Using a combined sample of adolescent twins, biological siblings, and adoptive siblings, we estimated and compared the differential shared-environmentality for high cognitive ability and the shared-environmental variance for the full range of ability during adolescence. Estimates obtained via multiple methods were in the neighborhood of 0.20, and suggest a modest effect of the shared environment on both high and full-range ability. We then examined the association of ability with three measures of the family environment in a subsample of adoptive siblings: parental occupational status, parental education, and disruptive life events. Only parental education showed significant (albeit modest) association with ability in both the biological and adoptive samples. We discuss these results in terms of the need for cognitive-development research to combine genetically sensitive designs and modern statistical methods with broad, thorough environmental measurement.
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Acknowledgments This work was supported by US Public Health Service grants # DA005147, AA009367, DA13240, AA11886, and MH66140, and by grant # 13575 from the John Templeton Foundation (‘‘The Genetics of High Cognitive Abilities’’). The authors give their special thanks to Brian M. Hicks for his assistance in the analysis of the life-events and parental-psychopathology data.
- Family environment
- High cognitive ability
- Shared environment