EAS temperaments during the last half of the life span: twins reared apart and twins reared together

In this first behavioral genetic study of personality in the last half of the life span, results are reported using the powerful adoption/twin design that compares identical and fraternal twins reared apart and identical and fraternal twins reared together. Traits studied were the EAS temperaments (emotionality, activity level, and sociability), traits that show substantial genetic influence in childhood. It was hypothesized that the EAS traits would also show significant genetic influence later in life and that most of the environmental variation would be nonshared--that is, twins reared together would show no greater resemblance for the EAS traits than twins reared apart. Both hypotheses are supported.     

Learning Abilities and Disabilities: Generalist Genes, Specialist Environments

ABSTRACT— Twin studies comparing identical and fraternal twins consistently show substantial genetic influence on individual differences in learning abilities such as reading and mathematics, as well as in other cognitive abilities such as spatial ability and memory. Multivariate genetic research has shown that the same set of genes is largely responsible for genetic influence on these diverse cognitive areas. We call these "generalist genes." What differentiates these abilities is largely the environment, especially nonshared environments that make children growing up in the same family different from one another. These multivariate genetic findings of generalist genes and specialist environments have far-reaching implications for diagnosis and treatment of learning disabilities and for understanding the brain mechanisms that mediate these effects.     

Genetic and Environmental Effects on Openness to Experience, Agreeableness, and Conscientiousness: An Adoption/Twin Study

ABSTRACT Previous research has indicated that extraversion and neuroticism are substantially affected both by genotype and environment. This study assesses genetic and environmental influences on the other three components of the five-factor model of personality: Openness to Experience, Agreeableness, and Conscientiousness. An abbreviated version of the NEO Personality Inventory (NEO-PI) was administered to 82 pairs of identical twins and 171 pairs of fraternal twins reared apart and 132 pairs of identical twins and 167 pairs of fraternal twins reared together. Estimates of genetic and environmental effects for Openness and Conscientiousness were similar to those found in other studies of personality: Genetic influence was substantial and there was little evidence of shared rearing environment. Results for Agreeableness were different: Genetic influence accounted for only 12% of the variance and shared rearing environment accounted for 21% of the variance. Few significant gender or age differences for genetic and environmental parameters were found in model-fitting analyses.     

Genetic mediation of the relationship between social support and psychological well-being.

This study assessed genetic and environmental influences on the association between social support and psychological functioning using the combined adoption/twin design from the Swedish Adoption/Twin Study of Aging. A subsample of 424 twin pairs, 50 years and older, was used: 64 pairs of identical twins reared apart, 95 pairs of identical twins reared together, 132 pairs of fraternal twins reared apart, and 133 pairs of fraternal twins reared together. Multivariate model-fitting analyses indicated that the relationship between the perceived adequacy of social support and psychological well-being (depression and life satisfaction) was mediated in part by genetic factors.     

The effects of shared environment on adult intelligence: A critical review of adoption, twin, and MZA studies

There has been a vigorous debate for decades concerning the heritability of intelligence. In recent years, the debate has been focused on whether the components of IQ variability change with age and on separating environmental effects into shared and unshared components. Citing evidence from adoption studies, studies comparing identical and fraternal twins, and studies of identical twins raised apart, some prominent psychologists have concluded that the shared environment has a significant effect on the intelligence of children but little or no effect on the intelligence of adults. In this article, the evidence from such studies is reviewed. The article reaches the conclusion that while there is some evidence from adoption studies supporting the claim that shared environment has little or no effect on adult intelligence, that evidence is inconclusive and is inconsistent with evidence from twin studies and from studies of identical twins reared apart. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Genetic influence on life events during the last half of the life span

Genetic influence on perceptions of major events later in life was assessed with a combination of twin and adoption designs as part of the Swedish Adoption/Twin Study of Aging (SATSA). The SATSA design includes 4 groups totaling 399 pairs of same-sex twins: identical and fraternal twins reared apart and matched twins reared together. The average age of the twins was 59 years. The results demonstrate significant genetic influence on reports of the occurrence of life events, especially for controllable events in which the individual can play an active role. Maximum likelihood model-fitting estimates of genetic influence indicate that 40% of the variance of the total life events score is due to genetic differences among individuals. How genetic factors can affect life experiences and directions for future research are discussed.     

Twins' reactions to delayed auditory feedback

10 pairs of identical and 10 pairs of fraternal twins, matched by age, spoke under conditions of 0.0-, 100-, 200-, 300-, 400-, and 500-msec. delayed auditory feedback. Length of spoken passages was controlled. Product-moment and intraclass correlations were calculated for speaking times and disfluencies. Significant Pearson rs for times were noted at 0.0 and 300 msec. for both groups and at 100, 200, and 400 msec. for identical twins, while fraternal twins' times were significantly correlated at 500 msec. Difference scores were significantly correlated at 100, 200, 300, and 400 msec. for identical twins. Disfluencies were significantly correlated for identical twins at 400 msec. Data were combined with those of Timmons' (1969) study, increasing subjects to 21 pairs per group. Intraclass correlations supported the contention that responses of identical twin pairs to delayed auditory feedback were more highly correlated than those for fraternal twin pairs.     

Nature,nurture and academic achievement: A twin study of teacher assessments of 7‐year‐olds

Background: Twin research has consistently shown substantial genetic influence on individual differences in cognitive ability; however, much less is known about the genetic and environmental aetiologies of school achievement. Aims: Our goal is to test the hypotheses that teacher‐assessed achievement in the early school years shows substantial genetic influence but only modest shared environmental influence when children are assessed by the same teachers and by different teachers. Sample: 1,189 monozygotic (MZ) and dizygotic (DZ) twin pairs born in 1994in England and Wales. Methods: Teachers evaluated academic achievement for 7‐year‐olds in Mathematics and English. Results were based on the twin method, which compares the similarity between identical and fraternal twins. Results: Suggested substantial genetic influence in that identical twins were almost twice as similar as fraternal twins when compared on teacher assessments for Mathematics, English and a total score. Conclusions: The results confirm prior research suggesting that teacher assessments of academic achievement are substantially influenced by genetics. This finding holds even when twins are assessed independently by different teachers.     

Importance of shared genes and shared environments for symptoms of depression in older adults.

The Center for Epidemiologic Studies-Depression scale was administered to 68 identical and 161 fraternal twin pairs reared apart and 114 identical and 138 fraternal pairs reared together to ascertain relative genetic and environmental contributions to individual differences in self-reported depressive symptoms. Intraclass correlations and model fitting indicated that genetic influences explained 16% of the variance in total depression scores and 19% for the Psychomotor Retardation and Somatic Complaints subscale, but heritability was minimal for the Depressed Mood and Well-Being subscales. Influence of family rearing context played a substantial role in explaining twin similarity, whereas unique life experiences accounted for the greatest proportion of variance. Significant age group differences were observed, with heritability greater in twins of 60 years of age or older than in twins under 60, especially for Psychomotor Retardation.     

Beyond genetic explanations for leadership: The moderating role of the social environment

Leadership role occupancy has recently been shown to have a genetic basis. We extend prior research by examining the moderating effects of the social environment during adolescence on the genetic influences on leadership role occupancy at work. Utilizing a sample of male twins (89 pairs of identical and 54 pairs of fraternal twins, with a mean age of 36.5 years), we found that genetic influences are weaker for those reared in enriched environments (i.e., higher family socioeconomic status, higher perceived parental support, and lower perceived conflict with parents). For those twins who had relatively poorer social environments, genetic influences on leadership role occupancy are significantly greater. These results have important implications for early interventions on leadership development inside and outside organizations.     

Do environmental similarities explain the similarity in intelligence of identical twins reared apart?

Taylor (1980) claims to show that the similarity in IQ between monozygotic twins reared apart (MZA's) in the three classic studies by Newman, Freeman, and Holzinger (1937), Shields (1962), and Juel-Nielsen (1965) is due to similarity in their environments. A reanalysis, using Taylor's classification of the twins into similar and dissimilar environments on the basis of four different criteria, but using the alternate IQ measure used in two of the studies, shows that his findings do not constructively replicate. Taylor's conclusion that “it seems reasonable to suggest that the IQ correlations characterizing pairs of individuals with absolutely identical genes and absolutely uncorrelated environments would be extremely low” cannot be substantiated from the evidence at hand.     

A Rorschach Study of Personality Development In Identical and Fraternal Twins

To determine whether identical twins show greater resemblances in their general personality make-up than fraternals, seven pairs of identical and eight pairs of fraternal twins were studied using the Rorschach Inkblot test. The results of the inter-twin correlations, on the various Rorschach categories indicated clearly striking similarity or resemblance in identical twins, but no similarity in the case of fraternal twins. This study also clearly demonstrated the usefulness of the Rorschach technique for the study of personality.     

Separated twins and the genetics of personality differences: a critique

This article discusses studies of separated twins, with special emphasis on the Minnesota Study of Twins Reared Apart (MISTRA), to determine whether they support the existence of an important genetic component in behavioral and personality differences. The methods and conclusions of the MISTRA team are discussed in the context of earlier studies of separated identical twins. I argue that volunteer-based studies are biased toward greater twin similarity. In addition, the MISTRA research team did not publish or share raw data and case history information. Reared-together and reared-apart monozygotic twins share important environmental similarities not controlled for by comparing personality correlations. I propose an alternative control group consisting of biologically unrelated pairs of strangers matched on all environmental factors common to pairs of separated monozygotic twins. I conclude that the evidence from studies of twins reared apart does not support the role of genetic factors in personality and behavioral differences.     

Understanding the genetic and environmental specificity and overlap between well‐being and internalizing symptoms in adolescence

Moderate inverse correlations are typically found between well‐being and mental illness. We aimed to investigate the role of genes and environments in explaining the relationships between two aspects of well‐being and two measures of internalizing symptoms. Altogether, 4700 pairs of 16‐year‐old twins contributed data on subjective happiness and life satisfaction, as well as symptoms of depression and emotional problems. Well‐being was moderately correlated with internalizing symptoms (range = ?0.45, ?0.58). Multivariate twin model‐fitting indicated both genetic and environmental overlap. Life satisfaction and happiness demonstrated different patterns of overlap, with stronger genetic links between life satisfaction and depression. Non‐shared environmental influences were largely specific to each trait. This study supports the theory of mental health and illness being partly (but not entirely) correlated dimensions. There are also significant genetic and environmental factors to identify for well‐being that go beyond the absence of mental illness. It is therefore possible that different interventions are needed for treating mental illness and promoting mental health.     

A TWIN STUDY OF SPATIAL ABILITY

A battery of spatial visualization land form percepthn plus some tests of arithmetic, vocabulary and social perception has been administered to 274 pairs of identical and 198 pairs of frabmal twins. To assess the importance of hereditary components in the individual differences observed, the within pair variance for fraternal paim was compared with the within pair vazianw for identical pains by the F ratio test. The results for 123 pairs of identiml twins and 91 pairs of fraternal twins on the spatial task, were classified in terms of the apparent psychological task requirements of the test. It appears that tests requiring three-dimensional manipdadion of drawings demonstrate more frequently a statistically significant hereditary component.     

Does More Money Make You Happier? Why so much Debate?

Easterlin’s famous paradox questioned standard economic assumptions about a fundamental relationship in economics: that between happiness and income. In recent years there has been renewed debate about the paradox. In this essay, I highlight some of the methodological issues and challenges underlying that debate. I focus on the sensitivity of the results to the method selected, the choice of micro or macro data, and the way that happiness questions are defined and framed, all of which result in divergent conclusions. I also note the mediating role of the pace and nature of economic growth, institutional frameworks, and inequality. What is most notable is the remarkable consistency in the determinants of individual happiness – including income – within countries of diverse income levels and, at the same time, how happiness is affected by cross-country differences that are related to average per-capita income levels, such as political freedom and public goods. Income clearly plays a role in determining both individual and country level happiness. Still, assessing its role relative to other more difficult to measure factors as countries develop in new ways and at different rates will remain a challenge for the foreseeable future.     

The extended genotype: the heritability of personality accounts for the heritability of recalled family environments in twins reared apart

Abstract How are retrospective accounts of family rearing environments linked to adult personality? We addressed this question by measuring both domains in a sample of 180 reared‐apart twins. Twins completed extensive measures of rearing environments (the Minnesota‐Briggs History Record, the Block Environmental Questionnaire, the Family Environment Scale, and the Physical Facilities Questionnaire) and an omnibus measure of adult personality (the Multidimensional Personality Questionnaire). Retrospective accounts of family environments were partially heritable and all the heritable variance in environmental measures could be accounted for by heritable variance in personality. In addition, differences between twins in their accounts of their rearing environments (nonshared environmental factors) were not significantly linked to differences between twins in their personalities. Hence, family environmental measures appear to be heritable because personality genes influence the way people shape and recall their rearing environments. In addition, differences in reared‐apart twins' retrospectively recalled rearing environments appear to have little impact on differences in their personalities in adulthood.     

Level and Inequality of Happiness in Nations: Does Greater Happiness of a Greater Number Imply Greater Inequality in Happiness?

Utilitarians and egalitarians have different priorities. Utilitarians prioritize the greatest level of happiness in society and are prepared to accept inequality, while egalitarians prioritize the smallest differences and are willing to accept a loss of happiness for this purpose. In theory these moral tenets conflict, but do they really clash in practice? This question is answered in two steps. First I consider the relation between level and inequality of happiness in nations; level of happiness is measured using average responses to a survey question on life satisfaction and inequality is measured with the standard deviation. There appears to be a strong negative correlation; in nations where average happiness is high, the standard deviation tends to be low. This indicates harmony instead of tension. Secondly I consider the institutional factors that are likely to affect happiness. It appears that level and equality of happiness depend largely on the same institutional context, which is another indication for harmony. We may conclude that the discussion between utilitarians and egalitarians is of little practical importance. This conclusion implies that increasing income inequality can go together with decreasing inequality in happiness and this conclusion provides moral support for Governments developing modern market economics     

Relationships between parenting and adolescent adjustment over time: genetic and environmental contributions.

The predictive association between parenting and adolescent adjustment has been assumed to be environmental; however, genetic and environmental contributions have not been examined. This article represents one effort to examine these associations in which a genetically informative design was used. Participants were 395 families with adolescent siblings who participated in the Nonshared Environment in Adolescent Development (D. Reiss et al., 1994) project at 2 times of assessment, 3 years apart. There were 5 sibling types in 2 types of families: 63 identical twins, 75 fraternal twins, and 58 full siblings in nondivorced families and 95 full, 60 half, and 44 genetically unrelated siblings in stepfamilies. Results indicate that the cross-lagged associations between parental conflict-negativity and adolescent antisocial behavior and depressive symptoms can be explained primarily by genetic factors. These findings emphasize the need to recognize and examine the impact that adolescents have on parenting and the contribution of genetic factors to developmental change.     

Separation—Individuation,Self-Concept,and Object Relations in Fraternal Twins,Identical Twins,and Singletons

Identical twins, fraternal twins, and singletons (n = 30 in each group) were compared on objective measures of separation–individuation, object relations, and self-esteem. No significant differences were found. The data did not support the popular notion that twins face special problems with respect to personality development or the idea that twins have more difficulty than others in establishing and maintaining close relationships. Twins and nontwins did not differ significantly with respect to marital status, number of years married, whether married before, number of previous marriages, number of years divorced, or living arrangements if single. The majority of twins had been raised in a way that encouraged at least some individual differences.