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There are the ones who pucker tightly before the kiss. There are the nibblers who chew around the edge of your lips. Then there are the ones who use lots of saliva, and others who are very dry. There are the firm ones, the tender ones, the fast ones and the slow, leisurely take-all-day ones. There are the teasers, who open their mouth slightly, and the prodders. A good kisser has an arsenal of techniques and can gauge the situation to decide which strategy to use.
One of the most expressive and complex acts that people can engage in is a kiss. A kiss can be a greeting, affectionate, sexual, romantic, consoling, and religious - and can occur between lovers, strangers, family members, friends, and out of respect for status. Although there are all of these contexts, we are obsessed, at least as reflected by the media, with sexual or romantic kissing. The media routinely shows us "stolen" kisses where someone simply can't help it - she or he must lip lock with the object of desire. It's as though two trains are on the same track, heading towards each other, and the engineers have checked out. Similarly, old movies give us these incredibly sweet romantic love scenes with prolonged kisses. 
Think of Casablanca, where we see the romance, not the sex, between Ilsa and Rick (aka Ingrid Bergman and Humphrey Bogart). Their final kiss is pure romance, the kind that grabs you in your gut and squeezes.It isn't a kiss that is meeting some sexual need - it's so very much deeper, and I think you all know the kind of kiss I'm talking about.
Numerous researchers in my field have been studying kissing. Some suggest that kissing is genetic, that we're hard-wired to do it, while others say it's learned. Some (like Vaughn Bryant) say that we kiss so that we can smell the pheromones of the person and decide if they are someone we want to have sex with either now or in the future. Helen Fisher (2009; no relation) proposes that men's saliva contains testosterone, which they transfer to women to increase the latter's sex drive. Likewise, men use the woman's saliva to learn about the woman's fertility. Colin Hendrie and Gayle Brewer (2009) outline various benefits, at a viral level, that can be gained through kissing.
Whether kissing is a way to measure various biochemistries of a potential partner is all well and good, but is it more than this? The idea of swapping saliva doesn't make me swoon, quite the opposite actually, but the idea of a prolonged, romantic kiss still stirs my heart. Why? What is it about a deeply romantic, emotion-packed, earth-shattering kiss that separates it from all other kisses? And why are we not studying the romance aspect of kissing, the part that lingers in one's soul, rather than in a more easily identifiable body part?
So, this is my plea: don't underestimate the emotional importance of a kiss. As any romance novel reader knows, that first kiss between the heroine and hero is like candy; there is some satisfaction that the characters are doing what they should be doing. (Yes, I read romance novels...but what's more is that I work for a leading romance novel publishing company, which is probably why I'm focusing on kissing here. More about that another time.) There is trust involved in kiss, and a curiosity. The first kiss with someone new is an exploration into another dimension of one's relationship - whether it's a brand new relationship that started 5 minutes ago, or one that has existed longer. It might end at the first kiss - after all, if the person can't kiss in a way that sets you a flutter, why bother? (Although I would certainly argue that you might want to try it again, just to be sure.) But what about the couples who have been together so long that a mere kiss doesn't ignite their desires? Why do they still kiss - even if it's just the perfunctory lip smack on the way out the door in the morning? Are these people acting out of habit, and if so, how did they establish the pattern? Does this couple still kiss romantically, but wait for the right time and place? Explanations such as viral resistance and hormonal analysis simply don't explain these decisions and behaviours.
Yes there is kissing for sexual pleasure. But, this type of kissing is not the type that really gets romance readers interested in plot lines, nor does it make for a fulfilling movie (except for maybe a risqué adult film), nor does it make a deeply meaningful relationship.
Kissing is not just about sex. It is an emotional act that has meaning; it represents an emotional bond. This seems particularly true for women. Women seem to place more importance on kissing than men, even when it is used in sex. Susan Hughes and colleagues (2007) found that women think of kissing as an integral part of sexual behaviour, and most will not engage in sex without kissing before, and often during, sexual interactions whereas the same is not true of most men. Is it because women want some emotional interaction? Perhaps.
So, here's my hypothesis. Kissing represents one of the most romantic acts that can be performed, and because women tend to like romance, they like kissing. Kissing is an act of emotion. Yes, it can be propelled out of sexual longing, but ultimately, it represents an emotional connection, even temporarily, between two people. The person is the center of your universe, for at least as long as that kiss. You are journeying somewhere together, connecting. It's fine and dandy if this means you can assess your partner's fertility, gain immunity to viruses and all that, but these explanations are missing out on the bigger picture. We need to start digging deeper and understand what the magic of a kiss truly is - and not be afraid, as scientists, that it's linked to romance and emotion. As Judy Garland is reported to have said, "T'was not my lips you kissed but my soul." She must have known a decent kisser.
