When the brain releases oxytocin during sex, childbirth, breastfeeding, and social interactions, the hormone supports strong feelings such as attachment, trust, and closeness. That’s why oxytocin is frequently nicknamed the love, cuddle, or happy hormone—even though it’s also linked with aggression. To continue investigating the biological role of oxytocin, a team of researchers studied it with scientist’s poster species for love and friendship, the prairie vole (Microtus ochrogaster). Within the context of building bonds, oxytocin seems to play a role particularly in the selectivity of friendships. “This broadens the view of oxytocin from being just the ‘love hormone’ to a more general ‘social relationship’ hormone that supports both romantic and platonic connections,” she says.