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Yawning…and why yawns are contagious: A theory on evolution and atavism
Medical Hypotheses (2008) 71, 307–325
http://intl.elsevierhealth.com/journals/mehy
Correspondence
Yawning. . .and why yawns are contagious: A theory on evolution and atavism I would like to congratulate Matikainen and Elo on their unearthing of mechanism giving rise to increased arousal, alertness and wakefulness, while yawning [1]. Observational studies on animal and human yawning yield important clues for understanding primate evolution. In response to this article, I would like to draw your attention to our observation regarding contagious yawn usage in humans, which I believe may help enhance our knowledge of human and primate evolution. We have all noticed that when one person yawns, it sets off a chain reaction of yawns amongst others in the group. However, the reason why yawns are contagious is a bit of a mystery. There is also very little research done, because for most people contagious yawning is not a problem. It was previously thought that, while yawning occurs in many animal species, only humans yawned contagiously. It turns out, chimps and stumptail macaques may yawn contagiously as well [2,3]. Its universal and widespread nature suggests that it must have either functional or atavistic basis, if not so [4]. In non-human animals, contagious yawning can serve as a warning signal. For example, baboons use yawn to threaten their enemies, possibly by displaying large, canine teeth [5]. Although human beings no longer require the use of displaying their unimpressive incisor teeth to exhibit dominance or anger, It is possible that a contagious yawn is a vestigial reflex, similar to the formation of goose bumps in humans under stress, because doi:10.1016/j.mehy.2008.03.006
at one time in evolutionary history, the yawn served to coordinate the aggressive social behaviour of a group of animals. I strongly believe that this unconscious automatic action is a non-anatomical, physiological atavistic trait present in humans.
References [1] Matikainen J, Elo H. Does yawning increase arousal through mechanical stimulation of the carotid body. Med Hypotheses 2008;70(3):488–92. [2] Anderson JR, Myowa-Yamakoshi M, Matsuzawa T. Contagious yawning in chimpanzees. Proc Biol Sci 2004;271(Suppl. 6): S468–70. [3] Paukner A, Anderson JR. Video-induced yawning in stumptail macaques (Macaca arctoides). Biol Lett 2006;2(1): 36–8. [4] Kumar A, Kumar CJ. Atavistic orofacial response to manually dextrous activities. Med Hypotheses 2005;65(1):196. [5] Darwin CR. Special expressions of animals. In the expression of the emotions in man and animals. 1st ed. London: John Murray; 1872. p. 116–46.
Hari Prasad Medical Research Faculty, Microbiology, K.S. Hegde Medical Academy, Deralakatte, Nithyanandanagar P.O., Mangalore, Karnataka 575 018, India Tel.: +91 99 45 300 360; fax: +91 824 2443875 E-mail address: [email protected]
http://intl.elsevierhealth.com/journals/mehy
Correspondence
Yawning. . .and why yawns are contagious: A theory on evolution and atavism I would like to congratulate Matikainen and Elo on their unearthing of mechanism giving rise to increased arousal, alertness and wakefulness, while yawning [1]. Observational studies on animal and human yawning yield important clues for understanding primate evolution. In response to this article, I would like to draw your attention to our observation regarding contagious yawn usage in humans, which I believe may help enhance our knowledge of human and primate evolution. We have all noticed that when one person yawns, it sets off a chain reaction of yawns amongst others in the group. However, the reason why yawns are contagious is a bit of a mystery. There is also very little research done, because for most people contagious yawning is not a problem. It was previously thought that, while yawning occurs in many animal species, only humans yawned contagiously. It turns out, chimps and stumptail macaques may yawn contagiously as well [2,3]. Its universal and widespread nature suggests that it must have either functional or atavistic basis, if not so [4]. In non-human animals, contagious yawning can serve as a warning signal. For example, baboons use yawn to threaten their enemies, possibly by displaying large, canine teeth [5]. Although human beings no longer require the use of displaying their unimpressive incisor teeth to exhibit dominance or anger, It is possible that a contagious yawn is a vestigial reflex, similar to the formation of goose bumps in humans under stress, because doi:10.1016/j.mehy.2008.03.006
at one time in evolutionary history, the yawn served to coordinate the aggressive social behaviour of a group of animals. I strongly believe that this unconscious automatic action is a non-anatomical, physiological atavistic trait present in humans.
References [1] Matikainen J, Elo H. Does yawning increase arousal through mechanical stimulation of the carotid body. Med Hypotheses 2008;70(3):488–92. [2] Anderson JR, Myowa-Yamakoshi M, Matsuzawa T. Contagious yawning in chimpanzees. Proc Biol Sci 2004;271(Suppl. 6): S468–70. [3] Paukner A, Anderson JR. Video-induced yawning in stumptail macaques (Macaca arctoides). Biol Lett 2006;2(1): 36–8. [4] Kumar A, Kumar CJ. Atavistic orofacial response to manually dextrous activities. Med Hypotheses 2005;65(1):196. [5] Darwin CR. Special expressions of animals. In the expression of the emotions in man and animals. 1st ed. London: John Murray; 1872. p. 116–46.
Hari Prasad Medical Research Faculty, Microbiology, K.S. Hegde Medical Academy, Deralakatte, Nithyanandanagar P.O., Mangalore, Karnataka 575 018, India Tel.: +91 99 45 300 360; fax: +91 824 2443875 E-mail address: [email protected]