Sources of human psychological differences: the Minnesota Study of Twins Reared Apart.
Level 4 - case-series / case-control
Level 4 by design analogy: observational natural experiment cross-sectional twin study.
PubMed 2218526 · doi:10.1126/science.2218526
What was done
The Minnesota Study of Twins Reared Apart evaluated more than 100 sets of monozygotic and dizygotic twins or triplets separated in infancy and reared apart. Participants completed a week of intensive psychological and physiological assessments covering IQ, personality, temperament, occupational and leisure-time interests, and social attitudes.
What was found
About 70% of the variance in IQ was associated with genetic variation. Across multiple measures of personality, temperament, occupational/leisure interests, and social attitudes, monozygotic twins reared apart were about as similar as monozygotic twins reared together. Exact numerical correlation values and confidence intervals were not reported in the abstract.
Why it matters
The findings demonstrate a strong genetic contribution to human cognitive ability and personality traits, indicating that shared rearing environment accounts for less psychological resemblance in adulthood than genetics.
Limits
The abstract does not provide exact subgroup sample sizes (monozygotic vs. dizygotic), specific test scores, or statistical confidence intervals. The degree of environmental separation and potential selective placement or adult reunion prior to testing are not described in the abstract.
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.