Our findings have important implications for how personality is positioned in an evolutionary framework. Results consistent with most of the genetic variation being due to rare variants and/or nonadditive genetic effects suggest that personality traits have been under selection, and results consistent with inbreeding depression suggest that three of the personality traits have been under directional selection. Directional selection does not necessarily mean that extremely high or low values are favoured, just that the mean trait level in the population deviates from the optimum. Several possibilities exist for why the means of personality traits are not at the evolutionarily optimal levels. One is that personality traits are condition-dependent; for example, Lukaszewski and Roney (2011) have argued that high extraversion (closely related to Novelty Seeking) is usually displayed by physically attractive individuals (through facultative calibration) because it is a more beneficial strategy for them than for less extraverted individuals. Under this model, the heritable variation in extraversion is a side effect of the heritable variation in physical attractiveness (which is presumably condition-dependent and under mutation-selection balance). Similarly, low (optimal) levels of
