Although it is well established that personality traits are heritable (Loehlin 1992; Bouchard 1994; Jang et al 1996), most theories of personality do not attempt to identify the specific genes involved. Cloninger and colleagues (1993), however, proposed a psychobiological model of personality that purports to map personality at the genetic level. They proposed that temperament and character traits can be described in terms of specific psychological factors, and that these traits are associated with genetically determined neurochemical substrates. An obvious implication of this model is that genes associated with neurotransmitters are related to the hypothesized temperament traits. Another implication is that traits hypothesized to have a shared genetic basis should covary at the phenotypic level.
