IQ correlations in transracial adoptive families

IQ tests were administered to all available members over 4 years old in 101 transracial adoptive families when the adopted children were an average of 7 years old and again when they averaged 17 years old. At both times, 426 members of 93 families were studied; 398 were seen in person and administered the WAIS-R or WISC-R. IQ correlations were calculated for adopted and biological parent-child pairs, and for genetically related and unrelated siblings. Educational levels of birth parents were correlated with the IQ scores of their adopted-away children. Results show that biologically related family members tended to resemble each other intellectually more than did adoptive family members at both time points. IQ correlations for biological parent-child pairs exceeded those for adoptive parent-child pairs, and correlations were greater for genetically related than unrelated siblings. In late adolescence, the IQ scores of unrelated siblings in the transracial adoptive families were more similar than those of unrelated adolescent siblings pairs reported in other studies. The pattern of IQ correlations for unrelated siblings suggested that familial environmental influences on IQ decline from childhood to late adolescence, but this conclusion was not supported by parent-child IQ correlations. The effects of selective placement on familial IQ correlations were small. Estimates of genetic and familial environmental influences on IQ were very similar to those of other studies. This suggests that the influences on intellectual development in this sample of black/interracial adoptees reared in white families are similar to those for children in the majority populations of the United States and Western Europe.     

Intellectual similarity of virtual twin pairs: Developmental trends

Virtual twins (VTs) are same-age unrelated siblings reared together from infancy who replicate twinship, but without the genetic relatedness. A 2005 report from the ongoing Fullerton Virtual Twin Study found an IQ intraclass correlation of .26 (p < .01, n = 113 pairs) and a within-pair difference of 13.22 IQ points. The average age of VTs in that study was 8.10 years (SD = 8.56, range: 4.01-54.84 years). An opportunity to retest members of 43 VT pairs, 1.70-8.96 years after their time 1 assessment, allowed additional analyses of genetic and environmental influences underlying general intellectual development. A decrease in the VT IQ correlation and an increase in the within-pair difference were indicated, consistent with increasing genetic and/or non-shared environmental influences and decreasing shared environmental influence on general intellectual development throughout childhood.     

Adolescents' relationships to siblings and mothers: a multivariate genetic analysis.

Research has consistently demonstrated that children's behavior toward their siblings tends to resemble interactions occurring in the parent-child relationship. This study examined the relative contributions of genetic and environmental influences to the covariation between sibling relationships and mother-adolescent relationships. Reported and observed family interactions were assessed for 719 same-sex sibling pairs of varying degrees of genetic relatedness. The covariance between mother-adolescent and sibling interactions was decomposed into genetic, shared, and nonshared environmental components. The overlapping effects of shared environment on the two relationship subsystems explained most of the covariance. Smaller but significant genetic and nonshared environmental effects were also found. The consistency of these findings with family processes, such as modeling, is discussed.     

Differential experiences of siblings in the same family as predictors of adolescent sibling personality differences

In the area of personality development, environmental influences operate to make siblings in the same family different rather than similar to each other. The goal of the present study was to determine whether differential experience of siblings can be used to explain the marked personality differences of siblings. The Sibling Inventory of Differential Experience (SIDE) along with personality information (the EAS Temperament Inventory and questions about career expectations) was administered to 50 biological sibling pairs and 98 adoptive sibling pairs in adolescence and young adulthood. The results indicated that differential sibling interaction and differential peer characteristics as self-reported on the SIDE explain 6%-26% of the variance in sibling personality difference scores. For example, the sibling who reports more sociability as compared to his sibling also experiences more sibling closeness and more peer popularity as compared to his sibling. Comparison between adoptive and biological siblings indicates that the SIDE relations are mediated environmentally rather than genetically.     

School Context and Genetic Influences on Aggression in Adolescence

Genetic and environmental contributions to variation in aggression were examined using adolescents' self-reports of aggressive behavior. The National Longitudinal Study of Adolescent Health provided a sample of 1,515 pairs of adolescents in five genetically informative groups (i.e., monozygotic twins, dizygotic twins, full siblings, half siblings, and unrelated siblings reared together). The analysis, a DeFries-Fulker regression within a hierarchical linear model, yielded findings on individual-level heritability (h2), shared environmental effects (c2), school-level effects, and school-level moderation of h2 and c2. The estimate of h2 for aggression in the full sample was .32, and c2 was .05. In the moderating effect, h2 increased and c2 decreased with greater school-level family warmth. Two effects on school means were found: Those schools with greater ethnic-racial heterogeneity had higher mean levels of aggression, and schools where students perceived greater family warmth had lower mean levels of aggression.     

Genetic and Environmental Contributions to Common Psychopathologies of Childhood and Adolescence: A Study of Twins and Their Siblings

We report findings based on analyses of self-reports of six common adolescent psychopathologies (attention deficit/hyperactivity disorder, ADHD; conduct disorder, CD; oppositional defiant disorder, ODD; generalized anxiety disorder, GAD; separation anxiety disorder, SAD; and major depressive disorder, MDD) in a sample of 1,162 male and female adolescent (12–19 years) twin pairs and 426 siblings. Prevalence statistics for past year and lifetime reports confirm differences between genders for CD, GAD, SAD, and MDD, and a lack of differences between twins and their non-twin siblings. Biometrical modeling was conducted to ascertain the relative influences of genes, and shared and non-shared environments contributing to these disorders. A more robust estimate of these parameters was obtained by including non-twin siblings. Age-specific thresholds were integrated into the analyses to appropriately model the developmental patterns of behavior. We found evidence for both genetic and non-shared environmental influences for all disorders. Shared environmental influences also seem to be important for MDD and lifetime GAD.     

Differential parent-child relationships and adolescent externalizing symptoms: cross-lagged analyses within a monozygotic twin differences design

Research has indicated that differential parental treatment is linked to differences in externalizing symptomology (EXT) across siblings, even those siblings who are genetically identical. However, the direction of causation and longitudinal significance of this relationship remains unclear. Thus, in the present study, the authors examined 486 monozygotic twin pairs, assessed at ages 11, 14, and 17 years, within a cross-lagged twin differences design. Results revealed that differential parent-child conflict at age 11 years uniquely contributed to differential sibling EXT 3 years later but only in the most discordant twin pairs. In the full, unselected sample, this relationship was not significant. These results suggest that markedly different parent-child conflict has an environmentally mediated impact on child behavior through mid-adolescence, findings that yield insights into environmental influences on behavior.     

Adolescent sibling differences in suicidal symptoms: The role of parent-child relationships

This study examined concordance for symptoms of suicide among 178 pairs of adolescent siblings, and the association of youth and maternal reports of parenting with variation in suicide ideation both across families and between siblings. Crosstabulation analyses indicated a significant risk of suicide ideation among siblings of adolescents who had made suicide attempts, as well as a significant degree of concordance for suicide ideation among pairs of siblings. Regression analyses indicated that reported levels of maternal warmth and harsh discipline, especially youth reports, were associated with suicide ideation, and that sibling differences on these parenting indices were associated with differences in suicide ideation both across families as well as between siblings. However, sibling differences in reported parenting did not contribute to prediction of suicide ideation above the variance accounted for by the simple levels of parenting reported by adolescents.     

Speech‐evoked auditory brainstem responses reflect familial and cognitive influences

Cortical function and related cognitive, language, and communication skills are genetically influenced. The auditory brainstem response to speech is linked to language skill, reading ability, cognitive skills, and speech‐in‐noise perception; however, the impact of shared genetic and environmental factors on the response has not been investigated. We assessed auditory brainstem responses to speech presented in quiet and background noise from (1) 23 pairs of same sex, same learning diagnosis siblings (Siblings), (2) 23 unrelated children matched on age, sex, IQ, and reading ability to one of the siblings (Reading‐Matched), and (3) 22 pairs of unrelated children matched on age and sex but not on reading ability to the same sibling (Age/Sex‐Matched). By quantifying response similarity as the intersubject response‐to‐response correlation for sibling pairs, reading‐matched pairs, and age‐ and sex‐matched pairs, we found that siblings had more similar responses than age‐ and sex‐matched pairs and reading‐matched pairs. Similarity of responses between siblings was as high as the similarity of responses collected from an individual over the course of the recording session. Responses from unrelated children matched on reading were more similar than responses from unrelated children matched only on age and sex, supporting previous data linking variations in auditory brainstem activity with variations in reading ability. These results suggest that auditory brainstem function can be influenced by siblingship and auditory‐based communication skills such as reading, motivating the use of speech‐evoked auditory brainstem responses for assessing risk of reading and communication impairments in family members.     

Cultural variation in the social organization of problem solving among African American and European American siblings

This study examined the social organization of a problem-solving task among 15 African American and 15 European American sibling pairs. The 30 sibling pairs between the ages of 6 and 12 were video recorded constructing a marble track together during a home visit. African American siblings were observed to collaborate more often than European American siblings who were more likely to divide up the labor and direct each other in constructing the marble track. In addition, older European American siblings made more proposals of step plans than older African American siblings. The findings provide insights into the cultural basis of the social organization of problem solving across African American and European American siblings.     

Differences in Nonshared Individual,School, and Family Variables Between Delinquent and Nondelinquent Hmong Adolescents

The purpose of the current study was to determine whether there were differences between Hmong immigrant siblings on multiple nonshared individual, school, and family variables. Participants were 58 sibling pairs (29 delinquent pairs and 29 nondelinquent pairs), who ranged in age from 13 to 21 years. There were 11 pairs of boys, 3 pairs of girls, and 15 pairs of opposite-sex siblings. Results of a multivariate analysis of variance indicated that delinquent and nondelinquent sibling groups were significantly different in participation in organized activities, antisocial attitudes, delinquent behaviors, school truancy, school performance, and parents' labeling. The findings have implications for future research on sibling delinquency in Hmong immigrant families and for program development and delivery.     

Differences in nonshared individual, school, and family variables between delinquent and nondelinquent Hmong adolescents

The purpose of the current study was to determine whether there were differences between Hmong immigrant siblings on multiple nonshared individual, school, and family variables. Participants were 58 sibling pairs (29 delinquent pairs and 29 nondelinquent pairs), who ranged in age from 13 to 21 years. There were 11 pairs of boys, 3 pairs of girls, and 15 pairs of opposite-sex siblings. Results of a multivariate analysis of variance indicated that delinquent and nondelinquent sibling groups were significantly different in participation in organized activities, antisocial attitudes, delinquent behaviors, school truancy, school performance, and parents' labeling. The findings have implications for future research on sibling delinquency in Hmong immigrant families and for program development and delivery.     

Longitudinal associations between parents' hostility and siblings' externalizing behavior in the context of marital discord.

This study examined longitudinal associations between parents' hostility and siblings' externalizing behavior in the context of interparental discord. The sample included 116 families (mothers, fathers, 2 siblings) assessed in middle childhood, when siblings were, on average, 8 and 10 years old, and in adolescence, at average ages of 14 and 16 years. Parents reported on their hostility toward each child and on each child's externalizing problems. Raters observed interparental hostility, and parents rated their marital quality. Results indicated both within-family and between-families effects. Specifically, the child who received more parental hostility than his or her sibling showed greater increases in externalizing problems than his or her sibling; this association was moderated by marital discord. In addition, the child who exhibited more behavioral problems than his or her sibling received greater increases in hostile mothering than did his or her sibling. Between-families effects were evident, in that children's externalizing problems were associated with increases in mothers' hostility toward both children in the family. Results support transactional models of development and family systems theory.     

Beauty is in the 'we' of the beholder: greater agreement on facial attractiveness among close relations

Scientific research on facial attractiveness has focused primarily on elucidating universal factors to which all raters respond consistently. However, recent work has shown that there is also substantial disagreement between raters, highlighting the importance of determining how attractiveness preferences vary among different individuals. We conducted a typical attractiveness ratings study, but took the unusual step of recruiting pairs of subjects who were spouses, siblings, or close friends. The agreement between pairs of affiliated friends, siblings, and spouses was significantly greater than between pairs of strangers drawn from the same race and culture, providing evidence that facial-attractiveness preferences are socially organized.     

Sibling deidentification in the clinic: devil vs. angel

A four-member family structure consisting of two siblings contrasting in personality (sibling deidentification) and each identified with a different parent (split-parent identification) was recently reported (15). In well-functioning families, this tetrad or quadrangle is wide-spread in the first pair of siblings in the family and tends to be more common in same-sex pairs, suggesting that sibling deidentification is designed to mitigate the relatively intense sibling rivalry characteristic of these pairs and hence to maintain family harmony. In this collated case report, deidentification is found to follow the same pattern in 39 clinic first pairs. However, contrasting attributes are varied and nonevaluative in nonclinic pairs but mainly "good-bad" in clinic pairs, with polarization extreme. Results suggest that nonclinic siblings negotiate their identity (being) much as they negotiate about possessions (having) and that negotiations are blocked in clinic pairs, freezing mythic devil or angel identity. Intervention is directed at dislodging this block.     

Interpersonal responses among sibling dyads tested for BRCA1/BRCA2 gene mutations.

OBJECTIVE: The familial context plays an important role in psychosocial responses to genetic testing. The purpose of this study was to compare sibling pairs with different combinations of BRCA1/BRCA2 test results on measures of affect, interpersonal responses, and physiological reactions. DESIGN: Forty-nine sibling dyads with different combinations of BRCA1/BRCA2 test results (i.e., mixed, positive, negative) completed a questionnaire, and 35 of the dyads also participated in a laboratory-based discussion of genetic testing. MAIN OUTCOME MEASURES: The primary outcome variables included participant reports of supportive actions toward their sibling, state anger and anxiety, perceptions of sibling behavior, and electrodermal responses. RESULTS: Compared to positive and negative dyads, mixed pairs reported less friendly general support actions, noted more anger, and perceived their sibling to be less friendly and more dominant during the interactions. In comparisons between same-result (i.e., positive, negative) pairs, positive dyads reported more dominant support behaviors and perceived their sibling to be friendlier during the interactions. CONCLUSION: Data suggest that siblings who have different test results may experience more interpersonal strain than siblings who have the same test result. Future research on genetic testing and family relationships can expand upon these findings.     

Genotype-environment interaction in personality development: identical twins reared apart

The focus of this study is to identify specific genotype-environment (GE) interactions as they contribute to individual differences in personality in later life. In behavioral genetics, GE interaction refers to the possibility that individuals of different genotypes may respond differently to specific environments. A sample of 99 pairs of identical twins reared apart, whose average age is 59 years, has been studied as part of the Swedish Adoption/Twin Study of Aging (SATSA). Hierarchical multiple regression was used to detect interactions between personality and environmental measures after the main effects of genotype and environment were removed. Analyses yield evidence for 11 significant interactions that provide the first evidence for GE interaction in human development using specific environmental measures. Thus, in addition to the main-effect contributions of heredity and environment, GE interactions contribute to individual differences in personality as measured in the second half of the life course.     

Exploring gene-environment interactions: socioregional moderation of alcohol use.

Examples of gene-environment interaction in human behavioral data are relatively rare; those that exist have used simple, dichotomous measures of the environment. The authors describe a model that allows for the specification of more continuous, more realistic variations in environments as moderators of genetic and environmental influences on behavior. Using data from a population-based Finnish twin study, the authors document strong moderating effects of socioregional environments on genetic and environmental influences on adolescent alcohol use, with nearly a five-fold difference in the magnitude of genetic effects between environmental extremes. The incorporation of specific environmental measures into genetically informative designs should prove to be a powerful method for better understanding the nature of gene-environment interaction and its contribution to the etiology of behavioral variation.     

Do the Predictors of Child Conduct Problems Vary by High- and Low-Levels of Socioeconomic and Neighborhood Risk?

This review seeks to examine whether the existing literature on child conduct problems (CP) supports the notion that certain CP risk factors vary in their importance across disadvantaged and better-off environments. Disadvantaged environments are represented by socioeconomic and/or neighborhood risk (SN risk) in this review. Three types of studies were reviewed: behavioral genetic studies that compare the importance of genetic and environmental influences on CP for youth from poor homes and/or disadvantaged communities versus youth from better-off contexts, studies that examine how SN risk and other CP risk factors interact, and studies that compare the antecedents for CP across levels of SN risk. Findings were inconsistent about the manner in which individual child risk factors interact with SN risk. However, familial risk factors were generally found to be of greater importance for youth from poor families and disadvantaged communities, particularly parental supervision. Most of the studies that indicated otherwise focused on physical discipline, or were limited to children from disadvantaged and extremely deprived environments. The findings suggest that in extremely deprived environments, familial influences are overwhelmed by the pervasiveness of other CP risk factors such as deviant peers. Implications for intervention and suggestions for future research are discussed.     

What Virtual Twins Reveal About General Intelligence and Other Behaviors

The Fullerton Virtual Twin Study has been assessing the behaviors of an unusual sibship since 1982. Virtual twins (VTs) are same-age, unrelated siblings reared together since infancy. They replicate the rearing situation of twins but without the genetic link, enabling direct assessment of shared environmental effects on behavior. An updated analysis of IQ data, based on an increased sample of 142 VT pairs (7.87 years, SD=8.22), is presented. Intraclass correlations of .28 (IQ) and .11 (subtest profile) indicated modest shared environmental influences on intelligence. Findings from the Twins, Adoptees, Peers and Siblings (TAPS) project that studies virtual twins and other kinships are described.