To explain the role of intrinsic maturation, proponents of the FFT often make an analogy between personality and height, a phenotype that obviously depends on environmental inputs (e.g., nutrition), but follows a developmental course largely determined by intrinsic mechanisms when sufficient environmental resources are available (e.g., genetic influences; McCrae & Costa, 2006). During childhood and adolescence, there are individual differences in terms of growth spurts that re-order the relative ranking of individuals. Therefore, in adolescence one would expect relatively low differential stability of height. In early adulthood, it is much less common for individuals to be re-ordered in terms of their height. McCrae and Costa (2006) argue that personality traits can be understood in a similar way. Ultimately, Costa and McCrae (2008) claim “the course of personality development is determined by biological maturation, not by life experiences” (p. 167). Thus, the FFT would predict high stability of genetic effects that would most likely peak near age 30. The phenotypic stability of traits would be predicted to be largely mediated by genetic factors, and the increase in phenotypic stability should be
