There are activities common to most humans that we enjoy immensely, without much thought. On occasion, researchers feel they need to know why.

Recently, experimental psychologists at Oxford University in Britain explored the function of kissing in romantic relationships. They found it is complicated.

After conducting an online survey with 308 men and 594 women, mostly from North America and Europe, who ranged in age from 18 to 63, the researchers have concluded that kissing may help people assess potential mates and then maintain those relationships.

"The repurposing of the behavior is very efficient," said Rafael Wlodarski, lead author of the study. But another hypothesis about kissing - that its function is to elevate sexual arousal and ready a couple for coitus - didn't hold up.

Participants in the survey were asked about their attitudes toward kissing in different phases of romantic relationships. They were then asked about their sexual history: for example, whether they had been more inclined toward casual encounters or long-term, committed relationships.

Earlier research had suggested that in a new relationship, a romantic kiss serves to pull two relative strangers into each other's space, their faces glued together, possibly transmitting pheromonal, sensory, even genetic cues to each other's brain. This could be a kind of primal interview: Could this person be mating material?

Mr. Wlodarski's results suggest a more nuanced dynamic.

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."

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. 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.

Among the study's participants who said they were in exclusive relationships, frequency of kissing, rather than of sexual intercourse, was best correlated with relationship happiness.

Particularly for men and women looking for long-term relationships, kissing serves other purposes, like relationship upkeep. They would use their orbicularis oris muscle to mediate, ameliorate and sustain their connections. They rated kissing equally important before sex and at "other times not related to sex."

For these participants, kissing was least important during sex.

The New York Times

(China Daily 11/10/2013 page11)