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The heritability of IQ
B Devlin1, M Daniels, K Roeder
1Department of Psychiatry, University of Pittsburgh School of Medicine, Pennsylvania 15213, USA. devlinbj@msx.upmc.edu
Nature
|July 31, 1997
Summary
New research suggests maternal effects significantly influence IQ heritability, not just genetics. A meta-analysis found shared maternal environments explain more IQ covariance in twins and siblings than previously thought.
Area of Science:
- Behavioral Genetics
- Developmental Psychology
- Human Intelligence
Background:
- IQ heritability, the genetic contribution to IQ variation, is debated.
- Previous models assumed distinct environmental influences for twins, siblings, and parent-offspring.
- Maternal effects have often been considered negligible in IQ heritability studies.
Purpose of the Study:
- To evaluate an alternative model incorporating maternal womb and common home environments.
- To compare the fit of a 'maternal-effects' model against traditional 'family-environments' models.
- To re-evaluate the contribution of genes and environment to IQ variability.
Main Methods:
- Meta-analysis of 212 previous studies on IQ heritability.
- Development and testing of a novel 'maternal-effects' model.
- Comparison of statistical support for maternal-effects versus family-environments models.
Main Results:
- The 'maternal-effects' model demonstrated a superior fit to existing data.
- Maternal effects accounted for 20% of twin covariance and 5% of sibling covariance.
- Heritability estimates were reduced, with two measures falling below 50%.
Conclusions:
- Shared maternal environments play a substantial, previously underestimated role in IQ covariance.
- The findings challenge traditional views of IQ heritability and highlight the importance of maternal influences.
- Understanding maternal effects is crucial for identifying potential avenues to enhance IQ.