GENETIC CHANGE AND CONTINUITY FROM 14 TO 20 MONTHS - THE MACARTHUR LONGITUDINAL TWIN STUDY

Genetic change as well as continuity was investigated within the domai ns of temperament, emotion, and cognition/language for 200 pairs of tw ins assessed at 14 and 20 months of age in the laboratory and home. Th e second year of life is marked by change rather than continuity: corr elations from 14 to 20 months averaged about .30 for observational mea sures of temperament and emotion, about .40 for language measures, and about .50 for mental development. 2 types of genetic change were exam ined: changes in the magnitude of genetic influence (heritability) and genetic contributions to change from 14 to 20 months. In general, her itability estimates were similar at 14 and 20 months. Evidence for gen etic influence on change from 14 to 20 months emerged for several meas ures, implying that heritability cannot be equated with stability. Ana lyses of continuity indicated that genetic factors are largely respons ible for continuity from 14 to 20 months.