Kissing helps people to assess potential partners and maintain affection and attachment in long-term relationships.
Oxford University researchers looked at the importance of kissing to try to establish its purpose to relationships, in both short-term and long-term relationships.
An online questionnaire devised by researchers Rafael Wlodarski and Robin Dunbar received 900 adult responses.
Wlodarski said: "Kissing in human sexual relationships is incredibly prevalent in various forms across just about every society and culture. 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."
He explained there are three theories about the purpose of kissing. That it helps assess genetic quality of potential partners, that it increases arousal and that it keeps relationships intact.
"We wanted to see which of these theories held up under closer scrutiny," he said.
In short term-relationships, kissing was more important before sex, less so during sex, was less important again after sex. In long-term relationships, kissing was equally important before sex as at times not-related to sex, suggesting it is a means of maintaining the relationship.
Waiting for Mr Darcy
Findings showed that in general, women rated kissing as more important than men. It was also considered more important to people who considered themselves attractive, or who had more short-term relationships.
The researchers say women likely place more importance on kissing because they have to invest more time than men in having children, so tend to be more selective when picking a partner.
In people who consider themselves attractive, they may feel they have more options so are waiting for their "Mr Darcy", the researchers suggest. It has previously been suggested that kissing allows people to pick up on biological cues for compatibility, fitness and health through taste and smell.
Dunbar 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.
"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 women 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 choosey 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."