title: The origins of reciprocity and social exchange in friendships.
authors.affiliation: Florida Atlantic University, USA.
authors.forename: Brett
authors.initials: B
authors.lastname: Laursen
authors.forename: Willard W
authors.initials: WW
authors.lastname: Hartup
mesh_terms: D002648:Child; D002657:Child Development; D003071:Cognition; D005260:Female; D006801:Humans; D007398:Interpersonal Relations; D008297:Male; D010379:Peer Group; D011582:Psychological Theory; D012919:Social Behavior