Last week, we talked about our love of sugar and I explained some of the reasons why we humans develop certain traits that seem contrary to our survival. This week, I thought we’d dig into why we develop some traits that aren’t so much contrary to our survival but may seem unnecessary. Specifically, why do we laugh?

People from all cultures laugh, although we may laugh at different things. (I once interviewed for a job in the Netherlands and none of my jokes landed. I didn’t get that job.) Apes also laugh. We know this because there are scientists whose job it is to tickle animals. I’m not even kidding. What a life!

Humans start laughing as early as 3 months into life, even before we can speak. This is true even for babies who are deaf or blind. Peekaboo, it turns out, is particularly a global crowd-pleaser. And we know this because studying baby laughter is an actual job, too.

So, the ubiquitous nature of laughter suggests that it must serve a purpose, but what?

Why do we laugh? Here are a few scientific reasons

Laughter clearly serves a social function. It is a way for us to signal to another person that we wish to connect with them. In fact, in a study of thousands of examples of laughter, the speakers in a conversation were found to be 46 percent more likely to laugh than the listeners.

We’re also 30 times more likely to laugh in a group. Young children between the ages of 2.5 and 4 were found to be eight times more likely to laugh at a cartoon when they watched it with another child even though they were just as likely to report that the cartoon was funny whether alone or not. 

Evolutionarily speaking, this signal of connection likely played an important role in survival. Upon meeting a stranger, we want to know: What are your intentions with me? And who else are you aligned with?

In a study that spanned 24 different societies and included 966 participants, scientists played short sound bites of pairs of people laughing together. In some cases, the pair were close friends, in others, the pair were strangers. 

Participants in the study were asked to listen to the simultaneous laughter and determine the level of friendship shared by the laughers. Using only the sound of the laughter as cues, they could reliably tell the difference between people who had just met and those who were long-time friends. These results suggest not only the link between true laughter and friendship but also that we aren’t fooling anyone when we pretend to laugh at another person’s joke. 

Another theory, which takes the person-to-person connection provided by laughter a step further, is that laughter may be a replacement for the act of grooming each other. Grooming another is a behavior seen in primates. To groom someone else is a generous, one-sided act. Because it requires trust and investment of time, it bonds the groomer and groomee as friends.

As our communities got larger, we couldn’t all go around grooming each other to establish bonds. So, this is no longer our preferred method of exhibiting an offer of friendship. (And that’s probably a good thing.) But laughter, like the commitment offered through grooming, is also hard to fake, at least not without being obvious. And, unlike grooming, it can be done in a larger group and gives a more immediate impression. When we genuinely laugh, we signal that we are comfortable and feel like we belong. 

According to the Mayo Clinic, there are also a multitude of physical health benefits to laughter. Laughter can increase your oxygen intake, which can in turn stimulate your heart, lungs, and muscles. Laughing further releases endorphins, the feel-good chemicals our bodies produce to make us feel happy and even relieve pain or stress. The act of increasing and then decreasing our heart rate and blood pressure through laughter is also ultimately calming and tension-relieving. Laughter can even boost our immune system response through the release of stress-and illness-reducing neuropeptides.

So laughter signals cooperation, a key aspect of human survival, and promotes a healthier body to boot. That’s the best excuse I’ve heard to make sure to take the time to enjoy a few laughs over dinner and drinks with friends.