\n<\/p>\n
A<\/span>ll vertebrates yawn, or indulge in a behaviour that\u2019s at least recognisable as yawn-adjacent. Sociable baboons yawn, but so do semi-solitary orangutans. Parakeets, penguins and crocodiles yawn \u2013 and so, probably, did the first ever jawed fish. Until relatively recently, the purpose of yawning wasn\u2019t clear, and it\u2019s still contested by researchers and scientists. But this commonality provides a clue to what it\u2019s really all about \u2013 and it\u2019s probably not what you\u2019re expecting.<\/p>\n \u201cWhen I poll audiences and ask: \u2018Why do you<\/em> think we yawn?\u2019, most people suggest that it has to do with breathing or respiration and might somehow increase oxygen in the blood,\u201d says Andrew Gallup, a professor in behavioural biology at Johns Hopkins University. \u201cAnd that\u2019s intuitive because most yawns do have this clear respiratory component, this deep inhalation of air. However, what most people don\u2019t realise is that that hypothesis has been explicitly tested and shown to be false.\u201d<\/p>\n <\/span>Is he tired \u2013 or increasing arterial blood supply to his cranium?<\/span> Photograph: Galina Zhigalova\/Getty Images<\/p>\n To test the idea that we yawn to bring in more oxygen or expel excess carbon dioxide, studies published in the 1980s manipulated the levels of both gases in air inhaled by volunteers \u2013 and they found that while changes did<\/em> significantly affect other respiratory processes, they didn\u2019t influence the regularity of yawns. There also doesn\u2019t seem to be any systematically measurable difference in the yawning behaviour of people suffering from illnesses associated with breathing and lung function \u2013 which is what you would expect if yawns were respiration-related.<\/p>\n This, more or less, was where Gallup came to the subject. \u201cWhen I was pursuing my honours thesis, my adviser at the time said, well, why not study yawning, because nobody knows why we do it?\u201d he says. \u201cThat was intriguing \u2013 we knew it had to serve some underlying physiological function. So I started to examine the motor action pattern it involves \u2013 this extended gaping of the jaw that\u2019s accompanied by this deep inhalation of air, followed by a rapid closure of the jaw and a quicker exhalation. And it occurred to me that this likely has important circulatory consequences that are localised to the skull.\u201d<\/p>\n We can think of the gaping of the jaw as a localised stretch, similar to stretching muscles in other areas of the body<\/p>\n This, in fact, seems to be exactly what\u2019s happening: several reviews of the medical literature suggest that yawning increases arterial blood supply to the cranium, and then venous return (the rate at which blood flows back from the head to the heart).<\/p>\n \u201cWe can think of the gaping of the jaw as a localised stretch, similar to stretching muscles in other areas of the body,\u201d says Gallup. \u201cIn the same way that stretching helps circulation in those extremities, yawns seem to do the same for the skull.\u201d<\/p>\n From here, Gallup and his fellow researchers started to develop the idea that yawning helps regulate heat in and around the skull. Your brain\u2019s temperature is mainly determined by three variables \u2013 the rate of arterial blood travelling to the brain, the temperature of that blood, and metabolic heat production that occurs within the brain, based on neuronal activity \u2013 and yawning, theoretically, can alter the first two. When you yawn, you take in a deep breath of air that moves across the moist surfaces of your mouth, tongue and nasal passages, a bit like air flowing across a car radiator \u2013 carrying heat away through evaporation and convection.<\/p>\n Studies seem to bear this out: ambient temperature has a pretty predictable effect on yawn frequency, which goes up when it\u2019s just slightly<\/em> too toasty (when it gets really hot, the air temperature is too high for the radiator effect to work, so other cooling mechanisms such as sweating kick in and yawning settles down again) and down when it\u2019s colder.<\/p>\n <\/span>Contagious, isn\u2019t it? A Turkish fox.<\/span> Photograph: Anadolu\/Getty Images<\/p>\n This also seems to explain why certain medical conditions are associated with excess yawning: either the conditions themselves, or the drugs used to treat them, cause elevated brain or body temperature. The \u201cneuronal activity\u201d explanation is also borne out by animal studies \u2013 the mammals and birds with more neurons in their brains yawn for longer durations, irrespective of the size of their actual brains.<\/p>\n This isn\u2019t to say that other hypotheses have been entirely put to rest. The one best supported by the evidence is the \u201carousal change\u201d theory: basically, that yawning helps the brain transition between states \u2013 from sleeping to wakefulness, boredom to alertness, and so on. \u201cOne possibility is that yawning helps the brain switch between using its \u2018default mode network\u2019 \u2013 the regions associated with daydreaming, recalling memories and self-reflection \u2013 and the attentional network responsible for preparing the body for action,\u201d says the historian of medicine Dr Olivier Walusinski, who has authored several papers on the subject. \u201cOne proposed mechanism for this would be that it helps with the circulation of cerebrospinal fluid, the liquid that surrounds and cushions your brain and spinal cord.\u201d<\/p>\n It could be the case, in fact, that this function evolved first, with the thermoregulation effect emerging as a useful after-effect: something we\u2019ll have better evidence for as studies are done on a wider array of animals. It could also be that the two explanations are directly related: these state changes probably mean changes in brain activity and temperature, meaning a need for enhanced blood flow and<\/em> neural cooling. This would explain why you yawn when you\u2019re bored: your brain\u2019s activity level may upshift as it starts to think of ways to move you into a more stimulating situation, and so do its circulatory needs.<\/p>\n Yawning\u2019s probably good for you, and it\u2019s probably helping your brain function better<\/p>\n Wait a minute, though: what about contagious<\/em> yawning? We\u2019re all aware of the phenomenon of one person in a room \u2013 or even on a TV screen \u2013 taking a gulp of air, only for everyone else to do the same. Some researchers have suggested that this sort of infectious behaviour brings groups together, perhaps because it\u2019s a hard-to-fake signal of sleepiness, boredom or vigilance \u2013 though it\u2019s unlikely to be yawning\u2019s main purpose, as plenty of solitary animals are regular yawners.<\/p>\n \u201cIt could be that contagious yawning doesn\u2019t have a function and is just a byproduct of advanced social cognitive mechanisms within highly social species,\u201d says Gallup.<\/p>\n To put that slightly more simply, lots of animals \u2013 including humans \u2013 have various ways of improving their empathy, including \u201cmirror neurons\u201d, which fire when an individual performs an action and when they see someone else perform a similar action. It might be, then, that seeing someone else yawn simply makes your mirror neurons kick in, prompting you to yawn yourself. But contagious yawning may<\/em> also play a role in group coordination through mechanisms related to the arousal change theory: helping every animal in the group switch states from relaxed to active.<\/p>\n One 2021 study that tested this effect in lions found that other behaviour can be contagious among yawners, so if one lying lion yawns and then gets up for a walk, other yawners follow.<\/p>\n Contagious yawning may also promote group vigilance: if one baboon in a troop triggers others to yawn, they may all become more alert. This may also work the other way around \u2013 helping to downregulate arousal before sleep.<\/p>\n So, in other words: yawning\u2019s probably good for you, and it\u2019s probably helping your brain function better. Oh, and if you\u2019ve been conspicuously yawning to get a five-year-old to go to sleep, don\u2019t stop \u2013 there\u2019s a chance it\u2019s really working.<\/p>\n","protected":false},"excerpt":{"rendered":" All vertebrates yawn, or indulge in a behaviour that\u2019s at least recognisable as yawn-adjacent. Sociable baboons yawn, but so do semi-solitary orangutans. Parakeets, penguins and crocodiles yawn \u2013 and so, probably, did the first ever jawed fish. Until relatively recently, the purpose of yawning wasn\u2019t clear, and it\u2019s still contested by researchers and scientists. But<\/p>\n","protected":false},"author":1,"featured_media":30689,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[58],"tags":[6962,10943,761,10646,17975],"class_list":{"0":"post-30688","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-biology","9":"tag-certainly","10":"tag-human","11":"tag-reason","12":"tag-yawn"},"_links":{"self":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/30688","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=30688"}],"version-history":[{"count":0,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/30688\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/media\/30689"}],"wp:attachment":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=30688"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=30688"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=30688"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}