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Parent-offspring resemblances in intelligence: theories and evidence.

A review of data on parent-offspring resemblances in intelligence is presented in the context of correlation, regression and variance predictions from the polygenic model and an environmental model. Consideration was given to reliability, test equivalence and long-term stability of IQ scores. Results indicate that much of the difference among offspring IQ scores is not directly attributable to parental IQ, and that some is due to other between-family variables. The magnitude of single-parent-offspring correlations was related to the degree of assortative mating present in samples. Evidence on whether parent-offspring resemblances in IQ are transmitted genetically or environmentally is on the whole lacking. A single study provides evidence for some degree of genetic transmission, but it is argued that the present polygenic model is inadequate.