The Dunedin Study is a long-running study of human health and development, based on roughly 1000 people born in Dunedin in 1972. In TV series Why Am I? , the far-reaching findings of the study are explored. This episode focuses on the interplay between nature and nurture, especially in regard to anti-social behaviour — as narrator Susie Ferguson says, "it's as if nature loads a gun, and nurture pulls the trigger." Much of the episode explores a rare mutation in the MAOA gene, a common denominator in violent criminals. Other subjects include depression, and when cannabis use can help cause psychosis.