It’s not Valentine’s Day yet, but I couldn’t pass up the opportunity to post about Chip Walter’s article in Scientific American called “Affairs of the Lips: Why We Kiss.”

According to Walter, ethologist Desmond Morris (who wrote The Naked Ape among other interesting books) suggested that human kissing evolved from a practice found in primate mothers, who may have pre-chewed food for their infants and then fed them mouth-to-mouth. Subsequently, pressing lips even without food may have provided a signal of comfort and love.

Whether our lips were influenced by the practice of kissing or not, they certainly have more than their fair share of sensitivity, as you may have noticed if you have ever had a paper cut from licking an envelope. Kissing also effects our biochemistry. Wendy Hill and Carey Wilson found that two substances, oxytocin and cortisol, were influenced by kissing. Cortisol levels, which usually rise when we’re alert or stressed, drop when couples kiss, talk, or hold hands. Oddly enough, oxytocin levels increased for males after kissing, but dropped in females. Oxytocin has been implicated in a number of social bonding activities, including orgasm and nursing an infant. Obviously, more research needs to happen in this area to see why men and women are reacting differently.

How important is kissing? Gordon Gallup and his colleagues argue that a first kiss is really important to people. Fifty-eight percent of men and 66 percent of women recalled an instance where they ended a promising relationship because the first kiss didn’t “feel right.” However, these same researchers argued that kissing means very different things to men and women. Men viewed kissing as a step towards more sexual activity, whereas women viewed kissing as a bonding mechanism.

Science has a way of making some very romantic things seem less so by dissecting them. I’m not sure if this is useful information for you, but apparently most people tilt their heads to the right in order to kiss (check out Clark Gable and Vivien Leigh above). The advantage for such laterality seems to be mysterious, but we can guess that brain laterality plays a role.

Here’s another interesting factoid from Walter–apparently about 10 percent of the world’s population do not kiss. I guess they don’t know what they’re missing.