A twin study of temperament in young children.

Temperament was assessed in 182 young children (91 pairs of twins, average age of 3.6 years) with use of the Colorado Childhood Temperament Inventory (CCTI). The CCTI represents a merger of dimensions suggested by two approaches to the study of the development of temperament: the New York Longitudinal Study and Buss and Plomin's temperament theory. Of the six traits measured by the CCTI, genetic factors were implicated in the etiology of five (sociability, emotionality, activity, attention span-persistence, and soothability). One trait, reaction to food, showed no genetic influence and indicated strong between-family environmental effects. A negative correlation between emotionality and soothability may also have a genetic basis. These results suggest that the development of certain personality traits--those that we include as temperament--are substantially influenced by heredity.