stage for personality development. They hold that lifespan trends, however, are primarily a function of exogenous forces, most notably the social environment. Importantly, even in the primary proponents’ most polemic work, both sides have acknowledged that genes are a substantial influence on stability (e.g., Roberts, Wood, & Caspi, 2005, p. 384) and that the environment is a likely influence on at least the expression of personality (McCrae et al., 2000, p. 175). Differences emerge in the interpretation of results as being primarily explained by intrinsic maturation processes or by social mechanisms (see e.g., Costa & McCrae, 2006; Roberts, Walton, & Viechtbauer, 2006). Below we provide a brief overview of these theories and how they account for the empirical trend of increasing trait stability.
