The Genetic and Environmental Architecture of Psychoticism, Extraversion and Neuroticism

Abstract

It is the purpose of the present chapter to discuss the causes of individual differences in Eysenck’s major personality dimensions, psychoticism, extraversion and neuroticism, using the concepts and analytical methods of biometrical genetics. From the point of view of the biological theory underlying these dimensions (Eysenck 1967), resolution into genetic and environmental components is of some importance. The presence of a strong genetic component, implying stable, constitutionally based individual differences combined with a relatively weak effect of the environment, particularly the social environment, would lend strong support to the theory. For this reason alone the investigation of the effects of nature and nurture on these personality dimensions is justified. However, the choice of biometrical genetics as the method of analysis, a relatively recent development in this area (Jinks and Fulker 1970), has the additional advantage of allowing a more searching investigation of these causes than alternative approaches based on the simple nature-nurture dichotomy. Using the biometrical approach, genetic and environmental effects can be further subdivided into more informative components and additional insight gained into how these components interact. As a result, biometrical analysis not only provides broad evidence concerning the validity of the underlying psychological theory but also allows us to place the theory within the wider framework of evolutionary biology by providing more detailed information concerning the genetic and environmental architecture of the traits.