Personality similarity in twins reared apart and together.
Level 4 - case-series / case-control
Cross-sectional twin study comparing reared-together and reared-apart pairs (by design analogy)
PubMed 3397862 · doi:10.1037//0022-3514.54.6.1031
What was done
Researchers administered the Multidimensional Personality Questionnaire (MPQ; 11 primary scales, 3 higher-order scales) to adult twin pairs across four groups: 217 monozygotic reared-together, 114 dizygotic reared-together, 44 monozygotic reared-apart, and 27 dizygotic reared-apart pairs (total 402 pairs). Using maximum-likelihood techniques, they fitted a full four-parameter biometric model (additive genetic, nonadditive genetic, shared family environment, and unshared environment) alongside five reduced models to evaluate the contributions of genes and environment.
What was found
Purely environmental models failed to fit any of the 14 MPQ scales. The full model provided a satisfactory fit for all scales, yielding heritability estimates ranging from .39 to .58. The contribution of shared family environment was negligible for 12 of the 14 measures, showing a meaningful effect in only 2 scales. In addition, 3 measures showed evidence of significant nonadditive genetic effects.
Why it matters
This landmark reared-apart twin study provided empirical evidence that adult personality traits are substantially heritable (roughly 40% to 60%) and that growing up in the same household accounts for very little similarity in adult personality.
Limits
The sample of reared-apart pairs was relatively small (44 MZ and 27 DZ pairs). Personality was assessed exclusively via self-report on a single instrument (the MPQ). The findings depend on the assumptions of biometric structural equation modeling, and the abstract does not report specific demographic characteristics or confidence intervals for the heritability parameters.
Cited by
- supports Studies of identical twins separated at birth conducted at the University of Minnesota show that positive and negative affect profiles are between 40% and 80% genetically determined.