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Why do identical twins differ in personality: shared environment reconsidered.
Anne Mari Torgersen1, Harald Janson
1Department of Psychology, University of Oslo, Norway. a.m.torgersen@psyki-atri.uio.no
Summary
Childhood life stressors significantly correlate with adult personality differences in identical twins, even when genetics are considered. Shared environmental factors, like stress, shape individual personality development over time.
Area of Science:
- Psychology
- Behavioral Genetics
- Developmental Psychology
Background:
- Heritability studies indicate genetics and non-shared environments largely explain adult personality variance.
- However, the impact of shared environmental influences on personality development remains significant.
Purpose of the Study:
- To investigate the relationship between childhood life stressors and adult personality differences.
- To examine the role of shared environmental factors in shaping personality within monozygotic twin pairs.
Main Methods:
- Utilized prospective data from 26 monozygotic (MZ) twin pairs studied from birth.
- Assessed life stressors experienced between ages 6 to 15.
- Correlated childhood stressors with Big Five personality traits at age 29.
Main Results:
- Found a significant positive correlation between childhood/early adolescent stressors and intrapair personality differences.
- Observed effects on Agreeableness, Openness, Conscientiousness, and overall five-factor profiles.
- Highlighted that shared environmental effects can be mislabeled as 'nonshared' when they increase sibling dissimilarity.
Conclusions:
- Childhood life stressors are linked to later personality divergence in genetically identical individuals.
- Shared environmental experiences, particularly stress, play a crucial role in adult personality formation.
- Suggests a need for further research into the mechanisms linking early stress to personality differences.