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Temperaments are often regarded as biologically based psychological tendencies with intrinsic paths of development. It is argued that this definition applies to the personality traits of the five-factor model. Evidence for the endogenous nature of traits is summarized from studies of behavior genetics, parent–child relations, personality structure, animal personality, and the longitudinal stability of individual differences. New evidence for intrinsic maturation is offered from analyses of NEO Five-Factor Inventory scores for men and women age 14 and over in German, British, Spanish, Czech, and Turkish samples (N = 5,085). These data support strong conceptual links to child temperament despite modest empirical associations. The intrinsic maturation of personality is complemented by the culturally conditioned development of characteristic adaptations that express personality; interventions in human development are best addressed to these.

There are both empirical and conceptual links between child temperaments and adult personality traits. The empirical associations are modest, but the conceptual relations are profound. Explaining how this is so requires a complicated chain of arguments and evidence. For example, we report cross-sectional data showing (among other things) that adolescents are lower in Conscientiousness than are middle-aged and older adults in Germany, the United Kingdom, Spain, the Czech Republic, and Turkey. The relevance of such data may not be immediately obvious, but in fact they speak to the transcontextual nature of personality traits and thus to the fundamental issue of nature versus nurture.

The gist of our argument is easily stated: Personality traits, like temperaments, are endogenous dispositions that follow intrinsic paths of development essentially independent of environmental influences. That idea is simple, but it is so foreign to the thinking of most psychologists that it requires a...