Quantitative genetic models of continuous psychological constructs, such as psychopathology and cognitive ability, overwhelmingly support a generalist genes model, where genetic factors account for covariance among phenotypes, and environmental factors account for specificity. Non-human animal models of personality suggest broad targets of biological influence, which may map more closely to the two-factor model of personality (e.g. approach versus avoidance) compared to the five-factor phenotypic model most commonly used in human research. This study will develop personality phenotypes on the basis of genetic and environmental overlap, rather than the other way around.