From interpersonal to extended fusion: relationships between fusion with siblings and fusion with the country / Desde la fusión interpersonal a la fusión extendida: Relaciones entre la fusión con los hermanos y la fusión con el país

Abstract Identity fusion is a visceral feeling of oneness with a group. Although research on identity fusion focuses on the alignment of individuals with groups, we propose that fusion can develop between two individuals. In particular, we explore for the first time identity fusion between siblings and its relation with endorsement of extreme behaviour to protect the sibling. In a study conducted with 761 couples of siblings we found that fusion with the sibling is positively associated with willingness to fight and die for the sibling. Additionally, we address the relation between interpersonal and extended fusion. Specifically, a positive association between fusion with the sibling and fusion with the country emerged. The hypothesis that extended fusion might require the projection of interpersonal ties to a large category is discussed.