One of sciences most baffling questions? Why we yawn By David Robson Health Brain Psychology Sleep Yawning is common throughout the animal kingdom, yet we still dont know what purpose it serves (Science Photo Library) Yawning has puzzled scientists for more than two millennia. But could a new theory settle the question once and for all? David Robson investigates. Mid-conversation with Robert Provine, I have a compelling urge, rising from deep inside my body. The more I try to quash it, the more it seems to spread, until it consumes my whole being. Eventually, it is all I can think about – but how can I stop myself from yawning? Provine tells me this often happens when people are talking to him; during presentations, he sometimes finds the majority of his audience with their mouths agape and tonsils swinging. Luckily, as a psychologist at the University of Maryland, Baltimore County and author of Curious Behavior: Yawning, Laughing, Hiccupping, and Beyond, he isn’t offended. “It makes a very effective lecture,” he says. “You talk and then the audience starts yawning. And then you can ask people to experiment on their yawns – like closing the lips, or inhaling through clenched teeth, or trying to yawn with the nose pinched closed.” It is through experiments like these that Provine has tried to explore a millennia-old mystery: why do we yawn? We all know that tiredness, boredom, or the sight of someone else can all bring along the almost irrepressible urge – but what purpose does it serve the body? When he first started work on so-called “chasmology” in the late 80s, Provine wrote that “yawning may have the dubious distinction of being the least understood, common human behaviour”. Nearly three decades later, we may be closer to an answer, but it’s one that has split the field. View image of Does infectious yawning ensure that we all go to bed at the same time? (Getty Images) Arguably the first studier of yawns was the Greek physician Hippocrates nearly 2,500 years ago. He believed that yawning helped to release noxious air, particularly during a fever. “Like the large quantities of steam that escape from cauldrons when water boils, the accumulated air in the body is violently expelled through the mouth when the body temperature rises,” he wrote. Different incarnations of the idea lingered until the 19th Century, when scientists instead proposed that yawning aids respiration – triggering a rush of oxygen into the blood supply, while flushing out the carbon dioxide. If that were true, you would expect people to yawn more or less frequently depending on the oxygen and carbon dioxide concentrations in the air. Yet when Provine asked volunteers to breathe various mixtures of gases, he found no such change. Many theories have instead focussed on the strange, contagious nature of yawning – a fact that I know only too well from my conversation with Provine. “Around 50% of people who observe a yawn will yawn in response,” he says. “It is so contagious that anything associated with it will trigger one… seeing or hearing another person, or even reading about yawning.” For this reason, some researchers have wondered if yawning might be a primitive form of communication – if so, what information is it transmitting? We often feel tired when we yawn, so one idea is that it helps set everyone’s biological clocks to the same rhythm. “In my view the most likely signalling role of yawning is to help to synchronize the behaviour of a social group – to make them go to sleep more or less at the same time,” says Christian Hess, at the University of Bern in Switzerland. With the same routine, a group can then work together more efficiently throughout the day. View image of Danario Alexander of the San Diego Chargers yawns before the start of a American football match (Getty Images) Yet we also yawn during times of stress: Olympic athletes often do it before a race, while musicians sometimes succumb before a concert. So some researchers, including Provine, believe that the strenuous movements might have a more general role in rebooting the brain – when you are sleepy they make you more alert, or when you are distracted they make you more focussed. Spreading through a group, contagious yawns could then help everyone reach the same level of attention, making them more vigilant to a threat, for instance. The mechanism is somewhat hazy – though one French researcher, Olivier Walusinski, proposes that yawning helps to pump cerebrospinal fluid around the brain, which could trigger a shift in neural activity. To be continue.
Posted on: Wed, 13 Aug 2014 06:07:32 +0000