Remember that guy you snogged randomly in the street? While your friends might be still ribbing you about it, be comforted in the knowledge that you were actually taking part in an ancient primal ritual to determine whether they make a suitable partner.
New research has revealed that when two people kiss, it allows each individual to assess the other through taste or smell.
The signals kissing provides may provide biological cues for compatibility, genetic fitness, or general health, scientists believe.
"Kissing in human sexual relationships is incredibly prevalent in various forms across just about every society and culture," said psychologist Rafael Wlodarski, from Oxford University, who led the study of 900 people.
"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."
However, men and women don't necessarily view kissing in the same way.
HuffPost UK Lifestyle spoke to Suzi Godson, sex columnist for The Times, who said: "Research suggests that women use kissing as a mate assessment device and as a means of initiating, maintaining, and monitoring the current status of their relationship with a long-term partner. In contrast, males place less importance on kissing, especially with short-term partners, and appear to use kissing to increase the likelihood of having sex (Hughes et al 2007). Yep, I could have told them that too."
The survey responses showed that men and women who rated themselves as being attractive, or who tended to have more short-term relationships and casual encounters, also saw kissing as more important.
Previous studies have shown women tend to be more selective than men when initially choosing a partner.
Both men and women who are more attractive, or have many casual partners, are also known to be extra picky when looking for a long-term potential mate.
Since, according to the survey, both groups also place a high value on kissing, it suggests that kissing may help in mate assessment.
Co-author Professor Robin Dunbar, from the Department of Experimental Psychology at Oxford University, said: "Mate choice and courtship in humans is complex. 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.
HuffPost UK Lifestyle blogger The Guyliner commented: "Kissing is vital in any relationship. While a gentle squeeze on the arm or the arse can remind your partner you care, a kiss on the lips – even if it's a quick peck in the supermarket – is internationally understood shorthand for intimacy.
"You have to really mean it, or your lacklustre kiss gives you away. Being denied a kiss is like ordering a full English only to find, instead of bacon, there's a small stone in its place. And you're expected to chew your way through it."
"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."
But what do you do with a bad kisser? Suzi advises: "Adolescents may be able to forgive the crash of dental braces, the odd remnant of egg mayonnaise or indeed, lizard tongue, but encountering bad kissing as an adult is the ultimate turn off. Sadly, there is not much you can do to correct it. I can't think of a good way to tell a person that they are a bad kisser without humiliating them. There is someone for everyone and chances are, your bad kisser is someone else's perfect snog."
The study also found that the significance of kissing changed according to the type of relationship people were in or seeking.
Women rated it as especially important in long-term relationships, suggesting that kissing also plays a key role in maintaining attachment between established couples.
While high levels of arousal might result from kissing, the researchers say sex does not appear to be the driving factor that explains why we kiss in romantic relationships.Suggest a correction