The science of the smooch

Why mash our mouths together? An expert explains the evolutionary reasons for kissing, and why men like more tongue

Published January 19, 2011 1:30AM (EST)

close up portrait of young caucasian couple kissing (Serg Zastavkin)
close up portrait of young caucasian couple kissing (Serg Zastavkin)

Let's be honest, a kiss is never just a kiss. It is the ultimate romantic symbol in our culture -- from Shakespearean tragedies to Gustav Klimt's gilded embrace to the legendary V-J Day smooch in Times Square to those critical words "you may kiss the bride." Sometimes it's instead an expression of affection, elation, loyalty or, on the other hand, disloyalty (see: the kiss of Judas). In cruder manifestations -- take Britney and Madonna's lip smacking, and the tonsil hockey of modern reality television -- it's a way to scandalize. But despite this breadth of meaning, we have very rigid ideas of what types of kissing are appropriate and acceptable -- as Stephanie Seymour recently discovered after photos circulated of an ocean-side embrace with her son.

This rich cultural history makes kissing seem so natural as to be fairly unremarkable, which is why many readers will greet the new book "The Science of Kissing: What Our Lips Are Telling Us" with skepticism. How much is there to say about locking lips, anyway? A whole lot, it turns out. Sheril Kirshenbaum, a research scientist at the University of Texas at Austin, gives an engaging overview of the possible evolutionary basis for two people mashing their mouths together -- a practice that is actually pretty odd, once you think about it. There's the way sexy red lipstick plays on our hunter-gatherer past, how swapping spit can help us develop immunity against disease and why it might have first developed as a way to literally sniff out genetically appropriate sexual partners.

That's not to mention the tremendous variety in kisses the world over -- from the Eskimo to the French variety -- and that's just in the human world (bonobos, for example, will suck on each other's tongues for as long as 12 minutes). Salon spoke with Kirshenbaum about how our lips are "genital echoes," the natural high of making out with a longtime crush and how technology will change kissing.

What is it about lips, why are we so drawn to them?

There are several theories. For starters, psychologists will tell you that red grabs our attention. I spoke to a neuroscientist and he thought it might have something to do with our ancestors looking for ripe fruit. Those that could detect the color red could find food the fastest and they had an advantage and survived to pass on their genes, and that might be why we notice the color red.

Red became pronounced in different areas of the body, and it became a sexual cue over time. Certain parts of the female anatomy, especially with our primate ancestors, were enhanced with red, and it especially had to do with the female being ready to reproduce. As our ancestors began to walk upright, rather than males being attracted to the female's posterior, they began to focus on the breasts and the lips -- they call this "genital echoes." In research on lip color, men consistently choose the women wearing the bright red lipstick as the most attractive -- there's this power to making the lips slightly redder. There's a lot of evidence to back up the existence of the makeup industry.

Much to my surprise, you make a connection between kissing and breast-feeding. Can you explain that?

Nursing is a very pleasurable activity. The lips are so sensitive to stimulus, and the hormone oxytocin, which is involved in social bonding and attachment, is stimulated in the infant and the mother during nursing. We start to associate this bonding with lip pressure. As adults, when we kiss there's this rise in oxytocin, which is so important in new relationships and in maintaining relationships. Nursing is very important in putting those neural pathways in place. When our lips are stimulated later in life there are these associations with those early experiences.

What about non-romantic kissing?

It's a really powerful means of expressing yourself. All of our senses are engaged in the behavior. Traditionally, scent was so important in terms of recognizing our friends and family members. In prehistory they were using scent to recognize each other and assess the health of someone. Social kissing probably evolved from a sniff to cheek kissing. It's one of the most powerful things we can do to connect with another individual.

How do kissing styles vary from culture to culture?

The mouth-to-mouth kiss that we recognize is definitely not the only universal style of kissing. Charles Darwin wrote about this: He suspected that if you talk about kissing in terms of touching the lips to any body part, and even behaviors like licking and blowing, then it's probably a universal practice.

Traditionally, many cultures around the world didn't mouth-to-mouth kiss. It was probably not the same experience before there was mouthwash [laughs]. I went into all these historical accounts written in the 1800s, mostly by European explorers. There's this great anecdote where an explorer goes to Africa and falls in love with the daughter of an African king, and one night he's brave enough to kiss her. She reacts by screaming and running from the room. He realizes later that she thought he was planning to eat her.

Has kissing changed much over time? Do certain styles of kissing come into fashion?

Well, I love the French kissing story. It turns out that when people were traveling through Europe, there was this notion that women in France were more openly affectionate. There became this saying: "While in France, get the girls to kiss you." That sort of evolved to be: "Get a French kiss." But in France they don't call it that, they call it a "tongue kiss" or a "soul kiss," because it's supposed to feel like two souls merging.

What happens physiologically when we kiss?

A lot. It depends on the kind of kiss, of course. If you're talking about a good kiss, our pulse quickens and our pupils dilate, which is probably part of the reason we close our eyes. There's also a rise in dopamine, which is responsible for the craving and longing, that can't-wait-to-be-with-you sensation. It's also stimulated by a lot of recreational drugs like cocaine; kissing sends us on a natural high. Dopamine spikes from really longing for something for a while and then getting it. When we've been dreaming about someone for a long time and then finally get it, dopamine is involved.

Serotonin causes obsessive feelings about someone. It's also the same neurotransmitter involved in people with obsessive-compulsive disorder. It sounds a lot like the symptoms of falling in love. Everyone loves to talk about sex, but kissing is probably the most intimate activity we can engage in. Look at the history of prostitution -- prostitutes won't kiss their johns because they don't want to get their emotions involved. And, overall, johns aren't that anxious to kiss their prostitutes either.

There's a strong gender divide in how we view kissing, isn't there?

Absolutely. There's a huge gender divide. In one large study of college-age students, strong patterns emerged: Women were constantly complaining about too much tongue and men were saying, "I really like wet kisses, lots of saliva!" The guys were usually eager to foray into sex without kissing and very few women were. Women paid a lot more attention to the teeth and breath of the person. Men tended to say they would consider starting a relation with someone just because they were a good kisser, and women were not that way. The act of kissing has a lot more significance for women than men. Men tend to report that kissing is a means to an end; women tend to try to figure out what the kiss means about their relationship, what it says about how their partner feels toward them.

Why might this be?

I started getting really frustrated by these findings, because I felt the results were very stereotypical. So I got together 80 of my own friends and acquaintances, and I was pretty shocked to see that they fell almost completely in the same pattern. When you start looking at reproductive strategies, it makes sense: A woman puts a lot more investment into the [sexual] decisions she makes, because she is fertile for a much shorter period of time each month, and a man can theoretically inseminate countless women throughout his life. Women are a lot more sensitive to smell and taste, which can tell a lot about a partner's health and reproductive capacity.

There's a great study looking at attraction and scent. It turns out that women are able to identify men who have a very different genetic code from their own, and they tend to be more attracted to them, because if they mate, their children would be healthier and stronger and more likely to survive because of the diversity in their genetics. Interestingly enough, women who are taking the birth control pill seem to have the opposite reaction. They're more attracted to men with genetic immunities similar to their own. It starts to make you wonder what all these hormones that we take are starting to do to our bodies and whether they're masking these signals that we've developed over thousands and thousands and thousands of years. I came across some pieces asking, "Is it possible that for some couples divorce is a result of the woman going off hormones and all of a sudden feeling less attracted to her partner?" It's certainly an important question to ask.

What can we expect from the future of kissing?

There are robots that are very eerily lifelike and starting to be able to kiss each other -- it's pretty convincing when you see the actual video. In terms of virtual reality, it might be possible that it could feel like you're kissing your idealized partner or celebrity.

Just last year, a robot debuted called Roxxxi. She's supposed to be the first sex robot. I called up the company and spoke to the engineer because I wanted to know whether she could kiss. His response was, "No, but her mouth is one of three inputs." It turns out kissing was not something they had programmed in. At the time they were about to debut their robot geared toward women and, given all this psychological research, it might be something that women clients would be more interested in seeing.

Speaking of technological changes, what about online dating -- how is it changing the courtship process?

Many of my friends were going online looking for love just as I was learning about all these important cues other than what we see in a profile -- things like voice and touch and smell taste. We are flying blind when we're dating online. We're only able to see a photo and a carefully worded profile. You might invest a lot of time getting to know someone and it might be imminently obvious when you're actually in the same room that it's star-crossed, or you might pass over someone who might have seemed ideal if you'd been in the same room together. A kiss just tells you so much more than a poke or a wink -- or whatever it is, depending on the service you're using. I've been calling it nature's litmus test.

By Tracy Clark-Flory

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