From Howstuffworks.com: “No one knows for sure, but anthropologists think kissing might have originated with human mothers feeding their babies much the way birds do. Mothers would chew the food and then pass it from their mouths to their babies’ mouths. After the babies learned to eat solid food, their mothers may have kissed them to comfort them or to show affection…Other researchers believe instead that kissing is instinctive. They use bonobo apes, which are closely related to humans, to support this idea. Bonobos kiss one another frequently. Regardless of sex or status within their social groups, bonobos kiss to reduce tension after disputes, to reassure one another, to develop social bonds and sometimes for no clear reason at all. Some researchers believe that kissing primates prove that the desire to kiss is instinctive.”