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Why are children in the same family so different from one another?
Robert Plomin1, Denise Daniels
1Department of Individual and Family Studies, Pennsylvania State University, University Park, PA 16802, USA.
International Journal of Epidemiology
|August 3, 2011
Summary
Environmental factors, not genetics, significantly shape personality, psychopathology, and cognition. Crucially, these environmental influences make siblings as different as strangers, highlighting the impact of nonshared environment.
Area of Science:
- Human Behavioral Genetics
- Developmental Psychology
- Quantitative Genetics
Background:
- Human behavioral genetics research increasingly emphasizes environmental influences over heredity.
- Environmental factors are critical for personality, psychopathology, and cognitive development.
- A key finding is that environmental influences create greater differences between siblings than between unrelated individuals.
Purpose of the Study:
- To present evidence that nonshared environmental influences are the primary drivers of psychological variation.
- To detail quantitative genetic methods supporting the role of nonshared environment.
- To explore specific nonshared environmental factors and their relation to behavioral differences.
Main Methods:
- Utilizing quantitative genetic methods to analyze behavioral variation.
- Examining correlations in pairs of adopted children reared together.
- Analyzing longitudinal data on cognitive abilities (IQ) and environmental influences.
Main Results:
- Correlations for adoptive siblings are near zero, indicating minimal shared environmental impact.
- Nonshared environmental factors account for the majority of environmental variance in psychological traits.
- Even cognitive abilities like IQ are primarily influenced by nonshared environment after adolescence.
Conclusions:
- Psychologically relevant environmental influences create differences, not similarities, among children within the same family.
- The concept of nonshared environment is crucial for understanding individual psychological development.
- Future research should focus on identifying specific nonshared environmental influences and their mechanisms.
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