Scientists now think that humans use kissing as a way to audition potential mates. It allows us to get all up in their pheromones and hormones, which convey subconscious clues as to their health, fertility, and if they’re at all related. And therefore, it makes sense that beautiful people enjoy kissing more – they can be pickier about who they choose as their partner.
Bonus finding: People who kiss and have sex often report more satisfaction with their relationships. No word on the effect of witnessing enthusiastic PDA has on people passing by.