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Page history last edited by Alex Backer, Ph.D. 13 years, 6 months ago

Analyzing humor is like dissecting a frog. Few people are interested and the frog dies of it. 

E. B. White


Humor is a deeply ingrained human behavior. It triggers reflex reactions across the globe. Clearly, it evolved for a reason. So what is humor for?



A theory for the evolutionary origin and selective advantage of laughter and humor is proposed. In brief, I propose that laughter evolved to signal to third parties that all is well with a situation that might otherwise seem disturbing, signaling the cause of the laugh as friend, and that humor co-opted this mechanism, with jokers developing signals (jokes or funny acts) that elicit laughter to gain the approval by others conferred by a laugh, which signals that the laugher considers the joker a friend.


Requirements of a successful theory of humor and laughter

Any theory of humor must explain:

* Why we laugh

* Why we tell jokes

* What came first, jokes or laughter?

* Why humor plays an important role in seduction, and women are attracted to funny men

* Why so many jokes revolve around laughing at someone

* What is funny

* Why tickling makes people laugh

* Why children are tickled by their parents

* Why the same actions by a friendly parent that trigger tickling do not tickle when done by a stranger, or by the tickled herself

* The paradox of tickling: why those tickled experience laughter and pleasure in being tickled, yet try frantically to escape it

* Why laughter is contagious 

* Why men are more likely to be comedians than women


 Dogs pee on trees while lifting a leg. Art courtesy of Joshua Eisenberg. See also The Adult Male Dog Peeing Behavior and Mathematics,-Language,-Poetry-and-Music:-A-Continuum.


By way of introduction, I will cite here some passages which I find particularly revealing from Polimeni and Reiss (2006) 's excellent review:


Theories of the Evolution of Humor

Several humor thinkers have emphasized how humor is often utilized to

demonstrate superiority or elevate social status. Weisfeld (1993) provides several

examples such as the Greenland Inuit who “traditionally resolved disputes by engaging in

public contests of ridiculing each other” (p. 154). Thomas Hobbes (1651/1981) in

Leviathan was the first to clearly articulate this idea, characterizing laughter as an

extension of “sudden glory.” Critics point out that most jokes do little to boost feelings of



Alexander (1986) was one of the first to methodically analyze humor and laughter

within an evolutionary context. Advancing an idea clearly rooted in Hobbes’ superiority

theory, Alexander figured humor led to greater reproductive success by enhancing one’s

social standing through ostracizing others. Ostracism steers “conflicts and confluences of

interest” ultimately altering access to resources. Humor is considered one method of

social ostracism. Thus, according to Alexander, the major benefits of telling jokes are

varied and include 1) raising one’s own status, 2) lowering the status of certain

individuals and 3) raising the status of designated listeners and thereby enhancing

camaraderie or social unity.


Weisfeld (1993) proposed a general humor theory suggesting humor provides

valuable social information to others while laughter provokes pleasurable feelings that

positively reinforce the humorist. In return, the humorist gets forthcoming reciprocation

by putting an ally in a favorable disposition. It is an interesting hypothesis although

difficult to critique given that the mechanics of mammalian cooperation are exceedingly

complex and yet unsolved (Wilson, 1975/2000).


W. E. Jung (2003) suggests that the fundamental evolutionary purpose of humor

and laughter was to facilitate cooperation between people. According to Jung, the ability

to attribute mental states to others (theory-of-mind) is humor’s most essential feature.

His “Inner Eye” theory proposes that “laughter is a signal that facilitates cooperation by

transfer of information on the laugher’s empathy with attributed mental states and his

sympathy levels for others” (p. 245) Ultimately, a laughing response signals that one is

both ready and able to cooperate.



Darwin (1872/1920) first recognized that the areas most vulnerable to tickling

such as the neck, abdomen and soles of the feet are perhaps equally the most vulnerable

areas to predator attack. Koestler (1964) framed tickling as a “mock attack” and therefore

evolutionary adaptive.


Animal models

When tickled, the higher primates (humans, chimpanzees, gorillas and orangutans)

all display a laughter-like behaviour (Caron, 2002; Fry, 1994). Fry dates the

“rudimentary elements of contemporary humor” to 6.5 million years ago - a figure

representing the last common ancestor of Homo sapiens and chimpanzees. However, it

appears that Fry inadvertently misses the last common ancestor of humans and orangutans,

which is approximately 14 millions old (Dawkins, 2004). This means that the

rudimentary origins of laughter could be at least 14 million years old.


"Chimpanzee politics"

Nicely captured in Frans De Waal’s (1982) phrase “chimpanzee politics,” primate

life is characterized by constant negotiations between empathic and aggressive

tendencies. Grooming engenders pleasurable feelings that countervail aggressive

tendencies. But with language replacing grooming, what mitigates aggressive tendencies

between lesser-related individuals? Humor seems to inject positive feelings while

hierarchal competition and other minor social quarrels are being worked out. Humor

can’t control pernicious disputes but for the more mundane disagreements, it diminishes

the risk of a contentious issue deteriorating to violence.


Social distribution of laughter

According to Provine (2000, pp. 27-28) women laugh 126% more than

men during conversations with each other. In this particular case, cultural factors such as

contemporary gender imbalances in social status are probably more important than

genetic differences (it has been observed that persons in higher positions of authority

seem to laugh less than those in lower positions).


Humor in traditional societies

Modern culture has a remarkable ability to transform adaptive behaviors so

completely that it makes it difficult to comprehend why certain behavioral propensities

exist at all. Listening to music alone through headphones for hours couldn’t possibly be

adaptive; however, witnessing a ceremony of song and dance in preparation for tribal

warfare puts an entirely different perspective on the potential evolutionary functions of

music. Similarly, can the use of humor in traditional societies provide any insight to the

possible evolutionary purposes of humor?


Joking relationships in preliterate societies are most commonly observed between extended

relatives. Nuclear families do not typically communicate extensively in this manner.

Siblings-in-law and cousins, particularly of the opposite sex, seem to most readily

demonstrate humor in their conversations. Second, there are definite customary

expectations associated with some joking relationships. The most common expectation is

that the participants not take offense. Third, a variety of topics are typically involved in

joking relationships although sexual humor between sibling-in-laws of opposite sex is

commonly witnessed. Reducing potential conflict and aggression is the usual explanation

for this type of communication.



The best documented case of a laughing epidemic originated in Tanzanian

schoolchildren in 1962 (Rankin and Philip, 1963). Over two hundred adolescents and

young adults were overcome by recurrent bouts of hysterical laughter and crying over a

period of a few months. Although no initiating factor was ever discovered, this incident

exemplifies the social and contagious aspects of laughter.


Neurobiology of Humor

Activation in the medial ventral prefrontal cortex (MVPFC) bilaterally correlated with how funny a joke

was rated. The authors suggest their results indicate “the affective appreciation of humor

involves access to a central reward system in the MVPFC” (p. 238).


Moran, Wig, Adams, Janata, and Kelley (2004) monitored humor detection versus

humor appreciation using The Simpsons and Seinfeld comedies in an event-related fMRI

experiment. They found significant activations in the left posterior middle temporal gyrus

and left inferior frontal gyrus, with additional activations in the bilateral anterior temporal

cortex, left inferior temporal gyrus, right posterior middle temporal gyrus and right

cerebellum. Of note, the authors point out that the left inferior frontal cortex has been

previously associated with “reconciling ambiguous semantic content with stored

knowledge” (p. 1058).


Mobbs, Greicius, Abdel-Azim, Menon, and Reiss (2003) event related fMRI

study used captioned funny cartoons versus non funny ones and showed that humorous

content primarily activated, the left temporal-occipital junction, left inferior frontal gyrus,

left temporal pole, left supplementary motor area, left dorsal anterior cingulate and

bilateral subcortical structures including ventral striatum, nucleus accumbens, ventral

tegmentum area and amygdale, which are key components of the mesolimbic

dopaminergic reward system. The authors point out a similar pattern is commonly

observed in “monetary and video-game reward tasks” (p. 1043).


It seems to me that several of the points made by others above are on the right path, yet a full explanation is still lacking --one might say that, like the jokes they seek to explain, they have a nugget of truth and a lot of uncertainty. 


Comedians are overwhelmingly male

English's gender ambiguity leads me to use Spanish for these experiments: a Google search for "el comediante" (Spanish for male comedian) yield almost ten times as many results as one for "la comediante" (Spanish for female comedian). In contrast, a search for actors yields only 10% more results than one for actress. Any theory of humor must explain this overwhelming sex bias, too.


Laughter as a measure of social dominance?

Humor seems to have co-opted an earlier laughing behavior that was triggered by stimuli such as tickling.


Animals --from lobsters to humans-- benefit from mechanisms to resolve conflict peacefully. Lobsters, for example, have aggressive displays that allow them to predict who would win a fight and accept the result without the need for the injuries of an actual fight --see the wonderful work by Ed Kravitz at Harvard. Tickling may thus originally have been a way to establish dominance without the costs of an actual fight, and laughter a way to accept dominance and gain the sympathy of the winner. In this theory, laughter is more primitive than humor and evolved to signal acceptance of dominance, and its selective advantage is clear: saving the laugher from probable injury by the dominant player, or tickler.


It is possible that laughter evolved originally as an exaggerated form of smiling that signals to an attacker goodwill and compliance. There is no better way to survive an attack than to befriend the attacker. But befriending someone during an attack is no easy task. Perhaps no better way to signal friendliness than to smile exaggeratedly and make audible signals. An animal that laughs when its vulnerable body parts are touched by surprise (in short, an animal capable of being tickled), may well increase its probability of surviving the attack. Setting out to find more examples of such animal tickling, I found that rats laugh when tickled. And anybody who's played with their dog knows they get tickled, too.


This would also explain why laughter is contagious: the more people who submit to a dominant male, the wiser it is to submit to him yourself.


It would also explain why persons in higher positions of authority seem to laugh less than those in lower positions: if laughing indicates submission, then those in lower positions of authority ought to do it more often.


Yet this hypothesis appears inconsistent with some animal laughter findings that suggest that tickling only happens in mock attacks.


Tickling requires friendliness

Jaak Panksepp, a neuroscientist from Bowling Green State University in Ohio who discovered rat laughter, said: "Tickling made the rats chirp happily, as long as the animal's friendly toward you". "If not, you won't get a single chirp, just like a child that might be suspicious of an adult. Rats that were repeatedly tickled became socially bonded to the researchers and would seek out tickles. The researchers also found that rats would rather spend time with animals that chirp a lot than with those that don't. During human laughter, the dopamine reward circuits in the brain light up. When researchers neurochemically tickled those same areas in rat brains, the rats chirped."


Tickle in chimp play

Psychologist and neuroscientist Robert Provine, author of "Laughter: A Scientific Investigation," tickled and played with chimpanzees at the Yerkes Regional Primate Center in Atlanta while researching the origins of the human laugh. Laughter in chimps, our closest genetic relatives, is associated with rough-and-tumble play and tickling, Provine found. "It's like the behavior of young children," said Provine, of the University of Maryland Baltimore County. "A tickle and laughter are the first means of communication between a mother and her baby, so laughter appears by about four months after birth." Regarding the importance of such an early behavior, Provine said: "We're talking about a life-and-death deal here--the bonding and survival of babies".


Yet it's clear that chimps don't only laugh when tickled; they have a sense of humor too:

Monkey Laughing At Dog - Awesome video clips here



Tickling makes dogs laugh, and laughing makes dogs play

University of Nevada, Reno, researcher Patricia Simonet discovered laughing in dogs: a "breathy, pronounced, forced exhalation" that sounds to the untrained ear like a normal dog pant. But a spectrograph showed a burst of frequencies, some beyond human hearing. A plain pant is simpler, limited to just a few frequencies.

Hearing a tape of the dog laugh made single animals take up toys and play by themselves, Simonet said. It never initiated aggressive responses. "If you want to invite your dog to play using the dog laugh, say `hee, hee, hee' without pronouncing the `ee,'" Simonet said. "Force out the air in a burst, as if you're receiving the Heimlich maneuver." When she played a recording of a laughing dog at an animal shelter, Simonet found that even 8-week-old puppies reacted by starting to play, something they hadn't done when exposed to other dog sounds. "Some sounds, like growls, confused the puppies. But the dog laugh caused sheer joy and brought down the stress levels in the shelter immediately." 


Laughing as a signal that an anxiety-producing situation is not harmful 

What exactly is tickling? It is quite a paradoxical behavior: something that gives pleasure and yet from which the animal frantically seeks to escape.  Darwin (1872) suggested that the primary response to tickling is not laughing, but a frantic attempt to avoid being tickled, by squirming, wriggling, and withdrawing the part of the body that is being tickled. 


What does tickling achieve? First, it achieves pleasure in those tickled, incenting them to either get tickled again or spend more time with the tickler. Second, perhaps it teaches the tickled how to avoid getting tickled areas exposed again, and how to escape. Third, perhaps it signals to everybody around that what is going on is tickling, and not an attack.


So perhaps laughing is a signal that an anxiety-producing situation (e.g. what looks like an attack), offers no cause for anxiety (e.g. is a mock attack), reducing stress in the community and preventing others from reacting inappropriately (e.g. turning a mock attack into a real battle).


How is this good for the tickled? If tickling truly serves to teach the tickled defensive techniques, then the value of sending a signal that allows it to continue is obvious. More generally, the value of communicating to your peers your assessment of an ambiguous situation is the same as that of all communications: enhancing the community's knowledge while acquiring individual respect in the community.


How is it good for the tickler? If animals tickle their young and close relatives, then the benefit of training accrues to their genes. 


What does the brain detect as a signal worthy of reacting with laughter to? Any few words used to define a given combination of emotions and percepts will necessarily simplify, but essentially, a surprise that is not unpleasant, a situation that is not as unpleasant or contradictory as it might at first seem. For example, a parent seemingly attacking a child who is really tickling him, a parent disappearing who has not really disappeared (peek-a-boo), an incongruency that is resolved. Laughter says to those who hear it: it may not seem so, but all is well here.


This role for laughter as a signal may explain its contagiousness on two levels. From an evolutionary perspective, a signal exists to be propagated, and so contagiousness helps it reach more targets. From a mechanistic perspective: if laughter is triggered by the realization that a seemingly vexing situation is harmless, then laughter signals its harmlessness, and triggers laugh in those around.


Why do the tickled recoil from the pleasurable act of tickling?

If tickling and chasing are practice for real threats of attacks, there is a clear advantage for animals that engage in what at first sight might appear like contradictory behavior: recoiling from the attack, to practice defense and flight, while simultaneously enjoying the process, so as to continue to practice, and broadcasting a signal (laughter) to others that no real danger exists.


Laughter in children: From tickling to peek-a-boo and chasing

We have looked at tickling because of its appearance in several species, but tickling is also prevalent in children. Because ontogeny sometimes recapitulates phylogeny, it is also of interest to look at laughter in infants. The interpretation above is consistent not just with tickling, but also with other stimuli that trigger laughter in children.


One of these is the game of peek-a-boo, in which infants who are just old enough to remember someone when they disappear and not old enough to know that their disappearance does not mean they cease to exist. As Shultz (1996) points out, infants laugh when their anxiety at the disappearance of a loved one is resolved by her/his reappearance.


Likewise, small children will laugh at the prospect of a chase, which Shultz interprets as the resolution of the anxiety of whether a chaser means harm when they recognize an expression in the chaser that he or she means no harm. That seems a stretch to me, as, except in extraordinary circumstances, I have not seen children truly afraid of a parent chasing them. Yet the idea of laughter as a stress-relieving signal to third parties makes sense for chases just as much as it does for tickling. Peek-a-boo presents more of a challenge for the signal theory of laughter, but if laughter evolved as a signal of when anxiety or stress is relieved due to its value in situations where the community might have reacted adversely to the stress, then its appearance in games which show the same sequence of arousal and relief such as peek-a-boo would be expected spandrels, non-adaptive consequences of evolution.


David, almost 3 years old, laughed after he thought he had lost a piece of a game and then saw me find it. Again, an anxiety-producing situation had been resolved in a favorable way.


What did laughing evolve from?

At first sight, laughing seems clearly related to smiling. Piaget (1951) noted that infants smile with the "pleasure of mastery" after mastering something that used to give them difficulty. In some ways, laughter is a subcase of such mastery of a previously ambiguous and difficult or unsettling situation. It thus might appear that smiling and pleasure in discovery, or curiosity, are related to laughing.


Hewitt (2002) suggests instead that laughing shares little with smiling and evolved from a more primitive broadcast signal of crying of submission. His arguments include the fact that crying and laughing are both involuntary while smiling is largely voluntary, the fact that both laughing and crying involve tears (sometimes) and similar breathing movements, that crying and laughter are broadcast signals whilst smiling is a form of one-to-one communication, and that both are gestures of submission (although as he points out, so is smiling).


The Genetics of Laughter: Ignorance to Laugh about 

Perhaps the question of the origin of laughter may have to await a better understanding of animal smiling, or the identification of the genetics of laughter --it is surprising and no laughing matter that a Google search for "genetics of laughter" today yields no results. This must change, for a behavior as old, universal and hard-wired as laughter undoubtedly has genes responsible for it, so there must be people and animals who cannot laugh.


A Whozat semantic search for "genetics of laughter" yields some more insight: a couple of uniparental disomy disorders suggest a genetic relationship between laughter and cry --at the very least suggesting that genes on the same chromosome, #15, are influential in both behaviors: inheriting both chromosomes #15 from the father causes Angelman syndrome, which often includes inappropriate outbursts of laughter. Inheriting both copies from the mother results in Prader-Willi syndrome, which includes a weak cry. More details on both syndromes can be found in this UVA article.


Humor co-opted laughter

Humor may have co-opted the same pathways but generalized laughter as a stresss-relieving signal that what could have previously been interpreted as verbal battles are not true attacks. 


This could explain why women are attracted to funny men: people who have the power of diffusing conflict and reducing stress.


It also explains the propensity of aggressive themes in humor or a loser in a joke, as the original laugh-inducing stimuli were an apparent attack on somebody revealed as harmless after all.


This explains also what is funny, and why: what's funny is a situation that creates tension and gets diffused by an alternative explanation or interpretation.


The theory also explains why it is usually males who engage in tickling and humor: like they are those who usually engage in attacks, and thus mock attacks.


Behind every joke is a nugget of truth

If the set up to a humorous situation is not threatening, no release of tension, thus no laughter, can occur. Thus, the setup of a joke must present a credible threat.


Like any confrontation, the outcome of humor is uncertain. The essence of humor is its ability to cope with this uncertainty of an ambiguous message that can be interpreted in more than one way by resolving it in an unexpected way. Humor thus provides "retractability" to a statement: the ability to portray the question or statement as a misunderstanding: "I am joking", "I was not serious", "I did not mean it". This is as useful for aggression as it is for seduction, providing the humorist with a safe way to probe the waters. Similarly, humor provides the aggrieved a way to pretend that the aggression was not "real", a way to save face. Similarly, a jester can say truths without as much risk of offending the reigning monarch by coaching them in humor, where their seriousness, and any affront diminished.


This explains the last element that remained to be explained, namely why what is funny is usually what is unexpected or incongruous but results finally congruous or understandable from a different viewpoint. Humor is a way to escape a tense situation with an alternative outcome different from what the tension had led listeners to believe would follow.


The theory also explains why humor is most common in traditional socities between parties, such as extended relatives, with an ongoing relationship, yet a relationship not close enough that things can be said plainly. The cost of saying something that is not well received (e.g. an unwelcome sexual advance) is too high to say without humor, yet the incentive to say them in case they are well received is high enough that humor is adaptive.


Humor as Ambiguous Communication Resolved in an Unexpected Amicable Way

More generally, there are times when saying or asking something could come at high cost, depending on elements that are uncertain at the time of saying them. In this sense, a mechanism to say something while simultaneously signaling lack of commitment to what is said, or flexibility, is very useful. Humor provides such a mechanism. A mechanism of exploration of reactions when there is uncertainty about the same. A way to say something that turns off the usual need for a response as a social signal to third parties.


Humor as an IFF (Identification, Friend or Foe) System?

John A. Hewitt (2002) , in a deeply thoughtful paper with several interesting ideas that deserves to be read carefully, suggests a very interesting theory for humor as an IFF (Identification, Friend or Foe) system which comes closest to the proposal contained herein. He(witt) wittily suggests, as I do, that laughter is an audible broadcast signal whose purpose is to indicate that the sender perceives no danger:

Children laugh incessantly while they are playing and their laughter sends signals to anyone within earshot. To any caring adults in the vicinity laughter says, "I'm OK; I'm happy and not worried." Generally speaking, the adult will not intervene.


He adds: The laughter says to other children in the group, "This is interesting. I get pleasure from it and from thinking about it. You too may get pleasure from it." So, other children come and investigate and learn from the same observation. In the end, each member of the group learns the same things and derives shared pleasure while doing so.


Hewitt goes on to argue that humor is a socially selected trait in which joker interrogates another party to identify himself as a friend (if he laughs) or foe (if he does not). This is where we diverge.


Laughter as an IF (Identification, Friend) System; Humor as a mechanism to be identified as a friend

Although Hewitt's idea is certainly appealing, it fails to explain the common basis of tickling, chasing laugh and adult humor. 


I believe the evidence favors humor as a system related to, but different from, IFF systems: a system in which the laugher identifies the joker, or tickler, or chaser, as a friend. In other words, unlike military IFF systems, humor and laughter are not primarily for the edification of the interrogator/joker/tickler/chaser, but for the edification of third parties observing the interaction. It seems clear that humor evolved from tickling and similar physical play that evokes laughter in animals, humans included. And I do not know of a single instance where the tickler is trying to find out if the tickled is friend or foe --the purpose of laugh is instead to signal to third parties that the tickler is a friend, not a foe, to stop them from intervening. 


Upon the background of laughter as a signal that clearly preceded humor and that signals that someone is not a threat, and indeed a friend, it is only natural that humor would develop as a parasitic behavior that exploits laughter, by mimicking the situations that elicit it, to become identified as a friend, not foe. The purpose of humor then is not for the "interrogator" to discover if the listeners are friends or foes, but rather for the listeners to signal the joker as a friend, not foe. This is consistent with the folkloric intuition of joking as a way to break into a social group or become popular within it. 


This is also consistent with the main test advanced by Hewitt of his theory, namely with the fact that males in traditional societies establish joking relationships with their maternal uncles but not their paternal uncles: given that maternal uncles belong to another patrilineal family, it is more important to try to win them as friends.


Further reading

  1. There is an excellent chapter by Thomas R. Shultz entitled A Cognitive-Developmental Analysis of Humour in 

Humor and Laughter

 by Anthony J. Chapman, Hugh C. Foot, Peter Derks (1996).

     2. The review by Polimeni and Reiss cited above has been published in Evolutionary Psychology: – 2006. 4: 347-366. 

     3. John A. Hewitt (2002) on Humor as an IFF system.


Alex Backer

Alcoy, Spain, Dec. 29-30, 2008


P.S. The first outline of this theory evolved during a cruise in the Baltic Sea during the summer of 2007 in which comedians performed almost nightly.


Read more of Alex Backer's Science articles here.


Comments (1)

Alex Backer, Ph.D. said

at 8:44 pm on Sep 14, 2011

Indeed, laughter releases endorphins, consistent with the theory propounded above (

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