In this article I hypothesize that the laughter elicited by the processing of what we characterize as humorous events is an exapted vocal fight-or-flight displacement response. A displacement activity is a reaction to change (or anticipation of change) in activity, internal conflict, or motivational ambivalence (Schniter, 2001).The motivational ambivalence and internal conflict aspects of the phenomenon are suggestive in explaining the efficacy of the particular structure of jokes in precipitating laughter. (Russell 1996; Kozintsev and Butovskaya 1999)

The idea that a displacement behaviour is at the heart of both laughter and humorous events is a bottom-up hypothesis that avoids the stunting effect of competing humour theories. It is the only hypothesis that I view as being able to give a meaningful explanation of the relationship that exists between laughter and the processing of events that cause its elicitation, doing away with vague explanations, such as the idea that we laugh with pleasure when we have resolved incongruities.

The three main humour theories (the relief, incongruity resolved and superiority theories) focus on particular stages and aspects of the sequence of events that take place during a laughter evoking episode.                                                                                                                                    Aggression and a feeling of superiority can be viewed as motivations for the instigation of humorous events - the intent being to disparage people who are disliked or seen as inferior. Aggression can also be an aspect of the content of a joke, and along with other topics such as religion, sex and politics, adds, what I term, "emotive weight", which increases arousal and thus the duration and volume of the laughter the event elicits. However, as I hope to demonstrate, it is fear, not aggression, that is at the centre of all laughter evoking events. It is the central thread that runs from the play fighting and tickling  exhibited by our closest evolutionary relatives to the verbal constructs of modern man.

As the incongruity theory of humour is concerned with, but does not fully explain, the mechanism by which laughter is disinhibited, it must take centre stage in our deliberations. The idea that jokes throw up contradictory, incongruous, or as I term them, conflicting, scenarios, is indisputable. This theory veers off course when it is designated the "incongruity resolved" theory. The consequences of believing we resolve the conflict engendered by the joke mechanism are explained in the next section.

The relief theory of humour is a "why" rather than a "how" theory, and basically views humour as been instrumental in the release or replacement of what has been variously characterized as "psychic energy" (Freud 1916)(Spencer 1860) and painful emotions. Relief theories deal with the general effects of laughter inducing events and give little insight into the neurophysiological source of pleasure or the nature of the laughter process.

None of the above theories encompass the diversity of laughter evoking events; nor do they address the biological underpinnings or explain the physiological effects of the laughter process.

The superiority and relief theories, and to a lesser extent, the incongruity resolved theory, suffer from the fact that they are not anchored within meaningful space-time frames. A humour theory that does not address the “where”, “when” and “how” - in other words, a theory that does not allow aspects of the phenomenon to be temporally and physically mapped (in the short term neurologically and the long term phylogenetically) must remain vague and, for the most part, will not lend itself to experimentation.

The misleadings effect of the vernacular

Before the advent of scientific methods explanations of human behaviours relied on the ideas and feelings expressed in the limiting context of our sociocultural existence. Our default language, the vernacular, developed to serve a particular function, that of communication in the cultural milieu, and although it is prone to ambiguity, it has served this purpose well for thousands of years.

Science required a different way of thinking and expression through a strictly defined vocabulary, and another problem that has hindered the elucidation of a coherent theory covering laughter and what we have termed “humour” is the use of the vernacular in scientific writing. When writing academic articles, authors feel obliged to use the accepted lexicon of their chosen field of study.The use of jargon can be detrimental to the dissemination of ideas; however, authors must be careful, as the use of the vernacular can bias and mislead. Scientific rigor demands that words that are pivotal to an author’s arguments are rightly applied and unambiguous. As a result of a top down approach,  humour research suffers greatly from both the use of words that are not applicable outside their common usage and the acceptance of words and phrases that give rise to circular statements.  

The very word “humour” defies any definition that is acceptable in a scientific discourse. It is a categorical noun, as is furniture, and not a process. There is no such thing as a humour process, and to use the phrases, “we experience humour"  and “humour takes place", as some authors do, is nonsensical.

Each of the following words: funny, humorous, comical and amusing, are defined in terms of one or more of the others, which leads to circular statements, and tells us nothing  about their natures. Even if we attempt to define humour  in terms of emotional and physical responses, we will find that there is little to connect the response to a light-hearted article in a newspaper and the response to a laughter eliciting joke. There is no doubt that both can, to varying degrees, produce a lowering of stress, but from the physical responses it is unlikely that the same brain areas are involved. 

Nothing has hindered the elucidation of the natures of laughter and humour more than the intellectualization of the common idea that we "get jokes". This has taken the form of the incongruity resolved theory, which lacks a neurological explanation and places laughter as a subsequential rather than a consequential response to the processing of the event in which it is elicited. 

Impulsive aggression is a behavioral disposition characterized by the inability to regulate negative affect and impulses to harm oneself or others. It is highly comorbid with depression, substance use, and suicidal behaviors (Hicks et al., 2004Horesh, Gothelf, Ofek, Weizman, & Apter, 1999Koller et al., 2002). The available literature suggests that deficient serotonergic activity in emotion regulation circuitry, such as the prefrontal cortex and the anterior cingulate cortex, may be an important predisposing factor to impulsive aggression (New et al., 2002Parsey, Oquendo, Simpson, Ogden, Van Heertum, Arango, & Mann, 2002Siever et al., 1999). Additionally, serotonergic hypofunction may contribute to the hyperactivity of the dopaminergic system, which further promotes impulsive and aggressive behaviors. Considering that serotonin hypofunction in impulsive aggression has been reported frequently across the literature and has a heritable foundation, serotonin hypofunction may be a neurochemical vulnerability marker of impulsive aggression. Dopamine hyperactivity may secondarily contribute to impulsive aggression, given the modulation of serotonin system over dopaminergic activity.

Role of Serotonin and Dopamine System Interactions in the Neurobiology of Impulsive Aggression and its Comorbidity with other Clinical Disorders