Resolution of cultural and biological inheritance by path analysis.

Analysis of family resemblance is developed in terms of three genetic parameters, six parameters for cultural inheritance, and one parameter for an index estimating family environment. With efficient use of nuclear families the model is fully determinate. Other biological and social relationship provide additional degrees of freedom for testing goodness of fit. Performance of the model is satisfactory on simulated data with extreme gene-environment interaction. Applied to a large body of published data on I.Q., neither genetic assortative mating nor gene-environment covariance is significant by a likelihood ratio test, but heritability is less and cultural inheritance is greater for adults than children. Whereas family resemblance of children is largely genetic, for adults it is largely due to their childhood environments, presumably acting on occupational aspirations. Further resolution is more likely to come from nuclear families than from the rare relationships that were favored by classical human genetics.