Human Behavior: The Mysteries of Laughter and Kissing

FROM THE LECTURE SERIES: UNDERSTANDING THE MYSTERIES OF HUMAN BEHAVIOR

By Mark Leary, Ph.D., Duke University

Laughter and kissing are two human behaviors that still baffle scientists. Why do people laugh, and why at some things but not at others? What function does kissing serve, and why do most people seem to enjoy it? Several explanations seem plausible, but none of them is entirely satisfactory.

A family sitting together and laughing.
A lot of human behavior is still shrouded in mystery, especially things like laughter. (Image: fizkes/Shutterstock)

Laughter: Not Just Funny Stuff

Laughter is so normal and so natural that you may have never thought about how strange it really is. Most people think of laughter as an involuntary physiological response to humor. You automatically laugh when something’s funny, right? Well, not necessarily.

Not only do we not laugh at everything that we think is funny—sometimes we just smile or feel amused—but we also laugh at things that are decidedly not funny.

For example, sometimes people laugh when they have embarrassed or humiliated themselves in public. And sometimes people laugh at things that are awkward, or dangerous, or even tragic. People even laugh involuntarily while recounting a horrible story in which someone is badly hurt or even killed. So, laughter isn’t just a natural reaction to things that are humorous.

The Stress Relief Theory

Some theorists have suggested that laughter is fundamentally about releasing stress, and others have offered the related idea that laughter may reflect an expression of relief after some danger has passed.

You may have experienced that kind of laughter yourself when you nearly had an accident, or a mishap. As soon as it was clear that everything was alright, you laughed. And laughing seemed to reflect your relief that things had turned out OK. And, likewise, laughter certainly does help people cope with stress and other negative emotions. But this doesn’t explain why we laugh most often when we are happy rather than when we are upset.

This is a transcript from the video series Understanding the Mysteries of Human Behavior. Watch it now, on The Great Courses Plus.

Laughter is Personal and Social

One important clue in trying to understand laughter is the fact that laughter almost always occurs in encounters with other people. Research shows that people are about 30 times more likely to laugh when interacting with other people.

Even humorous events are much more likely to make people laugh when they’re with other people. This observation suggests that laughter may be a social signal of some kind rather than just an expression of emotion or a release of tension. But what does laughter signal?

People laughing together in a social situation.
Social situations seem to prompt more laughter than when a person is alone. (Image: Monkey Business Images/Shutterstock)

Research shows that people who are engaged in a conversation are much more likely to laugh after they say something themselves than they are to laugh at what other people say. So, perhaps laughter conveys playfulness or is designed to promote social bonding. Perhaps laughter signals an openness or a receptivity to being connected with other people.

After all, we usually don’t laugh—I mean genuinely laugh—around people we dislike. And furthermore, research shows that laughing together brings people closer and improves social relationships. So, maybe laughter is a signal that indicates a desire for social connections.

Does Laughter Show Playfulness?

Some researchers have suggested that laughter evolved from the play signals that are used by nonhuman primates. Apes sometimes hoot and holler when they play with each other, and you can see similar behaviors in small children. They giggle and laugh and shriek while they are playing.

These playful sounds seem to be signals that say something like, “I’m having fun with you,” or “I’m enjoying our interaction”. And perhaps laughter sends the same signal among adults. So, laughter may signal or promote social bonding, although that’s still not a complete explanation.

For example, it doesn’t easily explain why we tend to laugh at certain things and not at other things. If laughter is a social signal that conveys closeness or connection, then it shouldn’t matter much what we laugh at. But some things really are funnier than others.

So, laughter remains a bit of a mystery. At present, we have many miniature theories of laughter, but no single theory that covers all instances in which people laugh.

Learn more about the complex processes by which nature and nurture interact to create differences in siblings.

But Why Kissing?

The same is true of kissing. Kissing between romantic or sexual partners occurs in about 90 percent of human cultures, and even in cultures where mouth-to-mouth kissing is not accepted, partners often lick, suck, or rub their partner’s faces.

Two bonobos kissing.
Many apes, like bonobos, kiss each other, much like humans do. (Image: Nuria Ruiz/Shutterstock)

Certain other species kiss, too. Bonobos not only kiss a great deal, but they also engage in deep tongue kissing. In any case, the origins of human kissing may lie deep in our animal past.

One theory is that kissing evolved from the behavior of primate mothers passing along chewed-up food to their toothless babies. Many animal parents chew-up food and pass it along from their own mouth to the mouth of infants who don’t yet have any teeth.

Kissing as a Method of Assessing Partners

Another explanation is that kissing evolved as a way of assessing things about a potential partner. Animals, such as dogs, size each other up by sniffing each other.

Well, human beings don’t have the same acute sense of smell that most other mammals do. Maybe we require very close physical contact to provide us with information about another person.

Research shows that the smell of another’s person’s breath and the taste of someone’s saliva can provide information about the person’s state of health. There’s also evidence that men can detect whether a woman is ovulating through taste and smell. It might also be that people assess the other person’s degree of interest and involvement in a relationship by how they kiss.

Of course, people are not purposefully assessing each other in these ways when they kiss. But it’s certainly possible that kissing evolved to put people into contact with the skin and saliva of potential partners to assess certain things about them.

Learn more about the three main “love systems” in the brain.

Kissing and Closeness

A third explanation is that, like laughter, kissing promotes social bonding. People report that kissing often increases a sense of closeness. Research studies show that kissing releases hormones, such as oxytocin, that increases feelings of social connection.

We typically don’t kiss people we don’t want to feel close to. Perhaps that’s why not only human beings, but also chimpanzees and bonobos, kiss each other to make up after conflicts and fights, which also supports the social bonding hypothesis.

A fourth perspective suggests that kissing increases sexual interest. But why kissing? Why don’t we rub each other’s ears or twiddle each other’s noses instead of touching lips?

We have several possible explanations for both kissing and laughter, each of which has a certain amount of support, both from people’s personal experiences and from scientific research. But there’s no general agreement about which one theory could be the most likely.

Common Questions About the Reasons for Laughter and Kissing

Q. Is laughter always a reaction to humorous things?

Laughter is not always a reaction to humorous things. People laugh when they have embarrassed or humiliated themselves in public. And sometimes people laugh at things that are awkward, or dangerous, or even tragic. People even laugh involuntarily while recounting horrible things in which people are badly hurt or even killed.

Q. In what way is laughter a social activity?

Research shows that people are about 30 times more likely to laugh when interacting with other people. Laughter may be a social signal of some kind rather than just an expression of emotion or a release of tension.

Q. What is the connection between laughter and playfulness?

Some researchers have suggested that laughter evolved from play signals. Small children giggle and laugh and shriek while they are playing. These playful sounds seem to say something like, “I’m having fun with you,” or “I’m enjoying our interaction”. Perhaps laughter sends the same signal among adults.

Q. What are the two theories that may explain kissing?

The two theories that may explain kissing are: kissing evolved from the behavior of primate mothers passing along chewed-up food to their toothless babies; or, kissing evolved as a way of assessing things about a potential partner.

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