Did you hear the one about the royal barber? When he asked the king how he wanted his hair cut, the king replied: “In silence.”

Granted, this may not be the funniest joke ever, but it gets bonus points for being one of the oldest. It’s one of 265 jokes in the world’s oldest surviving joke book, the Ancient Greek Philogelos, or “Laughter Lover”, dating from the late fourth or early fifth century AD.

While not all of the jokes have stood the test of time, it’s amazing how many we can still understand, and even laugh at. A case in point is the British standup comedian Jim Bowen, who in 2008 used some of the original Greek jokes in a live show and still had modern audiences splitting their sides.

In comedy, 1,500 years is no big deal, apparently. Chances are that some of today’s perennial YouTube favourites such as ‘paw de deux’ or ‘stuck up with contact cement’ would probably also have had our ancestors crack a smile.

All that is odd

There is no shortage of research papers that seek to get to the bottom of what we find funny. Even Darwin tried to explain it. Instinctively it feels like a matter of taste – some are suckers for slapstick, while others prefer more cerebral or politically savvy fare. Yet research reveals that most of the time, it comes down to one thing: incongruity. “Incongruity is essentially an error. You’re expecting x and you get y,” evolutionary biologist Jonathan Silvertown says. “There’s a lot of cognitive and psychological evidence that demonstrates that this is the essence of humour.” He’s written a book about it, The Comedy of Error.

In the history of our species, the theory goes, it was important to scan the environment for odd situations – errors – to avoid disaster. When the error turned out not to be dangerous, we could laugh it off. We still laugh as a release sometimes after a particularly narrow escape. The error has to be trivial to be funny. “If it isn’t trivial, it becomes a tragedy,” Silvertown says.

Shakespeare’s comedies are good examples. In his Comedy of Errors, mistaken identity is the error driving the humour, Silvertown says. “This occurs time and time again in Shakespeare’s plays.” While Shakespeare put the technique to good use, he didn’t invent it. “He got the plot of his Comedy of Errors from a Roman playwright, using exactly the same plot device. The audience is in on the joke but the people on stage are not.” The result? Mass hysterics.

Doubled-up daily

It’s clear that as a species, across the board, we really do love to laugh. In fact, we’re born to laugh. We laugh before we can even speak, trying it out for the first time as early as three or four months old. Even as adults, we still burst into laughter about 17 times a day.

Studies have shown that from the comedy clubs of London to the remote Namibian deserts of the Himba tribe, laughter is a universal sound that people the world over can recognise regardless of their culture or language. As Czech writer Milan Kundera so eloquently describes in The Book of Laughter and Forgetting, “the sound of laughter is like the vaulted dome of a temple of happiness.” And guess what? It’s incredibly contagious.

“If you look at what provokes laughter, most of the time, it’s not jokes – it’s being with other people,” says cognitive neuroscientist Sophie Scott of University College London. “It’s a social lubricant. We laugh to show that we understand someone, that we like them, that we agree with them.” She mentions American psychology professor Robert Provine’s research, which shows that we are 30 times more likely to laugh in the presence of others, than when we’re alone.

A sign of play

This social function has deep evolutionary roots. “As social animals, maintaining social bonds has always been vital. Play is an important behaviour for that, and laughter shows that you’re playing, or inviting someone to play,” Scott explains. Research with rats that have had their vocal cords removed so they can no longer laugh, reveals that they are more likely to be bitten by other rats. “If they can’t show that they’re playing, their behaviour can be seen as threatening,” Scott says.

Instead of rats, Sophie uses willing human guinea pigs in her research and one of her most recent studies reveals just how social laughter is. Her team at University College London put this to the test by collecting the 40 worst jokes they could find. They then added the sound of pre-recorded laughter to see what would happen.

The outcome was conclusive. “Adding laughter makes even the least funny jokes funnier. Seeing or hearing others laugh makes you want to laugh more.” But there is a limit, as demonstrated by this howler: When does a sandwich cook? When it’s bakin’ lettuce and tomato. This joke was so bad that adding laughter didn’t help.

Four other cringe-worthy jokes from the study:

– What US state has the smallest drinks? Mini-soda!
– What does a dinosaur use to pay the bills? Tyrannosaurus cheques!
– What’s orange and sounds like a parrot? A carrot!
– What do you call a man with a spade on his head? Dug!

Interestingly, people laughed more to the sound of genuine, spontaneous laughter than to fake laughter. “The more spontaneous the laughter, the funnier the joke,” Scott found. People are very good at recognising the difference. “Spontaneous laughter has lots of funny noises and squeaks that are hard to fake.” Knowing the person makes the laughter even more contagious.

Getting people to laugh in a lab setting isn’t easy, so over the years Scott has become something of an expert at eliciting laughter. Her secret weapon? A video of an American TV host trying to keep a straight face when faced with atrocious singing during a live phone in. “It works every time,” Scott says. Watch it and try and resist your evolutionary urge to join in.

Or better still, go ahead and have a proper belly laugh. You’ll be doing yourself a favour. There is broad medical evidence that laughter is good for your health. Laughing can produce endorphins, the ‘feel-good’ hormones that also minimise pain. It dilates blood vessels, which improves vascular function, decreases stress levels and boosts your immune system as well as your mood. In short, we should all be taking a daily dose.

But seriously

When it comes to mental health, laughter is not to be made light of. “Anomalies in laughter patterns can point to serious psychological issues,” Scott points out. “Boys at risk of psychopathy don’t process laughter in the same way. For them, it’s not as contagious.” Similarly, gelotophobia – a fear of being laughed at – is always linked to profound psychological disturbance, she says.

So, does studying laughter professionally make it harder for her to laugh? “The opposite. I value it a lot more and go out of my way to make sure that I do the things and see the people that make me laugh. During lockdown, I deliberately stopped working at 5pm to do something as a family that would make us laugh together,” she says. “A lot of people see laughter as the least important part of the day. I think it’s the most important thing to do. Especially now.” Looks like it’s time to dust off that ancient Greek joke book. Just don’t read it solo.