Thursday, February 9, 2012

A Brief History of Laughter

     A few months ago, while I was in the operating room giving anesthesia during a tonsillectomy, I joined an interesting conversation regarding whether or not other primates, like chimpanzees or gorillas, are capable of laughter. I don't remember exactly how the topic was introduced; it seemed like one of the scrub techs had seen a video or an episode of Animal Planet elaborating on this subject. The ENT surgeon was involved in the discussion, and what he had to say caught my attention. I'd always thought the main difference between humans and "lesser primates" was a nuance in the function of our opposable thumbs. The surgeon, speaking strictly in terms of the comparative laryngeal anatomy between humans and chimps, opined that because of anatomical differences in the musculature, these primates cannot laugh like humans, concluding that it is the ability to laugh which distinguishes us from them.
     Because I am a devout lover of laughter and silliness, I try to engage in mirthful behavior as many times as possible on a daily basis. Our dogs, Simon and Lilly, provide an endless supply of amusement. The other night, Spartacus and I had a good giggle, watching as Simon and Lilly began the complicated and bizarre process of folding and rearranging their dog beds. It's a canine nighttime ritual they've recently developed. First, they race to our bedroom to see who's going to get the "favorite" of the two identical beds, and then, they play-fight over them, turning them up against the wall until only one bed is fully on the floor, the loser of the battle getting the less desirable half-bed. I started thinking about how funny it would be if dogs could laugh, and then, I remembered the conversation from the OR. "Why do we laugh, and what's the mechanism?" I wondered. "How did the first humans 'start' laughing, and what exactly were they laughing at?" The answers surprised me, and hopefully, they'll intrigue and delight you.
     Laughter, perhaps the most ancient of human affective behaviors, has been around for at least 7 million years. (1) It is thought to predate human speech. Both laughter and speech are characterized by coordination of respiration, phonation, and resonance. Unlike laughter, speech requires articulation, or voluntary control over the vocal system. (2) Contrary to popular belief, laughter is not a uniquely human phenomenon; other mammals vocalize during play, while chimps and other great apes who are playing or being tickled, produce a breathy pant, similar to us. (1)  Human laughing involves breath control, a feature absent in nonhuman primate laughter, and this is why we can speak. When chimps and great apes laugh, only one vocalization occurs each time they inhale and exhale. The laughter of humans involves a pulsed cycle of choppy exhalations, accompanied by modulation of the laryngeal  cartilages and musculature, along with other structures, such as the tongue and facial muscles, producing our familiar "ha-ha-ha." (2) These differences are primarily a function of bipedalism. Running and breathing on all fours is coordinated in a one breath per stride ratio; this ensures that the lungs remain inflated to strengthen and prepare the thorax for forelimb impact. (1) As primate ambulation became more upright, these respiratory constraints were no longer necessary, as evidenced by our ability to walk and talk simultaneously. Because laughter and speech compete for the same vocal mechanism, with speech being dominant, laughter punctuates our speech. (1) Despite these differences, it is clear that laughter is the sound of play. (1)  Charles Darwin postulated that laughter in early humans evolved as an indicator of a group's cohesiveness and well being, conferring a survival advantage upon "happy" clans. (3)
      Laughing is a social phenomenon, a signal we send to others, the necessary stimulus being another person. (1) As babies, we receive lots of encouragement to smile and laugh. We begin smiling at about 5 weeks of age, and develop spontaneous laughter between 4 to 6 months, usually in response to being tickled by our parents. Tickling, in fact, may be one of the most ancient games played by primates, with the oldest joke being "I'm going to get you!" (1) We cannot tickle ourselves, for tickling, like spontaneous laughter, specifically requires an external stimulus. Our brains inhibit any self-induced responses to tickling; otherwise, we'd all be walking around like giggling idiots in a constant state of ticklish false alarm. (1) It is possible that tickling arose as a defense mechanism, a primitive neurocutaneous reflex which enabled us to protect ourselves from predators. In primates, the reciprocal smiling and laughing which occurs during tickling is felt to facilitate parent-offspring bonding. (4) Although most people don't like being tickled, it generally evokes laughter, creating a cycle of positive reinforcement with the tickler: "Stop! Ha-ha-ha! Do it again!" Laughter comes in two flavors, spontaneous (emotional) and voluntary (contrived). Both types of laughter arise from a single brain center, their pathways being modulated by different tracts and structures. (5) We can make ourselves laugh, but the emotionality of laughter involves a different neural pathway over which we have no control. Spontaneous, emotional laughing is enjoyable, producing an altered state of consciousness, where we temporarily lose ourselves in joy, forgetting about any physical pain or worldly worries. Our eyes truly "light up" when we laugh spontaneously because emotion sends a unique signal to the eye muscles, as well as the muscles around the mouth. Voluntary laughter sounds just like spontaneous laughter, involving a similar respiratory pattern, but is not typically accompanied by enjoyment. In the game of social acceptance, we fake laugh in order to please others, to give them the impression that we find what they've said clever or humorous. (2) Interestingly, as some of the yogis have recently demonstrated, voluntary laughter can progress to spontaneous laughter.(1, 7)
     Gelatology is the study of laughter and its effects on the body. Research in this field focuses on examining the biopsychosocial and physiologic impact laughter has on various aspects of human health. An excellent structural definition of laughter is a "buoyant immersion in the presence of unanticipated glimpsings prompting harmonious integrity which surfaces anew through contemplative visioning", the implied harmony, plenitude, and energy of which can be extrapolated more broadly to describe a state of health (5, 6) The benefits of laughter have been elucidated by a variety of studies examining its effects on the cardiovascular, neurological, respiratory, and immune systems, as well as its psychological impact on depression and terminal illness. In humans, there are two types of stress. Distress, or negative stress, is bad for us because it invokes the release of chemical mediators which constrict our blood vessels and suppress our immune systems. A positive form of stress, eustress, which is brought on by mirthful laughter, reverses this harmful neurohumoral cascade, thereby promoting health. Laughter has also been demonstrated to be the central mediator between mental well-being and disease. (5) Proponents of laugh yoga describe laughter as "a powerful form of exercise that gives you more of a cardiovascular workout than many 'regular' aerobic activities. (5,7) Indeed, laughter induces forceful, rhythmic contractions of the rib cage, activating muscles, such as the diaphragm, and rectus abdominis, which are normally passive during respiration, accompanied by an initial rise and subsequent lowering of the heart rate, dilation of the blood vessels, and an increase in lung capacity. (2, 5) Laughing, it seems, is just plain good for you!!
     In conclusion, we feel better when we laugh. Since we typically only laugh in the presence of others (the audience effect), it follows that if we want more laughter in our lives, we should seek the company of others, even if it's the family pet. (1) Since losing my job, I'm at home alone much of the day. Although I miss the human interaction I once enjoyed at work, Simon and Lilly's buffoonery is a wonderful substitute. It's a refreshingly reciprocal relationship, motivated purely by mutual adoration. I find myself tittering and laughing at their joyfully uninhibited frolicking, my outward amusement further fueling their canine mischief. To put it simply, we get a kick out of each other, and our playful interactions leave us all feeling happy and relaxed. I only wish they could laugh with me!

1. Provine, RR. Laughing, tickling, and the evolution of speech and self. Current Directions in Psychological Science, 2004. 13(6), 215-218.
2. Ruch, W. & Ekman, P. The expressive pattern of laughter. Emotions, Quality, & Consciousness Kazniak, A.W. (ed). Tokyo: World Scientific Publisher, 426-443.
3. Wild, B., Rodden, F.A., Grodd, W., & Ruch, W. Neural correlates of laughter and humour. Brain, 2003; 126, 2121-2138.
4. Harris, C.R. The mystery of ticklish laughter. American Scientist, 1999. 87; 344-351.
5. Hunaid, H., & Hasan, T.F. Laugh yourself into a healthier person: a cross cultural analysis of the effects of varying levels of laughter on human health. International Journal of Medical Sciences, 2009. 6(4): 200-211.
6. Parse, R.R. The experience of laughter: a phenomological study. Nursing Science Quarterly, 1993: 39-43.
7. [Internet] Kataria, M., & Kataria, M. Laughter Yoga International.


  1. What a wonderful post, and subject for a post. It's fascinating to read about laughter from a doctor's (scientist's) point of view. I learned so much. Is it considered spontaneous laughter if one makes oneself laugh, because I do that all the time? I don't mean I set out deliberately to give myself the giggles, but I think of something that sends me into hysterics. I seem to be able to amuse myself better than anyone else.

    1. great question, NP! although the literature suggests that spontaneous laughter requires some sort of external stimulus, i think that aspects of ourselves, like our own funny thoughts or inside jokes, can stimulate spontaneous laughter as well. if i repeat the word, "helmet" enough times out loud, i'll inevitably start laughing. it's probably associated with something funny i've seen or heard in the past, like a Monty Python skit, but the image/connection is still intact. i agree, i think sometimes we are better at making ourselves laugh than anyone else...laughing at ourselves is amusing and therapeutic!

  2. Greatly enjoyed reading your post! Why we laugh, why tickling produces laughter, etc - are questions that run in my mind too. Equally intriguing are the differences between spontaneous and voluntary laughter, as you pointed out. Most certainly, it can't be an excess of nitric oxide anytime laughter happens, it has to be a deeper physiological/psychological phenomenon. Its so nice to have an anesthesiologist on board (here at BC), who is also a philosopher and artist :) Cheers!

  3. Very interesting, and very informative. I had never thought of anyone studying laughter before this, but it seems an obvious thing to do. I would love to be a test subject.

    It is amazing to me that someone with such talents as yourself would not be employed, unless of course you just did not wish to be.

    1. Thanks, PBS...this is a subject that I was surprised to find a number of scholarly papers on. Wouldn't it be fun to be a test subject, unless of course, you had to agree to being tickled for hours on end :-) I am working part-time now...around the time I wrote this, I was in-between jobs.

  4. Great post, Kris! I really enjoyed learning about the history of laughter (had no idea it predated human speech!). Oh yes, we do feel better when we laugh. I am a devout lover of laughter and silliness too! Like the videos you included. Fascinating the way great apes laugh, and the laughter yoga classes and laughter club, fabulous idea that doctor had! I’d love to find one of those laughter clubs in my area!

    1. Thanks, Madilyn, glad you enjoyed it! I think laughing yoga is absolutely brilliant!