins but are different between sets of dizygotic twins, meaning that if monozygotic twins are more alike in terms of aggression than dizygotic twins are, this similarity can be attributed to genetics. These twin studies have generally found that almost 50% of variance in aggressive behaviour can be attributed to genetic factors (Coccaro et al 1997).
Adoption studies can help determine the relative contributions of environment and heredity in aggression. Positive correlation between adopted children and their biological parents implies a genetic effect, while positive correlation between the child and their adoptive parents implies an environmental effect. A study of over 14,000 adoptions in Denmark found that a significant number of adopted boys with criminal convictions had biological fathers with criminal convictions, demonstrating a genetic effect.
Having genes itself cannot determine behaviour, it depends on other factors such as environmental risk factors.