Forging one’s identity as a twin: Balancing sibling cohesion and deidentification

Little is known about how twins influence one another’s development during emerging adulthood. Although the exact mechanisms that underlie sibling influence have not been firmly established, they likely encompass processes that highlight either sibling identification (e.g., seeking similarities and imitation in the service of building cohesion) or deidentification (e.g., seeking differences that distinguish themselves to reduce competition, rivalry, and jealousy). Because past research inferred these processes rather than directly assess them, we conducted a mixed methods study in which 20 sets of monozygotic (MZ, n = 11 dyads) and dizygotic (DZ, n = 9 dyads) twins, aged 19.70 years (SD = 1.11), were interviewed individually regarding their personal identity development and sibling relationship. A grounded theory approach guided the qualitative analysis, which included coordinating twins’ interview responses at the dyadic level. Each twin also completed the Adult Sibling Relationship Questionnaire which provided a complementary quantitative assessment. 75% of the dyads prioritized differentiation and felt that college was the optimal time to pursue unique identities and goals. Those who prioritized seeking similarity were MZ twins who sought emotional closeness and support and attended the same college. Rather than pitting social learning and deidentification as opposing processes, the results suggest that deidentification is a developmental process in which twins increasingly take steps towards independence while seeking to retain the closeness, trust, and reliance they have long enjoyed in their relationship. Practical implications for helping twins balance their needs for autonomy and distinctiveness, while maintaining emotional closeness, are discussed.