In this study we test the strongest competing predictions of selective neutrality, mutation-selection balance, and balancing selection: (a) the extent to which all common genetic variants contribute to variation in personality; and (b) whether or not inbreeding affects personality traits. To do this, we use genotypic and phenotypic data from four community-based samples from Australia and Finland (total N>8,000) who were assessed on Cloninger's Harm Avoidance, Novelty Seeking, Reward Dependence, and Persistence dimensions. To test (a) above, we use recently-developed methodology (Visscher et al. 2010; Yang et al. 2010; Yang et al. 2011b) to estimate the proportion of variation in these personality traits that can be accounted for by ~270,000 SNPs taken together. This method captures the vast majority of the combined effect of common variants, but much less of the combined effect of rare (MAF<0.01) variants (Yang et al. 2010), since the rarer a variant is the less it can possibly be correlated with a common SNP in a sample of unrelated people (Wray 2005; Wray et al. 2011)1. To test (b), we examine the association between personality traits
