From the NYTimes:
The participants generally rated kissing in casual relationships as most important before sex, less important during sex, even less important after sex and least important “at other times.” (To clarify: researchers defined kissing as “on the lips or open-mouth (French).”)Past research has shown that three types of people tend to be choosier in selecting mates who are genetically fit and compatible: women, those who rate themselves highly attractive, and those favoring casual sex. In this study, these people said that kissing was important mostly at the start of a relationship.That may be because for these individuals, kissing turns out to be a quick, easy way to sample a partner’s suitability — a subconscious stop-go light. For them, “The Shoop Shoop Song (It’s in His Kiss)” might not be far off the mark.After that first kiss, these types are much more likely than other subjects to change their minds about a potential partner, researchers found. If it’s not in his kiss, forget about him.But other people might use different criteria to size up their mates: men, those who rate themselves as less sexually attractive, and people looking for commitment. In the grand search for a partner, these individuals screen for people who seem to have the inclination and resources for the long haul. And for them, this study showed, kissing has a lower priority at the beginning of dating.