Writing in the Journal of Personality, the researchers found that identical twins were twice as likely as non-identical twins to share the same personality traits, suggesting that their DNA was having the greatest impact. Genetics were most influential on people's sense of self-control and also affected their social and learning abilities and their sense of purpose. Prof Timothy Bates, who led the study, said: "Previously, the role of family and the environment around the home often dominated people's ideas about what affected psychological wellbeing. However, this work highlights a much more powerful influence from genetics."