A pilot study of attachment patterns in adult twins.

The hypothesis that attachment in adults is influenced by genetic factors was investigated. The within-pair differences in attachment representation in same-sex monozygotic and dizygotic twins were compared using the Adult Attachment Interview (AAI). The results showed a clear tendency toward monozygotic twins (n = 28) being more concordant than dizygotic twins (n = 13), but the within-pair similarity was also high in both zygosity groups. The results suggest, in behavior genetic terms, that heredity 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. Furthermore, the results showed that the distribution of the attachment pattern in twins had the same percentage distribution as reported for singletons. Consequently, there was no tendency toward more insecure attachment in twins than in singletons.