Multiple regression analysis of twin and sibling data

DeFries and Fulker (1985) employed a multiple regression analysis of twin data in which a cotwin's score is predicted from the proband's score, the coefficient of relationship (R = 1.0 for monozygotic twins and 0.5 for dizygotic twins), and their interaction to yield direct estimates of heritability (h²) and the proportion of variance due to common or shared environmental influences (c²). The purpose of the report is to extend this model to allow for the analysis of data from more than two familial relationships simultaneously. Data from identical twins, fraternal twins, and siblings pairs, in which one member of each pair was selected based on low reading performance, were analyzed. To analyze the data simultaneously, additional coefficients were added to the regression equation in order to differentiate shared environmental influences of twins and siblings. When the model was applied to the combined cognitive data, significant estimates for heritability were obtained in three of the six tests analyzed. The results also indicated a lack of justification for the separate twin and sibling environmental parameters, and a discussion of more parsimonious models is included.     

Investigating cognitive transfer within the framework of music practice: genetic pleiotropy rather than causality

The idea of far transfer effects in the cognitive sciences has received much attention in recent years. One domain where far transfer effects have frequently been reported is music education, with the prevailing idea that music practice entails an increase in cognitive ability (IQ). While cross‐sectional studies consistently find significant associations between music practice and IQ, randomized controlled trials, however, report mixed results. An alternative to the hypothesis of cognitive transfer effects is that some underlying factors, such as shared genes, influence practice behaviour and IQ causing associations on the phenotypic level. Here we explored the hypothesis of far transfer within the framework of music practice. A co‐twin control design combined with classical twin‐modelling based on a sample of more than 10,500 twins was used to explore causal associations between music practice and IQ as well as underlying genetic and environmental influences. As expected, phenotypic associations were moderate (r = 0.11 and r = 0.10 for males and females, respectively). However, the relationship disappeared when controlling for genetic and shared environmental influences using the co‐twin control method, indicating that a highly practiced twin did not have higher IQ than the untrained co‐twin. In line with that finding, the relationship between practice and IQ was mostly due to shared genetic influences. Findings strongly suggest that associations between music practice and IQ in the general population are non‐causal in nature. The implications of the present findings for research on plasticity, modularity, and transfer are discussed.     

Social closeness of MZ and DZ twin parents towards nieces and nephews

Twins' marriages to non‐twins yield genetically and socially informative kinships. Monozygotic (MZ) twins' genetic identity makes them ‘genetic parents’ of their nieces/nephews, and their nieces/nephews their ‘genetic children’. The present study is the first to apply twin‐family models to study social relatedness. Analyses of twin families (MZ: N = 248; DZ: N = 75) tested evolutionary‐based concepts concerning social closeness, perceived similarity and caretaking. Hypotheses based on Hamilton's inclusive fitness theory were supported: MZ twin aunts/uncles expressed greater social closeness towards their nieces/nephews than DZ twin aunts/uncles; and female twins from same‐sex pairs expressed greater closeness towards their nieces/nephews than male twins from same‐sex pairs. This study underlines benefits of associations between behavioural‐genetic and evolutionary psychological theories, methods and interpretations. Copyright © 2007 John Wiley & Sons, Ltd.     

J.P. Rushton’s contributions to the study of altruism

This essay describes Rushton’s work on altruism over the past 40 years. During his academic career, he changed his theoretical approach from social learning theory to trait theory to sociobiology. My essay includes five sections. The first gives an overview of Rushton’s work on altruism. The second reviews his early work based on social learning theory. His laboratory and naturalistic experiments led him to conclude that altruism could be increased by exposure to models exemplifying the behavior, and that, once engaged in, the behavior could be durable over months and generalizable across situations. The third section discusses his work on the genetic foundation of altruism with social biology including his twin studies of prosocial behaviors using different age groups of both western and Asian samples. He concluded that about 50% of the variance in prosocial behaviors is heritable. The fourth section will describe altruism as part of the general factor of personality, the apex of the personality hierarchy. The last section summarizes my review of Rushton’s work on altruism.     

In search of shared and nonshared environmental factors in security of attachment: a behavior-genetic study of the association between sensitivity and attachment security

The current article presents results from a twin study of genetic and environmental components of maternal sensitivity and infant attachment and their association. The sample consisted of 136 twin pairs from 2 sites: Leiden, the Netherlands, and London, UK. Maternal sensitivity was assessed in the home at 9-10 months, and infant attachment security was observed in the laboratory at 12 months. The study yielded little evidence that genetic factors are involved in variations between twins in maternal sensitivity ratings but did find that shared variance in maternal sensitivity was able to account for some of the similarity between twins in attachment security. Weak nonshared associations between sensitivity and attachment appeared to suppress the magnitude of the correlation between attachment and sensitivity in twin children. The results could indicate that the attachment security of one twin may depend on the relationship the parent has with the other twin. The results are brought to bear on the validity of attachment theory as a theory of primarily shared environmental effects in children's development and the continuing challenge posed to attachment theory by within-family differences in socioemotional processes.     

The nature of adult twin relationships: an attachment-theoretical perspective

Twin relationships have been hailed as one of the most unique and intimate kinds of relationships. Unfortunately, there is a paucity of empirical research that addresses the interpersonal nature of twin relationships. In this article, the authors argue that attachment theory may provide a useful framework for understanding the nature of twin relationships. The authors present data indicating that (a) twins are more likely than non-twin siblings to use their sibling as an attachment figure; (b) the developmental course of twin attachment differs from that of other attachments; and (c) certain factors, such as genetic relatedness, empathy, including the other in the self, and shared experiences, may impact the extent to which twins use one another as attachment figures.     

Nonshared environmental processes in social‐emotional development: an observational study of identical twin differences in the preschool period

Differences in mothers’ parenting behaviors toward their identical twin preschoolers were examined to identify nonshared environmental processes in social‐emotional development. The study included 62 pairs of 3½‐year‐old same‐sex identical twins. Indicators of each child’s social‐emotional development (temperament, prosocial behavior, behavior problems and noncompliance) and parenting environment (warmth and negativity, positive and negative control, responsiveness) were assessed using observers’, interviewers’, and parents’ ratings. Mothers treated their identical twins differently, and this differential treatment covaried in expected ways with identical twin differences in social‐emotional adjustment. The twin who received more supportive and less punitive forms of parenting was also higher in positive mood and prosocial behaviors and lower in negative mood and behavior problems when compared to her or his twin.     

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.     

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.     

A Problem in Schutz's Theory of the Historical Sciences with an Illustration from the Women's Liberation Movement

In the first part of this essay it is contended that Schutz's project is best called the philosophical theory of the cultural sciences; in the last parts it is shown that he offers satisfactory rudiments of a theory of the historical sciences except where the differentia specifica of those sciences is concerned. The central part is devoted to women's liberation as a case of contemporary history in relation to which Schutz's thought about the historical sciences needs correction.     

Type II twinning in devitrite,Na2Ca3Si6O16

Nanometre-scale twins found in the triclinic crystalline phase devitrite, Na₂Ca₃Si₆O₁₆, are shown to exhibit the relatively rare form of twinning, Type II twinning, in which the crystal structure of one of the parts is related to the crystal structure of the other by a rotation of 180° about η ₁?=?[1?0?0]. Although formally, the twin plane K ₁ is irrational, it is in essence (0?1?0).     

Growing up and growing apart: a developmental meta-analysis of twin studies

Developmental change in twin similarity was examined with age contrasts in a meta-analysis of twin studies from 1967 through 1985. Intraclass rs were coded from 103 papers that included data for monozygotic or dizygotic twins, or for both, on personality or intelligence variables. Analyses indicated that there was a general tendency for some intraclass rs to decrease with age. In other words, as twins grow up, they grow apart. There were also developmental differences associated with components of variance for heritability, the shared environment, and the nonshared environment. Mechanisms through which the nonshared environment may operate are discussed.     

Is there still a cognitive cost of being a twin in the UK?

ObjectiveTo investigate whether twins still perform below singletons in cognitive ability tests and in national educational attainment examinations in a recent UK cohort of 11-year-olds.DesignPopulation-based cohort study, using a validated method of twin extraction.SettingEnglish state schools.Participants178,599 pupils (mean age 11 years) attending English state schools in 2004, representing 93% of local educational authorities.Main outcome measuresVerbal, quantitative and nonverbal reasoning measured by the Cognitive Abilities Test — Third Edition (CAT3), and educational attainment in English, maths and science from Key Stage 2 national curriculum tests.ResultsTwin-singleton differences in cognitive ability were of negligible effect size. Mean performance of twins was 1% of a SD below singletons on general cognitive ability, 3% lower on verbal reasoning, and less than 1% of a SD lower on quantitative and nonverbal reasoning, with and without adjustment for sex. Almost identical proportions of twins and singletons attained the expected standards of educational performance in English (80.4% versus 80.5%, respectively), maths (77.4% versus 77.3%), and science (90.1% versus 88.8%). There were no differences in rates of twins and singletons achieving higher or lower performance levels.ConclusionThe cognitive cost of being a twin reported in previous cohorts of UK children no longer exists in a large, contemporary and population-representative sample.     

Maternal expressed emotion predicts children's antisocial behavior problems: using monozygotic-twin differences to identify environmental effects on behavioral development

If maternal expressed emotion is an environmental risk factor for children's antisocial behavior problems, it should account for behavioral differences between siblings growing up in the same family even after genetic influences on children's behavior problems are taken into account. This hypothesis was tested in the Environmental Risk Longitudinal Twin Study with a nationally representative 1994-1995 birth cohort of twins. The authors interviewed the mothers of 565 five-year-old monozygotic (MZ) twin pairs and established which twin in each family received more negative emotional expression and which twin received more warmth. Within MZ pairs, the twin receiving more maternal negativity and less warmth had more antisocial behavior problems. Qualitative interviews were used to generate hypotheses about why mothers treat their children differently. The results suggest that maternal emotional attitudes toward children may play a causal role in the development of antisocial behavior and illustrate how genetically informative research can inform tests of socialization hypotheses.     

HREM study of the chemical nature of twin planes in CuAlO2

Abstract

High-resolution electron microscopy has been used to study the atomic structure of twins in the binary oxide CuAlO₂. This compound is an occasional product of the bonding between pre-oxidized copper and alumina; its peculiarity is to exhibit a twinned microstructure, owing to the occurrence of two enantiomorphic right- and left-handed configurations. The microstructural examination at high resolution reveals that twin planes are located on copper basal planes rather than aluminium planes; this result is discussed on the basis of an analysis of the various possible stacking sequences which can reasonably be considered to occur at the twin interfaces.     

Tacit coordination in monozygotic twins, dizygotic twins and virtual twins: Effects and implications of genetic relatedness

Game theorists have long been interested in why some partners are more successful at achieving mutual goals than others. The present study was conducted to determine if tacit coordination (non-negotiated consensus) varies as a function of genetic relatedness between social partners. The sample included 7–13-year-old monozygotic (MZ) twin pairs (n = 53), dizygotic (DZ) twin pairs (n = 85) and virtual twin (VT) pairs (n = 42; same-age unrelated siblings). Co-twin agreement on questions completed under individual and coordination conditions was compared across the three groups. MZ twins showed significantly greater overall agreement than DZ twins and VTs, using multiple criteria. The implications of these findings are considered with reference to behavioral-genetic and evolutionary theories of behavior.     

From My Place: Teaching the Holocaust and Judaism at the University of Mississippi Fifty‐Three Years after James Meredith

This essay explores classroom dynamics when students identify and connect their own painful experiences to structural racism or ethnocentrism exhibited in the Holocaust or parts of Jewish history. The intrusion of this proximal knowledge can be an obstacle to student learning. If engaged by professors, however, I argue that proximal knowledge can be a catalyst that promotes learning. Social scientific theory provides a useful lens for helping students to better grasp and contextualize both their old experiences and the new materials that are being taught in the course within the larger structural frames of race, religion, and ethnicity that they have selected, but may not fully appreciate. Reflective guided journaling is an essential part of the learning experience.     

In situ observation of twin boundary migration in copper with nanoscale twins during tensile deformation

In situ transmission electron microscopy observations are reported of the dynamic process of twin boundary migration in Cu with nanoscale twins. The experiment provides the first direct evidence of twin boundary migration via Shockley partial dislocation emission from the twin boundary/grain boundary intersections, and reveals that such migration is the dominant deformation mechanism in the initial stage of plastic straining. The behaviour is discussed in comparison with molecular dynamics simulations and in terms of the unique characteristics of the sample microstructure.     

A General Theory of Location Based on the Notion of Entire Location

It would be a good thing to have at our disposal a general theory of location that is neutral with respect to (i.e. that does not rule out or entail) (i) the view that some objects have more than one exact location, (ii) the view that some objects are located without having an exact location, and (iii) the view that some objects are “spanners”—where a spanner is an object exactly located at a region that has proper parts but which has no proper part exactly located at a proper part of the region. As far as I know, no theory of location that can be found in the literature has this feature. I put forward a new theory that does—or so I argue. The theory takes as its sole locational primitive the notion of being entirely located at.

     

A Comparison of Selected Behaviors of Identical Twins,One Blind from Birth

The purpose of this study was to compare differences in mental-emotional, fine perceptual-motor and gross motor behaviors of a set of 13 year-old identical twins, one of whom was blind from birth. In general, the blind twin was superior in performances where total body involvements were minimal and fine manipulative movements of the hands and/or fingers were stressed. The blind twin also appeared to be more well-adjusted emotionally than the sighted twin.