The objective of this study was to examine the genetic and environmental contributions to shyness throughout the school-age period. Participants were 553 twin pairs from the ongoing prospective longitudinal Quebec Newborn Twin Study. Teacher-rated measures of shyness were collected at five time-points from age 6-12 years. On average, shyness was moderately stable over time (r = 0.23-0.33) and this stability was almost entirely accounted for by genetic factors. Genetic factors at age 6 accounted for 44% of individual differences and these early genetic factors also explained individual differences at all subsequent ages (6-22%). Non-shared environmental factors explained most of individual differences at single time-points (51-63%), and did not account for stability in shyness. Contributions of shared environment were not significant. Our results suggest that the stability in shyness is mostly accounted for by early and persistent genetic contributions.
Keywords: Development; Longitudinal study; School-age; Shyness; Twins.