Peer network overlap in twin, sibling, and friend dyads.

Research suggests that sibling-peer connections are important for understanding adolescent problem behaviors. Using a novel behavioral genetic design, the current study investigated peer network overlap in 300 child-child pairs (aged 7-13 years) in 5 dyad types: monozygotic (MZ), dizygotic twins, full siblings (FSs), friend pairs, and virtual twins (i.e., same-aged, genetically unrelated siblings). Genetic relatedness, sex composition, and age differences contributed to peer overlap in sibling dyads. MZ twins showed the highest overlap (82%), opposite-sex FS pairs showed the lowest overlap (27%), and friend pairs (48%) were close to the mean (53%). Social contact variables and self-reported relationship intimacy predicted additional variance in peer overlap. The roles of genotype-environment correlational and shared environmental processes in the sibling-peer connections are discussed.