A model is presented for the changes in familial resemblance as a function of age. The model allows for separate developmental components of genetic and environmental effects and for the influence of earlier phenotypic values on current measurements. Genetic and environmental effects may be specific to occasions or constant over time. Expected covariances are derived within individuals and between relatives measured at different ages. Parameter substitution shows that models with different assumptions about the mechanism of development yield different predictions for temporal changes in family resemblance. The application of the model is illustrated by the analysis of published longitudinal data on cognitive development. The data suggest that the continuity of cognitive performance over time and the increase in heritability with age reflect the cumulative long-term effects of a single set of genes expressed throughout development. The quality of the shared environment changes from family to family over time but appears to exercise a long-term effect on cognitive development.

Original languageEnglish
Pages (from-to)143-162
Number of pages20
JournalBehavior genetics
Issue number1
StatePublished - Jan 1986


  • aging
  • cognition
  • development
  • family resemblance
  • heritability
  • path analysis
  • quantitative inheritance
  • twins


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