A recent development affecting personality theory and research comes from behaviour genetics. Overwhelming success in the behaviour genetic analysis of personality traits has urged personality psychologists to redefine their object as well as to reconsider the most expedient ways to study it. Particularly the assessment and explanation of individual

differences may benefit from the new frame of reference offered by behaviour genetics. Recent studies suggest considerable genetic contributions in several personality traits including altruism, empathy, nurturance, aggression and assertiveness (Rushton et al., 1986), the Big Five personality dimensions (Bouchard, 1993), interest patterns (Nichols, 1978; Lykken et al., 1993; Waller et al., 1995), vocational interests (Moloney et al., 1991; Betsworth et al., 1994), religious interests (Waller et al., 1990), work values (Keller et al., 1992), and special mental abilities (Nichols, 1978; Bouchard et al., 1990). From a behaviour genetics point of view, traits are to be seen as phenotypes, i.e. manifestations of genotypic propensities. Underlying traits are physiological, biochemical and neurological processes, ultimately genes at the most distal level. Classical biological approaches to personality have proposed a rather direct relationship between biological structures and processes on the one hand and traits like neuroticism, extraversion (Eysenck, 1967), or impulsivity and anxiety (Gray, 1991) on the other. Those approaches have been among the foremost exponents of the hypothesis that personality traits provide a window on individual differences in brain functioning. However, recent comments have concluded that the assumptions of the biological approach to personality are in need of reassessment. In particular it has been suggested that trait research should place more emphasis on the social-cognitive bases of personality (Matthews and Gilliland, 1999). A more systematic ordering of the diverse conditions underlying personality has been proposed in Zuckerman’s (1993) seven turtles model. According to this model personality traits are based on social behaviour that, in turn, is the fruit of learning. Physiological conditions underlie learning but are based on biochemical processes that rest on neurological conditions themselves. Finally, the major foundations of neurology are genes, controlling the production of proteins, which in turn exert profound effects on behavioural structures and processes via the nervous system and production of behaviourally relevant hormones and neurotransmitters. Thus, summarizing, traits, social behaviour, learning, physiology, biochemistry, neurology and genes are the stations along which genotypes are translated into phenotypes. To explore the ways in which the different levels exert their influence is a major task for current personality psychology.