This study investigated the influence of genetic factor and personality on leadership role occupancy among a sample of male twins. Identical twins (n =238) who share 100% of their genetic background were compared with fraternal twins (n =188) who are expected to share only 50% of their genetic background. Results indicated that 30% of the variance in leadership role occupancy could be accounted...

This paper examines why parents of twins or adult twins themselves request zygosity testing. Of 405 multiples including 8 sets of triplets, the majority (93%) were monozygotic. Age of testing ranged from 0 days to 73 years. About 50% of requests came from parents or twins who were curious about, or expressed a need to be certain of, their zygosity. Other reasons included health concerns (curren...

This article describes the design and data availability for samples of genetic pairs in the National Longitudinal Study of Adolescent Health (Add Health). Add Health provides unique samples of genetic pairs that are nationally representative and followed longitudinally from early adolescence into young adulthood with 3 in-home interviews and a 4th interview planned for 2007 to 2008. The design ...

Environmental measures used widely in the behavioral sciences show nearly as much genetic influence as behavioral measures, a critical finding for interpreting associations between environmental factors and children's development. This research depends on the twin method that compares monozygotic and dizygotic twins, but key aspects of children's environment such as socioeconomic status (SES) c...

Men outperform women in mental rotation by about one standard deviation. Prenatal exposure to testosterone has been suggested as one cause. In animals it has been shown that a female fetus located between two male ones is exposed to higher levels of testosterone. It is still unclear whether intra-uterine hormone transfer exists in humans. Therefore, the influence of an intra-uterine presence of...