Being Opposite: Is there Advantage for Social Competence and Friendships in Being an Opposite Sex Twin?

Abstract

A recent large-scale study of Finnish adolescent twins (Pulkkinen et. al, 2003) reported that individuals from opposite sex twin pairs were more socially adaptive than either individuals from same sex pairs or singletons. This finding raises questions about the social learning effects of being an opposite sex twin. The current paper hypothesised on the basis of this finding, and evidence from singleton populations, that having an opposite sex sibling would yield social advantage. It sought to examine the social competencies of opposite sex pairs and compare them with same sex twins and singletons. The study focused on the preschool years (age 3-6), a period in which the majority of children encounter their first large group, non-familial social experiences.
The study obtained reports from parents and teachers of children aged 3-6 years: 72 children (36 pairs) who were dizygotic opposite sex twins (DZOS), 50 children (25 pairs) who were dizygotic same sex twins (DZSS), and 85 singletons of the same age and sex as the twins, who had at least one sibling. Reports were made using standardised measures of social competencies, behaviour problems, language development and friendships. The main effects found were of differences in social competency between twins and singletons. Twins had lower social competency scores. No differences between same sex and opposite sex twins were found. The findings did not support the hypothesis of social advantage for opposite sex twins in early childhood.