Laughter beats hunting fleas

Imagine yourself sitting on the edge of your seat in a crowded comedy club, listening to the hilarious stand-up comic on stage.

You're hanging on every word, and as he delivers the punchline the crowd erupts in laughter.

You wipe away tears and feel a warm sense of belonging, of having a bond with others sharing the joke.

Why does laughter make us feel this way, and are we the only animals with a sense of humour? Chimpanzees have laughter of sorts: youngsters when tickled make panting noises. But theirs is the type of laughter we associate with children at play, not the full-blown belly laugh of adults.

According to Professor Robin Dunbar, of the school of biological sciences at the University of Liverpool, chimpanzees don't need to laugh like we do because, like other apes and monkeys, they use grooming as a kind of social cement. The grooming consolidates alliances, and monkeys might trade grooming for help in conflicts.

For apes and monkeys, grooming is vital for maintaining relationships, which in turn helps to keep groups together.

Grooming can strengthen relationships in two ways: if you're grooming with Bob rather than someone else, you're saying to him that he's important to you. But as well as having your time and attention, Bob will be experiencing the release of endorphins and oxytocin - hormones which will make him feel well-disposed towards you.

With the exception of people in intimate relationships, humans don't "groom" one another, at least not without the risk of causing outrage. During our evolution, group sizes got so big that our ancestors simply could not afford to put in the amount of time needed for grooming so many social partners.

Professor Dunbar proposes that vocalisations in our ancestors became more complex, allowing us to vocally "groom" our group-mates, and this, he says, gave the push towards the evolution of language.

But how can humans get their relationship-cementing endorphin kick? Laughter, he suggests.

Researchers have experimented to see if laughter does indeed cause the release of endorphins. While most have yielded positive results, the endorphin increase was not always significant.

But a problem with these experiments is the fact that the subjects were isolated.

"Laughter is a contagiously social phenomenon," says Professor Dunbar. "People can be made to laugh merely by hearing someone else laughing."

People rarely laugh out loud when alone, and if laughter strengthens relationships, then it would make sense to look at what happens to people in groups.

Professor Dunbar and his colleagues carried out an experiment whereby people in small groups were shown different videos. This experiment relied on the assumption that endorphin release raises pain thresholds, and so the ability to withstand pain was used as a proxy for endorphin levels.

This was measured in each subject before and after watching the video by measuring how long they could keep a frozen wine-cooler sleeve on their arm.

Subjects who had watched a comedy video, as opposed to a documentary, kept the cooler on for much longer, and the more time they spent laughing during the video, the higher their apparent pain threshold.

"Endorphins were the first natural opiates, and they make us feel relaxed," says Professor Gareth Leng, neuroscientist at the University of Edinburgh.

"Oxytocin and endorphins have been associated with reduction in stress, and they encourage social and sexual interaction."

A recent study showed oxytocin also increased trust.

The idea that laughter evolved as a relationship-bonding exercise would explain why we try to be funny and make one another laugh. Conversely, failing to elicit laughter when trying to be amusing is awkward and bad for the relationship. It's also guaranteed to make you want to find someone else to talk to.

"Laughter is a big part of popular culture," says Stephen Wagg, of the school of life and human sciences at Roehampton University.

"Just as people are expected to have a sports team, they're also expected to have a favourite comedian - there's one for everyone. We live in a disciplined age, and often can't show our feelings."

He says laughter may have evolved long before language.

"The fact that laughter is so contagious suggests it was used in a communal ritual alongside conventional primate calls."

Having a good laugh with your mates would seem to have ancient origins.

- INDEPENDENT