Laughter is weird – and we do it a lot. One study found that people laugh seven times for every 10 minutes of conversation.
We don’t do it when we think we do. It’s been found that if you ask people what makes them laugh they’ll talk about jokes and humour, but we laugh most frequently when we are with other people – and hardly ever at jokes.
It’s a social emotion and we use it to make and maintain social bonds.
We also make very strange noises when we laugh – from wheezes and squeaks to gasps and snorts – and each sound simply reflects the muscles in the chest squeezing out air from our ribcages under very high pressures.
My laugh is very high-pitched, far higher than I could produce when trying to sing, for example.
Laughter is also a very primitive way of making a sound.
Image captionProf Sophie Scott explains how our bodies produce the sound of laughter
MRI images show that when someone laughs, there is no real movement of the tongue, jaw, soft palate and lips. All the action is happening at the ribcage.
Image captionFacial expressions of emotion are mirrored across species
Laughter is a non-verbal emotional expression and these sounds, which we typically make when in the grip of quite strong emotions, are more like animal calls than they are like our normal speech.
We make them in very simple ways (unlike speech) and they are controlled by an evolutionarily “older” brain system, one that looks after vocalisation in all mammals (unlike speech).
This is why a stroke can rob someone of the ability to speak, but leave them able to laugh and cry. They have suffered damage to the brain areas that enable them to speak, but the older emotional system is still intact.
Image captionNeuroscientist Prof Jaak Panksepp tickles rats to make them laugh
These non-verbal expressions are frequently associated with expressions of emotion. The emotions themselves are called the “basic” ones, because they’re recognised by all human groups and are also found in other mammals.
This explains why some emotions are quite similar across species – think about similarities between the face of an angry human and an angry wolf.
People recognise laughter as laughter even if it is produced by someone from a very unfamiliar culture.
Image captionHimba people produce an almost song-like “ay-ay-ay” sound when they are celebrating but laughter is universal
Other, very positive emotions such as triumph, which are meaningful across cultures, are expressed very differently in different cultures and so are not basic expressions.
For example, in the UK, it’s not unusual for people to cheer to express triumph, while the Himba people produce an almost song-like “ay-ay-ay” sound when they are celebrating.
Of course, we are certainly not the only animals that laugh. Laughter has been well described in other primates such as gorillas, chimpanzees and orang-utans – as shown in this video, where a zookeeper is talking about the slightly nerve-shredding activity of tickling a gorilla and how it makes her laugh.