ABSTRACT
This chapter illustrates the context of a uniquely large-sample study of early language delay, the Twins' Early Development Study (TEDS), which will eventually include measures of language development. TEDS analyses of individual differences support the conclusion emerging from research on older children that genetic factors play a significant role in normal language development in infancy. The chapter discusses twin and adoption studies suggest that language abilities and disabilities may be among the most heritable cognitive traits. Twin and adoption studies consistently suggest substantial genetic influence on measures of verbal ability as do measures of specific language structures and processes. Many studies have demonstrated that the quantity and quality of parental language is correlated with children's rate of language development. A more subtle point is that finding genetic influence on individual differences in language development offers a different interpretation of research showing correlations between the quantity and quality of parental language and children's language development.
