Science Interviews


Tue, 15th Oct 2013

Why do people kiss?

Rafael Wlodarski, University of Oxford

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Oxford researcher Rafael Wlodarski has been quizzing people about their kissing habits and what it actually means to them.  kissChris Smith spoke to Rafael to find out more.

Rafael -   Hello.  How is it going?

Chris -   Very well, thank you.  Why on Earth did you do this?

Rafael -   Well, itís a fascinating topic.  I think you probably agree.  Kissing is quite interesting and itís one of those behaviours in courtship rituals that is actually surprisingly common across most of the worldís cultures in various different forms.  If we find something usually that's this common and usually, not the most safest thing to do to approach a stranger and exchange microbes and so forthÖ

Chris -   Indeed.  There was another website thatís describe kissing as a biological biohazard Ė putting yourself at considerable risk of exposure to all kinds of microbes and viruses.

Rafael -   Thatís exactly right and if people overcome these fears and manage to do this on such a regular basis and then there's usually must be some kind of reason for it.  So, we try to figure out if we could find any supporting evidence to sort of figure out if kissing serve some kind of function in the mating ritual of humans.

Chris -   How did you do this?  Presumably, not by kissing loads of people.

Rafael -   No, that would be very complicated.  Now, we had to go in a very roundabout way as you can imagine with the sort of sensitive topic.  So, we had a very large survey of over 900 people from 20 countries that we put out into the wild, asking people about their sort of general attitudes towards kissing and to different partners in short term, long term situations, and so forth.  And we also took a lot of information about individual variables Ė so obviously, their gender, how attractive they were, at the variables to do with their sexual history.  What we did was when we looked at these answers and we went to see how they correlated with other factors that we know correlate with certain behaviours, so what we ended up finding was that individuals that have previously been shown to be extremely selective when it comes to choosing a mate.  Particularly, when it comes to genetic quality were also individuals that thought kissing was extra important at the beginning stages of their relationship.

Chris -   So, in other words, if someone is really fussy, if they say, ďI donít just kind of go down the pub and pick up the first person who sort of winks at meĒ then they set greater store by a kiss.

Rafael -   Yeah, I mean, this wasnít a self-report thing,  we didnít ask people, ďAre you fussy?  Are you not?Ē  I imagine most people would consider they're fussy on some level, but what we did was we looked at, for example, females have previously been shown again and again to be more fussy.  So, we just asked them their gender.  We also asked them to rate their own attractiveness and past researchers found that even though everyone thinks they're more attractive than average, there's actually people who are very good at rating how attractive they are in the whole mating market.  So, the more attractive you are, sort of the more resources you have to offer and the more chance you have to be picky and so obviously, you'll be more selective. So, those individuals in the past have been shown to be much more selective when it comes to choosing mates. 

And also, individuals who are interested in short term relationships who preferred to judge potential partners solely on physical characteristics and sort of good quality genetic traits.  All those three individuals were more likely to sort of say that kissing is really important in early stages and all three of those types of individuals were also much more likely to say that their attraction had changed to an individual after they had kissed them for the first time.  Whereas people who are less fussy said that this wasnít usually the case.  So, itís a roundabout way to try and tease out whether kissing might play a role in this stage.  We also managed to sort of find support for the idea that kissing is also used as a secondary function in long term relationships, sort of keep relationships intimate and bonded.

Chris -   What about the menstrual cycle because weíve seen a number of publications in recent years showing that womenís attractiveness to men, menís behaviour towards women, and womenís behaviour towards men definitely changes menstrually, specifically when they're more likely to fall pregnant at certain times of the month?  So, does the kissing get ranked differently at different times of the month?

Rafael -   Exactly.  So, this was after Ė we had two papers.  The first paper was just a sort of analysis of this major survey and the second paper was a subanalysis, looking at womenís menstrual cycles and whether their opinion of kissing change close to menstrual cycle.  And very interestingly, and for us, not that surprisingly, but itís got a good piece of corroborating evidence, what we found is that these women at the stage of the cycle where they're most likely to fall to conceive or to fall pregnant, at that stage, they thought kissing was much more important than other stages of the cycle.  Again, only at the initial stages of a relationship.  Again, sort of more corroborating evidence suggesting that these women who are extremely fussy at this stage of their relationship and also, very selective in terms of genetic quality of a potential mate at that same time is when they also valued kissing the most.

Chris -   What do you think you can learn from a kiss that you can't learn just by talking to someone or going out to dinner with them?

Rafael -   Yeah, itís a good question.  We didnít specifically obviously examine this, but I think based on what we know about sort of human mating rituals, I think the most likely scenario is that there's ceremonial cues being exchanged.  Ever since the Ď70s, there's been considerable research showing that human beings are actually quite adept at assessing the genetic quality and genetic compatibility even of mates based on MHC immunocompetence, solely based on smell alone.  And I think this is probably why kissing is such a great socially accepted way around the world of getting two individuals who otherwise wouldnít have an excuse to get extremely close to each other.  Itís a kind of a socially accepted way for two people to get close enough together to get that a little bit of extra information from pheromones that you just won't be able to get by having a chat on the bar or sort of winking over the end of the village sort of thing.

Chris -   Do you have to do the Ďfull-on television kissí as my kids would dub it in order to get that information or does the classic air kiss also?

Rafael -   No, I donít think you really do.  I mean, when I talk about sort of kissing, I talk about the most generalised form of kissing which really doesnít always necessarily involve sort of full mouth and tongue contact.  Itís a relatively recent invention.  But in many cultures, the most common form of kissing involves some kind of very close physical proximity and most interestingly, and the sort of thing that leads me to believe that pheromones are involved, a load of these cultures involve sniffing and inhaling. Like what we think of as the Eskimo kiss, which isn't really rubbing noses:  the actual custom involves placing your nose on someoneís cheek or their forehead and inhaling deeply.  That is the sort of the greeting thatís involved between romantic partners.

Chris -   Rafael, we must leave it there, but thank you for joining us.  Rafael Wlodarski from Oxford University.  Heís published that work this week in The Archives of Sexual Behaviour and also in the journal Human Nature.


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Why do we kiss? Easy. Because we can. :) Pmb, Tue, 22nd Oct 2013

a similar question ... RD, Tue, 22nd Oct 2013

Racing Pigeons kiss quite frequently, it last for about 5 seconds, and takes place after the cock bird indicates to the hen that he fancies a spot of sex with her, the hen signals her acceptance by bowing down slightly and shuffling herself towards him to have a quick snog. After the kissing takes place the hen then squats down and is treaded by the cock bird, following this sexual encounter they both strut about looking rather pleased with themselves and the cock bird often flies off for a celebration fly past around the pigeon loft. It may well be there is a connection between humans kissing and this act between birds.    Sherwood Forester, Sun, 5th Jan 2014

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