Broadly, there are three main possibilities for explaining the maintenance of genetic variation in personality. The first, selective neutrality, is that genetic variants underlying personality traits do not affect individuals' fitness and so are free to randomly drift in frequency without being affected by selection. Under selective neutrality, individual genetic variants will be lost due to drift, but in the meantime new mutations will also arise and maintain genetic variation in the population (i.e. a mutation-drift balance). An argument against selective neutrality in humans is that personality traits are associated with traits that are presumably related to fitness such as mental and physical health (Lahey 2009; Kotov et al. 2010), mortality (Shipley et al. 2007; Mosing et al. 2012), attractiveness (Lukaszewski and Roney 2011), mating behaviour (Zietsch et al. 2010), and number of offspring (Eaves et al. 1990; Jokela et al. 2009; Alvergne et al. 2010; Jokela et al. 2010). However, positive correlations with one fitness component can be counterbalanced by negative correlations with other fitness components (e.g. Nettle 2005; Alvergne et al. 2010), which could potentially result in a
