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A sailor and a nurse kiss in New York's Times Square as the U.S. celebrates the announcement of the Japanses surrender August 14 1945.Reuters

How do you like your kisses, wet or dry?

If you've never stopped to ponder the deep psychological ramifications of your answer, fear not: U.S. researchers are on the case.

They have discovered, in research published in last month's issue of Evolutionary Psychology, that a kiss is definitely not just a kiss.

Planting a wet one on your sweetie is, in fact, a deliberate step in a mating dance choreographed by millennia of evolution. According to the study of 1,041 college students at the University at Albany, men and women kiss for very different reasons - and we're hard-wired to prefer different techniques.

Women kiss to assess the commitment of a mate - is he really that into me? - while men kiss as a means to an end - let's get it on. The study determined that men like their kisses wetter and with more tongue: To be precise, 33 per cent wetter and with 11 per cent more tongue, on average, than women do.

Blame our differences not on Mars and Venus, but on evolutionary history, researchers say. Women use kissing as pre-sex screening to determine whether their partner is healthy and sufficiently bonded to stick around for the long haul of child rearing. Men's biological imperative tells them to hit it and quit it, the better to share their DNA with more lucky ladies.

"From an evolutionary perspective, the costs and consequences for reproduction are dramatically different for females and males," says Gordon Gallup, a psychology professor at the University at Albany, State University of New York, who co-authored the study.

"Insemination is the name of the game for males, while insemination is the mere beginning of the reproductive process for females. So females put a lot of emphasis on making judicious mate choices."

Of course, college students aren't thinking about judicious mate choices when they grab someone cute to snog at last call. But evolutionary habits die hard, researchers say.

"This all happens on a very subconscious level," says study co-author Susan Hughes, an assistant professor of psychology at Albright College in Pennsylvania.

She acknowledges that what's true for college students may not hold for older adults; but, she notes, college students are in their reproductive prime, from an evolutionary if not an emotional standpoint.

Women in the study rate kissing as more important than men do at all stages of a relationship. Men are much more likely to skip to the main event: 53 per cent said they would have sex with someone without kissing, compared with only 15 per cent of women. Men are also much more likely to have sex with someone who's a bad kisser.

Nice-looking teeth and lips figure strongly in women's decision whether to kiss someone, and their kissing partner's breath and mouth taste is important. Men, meanwhile, are more concerned with their potential partner's body shape and weight, and they say a good kiss includes their partner making moaning noises.

"At the moment of a kiss, there is an exceedingly rich and complex exchange of postural, tactile and chemical cues," the study says.

Men may have an ulterior motive for preferring wetter kisses, Dr. Gallup says. Swapping spit involves an exchange of hormones, and one hormone in male saliva is testosterone, which increases female arousal, thus increasing the chances for sex.

One thing men and women seem to agree on: Kissing can nip a relationship in the bud as easily as it can spark a romance.

A separate survey conducted by Dr. Gallup found that 59 per cent of men and 66 per cent of women said they'd lost attraction for someone after kissing them for the first time.

"A kiss can't make a relationship, but clearly the evidence shows it can break or kill a relationship," Dr. Gallup says.

Does scientific analysis suck the romance out of kissing?

Smooch expert Michael Christian thinks so.

Sure, men's and women's kissing styles differ, but "there are more similarities than differences," says Mr. Christian, who wrote The Art of Kissing under the name William Cane. He thinks the psychology researchers may have overlooked one obvious motivation for puckering up: It's pleasurable.

"We all experience oral pleasure," Mr. Christian says. "That's one of the greatest things uniting people all over the globe. They enjoy it because it feels good."

Still, Mr. Christian can't argue with the statistics collected by the University at Albany researchers. The No. 1 complaint he hears from women is that men kiss with too much tongue, and men's No. 1 complaint is that women don't use enough tongue.

Mr. Christian complains that an evolutionary approach tends to unfairly paint women as the romantic ones and men as sex-crazed, when in reality it's a bit of both.

"Men also get romantic pleasure and connection from kissing, and both men and women will use kissing to advance to more intimate sexual acts," Mr. Christian says. "... We're all sensitive people - Marvin Gaye said that, and he was right. Women have a sexual side that's very powerful as well."

For Dr. Gallup and his study co-authors, romance is just another evolved courtship strategy. As for that fluttery feeling you get when you kiss your beloved?

"The romance is an evolutionary cue that prompts and leads to the creation of pair bonds that are absolutely crucial to the survival of the young," Dr. Gallup says.

Kissing research remains in its infancy, Dr. Hughes says. Despite humanity's never-ending interest in relationships and sex, the reasons and methods for kissing seem to have escaped scientific scrutiny, until now.

"This is among the first studies that has really looked at it from this perspective," Dr. Hughes says. "It's shocking there hasn't been more investigation."


Smooching styles

Men and women kiss for different reasons and prefer different techniques, according to a recent study of more than 1,000 college students. More men than women think kissing will end a fight, and men are more likely to have sex without kissing. When they do pucker up, men prefer their kisses wetter and with more tongue. Researchers say our evolutionary history explains why we make out the way we do.


KISSING AND SEXUAL BEHAVIOUR: The percentage of participants who said they would have sex with someone without kissing:

Men: 52.8%

Women: 14.6%


KISSING AND RECONCILIATION: When it comes to kissing as a form of reconciliation, the percentage that thought kissing a romantic partner could end a fight:

Men: 70.1%

Women: 58%


SALIVARY EXCHANGE: Respondents were asked how "wet" they preferred their kisses when kissing a short - or long-term partner, where responses were scaled as 0 = totally dry, 1 = slightly moist, 2 = somewhat wet, 3 = very wet and 4 = extremely wet.

Men: average preference = 1.83 %

Women: average preference = 1.38%


TONGUE CONTACT: Participants were asked to indicate their preference for tongue contact during a first kiss (based on a Likert scale of 0 = no tongue and 4 = a lot of tongue).

Men: average preference = 2.49%

Women: average preference = 2.09 %



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