Social functional theory proposes that emotions enable people to form, maintain, and negotiate the relationships that matter most, such as romantic bonds, friendships, social hierarchies, and collective and cultural identities. Emotions help solve the "commitment problem," enabling people to express sincere commitment and to behave in ways that benefit others' well-being, thus strengthening social relationships. The chemical oxytocin, when circulating throughout the blood, contributes to building commitment and trust.