Analysis of genetic influences on the consistency and variability of the Big Five across different stressful situations

The Oslo University Adolescent and Young Adult Twin Project: Recruitment and Attrition

The Oslo University Adolescent and Young Adult Twin Project started in 2006 with the first of three questionnaire data collection waves, 2 years apart. All twins from the birth cohorts 1988-1994 were invited to participate, and both the twins and their parents were asked to sign consent forms. The twins were 12-18 years old at Wave 1, at which time parents were asked to complete similar questionnaires. The parents' questionnaire enquired about the parents' ratings of their twin's traits. In addition, the parents answered questions regarding their own education, demographics and socioeconomic situation. When the twins were 18 years old, they were invited to a face-to-face interview and two new questionnaires were presented. The questionnaires for the waves included a number of personality scales, internalization and externalization traits, affective and behavioral problems, as well as measures of environment and coping. The most common DSM-IV mental disorders and all personality disorders were covered in the interview. Zygosity was established both by questionnaire and gene markers. The original sample consisted of 5374 twin families, and among these, 4668 pairs were alive and living in Norway. Of these, 2486 families (53.3%) consented to participate. Of these, again 1538 twin families (61.9%) actually participated in at least one wave and twins from 1422 pairs (57.3%) participated in the interview. Female gender, but not zygosity, predicted staying in the project. Moreover, having a planning, structured personality (being more conscientious, open to experience [i.e., curious and interested in learning], having higher resilience and better school habits) increased the chance of carrying on in the project. Interestingly, the attrition did not seem to bias the heritability estimates.

A Trio of Concerns

This essay assesses the two most significant changes in psychology over the past century: the attempt to localize psychological phenomena in restricted brain sites and the search for genetic contributions to behavior and psychopathology. Although there are advantages to these new developments, they are accompanied by some questionable assumptions. Because the investigators in these domains often relate variation in their biological measures to variation in personality traits evaluated with questionnaires, an analysis of the unique properties of the verbalreport questionnaires is presented. It is suggested that future research on human personality should try to combine semantic reports with behaviors and biological data in order to arrive at more fruitful constructs.

Genetic and environmental influences on impulsivity: a meta-analysis of twin, family and adoption studies

A meta-analysis of twin, family and adoption studies was conducted to estimate the magnitude of genetic and environmental influences on impulsivity. The best fitting model for 41 key studies (58 independent samples from 14 month old infants to adults; N=27,147) included equal proportions of variance due to genetic (0.50) and non-shared environmental (0.50) influences, with genetic effects being both additive (0.38) and non-additive (0.12). Shared environmental effects were unimportant in explaining individual differences in impulsivity. Age, sex, and study design (twin vs. adoption) were all significant moderators of the magnitude of genetic and environmental influences on impulsivity. The relative contribution of genetic effects (broad sense heritability) and unique environmental effects were also found to be important throughout development from childhood to adulthood. Total genetic effects were found to be important for all ages, but appeared to be strongest in children. Analyses also demonstrated that genetic effects appeared to be stronger in males than in females. Method of assessment (laboratory tasks vs. questionnaires), however, was not a significant moderator of the genetic and environmental influences on impulsivity. These results provide a structured synthesis of existing behavior genetic studies on impulsivity by providing a clearer understanding of the relative genetic and environmental contributions in impulsive traits through various stages of development.

Genetic and Environmental Influences on Person × Situation Profiles

Genetic and environmental influences on Person x Situation interactions were studied using data of the German Observational Study of Adult Twins. The performance of 168 monozygotic and 132 dizygotic twin pairs in 15 tasks was observed by 120 judges who never met the twins in person. Four judges observed one twin of each pair in one task. Twin similarities in Person x Situation profiles were analyzed via (a) correlations across tasks between co-twins' Person x Situation profiles (their personality signatures) and (b) common-pathway genetic models that partitioned genetic and environmental contributions to trait levels and to Person x Situation interactions. Genes accounted for about 25% of the reliable Person x Situation interactions, whereas shared environmental influences were negligible.

Behavioral genetics of personality

Behavioral genetic personality research has moved from findings of genetic and environmental effects to new areas. Personality disorders have been included, children and adolescents studied, gender effects evaluated, and the importance of rater sources investigated. Recently, multivariate methods have been applied to disentangle the genetic and environmental latent structure, and investigate covariance in mental disorders. Perhaps the most exciting recent developments are the investigations of situation variables, the studies of how genotypes influence how individuals select themselves into situations and other form of gene-environment correlations, and how genotype moderates the effect of situations and circumstances on behavior (gene-environment interaction). In the future, we will learn how personality, partly determined by heredity, influences our entire lives. We will better understand what we experience, how we interpret the experiences and how to react to them effectively. We will learn how our mental lives develop while we interact with the environment, and we will broaden our understanding of which genes are coding for mental health and mental disorders.

Traits and Biology: A Response to Joseph and Howley

This rejoinder questions lines of criticism used by A. Howley and J. Joseph in their respective reviews of Eigenberger and Sealander's proposal in 2001 that anti-intellectualism be under consideration as a facet-level component, conceptually fitting into the so-called ‘Big Five’ personality dimensions and encompassed by the term ‘intellectual openness’.