McCrae and Costa have proposed a theoretical model, the fi ve-factor model, that emphasizes the biological basis of traits, which are construed in the model as basic tendencies

McCrae and Costa have proposed a theoretical model, the fi ve-factor model, that emphasizes the biological basis of traits, which are construed in the model as basic tendencies. Substantial evidence of stability of overall trait structures and of individual differences in trait levels is consistent with this theoretical model. However, the model is questioned by evidence of change in personality trait levels and by uncertainty concerning the limits of environmental infl uence on personality development. In addition, there is evidence that at least one more trait factor is required to capture all major individual differences.