title: Family environment and the malleability of cognitive ability: a Swedish national home-reared and adopted-away cosibling control study.
abstract: Cognitive ability strongly aggregates in families, and prior twin and adoption studies have suggested that this is the result of both genetic and environmental factors. In this study, we used a powerful design--home-reared and adopted-away cosibling controls--to investigate the role of the rearing environment in cognitive ability. We identified, from a complete national Swedish sample of male-male siblings, 436 full-sibships in which at least one member was reared by one or more biological parents and the other by adoptive parents. IQ was measured at age 18-20 as part of the Swedish military service conscription examination. Parental educational level was rated on a 5-point scale. Controlling for clustering of offspring within biological families, the adopted siblings had an IQ 4.41 (SE = 0.75) points higher than their nonadopted siblings. Each additional unit of rearing parental education was associated with 1.71 (SE = 0.44) units of IQ. We replicated these results in 2,341 male-male half-sibships, in which, controlling for clustering within families, adoption was associated with a gain of IQ of 3.18 (SE = 0.34) points. Each additional unit of rearing parental education was associated with 1.94 (SE = 0.18) IQ units. Using full- and half-sibling sets matched for genetic background, we found replicated evidence that (i) rearing environment affects IQ measured in late adolescence, and (ii) a portion of the IQ of adopted siblings could be explained by the educational level of their adoptive parents.
authors.affiliation: Virginia Institute for Psychiatric and Behavioral Genetics and Departments of Psychiatry and Human and Molecular Genetics, Virginia Commonwealth University, Richmond, VA 23298; ent3c@virginia.edu kendler@vcu.edu.
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
authors.affiliation: Department of Psychology, University of Virginia, Charlottesville, VA 22904; ent3c@virginia.edu kendler@vcu.edu.
authors.forename: Eric
authors.initials: E
authors.lastname: Turkheimer
authors.affiliation: Center for Primary Health Care Research, Lund University, SE-205 02 Malmö, Sweden; and.
authors.forename: Henrik
authors.initials: H
authors.lastname: Ohlsson
authors.affiliation: Center for Primary Health Care Research, Lund University, SE-205 02 Malmö, Sweden; and Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, CA 94305.
authors.forename: Jan
authors.initials: J
authors.lastname: Sundquist
authors.affiliation: Center for Primary Health Care Research, Lund University, SE-205 02 Malmö, Sweden; and Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, CA 94305.
authors.forename: Kristina
authors.initials: K
authors.lastname: Sundquist
mesh_terms: D000300:Adoption / Q000523:psychology*; D003071:Cognition; D004522:Educational Status; D005190:Family / Q000523:psychology*; D059647:Gene-Environment Interaction; D006801:Humans; D007360:Intelligence; D010287:Parent-Child Relations; D010290:Parents / Q000523:psychology; D035781:Siblings / Q000523:psychology*; D012931:Social Environment; D013548:Sweden
keywords: adoption; cognitive ability; cosibling control; environment; rearing
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