by Emrys Westacott
Why do human beings laugh? The question is ambiguous. It could be understood in at least three ways:
1) What features of jokes or amusing situations prompt us to laugh?
2) What psychological mechanism is called into play by the things we find amusing?
3) What evolutionary process led to the phenomenon of human laughter and our capacity for humor?
The first question has often been posed by thinkers seeking to identify the essence of humor, the thing that all amusing phenomena have in common. The second question sees humor as a possible avenue of insight into human nature. Philosophers and psychologists who have sought to understand humor and laughter have typically focused on (1) and (2). The third question has only been asked more recently as the popularity of evolutionist thinking has grown.
The evolutionary question is certainly fascinating and has produced some ingenious hypotheses. Perhaps the simplest view is that laughter originated in the cry of triumph let out by a victorious hunter or warrior. As Stephen Leacock puts it: “The savage who first cracked his enemy over the head with a tomahawk and shouted “Ha ha!” was the first humorist.
More subtle is the “false alarm” theory which notes that we typically laugh after some gradually built-up expectation is resolved in a non-threatening way. This happens, for instance, when we hear the punch line of a joke, when we are saved from danger, or when the monster threatening us with outstretched talons turns out to be a tickling monster. The theory suggests that laughter began as a specific kind of signal from one individual to others that what had seemed threatening was in fact harmless.
A variation on the false alarm theory is the idea that smiling and laughing evolved as ways of indicating that an apparent act of aggression was intended playfully rather than seriously. This is the function it still serves in rough and tumble play and when it accompanies practical jokes or teasing. It lets everyone know that the safety catch is still on. Along related lines, psychologist Robert Provine speculates that laughter originated in the sort of panting that accompanies boisterous play (including sexual play), and eventually came to symbolize the playful state itself.
The essentially social nature of laughter would also seem to give it evolutionary value. We rarely laugh alone, but in groups laughter is contagious–which is why sit coms are funnier if accompanied by laugh tracks. This indicates that it has a bonding function, promoting solidarity and trust within a group. At the same time, the fact that smiling bares one's teeth suggests the possibility that it evolved from what was initially an aggressive display. This idea hooks up both to the idea that laughter accompanies the transition from feeling threatened to feeling safe, and to the theory that it is prompted by feelings of superiority.
Evolutionary accounts such as these can certainly suggest things to look for when trying to understand what amuses us today and why. Nevertheless, these latter questions are distinct from the question of origins. In Western thought many accounts of the nature of humor have been offered, often presented as explanations of laughter, but three have been especially influential.
Laughter expresses feelings of superiority
This is the oldest theory, suggested by Plato, taken up by Aristotle, and given its best-known expression by Hobbes. It is easy to see its appeal. So much humor involves someone being represented as suffering a misfortune or exhibiting some kind of failing: e.g. the clown with outsized ears and a big red nose who slips on a banana skin, sits on a hot plate, or gets a pie in the face; jokes about people who are ignorant, stupid, ugly, impotent, humiliated, immoral, sick, or about to be eaten by cannibals; or simple teasing, where we typically suggest that a person is inadequate in some way.
The superiority theory coheres easily with the evolutionary accounts of laughter that see it as originating in displays of aggression or in the triumphant roar of the victor over the vanquished. An obvious weakness of the theory, however, is that it does not seem to fit cases where the laughter is entirely good natured, as when two friends meet each other unexpectedly. Nor does it apply in any obvious way to neutral sorts of humor like simple wordplay. Nor does it easily explain the many occasions where we laugh at ourselves. A more sweeping criticism of the theory is that it generalizes from the kind of humor that is mainly popular among men and overlooks the typically less aggressive sort of humor preferred by women.
Laughter is a reaction to incongruity
This theory was first articulated by Kant in the late eighteenth century, although earlier writers on humor had noted that surprise was often an important ingredient. Incongruity is a broad term covering many things, including absurdity, impossibility, strangeness, inappropriateness, irrelevance, ambiguity and unexpectedness. The theory certainly seems to offer an important insight into what it is in so many jokes, witty remarks, comic routines and other humorous situations that prompts laughter. Take a simple joke:
Two cannibals are eating a clown. One says to the other, “Does this taste funny to you?”
The joke hinges on the ambiguity of the word “funny” which can mean “unusual” as well as “humorous.” The incongruity lies in applying the first of these senses to a piece of food being eaten, suggesting that something could have a humorous taste, which is absurd.
In a lot of humor the incongruity is so obvious as to require no analysis: animals dressed as humans; adults acting like children; Greek philosophers in togas strolling around a soccer pitch (a famous Monty Python sketch); someone who is supposed to be respectable (for instance a priest or a rabbi) breaking the rules. The list is endless.
The incongruity theory seems to catch more in its net than the superiority theory, applying to slapstick as well as to simple puns. But stated in general terms—as it usually is—it does not seem to explain very much. The problem is that not all incongruity is funny, only some. If the cannibal eating the clown had said, “Does this taste metaphorical to you?” there would be incongruity but no joke. We only laugh when the incongruity is significant in some way, when it fits the situation and gives us some sort of intellectual satisfaction.
Laughter is a release of nervous energy
This is the view made famous by Freud in Jokes and Their Relation to the Unconscious. Freud's basic idea is that when we laugh we are discharging surplus psychic energy that is suddenly no longer needed. The energy can be cognitive or emotional, but his theory seems most plausible when the energy in question is being used to repress thoughts, feelings and desires surrounded by social taboos. In this respect jokes are similar to dreams, a place where forbidden desires surface into consciousness.
For Freud, the forbidden desires are primarily sexual or aggressive, and this certainly helps to explain the high proportion of jokes that concern sex, body parts, bodily functions, and victims of cruelty, violence, accidents and other misfortunes. But one can easily extend the basic idea to include the constraints imposed by other social norms or even by reason itself. A lot of humor involves violating expectations established by logical thinking (cold baths are a lot nicer when the water is warm) or by our experience of a familiar order, either natural or social. (Q: Why do elephants sit on marshmallows? A: To avoid drowning in the hot chocolate.) This theory also fits quite well with some evolutionary accounts of laughter since cackling over a vanquished foe or laughing from relief at the removal of danger can also be understood as expending sudden superfluous energy. Like the other two theories, though, it seems to capture one aspect of humor rather than provide a key to the whole. Many jokes and humorous routines involve a build up of tension that is released when the punch line is delivered; but just as many are not of this sort. And while humor certainly gives us a safe form of transgression, if Freud's explanation of laughter were correct we would expect the people who are normally the most repressed to be the ones most prone to explosive laughter; yet the reverse seems to be true.
There are, of course, other accounts of humor. Max Eastman argues that humor is a form of play in which we are able to adopt a disinterested attitude to matters that we would normally take seriously. Henri Bergson argues that humor typically involves an incongruous mixing of the human and the inhuman, as when a person is represented as a thing controlled by mechanical laws. But these other theories, like the three just discussed, are open to the charge that they fail to cover every form of humor or humorous situation. The attempt to find something common to all humor is a classic example of a misguided essentialism, looking for the quality that all instances of a thing share when they may, to use Wittgenstein's metaphor, only be linked by a series of family resemblances.
Similarly, the search for a single fundamental explanation of why we laugh offers a case study in failed reductionism. It would be nice to do for the many kinds of laughter what Newton did for planetary orbits, falling apples, and tides–viz. show them all to be manifestations of the same underlying principle. But it seems unlikely that this is possible. The various explanations of laughter are not mutually exclusive, so we should not view them as competitors. Each one highlights important but not universal features of humor or laughter, and thereby deepens our understanding of a phenomenon that remains somewhat mysterious despite its familiarity.
 See Robert Provine, Laughter: A Scientific Investigation (New York: Viking, 2000), pp. 75-97.
 For a critical review of all three theories, see John Morreall, Taking Laughter Seriously (Albany: SUNY, 1983). We might note here the distinction between laughter and humor. Laughter is a physiological phenomenon that can have causes that are not in themselves humorous. Humor covers a range of discourse and behavior from pulling a face to using an inappropriate word. Not all humor produces laughter, even when successful.
 ” [W]omen's humor generally lacks the aggressive and hostile quality of men's humor. The use of humor to compete with or to belittle others, thereby enhancing a person's own status, or to humiliate others either psychologically or physically, seems generally absent among women.” Nancy A. Walker and Zita Dresner, “Women's Humor in America,” in Nancy A. Walker (ed.), What's So Funny? Humor in American Culture (Wilmington: Scholarly Resources Inc., 1998), p. 172.
 This article is adapted from Chapter Four of The Virtues of our Vices(Princeton University Press).