Heterosis versus Inbreeding Depression Effects: An Investigation of Personality, Digit Ratio (2D:4D), and Laterality Traits

The opposed genetic effects of heterosis and inbreeding depression consist of beneficial augmentations (vs. detrimental reductions) of phenotypic trait values in offspring of genetically distant (vs. related) parents. This is due to increased offspring heterozygosity for heterosis vs. increased homozygosity for inbreeding depression, with the consequence of escape from (vs. falling prey to) the cumulative effects of deleterious recessive alleles. Heterosis/inbreeding depression is well documented for human health outcomes and psychometric intelligence, but has only sporadically been investigated for heritable personality traits. This study of 129 adults from a geographically isolated region in westernmost Austria examined heterosis/inbreeding depression in differentially heritable individual difference variables: personality dimensions (Big Five, sensation seeking), digit ratio (2D:4D), and laterality traits. Consistent with heterosis/inbreeding depression effects, 2D:4D (strongly genetically influenced) of both hands was expressed more sex-typically with farther birthplace distance of relatives (approximating genetic distance) among women (but not men), whereas no effects emerged for directional asymmetry in 2D:4D (almost nonheritable) or laterality traits (only weakly heritable). However, not replicating recent suggestive findings, effects were also largely absent for the (strongly heritable) Big Five and sensation seeking personality dimensions. Future directions for exploring heterosis and inbreeding depression in the personality and individual differences domain are discussed.