Hierarchy of attachment figures among adult twins and non-twins

This study concerns attachment in adult twins and siblings from a psychological perspective. Our objectives were to translate from English to Portuguese and adapt the 16-items Attachment Features and Functions Measure (AFF) to Brazilian population and to compare the attachment hierarchy of monozygotic (MZ), dizygotic (DZ) twins and nontwin siblings (NT). The Brazilian version of the AFF was answered by adults, of whom 132 had twin siblings and 98 had non-twin siblings. Only one representative of a twinship or a sibling relationship participated in our study. The four attachment dimensions (proximity seeking, safe haven, secure base and separation distress) were highly intercorrelated within each attachment target (sibling, mother, father), suggesting a single-component structure. We considered the existence of a single attachment factor in the AFF Questionnaire and the internal consistency of the composite score was high. The results indicated that MZ twins reported higher levels of attachment to their siblings than DZ twins and non-twins, as expected by both attachment and inclusive fitness perspectives. In addition, mothers were considered the main attachment figures by all groups, while fathers occupied the bottom of the hierarchy. Our study contributes to a better understanding of the relationship between twins and their families in Brazil.