Yawn#Social function

The English yawn continues a number of Middle English forms: {{lang|enm|yanen}} from Old English {{lang|ang|ġānian}}, and {{lang|enm|yenen, yonen}} from Old English frequentatives {{lang|ang|ġinian, ġionian}}, from a Germanic root *gīn-. The Germanic root has Proto-Indo-European cognates, from a root {{PIE|*g̑hēi-}}Pokorny (1959:419-422): "g̑hē- : ghə-, and g̑hēi- 'to gape, yawn'", Pokorny (1959:449): "g̑hēu- : g̑hō(u)- : g̑həu- 'to gape, yawn'" found also with -n- suffix in Greek {{lang|grc|χαίνω}} ('to yawn'), and without the -n- in English gap (compare the figura etymologica in Norse {{lang|non|ginnunga-gap}}), gum ('palate') and gasp (via Old Norse), Latin {{lang|la|hiō, hiatus}}, and Greek {{transliteration|grc|chasm, chaos}}.

The Latin term used in medicine is {{lang|la|oscitatio}} (anglicized as oscitation), from the verb oscito ('to open the mouth').

Pandiculation is the act of yawning and stretching simultaneously.[http://www.medterms.com/script/main/art.asp?articlekey=4752 MedOnline.net] {{Webarchive|url=https://web.archive.org/web/20070502002255/http://www.medterms.com/script/main/art.asp?articlekey=4752 |date=2007-05-02 }}, "pandiculate"

File:Fetal yawning 4D ultrasound ecografia 4D Dr. Wolfgang Moroder.theora.ogv

There are a number of theories that attempt to explain why humans and other animals yawn.{{cite web|url=https://www.nbcnews.com/id/wbna3076713|archive-url=https://web.archive.org/web/20130417063112/http://www.nbcnews.com/id/3076713/t/little-mystery-why-do-we-yawn|url-status=live|archive-date=17 April 2013|title=Little mystery: Why do we yawn?|year=2013|publisher=MSNBC Interactive|access-date=16 September 2013}}{{cite web |last=Chudler |first=Eric H |title=Yawning...and Why Yawns are Contagious |url=http://faculty.washington.edu/chudler/yawning.html |date=July 31, 2007 |publisher=University of Washington |access-date=2009-10-03 |archive-url=https://web.archive.org/web/20060112122510/http://faculty.washington.edu/chudler/yawning.html |archive-date=January 12, 2006}}{{cite journal|last1=Gupta|first1=S|last2=Mittal|first2=S|title=Yawning and its physiological significance.|journal=International Journal of Applied & Basic Medical Research|date=January 2013|volume=3|issue=1|pages=11–5|pmid=23776833|doi=10.4103/2229-516x.112230|pmc=3678674|doi-access=free}}

One study states that yawning occurs when one's blood contains increased amounts of carbon dioxide and therefore becomes in need of the influx of oxygen (or expulsion of carbon dioxide) that a yawn can provide. Yawning may reduce oxygen intake compared to normal respiration; however, the frequency of yawning is not decreased by providing more oxygen or reducing carbon dioxide in the air.{{cite web |url=http://faculty.washington.edu/chudler/yawning.html |title=Yawning.. and why yawning is contagious |date=31 July 2007 |publisher=University of Washington |access-date=2012-11-16 |archive-date=2006-01-12 |archive-url=https://web.archive.org/web/20060112122510/http://faculty.washington.edu/chudler/yawning.html |url-status=live }}

Animals subject to predation or other dangers must be ready to physically exert themselves at any given moment. At least one study suggests that yawning, especially psychological "contagious" yawning, may have developed as a way of keeping a group of animals alert.{{cite web |url=http://www.albany.edu/campusnews/releases_368.htm |title=UAlbany News Release - What's in a Yawn ask UAlbany Researchers |publisher=University at Albany |date=29 June 2007 |access-date=7 December 2013 |archive-date=4 April 2014 |archive-url=https://web.archive.org/web/20140404231613/http://www.albany.edu/campusnews/releases_368.htm |url-status=live }} If an animal is drowsy or bored, it will be less alert than when fully awake and less prepared to spring into action. "Contagious" yawning could be an instinctual signal between group members to stay alert.

File:Yawning Infant, August 2018.jpg

Nervousness, which often indicates the perception of an impending need for action, has also been suggested as a cause. Anecdotal evidence suggests that yawning helps increase a person's alertness. Paratroopers have been noted to yawn during the moments before they exit their aircraft.{{cite magazine |url=https://www.newscientist.com/article/mg19426104.400-yawning-may-boost-brains-alertness.html |title=Yawning may boost brain's alertness |last=Hooper |first=Rowan |date=2 July 2007 |magazine=New Scientist |access-date=2009-09-01 |archive-date=2009-04-27 |archive-url=https://web.archive.org/web/20090427221054/http://www.newscientist.com/article/mg19426104.400-yawning-may-boost-brains-alertness.html |url-status=live }}

Another notion states that yawning is the body's way of controlling brain temperature.{{cite journal |first1=Andrew C. |last1=Gallup |last2=Gallup |title=Yawning as a brain cooling mechanism: Nasal breathing and forehead cooling diminish the incidence of contagious yawning |journal=Evolutionary Psychology |volume=5 |issue=1 |pages=92–101 |date=June 21, 2007 |doi=10.1177/147470490700500109 |doi-access=free }}{{cite web |url=http://dsc.discovery.com/news/2008/12/15/yawn-brain-head.html |title=Discovery News |access-date=2008-12-15 |archive-date=2008-12-16 |archive-url=https://web.archive.org/web/20081216015403/http://dsc.discovery.com/news/2008/12/15/yawn-brain-head.html |url-status=live }} In 2007, researchers, including a professor of psychology from the SUNY Albany (US), proposed yawning may be a means to keep the brain cool. Mammalian brains operate best within a narrow temperature range. In two experiments, subjects with cold packs attached to their foreheads and subjects asked to breathe strictly nasally exhibited reduced contagious yawning when watching videos of people yawning.{{cite video |people=Gordon G. Gallup |title=Good Morning America – The Science of Yawning (July 30, 2007) |url=https://abcnews.go.com/GMA/Story?id=3425960&page=1 |medium=TV-Series |publisher=ABC |location=USA |date=2007}}

A similar hypothesis suggests yawning is used for regulation of body temperature. Similarly, Guttmann and Dopart (2011) found that when a subject wearing earplugs yawns, the air moving between the subject's ear and the environment causes a breeze to be heard.{{cite web |url=http://www.enn.com/health/article/43278/print |title=Global Health and Wellness News: Yawn! |publisher=Enn.com |date=2011-09-20 |access-date=2014-03-02 |archive-date=2014-02-02 |archive-url=https://web.archive.org/web/20140202112349/http://www.enn.com/health/article/43278/print |url-status=live }} Guttmann and Dopart determined that a yawn causes one of three possible situations to occur: the brain cools down due to an influx or outflux of oxygen; pressure in the brain is reduced by an outflux of oxygen; or the pressure of the brain is increased by an influx of air caused by increased cranial space.

One review hypothesized that yawning's goal is to periodically stretch the muscles of the throat, which may be important for efficient vocalization, swallowing, chewing, and also keeping the airway wide.{{Cite journal |last1=Doelman |first1=Christiaan Jacob |last2=Rijken |first2=Johannes Adriaan |date=2022-02-05 |title=Yawning and airway physiology: a scoping review and novel hypothesis |journal=Sleep & Breathing = Schlaf & Atmung |volume=26 |issue=4 |pages=1561–1572 |doi=10.1007/s11325-022-02565-7 |pmid=35122606 |pmc=9663362 |s2cid=246534682 }}

Yawning behavior may be altered as a result of medical issues such as diabetes,{{cite journal |doi=10.1152/ajpregu.00429.2006 |title=Lack of central nitric oxide triggers erectile dysfunction in diabetes |year=2006 |last1=Zheng |first1=Hong |last2=Bidasee |first2=Keshore R. |last3=Mayhan |first3=William G. |last4=Patel |first4=Kaushik P. |journal=AJP: Regulatory, Integrative and Comparative Physiology |volume=292 |issue=3 |pmid=17095652 |pages=R1158–64}} stroke,{{cite web|author=Steve Jones |url=https://www.telegraph.co.uk/science/steve-jones/6583820/Yawning-is-part-of-what-makes-us-human.html |archive-url=https://web.archive.org/web/20091120065150/http://www.telegraph.co.uk/science/steve-jones/6583820/Yawning-is-part-of-what-makes-us-human.html |url-status=dead |archive-date=2009-11-20 |title=Telegraph.co.uk |publisher=Telegraph.co.uk |access-date=2013-07-20}} or adrenal conditions.{{cite journal |doi=10.1016/j.bbr.2004.02.013 |title=Adrenalectomy and dexamethasone replacement on yawning behavior |year=2004 |last1=Anías-Calderón |first1=José |last2=Verdugo-Díaz |first2=Leticia |last3=Drucker-Colín |first3=René |journal=Behavioural Brain Research |volume=154 |pages=255–9 |pmid=15302132 |issue=1|s2cid=37006215 }} Excessive yawning is seen in immunosuppressed patients such as those with multiple sclerosis.{{cite journal |doi=10.1016/j.msard.2018.04.019 |title=Yawning and cortisol levels in multiple sclerosis: potential new diagnostic tool |year=2018 |last1=Thompson |first1=S.B.N. |last2=Coleman |first2=A. |last3=Williams |first3=N. |journal=Multiple Sclerosis & Related Disorders |volume=23 |pages=51–5 |pmid=29772467 |s2cid=21715886 |url=http://eprints.bournemouth.ac.uk/31829/7/Manuscript.pdf }} A professor of clinical and forensic neuropsychology at Bournemouth University has demonstrated that cortisol levels rise during yawning.{{cite journal |doi=10.2196/ijmr.2241 |title=Born to yawn? Understanding yawning as a warning of the rise in cortisol levels: randomized trial |year=2012 |last1=Thompson |first1=S.B.N. |last2=Bishop |first2=P. |journal=Interactive Journal of Medical Research |volume=1 |number=2 |pages=1–9|pmid=23611879 |doi-access=free |pmc=3626133 }}{{cite journal|url=http://eprints.bournemouth.ac.uk/22534/1/Cortisol-Frankham-Bishop.pdf |title=The art of capturing a yawn using the science of nerve impulses and cortisol levels in a randomized controlled trial. Thompson Cortisol Hypothesis as a potential predictor of neurological impairment |year=2014 |last1=Thompson |first1=S.B.N. |last2=Frankham |first2=C. |last3=Bishop |first3=P. |journal=Interactive Journal of Arts & Sciences |volume=7 |number=3 |pages=543–57}}

File:Edgar Germain Hilaire Degas 084.jpg]]

With respect to a possible evolutionary advantage, yawning might be a herd instinct.{{cite journal |doi=10.1016/j.neuroimage.2004.10.022 |title=Yearning to yawn: The neural basis of contagious yawning |year=2005 |last1=Schürmann |first1=Martin |last2=Hesse |first2=Maike D. |last3=Stephan |first3=Klaas E. |last4=Saarela |first4=Miiamaaria |last5=Zilles |first5=Karl |last6=Hari |first6=Riitta |last7=Fink |first7=Gereon R. |journal=NeuroImage |volume=24 |issue=4 |pages=1260–4 |pmid=15670705|s2cid=6269514 }} (see also {{cite journal |doi=10.1016/j.cogbrainres.2004.11.011 |title=Contagious yawning and the brain |year=2005 |last1=Platek |first1=Steven M. |last2=Mohamed |first2=Feroze B. |last3=Gallup |first3=Gordon G. |journal=Cognitive Brain Research |volume=23 |issue=2–3 |pages=448–52 |pmid=15820652}}) Theories suggest that the yawn serves to synchronize mood in gregarious animals, similar to howling in a wolf pack. It signals fatigue among members of a group in order to synchronize sleeping patterns and periods.

Research by Garrett Norris (2013) involving monitoring the behaviour of students kept waiting in a reception area indicates a connection (supported by neuro-imaging research) between empathic ability and yawning. "We believe that contagious yawning indicates empathy. It indicates an appreciation of other peoples' behavioral and physiological state," says Norris.{{cite news |last=Seward |first=Liz |url=http://news.bbc.co.uk/2/hi/science/nature/6988155.stm |title=Sign of empathy |work=BBC News |date=2007-09-10 |access-date=2013-07-20 |archive-date=2014-03-01 |archive-url=https://web.archive.org/web/20140301065827/http://news.bbc.co.uk/2/hi/science/nature/6988155.stm |url-status=live }}

The yawn reflex has long been observed to be contagious. In 1508, Erasmus wrote, "One man's yawning makes another yawn",Erasmus Adagio Chil. III, cent. iv, No 95 (1508) quoted in Stevenson, Burton ed. (1948) The Macmillan Book of Proverbs, Maxims, and Famous Phrases. New York: Macmillan. and the French proverbialized the idea to {{lang|fr|"Un bon bâilleur en fait bâiller sept"}} ('One good gaper makes seven others gape').Stevenson, Burton ed. (1948) The Macmillan Book of Proverbs, Maxims, and Famous Phrases. New York: Macmillan. Often, if one person yawns, this may cause another person to "empathetically" yawn.{{cite journal |doi=10.1511/2005.6.532 |title=Yawning |year=2005 |last1=Provine |first1=Robert |journal=American Scientist |volume=93 |issue=6 |page=532}} Observing another person's yawning face (especially their eyes), reading or thinking about yawning, or looking at a yawning picture can cause a person to yawn.{{cite journal |doi=10.1111/j.1439-0310.1986.tb00611.x |title=Yawning as a Stereotyped Action Pattern and Releasing Stimulus |year=2010 |last1=Provine |first1=Robert R. |journal=Ethology |volume=72 |issue=2 |pages=109–22|bibcode=1986Ethol..72..109P }}{{cite web |url=https://www.npr.org/templates/story/story.php?storyId=14654608 |title=The Quest to Design the Perfect Yawn: NPR |last=Krulwich |first=Robert |date=September 24, 2007 |publisher=NPR |access-date=2009-09-01 |archive-date=2010-01-22 |archive-url=https://web.archive.org/web/20100122151932/http://www.npr.org/templates/story/story.php?storyId=14654608 |url-status=live }} The proximate cause for contagious yawning may lie with mirror neurons in the frontal cortex of certain vertebrates, which, upon being exposed to a stimulus from conspecific (same species) and occasionally interspecific organisms, activates the same regions in the brain.{{cite magazine |first1=V. S. |last1=Ramachandran |year=2000 |title=Mirror Neurons and Imitation Learning as the Driving Force Behind 'the Great Leap Forward' in Human Evolution |magazine=Edge |volume=69 |url=http://www.edge.org/3rd_culture/ramachandran/ramachandran_index.html |access-date=2012-05-15 |archive-date=2019-03-08 |archive-url=https://web.archive.org/web/20190308010928/https://www.edge.org/3rd_culture/ramachandran/ramachandran_index.html |url-status=live }} Mirror neurons have been proposed as a driving force for imitation, which lies at the root of much human learning, such as language acquisition. Yawning may be an offshoot of the same imitative impulse.

A 2007 study found that young children with autism spectrum disorders do not increase their yawning frequency after seeing videos of other people yawning, in contrast to non-autistic children. In fact, the autistic children actually yawned less during the videos of yawning than during the control videos.{{cite journal |doi=10.1098/rsbl.2007.0337 |title=Absence of contagious yawning in children with autism spectrum disorder |year=2007 |last1=Senju |first1=A. |last2=Maeda |first2=M. |last3=Kikuchi |first3=Y. |last4=Hasegawa |first4=T. |last5=Tojo |first5=Y. |last6=Osanai |first6=H. |journal=Biology Letters |volume=3 |issue=6 |pages=706–8 |pmid=17698452 |pmc=2391210}}

File:Joseph Ducreux (French - Self-Portrait, Yawning - Google Art Project.jpg pandiculating (both yawning and stretching); self-portrait c. 1783]]

The relationship between yawn contagion and empathy is strongly supported by a 2011 behavioural study, conducted by Ivan Norscia and Elisabetta Palagi (University of Pisa, Italy). The study revealed that—among other variables such as nationality, gender, and sensory modality—only social bonding predicted the occurrence, frequency, and latency of yawn contagion.{{cite journal |doi=10.1371/journal.pone.0028472 |title=Yawn Contagion and Empathy in Homo sapiens |year=2011 |editor1-last=Rogers |editor1-first=Lesley Joy |last1=Norscia |first1=Ivan |last2=Palagi |first2=Elisabetta |journal=PLOS ONE |volume=6 |issue=12 |pages=e28472 |pmid=22163307 |pmc=3233580|bibcode=2011PLoSO...628472N |doi-access=free }} As with other measures of empathy, the rate of contagion was found to be greatest in response to kin, then friends, then acquaintances, and lastly strangers. Related individuals (r≥0.25) showed the greatest contagion, in terms of both occurrence of yawning and frequency of yawns. Strangers and acquaintances showed a longer delay in the yawn response (latency) compared to friends and kin. Hence, yawn contagion appears to be primarily driven by the emotional closeness between individuals. The social asymmetry in contagious yawning (with contagious yawning being more frequent between familiar subjects than between strangers) remains when only yawns that are heard, but not seen, are considered. This finding makes it unlikely that visual attentional biases are at the basis of the social asymmetry observed in contagious yawning.{{cite journal |doi=10.3389/fpsyg.2020.00442 |title=Auditory Contagious Yawning Is Highest Between Friends and Family Members: Support to the Emotional Bias Hypothesis |year=2020 |last1=Norscia |first1=Ivan |last2=Zanoli |first2=Anna|last3=Gamba |first3=Marco |last4=Palagi |first4=Elisabetta |journal= Frontiers in Psychology |volume=11 |page=442 |pmid=32317997 |pmc=7147458 | id=1664-1078 |doi-access=free }}

Two classes of yawning have been observed among primates.{{cite journal |last1=Deputte |first1=Bertrand L. |title=Ethological Study of Yawning in Primates. I. Quantitative Analysis and Study of Causation in Two Species of Old World Monkeys (Cercocebus albigena and Macaca fascicularis) |journal=Ethology |date=26 April 2010 |volume=98 |issue=3–4 |pages=221–245 |doi=10.1111/j.1439-0310.1994.tb01073.x }} In some cases, the yawn is used as a threat gesture as a way of maintaining order in the primates' social structure.{{cite web |last1=Laura |first1=Poppick |title=Baboons Use Yawns to Convey Social Messages|date=February 18, 2014 |url=https://www.scientificamerican.com/article/baboons-use-yawns-to-convey-social-messages/ |website=Scientific American}} Specific studies were conducted on chimpanzees{{cite journal |doi=10.1098/rsbl.2004.0224 |pmid=15801606 |title=Contagious yawning in chimpanzees |year=2004 |last1=Anderson |first1=J. R. |last2=Myowa-Yamakoshi |first2=M. |last3=Matsuzawa |first3=T. |journal=Proceedings of the Royal Society B: Biological Sciences |volume=271 |issue=Suppl 6 |pages=S468–S470|pmc=1810104 }} and stumptail macaques.{{cite journal |doi=10.1098/rsbl.2005.0411 |title=Video-induced yawning in stumptail macaques (Macaca arctoides) |year=2006 |last1=Paukner |first1=A. |last2=Anderson |first2=J. R |journal=Biology Letters |volume=2 |pages=36–8 |pmid=17148320 |issue=1 |pmc=1617183}} A group of these animals was shown a video of other members of their own species yawning; both species yawned as well. This helps to partly confirm a yawn's "contagiousness".

The Discovery Channel's show MythBusters also tested this concept. In their small-scale, informal study they concluded that yawning is contagious.{{Cite web|url=http://dsc.discovery.com/fansites/mythbusters/episode/episode-tab-06.html|title=DSC.discovery.com|access-date=2010-06-22|archive-date=2010-07-23|archive-url=https://web.archive.org/web/20100723110724/http://dsc.discovery.com/fansites/mythbusters/episode/episode-tab-06.html|url-status=live}}

Gordon Gallup, who hypothesizes that yawning may be a means of keeping the brain cool, also hypothesizes that "contagious" yawning may be a survival instinct inherited from our evolutionary past. "During human evolutionary history, when we were subject to predation and attacks by other groups, if everybody yawns in response to seeing someone yawn the whole group becomes much more vigilant and much better at being able to detect danger."

A study by the University of London has suggested that the "contagiousness" of yawns by a human will pass to dogs. The study observed that 21 of 29 dogs yawned when a stranger yawned in front of them but did not yawn when the stranger only opened his mouth.

Helt and Eigsti (2010) showed that dogs, like humans,{{cite journal |doi=10.1111/j.1467-8624.2010.01495.x|title=Contagious Yawning in Autistic and Typical Development |year=2010 |last1=Helt |first1=Molly |last2=Eigsti |first2=Inge-Marie |journal=Child Development |volume=81 |issue=5 |pages=1620–1631 |pmid=20840244 }} develop a susceptibility to contagious yawning gradually, and that while dogs above seven months 'catch' yawns from humans, younger dogs are immune to contagion.{{cite journal |doi=10.1007/s10071-012-0568-9|pmid=23076724|title=Contagious yawning in domestic dog puppies (Canis lupus familiaris): the effect of ontogeny and emotional closeness on low-level imitation in dogs|year=2012 |last1=Madsen |first1=Elainie Alenkær |last2=Perssson |first2=Tomas |journal=Animal Cognition |volume=16|issue=2|pages=233–40|s2cid=18440582}} The study also indicated that nearly half of the dogs responded to the human's yawn by becoming relaxed and sleepy, suggesting that the dogs copied not just the yawn, but also the physical state that yawns typically reflect.

In a study involving gelada baboons, yawning was contagious between individuals, especially those that were socially close. This suggests that emotional proximity rather than spatial proximity is an indicator of yawn contagion.{{cite journal |author1=Palagi E. |author2=Leone A. |author3=Mancini G. |author4=Ferrari P. F. | year = 2009 | title = Contagious yawning in gelada baboons as a possible expression of empathy | journal = Proceedings of the National Academy of Sciences | volume = 106 | issue = 46| pages = 19262–19267 | doi=10.1073/pnas.0910891106 |bibcode=2009PNAS..10619262P | pmid=19889980 | pmc=2780782|hdl=11381/2292627 |doi-access=free }}

Evidence for the occurrence of contagious yawning linked to empathy is rare outside of primates. It has been studied in Canidae species, such as the domestic dog and wolf. Domestic dogs have shown the ability to yawn contagiously in response to human yawns. Domestic dogs have demonstrated they are skilled at reading human communication behaviours. This ability makes it difficult to ascertain whether yawn contagion among domestic dogs is deeply rooted in their evolutionary history or is a result of domestication.

In a 2014 study, wolves were observed in an effort to answer this question. The results of the study showed that wolves are capable of yawn contagion.{{cite journal |author1=Romero T. |author2=Ito M. |author3=Saito A. |author4=Hasegawa T. | year = 2014 | title = Social Modulation of Contagious Yawning in Wolves | journal = PLOS ONE | volume = 9 | issue = 8| page = e105963 | doi=10.1371/journal.pone.0105963|pmid=25162677 |pmc=4146576 |bibcode=2014PLoSO...9j5963R |doi-access=free }} This study also found that the social bond strength between individuals affected the frequency of contagious yawning in wolves, supporting previous research which ties contagious yawning to emotional proximity.

Some evidence for contagious yawning has also been found in budgerigars (Melopsittacus undulatus), a species of social parrots.{{cite journal |last1=Gallup |first1=A |last2=Swartwood |first2=L |last3=Militello |first3=J |last4=Sackett |first4=S |title=Experimental evidence of contagious yawning in budgerigars (Melopsittacus undulatus) |journal=Animal Cognition |date=2015 |volume=18|issue=5 |pages=1051–8 |doi=10.1007/s10071-015-0873-1 |pmid=26012708 |s2cid=17105459 }} This indicates that contagious yawning may have evolved several times in different lineages. In budgerigars, contagious yawning does not seem to be related to social closeness.

In certain neurological and psychiatric disorders, such as schizophrenia and autism, the patient has an impaired ability to infer the mental states of others. In such cases, yawn contagion can be used to evaluate their ability to infer or empathize with others. Autism spectrum disorder (ASD) is a developmental disorder which severely affects social and communicative development, including empathy.{{Citation needed|date=August 2023}} The results of various studies have shown a diminished susceptibility to contagious yawn, compared to the control group of typically developing children.{{cite journal |author1=Helt M. S. |author2=Eigsti I. M. |author3=Snyder P. J. |author4=Fein D. A. | year = 2010 | title = Contagious yawning in autistic and typical development | journal = Child Development | volume = 81 | issue = 5| pages = 1620–1631 | doi=10.1111/j.1467-8624.2010.01495.x | pmid=20840244}} Since atypical development of empathy is reported in autism spectrum disorder, results support the claim that contagious yawning and the capacity of empathy share common neural and cognitive mechanisms.{{Citation needed|reason=which results?|date=August 2023}} Similarly, patients with neurological and psychiatric conditions, such as schizophrenia, have shown an impaired ability to empathize with others. Contagious yawning is one means of evaluating such disorders.{{Citation needed|date=August 2023}} The Canadian psychiatrist Heinz Lehmann claimed that increases in yawning could predict recovery in schizophrenia.{{cite journal | author = Provine R. R. | year = 2005 | title = Yawning: the yawn is primal, unstoppable and contagious, revealing the evolutionary and neural basis of empathy and unconscious behavior | journal = American Scientist | volume = 93| pages = 532–539 | doi = 10.1511/2005.56.532 }} The impairment of contagious yawning can provide greater insight into its connection to the underlying causes of empathy.

There is still substantial disagreement in the existing literature about whether or not yawn contagion is related to empathy at all.{{cite journal |last1=Massen |first1=J |last2=Gallup |first2=A |title=Why contagious yawning does not (yet) equate to empathy. |journal=Neuroscience & Biobehavioral Reviews |date=2017 |volume=80 |pages=573–585 |doi=10.1016/j.neubiorev.2017.07.006|pmid=28735879 |doi-access=free |hdl=1887/76849 |hdl-access=free }} Empathy is a notoriously difficult trait to measure, and the literature on the subject is confused, with the same species sometimes displaying a connection between contagious yawning and social closeness, and sometimes apparently not. Different experimenters typically use slightly different measures of empathy, making comparisons between studies difficult, and there may be a publication bias, where studies which find a significant correlation between the two tested variables are more likely to be published than studies which do not. By revising in critical way the literature for and against yawn contagion as an empathy-related phenomenon, a 2020 review has shown that the social and emotional relevance of the stimulus (based on who the yawner is) can be related to the levels of yawn contagion, as suggested by neurobiological, ethological and psychological findings.{{cite journal |doi=10.1016/j.neubiorev.2020.01.020 |title= The neuroethology of spontaneous mimicry and emotional contagion in human and non-human animals |year=2020 |last1=Palagi |first1=Elisabetta |last2=Celeghin |first2=Alessia|last3= Tamietto |first3=Marco |last4=Winkielman |first4=Piotr |last5=Norscia |first5=Ivan|journal= Neuroscience & Biobehavioral Reviews |volume=111 |pages= 149–165 |pmid= 31972204 |hdl= 2318/1724362 |s2cid= 210836319 |url= https://research.tilburguniversity.edu/en/publications/6df2bd63-9c07-4070-96de-fdc039324355 | id=0149-7634 |hdl-access=free }} Therefore, the discussion over the issue remains open.

{{Quote box

|quote = Seeing a dog & horse & man yawn, makes me
feel how much all animals are built on one structure.

|align = right

|qalign = left

|author = Charles Darwin

|source = Notebook M (1838), [http://darwin-online.org.uk/content/frameset?pageseq=79&itemID=CUL-DAR125.-&viewtype=side 65]

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File:Close-up view of the head of a white tiger, yawning with the tongue out.jpg

File:Cougar Yawn.gif

Mammals, birds, and other vertebrates yawn.{{cite journal |last=Smith |first=E. O. |date=1999-07-01 |title=Yawning: An evolutionary perspective |journal=Human Evolution |volume=14 |issue=3 |pages=191–198 |doi=10.1007/BF02440156 |s2cid=14876709 }}

In animals, yawning can serve as a warning signal. Charles Darwin's book, The Expression of the Emotions in Man and Animals, mentions that baboons yawn to threaten their enemies, possibly by displaying large canine teeth.{{Cite book |url=https://books.google.com/books?id=SDiB_dDG8vYC&q=baboon+yawn&pg=PA48 |title=Developing a social psychology of monkeys and apes |first=John K. |last=Chadwick-Jones |publisher=Taylor and Francis |year=1998 |page=48 |isbn=978-0-86377-820-9 |access-date=2020-10-21 |archive-date=2021-09-21 |archive-url=https://web.archive.org/web/20210921091408/https://books.google.com/books?id=SDiB_dDG8vYC&q=baboon+yawn&pg=PA48 |url-status=live }} Similarly, Siamese fighting fish yawn only when they see a conspecific (same species) or their own mirror-image, and their yawn often accompanies aggressive attack.{{cite journal |title=Some comparative aspects of yawning in Betta splendens, Homo sapiens, Pantera leo, and Papio sphinx |author=Baenninger R |journal=Journal of Comparative Psychology |year=1987 |volume=101 |issue=4 |pages=349–354 |doi=10.1037/0735-7036.101.4.349}} Guinea pigs also yawn in a display of dominance or anger, displaying their impressive incisor teeth. This is often accompanied by teeth chattering, purring and scent marking.

Adelie penguins employ yawning as part of their courtship ritual. Penguin couples face off and the males engage in what is described as an "ecstatic display", opening their beaks and pointing their faces skyward. This trait has also been seen among emperor penguins. Researchers have been attempting to discover why these two different species share this trait, despite not sharing a habitat. Snakes yawn, both to realign their jaws after a meal and for respiratory reasons, as their trachea can be seen to expand when they do this. Dogs, and occasionally cats, often yawn after seeing people yawn{{cite web|title=Why Do Cats Yawn|url=http://www.cathealth.com/how-and-why/why-do-cats-yawn|publisher=CatHealth|access-date=10 March 2016|archive-date=11 March 2016|archive-url=https://web.archive.org/web/20160311014322/http://www.cathealth.com/how-and-why/why-do-cats-yawn|url-status=live}} and when they feel uncertain.{{cite book |first=Turid |last=Rugaas |year=2005 |chapter=Yawning |chapter-url=https://books.google.com/books?id=tB7tONlHCVQC&pg=PA25 |pages=[https://archive.org/details/ontalkingtermswi0000ruga/page/25 25–7] |title=On Talking Terms With Dogs: Calming Signals |publisher=Dogwise |location=Wenatchee |isbn=978-1-929242-36-8 |url=https://archive.org/details/ontalkingtermswi0000ruga/page/25 }} Dogs demonstrate contagious yawning when exposed to human yawning. Dogs are very adept at reading human communication actions, so it is unclear if this phenomenon is rooted in evolutionary history or a result of domestication.{{Cite journal | doi=10.1371/journal.pone.0105963| pmid=25162677| pmc=4146576|title = Social Modulation of Contagious Yawning in Wolves| journal=PLOS ONE| volume=9| issue=8| pages=e105963|year = 2014|last1 = Romero|first1 = Teresa| last2=Ito| first2=Marie| last3=Saito| first3=Atsuko| last4=Hasegawa| first4=Toshikazu| bibcode=2014PLoSO...9j5963R| doi-access=free}} Fish can also yawn, and they will increase this behavior when experiencing a lack of oxygen.{{cite journal |last1=Hasler |first1=C |last2=Suski |first2=C |last3=Hanson |first3=K |last4=Cooke |first4=S |last5=Tufts |first5=B |title=The Influence of Dissolved Oxygen on Winter Habitat Selection by Largemouth Bass: An Integration of Field Biotelemetry Studies and Laboratory Experiments |journal=Physiological and Biochemical Zoology|pmid=19199559 |doi=10.1086/591806 |volume=82 |year=2009 |issue=2 |pages=143–52 |hdl=10680/1815 |s2cid=23493633 |hdl-access=free }} Socially contagious yawning has been observed in budgerigars, and anecdotally when tired in other parrot species.{{cite web |title=Why Does My Parrot Yawn? |url=https://www.forbirdsonlyny.com/blog/2017/10/24/why-does-my-parrot-yawn |website=For Birds Only Blog |access-date=17 June 2021 |archive-date=24 June 2021 |archive-url=https://web.archive.org/web/20210624200634/https://www.forbirdsonlyny.com/blog/2017/10/24/why-does-my-parrot-yawn |url-status=live|date=2017-10-24 }}

File:Oscar Bluhm Ermüdende Konversation crop.jpg titled Ermüdende Konversation, or "Wearisome conversation".]]

Some cultures lend yawning moral or spiritual significance. An open mouth has been associated with letting good immaterial things (such as the soul) escape or letting bad ones (evil spirits) enter, and yawning may have been thought to increase these risks.{{cite journal |last= Walusinski |first=O. |title= Yawning Comparative study of knowledge and beliefs |journal= BMJ |volume= 328 |issue= 7445 |year= 2004 |page=328:963.2|doi= 10.1136/bmj.328.7445.963-a |pmc= 390270 }} Covering the mouth when yawning may have been a way to prevent such transmission. Exorcists believe yawning can indicate that a demon or possessive spirit is leaving its human host during the course of an exorcism.{{cite magazine|last1=Cruz|first1=Gilbert|title=The Story of a Modern-Day Exorcist|url=http://content.time.com/time/nation/article/0,8599,1885372,00.html|magazine=Time|access-date=25 August 2015|date=16 Mar 2009|archive-date=7 March 2018|archive-url=https://web.archive.org/web/20180307104155/http://content.time.com/time/nation/article/0,8599,1885372,00.html|url-status=live}} Thus, covering one's mouth has been conceived as a protective measure against this.

Yawning has also been described as disrespectful (when done before others) or improper (when done alone). For example, in his commentary on Al-Bukhari's hadith collection, Ibn Hajar, an Islamic theologian, mentions that yawning, in addition to its risks of letting demons enter or take hold of one's body, is unbefitting for humans as it makes them look and sound like dogs by crooking men's upright posture and making them howl:

{{Blockquote|He [Prophet Muhammad] likened excessive yawning to the howling of dogs to deter people from it and to make it seem repulsive, for when a dog howls, it raises its head and opens its mouth widely, and the yawner resembles it when he yawns too much. This is why the Devil laughs at those who yawn, for he succeeds in playing with them and deforming them.}}

Superstitions regarding the act of yawning may have arisen from concerns over public health. Polydore Vergil ({{circa|1470}}–1555), in his De Rerum Inventoribus, writes that it was customary to make the Sign of the Cross over one's mouth, since "alike deadly plague was sometime in yawning, wherefore men used to fence themselves with the sign of the cross{{nbsp}}... which custom we retain at this day."Iona Opie and Moira Tatem, A Dictionary of Superstitions (Oxford: Oxford University Press, 1992), 454.

Yawning is often perceived as implying boredom, and yawning conspicuously in another's presence has historically been a faux pas. In 1663 Francis Hawkins advised, "In yawning howl not, and thou shouldst abstain as much as thou can to yawn, especially when thou speakest."Hawkins, Francis Youth's Behavior, or, Decency in Conversation amongst Men (1663) quoted in Mencken, H.L. A New Dictionary of Quotations on Historical Principles from Ancient and Modern Sources New York: Vintage, 1942{{page needed|date=May 2012}} George Washington said, "If You Cough, Sneeze, Sigh, or Yawn, do it not Loud but Privately; and Speak not in your Yawning, but put Your handkerchief or Hand before your face and turn aside."{{cite book|last1=Washington|first1=George|last2=Conway|first2=Moncure Daniel|title=George Washington's Rules of civility: traced to their sources and restored|page=59|year=1890|publisher=University of California|isbn=9781463506391 |url=https://books.google.com/books?id=_bZEAAAAIAAJ&q=If+You+Cough,+Sneeze,+Sigh,+or+Yawn,+do+it+not+Loud+but+Privately;+and+Speak+not+in+your+Yawning,+but+put+Your+handkercheif+or+Hand+before+your+face+and+turn+aside&pg=PA59|access-date=2020-10-21|archive-date=2021-11-01|archive-url=https://web.archive.org/web/20211101023417/https://books.google.com/books?id=_bZEAAAAIAAJ&q=If+You+Cough%2C+Sneeze%2C+Sigh%2C+or+Yawn%2C+do+it+not+Loud+but+Privately&+and+Speak+not+in+your+Yawning%2C+but+put+Your+handkercheif+or+Hand+before+your+face+and+turn+aside=&pg=PA59|url-status=live}} These customary beliefs persist in the modern age. One of Mason Cooley's aphorisms is "A yawn is more disconcerting than a contradiction." A loud yawn may even lead to penalties for contempt of court.{{Cite news |url=https://www.latimes.com/archives/la-xpm-2005-apr-20-me-yawn20-story.html |title=Sleepy Juror Gets Rude Awakening |last=Liu |first=Caitlin |date=April 20, 2005 |work=Los Angeles Times |access-date=May 7, 2010 |archive-date=October 21, 2010 |archive-url=https://web.archive.org/web/20101021020348/http://articles.latimes.com/2005/apr/20/local/me-yawn20 |url-status=live }}

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{{Reflist|30em}}

• Provine, Robert R. Curious Behavior: Yawning, Laughing, Hiccupping, and Beyond (Harvard University Press; 2012) 246 pages; examines the evolutionary context for humans.

{{wiktionary|yawn}}

{{Commons category|Yawning}}

• [http://www.scholarpedia.org/article/Yawn Yawn] article in Scholarpedia.
• [http://www.uc.edu/news/ebriefs/yawn.htm A Real Yawner: Causes, Concerns and Communications of the Yawn], Mary Bridget Reilly, University of Cincinnati, 23 October 2003

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