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This Wikipedia article defines laughter in many terms, such as...

"a visual expression of happiness, or an inward feeling of joy"


"a part of human behavior regulated by the brain, helping humans clarify their intentions in social interaction and providing an emotional context to conversations".

Note: the emphasis was added by myself.

The article also states that laughter is "probably genetic", and that

"Scientists have noted the similarity in forms of laughter induced by tickling among various primates, which suggests that laughter derives from a common origin among primate species."

According to this report which the Wikipedia referenced, the expression of laughter in general is present among other great apes. Phylogenetic trees were reconstructed to represent the evolution of this trait among primates (which concludes that the ability to laugh must have a genetic basis, at least to some degree).

Note: I also found this WikiAnswers post, but it clearly can't be that reliable.

A search on the OMIM database yielded this result, where children with Angelman syndrome were characterized with "excessive laughter", this result, in which Charles Bonnet syndrome was characterized with "inappropriate laughter", as well as many other genetic mutations which resulted in some sort of uncontrollable laughter.

I understand that laughter is a complex psychological expression of emotion likely associated with more abstract thought, and that there simply can't be "a laughter gene", but my question is:

Is there any known genetic or physiological origin of laughter? What is biologically different in great apes which allows for laughter, in comparison with a panoply of other animals? I'm looking for more of a molecular answer rather than an ecological or psychological one.

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this question (or any follow ups you might have) would also find a good home at CogSci.SE. –  Artem Kaznatcheev Jun 17 '12 at 1:54
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1 Answer

I recommend this article: The Evolution and Functions of Laughter and Humor: A Synthetic Approach by M Gervais and DS Wilson, 2005, University of Chicago Press.

For your question about the origin, firstly they explain that all laughter is induced by stimuli which are unexpected or unpredictable, experienced in a non-serious (unthreatening, safe) context. Given examples include peek-a-boo, which can make a child laugh but also cry if the child is not perceiving the situation as safe. Also that we can't tickle ourselves and tickling is induced by stimulating vulnerable body areas. Similarily, apparently in apes laughter is mainly induced by "tickling in conjunction with mock aggression and chasing".

They explain the function of (Duchenne, that is stimulus-driven "honest" as opposed to voluntary) laughter to be propagation of "positive affect" in a group, as it utilises the chameleon effect (it is contagious) which apparently has been shown to exist for its "cooperative value". Other studies seem to have shown that a) we are thirty times more likely to laugh in a social context than by ourselves and b) the contagiousness of laughter response increases with group size, making it an efficient tool for coordinating a group and getting everyone into the same emotional state.

As for other animals, the article doesn't address that. It does seem like a different question to me so I would consider separating that into a second one.

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Molecular in what sense? The neural pathways, anatomy? –  Armatus May 6 '12 at 21:41
Could you give a different (unrelated if you wish) example that could explain what you mean by molecular genetics in relation to a pattern of behaviour? –  Armatus May 6 '12 at 22:52
Rather than the behavioural act of laughing itself, I'm more concerned with the biological ability to laugh that humans and some great apes have, according to the report. As laughter also has some sort of genetic component, there must be some genes being expressed within specifically primates that allows us to laugh. I'm thus interested in the expression of these genes, and how they interact to create the phenotype of being able to laugh. –  LanceLafontaine May 7 '12 at 2:39
@LanceLafontaine The road from genes, to proteins, to neurons, to neural systems, to behavior is a very long one. It has not been parsed out yet so what you're asking for can not yet be delivered. Keep in mind that laughter (like all behavior) is an extremely complicated emergent property of many underlying systems. It's never as simple as "having some genes for X". Basically, the question your asking is too vast. –  Preece May 7 '12 at 9:58
@Preece, notice that I mention exactly that in the question. I'm not looking for the impossible, but rather what's already known, if anything. And if nothing is known, an answer explaining why would be sufficient. –  LanceLafontaine May 7 '12 at 13:51
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