The Influence of "Family Background" on Intellectual Attainment

Family background frequently has been found to have long-term effects on adult intellectual, occupational, and economic outcomes. Since families differ both genetically and environmentally, it has been difficult to interpret family effects in studies of individuals or biological relatives. This study includes samples of adoptive and biologically-related families with children between 16 and 22 years of age. We regressed child IQ on several family demographic variables, on parental IQ, and on natural parent characteristics (for the adopted children) to estimate the degree of genetic bias in the coefficients on measured family background. The results indicate that there is little effect of those family environmental differences studied on IQ differences among the adolescents in the SES range of working to upper middle class. Parent-child and sibling correlations further indicate that genetic differences among families account for the major part of the long-term effects of 'family background on IQ.