Personality similarity in twins reared apart and together.

TLDR

The study administered the Multidimensional Personality Questionnaire to 217 monozygotic and 114 dizygotic reared‑together adult twin pairs and 44 monozygotic and 27 dizygotic reared‑apart pairs, then fitted a four‑parameter biometric model—including genetic, additive, nonadditive, shared family‑environment, and unshared environment components—to the 11 primary and 3 higher‑order MPQ scales using maximum‑likelihood techniques. Environmental models failed to fit any scale, whereas the full biometric model fit all scales, yielding heritabilities of .39 to .58, a negligible common family‑environment effect for all but two of 14 measures, and significant nonadditive genetic effects for three measures.

Abstract

We administered the Multidimensional Personality Questionnaire (MPQ) to 217 monozygotic and 114 dizygotic reared-together adult twin pairs and 44 monozygotic and 27 dizygotic reared-apart adult twin pairs. A four-parameter biometric model (incorporating genetic, additive versus nonadditive, shared family-environment, and unshared environment components) and five reduced models were fitted through maximum-likelihood techniques to data obtained with the 11 primary MPQ scales and its 3 higher order scales. Solely environmental models did not fit any of the scales. Although the other reduced models, including the simple additive model, did fit many of the scales, only the full model provided a satisfactory fit for all scales. Heritabilities estimated by the full model ranged from .39 to .58. Consistent with previous reports, but contrary to widely held beliefs, the overall contribution of a common family-environment component was small and negligible for all but 2 of the 14 personality measures. Evidence of significant nonadditive genetic effects, possibly emergenic (epistatic) in nature, was obtained for 3 of the measures.