Why Do Humans and Animals Laugh?

If you tickle a rat's belly, it squeals with laughter. However, we are unable to perceive this laughter as its frequency, around 50 kHz, exceeds the range of human hearing. Neuroscientist Jaak Panksepp and his colleagues discovered this phenomenon a few decades ago. They had noticed that rats emit brief bursts of high-frequency sound during play. They tickled the rats on their stomachs and necks to investigate whether this sound was a form of laughter. The sound was much more frequent than when the rats were playing.

Numerous animal species exhibit laughter-like behavior, as indicated in a review article by bioanthropologist Sasha Winkler and communication scientist Gregory Bryant. Their comprehensive study encompasses 65 animal species, primarily mammals, including a kangaroo species and three bird species. What the laughter-like behaviors share is that they occur during play and when the animals are tickled. Given the prevalence of laughter across species, it is reasonable to assume that survival benefits are associated with this behavior. However, the exact nature of these benefits remains a significant question.

While individuals who interact with animals recognize that they possess distinct emotions, there is a tendency to attribute human-like emotions to them. Darwin emphasized the continuity between humans and animals and was the first to study the expression of emotions in animals systematically. He saw humor as "tickling the mind." Modern scientists try to avoid assuming that animals have the same emotions as humans, which would be a form of anthropomorphism.

How do we know that the sounds made by rats are really laughter? The best method is to compare the behavior of different species. Panksepp draws several parallels between the rat sounds and the laughter of human children: (i) rats laugh most before sexual maturity, (ii) if frightened, they stop laughing when you tickle them, (iii) young rats prefer socializing with older rats that laugh a lot, and (iv) rats that have experience social isolation laughs more when they are allowed to socialize with other rats. All these parallels with human laughter behavior strongly suggest that the rats' sounds correspond to human laughter. Panksepp proposes that joy and other emotions we experience are linked to neurological processes. He speculates that the mechanisms underlying laughter are evolutionarily old and deeply rooted in the brain.

A prevailing theory posits that laughter serves to encourage continued play. Many animals employ play signals–dogs extend their front legs and bow their heads with upturned mouths, and chimpanzees have a special "play face" resembling a wide smile. Young mammals frequently engage in play-fighting–they tumble around and nibble each other, often with a tickling effect. The point of play signals is that the participants know that wrestling and nibbling are not serious. Unlike a real fight, the intention is not to hurt each other. They communicate friendly intentions.

While familiar with human laughter, what does it sound like in other animals? Typically, laughter is not particularly loud. One illustration comes from Nobel Prize winner Konrad Lorenz, who was one of the first to study laughter in dogs. He noted that dogs laugh during intense play and pant in addition to their raised mouths. In the species of monkeys studied, the play face is also associated with panting or laughing. Lorenz initially proposed that laughter evolved from an aggressive signal where the animal displays its teeth, but this theory has not been supported. A more recent hypothesis suggests that laughter evolved from the panting that occurs during play.

Only a limited number of animal species, such as elephants and seals, exhibit loud laughter. In the case of elephants, this is likely related to their tendency to trumpet when they gasp intensely. Humans are the sole species among great apes that laugh loudly. One possible explanation for this is the differing anatomy of chimpanzees. As humans evolved to walk upright, they no longer needed to use their chests to control their arms while walking. As a result, breathing can be better controlled, and we can more easily create sounds with our vocal cords.

Another reason animals should refrain from laughing out loud is the potential attraction of predators. A gasp can only be heard by those participating in the game. Elephants and humans in groups are not as vulnerable to predators; they can afford to laugh out loud. Rats' laughter is so high-pitched that predators cannot hear it.

Humans don't only laugh when they are playing or being tickled. With us, animal laughter has been extended to other social contexts. However, the animal origin is evident in that those who laugh most when tickled are also those who laugh most in humorous contexts.

As noted by Darwin, humor can be described as something that tickles the mind. So, what is it that provokes mirth? A common description is that it is unexpected and social while not perceived as dangerous. You don't laugh if you feel threatened. This is a rather soulless characteristic, as many things possess these qualities without leading to laughter. And what is perceived as very funny by one person only makes another person frown.

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Experiments involving chimpanzees' laughter have demonstrated that it also creates laughter in other group members and is important for play to continue. How can laughter be contagious? Over the last decade, cognitive scientists and neurologists have become increasingly interested in 'coupled' brains, that is, social activities where two or more people's brain activities can be shown to be synchronized. Researchers often assume that so-called mirror neurons are involved when explaining such connections, but the underlying mechanisms are still poorly understood.

Laughter serves many functions for humans. It synchronizes emotions within a group, fostering increased cohesion. Above all, it signals a willingness to cooperate among those who laugh. Laughter reduces stress in challenging situations. Instead of fake laughter, genuine laughter evokes positive responses from listeners toward the person laughing. Some people laugh nervously to make others more friendly, but this often fails.

Laughter can also wield power. A group laughing at something outside the group creates a separation between "us" and "them," hindering group cooperation. An individual can be excluded from a community by being laughed at. A mocking laugh is an insincere expression often used to degrade or exclude, and it demonstrates power.

Research on animal laughter is valuable because laughter has deep biological roots. We can enhance our understanding of the human condition by unraveling the evolutionary, neurological, and social mechanisms behind laughter.