P: There is research support for the influence of genes on aggression from twin studies

E: Twin studies have found a higher concordance rate for criminal behaviour among monozygotic twins than dizygotic twins

E: This demonstrates that genetics play a role in influencing the likelihood of aggressive behaviour, as MZ twins share more genes than DZ twins, providing further support for the explanation

P: There is research support for the influence of genes on aggression from adoption studies

E: An adoption study found that children who displayed criminal behaviour were significantly more likely to have biological parents who also displayed criminal behaviour

E: Thus, this similarity between the adopted children and their biological parents, must be due to genetics

P: There is research support for the role of the MAOA gene in aggression

E: For example, Frazzetto et al found a correlation between low activity in the MOAO gene and higher levels of aggression in adult men.

E: This increases the validity of the explanation by providing real-life support.