The meeting of lips may feel harmonious, but it isn't. Men are always pushing to make kisses sloppier, while women always want to keep at them long after the show's over. And kissing style isn't the only point of contrast: In light of recent findings by psychologists, a kiss shared between a man and a woman seems more like a clash of spirits than a meeting of souls.
"Women tend to use kissing to create a bond with their partners, and to assess them as potential mates," Susan Hughes, a psychologist at Albright College in Pennsylvania, told Life's Little Mysteries. "Meanwhile, men use kissing as a means to an end." That end being sex. "Males are kissing primarily to increase arousal for their partner," Hughes said.
Those statements may strike some as obvious and others as old-fashioned, but regardless, they're scientifically proven. Hughes and her colleagues published a study in the journal Evolutionary Psychology three years ago that helped test, and prove, several theories evolutionary psychologists have long held about kissing. The researchers probed the kissing preferences and opinions of more than 1,000 males and females in their sexual prime — college undergraduates — who were asked to mark their answers to a series of detailed kissing questions on a 5-point scale.
The results showed that both men and women consider kissing an important and highly intimate interaction. Both sexes use kissing to gauge the relationship compatibility of themselves and their partners. Furthermore, both may become more or less attracted to their partners based solely on their experience kissing them, a result that lends support to the theory that pheromones and other important biochemical signals get exchanged when people kiss.
But the similarities end there. While women usually consider a bad kiss to be a deal-breaker, men reported that they would more than likely still have sex with a woman even if she were a bad kisser. In other words, biochemical cues be damned!
In fact, the data showed that males feel much more strongly that kissing should lead to sex than females do, period. "Whereas females felt there was a greater likelihood that kissing should lead to sex with a long-term partner than a short-term partner, males felt that in either instance, kissing should lead to sex," the researchers wrote in their article.
Men also like significantly wetter kisses. The gender divide becomes drastic when the kissing involves short-term partners, who presumably hold primarily sexual rather than romantic appeal. In the short-term, men like kisses to be wet, while women do not. Psychologists hypothesize that males "perceive a greater wetness or salivary exchange during kissing as an index of the female’s sexual arousal/receptivity, similar to the act of sexual intercourse," Hughes wrote.
Follow-up research conducted by Helen Fisher, an anthropologist at Rutgers University, in 2009 even found that men pass testosterone to women via their saliva, which may momentarily increase the women's sex drive.
Perhaps more surprising than the fact that men like sloppy kisses is that "they'll even forgo kissing altogether if they can just have sex," Hughes told Life's Little Mysteries. Indeed, Hughes' survey found that over half of men would be willing to have sex with someone without kissing them, while only 14 percent of women would do so.
Sheril Kirshenbaum, a science journalist, extended that finding to adult men and women for publication in her book, "The Science of Kissing" (Grand Central Publishing 2011). She found that guys really don't grow out of their indifference to kissing: As in Hughes' survey, the adult men in her survey did more often than not express a willingness to have sex without kissing. Meanwhile, "Several women actually called or e-mailed asking why they'd even be in that situation in the first place," Kirshenbaum wrote. Two women asked if the survey question was referring to prostitution.
The gender divide is indeed dramatic; it even extends to when men and women like to kiss. "Basically, most men don't like to kiss after sex," Hughes said. "This is even true of men in long-term, committed relationships, which we thought was a bit surprising." Though men typically want to kiss only until the sex starts, women like kissing before, during and after intercourse.
Why all the differences? "From an evolutionary perspective," Hughes explained, "females are limited reproductively, so they want to bond with a mate, whereas males can have a lot of partners and so are generally more interested in having promiscuous sex. Both use kissing to get what they want."
In summary, women use kissing as a screening tool — to find a man with the right pheromones. Then, when a good mate is found, kissing is used to increase mutual feelings of attachment. Men, on the other hand, kiss primarily to gain sexual access.
A great kiss, then, by no means results from great minds thinking alike.
This article was provided by Life’s Little Mysteries, a sister site to LiveScience.com.
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Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.