Laura A. Baker

Genetic Variation in Political Participation

The decision to vote has puzzled scholars for decades. Theoretical models predict little or no variation in participation in large population elections and empirical models have typically accounted for only a relatively small portion of individual-level variance in turnout behavior. However, these models have not considered the hypothesis that part of the variation in voting behavior can be attributed to genetic effects. Matching public voter turnout records in Los Angeles to a twin registry, we study the heritability of political behavior in monozygotic and dizygotic twins. The results show that a significant proportion of the variation in voting turnout can be accounted for by genes. We also replicate these results with data from the National Longitudinal Study of Adolescent Health and show that they extend to a broad class of acts of political participation. These are the first findings to suggest that humans exhibit genetic variation in their tendency to participate in political activities.

Genetics of Educational Attainment in Australian Twins: Sex Differences and Secular Changes

The relative effects of genetic and environmental factors in producing individual differences in educational achievement are compared across women and men and over birth cohorts. In a large sample of Australian twin pairs, the heritability of self-reported educational attainment did not vary among women and men born before and after 1950. In a “psychometric” model of twin resemblance, based on separate self-reports in 1981 and 1989, genetic factors explained 57% of the stable variance in educational achievement, while environmental factors shared by twins accounted for 24% of the variance. Corrections for phenotypic assortative mating for educational level, however, suggested that estimated common-environmental effects could be entirely explained by the correlation between additive genetic values for mates. Taking this into account, heritability of “true” educational attainment in Australia may be as high as 82% with the remaining variation being due to individual environments or experiences. Unlike previous studies in Scandinavian countries, results in Australia suggest that factors influencing educational success are comparable between women and men and for individuals born at different points during this century.

Genetic and environmental influences on positive and negative affect: support for a two-factor theory.

Genetic and environmental etiologies of positive and negative affect, as measured by the Bradburn Affect Balance Scale, were studied to gain understanding of a two-factor theory of well-being. It was hypothesized that negative affect would demonstrate significant genetic and environmental variance and positive affect would be explained primarily by environmental influences. Data were combined from 105 pairs of twins (ages 18-72) and 220 multigenerational families (ages 16-98). Simultaneous model fitting indicated significant heritable effects for negative affect and a significant effect of common environment for twins. Significant effects for positive affect included common environment (for parents and offspring and for twin pairs) and assortative mating. These results, documenting differential genetic and environmental influences on positive and negative affect, provide further support for their being separate components of well-being.

Sex differences in property crime in a Danish adoption cohort

Sex differences in genetic and environmental influences on criminal behavior against property were studied in a birth cohort of 6129 male and 7065 female Danish adoptees and their biological and adoptive parents. Both genetic and environmental factors were found to contribute to variation in liability to property criminality, the relative proportions of variance explained being similar in males and females. Important shared- and nonshared-family environmental factors were present. In separate analyses of average liability toward property criminality, however, convicted females appeared to be more genetically predisposed than convicted males, a conclusion based on the finding that female property offenders were more likely than male offenders to have convicted biological (but adopted-away) offspring. On the other hand, property-offending males and females did not appear to differ in their average shared-family environmental liabilities, since conviction rates did not differ for adoptees of convicted adoptive mothers and fathers. Also, social class in the adopitive parents of convicted sons and daughters were comparable, further indicating that average shared-family environmental liabilities do not differ between the sexes.

The Southern California Twin Register at the University of Southern California: II

The Southern California Twin Register at the University of Southern California (USC) was initiated in 1984 and continues to provide an important resource for studies investigating genetic and environmental influences on human behavior. This article provides an update on the current register and its potential for future twin studies using recruitment through school district databases and voter records. An overview is also provided for an ongoing longitudinal twin study investigating the development of externalizing psychopathology from childhood to young adulthood, the USC Study of Risk Factors for Antisocial Behavior. Characteristics of the twins and their families are presented, including recruitment and participation rates, as well as attrition analyses and a summary of key findings to date.

Spouse similarity in attitudes, personality, and psychological well-being

The study of the origin of spouse similarity is interesting because the extent to which spouse similarity reflects genetic resemblance between husbands and wives affects the genetic structure of a population. The sources of observed spouse similarity in attitudes, personality, and psychological well-being are discussed. Analyses based on data collected from an American adult sample assessed longitudinally showed that spouse correlations were high for attitudes and low to moderate for personality and psychological well-being. Four competing explanations to spouse similarity were compared: initial similarity, attrition, convergence, and age covariation. The results did not support the latter three explanations, indicating that initial similarity may be an appropriate interpretation of observed spouse similarity. The findings are consistent with those of other comparable studies.

Genetic and environmental stability differs in reactive and proactive aggression

The aim of this study was to examine stability and change in genetic and environmental influences on reactive (impulsive and affective) and proactive (planned and instrumental) aggression from childhood to early adolescence. The sample was drawn from an ongoing longitudinal twin study of risk factors for antisocial behavior at the University of Southern California (USC). The twins were measured on two occasions: ages 9-10 years (N=1,241) and 11-14 years (N=874). Reactive and proactive aggressive behaviors were rated by parents. The stability in reactive aggression was due to genetic and nonshared environmental influences, whereas the continuity in proactive aggression was primarily genetically mediated. Change in both reactive and proactive aggression between the two occasions was mainly explained by nonshared environmental influences, although some evidence for new genetic variance at the second occasion was found for both forms of aggression. These results suggest that proactive and reactive aggression differ in their genetic and environmental stability, and provide further evidence for some distinction between reactive and proactive forms of aggression.

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.

Assessing Inattention and Impulsivity in Children during the Go/NoGo Task.

Behavioural performance in the Go/NoGo task was compared with caregiver and teacher reports of inattention and hyperactivity-impulsivity in 1,151 children (N = 557 boys; N = 594 girls) age 9- 10-years-old. Errors of commission (NoGo errors) were significantly correlated with symptom counts of hyperactivity-impulsivity, while errors of omission (Go errors) were significantly correlated with symptom counts for inattention in both caregiver and teacher reports. Cross-correlations were also evident, however, such that errors of commission were related to inattention symptoms, and errors of omission were related to hyperactivity-impulsivity. Moreover, hyperactivity-impulsivity and inattention symptoms were highly intercorrelated in both caregiver (r = .52) and teacher reports (r = .70), while errors of commission and omission were virtually uncorrelated in the Go/NoGo task (r = .06). The results highlight the difficulty in disentangling hyperactivity-impulsivity and inattention in questionnaires, and suggest that these constructs may be more clearly distinguished in laboratory measures such as the Go/NoGo task.

Relationships Among Life Events and Psychological Well-Being: More Evidence for a Two-Factor Theory of Well-Being

Relationships between 11 major life events and changes in psychological well-being were examined in a three-generation sample: grandparents, their adult children, and their young adult grandchildren. Psychological well-being was measured using the Bradburn Affect Balance Scale. Life events included marriages; divorces; births of children; deaths of spouses, children, and parents; health declines; hospitalizations; improved standard of living; retirement; and retirement of ones spouse. Both positive and negative affect demonstrated similar stability over 14 years and were equally predictable from the life events. However, consistent with a two-factor conceptualization of psychological well-being, for all generations, desirable life events predicted change in positive affect whereas undesirable events predicted change in negative affect; cross-domain prediction was minimal. Results further indicated that whether life events are expected may be more important in predicting subsequent psychological well-being than whether they are desirable or undesirable.