Why do humans kiss?
-- asks Roberto Morabito from Brooklyn, NY.
Kristina Fiore • October 2, 2006
Scientists currently have no explanation for this particular KISS. (CREDIT: Wok)
Her eyes are wide as they stare into yours. You wrap your arm around her waist and pull her in close. She touches your face and you lean in, tilt your head – to the right, of course – and your lips connect. The rushing sensation leaves you little room to wonder, “Why the hell am I doing this anyway?”
Of course, the simplest answer is that humans kiss because it just feels good. But there are people for whom this explanation isn’t quite sufficient. They formally study the anatomy and evolutionary history of kissing and call themselves philematologists.
So far, these kiss scientists haven’t conclusively explained how human smooching originated, but they’ve come up with a few theories, and they’ve mapped out how our biology is affected by a passionate lip-lock.
A big question is whether kissing is learned or instinctual. Some say it is a learned behavior, dating back to the days of our early human ancestors. Back then, mothers may have chewed food and passed it from their mouths into those of their toothless infants. Even after babies cut their teeth, mothers would continue to press their lips against their toddlers’ cheeks to comfort them.
Supporting the idea that kissing is learned rather than instinctual is the fact that not all humans kiss. Certain tribes around the world just don’t make out, anthropologists say. While 90 percent of humans actually do kiss, 10 percent have no idea what they’re missing.
Others believe kissing is indeed an instinctive behavior, and cite animals’ kissing-like behaviors as proof. While most animals rub noses with each other as a gesture of affection, others like to pucker up just like humans. Bonobos, for example, make up tons of excuses to swap some spit. They do it to make up after fights, to comfort each other, to develop social bonds, and sometimes for no clear reason at all – just like us.
Today, the most widely accepted theory of kissing is that humans do it because it helps us sniff out a quality mate. When our faces are close together, our pheromones “talk” – exchanging biological information about whether or not two people will make strong offspring. Women, for example, subconsciously prefer the scent of men whose genes for certain immune system proteins are different from their own. This kind of match could yield offspring with stronger immune systems, and better chances for survival.
Still, most people are satisfied with the explanation that humans kiss because it feels good. Our lips and tongues are packed with nerve endings, which help intensify all those dizzying sensations of being in love when we press our mouths to someone else’s. Experiencing such feelings doesn’t usually make us think too hard about why we kiss – instead, it drives us to find ways to do it more often.
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About the Author
Kristina Fiore
By day, a mild-mannered reporter(former Newsday intern, current Daily Record part-timer); Alter-ego: lover of non-fiction narrative. “If he stays beholden to dry, yeastless factuality, he will, to the very end, lack imagination and miss the better story.” — Life of Pi
353 Comments
I had read somewhere else that some theorized it originated from a tradition of men and women swapping tobacco. Not sure of the source.
Jim
http://www.runfatboy.net – Exercise for the rest of us.
I agree with the ‘it feels good’ camp. That HAS to be the reason :) Still it IS odd that chimps and other animals do it.
@the english guy
Just saying “it feels good” doesn’t explain anything. If you believe that humans evolved, as the vast, vast majority of scientists do, then you’ll be curious to find a reason for kissing that makes it advantageous for reproduction somehow. The fact that it feels so good lends support to the idea that there is such a reason. Also, it would be even more odd if no other mammals did it, since most of the things that really make humans unique are more directly related to intellect.
Kissing is learned. Thais don’t kiss…they sniff each other’s cheeks. Put your tongue down a Thai girl’s throat and she is more likely to puke on you.
Then again, if you kiss her down below she is more likely to explode in ecstacy. I guess it all comes down to where you do your kissing, doesn’t it?
Regardless, it’s still disgusting. They don’t mention that over 200 bacteria colonies are exchanged during a kiss.
Not everything has an obvious evolutionary reason for existing. Humans evolved consciousness, and the ability to think about what feels good and what doesn’t. There are several sexual practices engaged by humans that really have no bearing on improved reproduction.
Bacteria… I believe that is one of the reasons. Many South American cultures share spit in other ways, through community meals and ‘special’ beverages. I have always suspected that this leads to a shared immune response, and makes a group stronger as a whole. Just my 2 cents.
sounds like someone is disappointed he isn’t getting any bacteria.
There would be a counter advantageous element to the kiss too from an evolutionary stand point. The kiss would greatly increase the chance of transmitting pathogens. If there is a genetic underpinning to this activity it would mean that the advantages must outweigh the negative aspects otherwise selective pressure would have favored individuals that didn’t kiss it or even were repulsed by this type on non-reproductive activity.
@Anon
Your point…?
@Chad
Yea I agree. lol!
@Joe
First, evolution is dead in informed circles. Entropy and information theory work against it.
Second, why must the ‘it feels good’ answer be wrong? Take an example of the inverse – I do not hit my finger with a hammer because it does not feel good. Does that mean that my continued persistance in NOT hitting my finger with a hammer comes from some deeply significant human-promotional act? Perhaps it’s just because I accidentally hit my finger with a hammer one time, and decided I didn’t want to do that again thanks to subsequent throbbing pain, so I avoid it. Similarly, perhaps kissing just feels good to many of us, and therefore we are attracted to the act, akin to how I’m repulsed from the painful hammer-to-a-finger act.
i’ve read somewhere that it begun with men trying to know if there women had drunk wine.. O.o
michael, are you from south america? ¬¬
Even in America, “French Kissing” was fairly uncommon until after Victorian times… I am fairly sure my parents (now aged 80) never did it. When the Clinton scandal broke, Mom expressed disgust that anyone would do *that* kind of thing either.
@Matt,
ahh… but then one has to ask, “Why does it hurt when you hit your hand with a hammer?” and you thus come back to the “must stay alive” mentality. When you make yourself less “survivable”, your body tells you it’s bad to do what you’re doing through pain. A broken finger would put you a few rungs down on the ladder of traits, so your body reacts by saying “Don’t do that”. Thus human-promotional act.
@Matt
Funny because the majority of scientist in the world all reguard evolution is fact. Quit making up stuff, unless creationists are informed circles to you.
As for kissing, I believe it’s a combination of feel good/instinctual behavior. I believe it feels good because we are programmed genetically to enjoy kissing because of the advantages that come from it. Still if passing on bacteria is so great, why do we only kiss our mates on the lips?
“@Joe
First, evolution is dead in informed circles. Entropy and information theory work against it.”
Evolution dead in informed circles? I bet the informed professors would disagree if I’d used that argument in any of the Bio courses that I’ve taken in the past few years. Entropy argues against a sustained complex system, but that doesn’t rule out the existence of any complex systems. Nature is full of complex systems, so a few proteins folding in just the right way on one planet out of trillions of stars in the known universe hardly seems unreasonable.
@Todd
You only kiss your mate on the (oral) lips?
Poor mate.
And poor you!
I see what Matt is saying, though. Making sure not to hit your finger with a hammer is not something that evolved evolutionarily exactly. The ability to have things feel good or feel bad evolved first, and then hitting your finger with a hammer happened to feel good. It’s not like cave men were hitting their fingers with hammers and then the ones with nerve endings survived and reproduced.
Similarly, being close face-to-face with someone, touching something soft to your lips, etc… it just feels good. We don’t need to have evolved kissing… It’s just something that feels good because of the way we evolved already, apart from kissing.
To say that people who don’t kiss were at any significant disadvantage to reproduce or survive seems ridiculous, IMO.
Oh, btw, this is a different Joe from the other Joe up there.
I think kissing helps us determine genetic diversification before mating. For example, my naive theory is that people’s saliva tastes different based on their chemical makeup, and perhaps blood type. If you get the same taste if you kiss someone, you are likely to be too alike, and its not as good for the success of your offspring to mix two alike people. If they taste different, I seem to favor kissing my mate more, and therefore more chance of successful mating with diverse genes in my children. Just a guess, but I haven’t seen any research to that effect.
Why do humans kiss?
What no one has mentioned is that kissing is actually sexually stimulating. Somehow and for some reason, kissing is foreplay. Ear nibbling, hand-holding, and foot rubbing are also sexually stimulating. It could simply be arbitrary. As long as it leads to sex, that’s all that matters. Maybe the cultures that aren’t that into kissing just aren’t that into the aesthetics of sex. Just like the old blue-noses who are offended by oral sex.
@Zebov,
Yes, that’s true. That occurred to me as I was contemplating this. The hammer-on-the-finger does sound like an act that would decrease survivability. Perhaps that wasn’t the best example to use. My point was that the “feel goodness” of kissing may be enough to cause us to do it again, similar to the hammer-finger is enough to cause me to never do it again. Also, I would assert that pain does not necessarily govern what is best for our survival. Silly example: growing pains (e.g. aches, etc.) are a part of maturing physically. They hurt, but yet it’s a necessary part of my overall survivability. Maybe I’m thinking too much about this – this is just off-the-cuff theorizing on the topic.
@Todd & Andrew,
Not planning to make this an evolution debate, but since one of you suggested that I’m (or “we’re”, more likely) making this stuff up, I’ll play along.
Entropy & sustained complex systems – sure, that’s fine…except that all systems tend toward decay without purposeful and continued input, implying strategic organization when the system first existed. And where do these complex systems originate? They don’t occur randomly. You need information – articulated design decisions to create a system. Assuming a system defied all probability and was randomly generated, entropy kicks in and decays it. And then on top of that when you complicate the matter with most systems’ irreducible complexity, then the already tiny chances of any non-trivial system evolving become astronomically small.
I’ve read what learned people say about this, e.g. irreducible complexity. They tend to ignore either entropy (continued decay without information / energy input) or information theory (how the system got there to begin with). Talking about one in a vacuum is useless.
Stop to consider this.
Kissing is just another form of touch, just as is a stroke on the back. Both can be innocent, comforting, and arousing. Touch is the ultimate way to excite your senses. I hope we all know what happens when you excite the senses of your potential mate. Well, we all hope it won’t be blue balls.
If my girlfriend began rubbing my back in an intimate way, she would get a response that would encourage reproduction. But if I was feeling a bit down, and my girlfriend was doing it to bring me comfort, it would encourage a different set of emotions.
As stated before, there are a shit load of nerve bundles in the mouth and on the tongue, which make a great roadway for excitement. Our society dictates that kissing is a great starting point toward intercourse. If it was giving high-fives, basketball would be a lot more interesting.
I read somewhere (in Discovery mag I think but i’m probably wrong) that kissing is more about smelling your partner’s unique scent; i.e., while your lips are locked together, you are in a uniquely intimate position to smell your partner. It sounds sketchy and could be pure bollocks but …
Matt,
You are mistaken in thinking that a system of life on earth would decay due to entropy. Entropy is not disorder; entropy is energy that can not be used to perform work. New, non-entropy energy is constantly being introduced by solar radiation.
And don’t babble on about “irreducible complexity;” that’s just a buzzword designed to sound scientific but meaning “we don’t feel like imagining how this would have come to be.” Complexity arises from simplicity all the time. Observe how evaporating water, set to spin from the rotation of the earth, becomes a hurricane.
@Matt
What do you call the sun? I’d say that’s somewhat of a lot of energy input. Solar power may be inefficient, but it’s not nonexistent.
But yeah, entropy only applies in a closed system. The earth is quite thoroughly not a closed system. The sun is becoming more disorderly all the time, which in turn allows the earth to become more orderly. Thus, the complete sun-earth system always increases in average entropy, but that doesn’t mean parts of it can’t become more orderly.
And I think this debate sort of stems from a confusion regarding whether pleasure and pain serve a purpose. If they are things that are just there for no reason, then Matt could be right. If, on the other hand, they are indeed survival mechanisms, and our genes are punishing self-destructive behaviour such as thumb-hammering and rewarding self-reproductive behaviour such as sex, then the logical assumption is that, yes, we kiss because it feels good, but in addition to that, kissing feels good for a reason. So the underlying question the article was originally trying to ask was not “Why do we kiss?”, but is instead “Why does kissing feel good?”
“They tend to ignore either entropy (continued decay without information / energy input)”
*ahem* THE SUN!
Next!
(99.85% of all scientists in related fields support evolution theory, 95% in non-related fields do also, your “informed circle” must be pretty small)
It does feel good. And it tends to bond people together, because its an intimate experience. People who wouldn’t dare use each other’s toothbrushes will kiss like there’s no tomorrow. The bonding experience may explain the evolutionary benefits of kissing.
@scosol – I think Todd was saying something else. Not that lips are the only places we kiss our mates, but our mates are the only ones we kiss. Like, if bacteria swapping is so great, why don’t we kiss the smelly old man at the bus stop?
Why do we kiss???
Q. Why does a dog lick its butt?
A. Cause it can.
@ Sean, DannyDrak
Glad somebody mentioned this point. Typical of the scientists to miss it :) – yet the ‘lovers’ amongst us know that kissing isn’t just for the lips – either pair.
But to the assertion that as some cultures do not engage in kissing therefore it is a ‘learned’ behaviour, that seems a bit flawed. Can we be sure that the absence of kissing in those cultures is not due to latterly imposed social or ideological rules, rather like the those of many established religions? I can’t, so I’m with the ‘instinctual’ camp. It’s for sexual stimulation. The fact that it feels good is indicative of the purpose why it triggers our instincts.
Sexual stimulation is all about finding the best mate for procreation and, as evidenced in other animals at least, in the most efficient and fastest way possible, after all, all animals are extremely vulnerable to predators during this act. In our history, human’s were no less vulnerable.
Perhaps the act of kissing parts of the body other than the mouth is learned however, in the same way that sign language developed to better communicate the acts of the hunters and now we prattle on about all kinds of trivia on the Internet :)
Could it just be part of the mating ritual that’s evolved along with the notions of love, and from there has become a learned thing?
@ Matt
>First, evolution is dead in informed circles. >Entropy and information theory work against it.
You mean uninformed circles?
Entropy would work against it in a closed system, but guess what the only closed system in the universe is? That’s right… the universe!
Earth recieves energy from the sun, therefore the law of increasing entropy in a closed system does NOT apply. Take some physics and get back to us, mmmkay? :)
Kissing is of course the smallest favor that leads to sex, it feels good and everyone knows that when you kiss that certain spot, whether it be the ears or what not, it leads to heavy excitement, therefore increasing your chances of reproduction. Sure it could have evolved over time from some mom giving food to her kids or whatever, the fact of the matter is it’s still done today, it improves everyday and it evolves in a sense from just a peck on the lips to full on tonsel hockey. Kissing is something that mates do when they feel comfortable around each other enough to engage in further commitment and bonding. you wouldnt just sit there and twiddle your thumbs to get the night going. NO! it is a common activity to do with a mate and you can think that it evolved from cave men if you want to, but i think everyone is missing the big picture of what kissing really means and what it brings to a relationship. it’s also a tell tale sign that the other mate likes you and wants to take things further and its relaxing and intimate and anyone who doesnt like to kiss or hasnt been exposed to it, should be.
most mammles clean one another. for instance my two cats clean each other, and so do my two rats. It is just a way to show love and care to another. but we do it by kissing.
Matt..
As nicely as I can put it – you’re uninformed, if not an outright idiot.
First off, the notion that Evolution somehow breaks the laws of entropy is just silly. (The 2nd law of Thermodynamics is what you’re referring to, I believe, there is no ‘law of entropy’..): You can read several explanations of why your claim is wrong here: http://www.talkorigins.org/faqs/thermo.html
Short and sweet, your own words above invalidate this claim! ‘Systems decay without constant input’ – What do you think the SUN is, anyway? It’s a gigantic energy source, pouring vast amounts of energy out into space and onto the earth. The earth is NOT a closed system, so complexity most certainly CAN increase. It’s only in a closed system that the ‘Law’ states that complexity will tend to decrease.
Snowflakes are far more complex than drops of water, yet they occur all the time. Why? Due to interactions with the sun, air, and water on our planet, we have this nifty process called ‘weather’, where heat energy and water vapor are circulated all around the planet, forming complex patterns in a myriad of forms, from lightning to clouds to snowflakes. There are many other forms of ‘simple’ complexity being created around us constantly.
As for this need for ‘information’ that you claim, I don’t suppose you could quote any honest science (You know, *real, peer-reviewed* science) that explains this need, or even properly quantifies what ‘information’ is, exactly? It’s a nice claim, but it’s nothing but babbling in an attempt to sound scientific. There is no law or even a proper theory that requires ‘articulated design decisions’ for weather, evolution, or any of the other processes around us. All they take is energy, and we get it from the sun in abundance.
‘Irreducible Complexity’ is a farce. Intelligent Design is a farce. It has no science behind it, and everytime one of these creationists hiding as a scientist brings it up, they are quickly shot down by real scientists all around them. Everytime they point to an example and say ‘See? Irreducible Complexity!’, they’re shown to be wrong. Bacterial flagella, the blood clotting cascade, the eye, the immune system, even something as simple as mousetraps! Michael Behe himself had to admit in court that none of his examples either showed IC or ruled out evolution as described in the neo-darwinian synthesis.
Here. Read about it at http://www.talkorigins.org/indexcc/CB/CB200.html .
Try reading the whole site, or at least the sections that explain those particular subjects. Read about the Dover Trial itself here.
Go to PubMed and search for articles referring to ‘Evolution’, and compare it to articles referencing ‘Irreducible Complexity’. You -might- find half a dozen that mention IC, and all of them showing how it’s wrong. You’ll find tens or even hundreds of thousands of real, peer-reviewed studies, each one validating or explaining yet another tiny piece of the Theory of Evolution.
There IS no ‘Theory of Intelligent Design’, unlike the Theory of Evolution. After many years of questioning, I have yet to see any ID proponent articulate an actual theory that doesn’t involve ‘and then god’s magic happens’.
Really, just having you say ‘Evolution is dead in informed circles.’ tells me that you don’t actually travel in any informed circles. Could you give us some examples of these ‘informed circles’ who feel that Evolution is dead?
Please. Educate yourself about REAL science, and then come back to talk to us about informed circles’ and the laws of thermodynamics (entropy).
Just today I started seeing articles about the most recent Nobel Prize being given out. To whom?
http://nobelprize.org/nobel_prizes/medicine/laureates/2006/
A pair of researchers who jointly discovered RNA Interference – gene silencing by double-stranded RNA. Try reading the advanced information about the breakthrough and see how many times it refers to evolutionary implications, and then tell me that evolution is dead!
Ermine
Grait stuff. I knid of knew the answer – but it’s nice to be confirmed. Good work – nice (short) reading :-)
why does everyone want so badly to think that there MUST be an evolutionary process behind kissing? somethings are done simply for pleasure… look at masterbating, it has no reproductive benefits, it doesnt significantly impact our health, why do we do it then… oh that’s right b/c it feels good. while kissing may have some big chain of events leading to it being ingrained in our brains, it seems more likely that its one of those things we do b/c we like the way it makes us feel.
I think tis because public oral sex became taboo thousands of years ago.
but it isnt now..and kissing isnt public oral sex unless you are actually that daring and out there..kissing is a public thing, i see couples making out in the parks all the time, hell i do it. i have to agree with this is silly, because it is virtually the same concept, it just feels good and honest to god when you find something that feels good and gives you pleasure do you really want to give it up and stop doing it??
*raises hand*
There are some of us who do not find any pleasure in kissing and wonder what the hell the rest of you are so excited about. To me, finding kissing pleasurable is like being ticklish — if you are ticklish, you react to being tickled, otherwise it’s just weird touching. And like being ticklish, it doesn’t mean you’re abnormal in any other way.
i though masterbation did serve a purpose…cleaning out the tubes and what not. not to mention the endorphins released. am i wrong on this??? here i thought i was being healthy :-(
what about if you aren’t in love? people seem to be satisfied by kissing still, and i would never understand why making out witha random stranger would be pleasant in any way.
@beer
actually you are correct..i learned this in bio..you are being healthy and plus it builds up the muscles in ur arm..well both if you’re multi talented..plus when you eat healthy too, like lots of fruits and vegies and protien, it makes it taste sweeter and better because its all vitamins and proteins that you release.. so yea just a lil tip watch what you eat, cuz we swallow it too… (hah) and of course making out with a complete stranger isnt pleasurable, its gross cuz you dont know them, for it to mean something you have to be friends with the person first.
@Jason
The ‘physical’ universe is not a closed system. It’s not that difficult to see this if you look with a disciplined mind. Of course, if you only observe physical law being played out, and take probabilities to be governed by such law (as opposed to sentience), you aren’t going to percieve that which lies before you, within you, ohh, basically everywhere.
@Plasma
I don’t know why people associate increased entropy with increased disorder. Here is a little definition for you from a popular book:
“entropy: the degradation of the matter and energy in the universe to an ultimate state of inert uniformity”
Like, what if everything was Iron? Would Ozzy be the alpha Fe-Male then? :p
Joe says…
“If you believe that humans evolved, as the vast, vast majority of scientists do”
Joe, you are full of shit. Interesting that when someone knows subconsciously that they are full of shit, they have to use superlatives. The word “vast” would be unnecessary even once if you believed what you are saying. Twice is absurd, and focuses your self doubt like a laser beam on your statement. Anyone who has a passing familiarity with the scientific community knows that evolutionism is not nearly as popular as you so fervently hope.
Matt Says…
Funny because the majority of scientist in the world all reguard evolution is fact. Quit making up stuff, unless creationists are informed circles to you.
Matt,
Provide some sources. You made a fool of yourself with that comment. It is utter nonsense.
Also, you should repeat 7th grade English class.
Matt, I apologize.
In the above post, I meant to say, “Todd says”
FAB says…
(99.85% of all scientists in related fields support evolution theory, 95% in non-related fields do also, your “informed circle” must be pretty small)
Bachelor’s degree in physics, grad study in electrical engineering here.
I know no one with a real scientific background who supports evolution theory. Not ONE. Where do you guys get these numbers? From your freshman biology professor? He is probably not a scientist, but a political activist, memorizer, and wishful thinking secular humanist with an agenda. Wake up, guys.