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 pant-like 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 they might trade grooming for help in conflicts. For monkeys and apes, 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 in his brain which will make him feel well disposed towards you.
With the exception of those 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 couldn't afford to put in the amount of time needed for grooming so many social partners.
Dunbar proposes that vocalisations in our ancestors became more varied and complex, allowing us to vocally "groom" our group-mates, and this, he says, gave the push towards the evolution of language. But what means do humans have to get their relationship-cementing endorphin kick? The answer, suggests Dunbar, is laughter.
Several researchers have carried out experiments 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 during the studies. "Laughter is a contagiously social phenomenon," says 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.
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 significantly longer, and the more time they spent laughing during the video, the bigger the increase in their apparent pain threshold.
"Endorphins were the first natural opiates known, and they make us feel relaxed," says Professor Gareth Leng, a neuroscientist at the University of Edinburgh. "Oxytocin and endorphins have been associated with an apparent reduction in stress, and they encourage social and sexual interaction." A recent study showed that oxytocin also increases levels of trust.
The idea that laughter has evolved as a relationship-bonding exercise would explain why we spend so much of our time trying to be funny and make each other laugh. There is no doubt that we are drawn to witty people: someone who peppers their conversation with funny anecdotes invariably becomes a social magnet, and many a teacher will attest to the fact that children play the fool to get accepted by their peers.
Conversely, failing to elicit laughter in one's partner 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. And there is a difference between being laughed at and laughed with: most of us know how isolated we feel if we are the butt of the joke. Stephen Wagg, of the school of life and human sciences at Roehampton University, agrees that laughter can help people to bond, and suggests that different sections of society may unite through their own sort of comedian. "Laughter is a big part of popular culture," he says. "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 we often can't show our feelings."
For instance, he suggests that it is still difficult for women to express themselves about issues such as discrimination and domestic abuse. "That makes it all the more important to get along to a Jo Brand gig and laugh your socks off." Joking is cognitively demanding, and depends on play on words, double meanings, surprise and so on. It probably requires more brain power than any animals, other than ourselves, possess. However, humour itself is an emotional, rather than linguistic phenomenon. This idea is supported by the fact that a part of the brain that is crucial for the appreciation of humour is far removed from the language processing area, and has neural connections to the amygdala, which is involved in processing of emotion.
"Laughter may well have evolved long before language," says Dunbar. "The fact that laughter is so contagious perhaps suggests that it was used in a kind of communal ritual alongside conventional primate calls." Dunbar suggests that laughter was evolved in Homo erectus as a chorusing display, perhaps around a million years ago. As language abilities evolved in our ancestors, so then came the opportunity to tell jokes. Having a good laugh with your mates, then, would seem to have ancient origins.
Robin Dunbar is the author of 'The Human Story', Faber & Faber, £7.99Reuse content