KEY POINTS:
Valentine's Day is just around the corner and with it comes the promise of romantic outings, romantic presents and a lot of something many of us take for granted, kissing.
Ninety per cent of human cultures do it, but until recently no one really knew why.
It was generally accepted that the practice evolved from women chewing up food for their children and giving it to them by mouth.
However a study published in the online journal Evolutionary Psychology busts that myth.
Researchers Susan M. Hughes, Marissa A. Harrison and Gordon G. Gallup Jr. found that kissing is in fact part of an evolved courtship ritual.
"When two people kiss there is a rich and complicated exchange of information involving chemical, tactile, and postural cues," said Gallup.
"This may activate evolved mechanisms that function to discourage reproduction among individuals who are genetically incompatible."
Psychology students at the University at Albany in New York were the researcher's guinea pigs.
Using anonymous questionnaires, 1041 students were asked about their kissing history. Research participants who indicated they had never romantically kissed another person were excluded from the analysis.
Bad kissers, the study unsurprisingly concluded, are a real turn off. In fact 59 per cent of males and 66 per cent of females said they had been in a situation where their romantic interest in a person had waned following a "bad" first kiss.
"In other words," said Gallup, while many forces lead two people to connect romantically, the kiss, particularly the first kiss, can be a deal breaker."
The study's results indicate that, whether we like it or not, kissing is a way of establishing the likelihood of long-term romantic connection with another person.
Women were more likely to view kissing as an important part of a relationship, whereas men were more likely to view it as a pre-cursor to sex.
Hughes told The Washington Post women used kissing as a way to make an assessment about the person they were with.
"If he's a bad kisser, then she's not going to want to have sex with him. She's getting a lot of information from that kiss," she said.
Men, on the other hand, were found to be less critical of things like bad breath and indicated a preference for wetter kisses with more tongue contact.
However the importance of kissing as an indicator of reproductive capability was evident in the results for both sexes.
The researchers hypothesised that the male preference for open-mouthed, wet kisses allowed them to access subtle information about a female's reproductive status because a woman's saliva and breath odour is known to change across her menstrual cycle.
Male saliva also contains measurable amounts of the sex hormone testosterone which can affect libido.
Women were far less likely than men to engage in sex without kissing, and to become jealous if they discovered their partner had kissed someone else - regardless of whether the relationship was long- or short-term.
This indicates that women use kissing as a way to monitor the status of their relationship, and to assess and periodically update the level of commitment on the part of their partner.
However it appears men have taken the adage "a kiss will make it all better" more to heart than their female counterparts.
Seventy per cent of men said they thought kissing their partner was an appropriate way to reconcile following a fight, compared with just 58 per cent of women.
