INDIVIDUAL-DIFFERENCES IN ADULT EGO DEVELOPMENT - SOURCES OF INFLUENCE IN TWINS REARED APART

A behavior genetic analysis of the personality dimension of ego develo pment, as assessed by the Washington University Sentence Completion Te st, was carried out on a sample of 45 pairs of monozygotic twins and 2 8 pairs of same-sex dizygotic twins. The twins ranged in age from 16 t o 70 years at the time of assessment, had been separated during infanc y, and had been raised apart in adoptive homes before being reunited i n adulthood. Analyses indicated that reared-apart twins were similar i n trait levels of ego development and that such similarity could not s olely be attributed to measured similarity in cognitive ability, inclu ding verbal reasoning. Estimates of broad heritability for ego develop ment (46%) were comparable to values reported for other major personal ity dimensions. Phenotypic variance in adult levels of ego development appears to have substantial genetic and environmental sources.