Socializing is found across the animal kingdom, but osculation — or kissing — seems to a human behavior. How did it start and why? The Science of Kissing author Sheril Kirshenbaum discusses the history and biology behind kissing.
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IRA FLATOW, host:
You're listening to SCIENCE FRIDAY. I'm Ira Flatow.
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Up next, our Valentine's Day gift to you: the science of kissing. I know, you're saying science, you're saying kissing. Kissing is an art, not a science, right? Well, my next guest has written a book called "The Science of Kissing," which covers not only osculation - there's the word for today - the scientific word for kissing - but its history and all kinds of stuff having to do with kissing, when and why did it start, why did giraffes neck and dogs lick but we're the only species that kiss, besides bonobos? Yeah.
Sheril Kirshenbaum is the author of "The Science of Kissing" and research associate at the Center for International Energy and Environmental Policy at the University of Texas at Austin. She joins us by phone from there.
Welcome back to SCIENCE FRIDAY.
Ms. SHERIL KIRSHENBAUM (Author, "The Science of Kissing"): Hi, Ira. Thanks so much for having me back.
FLATOW: I'm hoping that we can give some people, you know, good reason to appreciate Valentine's Day more.
Ms. KIRSHENBAUM: Well, I hope they kiss more. That's definitely something good for us.
(Soundbite of laughter)
FLATOW: Is it really good for us?
Ms. KIRSHENBAUM: Oh, it's great for us. I think more than anything it firms up our relationships. It let's someone know how we feel, expresses - we can express ourselves in ways that words just don't.
FLATOW: Can you actually measure bodily changes that go on if - during kissing?
Ms. KIRSHENBAUM: Yeah. There's been some great research on this. At Lafayette, two endocrinologists were interested in the way hormones changed, both oxytocin, the love hormone, and cortisol, known as the stress hormone. They invited student volunteers into their laboratory, had them - well, actually into their health facility, had them make out and prodded them with needles and had them spit in a cup and measured how things were changing in their bodies.
FLATOW: I'll bet you they had - they paid them to do that.
(Soundbite of laughter)
Ms. KIRSHENBAUM: I think it was pretty much a volunteer basis, but the funny thing about that experiment was the results weren't quite what they expected. And then over time it dawned on them that maybe a health center and being poked with needles wasn't the most relaxed environment and that might have had something to do with it. So they re-did the experiment in a dark quiet room with candlelight and music...
Ms. KIRSHENBAUM: ...and had some different results.
FLATOW: That or the back of a movie theater somewhere...
Ms. KIRSHENBAUM: That could probably work too.
(Soundbite of laughter)
FLATOW: ...or a '57 Chevy. Is there a scientific definition for a kiss?
Ms. KIRSHENBAUM: You know, what surprised me most writing this book was how little research has gone into study the science of kissing, because it's a near universal behavior so many of us can relate to, and we spend so much time and energy studying behaviors in other species, like foraging behavior in birds, like ants carrying leaves, which are also interesting, but why not put the microscope under, you know, to ourselves.
And so there isn't any kind of taxonomy, like there would be in most things that scientists would study. But in - for the purpose of my book, I defined a kiss as pressing of one's lips to another, well, to someone else's lips or body part or even an object.
FLATOW: Uh-huh. 1-800-989-8255 is our number. We're talking about the science of kissing with Sheril Kirshenbaum.
Is it true that we are the only species that kisses?
Ms. KIRSHENBAUM: That is a great question. Well, scientists have to be very careful when we want to talk about the emotions and the motivations of other species, because we can't pretend to know what drives them. So instead of words like love, we'll say things like mate selection or selective perceptivity.
But then when you look around the animal kingdom, that said, we see a lot of behaviors that look a lot like kissing. As mentioned before, bonobos have been spotted to suck on each other's tongues for about 12 minutes straight. We see turtles tapping heads, giraffes entwining their necks. I have a dog. Dogs will lick any noun - you know, person, place or thing.
Ms. KIRSHENBAUM: So we see a lot of similar-looking behaviors, and if we're willing to broaden the definition of kissing to this kissing-like behavior, which is actually what Charles Darwin did, then I think that we can say that we do see similar behaviors in other species for reasons from affection to grooming to social hierarchy to conflict.
FLATOW: Is there any way to pin down how long human beings have been -when they first started kissing?
Ms. KIRSHENBAUM: Well, the earliest literary evidence we have for kissing dates back to India's (unintelligible) Sanskrit texts, which are about 3,500 years old. But I would suspect, especially given all of these behaviors that I was talking about across the animal kingdom, humans have probably been connecting in some kind of similar way for as long as we've been here.
FLATOW: And are our lips, I mean, designed for a special function like kissing?
Ms. KIRSHENBAUM: Well, our lips are packed with sensitive nerve endings, so even the slightest brush sends a cascade of signals and information to our brains, and the amount of our brains associated with lip stimulation - sort of the brain's-eye view of the body in terms of touch - is enormous. It's very disproportionate to other organs. So in that way our lips are our almost exposed erogenous zones, and they're really our way of interpreting the world. And for all sort of reasons, we're drawn to another person's lips. It's a wonderful example of a behavior that's both nature and nurture. So humans seem to have this instinctive drive to connect with someone this way, but it's also very much influenced by our culture and personal experiences.
FLATOW: It's interesting, you talked about Bonobos. And we know Bonobos to be among the most affectionate animals.
Ms. KIRSHENBAUM: They are quite amorous, yes.
FLATOW: Yeah. And so they - and they're sort of doing their own kind of kissing there too, that's interesting.
Ms. KIRSHENBAUM: Mm-hmm. They also have pink lips like we do.
FLATOW: Is that right?
Ms. KIRSHENBAUM: Mm-hmm. Mm-hmm. Although human lips are uniquely averted so they purse outwardly. And they're probably more sensitive than other species. So in species like chimpanzees, which also kiss, they're probably not as sensitive and it's almost more like a hug (unintelligible).
FLATOW: Hmm. Do we give off any, you know, pheromones, any odors that start - might want us to kiss somebody?
Ms. KIRSHENBAUM: Two parts to that question. So scent plays a very big role in kissing. When we're kissing someone, we're engaging all of our senses. So rather than just getting visual information up until that point, all of a sudden our noses play a big role, our sense of taste, our touch.
And there's actually been research on - perhaps you've talked about this on the show, the major histocompatibility complex. So the set of genes, the MHC, which codes for immunity. And women seemed to be most attracted to men whose genetics for immunity are very distinct from their own. And so - I'm sorry - women seemed to be most attracted to the scents of men with an MHC distinct from their own. And so when we're kissing, we're in what we call our personal space. It's a perfect opportunity to get that sample and to sense whether this might be a good match for us. And the advantage of that would be, if two people with more genetic diversity in this region got together, their child might be stronger, healthier, have a better immune system, be more likely to pass on their genes.
So pheromones are a very controversial topic. Humans definitely secrete chemicals that we recognize as pheromones in other animals. But we're not quite sure whether humans have immunity to detect them.
FLATOW: Hmm. That's interesting. You talk about - in the section of your book called "The Anatomy of a Kiss"...
Ms. KIRSHENBAUM: Mm-hmm.
FLATOW: ...and how there's a certain, you know, turning of the head that's important.
Ms. KIRSHENBAUM: Yeah. Two-thirds of us seemed to tilt our heads to the right. There is a study where someone went around to airports, public parks and beaches and observed couples kissing. And they couldn't be encumbered by luggage. There were strict protocols to follow. He watched people making out and recorded what he saw and came up with a figure, two-thirds, and this study was actually published in the journal Nature.
And we're not quite sure why that might be. But one possibly is that it might have to do with the direction of fetuses tilting its head in the womb or many women are nursing to the left, so the infant would be turning up to the right. But we're not...
FLATOW: What about if you're a righty or a lefty? Left-handed...
Ms. KIRSHENBAUM: No, it's not correlated, which is so interesting.
FLATOW: It's not?
Ms. KIRSHENBAUM: No. It doesn't seem to be.
FLATOW: You know, everybody thinks they're a great kisser, right?
(Soundbite of laughter)
FLATOW: I mean, what makes a good kisser?
Ms. KIRSHENBAUM: Oh, there's so much involved. I mean, there's things that we can and can't control. So a good kiss is very much about the individuals involved, understanding kind of the needs and desires of the other person. But environment is so important. I mean, a kiss that takes place when two people are feeling very comfortable is going to feel very different than a kiss happening - there was bad timing or someone feels a lot of pressure, because then you're going to have this stress hormone, this cortisol, in your body, and kissing and cortisol don't mix.
But there are a whole bunch of different factors. And also, even if this sort of natural scent can play a role well beyond our control, but it tells our body a lot of information about whether to pursue a deeper relationship or maybe look elsewhere. And, in fact, 59 percent of men, 66 percent of women, say they've ended a budding relationship because of a bad first kiss. So we're really, really paying attention to what's going on. Not always, again, consciously, but it matters. It's a really significant moment in our lives. It creates extremely vivid memory for us to go back to and sort of figure out what's going on.
FLATOW: Here's a tweet from Brian(ph) in Stockdale(ph), who says: Any research on the healing powers of a kiss? My wife kisses my booboos and it feels better.
(Soundbite of laughter)
Ms. KIRSHENBAUM: I love that question, Brian. Well, no research specifically on I guess correlation with healing. But kissing is associated with feelings of attachment, of really firming up an important relationship that you have. So when you're around someone you love, you're very comforted. There have been studies that people seem to experience a lesser degree of pain when they're holding the hand of a husband or wife. And so I wouldn't be surprised that your wife's kiss makes you feel a bit better.
FLATOW: Mm-hmm. Let's go to Maya(ph) in Dayton. Hi, Maya. Welcome to SCIENCE FRIDAY.
MAYA (Caller): Hello.
FLATOW: Hi, there.
MAYA: Well, thank you. My question is, basically - I might not be asking it correctly, but I've been criticized on several occasions by, you know, by boyfriends that I'm not a good kisser. And I've never truly enjoyed kissing. I don't know why. I don't know if it's, you know, for sanitary purposes or whatnot. But I'm a very emotional, amorous person. So is a person who doesn't like to kiss, are they - is there any reason behind it that you would be aware of?
FLATOW: There's something wrong with Maya...
Ms. KIRSHENBAUM: No.
(Soundbite of laughter)
Ms. KIRSHENBAUM: You're just fine. Don't worry at all. No. I mean, you know, a lot of it has to do with our own experiences, what we're comfortable with. And in your case, it's possible that all of these people who have been criticizing you are making you pretty uncomfortable when you're going in each time to give it another chance. But - you know, there are a lot of people who just don't like kissing. It doesn't mean that there's anything wrong.
There are varied different ways for us to connect with individuals. Our lips are just a really good one because, as I was saying before, they are so sensitive. And in our earliest memories, they're also - our earliest experiences as children, our lips are often associated as we're feeding and nursing, doing similar movements with our first feelings of security and love and comfort. So often that - the same neural pathways are involved later on with a romantic partner. But there are many ways to connect.
FLATOW: Maya, you just have to practice it some more, right?
MAYA: (Unintelligible) not to do it. I don't know why. I just - I've never really liked kissing. And you know, my whole, my entire family, we see each other, we kiss on lips.
MAYA: And you know, as long as it's a nice quick kiss, that's fine with me.
(Soundbite of laughter)
MAYA: But with, you know, a significant other...
MAYA: ...I like, you know, quick kisses but not long, drawn-out kisses...
FLATOW: Well, I'm sure - I'm sure it's working for you anyhow. Thanks for calling, Maya. That's about all the time we have for today. Sheril, thank you for taking time. That was great.
Ms. KIRSHENBAUM: Thank you so much for having me on. And Happy Valentine's...
FLATOW: We're going to give you a few more minutes here, because a lot more people want to talk to you about kissing.
Ms. KIRSHENBAUM: Oh, terrific.
FLATOW: So let's see if we can get some more folks on here. This is what's interesting to me, is this question, because I'm an Aquarius. Go to Todd in Cleveland, who's going to talk about the kissing gourami, right, Todd?
TODD (Caller): That's right. Thanks so much for taking my call.
FLATOW: Go ahead.
TODD: I'm an aquarium enthusiast. And there are several different species of gouramis, but one of my favorite species is called the kissing gourami. And it's a pink fish, ironically. And many of the other different species have poor eyesight. And they have elongated pectoral fins that almost look like antennae, but the kissing gourami does not have these. And it was long thought that they kiss, actually pursing their lips and kiss as an identifier. But the interesting part is that it's only breeding pairs that kiss.
FLATOW: Huh. Is that right?
TODD: So there is some kind of connection between the kissing and breeding. And they actually breed with bubble nests(ph) they're very interesting fish. They're labyrinth fish, so they can store airborne oxygen to breathe, et cetera, et cetera.
FLATOW: Let me just remind everybody that this is SCIENCE FRIDAY from NPR. I'm Ira Flatow, talking with Sheril Kirshenbaum, author of "The Science of Kissing." Do gouramis really kiss, Sheril?
Ms. KIRSHENBAUM: Well, my understanding of the species - my background is actually in marine science - is that they'll also touch lips in conflict. So it's sort of a socially significant behavior that can take on many forms within individuals and among the species. Because we also have to remember with animal behavior...
Ms. KIRSHENBAUM: ...we can't - it's hard to generalize since we have so few - so little to sample from. So one individual could do something different than another individual in a different part of the country or the world.
FLATOW: Right, right. Let's go to Randy in Pullman, Washington. Hi, Randy.
RANDY (Caller): How are you doing?
FLATOW: Hi there.
RANDY: Great. I just wanted to make a comment. I have a really, really autistic son. And when he goes into autism land, we call it, I'll go over and kiss him on the forehead or kiss him on the cheek or kiss him on the hand and he comes out of it and he's smiling, and he's quite happy.
FLATOW: Wow. You just - you just have to keep doing that.
RANDY: I've been doing it for 22 years.
(Soundbite of laughter)
FLATOW: There you go. Well, good for you. Thanks for calling.
RANDY: You're welcome.
FLATOW: 1-800-989-8255. Let's see if we can get a lot of people -Valentine's Day coming up. Any hints for Valentine's Day, Sheril?
Ms. KIRSHENBAUM: Yeah. Absolutely. Well, women pay a lot of attention to the scent. Sorry scent too(ph) - but to the breath and teeth of a partner. So keeping things like that in mind is definitely a good idea. There's also a lot of gender differences in kissing, which are really interesting.
Women place a lot more emphasis on the act of kissing itself. So it's a good idea for men to kind of take that into consideration and recognize how important it can be as, you know, she's consciously and subconsciously trying to learn a bit more about you.
FLATOW: Do you have to set up the kiss well? Should you set it up?
Ms. KIRSHENBAUM: The moment definitely does matter. You go in too soon and, again, you're going to be pumping lots of cortisol - not the best moment. But on top of that, I think the best advice I can give is when you do find someone special, kiss and kiss often, because it's not just about a new relationship. It's about maintaining that special bond, getting that oxytocin flowing. And it's partly responsible for - you know, kissing and oxytocin - similar behaviors keep couples together. It's a way to reconnect, and it matters tremendously in a relationship.
FLATOW: Mm-hmm. And so it's a good thing to practice.
Ms. KIRSHENBAUM: Absolutely. We should all be kissing more.
FLATOW: Practice till you get it right. I want to thank you for taking the time to be with us today.
Ms. KIRSHENBAUM: Thank you so much for having me on. This was fun.
FLATOW: You're welcome. Sheril Kirshenbaum is the author of "The Science of Kissing." And she's research associate of the Center of International Energy and Environmental Policy at the University of Texas at Austin in Texas.
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