Twin and sibling attachment in a nationally representative sample

The objective of this research was to evaluate the hypothesis that twin relationships are attachments, using data from a nationally representative sample. The results indicated that twin siblings were more likely than nontwin siblings to be attached to their siblings. Moreover, analyses indicated that both attachment theoretical and inclusive fitness perspectives are necessary for explaining these findings. Namely, twins were more likely to be attached than nontwin siblings, as expected from an attachment perspective. But identical twins were more likely than fraternal twins to be attached to one another, as might be expected from an inclusive fitness perspective. Cross-sectional analyses indicated that older people are less likely than younger people to use their sibling as an attachment figure compared to younger people and that married adults are less likely to use their sibling as an attachment figure than nonmarried people.     

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.     

Aspects of narcissism and symbiosis, or, essential neurosis of twins

Following a brief introduction I address the relationships of twins from five different perspectives: the Intimate Connection, the Mirror Image and Complementarity, Object- and Self-Representation, Self and Object or Rivalry, and Intersubjective Communication. This approach attempts to understand twin relationships and the individual development of twins in terms of their intense mutual dependence, akin to infantile symbiosis, and in terms of narcissism. In their similarity to each other, twins may choose each other as love objects even as they see themselves in the other. That is, a twin may "love what he himself is" or "someone who was once part of himself." This "type of object-choice … must be termed 'narcissistic'" (Freud, 1914, pp. 90, 88). Such "cathexis of an undifferentiated self-object" is considered to be "primary narcissism" (Burstein, 1977, p. 103). Hoffer (1952) describes primary narcissism as "the lack of all qualities discriminating between self and not-self, inside and outside" (p. 33).     

Observed Mother– and Father–Child Interaction Differences in Families with Medically Assisted Reproduction‐Conceived Twins and Singletons

Increased medically assisted reproduction (MAR) use to treat infertility has resulted in a growing twin birth rate. Little is known about parent–child relationships for twin relative to singleton children in middle childhood. This study fills this gap by examining parent–child relationships in 57 families with eighty 6‐ to 12‐year‐old MAR twin and singleton children using observational data (warm and supportive communication, control, and hostility). Nested ANCOVAs indicate that while mothers exhibit similar interactional behaviors toward twins and singletons, fathers have less optimum behaviors toward twins relative to singletons. Twins displayed less engaged behavior with mothers and fathers relative to singletons. Given the vitality of parent–child relationships for family and child adjustment, future studies should examine determinants and outcomes of twin–singleton relationship differences to bolster twins’ and their families’ functioning.     

Maternal speech style with prelinguistic twin infants

The mother–infant communicative speech of a group of mothers of 4‐month‐old first‐born twin infants was compared to the speech of a group of mothers of first‐born singleton infants. Maternal groups were matched on age, education level, mother–infant attachment status and infant gender, and maternal depression was assessed as a control variable. Maternal speech was coded for focus, content, complexity and syntax of mothers' utterances. The findings of earlier studies with toddler age twins, that maternal speech style was more directive and less infant‐focused, were replicated in this prelinguistic period of infancy. Compared to mothers of singletons, mothers of twins used less infant‐focused speech, were less responsive to their infants' cues, and attributed less agency to their infants. Mothers of twins also used fewer questions and requests but did not differ from mothers of singletons in their use of negatives and imperatives. These early differences in the language learning environments of twin and singleton infants may be due to the reduced opportunities that mothers of twins have to establish dyadic communicative routines with their infants and to familiarize themselves with their infants as interactive partners, and may have implications for the early language development of twins. Copyright © 2002 John Wiley & Sons, Ltd.     

A comparison of twins for degree of closeness and field dependency

An examination of Witkin's construct of field dependency was undertaken with a sample of adolescent twin pairs to determine if the degree of closeness in twin relationships would be reflected in the twins' degree of field dependency. Sixteen pairs of monozygotic (MZ) adolescent male twins and the same number of dizygotic (DZ) same-sexed male twins were administered three measures: Nichols and Bilbro's (1966) zygosity questionnaire, Paluszny and Beit Hallahmi's (1974) semantic differential measure of closeness, and Jackson's (1956) short form of the Embedded Figures Test. No significant differences were found between the MZ and DZ twin groups with regard to their expressed closeness to one another, as measured with Paluszny and Beit-Hallahmi's index of closeness; in addition, there were no significant differences between the two twin groups on the measure of field dependency. However, significant relationships of these two variables with intelligence were found and possible reasons for such an occurrence were offered.     

Twin imitation for antisocial behavior: implications for genetic and family environment research.

When twin pairs influence each other's behavior, observed variance is greater for MZ twins than for DZ twins under at least 1 of 2 conditions: (a) the trait has some heritability and (b) MZ twins influence each other more than do DZ twins. Applied to a trait that has an underlying continuous distribution but is measured as a dichotomy, the presence of reciprocal twin influence predicts that if the base rate for the trait is not exactly 50%, then the prevalence of the trait should differ in MZ and DZ twin pairs. This prediction held for registered criminality in a large twin cohort. Methods of analysis that permit reciprocal twin interaction not only provide better statistical fits to the data but also yield estimates of heritability that agree with adoption data. The results suggest that the genetic influence on registered criminality may be more modest than previously thought.     

The equal environments assumption of classical twin studies may not hold

The classical twin method ‐ comprising comparisons of monozygotic (MZ) and dizygotic (DZ) twins ‐ in the domain of cognitive abilities and attainments has led to wide acceptance of results suggesting a large amount of additive genetic variance, with far‐reaching implications both for the nature of future studies on the causes of cognitive variance and for intervention policies, as in education. However, this interpretation is only valid if the method observes a number of conditions, which have to hold. Here, we show that the most crucial of these, namely, the equal environments assumption (EEA), may not hold. Consequently, differences in twin correlations might be at least partly explained by treatment effects from parents, teachers, peers, and so on. In addition, well‐known interactions at various levels confound the model of simple additive effects on which the classical twin method is predicated and results are interpreted. For example, at a socio‐cognitive level, DZ twins may respond to treatments differently from MZ twins. This interaction may further explain MZ—DZ correlation differences. There is abundant evidence for such interactive effects in published twin data. We suggest that there is a need for a more thorough examination of these problems.     

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.     

Are twins different from singletons during early childhood?

This paper examines the specificity of intrafamilial experiences to which twins are exposed during early childhood, and the impact of this family context on the psychological development of twins. An overview of the literature on the psychological development of twins indicates two broad categories of findings. The first category covers studies dealing with the developmental features that appear early in twins. Although there are numerous studies comparing the psychomotor and verbal development of twins to singletons, only a few have dealt with the emergence of personality and identity, and most have been conducted in clinical settings. The second set of studies deals with mother-twin relations, explored in recent years in terms of the psychosocial stress created by twin births. Few studies have examined the mother-twin relationship in the light of major theories on mother-child bonding (psychoanalysis, attachment, interactionist model). These developmental models have mainly focused on mother-infant dyads, while the construction of this specific mother-twin relationship needs to be set within the framework of a triadic situation. Rather than describing a specific ‘twin mentality’, it is argued here that the twin situation should be seen as a special case of adaptative development, both for the mother and the child, which has effects on the formation of the individual.     

The Association Between Childhood Maltreatment and Coping Strategies: The Indirect Effect Through Attachment

Maladaptive coping strategies represent a potentially treatable component of psychopathologies associated with childhood abuse and neglect. Coping strategies are relatively stable constructs that may be viewed as trait-like behavioral manifestations of larger, albeit less accessible, intra- and interpersonal processes, such as activation of the attachment system. The authors investigated a potential mediational pathway from childhood maltreatment (in the form of physical and emotional abuse experiences) to coping strategies developed in emerging adulthood through attachment organization in a sample of undergraduate psychology research participants at a public Midwestern university (N = 225). Avoidant attachment patterns helped to explain the relationship between increased instances of childhood maltreatment and a decreased use of adaptive coping strategies. Further, both anxious and avoidant attachment mediated the relationship between childhood maltreatment and an increased use of maladaptive coping. By utilizing an attachment theory–informed approach as an explanatory guide, researchers and clinicians may be better able to conceptualize, study, and treat complex cases by understanding the underlying relationships between childhood maltreatment, attachment, and coping.     

Mothers' representations of their 13-month-old twins and child-raising attitudes

The purpose of this study was to describe maternal representations of the twin sibling relationship and of the children's differences and similarities. Mothers' mental representations were also analyzed with regard to two aspects of their child-raising attitudes: individualization of childcare routines, and the question of differentiation by “external signs of twinship” (dress, toys, and first names). Data from interviews with 44 mothers of twins conducted 13 months after the birth were analyzed in terms of 8 categories—complicity, rivalry/jealousy, agonistic relations, dominance, imitation, physical appearance, development, and personality. A multiple correspondence analysis of the data pointed out that the first dimension describing the mothers' representations concerns the contrast between the “unalike” representation of dizygotic twins and the “alike” representation of monozygotic twins. The second dimension corresponds to the casual, twinship-minimizing representations generated by the twin condition. Two other dimensions express the issues of aggression and dominance. The relationship between the child-raising behavior of the mothers and their representations of the twin couple turned out to be more complex than expected. The results are discussed in terms of the specificity of the psychological issues facing mothers of twins. Defense mechanisms used by some mothers to cope with the exceptional nature of the twin phenomenon are also suggested. © 1998 Michigan Association for Infant Mental Health     

Sharing genes fosters identity fusion and altruism

Researchers have shown that the more genes twins share, the more they care about one another. Here, we examine a psychological mediator of such genetic influences, “identity fusion” (a visceral sense of oneness with them). Results supported this hypothesis. Relative to dizygotic twins, monozygotic twins reported stronger fusion and elevated desire to have contact and share experiences with their twin (Study 1), to forgive and grant favors to their twin after being disappointed by him/her (Study 2), and willingness to make sacrifices for their twin (Study 3). Fusion with the twin mediated the impact of zygosity on these outcomes. These findings demonstrate that genetic relatedness fosters a powerful feeling of union with one’s twin that predicts sharing, tolerance, and self-sacrificial behavior toward him or her.     

The evolution and function of adult attachment: a comparative and phylogenetic analysis

Although the evolutionary functions of attachment in infant-caregiver relationships are undisputed, it is unclear what functions--if any--attachment serves in adult romantic relationships. The objective of this research was to examine the evolution and function of adult attachment (i.e., pair bonding) by applying comparative and phylogenetic methods to archival data collected on 2 diverse samples of mammalian species. The authors found that species exhibiting adult attachment were more likely than others to be characterized by paternal care, developmental immaturity or neoteny, small social groups, and small body sizes. The authors also used phylogenetic techniques to reconstruct the evolution of adult attachment and test alternative evolutionary models of the comparative correlates of pair bonding. Phylogenetic analyses suggested that the relationship between paternal care and adult attachment may be a functional one (i.e., due to convergent evolution) but that the relationship between neoteny and adult attachment may be due to homology (i.e., shared ancestry). Discussion focuses on the potential of comparative and phylogenetic methods for advancing the science of social and personality psychology.     

The ethics of separating conjoined twins: two arguments against

I argue that the separation of conjoined twins in infancy or early childhood is unethical (rare exceptions aside). Cases may be divided into three types: both twins suffer from lethal abnormalities, only one twin has a lethal abnormality, or neither twin does. In the first kind of case, there is no reason to separate, since both twins will die regardless of treatment. In the third kind of case, I argue that separation at an early age is unethical because the twins are likely to achieve an irreplaceably good quality of life—the goods of conjoinment—that separation takes away. Evaluation of this possibility requires maturation past early childhood. Regarding the second type, I point out that with conceivable but unrecorded exceptions, these cases will consistently involve sacrifice separation. I present an argument that sacrifice separation is unethical, but in some cases a moral dilemma may exist in which separation and refraining from separation are both unethical. Perhaps in such cases a decision can be made on non-moral grounds; however, the possibility of such a decision serves not to mitigate but to underscore the fact that the separation is unethical. My conclusion, which applies to all three types of cases, is that it is unethical to separate conjoined twins before their developing personalities give some reliable indication as to whether they desire separation and whether they will achieve those goods of conjoinment.     

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.     

Left-handedness in twin families: support of an environmental hypothesis

Information on handedness, assessed as writing-hand, was collected from 197 MZ twin pairs and 203 DZ twin pairs and from their parents, spouses, and children. Associations for pairs of relatives were studied by 2 X 2 tables, computing chi squared-values and tetrachoric correlations. Correlations of about .3 were obtained for mother-offspring and sibling pairs, while for cousins the correlation was .25 (in a small sample). No other significant associations were found, not even for twins. These results suggest only a small, if any, genetic effect, and only a small environmental between family effect, most of which seems to be a maternal effect. The lack of cotwin correlations and correlations for one of the twins with her/his ordinary brothers/sisters suggest the existence of an effect specific to twins, since the correlation for pairs of ordinary siblings is significant. Conclusions drawn from twin studies alone may be biased. The frequency of left-hand writers has increased from 1% to 10% in the different age groups born during the last century in Norway. This age effect is present mainly in hand writing and not so much in handedness generally, suggesting a decrease in cultural repression against left-hand writing.     

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.     

“Principles in his nature which interest him in the fortune of others…”: The heritability of empathic concern for others1

The present research was conducted to explore genetic influences on empathic concern for others. First, an index of empathic concern was created by combining relevant items from Gough's Adjective Check List (ACL). This index was validated by correlating scores of 88 undergraduates on the index with their scores on a self-report measure of empathy, which has been related to prosocial behavior. Correlations were sufficiently high to accept the validity of the index. Next, previously collected ACL responses of 114 monozygotic (MZ) and 116 dizygotic (DZ) twins were reanalyzed in order to create an empathic concern score for each twin. The twins were middle-aged males initially raised together but living apart at the time they completed the ACL. Comparison of intraclass correlations for MZ and DZ twins revealed, as predicted by the genetic hypothesis, significant (p < .005) heritability in empathic concern scores. This finding suggests that there may, indeed, be a genetic influence on individual differences in empathic concern for others. Some limitations of the present data are also considered. How selfish soever man may be supposed, there are evidently some principles in his nature which interest him in the fortune of others, and render their happiness necessary to him.