Why do humans kiss? You might think it is a universal trait, something that we all do. But when European explorers travelled the world, they met tribes that didn’t kiss. So is it a learnt response after all? ? It can be as a greeting, or a sign of reverence or supplication - but we will be talking about the romantic kiss - face to face, lips to lips. We examine the biochemistry, psychology, anthropology and history of kissing. Where does it come from? (Image of two women kissing at a festival, credit AFP/Getty Images)