Pucker up: we use kissing to size up a potential partner

A kiss is just a kiss according to the words of the song but maybe not. A research study from Oxford University suggests it might be a sneaky way to size up a potential partner by testing genetic fitness or general health.

Kissing in human sexual relationships is incredibly prevalent across just about every society and culture, but why do we do it, asked research student Rafael Wlodarski. This is not a trick question.

He and prof Robin Dunbar set up an online questionnaire to get to the bottom of this mystery, which attracted 900 respondents.

To most of us the answer might seem as obvious as the nose or perhaps the lips on your face, but they raised legitimate questions when publishing their findings this morning in the Archives of Sexual Behavior and the journal Human Nature, both published by Springer.

There were currently three main theories about the role of kissing in sexual relationships: it helps us choose better mates because we can assess their genetic fitness or detect disease; we do it to increase arousal; or it helps to keep existing relationships together, Mr Wlodarski said. “We wanted to see which of these theories held up under closer scrutiny.”

They found men and women who were more attractive or had more casual sex tended to be more picky when choosing a mate and valued kissing quality as a way to assess them.

Things get more complex as the relationship deepens because kissing then becomes more important for bonding.

The researchers linked more frequent kissing to the quality of a relationship, with the more the better.

Yet more frequent sex did not reflect the quality of a relationship.

Rather alarmingly women valued kissing most when they were in the part of their menstrual cycle when they were most likely to conceive.

They put this down as a way for women to assess genetic quality just at the time when it might be most important to know this.

Then there is the "Jane Austen problem" as the researchers put it. A couple may be prevaricating on whether to advance or retreat in a relationship, but there are risks. How long do you wait for Mr Darcy to arrive, because you can't wait forever, but there may be other women waiting for him too. At what point do you have to compromise and go for the curate instead, the researchers posit.

Longer term, kissing seems to provide a useful glue to help couples stick together and strengthen attachment.

Kissing is more useful than sex in accomplishing this in an established relationship.