“You and me”: Parental perceptions on asymmetry in twins' development and their dominance relationship dynamics

Objective: This study investigated the role of nontypical development in the relative dominance in twins' relationships throughout childhood. Background: Dominance dynamics, affecting siblings' well-being, are different in twins than in singletons for whom age and development often dictate sibling hierarchy. These dynamics in twins, who share similar ages and developmental contexts, remain underexplored and demand further understanding. Method: A longitudinal study surveyed 1,547 mothers and 536 fathers of 322 monozygotic (sharing nearly 100% genes) and 1,199 dizygotic (sharing 50% genetic variance) twin pairs, aged 3 to 8–9. Both parents reported on the twins' relationships. Mothers reported whether either twin had a developmental condition. Results: No dominance difference was found in similar developmental conditions dyads, whether both twins had typical or nontypical development. However, in dyads where twins differed in the developmental condition, nontypically developing twins were less dominant than their typically developing cotwins. This dominance imbalance persisted throughout childhood, even if initial developmental issues were resolved. Conclusion: From parents' perspectives, nontypical development does not, in itself, prevent children from demonstrating dominance behaviors in twinship, but it is more likely that the asymmetry in developmental conditions is associated with the relationship between the twins. Implications and Recommendations: According to parents' perceptions, twins with nontypical development might experience imbalances in their relationship throughout childhood when their co-twin is a typically developing child. However, demonstrating dominance might be possible for them in other contexts. Understanding these dominance dynamics is vital for caregivers, informing tailored parenting strategies and interventions to support the well-being of children.