Twins', siblings', and friends' social relationships and their temperamental correlates

Friendship and sibling relationships differ because friends choose each other, while siblings do not. The present study investigates these two relationship contexts and their temperamental correlates. Monozygotic twins (MZ), dizygotic twins (DZ), virtual twins (VT), and full sibling (FS) pairs were compared on ratings of friend and sibling relationships and on their temperamental similarity. Analyses revealed that negative aspects of both the sibling relationship and friendship were related to negative affect, while the positive aspects of these relationships were associated with effortful control. Surgency was associated with negative aspects of the friend relationship. In addition, MZ twins rated their relationships as more intimate than did DZ, VT, and FS pairs. Same-sex dyads were also found to rate their sibling more intimately than children in opposite-sex dyads. Females rated both their sibling and friend relationships more intimately than did males. Intraclass correlations show that MZ twins display more temperamental similarity than DZ, VT, and FS pairs. From the findings, temperament appears to be genetically influenced.