The researchers found that even though they had been brought up apart, identical twins like Jack and Oskar had a lot more in common than the 40 sets of fraternal twins brought up together who were also subjects of the study. But not everything was written in their genes. Jack and Oskar never agreed on Middle Eastern politics; Nancy Segal, Bouchard’s co-researcher, described them as having an “extraordinary love-hate relationship... They were repelled and fascinated by each other.”