Genetic and environmental influences on imitation in toddlers
Despite evidence for considerable variability, few studies have sought to explore the factors underlying individual differences in children's imitative behavior. The primary aim of the present research was to ascertain the relative contributions of genetic and environmental factors to observed variability in elicited imitation. Additional aims were to examine phenotypic relations of elicited imitation with mental development, temperament, and spontaneous imitation and, where strong relations exist, to investigate to what degree these associations reflect overlapping genetic and environmental influences. The elicited imitation of 311 24-month old twin pairs (143 MZ, 168 DZ) was assessed using three separate experimenter-modeled multi-step paradigms adapted from the cognitive developmental literature. Mental development was assessed via the Bayley Scales of Infant Development-II (MDI). Both parents and observers provided ratings of temperament. In addition, a per-minute score of spontaneous imitation behaviors was derived from 20-minute videotaped segments of a laboratory testing situation.
Univariate model-fitting procedures revealed that variability in children's elicited imitation at age two can be attributed to both broad heritability and nonshared environmental influences (approximately 48% and 52% of the variance, respectively). Similar results were found for spontaneous imitation, with genetic factors accounting for 43% of the variance. Moderate phenotypic associations were found between elicited imitation and MDI, as well as between elicited imitation and the temperament dimensions of Affect/Extraversion and Task Orientation. Applying multivariate behavior genetic models to the data revealed although there was some moderate genetic and environmental overlap between elicited imitation, MDI, and temperament, 62% of the total genetic variance on elicited imitation was found to be unique from genetic influences on cognition or temperament. Exploratory analyses of the relation between elicited and spontaneous imitation evinced a surprisingly low phenotypic association (.14). This correlation was due entirely to overlapping genetic influences, with no significant environmental covariance.
This research represents the first study to examine the relative contributions of genetic and environmental influences to laboratory-assessed imitation. The present findings thus contribute novel and important information to the existing literature with regard to the overall etiology of children's imitative behavior, with considerable implications for both cognitive and social development.