The Volokh Conspiracy
[Eugene Volokh, July 6, 2005 at 12:50pm] Trackbacks
Why Do People Enjoy Kissing?

I think I know the reasons people enjoy sex -- both the proximate reason and the likely evolutionary reason (though I realize that the question there is quite complex, especially when it comes to the female orgasm).

But why do people enjoy kissing (I speak here of serious kissing on the lips, not just pecks on the cheek)? Is it purely social convention, or is it biological? Some people say that it's because there are lots of nerve endings in the lips, just as there are in the genitals; but I don't think that can be quite right -- one piece of evidence is that self-stimulation of the genitals is pleasant, but you never hear of people touching their own lips for sexual gratification.

If anyone actually knows the answer to this, I'd love to hear it.

(This post is prompted by Amber Taylor's Kissing Day post; thanks to InstaPundit for the link.)

Steve R:
I suspect there is a sexual selection answer for kissing the same as for intercourse. For one thing note the universality of kissing both as foreplay and as part of the overall sexual act. Further evidence for the evolutionary connection is our uniqueness in having everted lips, unlike all other existing mammals.

Lastly for now, you note the lack of touching ones own lips for sexual gratification, however, during sexual gratification, self or otherwise, licking ones lips is known.
7.6.2005 1:14pm
Buck Turgidson (mail):
Judging from ape and monkey behavior, I'd say it's not a mere social convention. Having witnessed monkey anal sex (two males, no less), I'd say some other things that have been claimed to be unnatural are actually quite common in the animal world (and there are plenty of zoologists who'd back me up on this). Pontificating about God or divine retribution, on the other hand, is purely a human vice, a social convention.
7.6.2005 1:16pm
jurisprude:
I don't know if there's anything about kissing in it (it's been a while since I read it), but for a good read on why people enjoy sexual activity in general, I'd recommend Jared Diamond's "Why Is Sex Fun?" The amazon.com link also has some links to other books on the same topic.
7.6.2005 1:19pm
A F:
Why do baseball fans like seeing their team hit a single? A single, without more, is of no moment -- it does not count in the final score, and as often as not does not contribute to victory. But a well timed single is a sign of greater things to come!
7.6.2005 1:34pm
A. Nonymous (mail) (www):
I've heard that the lips have an enourmous amount of nerve endings, both in raw numbers and in nerve endings per surface area. This column suggests that these are just some of the reasons...

http://www.edwardwillett.com/Columns/kissing.htm
7.6.2005 1:36pm
Kipp (mail):
"but you never hear of people touching their own lips for sexual gratification"

I think you're under-appreciating how much action the lips get during sex and other amorous activity. The lips don't really need to be manipulated like the genitals do since they are "self-touching" and surrounded by other mouthparts (the tongue and teeth) that can stimulate them just fine without the assistance of a stroking hand (or foot?). Watch most people during sex and you'd probobly see their lips are getting plenty of auto-stimulation quite apart from kissing a partner: pursing, licking, that quintessentially sexy gesture of biting the bottom lip. I would also wager than such stimulation - lip biting, licking the lips, etc - also occurs when many people masturbate. Since we do it subconsciously for the most part, we don't notice it...

...does this mean lip balm is a marital aid now?
7.6.2005 1:45pm
Scipio (mail) (www):
Loss of oxygen. ;)
7.6.2005 2:01pm
arbitraryaardvark (mail):
(uninformed guess:) primates are social animals. solipcism is a big issue - are we alone in the universe, or can we meaningfully interact with others? kissing is one of the more intimate things two people can do. your bundles of sensory organs are getting feedback from each other - touch taste smell hearing sometimes sight. until we can link minds with a cable, it's about as close as you can get. dr susan block at blockbonobofoundation.org (not entirely worksafe) has some theories about what pygmy chimp culture has to teach us about ourselves. kissing may predate language as a communications device. intimacy and closeness relate to trust, and trust is key to transactions costs in trading. kissing can be an indication of willingness to cooperate and form alliances. with those we kiss, we tend to enagage in informal reciprocal altruism of favor exchanges, while others pay cash or otherwise use formal trust-resolution processes like credit ratings and written contracts.
7.6.2005 2:20pm
Anderson (mail) (www):
This is one place where Freud is useful (there are indeed such places). You don't see people "touching their lips" for sexual pleasure, but you do see them sucking lollipops, chewing gum, smoking, etc.

Serious "sexual" kissing is a lot more like sucking or chewing than is a mere peck on the lips. The latter is presumably a toned-down version that had selection value as a gesture of amicability.

(I read the comments, logged in, wrote this comment, &then saw that Kipp's comment had just posted. So, "hear, hear" to Kipp.)
7.6.2005 2:56pm
Windypundit (www):
I suspect that kissing other people is more fun than self-stimulation of the lips because the human perceptual process is able to filter out stimuli that are self-caused. For instance, if you are transporting a pet in a carrier, you don't get much of a sensation of changing forces on your hand when you move the carrier around, but you can tell instantly when your pet moves inside. A more relevant example is that it's very hard to tickle yourself because your own contribution is filtered out. As for touching the genitals, I think it's a matter of degree. I believe many people would argue that it's more fun when someone else does it.
7.6.2005 3:13pm
Robert Schwartz (mail):
There are just somethings that need not be rationalized.

Play It Sam!

You must remember this
A kisss is till a kiss ...
7.6.2005 3:25pm
Fishbane:
IANA(evolutionary biologist), but what else is a blog for than making up theories?

I can see good evolutionary reasoning for it - intimate exchange of air, saliva, etc. could help identify some impending health problems that would make the victim a less effective mate. (My mother, a doctor, has mentioned that many people would be freaked out if they knew to what extent doctors (or at least GPs) depend on their sense of smell in intial diagnosis.)

Also, I remember reading somewhere (quite some time ago, can't recall where) that immune system compatibility seems to have a great deal to do with whether one smells attractive to specific others; kissing gets one a very close sample.
7.6.2005 4:32pm
Drew (mail):
Fishbane's reasons sound decent. Also I would add that there might be some evolutionary benefit to sharing germs before intercoures (don't laugh). You'll very quickly determine if the person is actually healthy (though at the risk of getting sick yourself). Also there may be some benefit to being ill shortly after a person you are close to (such as reducing the chances of relapse/reinfection).
7.6.2005 4:45pm
Zywicki (mail):
It is biological and it is an evolutionary residue of food sharing in primates, which is often done mouth-to-mouth. Pictures of chimpanzees often show them "kissing" as part of a food-sharing rituatl. I believe that either Ridley or de Waal has a discussion of the food-sharing roots of kissing in one of their books.

As for the larger associations, food is often directly exchanged for sex in both primate and hunter-gatherer societies. It may be no coincidence that in advanced societies what we call a "date" typically involves some meal, usually protein-based, still today.
7.6.2005 4:57pm
Joe Behrmann (mail) (www):
I am a biologist :)

When we kiss, the hormone oxytocin is released, which stimulates us and produces the "feel good all over" sensation associated with kissing. Also, when kissing, our mouths produce chemicals which induce a further desire for kissing.

The oils on the lips are different from person to person and certain combinations produce a stronger response than others, which is why kissing some people stimulates us and some people don't. We literally become mildly addicted to kissing a certain person. The pleasure stimulation, which is caused by elevated levels of dopamine, is addictive just like adrenaline rushes and other intense stimulations.

One of the worst things about being a biologist is knowing how your body tricks you into liking or disliking certain people and certain activities. The lip oil addictions, the preference for a certain person's smell based on their histone complexes, the changing of that smell preference based on pregnancy or taking the pill, etc.
7.6.2005 5:05pm
lcooker2 (mail):
Leonardo de Vinci described the attractiveness of a woman's face in precise geometric terms,ie spacing between
the eyes and the base of the nose, ideal ratio of the
thickness of the lower lip to the upper(2:1). A woman's
forehead is different,eyes are different,mouth is different. Facial muscles are stronger than men's, which is where the big smile comes from. Lots more differences
and I say the differences are the answer, for her too.
7.6.2005 6:03pm
Attila (Pillage Idiot) (mail) (www):
If you have to ask....
7.6.2005 8:15pm
Thief (mail) (www):
I will leave this to the poets, and not the biologists. Needless to say, I think the answer is "because."


since feeling is first
who pays any attention
to the syntax of things
will never wholly kiss you;

wholly to be a fool
while Spring is in the world

my blood approves,
and kisses are a better fate
than wisdom
lady i swear by all flowers. Don't cry
- the best gesture of my brain is less than
your eyelids' flutter which says

we are for each other; then
laugh, leaning back in my arms
for life's not a paragraph

And death i think is no parenthesis



-- e.e. cummings
7.7.2005 2:38am
Fred (mail) (www):
Food sharing is common not only among primates, but also among certain tribes. It's not unheard of in suburban America.
7.7.2005 2:50pm
bago (mail):
Labia means lips.

The rest I leave to your imagination.
7.8.2005 5:29am

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