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AbstractMeasures of self-transcendence, physical health and psychological well-being were included in a self-report Health and Lifestyle questionnaire administered to Australian twins aged over 50 between 1993 and 1995. Self-transcendence appears to be higher among older Australian women than men, and was significantly associated with religious affiliation, marital status (in women) and age (in men). No strong correlations were observed between self-transcendence and any measure of psychological or physical health. Additive genetic effects were found to be important in influencing self-transcendence, with heritability estimates of 0.37 and 0.41 for men and women respectively, whilst shared environment effects were not found to be significant. Multivariate modelling of self-transcendence scores and self-reported church attendance behavior indicated substantially different etiologies for these variables, with implications for methods of investigation of religiosity and spirituality.

AbstractDepression scores (DSSI) were available for 1232 MZ and 751 DZ female twin pairs who completed a mailed questionnaire. Pairs were divided into those concordant for being in a marriage-like state, concordant for having no partners, and those discordant. The pattern of twin correlations differed according to marital status. Our results suggest that having a marriage-like relationship acts as a protective factor in reducing the impact of inherited liability to symptoms of depression in the general population.

AbstractConsiderable evidence from twin and adoption studies indicates that both genetic and shared environmental factors play a substantial role in the liability to antisocial behavior. Although twin and adoption designs can resolve genetic and environmental influences, they do not provide information about assortative mating, parent–offspring transmission, or the contribution of these factors to trait variation. We examined the role of genetic and environmental factors for conduct disorder (CD) using a twin–parent design. This design allows the simultaneous estimation of additive genetic, shared and individual-specific environmental effects, as well as sex differences in the expression of genes and environment in the presence of assortative mating and combined genetic and cultural transmission. A retrospective measure of CD was obtained from twins and their parents or guardians in the Virginia Twin Study of Adolescent Behavior Development and its Young Adult Follow up sample. Both genetic and environmental factors play a significant role in the liability to CD. Major influences on individual differences appeared to be additive genetic (38%–40%) and unique environmental (39%–42%) effects, with smaller contributions from the shared environment (18%–23%), assortative mating (~2%), cultural transmission (~2%) and resulting genotype-environment covariance. This study showed significant heritability, which is slightly increased by assortative mating, and significant effects of primarily nonparental shared environment on CD.

AbstractNon-linear epigenetic processes are a potential underlying source of phenotypic differences in development. Simulation studies of twin pairs using simple non-linear development models characterised by chaotic or near-chaotic behavior are presented. The effect of chaotic processes on correlations is to lower them from their initial values, but high initial correlations are affected much less by chaotic and near-chaotic processes than intermediate correlations. Therefore, we would predict that traits affected by chaotic processes would have high MZ and low DZ twin correlations and this is reminiscent of certain traits such as EEG spectra. However the much more frequent observation of MZ correlations close to twice their DZ counterparts would suggest that the role of chaos in development is quite limited.

AbstractThe effects on sleep pattern ('short-sleep' versus 'long-sleep') and subjective sleep disturbance of genotype, personality, symptoms of anxiety and depression, and lifestyle, were examined using survey data on a clinically unselected sample of adult Australian twin pairs, aged 17–88 years. When the effects of genotype, personality and symptoms were ignored, lifestyle variables appeared to account for roughly 4% of the variance in sleep disturbance, and 9% of the variance in sleep pattern. Significant genetic effects on sleep disturbance and sleep pattern were found, which were only partly explained by the effects of personality and symptoms of anxiety and depression. Much of the association between sleep disturbance and lifestyle appeared to be explained by separate effects of personality and symptoms of anxiety and depression on sleep and lifestyle ('genotype – risk-factor correlation'). There was little evidence for genetically determined differences in sensitivity to the lifestyle variables ('genotype × risk-factor interaction').

AbstractThe analysis of genetic and environmental contributions to preterm birth is not straightforward in family studies, as etiology could involve both maternal and fetal genes. Markov Chain Monte Carlo (MCMC) methods are presented as a flexible approach for defining user-specified covariance structures to handle multiple random effects and hierarchical dependencies inherent in children of twin (COT) studies of pregnancy outcomes. The proposed method is easily modified to allow for the study of gestational age as a continuous trait and as a binary outcome reflecting the presence or absence of preterm birth. Estimation of fetal and maternal genetic factors and the effect of the environment are demonstrated using MCMC methods implemented in WinBUGS and maximum likelihood methods in a Virginia COT sample comprising 7,061 births. In summary, although the contribution of maternal and fetal genetic factors was supported using both outcomes, additional births and/or extended relationships are required to precisely estimate both genetic effects simultaneously. We anticipate the flexibility of MCMC methods to handle increasingly complex models to be of particular relevance for the study of birth outcomes.

Fear is a pervasive aspect of political life and is often explored as a transient emotional state manipulated by events or exploited by elites for political purposes. The psychological and psychiatric literatures, however, have also established fear as a genetically informed trait, and people differ in their underlying fear dispositions. Here we propose these differences hold important implications for political preferences, particularly toward out‐groups. Using a large sample of related individuals, we find that individuals with a higher degree of social fear have more negative out‐group opinions, which, in this study, manifest as anti‐immigration and prosegregation attitudes. We decompose the covariation between social fear and attitudes and find the principal pathway by which the two are related is through a shared genetic foundation. Our findings present a novel mechanism explicating how fear manifests as out‐group attitudes and accounts for some portion of the genetic influences on political attitudes.

Utilizing quantitative genetic models, the authors examine the sources of party identification and the intensity of that identification. The results indicate genes exert little, if any, influence on party identification, directly or indirectly through covariates. However, we find that genes appear to play a pivotal role in shaping the strength of an individual's party identification. Together with recent examinations of political attitudes and vote choice, these findings begin to provide a more complete picture of the source of partisanship and the complex nature of the political phenotype. Adapted from the source document.

Utilizing quantitative genetic models, the authors examine the sources of party identification and the intensity of that identification. The results indicate genes exert little, if any, influence on party identification, directly or indirectly through covariates. However, we find that genes appear to play a pivotal role in shaping the strength of an individual's party identification. Together with recent examinations of political attitudes and vote choice, these findings begin to provide a more complete picture of the source of partisanship and the complex nature of the political phenotype.