Attachment to the Romantic Partner and Sibling: Attachment Hierarchies of Twins and Non-Twin Siblings

What is it about?

The strongest emotional bond between two persons is, for most people, the emotinal bond to their romantic partner. However, people also form strong emotional bonds to their sibling. Empirical research suggested, that people form especially strong emotional bonds to their (monozygotic) twin. In this study, we compared the emotional bonds of people to their romantic partner and their sibling, comparing monozygotic twins, dizygotic twins, and non-twin sibling relationships. The results show that monozygotic twins prefer their sibling to their romantic partner whereas dizygotic twins are equally attached to their sibling and romantic partner. In contrast, non-twin siblings are more attached to their romantic partner compared to their sibling. These results indicate that genetic relatedness has profound impact on a person’s attachment hierarchy and the relative rank of the romantic partner and the sibling.

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Why is it important?

This finding has several important implications for research on close relationships. For example, the strong relationship between twins –– especially MZ twins –– might cause conflicts in close relationships, especially when the romantic partner expects to be the first in the attachment hierarchy (Pietilä, Bülow, & Björklund, 2012). Petersen, Martinussen, McGue, Bingley, and Christensen (2011) found that twins are less likely to marry and have lower divorce rates than non-twin siblings. It might be valuable for future research to consider the impact of the strong sibling relationship on the satisfaction in and the stability of a couple’s relationship. On the other hand, it would also be interesting to investigate the impact of a close relationship on the relationship between siblings. As far as we know this idea has not been tested before, but we would predict that the quality of the relationship between twins would suffer less from a new romantic relationship than the quality of the relationship between non-twin siblings. Further studies are needed to test these predictions.