title: Are stepfathers' education levels associated with the intelligence of their stepsons? A register-based study of Norwegian half-brothers.
abstract: We examined the relationship between the parents' education levels and the adult intelligence of their children in a population-based, nationwide sample of Norwegian half-brothers with different fathers (2,016 pairs of half-brothers). In a family where the mother has two children with different men, the firstborn child usually lives with the younger child's father during a period of their childhood. This makes it possible to study the non-genetic effects of paternal education on children's development. Results showed that the education level of the younger half-brother's father was positively associated with the intelligence score of the older half-brother. The education level of the older half-brother's father was not associated with the intelligence score of the younger half-brother. Firstborn men whose half-brothers' fathers had high levels of education had intelligence scores that were 33% (95% confidence interval: 18-47%) of a standard deviation higher than those of firstborn men whose half-brothers' fathers had low levels of education, after adjustment for the biological fathers' education levels, mothers' education levels, and other background factors. These findings are compatible with the hypothesis that a child's family environment exerts an effect on the cognitive abilities of the child that lasts into adulthood.
authors.affiliation: Division of Mental Health, Norwegian Institute of Public Health, Oslo, Norway. w-bjarer@online.no
authors.forename: Willy
authors.initials: W
authors.lastname: Eriksen
authors.forename: Jon M
authors.initials: JM
authors.lastname: Sundet
authors.forename: Kristian
authors.initials: K
authors.lastname: Tambs
mesh_terms: D000328:Adult; D004522:Educational Status; D005220:Fathers / Q000523:psychology*; D006801:Humans; D007360:Intelligence / Q000502:physiology*; D008297:Male; D009664:Norway; D035781:Siblings / Q000523:psychology*