A US study has found women use kissing as a means to assess a relationship and its future while men appear to kiss in a bid to increase the likelihood of having sex.
The study found women place more importance on kissing and are more likely to evaluate their partner's kissing ability on factors such as the smell of their breath and the appearance of their teeth.
The study of more than one thousand students at the New York State University also found fewer women than men are willing to have sex without kissing their partners first.
Women also feel a bad kisser is less attractive.
The study published in Evolutionary Psychology found men are less discriminating when it comes to deciding who to kiss or who to have sex with.
Further findings show men tend to employ romantic kissing as a means of increasing sexual receptivity and gaining sexual access to affect conflict resolution and to possibly monitor the fertility of his mate.
Women meanwhile place a greater importance on kissing not only to make more judicious mate assessments but for those in committed relationships kissing is used to update monitor and assess the status of their partner's continuing commitment or lack thereof to the relationship
Fate of a couple is sealed with first kiss
It is a moment of high anxiety in any romantic relationship. But now researchers have found that the first kiss may be even more important than anyone suspected.
While a kiss may just be a kiss for a man, for a woman it's an all-important means of gauging a prospective partner's compatability. She uses it, the study suggests, to assess a "rich and complex exchange" of romantic and chemical clues that pass between partners as their lips touch.
A "good kiss" will help convince her that the partner is worth perservering with but a man who is judged to be a bad kisser is unlikely to find himself invited in for coffee.
In the longer term the woman treats kissing as a means to induce bonding and to help her assess whether her partner has remained faithful and interested.
For men the kiss is much less important. It might be a source of hormonal information but it's mostly regarded as a preliminary to sex. A man tends to regard a good kiss as one in which he's allowed to use his tongue and is rewarded with moans of pleasure, the study found.
Dr Gordon Gallup, of the University at Albany in the United States, said: "The information conveyed by a kiss can have profound consequences for romantic relationships, and can even be a major factor in ending one.
"While many forces lead two people to connect romantically, the kiss - particularly the first one - can be a deal-breaker."
The study, published in the online journal Evolutionary Psychology, suggests that clues to a person's health are passed on by kissing.
These clues are picked up and understood - consciously or unconsciousy - by the kissers but are more important to the female, the researchers said, because she is more interested in a long-term relationship compared with the man who is often an "opportunistic mater".
Women were more likely than men to take into account the smell of their partner's breath, the taste of their mouth and the state of their teeth during a kiss.
"Females place a greater emphasis on kissing for making mate assessments," the researchers reported. "Our data shows that females are more likely to base evaluations of their partner's kissing ability on chemical clues, ie, the breath and taste.
"This study provides evidence that romantic kissing may have evolved as an adaptive courtship strategy that functions as a mate-assessment technique, a means of initiating sexual arousal and receptivity, and a way of maintaining a bonded relationship."
Women were less than half as likely to have sex with a man without first enjoying a kiss, and the study also found they were less likely to tolerate the use of tongues on a first date.
By contrast, men showed themselves to be far less fussy and were much more likely both to continue to want sex even with a bad kisser or without bothering with a kiss.
Once a relationship was established, the researchers found, men grew less interested in kissing whereas women continued to give kisses a high priority. They were much more likely to kiss a partner after sex than men were.
Researchers made their findings after analysing three surveys of a total of 1,041 college students, most of them aged 18 to 25.
The study was conducted by academics from the University at Albany, the City University of New York and Albright College, all in the United States.
The Richard Gere/Shilpa Shetty kiss: made in Bollywood
Richard Gere kisses Shilpa Shetty. Photograph: Tanushree Punwani
The outrage in India over the Richard Gere/Shilpa Shetty kiss has a dreary predictability about it. Putting aside the fact that Gere was rather embarrassingly parodying his Shall We Dance? moves after Shetty complimented him on his performance in that film, this is a controversy that has its own history.
In 1980, actress Padmini Kholapure (who famously portrayed Raj Kapoor's teenage widow in the pioneering film Prem Rog) scandalised the nation by kissing Prince Charles on the cheek when he visited the country. Actress Shabana Azmi's "freedom kiss" planted on Nelson Mandela's cheek in 1993 inflamed the righteous once more. This latest story demonstrates with brutal clarity one difference between Holly and Bollywood. The celebrities of the west have the paparazzi snapping at their heels but Bollywood babes come under the judgment of the holier-than-thou crowd.
Give or take a song, the scenario itself has played out like a Bollywood storyline - two lone innocents representing common sense and human values battling against an unjust and repressive society. The furious activists, including those burning effigies of both actors, mainly hail from Hindu fundamentalist groups: Shiv Sena, and the rather sinister youth wing of the rightwing BJP. Both have appointed themselves the guardians of Indian womanhood against corrupt western influences.
Bollywood has long drawn objections from such folk; from the beehive hairdos of the 50s and 60s to the famously sexy cabaret numbers of the 70s, the "western" accusation has been flung about willy-nilly. From this comes the notion, once prevalent about actresses in the film industries of the west (and the theatre before that), and still commonplace in mainstream India, that the women of Bollywood are "modern" anyway; as distinguished from the good Indian girls of the real world.
But while kissing is rare, it isn't new to Bollywood fans. Pioneering smoochers go right back to the 30s, while a raunchier recent release, Khwaish, boasts no less than 17 lip-clinches.
Interestingly, independent Indian cinema and that of the diaspora is frequently filled with the kind of naughtiness that a general Bollywood formula excludes. Monsoon Wedding has adultery, half-naked kisses galore and even the odd cigarette. Hey Ram, an intriguing modern film about Indian independence which sketches a psychological portrait of a man who almost assassinates Gandhi, features songs accompanying sex on a balcony.
As the landscape of Indian cinema changes, more kisses arrive, along with more radical stories. It's when that fantasy spills out of the cinema screen into real life that the golden-robed rent-a crowd emerges.