(CNN)Everyone likes a good belly laugh from time to time, and science supports that feeling.
Studies have shown that laughing is linked to our physical, emotional and mental well-being -- even our relationships.
Here are some things you might not know about laughter.
Laughter was a survival tool
Laughter is thought to have evolved as a form of social bonding in animals and as a way to express playful intention. Many mammals laugh when they are tickled and when they engage in physical play.
But humans don't need a physical trigger to laugh -- though generally we can't help but laugh if we're tickled.
Janet Gibson, a professor emerita of cognitive psychology at Grinnell College in Iowa, said that laughter evolved in humans as a communication signal.
Hundreds of years ago, "laughter was the glue that kept the group together," she told CNN Chief Medical Correspondent Dr. Sanjay Gupta on his Chasing Life podcast.
"The idea was that laughter was an external signal that can tell the group everything is OK, we can relax. (There is) no need to be anxious or threatened by what's happening around us. And so this would really be a great survival tool for groups of humans," she explained.
"And the belief is, is that over the centuries, the brain kept these connections so that we now laugh when ... we hear things that are relaxing, funny, surprising, amusing."
Anthropologists think that laughter is universal, but that doesn't mean every culture finds the same things funny.
Laughing is a primitive noise
Laughter is a surprisingly complicated process, engaging multiple regions of the brain and the body.
The frontal lobe is thought to help you interpret the various bits of information you receive -- the sounds and images -- and then it decides whether they are funny. That triggers an emotional response in the limbic system, which controls feelings like pleasure and fear and that in turn stimulates your motor cortex, explained Gupta in the podcast.
This controls your physical response -- the guffaws, snorts and chuckles we recognize as laughter.
"When you start to laugh you get a fairly large contraction in the rib cage -- very large and very fast. Those contractions push air -- ha, ha, ha. It's a very primitive way of making noise. At the brain level, it's associated with a change in the circulating endorphins," said Sophie Scott, a professor of cognitive neuroscience at University College London.
This can give you a pain-killing sensation. As you laugh, it lowers your adrenaline levels and over a longer time frame your levels of the stress hormone cortisol, she explained. As such, laughter can improve your mood and make your physical and emotional response to stress less intense.
"You're more relaxed, less stressed, and you have a pleasant buzzy feeling," she said.
Couples who laugh together stay together
A long-running study of couples at the University of California, Berkeley, of more than 150 long-term relationships that started in 1989 has suggested that laughter is the glue that keeps people together.
Satisfied couples laugh more than unsatisfied ones, found the study team, led by Robert Levenson, professor of psychology. In one experiment, the couples were asked to discuss a problem or conflict in their relationship while they were videotaped, and a polygraph measured different physiological and emotional signs.
Laughter during the stressful conversation was associated with emotions becoming more positive.
"You see people starting to get stressed, and what you find is that couples who deal with increased feeling of stress, the ones who react to that with laughter not only get less stressed immediately but they are couples that tend to be happier in their relationships and tend to stay together longer," said Scott, who was not involved in the study.
"It's not that the laughter is magic dust. It's more like laughter is a sign of a relationship where people can use laughter to negotiate a better way together," she added.
In defusing tense situations, she said that laughter can make it easier for couples to communicate and maintain relationship bonds -- important planks of relationship satisfaction.
It's very hard to explain why something is funny
While psychologists and comedians have tried to come up with one, there is no universal theory for what makes something funny.
People sometimes find amusement in the misfortunes of others, in the expression of otherwise forbidden emotions, or in violating a norm but in a nonthreatening way, Scott said.
But sometimes sounds or words can just be inherently funny.
"Any theory of humor always falls down because we can't explain all the things that are funny, and it can't be used to generate jokes. Laughter is a really important part of play, and maybe that's where a lot of adult human play behavior goes, it feeds into humor."
Laughter can also have a dark side.
Inappropriate laughter can sometimes be a sign that something is cognitively amiss. An early sign of dementia is an altered sense of humor and laughing at inappropriate moments, one study found.
What's more, laughter doesn't always accompany genuinely felt emotions -- it can also be for social display. People will use laughter to defuse a stressful situation or a joke to break the ice. However, whether it works or not depends on whether the other person joins in and laughs with you, as anyone who has had a punch line fall flat knows.
Laughter is about people, not jokes
Laughter is 30 times more likely to occur in the company of others than when one is alone. It's also contagious. You're much more likely to laugh if you hear someone else laughing.
"When you have endorphins circulating through the brain, you feel good. When you laugh, you're inhaling more oxygen. So, all the cells of your brain are getting more oxygen, as well as the cells of your body," Gibson said.
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"It's just a tool in your medicine cabinet to help you feel better. And I'd say it's free, and it brings in all these other benefits that it's a great tool to use and not to be dismissed as silly or worthless. "
It's hard to separate the benefits of laughter and the context in which you would laugh. As such, if you want to harness the healing power of laughter, a funny movie might help -- but it's really the connections laughter builds with other people that count.
