The state of the kiss, 2009

OK, so: kissing. Here's what we know.

It has major evolutionary advantages. Only the hottest and highest species do it.

Yet among current humans, the future of kissing seems an open question. In our liberated era, have we become so quick to get past the kiss and further into lovemaking that we have devalued the icons, wisdoms, and traditions of the ancestors? Have we diminished the meaning and memory of the lingering smooch?

If so, this is a horrifying situation. Kissers of the world, unite.

"A kiss is a blast of information that you are sending out and information that you are receiving," says Helen Fisher, the Rutgers anthropologist who is the author of Why We Love: The Nature and Chemistry of Romantic Love.

"Basically it's a mate assessment tool. Much of the cortex is devoted to picking up sensations from around the lips, cheeks, tongue and nose. Out of 12 cranial nerves, five of them are picking up the data from around the mouth. . . . So kissing is not just kissing. It is a profound advertisement of who you are, what you want, and what you can give."

Gordon Gallup, a professor of evolutionary psychology at the State University of New York at Albany, says there are hard-wired mechanisms during a kiss that assess health, reproductive status, and genetic compatibility.

"Therefore, what happens during that first kiss can be a make-or-break proposition."

For example, a woman can sense whether the man's immune-system proteins are different from hers, thus increasing the odds of healthy offspring. "Women apparently are quite drawn to men who have differences rather than similarities in their histocompatibility system. They pick it up by smell, and they can pick it up from kissing," says Fisher, who is also science adviser to Chemistry.com, a division of Match.com.

Kissing thus not only conveys evolutionary advantage. It also can dramatically alter the outcome of Saturday night.

A survey of 1,041 college students led by SUNY Albany's Gallup found that 59 percent of men and 66 percent of women reported at least once finding someone attractive only to discover after the first kiss that they weren't.

"I think we have evolved three distinctly different brain systems for mating and reproduction," Fisher says. "One is the sex drive. The second one is romantic love - that elation, the craving, the obsessive thinking - and the third is attachment, the sense of calm and security you can feel with a long-term partner." And it all starts with kissing.

OK, but if kissing is all that important, why has kissing lost its iconic status? Why, according to the giant Gallup survey, do 52.9 percent of men and 14.6 percent of women feel they can readily skip the smooch and dive right into the sack?

The meaning of a kiss has varied over the centuries. St. Paul told us to "salute another with a holy kiss." That rapidly got out of hand. "By the high Middle Ages, the 'holy kiss' was given or exchanged in Christian rituals of baptism, ordination, the consecration of bishops, coronations, absolution of penitents, and in the marriage ceremony," historian Craig Koslofsky told New Scientist. During the Reformation, Protestants found all this public kissing treacherous.

Nonetheless, public displays of affection in England 400 years ago remained bold even by our standards.

Foreign visitors commented on women of the household greeting strangers with a kiss on the mouth.

Compare that with today. In some quarters, you can't pay to get kissed. As a rule, prostitutes avoid it specifically because it connotes attachment and intimacy.

There is still plenty of ritual kissing. The pope's ring. The cup at Wimbledon. The Blarney Stone. The dice.

There are also therapeutic kisses - on a boo-boo to make it better. Kisses of death - The Godfather. The chivalrous hand kiss, the Hollywood air kiss.

Kisses used to be iconic. Rodin's statue. The sailor and the nurse in Times Square at the end of World War II. Lady and the Tramp.

The memorable kisses of this young century, by contrast, are mainly those that are remarkable for examining the edges. Think Brokeback Mountain. Or Madonna and Britney.

Popular music really knows how to make the meaning of kissing seem quaint beyond superfluous. This is not to say that kissing is history just because pop lyrics have come a long way since "I Want to Hold Your Hand," notes Joe Levy, editor in chief of Blender, a music magazine whose readership skews young. "I'm not sure because we're talking about it less in pop lyrics, it happens less or is less important," he says. "What used to start with a kiss still starts with a kiss. You just hear exactly where it went after that."

About two-thirds of all humans, male and female, tilt their heads to the right when kissing. It does not matter whether they are left- or right-handed.

Men think kissing is a highly effective way to end a fight. Women think that's hooey. For once, the women are incorrect. "The evidence shows," evolutionary psychology professor Gordon Gallup says, that "kissing is so powerful for females that even though they deny it, once it occurs, they're so affected by a kiss ..." That they're helpless in its grip? "Yup."

Remember those great standing kisses in old movies, where the girl demonstrates ecstasy by lifting her delicately shod tootsie behind her? That move was called a "foot pop."

The science of kissing is known as philematology.

More men than women describe a good kiss as one that involves tongue contact, saliva exchange, and moaning.

After a relationship is established, women are much more likely than men to use kissing to monitor the commitment. "There is good evidence that the frequency of kissing is a pretty good barometer of the status of a relationship," Gallup says.

Kissing, of course, is not all moonlight and roses. It is implicated in the spread of mononucleosis and oral herpes. The connection to meningitis and gastric ulcers is more distant but exists.

The hormonal and neurotransmitter cascade triggered by kissing includes adrenaline (which increases heart rate), endorphins (which produce euphoria), oxytocin (which helps development attachment), serotonin (which affects mood), and dopamine (which helps the brain process emotions). Your heart rate increases, your blood vessels dilate, your body receives more oxygen. Your earlobes swell.

When kissing, cortisol levels drop for both sexes, meaning that kissing does in fact reduce stress. During kissing under laboratory conditions, oxytocin rises for males but unexpectedly drops for females. Neuroscientist Wendy Hill speculates this means that to bond, females may require a more romantic atmosphere than the experimental setting provided. Hill presented a paper Saturday at the American Association for the Advancement of Science annual meeting titled "Kissing Chemicals: Hormonal Changes in Responses to Kissing."

Very few creatures other than humans are great kissers. The marked exceptions are our close relatives the chimpanzees and bonobos.

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