Genetic and Sociocultural Influence on Language Development

The present study was designed to assess the relative contribution of genetic and environmental variance to the phenotypic expression of language skills. The classical twin method is used, comparing intrapair similarity for identical and like-sexed fraternal twins on measures of phonological, morphological, syntactic and semantic development. In addition, the mother's interactions with her child are measured, both in terms of the verbal complexity of her speech and her speaking style. Comparisons will he made for all measures: one, between children reared by the . same mother but who differ in genetic relatedness (MZ vz. DZ pairs); and two, between children reared in different families whose mothers vary in I.Q., speaking styles, and speech complexity (between families).