international-kissing-day Romantic kissing is one of those things that come to us “naturally.” Kissing between romantic partners is universal among humans and is documented in over 90 percent of human cultures throughout the world (Fisher, 1992). Even in those cultures where kissing is non-existent or chastised, partners still blow, lick, sub or rub each other’s faces before the intercourse takes place (Ford and Beach, 1951).

Evolutionary psychology researches investigate various types of human sexual behaviors from kissing to handholding and orgasm because it helps express the conditions of complex human mating psychology (Fisher, 2004). In Darwinian perspectives, mating is the central role because the genes only pass via successful mating.

In this article, I summarize most of the findings mentioned in the study conducted by Hughes et al. (2007). (Dr. Hughes is an evolutionary psychologist, currently teaching at Albright College.) I read this article in one of her college classes. It’s really cool. The study explores the adaptive significance of kissing behaviors. First we have to understand the biological sex differences between men and women in terms of reproduction.

1. Sex differences between men and women

Evolutionarily speaking, women bear heavier costs with internal fertilization, higher parental investment shorter reproductive lifespans and number of potential offspring in life (Buss, 2003). From conception, women have to bear the child internally for about 9 months while the man’s duty is biologically done. Because of lactation even after the conception, the female parental investment is still very much higher than males (Although human males are one of the primate species with heavy usually lifelong paternal investment, maternal investment is higher. The egg from female is more “expensive” than the sperm.)

Men and women also have differential reproductive potentials and lifespans. Ideally, men can farther more than hundreds of offspring, as long as he can find fertile mates while women’s biology limits the number of offspring below 20. Women also have limited number of reproductive life span. While men may procreate even after 75, women have almost 0 percent chance of conception because menopause in woman kicks in. With that in mind, evolutionary theory predicts, and finds that women are choosier than men in choosing their mate.

I heard about this analogy in one of the videos I watched, possibly from David Buss- “If you are eating the food that costs you about 5 bucks, you won’t be complaining so much, even if the food is bad. However, if you are spending about 200, or 300 bucks on the food, you are going to be choosier in terms of what you order and complain when the food is bad.”

2. Evolutionary Explanations of kissing behaviors

Before I tell you about the findings from the study, let’s look at adaptive function romantic kissing might serve, as hypothesized in the study.

  • Kissing as a mate assessment device.

Studies have shown that the taste and breadth of the mouth can indicate underlying health problems (Durham et al., 1993; Service 1998). Females also have a higher olfactory and taste detection compared to males and are heightened near the ovulation, the period where the likelihood of conception is highest (Pause et al. 1996). Women are therefore hypothesized to be more sensitive and cautious about what kissing from the partner indicates.

  • Kissing promotes bonding between partners.

Kissing on the lips is a signal that one is willing to take risks in contracting the illness. Kissing also may exchange chemicals such as oxytocin, which could promote bonding and trust between partners (Hughes et al., 2007). Both men and women also agreed that kissing on the lips is more intimate than cuddling, holding hands, hugging, stroking, backrubs, kissing on the face (Gulledge et al., 2003).

  • Kissing increases sexual receptivity.

Studies suggested that men who have been kissing their partners felt more entitled to force sexual intercourse. Christopher (1988) also reported that 57% of college-aged women had been forced into kissing by physical attempts to make them agree to intercourse. Another speculative hypothesis in the study says men may use kissing to introduce hormones and proteins through saliva to manipulate female mating psychology. Plus, the wetness in kissing may be perceived by males as a sign of sexual arousal. Males are hypothesized to enjoy wetter kisses more than women.

3. Key Findings From Hughes et al. (2007)

  • While 52.8% of males reported that they would have sex without kissing, only about one in seven females (14.6%) said they would consider having sex with someone without kissing. And 85.4 % of the females said NO- they would not have sex without kissing.
  • Women also rated higher than males in the importance of kissing in all 3 situations: before, during and after sex.
  • Males were significantly more likely than females to have sex with someone who was a bad kisser. (Males are less discriminating in their mate choice because of the fewer biological costs and greater benefits associated.)
  • Males significantly preferred wetter kisses with more tongue contacts and open mouth kisses than females.
  • Males reported the significantly decreased importance of kissing as the relationship progressed over time.

4. Females are more interested in having a causal sex with good kisser.

The experimental study by Wlodarski and Robin (2014) showed that females were significantly more interested in having a causal sex with someone who is a good kisser; a good or bad kisser was manipulated in the vignettes they read. (While, the results were the same in men, the effects are more pronounced in females.)

Now that you have read about some of the findings and researches related to romantic kissing. Of course, like any other studies in psychology, the study is based on a small group of sample, and there are always individual differences. Again, evolutionary psychology does not condone any behavior as being “right” because of the findings.

Next, I hope reading about this article and the study does not change your feelings of romance towards kissing or partner or whatsoever. Cartwright (2008) said, “Newtonian optics can account for the formation and position of the rainbow but rainbows remain.” The beauty of the rainbow should not be affected by Newtonian theory of optics. We have and shall continue to kiss our partners.

Helen Fisher also said in one of the Ted talks, “You can know every single ingredient in a piece of chocolate cake, and then when you sit down and eat that cake, you can still feel that joy. “ Enjoy kissing with your partner!




This wonderful study by Hughes et al., (2007) was conducted as a survey study among college students. This published article was introduced to me and my fellow classmates in Evolutionary Psychology. Over this summer 2015, I went back to the article, read and wrote about key findings for the public. To read the free full original article for (Hughes et al., 2007), click here ( ). To access (Wlodarski and Robin, 2014) click here:


Buss, D. M. (2003). The evolution of desire: Strategies of human mating (2nd ed). New York: Basic Books.

Cartwright, J. (2008). Evolution and Human Behavior (2nd ed). Cambridge, Massachusetts, The MIT press.

Chirstopher, F.S. (1988). An initial investigation into a continuum of premarital sexual pressure. The Journal of Sex Research, 25, 255-266.

Durham, T.M., Malloy, T., and Hodges, E.D. (1993). Halitosis: Knowing when “bad breath” signals systemic disease. Geriatrics, 48, 55-59.

Fisher, H. (1992). Anatomy of Love: A Natural History of Monogamy, Adultery, and Divorce. New York: W.W. Norton

Fisher, H. (2004). Why we love: The nature and chemistry of romantic love. New York, NY: Holt.

Ford, C.S. and Beach, F.A. (1951). Patterns of Sexual Behavior. New York: Harper and Row.

Gulledge, A.K., Gulledge, M.H., and Stahmann, R.F. (2003). Romantic physical affection types and relationship satisfaction. The American Journal of Family Therapy, 31, 233-242.

Hughes, S. M., Harrison, M. A., & Gallup G. G. (2007). Sex differences in romantic kissing among college students: An evolutionary perspective, 5(3), 612-631.

Pause, B.M., Sojka, B., Krauel, K., Fehm-Wolfsdorf, G., and Ferstl, R. (1996). Olfactory information processing during the course of the menstrual cycle. Biological Psychology, 44, 31-54.

Service, R. (1998). Breathalyzer device sniffs for disease. Science, 281, 1431.

Wlodarski, R., & Dunbar, R. I. (2014). What’s in a kiss? The effect of romantic kissing on mate desirability. Evolutionary Psychology, 12(1), 178-199.


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