It’s not Valentine’s Day yet, but I couldn’t pass up the opportunity to post about Chip Walter’s article in Scientific American called “Affairs of the Lips: Why We Kiss.”

According to Walter, ethologist Desmond Morris (who wrote The Naked Ape among other interesting books) suggested that human kissing evolved from a practice found in primate mothers, who may have pre-chewed food for their infants and then fed them mouth-to-mouth. Subsequently, pressing lips even without food may have provided a signal of comfort and love.

Whether our lips were influenced by the practice of kissing or not, they certainly have more than their fair share of sensitivity, as you may have noticed if you have ever had a paper cut from licking an envelope. Kissing also effects our biochemistry. Wendy Hill and Carey Wilson found that two substances, oxytocin and cortisol, were influenced by kissing. Cortisol levels, which usually rise when we’re alert or stressed, drop when couples kiss, talk, or hold hands. Oddly enough, oxytocin levels increased for males after kissing, but dropped in females. Oxytocin has been implicated in a number of social bonding activities, including orgasm and nursing an infant. Obviously, more research needs to happen in this area to see why men and women are reacting differently.

How important is kissing? Gordon Gallup and his colleagues argue that a first kiss is really important to people. Fifty-eight percent of men and 66 percent of women recalled an instance where they ended a promising relationship because the first kiss didn’t “feel right.” However, these same researchers argued that kissing means very different things to men and women. Men viewed kissing as a step towards more sexual activity, whereas women viewed kissing as a bonding mechanism.

Science has a way of making some very romantic things seem less so by dissecting them. I’m not sure if this is useful information for you, but apparently most people tilt their heads to the right in order to kiss (check out Clark Gable and Vivien Leigh above). The advantage for such laterality seems to be mysterious, but we can guess that brain laterality plays a role.

Here’s another interesting factoid from Walter–apparently about 10 percent of the world’s population do not kiss. I guess they don’t know what they’re missing.



bhidahl · February 3, 2008 at 9:58 pm

this is an interesting article! i guess i never really thought about why we kiss before. kissing just seems like another way to show affection to me and it doesn’t have to be sexual. then again, it depends on how you’re kissing of course. obviously parents kiss their children, and pecks on the cheek or forhead are not the same as deep kisses on the lips. i find it interesting that oxytocin levels drop in women when kissing, but rise in men. perhaps it has to do with the view of kissing described – that men view it as leading into something more, but women don’t necessarily think a kiss has to lead to anything. that actually reminds me of a scene from a 90’s tv show called “My-So Called Life.” The mom/wife complains about how her husband doesn’t kiss her goodbye in the morning and he replied that they don’t have time to start anything so why bother. apparently this stereotype has been around long enough to appear in our pop culture. i can definitely relate to the cortisol levels dropping though…a good cuddle or kiss can do wonders for my stress level!

aoneil · February 3, 2008 at 10:32 pm

It seems that Valentine’s Day is one of those days that people either look forward to or completely dread. For those of us in a relationship, it’s a day to remind us how much we care for our significant others. But for those of us who are single it seems to also be a reminder that we still haven’t found that “special someone.” At least one positive aspect is the chocolate, which is said to signal “feel good” chemicals in the brain 🙂 And it can even be good for you, if it’s dark with antioxidants.

biopsych · February 5, 2008 at 4:40 pm

I really liked this article. It was interesting to hear that “10 percent of the world’s population doesn’t kiss.” I would be interested to know what areas this predominately occurs in. I agree that many people put high stakes on the first kiss because you always hear people (well usually women) talking about if there were “sparks” and if they felt an instant connection.

bblaine · February 5, 2008 at 6:47 pm

I am like many other women in the world who believe a good kiss can say a lot. Kissing is extremely important. I am shocked to hear that 10 percent of the world’s population don’t kiss. However, I do believe that Valentine’s Day is not that important. This day was literally put in place as a marketing mechanism. Loads of people spending money for no reason except that they are “told to.” On the other hand, kissing on Valentine’s Day seems much more romantic than kissing on any other day. But, that’s probably just a mental thing.

bldrysdale · February 6, 2008 at 12:40 pm

This article was very interesting. I was also surprised that 10% of the world doesn’t kiss. In the study about tilting our heads to the left, I wonder of case studies have been done on the people who tilted their head to the left. It would be interesting to know if their were any other differences with these people. Also while the study by Morris about the apes really didn’t make kissing seem as romantic, it does make one think that this is connected with food as comfort. Maybe instead of over eating when one feels bad, one could over kiss instead?

Laura Freberg · February 17, 2008 at 10:55 am

The 10% figure all of you seem to find interesting is from a 1972 book by Irenaus Eibl-Eibesfeldt entitled “Love and Hate: The Natural History of Behavior Patterns. You can read more about the book here:

Unfortunately, this is not available at the Cal Poly library, although an earlier title by Eibl-Eibesfeldt (Human Ecology) is.

trubio · February 23, 2008 at 9:35 pm

I’ve never really thought about where the kiss originated either… I kind of just figured it’s always been done. I don’t really like the idea that it started with primates though, for some reason.

I’m interested in knowing what’s different about someone who typically tilts their head to the left when kissing. Does it relate to left handedness at all?

amandam · March 5, 2008 at 11:47 pm

I was very intrigued when I seen the title of this topic, I do have to say it pulled me in. It was very odd to find out that 10% of the population don’t kiss and I’m going to have to agree with you, they do not know what they are missing out on. Well I’m going to have to say that with me a kiss means a lot for a relationship. I once kissed a guy who’s lips were so stiff and cold that it totally made me unattracted to him. On the other hand I would have to say that with my first kiss, it was so great I literally almost fell, I was weak in the knees, no lie.

reggie · March 13, 2008 at 3:39 pm

This topic really seemed to interest me. I have to say a kiss is a very big part of intimacy for me in a relationship. And sometimes if the kiss isn’t good the first time, there’s always room to make up for it. Maybe the next time will be better…hopefully. I also think the intensity of the kiss is flexible and depends on your feeling at the time of the kiss. I feel you can kiss your GF/BF to show a deep affection…and if the mood is right…it will probably turn into something sexual. Kissing or not, I believe everyone should experience it, it’s one of those simple things that make us feel better.

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