Laughter

A very short, very simple question today.

Why do humans laugh?

It turns out that humans are not unique in possessing the ability to laugh: rats, mice and dogs have shown an ability to laugh, as have other primates such as chimpanzees and orang-utans. Indeed, our ability to laugh may have been inherited from the primate ancestors from which Homo sapiens evolved.

Not only chimps, the closest apes to men, laugh. Orangutans too possess a sense of empathy and mimicry essential for a laughter and this pushes the age of human laughter to at least 12-16 million years ago, when orangutans split from the line that led to humans, chimps and gorillas.

Facial expressions, like the open mouth resembling laughter, have been observed in orangutans. The speed of the imitation (0.4 seconds) revealed that those expressions were involuntary, thus orangutan laughing is contagious.

Some experts might say that to laugh requires empathy - the capacity to understand the suffering of others; to understand the circumstances behind the suffering of others. It is, in humans, not enough to understand that the sound of sobbing, the tears streaming from tear ducts, the flushed face covered by hands indicate that a human is suffering and in tears. Empathy comes from the understanding of the different causes of lachrymation - grief, shame, relief ... even joy.

In at least one example of fiction, a scene featuring some primates in a zoo in the Robert A Heinlein story Stranger In A Strange Land, the author posits that laughter stems from the release of fear, based on the perception of suffering in others and the expectation that the suffering may spread to inflict itself on the observer, only for that tension and fear to be released as laughter when the observer realised that he or she is not going to be the recipient of the suffering.

Larry Niven also wrote along similar lines in his novel Ringworld, positing that laughter is an interrupted defense mechanism, and that no sane sentient being interrupts a defense mechanism.

Lastly, in the Babylon 5 television series' season 5 episode "Day of The Dead," written by author Neil Gaiman, one character maintains that the humour of a species known as the Minbari is not based on the human perception of suffering or embarrassment, but on the inability to achieve spiritual enlightenment - a further assertion from the ranks of science fiction authors that human laughter comes from our capacity for empathy and to perceive the causes of suffering in others.

How likely, in your view, is the empathy explanation to be the actual cause of human laughter?