Nancy L. Segal

Personality similarity in twins reared apart and together.

We administered the Multidimensional Personality Questionnaire (MPQ) to 217 monozygotic and 114 dizygotic reared-together adult twin pairs and 44 monozygotic and 27 dizygotic reared-apart adult twin pairs. A four-parameter biometric model (incorporating genetic, additive versus nonadditive, shared family-environment, and unshared environment components) and five reduced models were fitted through maximum-likelihood techniques to data obtained with the 11 primary MPQ scales and its 3 higher order scales. Solely environmental models did not fit any of the scales. Although the other reduced models, including the simple additive model, did fit many of the scales, only the full model provided a satisfactory fit for all scales. Heritabilities estimated by the full model ranged from .39 to .58. Consistent with previous reports, but contrary to widely held beliefs, the overall contribution of a common family-environment component was small and negligible for all but 2 of the 14 personality measures. Evidence of significant nonadditive genetic effects, possibly emergenic (epistatic) in nature, was obtained for 3 of the measures.

Job Satisfaction: Environmental and Genetic Components

Monozygotic twins reared apart from an early age were used to test the hypothesis that there is a significant genetic component to job satisfaction. Thirty-four monozygotic twin pairs who had been reared apart completed the Minnesota Job Satisfaction Questionnaire as part of a comprehensive work-history assessment. Three subscales were formed from the job satisfaction items to reflect intrinsic, extrinsic, and general satisfaction with the current (or major) job. Intraclass correlations were computed to estimate the proportion of observed variability resulting from genetic factors for all job satisfaction items and for the three subscales. Resulting values indicated that approximately 30% of the observed variance in general job satisfaction was due to genetic factors. Additional analysis indicated that these results obtained even when job characteristics such as complexity, motor skill requirements, and the physical demands were held constant via partialing methods. Finally, the data indicated significant heritabilities for several of these job characteristics, which is consistent with the hypothesis of a genetic disposition to seek and remain in similar environments (jobs). Implications of these findings for theories of job satisfaction, selection, and job enrichment are discussed.

Heritability of substance abuse and antisocial behavior: A study of monozygotic twins reared apart ☆

Thirty-two sets of monozygotic twins reared apart since shortly after birth (31 pairs and one set of triplets; median age at separation was 0.2 years) were interviewed separately and blindly using the Diagnostic Interview Schedule for presence of DSM-III Axis I psychiatric disorders and antisocial personality. Because the sample was recruited from a nonclinical population, predictably few subjects met criteria for such disorders. However, items counting toward diagnoses were cumulated into four scores: alcohol-related problems, drug-related problems, childhood antisocial behavior, and adult antisocial behavior. The scores showed within-scale cohesion as measured by Cronbachs coefficient alpha. The drug scale and both antisocial scales showed significant heritability (p less than 0.1), but the alcohol scale had an estimated heritability of zero (albeit with a broad confidence interval). There appeared to be substantial commonalities in the genetic factors responsible for these traits.

Work values: Genetic and environmental influences.

The Minnesota Importance Questionnaire (MIQ), measuring work values, was administered to 23 monozygotic and 20 dizygotic reared-apart twin pairs to test the hypothesis that genetic factors are associated with work values. Both univariate and multivariate analyses were performed. In the univariate analysis, intraclass correlations were computed to estimate the proportion of variability in work values associated with genetic factors for each of the 20 MIQ scales and for the 6 higher order work value scales. The multivariate analysis used maximum likelihood estimation to separate the genetic and environmental factors for the correlated higher order scales. Results from both analyses indicated that, on average, 40% of the variance in measured work values was related to genetic factors.

Twins and virtual twins: bases of relative body weight revisited

OBJECTIVE: Application of a new investigative strategy to assess genetic and environmental influences on relative body weight.DESIGN: Covariance structure analysis of body mass index (BMI) using genetically informative samples.SUBJECTS: One-hundred and fourteen monozygotic (MZ) twin pairs (age 5.04–22.93 y), 81 dizygotic (DZ) twin pairs (age 6.05–16.52 y), and 98 virtual twin (VT) pairs, ie same-age unrelated siblings (3.68–54.75 y).MEASUREMENTS: Height, weight, BMI variously obtained by direct measurement and self-report.RESULTS: In contrast with most previous studies, significant common environmental influence on BMI was observed.CONCLUSION: Much past research may have underestimated common environmental effects on BMI because the designs lacked the power or ability to detect them.

Heritable and environmental variables affect reproduction-related behaviors, but not ultimate reproductive success

Abstract The present study is an attempt to integrate a behavior—genetic approach and methodology with the goals of sociobiology, using a life history analysis. The study seeks to determine (a) whether differences in reproduction-related behaviors show evidence of heritability; and (b) what factors contribute to observed variance in reproduction-related activities. In accordance with sociobiological theory, the reproduction-related behaviors of males were found to be more variably influenced by both heritable and environmental factors than those of females. The results also suggest, however, that while some reproduction-related behaviors are associated in a proximate sense with heritable personality and health-related factors, this association does not ultimately translate into predictable differences in total number of children.

Suicidal behavior in twins : a replication

OBJECTIVE Our two previous reports showed that monozygotic (MZ) twins were significantly more concordant for both completed suicide and attempted suicide than dizygotic (DZ) twins. We wished to replicate the finding that MZ co-twins showed greater concordance for suicidal behavior. METHOD We collected a new series of 28 twin pairs in which one twin had committed suicide. RESULTS We found that 4 of the 13 MZ twin pairs were concordant for suicidal behavior compared with 0 of the 15 DZ twin pairs (P=0.035). CONCLUSIONS These data confirm our previous reports that MZ co-twins show greater concordance for suicidal behavior than DZ co-twins, consistent with genetic influence.

Uniting psychology and biology : integrative perspectives on human development

The Scholarship of Daniel G. Freedman Pursuing the Big Picture My Three Mentors Is Nonduality Possible in the Social and Biological Sciences? Small Essays on Holism and Related Issues Are Genetically-Based Individual Differences Compatible with Species-Wide Adaptations? Genetic Bases of Behaviour Contributions to Psychological Research A Developmental and a Genetic Perspective on Aggression Genetic Analysis of Social Behaviour Twin Research Perspective on Human Development Biological Approaches to Developmental Issues - Rethinking the Data Ethological and General Systems Perspectives on Child-Parent Attachment During the Toddler and Preschool Years Sexual Orientation as a Developmental Context for Lesbians, Gays, and Bisexuals - Biological Perspectives What Can the Genotype Tell Us About Complex Human Conditions? Naturalistic Studies of Behaviour - How Does a Cross-Cultural Approach Inform Ongoing Research? Why Do Hadza Children Forage? Expression or Communication About Emotion Mother-Infant Interaction in Cross-Cultural Perspective Marriage in a Cross-Cultural Perspective Evolutionary Analyses - New Issues and Continuing Controversies Genetic Basis of Intrapsychic Conflict Is Human Happiness Universal? An Evolutionary Perspective Discrete Emotions Theory with Specific Reference to Pride and Shame Film Retrospective - The Method and the Medium Film Commentaries Behaviour Genetics, Human Ethology, Evolutionary Psychology and Culture - Looking to the Future Pair-Bonding Deconstructed by Twin Studies of Marital Status - What is Normative? An Ethological Perspective on Normal Behaviour, Especially as it Relates to Mating Systems Evolving Beyond Evolutionary Psychology - A Look at Family Violence Final Overview - Uniting Psychology and Biology.

Genetic factors in the electrocardiogram and heart rate of twins reared apart and together

Important physiologic mechanisms have been thought not to exhibit large amounts of variability, due in part to the assumption that critical biologic functions will have evolved to an evolutionary optimum. The attainment of this optimum would necessarily eliminate individual differences in these variables. Using a sample of monozygotic and dizygotic twins reared apart since birth or early infancy, 12-lead electrocardiographic recordings and vectorcardiograms were obtained. Values of these variables for monozygotic and dizygotic twins reared together were obtained from other studies. Maximum likelihood tests of genetic and environmental components of variation for PR interval, QRS duration, QT interval and ventricular rate indicated a significant contribution of genetic effects (most heritabilities ranged from 30 to 60%), with a negligible contribution from common familial environmental effects.

Twin, sibling, and adoption methods. Tests of evolutionary hypotheses.

: Twin, sibling, and adoption studies have long been used by behavioral geneticists to identify genetic and environmental influences underlying human behavioral and physical variation. The full potential of these methodologies for unraveling the blend of biological, cultural, and experiential factors affecting human development has been insufficiently appreciated. The application of twin, sibling, and adoption designs for examining hypotheses generated by evolutionary theory is described. Potential contributions from a closer association between these disciplines are underlined.