Why do human beings kiss? Does kissing serve an evolutionary purpose? This article explores some of the research about kissing and why we do it. The lips have the thinnest skin on the human body and a dense concentration of blood and nerve endings, which is why they are so sensitive. Kissing releases important chemicals like oxytocin, and has other physical effects, like causing pupils to dilate. One scientist surmises that kissing evolved from the way primate mothers fed their young (chewing it up and feeding it to them mouth-to-mouth). Others suggest that its a way we transmit subtle genetic information to each other via pheromones. This research is intriguing, but not conclusive. So for the time being, we’ll have to enjoy kissing without knowing exactly why!