42. Cherny, S. S., Fulker, D. W., Corley, R. P., Plomin, R., & DeFries, J. C. (1994). Continuity and change in infant shyness from 14 to 20 months. Behavior Genetics, 24, 365-379.

Objective measures of shyness were obtained from 163 MZ and 138 same-sex DZ twins pairs in two testing situations: the laboratory and the home. Results indicated that developmental change from 14 to 20 months and situational specificity between the laboratory and the home are mediated largely by environmental influences. Genetic variation is largely responsible for both the stability in shyness from 14 to 20 months and the phenotypic correlations between the two settings.