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The Punch behind the Peck: A Behavioral and Physiological Analysis of the Kiss

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Biology 202
2004 Second Web Paper
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The Punch behind the Peck: A Behavioral and Physiological Analysis of the Kiss

Ginger Kelly

Robin Hood, reeling in the corner from nearly being skewered, gazes across the room to his Maid Merion. Disheveled from worry about her love, she lets out a sob. Then with joy she rushes forward to embrace her man. Miraculously, a second wind innervates Robin as he jumps up to..... Shake hands with his lady fair. Just doesn't have the momentum without the dramatic lip lock, does it (1)?

The kiss is arguably the most popular franchise of all time. Butterflies, Eskimos, and the French each have their own brand. Hospitals are fitted with equipment to bestow "kisses of life" to their patients (2). Teenagers, taking advantage of the dark, awkwardly embrace on front porch steps. Poets muse about it. Cher sings about it. Movies revere those who die for it. To make a long story short, mankind is batty for this simple act. Yet, there are organisms in nature that reproduce and thrive without smooching. Why is the kiss such a vital part of the human experience? What is the origin of this kissing behavior? Are people the only living creatures that find merit in the deed?

The average human being will spend two full weeks of his or her life kissing (3). For an organism to focus that much energy on any endeavor, there must be some advantage to negate the cost. Kissing is a positive re-enforcement behavior. To promote habit formation, participants in the activity are rewarded with pleasurable sensations. The organs involved in the kiss are well suited to this function. The lips and the area around the mouth happen to have the highest concentration of sensory nerves endings of all the tactile senses (4). As icing to the cake, the lips are also outfitted with a very thin layer of skin making them the most sensitive part of the body (5). So, could one claim the structure of the mouth was patterned by the kissing function? No, most likely, the lips are ultra sensitive to make humans more discriminating critics regarding what they should ingest. The pleasure potential of the mouth is a parallel role. What then causes a co-mingling of two sets of lips to be pleasurable? The warm and tingly feelings associated with pleasure are the outcome of a potent surge of dopamine, norepinephrine, and phenylethylamine in the brain (6). This "cocktail" of neurotransmitters, which is triggered by electrical signals from the lips, is received by the emotional portions of the brain (5). Almost immediately, the brain responds by producing feelings of elation similar to those induced by certain drugs--kisses: the ultimate anti-depressant?

The euphoria experienced from a kiss has a purpose. To repeat the above assertion, the body is not an altruistic entity. There is a catch to every gift. So, why does the body encourage the act of kissing? It can be a risky activity after all: a single kiss can exchange 278 species of helpful and harmful bacteria in the saliva, not to mention diseases (e.g. herpes and mononucleosis) and viruses (7). There are health benefits to kissing too. Studies have shown that kisses assist in the prevention of tooth decay, stress relief, weight loss, and can raise self confidence (8). However, it is possible that a few of these results may fall more directly under the Placebo Effect sphere. For example, my previous statement implies that kissing is a direct treatment for stress. This could be true, but it could also be faith in the treatment that really yields the desired result.

Have I answered the question I posed in the previous paragraph? Is dental hygiene reason enough to necessitate the use of satisfaction hormones? Contrary to how my dentist may feel, I'm inclined to say no. Evolutionarily, nature favors organisms that can survive to perpetuate the species. Thus, most resources in the body are devoted to bettering the odds of producing viable offspring. It is logical then to assume kissing would have a reproductive function as well. Kissing is oftentimes a precursor to sexual activity. So, the act of kissing could serve as a trigger for the release of sexual hormones. One of the theories behind the development of the kiss builds on this procreation principle. Many philematologists (people who study kissing) feel that the mouth kiss is a derivation of the "Eskimo" kiss. In this genre of kissing, companions rub noses as an act of greeting (9). This motion of noses creates a proximity that allows olfactory neurons to detect the other person's pheromones (5). Pheromones are an organisms' unique scent. They reveal the mood, health, disposition, and recent exploits of the particular individual (9). Thus, pheromones could be used as evaluation of compatibility as a mate. It is important to note that the "Eskimo" kiss is not exclusive to human beings. In fact, many animals practice this exchange of information (10). When your cat rubs his face against yours, he's sizing you up.

Is it plausible that mouth kissing could have evolved as a means of further testing genetic fitness? Perhaps, body fluids are a pretty intimate aspect of a person after all. In addition to bacteria, saliva contains immunoglobulin (a compound that binds to bacteria to signal disposal by the immune system). Stress and anxiety levels can also be measured in saliva by monitoring the breakdown of noradrenaline (11). In other words, a person can make a pretty educated guess about a potential mates' health just by swapping spit.

Kissing is somewhat of an enigma. In comparison to other aspects of life, scientists know relatively little about the embrace. The theory about kissing originating as a means of data collection (as explained above) is only one in many. Some experts feel that the kiss's roots are more superstitious. There was a belief, at a time, that "the human breath carried the power of one's soul (9)." Thus, kissing was a way for loved one's to exchange this power and merge their souls forever. Although tempting to toss this theory aside, it has as much credibility as any other theory. Remnants of this faith are still seen today: after all, why do you think the bride and groom kiss at the end of a marriage ceremony? Another theory asserts that kissing began as a descent from a prehistoric feeding practice. Frequently, mothers would do as the birds do—chew up food then push it into their children's mouths (10). Kissing later developed as a way the mother could convey her love for the child. This theory is interesting because it allows for the association of emotion with kissing (10). What began as a symbol of the mother child connection may have evolved to become the poster child for fondness in all relationships.

Why do all these theories vary vastly from one to another? Is kissing that challenging of a concept to pin down? It appears so based on what I have presented to you. The real issue in philematology, however, is whether kisses come from a genetic or a cultural origin; the classic "nature" versus "nurture" argument once again rears its ugly head. Scientists cannot formulate accurate "source" hypothesis without knowing if it needs to look in science or anthropology. Most modern research is taking a step backward to try to solve that conundrum. A German researcher, Onur Hunturkun, spent two years documenting the trends in how couples kiss. He found that most couples lean to the right when kissing; he interpreted this as evidence of genetic asymmetries of motor and sensory functions (12). However, he also noted that cultural identity affects the way that couples kissed (12). Hunturkun's findings give more insight into kissing's mysterious parents, yet we are still left at an uncomfortable place. Most couples lean right, which implies a genetic pre-disposition for kissing to the right. However, whatever codes for this asymmetry probably codes for all motor functions (e.g. right handedness); kissing just happen fall under its jurisdiction. Hunturkun also mentions the effect of culture patterns on kissing. This is further evidence that kissing probably comes from a mostly "nurture" background. Yet, to not exclude the theories of origin previous mentioned, it is possible that the "nurture" act may have stemmed from a "nature" need. Yet, without conclusive evidence, philematology continues to be a study of near leads and suggestion.

You don't usually walk out into a field and see two horses engaged in a passionate embrace. So are humans the only species that practices the kooky art of kissing? Surprisingly, no we are not. Although you will never see two horses making out, you will oftentimes see them smelling one another's head—the "Eskimo" kiss. Lawrence Katz, a neurobiology researcher who did studies mice, found that pheromones are critical for animals to receive information (13). Mice and other creatures have developed very powerful vomeronasal organs to read pheromones in detail. Humans have this ability as well, but to a much lesser extent; our evolution placed emphasis on sense of sight over sense of smell. Katz also deduced that pheromones are nature's prevention against inbreeding: "When mice met their genetic twin, certain neurons fired. When they encountered mice from a different strain, different neurons activated (13)." Thus, in animals, kissing serves a vital reproductive function: for finding both a responsive and genetically different mate. Could this research be further evidence that kissing in humans has a reproductive basis as well?

Ingrid Bergman mused that "a kiss is a lovely trick designed by nature to stop speech when words become superfluous (14)." In other words, a kiss is an act that communicates unmistakably without words. The bulk of this paper has been devoted to the scientific aspects of kissing. Yet, there are volumes of emotional and psychological implications behind the practice that I haven't even touched upon. Kissing may have evolved as a way to increase the fitness of a species, but it quickly became intertwined with emotion. It has since become a physicalization of untangible qualities like love, commradery, and devotion. Because kissing means so much in human culture, we owe it to ourselves to understand it fully. Maybe then we'll understand why marriages that lack kissing usually result in divorce (7).


1) Self Written Scene Parody of Robin Hood: Prince of Thieves, prod. by Morgan Creek, dir. by James G. Robinson, 144 min. , Warner Brothers, 1991, videocassette.
2) Kissing, Written by Peta Heskell
3) Fun Facts About Kissing, from HiCards
4) Kissing, from Barbelith Underground Community
5) Can a Kiss be Bettter than Sex?, Written by John Triggs
6) News: The Science of Kissing, Written by Rob Bhatt
7) Science of a kiss, Written by Raj Kaushik
8) Reasons Why Kissing is Good for You, from CoolNurse
9) First Kisses, Written by David Templeton
10) The Science of Kissing,Written by Edward Willett
11) Kissing—how it all began..., from NZGirl
12) Your Kiss is All Right With Me, Written by Amanda Gardner
13) There's No Mistaking Mouse Lust, Written by Jennifer Thomas
14) Quotations About Kisses, from The Quote Garden



Comments made prior to 2007
Hello, I'm interested in hearing from men from cultures and countires where the men kiss each otehr on the lps as a greeting only and not soemthing imoral. I want to talk to men woh do this only as a greting, especially if your a man and have a brotehr that you kiss like that as a greeitng and nothing more.


I'd also like to konw if there are any countires and cu8ltures where any man might be from where he and another man might kiss for as long as tow or three seconds on the lips like Samuel kisses David in hte movie "David" from teh Bible colleciotn. I want to see if there are cultures where men kiss that long only as a greeting and nothing fore ... Darrell Waters, 30 May 2006