Laughter as social lubricant - Mark van Vugt

Laughter as social lubricant - Mark van Vugt


Laughter as Social Lubricant:

A Biosocial Hypothesis about the Pro-social Functions

of Laughter and Humor

Mark Van Vugt, Charlie Hardy, Julie Stow, & Robin Dunbar

Please do not cite or circulate without permission from the authors




We test the hypothesis that laughter acts as a social lubricant to enhance a sense of

group membership through the release of endorphins. Using a public good game, we

show that laughter increases social bonding and cooperation between strangers and

that it increases the subjective experience of positive affect, while reducing negative

affect. We also show that laughter stimulates the release of endorphins (as indexed by

levels of pain tolerance) and that endorphin release is approximately proportional to

the amount of laughter performed. We propose a biosocial hypothesis of laughter

which addresses both the ultimate and proximate functions of laughter for connecting

individuals within groups.



Laughter as Social Lubricant:

A Biosocial Hypothesis about the Pro-social Functions

of Laughter and Humor

“In laughter we emit sounds and express emotions that come from deep within our

biological being—grunts and cackles from our animal unconscious. But what do these

vocalizations signify? More than 2,000 years of the contemplation of laughter by

some of history’s great philosophers, writers, scientists, and physicians certify the

importance of the question but provide only the vaguest of answers.”

--- R. Provine (2000; p. 2)

Humans are a uniquely social species. They are able to empathize and form deep

emotional connections with non-kin (Baumeister & Leary, 1995). They come to the

rescue of complete strangers in need (Becker & Eagly, 2004). And, they are capable

of sacrificing themselves for the welfare of others in sometimes very large groups

(Van Vugt & Van Lange, 2006). Humans are also unique in their capacity to laugh,

talk, sing and dance (Dunbar, 2004a). These social capacities are not unrelated. The

scale and intensity of human cooperation requires mechanisms to facilitate

communication and affective bonding between people.

Here we propose one such bonding mechanism, human laughter. We develop a

biosocial theory of laughter in which we argue that laughter promotes psychological

well-being, which in turn enables individuals to cooperate and function better in

groups. The effects of laughter are complex and diverse. At the basic physiological

level, we suggest that laughter is involved in the release of endorphins, which create

the experience of positive affect. At the individual psychological level, we predict that

laughter elicits positive mood states while decreasing their negative mood. At the



social psychological level, we predict that laughter promotes group identification as a

direct consequence of this shift in affect. At the behavioral level, we predict that

laughter improves group functioning by increasing altruistic group contributions.

Our biosocial theory of laughter is rooted in both the (evolutionary) biological

and (social) psychological literatures. We will first review the empirical literature on

laughter to summarize a number of key empirical points. Based on the literature

review, we discuss the various proximate functions of laughter and embed them

within an evolutionary hypothesis about the origins of human laughter. Our biosocial

hypothesis leads to a number of specific predictions concerning the effects of

laughter, some of which we test here. Our primary hypothesis is that laughter induces

positive affect and this enables individuals to feel and function better in groups.

Universality of Human Laughter

A Review of the Laughter Literature

Humans have long been characterized as the “laughing animal” (McComas, 1923)

and for some very good reasons. The scientific study of laughter and humor,

gelotology, has produced a number of important insights. Laughter is a universal

human behavior (Dunbar, 2004a; Eibl-Eibelsfeldt, 1999; Provine, 2000). It is

universally recognizable and occurs in a characteristic, stereotyped form (Eibl-

Eibelsfeldt, 1999). Ontogenetically, laughter emerges spontaneously in children as

young as 17 days old and it is one of the first social vocalizations (Deacon, 1997;

Kawakami et al., 2006). Laughter has also been observed in children who are blind

and deaf at birth and who therefore cannot possibly have learnt it from others

(Provine, 2000). This suggests that humans are strongly genetically disposed to

produce laughter.



The evolved basis of laughter is further strengthened by phylogenetic and cross-

cultural comparisons. Some nonhuman primates, notably the chimpanzee (Van Hooff,

1972; Waller & Dunbar 2005), display facial expressions and emit vocalizations

during social play that resemble (and are homologous with) human laughter. Some

theorists have argued that laughter supplements grooming as a bonding device in

primates (Dunbar, 2004a). This suggests that human laughter may have an ancient

evolutionary basis and that a primordial form of laughter may have already been

present in our common ancestor, from which humans and chimpanzees departed some

six million years ago. Cross-culturally, there are important similarities in the stimuli

that elicit laughter. Humor is perhaps the most familiar stimulus, but others include

social play and tickling. Interestingly, Darwin (1872) considered laughter to be the

“tickling of the mind.”

In the literature, there is a general consensus that laughter occurs mostly in

response to unexpected non-serious social events – the stuff that, for example, jokes

are made of (Gervais & Wilson, 2005). We ought to draw a distinction here between

Duchenne and non-Duchenne forms of laughter (Keltner & Bonanno, 1997). The first

is the spontaneous, emotional, stimulus-driven laughter which we are interested in

explaining. The second is primarily self-generated and emotionless, such as when

people laugh out of appeasement, embarrassment or in response to derision. Brain

imaging data show that these two forms of laughter are supported by different neural

systems (Iwase et al., 2002). Duchenne laughter emerges in the subcortical, limbic

system and is connected to a laughter-coordination centre in the dorsal pons (Wild,

Rodden, Grodd, & Ruch, 2003). In contrast, the non-Duchenne laughter originates in

the premotor region and directly influences the primary motor cortex (Wild et al.,




Although Duchenne laughter is presumably hardwired, it is not insensitive to

cultural factors. Cultural norms can dictate what people laugh about and in what

situations laughter is appropriate or inappropriate. For example, in some cultures there

is a greater emphasis on sexual and toilet humor in eliciting laughs, whereas in others

the focus is more on, say, political humor (Provine, 2000). Furthermore, the intensity

and context of laughter are also variable in different cultures (Provine, 2000). This

indicates that laughter can be reinforced or inhibited in accordance with local social

norms and customs (Apte, 1985).

The Functions of Laughter

Laughter theorists have proposed a diversity of proximate, psychological

functions of laughter. First, laughter has been linked to positive emotional

experiences. Brain imaging studies show that laughter involves affective reward

networks in the brain (Iwase et al., 2002), while several clinical studies have revealed

that significant health benefits can be derived from laughter, for example, in immune

system protection (Rosner, 2002). Also, social-psychological studies have found that

humor and laughter are associated with stress relief and a reduction in negative affect

while experiencing the stress of, for example, bereavement (Keltner & Bonanno,

1997). A recent study shows that as little as one minute of laughter increases people’s

self-reported mood (Neuhoff & Schaeffer, 2002). The mood effects of laughter have

been attributed to the release of “feel-good” neuropeptides like endorphins but this

still awaits investigation (Provine, 2000).

Another proposed function of laughter is communicative. Laughter has been

conceptualized as a signal designed to communicate the subjective emotional state of

a sender to receivers. The meaning of laughter is considered something like “that was

social play” to indicate that the situation is not serious (Gervais & Wilson, 2005). A



related signaling function of laughter is to induce positive affect in others (Owren &

Bachoroskwi, 2003). There is support for this theory in a study showing that

particular forms of laughter (like voiced laughter) elicits positive affect in others

(Bachorowski & Owren, 2001). Furthermore, an fMRI study shows that hearing

laughter activates the amygdala, a key emotion area in the brain (Sander & Scheich,


Third, laughter has been proposed to have an emotional contagion function

(Provine, 2000). Research strongly suggests that laughter activates laughter, which is

why many TV-comedies use canned laughter (Provine, 2000). Thus, there might be a

mimicking effect of laughter which results in a convergence of the emotional states

and behaviors of people, the chameleon effect (Chartrand & Bargh, 1999). This shared

affect (as a result of laughter) might be a good way of coupling the emotional states of

individuals within groups enabling them to better coordinate their actions and


A final proposed function of laughter is affiliative. Laughter has been proposed to

foster the integration of new individuals into existing groups (Gamble, 2001). Some

research suggests that laughter plays a role in delineating ingroup and outgroup

boundaries by establishing exclusionary group identities and by fostering aggression

towards members of outgroups (Platow et al., 2005). Others propose that laughter, as

a function of humor, increases the cohesiveness and performance of goal-oriented

groups (Graetbach & Clark, 2003).

Laughter as Social Lubricant: A Biosocial Hypothesis

The evolutionary perspective is premised on the assumption that traits which

enhanced the survival and reproductive success of our ancestors have spread through

the population at the cost of alternative, less successful traits (Barrett, Dunbar, &



Lycett, 2002). By this logic, a legitimate question to ask is what function laughter

would have served our hominid ancestors in order for it to become a design feature of

modern humans.

Our evolutionary hypothesis links laughter to individual well-being and the

welfare of their social groups through its impact on positive affect. Fredrickson’s

(1998) Broaden-and-Build hypothesis suggests that positive emotions “serve to

broaden an individual’s momentary though-action repertoire, which in turn has the

effect of building that individual’s physical, intellectual, and social resources”

(Fredrickson, 1998, p. 300). Emotions such as joy, happiness, and pleasure that are

elicited by laughter foster the urge of people to engage in social play and these play

activities help build resources that can be relied upon when individuals or groups face

a variety of different challenges.

Life in ancestral times is thought to have been extremely stressful. The transition

of hominids to more open savannah type environments meant increased daily travel

times to gather food and water, and increased risks of being exposed to predators and

hostile outgroups (Foley, 1996). These threats, in turn, increased the pressures on

groups to expand in size -- in some cases by adding non-kin group members -- and

develop a more complex social organization. These demographic changes would

inevitably have added further stress, not least because large groups increase the extent

to which free-riders -- those who take the benefits of sociality without paying all the

costs -- can prosper at the expense of other group members (Dunbar, 2004ab; Van

Vugt & Van Lange, 2006).

During this transition, there would have been selection for an adaptive mechanism

that could quickly and effectively release positive emotions in people that had the

effect of increasing group cohesiveness and social cooperation. Laughter could



potentially have served this particular purpose. Additionally, if positive emotions

could be easily and efficiently transmitted between individuals – through a

mechanism such as laughter -- then even those with a negative mood could be

recruited into social activities through the inducement of positive affect. Laughter as

well as the stimuli to produce it, notably humor, could potentially have functioned in

this fashion. Furthermore, the contagious effect of laughter could have facilitated the

social interactions between individuals, allowing them to operate in larger social

networks with minimal costs to group cohesiveness and performance.

Thus, laughter may have been selected for in early humans as a mechanism

whereby individuals, through social play, could build their individual and group

resources to cope with a variety of physical and social dangers. Although the

phylogenetic evidence suggests that laughter was already present in the common

ancestor of humans and chimpanzee -- where it might have played a role in social

bonding and grooming (Dunbar, 2004ab) -- it might not have become a strong

selection force until hominids started to live and move around in large social groups

(Gervais & Wilson, 2005).

The Experiments

Here we propose a biosocial theory of laughter, which integrates the evolutionary

and proximate, psychological functions of laughter into a single coherent theoretical

framework. Evidence from multiple sources, including for example social-

psychological, cognitive-psychological, neuro-endocrinal and neuro-imagining

studies should help build a comprehensive picture of the functions and consequences

of human laughter.

The primary hypothesis derived from this theory is that laughter acts as social

lubricant by facilitating group cohesiveness and social cooperation through eliciting



positive affect. This hypothesis makes a number of specific predictions about the

individual and group-level effects of laughter, some of which will be tested in this

study. In the experiments, we first consider the behavioral effects of laughter by

examining the effects of a laughing experience on decision-making in a public good

dilemma, a group game measuring people’s cooperative inclinations towards groups

(Fehr & Gaechter, 2002; Van Vugt, De Cremer, & Janssen, 2007). We also examine

the extent to which laughter promotes group cohesiveness more directly by measuring

its effect on people’s identification with their group. We then turn our attention to the

role of laughter in inducing positive affect and reducing negative affect. Finally, we

consider the basic physiological processes underlying the social lubricant effect,

particularly the role of laughter in the release of endorphins, the “feel good”

neuropeptides (Keverne, Martensz, & Tuite, 1989). More specifically, the laughter-as-

social lubricant hypothesis generates several predictions.

The first prediction concerns the behavioral effects of laughter. We predict that,

after a laughing experience, people will be more inclined to act altruistically when

interacting with strangers. Cooperation, especially between strangers, can be quite

risky because it is not clear whether one’s contributions will be matched by others in

the group (Van Vugt & Van Lange, 2006). In contexts where reciprocity is the only

basis for balancing the altruism equation, the risk of free-riders reneging on their

debts is greatly increased. Laughter might make people more optimistic so that they

are more willing to increase their cooperation levels by taking others on trust.

A second prediction from our model concerns the affiliative consequences of

laughter. If the social lubricant hypothesis is correct, we would expect an increase in

the social cohesiveness of a group after laughter. One way to measure this is to


examine the extent to which people identify with a group of strangers after

undergoing a laughter experience (Hogg, 1992).

Third, laughter should increase people’s positive affect on a range of specific

subjectively experienced emotions, while decreasing their negative affect. There has

been much speculation on this relationship, but not a great deal of evidence that

laughter is directly responsible for inducing positive mood (for an exception, see

Keltner & Bonanno, 1997). We therefore induce laughter experimentally in people

and examine the resulting mood change by administering the validated and well-

established emotional state scale, PANAS, to measure temporary positive and

negative affect states (Watson, Tellegen & Clark, 1980). Ideally, we should see an

increase in positive emotions such as joy and happiness and a reduction in negative

emotions like sadness which would mediate the effects of laughter.

Laughter and Endorphins

Our final prediction concerns the neurophysiological basis of laughter. If laughter

facilitates social cooperation through its effects on positive affect, then we might

expect laughter to correlate with various physiological indices of positive affect. This

prediction arises from our hypothesis that in the human lineage laughter might have

emerged as a “social grooming” device to connect individuals to groups. Grooming is

known to trigger endorphin release from the hypothalamus (Keverne et al., 1989).

Endorphins are associated with the pain control mechanisms, one of whose by-

products is to make people feel happy and allow them to cope better with aversive

stimuli (Pert & Snyder, 1973). Endorphins create a state of mild euphoria which, for

example, enables individuals to maintain physically stressful physical activities (e.g.,

the famous runners high; see Howlett et al., 1984). Their release during social

grooming produces a sense of mild euphoria which appears to be instrumental in


creating the internal psychological environment conducive for social cooperation. At

the basic neuro-endocrinal level, laughter is therefore expected to be linked to

endorphins, creating the same kind of “high” (Dunbar, 2004b).

Unfortunately, measuring endorphins is a challenge. Because endorphins are

released in the brain, assaying their production can only be done by taking spinal fluid

samples using lumber puncture (Mosby, 1994). However, experts agree that a good

proxy is provided by pain tolerance, since increased pain thresholds are one functional

consequence of endorphin release (Provine, 2000; Zillmann, Rockwell, Schweitzer, &

Sundar, 1993). Therefore, in the final experiment, we induce laughter in participants

and subsequently examine how they cope with a painful task. We predict that laughter

increases pain tolerance levels and argue that this effect is likely caused by the release

of endorphins as a direct result of laughter.

In each of these experiments, we induce laughter by exposing people to carefully

selected comedy clips for a 10-15 minute period, before measuring the main

dependent variables of interest. Consistent with other laughter studies (Provine,

2000), we also examine potential sex differences in our experiments.

Experiment 1: Laughter and Cooperation with Strangers

Does laughter induce cooperation between strangers? To put this suggestion to the

test we exposed people to a brief laughing experience – watching a comedy video clip

-- before examining their decision-making in a cooperative group game. In order to

separate the laughter effects from social bonding that occurs through spending time

together, we compared a condition in which people, before playing the group game,

watched the clip together with their fellow group members (acquaintances condition),

versus a condition where people first watched the clip individually before playing the

game with others (strangers condition). If laughter acts as social lubricant, we


predicted that after a laughter experience people would cooperate more easily with

strangers. We also predicted that this effect would be related to the degree of laughter.

Design and Participants


One hundred and twelve students, 78 women and 34 men, from the University of

Kent participated in this study. Their age range varied from 18 to 51 years, with a

median age of 20. Participants were randomly assigned to one of four experimental

conditions, with a 2 (clip: neutral vs. comedy) x 2 (grouping: strangers vs.

acquaintances) between subjects design. There were 28 experimental sessions in total,

each session containing four individuals each. One group was removed from the

experiment (session 10), because their data were incomplete due to a technical failure,

thus leaving 27 group sessions.


Participants were recruited via the Department of Psychology research

participation scheme and the student webpages at the University of Kent, and signed

up individually for the experiment. Four individuals arrived simultaneously at the

meeting room of the social psychological laboratory, where they were welcomed by

two experimenters and completed an informed consent form.

Manipulation of grouping. To watch the clip, depending upon the grouping

condition, participants were placed either in separate soundproof experimental

cubicles (strangers condition) or in a larger room with three other participants with

whom they formed a group (acquaintances condition). Each room had a single

desktop computer with a 15 inch screen.

Manipulation of clip. Windows media player was used to play the video clips.

The neutral clip showed a 10-minute excerpt from the BBC-series Walking with


Dinosaurs (the actual episode was from Series 1, the “Giant of the Skies”), filmed in

the style of a nature documentary. The comedy clip consisted of a 10-minute excerpt

of a home video comedy show called You Have Been Framed The show contains a

compilation of viewers’ funny home videos, which commonly stimulate Duchenne

laughter. For instance, one clip shows a man jumping on a trampoline when seconds

later he falls straight through the canvas. The show uses canned laughter to maximize

laughter in viewers.

Public good game. After watching the video, individuals were led back to the

meeting room where they played a one-shot public good task with the three other

participants with whom they had already interacted (acquaintances) or not (strangers).

We used a public goods game without a step-level (for a similar procedure, see De

Cremer & Van Vugt, 1999), and the instructions were given on paper. Each member

received an endowment of £2.50 (approximately $5) in an envelope and was told that

they could invest any amount in a group fund or a private fund. They could keep

whatever they put in their private fund. Whatever ended up in the group fund would

be doubled and divided equally among the four of them, regardless of their individual

group contribution. We ran a few practice trials to enhance their understanding of the

game and its pay-offs. The participants were then asked to split the money between

their private fund and the group fund and complete a short questionnaire about the


Subsequently, participants received a careful debriefing about the experiment

and its manipulations from one experimenter, while the other calculated the amount

each person had earned. They were then paid off and asked not to convey the purpose

of the experiment to any other students.


Manipulation Checks


We asked the participants several questions about the clip they had watched, for

example, “How funny did you find the clip?” (1 = not funny at all, 5 = very funny).

This was analyzed with a 2 (Sex) x 2 (Clip) x 2 (Grouping) between-subjects design.

It produced a significant main effect for clip, F(1, 100) = 49.80, p


Looking at the conditions separately shows that in the strangers condition people

contributed more after watching the comedy clip (M = 1.34, SD = 0.60) than the

neutral clip (M = 1.04, SD = 0.57), F(1, 48) = 4.00, p =.05. There was no difference

between the two clips (M’s = 1.41 vs. 1.32, SD’s = 0.69 and 0.63) in the acquaintances

condition, F(1, 52) = 1.24, p =.27. Furthermore, the contribution level in the

comedy/strangers condition was virtually the same as in the two acquaintances

conditions in which people had already interacted with their fellow group members

before playing the game (both p’s >.05).

There was also an unexpected three way interaction between sex, clip and

grouping, F(1, 100) = 3.94, p =.05. The means associated with this interaction are

given in Table 1. They suggest that this three-way interaction was caused by males

being particularly cooperative towards strangers after watching the neutral clip (M =

1.73, SD = 0.61) and that this, in turn, was mainly due to one particular group of three

males and one female (session 20) in which the three men contributed an unusually

large amount of money to the group fund (M = 1.83). This suggests that the sex

composition of the group might be an important factor, something which we will

address later. (Incidentally, when this particular group was eliminated from the

analysis, the two-way interaction between clip and grouping became significant, F(1,

96) = 3.55, p


As expected, there was a positive correlation between laughter and contribution in

the strangers condition (r = .33, p


literature, but not directly tested; but see Neuhoff & Schaefer, 2002). Hence, we

included the PANAS to measure people’s affective states. A third aim was to

determine whether laughter would increase social cohesiveness in groups of strangers.

To do this, we added a group identification scale (De Cremer & Van Vugt, 1999) to

measure the extent to which members felt emotionally attached to their group during

the game.

We used different clips in this experiment, for two reasons. First, although the

comedy clip in Experiment 1 was rated funnier than the neutral clip, it was not rated

very funny in absolute terms. Second, there was an unexplained sex difference in the

rating of the neutral clip in the first study. Although we were not quite sure what

caused this, we nevertheless decided to use a different clip.

Design and Participants


Eighty students, 46 women and 34 men, from the University of Kent participated

in this study. Their age range varied from 18 to 28 years, with a median age of 20.

Participants were randomly assigned to one of four experimental conditions,

following a 2 (clip: comedy vs. neutral) x 2 (grouping: strangers vs. acquaintances)

between-participants design. There were 20 experimental sessions, containing four

individuals each. 2


The procedure was essentially the same as in the first experiment with a few

notable exceptions. First, we used different video clips. For the comedy clip, we opted

for a 10 minute clip of an episode from the Simpsons (episode 3F31; “The Simpsons

138 th episode spectacular”), which the experimental assistants (who were themselves


university students) rated as funny. For the neutral clip, we took a clip from a sports

documentary entitled “Go Tigers”, which the assistants rated as boring.

Second, we measured actual laughter during the clip. We used audio-recorders,

because we did not want the participants to watch the clip in the same room as the

experimenters. After each experimental session, two experimental assistants listened

to the audio-tape and wrote down independently the number of laughs they heard

during the 10 minute clip. Their ratings were highly consistent (Cohen’s kappa = .88).

For analysis, we averaged their scores in those cases where there were discrepancies.

Once again, in the strangers condition we placed people in separate

soundproof cubicles and in the acquaintances condition they were placed in a room

together with their fellow group members to watch the clip.

After watching the clip, they were brought together in a meeting room. Before

playing the group game, we asked the participants to rate their feelings by completing

the 20 item PANAS (e.g., “At this moment I feel happy, …sad, …excited, …upset; 1

= very slightly or not at all, 5 = extremely).

Thereafter they played the group game, which was essentially the same as in the

previous experiment with one exception. In order to determine whether the results in

Experiment 1 were due to a ceiling effect, we increased the stakes of the game, giving

each participant a £5 endowment which they had to divide between their private fund

and the group fund. After this, they completed a 10 item group identification scale

(adopted from Brown et al., 1986) asking them how they felt about the group with

whom they played the game: Items included “I am a person who is glad to belong to

this group” “…who feels strong ties to the group” (1 = never, 5 = very often).


After some final questions about the experiment (including some manipulation

checks), the participants were debriefed by one experimenter while the other

calculated the amount each individual had earned and paid it out to them.

Manipulation Checks


We asked participants the question: “How funny did you find the clip?” (1 =

not funny at all, 5 = very funny). This was analyzed with a 2 (Sex) x 2 (Clip) x 2

(Grouping) design. This analysis only revealed a significant main effect for clip, F(1,

72) = 44.63, p


Taken together, it seems that the laughter manipulation was successfully

induced. The comedy clip was considered funnier and produced considerably more

laughter than the neutral clip.

Group Cooperation

The main dependent variable was the contribution to the group fund (0 - 5 GBP)

in the public good game. We analyzed this using a 2 (Sex) x 2 (Clip) x 2 (Grouping)

design. Recall that we expected group contributions to increase after watching the

comedy clip, particularly among groups of strangers. We found two main effects, for

clip, F(1, 72) = 10.52, p


social cooperation, participants identified more strongly with a group of strangers

after watching the comedy clip (M = 3.19, SD = 0.86) than the neutral clip (M = 1.65,

SD = 0.32), F(1, 36) = 54.12, p


virtually the same as in the two acquaintances conditions where people had interacted

with each other before.

This analysis also revealed a multivariate main effect for Sex, F(2, 71) = 4.65, p



Experiment 3: Laughter and Pain Tolerance

In the third experiment, we examine the hypothesis that laughter stimulates the

production of endorphins, arguing that it is the relaxing effect of these endorphins that

is responsible for the increased positive affect and willingness to cooperate in groups.

Since direct assays for endorphin production can only be done using lumber puncture

(a process that is itself painful, as well as being fraught with adverse side-effects:

Mosby, 1994), we followed conventional practice (e.g., Zillman et al., 1993) and used

pain tolerance as an index of endorphin production. In this study we used slightly

longer clips (15 rather than 10 minutes), because we were not sure how quickly the

impact of endorphins would set in. Furthermore, we used a more refined measure of

laughter, measuring whether or not the participant was laughing on instantaneous scan

samples taken at 30 second intervals, which we used to calculate a percentage score of

laughter (out of 30 events).

Design and Participants


This experiment employed a between subject design and consisted of 32

participants (14 female and 18 male) who were recruited from the student population

at the University of Liverpool. Half of them watched a comedy clip and half watched

a neutral clip. All participants completed a questionnaire before the experiment which

provided background information on their attitudes to humor, and also provided

confirmation of their willingness to take part in the project. Participants ranged in age

from 18-60 years.


For each session, participants undertook a pain tolerance assay (see below), then

watched a 15-minute video, and repeated the pain tolerance assay. Participants were


told that they were taking part in a study of pain tolerance (which had to be measured

twice), but not about the relationship between pain and endorphins or the relationship

between laughter and endorphins. They were fully debriefed after the experiment.

While they were watching the video, the experimenter recorded whether or not each

participant was laughing at 30-sec intervals.

Participants watched the clips in groups of 2-6 individuals, and were asked not

to talk to each other while watching the clips. We used a variety of comedy clips such

as Mr Bean, You’ve Been Framed, Eddie Izzard, Father Ted, Friends and The

Simpsons, all of which were regular comedy slots on UK television which had been

selected by the experimental assistants who were students themselves. The neutral

clips were either from a News programme, Eastenders (a TV soap), Songs of Praise

(a Sunday evening religious slot), a science documentary and a sports programme (on


Pain tolerance was examined using a frozen vacuum wine cooler sleeve,

frozen to -16 o C for the start of each test. Participants were asked to put a sleeve over

their forearm and to keep it there for as long as they could stand it (but, in any case,

for a maximum of 180 seconds to avoid skin damage). A stopwatch was used to

determine (to the nearest complete second) how long they kept the sleeve on. This

procedure was approved by the University’s strict ethical guidelines for conducting

research with human participants.


We assessed endorphin production by the change in pain tolerance (indexed as

the number of seconds for which the frozen wine cooler could be kept on the arm)

before and after watching the clip. Figure 3 plots the difference in pain tolerance

(after minus before) against the proportion of laughs (0-100%) for individual


participants. Laughter was a significant predictor of the difference in pain tolerance,

t(31) = 3.12, p


link between the laughter produced by the comedy clip and the increase in pain

tolerance of participants. 3


Thus, watching a comedy clip seems to be associated with a significant

increase in serum endorphin titre (as indexed by pain tolerance), and the magnitude of

this effect is a linear function of the degree of laughter among participants. There was

an interesting sex difference with males showing an increased pain tolerance after

watching a comedy clip, which was related to the proportion of laughter (we address

this in the General Discussion).

General Discussion

This research yields convergent support for the idea that laughter acts as social

lubricant by enhancing a sense of group membership via the release of endorphins.

Laughter was induced through exposure to a comedy (vs. neutral) clip. We then

measured participants’ physiological, affective, and behavioral reactions in various

experimental tasks. Our findings revealed that laughter – through watching a comedy

– induces positive affect, while reducing negative affect. Furthermore laughter

facilitates social bonding and social cooperation particularly among strangers.

Laughter also significantly increases pain tolerance, which suggests that laughter is

associated with endorphin release. Our research is one of the first to show that

laughter is directly responsible for these effects. Below we discuss the implications of

our findings, attempting to integrate them into a broader biosocial hypothesis about

the functions of laughter in groups.

Social Lubricant Theory of Laughter

The social lubricant theory is inspired by social, evolutionary, and positive

psychological approaches to the study of laughter. It assumes that laughter fosters


people’s attachment to groups through the release of mood-inducing endorphins.

Laughter serves to enhance a sense of social identity which facilitates cooperation

among strangers. Our theory connects different levels of analysis about the proposed

functions of laughter. At the proximate level, we can look at the immediate functions

of laughter, the way it affects individual well-being and group welfare.

Consistent with our theory, our research reveals a myriad of beneficial effects of

laughter. In terms of neurophysiology, our research is among the first to show the

effects of laughter on endorphin production. Endorphins are neuropeptides that create

a mild sense of euphoria in organisms which is believed to have a range of benefits

for health and mood (Provine, 2000). Laughter is used, for example, in health

intervention programs to overcome depression (Rosner, 2002) and cope with pre-

surgery anxiety (Vagnoli, 2005). Procedures to measure endorphins directly in

humans are quite invasive (via a spinal puncture) and so we obtained a reliable

indirect measure in the form of pain tolerance during a physical task (Zillman et al.,

1993). Laughter significantly predicted pain tolerance.

Mirroring the endorphin effects, our research also shows that laughter affects

people’s subjective mood state. Laughter increased positive affect while reducing

negative affect. Participants who watched a comedy clip were happier, more excited,

more inspired, less sad and less bored. Furthermore, their mood changes could be

attributed to the amount of laughter. These data are consistent with other research

showing, for example, that a one-minute laughter experience enhances mood

(Neuhoff & Schaeffer, 2002)

The social lubricant theory proposes that laughter (through the above effects)

facilitates social cooperation between strangers. For this purpose, we utilized a public

goods game to measure the impact of laughter on the convergence between individual


and group interests (Van Vugt et al., 2007). Our research shows that people who

watched a comedy became more cooperative toward strangers, thus improving the

performance of their group. As expected, the amount of laughter was directly

responsible for these effects. Paralleling these results, we also found that laughter

positively affected group cohesiveness by raising the extent to which people identified

with their group.

This suggests that the effects of laughter are primarily the result of a

transformation of motives, whereby the collective group interest starts to weigh more

heavily than self-interest (Brewer & Kramer, 1994; De Cremer & Van Vugt, 1999).

Interestingly, in the acquaintances conditions, laughter did not produce a significant

increase in cooperation. The second experiment (in which endowments were doubled)

revealed that this was not simply due to a ceiling effect. The most probable reason is

that, in these conditions, participants already trusted each other through talking to

each other. This suggests that laughter and language serve as complimentary

mechanisms for inducing cooperation, possibly with laughter having a stronger effect

on group-based affect and language on group-based trust (Dawes, McTavish, &

Shaklee, 1977). This awaits further investigation.

This brings us to speculate about the ultimate functions of laughter. We

hypothesize that the capacity for laughter originates in the importance of group living

for hominids. Group living enabled our ancestor to solve many important problems of

survival and reproduction such as food sharing, communal child care, and coalitional

defense. As group life became more socially complex – perhaps due to an increase in

group size (Dunbar, 2004a) – this development created a need for mechanisms that

could foster the integration of individuals within groups. Laughter may be one such

mechanism. Because laughter quickly releases positive emotions, it is an effective


way to smoothen social interaction between individuals (especially in potentially

conflicting relations between strangers), thus enabling them to create and operate in

highly cooperative units necessary for survival. In this view, laughter might have

evolved as an adaptive mechanism to build up social reserves that groups could rely

upon in times of crises, a view that is consistent with positive psychology (cf.

Fredrickson, 1998).

Albeit somewhat speculative, this evolutionary scenario is not a “just-so story.”

Experts agree that the human capacity for laughter has very ancient origins, and is

probably older than our language ability itself (Gervais & Wilson, 2005). Laughter is

found across all human cultures, and is one of the first vocal expressions of babies

(Provine, 2000). Neuro-imagining studies strongly suggest the presence of a

“laughter-coordination centre” in the human brain (Wild et al., 2003). And, a

rudimentary form of laughter is present among our closest primate cousin, the

chimpanzee, which is elicited during social play and tickling (Van Hooff, 1972;

Waller & Dunbar 2005). Human laughter may have co-evolved with the language

capacity to create typically human phenomena such as humor, a very potent stimulus

to elicit Duchenne laughter, as well as non-Duchenne laughter, a form of laughter that

lacks a strong emotional component (e.g., the nervous laugh; Keltner & Bonanno,


Sex Differences

There were various sex differences in our studies and they deserve some special

attention. The research on sex differences in laughter is a mixed bag. In social

contexts, there seem to be few differences between males and females in laughter

production (Owren & Bachorowski, 2003). However, it is quite likely that males and

females differ in laughter as a function of differences in what they consider to be


funny (Provine, 2000). For example, the comedy clips that were used in Experiments

2 and 3 such as the Simpsons produced more laughter from men than from women.

But there were no differences in laughter for the Have you Been Framed clips (funny

home videos). The fact that the effects of laughter itself did not differ between the

sexes is encouraging for our theory. The final experiment showed that differences in

pain tolerance between males and females were fully accounted for by the sex

differences in laughter production. Nevertheless it is important for future research to

be aware of sex differences when developing stimulus materials (Azim, 2005).

Another issue to consider in future research is the sex composition of the groups.

A consistent finding in the literature is that females tend to laugh more around males

in conversational interactions (Owren & Bachorowski, 2003). The results of the

second experiment confirm this: Females laugh more in mixed sex groups (5.3 laughs

on average) than in all female groups (3.5 laughs). The other group composition effect

we obtained was for cooperation rates in Experiment 1. Within a complicated three-

way interaction there was evidence for increased male group contributions in one

particular condition. This happened to be a group in which three males were paired

with one female (we avoided this grouping in the second experiment). There is

evidence to suggest that males sometimes use generosity as a strategy to attract the

interest of a female (sexual selection theory; Buss, 1994; Hardy & Van Vugt, 2006),

which is what may have happened in this case.

Limitations of the Present Research and Directions for the Future

The first obvious criticism concerns the ecological validity of our findings. How

important is laughter in real life? We can only speculate about this. Obviously we only

examined relative small personal sacrifices from participants, particularly in the first

experiment (up to $5). Although such amounts are quite common in economic games


experiments (Komorita & Parks, 1994), the question is whether laughter promotes

more substantial group sacrifices. The short answer is: We don’t know. But

interestingly, once we doubled the endowment in Experiment 2, laughter produced

similar pro-social effects, suggesting that the amount of personal sacrifice makes little


Setting aside these results, it is noteworthy that one of the most desirable traits in

potential partners is sense of humor (Buss, 1994), suggesting the importance of

laughter for mating relationships. In addition, many experts on the human condition

from the Bible to Shakespeare to modern day health professionals have reminded us

that “laughter is the best medicine.” In support of this, various health programs use

laughter therapy to help people cope with various stressors like bereavement, surgery,

and fertility treatment (Rosner, 2002). Yet, as Provine (2000) suggests, many studies

suffer from poor experimental designs and further research into the health benefits of

laughter is desperately needed.

A second potential criticism is the absence of any direct neurophysiological

evidence for the impact of laughter. For example, our claim that endorphins are

involved in laughter is based on indirect evidence. It is therefore important to collect

further neurobiological data on laughter. For example, via saliva and urinary samples

it is currently possible to measure oxytocin, a neuro-hormone that is believed to be

involved in attachment processes (Taylor et al., 2000). It may well be that laughter

stimulates the release of oxytocin in addition to endorphins. In addition, neuro-

imagining studies may be useful to examine the neuropsychological correlates of

laughter production. So far, the constraints of imaging technology mean that it is

virtually impossible to study laughter in any detail: Accurate imaging requires the


subject to remain very still, but full-blown Duchenne laughter commonly involves

gross head and body movements.

Another recommendation for research is to compare the effects of Duchenne with

non-Duchenne laughter. Our theory predicts beneficial effects from laughter, but our

research has focused on Duchenne laughter, that is, spontaneous stimulus-driven

laughter which is elicited when people are exposed to humor. What are the effects of

non-Duchenne laughter, which occurs in the absence of attempts at humor? Because

this type of laughter lacks a strong emotional component, we expect it will be less

effective in social bonding. In a similar set-up as the present studies, we could ask

people to laugh out loud for a certain duration and contrast the effects with the

Duchenne laughter generated by humor.

Conclusions and Implications

The main goal of this research has been to introduce a new theoretical perspective

on laughter, the laughter-as-social-lubricant hypothesis, and provide some data in

support of this hypothesis. This hypothesis integrates findings from many different

disciplines that have studied laughter, including social psychology, positive

psychology, evolutionary psychology, cognitive neurosciences, and gelotology (the

scientific study of laughter). Through controlled experimental research we have

shown that laughter enhances a sense of group membership which enables individuals

to engage in profitable social exchanges with strangers. Our research suggests a role

for endorphins in producing these effects of laughter. More research is obviously

needed to test different elements of the social lubricant theory of laughter and we have

given some recommendations for future inquiry. Laughter is a serious topic of

scientific inquiry and deserves more attention from researchers interested in human

social behavior.



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1 There was a three-way interaction between sex, clip and grouping, F(1, 100) =

5.08, p



Table 1. Cooperation as a function of sex, clip, and grouping (Experiment 1)


Strangers Acquaintances



Male 0.92 a (.62) 1.73 b (.61)

Female 1.08 a (.57) 1.16 b (.57)


Male 1.52 b (.68) 1.32 b (.76)

Female 1.30 b (.59) 1.48 b (.64)


Notes: cooperation ranges from 0-2.5 GBP; standard deviations are in between

parentheses; means with a different superscript differ from each other; p


Table 2. Affect as a function of clip and grouping (Experiment 2)





Comedy 3.24 a (.68) 1.58 b (.68)

Neutral 1.89 b (.36) 2.65 a (.39)


Comedy 3.01 a (.68) 1.48 b (.44)

Neutral 2.51 a (.95) 1.65 b (.48)


Notes: scales range from 1 (not at all) to 5 (extremely); standard deviations appear in

between parentheses; means with a different superscript differ from each other; p

Control Group Experimental Group


Figure Captions

Figure 1. Cooperation as a function of clip and grouping; Experiment 2

Figure 2. Group identification as a function of clip and grouping; Experiment 2

Figure 3. Relationship between laughter and pain tolerance, r = .50; paindiff is the

difference in pain tolerance between posttest and pretest; Experiment 3


(in GBP)












Strangers Acquaintances















Strangers Acquaintances























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