Abstract
The imitative performance of 311 pairs of 24-month old twins (143 MZ, 168 same-sex DZ) was assessed via three multi-step imitative sequences. Composite imitation score correlations suggested the presence of genetic influences on imitation, with MZ correlations significantly exceeding DZ correlations. Univariate model-fitting procedures supported this finding. Substantial broad heritability was found for imitative performance, with no evidence for shared environment. However, we are unable to say with certainty to what extent this heritability is represented by additive and nonadditive genetic variance. Estimates of heritability derived from both ACE and ADE model-fitting procedures accounted for approximately 50% of the total variance, with the remaining variance in imitative performance attributable to nonshared environmental factors.