It’s a Twin Thing

by hcoms1 on March 13, 2014 - 7:32pm

In a recent article published in 2013, Chisato Hayashi, Hiroshi Mikami, Reiko Nishihara, Chiho Maeda, and Kazuo Hayakawa examine the relationship between twins and how the development of twins creating their own language relates to their social capacity. Hayashi and colleagues hypothesized that twins who have a closer tie, or relationship with one another, are more likely to develop a twin language, and therefore will have less social competence. Twin language is a unique language or system of communication that twins develop that only they can understand. Another hypothesis of the study was that environmental factors such as having an older sibling and attending preschool, and genetic differences such as zygosity (being an identical or fraternal twin), and sex of the twins would have an influence on twins’ close ties, twin language, and social competence. The data for this study was collected through a questionnaire given in 1999 to 958 women who were members of the Twin Mothers’ Club in Japan who had given birth to twins between April 1997 and April 1998. A follow-up questionnaire was administered in 2004 to the same mothers who answered the 1999 survey, and 53.9% of mothers who answered the first survey responded to the second. Respondents to the survey answered questions to identify the sex and zygosity of their twins, and basic facts about their family structure. Other questions were designed to assess the twins’ closeness and whether or not they had developed their own language, and to determine the twins’ social abilities in home and school settings. Through a statistical analysis of the responses from the questionnaires, Hayashi and colleagues concluded that twins who had developed a twin language showed more social competence issues. Though it was not found that twins’ close ties directly affects their social competence, twins with a closer tie were more likely to develop their own language, and therefore suffer socially. It was also found that environmental factors such as having an older sibling and attending preschool did not affect twins’ close tie, twin language, or social competence, while zygosity and sex were correlated with twins’ close tie. Identical female twins showed significantly closer relationships than other twin pairings, although this factor, again, did not directly affect twin language or social competence.


Hayashi and colleagues’ research article posed many interesting conclusions about the relationships of twins and their social competence, yet some assumptions throughout the article limit the scope of the research. For example, Hayashi et al. (2013) collected the data for this study through a survey given to mothers who answered questions about their twins to the best of their ability. Researchers for this study made the assumption that these mothers correctly knew how to identify twin language and other aspects of their twins’ social life and competencies that are crucial for the findings of this study. Some of the questions in the survey asked mothers to identify how sociable their twins are with other children and how their children behave at school in order to assess their social abilities. Accepting the responses given by these mothers, again, is making the assumption that these mothers correctly know how their twins behave among others even when they are not directly present to observe their children’s interactions. Some mothers may have been biased and recorded all positive results for their twins’ sociability, or simply may not have known the full extent of their twins’ sociability, yet completed and returned the survey anyway, leading to flawed or inaccurate information about the twins’ competencies. Another assumption is found in how Hayashi and colleagues determined zygosity of the twins studied. In order to determine whether twins were identical or fraternal, the survey asked whether the twins were “as alike as two peas in a pod” (Hayashi et al., 2013, p. 30). Mothers who answered this question with a “yes” were classified to have monozygotic (identical) twins, while those who answered “no” were recorded to have dizygotic (fraternal) twins. Researchers for this study assumed that twins who were “as alike as two peas in a pod” are identical, though that may not always be the case. Mothers could have all different interpretations of the question, ranking their children as alike in physical characteristics, personality components, or both. Speaking from personal experience as myself being a fraternal twin, my mother frequently used to refer to my twin sister and I as “two peas in a pod” because of our close relationship, but we are not identical twins. The assumption that two twins who are merely “alike” can be classified as identical is extremely strong, and may not provide the most accurate results possible for the study. A final assumption Hayashi et al. makes is that twin siblings can be assessed as one unit with equal characteristics regarding their social competence. All twins in this study were researched together as one twin pair, making no distinction between the first and second twin’s social capacities. Hayashi and colleagues are making the assumption that twin pairs develop identically in the social realm, which certainly is not always the case. My twin and I have had a very close relationship ever since we were toddlers, but we are extremely opposite of one another when it comes to our social personalities. The assumption that twins act the same way in social settings with other children and in school is rather broad as twins are individuals and are not the same in every aspect of life, regardless if they are genetically identical or not. The credibility of Hayashi et al.’s findings is limited due to the fact that many methods of data collection rely on broad assumptions that should not necessarily be taken for granted.

Hayashi, C., Mikami, H., Nishihara, R., Maeda, C., & Hayakawa, K. (2013). The relationship between twin language, twins’ close ties, and social competence. Twin Research and Human Genetics, 17, 27-37.

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