What's in a kiss? A study by Oxford University researchers suggests kissing helps us size up potential partners and, once in a relationship, may be a way of getting a partner to stick around.
'Kissing in human sexual relationships is incredibly prevalent in various forms across just about every society and culture,' says Rafael Wlodarski, the DPhil student who carried out the research in the Department of Experimental Psychology at Oxford University. 'Kissing is seen in our closest primate relatives, chimps and bonobos, but it is much less intense and less commonly used.
'So here's a human courtship behaviour which is incredibly widespread and common and, in extent, is quite unique. And we are still not exactly sure why it is so widespread or what purpose it serves.'
To understand more, Rafael Wlodarski and Professor Robin Dunbar set up an online questionnaire in which over 900 adults answered questions about the importance of kissing in both short-term and long-term relationships.
Rafael Wlodarski explains: 'There are three main theories about the role that kissing plays in sexual relationships: that it somehow helps assess the genetic quality of potential mates; that it is used to increase arousal (to initiate sex for example); and that it is useful in keeping relationships together. We wanted to see which of these theories held up under closer scrutiny.'
The researchers report their findings in two papers, one in the journal Archives of Sexual Behavior and the second in the journal Human Nature. They were funded by the European Research Council.
The survey responses showed that women rated kissing as generally more important in relationships than men. Furthermore, men and women who rated themselves as being attractive, or who tended to have more short-term relationships and casual encounters, also rated kissing as being more important.
In humans, as in all mammals, females must invest more time than men in having offspring - pregnancy takes nine months and breast-feeding may take up to several years. Previous studies have shown women tend to be more selective when initially choosing a partner. Men and women who are more attractive, or have more casual sex partners, have also been found to be more selective in choosing potential mates. As it is these groups which tended to value kissing more in their survey responses, it suggests that kissing helps in assessing potential mates.
It has been suggested previously that kissing may allow people to subconsciously assess a potential partner through taste or smell, picking up on biological cues for compatibility, genetic fitness or general health.
'Mate choice and courtship in humans is complex,' says Professor Robin Dunbar. 'It involves a series of periods of assessments where people ask themselves "shall I carry on deeper into this relationship?" Initial attraction may include facial, body and social cues. Then assessments become more and more intimate as we go deeper into the courtship stages, and this is where kissing comes in.'
He adds: 'In choosing partners, we have to deal with the "Jane Austen problem": How long do you wait for Mr Darcy to come along when you can't wait forever and there may be lots of you waiting just for him? At what point do you have to compromise for the curate?
'What Jane Austen realised is that people are extremely good at assessing where they are in the "mating market" and pitch their demands accordingly. It depends what kind of poker hand you've been dealt. If you have a strong bidding hand, you can afford to be much more demanding and choosy when it comes to prospective mates.
'We see some of that coming out in the results of our survey, suggesting that kissing plays a role in assessing a potential partner,' Professor Dunbar explains.
Past research has also found that women place greater value on activities that strengthen long-term relationships (since raising offspring is made easier with two parents present).
In the current study, the team found that kissing's importance changed for people according to whether it was being done in long-term or short-term relationships. Particularly, it was rated by women as more important in long-term relationships, suggesting that kissing also plays an important role in mediating affection and attachment among established couples.
While high levels of arousal might be a consequence of kissing (particularly as a prelude to sex), the researchers say it does not appear to be a driving factor that explains why we kiss in romantic relationships.
Other findings included:
Notes to Editors
In total, just over 900 adults aged between 18 and 63 took part in the online survey, with around 55% in a long-term relationship at that time. 308 men and 594 women answered questions like: 'How important do you think kissing is at the very initial stages of a relationship?' or 'How important do you think kissing is with a committed long-term partner immediately before sex/during sex/after sex/at all other times?'
The researchers began the work by considering that there could be three possible functions for kissing: it plays a role in assessing a potential mate, it could mediate the attachment felt between established couples, and it could be important in raising levels of arousal leading to sex.
They used differences between men and women, in being in short- or long-term relationships, and with people who might be more attractive or tended to have more relationships, to tease out which of these hypotheses might best explain why we kiss.
They explain the patterns of people's survey responses fit with the first two hypotheses but there is little evidence that arousal is an important driver for why we kiss, although it could well be a consequence of kissing.
Oxford University's Medical Sciences Division is one of the largest biomedical research centres in Europe, with over 2,500 people involved in research and more than 2,800 students. The University is rated the best in the world for medicine, and it is home to the UK's top-ranked medical school.
From the genetic and molecular basis of disease to the latest advances in neuroscience, Oxford is at the forefront of medical research. It has one of the largest clinical trial portfolios in the UK and great expertise in taking discoveries from the lab into the clinic. Partnerships with the local NHS Trusts enable patients to benefit from close links between medical research and healthcare delivery.
A great strength of Oxford medicine is its long-standing network of clinical research units in Asia and Africa, enabling world-leading research on the most pressing global health challenges such as malaria, TB, HIV/AIDS and flu. Oxford is also renowned for its large-scale studies which examine the role of factors such as smoking, alcohol and diet on cancer, heart disease and other conditions.
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