One of science's most baffling questions? Why we

yawn

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?

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.

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.

I’m willing to bet you’ve been stifling a few yawns yourself by this point – as Provine points out, reading or even thinking about yawning can be enough to set us off. So go ahead, let it out – and do so in the knowledge that you are enjoying one of life’s most enduring mysteries.

Disponível em: http://www.bbc.com/. Acesso em 12 ago 2014.

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