ABSTRACT
Most commentators on human nature have noted that the variation in the reaction to unfamiliarity and possible risk is a major characteristic that differentiates adults. Even though it is rare to find a large number of people who are consistently shy, cautious, and timid, or, on the other hand, outgoing, relaxed, and bold in all contexts, there is a small group, perhaps 10%, who consistently bring one or the other of these behavioral styles to untried situations that have the potential to create uncertainty. Jung’s category of introversion–extraversion represents the most complete elaboration of this idea, and empirical indices of these and related constructs are among the most stable and the most heritable in contemporary psychological research (Conley, 1985; Loehlin, 1982; Plomin, 1986). The actualization of these two qualities in childhood has been described by Thomas and Chess (1977), who generated great interest among psychologists in the study of temperament.
