Attachment in adult twins: Genetic influence on twins' close relationships

In a preliminary study of attachment in adult twins, 41 pairs of same-sexed 30 years old twins (28 MZ and 13 DZ), were assessed with the Adult Attachment Interview (AAI). The results suggested in behaviour genetic terms, that heritability and shared environment may contribute to attachment status in adulthood. This differs from studies of attachment in infancy and early childhood which report attachment to be explained mainly by shared environment with minimal influence from genetic factors. The twins were also interviewed about the attachment to their twin with the AAI methodology. Results showed that the genetic influence also manifests itself in the twins co-relationships, i.e MZ twins are more similar than DZ in attachment style. The twins attachment to co-twin (AAT) in DZ twin pairs were more often secure than in MZ pairs, compaired to attachment to parents (AAI) where the tendency is that more MZ twins classified as secure. None of these tendencies reached significance level.