Researchers have implicated both nurture and nature in these individual differences. Some aspects of shyness are learned. Children's cultural background and family environment offer models of social behavior. Chinese children in day care have been found to be more socially reticent than Caucasians, and Swedish children report more social discomfort than Americans. There is growing evidence of a hereditary or temperamental basis for some variations of dispositional shyness.
Adoption studies can predict shyness in adopted children from the biological mother's sociability.
Extremely inhibited children show physiological differences from uninhibited children, including higher and more stable heart rates. Patterns of social passivity or inhibition are remarkably consistent in longitudinal studies of personality development. Despite this evidence, most researchers emphasize that genetic influences probably account for only a small proportion of self-labeled shyness. Even hereditary predispositions can be modified. Shyness can be a normal, adaptive response to potentially overwhelming social experience.