Twin study of personality

The term personality is understood as trait factors in a narrow sense, such as the Big Five, from a broader psychological perspective, as any kinds of individual dimensions other than cognitive abilities. Twin studies investigating the genetic and environmental influence of personality reveal common and robust results concerning personality; additive genetic and nonshared environmental factors are the main sources of variations in most personality traits, nonadditive genetic (genetic contribution explained not by the simple addition of related genes but by combinational and interactional effects of multiple genes) and shared environmental effects are relatively rare if not negligible at all. The structures of personality traits are also explained as genetic structure universally from the top general factor to each item level. Developmental genetic contribution to personality tends to decrease throughout life. Other-related traits such as social behavior (political, economic, religious, criminal) have also been investigated. Two elegant applications of twin methodology, the discordant twin method, direction of causation model were introduced.