There is an area you might call the brain’s funny bone. It sits within the brain just behind the right eyebrow in a place called the ventromedial prefrontal cortex. This is where we “see” incongruity, and then register the surprise that makes us laugh. It’s the part of the brain that “gets” the joke, the whiplash effect. This may explain why you never see a laugh coming. It always surprises you. If it doesn’t, the laugh isn’t genuine.

Two cannibals are sitting in front of a campfire. One says to the other:

“Your husband sure makes a great roast.”

Second cannibal nods.

“Yeah. I’m going to miss him.”

Laughter is one of the great mysteries of human behavior. We make these noises at one another and though they have no specific meaning, we would be lost without them. This is because laughter’s roots are primal. They reach back long before language evolved. This is also why laughing is universal. Everyone laughs, no matter their station or language, whether they hunt corporate heads among the skyscrapers of Manhattan or real ones in the forests of Borneo. And it’s contagious. A television technician named Charles Douglas proved that when he invented the laugh track in 1953. It’s still standard equipment for every sitcom. When others laugh, it is difficult to not laugh with them.

Laughing is usually related to play and fun, but not always. Dante once remarked, “He is not always at ease who laughs.” And Darwin pointed out that people laugh not just when they’re enjoying themselves, but when they feel shame and anger, are uncomfortable, or want to mask an emotion. Sometimes it’s a signal of subservience; when an employee laughs at a less than funny joke the boss just made, for example. And one of the worst feelings in the world is to feel laughed at rather than laughed with. It’s an instant signal that you’ve been left out, aren’t in on the joke, or worse, are the joke.

The uncomfortable and primal nature of laughter makes it difficult to sensibly dissect exactly how it happens because it predates the evolution of the language we try to use to explain it. Several years ago a psychologist at the University of Hertfordshire named Richard Wiseman decided he’d attempt to gain a little insight and created a project he called LaughLab. Wiseman and his colleagues set up a website and asked people to submit their favorite jokes and at the same time asked people to rate which they thought were funniest. Three hundred and fifty-thousand people submitted 40,000 jokes and two million ratings. This was the winning joke:

A couple of New Jersey hunters are out in the woods when one of them falls to the ground. He doesn't seem to be breathing; his eyes are rolled back in his head. The other guy whips out his cell phone and calls the emergency services. He gasps to the operator: “My friend is dead! What can I do?” The operator, in a calm soothing voice says: “Just take it easy. I can help. First, let's make sure he's dead.” There is a silence, then a shot. The guy's voice comes back on the line. He says: “OK, now what?"

Why was this joke chosen the funniest? Because of its broad appeal, said Wiseman. No matter who read it, men, women, young old, all nationalities, everyone laughed. Wiseman also theorized that readers felt superior to the witless hunter who eventually did in his own companion.  Another appeal was that it provided a release for people’s own fear of death, something we all share.

Sigmund Freud agreed. In 1905 he wrote that jokes reveal fears and feelings in all of us that might otherwise be inappropriate, not unlike dreams. The laugh itself was a physical expression of the relief. Maybe, he suggested, feelings that were dark and startling, even angry, lurked behind every joke or one-liner, but the joke made its expression publicly acceptable because it masquerades as positive.

On the other hand, sometimes a cigar is just a cigar.

It is true, though, that the uncomfortable positioning of two opposites in a joke has a way of creating a kind of whiplash effect in the mind. In the case of the LaughLab joke the story takes you in one direction leading you to think that someone concerned enough to call 911 about an injured friend would be more likely to go back and delicately check his pulse rather than un-shoulder his rifle and shoot him. That’s completely the opposite of what you’re expecting, and under the circumstances, it’s hilarious because the whiplash is so sharp.

All jokes have this in common, whether its Dorothy Parker’s “Don’t put all of your eggs in one bastard,” or “I just flew in from Pittsburgh, and boy are my arms tired.” To be amused, our minds have to be zipping along in one direction and unceremoniously yanked in the other.

Wiseman’s lab didn’t simply observe and speculate on this whiplash effect, it measured it using functional magnetic resonance imaging (fMRI). The scans found that we have, cerebrally at least, no Comedy Central; humor and laughter are scattered all over the brain because different areas of it light up depending on whether it’s processing visual or verbal humor, parsing a pun or processing a pratfall. A different part of the brain even devotes itself to sensing when others are laughing (this helps explain the contagious part of laughter), and still another area marshals the forces that generate the short explosive sounds that are the signature of every kind of laugh from timid giggles to wild guffaws.

There is, however, an area you might call the brain’s funny bone. It sits just above the right eyebrow in a place called the ventromedial prefrontal cortex. This is where we “see” incongruity, and then register the surprise that makes us laugh. It’s the part of the brain that “gets” the joke, the whiplash effect. This may explain why you never see a laugh coming. It always surprises you. If it doesn’t, the laugh isn’t genuine.

The reason we’re surprised when we laugh is connected to its primal origins. A lot of animals have developed involuntary sounds they make that are hardwired into their behavior: the songs of birds, or the howling of a pack of wolves. When chimpanzees are foraging in a forest for food they involuntarily call out in a particular way when they find it. Their DNA dictates the behavior and they can’t help it. It’s a little evolutionary trick that ups the chances of the troop’s common survival by spreading the word that nourishment has been found.

Jane Goodall tells the story of watching a chimp in the wild who was foraging alone in the forest and found some food. The chimp wanted to stop the food call, and even tried to cover its mouth to keep the food for itself, but it couldn’t stop. Laughter is like this too. It has one of its feet in the primal world, and another in the modern one, the one that requires sophisticated intelligence.

Given all of this research you’d think we do most of our laughing when we’re sitting in front of the television or in a movie theater passively watching a comedian or some hilarious comic scene. We don’t. Mostly we laugh when we are simply enjoying one another’s company. Psychologist Robert Provine at the University of Maryland says we are thirty times more likely to laugh when we are hanging out with others then when we are alone. That’s because in the end laughter is really less about humor and more about bonding and communicating.

Provine and his students came to this conclusion after years of research in bars, restaurants, malls and anywhere people gathered, talked and laughed. They attentively studied what all the laughing was about and made some fascinating discoveries. We laugh, it turns out, more when we are doing the talking than when we are listening—46 percent more. When we are in mixed company, no matter who is talking, women laugh 127 percent more often than men do. And men, when they are talking, laugh seven percent less than their female audience does. Put another way, when male and female humans get together, women do most of the laughing, and when women are talking both men and women laugh less than if men are talking.

This isn’t because men are incredibly witty and women are hanging on their every word. Instead this is what what zoologists call lekking, the behavior of a male animal when he’s strutting his stuff, like a peacock. By laughing women encourage men to strut so that they can survey them, and see what they have to offer. Good companion? Smart? Worth my time? The more she laughs, the more he may reveal. Not that any of this is happening consciously. It’s wired into us and we’re almost entirely unaware of it.

Provine’s work also revealed that, contrary to what you may think, we don’t spend most of our time laughing at sidesplitting, Woody Allensque one-liners. A mere 20 percent of laughter follows a good joke. Mostly we just laugh at comments because of the context, the relationships, the delivery and the people. Or, again, because everyone else is laughing. The funniest line that the researchers found was, “Do you date within your own species?” Amusing, but not Woody Allen, which is why, I suppose, we have all told someone else a story we found hilarious, but they didn’t, and then find ourselves explaining, “Well, I guess you had to be there.”

The central point is that when people laugh together, they are connecting on some unconscious level the way coyotes do when they howl in chorus at the  moon. We cohere and grow closer. One theory is that laughter evolved out of a primal need to get the attention of the others around us (something like the way a baby’s cry gets the attention of a parent). It supercharges our efforts be attractive, important, accessible, accepted. It might be a way of reaching out (playfully) and saying, “I want you to know I am here and that I matter. And if you are laughing with me, then I guess I’m succeeding.”

It might be as simple as this: when we laugh with someone, we are bonding with them. We laugh most with the people we like, and we most like the people that we laugh with. It’s a feedback loop. We are members of the same troop. It is the one time in our mental and emotional lives when we completely drop our guard; when we are not wondering what the other people around us are feeling or thinking.

And it’s good for you. Various studies have shown that laughing increases endorphins, reduces blood glucose levels, strengthens the immune system and increases heart health.

That’s the power of laughter. Somehow these odd noises we share spontaneously draw us together in ways that are uniquely human and that words can’t express. As emotional human glues go, it may be the most powerful one of all.

This article was drawn from Chip Walter’s book Thumbs, Toes and Tears (And Other Traits That Make Us Human).