Genetic analyses of focal aspects of infant temperament

The authors explored the genetic and environmental underpinnings of individ ual differences in temperament with a sample of 604 3- to 16-month-old infa nt twins and their parents. Mothers completed Rothbart's Infant Behavior Qu estionnaire (IBQ) and a subsample of 140 9-month-old twins participated in behavioral assessment of temperament in the laboratory as well. For IBQ Smi ling and Laughter and Duration of Orienting, both additive genetic and shar ed environmental effects were needed to best represent the data. Shared env ironmental effects fully accounted for cotwin similarity for IBQ Soothabili ty, and conversely, additive genetic effects fully accounted for cotwin sim ilarity for the IBC! Distress to Limitations, Distress to Novelty, and Acti vity Level scales. With the subsample, the authors fit a multivariate model to mother report, father report, and lab measures of stranger distress and found that genetic influences were most important for the covariation amon g these measures.