Sophie Scott is Professor of Cognitive Neuroscience at UCL, where she is Deputy Director of the Institute for Cognitive Neuroscience and group leader for the Speech Communication Lab. In her spare time she performs stand-up comedy. She is the 2017 Royal Institution Christmas Lecturer. She was elected to the Academy of Medical Sciences in 2012 and the British Academy in 2016.

Laughter – the expression of play – is vital to bring us together.

Play – the performance of and engagement with activities that have no purpose beyond recreation and enjoyment – is a ubiquitous aspect of mammal behaviour. All mammals play as juveniles; some mammals continue for their whole lives. Play appears to be critical to the development of the mammalian brain: mammals have an extended juvenile period during which their large brains develop and grow, and play is an important mechanism for learning about adult activities and the social world. Play can be hard to define, but is easy to recognise, and this is partly due to some general cues mammals use to indicate that an activity is playful. These include so-called “play face”, which is a loose, open, unthreatening smile, and body posture, such as the “play bow” that dogs adopt to show that what follows is a game. These signs are important because the same behaviour can be threatening or enjoyable, depending on whether it is perceived as playful. When there is a sound associated with play, it’s laughter. In fact laughter has been described as, at its heart, an invitation to play.

Adult humans like laughter a lot – we pay attention to it, we seek it out, and we will pay good money for the opportunity to laugh. Our laughter has its roots in the interactions we had as babies, with our parents. Human babies first laugh at around two to three months, and this is always linked to interactions such as being tickled or playing peekaboo. The role of this laughter seems to be to do with social bonding, although this rapidly becomes more nuanced: by the time a baby is a toddler he or she will pay a lot of attention to parental laughter, will use parental laughter to know if the situation is safe or threatening, and will be able to perform actions specifically designed to make parents laugh. As detailed above, laughter can also be deployed to signal or encourage play, and play in human childhood can be awash with laughter. Humans, though, are mammals – like dogs and otters – who continue to play our whole lives. What happens to our laughter as we become adults?

The US psychologist Robert Provine has shown that if you ask adult humans what makes them laugh, they will talk about jokes, comedy, and humour. Provine has also shown that laughter is still primarily driven by social context – we are 30 times more likely to laugh if there is someone else with us than if we are on our own, and we will laugh more if we know the people we’re with, and more still if we like them. What this means in practice is that most of our laughter as adults is associated with social interactions and conversations. Within these interactions we’re very rarely laughing at actual jokes. People laugh at statements and comments like “I will have another cup of coffee” or “I might miss my bus”, because people are laughing to show social affiliation, familiarity, affection, agreement and understanding as much as humour. In the middle of human language, we fall into an old mammal behaviour to enable us to do much of the social “heavy lifting” in conversations.

But maybe laughter also still functions as an invitation to play, as a sign that the conversation is not serious or threatening, as an interpretation of other people’s speech that might render it playful, or as a relatively safe emotional space where a conversation can live. We don’t laugh when anxious or exposed, but we do laugh when we’re trying to stop feeling anxious or exposed, or feeling unsure about membership of the group. There is good evidence that couples who deal with stressful situations by laughing together not only feel less stressed but also are typically happier in their relationship: their relationships also last longer. This effect is only seen if both members of the couple laugh, however – laughter has to be shared for it to work. This effect is unlikely to be limited to romantic relationships: one of the properties of friendship may be that we can use laughter, together, to negotiate a more positive emotional state, to get on better with one another and reach accommodations.

There is data showing that the amount of laughter in an interaction is associated with the amount of social information – we laugh most when we are face to face with someone. Laughter drops off when there is only a voice, and becomes most infrequent when we are using entirely text-based interactions, such as SMS and email, that rob us of the social information and spontaneity of face-to-face conversation. Text, stripped of the melody and nuance of the speaking face and voice, is ripe for misunderstanding. The recent explosion in the use of emojis and gifs can be seen as attempts to get the laughter back into text interactions. Maybe we need to think about laughter when we’re designing spaces (real and virtual) where people interact. It’s probably worth taking laughter, and play, a bit more seriously.