Behavioral Inhibition as a Function of Relationship in Preschool Twins and Siblings

Abstract

M onozygotic (MZ) twins spend more time with each other and are more genetically alike than are dizygotic (DZ) twins or nontwin siblings and therefore probably experience less diversity in their playmates than DZ twins, who in turn may experience less diversity than other-age siblings. Thus MZ twins may be more inhibited than DZ twins, who may in turn be more inhibited than nontwin siblings. To test this, 205 children (42 MZ twins, 94 DZ twins, and 69 nontwin siblings) were assessed in a playroom laboratory during free play with an unfamiliar peer. Children's inhibition was rated based on latency to touch a toy for the first time and amount of time spent interacting with the other child. Additionally, the Child Behavior Checklist (CBCL) withdrawn scale was used to assess inhibition according to parent report. Behavioral ratings showed that MZ and DZ twins did not significantly differ on the inhibition or withdrawn ratings. DZ twins were significantly more inhibited than were nontwin siblings, according to laboratory ratings. Greater inhibition of twins during the free peer play situation can be explained by their relative lack of experience in playing with children who are less genetically and phenotypically like themselves. Parental ratings showed exactly the opposite pattern, suggesting a rater bias effect.Monozygotic (MZ) twins, who spend a lot of time with each other and are very much alike, may spend more time playing with each other than with other friends, and they may do this to a greater extent than do dizygotic (DZ) co-twins because MZ twins are more similar to each other genetically and therefore may have more similar interests and play behaviors. In one study of preteen twins, MZ twins reported each other as being one of their best friends more often than did DZ twins (Rose, 2002), suggesting that they play together more often than do DZ twins. Therefore, MZ twins probably experience less diversity in their playmates than do DZ twins. This lack of diverse experiences with other children may negatively impact MZ twins' behaviors with other children, leading them to be more inhibited than DZ twins or nontwins. Similarly, DZ twins, being the same age as each other, are likely to play together more often than do nontwin siblings, and therefore they may experience less diversity in their friendships than do nontwin siblings. Thus, in line with developmental social genetics theory (Scott, 1977), we would predict that MZ twins will be more socially withdrawn than DZ twins, who will be more withdrawn than nontwin siblings.This idea, based on the developmental social genetics theory that children's social interactions rely in part on the genotypes of each of the children (Segal, 1997), suggests that the degree to which two children share genotypes will influence the way in which they play together. Studies on cooperation among twin children have found that MZ twins are more cooperative with each other than are DZ twins (Segal, 1988;Segal & Hershberger, 1999). It may be the case that children who spend most of...

Conflict, Closeness and Comfort: The Inter-Twin Relationship as a Risk Factor for Behavioral Difficulties

“…In line with previous research (DiLalla & Caraway, 2004) the current study found mean differences across measures of sibling relationship between MZ and DZ pairs. However, in regard to the question concerning patterns of association between measures of sibling relationship and behavioral outcome our findings indicate no significant differences.…”

Testing Alternative Hypotheses Regarding the Association Between Behavioral Inhibition and Language Development in Toddlerhood

“…However, it is important to note that the longitudinal design of the present study brings us one step closer to testing the alternative hypotheses directly by allowing examination of the directionality of the association. Additionally, the present study examined a general population sample of same-sex twins, and prior studies have reported that twins have higher incidence of language delay than singletons at early ages (e.g., Rutter et al, 2003; Thorpe, 2008) and are more behaviorally inhibited compared to singletons in a preschool sample (DiLalla & Caraway, 2004). If these mean differences between twins and singletons are accompanied by differences in how behavioral inhibition and language relate to each other, it will be important to replicate the results in other samples to determine generalizability.…”

“…Also, we examined two different measures of behavioral inhibition (observed and parent-reported), which have been shown to be significantly associated but distinct in an earlier study using the present sample (Smith et al, 2012). Some of the associations between behavioral inhibition and language development were limited to parent-reported behavioral inhibition, which may reflect the rater-driven differences specific to parent-reported behavioral inhibition (e.g., DiLalla & Caraway, 2004); for example, parents have a larger sampling of behavioral observations on which to rate their children’s behavior, and likely use different reference points for comparisons (e.g., other children in their family). We also had multiple measures of observed and parent-reported behavioral inhibition, which reduced measurement error and led to a more reliable assessment.…”

Genetic and Environmental Influences on the Stability of Withdrawn Behavior in Children: A Longitudinal, Multi-informant Twin Study

“…In a large twin-singleton comparison study (Pulkkinen et al 2003), 12-year-old twins were reported to be more socially adaptable than non-twins, but no twin-singleton differences were found for social anxiety. A twinsingleton comparison of both maternal CBCL withdrawn ratings and laboratory assessment of inhibition in 5-yearolds yielded inconsistent results (DiLalla and Caraway 2004). According to laboratory ratings, twins were more inhibited than non-twins, whilst maternal ratings showed the opposite.…”