Life Science

Why do humans kiss?

-- asks Roberto Morabito from Brooklyn, NY.

October 2, 2006
Scientists currently have no explanation for this particular KISS. (CREDIT: Wok)
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.

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



adam bold says:

Please someone tell me the tricks of kissing….Whenever I go in front of her it feels like avoiding.But after wards feels to kiss.I want to kiss very soon!!

Kay Ess says:

Well, recently I’ve read that French kissing is one way a man can actually transfer testosterone to a woman, which will up her arousal. So kissing as a precursor to sex/procreation makes sense from an evoluntionary standpoint.

Aisha says:

hey hey @Beer

oh come on… of course you are true, if i wanked off my arm i would gain muscle, all those just happen to be the result of masterbating, people say its healhty maybe to make us feel better about doing it, but really your just doing it coz it feels good and relieves stress for men.

as for kissing, it was probably learned or all of the above, but what matters is we still do it now, if it was bad we wouldn’t do it today. So it’s just a harmfull act, now pucker up and stop wondering about pointless stuff and just accept it…



Rox says:

I find that when kissing leads to more enjoyable things we do it more often but when the ‘spark’ is not there it often leads to less kissing. So I’m with the “it feels good theory”.

Delaney says:

It’s a learned thing I think, IF it was instinctual then why would people in other remote areas not do it?
Then again, there are instinctual things people in certain regions that others don’t.

It’s a very interesting subject though.

Honey says:

I think a woman can get more information about a man’s heart and intentions with one kiss than in hours of ego driven conversation. The tenderness and controlled passion, or the fumbling indecisiveness, the timing, and even responsiveness to the slight movements during the kiss are all clues to a compatibility that cannot be expressed easily with vocabulary. One kiss can make me “ready” and another can forever turn me off. I think there is an old R & B song: It’s in his kiss.

Dr Don says:


In Kissing, there is SALIVA exchange. Saliva contains Chemicals, enzymes, Ant-bacteria etc.

The partners have different concentration of these chemicals due to diet difference and just their sex (male and Female)

Kissing… is an evolutionary concept meant to Allow Bonding to TAKE place between Man and Woman. so if you WANT to BOND to a lot of KISSING b4 Sex.

its Gods design for Bonding Physically.

dont over complicate it ppl says:

People are making a huge assumption that everybody finds kissing pleasurable. I don’t. Though, strangely, i do feel closer to those i kiss.
I dont think kissing developed as a means to check out the levels of genetic variance between two people etc cuz otherwise it would’ve evolved alot earlier and it would be more universal (someone said up there that French kissing only really came about after the Victorian era in America; the 10% of humans who dont kiss). I think its just a means to increase bonding. I mean, we subconsciously analyze the smell of potential mates and this helps determine the level of attraction and compatibility, so if kissing were for compatibility and such then people wouldve evolved to skip straight to the kissing stage when scouting for potential partners right? i mean the order of things would be different e.g. ‘kiss, then flirt’ not ‘flirt, then kiss’. (And yes im discounting the club scene whereby people kiss whoever they hope to end up in bed with :-P But seriously, not all cultures would find the idea of kissing a stranger based on physical attraction attractive- this alone confirms the idea kissing is for strengthening a relationship).

Asking why people kiss is like asking why people tickle one another. Some people are ticklish- while others arent. While we cant say for sure how tickling came about and why some people arent ticklish – its true that for those who are it is a bonding experience and neither would you tickle a complete stranger.

Harvester says:

@ Ermine, October 3, 2006 at 1:19 am

Regarding your comment about quantifying ‘information’ and there being no ‘real’ science available on the need of information. I assume you’re talking about the need of information in relation to individuals?

There is in fact a whole field of biological research concerned with the ecology of information use. As you may guess information has to be defined in this field in order to be studied, so a definition does exist and it actually fiercely debated. Individuals gain information from the environment- within the scope of their gambit- on a day to day, second by second basis.

The ability to act on this information is what drives the behaviour of individuals. I suggest before you mount your high horse you should carry out some research of your own.

Soham Dongargaonkar says:

@chad, thunb up to you frm me too!

Marisano says:

Huh. Well, citing kissing among bonobos as evidence of it being instinctual is problematic since they are not any old animal, and can learn and pass learned things down culturally. [Also, even if kissing were to be instinctual in bonobos it would not necessarily be so in humans.]

sam says:

Kissing is practised or instinct is not important because kissing has a mojor role in pre sexual play

cry35- rennes- france says:

in fact i’m 32 years old bat i just use my mouth for eating I’ve never kissed so i can’t give you any opinion

sean says:

in addition to the above stated theories I believe kissing to be an act of trust. As is sharing a bed with another person. We are at our most vulnerable when asleep and to allow someone to sleep with us is a huge act of trust. To allow someone to touch you with their mouth is equally trusting. By doing this it is assumed you will not be bitten when you very well could be. This could have started very early on even before modern-humans were on the scene but this is pure speculation.

mckenna says:

i think its because we like it i am 11 and i love kissing it is awesome

krevez says:

in the artical it said that it’s an evolutionary thing that people are born with,which would mean that all cultures do it,but as the writer stated,no everyone does it!

I would think it would be a mixture of the learned thing,cause if it was learned,that means it would be in a specific group of people who do it.

there is also how it helps our immune system (exchanging bacteria and building immunities to it) and how it does help us find a mate.

the fact that “it feels good” is relative,cause it doesn’t for everyone.which would point to kissing being a learned thing,or maybe a certain evolutionary thing that comes out in some people,and not in others.

Jared says:

Why do Africans kiss? Because they aped it frm westerners,..why do westeners kiss?..avoidance of strange sounds a woman makes in sex by shutting her mouth,then they realise its good..
Again kissing is a temptation,we kiss when tempted to do so

VJ says:

I think a married guy can give us some hint here O.o

patrick roos says:

People and other animals kiss so the wife get infected with the viruses the man has but she doesn’t. This will lower the change of a primo-infection during pregnancy which can be disastrous. When they kiss, she get infected and form anitbodies.

patrick roos says:

It is bad for a women to get a primo-infection, with for example CMV when she is pregnant. When the man of the couple has for example CMV, and the wife does not, it is very beneficial for the women and the future kid, that the wife get in contact with CMV, BEFORE she get pregnant. Kissing is a very efficient way to infect the wife with viruses the man has and the wife not, which she did not encounter before. THAT S THE REASON. And to motivate animals/people to kiss, it gives a good feeling.

Kuunal says:

I would like to make a simple point. Probably its too raw and Basic as i havent studied evolution or psychology…I suppose a kiss is the only other way where a person’s insides connect with another person’s insides. So its the only possible option to sexual intercourse(the feeling to get inside the other person is what i mean here and not Sex)

Gaino says:

Kiss is the best!

Anonymous says:

i personally believe kissing is learned because, i live in a part of the world where people don’t kiss, well at least not in public. it’s considered obscene and i think i wouldn’t have learned to kiss unless i saw all those western movies

Anna says:

Interesting and funny that most comments are from men trying to find a logical reason for kissing. Its fun! Keep It Simple Stupid (KISS) :DDD

kenneth says:

we kiss cause we wanna. nothin’ gonna stop us from doing what we like. matters not what in the heck the reason is, we do what we do. kissing came bout as a way to feel good and show afection. dont go and make in complicated an hurt me head; math does enough of that that ye very much. just leave kissin’ as it truly is and stop trying to complicate every little thing in this world born of crimson flames and resolve of sword

Brian says:

“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.”

But then why do homosexuals kiss? Or elderly people? This theory doesn’t also work because, as mentioned earlier, the other then per cent who have no idea about kissing obviously breed as well, and also the majority of animals. I suppose it’s just another degeneration, such as oral sex.

Sunita says:

Kissing is universal trend of showing love ,affection and respect.There are unlimited reasons for kissing.I think kissing is as old as human civilization.There can never be one theory or reason for kissing.Interesting views are given in this article.

suomynonA says:


Could I possibly contact you in some way? I found your arguments quite interesting. Wouldn’t mind discussing further. Dot me at my e-mail: <- aka if you feel like it!

Me says:

Why do you all have to make such a scientific thing of it? It makes it harder to enjoy when all you can think of is exchanging bacteria!

joe common says:

Kissing has evolved from our relationship and domestication of canines. The act is the ultimate sign of respect and caregiving. Jesus used this analogy at the last supper. We as humans naturally overthink, it is about survival cut and dried.

Julis & the 10 dwarfs says:

i love this post. i also wondered why we kiss and the pleasure we got from it. i guess i will be content with this answer or I will derive the answer of my questions from the way i feel about who i kiss.

haibara says:

to scott #248
yup. evolution makes total sense. *eye roll* do you know how many times i have heard people say stuff like that? seriously. “we evolved from apes” then why the hell are they still around today?! as for adapting to habitats, where are the mammoths? saber tigers? what about all the species disapearing today like tigers and polar bears? did they forget how to evolve? of course not because it never happend! as for new species appearing, they arent compleatly new! for example, almost all dogs came from certain speicies of wolves and foxes. different species of wolves/foxes bred, making a new breed that carries the genes of both parents. say if a crossed a poodle and a yorkshire terrier. then thhier puppies would be yorkiepoos,correct? did the yorkie “evolve”? no! not to mention animals can change due to dna mutations, which mutates the rna which mutates the protiens that build the organism.
then theres the matter of the so-called “evidence” in the whale. why do they have tiny, useless hip bones? well for one thing, they could have a use that we simply havent discovered yet. if they dont have a use, then they have them for the same reason male humans have nipples. they are just there with no particular use. it coould be a growth caused by a gene from a different species of wale that mated with another, then went extinct, passing its genes on. either that or it could be as passed down mutation.
as for all the other people on this site who are calling everyone else that does not support darwins theory, quit calling them religouse and creationist freaks.there is scientifical support for THIS view too. the idea of evolution is just silly. if any organism could evolve then there would be no such thing as natural extinction.

Curt Welch says:

I think we kiss because it feels good. I think it feels good, because we are hard wired by evolution to make some things feel good and others feel bad because these hard wired “feelings” are the foundation of all our learning – the foundation of why we do everything we do – the foundation of how our brain’s learning system itself works.

The reason stimulating the lips and mouth is hardwired to feel-good, is because as strong learning machines, we must _learn_ to EAT after birth. We must learn to use our hands and arms to put food in our mouth. And even more important we must learn to breastfeed very quickly, or we will die. So evolution hard wired lip simulation as a reward to help us learn not to pull our head away while breast feeding, such as by kicking our legs, or moving our arms in the wrong way. That learning only works well if there’s a simple and obvious reward associated with it – which is why lip stimulation was hard wired as a reward – just as sex is hard wired as a reward in our brain so as to motivate us to do another very “odd” act to reproduce.

Kissing just evolved naturally as a social tradition because lip stimulation is hard wired as a reward for us.

james says:

kissing in an evolutionary way would have nothing but reduce the chance of survival by increasing the risk of disease.However maybe just perhaps ,if a man thought that my kissing a woman she would become more responsive to breeding with him then he might risk the chance of disease so as to increase his chance of mating .This of course makes no sense to the caveman like picture of dragging a woman by her hair to rape her …but says:

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elias says:

Adam And Eve did the first kiss.

harmoni says:

why people kiss? that’s because it’s the second sexual desire for most people in the world – why do people have sex? because it’s the first sexual desire for all people in the world and it makes people feel good,that their wanted by some one even if it’s a one night stand.

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Mike says:

Has anyone posted this yet? –
Kissing may be an offshoot of the sucking behavior of a nursing infant ?
So it’s an adult behavior that has that calming effect ?

pranav says:

kiss is the most beautyfull moment in the world……
one kiss ,it will change the world…
it is a wonderfull romantik feeling

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Shaun says:

Given that most mammals use smell to check out their partners esp their butts, the real question is why don’t humans smell their partners butt?

paris plan q says:

Thanks for finally talking about > Why do humans kiss?

Greg Greatew says:

This is a great source, I think!

Dinah Neri says:

I think that the reason we ‘evolved’ kissing is because to relates to mothers chewing food for babies and then putting it in the babies mouths directly from their own. Just like my dog wants to lick my face because she instinctively knows that the mother dog would give her ready chewed food if she does this. So it starts as caring for babies, and is thus already intimate. Then it gets mixed up with other intimacies.

It also expresses affection because providing for another does this. we don’t provide those we are not feeling affection for.

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